Recombinant von Willebrand factor: preclinical development.

PubMed

Plaimauer, B; Schlokat, U; Turecek, P L; Mitterer, A; Mundt, W; Auer, W; Pichler, L; Gritsch, H; Schwarz, H P

2001-08-01

Von Willebrand factor (vWF) is a multimeric glycoprotein (GP) that attracts platelets to the site of vascular injury, mediates platelet-platelet interaction, and stabilizes factor VIII (FVIII) in the circulation. Quantitative and qualitative defects of vWF result in von Willebrand disease (vWD), manifested by modest to severe bleeding episodes. Substitution therapy, with plasma-derived FVIII/vWF complex concentrates, is used for patients suffering the more severe forms of vWD. Efficacy of these preparations is often unsatisfactory because inadvertent proteolytic degradation during the manufacturing process causes them to lack the hemostatically most active high-molecular-weight multimers. In contrast, recombinant vWF (r-vWF), which is constitutively expressed at high yields in Chinese hamster ovary (CHO) cells and secreted into the conditioned medium under perfusion fermentation in "protein-free" medium, has high-molecular-weight multimers of extraordinary structural integrity. Functional analysis has shown that r-vWF promotes ristocetin cofactor-mediated platelet aggregation, collagen interaction and FVIII binding, and platelet-collagen adhesion under shear stress. Infusing vWF-deficient animals with r-vWF corrected vWF concentration and reduced blood loss, subsequently stabilizing endogenous FVIII associated with the reduction of bleeding time. Compared with plasma-derived vWF preparations, r-vWF was found to have a prolonged half-life, further enhancing the potential value of r-vWF as a therapeutic agent for treating patients suffering from vWD.

Single-molecule force measurements of the polymerizing dimeric subunit of von Willebrand factor

NASA Astrophysics Data System (ADS)

Wijeratne, Sithara S.; Li, Jingqiang; Yeh, Hui-Chun; Nolasco, Leticia; Zhou, Zhou; Bergeron, Angela; Frey, Eric W.; Moake, Joel L.; Dong, Jing-fei; Kiang, Ching-Hwa

2016-01-01

Von Willebrand factor (VWF) multimers are large adhesive proteins that are essential to the initiation of hemostatic plugs at sites of vascular injury. The binding of VWF multimers to platelets, as well as VWF proteolysis, is regulated by shear stresses that alter VWF multimeric conformation. We used single molecule manipulation with atomic force microscopy (AFM) to investigate the effect of high fluid shear stress on soluble dimeric and multimeric forms of VWF. VWF dimers are the smallest unit that polymerizes to construct large VWF multimers. The resistance to mechanical unfolding with or without exposure to shear stress was used to evaluate VWF conformational forms. Our data indicate that, unlike recombinant VWF multimers (RVWF), recombinant dimeric VWF (RDVWF) unfolding force is not altered by high shear stress (100 dynes/cm2 for 3 min at 37°C ). We conclude that under the shear conditions used (100 dynes/cm2 for 3 min at 37°C ) , VWF dimers do not self-associate into a conformation analogous to that attained by sheared large VWF multimers.

Agglomeration of Celecoxib by Quasi Emulsion Solvent Diffusion Method: Effect of Stabilizer.

PubMed

Maghsoodi, Maryam; Nokhodchi, Ali

2016-12-01

Purpose: The quasi-emulsion solvent diffusion (QESD) has evolved into an effective technique to manufacture agglomerates of API crystals. Although, the proposed technique showed benefits, such as cost effectiveness, that is considerably sensitive to the choice of a stabilizer, which agonizes from a absence of systemic understanding in this field. In the present study, the combination of different solvents and stabilizers were compared to investigate any connections between the solvents and stabilizers. Methods: Agglomerates of celecoxib were prepared by QESD method using four different stabilizers (Tween 80, HPMC, PVP and SLS) and three different solvents (methyl acetate, ethyl acetate and isopropyl acetate). The solid state of obtained particles was investigated by differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy. The agglomerated were also evaluated in term of production yield, distribution of particles and dissolution behavior. Results: The results showed that the effectiveness of stabilizer in terms of particle size and particle size distribution is specific to each solvent candidate. A stabilizer with a lower HLB value is preferred which actually increased its effectiveness with the solvent candidates with higher lipophilicity. HPMC appeared to be the most versatile stabilizer because it showed a better stabilizing effect compared to other stabilizers in all solvents used. Conclusion: This study demonstrated that the efficiency of stabilizers in forming the celecoxib agglomerates by QESD was influenced by the HLB of the stabilizer and lipophilicity of the solvents.

Monomeric rhodopsin is the minimal functional unit required for arrestin binding.

PubMed

Tsukamoto, Hisao; Sinha, Abhinav; DeWitt, Mark; Farrens, David L

2010-06-11

We have tested whether arrestin binding requires the G-protein-coupled receptor be a dimer or a multimer. To do this, we encapsulated single-rhodopsin molecules into nanoscale phospholipid particles (so-called nanodiscs) and measured their ability to bind arrestin. Our data clearly show that both visual arrestin and beta-arrestin 1 can bind to monomeric rhodopsin and stabilize the active metarhodopsin II form. Interestingly, we find that the monomeric rhodopsin in nanodiscs has a higher affinity for wild-type arrestin binding than does oligomeric rhodopsin in liposomes or nanodiscs, as assessed by stabilization of metarhodopsin II. Together, these results establish that rhodopsin self-association is not required to enable arrestin binding. Copyright 2010 Elsevier Ltd. All rights reserved.

Role of CD40 and ADAMTS13 in von Willebrand factor-mediated endothelial cell-platelet-monocyte interaction.

PubMed

Popa, Miruna; Tahir, Sibgha; Elrod, Julia; Kim, Su Hwan; Leuschner, Florian; Kessler, Thorsten; Bugert, Peter; Pohl, Ulrich; Wagner, Andreas H; Hecker, Markus

2018-06-12

Monocyte extravasation into the vessel wall is a key step in atherogenesis. It is still elusive how monocytes transmigrate through the endothelial cell (EC) monolayer at atherosclerosis predilection sites. Platelets tethered to ultra-large von Willebrand factor (ULVWF) multimers deposited on the luminal EC surface following CD40 ligand (CD154) stimulation may facilitate monocyte diapedesis. Human ECs grown in a parallel plate flow chamber for live-cell imaging or Transwell permeable supports for transmigration assay were exposed to fluid or orbital shear stress and CD154. Human isolated platelets and/or monocytes were superfused over or added on top of the EC monolayer. Plasma levels and activity of the ULVWF multimer-cleaving protease ADAMTS13 were compared between coronary artery disease (CAD) patients and controls and were verified by the bioassay. Two-photon intravital microscopy was performed to monitor CD154-dependent leukocyte recruitment in the cremaster microcirculation of ADAMTS13-deficient versus wild-type mice. CD154-induced ULVWF multimer-platelet string formation on the EC surface trapped monocytes and facilitated transmigration through the EC monolayer despite high shear stress. Two-photon intravital microscopy revealed CD154-induced ULVWF multimer-platelet string formation preferentially in venules, due to strong EC expression of CD40, causing prominent downstream leukocyte extravasation. Plasma ADAMTS13 abundance and activity were significantly reduced in CAD patients and strongly facilitated both ULVWF multimer-platelet string formation and monocyte trapping in vitro. Moderate ADAMTS13 deficiency in CAD patients augments CD154-mediated deposition of platelet-decorated ULVWF multimers on the luminal EC surface, reinforcing the trapping of circulating monocytes at atherosclerosis predilection sites and promoting their diapedesis.

Low-loss resonance modes in a gain-assisted plasmonic multimer

NASA Astrophysics Data System (ADS)

Pan, Gui-Ming; Yang, Da-Jie; Zhou, Li; Hao, Zhong-Hua

2018-03-01

We theoretically study the properties of optical losses in a plasmonic multimer and find modes with lower radiative losses due to the cancellation of the dipole moment. High order plasmonic resonances, including electric quadrupole and magnetic dipole resonances, can be achieved by the reduction of symmetry in a multimer. Meanwhile, the dipole moment can be significantly reduced in these high order modes, and consequently, the radiative losses decrease efficiently. The low-loss modes can lead to a lower gain threshold in the gain-assisted nanosystem. In particular, compared with the electric dipolar mode in a single nanoshell, the gain threshold of the electric quadrupolar and magnetic dipolar modes in a multimer can drop by 57.66% and 59.22%, respectively. On the other hand, the gain threshold can reflect the extent of the optical losses of the plasmonic mode in a nanosystem. These findings may have potential applications in the design of a nanolaser, plasmon waveguide and photo-thermal device.

Can green solvents be alternatives for thermal stabilization of collagen?

PubMed

Mehta, Ami; Rao, J Raghava; Fathima, Nishter Nishad

2014-08-01

"Go Green" campaign is gaining light for various industrial applications where water consumption needs to be reduced. To resolve this, industries have adopted usage of green, organic solvents, as an alternative to water. For leather making, tanning industry consumes gallons of water. Therefore, for adopting green solvents in leather making, it is necessary to evaluate its influence on type I collagen, the major protein present in the skin matrix. The thermal stability of collagen from rat tail tendon fiber (RTT) treated with seven green solvents namely, ethanol, ethyl lactate, ethyl acetate, propylene carbonate, propylene glycol, polyethylene glycol-200 and heptane was determined using differential scanning calorimetry (DSC). Crosslinking efficiency of basic chromium sulfate and wattle on RTT in green solvents was determined. DSC thermograms show increase in thermal stability of RTT collagen against heat with green solvents (>78°C) compared to water (63°C). In the presence of crosslinkers, RTT demonstrated thermal stability >100°C in some green solvents, resulting in increased intermolecular forces between collagen, solvent and crosslinkers. The significant improvement in thermal stability of collagen potentiates the capability of green solvents as an alternative for water. Copyright © 2014 Elsevier B.V. All rights reserved.

Stabilization of Proteins by Polymer Conjugation via ATRP

DTIC Science & Technology

2008-08-31

to increase their solubility and utility in organic solvents and to increase their stability in body. Protein-initiated ATRP would enable us to... Solvent solubilization, therapeutic proteins, hydrophilic polymers, protein stabilization Lance Mabus, Jason Berberich, Bhalchandra Lele, Virginia Depp... solvents and to increase their stability in body. Protein-initiated ATRP would enable us to overcome many problems in conventional technology that

Polymer Latex Stability Modification by Exposure to Hydrophobic Solvents.

PubMed

de Oliveira Cardoso A; Galembeck

1998-08-01

The stability of latex particles toward coagulation in the presence of salt is modified by swelling the latex with toluene and chloroform vapors. Short-term stability was determined by turbidimetric titrations, and the long-term stability was evaluated by adding latex and salt solutions, allowing the mixture to age for 24 or 48 h and determining the characteristics of the supernatant and of the sediment. Nine different latexes were examined, with variable results: in some cases, both apolar solvents stabilize the latex; in other cases, increased stability is induced by only one of the solvents, either toluene or chloroform. There is also coherence, but not a strict correlation, between the solvent effects on short- and long-term stability. For instance, in the case of a core-and-shell styrene-butyl methacrylate latex, chloroform has a small stabilizing effect in the titration experiment, but it prevents the formation of a coagulated latex sediment even 48 h after mixing latex and salt. Two hypotheses are discussed to account for these observations: (i) swelling solvents decrease the particles ability to dissipate the collision kinetic energy, so that particles collide but without joining each other; (ii) the solvents induce the release of trapped charged groups from the particle interior to the interface, enhancing the usual (electrostatic, steric, hydration) stability factors. Copyright 1998 Academic Press.

Tuning aggregation of microemulsion droplets and silica nanoparticles using solvent mixtures.

PubMed

Salabat, Alireza; Eastoe, Julian; Mutch, Kevin J; Tabor, Rico F

2008-02-15

The effect of solvent on stability of water-in-oil microemulsions has been studied with AOT (sodium bis(2-ethylhexyl)sulfosuccinate) and different solvent mixtures of n-heptane, toluene and dodecane. Dynamic light scattering DLS was used to monitor the apparent diffusion coefficient D(A) and effective microemulsion droplet diameter on changing composition of the solvent. Interdroplet attractive interactions, as indicated by variations in D(A), can be tuned by formulation of appropriate solvent mixtures using heptane, toluene, and dodecane. In extreme cases, solvent mixtures can be used to induce phase transitions in the microemulsions. Aggregation and stability of model AOT-stabilized silica nanoparticles in different solvents were also investigated to explore further these solvent effects. For both systems the state of aggregation can be correlated with the effective molecular volume of the solvent V(mol)(eff) mixture.

Functional Importance of Covalent Homodimer of Reelin Protein Linked via Its Central Region*

PubMed Central

Yasui, Norihisa; Kitago, Yu; Beppu, Ayako; Kohno, Takao; Morishita, Shunsuke; Gomi, Hiroki; Nagae, Masamichi; Hattori, Mitsuharu; Takagi, Junichi

2011-01-01

Reelin is a 3461-residue secreted glycoprotein that plays a critical role in brain development through its action on target neurons. Although it is known that functional reelin protein exists as multimer formed by interchain disulfide bond(s) as well as through non-covalent interactions, the chemical nature of the multimer assembly has been elusive. In the present study, we identified, among 122 cysteines present in full-length reelin, the single critical cysteine residue (Cys2101) responsible for the covalent multimerization. C2101A mutant reelin failed to assemble into disulfide-bonded multimers, whereas it still exhibited non-covalently associated high molecular weight oligomeric states in solution. Detailed analysis of tryptic fragments produced from the purified reelin proteins revealed that the minimum unit of the multimer is a homodimeric reelin linked via Cys2101 present in the central region and that this cysteine does not connect to the N-terminal region of reelin, which had been postulated as the primary oligomerization domain. A surface plasmon resonance binding assay confirmed that C2101A mutant reelin retained binding capability toward two neuronal receptors apolipoprotein E receptor 2 and very low density lipoprotein receptor. However, it failed to show signaling activity in the assay using the cultured neurons. These results indicate that an intact higher order architecture of reelin multimer maintained by both Cys2101-mediated homodimerization and other non-covalent association present elsewhere in the reelin primary structure are essential for exerting its full biological activity. PMID:21844191

A BENCHMARKING ANALYSIS FOR FIVE RADIONUCLIDE VADOSE ZONE MODELS (CHAIN, MULTIMED_DP, FECTUZ, HYDRUS, AND CHAIN 2D) IN SOIL SCREENING LEVEL CALCULATIONS

EPA Science Inventory

Five radionuclide vadose zone models with different degrees of complexity (CHAIN, MULTIMED_DP, FECTUZ, HYDRUS, and CHAIN 2D) were selected for use in soil screening level (SSL) calculations. A benchmarking analysis between the models was conducted for a radionuclide (99Tc) rele...

Prediction of the solvent affecting site and the computational design of stable Candida antarctica lipase B in a hydrophilic organic solvent.

PubMed

Park, Hyun June; Joo, Jeong Chan; Park, Kyungmoon; Kim, Yong Hwan; Yoo, Young Je

2013-02-10

Enzyme reactions in organic solvent such as for organic synthesis have great industrial potential. However, enzymes lose their stability in hydrophilic organic solvents due to the deformation of the enzyme by the solvent. It is thus important to enhance the stability of enzymes in hydrophilic organic solvents. Previous approaches have not considered on the interaction between enzymes and solvents due to the lack of information. In this study, the structural motions of the enzyme in methanol cosolvent and the interaction between the enzyme surface and the solvent molecule were investigated using molecular dynamics simulation (MD). By analyzing the MD simulation results, the surface residues of Candida antarctica lipase B (CalB) with higher root mean square deviation (RMSD) in a methanol solvent were considered as methanol affecting site and selected for site-directed mutagenesis. The methanol affecting site was computationally redesigned by lowering the RMSD. Among the candidate mutants, the A8T, A92E, N97Q and T245S mutants showed higher organic solvent stability at various methanol concentrations. The rational approach developed in this study could be applied to the stabilization of other industrial enzymes used in organic solvents. Copyright © 2012 Elsevier B.V. All rights reserved.

Pharmacokinetics and safety of a novel recombinant human von Willebrand factor manufactured with a plasma-free method: a prospective clinical trial.

PubMed

Mannucci, Pier Mannuccio; Kempton, Christine; Millar, Carolyn; Romond, Edward; Shapiro, Amy; Birschmann, Ingvild; Ragni, Margaret V; Gill, Joan Cox; Yee, Thynn Thynn; Klamroth, Robert; Wong, Wing-Yen; Chapman, Miranda; Engl, Werner; Turecek, Peter L; Suiter, Tobias M; Ewenstein, Bruce M

2013-08-01

Safety and pharmacokinetics (PK) of recombinant von Willebrand factor (rVWF) combined at a fixed ratio with recombinant factor VIII (rFVIII) were investigated in 32 subjects with type 3 or severe type 1 von Willebrand disease (VWD) in a prospective phase 1, multicenter, randomized clinical trial. rVWF was well tolerated and no thrombotic events, inhibitors, or serious adverse events were observed. The PK of rVWF ristocetin cofactor activity, VWF antigen, and collagen-binding activity were similar to those of the comparator plasma-derived (pd) VWF-pdFVIII. In vivo cleavage of ultra-large molecular-weight rVWF multimers by ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13; the endogenous VWF protease) and generation of characteristic satellite bands were demonstrated. In 2 subjects with specific nonneutralizing anti-VWF-binding antibodies already detectable before rVWF infusion, a reduction in VWF multimers and VWF activity was observed. Stabilization of endogenous FVIII was enhanced following post-rVWF-rFVIII infusion as shown by the difference in area under the plasma concentration curve compared with pdVWF-pdFVIII (AUC0-∞) (P < .01). These data support the concept of administering rVWF alone once a therapeutic level of endogenous FVIII is achieved.

ADAMTS-13 rapidly cleaves newly secreted ultralarge von Willebrand factor multimers on the endothelial surface under flowing conditions.

PubMed

Dong, Jing-fei; Moake, Joel L; Nolasco, Leticia; Bernardo, Aubrey; Arceneaux, Wendy; Shrimpton, Corie N; Schade, Alicia J; McIntire, Larry V; Fujikawa, Kazuo; López, José A

2002-12-01

Thrombotic thrombocytopenic purpura (TTP) is a devastating thrombotic disorder caused by widespread microvascular thrombi composed of platelets and von Willebrand factor (VWF). The disorder is associated with a deficiency of the VWF-cleaving metalloprotease, ADAMTS-13, with consequent accumulation of ultralarge (UL) VWF multimers in the plasma. ULVWF multimers, unlike plasma forms of VWF, attach spontaneously to platelet GP Ibalpha, a component of the GP Ib-IX-V complex. We have found that ULVWF multimers secreted from stimulated endothelial cells (ECs) remained anchored to the endothelial surface where platelets and Chinese hamster ovary cells expressing the GP Ib-IX-V complex attached to form long beads-on-a-string structures in the presence of fluid shear stresses in both the venous (2.5 dyne/cm(2)) and arterial (20 and 50 dyne/cm(2)) ranges. Although measurement of the activity of the ADAMTS-13 VWF-cleaving metalloprotease in vitro requires prolonged incubation of the enzyme with VWF under nonphysiologic conditions, EC-derived ULVWF strings with attached platelets were cleaved within seconds to minutes in the presence of normal plasma (containing approximately 100% ADAMTS-13 activity) or in the presence of partially purified ADAMTS-13. By contrast, the strings persisted for the entire period of perfusion (10 minutes) in the presence of plasma from patients with TTP containing 0% to 10% ADAMTS-13 activity. These results suggest that cleavage of EC-derived ULVWF multimers by ADAMTS-13 is a rapid physiologic process that occurs on endothelial cell surfaces.

Effect of dynamic surface polarization on the oxidative stability of solvents in nonaqueous Li-O 2 batteries

NASA Astrophysics Data System (ADS)

Khetan, Abhishek; Pitsch, Heinz; Viswanathan, Venkatasubramanian

2017-09-01

Polarization-induced renormalization of the frontier energy levels of interacting molecules and surfaces can cause significant shifts in the excitation and transport behavior of electrons. This phenomenon is crucial in determining the oxidative stability of nonaqueous electrolytes in high-energy density electrochemical systems such as the Li-O2 battery. On the basis of partially self-consistent first-principles Sc G W0 calculations, we systematically study how the electronic energy levels of four commonly used solvent molecules, namely, dimethylsulfoxide (DMSO), dimethoxyethane (DME), tetrahydrofuran (THF), and acetonitrile (ACN), renormalize when physisorbed on the different stable surfaces of Li2O2 , the main discharge product. Using band level alignment arguments, we propose that the difference between the solvent's highest occupied molecular orbital (HOMO) level and the surface's valence-band maximum (VBM) is a refined metric of oxidative stability. This metric and a previously used descriptor, solvent's gas phase HOMO level, agree quite well for physisorbed cases on pristine surfaces where ACN is oxidatively most stable followed by DME, THF, and DMSO. However, this effect is intrinsically linked to the surface chemistry of the solvent's interaction with the surface states and defects, and depends strongly on their nature. We conclusively show that the propensity of solvent molecules to oxidize will be significantly higher on Li2O2 surfaces with defects as compared to pristine surfaces. This suggests that the oxidative stability of a solvent is dynamic and is a strong function of surface electronic properties. Thus, while gas phase HOMO levels could be used for preliminary solvent candidate screening, a more refined picture of solvent stability requires mapping out the solvent stability as a function of the state of the surface under operating conditions.

Effect of sorbitol and glycerol on the stability of trypsin and difference between their stabilization effects in the various solvents.

PubMed

Pazhang, Mohammad; Mehrnejad, Faramarz; Pazhang, Yaghub; Falahati, Hanieh; Chaparzadeh, Nader

2016-01-01

The effect of glycerol and sorbitol on the stability of porcine pancreas trypsin was investigated in this work. Molecular dynamics simulation and thermostability results showed that trypsin has two flexible regions, and polyols (sorbitol and glycerol) stabilize the enzyme by decreasing the flexibility of these regions. Radial distribution function results exhibited that sorbitol and glycerol were excluded from the first water layer of the enzyme, therefore decrease the flexibility of the regions by preferential exclusion. Also, results showed that the stabilization effect of sorbitol is more than glycerol. This observation could be because of the larger decrease in the fluctuations of trypsin in the presence of sorbitol. We also examined the role of solvent's hydrophobicity in enzyme stabilization by sorbitol and glycerol. To do so, the thermostability of trypsin was evaluated in the presence of solvents with different hydrophobicity (methanol, ethanol, isopropanol and n-propanol) in addition to the polyols. Our results depicted that glycerol is a better stabilizer than sorbitol in the presence of hydrophobic solvents (n-propanol), whereas sorbitol is a better stabilizer than glycerol in the presence of hydrophilic solvents (methanol). © 2015 International Union of Biochemistry and Molecular Biology, Inc.

Supramolecular curcumin-barium prodrugs for formulating with ceramic particles.

PubMed

Kamalasanan, Kaladhar; Anupriya; Deepa, M K; Sharma, Chandra P

2014-10-01

A simple and stable curcumin-ceramic combined formulation was developed with an aim to improve curcumin stability and release profile in the presence of reactive ceramic particles for potential dental and orthopedic applications. For that, curcumin was complexed with barium (Ba(2+)) to prepare curcumin-barium (BaCur) complex. Upon removal of the unbound curcumin and Ba(2+) by dialysis, a water-soluble BaCur complex was obtained. The complex was showing [M+1](+) peak at 10,000-20,000 with multiple fractionation peaks of MALDI-TOF-MS studies, showed that the complex was a supramolecular multimer. The (1)H NMR and FTIR studies revealed that, divalent Ba(2+) interacted predominantly through di-phenolic groups of curcumin to form an end-to-end complex resulted in supramolecular multimer. The overall crystallinity of the BaCur was lower than curcumin as per XRD analysis. The complexation of Ba(2+) to curcumin did not degrade curcumin as per HPLC studies. The fluorescence spectrum was blue shifted upon Ba(2+) complexation with curcumin. Monodisperse nanoparticles with size less than 200dnm was formed, out of the supramolecular complex upon dialysis, as per DLS, and upon loading into pluronic micelles the size was remaining in similar order of magnitude as per DLS and AFM studies. Stability of the curcumin was improved greater than 50% after complexation with Ba(2+) as per UV/Vis spectroscopy. Loading of the supramloecular nanoparticles into pluronic micelles had further improved the stability of curcumin to approx. 70% in water. These BaCur supramolecule nanoparticles can be considered as a new class of prodrugs with improved solubility and stability. Subsequently, ceramic nanoparticles with varying chemical composition were prepared for changing the material surface reactivity in terms of the increase in, degradability, surface pH and protein adsorption. Further, these ceramic particles were combined with curcumin prodrug formulations and optimized the curcumin release properties in the combined formulations. Our proof concept study shows that, the conversion of curcumin to a metal-organic supramolecular prodrug improved the solubility, stability and release profile of curcumin. The prodrug approach with the micellisation strategy appears to be more appropriate to deliver intact curcumin in the presence of ceramic particles of varying surface reactivity. Copyright © 2014 Elsevier B.V. All rights reserved.

Stabilization of Li Metal Anode in DMSO-Based Electrolytes via Optimization of Salt-Solvent Coordination for Li-O 2 Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Bin; Xu, Wu; Yan, Pengfei

The conventional DMSO-based electrolyte (1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in DMSO) is unstable against the Li metal anode and therefore cannot be used directly in practical Li-O2 batteries. Here, we demonstrate that a highly concentrated electrolyte based on LiTFSI in DMSO (with a molar ratio of 1:3) can greatly improve the stability of the Li metal anode against DMSO and significantly improve the cycling stability of Li-O2 batteries. This highly concentrated electrolyte contains no free DMSO solvent molecules, but only complexes of (TFSI–)a-Li+-(DMSO)b (where a + b = 4), and thus enhances their stability with Li metal anodes. In addition,more » such salt-solvent complexes have higher Gibbs activation energy barriers than the free DMSO solvent molecules, indicating improved stability of the electrolyte against the attack of superoxide radical anions. Therefore, the stability of this highly concentrated electrolyte at both Li metal anodes and carbon-based air electrodes has been greatly enhanced, resulting in improved cyclic stability of Li-O2 batteries. The fundamental stability of the electrolyte with free-solvent against the chemical and electrochemical reactions can also be used to enhance the stability of other electrochemical systems.« less

High-throughput 96-well solvent mediated sonic blending synthesis and on-plate solid/solution stability characterization of pharmaceutical cocrystals.

PubMed

Luu, Van; Jona, Janan; Stanton, Mary K; Peterson, Matthew L; Morrison, Henry G; Nagapudi, Karthik; Tan, Helming

2013-01-30

A 96-well high-throughput cocrystal screening workflow has been developed consisting of solvent-mediated sonic blending synthesis and on-plate solid/solution stability characterization by XRPD. A strategy of cocrystallization screening in selected blend solvents including water mixtures is proposed to not only manipulate solubility of the cocrystal components but also differentiate physical stability of the cocrystal products. Caffeine-oxalic acid and theophylline-oxalic acid cocrystals were prepared and evaluated in relation to saturation levels of the cocrystal components and stability of the cocrystal products in anhydrous and hydrous solvents. AMG 517 was screened with a number of coformers, and solid/solution stability of the resulting cocrystals on the 96-well plate was investigated. A stability trend was observed and confirmed that cocrystals comprised of lower aqueous solubility coformers tended to be more stable in water. Furthermore, cocrystals which could be isolated under hydrous solvent blending condition exhibited superior physical stability to those which could only be obtained under anhydrous condition. This integrated HTS workflow provides an efficient route in an API-sparing approach to screen and identify cocrystal candidates with proper solubility and solid/solution stability properties. Copyright © 2012 Elsevier B.V. All rights reserved.

Gels with exceptional thermal stability formed by bis(amino acid) oxalamide gelators and solvents of low polarity.

PubMed

Makarević, Janja; Jokić, Milan; Frkanec, Leo; Katalenić, Darinka; Zinić, Mladen

2002-10-07

Some bis (amino acid) oxalamide gelators form common thermo-reversible gels with various organic solvents but also gels of exceptional thermal stability with some solvents of medium and low polarity; the latter gels can be heated up to 50 degrees C higher temperatures than the bp of the solvent without apparent gel-to-sol transition.

The thrombospondin-1 N700S polymorphism is associated with early myocardial infarction without altering von Willebrand factor multimer size.

PubMed

Zwicker, Jeffrey I; Peyvandi, Flora; Palla, Roberta; Lombardi, Rossana; Canciani, Maria Teresa; Cairo, Andrea; Ardissino, Diego; Bernardinelli, Luisa; Bauer, Kenneth A; Lawler, Jack; Mannucci, Pier

2006-08-15

The N700S polymorphism of thrombospondin-1 (TSP-1) has been identified as a potential genetic risk factor for myocardial infarction (MI). In a large case-control study of 1425 individuals who survived a myocardial infarction prior to age 45, the N700S polymorphism was a significant risk factor for myocardial infarction in both homozygous (odds ratio [OR] 1.9, 95% confidence interval [CI] 1.1-3.3, P = .01) and heterozygous carriers of the S700 allele (OR 1.4, 95% CI 1.1-3.3, P = .01). TSP-1 has been shown to reduce von Willebrand factor (VWF) multimer size, and the domain responsible for VWF-reducing activity has been localized to the calcium-binding C-terminal sequence. As the N700S polymorphism was previously shown to alter the function of this domain, we investigated whether the altered VWF-reducing activity of TSP-1 underlies the observed prothrombotic phenotype. The TSP1 N700S polymorphism did not influence VWF multimer size in patients homozygous for either allele nor was there a significant reduction of VWF multimer size following incubation with recombinant N700S fragments or platelet-derived TSP-1.

The thrombospondin-1 N700S polymorphism is associated with early myocardial infarction without altering von Willebrand factor multimer size

PubMed Central

Zwicker, Jeffrey I.; Peyvandi, Flora; Palla, Roberta; Lombardi, Rossana; Canciani, Maria Teresa; Cairo, Andrea; Ardissino, Diego; Bernardinelli, Luisa; Bauer, Kenneth A.; Lawler, Jack; Mannucci, Pier

2006-01-01

The N700S polymorphism of thrombospondin-1 (TSP-1) has been identified as a potential genetic risk factor for myocardial infarction (MI). In a large case-control study of 1425 individuals who survived a myocardial infarction prior to age 45, the N700S polymorphism was a significant risk factor for myocardial infarction in both homozygous (odds ratio [OR] 1.9, 95% confidence interval [CI] 1.1-3.3, P = .01) and heterozygous carriers of the S700 allele (OR 1.4, 95% CI 1.1-3.3, P = .01). TSP-1 has been shown to reduce von Willebrand factor (VWF) multimer size, and the domain responsible for VWF-reducing activity has been localized to the calcium-binding C-terminal sequence. As the N700S polymorphism was previously shown to alter the function of this domain, we investigated whether the altered VWF-reducing activity of TSP-1 underlies the observed prothrombotic phenotype. The TSP1 N700S polymorphism did not influence VWF multimer size in patients homozygous for either allele nor was there a significant reduction of VWF multimer size following incubation with recombinant N700S fragments or platelet-derived TSP-1. PMID:16684956

Role of carbohydrate in multimeric structure of factor VIII/von Willebrand factor protein.

PubMed Central

Gralnick, H R; Williams, S B; Rick, M E

1983-01-01

The carbohydrate moiety of the factor VIII/von Willebrand (vW) factor protein is important in the expression of vW factor activity and the intravascular survival of the protein. Studies of normal human factor VIII/vW factor protein indicate that there is a requirement of a full complement of penultimate galactose for the maintenance of a normal multimeric structure. Release of penultimate galactose by beta-galactosidase or modification by galactose oxidase results in loss of the largest molecular weight multimers and increased numbers of intermediate and smaller multimers. In contrast, terminal galactose on the factor VIII/vW factor protein does not appear to play a significant role in the maintenance of the multimer organization. The abnormalities in multimeric structure and molecular size were demonstrated by NaDodSO4/polyacrylamide/agarose gel electrophoresis, NaDodSO4/glyoxyl-agarose electrophoresis, and sucrose density ultracentrifugation. These studies indicate that the penultimate galactose plays a role in the maintenance of the largest multimers of the factor VIII/vW factor protein. This may explain why, in some patients with variant forms of vW disease, a carbohydrate abnormality also may affect the multimeric structure of the plasma factor VIII/vW factor protein. Images PMID:6601805

Stability-limit "Ouzo region" boundaries for poly(lactide-co-glycolide) nanoparticles prepared by nanoprecipitation.

PubMed

Beck-Broichsitter, Moritz

2016-09-10

The introduction of "Ouzo diagrams" has enhanced the applicability of the basic nanoprecipitation process for drug delivery research. The current study investigated the interaction of two relevant polymer/solvent systems, which is thought to impact the location of the stability-limit "Ouzo boundary". Viscosity measurements (Kurata-Stockmayer-Fixman approach) and static light scattering (Debye method) underlined a distinct interplay of the employed polymer (poly(lactide-co-glycolide)) with the utilized organic solvents (acetone and tetrahydrofuran). Both methods indicated that tetrahydrofuran was the "better" solvent for poly(lactide-co-glycolide). Thus, nanoprecipitation of this polymer/solvent composition resulted in larger nanoparticles. This observation can be attributed to the chain configuration of poly(lactide-co-glycolide) in the organic solvent, which influenced the extent of the break-up of the injected solvent layer. Accordingly, the stability-limit curve of the "Ouzo region" was shifted to lower poly(lactide-co-glycolide) fractions for tetrahydrofuran. Overall, the location of the "Ouzo region", which is an essential tool for drug delivery research, is influenced by the employed organic solvent. The current study described two distinct methods suitable to identify relevant polymer-solvent interactions, which dictate the stability-limit "Ouzo boundary" for relevant poly(lactide-co-glycolide). Copyright © 2016 Elsevier B.V. All rights reserved.

Constitutive dimerization of the G-protein coupled receptor, neurotensin receptor 1, reconstituted into phospholipid bilayers.

PubMed

Harding, Peter J; Attrill, Helen; Boehringer, Jonas; Ross, Simon; Wadhams, George H; Smith, Eleanor; Armitage, Judith P; Watts, Anthony

2009-02-01

Neurotensin receptor 1 (NTS1), a Family A G-protein coupled receptor (GPCR), was expressed in Escherichia coli as a fusion with the fluorescent proteins eCFP or eYFP. A fluorophore-tagged receptor was used to study the multimerization of NTS1 in detergent solution and in brain polar lipid bilayers, using fluorescence resonance energy transfer (FRET). A detergent-solubilized receptor was unable to form FRET-competent complexes at concentrations of up to 200 nM, suggesting that the receptor is monomeric in this environment. When reconstituted into a model membrane system at low receptor density, the observed FRET was independent of agonist binding, suggesting constitutive multimer formation. In competition studies, decreased FRET in the presence of untagged NTS1 excludes the possibility of fluorescent protein-induced interactions. A simulation of the experimental data indicates that NTS1 exists predominantly as a homodimer, rather than as higher-order multimers. These observations suggest that, in common with several other Family A GPCRs, NTS1 forms a constitutive dimer in lipid bilayers, stabilized through receptor-receptor interactions in the absence of other cellular signaling components. Therefore, this work demonstrates that well-characterized model membrane systems are useful tools for the study of GPCR multimerization, allowing fine control over system composition and complexity, provided that rigorous control experiments are performed.

Application of precipitation methods for the production of water-insoluble drug nanocrystals: production techniques and stability of nanocrystals.

PubMed

Xia, Dengning; Gan, Yong; Cui, Fude

2014-01-01

This review focuses on using precipitation (bottom-up) method to produce water-insoluble drug nanocrystals, and the stability issues of nanocrystals. The precipitation techniques for production of ultra-fine particles have been widely researched for last few decades. In these techniques, precipitation of solute is achieved by addition of a non-solvent for solute called anti-solvent to decrease the solvent power for the solute dissolved in a solution. The anti-solvent can be water, organic solvents or supercritical fluids. In this paper, efforts have been made to review the precipitation techniques involving the anti-solvent precipitation by simple mixing, impinging jet mixing, multi-inlet vortex mixing, the using of high-gravity, ultrasonic waves and supercritical fluids. The key to the success of yielding stable nanocrystals in these techniques is to control the nucleation kinetics and particle growth through mixing during precipitation based on crystallization theories. The stability issues of the nanocrystals, such as sedimentation, Ostwald ripening, agglomeration and cementing of crystals, change of crystalline state, and the approaches to stabilizing nanocrystals are also discussed in detail.

Theoretical study of structure and stability of small gadolinium carboxylate complexes in liquid scintillator solvents.

PubMed

Huang, Pin-Wen

2014-09-01

The structural properties of three small gadolinium carboxylate complexes in three liquid scintillator solvents (pseudocumene, linear alkylbenzene, and phenyl xylylethane) were theoretically investigated using density functional theory (B3LYP/LC-RECP) and polarizable continuum model (PCM). The average interaction energy between gadolinium atom and carboxylate ligand (E(int)) and the energy difference of the highest singly occupied molecular orbital and lowest unoccupied molecular orbital (Δ(SL)) were calculated to evaluate and compare the relative stability of these complexes in solvents. The calculation results show that the larger (with a longer alkyl chain) gadolinium carboxylate complex has greater stability than the smaller one, while these gadolinium carboxylates in linear alkylbenzene were found to have greater stability than those in the other two solvents.

Clinical application of a rapid method using agarose gel electrophoresis and Western blotting to evaluate von Willebrand factor protease activity.

PubMed

Kirzek, D M; Rick, M E

2001-03-01

A method for evaluating the activity of the von Willebrand factor (vWF) protease is described, and a clinical application is illustrated. The procedure utilizes gel electrophoresis, Western blotting, and luminographic detection methods to evaluate the distribution of vWF multimers before and after incubation of clinical samples under conditions that favor proteolysis by this enzyme. Physiologically, the high-molecular-weight multimers of vWF are cleaved by the vWF protease under conditions of high shear stress in parts of the arterial circulation; cleavage of vWF multimers is also observed after exposure of vWF to denaturing agents in vitro and thus can serve as a laboratory test for the activity of the protease. vWF protease activity is decreased or absent in patients with thrombotic thrombocytopenic purpura due to an inhibiting autoantibody, and this leads to high levels of noncleaved vWF and to life-threatening thrombosis, thrombocytopenia and anemia. The assay evaluates the activity of the protease by assessing the cleavage of vWF multimers after patient plasmas are incubated in vitro under denaturing conditions. With the use of these electrophoresis and Western blotting techniques, patient plasmas can be rapidly assessed for the activity of the vWF protease which may aid in the treatment strategy for these patients.

Frequency and reactivity of antigen-specific T cells were concurrently measured through the combination of artificial antigen-presenting cell, MACS and ELISPOT.

PubMed

Shen, Chuanlai; Xu, Tao; Wu, You; Li, Xiaoe; Xia, Lingzhi; Wang, Wei; Shahzad, Khawar Ali; Zhang, Lei; Wan, Xin; Qiu, Jie

2017-11-27

Conventional peptide-major histocompatibility complex (pMHC) multimer staining, intracellular cytokine staining, and enzyme-linked immunospot (ELISPOT) assay cannot concurrently determine the frequency and reactivity of antigen-specific T cells (AST) in a single assay. In this report, pMHC multimer, magnetic-activated cell sorting (MACS), and ELISPOT techniques have been integrated into a micro well by coupling pMHC multimers onto cell-sized magnetic beads to characterize AST cell populations in a 96-well microplate which pre-coated with cytokine-capture antibodies. This method, termed AAPC-microplate, allows the enumeration and local cytokine production of AST cells in a single assay without using flow cytometry or fluorescence intensity scanning, thus will be widely applicable. Here, ovalbumin 257-264 -specific CD8 + T cells from OT-1 T cell receptor (TCR) transgenic mice were measured. The methodological accuracy, specificity, reproducibility, and sensitivity in enumerating AST cells compared well with conventional pMHC multimer staining. Furthermore, the AAPC-microplate was applied to detect the frequency and reactivity of Hepatitis B virus (HBV) core antigen 18-27 - and surface antigen 183-191 -specific CD8 + T cells for the patients, and was compared with conventional method. This method without the need of high-end instruments may facilitate the routine analysis of patient-specific cellular immune response pattern to a given antigen in translational studies.

Purification and protective efficacy of monomeric and modified Yersinia pestis capsular F1-V antigen fusion proteins for vaccination against plague

PubMed Central

Goodin, Jeremy L.; Nellis, David F.; Powell, Bradford S.; Vyas, Vinay V.; Enama, Jeffrey T.; Wang, Lena C.; Clark, Patrick K.; Giardina, Steven L.; Adamovicz, Jeffery. J.; Michiel, Dennis F.

2009-01-01

The F1-V vaccine antigen, protective against Yersinia pestis, exhibits a strong tendency to multimerize that affects larger-scale manufacture and characterization. In this work, the sole F1-V cysteine was replaced with serine by site-directed mutagenesis for characterization of F1-V non-covalent multimer interactions and protective potency without participation by disulfide-linkages. F1-V and F1-VC424S proteins were over-expressed in Escherichia coli, recovered using mechanical lysis/pH-modulation and purified from urea-solubilized soft inclusion bodies, using successive ion-exchange, ceramic hydroxyapatite, and size-exclusion chromatography. This purification method resulted in up to 2 mg per gram of cell paste of 95% pure, mono-disperse protein having ≤ 0.5 endotoxin units per mg by a kinetic chromogenic limulus amoebocyte lysate reactivity assay. Both F1-V and F1-VC424S were monomeric at pH 10.0 and progressively self-associated as pH conditions decreased to pH 6.0. Solution additives were screened for their ability to inhibit F1-V self-association at pH 6.5. An L-arginine buffer provided the greatest stabilizing effect. Conversion to >500-kDa multimers occurred between pH 6.0 and 5.0. Conditions for efficient F1-V adsorption to the cGMP-compatible Alhydrogel® adjuvant were optimized. Side-by-side evaluation for protective potency against subcutaneous plague infection in mice was conducted for F1-VC424S monomer; cysteine-capped F1-V monomer; cysteine-capped F1-V multimer; and a F1-V standard reported previously. After a two-dose vaccination with 2 × 20 µg of F1-V, respectively, 100, 80, 80, and 70% of injected mice survived a subcutaneous lethal plague challenge with 108 LD50 Y. pestis CO92. Thus, vaccination with F1-V monomer and multimeric forms resulted in significant, and essentially equivalent, protection. PMID:17293124

STABILITY OF A CYLINDRICAL SOLUTE-SOLVENT INTERFACE: EFFECT OF GEOMETRY, ELECTROSTATICS, AND HYDRODYNAMICS.

PubMed

Li, B O; Sun, Hui; Zhou, Shenggao

The solute-solvent interface that separates biological molecules from their surrounding aqueous solvent characterizes the conformation and dynamics of such molecules. In this work, we construct a solvent fluid dielectric boundary model for the solvation of charged molecules and apply it to study the stability of a model cylindrical solute-solvent interface. The motion of the solute-solvent interface is defined to be the same as that of solvent fluid at the interface. The solvent fluid is assumed to be incompressible and is described by the Stokes equation. The solute is modeled simply by the ideal-gas law. All the viscous force, hydrostatic pressure, solute-solvent van der Waals interaction, surface tension, and electrostatic force are balanced at the solute-solvent interface. We model the electrostatics by Poisson's equation in which the solute-solvent interface is treated as a dielectric boundary that separates the low-dielectric solute from the high-dielectric solvent. For a cylindrical geometry, we find multiple cylindrically shaped equilibrium interfaces that describe polymodal (e.g., dry and wet) states of hydration of an underlying molecular system. These steady-state solutions exhibit bifurcation behavior with respect to the charge density. For their linearized systems, we use the projection method to solve the fluid equation and find the dispersion relation. Our asymptotic analysis shows that, for large wavenumbers, the decay rate is proportional to wavenumber with the proportionality half of the ratio of surface tension to solvent viscosity, indicating that the solvent viscosity does affect the stability of a solute-solvent interface. Consequences of our analysis in the context of biomolecular interactions are discussed.

Comparative analysis of von Willebrand factor profiles after implantation of left ventricular assist device and total artificial heart.

PubMed

Reich, H J; Morgan, J; Arabia, F; Czer, L; Moriguchi, J; Ramzy, D; Esmailian, F; Lam, L; Dunhill, J; Volod, O

2017-08-01

Essentials Bleeding is a major source of morbidity during mechanical circulatory support. von Willebrand factor (VWF) multimer loss may contribute to bleeding. Different patterns of VWF multimer loss were seen with the two device types. This is the first report of total artificial heart associated VWF multimer loss. Background Bleeding remains a challenge during mechanical circulatory support and underlying mechanisms are incompletely understood. Functional von Willebrand factor (VWF) impairment because of loss of high-molecular-weight multimers (MWMs) produces acquired von Willebrand disease (VWD) after left ventricular assist device (LVAD). Little is known about VWF multimers with total artificial hearts (TAHs). Here, VWF profiles with LVADs and TAHs are compared using a VWD panel. Methods VWD evaluations for patients with LVAD or TAH (2013-14) were retrospectively analyzed and included: VWF activity (ristocetin cofactor, VWF:RCo), VWF antigen (VWF:Ag), ratio of VWF:RCo to VWF:Ag, and quantitative VWF multimeric analysis. Results Twelve patients with LVADs and 12 with TAHs underwent VWD evaluation. All had either normal (47.8%) or elevated (52.2%) VWF:RCo, normal (26.1%) or elevated (73.9%) VWF:Ag and 50.0% were disproportional (ratio ≤ 0.7). Multimeric analysis showed abnormal patterns in all patients with LVADs: seven with high MWM loss; five with highest MWM loss. With TAH, 10/12 patients had abnormal patterns: all with highest MWM loss. High MWM loss correlated with presence of LVAD and highest MWM loss with TAH. Increased low MWMs were detected in 22/24. Conclusion Using VWF multimeric analysis, abnormalities after LVAD or TAH were detected that would be missed with measurements of VWF level alone: loss of high MWM predominantly in LVAD, loss of highest MWM in TAH, and elevated levels of low MWM in both. This is the first study to describe TAH-associated highest MWM loss, which may contribute to bleeding. © 2017 International Society on Thrombosis and Haemostasis.

Solvent effects on the relative stability of radicals derived from artemisinin: DFT study using the PCM/COSMO approach

NASA Astrophysics Data System (ADS)

Araujo, M. T. De; Carneiro, J. W. De M.; Taranto, A. G.

The PCM/COSMO approach was employed to calculate the relative stability of radicals derived from the antimalarial artemisinin. The calculations were performed in polar (water) and apolar (THF) solvent at the density functional level [B3LYP/6-31g(d)]. Relative stabilities were calculated by means of isodesmic equations using artemisinin as reference. Replacement of oxygen atoms by CH2 unities was found to decrease the relative stability of the anionic radical intermediates. The degree of destabilization is reduced in the presence of solvent, being less in water than in THF. The dipole moment and the corresponding solvation free energies of these species modulate this effect. Derivatives with inverted stereochemistry are more stable than those with the artemisinin-like stereochemistry, although the solvent attenuates this stabilization effect. As was found in the in vacuo calculations, the radicals centered on carbon are always more stable than the corresponding radicals centered on oxygen.

Thermal stability study of a new guanidine suppressor for the next-generation caustic-side solvent extraction process

DOE PAGES

Hill, Talon G.; Ensor, Dale D.; Delmau, Lætitia Helene; ...

2016-02-06

Cesium stripping performance of thermally stressed solvent degrades slowly over time in batch tests of the Next Generation Caustic-Side Solvent Extraction (NGS) process. NGS is currently used at pilot scale at the Savannah River Site for the selective removal of cesium from high-level salt waste. Recently a new guanidine, N,N',N" -tris(3,7-dimethyloctyl)guanidine (TiDG), was chosen for use as the suppressor, a lipophilic organic base needed for stripping, and the present study was undertaken to address the question of its stability. The NGS process solvent was evaluated for a period of three months under a variety of temperature and storage conditions. Themore » performance of the solvent was tested at 30-day increments using a standard extraction, scrub, strip, and extraction (ES 2S 3E) sequence. Lastly, the results provide insight on the effects of storage and process conditions, the stripping behavior of TiDG, and the stability of the new solvent composition.« less

Thermal stability study of a new guanidine suppressor for the next-generation caustic-side solvent extraction process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hill, Talon G.; Ensor, Dale D.; Delmau, Lætitia Helene

Cesium stripping performance of thermally stressed solvent degrades slowly over time in batch tests of the Next Generation Caustic-Side Solvent Extraction (NGS) process. NGS is currently used at pilot scale at the Savannah River Site for the selective removal of cesium from high-level salt waste. Recently a new guanidine, N,N',N" -tris(3,7-dimethyloctyl)guanidine (TiDG), was chosen for use as the suppressor, a lipophilic organic base needed for stripping, and the present study was undertaken to address the question of its stability. The NGS process solvent was evaluated for a period of three months under a variety of temperature and storage conditions. Themore » performance of the solvent was tested at 30-day increments using a standard extraction, scrub, strip, and extraction (ES 2S 3E) sequence. Lastly, the results provide insight on the effects of storage and process conditions, the stripping behavior of TiDG, and the stability of the new solvent composition.« less

Application of natural deep eutectic solvents to the extraction of anthocyanins from Catharanthus roseus with high extractability and stability replacing conventional organic solvents.

PubMed

Dai, Yuntao; Rozema, Evelien; Verpoorte, Robert; Choi, Young Hae

2016-02-19

Natural deep eutectic solvents (NADES) have attracted a great deal of attention in recent times as promising green media. They are generally composed of neutral, acidic or basic compounds that form liquids of high viscosity when mixed in certain molar ratio. Despite their potential, viscosity and acid or basic nature of some ingredients may affect the extraction capacity and stabilizing ability of the target compounds. To investigate these effects, extraction with a series of NADES was employed for the analysis of anthocyanins in flower petals of Catharanthus roseus in combination with HPLC-DAD-based metabolic profiling. Along with the extraction yields of anthocyanins their stability in NADES was also studied. Multivariate data analysis indicates that the lactic acid-glucose (LGH), and 1,2-propanediol-choline chloride (PCH) NADES present a similar extraction power for anthocyanins as conventional organic solvents. Furthermore, among the NADES employed, LGH exhibits an at least three times higher stabilizing capacity for cyanidins than acidified ethanol, which facilitates their extraction and analysis process. Comparing NADES to the conventional organic solvents, in addition to their reduced environmental impact, they proved to provide higher stability for anthocyanins, and therefore have a great potential as possible alternatives to those organic solvents in health related areas such as food, pharmaceuticals and cosmetics. Copyright © 2016 Elsevier B.V. All rights reserved.

Lid opening and conformational stability of T1 Lipase is mediated by increasing chain length polar solvents

PubMed Central

Mohamad Ali, Mohd Shukuri; Salleh, Abu Bakar; Rahman, Raja Noor Zaliha Raja Abd; Normi, Yahaya M.; Mohd Shariff, Fairolniza

2017-01-01

The dynamics and conformational landscape of proteins in organic solvents are events of potential interest in nonaqueous process catalysis. Conformational changes, folding transitions, and stability often correspond to structural rearrangements that alter contacts between solvent molecules and amino acid residues. However, in nonaqueous enzymology, organic solvents limit stability and further application of proteins. In the present study, molecular dynamics (MD) of a thermostable Geobacillus zalihae T1 lipase was performed in different chain length polar organic solvents (methanol, ethanol, propanol, butanol, and pentanol) and water mixture systems to a concentration of 50%. On the basis of the MD results, the structural deviations of the backbone atoms elucidated the dynamic effects of water/organic solvent mixtures on the equilibrium state of the protein simulations in decreasing solvent polarity. The results show that the solvent mixture gives rise to deviations in enzyme structure from the native one simulated in water. The drop in the flexibility in H2O, MtOH, EtOH and PrOH simulation mixtures shows that greater motions of residues were influenced in BtOH and PtOH simulation mixtures. Comparing the root mean square fluctuations value with the accessible solvent area (SASA) for every residue showed an almost correspondingly high SASA value of residues to high flexibility and low SASA value to low flexibility. The study further revealed that the organic solvents influenced the formation of more hydrogen bonds in MtOH, EtOH and PrOH and thus, it is assumed that increased intraprotein hydrogen bonding is ultimately correlated to the stability of the protein. However, the solvent accessibility analysis showed that in all solvent systems, hydrophobic residues were exposed and polar residues tended to be buried away from the solvent. Distance variation of the tetrahedral intermediate packing of the active pocket was not conserved in organic solvent systems, which could lead to weaknesses in the catalytic H-bond network and most likely a drop in catalytic activity. The conformational variation of the lid domain caused by the solvent molecules influenced its gradual opening. Formation of additional hydrogen bonds and hydrophobic interactions indicates that the contribution of the cooperative network of interactions could retain the stability of the protein in some solvent systems. Time-correlated atomic motions were used to characterize the correlations between the motions of the atoms from atomic coordinates. The resulting cross-correlation map revealed that the organic solvent mixtures performed functional, concerted, correlated motions in regions of residues of the lid domain to other residues. These observations suggest that varying lengths of polar organic solvents play a significant role in introducing dynamic conformational diversity in proteins in a decreasing order of polarity. PMID:28533982

Anion-π aromatic neutral tweezers complexes: are they stable in polar solvents?

PubMed

Sánchez-Lozano, Marta; Otero, Nicolás; Hermida-Ramón, Jose M; Estévez, Carlos M; Mandado, Marcos

2011-03-17

The impact of the solvent environment on the stabilization of the complexes formed by fluorine (T-F) and cyanide (T-CN) substituted tweezers with halide anions has been investigated theoretically. The study was carried out using computational methodologies based on density functional theory (DFT) and symmetry adapted perturbation theory (SAPT). Interaction energies were obtained at the M05-2X/6-31+G* level. The obtained results show a large stability of the complexes in solvents with large dielectric constant and prove the suitability of these molecular tweezers as potential hosts for anion recognition in solution. A detailed analysis of the effects of the solvent on the electron withdrawing ability of the substituents and its influence on the complex stability has been performed. In particular, the interaction energy in solution was split up into intermonomer and solvent-complex terms. In turn, the intermonomer interaction energy was partitioned into electrostatic, exchange, and polarization terms. Polar resonance structures in T-CN complexes are favored by polar solvents, giving rise to a stabilization of the intermonomer interaction, the opposite is found for T-F complexes. The solvent-complex energy increases with the polarity of the solvent in T-CN complexes, nonetheless the energy reaches a maximum and then decreases slowly in T-F complexes. An electron density analysis was also performed before and after complexation, providing an explanation to the trends followed by the interaction energies and their different components in solution.

VP08R from Infectious Spleen and Kidney Necrosis Virus Is a Novel Component of the Virus-Mock Basement Membrane

PubMed Central

Xu, Xiaopeng; Yan, Muting; Wang, Rui; Lin, Ting; Tang, Junliang; Li, Chaozheng; Weng, Shaoping

2014-01-01

ABSTRACT Infectious spleen and kidney necrosis virus (ISKNV), the type species of the genus Megalocytivirus, family Iridoviridae, brings great harm to fish farming. In infected tissues, ISKNV infection is characterized by a unique phenomenon, in that the infected cells are attached by lymphatic endothelial cells (LECs), which are speculated to wall off the infected cells from host immune attack. A viral membrane protein, VP23R, binds and recruits the host nidogen-1 protein to construct a basement membrane (BM)-like structure, termed virus-mock basement membrane (VMBM), on the surface of infected cells to provide attaching sites for LECs. VMBMs do not contain collagen IV protein, which is essential for maintenance of BM integrity and functions. In this study, we identified the VP08R protein encoded by ISKNV. VP08R was predicted to be a secreted protein with a signal peptide but without a transmembrane domain. However, immunofluorescence assays demonstrated that VP08R is located on the plasma membrane of infected cells and shows an expression profile similar to that of VP23R. Coimmunoprecipitation showed that VP08R interacts with both VP23R and nidogen-1, indicating that VP08R is a component of VMBM and is present on the cell membrane by binding to VP23R. Through formation of intermolecular disulfide bonds, VP08R molecules self-organized into a multimer, which may play a role in the maintenance of VMBM integrity and stability. Moreover, the VP08R multimer was easily degraded when the ISKNV-infected cells were lysed, which may be a mechanism for VMBM disassembly when necessary to free LECs and release the mature virions. IMPORTANCE Infectious spleen and kidney necrosis virus (ISKNV; genus Megalocytivirus, family Iridovirus) is most harmful to cultured fishes. In tissues, the ISKNV-infected cells are attached by lymphatic endothelial cells (LECs), which are speculated to segregate the host immune system. A viral membrane protein, VP23R, binds and recruits the host nidogen-1 protein to construct virus-mock basement membranes (VMBMs) on the surface of infected cells to provide attaching sites for LECs. Although VMBMs lack the collagen IV network, which is an essential structural part of true BMs, VMBMs still show an intact structure. An ISKNV-encoded VP08R protein can self-assemble into a multimer and bind both VP23R and nidogen-1 to maintain the integrity and stability of VMBMs. On the basis of these facts, we redrew the putative schematic illustration of the VMBM structure. Our study suggests that the virus adopts a strategy to remodel the cellular matrix and may provide an important reference to elucidate BM functions and the mechanisms of lymphangiogenesis. PMID:24599992

The Carmat Bioprosthetic Total Artificial Heart Is Associated With Early Hemostatic Recovery and no Acquired von Willebrand Syndrome in Calves.

PubMed

Smadja, David M; Susen, Sophie; Rauch, Antoine; Cholley, Bernard; Latrémouille, Christian; Duveau, Daniel; Zilberstein, Luca; Méléard, Denis; Boughenou, Marie-Fazia; Belle, Eric Van; Gaussem, Pascale; Capel, Antoine; Jansen, Piet; Carpentier, Alain

2017-10-01

To determine hemostasis perturbations, including von Willebrand factor (VWF) multimers, after implantation of a new bioprosthetic and pulsatile total artificial heart (TAH). Preclinical study SETTING: Single-center biosurgical research laboratory. Female Charolais calves, 2-to-6 months old, weighing 102-to-122 kg. Surgical implantation of TAH through a mid-sternotomy approach. Four of 12 calves had a support duration of several days (4, 4, 8, and 10 days), allowing for the exploration of early steps of hemostasis parameters, including prothrombin time; coagulation factor levels (II, V, VII+X, and fibrinogen); and platelet count. Multimeric analysis of VWF was performed to detect a potential loss of high-molecular weight (HMW) multimers, as previously described for continuous flow rotary blood pumps. Despite the absence of anticoagulant treatment administered in the postoperative phase, no signs of coagulation activation were detected. Indeed, after an immediate postsurgery decrease of prothrombin time, platelet count, and coagulation factor levels, most parameters returned to baseline values. HMW multimers of VWF remained stable either after initiation or during days of support. Coagulation parameters and platelet count recovery in the postoperative phase of the Carmat TAH (Camat SA, Velizy Villacoublay Cedex, France) implantation in calves, in the absence of anticoagulant treatment and associated with the absence of decrease in HMW multimers of VWF, is in line with early hemocompatibility that is currently being validated in human clinical studies. Copyright © 2017 Elsevier Inc. All rights reserved.

A novel and organic solvent-free preparation of solid lipid nanoparticles using natural biopolymers as emulsifier and stabilizer.

PubMed

Xue, Jingyi; Wang, Taoran; Hu, Qiaobin; Zhou, Mingyong; Luo, Yangchao

2017-10-05

In this work, a new and novel organic solvent-free and synthetic surfactant-free method was reported to fabricate stable solid lipid nanoparticles (SLNs) from stearic acid, sodium caseinate (NaCas) and pectin, as well as water. Melted stearic acid was directly emulsified into an aqueous phase containing NaCas and pectin, followed by pH adjustment and thermal treatment to induce the formation of a compact and dense polymeric coating which stabilized SLNs. The preparation procedures and formulations were comprehensively optimized. The inter- and intra-molecular interactions among three ingredients were characterized by fluorescence and Fourier transform infrared spectroscopies. The stability of as-prepared SLNs was evaluated under simulated gastrointestinal conditions, and compared with traditional SLNs prepared with organic solvents. Our results revealed that the SLNs prepared from this organic solvent-free method had superior physicochemical properties over the traditional SLNs, including smaller size and better stability. Furthermore, redispersible SLNs powders were obtained by nano spray drying, but only the SLNs prepared by organic solvent-free method had sub-micron scale, uniform and spherical morphology. The organic solvent-free preparation method was proved to be a promising approach to prepare stable and uniform SLNs for potential oral delivery applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Microcalorimetric study of thermal unfolding of lysozyme in water/glycerol mixtures: An analysis by solvent exchange model

NASA Astrophysics Data System (ADS)

Spinozzi, Francesco; Ortore, Maria Grazia; Sinibaldi, Raffaele; Mariani, Paolo; Esposito, Alessandro; Cinelli, Stefania; Onori, Giuseppe

2008-07-01

Folded protein stabilization or destabilization induced by cosolvent in mixed aqueous solutions has been studied by differential scanning microcalorimetry and related to difference in preferential solvation of native and denatured states. In particular, the thermal denaturation of a model system formed by lysozyme dissolved in water in the presence of the stabilizing cosolvent glycerol has been considered. Transition temperatures and enthalpies, heat capacity, and standard free energy changes have been determined when applying a two-state denaturation model to microcalorimetric data. Thermodynamic parameters show an unexpected, not linear, trend as a function of solvent composition; in particular, the lysozyme thermodynamic stability shows a maximum centered at water molar fraction of about 0.6. Using a thermodynamic hydration model based on the exchange equilibrium between glycerol and water molecules from the protein solvation layer to the bulk, the contribution of protein-solvent interactions to the unfolding free energy and the changes of this contribution with solvent composition have been derived. The preferential solvation data indicate that lysozyme unfolding involves an increase in the solvation surface, with a small reduction of the protein-preferential hydration. Moreover, the derived changes in the excess solvation numbers at denaturation show that only few solvent molecules are responsible for the variation of lysozyme stability in relation to the solvent composition.

Effect of stearic acid modified HAp nanoparticles in different solvents on the properties of Pickering emulsions and HAp/PLLA composites.

PubMed

Zhang, Ming; Wang, Ai-Juan; Li, Jun-Ming; Song, Na

2017-10-01

Stearic acid (Sa) was used to modify the surface properties of hydroxyapatite (HAp) in different solvents (water, ethanol or dichloromethane(CH 2 Cl 2 )). Effect of different solvents on the properties of HAp particles (activation ratio, grafting ratio, chemical properties), emulsion properties (emulsion stability, emulsion type, droplet morphology) as well as the cured materials (morphology, average pore size) were studied. FT-IR and XPS results confirmed the interaction occurred between stearic acid and HAp particles. Stable O/W and W/O type Pickering emulsions were prepared using unmodified and Sa modified HAp nanoparticles respectively, which indicated a catastrophic inversion of the Pickering emulsion happened possibly because of the enhanced hydrophobicity of HAp particles after surface modification. Porous materials with different structures and pore sizes were obtained using Pickering emulsion as the template via in situ evaporation solvent method. The results indicated the microstructures of cured samples are different form each other when HAp was surface modified in different solvents. HAp particles fabricated using ethanol as solvent has higher activation ratio and grafting ratio. Pickering emulsion with higher stability and cured porous materials with uniform morphology were obtained compared with samples prepared using water and CH 2 Cl 2 as solvents. In conclusion, surface modification of HAp in different solvents played a very important role for its stabilized Pickering emulsion as well as the microstructure of cured samples. It is better to use ethanol as the solvent for Sa modified HAp particles, which could increase the stability of Pickering emulsion and obtain cured samples with uniform pore size. Copyright © 2017 Elsevier B.V. All rights reserved.

Thermodynamic study of complex formation between Ce3+ and cryptand 222 in some binary mixed nonaqueous solvents

NASA Astrophysics Data System (ADS)

Rounaghi, G. H.; Dolatshahi, S.; Tarahomi, S.

2014-12-01

The stoichiometry, stability and the thermodynamic parameters of complex formation between cerium(III) cation and cryptand 222 (4,7,13,16,21,24-hexaoxa-1,10-diazabycyclo[8.8.8]-hexacosane) were studied by conductometric titration method in some binary solvent mixtures of dimethylformamide (DMF), 1,2-dichloroethane (DCE), ethyl acetate (EtOAc) and methyl acetate (MeOAc) with methanol (MeOH), at 288, 298, 308, and 318 K. A model based on 1: 1 stoichiometry has been used to analyze the conductivity data. The data have been fitted according to a non-linear least-squares analysis that provide the stability constant, K f, for the cation-ligand inclusion complex. The results revealed that the stability order of [Ce(cryptand 222)]3+ complex changes with the nature and composition of the solvent system. A non-linear relationship was observed between the stability constant (log K f) of [Ce(cryptand 222)]3+ complex versus the composition of the binary mixed solvent. Standard thermodynamic values were obtained from temperature dependence of the stability constant of the complex, show that the studied complexation process is mainly entropy governed and are influenced by the nature and composition of the binary mixed solvent solutions.

Method for determining asphaltene stability of a hydrocarbon-containing material

DOEpatents

Schabron, John F; Rovani, Jr., Joseph F

2013-02-05

A method for determining asphaltene stability in a hydrocarbon-containing material having solvated asphaltenes therein is disclosed. In at least one embodiment, it involves the steps of: (a) precipitating an amount of the asphaltenes from a liquid sample of the hydrocarbon-containing material with an alkane mobile phase solvent in a column; (b) dissolving a first amount and a second amount of the precipitated asphaltenes by changing the alkane mobile phase solvent to a final mobile phase solvent having a solubility parameter that is higher than the alkane mobile phase solvent; (c) monitoring the concentration of eluted fractions from the column; (d) creating a solubility profile of the dissolved asphaltenes in the hydrocarbon-containing material; and (e) determining one or more asphaltene stability parameters of the hydrocarbon-containing material.

Activity and conformation of lysozyme in molecular solvents, protic ionic liquids (PILs) and salt-water systems.

PubMed

Wijaya, Emmy C; Separovic, Frances; Drummond, Calum J; Greaves, Tamar L

2016-09-21

Improving protein stabilisation is important for the further development of many applications in the pharmaceutical, specialty chemical, consumer product and agricultural sectors. However, protein stabilization is highly dependent on the solvent environment and, hence, it is very complex to tailor protein-solvent combinations for stable protein maintenance. Understanding solvent features that govern protein stabilization will enable selection or design of suitable media with favourable solution environments to retain protein native conformation. In this work the structural conformation and activity of lysozyme in 29 solvent systems were investigated to determine the role of various solvent features on the stability of the enzyme. The solvent systems consisted of 19 low molecular weight polar solvents and 4 protic ionic liquids (PILs), both at different water content levels, and 6 aqueous salt solutions. Small angle X-ray scattering, Fourier transform infrared spectroscopy and UV-vis spectroscopy were used to investigate the tertiary and secondary structure of lysozyme along with the corresponding activity in various solvation systems. At low non-aqueous solvent concentrations (high water content), the presence of solvents and salts generally maintained lysozyme in its native structure and enhanced its activity. Due to the presence of a net surface charge on lysozyme, electrostatic interactions in PIL-water systems and salt solutions enhanced lysozyme activity more than the specific hydrogen-bond interactions present in non-ionic molecular solvents. At higher solvent concentrations (lower water content), solvents with a propensity to exhibit the solvophobic effect, analogous to the hydrophobic effect in water, retained lysozyme native conformation and activity. This solvophobic effect was observed particularly for solvents which contained hydroxyl moieties. Preferential solvophobic effects along with bulky chemical structures were postulated to result in less competition with water at the specific hydration layer around the protein, thus reducing protein-solvent interactions and retaining lysozyme's native conformation. The structure-property links established in this study are considered to be applicable to other proteins.

Large-scale detection of antigen-specific T cells using peptide-MHC-I multimers labeled with DNA barcodes.

PubMed

Bentzen, Amalie Kai; Marquard, Andrea Marion; Lyngaa, Rikke; Saini, Sunil Kumar; Ramskov, Sofie; Donia, Marco; Such, Lina; Furness, Andrew J S; McGranahan, Nicholas; Rosenthal, Rachel; Straten, Per Thor; Szallasi, Zoltan; Svane, Inge Marie; Swanton, Charles; Quezada, Sergio A; Jakobsen, Søren Nyboe; Eklund, Aron Charles; Hadrup, Sine Reker

2016-10-01

Identification of the peptides recognized by individual T cells is important for understanding and treating immune-related diseases. Current cytometry-based approaches are limited to the simultaneous screening of 10-100 distinct T-cell specificities in one sample. Here we use peptide-major histocompatibility complex (MHC) multimers labeled with individual DNA barcodes to screen >1,000 peptide specificities in a single sample, and detect low-frequency CD8 T cells specific for virus- or cancer-restricted antigens. When analyzing T-cell recognition of shared melanoma antigens before and after adoptive cell therapy in melanoma patients, we observe a greater number of melanoma-specific T-cell populations compared with cytometry-based approaches. Furthermore, we detect neoepitope-specific T cells in tumor-infiltrating lymphocytes and peripheral blood from patients with non-small cell lung cancer. Barcode-labeled pMHC multimers enable the combination of functional T-cell analysis with large-scale epitope recognition profiling for the characterization of T-cell recognition in various diseases, including in small clinical samples.

Enhanced Detection of Antigen-Specific CD4+ T Cells Using Altered Peptide Flanking Residue Peptide–MHC Class II Multimers

PubMed Central

Holland, Christopher J.; Dolton, Garry; Scurr, Martin; Ladell, Kristin; Schauenburg, Andrea J.; Miners, Kelly; Madura, Florian; Sewell, Andrew K.; Price, David A.

2015-01-01

Fluorochrome-conjugated peptide–MHC (pMHC) class I multimers are staple components of the immunologist’s toolbox, enabling reliable quantification and analysis of Ag-specific CD8+ T cells irrespective of functional outputs. In contrast, widespread use of the equivalent pMHC class II (pMHC-II) reagents has been hindered by intrinsically weaker TCR affinities for pMHC-II, a lack of cooperative binding between the TCR and CD4 coreceptor, and a low frequency of Ag-specific CD4+ T cell populations in the peripheral blood. In this study, we show that peptide flanking regions, extending beyond the central nonamer core of MHC-II–bound peptides, can enhance TCR–pMHC-II binding and T cell activation without loss of specificity. Consistent with these findings, pMHC-II multimers incorporating peptide flanking residue modifications proved superior for the ex vivo detection, characterization, and manipulation of Ag-specific CD4+ T cells, highlighting an unappreciated feature of TCR–pMHC-II interactions. PMID:26553072

Study of complexation process between 4'-nitrobenzo-15-crown-5 and yttrium(III) cation in binary mixed non-aqueous solvents using conductometric method

NASA Astrophysics Data System (ADS)

Habibi, N.; Rounaghi, G. H.; Mohajeri, M.

2012-12-01

The complexation reaction of macrocyclic ligand (4'-nitrobenzo-15C5) with Y3+ cation was studied in acetonitrile-methanol (AN-MeOH), acetonitrile-ethanol (AN-EtOH), acetonitrile-dimethylformamide (AN-DMF) and ethylacetate-methanol (EtOAc-MeOH) binary mixtures at different temperatures using conductometry method. The conductivity data show that in all solvent systems, the stoichiometry of the complex formed between 4'-nitrobenzo-15C5 and Y3+ cation is 1: 1 (ML). The stability order of (4'-nitrobenzo-15C5). Y3+ complex in pure non-aqueous solvents at 25°C was found to be: EtOAc > EtOH > AN ≈ DMF > MeOH, and in the case of most compositions of the binary mixed solvents at 25°C it was: AN≈MeOH ≈ AN-EtOH > AN-DMF > EtOAc-MeOH. But the results indicate that the sequence of the stability of the complex in the binary mixed solutions changes with temperature. A non-linear behavior was observed for changes of log K f of (4'-nitrobenzo-15C5 · Y3+) complex versus the composition of the binary mixed solvents, which was explained in terms of solvent-solvent interactions and also the hetero-selective solvation of the species involved in the complexation reaction. The values of thermodynamic parameters (Δ H {c/ℴ} and Δ S {c/ℴ}) for formation of the complex were obtained from temperature dependent of the stability constant using the van't Hoff plots. The results represent that in most cases, the complex is both enthalpy and entropy stabilized and the values and also the sign of thermodynamic parameters are influenced by the nature and composition of the mixed solvents.

Mechanism of protein precipitation and stabilization by co-solvents

NASA Astrophysics Data System (ADS)

Timasheff, Serge N.; Arakawa, Tsutomu

1988-07-01

The interactions between proteins and a number of substances which, when present at high concentration, stabilize or precipitate proteins, have been analyzed in terms of the preferential interactions of these co-solvents with proteins. In all cases, stabilization or precipitation was accompanied by preferential exclusion of the co-solvent from the immediate domain of the protein, i.e., preferential hydration of the protein. This means that addition of the co-solvent to the aqueous protein solution increased the chemical potentials of both components. The thermodynamic interaction parameters derived from such data make it possible to calculate the salting out constant, Ks, as well as to construct a phase isotherm for any given solvent mixture which indicates the limiting protein solubility. The salting-out effect can be decomposed into contributions from non-specific preferential exclusion and specific binding of the ligand to the protein, the balance leading to solubilization or precipitation. In reactions, such as denaturation, the effect of co-solvent on the reaction depends on the difference in the preferential interactions of the two end states of the protein. Principal sources of preferential exclusion have been identified as steric exclusion, increase of the surface tension of water by the co-solvent, repulsion by charged loci on the protein and solvophobicity.

Functionalization of Cadmium Selenide Quantum Dots with Poly(ethylene glycol): Ligand Exchange, Surface Coverage, and Dispersion Stability.

PubMed

Wenger, Whitney Nowak; Bates, Frank S; Aydil, Eray S

2017-08-22

Semiconductor quantum dots synthesized using rapid mixing of precursors by injection into a hot solution of solvents and surfactants have surface ligands that sterically stabilize the dispersions in nonpolar solvents. Often, these ligands are exchanged to disperse the quantum dots in polar solvents, but quantitative studies of quantum dot surfaces before and after ligand exchange are scarce. We studied exchanging trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) ligands on as-synthesized CdSe quantum dots dispersed in hexane with a 2000 g/mol thiolated poly(ethylene glycol) (PEG) polymer. Using infrared spectroscopy we quantify the absolute surface concentration of TOP/TOPO and PEG ligands per unit area before and after ligand exchange. While 50-85% of the TOP/TOPO ligands are removed upon ligand exchange, only a few are replaced with PEG. Surprisingly, the remaining TOP/TOPO ligands outnumber the PEG ligands, but these few PEG ligands are sufficient to disperse the quantum dots in polar solvents such as chloroform, tetrahydrofuran, and water. Moreover, as-synthesized quantum dots once easily dispersed in hexane are no longer dispersible in nonpolar solvents after ligand exchange. A subtle coverage-dependent balance between attractive PEG-solvent interactions and repulsive TOP/TOPO-solvent interactions determines the dispersion stability.

AN INVESTIGATION OF THE CHEMICAL STABILITY OF ARSENOSUGARS IN BASIC ENVIRONMENTS USING IC-ICP-MS AND IC-ESI-MS/MS

EPA Science Inventory

This paper evaluates the chemical stability of four arsenosugars using tetramethylammonium hydroxide (TMAOH) as an extraction solvent. This solvent was chosen because of the near quantitative removal of these arsenicals from difficult to extract seafood (oysters and shellfish). ...

Next Generation Solvent Performance in the Modular Caustic Side Solvent Extraction Process - 15495

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Tara E.; Scherman, Carl; Martin, David

Changes to the Modular Caustic Side Solvent Extraction Unit (MCU) flow-sheet were implemented in the facility. Implementation included changing the scrub and strip chemicals and concentrations, modifying the O/A ratios for the strip, scrub, and extraction contactor banks, and blending the current BoBCalixC6 extractant-based solvent in MCU with clean MaxCalix extractant-based solvent. During the successful demonstration period, the MCU process was subject to rigorous oversight to ensure hydraulic stability and chemical/radionuclide analysis of the key process tanks (caustic wash tank, solvent hold tank, strip effluent hold tank, and decontaminated salt solution hold tank) to evaluate solvent carryover to downstream facilitiesmore » and the effectiveness of cesium removal from the liquid salt waste. Results indicated the extraction of cesium was significantly more effective with an average Decontamination Factor (DF) of 1,129 (range was 107 to 1,824) and that stripping was effective. The contactor hydraulic performance was stable and satisfactory, as indicated by contactor vibration, contactor rotational speed, and flow stability; all of which remained at or near target values. Furthermore, the Solvent Hold Tank (SHT) level and specific gravity was as expected, indicating that solvent integrity and organic hydraulic stability were maintained. The coalescer performances were in the range of processing results under the BOBCalixC6 flow sheet, indicating negligible adverse impact of NGS deployment. After the Demonstration period, MCU began processing via routine operations. Results to date reiterate the enhanced cesium extraction and stripping capability of the Next Generation Solvent (NGS) flow sheet. This paper presents process performance results of the NGS Demonstration and continued operations of MCU utilizing the blended BobCalixC6-MaxCalix solvent under the NGS flowsheet.« less

DYSREGULATION OF MATERNAL SERUM ADIPONECTIN IN PRETERM LABOR

PubMed Central

Mazaki-Tovi, Shali; Romero, Roberto; Vaisbuch, Edi; Erez, Offer; Mittal, Pooja; Chaiworapongsa, Tinnakorn; Kim, Sun Kwon; Pacora, Percy; Yeo, Lami; Gotsch, Francesca; Dong, Zhong; Nhan-Chang, Chia-Ling; Jodicke, Cristiano; Yoon, Bo Hyun; Hassan, Sonia S.; Kusanovic, Juan Pedro

2013-01-01

Objective Intra-amniotic and systemic infection/inflammation have been causally linked to preterm parturition and fetal injury. An emerging theme is that adipose tissue can orchestrate a metabolic response to insults, but also an inflammatory response via the production of adipocytokines, and that these two phenomenon are interrelated. Adiponectin, an insulin-sensitizing, anti-inflammatory adipocytokine, circulates in multimeric complexes including low-molecular-weight (LMW) trimers, medium-molecular-weight (MMW) hexamers and high-molecular-weight (HMW) isoforms. Each of these complexes can exert differential biological effects. The aim of this study was to determine whether spontaneous preterm labor (PTL) with intact membranes and intra-amniotic infection/inflammation (IAI) is associated with changes in maternal serum circulating adiponectin multimers. Study design This cross-sectional study included patients in the following groups: 1) normal pregnant women (n=158); 2) patients with an episode of preterm labor and intact membranes without IAI who delivered at term (n=41); 3) preterm labor without IAI who delivered preterm (n=27); and 4) preterm labor with IAI who delivered preterm (n=36). Serum adiponectin multimers (total, HMW, MMW and LMW) concentrations were determined by ELISA. Non-parametric statistics were used for analyses. Results 1) Preterm labor leading to preterm delivery or an episode of preterm labor which does not lead to preterm delivery, was associated with a lower median maternal serum concentration of total and HMW adiponectin, a lower median HMW/total adiponectin ratio, and a higher median LMW/total adiponectin ratio than normal pregnancy; 2) among patients with preterm labor, those with IAI had the lowest median concentration of total and HMW adiponectin, as well as the lowest median HMW/total adiponectin ratio; 3) The changes in maternal adiponectin and adiponectin multimers remained significant after adjusting for confounding factors such as maternal age, BMI, gestational age at sampling, and parity. Conclusion 1) Preterm labor is characterized by a change in the profile of adiponectin multimers concentrations and their relative isoforms. These changes were observed in patients with an episode of preterm labor not leading to preterm delivery, in patients with intra-amniotic inflammation, or in those without evidence of intra-amniotic inflammation; 2) The changes in adiponectin multimer concentrations reported in preterm labor are different from those previously reported in spontaneous labor at term, suggesting that there is a fundamental difference between preterm labor and labor at term; 3) The findings reported herein, provide the first evidence for the participation of adiponectin multimer in preterm parturition. We propose that adiponectins and adipokines in general provide a mechanism to organize the metabolic demands generated by the process of preterm parturition regardless of the nature of the insult (intra-amniotic inflammation or not). PMID:19579094

Laboratory diagnosis of von Willebrand disease type 1/2E (2A subtype IIE), type 1 Vicenza and mild type 1 caused by mutations in the D3, D4, B1-B3 and C1-C2 domains of the von Willebrand factor gene. Role of von Willebrand factor multimers and the von Willebrand factor propeptide/antigen ratio.

PubMed

Gadisseur, Alain; Berneman, Zwi; Schroyens, Wilfried; Michiels, Jan Jacques

2009-01-01

Autosomal dominant von Willebrand disease (VWD) type 1/2E is a quantitative/qualitative defect in the von Willebrand factor (VWF) caused by heterozygous cysteine and non-cysteine mutations in the D3 domain of the VWF gene and results in a secretion-multimerization-clearance defect in mutant VWF with the loss of large VWF multimers not due to proteolysis. The multimers of patients with dominant VWD type 1/2E due to mutations in the D3 domain show an aberrant triplet structure with lack of outer bands but with pronounced inner bands of the triplet structure combined with a relative decrease in large multimers reflecting heterozygosity for multimerization defects. There is a good response to desmopressin (DDAVP) followed by rapid clearance of VWF:antigen (Ag), factor VIII coagulant activity (FVIII:C) and VWF:ristocetin cofactor activity (RCo) as the main cause of VWD type 1 or 2 with typical 2E multimeric pattern (VWD type 1/2E). Cysteine mutations in the D3 domains (C1130, C1149 and C1190) show pronounced features of VWD 1/2E with the relative loss of large and relative increase in small VWF multimers with abnormal triplet structure in heterozygotes. Such abnormalities are less pronounced in patients with a milder form of VWD type 1 due to non-cysteine mutations W1144G, T1156M and W1120S in the D3 domain. VWD type 1 Vicenza is caused by the R1205H mutation in the D3 domain and characterized by equally low levels of FVIII:C, VWF:Ag and VWF:RCo. The response to DDAVP in VWD Vicenza is good for FVIII:C, VWF:Ag and VWF:RCo, which is followed by a rapid clearance in less than a few hours of FVIII:C and VWF parameters. The ratios for FVIII:C/VWF:Ag, VWF:RCo/Ag and VWF:CB/Ag remain normal before and after DDAVP indicating that VWD Vicenza clearly differs from VWD type 1, 1/2E and 2M. A new set of missense mutations in D4, B1-B3 and C1-C2 domains has been discovered as the cause of a mild VWD type 1 secretion defect with normal VWF multimers or smeary VWF multimeric pattern. Cysteine mutations in exons 38, 40, 42 and 43 (D4, B1-B3 and C1 domain), show smeary patterns (either smf or sm), with the presence of large VWF multimers and a laboratory phenotype of mild VWD type 1 with variable penetrance of bleeding manifestations. Recent studies showed that the ratio of VWF propeptide (pp) to VWF:Ag can be used to predict a shorter than normal half-life for VWF:Ag. There is a strong inverse correlation between rapid clearance of VWF:Ag after DDAVP and increased VWFpp/Ag ratios >10 in VWD type 1 Vicenza, and >2 in VWD type 1/2E but normal or slightly increased (1-<2) VWFpp/Ag ratios in mild-type VWD due to nonsense or missense mutations in the D1, D2, D4, B and C domains. Copyright (c) 2009 S. Karger AG, Basel.

In situ crosslinking of surface-initiated ring opening metathesis polymerization of polynorbornene for improved stability.

PubMed

Fursule, Ishan A; Abtahi, Ashkan; Watkins, Charles B; Graham, Kenneth R; Berron, Brad J

2018-01-15

In situ crosslinking is expected to increase the solvent stability of coatings formed by surface-initiated ring opening metathesis polymerization (SI ROMP). Solvent-associated degradation limits the utility of SI ROMP coatings. SI ROMP coatings have a unique capacity for post-functionalization through reaction of the unsaturated site on the polymer backbone. Any post-reaction scheme which requires a liquid solvent has the potential to degrade the coating and lower the thickness of the resulting film. We designed a macromolecular crosslinking group based on PEG dinorbornene. The PEG length is tailored to the expected mean chain to chain distance during surface-initiated polymerization. This crosslinking macromer is randomly copolymerized with norbornene through SI ROMP on a gold coated substrate. The solvent stability of polynorbornene coatings with and without PEG dinorbornene is quantitatively determined, and the mechanism of degradation is further supported through XPS and AFM analyses. The addition of the 0.25mol% PEG dinorbornene significantly increases the solvent stability of the SI ROMP coatings. The crosslinker presence in the more stable films is supported with observable PEG absorbances by FTIR and an increase in contact angle hysteresis when compared to non-crosslinked coatings. The oxidation of the SI ROMP coatings is supported by the observation of carbonyl oxygen in the polynorbornene coatings. The rapid loss of the non-crosslinked SI ROMP coating corresponds to nanoscale pitting across the surface and micron-scale regions of widespread film loss. The crosslinked coatings have uniform nanoscale pitting, but the crosslinked films show no evidence of micron-scale film damage. In all, the incorporation of minimal crosslinking content is a simple strategy for improving the solvent stability of SI ROMP coatings. Copyright © 2017 Elsevier Inc. All rights reserved.

Development of a Gas Chromatography/Mass Spectrometry Method for the Analysis of the Solvent Stabilizer 1,4-Dioxane in Drinking Water

EPA Science Inventory

The solvent stabilizer 1,4-dioxane was named to the latest draft Drinking Water Contaminant Candidate List (CCL3) in February 2008 by the United States Environmental Protection Agency (USEPA). To collect occurrence data under the Unregulated Contaminant Monitoring Regulation (UC...

Comparative theoretical study of the structures and stabilities of four typical gadolinium carboxylates in different scintillator solvents.

PubMed

Huang, Pin-Wen

2016-03-01

The structural properties and stabilities of four typical gadolinium carboxylates (Gd-CBX) in toluene, linear alkyl benzene (LAB), and phenyl xylyl ethane (PXE) solvents were theoretically studied using density functional theory (DFT/B3LYP with the basis sets 6-311G(d) and MWB54) and the polarizable continuum model (PCM). The average Gd-ligand interaction energies (E int, corrected for dispersion) and the values of the energy gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital (ΔHL) for the gadolinium complexes were calculated to compare the relative stabilities of the four Gd-CBX molecules in the three liquid scintillator solvents. According to the calculations, the values of E int and ΔHL for Gd-CBX in LAB are larger than the corresponding values in PXE and toluene. Gd-CBX may therefore be more compatible with LAB than with PXE and toluene. It was also found that, in the three scintillator solvents, the stabilities of the four Gd-CBX molecules increase in the order Gd-2EHA < Gd-2MVA < Gd-pivalate < Gd-TMHA.

Evidence that the rabbit proton-peptide co-transporter PepT1 is a multimer when expressed in Xenopus laevis oocytes.

PubMed

Panitsas, Konstantinos-E; Boyd, C A R; Meredith, David

2006-04-01

To test whether the rabbit proton-coupled peptide transporter PepT1 is a multimer, we have employed a combination of transport assays, luminometry and site-directed mutagenesis. A functional epitope-tagged PepT1 construct (PepT1-FLAG) was co-expressed in Xenopus laevis oocytes with a non-functional but normally trafficked mutant form of the same transporter (W294F-PepT1). The amount of PepT1-FLAG cRNA injected into the oocytes was kept constant, while the amount of W294F-PepT1 cRNA was increased over the mole fraction range of 0 to 1. The uptake of [(3)H]-D: -Phe-L: -Gln into the oocytes was measured at pH(out) 5.5, and the surface expression of PepT1-FLAG was quantified by luminometry. As the mole fraction of injected W294F-PepT1 increased, the uptake of D: -Phe-L: -Gln decreased. This occurred despite the surface expression of PepT1-FLAG remaining constant, and so we can conclude that PepT1 must be a multimer. Assuming that PepT1 acts as a homomultimer, the best fit for the modelling suggests that PepT1 could be a tetramer, with a minimum requirement of two functional subunits in each protein complex. Western blotting also showed the presence of higher-order complexes of PepT1-FLAG in oocyte membranes. It should be noted that we cannot formally exclude the possibility that PepT1 interacts with unidentified Xenopus protein(s). The finding that PepT1 is a multimer has important implications for the molecular modelling of this protein.

Native multimer analysis of plasma and platelet von Willebrand factor compared to denaturing separation: implication for the interpretation of satellite bands.

PubMed

Hohenstein, Kurt; Griesmacher, Andrea; Weigel, Günter; Golderer, Georg; Ott, Helmut Werner

2011-06-01

Blue native electrophoresis (BNE) was applied to analyze the von Willebrand factor (vWF) multimers in their native state and to present a methodology to perform blue native electrophoresis on human plasma proteins, which has not been done before. The major difference between this method and the commonly used SDS-agarose gel electrophoresis is the lack of satellite bands in the high-resolution native gel. To further analyze this phenomenon, a second dimension was performed under denaturing conditions. Thereby, we obtained a pattern in which each protein sub-unit from the first dimension dissociates into three distinct sub-bands. These bands confirm the triplet structure, which consists of an intermediate band and two satellite bands. By introducing the second dimension, our novel method separates the triplet structure into a higher resolution than the commonly used SDS-agarose gel electrophoresis does. This helps considerably in the classification of ambiguous von Willebrand's disease subtypes. In addition, our method has the additional advantage of being able to resolve the triplet structure of platelet vWF multimers, which has not been identified previously through conventional SDS-agarose electrophoresis multimer analysis. This potential enables us to compare the triplet structure from platelet and plasmatic vWF, and may help to find out whether structural abnormalities concern the vWF molecule in the platelet itself, or whether they are due to the physiological processing of vWF shed into circulation. Owing to its resolution and sensitivity, this native separation technique offers a promising tool for the analysis and detection of von Willebrand disorder, and for the classification of von Willebrand's disease subtypes. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The effect of solvents on the stabilities (color and Fe) of anthocyanin isolated from the red-color-melinjo peels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tarmizi, Ermiziar, E-mail: uph-ermi@yahoo.com, E-mail: ermitarmizi@gmail.com; Saragih, Raskita, E-mail: raskitasaragih@yahoo.com; Lalasari, Latifa Hanum, E-mail: ifa-sari@yahoo.com, E-mail: lati003@lipi.go.id

Anthocyanin from the red-color-melinjo peels could be isolated using a polar solvent (ethanol) [ermiziar, 2010]. The amount of hydrocarbons in the structure of anthocyanin might cause that anthocyanin could be isolated using a non polar solvent. The purpose of research is to isolate anthocyanin using non polar solvents (hexane and petroleum ether) with maceration steps for 24 hours and separate solvents using rotary evaporator equipment. The stability of anthocyanin could be observed every week (1,2,3 and 4 weeks) in various environmental conditions (with or without light in refrigerator and open or closed storage). The characterization of anthocyanin was analyzed withmore » visual (physic photo) and or using equipments such as Fourier Transform Infrared Spectroscopy (FTIR) for determining functional groups, Ultraviolet–Visible Spectroscopy (UV/Vis) with 500-550 nm wavelengths for deciding absorption of anthocyanin and atomic absorption spectroscopy (AAS) for analyzing Fe element. The result showed that anthocyanin isolation with hexane solvent has yield higher than petroleum eter solvent. From the results of physic observation for 4 weeks looked that there are changing colors of samples significant after 3 and 4 weeks in cooler with or without light. The stability of anthocyanin color was the best on the storage time until 2 weeks using hexane solvent in refrigerator and closed condition that it has absorption of 0.6740 with 500 nm wavelengths and Fe concentration 6.29 ppm.« less

Molecular dynamics studies of the 3D structure and planar ligand binding of a quadruplex dimer.

PubMed

Li, Ming-Hui; Luo, Quan; Xue, Xiang-Gui; Li, Ze-Sheng

2011-03-01

G-rich sequences can fold into a four-stranded structure called a G-quadruplex, and sequences with short loops are able to aggregate to form stable quadruplex multimers. Few studies have characterized the properties of this variety of quadruplex multimers. Using molecular modeling and molecular dynamics simulations, the present study investigated a dimeric G-quadruplex structure formed from a simple sequence of d(GGGTGGGTGGGTGGGT) (G1), and its interactions with a planar ligand of a perylene derivative (Tel03). A series of analytical methods, including free energy calculations and principal components analysis (PCA), was used. The results show that a dimer structure with stacked parallel monomer structures is maintained well during the entire simulation. Tel03 can bind to the dimer efficiently through end stacking, and the binding mode of the ligand stacked with the 3'-terminal thymine base is most favorable. PCA showed that the dominant motions in the free dimer occur on the loop regions, and the presence of the ligand reduces the flexibility of the loops. Our investigation will assist in understanding the geometric structure of stacked G-quadruplex multimers and may be helpful as a platform for rational drug design.

Recent advances in exploiting ionic liquids for biomolecules: Solubility, stability and applications.

PubMed

Sivapragasam, Magaret; Moniruzzaman, Muhammad; Goto, Masahiro

2016-08-01

The technological utility of biomolecules (e.g. proteins, enzymes and DNA) can be significantly enhanced by combining them with ionic liquids (ILs) - potentially attractive "green" and "designer" solvents - rather than using in conventional organic solvents or water. In recent years, ILs have been used as solvents, cosolvents, and reagents for biocatalysis, biotransformation, protein preservation and stabilization, DNA solubilization and stabilization, and other biomolecule-based applications. Using ILs can dramatically enhance the structural and chemical stability of proteins, DNA, and enzymes. This article reviews the recent technological developments of ILs in protein-, enzyme-, and DNA-based applications. We discuss the different routes to increase biomolecule stability and activity in ILs, and the design of biomolecule-friendly ILs that can dissolve biomolecules with minimum alteration to their structure. This information will be helpful to design IL-based processes in biotechnology and the biological sciences that can serve as novel and selective processes for enzymatic reactions, protein and DNA stability, and other biomolecule-based applications. Copyright © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Contribution of Charged Groups to the Enthalpic Stabilization of the Folded States of Globular Proteins

PubMed Central

Dadarlat, Voichita M.; Post, Carol Beth

2016-01-01

In this paper we use the results from all atom MD simulations of proteins and peptides to assess individual contribution of charged atomic groups to the enthalpic stability of the native state of globular proteins and investigate how the distribution of charged atomic groups in terms of solvent accessibility relates to protein enthalpic stability. The contributions of charged groups is calculated using a comparison of nonbonded interaction energy terms from equilibrium simulations of charged amino acid dipeptides in water (the “unfolded state”) and charged amino acids in globular proteins (the “folded state”). Contrary to expectation, the analysis shows that many buried, charged atomic groups contribute favorably to protein enthalpic stability. The strongest enthalpic contributions favoring the folded state come from the carboxylate (COO−) groups of either Glu or Asp. The contributions from Arg guanidinium groups are generally somewhat stabilizing, while NH3+ groups from Lys contribute little toward stabilizing the folded state. The average enthalpic gain due to the transfer of a methyl group in an apolar amino acid from solution to the protein interior is described for comparison. Notably, charged groups that are less exposed to solvent contribute more favorably to protein native-state enthalpic stability than charged groups that are solvent exposed. While solvent reorganization/release has favorable contributions to folding for all charged atomic groups, the variation in folded state stability among proteins comes mainly from the change in the nonbonded interaction energy of charged groups between the unfolded and folded states. A key outcome is that the calculated enthalpic stabilization is found to be inversely proportional to the excess charge density on the surface, in support of an hypothesis proposed previously. PMID:18303881

Enzymes from solvent-tolerant microbes: useful biocatalysts for non-aqueous enzymology.

PubMed

Gupta, Anshu; Khare, S K

2009-01-01

Solvent-tolerant microbes are a newly emerging class that possesses the unique ability to thrive in the presence of organic solvents. Their enzymes adapted to mediate cellular and metabolic processes in a solvent-rich environment and are logically stable in the presence of organic solvents. Enzyme catalysis in non-aqueous/low-water media is finding increasing applications for the synthesis of industrially important products, namely peptides, esters, and other trans-esterification products. Solvent stability, however, remains a prerequisite for employing enzymes in non-aqueous systems. Enzymes, in general, get inactivated or give very low rates of reaction in non-aqueous media. Thus, early efforts, and even some recent ones, have aimed at stabilization of enzymes in organic media by immobilization, surface modifications, mutagenesis, and protein engineering. Enzymes from solvent-tolerant microbes appear to be the choicest source for studying solvent-stable enzymes because of their unique ability to survive in the presence of a range of organic solvents. These bacteria circumvent the solvent's toxic effects by virtue of various adaptations, e.g. at the level of the cytoplasmic membrane, by degradation and transformation of solvents, and by active excretion of solvents. The recent screening of these exotic microbes has generated some naturally solvent-stable proteases, lipases, cholesterol oxidase, cholesterol esterase, cyclodextrin glucanotransferase, and other important enzymes. The unique properties of these novel biocatalysts have great potential for applications in non-aqueous enzymology for a range of industrial processes.

Stable colloids in molten inorganic salts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Hao; Dasbiswas, Kinjal; Ludwig, Nicholas B.

2017-02-15

A colloidal solution is a homogeneous dispersion of particles or droplets of one phase (solute) in a second, typically liquid, phase (solvent). Colloids are ubiquitous in biological, chemical and technological processes1, 2, homogenizing highly dissimilar constituents. To stabilize a colloidal system against coalescence and aggregation, the surface of each solute particle is engineered to impose repulsive forces strong enough to overpower van der Waals attraction and keep the particles separated from each other2. Electrostatic stabilization3, 4 of charged solutes works well in solvents with high dielectric constants, such as water (dielectric constant of 80). In contrast, colloidal stabilization in solventsmore » with low polarity, such as hexane (dielectric constant of about 2), can be achieved by decorating the surface of each particle of the solute with molecules (surfactants) containing flexible, brush-like chains2, 5. Here we report a class of colloidal systems in which solute particles (including metals, semiconductors and magnetic materials) form stable colloids in various molten inorganic salts. The stability of such colloids cannot be explained by traditional electrostatic and steric mechanisms. Screening of many solute–solvent combinations shows that colloidal stability can be traced to the strength of chemical bonding at the solute–solvent interface. Theoretical analysis and molecular dynamics modelling suggest that a layer of surface-bound solvent ions produces long-ranged charge-density oscillations in the molten salt around solute particles, preventing their aggregation. Colloids composed of inorganic particles in inorganic melts offer opportunities for introducing colloidal techniques to solid-state science and engineering applications.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devadoss, C.; Fessenden, R.W.

The transient that is produced in the quenching of triplet benzophenone by 1,4-diazabicyclo(2.2.2)octane (DABCO) has been examined by use of nano- and picosecond laser photolysis. The initial step in all solvents, both polar and nonpolar, is electron transfer to form a triplet contact ion pair. In nonpolar solvents, the ion pair remains in this form until it decays. For polar solvents, the spectra change somewhat over the first 100 ps showing that the solvation changes and the ion pair becomes solvent separated. The lifetime of the ion pair varies greatly with the solvent. In saturated hydrocarbons it is about 80more » ps. Nonpolar solvents with either {pi} electrons or a lone pair of electrons stabilize the ion pair on the nanosecond to microsecond time scale. A small amount of alcohol in benzene also stabilizes the ion pair by hydrogen bonding. A shift in the peak position with time toward the blue accompanies the formation of hydrogen bonds in this case.« less

Development of novel zein-sodium caseinate nanoparticle (ZP)-stabilized emulsion films for improved water barrier properties via emulsion/solvent evaporation.

PubMed

Wang, Li-Juan; Yin, Ye-Chong; Yin, Shou-Wei; Yang, Xiao-Quan; Shi, Wei-Jian; Tang, Chuan-He; Wang, Jin-Mei

2013-11-20

This work attempted to develop novel high barrier zein/SC nanoparticle (ZP)-stabilized emulsion films through microfluidic emulsification (ZPE films) or in combination with solvent (ethyl acetate) evaporation techniques (ZPE-EA films). Some physical properties, including tensile and optical properties, water vapor permeability (WVP), and surface hydrophobicity, as well as the microstructure of ZP-stabilized emulsion films were evaluated and compared with SC emulsion (SCE) films. The emulsion/solvent evaporation approach reduced lipid droplets of ZP-stabilized emulsions, and lipid droplets of ZP-stabilized emulsions were similar to or slightly lower than that of SC emulsions. However, ZP- and SC-stabilized emulsion films exhibited a completely different microstructure, nanoscalar lipid droplets were homogeneously distributed in the ZPE film matrix and interpenetrating protein-oil complex networks occurred within ZPE-EA films, whereas SCE films presented a heterogeneous microstructure. The different stabilization mechanisms against creaming or coalescence during film formation accounted for the preceding discrepancy of the microstructures between ZP-and SC-stabilized emulsion films. Interestingly, ZP-stabilized emulsion films exhibited a better water barrier efficiency, and the WVP values were only 40-50% of SCE films. A schematic representation for the formation of ZP-stabilized emulsion films was proposed to relate the physical performance of the films with their microstructure and to elucidate the possible forming mechanism of the films.

Determination of residual solvents and investigation of their effect on ampicillin trihydrate crystal structure.

PubMed

Nojavan, Saeed; Ghassempour, Alireza; Bashour, Yosef; Darbandi, Masoud Khalilian; Ahmadi, Seyyed Hamid

2005-01-04

In the present work, the relationship between residual solvents concentration and ampicillin trihydrate crystals stability has been investigated. The amounts of residual solvents determined by GC, X-ray powder diffraction (XRPD) and Fourier transform infrared spectroscopy (FT-IR) were used for characterization of solid state. The obtained results have shown good relationship between concentration of methylene chloride (as a critical residue solvent) and degree of ampicillin trihydrate crystallinity. As with the increasing methylene chloride concentration in the sample the degree of crystallinity decreased after stability test. From this relationship, critical concentration of methylene chloride into the ampicillin trihydrate is obtained and the results can be used for improving the large-scale production of ampicillin trihydrate.

The theoretical investigation of solvent effects on the relative stability and 15N NMR shielding of antidepressant heterocyclic drug

NASA Astrophysics Data System (ADS)

Tahan, Arezoo; Khojandi, Mahya; Salari, Ali Akbar

2016-01-01

The density functional theory (DFT) and Tomasi's polarized continuum model (PCM) were used for the investigation of solvent polarity and its dielectric constant effects on the relative stability and NMR shielding tensors of antidepressant mirtazapine (MIR). The obtained results indicated that the relative stability in the polar solvents is higher than that in non-polar solvents and the most stable structure was observed in the water at the B3LYP/6-311++G ( d, p) level of theory. Also, natural bond orbital (NBO) interpretation demonstrated that by increase of solvent dielectric constant, negative charge on nitrogen atoms of heterocycles and resonance energy for LP(N10) → σ* and π* delocalization of the structure's azepine ring increase and the highest values of them were observed in water. On the other hand, NMR calculations showed that with an increase in negative charge of nitrogen atoms, isotropic chemical shielding (σiso) around them increase and nitrogen of piperazine ring (N19) has the highest values of negative charge and σiso among nitrogen atoms. NMR calculations also represented that direct solvent effect on nitrogen of pyridine ring (N15) is more than other nitrogens, while its effect on N19 is less than other ones. Based on NMR data and NBO interpretation, it can be deduced that with a decrease in the negative charge on nitrogen atoms, the intramolecular effects on them decrease, while direct solvent effect increases.

Influence of a Confined Methanol Solvent on the Reactivity of Active Sites in UiO-66.

PubMed

Caratelli, Chiara; Hajek, Julianna; Rogge, Sven M J; Vandenbrande, Steven; Meijer, Evert Jan; Waroquier, Michel; Van Speybroeck, Veronique

2018-02-19

UiO-66, composed of Zr-oxide bricks and terephthalate linkers, is currently one of the most studied metal-organic frameworks due to its exceptional stability. Defects can be introduced in the structure, creating undercoordinated Zr atoms which are Lewis acid sites. Here, additional Brønsted sites can be generated by coordinated protic species from the solvent. In this Article, a multilevel modeling approach was applied to unravel the effect of a confined methanol solvent on the active sites in UiO-66. First, active sites were explored with static periodic density functional theory calculations to investigate adsorption of water and methanol. Solvent was then introduced in the pores with grand canonical Monte Carlo simulations, followed by a series of molecular dynamics simulations at operating conditions. A hydrogen-bonded network of methanol molecules is formed, allowing the protons to shuttle between solvent methanol, adsorbed water, and the inorganic brick. Upon deprotonation of an active site, the methanol solvent aids the transfer of protons and stabilizes charged configurations via hydrogen bonding, which could be crucial in stabilizing reactive intermediates. The multilevel modeling approach adopted here sheds light on the important role of a confined solvent on the active sites in the UiO-66 material, introducing dynamic acidity in the system at finite temperatures by which protons may be easily shuttled from various positions at the active sites. © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Understanding the influence of solvent field and fluctuations on the stability of photo-induced charge-separated state in molecular triad

NASA Astrophysics Data System (ADS)

Balamurugan, D.; Aquino, Adelia; Lischka, Hans; Dios, Francis; Flores, Lionel; Cheung, Margaret

2013-03-01

Molecular triad composed of fullerene, porphyrin, and carotene is an artificial analogue of natural photosynthetic system and is considered for applications in solar energy conversion because of its ability to produce long-lived photo-induced charge separated state. The goal of the present multiscale simulation is to understand how the stability of photo-induced charge-separated state in molecular triad is influenced by a polar organic solvent, namely tetrahydrofuran (THF). The multiscale approach is based on combined quantum, classical molecular dynamics, and statistical physics calculations. The quantum chemical calculations were performed on the triad using the second order algebraic diagrammatic perturbation and time-dependent density functional theory. Molecular dynamics simulations were performed on triad in a box of THF solvent with the replica exchange method. The two methods on different length and time scales are bridged through an important sampling technique. We have analyzed the free energy landscape, structural fluctuations, and the long- range electrostatic interactions between triad and solvent molecules. The results suggest that the polarity and re-organization of the solvent is critical in stabilization of charge-separated state in triad. Supported by DOE (DE-FG02-10ER16175)

Solubility, stability, and electrochemical studies of sulfur-sulfide solutions in organic solvents

NASA Technical Reports Server (NTRS)

Fielder, W. L.; Singer, J.

1978-01-01

A preliminary study of the sulfur electrode in organic solvents suggests that the system warrants further investigation for use in a low temperature (100 deg to 120 C) Na-S secondary battery. A qualitative screening was undertaken at 120 C to determine the solubilities and stabilities of Na2S and Na2S2 in representatives of many classes of organic solvents. From the screening and quantitative studies, two classes of solvents were selected for work; amides and cyclic polyalcohols. Voltammetric and Na-S cell charge discharge studies of sulfide solutions in organic solvents (e.g., N, N-dimethylformamide) at 120 C suggested that the reversibilities of the reactions on Pt or high density graphite were moderately poor. However, the sulfur electrode was indeed reducible (and oxidizable) through the range of elemental sulfur to Na2S. Reactions and mechanisms are proposed for the oxidation reduction processes occurring at the sulfur electrode.

Effects of solvents and salt on the thermal stability of lithiated graphite used in lithium ion battery.

PubMed

Wang, Qingsong; Sun, Jinhua; Chen, Chunhua

2009-08-15

The thermal stability of lithiated graphite in the presence of solvents, electrolytes and LiPF(6) salt was studied using C80 micro-calorimeter. The presence of cyclic carbonates or linear carbonates increases the activity of Li(x)C(6)-solvent coexisting system, especially for the Li(x)C(6)-linear carbonates one. LiPF(6) was detected that it increases the activity greatly of its coexisting system with lithiated graphite. The coexisting system of Li(x)C(6) with the electrolyte of LiPF(6)/ethylene carbonate+diethyl carbonate shows less thermal stability, which is attributed to the activity between diethyl carbonate and Li(x)C(6). This also agrees with the experiment result of Li(x)C(6)-diethyl carbonate coexisting system.

Effect of Solvent Choice on the Self-Assembly Properties of a Diphenylalanine Amphiphile Stabilized by an Ion Pair.

PubMed

Mayans, Enric; Ballano, Gema; Sendros, Javier; Font-Bardia, Merçè; Campos, J Lourdes; Puiggalí, Jordi; Cativiela, Carlos; Alemán, Carlos

2017-07-19

A diphenylalanine (FF) amphiphile blocked at the C terminus with a benzyl ester (OBzl) and stabilized at the N terminus with a trifluoroacetate (TFA) anion was synthetized and characterized. Aggregation of peptide molecules was studied by considering a peptide solution in an organic solvent and adding pure water, a KCl solution, or another organic solvent as co-solvent. The choice of the organic solvent and co-solvent and the solvent/co-solvent ratio allowed the mixture to be tuned by modulating the polarity, the ionic strength, and the peptide concentration. Differences in the properties of the media used to dissolve the peptides resulted in the formation of different self-assembled microstructures (e.g. fibers, branched-like structures, plates, and spherulites). Furthermore, crystals of TFA⋅FF-OBzl were obtained from the aqueous peptide solutions for X-ray diffraction analysis. The results revealed a hydrophilic core constituted by carboxylate (from TFA), ester, and amide groups, and the core was found to be surrounded by a hydrophobic crown with ten aromatic rings. This segregated organization explains the assemblies observed in the different solvent mixtures as a function of the environmental polarity, ionic strength, and peptide concentration. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Roles of Gag-RNA interactions in HIV-1 virus assembly deciphered by single-molecule localization microscopy.

PubMed

Yang, Yantao; Qu, Na; Tan, Jie; Rushdi, Muaz N; Krueger, Christopher J; Chen, Antony K

2018-06-11

During HIV-1 assembly, the retroviral structural protein Gag forms an immature capsid, containing thousands of Gag molecules, at the plasma membrane (PM). Interactions between Gag nucleocapsid (NC) and viral RNA (vRNA) are thought to drive assembly, but the exact roles of these interactions have remained poorly understood. Since previous studies have shown that Gag dimer- or trimer-forming mutants (Gag ZiL ) lacking an NC domain can form immature capsids independent of RNA binding, it is often hypothesized that vRNA drives Gag assembly by inducing Gag to form low-ordered multimers, but is dispensable for subsequent assembly. In this study, we examined the role of vRNA in HIV-1 assembly by characterizing the distribution and mobility of Gag and Gag NC mutants at the PM using photoactivated localization microscopy (PALM) and single-particle tracking PALM (spt-PALM). We showed that both Gag and Gag ZiL assembly involve a similar basic assembly unit, as expected. Unexpectedly, the two proteins underwent different subsequent assembly pathways, with Gag cluster density increasing asymptotically, while Gag ZiL cluster density increased linearly. Additionally, the directed movement of Gag, but not Gag ZiL , was maintained at a constant speed, suggesting that the two proteins experience different external driving forces. Assembly was abolished when Gag was rendered monomeric by NC deletion. Collectively, these results suggest that, beyond inducing Gag to form low-ordered multimer basic assembly units, vRNA is essential in scaffolding and maintaining the stability of the subsequent assembly process. This finding should advance the current understanding of HIV-1 and, potentially, other retroviruses. Copyright © 2018 the Author(s). Published by PNAS.

The Vitamin K Oxidoreductase Is a Multimer That Efficiently Reduces Vitamin K Epoxide to Hydroquinone to Allow Vitamin K-dependent Protein Carboxylation*

PubMed Central

Rishavy, Mark A.; Hallgren, Kevin W.; Wilson, Lee A.; Usubalieva, Aisulu; Runge, Kurt W.; Berkner, Kathleen L.

2013-01-01

The vitamin K oxidoreductase (VKORC1) recycles vitamin K to support the activation of vitamin K-dependent (VKD) proteins, which have diverse functions that include hemostasis and calcification. VKD proteins are activated by Glu carboxylation, which depends upon the oxygenation of vitamin K hydroquinone (KH2). The vitamin K epoxide (KO) product is recycled by two reactions, i.e. KO reduction to vitamin K quinone (K) and then to KH2, and recent studies have called into question whether VKORC1 reduces K to KH2. Analysis in insect cells lacking endogenous carboxylation components showed that r-VKORC1 reduces KO to efficiently drive carboxylation, indicating KH2 production. Direct detection of the vitamin K reaction products is confounded by KH2 oxidation, and we therefore developed a new assay that stabilized KH2 and allowed quantitation. Purified VKORC1 analyzed in this assay showed efficient KO to KH2 reduction. Studies in 293 cells expressing tagged r-VKORC1 revealed that VKORC1 is a multimer, most likely a dimer. A monomer can only perform one reaction, and a dimer is therefore interesting in explaining how VKORC1 accomplishes both reactions. An inactive mutant (VKORC1(C132A/C135A)) was dominant negative in heterodimers with wild type VKORC1, resulting in decreased KO reduction in cells and carboxylation in vitro. The results are significant regarding human VKORC1 mutations, as warfarin-resistant patients have mutant and wild type VKORC1 alleles. A VKORC1 dimer indicates a mixed population of homodimers and heterodimers that may have different functional properties, and VKORC1 reduction may therefore be more complex in these patients than appreciated previously. PMID:23918929

Thermometric sensing of peroxide in organic media. Application to monitor the stability of RBP-retinol-HRP complex.

PubMed

Ramanathan, K; Jönsson, B R; Danielsson, B

2000-08-01

The stability of horseradish peroxidase (HRP) in aqueous and organic solvents is applied to develop a simple thermometric procedure to detect the binding of retinoic acid-HRP conjugate to retinol binding protein (RBP). Butanone peroxide (BP) in organic phase and hydrogen peroxide in aqueous phase is detected thermometrically on a HRP column, immobilized by cross-linking with glutaraldehyde on controlled pore glass (CPG). Acetone, acetonitrile, methanol, and 2-butanol are used for detection of BP, in the flow injection analysis (FIA) mode. A linear range between 1 and 50 mM BP is obtained in all the organic solvents with a precision of 5-7% (CV%). The magnitude and nature of the thermometric response is significantly different in each organic solvent. The stability of HRP in the organic phase is used to study the stability of a retinoic acid-HRP conjugate bound to immobilized RBP. The response of HRP (to 20 mM BP) in the retinoic acid-HRP conjugate is used as an indicator of the stability of the RBP-retinoic acid-HRP complex, after challenges with various organic/aqueous solvents. Both immobilized HRP and RBP are stable at least for 6 months. The effect of o-phenylene diamine on the thermometric response of HRP is also investigated. A scheme for the design of a thermometric retinol (vitamin A) biosensor is proposed.

DNA Architectures for Templated Material Growth

DTIC Science & Technology

2011-09-01

Solubilization of the DNA in non-aqueous solvents is achieved by replacing charge stabilizing salts with surfactants. Retention of DNA hierarchical structure...solvents is achieved by replacing charge stabilizing salts with surfactants. Retention of DNA hierarchical structure under both conditions will be...studied and explained, and is only being reproduced in this experiment.12-14 Both CTAB and CTAC, were reacted with the reconstituted DNA (salmon sperm

Exploration of the Detailed Conditions for Reductive Stability of Mg(TFSI) 2 in Diglyme: Implications for Multivalent Electrolytes

DOE PAGES

Baskin, Artem; Prendergast, David

2016-02-05

In this paper, we reveal the general mechanisms of partial reduction of multivalent complex cations in conditions specific for the bulk solvent and in the vicinity of the electrified metal electrode surface and disclose the factors affecting the reductive stability of electrolytes for multivalent electrochemistry. Using a combination of ab initio techniques, we clarify the relation between the reductive stability of contact-ion pairs comprising a multivalent cation and a complex anion, their solvation structures, solvent dynamics, and the electrode overpotential. We found that for ion pairs with multiple configurations of the complex anion and the Mg cation whose available orbitalsmore » are partially delocalized over the molecular complex and have antibonding character, the primary factor of the reductive stability is the shape factor of the solvation sphere of the metal cation center and the degree of the convexity of a polyhedron formed by the metal cation and its coordinating atoms. We focused specifically on the details of Mg (II) bis(trifluoromethanesulfonyl)imide in diethylene glycol dimethyl ether (Mg(TFSI) 2)/diglyme) and its singly charged ion pair, MgTFSI +. In particular, we found that both stable (MgTFSI) + and (MgTFSI) 0 ion pairs have the same TFSI configuration but drastically different solvation structures in the bulk solution. This implies that the MgTFSI/dyglyme reductive stability is ultimately determined by the relative time scale of the solvent dynamics and electron transfer at the Mg–anode interface. In the vicinity of the anode surface, steric factors and hindered solvent dynamics may increase the reductive stability of (MgTFSI) + ion pairs at lower overpotential by reducing the metal cation coordination, in stark contrast to the reduction at high overpotential accompanied by TFSI decomposition. By examining other solute/solvent combinations, we conclude that the electrolytes with highly coordinated Mg cation centers are more prone to reductive instability due to the chemical decomposition of the anion or solvent molecules. Finally, the obtained findings disclose critical factors for stable electrolyte design and show the role of interfacial phenomena in reduction of multivalent ions.« less

Exploration of ethyl anthranilate-loaded monolithic matrix-type prophylactic polymeric patch.

PubMed

Islam, Johirul; Zaman, Kamaruz; Chakrabarti, Srijita; Bora, Nilutpal Sharma; Pathak, Manash Pratim; Mandal, Santa; Junejo, Julfikar Ali; Chattopadhyay, Pronobesh

2017-10-01

Compromised stability of pharmaceutical formulations loaded with volatiles is a serious problem associated with devices designed to deliver volatile compounds. The present study has been focused to evaluate the stability potential of matrix-type polymeric patches composed of volatile ethyl anthranilate for prophylaxis against vector-borne diseases. Ethyl anthranilate-loaded matrix-type polymeric patches were fabricated by solvent evaporation method on an impermeable backing membrane and attached to temporary release liners. Stability testing of the polymeric patches was performed as per the International Conference on Harmonization (ICH) guidelines for 6 months under accelerated conditions. In addition, the quantification of residual solvents was also performed as per the ICH guidelines. After conducting the stability studies for 6 months, the optimized patches showed the best possible results with respect to uniformity of drug content, physical appearance, and other analytical parameters. Furthermore, the amount of residual solvent was found well below the accepted limit. Thus, the present report outlined the analytical parameters to be evaluated to ensure the stability of a certain devices consisting of volatile compounds. Copyright © 2016. Published by Elsevier B.V.

Stability and thermophysical studies on deep eutectic solvent based carbon nanotube nanofluid

NASA Astrophysics Data System (ADS)

Chen, Yan Yao; Walvekar, Rashmi; Khalid, Mohammad; Shahbaz, Kaveh; Gupta, T. C. S. M.

2017-07-01

Commercial coolants such as water, ethylene glycol and triethylene glycol possess very low thermal conductivity, high vapor pressure, corrosion issues and low thermal stability thus limiting the thermal enhancement of the nanofluids. Thus, a new type of base fluid known as deep eutectic solvents (DESs) is proposed in this work as a potential substitute for the conventional base fluid due to their unique solvent properties such as low vapor pressure, high thermal stability, biodegradability and non-flammability. In this work, 33 different DESs derived from phosphonium halide salt and ammonium halide salts were synthesised. Carbon nantubes (CNTs) with different concentrations (0.01 wt%-0.08 wt%) were dispersed into DESs with the help of sonication. Stability of the nanofluids were determined using both qualitative (visual observation) and quantitative (UV spectroscopy) approach. In addition, thermo-physical properties such as thermal conductivity, specific heat, viscosity and density were investigated. The stability results indicated that phosphonium based DESs have higher stability (up to 4 d) as compared to ammonium-based DESs (up to 3 d). Thermal enhancement of 30% was observed for ammonium based DES-CNT nanofluid whereas negative thermal enhancement was observed in phosphonium based DES-CNT nanofluid.

Thermodynamically based solvent design for enzymatic saccharide acylation with hydroxycinnamic acids in non-conventional media.

PubMed

Zeuner, Birgitte; Kontogeorgis, Georgios M; Riisager, Anders; Meyer, Anne S

2012-02-15

Enzyme-catalyzed synthesis has been widely studied with lipases (EC 3.1.1.3), but feruloyl esterases (FAEs; EC 3.1.1.73) may provide advantages such as higher substrate affinity and regioselectivity in the synthesis of hydroxycinnamate saccharide esters. These compounds are interesting because of their amphiphilicity and antioxidative potential. Synthetic reactions using mono- or disaccharides as one of the substrates may moreover direct new routes for biomass upgrading in the biorefinery. The paper reviews the available data for enzymatic hydroxycinnamate saccharide ester synthesis in organic solvent systems as well as other enzymatic hydroxycinnamate acylations in ionic liquid systems. The choice of solvent system is highly decisive for enzyme stability, selectivity, and reaction yields in these synthesis reactions. To increase the understanding of the reaction environment and to facilitate solvent screening as a crucial part of the reaction design, the review explores the use of activity coefficient models for describing these systems and - more importantly - the use of group contribution model UNIFAC and quantum chemistry based COSMO-RS for thermodynamic predictions and preliminary solvent screening. Surfactant-free microemulsions of a hydrocarbon, a polar alcohol, and water are interesting solvent systems because they accommodate different substrate and product solubilities and maintain enzyme stability. Ionic liquids may provide advantages as solvents in terms of increased substrate and product solubility, higher reactivity and selectivity, as well as tunable physicochemical properties, but their design should be carefully considered in relation to enzyme stability. The treatise shows that thermodynamic modeling tools for solvent design provide a new toolbox to design enzyme-catalyzed synthetic reactions from biomass sources. Copyright © 2011 Elsevier B.V. All rights reserved.

Solvent dielectric effect and side chain mutation on the structural stability of Burkholderia cepacia lipase active site: a quantum mechanical/molecular mechanics study.

PubMed

Tahan, A; Monajjemi, M

2011-12-01

Quantum mechanical and molecular dynamics methods were used to analyze the structure and stability of neutral and zwitterionic configurations of the extracted active site sequence from a Burkholderia cepacia lipase, histidyl-seryl-glutamin (His86-Ser87-Gln88) and its mutated form, histidyl-cysteyl-glutamin (His86-Cys87-Gln88) in vacuum and different solvents. The effects of solvent dielectric constant, explicit and implicit water molecules and side chain mutation on the structure and stability of this sequence in both neutral and zwitterionic forms are represented. The quantum mechanics computations represent that the relative stability of zwitterionic and neutral configurations depends on the solvent structure and its dielectric constant. Therefore, in vacuum and the considered non-polar solvents, the neutral form of the interested sequences is more stable than the zwitterionic form, while their zwitterionic form is more stable than the neutral form in the aqueous solution and the investigated polar solvents in most cases. However, on the potential energy surfaces calculated, there is a barrier to proton transfer from the positively charged ammonium group to the negatively charged carboxylat group or from the ammonium group to the adjacent carbonyl oxygen and or from side chain oxygen and sulfur to negatively charged carboxylat group. Molecular dynamics simulations (MD) were also performed by using periodic boundary conditions for the zwitterionic configuration of the hydrated molecules in a box of water molecules. The obtained results demonstrated that the presence of explicit water molecules provides the more compact structures of the studied molecules. These simulations also indicated that side chain mutation and replacement of sulfur with oxygen leads to reduction of molecular flexibility and packing.

Structure, stability and behaviour of nucleic acids in ionic liquids

PubMed Central

Tateishi-Karimata, Hisae; Sugimoto, Naoki

2014-01-01

Nucleic acids have become a powerful tool in nanotechnology because of their conformational polymorphism. However, lack of a medium in which nucleic acid structures exhibit long-term stability has been a bottleneck. Ionic liquids (ILs) are potential solvents in the nanotechnology field. Hydrated ILs, such as choline dihydrogen phosphate (choline dhp) and deep eutectic solvent (DES) prepared from choline chloride and urea, are ‘green’ solvents that ensure long-term stability of biomolecules. An understanding of the behaviour of nucleic acids in hydrated ILs is necessary for developing DNA materials. We here review current knowledge about the structures and stabilities of nucleic acids in choline dhp and DES. Interestingly, in choline dhp, A–T base pairs are more stable than G–C base pairs, the reverse of the situation in buffered NaCl solution. Moreover, DNA triplex formation is markedly stabilized in hydrated ILs compared with aqueous solution. In choline dhp, the stability of Hoogsteen base pairs is comparable to that of Watson–Crick base pairs. Moreover, the parallel form of the G-quadruplex is stabilized in DES compared with aqueous solution. The behaviours of various DNA molecules in ILs detailed here should be useful for designing oligonucleotides for the development of nanomaterials and nanodevices. PMID:25013178

Pre-formulation and chemical stability studies of penethamate, a benzylpenicillin ester prodrug, in aqueous vehicles.

PubMed

Jain, Rohit; Wu, Zimei; Bork, Olaf; Tucker, Ian G

2012-01-01

Penethamate (PNT) is a diethylaminoethyl ester prodrug of benzylpenicillin used to treat bovine mastitis via the intramuscular route. Because of its instability, PNT products must be reconstituted before administration and the reconstituted injection has a short shelf life (7 days at 2-8°C). The purpose of this paper was to investigate whether the stability of PNT can be improved in order to achieve a chemically stable ready-to-use aqueous-based PNT formulation or at least to extend the shelf life of the reconstituted suspension. A chemical stability study of PNT in aqueous-based solutions as a function of pH, buffer strength, solvent mixtures and temperature, supported by studies of its solubility in mixed solvents, allowed predictions of the shelf life of PNT solution and suspension formulations. PNT degraded in aqueous solutions by several pathways over the pH range 2.0-9.3 with a V-shaped pH-rate profile and a minimum pH of around 4.5. The stability of PNT solutions in mixed solvents was greater than in aqueous solutions. For example, in propylene glycol:citrate buffer (60:40, v/v, pH 4.5), the half-life of PNT was 4.3 days compared with 1.8 days in aqueous buffer. However, solubility of PNT in the mixed solvent was higher than that in aqueous solution and this had an adverse effect on the stability of suspensions. By judicious choosing of pH and mixed solvent, it is possible to achieve a storage life of a PNT suspension of 5.5 months at 5°C, not sufficient for a ready-to-use product but a dramatic improvement in the storage life of the reconstituted product.

Molecular switching behavior in isosteric DNA base pairs.

PubMed

Jissy, A K; Konar, Sukanya; Datta, Ayan

2013-04-15

The structures and proton-coupled behavior of adenine-thymine (A-T) and a modified base pair containing a thymine isostere, adenine-difluorotoluene (A-F), are studied in different solvents by dispersion-corrected density functional theory. The stability of the canonical Watson-Crick base pair and the mismatched pair in various solvents with low and high dielectric constants is analyzed. It is demonstrated that A-F base pairing is favored in solvents with low dielectric constant. The stabilization and conformational changes induced by protonation are also analyzed for the natural as well as the mismatched base pair. DNA sequences capable of changing their sequence conformation on protonation are used in the construction of pH-based molecular switches. An acidic medium has a profound influence in stabilizing the isostere base pair. Such a large gain in stability on protonation leads to an interesting pH-controlled molecular switch, which can be incorporated in a natural DNA tract. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Competitive interactions and controlled release of a natural antioxidant from halloysite nanotubes.

PubMed

Hári, József; Gyürki, Ádám; Sárközi, Márk; Földes, Enikő; Pukánszky, Béla

2016-01-15

Halloysite nanotubes used as potential carrier material for a controlled release stabilizer in polyethylene were thoroughly characterized with several techniques including the measurement of specific surface area, pore volume and surface energy. The high surface energy of the halloysite results in the strong bonding of the additive to the surface. Dissolution experiments carried out with eight different solvents for the determination of the effect of solvent characteristics on the amount of irreversibly bonded quercetin proved that adsorption and dissolution depend on competitive interactions prevailing in the system. Solvents with low polarity dissolve only surplus quercetin adsorbed in multilayers. Polyethylene is a very apolar polymer forming weak interactions with every substance; quercetin dissolves into it from the halloysite surface only above a critical surface coverage. Stabilization experiments confirmed that strong adhesion prevents dissolution and results in limited stabilization efficiency. At larger adsorbed amounts better stability and extended effect were measured indicating dissolution and controlled release. Copyright © 2015 Elsevier Inc. All rights reserved.

Double stabilization of nanocrystalline silicon: a bonus from solvent

NASA Astrophysics Data System (ADS)

Kolyagin, Y. G.; Zakharov, V. N.; Yatsenko, A. V.; Paseshnichenko, K. A.; Savilov, S. V.; Aslanov, L. A.

2016-01-01

Double stabilization of the silicon nanocrystals was observed for the first time by 29Si and 13C MAS NMR spectroscopy. The role of solvent, 1,2-dimethoxyethane (glyme), in formation and stabilization of silicon nanocrystals as well as mechanism of modification of the surface of silicon nanocrystals by nitrogen-heterocyclic carbene (NHC) was studied in this research. It was shown that silicon nanocrystals were stabilized by the products of cleavage of the C-O bonds in ethers and similar compounds. The fact of stabilization of silicon nanoparticles with NHC ligands in glyme was experimentally detected. It was demonstrated that MAS NMR spectroscopy is rather informative for study of the surface of silicon nanoparticles but it needs very pure samples.

Stability of coordination compounds of Ni2+ and Co2+ ions with succinic acid anion in water-ethanol solvents

NASA Astrophysics Data System (ADS)

Tukumova, N. V.; Dieu Thuan, Tran Thi; Usacheva, T. R.; Koryshev, N. E.; Sharnin, V. A.

2017-04-01

Stability constants of the coordination compounds of nickel(II) and cobalt(II) ions with succinic acid anion in water-ethanol solvents are determined via potentiometric titration at ionic strength of 0.1 and at T = 298.15 K. It is found that logβ values of monoligand complexes of these ions and succinic acid anions rise along with the content of ethanol in solution ( X EtOH = 0-0.7 mole fractions). Based on an analysis of the thermodynamic characteristics of the solvation of the reagents involved in complex formation, it is found that the increased stability of succinate complexes of nickel(II) and cobalt(II) ions in water-ethanol solvents is mainly determined by the weakening of the solvation of succinic acid anion (Y2-).

ATZ11 recognizes not only Z-α1-antitrypsin-polymers and complexed forms of non-Z-α1-antitrypsin but also the von Willebrand factor.

PubMed

Goltz, Diane; Hittetiya, Kanishka; Yadegari, Hamideh; Driesen, Julia; Kirfel, Jutta; Neuhaus, Thomas; Steiner, Susanne; Esch, Christiane; Bedorf, Jörg; Hertfelder, Hans-Jörg; Fischer, Hans-Peter

2014-01-01

The ATZ11 antibody has been well established for the identification of α1-anti-trypsin (AAT) molecule type PiZ (Z-AAT) in blood samples and liver tissue. In this study, we systematically analyzed the antibody for additional binding sites in human tissue. Ultrastructural ATZ11 binding was investigated immunoelectron microscopically in human umbilical vein endothelial cells (HUVECs) and in platelets of a healthy individual. Human embryonic kidney (HEK293) cells were transiently transfected with Von Willebrand factor (VWF) and analyzed immunocytochemically using confocal microscopy and SDS-PAGE electrophoresis followed by western blotting (WB). Platelets and serum samples of VWF-competent and VWF-deficient patients were investigated using native PAGE and SDS-PAGE electrophoresis followed by WB. The specificity of the ATZ11 reaction was tested immunohistochemically by extensive antibody-mediated blocking of AAT- and VWF-antigens. ATZ11-positive epitopes could be detected in Weibel-Palade bodies (WPBs) of HUVECs and α-granules of platelets. ATZ11 stains pseudo-WBP containing recombinant wild-type VWF (rVWF-WT) in HEK293 cells. In SDS-PAGE electrophoresis followed by WB, anti-VWF and ATZ11 both identified rVWF-WT. However, neither rVWF-WT-multimers, human VWF-multimers, nor serum proteins of VWF-deficient patients were detected using ATZ11 by WB, whereas anti-VWF antibody (anti-VWF) detected rVWF-WT-multimers as well as human VWF-multimers. In human tissue specimens, AAT-antigen blockade using anti-AAT antibody abolished ATZ11 staining of Z-AAT in a heterozygous AAT-deficient patient, whereas VWF-antigen blockade using anti-VWF abolished ATZ11 staining of endothelial cells and megakaryocytes. ATZ11 reacts with cellular bound and denatured rVWF-WT and human VWF as shown using immunocytochemistry and subsequent confocal imaging, immunoelectron microscopy, SDS-PAGE and WB, and immunohistology. These immunoreactions are independent of the binding of Z-AAT-molecules and non-Z-AAT complexes.

CMV-specific T cell isolation from G-CSF mobilized peripheral blood: depletion of myeloid progenitors eliminates non-specific binding of MHC-multimers.

PubMed

Beloki, Lorea; Ciaurriz, Miriam; Mansilla, Cristina; Zabalza, Amaya; Perez-Valderrama, Estela; Samuel, Edward R; Lowdell, Mark W; Ramirez, Natalia; Olavarria, Eduardo

2014-11-19

Cytomegalovirus (CMV)-specific T cell infusion to immunocompromised patients following allogeneic Hematopoietic Stem Cell Transplantation (allo-HSCT) is able to induce a successful anti-viral response. These cells have classically been manufactured from steady-state apheresis samples collected from the donor in an additional harvest prior to G-CSF mobilization, treatment that induces hematopoietic stem cell (HSC) mobilization to the periphery. However, two closely-timed cellular collections are not usually available in the unrelated donor setting, which limits the accessibility of anti-viral cells for adoptive immunotherapy. CMV-specific cytotoxic T cell (CTL) manufacture from the same G-CSF mobilized donor stem cell harvest offers great regulatory advantages, but the isolation using MHC-multimers is hampered by the high non-specific binding to myeloid progenitors, which reduces the purity of the cellular product. In the present study we describe an easy and fast method based on plastic adherence to remove myeloid cell subsets from 11 G-CSF mobilized donor samples. CMV-specific CTLs were isolated from the non-adherent fraction using pentamers and purity and yield of the process were compared to products obtained from unmanipulated samples. After the elimination of unwanted cell subtypes, non-specific binding of pentamers was notably reduced. Accordingly, following the isolation process the purity of the obtained cellular product was significantly improved. G-CSF mobilized leukapheresis samples can successfully be used to isolate antigen-specific T cells with MHC-multimers to be adoptively transferred following allo-HSCT, widening the accessibility of this therapy in the unrelated donor setting. The combination of the clinically translatable plastic adherence process to the antigen-specific cell isolation using MHC-multimers improves the quality of the therapeutic cellular product, thereby reducing the clinical negative effects associated with undesired alloreactive cell infusion.

Improvement of bias-stability in amorphous-indium-gallium-zinc-oxide thin-film transistors by using solution-processed Y{sub 2}O{sub 3} passivation

DOE Office of Scientific and Technical Information (OSTI.GOV)

An, Sungjin; Mativenga, Mallory; Kim, Youngoo

2014-08-04

We demonstrate back channel improvement of back-channel-etch amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors by using solution-processed yttrium oxide (Y{sub 2}O{sub 3}) passivation. Two different solvents, which are acetonitrile (35%) + ethylene glycol (65%), solvent A and deionized water, solvent B are investigated for the spin-on process of the Y{sub 2}O{sub 3} passivation—performed after patterning source/drain (S/D) Mo electrodes by a conventional HNO{sub 3}-based wet-etch process. Both solvents yield devices with good performance but those passivated by using solvent B exhibit better light and bias stability. Presence of yttrium at the a-IGZO back interface, where it occupies metal vacancy sites, is confirmed by X-ray photoelectronmore » spectroscopy. The passivation effect of yttrium is more significant when solvent A is used because of the existence of more metal vacancies, given that the alcohol (65% ethylene glycol) in solvent A may dissolve the metal oxide (a-IGZO) through the formation of alkoxides and water.« less

Solvent effects on enzymes - Implications for extraterrestrial life.

NASA Technical Reports Server (NTRS)

Heinrich, M. R.

1972-01-01

Review of several studies on the alterations taking place in the structure, catalytic activity, specificity, and stability of an enzyme when some or all of the water in the medium is replaced by another solvent. These studies show the utility of solvents as a tool for probing enzyme function. They also suggest that solvents other than water should be investigated as media for controlling and directing enzyme reactions.

Laboratory Evaluation of Drop-in Solvent Alternatives to n-Propyl Bromide for Vapor Degreasing

NASA Technical Reports Server (NTRS)

Mitchell, Mark A.; Lowrey, Nikki M.

2012-01-01

Based on this limited laboratory study, solvent blends of trans-1,2 dichloroethylene with HFEs, HFCs, or PFCs appear to be viable alternatives to n-propyl bromide for vapor degreasing. The lower boiling points of these blends may lead to greater solvent loss during use. Additional factors must be considered when selecting a solvent substitute, including stability over time, VOC, GWP, toxicity, and business considerations.

Imagens do céu ontem e hoje - um multimídia interativo de astronomia e uma nova exposição no MAST

NASA Astrophysics Data System (ADS)

Caretta, C. A.; Lima, F. P.; Requeijo, F.; Vieira, G. G.; Alves, F.; Valente, M. E. A.; de Almeida, R.; de Garcia, G. C.; Quixadá, A. C.

2003-08-01

"Imagens do Céu Ontem e Hoje" é o título de uma nova exposição que está sendo inaugurada no Museu de Astronomia e Ciências Afins (MCT), que inclui experimentos interativos, maquetes, réplicas e 8 terminais de computador com um multimídia interativo sobre Astronomia para consulta dos visitantes. O multimídia apresenta um conteúdo bastante extenso, que engloba quase todos os temas em Astronomia, consistindo numa fonte de divulgação e pesquisa para um público que vai das crianças até estudantes universitários. O conteúdo está distribuído em mais de 500 páginas de texto divididas em 4 módulos: "O Universo", "Espectroscopia", "Telescópios" e "Observando o Céu". Cada módulo é subdividido em 5 seções, em média, cada uma iniciada por uma animação que ilustra os temas a serem abordados na seção. Ao final da animação, uma lista de temas é apresentada sob o título "Saiba Mais". Para exemplificar, o módulo "O Universo" contém as seguintes seções: "O Universo visto pelo homem", "Conhecendo o Sistema Solar", "Indo além do Sistema Solar", "Nossa Galáxia, a Via-Láctea" e "Indo mais além, a imensidão do Universo". A seção "Conhecendo o Sistema Solar", por sua vez, tem os seguintes temas: "A origem do Sistema Solar", "O Sol", "Os planetas", "Satélites, asteróides, cometas e outros bichos..." e "O Sistema Solar em números". Cada texto é repleto de imagens, quadros, desenhos, esquemas, etc, além de passatempos ao final de cada seção, incluindo jogos interativos, quadrinhos e curiosidades, que auxiliam o aprendizado de forma divertida. Apresentamos neste trabalho as idéias gerais que permearam a produção da exposição, e uma viagem pelo multimídia para exemplificar sua estrutura e conteúdo. O multimídia será posteriormente disponibilizado para o público externo pela página eletrônica do MAst e/ou por intermédio de uma publicação comercial.

A combined interfacial and in-situ polymerization strategy to construct well-defined core-shell epoxy-containing SiO2-based microcapsules with high encapsulation loading, super thermal stability and nonpolar solvent tolerance

NASA Astrophysics Data System (ADS)

Jia; Wang; Tian; Li; Xu; Jiao; Cao; Wu

2016-10-01

SiO2-based microcapsules containing hydrophobic molecules exhibited potential applications such as extrinsic self-healing, drug delivery, due to outstanding thermal and chemical stability of SiO2. However, to construct SiO2-based microcapsules with both high encapsulation loading and long-term structural stability is still a troublesome issue, limiting their further utilization. We herein design a single-batch route, a combined interfacial and in-situ polymerization strategy, to fabricate epoxy-containing SiO2-based microcapsules with both high encapsulation loading and long-term structural stability. The final SiO2-based microcapsules preserve high encapsulation loading of 85.7 wt% by controlling exclusively hydrolysis and condensed polymerization at oil/water interface in the initial interfacial polymerization step. In the subsequent in-situ polymerization step, the initial SiO2-based microcapsules as seeds could efficiently harvest SiO2 precursors and primary SiO2 particles to finely tune the SiO2 wall thickness, thereby enhancing long-term structural stability of the final SiO2-based microcapsules including high thermal stability with almost no any weight loss until 250°C, and strong tolerance against nonpolar solvents such as CCl4 with almost unchanged core-shell structure and unchanged core weight after immersing into strong solvents for up to 5 days. These SiO2-based microcapsules are extremely suited for processing them into anticorrosive coating in the presence of nonpolar solvents for self-healing application.

Non-Aqueous Sol-Gel Synthesis of FePt Nanoparticles in the Absence of In Situ Stabilizers

PubMed Central

Preller, Tobias; Knickmeier, Saskia; Porsiel, Julian Cedric; Temel, Bilal

2018-01-01

The synthesis of FePt nanocrystals is typically performed in an organic solvent at rather high temperatures, demanding the addition of the in situ stabilizers oleic acid and oleylamine to produce monomodal particles with well-defined morphologies. Replacing frequently-used solvents with organic media bearing functional moieties, the use of the stabilizers can be completely circumvented. In addition, various morphologies and sizes of the nanocrystals can be achieved by the choice of organic solvent. The kinetics of particle growth and the change in the magnetic behavior of the superparamagnetic FePt nanocrystals during the synthesis with a set of different solvents, as well as the resulting morphologies and stoichiometries of the nanoparticles were determined by powder X-ray diffraction (PXRD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES)/mass spectrometry (ICP-MS), and superconducting quantum interference device (SQUID) measurements. Furthermore, annealing of the as-prepared FePt nanoparticles led to the ordered L10 phase and, thus, to hard magnetic materials with varying saturation magnetizations and magnetic coercivities. PMID:29751508

Effect of spray-drying with organic solvents on the encapsulation, release and stability of fish oil.

PubMed

Encina, Cristian; Márquez-Ruiz, Gloria; Holgado, Francisca; Giménez, Begoña; Vergara, Cristina; Robert, Paz

2018-10-15

Fish-oil (FO) was encapsulated with hydroxypropylcelullose (HPC) by conventional spray-drying with water (FO-water) and solvent spray-drying with ethanol (FO-EtOH), methanol (FO-MeOH) and acetone (FO-Acet) in order to study the effect of the solvent on the encapsulation efficiency (EE), microparticle properties and stability of FO during storage at 40 °C. Results showed that FO-Acet presented the highest EE of FO (92.0%), followed by FO-EtOH (80.4%), FO-MeOH (75.0%) and FO-water (71.1%). A decrease of the dielectric constant increased the EE of FO, promoting triglyceride-polymer interactions instead of oil-in-water emulsion retention. FO release profile in aqueous model was similar for all FO-microparticles, releasing only the surface FO, according to Higuchi model. Oxidative stability of FO significantly improved by spray-drying with MeOH, both in surface and encapsulated oil fractions. In conclusion, encapsulation of FO by solvent spray-drying can be proposed as an alternative technology for encapsulation of hydrophobic molecules. Copyright © 2018 Elsevier Ltd. All rights reserved.

Solvation Effect on Complexation of Alkali Metal Cations by a Calix[4]arene Ketone Derivative.

PubMed

Požar, Josip; Nikšić-Franjić, Ivana; Cvetnić, Marija; Leko, Katarina; Cindro, Nikola; Pičuljan, Katarina; Borilović, Ivana; Frkanec, Leo; Tomišić, Vladislav

2017-09-14

The medium effect on the complexation of alkali metal cations with a calix[4]arene ketone derivative (L) was systematically examined in methanol, ethanol, N-methylformamide, N,N-dimethylformamide, dimethyl sulfoxide, and acetonitrile. In all solvents the binding of Na + cation by L was rather efficient, whereas the complexation of other alkali metal cations was observed only in methanol and acetonitrile. Complexation reactions were enthalpically controlled, while ligand dissolution was endothermic in all cases. A notable influence of the solvent on NaL + complex stability could be mainly attributed to the differences in complexation entropies. The higher NaL + stability in comparison to complexes with other alkali metal cations in acetonitrile was predominantly due to a more favorable complexation enthalpy. The 1 H NMR investigations revealed a relatively low affinity of the calixarene sodium complex for inclusion of the solvent molecule in the calixarene hydrophobic cavity, with the exception of acetonitrile. Differences in complex stabilities in the explored solvents, apart from N,N-dimethylformamide and acetonitrile, could be mostly explained by taking into account solely the cation and complex solvation. A considerable solvent effect on the complexation equilibria was proven to be due to an interesting interplay between the transfer enthalpies and entropies of the reactants and the complexes formed.

Homotypic Interaction of Bunyamwera Virus Nucleocapsid Protein

PubMed Central

Leonard, Vincent H. J.; Kohl, Alain; Osborne, Jane C.; McLees, Angela; Elliott, Richard M.

2005-01-01

The bunyavirus nucleocapsid protein, N, plays a central role in viral replication in encapsidating the three genomic RNA segments to form functional templates for transcription and replication by the viral RNA-dependent RNA polymerase. Here we report functional mapping of interacting domains of the Bunyamwera orthobunyavirus N protein by yeast and mammalian two-hybrid systems, immunoprecipitation experiments, and chemical cross-linking studies. N forms a range of multimers from dimers to high-molecular-weight structures, independently of the presence of RNA. Deletion of the N- or C-terminal domains resulted in loss of activity in a minireplicon assay and a decreased capacity for N to form higher multimers. Our data suggest a head-to-head and tail-to-tail multimerization model for the orthobunyavirus N protein. PMID:16189017

Effects of dispersion solvent on the formation of silicon nanoparticles synthesized via microemulsion route

NASA Astrophysics Data System (ADS)

Liong, W. L.; Sreekantan, S.; Hutagalung, S. D.

2010-05-01

Silicon nanoparticles are synthesized by microemulsion route. Silicon tetrachloride (SiCl4) is used as a silicon source. Meanwhile, hydrazine (N2H5OH), sodium hydroxide (NaOH), and polyethylene glycol (PEG) are used as reduction agent, stabilizer, and capping agent, respectively. In this study, the effects of different solvents (methanol, 1-butanol, 2-propanol, ethanol, acetone, and toluene) on the dispersion and the stabilization of silicon nanoparticles are studied intensively. The results in this study show that ethanol solvent has given smaller particle size, better size distribution, stable suspension and well dispersion of silicon nanoparticles. The diameter of synthesized silicon nanoparticles is in the range of 30-100 nm. Moreover, the absorption edge of silicon nanoparticles in ethanol is observed at a shorter wavelength compared to the others solvent.

Lipase in aqueous-polar organic solvents: Activity, structure, and stability

PubMed Central

Kamal, Md Zahid; Yedavalli, Poornima; Deshmukh, Mandar V; Rao, Nalam Madhusudhana

2013-01-01

Studying alterations in biophysical and biochemical behavior of enzymes in the presence of organic solvents and the underlying cause(s) has important implications in biotechnology. We investigated the effects of aqueous solutions of polar organic solvents on ester hydrolytic activity, structure and stability of a lipase. Relative activity of the lipase monotonically decreased with increasing concentration of acetone, acetonitrile, and DMF but increased at lower concentrations (upto ∼20% v/v) of dimethylsulfoxide, isopropanol, and methanol. None of the organic solvents caused any appreciable structural change as evident from circular dichorism and NMR studies, thus do not support any significant role of enzyme denaturation in activity change. Change in 2D [15N, 1H]-HSQC chemical shifts suggested that all the organic solvents preferentially localize to a hydrophobic patch in the active-site vicinity and no chemical shift perturbation was observed for residues present in protein's core. This suggests that activity alteration might be directly linked to change in active site environment only. All organic solvents decreased the apparent binding of substrate to the enzyme (increased Km); however significantly enhanced the kcat. Melting temperature (Tm) of lipase, measured by circular dichroism and differential scanning calorimetry, altered in all solvents, albeit to a variable extent. Interestingly, although the effect of all organic solvents on various properties on lipase is qualitatively similar, our study suggest that magnitudes of effects do not appear to follow bulk solvent properties like polarity and the solvent effects are apparently dictated by specific and local interactions of solvent molecule(s) with the protein. PMID:23625694

In Search of Functional Advantages of Knots in Proteins.

PubMed

Dabrowski-Tumanski, Pawel; Stasiak, Andrzej; Sulkowska, Joanna I

2016-01-01

We analysed the structure of deeply knotted proteins representing three unrelated families of knotted proteins. We looked at the correlation between positions of knotted cores in these proteins and such local structural characteristics as the number of intra-chain contacts, structural stability and solvent accessibility. We observed that the knotted cores and especially their borders showed strong enrichment in the number of contacts. These regions showed also increased thermal stability, whereas their solvent accessibility was decreased. Interestingly, the active sites within these knotted proteins preferentially located in the regions with increased number of contacts that also have increased thermal stability and decreased solvent accessibility. Our results suggest that knotting of polypeptide chains provides a favourable environment for the active sites observed in knotted proteins. Some knotted proteins have homologues without a knot. Interestingly, these unknotted homologues form local entanglements that retain structural characteristics of the knotted cores.

Ionic liquid electrolytes for dye-sensitized solar cells.

PubMed

Gorlov, Mikhail; Kloo, Lars

2008-05-28

The potential of room-temperature molten salts (ionic liquids) as solvents for electrolytes for dye-sensitized solar cells has been investigated during the last decade. The non-volatility, good solvent properties and high electrochemical stability of ionic liquids make them attractive solvents in contrast to volatile organic solvents. Despite this, the relatively high viscosity of ionic liquids leads to mass-transport limitations. Here we review recent developments in the application of different ionic liquids as solvents or components of liquid and quasi-solid electrolytes for dye-sensitized solar cells.

Effects of monohydric alcohols and polyols on the thermal stability of a protein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murakami, Shota; Kinoshita, Masahiro, E-mail: kinoshit@iae.kyoto-u.ac.jp

2016-03-28

The thermal stability of a protein is lowered by the addition of a monohydric alcohol, and this effect becomes larger as the size of hydrophobic group in an alcohol molecule increases. By contrast, it is enhanced by the addition of a polyol possessing two or more hydroxyl groups per molecule, and this effect becomes larger as the number of hydroxyl groups increases. Here, we show that all of these experimental observations can be reproduced even in a quantitative sense by rigid-body models focused on the entropic effect originating from the translational displacement of solvent molecules. The solvent is either puremore » water or water-cosolvent solution. Three monohydric alcohols and five polyols are considered as cosolvents. In the rigid-body models, a protein is a fused hard spheres accounting for the polyatomic structure in the atomic detail, and the solvent is formed by hard spheres or a binary mixture of hard spheres with different diameters. The effective diameter of cosolvent molecules and the packing fractions of water and cosolvent, which are crucially important parameters, are carefully estimated using the experimental data of properties such as the density of solid crystal of cosolvent, parameters in the pertinent cosolvent-cosolvent interaction potential, and density of water-cosolvent solution. We employ the morphometric approach combined with the integral equation theory, which is best suited to the physical interpretation of the calculation result. It is argued that the degree of solvent crowding in the bulk is the key factor. When it is made more serious by the cosolvent addition, the solvent-entropy gain upon protein folding is magnified, leading to the enhanced thermal stability. When it is made less serious, the opposite is true. The mechanism of the effects of monohydric alcohols and polyols is physically the same as that of sugars. However, when the rigid-body models are employed for the effect of urea, its addition is predicted to enhance the thermal stability, which conflicts with the experimental fact. We then propose, as two essential factors, not only the solvent-entropy gain but also the loss of protein-solvent interaction energy upon protein folding. The competition of changes in these two factors induced by the cosolvent addition determines the thermal-stability change.« less

Effects of monohydric alcohols and polyols on the thermal stability of a protein

NASA Astrophysics Data System (ADS)

Murakami, Shota; Kinoshita, Masahiro

2016-03-01

The thermal stability of a protein is lowered by the addition of a monohydric alcohol, and this effect becomes larger as the size of hydrophobic group in an alcohol molecule increases. By contrast, it is enhanced by the addition of a polyol possessing two or more hydroxyl groups per molecule, and this effect becomes larger as the number of hydroxyl groups increases. Here, we show that all of these experimental observations can be reproduced even in a quantitative sense by rigid-body models focused on the entropic effect originating from the translational displacement of solvent molecules. The solvent is either pure water or water-cosolvent solution. Three monohydric alcohols and five polyols are considered as cosolvents. In the rigid-body models, a protein is a fused hard spheres accounting for the polyatomic structure in the atomic detail, and the solvent is formed by hard spheres or a binary mixture of hard spheres with different diameters. The effective diameter of cosolvent molecules and the packing fractions of water and cosolvent, which are crucially important parameters, are carefully estimated using the experimental data of properties such as the density of solid crystal of cosolvent, parameters in the pertinent cosolvent-cosolvent interaction potential, and density of water-cosolvent solution. We employ the morphometric approach combined with the integral equation theory, which is best suited to the physical interpretation of the calculation result. It is argued that the degree of solvent crowding in the bulk is the key factor. When it is made more serious by the cosolvent addition, the solvent-entropy gain upon protein folding is magnified, leading to the enhanced thermal stability. When it is made less serious, the opposite is true. The mechanism of the effects of monohydric alcohols and polyols is physically the same as that of sugars. However, when the rigid-body models are employed for the effect of urea, its addition is predicted to enhance the thermal stability, which conflicts with the experimental fact. We then propose, as two essential factors, not only the solvent-entropy gain but also the loss of protein-solvent interaction energy upon protein folding. The competition of changes in these two factors induced by the cosolvent addition determines the thermal-stability change.

Viscoelastic stability of resin-composites aged in food-simulating solvents.

PubMed

Marghalani, Hanadi Y; Watts, David C

2013-09-01

To study time-dependent viscoelastic deformation (creep and recovery) of resin-composites, after conditioning in food-simulating solvents, under a compressive stress at 37°C. Five dimethacrylate-based composites: (Spectrum TPH, Premise Body, Tetric Ceram HB, Filtek P60, X-tra fil), and two Ormocers (Experimental Ormocer V 28407, Admira) were studied. Three groups of cylindrical specimens (4mm×6mm) were prepared and then conditioned in 3 solvents: methyl ethyl ketone (MEK), ethanol, and water for 1 month at 37°C. The compressive creep-strain under 35MPa in 37°C water was recorded continuously for 2h and then the unloaded recovery-strain was monitored for another 2h. The data were analyzed by one-way ANOVA and Bonferroni's test. The materials all exhibited classic creep and recovery curves, with most parameters being significantly different (p<0.0001) for each solvent condition. All materials showed lower creep-strain in water than in ethanol or MEK solvents. Maximum creep-strain and permanent-set gave negative linear-regression (r(2)>0.98) with logarithm of the solvent solubility-parameter. The % mean (SD) creep-strain ranged from a minimum of 0.82 (0.01) for the Exp. Ormocer in water to the maximum of 4.19 (0.30) for Admira in MEK. Similar trends were found for permanent-set. The dimethacrylate-based composites behaved as an intermediate group, apart from X-tra fil that had similar stability to the Exp. Ormocer. The viscoelastic stability (low creep and permanent-set) of the Exp. Ormocer, compared to many dimethacrylate-based composites, in food-simulating solvents may be due to its diluent-free formulation. This was closely matched by a highly-filled dimethacrylate material (X-tra fil). Copyright © 2013 Academy of Dental Materials. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baskin, Artem; Prendergast, David

In this paper, we reveal the general mechanisms of partial reduction of multivalent complex cations in conditions specific for the bulk solvent and in the vicinity of the electrified metal electrode surface and disclose the factors affecting the reductive stability of electrolytes for multivalent electrochemistry. Using a combination of ab initio techniques, we clarify the relation between the reductive stability of contact-ion pairs comprising a multivalent cation and a complex anion, their solvation structures, solvent dynamics, and the electrode overpotential. We found that for ion pairs with multiple configurations of the complex anion and the Mg cation whose available orbitalsmore » are partially delocalized over the molecular complex and have antibonding character, the primary factor of the reductive stability is the shape factor of the solvation sphere of the metal cation center and the degree of the convexity of a polyhedron formed by the metal cation and its coordinating atoms. We focused specifically on the details of Mg (II) bis(trifluoromethanesulfonyl)imide in diethylene glycol dimethyl ether (Mg(TFSI) 2)/diglyme) and its singly charged ion pair, MgTFSI +. In particular, we found that both stable (MgTFSI) + and (MgTFSI) 0 ion pairs have the same TFSI configuration but drastically different solvation structures in the bulk solution. This implies that the MgTFSI/dyglyme reductive stability is ultimately determined by the relative time scale of the solvent dynamics and electron transfer at the Mg–anode interface. In the vicinity of the anode surface, steric factors and hindered solvent dynamics may increase the reductive stability of (MgTFSI) + ion pairs at lower overpotential by reducing the metal cation coordination, in stark contrast to the reduction at high overpotential accompanied by TFSI decomposition. By examining other solute/solvent combinations, we conclude that the electrolytes with highly coordinated Mg cation centers are more prone to reductive instability due to the chemical decomposition of the anion or solvent molecules. Finally, the obtained findings disclose critical factors for stable electrolyte design and show the role of interfacial phenomena in reduction of multivalent ions.« less

Easy preparation of a large-size random gene mutagenesis library in Escherichia coli.

PubMed

You, Chun; Percival Zhang, Y-H

2012-09-01

A simple and fast protocol for the preparation of a large-size mutant library for directed evolution in Escherichia coli was developed based on the DNA multimers generated by prolonged overlap extension polymerase chain reaction (POE-PCR). This protocol comprised the following: (i) a linear DNA mutant library was generated by error-prone PCR or shuffling, and a linear vector backbone was prepared by regular PCR; (ii) the DNA multimers were generated based on these two DNA templates by POE-PCR; and (iii) the one restriction enzyme-digested DNA multimers were ligated to circular plasmids, followed by transformation to E. coli. Because the ligation efficiency of one DNA fragment was several orders of magnitude higher than that of two DNA fragments for typical mutant library construction, it was very easy to generate a mutant library with a size of more than 10(7) protein mutants per 50 μl of the POE-PCR product. Via this method, four new fluorescent protein mutants were obtained based on monomeric cherry fluorescent protein. This new protocol was simple and fast because it did not require labor-intensive optimizations in restriction enzyme digestion and ligation, did not involve special plasmid design, and enabled constructing a large-size mutant library for directed enzyme evolution within 1 day. Copyright © 2012 Elsevier Inc. All rights reserved.

Adiponectin isoform patterns in ethnic-specific ADIPOQ mutation carriers: The IRAS Family Study

PubMed Central

Tabb, Keri L.; Gao, Chuan; Hicks, Pamela J.; Hawkins, Gregory A.; Rotter, Jerome I.; da Chen, Yii-Der I; Guo, Xiuqing; Norris, Jill M.; Lorenzo, Carlos; Freedman, Barry I.; Bowden, Donald W.; Palmer, Nicholette D.

2017-01-01

Objective Adiponectin is found in human serum in three groups of multimers (high, medium, and low molecular weight). Previously, we reported two ethnic-specific variants in ADIPOQ, G45R (Hispanic Americans) and R55C (African Americans). Although carriers of both variants had mean adiponectin levels ≤20% of those of non-carriers, they were not clinically different from non-carriers. To compare carriers of both variants and non-carriers, relative quantification of adiponectin isoforms to total adiponectin was performed on serum samples. Methods The multimeric patterns of serum adiponectin in G45R carriers (n=23), R55C carriers (n=3), and Hispanic and African American non-carriers (n=84 and 44, respectively) from the IRAS Family Study were explored using native western blotting and densitometry. Results Serum samples from carriers showed an absence of the high molecular weight (HMW) isoform and a marked reduction in the medium molecular weight isoform but an approximate two-fold increase in the amount of the low molecular weight isoform (LMW). Thus, individuals making only LMW adiponectin are metabolically normal. Conclusions The results contrast with the proposed biological importance of the HMW multimer. This suggests that the LMW isoform may functionally compensate for some of the loss/reduction of the higher-order multimers in carriers of the G45R and R55C mutations. PMID:28643464

Platelet-independent adhesion of calcium-loaded erythrocytes to von Willebrand factor

PubMed Central

Bierings, Ruben; Meems, Henriet; Mul, Frederik P. J.; Geerts, Dirk; Vlaar, Alexander P. J.; Voorberg, Jan; Hordijk, Peter L.

2017-01-01

Adhesion of erythrocytes to endothelial cells lining the vascular wall can cause vaso-occlusive events that impair blood flow which in turn may result in ischemia and tissue damage. Adhesion of erythrocytes to vascular endothelial cells has been described in multiple hemolytic disorders, especially in sickle cell disease, but the adhesion of normal erythrocytes to endothelial cells has hardly been described. It was shown that calcium-loaded erythrocytes can adhere to endothelial cells. Because sickle erythrocyte adhesion to ECs can be enhanced by ultra-large von Willebrand factor multimers, we investigated whether calcium loading of erythrocytes could promote binding to endothelial cells via ultra-large von Willebrand factor multimers. We used (immunofluorescent) live-cell imaging of washed erythrocytes perfused over primary endothelial cells at venular flow rate. Using this approach, we show that calcium-loaded erythrocytes strongly adhere to histamine-stimulated primary human endothelial cells. This adhesion is mediated by ultra-large von Willebrand factor multimers. Von Willebrand factor knockdown or ADAMTS13 cleavage abolished the binding of erythrocytes to activated endothelial cells under flow. Platelet depletion did not interfere with erythrocyte binding to von Willebrand factor. Our results reveal platelet-independent adhesion of calcium-loaded erythrocytes to endothelium-derived von Willebrand factor. Erythrocyte adhesion to von Willebrand factor may be particularly relevant for venous thrombosis, which is characterized by the formation of erythrocyte-rich thrombi. PMID:28249049

Adiponectin and markers of metabolic syndrome in obese children and adolescents: impact of 8-mo regular physical exercise program.

PubMed

Nascimento, Henrique; Costa, Elísio; Rocha, Susana; Lucena, Clarice; Rocha-Pereira, Petronila; Rêgo, Carla; Mansilha, Helena Ferreira; Quintanilha, Alexandre; Aires, Luísa; Mota, Jorge; Santos-Silva, Alice; Belo, Luís

2014-08-01

Adiponectin circulates as low-, medium-, and high-molecular-weight multimers (LMW, MMW, and HMW) and influences lipid profile and insulin resistance (IR), HMW being considered as the most biologically active form. We aimed to study the relation between adiponectin and markers of metabolic syndrome (MS) in pediatric obesity, and the impact of physical exercise. The study consisted of a cross-sectional part and an 8-mo physical exercise program. Lipid profile, insulin, glucose, C-reactive protein (CRP), total adiponectin (TA), and homeostasis model assessment IR (HOMA-IR) were measured. Adiponectin multimers were studied in a prepubertal group. Obesity is associated with increased dyslipidemia, IR, and inflammation. TA is correlated inversely with adiposity, triglycerides, HOMA-IR, and CRP, and positively with high-density lipoprotein cholesterol (HDLc)/total cholesterol (TC) ratio. HMW mimicked TA associations. The intervention program led to a reduction of TC, low-density lipoprotein cholesterol (LDLc), insulin, HOMA-IR, and trunk percentage of fat, and an increase of HDLc/TC ratio, in the obese group. BMI improvements prevented adiponectin reduction and correlated with increments in HMW and MMW. Obesity-related increase in MS features might be linked to lower adiponectin. HMW and MMW were the multimers that most explained the MS features. The intervention program improved the lipid profile and IR, and prevented the reduction of adiponectin.

Monomer-dimer control of the ColE1 P(cer) promoter.

PubMed

Chatwin, H M; Summers, D K

2001-11-01

XerCD-mediated recombination at cer converts multimers of plasmid ColE1 to monomers, maximizing the number of independently segregating molecules and minimizing the frequency of plasmid loss. In addition to XerCD, recombination requires the accessory factors ArgR and PepA. The promoter P(cer), located centrally within cer, is also required for stable plasmid maintenance. P(cer) is active in plasmid multimers and directs transcription of a short RNA, Rcd, which appears to inhibit cell division. It has been proposed that Rcd is part of a checkpoint which ensures that multimer resolution is complete before the cell divides. This study has shown that ArgR does not act as a transcriptional repressor of P(cer) in plasmid monomers. P(cer) is unusual in that the -35 and -10 hexamers are separated by only 15 bp and this study has demonstrated that increasing this to a more conventional spacing results in elevated activity. An increase to 17 bp resulted in a 10- to 20-fold increase in activity, while smaller effects were seen when the spacer was increased to 16 bp or 18 bp. These observations are consistent with the hypothesis that P(cer) activation involves realignment of the -35 and -10 sequences within a recombinational synaptic complex. This predicts that a 17 bp spacer promoter derivative should be down-regulated by plasmid multimerization, and this is confirmed experimentally.

Rational modification of protein stability by targeting surface sites leads to complicated results

PubMed Central

Xiao, Shifeng; Patsalo, Vadim; Shan, Bing; Bi, Yuan; Green, David F.; Raleigh, Daniel P.

2013-01-01

The rational modification of protein stability is an important goal of protein design. Protein surface electrostatic interactions are not evolutionarily optimized for stability and are an attractive target for the rational redesign of proteins. We show that surface charge mutants can exert stabilizing effects in distinct and unanticipated ways, including ones that are not predicted by existing methods, even when only solvent-exposed sites are targeted. Individual mutation of three solvent-exposed lysines in the villin headpiece subdomain significantly stabilizes the protein, but the mechanism of stabilization is very different in each case. One mutation destabilizes native-state electrostatic interactions but has a larger destabilizing effect on the denatured state, a second removes the desolvation penalty paid by the charged residue, whereas the third introduces unanticipated native-state interactions but does not alter electrostatics. Our results show that even seemingly intuitive mutations can exert their effects through unforeseen and complex interactions. PMID:23798426

Analysis of the Efficiency of Surfactant-Mediated Stabilization Reactions of EGaIn Nanodroplets.

PubMed

Finkenauer, Lauren R; Lu, Qingyun; Hakem, Ilhem F; Majidi, Carmel; Bockstaller, Michael R

2017-09-26

A methodology based on light scattering and spectrophotometry was developed to evaluate the effect of organic surfactants on the size and yield of eutectic gallium/indium (EGaIn) nanodroplets formed in organic solvents by ultrasonication. The process was subsequently applied to systematically evaluate the role of headgroup chemistry as well as polar/apolar interactions of aliphatic surfactant systems on the efficiency of nanodroplet formation. Ethanol was found to be the most effective solvent medium in promoting the formation and stabilization of EGaIn nanodroplets. For the case of thiol-based surfactants in ethanol, the yield of nanodroplet formation increased with the number of carbon atoms in the aliphatic part. In the case of the most effective surfactant system-octadecanethiol-the nanodroplet yield increased by about 370% as compared to pristine ethanol. The rather low overall efficiency of the reaction process along with the incompatibility of surfactant-stabilized EGaIn nanodroplets in nonpolar organic solvents suggests that the stabilization mechanism differs from the established self-assembled monolayer formation process that has been widely observed in nanoparticle formation.

Organic microchemical performance of solvent resistant polycarbosilane based microreactor.

PubMed

Yoon, Tae-Ho; Jung, Sang-Hee; Kim, Dong-Pyo

2011-05-01

We report the successful fabrication of preceramic polymer allylhydridopolycarbosilane (AHPCS) derived microchannels with excellent organic solvent resistance and optical transparency via economic imprinting process, followed by UV and post thermal curing process at 160 degrees C for 3 h. The microchemical performance of the fabricated microreactors was evaluated by choosing two model micro chemical reactions under organic solvent conditions; syntheses of 2-aminothiazole in DMF and dimethylpyrazole in THF, and compared with glass-based microreactor having identical dimensions and batch system with analogy. It is clear that AHPCS derived microreactor showed excellent solvent resistance and chemical stability compare with glass derived microreactor made by high cost of photolithography and thermal bonding process. The novel preceramic polymer derived microreactors showed reliable mechanical and chemical stability and conversion yields compare with that of glass derived microreactors, which is very promising for developing an integrated microfluidics by adopting available microstructuring techniques of the polymers.

Tautomerism and spectroscopic properties of the immunosuppressant azathioprine.

PubMed

Makhyoun, Mohamed A; Massoud, Raghdaa A; Soliman, Saied M

2013-10-01

The molecular structure and the relative stabilities of the four possible tautomers of the immunosuppressant azathioprine (AZA) are calculated by DFT/B3LYP method using different basis sets. The results of the energy analysis and thermodynamic treatment of the obtained data are used to predict the relative stabilities of the AZA tautomers. The effect of solvents such as DMSO and water on the stability of the AZA tautomers was studied using the polarized continuum method (PCM) at the same level of theory. The calculation predicted that, the total energies of all tautomers are decreased indicating that all tautomers are more or less stabilized by the solvent effect. The vibrational spectra of AZA are calculated using the same level of theory and the results are compared with the experimentally measured FTIR spectra. Good correlation is obtained between the experimental and calculated vibrational frequencies (R(2)=0.997). The electronic spectra of AZA in gas phase and in methanol as solvent are calculated using the TD-DFT method. The calculations predicted bathochromic shift in all the spectral bands in presence of solvent compared to the gas phase. Also the NMR spectra of all tautomers are calculated and the results are correlated with the experimental NMR chemical shifts where the most stable tautomer gives the best correlation coefficient (R(2)=0.996). Copyright © 2013 Elsevier B.V. All rights reserved.

Stability of the solid electrolyte Li{sub 3}OBr to common battery solvents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schroeder, D.J.; Hubaud, A.A.; Vaughey, J.T., E-mail: vaughey@anl.gov

2014-01-01

Graphical abstract: The stability of the anti-perovskite phase Li{sub 3}OBr has been assessed in a variety of battery solvents. - Highlights: • Lithium stable solid electrolyte Li{sub 3}OBr unstable to polar organic solvents. • Solvation with no dissolution destroys long-range structure. • Ion exchange with protons observed. - Abstract: Recently a new class of solid lithium ion conductors was reported based on the anti-perovskite structure, notably Li{sub 3}OCl and Li{sub 3}OBr. For many beyond lithium-ion battery uses, the solid electrolyte is envisioned to be in direct contact with liquid electrolytes and lithium metal. In this study we evaluated the stabilitymore » of the Li{sub 3}OBr phase against common battery solvents electrolytes, including diethylcarbonate (DEC) and dimethylcarbonate (DMC), as well as a LiPF{sub 6} containing commercial electrolyte. In contact with battery-grade organic solvents, Li{sub 3}OBr was typically found to be insoluble but lost its crystallinity and reacted with available protons and in some cases with the solvent. A low temperature heat treatment was able to restore crystallinity of the samples; however evidence of proton ion exchange was conserved.« less

Integrating a post-column makeup pump into preparative supercritical fluid chromatography systems to address stability and recovery issues during purifications.

PubMed

Bajpai, Lakshmikant; Naidu, Harshavardhan; Asokan, Kathiravan; Shaik, Khaja Mohiddin; Kaspady, Mahammed; Arunachalam, Piramanayagam; Wu, Dauh-Rurng; Mathur, Arvind; Sarabu, Ramakanth

2017-08-18

Purification of many pharmaceutical compounds by supercritical fluid chromatography (SFC) has always been challenging because of degradation of compound during the isolation step in the presence of acidic or basic modifiers in the mobile phase. Stability of such acid or base-sensitive compounds could be improved by post-column addition of a solvent containing base or acid modifier as counter ion through a make-up pump respectively to neutralize the compound fraction without affecting the resolution. One such case study has been presented in this work where the stability of a base-sensitive compound was addressed by the addition of acidic co-solvent through the make-up pump. Details of this setup and the investigation of degradation of the in-house base-sensitive compound are discussed in this paper. In addition, poor retentivity and low recovery of many non-polar compounds in SFC eluting under low co-solvent percentage is another major concern. Even though the desired separation could be achieved with low percentage of co-solvent, it's difficult to get the proper recovery after purification due to precipitation of the sample and significant aerosol formation inside the cyclone. We have demonstrated the first-time use of a post-column make-up pump on SFC 350 system to introduce additional solvent prior to cyclone to avoid the precipitation, reduce the aerosol formation and thus improve the recovery of non-polar compounds eluting under less than 10% of co-solvent. Copyright © 2017 Elsevier B.V. All rights reserved.

Mercaptobenzothiazole-on-gold organic phase biosensor systems: 1. Enhanced organosphosphate pesticide determination.

PubMed

Somerset, V; Baker, P; Iwuoha, E

2009-02-01

This paper reports the construction of the gold/mercaptobenzothiazole/polyaniline/acetylcholinesterase/polyvinylacetate (Au/ MBT/PANI/AChE/PVAc) thick-film biosensor for the determination of certain organophosphate pesticide solutions in selected aqueous organic solvent solutions. The Au/MBT/PANI/AChE/PVAc electrocatalytic biosensor device was constructed by encapsulating acetylcholinesterase (AChE) enzyme in the PANI polymer composite, followed by the coating of poly(vinyl acetate) (PVAc) on top to secure the biosensor film from disintegration in the organic solvents evaluated. The electroactive substrate called acetylthiocholine (ATCh) was employed to provide the movement of electrons in the amperometric biosensor. The voltammetric results have shown that the current shifts more anodically as the Au/MBT/PANI/AChE/PVAc biosensor responded to successive acetylthiocholine (ATCh) substrate addition under anaerobic conditions in 0.1 M phosphate buffer, KCl (pH 7.2) solution and aqueous organic solvent solutions. For the Au/MBT/PANI/AChE/PVAc biosensor, various performance and stability parameters were evaluated. These factors include the optimal enzyme loading, effect of pH, long-term stability of the biosensor, temperature stability of the biosensor, the effect of polar organic solvents, and the effect of non-polar organic solvents on the amperometric behavior of the biosensor. The biosensor was then applied to detect a series of 5 organophosphorous pesticides in aqueous organic solvents and the pesticides studied were parathion-methyl, malathion and chlorpyrifos. The results obtained have shown that the detection limit values for the individual pesticides were 1.332 nM (parathion-methyl), 0.189 nM (malathion), 0.018 nM (chlorpyrifos).

The Importance of Water for High Fidelity Information Processing and for Life

NASA Technical Reports Server (NTRS)

Hoehler, Tori M.; Pohorille, Andrew

2011-01-01

Is water an absolute prerequisite for life? Life depends on a variety of non-covalent interactions among molecules, the nature of which is determined as much by the solvent in which they occur as by the molecules themselves. Catalysis and information processing, two essential functions of life, require non-covalent molecular recognition with very high specificity. For example, to correctly reproduce a string consisting of 600,000 units of information (e.g ., 600 kilobases, equivalent to the genome of the smallest free living terrestrial organisms) with a 90% success rate requires specificity > 107 : 1 for the target molecule vs. incorrect alternatives. Such specificity requires (i) that the correct molecular association is energetically stabilized by at least 40 kJ/mol relative to alternatives, and (ii) that the system is able to sample among possible states (alternative molecular associations) rapidly enough to allow the system to fall under thermodynamic control and express the energetic stabilization. We argue that electrostatic interactions are required to confer the necessary energetic stabilization vs. a large library of molecular alternatives, and that a solvent with polarity and dielectric properties comparable to water is required for the system to sample among possible states and express thermodynamic control. Electrostatic associations can be made in non-polar solvents, but the resulting complexes are too stable to be "unmade" with sufficient frequency to confer thermodynamic control on the system. An electrostatic molecular complex representing 3 units of information (e.g., 3 base pairs) with specificity > 107 per unit has a stability in non-polar solvent comparable to that of a carbon-carbon bond at room temperature. These considerations suggest that water, or a solvent with properties very like water, is necessary to support high-fidelity information processing, and can therefore be considered a critical prerequisite for life.

Carbonic Anhydrase Generates CO2 and H+ That Drive Spider Silk Formation Via Opposite Effects on the Terminal Domains

PubMed Central

Otikovs, Martins; Landreh, Michael; Nordling, Kerstin; Kronqvist, Nina; Westermark, Per; Jörnvall, Hans; Knight, Stefan; Ridderstråle, Yvonne; Holm, Lena; Meng, Qing; Jaudzems, Kristaps; Chesler, Mitchell; Johansson, Jan; Rising, Anna

2014-01-01

Spider silk fibers are produced from soluble proteins (spidroins) under ambient conditions in a complex but poorly understood process. Spidroins are highly repetitive in sequence but capped by nonrepetitive N- and C-terminal domains (NT and CT) that are suggested to regulate fiber conversion in similar manners. By using ion selective microelectrodes we found that the pH gradient in the silk gland is much broader than previously known. Surprisingly, the terminal domains respond in opposite ways when pH is decreased from 7 to 5: Urea denaturation and temperature stability assays show that NT dimers get significantly stabilized and then lock the spidroins into multimers, whereas CT on the other hand is destabilized and unfolds into ThT-positive β-sheet amyloid fibrils, which can trigger fiber formation. There is a high carbon dioxide pressure (pCO2) in distal parts of the gland, and a CO2 analogue interacts with buried regions in CT as determined by nuclear magnetic resonance (NMR) spectroscopy. Activity staining of histological sections and inhibition experiments reveal that the pH gradient is created by carbonic anhydrase. Carbonic anhydrase activity emerges in the same region of the gland as the opposite effects on NT and CT stability occur. These synchronous events suggest a novel CO2 and proton-dependent lock and trigger mechanism of spider silk formation. PMID:25093327

New solvent-stabilized few-layer black phosphorus for antibacterial applications.

PubMed

Sun, Zhenyu; Zhang, Yuqin; Yu, Hao; Yan, Chao; Liu, Yongchao; Hong, Song; Tao, Hengcong; Robertson, Alex W; Wang, Zhuo; Pádua, Agílio A H

2018-06-22

Discovering highly efficient, environmentally friendly, and low-cost exfoliating media that can both disperse and protect black phosphorus (BP) remains a challenge. Herein, we demonstrate such a new molecule, N,N'-dimethylpropyleneurea (DMPU), for effective exfoliation and dispersion of two-dimensional BP nanosheets. A very high exfoliation efficiency of up to 16% was achieved in DMPU, significantly surpassing other good solvents. Exfoliated flakes are free from structural disorder or oxidation. Nanosheets retain high stability in DMPU even after addition of 25 vol% of common solvents. The solvation shell appears to protect the nanosheets from reacting with water and air, more remarkably than the best solvent N-cyclohexyl-2-pyrrolidone reported so far. Molecular dynamics simulations of the exfoliation process show that DMPU is among the effective solvents, although energetically it does not appear as favorable as some other amides. We also demonstrate that our exfoliated BP nanosheets exhibit excellent antimicrobial activities against both Escherichia coli and Staphylococcus aureus, outperforming other common two-dimensional materials of graphene and MoS2, suggesting promise in biomedical applications.

Solvent influence on complex formation between Cd2+ and 2-hydroxy-1,4-naphthoquinone in binary mixed nonaqueous solvents at 15-45°C

NASA Astrophysics Data System (ADS)

Farazandeh, R.; Rounaghi, G. H.; Ebrahimi, M.; Basafa, S.

2017-04-01

The complexation reaction of Cd2+ cation with 2-hydroxy-1,4-naphthoquinone (HNQ) was studied in acetonitrile (AN), 2-PrOH, ethyl acetate (EtOAc), EtOH, dimethylformamide (DMF) and in binary solutions AN-2-PrOH, AN-DMF, AN-EtOH, and AN-EtOAc using conductometric method at 15-45°C. The conductance data show that the stoichiometry of the Cd2+ complex with HNQ in all solvent systems is 1 : 1. In the pure solvents the stability of the complex changes in the order AN > 2-PrOH > EtOH > DMF. The stability of the complex at 25°C in the studied mixtures changes in the following order : AN-EtOAc > AN-2-PrOH > AN-EtOH > AN-DMF. These orders are affected by the nature and composition of the solvent systems and by the temperature. From the temperature dependence data, the thermodynamic functions values (Δ H° and Δ S°) for the complex formation were calculated.

A Flemion-based actuator with ionic liquid as solvent

NASA Astrophysics Data System (ADS)

Wang, Jin; Xu, Chunye; Taya, Minoru; Kuga, Yasuo

2007-04-01

A perfluorinated carboxylic acid membrane, i.e. Flemion, shows improved performance as actuator material compared with Nafion (perfluorinated sulfonic acid). Flemion has a higher ion exchange capacity and good mechanical strength. In particular, Flemion will deform with no back relaxation under applied electrical stimulus. However, with water as solvent, the operation of Flemion in air has serious problems, since water would evaporate quickly in air. Moreover, the electrochemical stability for use in water is around 1 V at room temperature. In previous work, investigations on Nafion with ionic liquid as solvents have been carried out by some researchers and good results have been obtained. In this work, we explore the use of highly stable ionic liquid instead of water as solvent in Flemion. Experimental results indicate that Flemion-based actuators with ionic liquid as solvent have improved stability as compared to the water samples. Although the forces exhibited by Flemion-based actuators with the use of ionic liquid decreased dramatically compared to water, these preliminary results suggest good potential for the use of Flemion with ionic liquid in future applications.

Flemion-based actuator with ionic liquid as solvent

NASA Astrophysics Data System (ADS)

Wang, Jin; Xu, Chunye; Taya, Minoru; Kuga, Yasuo

2006-03-01

A perfluorinated carboxylic acid membrane, i.e. Flemion, shows improved performance as actuator material compared with Nafion (perfluorinated sulfonic acide). Flemion has a higher ion exchange capacity and good mechanical strength. Especially, Flemion will deform with no back relaxation when applied electrical stimulus. However, with water as solvent, the operation of Flemion in air has serious problems. Since water would evaporate quickly in air. Moreover, the electrochemical stability for use in water is around 1V at room temperature. In previous work, investigations on Nafion with ionic liquid as solvents have been carried out and good results have been obtained. In this work, we explore the use of highly stable ionic liquid instead of water as solvent in Flemion. Experimental results indicate that Flemion based actuators with ionic liquid as solvent have improved stability as compared to the water samples. Although the forces exhibited by Flemion based actuators with the use of ionic liquid decreased dramatically as compared to water, these preliminary results suggest a good potential for use of Flemion with ionic liquid in some applications.

Potential of mean force between two hydrophobic solutes in water.

PubMed

Southall, Noel T; Dill, Ken A

2002-12-10

We study the potential of mean force between two nonpolar solutes in the Mercedes Benz model of water. Using NPT Monte Carlo simulations, we find that the solute size determines the relative preference of two solute molecules to come into contact ('contact minimum') or to be separated by a single layer of water ('solvent-separated minimum'). Larger solutes more strongly prefer the contacting state, while smaller solutes have more tendency to become solvent-separated, particularly in cold water. The thermal driving forces oscillate with solute separation. Contacts are stabilized by entropy, whereas solvent-separated solute pairing is stabilized by enthalpy. The free energy of interaction for small solutes is well-approximated by scaled-particle theory. Copyright 2002 Elsevier Science B.V.

Self-healing Microencapsulation of Biomacromolecules without Organic Solvents**

PubMed Central

Reinhold, Samuel E.; Desai, Kashappa-Goud H.; Zhang, Li; Olsen, Karl F.

2012-01-01

Microencapsulation of biomacromolecules in PLGA is routinely performed with organic solvent through multiple complex steps deleterious to the biomacromolecule. The new self-healing based PLGA microencapsulation obviates micronization- and organic solvent-induced protein damage, provides very high encapsulation efficiency, exhibit stabilization and slow release of labile tetanus protein antigen, and provides long-term testosterone suppression in rats following a single injection of encapsulated leuprolide. PMID:23011773

Recombinant MHC Tetramers for Isolation of Virus-Specific CD8+ Cells from Healthy Donors: Potential Approach for Cell Therapy of Posttransplant Cytomegalovirus Infection.

PubMed

Vdovin, A S; Filkin, S Y; Yefimova, P R; Sheetikov, S A; Kapranov, N M; Davydova, Y O; Egorov, E S; Khamaganova, E G; Drokov, M Y; Kuzmina, L A; Parovichnikova, E N; Efimov, G A; Savchenko, V G

2016-11-01

Patients undergoing allogeneic hematopoietic stem cell transplantation have a high risk of cytomegalovirus reactivation, which in the absence of T-cell immunity can result in the development of an acute inflammatory reaction and damage of internal organs. Transfusion of the virus-specific donor T-lymphocytes represents an alternative to a highly toxic and often ineffective antiviral therapy. Potentially promising cell therapy approach comprises transfusion of cytotoxic T-lymphocytes, specific to the viral antigens, immediately after their isolation from the donor's blood circulation without any in vitro expansion. Specific T-cells could be separated from potentially alloreactive lymphocytes using recombinant major histocompatibility complex (MHC) multimers, carrying synthetic viral peptides. Rapid transfusion of virus-specific T-cells to patients has several crucial advantages in comparison with methods based on the in vitro expansion of the cells. About 30% of hematopoietic stem cell donors and 46% of transplant recipients at the National Research Center for Hematology were carriers of the HLA-A*02 allele. Moreover, 94% of Russian donors have an immune response against the cytomegalovirus (CMV). Using recombinant HLA-A*02 multimers carrying an immunodominant cytomegalovirus peptide (NLV), we have shown that the majority of healthy donors have pronounced T-cell immunity against this antigen, whereas shortly after the transplantation the patients do not have specific T-lymphocytes. The donor cells have the immune phenotype of memory cells and can be activated and proliferate after stimulation with the specific antigen. Donor lymphocytes can be substantially enriched to significant purity by magnetic separation with recombinant MHC multimers and are not activated upon cocultivation with the antigen-presenting cells from HLA-incompatible donors without addition of the specific antigen. This study demonstrated that strong immune response to CMV of healthy donors and prevalence of HLA-A*02 allele in the Russian population make it possible to isolate a significant number of virus-specific cells using HLA-A*02-NLV multimers. After the transfusion, these cells should protect patients from CMV without development of allogeneic immune response.

ATZ11 Recognizes Not Only Z-α1-Antitrypsin-Polymers and Complexed Forms of Non-Z-α1-Antitrypsin but Also the von Willebrand Factor

PubMed Central

Yadegari, Hamideh; Driesen, Julia; Kirfel, Jutta; Neuhaus, Thomas; Steiner, Susanne; Esch, Christiane; Bedorf, Jörg; Hertfelder, Hans-Jörg; Fischer, Hans-Peter

2014-01-01

Aims The ATZ11 antibody has been well established for the identification of α1-anti-trypsin (AAT) molecule type PiZ (Z-AAT) in blood samples and liver tissue. In this study, we systematically analyzed the antibody for additional binding sites in human tissue. Methods and Results Ultrastructural ATZ11 binding was investigated immunoelectron microscopically in human umbilical vein endothelial cells (HUVECs) and in platelets of a healthy individual. Human embryonic kidney (HEK293) cells were transiently transfected with Von Willebrand factor (VWF) and analyzed immunocytochemically using confocal microscopy and SDS-PAGE electrophoresis followed by western blotting (WB). Platelets and serum samples of VWF-competent and VWF-deficient patients were investigated using native PAGE and SDS-PAGE electrophoresis followed by WB. The specificity of the ATZ11 reaction was tested immunohistochemically by extensive antibody-mediated blocking of AAT- and VWF-antigens. ATZ11-positive epitopes could be detected in Weibel-Palade bodies (WPBs) of HUVECs and α-granules of platelets. ATZ11 stains pseudo-WBP containing recombinant wild-type VWF (rVWF-WT) in HEK293 cells. In SDS-PAGE electrophoresis followed by WB, anti-VWF and ATZ11 both identified rVWF-WT. However, neither rVWF-WT-multimers, human VWF-multimers, nor serum proteins of VWF-deficient patients were detected using ATZ11 by WB, whereas anti-VWF antibody (anti-VWF) detected rVWF-WT-multimers as well as human VWF-multimers. In human tissue specimens, AAT-antigen blockade using anti-AAT antibody abolished ATZ11 staining of Z-AAT in a heterozygous AAT-deficient patient, whereas VWF-antigen blockade using anti-VWF abolished ATZ11 staining of endothelial cells and megakaryocytes. Conclusions ATZ11 reacts with cellular bound and denatured rVWF-WT and human VWF as shown using immunocytochemistry and subsequent confocal imaging, immunoelectron microscopy, SDS-PAGE and WB, and immunohistology. These immunoreactions are independent of the binding of Z-AAT-molecules and non-Z-AAT complexes. PMID:24646657

Synthesis, fractionation, and thin film processing of nanoparticles using the tunable solvent properties of carbon dioxide gas expanded liquids

NASA Astrophysics Data System (ADS)

Anand, Madhu

Nanoparticles have received significant attention because of their unusual characteristics including high surface area to volume ratios. Materials built from nanoparticles possess unique chemical, physical, mechanical and optical properties. Due to these properties, they hold potential in application areas such as catalysts, sensors, semiconductors and optics. At the same time, CO 2 in the form of supercritical fluid or CO2 gas-expanded liquid mixtures has gained significant attention in the area of processing nanostructures. This dissertation focuses on the synthesis and processing of nanoparticles using CO2 tunable solvent systems. Nanoparticle properties depend heavily on their size and, as such, the ability to finely control the size and uniformity of nanoparticles is of utmost importance. Solution based nanoparticle formation techniques are attractive due to their simplicity, but they often result in the synthesis of particles with a wide size range. To address this limitation, a post-synthesis technique has been developed in this dissertation to fractionate polydisperse nanoparticles ( s . = 30%) into monodisperse fractions ( s . = 8%) using tunable physicochemical properties of CO 2 expanded liquids, where CO2 is employed as an antisolvent. This work demonstrates that by controlling the addition of CO2 (pressurization) to an organic dispersion of nanoparticles, the ligand stabilized nanoparticles can be size selectively precipitated within a novel high pressure apparatus that confines the particle precipitation to a specified location on a surface. Unlike current techniques, this CO2 expanded liquid approach provides faster and more efficient particle size separation, reduction in organic solvent usage, and pressure tunable size selection in a single process. To improve our fundamental understanding and to further refine the size separation process, a detailed study has been performed to identify the key parameters enabling size separation of various nanoparticle populations. This study details the influence of various factors on the size separation process, such as the types of nanoparticles, ligand type and solvent type as well as the use of recursive fractionation and the time allowed for settling during each fractionation step. This size selective precipitation technique was also applied to fractionate and separate polydisperse dispersions of CdSe/ZnS semiconductor nanocrystals into very distinct size and color fractions based solely on the pressure tunable solvent properties of CO2 expanded liquids. This size selective precipitation of nanoparticles is achieved by finely tuning the solvent strength of the CO2/organic solvent medium by simply adjusting the applied CO2 pressure. These subtle changes affect the balance between osmotic repulsive and van der Waals attractive forces thereby allowing fractionation of the nanocrystals into multiple narrow size populations. Thermodynamic analysis of nanoparticle size selective fractionation was performed to develop a theoretical model based on the thermodynamic properties of gas expanded liquids. We have used the general phenomenon of nanoparticle precipitation with CO2 expanded liquids to create dodecanethiol stabilized gold nanoparticle thin films. This method utilizes CO2 as an anti-solvent for low defect, wide area gold nanoparticle film formation employing monodisperse gold nanoparticles. Dodecanethiol stabilized gold particles are precipitated from hexane by controllably expanding the solution with carbon dioxide. Subsequent addition of carbon dioxide as a dense supercritical fluid then provides for removal of the organic solvent while avoiding the dewetting effects common to evaporating solvents. Unfortunately, the use of carbon dioxide as a neat solvent in nanoparticles synthesis and processing is limited by the very poor solvent strength of dense phase CO2. As a result, most current techniques employed to synthesize and disperse nanoparticles in neat carbon dioxide require the use of environmentally persistent fluorinated compounds as metal precursors and/or stabilizing ligands. This dissertation presents the first report of the simultaneous synthesis and stabilization of metallic nanoparticles in carbon dioxide solvent without the use of any fluorinated compounds thereby further enabling the use of CO 2 as a green solvent medium in nanomaterials synthesis and processing.

[The effect of hydrophobic surface properties of protein on its resistance to denaturation by organic solvents (using modified alpha-chymotrypsin as an example].

PubMed

Kudriashova, E V; Belova, A B; Vinogradov, A A; Mozhaev, V V

1994-03-01

Catalytic activity of covalently modified alpha-chymotrypsin in water/cosolvent solutions was investigated. The stability of chymotrypsin increases upon modification with hydrophilic reagents, such as glyceraldehyde, pyrometallic and succinic anhydrides, and glucosamine. Correlation was observed between the protein's stability in organic solvents and the degree of hydrophilization of the protein's surface. The protein is the more stable, the higher are the modification degree and the hydrophilicity of the modifying residue. At a certain critical hydrophilization degree of chymotrypsin a limit of stability is achieved. The stabilization effect can be accounted for by the fact that the interaction between water molecules on the surface and protein's functional groups become stronger in the hydrophilized protein.

Multidimensional equilibria and their stability in copolymer-solvent mixtures

NASA Astrophysics Data System (ADS)

Glasner, Karl; Orizaga, Saulo

2018-06-01

This paper discusses localized equilibria which arise in copolymer-solvent mixtures. A free boundary problem associated with the sharp-interface limit of a density functional model is used to identify both lamellar and concentric domain patterns composed of a finite number of layers. Stability of these morphologies is studied through explicit linearization of the free boundary evolution. For the multilayered lamellar configuration, transverse instability is observed for sufficiently small dimensionless interfacial energies. Additionally, a crossover between small and large wavelength instabilities is observed depending on whether solvent-polymer or monomer-monomer interfacial energy is dominant. Concentric domain patterns resembling multilayered micelles and vesicles exhibit bifurcations wherein they only exist for sufficiently small dimensionless interfacial energies. The bifurcation of large radii vesicle solutions is studied analytically, and a crossover from a supercritical case with only one solution branch to a subcritical case with two is observed. Linearized stability of these configurations shows that azimuthal perturbation may lead to instabilities as interfacial energy is decreased.

Pseudolatex preparation using a novel emulsion-diffusion process involving direct displacement of partially water-miscible solvents by distillation.

PubMed

Quintanar-Guerrero, D; Allémann, E; Fessi, H; Doelker, E

1999-10-25

Pseudolatexes were obtained by a new process based on an emulsification-diffusion technique involving partially water-miscible solvents. The preparation method consisted of emulsifying an organic solution of polymer (saturated with water) in an aqueous solution of a stabilizing agent (saturated with solvent) using conventional stirrers, followed by direct solvent distillation. The technique relies on the rapid displacement of the solvent from the internal into the external phase which thereby provokes polymer aggregation. Nanoparticle formation is believed to occur because rapid solvent diffusion produces regions of local supersaturation near the interface, and nanoparticles are formed due to the ensuing interfacial phase transformations and polymer aggregation that occur in these interfacial domains. Using this method, it was possible to prepare pseudolatexes of biodegradable and non-biodegradable polymers such as poly(D,L-lactic acid) and poly(epsilon-caprolactone), Eudragit E, cellulose acetate phthalate, cellulose acetate trimellitate using ethyl acetate or 2-butanone as partially water-miscible solvents and poly(vinyl alcohol) or poloxamer 407 as stabilizing agent. A transition from nano- to microparticles was observed at high polymer concentrations. At concentrations above 30% w/v of Eudragit E in ethyl acetate or cellulose acetate phthalate in 2-butanone only microparticles were obtained. This behaviour was attributed to decreased transport of polymer molecules into the aqueous phase.

Improvement of activity and stability of chloroperoxidase by chemical modification

PubMed Central

Liu, Jian-Zhong; Wang, Min

2007-01-01

Background Enzymes show relative instability in solvents or at elevated temperature and lower activity in organic solvent than in water. These limit the industrial applications of enzymes. Results In order to improve the activity and stability of chloroperoxidase, chloroperoxidase was modified by citraconic anhydride, maleic anhydride or phthalic anhydride. The catalytic activities, thermostabilities and organic solvent tolerances of native and modified enzymes were compared. In aqueous buffer, modified chloroperoxidases showed similar Km values and greater catalytic efficiencies kcat/Km for both sulfoxidation and oxidation of phenol compared to native chloroperoxidase. Of these modified chloroperoxidases, citraconic anhydride-modified chloroperoxidase showed the greatest catalytic efficiency in aqueous buffer. These modifications of chloroperoxidase increased their catalytic efficiencies for sulfoxidation by 12%~26% and catalytic efficiencies for phenol oxidation by 7%~53% in aqueous buffer. However, in organic solvent (DMF), modified chloroperoxidases had lower Km values and higher catalytic efficiencies kcat/Km than native chloroperoxidase. These modifications also improved their thermostabilities by 1~2-fold and solvent tolerances of DMF. CD studies show that these modifications did not change the secondary structure of chloroperoxidase. Fluorescence spectra proved that these modifications changed the environment of tryptophan. Conclusion Chemical modification of epsilon-amino groups of lysine residues of chloroperoxidase using citraconic anhydride, maleic anhydride or phthalic anhydride is a simple and powerful method to enhance catalytic properties of enzyme. The improvements of the activity and stability of chloroperoxidase are related to side chain reorientations of aromatics upon both modifications. PMID:17511866

A comparative study of spray-dried and freeze-dried hydrocortisone/polyvinyl pyrrolidone solid dispersions.

PubMed

Dontireddy, Rakesh; Crean, Abina M

2011-10-01

Poor water solubility of new chemical entities (NCEs) is one of the major challenges the pharmaceutical industry currently faces. The purpose of this study was to investigate the feasibility of freeze-drying as an alternative technique to spray-drying to produce solid dispersions of poorly water-soluble drugs. Also investigated was the use of aqueous solvent mixtures in place of pure solvent for the production of solid dispersions. Aqueous solvent systems would reduce the environmental impact of pure organic solvent systems. Spray-dried and freeze-dried hydrocortisone/polyvinyl pyrrolidone solid dispersions exhibited differences in dissolution behavior. Freeze-dried dispersions exhibited faster dissolution rates than the corresponding spray-dried dispersions. Spray-dried systems prepared using both solvent systems (20% v/v and 96% v/v ethanol) displayed similar dissolution performance despite displaying differences in glass transition temperatures (T(g)) and surface areas. All dispersions showed drug/polymer interactions indicated by positive deviations in T(g) from the predicted values calculated using the Couchman-Karasz equation. Fourier transform infrared (FTIR) spectroscopic results confirmed the conversion of crystalline drug to the amorphous in the dispersions. Stability studies were preformed at 40°C and 75% relative humidity to investigate the physical stability of prepared dispersions. Recrystallization was observed after a month and the resultant dispersions were tested for their dissolution performance to compare with the dissolution performance of the dispersions prior to the stability study. The dissolution rate of the freeze-dried dispersions remained higher than both spray-dried dispersions after storage.

Photoinduced intramolecular charge transfer (ICT) reaction in trans-methyl p-(dimethylamino) cinnamate: A combined fluorescence measurement and quantum chemical calculations

NASA Astrophysics Data System (ADS)

Chakraborty, Amrita; Kar, Samiran; Guchhait, Nikhil

2006-01-01

The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate ( t-MDMAC) donor-acceptor system has been investigated by steady-state absorption and emission spectroscopy and quantum chemical calculations. The molecule t-MDMAC shows an emission from the locally excited state in non-polar solvents. In addition to weak local emission, a strong solvent dependent red shifted fluorescence in polar aprotic solvents is attributed to highly polar intramolecular charge transfer state. However, the formation of hydrogen-bonded clusters with polar protic solvents has been suggested from a linear correlation between the observed red shifted fluorescence band maxima with hydrogen bonding parameters ( α). Calculations by ab initio and density functional theory show that the lone pair electron at nitrogen center is out of plane of the benzene ring in the global minimum ground state structure. In the gas phase, a potential energy surface along the twist coordinate at the donor (-NMe 2) and acceptor (-CH = CHCOOMe) sites shows stabilization of S 1 state and destabilization S 2 and S 0 states. A similar potential energy calculation along the twist coordinate in acetonitrile solvent using non-equilibrium polarized continuum model also shows more stabilization of S 1 state relative to other states and supports solvent dependent red shifted emission properties. In all types of calculations it is found that the nitrogen lone pair is delocalized over the benzene ring in the global minimum ground state and is localized on the nitrogen centre at the 90° twisted configuration. The S 1 energy state stabilization along the twist coordinate at the donor site and localized nitrogen lone pair at the perpendicular configuration support well the observed dual fluorescence in terms of proposed twisted intramolecular charge transfer (TICT) model.

A rapid method to visualize von willebrand factor multimers by using agarose gel electrophoresis, immunolocalization and luminographic detection.

PubMed

Krizek, D R; Rick, M E

2000-03-15

A highly sensitive and rapid clinical method for the visualization of the multimeric structure of von Willebrand Factor in plasma and platelets is described. The method utilizes submerged horizontal agarose gel electrophoresis, followed by transfer of the von Willebrand Factor onto a polyvinylidine fluoride membrane, and immunolocalization and luminographic visualization of the von Willebrand Factor multimeric pattern. This method distinguishes type 1 from types 2A and 2B von Willebrand disease, allowing timely evaluation and classification of von Willebrand Factor in patient plasma. It also allows visualization of the unusually high molecular weight multimers present in platelets. There are several major advantages to this method including rapid processing, simplicity of gel preparation, high sensitivity to low concentrations of von Willebrand Factor, and elimination of radioactivity.

Sonic hedgehog multimerization: a self-organizing event driven by post-translational modifications?

PubMed

Koleva, Mirella V; Rothery, Stephen; Spitaler, Martin; Neil, Mark A A; Magee, Anthony I

2015-01-01

Sonic hedgehog (Shh) is a morphogen active during vertebrate development and tissue homeostasis in adulthood. Dysregulation of the Shh signalling pathway is known to incite carcinogenesis. Due to the highly lipophilic nature of this protein imparted by two post-translational modifications, Shh's method of transit through the aqueous extracellular milieu has been a long-standing conundrum, prompting the proposition of numerous hypotheses to explain the manner of its displacement from the surface of the producing cell. Detection of high molecular-weight complexes of Shh in the intercellular environment has indicated that the protein achieves this by accumulating into multimeric structures prior to release from producing cells. The mechanism of assembly of the multimers, however, has hitherto remained mysterious and contentious. Here, with the aid of high-resolution optical imaging and post-translational modification mutants of Shh, we show that the C-terminal cholesterol and the N-terminal palmitate adducts contribute to the assembly of large multimers and regulate their shape. Moreover, we show that small Shh multimers are produced in the absence of any lipid modifications. Based on an assessment of the distribution of various dimensional characteristics of individual Shh clusters, in parallel with deductions about the kinetics of release of the protein from the producing cells, we conclude that multimerization is driven by self-assembly underpinned by the law of mass action. We speculate that the lipid modifications augment the size of the multimolecular complexes through prolonging their association with the exoplasmic membrane.

Ultrathin Hydrophobic Coatings Obtained on Polyethylene Terephthalate Materials in Supercritical Carbon Dioxide with Co-Solvents

NASA Astrophysics Data System (ADS)

Kumeeva, T. Yu.; Prorokova, N. P.

2018-02-01

The surface properties of ultradisperse polytetrafluoroethylene coatings on polyethylene terephthalate materials modified in a supercritical carbon dioxide medium with co-solvent additions (aliphatic alcohols) were analyzed. An atomic force microscopy study revealed the peculiarities of the morphology of the hydrophobic coatings formed in the presence of co-solvents. The contribution of the co-solvents to the formation of the surface layer with a low surface energy was evaluated from the surface energy components of the modified polyester material. The stability of the coatings against dry friction was analyzed.

A comprehensive study of the complexation of alkali metal cations by lower rim calix[4]arene amide derivatives.

PubMed

Horvat, Gordan; Frkanec, Leo; Cindro, Nikola; Tomišić, Vladislav

2017-09-13

The complexation of alkali metal cations by lower rim N,N-dihexylacetamide (L1) and newly synthesized N-hexyl-N-methylacetamide (L2) calix[4]arene tertiary-amide derivatives was thoroughly studied at 25 °C in acetonitrile (MeCN), benzonitrile (PhCN), and methanol (MeOH) by means of direct and competitive microcalorimetric titrations, and UV and 1 H NMR spectroscopies. In addition, by measuring the ligands' solubilities, the solution (transfer) Gibbs energies of the ligands and their alkali metal complexes were obtained. The inclusion of solvent molecules in the free and complexed calixarene hydrophobic cavities was also investigated. Computational (classical molecular dynamics) investigations of the studied systems were also carried out. The obtained results were compared with those previously obtained by studying the complexation ability of an N-hexylacetamidecalix[4]arene secondary-amide derivative (L3). The stability constants of 1 : 1 complexes were determined in all solvents used (the values obtained by different methods being in excellent agreement), as were the corresponding complexation enthalpies and entropies. Almost all of the examined reactions were enthalpically controlled. The most striking exceptions were reactions of Li + with both ligands in methanol, for which the entropic contribution to the reaction Gibbs energy was substantial due the entropically favourable desolvation of the smallest lithium cation. The thermodynamic stabilities of the complexes were quite solvent dependent (the stability decreased in the solvent order: MeCN > PhCN ≫ MeOH), which could be accounted for by considering the differences in the solvation of the ligand and free and complexed alkali metal cations in the solvents used. Comparison of the stability constants of the ligand L1 and L2 complexes clearly revealed that the higher electron-donating ability of the hexyl with respect to the methyl group is of considerable importance in determining the equilibria of the complexation reactions. Additionally, the quite strong influence of intramolecular hydrogen bond formation in compound L3 (not present in ligands L1 and L2) and that of the inclusion of solvent molecules in the calixarene hydrophobic cone were shown to be of great importance in determining the thermodynamic stability of the calixarene-cation complexes. The experimental results were fully supported by those obtained by MD simulations.

IRIS TOXICOLOGICAL REVIEW AND SUMMARY DOCUMENTS FOR 1,4 - DIOXANE

EPA Science Inventory

1,4 -Dioxane is a cyclic ether that is primarily utilized for industrial applications. These applications include 1,4 -dioxane as a solvent, reaction medium, wetting, degreasing, and dispersing agent, and for stabilization of chlorinated solvents (e.g. 1,1,1 -trichloroethane). ...

How a protein can remain stable in a solvent with high content of urea: insights from molecular dynamics simulation of Candida antarctica lipase B in urea : choline chloride deep eutectic solvent.

PubMed

Monhemi, Hassan; Housaindokht, Mohammad Reza; Moosavi-Movahedi, Ali Akbar; Bozorgmehr, Mohammad Reza

2014-07-28

Deep eutectic solvents (DESs) are utilized as green and inexpensive alternatives to classical ionic liquids. It has been known that some of DESs can be used as solvent in the enzymatic reactions to obtain very green chemical processes. DESs are quite poorly understood at the molecular level. Moreover, we do not know much about the enzyme microstructure in such systems. For example, how some hydrolase can remain active and stable in a deep eutectic solvent including 9 M of urea? In this study, the molecular dynamics of DESs as a liquid was simulated at the molecular level. Urea : choline chloride as a well-known eutectic mixture was chosen as a model DES. The behavior of the lipase as a biocatalyst was studied in this system. For comparison, the enzyme structure was also simulated in 8M urea. The thermal stability of the enzyme was also evaluated in DESs, water, and 8M urea. The enzyme showed very good conformational stability in the urea : choline chloride mixture with about 66% urea (9 M) even at high temperatures. The results are in good agreement with recent experimental observations. In contrast, complete enzyme denaturation occurred in 8M urea with only 12% urea in water. It was found that urea molecules denature the enzyme by interrupting the intra-chain hydrogen bonds in a "direct denaturation mechanism". However, in a urea : choline chloride deep eutectic solvent, as a result of hydrogen bonding with choline and chloride ions, urea molecules have a low diffusion coefficient and cannot reach the protein domains. Interestingly, urea, choline, and chloride ions form hydrogen bonds with the surface residues of the enzyme which, instead of lipase denaturation, leads to greater enzyme stability. To the best of our knowledge, this is the first study in which the microstructural properties of a macromolecule are examined in a deep eutectic solvent.

Stability improvement of gel-state dye-sensitized solar cells by utilization the co-solvent effect of propionitrile/acetonitrile and 3-methoxypropionitrile/acetonitrile with poly(acrylonitrile-co-vinyl acetate)

NASA Astrophysics Data System (ADS)

Venkatesan, Shanmugam; Su, Song-Chuan; Kao, Shon-Chen; Teng, Hsisheng; Lee, Yuh-Lang

2015-01-01

Propionitrile (PPN) or 3-methoxypropionitrile (MPN) is mixed with acetonitrile (ACN) to prepare ACN/PPN and ACN/MPN co-solvents and used to fabricate polymer gel electrolytes (PGEs) of dye-sensitized solar cells (DSSCs), aiming at improving the stability of gel-state DSSCs. Co-solvents with various ratios are utilized to prepare PGEs using poly(acrylonitrile-co-vinyl acetate) (PAN-VA) as the gelator. The ratio effects of the co-solvents on the properties of PGEs and the performances of the corresponding DSSCs are studied. The results show that in-situ gelation of the gel-electrolytes can still be performed at the presence of 40% PPN or 30% MPN. However, increasing the composition of PPN and MPN in the co-solvents triggers a decrease in the diffusivity and conductivity of the PGEs, but an increase in the viscosity. Therefore, the energy conversion efficiencies of the cells decrease as a result. However, the introduction of PPN and MPN elevates the gel-to-liquid transition temperature (Tp) of the PGEs which significantly increases the stability of the gel-state DSSCs. Comparing between the effects of the two co-solvents, PPN and MPN have similar effect on elevation of Tp, but the conductivity of PGEs and the corresponding cell efficiency are higher for the ACN/PPN system, attributed to its lower viscosity compared with ACN/MPN system. By using the ACN/PPN (60/40) co-solvent at the presence of TiO2 fillers, gel-state cell with an efficiency of 8.3% can be achieved, which is even higher than that obtained by the liquid state cell (8%). After 500 h test at 60 °C, the cell can retain 95.4% of its initial efficiency.

"Inverted" Solvent Effect on Charge Transfer in the Excited State.

PubMed

Nau; Pischel

1999-10-04

Faster in cyclohexane than in acetonitrile is the fluorescence quenching of the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by amines and sulfides. Although this photoreaction is induced by charge transfer (CT; see picture) and exciplexes are formed, the increase in the dipole moment of the exciplex is not large enough to offset the solvent stabilization of the excited reactants, and an "inverted" solvent effect results.

Effect of the type and level of hydration of alcoholic solvents on the simultaneous extraction of oil and chlorogenic acids from sunflower seed press cake.

PubMed

Scharlack, Nayara K; Aracava, Keila K; Rodrigues, Christianne Ec

2017-10-01

The present study aimed to evaluate the replacement of hexane by alcoholic solvents in oil extraction from sunflower seed press cake. The use of ethanol and isopropanol has important advantages, including low toxicity and good operational safety. Thus, in the present study, solid-liquid extractions were performed in a single stage from 60 to 90 °C and in consecutive extractions in three stages at 90 °C. Solvent hydration negatively affected the extraction of oil but favored the extraction of chlorogenic acids (CAs), especially when ethanol was used. Regarding oxidative stability, the oils extracted using ethanol presented long induction times, which could be related to the high levels of not only CAs and tocopherols, but also phospholipids. Alcoholic solvents can be used for extraction to produce sunflower seed oil containing minor compounds that give it greater oxidative stability. In addition, the results obtained using hydrous ethanol showed that this solvent can yield defatted sunflower seed meal with a low content of CAs, enabling future use of the protein fraction. © 2017 Society of Chemical Industry. © 2017 Society of Chemical Industry.

Towards more thermally stable Li-ion battery electrolytes with salts and solvents sharing nitrile functionality

NASA Astrophysics Data System (ADS)

Kerner, Manfred; Lim, Du-Hyun; Jeschke, Steffen; Rydholm, Tomas; Ahn, Jou-Hyeon; Scheers, Johan

2016-11-01

The overall safety of Li-ion batteries is compromised by the state-of-the-art electrolytes; the thermally unstable lithium salt, lithium hexafluorophosphate (LiPF6), and flammable carbonate solvent mixtures. The problem is best addressed by new electrolyte compositions with thermally robust salts in low flammability solvents. In this work we introduce electrolytes with either of two lithium nitrile salts, lithium 4,5-dicyano-1,2,3-triazolate (LiDCTA) or lithium 4,5-dicyano-2-trifluoromethylimidazolide (LiTDI), in solvent mixtures with high flashpoint adiponitrile (ADN), as the main component. With sulfolane (SL) and ethylene carbonate (EC) as co-solvents the liquid temperature range of the electrolytes are extended to lower temperatures without lowering the flashpoint, but at the expense of high viscosities and moderate ionic conductivities. The anodic stabilities of the electrolytes are sufficient for LiFePO4 cathodes and can be charged/discharged for 20 cycles in Li/LiFePO4 cells with coulombic efficiencies exceeding 99% at best. The excellent thermal stabilities of the electrolytes with the solvent combination ADN:SL are promising for future electrochemical investigations at elevated temperatures (> 60 °C) to compensate the moderate transport properties and rate capability. The electrolytes with EC as a co-solvent, however, release CO2 by decomposition of EC in presence of a lithium salt, which potentially makes EC unsuitable for any application targeting higher operating temperatures.

Electrode stabilizing materials

DOEpatents

Amine, Khalil; Abouimrane, Ali; Moore, Jeffrey S.; Odom, Susan A.

2015-11-03

An electrolyte includes a polar aprotic solvent; an alkali metal salt; and an electrode stabilizing compound that is a monomer, which when polymerized forms an electrically conductive polymer. The electrode stabilizing compound is a thiophene, a imidazole, a anilines, a benzene, a azulene, a carbazole, or a thiol. Electrochemical devices may incorporate such electrolytes.

Bio-Oil Separation and Stabilization by Near-Critical Propane Fractionation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ginosar, Daniel M.; Petkovic, Lucia M.; Agblevor, Foster A.

Bio-oils produced by thermal process are promising sources of sustainable, low greenhouse gas alternative fuels. These thermal processes are also well suited to decentralized energy production due to low capital and operating costs. Algae feedstocks for bio-oil production are of particular interest, due in part to their high-energy growth yields. Further, algae can be grown in non-arable areas in fresh, brackish, salt water, or even waste water. Unfortunately, bio-oils produced by thermal processes present significant stability challenges. These oils have complex chemical compositions, are viscous, reactive, and thermally unstable. Further, the components within the oils are difficult to separate bymore » fractional distillation. By far, the most effective separation and stabilization method has been solvent extraction. However, liquid phase extraction processes pose two main obstacles to commercialization; they require a significant amount of energy to remove and recover the solvent from the product, and they have a propensity for the solvent to become contaminated with minerals from the char and ash present in the original bio-oil. Separation and fractionation of thermally produced bio-oils using supercritical fluids (SCF) offers the advantages of liquid solvent extraction while drastically reducing energy demands and the predisposition to carry over solids into the extracted phase. SCFs are dense fluids with liquid-like solvent properties and gas-like transport properties. Further, SCF density and solvent strength can be tuned with minor adjustments in pressure, co-solvent addition, or gas anti-solvent addition. Catalytic pyrolysis oils were produced from Scenedesmus dimorphus algae using a fluid catalytic cracking catalyst. Bio-oil produced from catalytic fast pyrolysis (CFP) was separated using critical fluids. Propane extraction was performed at 65 °C at a fluid reduced pressure of 2.0 (85 bar) using an eight to one solvent to feed ratio by weight. Extraction of catalytic fast pyrolysis oil with near critical propane produced an oil extract that was physically and chemically different from and more stable than the original oil. The propane extract displayed lower viscosity and lower average molecular weight. The species present in the propane extract were likely the less polar that would be expected from using a non-polar solvent (propane). Carbonyl containing species in the extract were likely ketones and esters. The raffinate contained a higher amnount of OH bonded species along with the more polar more polar acids, amides, and alcohols. The higher concentration of nitrogen in the raffinate may confirm the presence of amides. Viscosity of the propane extract increased only half as much as that of the CFP bio-oil. Further, In situ NMR aging studies showed that the propane extract was more stable than the raw oil. In conclusion, propane extraction is a promising method to decrease the nitrogen content of bio-oils and to improve the stability of bio-oils obtained by the catalytic pyrolysis of algae based biomass.« less

Triplet-sensitized photon upconversion in deep eutectic solvents.

PubMed

Murakami, Yoichi; Das, Sudhir Kumar; Himuro, Yuki; Maeda, Satoshi

2017-11-22

Photon upconversion (UC) is a technology that can increase solar utilization efficiencies in broad photoenergy conversion systems by converting lower-energy photons into usable higher-energy photons. Recently, UC using triplet-triplet annihilation (TTA) of organic molecules has drawn attention because it is presently the only method applicable to weak and noncoherent light. To date, many attempts have been made to realize this UC technology in forms suitable for applications, but they typically suffer from either high cost or insufficient stability and/or safety of materials. Recently, a new class of liquid called deep eutectic solvents (DESs) has emerged as low-cost green fluids that possess low toxicity and vapor pressure, biodegradability, and high thermal stability. DESs have been proposed as an alternative to ionic liquids. This article develops triplet-sensitized UC samples using DESs that are found to be suitable solvents for this purpose, attaining a new materials platform for UC with the aforementioned advantages. The high thermal stability of the samples is qualitatively confirmed and their UC quantum yields are determined to be 0.11-0.21 (based on the definition that the maximum quantum yield is 0.5) depending on the DES composition. The triplet lifetime of the emitter 9,10-diphenylanthracene increases with DES viscosity, resulting in unique kinetics. Analysis of photophysical experimental results allows the relevant physics governing the performance of this sample system to be determined and discussed. Overall, a novel UC platform that simultaneously achieves high thermal stability, low cost, and environmental friendliness is developed using DESs as the solvent.

Conformational analysis of glutamic acid: a density functional approach using implicit continuum solvent model.

PubMed

Turan, Başak; Selçuki, Cenk

2014-09-01

Amino acids are constituents of proteins and enzymes which take part almost in all metabolic reactions. Glutamic acid, with an ability to form a negatively charged side chain, plays a major role in intra and intermolecular interactions of proteins, peptides, and enzymes. An exhaustive conformational analysis has been performed for all eight possible forms at B3LYP/cc-pVTZ level. All possible neutral, zwitterionic, protonated, and deprotonated forms of glutamic acid structures have been investigated in solution by using polarizable continuum model mimicking water as the solvent. Nine families based on the dihedral angles have been classified for eight glutamic acid forms. The electrostatic effects included in the solvent model usually stabilize the charged forms more. However, the stability of the zwitterionic form has been underestimated due to the lack of hydrogen bonding between the solute and solvent; therefore, it is observed that compact neutral glutamic acid structures are more stable in solution than they are in vacuum. Our calculations have shown that among all eight possible forms, some are not stable in solution and are immediately converted to other more stable forms. Comparison of isoelectronic glutamic acid forms indicated that one of the structures among possible zwitterionic and anionic forms may dominate over the other possible forms. Additional investigations using explicit solvent models are necessary to determine the stability of charged forms of glutamic acid in solution as our results clearly indicate that hydrogen bonding and its type have a major role in the structure and energy of conformers.

Study of the solubility and stability of polystyrene wastes in a dissolution recycling process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garcia, Maria Teresa; Gracia, Ignacio; Duque, Gema

2009-06-15

Dissolution with suitable solvents is one of the cheapest and more efficient processes for polystyrene waste management. In this work the solubility of polystyrene foams in several solvents benzene, toluene, xylene, tetrahydrofuran, chloroform, 1,3-butanediol, 2-butanol, linalool, geraniol, d-limonene, p-cymene, terpinene, phellandrene, terpineol, menthol, eucalyptol, cinnamaldheyde, nitrobenzene, N,N-dimethylformamide and water has been determined. Experimental results have shown that to develop a 'green process' the constituents of essential oils, d-limonene, p-cymene, terpinene, phellandrene, are the most appropriate solvents. The action of these solvent does not produce any degradation of polymer chains. The solubility of the polymer in the mentioned solvents at differentmore » temperatures has been investigated. The solvent can be easily recycled by distillation.« less

Effects of salt or cosolvent addition on solubility of a hydrophobic solute in water: Relevance to those on thermal stability of a protein

NASA Astrophysics Data System (ADS)

Murakami, Shota; Hayashi, Tomohiko; Kinoshita, Masahiro

2017-02-01

The solubility of a nonpolar solute in water is changed upon addition of a salt or cosolvent. Hereafter, "solvent" is formed by water molecules for pure water, by water molecules, cations, and anions for water-salt solution, and by water and cosolvent molecules for water-cosolvent solution. Decrease and increase in the solubility, respectively, are ascribed to enhancement and reduction of the hydrophobic effect. Plenty of experimental data are available for the change in solubility of argon or methane arising from the addition. We show that the integral equation theory combined with a rigid-body model, in which the solute and solvent particles are modeled as hard spheres with different diameters, can reproduce the data for the following items: salting out by an alkali halide and salting in by tetramethylammonium bromide, increase in solubility by a monohydric alcohol, and decrease in solubility by sucrose or urea. The orders of cation or anion species in terms of the power of decreasing the solubility can also be reproduced for alkali halides. With the rigid-body model, the analyses are focused on the roles of entropy originating from the translational displacement of solvent particles. It is argued by decomposing the solvation entropy of a nonpolar solute into physically insightful constituents that the solvent crowding in the bulk is a pivotal factor of the hydrophobic effect: When the solvent crowding in the bulk becomes more serious, the effect is strengthened, and when it becomes less serious, the effect is weakened. It is experimentally known that the thermal stability of a protein is also influenced by the salt or cosolvent addition. The additions which decrease and increase the solubility of a nonpolar solute, respectively, usually enhance and lower the thermal stability. This suggests that the enhanced or reduced hydrophobic effect is also a principal factor governing the stability change. However, urea decreases the solubility but lowers the stability. Bromide and iodide ions decrease the solubility but lower the stability of a protein with a large, positive total charge. In these cases, the urea- or ion-protein van der Waals interaction energy as well as the hydrophobic effect needs to be taken into account in arguing the stability change. We also present a new view on the so-called Hofmeister series: We show how it is expressed when the change in hydrophobic effect dominates and how it is modified when other factors are also influential.

Microchip electrospray: improvements in spray and signal stability during gradient elution by an inverted postcolumn makeup flow.

PubMed

Jung, Stephanie; Effelsberg, Uwe; Tallarek, Ulrich

2011-12-01

Dynamic changes in mobile phase composition during high-performance liquid chromatography (HPLC) gradient elution coupled to mass spectrometry (MS) sensitively affect electrospray modes. We investigate the impact of the eluent composition on spray stability and MS response by infusion and injection experiments with a small tetrapeptide in water-acetonitrile mixtures. The employed HPLC/electrospray (ESI)-MS configuration uses a microchip equipped with an enrichment column, a separation column, and a makeup flow (MUF) channel. One nano pump is connected to the separation column, while a second one delivers solvent of exactly inverted composition to the MUF channel. Both solvent streams are united behind the separation column, before the ESI tip, such that the resulting electrosprayed solution always has identical composition during a gradient elution. Analyte peak parameters without and with MUF compensation are determined and discussed with respect to the electrospray mode and eluent composition. The postcolumn MUF significantly improves spray and signal stability over the entire solvent gradient, without compromising the performance of the HPLC separation column. It can also be conveniently implemented on microchip platforms.

Liquid Salt as Green Solvent: A Novel Eco-Friendly Technique to Enhance Solubility and Stability of Poorly Soluble Drugs

NASA Astrophysics Data System (ADS)

Patel, Anant A.

As a result of tremendous efforts in past few decades, various techniques have been developed in order to resolve solubility issues associated with class II and IV drugs, However, majority of these techniques offer benefits associated with certain drawbacks; majorly including low drug loading, physical instability on storage and excessive use of environmentally challenging organic solvents. Hence, current effort was to develop an eco-friendly technique using liquid salt as green solvent, which can offer improvement in dissolution while maintaining long term stability. The liquid salt formulations (LSF) of poorly soluble model drugs ibuprofen, gemfibrozil and indomethacin were developed using 1-Ethyl-3-methylimidazolium ethyl sulfate (EMIM ES) as a non-toxic and environmentally friendly alternate to organic solvents. Liquid medications containing clear solutions of drug, EMIM ES and polysorbate 20, were adsorbed onto porous carrier Neusilin US2 to form free flowing powder. The LSF demonstrated greater rate and extent of dissolution compared to crystalline drugs. The dissolution data revealed that more than 80% drug release from LSF within 20 mins compared to less than 18% release from pure drugs. As high as 70% w/w liquid loading was achieved while maintaining good flowability and compressibility. In addition, the LSF samples exposed to high temperature and high humidity i.e. 40°C/80% RH for 8 weeks, demonstrated excellent physical stability without any signs of precipitation or crystallization. As most desirable form of administration is tablet, the developed liquid salt formulations were transformed into tablets using design of experiment approach by Design Expert Software. The tablet formulation composition and critical parameter were optimized using Box-Behnken Design. This innovative liquid salt formulation technique offered improvement in dissolution rate and extent as well as contributed to excellent physical stability on storage. Moreover, this formulation approach served as eco-friendly compelling alternate to conventional techniques involving organic solvents.

Synthesis, stabilization, and characterization of metal nanoparticles

NASA Astrophysics Data System (ADS)

White, Gregory Von, II

Wet chemical synthesis techniques offer the ability to control various nanoparticle characteristics including size, shape, dispersibility in both aqueous and organic solvents, and tailored surface chemistries appropriate for different applications. Large quantities of stabilizing ligands or surfactants are often required during synthesis to achieve these nanoparticle characteristics. Unfortunately, excess reaction byproducts, surfactants, and ligands remaining in solution after nanoparticle synthesis can impede application, and therefore post-synthesis purification must be employed. A liquid-liquid solvent/antisolvent pair (typically ethanol/toluene or ethanol/hexane for gold nanoparticles, GNPs) can be used to both purify and size-selectively fractionate hydrophobically modified nanoparticles. Alternatively, carbon dioxide may be used in place of a liquid antisolvent, a "green" approach, enabling both nanoparticle purification and size-selective fractionation while simultaneously eliminating mixed solvent waste and allowing solvent recycle. We have used small-angle neutron scattering (SANS) to investigate the ligand structure and composition response of alkanethiol modified gold and silver nanoparticles at varying anti-solvent conditions (CO2 or ethanol). The ligand lengths and ligand solvation for alkanethiol gold and silver NPs were found to decrease with increased antisolvent concentrations directly impacting their dispersibility in solution. Calculated Flory-Huggins interaction parameters support our SANS study for dodecanethiol dispersibility in the mixed organic solvents. This research has led to a greater understanding of the liquid-liquid precipitation process for metal nanoparticles, and provides critical results for future interaction energy modeling.

Recent advances in the applications of ionic liquids in protein stability and activity: a review.

PubMed

Patel, Rajan; Kumari, Meena; Khan, Abbul Bashar

2014-04-01

Room temperatures ionic liquids are considered as miraculous solvents for biological system. Due to their inimitable properties and large variety of applications, they have been widely used in enzyme catalysis and protein stability and separation. The related information present in the current review is helpful to the researchers working in the field of biotechnology and biochemistry to design or choose an ionic liquid that can serve as a noble and selective solvent for any particular enzymatic reaction, protein preservation and other protein based applications. We have extensively analyzed the methods used for studying the protein-IL interaction which is useful in providing information about structural and conformational dynamics of protein. This can be helpful to develop and understanding about the effect of ionic liquids on stability and activity of proteins. In addition, the affect of physico-chemical properties of ionic liquids, viz. hydrogen bond capacity and hydrophobicity on protein stability are discussed.

Assessment of the effector function of CMV-specific CTLs isolated using MHC-multimers from granulocyte-colony stimulating factor mobilized peripheral blood.

PubMed

Beloki, Lorea; Ciaurriz, Miriam; Mansilla, Cristina; Zabalza, Amaya; Perez-Valderrama, Estela; Samuel, Edward R; Lowdell, Mark W; Ramirez, Natalia; Olavarria, Eduardo

2015-05-20

Adoptive transfer of CMV-specific T cells has shown promising results in preventing pathological effects caused by opportunistic CMV infection in immunocompromised patients following allogeneic hematopoietic stem cell transplantation. The majority of studies have used steady-state leukapheresis for CMV-reactive product manufacture, a collection obtained prior to or months after G-CSF mobilization, but the procurement of this additional sample is often not available in the unrelated donor setting. If the cellular product for adoptive immunotherapy could be generated from the same G-CSF mobilized collection, the problems associated with the additional harvest could be overcome. Despite the tolerogenic effects associated with G-CSF mobilization, recent studies described that CMV-primed T cells generated from mobilized donors remain functional. MHC-multimers are potent tools that allow the rapid production of antigen-specific CTLs. Therefore, in the present study we have assessed the feasibility and efficacy of CMV-specific CTL manufacture from G-CSF mobilized apheresis using MHC-multimers. CMV-specific CTLs can be efficiently isolated from G-CSF mobilized samples with Streptamers and are able to express activation markers and produce cytokines in response to antigenic stimulation. However, this anti-viral functionality is moderately reduced when compared to non-mobilized products. The translation of Streptamer technology for the isolation of anti-viral CTLs from G-CSF mobilized PBMCs into clinical practice would widen the number of patients that could benefit from this therapeutic strategy, although our results need to be taken into consideration before the infusion of antigen-specific T cells obtained from G-CSF mobilized samples.

Dynamic Oligomerization of Integrase Orchestrates HIV Nuclear Entry.

PubMed

Borrenberghs, Doortje; Dirix, Lieve; De Wit, Flore; Rocha, Susana; Blokken, Jolien; De Houwer, Stéphanie; Gijsbers, Rik; Christ, Frauke; Hofkens, Johan; Hendrix, Jelle; Debyser, Zeger

2016-11-10

Nuclear entry is a selective, dynamic process granting the HIV-1 pre-integration complex (PIC) access to the chromatin. Classical analysis of nuclear entry of heterogeneous viral particles only yields averaged information. We now have employed single-virus fluorescence methods to follow the fate of single viral pre-integration complexes (PICs) during infection by visualizing HIV-1 integrase (IN). Nuclear entry is associated with a reduction in the number of IN molecules in the complexes while the interaction with LEDGF/p75 enhances IN oligomerization in the nucleus. Addition of LEDGINs, small molecule inhibitors of the IN-LEDGF/p75 interaction, during virus production, prematurely stabilizes a higher-order IN multimeric state, resulting in stable IN multimers resistant to a reduction in IN content and defective for nuclear entry. This suggests that a stringent size restriction determines nuclear pore entry. Taken together, this work demonstrates the power of single-virus imaging providing crucial insights in HIV replication and enabling mechanism-of-action studies.

Stability and activity of lysozyme in stoichiometric and non-stoichiometric protic ionic liquid (PIL)-water systems

NASA Astrophysics Data System (ADS)

Wijaya, Emmy C.; Separovic, Frances; Drummond, Calum J.; Greaves, Tamar L.

2018-05-01

There has been a substantial increase in enzyme applications within the biochemical and pharmaceutical industries, for example, as industrial biocatalysts. However, enzymes have narrow marginal stability which makes them prone to become inactive and/or denature with a slight change in the solvent environment. Typically industrial applications require harsher solvent environments than enzyme native environments, and hence there is a need to understand solvent-protein interactions in order to develop strategies to maintain, or enhance, the enzymatic activity under industrially relevant solvent conditions. Previously we have shown that protic ionic liquids (PILs) with water can have a stabilising effect on lysozyme, with a large variation dependent on which PIL ions are present, and the water concentration [E. C. Wijaya et al., Phys. Chem. Chem. Phys. 18(37), 25926-25936 (2016)]. Here we extend on this work using non-stoichiometric aqueous PIL solvents to investigate, and isolate, the role of pH and ionicity on enzymes. We have used the PILs ethylammonium nitrate (EAN) and ethanolammonium formate (EOAF) since our previous work has identified these as good solvents for lysozyme. Solvent libraries were made from these two PILs with an additional precursor acid or base to modify the acidity/basicity of the neutral stoichiometric PIL, and with water added, to have solutions with 4-17 mol. % of the PIL ions in water. Molar ratios of base:acid were varied between 1:1.05 and 2:1 for EAN and 1:1.25 and 2:1 for EOAF, which enabled from highly basic to highly acidic solutions to be obtained. This was to modify the acidity/basicity of the neutral stoichiometric PILs, without the addition of buffers. The structure and stability of hen egg white lysozyme (HEWL) were explored under these solvent conditions using synchrotron small angle X-ray scattering (SAXS), Fourier transform infrared (FTIR), and activity assays. The radius of gyration and Kratky plots obtained from the SAXS data showed little change with varying ionicity or acid:base ratio. FTIR showed that α-helix was maintained in all, except for the most acidic solvent conditions. The activity data show that HEWL was active between pH 0 and 11 for the EA:N-water system and pH 4.4 and 11 for the EOA:F-water system. This work indicates that ionic liquids have the potential to enable enzymes to maintain activity across a broader range of solvent conditions.

Mechanistic principles of colloidal crystal growth by evaporation-induced convective steering.

PubMed

Brewer, Damien D; Allen, Joshua; Miller, Michael R; de Santos, Juan M; Kumar, Satish; Norris, David J; Tsapatsis, Michael; Scriven, L E

2008-12-02

We simulate evaporation-driven self-assembly of colloidal crystals using an equivalent network model. Relationships between a regular hexagonally close-packed array of hard, monodisperse spheres, the associated pore space, and selectivity mechanisms for face-centered cubic microstructure propagation are described. By accounting for contact line rearrangement and evaporation at a series of exposed menisci, the equivalent network model describes creeping flow of solvent into and through a rigid colloidal crystal. Observations concerning colloidal crystal growth are interpreted in terms of the convective steering hypothesis, which posits that solvent flow into and through the pore space of the crystal may play a major role in colloidal self-assembly. Aspects of the convective steering and deposition of high-Peclet-number rigid spherical particles at a crystal boundary are inferred from spatially resolved solvent flow into the crystal. Gradients in local flow through boundary channels were predicted due to the channels' spatial distribution relative to a pinned free surface contact line. On the basis of a uniform solvent and particle flux as the criterion for stability of a particular growth plane, these network simulations suggest the stability of a declining {311} crystal interface, a symmetry plane which exclusively propagates fcc microstructure. Network simulations of alternate crystal planes suggest preferential growth front evolution to the declining {311} interface, in consistent agreement with the proposed stability mechanism for preferential fcc microstructure propagation in convective assembly.

Temperature responses of individual soil organic matter components

NASA Astrophysics Data System (ADS)

Feng, Xiaojuan; Simpson, Myrna J.

2008-09-01

Temperature responses of soil organic matter (SOM) remain unclear partly due to its chemical and compositional heterogeneity. In this study, the decomposition of SOM from two grassland soils was investigated in a 1-year laboratory incubation at six different temperatures. SOM was separated into solvent extractable compounds, suberin- and cutin-derived compounds, and lignin-derived monomers by solvent extraction, base hydrolysis, and CuO oxidation, respectively. These SOM components have distinct chemical structures and stabilities and their decomposition patterns over the course of the experiment were fitted with a two-pool exponential decay model. The stability of SOM components was also assessed using geochemical parameters and kinetic parameters derived from model fitting. Compared with the solvent extractable compounds, a low percentage of lignin monomers partitioned into the labile SOM pool. Suberin- and cutin-derived compounds were poorly fitted by the decay model, and their recalcitrance was shown by the geochemical degradation parameter (ω - C16/∑C16), which was observed to stabilize during the incubation. The temperature sensitivity of decomposition, expressed as Q10, was derived from the relationship between temperature and SOM decay rates. SOM components exhibited varying temperature responses and the decomposition of lignin monomers exhibited higher Q10 values than the decomposition of solvent extractable compounds. Our study shows that Q10 values derived from soil respiration measurements may not be reliable indicators of temperature responses of individual SOM components.

Multipoint attachment to a support protects enzyme from inactivation by organic solvents: alpha-Chymotrypsin in aqueous solutions of alcohols and diols.

PubMed

Mozhaev, V V; Sergeeva, M V; Belova, A B; Khmelnitsky, Y L

1990-03-25

Inactivation of alpha-chymotrypsin in aqueous solutions of alcohols and diols proceeds both reversibly and irreversibly. Reversible loss of the specific enzyme activity results from conformational changes (unfolding) of the enzyme detected by fluorescence spectroscopy. Multipoint covalent attachment to the matrix of polyacryl-amide gel by copolymerization method stabilizes alpha-chymotrypsin from denaturation by alcohols, the stabilizing effect increasing with the number of bonds between the protein and the support. Immobilization protects the enzyme also from irreversible inactivation by organic solvents resulting from bimolecular aggregation and autolysis.

Stability and precipitation of diverse nanoparticles

NASA Astrophysics Data System (ADS)

Desai, Chintal

Nanotechnology is a rapidly growing industry that is exploiting the novel characteristics of materials manufactured at the nanoscale. Carbon based nanomaterials such as Carbon Nanotubes (CNTs) and Detonation Nanodiamond (DND) possess unique properties and find a wide range of industrial applications. With the advent of mass production of such materials, there is a possibility of contamination of water resources. Depending on the surface properties and structures, they might aggregate and settle down, or be dispersed and transported by the water. Therefore, there is a need to develop an understanding of the fate of such materials in aqueous media. The understanding and effect of solution chemistry is a key to predicting their deposition, transport, reactivity, and bioavailability in aquatic environments. The colloidal behavior of organic dispersed CNTs and water dispersed DNDs is investigated. The aggregation behavior of these two colloidal systems is quite different from that of hydrophilic, water soluble functionalized CNTs (F-CNTs). The values of the Fuchs stability ratio or the critical coagulant concentration are determined experimentally using time-resolved dynamic light scattering and are used to predict the stability of such systems. It is found that the aggregation behavior of the organic dispersed, antisolvent precipitated system does not follow the conventional Derjaguin--Landau--Verwey-- Overbeek (DLVO) theory. But they stabilize in the long term, which is attributed to the supersaturation generated by different solubility of a solute in the solvent/antisolvent. Based on particle size distribution, zeta potential as well as the aggregation kinetics, the water dispersed DNDs are found to be relatively stable in aqueous solutions, but aggregate rapidly in presence of mono and divalent salts. Also, the formation of carboxylic groups on the DND surface does not alter colloidal behavior as dramatically as it does for other nanocarbons especially carbon nanotubes. Formation of colloidal dispersions via precipitation processes has been widely used in the chemical and pharmaceutical industries. The synthesis of micro- particles for hydrophobic drugs is effectively carried out via anti-solvent precipitation method. The formation of small particles in the precipitation method is strongly influenced by colloidal interactions, and therefore, dependent on the properties of the particles and the liquid. The effect of solvent on the colloidal stability of the micro-drug particles is studied in detail. It is found that the organic solvent plays an important role on particle formation, polymorphism and stability of micron scale drug particles in aqueous media. Also, the supersaturation can be varied by using different solvents and the physicochemical characteristics of the suspension can be altered, which affects stability. Understanding of the colloidal stability and the aggregation kinetics has great importance not only for fundamental researches, but also for their applications.

Effect of disulfide bonding and multimerization on proteoglycan 4's cartilage boundary lubricating ability and adsorption.

PubMed

Abubacker, Saleem; Ponjevic, Dragana; Ham, Hyun O; Messersmith, Phillip B; Matyas, John R; Schmidt, Tannin A

2016-01-01

The objectives of this study were to assess the cartilage boundary lubricating ability of (1) nonreduced (NR) disulfide-bonded proteoglycan 4 (PRG4) multimers versus PRG4 monomers and (2) NR versus reduced and alkylated (R/A) PRG4 monomers and to assess (3) the ability of NR PRG4 multimers versus monomers to adsorb to an articular cartilage surface. PRG4 was separated into two preparations, PRG4 multimer enriched (PRG4Multi+) and PRG4 multimer deficient (PRG4Multi-), using size exclusion chromatography (SEC) and characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The cartilage boundary lubricating ability of PRG4Multi+ and PRG4Multi- was compared at a physiological concentration (450 μg/mL) and assessed over a range of concentrations (45, 150, and 450 μg/mL). R/A and NR PRG4Multi- were evaluated at 450 μg/mL. Immunohistochemistry with anti-PRG4 antibody 4D6 was performed to visualize the adsorption of PRG4 preparations to the surface of articular cartilage explants. Separation into enriched populations of PRG4Multi+ and PRG4Multi- was achieved using SEC and was confirmed by SDS-PAGE. PRG4Multi+ and PRG4Multi- both functioned as effective friction-reducing cartilage boundary lubricants at 450 μg/mL, with PRG4Multi+ being more effective than PRG4Multi-. PRG4Multi+ lubricated in a dose-dependent manner, however, PRG4Multi- did not. R/A PRG4Multi- lubricated similar to NR PRG4Multi-. PRG4-containing solutions showed 4D6 immunoreactivity at the articular surface; the immunoreactive intensity of PRG4Multi+ appeared to be similar to SF, whereas PRG4Multi- appeared to have less intensity. These results demonstrate that the intermolecular disulfide-bonded multimeric structure of PRG4 is important for its ability to adsorb to a cartilage surface and function as a boundary lubricant. These findings contribute to a greater understanding of the molecular basis of cartilage boundary lubrication of PRG4. Elucidating the PRG4 structure-lubrication function relationship will further contribute to the understanding of PRG4's role in diarthrodial joint homeostasis and disease.

Traumatic Hemothorax Blood Contains Elevated Levels of Microparticles that are Prothrombotic but Inhibit Platelet Aggregation.

PubMed

Mitchell, Thomas A; Herzig, Maryanne C; Fedyk, Chriselda G; Salhanick, Marc A; Henderson, Aaron T; Parida, Bijaya K; Prat, Nicolas J; Dent, Daniel L; Schwacha, Martin G; Cap, Andrew P

2017-06-01

Autotransfusion of shed blood from traumatic hemothorax is an attractive option for resuscitation of trauma patients in austere environments. However, previous analyses revealed that shed hemothorax (HX) blood is defibrinated, thrombocytopenic, and contains elevated levels of D-dimer. Mixing studies with normal pooled plasma demonstrated hypercoagulability, evoking concern for potentiation of acute traumatic coagulopathy. We hypothesized that induction of coagulopathic changes by shed HX blood may be due to increases in cellular microparticles (MP) and that these may also affect recipient platelet function. Shed HX blood was obtained from 17 adult trauma patients under an Institutional Review Board approved prospective observational protocol. Blood samples were collected every hour up to 4 h after thoracostomy tube placement. The corresponding plasma was isolated and frozen for analysis. The effects of shed HX frozen plasma (HFP) and isolated HX microparticles (HMP) on coagulation and platelet function were assessed through mixing studies with platelet-rich plasma at various dilutions followed by analysis with thromboelastometry (ROTEM), platelet aggregometry (Multiplate), enzyme-linked immunosorbent assays, and flow cytometry. Furthermore, HFP was assessed for von Willebrand factor antigen levels and multimer content, and plasma-free hemoglobin. ROTEM analysis demonstrated that diluted HFP and isolated HMP samples decreased clotting time, clotting formation time, and increased α angle, irrespective of sample concentrations, when compared with diluted control plasma. Isolated HMP inhibited platelet aggregation in response to adenosine diphosphate, arachidonic acid, and collagen. HFP contained elevated levels of fibrin-degradation products and tissue factor compared with control fresh frozen plasma samples. MP concentrations in HFP were significantly increased and enriched in events positive for phosphatidylserine, tissue factor, CD235, CD45, CD41a, and CD14. von Willebrand factor (vWF) multimer analysis revealed significant loss of high molecular weight multimers in HFP samples. Plasma-free hemoglobin levels were 8-fold higher in HFP compared with fresh frozen plasma. HFP induces plasma hypercoagulability that is likely related to increased tissue factor and phosphatidylserine expression originating from cell-derived MP. In contrast, platelet dysfunction is induced by HMP, potentially aggravated by depletion of high molecular weight multimers of vWF. Thus, autologous transfusion of shed traumatic hemothorax blood may induce a range of undesirable effects in patients with acute traumatic coagulopathy.

Annatto Polymeric Microparticles: Natural Product Encapsulation by the Emulsion-Solvent Evaporation Method

ERIC Educational Resources Information Center

Teixeira, Zaine; Duran, Nelson; Guterres, Silvia S.

2008-01-01

In this experiment, the extract from annatto seeds was encapsulated in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) particles by the emulsion-solvent evaporation method. The particles were washed and centrifuged to remove excess stabilizer and then freeze-dried. The main compound of annatto seeds, bixin, has antioxidant properties as well…

Properties of electrospun pollock gelatin/poly(vinyl alcohol) and pollock gelatin/poly(lactic acid) fibers

USDA-ARS?s Scientific Manuscript database

Pollock gelatin/poly(vinyl alcohol) (PVA) fibers were electrospun using deionized water as the solvent and pollock gelatin/poly(lactic acid) (PLA) fibers were electrospun using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as the solvent. The chemical, thermal, and thermal stability properties were exami...

Electropolymerized carbonic anhydrase immobilization for carbon dioxide capture.

PubMed

Merle, Geraldine; Fradette, Sylvie; Madore, Eric; Barralet, Jake E

2014-06-17

Biomimetic carbonation carried out with carbonic anhydrase (CA) in CO2-absorbing solutions, such as methyldiethanolamine (MDEA), is one approach that has been developed to accelerate the capture of CO2. However, there are several practical issues, such as high cost and limited enzyme stability, that need to be overcome. In this study, the capacity of CA immobilization on a porous solid support was studied to improve the instability in the tertiary amine solvent. We have shown that a 63% porosity macroporous carbon foam support makes separation and reuse facile and allows for an efficient supply and presentation of CO2 to an aqueous solvent and the enzyme catalytic center. These enzymatic supports conserved 40% of their initial activity after 42 days at 70 °C in an amine solvent, whereas the free enzyme shows no activity after 1 h in the same conditions. In this work, we have overcome the technical barrier associated with the recovery of the biocatalyst after operation, and most of all, these electropolymerized enzymatic supports have shown a remarkable increase of thermal stability in an amine-based CO2 sequestration solvent.

UV-Vis spectrophotometric studies of self-oxidation/dissociation of quaternary ammonium permanganates (QAP) - impact of solvent polarity

NASA Astrophysics Data System (ADS)

Bank, Suraj Prakash; Guru, Partha Sarathi; Dash, Sukalyan

2015-05-01

Self-oxidation/dissociation of some quaternary ammonium permanganates (QAPs), such as cetyltrimethylammonium permanganate (CTAP) and tetrabutylammonium permanganate (TBAP), have been studied spectrophotometrically in six different organic solvent media of different polarities wherein the compounds show good solubility and stability. The optical densities of the substrates at zero time (ODo) and first-order rate constants of dissociation (k1) have been determined from their successive scanning for 40 min. At comparable experimental conditions, absorption capabilities of the substrates are compared from the ODo values in various organic media; the stability of the solutions is compared from the successive scan spectra in those media. The ODo values and the k1 values have been plotted against some solvent parameters to understand their effects on the absorbance and reactivity of the QAPs. These data are also subjected to multiple regression analysis to explain the influence of various solvent parameters on the ion-pairing properties of the substrates, thus elucidating their effects on the process of self-oxidation/dissociation of the substrates.

Long-Term Stability of Polymer-Coated Surface Transverse Wave Sensors for the Detection of Organic Solvent Vapors.

PubMed

Stahl, Ullrich; Voigt, Achim; Dirschka, Marian; Barié, Nicole; Richter, Christiane; Waldbaur, Ansgar; Gruhl, Friederike J; Rapp, Bastian E; Rapp, Michael; Länge, Kerstin

2017-11-03

Arrays with polymer-coated acoustic sensors, such as surface acoustic wave (SAW) and surface transverse wave (STW) sensors, have successfully been applied for a variety of gas sensing applications. However, the stability of the sensors' polymer coatings over a longer period of use has hardly been investigated. We used an array of eight STW resonator sensors coated with different polymers. This sensor array was used at semi-annual intervals for a three-year period to detect organic solvent vapors of three different chemical classes: a halogenated hydrocarbon (chloroform), an aliphatic hydrocarbon (octane), and an aromatic hydrocarbon (xylene). The sensor signals were evaluated with regard to absolute signal shifts and normalized signal shifts leading to signal patterns characteristic of the respective solvent vapors. No significant time-related changes of sensor signals or signal patterns were observed, i.e., the polymer coatings kept their performance during the course of the study. Therefore, the polymer-coated STW sensors proved to be robust devices which can be used for detecting organic solvent vapors both qualitatively and quantitatively for several years.

Stabilized aqueous foam systems and concentrate and method for making them

DOEpatents

Rand, Peter B.

1984-01-01

This invention comprises a combination of a water soluble polymer of the polyacrylic acid type, a foam stabilizer of dodecyl alcohol, a surfactant, a solvent and water as a concentrate for use in producing stabilized aqueous foams. In another aspect, the invention comprises a solution of the concentrate with water. In still another aspect the invention includes a method of generating stabilized aqueous foams.

Colloidal 3-Mercaptopropionic Acid Capped Lead Sulfide Quantum Dots in a Low Boiling Point Solvent.

PubMed

Reinhart, Chase C; Johansson, Erik

2017-04-26

Colloidal 3-mercaptopropionic acid (3-MPA) capped lead sulfide quantum dots were prepared in a variety of organic solvents stabilized with a quaternary ammonium halide salt. The stabilized colloids' optical properties were studied through optical absorption and emission spectroscopy and found to be dependent on both the concentration of a new ligand and stabilizer, and sample age. Nanocrystal ligand chemistry was studied through a combination of 1 H NMR and two-dimensional Nuclear Overhauser Effect Spectroscopy (NOESY) which revealed full displacement of the original oleate ligand to form a dynamically exchanging ligand shell. The colloids were studied optically and via NMR as they aged and revealed a quantitative conversion of monomeric 3-mercaptopropionic acid to its dimer, dithiodipropionic acid (dTdPA).

Solvent effects on adsorption of CO over CuCl(1 1 1) surface: A density functional theory study

NASA Astrophysics Data System (ADS)

Zhang, Riguang; Ling, Lixia; Wang, Baojun; Huang, Wei

2010-09-01

DFT calculations have been performed to investigate the effect of dielectric responses of the solvent environment on the CO adsorption over CuCl(1 1 1) surface by using COSMO (conductor-like solvent model) model in Dmol 3. Different dielectric constants, including vacuum, liquid paraffin, methylene chloride, methanol and water solution, are considered. The effects of solvent model on the structural parameters, adsorption energies and vibrational frequency of CO adsorption over CuCl(1 1 1) surface have been investigated. The calculation results suggest that solvent effects can improve the stability of CO adsorption and reduce the intensity of C-O bond, which might mean that solvent is in favor of C-O bond activation and improve the reaction activity of oxidative carbonylation in a slurry reactor.

High drug load, stable, manufacturable and bioavailable fenofibrate formulations in mesoporous silica: a comparison of spray drying versus solvent impregnation methods.

PubMed

Hong, Shiqi; Shen, Shoucang; Tan, David Cheng Thiam; Ng, Wai Kiong; Liu, Xueming; Chia, Leonard S O; Irwan, Anastasia W; Tan, Reginald; Nowak, Steven A; Marsh, Kennan; Gokhale, Rajeev

2016-01-01

Encapsulation of drugs in mesoporous silica using co-spray drying process has been recently explored as potential industrial method. However, the impact of spray drying on manufacturability, physiochemical stability and bioavailability in relation to conventional drug load processes are yet to be fully investigated. Using a 2(3) factorial design, this study aims to investigate the effect of drug-loading process (co-spray drying and solvent impregnation), mesoporous silica pore size (SBA-15, 6.5 nm and MCM-41, 2.5 nm) and percentage drug load (30% w/w and 50% w/w) on material properties, crystallinity, physicochemical stability, release profiles and bioavailability of fenofibrate (FEN) loaded into mesoporous silica. From the scanning electronic microscopy (SEM) images, powder X-ray diffraction and Differential scanning calorimetry measurements, it is indicated that the co-spray drying process was able to load up to 50% (w/w) FEN in amorphous form onto the mesoporous silica as compared to the 30% (w/w) for solvent impregnation. The in vitro dissolution rate of the co-spray dried formulations was also significantly (p = 0.044) better than solvent impregnated formulations at the same drug loading. Six-month accelerated stability test at 40 °C/75 RH in open dish indicated excellent physical and chemical stability of formulations prepared by both methods. The amorphous state of FEN and the enhanced dissolution profiles were well preserved, and very low levels of degradation were detected after storage. The dog data for the three selected co-spray-dried formulations revealed multiple fold increment in FEN bioavailability compared to the reference crystalline FEN. These results validate the viability of co-spray-dried mesoporous silica formulations with high amorphous drug load as potential drug delivery systems for poorly water soluble drugs.

Relaxation pathways of photoexcited iodide-methanol clusters: a computational investigation.

PubMed

Mak, Chun C; Peslherbe, Gilles H

2014-06-26

Upon photoexcitation of iodide-methanol clusters, I(-)(CH3OH)n, to a charge-transfer-to-solvent (CTTS) excited state, extensive relaxation was found to occur, accompanied by a convoluted modulation of the stability of the excited electron, which ultimately decreases substantially. In order to develop a molecular-level understanding of the relaxation processes of CTTS excited I(-)(CH3OH)n, high-level quantum chemical calculations are first used to investigate the ground, excited, and ionized states of I(-)(CH3OH)n (n = 2). Because of the relatively small size of I(-)(CH3OH)2, it was possible to characterize the contributions of solvent-solvent interactions to the stability of the CTTS excited cluster relative to dissociation into methanol, iodine, and a free electron, which exhibits a substantial dependence on the cluster geometric configuration. Ab initio molecular dynamics simulations of CTTS excited I(-)(CH3OH)3 are then performed to shed some light onto the nature of the relaxation pathways involved in the modulation of the stability of the excited electron in larger clusters. Simulation results suggest that separation of I and (CH3OH)3(-) accompanied by solvent reorganization in the latter can initially stabilize the excited electron, while gradual cluster fragmentation to I, (CH3OH)2(-), and CH3OH ultimately destabilizes it. This work shows, for the first time, that the inability of small CTTS excited I(-)(CH3OH)n to retain a solvated electron may be attributed to the limited hydrogen-bonding capacity of CH3OH, which increases the propensity for fragmentation to smaller clusters with lower excess-electron binding energies, and highlights the critical role of intricate molecular interactions in the electron solvation process.

Improved performance and safety of lithium ion cells with the use of fluorinated carbonate-based electrolytes

NASA Technical Reports Server (NTRS)

Smart, M. C.; Ratnakumar, B. V.; Ryan, V. S.; Surampudi, S.; Prakashi, G. K. S.; Hu, J.; Cheung, I.

2002-01-01

There has been increasing interest in developing lithium-ion electrolytes that possess enhanced safety characteristics, while still able to provide the desired stability and performance. Toward this end, our efforts have been focused on the development of lithium-ion electrolytes which contain partially and fully fluorinated carbonate solvents. The advantage of using such solvents is that they possess the requisite stability demonstrated by the hydrocarbon-based carbonates, while also possessing more desirable physical properties imparted by the presence of the fluorine substituents, such as lower melting points, increased stability toward oxidation, and favorable SEI film forming Characteristics on carbon. Specifically, we have demonstrated the beneficial effect of electrolytes which contain the following fluorinated carbonate-based solvents: methyl 2,2,2-trifluoroethyl carbonate (MTFEC), ethyl-2,2,2 trifluoroethyl carbonate (ETFEC), propyl 2,2,2-trifluoroethyl carbonate (PTFEC), methyl-2,2,2,2',2',2' -hexafluoro-i-propyl carbonate (MHFPC), ethyl- 2,2,2,2',2',2' -hexafluoro-i-propyl carbonate (EHFPC), and di-2,2,2-trifluoroethyl carbonate (DTFEC). These solvents have been incorporated into multi-component ternary and quaternary carbonate-based electrolytes and evaluated in lithium-carbon and carbon-LiNio.8Coo.202 cells (equipped with lithium reference electrodes). In addition to determining the charge/discharge behavior of these cells, a number of electrochemical techniques were employed (i.e., Tafel polarization measurements, linear polarization measurements, and electrochemical impedance spectroscopy (EIS)) to further characterize the performance of these electrolytes, including the SEI formation characteristics and lithium intercalatiodde-intercalation kinetics. In addition to their evaluation in experimental cells, cyclic voltammetry (CV) and conductivity measurements were performed on select electrolyte formulations to further our understanding of the trends in stability and ionic mobility imparted by different alkyl substituents in linear carbonates.

FT-IR study and solvent-implicit and explicit effect on stepwise tautomerism of Guanylurea: M06-2X as a case of study

NASA Astrophysics Data System (ADS)

Karimzadeh, Morteza; Manouchehri, Neda; Saberi, Dariush; Niknam, Khodabakhsh

2018-06-01

All 66 conformers of guanylurea were optimized and frequency calculations were performed at M06-2X/6-311++G(d,p) level of theory. Theses conformers were categorized into five tautomers, and the most stable conformer of each tautomer were found. Geometrical parameters indicated that these tautomers have almost planar structure. Complete stepwise tautomerism were studied through both intramolecular proton transfer routs and internal rotations. Results indicated that the proton transfer routs involving four-membered heterocyclic structures were rate-determining steps. Also, intramolecular proton movement having six-membered transition state structures had very low energy barrier comparable to the transition states of internal rotation routs. Differentiation of studied tautomers could easily be done through their FT-IR spectra in the range of 3200 to 3900 cm-1 by comparing absorption bands and intensity of peaks. Solvent-implicit effects on the stability of tautomers were also studied through re-optimization and frequency calculation in four solvents. Water, DMSO, acetone and toluene had stabilization effect on all considered tautomers, but the order of stabilization effect was as follows: water > DMSO > acetone > toluene. Finally, solvent-explicit, base-explicit and acid-explicit effect were also studied by taking place of studied tautomer nearside of acid, base or solvent and optimization of them. Frequency calculation for proton movement by contribution of explicit effect showed that formic acid had a very strong effect on proton transfer from tautomer A1 to tautomer D8 by lowering the energy barrier from 42.57 to 0.8 kcal/mol. In addition, ammonia-explicit effect was found to lower the barrier from 42.57 to 22.46 kcal/mol, but this effect is lower than that of water and methanol-explicit effect.

Elucidating sequence and solvent specific design targets to protect and stabilize enzymes for biocatalysis in ionic liquids.

PubMed

Sprenger, K G; Plaks, J G; Kaar, J L; Pfaendtner, J

2017-07-05

For many different frameworks, the structure, function, and dynamics of an enzyme is largely determined by the nature of its interactions with the surrounding host environment, thus a molecular level understanding of enzyme/host interactions is essential to the design of new processes and applications. Ionic liquid (IL) solvents are a popular class of solvents in which to study enzyme behavior, yet it is still not possible to predict how a given enzyme will behave in a given IL solvent. Furthermore, a dearth of experimental data with which to evaluate simulation force fields has prevented the full integration of experimental and computational techniques to gain a complete picture of enzyme/IL interactions. Utilizing recently published crystallographic data of an enzyme in complex with an IL, this study aims to validate the use of current molecular force fields for studying enzyme/IL interactions, and to provide new mechanistic insight into enzyme stabilization in IL solvents. Classical molecular dynamics (MD) simulations have been performed on both the folded and unfolded state of Bacillus subtilis lipase A and a quadruple-mutant version of lipase A, in solutions of aqueous 1-butyl-3-methylimidazolium chloride. Results show classical MD simulations can predict the preferred surface binding locations of IL cations as well as reductions in IL anion binding to mutated surface residues with high accuracy. The results also point to a mechanistic difference between IL binding to the folded and unfolded state of an enzyme, which we call the "counter-ion effect". These findings could have important implications for future rational design efforts to stabilize enzymes in non-conventional media.

Preparation of DPPE-Stabilized Gold Nanoparticles

ERIC Educational Resources Information Center

Dungey, Keenan E.; Muller, David P.; Gunter, Tammy

2005-01-01

An experiment is presented that introduces students to nanotechnology through the preparation of nanoparticles and their visualization using transmission electron microscopy (TEM). The experiment familiarizes the students with nonaqueous solvents, biphasic reactions, phase-transfer agents, ligands to stabilize growing nanoparticles, and bidentate…

Thermal degradation of the solvent employed in the next-generation caustic-side solvent extraction process and its effect on the extraction, scrubbing, and stripping of cesium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roach, Benjamin D.; Williams, Neil J.; Moyer, Bruce A.

As part of the ongoing development of the Next-Generation Caustic-Side Solvent Extraction (NGS) process, the thermal stability of the process solvent was investigated and shown to be adequate for industrial application. The solvent was thermally treated at 35 C over a period of 13 months whilst in dynamic contact with each of the aqueous phases of the current NGS process, namely SRS 15 (a highly caustic waste simulant), sodium hydroxide scrub solution (0.025 M), and boric acid strip solution (0.01 M). The effect of thermal treatment was evaluated by assessing batch extract/scrub/strip performance as a function of time, by monitoringmore » the sodium extraction capacity of the solvent, and by analysis of the solvent using electrospray mass spectrometry. Current studies indicate that the NGS solvent should be thermally robust for a period of XXX months at the Modular Caustic-Side Solvent Extraction Unit (MCU) pilot plant located at Savannah River Site. Furthermore, the guanidine suppressor appears to be the solvent component most significantly impacted by thermal treatment of the solvent, showing significant degradation over time.« less

Thermal degradation of the solvent employed in the next-generation caustic-side solvent extraction process and its effect on the extraction, scrubbing, and stripping of cesium

DOE PAGES

Roach, Benjamin D.; Williams, Neil J.; Moyer, Bruce A.

2015-09-02

As part of the ongoing development of the Next-Generation Caustic-Side Solvent Extraction (NGS) process, the thermal stability of the process solvent was investigated and shown to be adequate for industrial application. The solvent was thermally treated at 35 C over a period of 13 months whilst in dynamic contact with each of the aqueous phases of the current NGS process, namely SRS 15 (a highly caustic waste simulant), sodium hydroxide scrub solution (0.025 M), and boric acid strip solution (0.01 M). The effect of thermal treatment was evaluated by assessing batch extract/scrub/strip performance as a function of time, by monitoringmore » the sodium extraction capacity of the solvent, and by analysis of the solvent using electrospray mass spectrometry. Current studies indicate that the NGS solvent should be thermally robust for a period of XXX months at the Modular Caustic-Side Solvent Extraction Unit (MCU) pilot plant located at Savannah River Site. Furthermore, the guanidine suppressor appears to be the solvent component most significantly impacted by thermal treatment of the solvent, showing significant degradation over time.« less

Efficient production of fatty acid methyl ester from waste activated bleaching earth using diesel oil as organic solvent.

PubMed

Kojima, Seiji; Du, Dongning; Sato, Masayasu; Park, Enoch Y

2004-01-01

Fatty acid methyl ester (FAME) production from waste activated bleaching earth (ABE) discarded by the crude oil refining industry was investigated using fossil fuel as a solvent in the esterification of triglycerides. Lipase from Candida cylindracea showed the highest stability in diesel oil. Using diesel oil as a solvent, 3 h was sufficient to obtain a yield of approximately 100% of FAME in the presence of 10% lipase from waste ABE. Kerosene was also a good solvent in the esterification of triglycerides embedded in the waste ABE. Fuel analysis showed that the FAME produced using diesel oil as a solvent complied with the Japanese diesel standard and the 10% residual carbon amount was lower than that of FAME produced using other solvents. Use of diesel oil as solvent in the FAME production from the waste ABE simplified the process, because there was no need to separate the organic solvent from the FAME-solvent mixture. These results demonstrate a promising reutilization method for the production of FAME, for use as a biodiesel, from industrial waste resources containing waste vegetable oils.

Characterization and Higher-Order Structure Assessment of an Interchain Cysteine-Based ADC: Impact of Drug Loading and Distribution on the Mechanism of Aggregation.

PubMed

Guo, Jianxin; Kumar, Sandeep; Chipley, Mark; Marcq, Olivier; Gupta, Devansh; Jin, Zhaowei; Tomar, Dheeraj S; Swabowski, Cecily; Smith, Jacquelynn; Starkey, Jason A; Singh, Satish K

2016-03-16

The impact of drug loading and distribution on higher order structure and physical stability of an interchain cysteine-based antibody drug conjugate (ADC) has been studied. An IgG1 mAb was conjugated with a cytotoxic auristatin payload following the reduction of interchain disulfides. The 2-D LC-MS analysis shows that there is a preference for certain isomers within the various drug to antibody ratios (DARs). The physical stability of the unconjugated monoclonal antibody, the ADC, and isolated conjugated species with specific DAR, were compared using calorimetric, thermal, chemical denaturation and molecular modeling techniques, as well as techniques to assess hydrophobicity. The DAR was determined to have a significant impact on the biophysical properties and stability of the ADC. The CH2 domain was significantly perturbed in the DAR6 species, which was attributable to quaternary structural changes as assessed by molecular modeling. At accelerated storage temperatures, the DAR6 rapidly forms higher molecular mass species, whereas the DAR2 and the unconjugated mAb were largely stable. Chemical denaturation study indicates that DAR6 may form multimers while DAR2 and DAR4 primarily exist in monomeric forms in solution at ambient conditions. The physical state differences were correlated with a dramatic increase in the hydrophobicity and a reduction in the surface tension of the DAR6 compared to lower DAR species. Molecular modeling of the various DAR species and their conformers demonstrates that the auristatin-based linker payload directly contributes to the hydrophobicity of the ADC molecule. Higher order structural characterization provides insight into the impact of conjugation on the conformational and colloidal factors that determine the physical stability of cysteine-based ADCs, with implications for process and formulation development.

Determining the Energetics of the Hydrogen Bond through FTIR: A Hands-On Physical Chemistry Lab Experiment

ERIC Educational Resources Information Center

Guerin, Abby C.; Riley, Kristi; Rupnik, Kresimir; Kuroda, Daniel G.

2016-01-01

Hydrogen bonds are very important chemical structures that are responsible for many unique and important properties of solvents, such as the solvation power of water. These distinctive features are directly related to the stabilization energy conferred by hydrogen bonds to the solvent. Thus, the characterization of hydrogen bond energetics has…

Structural stability of proteins in aqueous and nonpolar environments

NASA Astrophysics Data System (ADS)

Yasuda, Satoshi; Oshima, Hiraku; Kinoshita, Masahiro

2012-10-01

A protein folds into its native structure with the α-helix and/or β-sheet in aqueous solution under the physiological condition. The relative content of these secondary structures largely varies from protein to protein. However, such structural variability is not exhibited in nonaqueous environment. For example, there is a strong trend that alcohol induces a protein to form α-helices, and many of the membrane proteins within the lipid bilayer consists of α-helices. Here we investigate the structural stability of proteins in aqueous and nonpolar environments using our recently developed free-energy function F = (Λ - TS)/(kBT0) = Λ/(kBT0) - S/kB (T0 = 298 K and the absolute temperature T is set at T0) which is based on statistical thermodynamics. Λ/(kBT0) and S/kB are the energetic and entropic components, respectively, and kB is Boltzmann's constant. A smaller value of the positive quantity, -S, represents higher efficiency of the backbone and side-chain packing promoted by the entropic effect arising from the translational displacement of solvent molecules or the CH2, CH3, and CH groups which constitute nonpolar chains of lipid molecules. As for Λ, in aqueous solution, a transition to a more compact structure of a protein accompanies the break of protein-solvent hydrogen bonds: As the number of donors and acceptors buried without protein intramolecular hydrogen bonding increases, Λ becomes higher. In nonpolar solvent, lower Λ simply implies more intramolecular hydrogen bonds formed. We find the following. The α-helix and β-sheet are advantageous with respect to -S as well as Λ and to be formed as much as possible. In aqueous solution, the solvent-entropy effect on the structural stability is so strong that the close packing of side chains is dominantly important, and the α-helix and β-sheet contents are judiciously adjusted to accomplish it. In nonpolar solvent, the solvent-entropy effect is substantially weaker than in aqueous solution. Λ is crucial and the α-helix is more stable than the β-sheet in terms of Λ, which develops a tendency that α-helices are exclusively chosen. For a membrane protein, α-helices are stabilized as fundamental structural units for the same reason, but their arrangement is performed through the entropic effect mentioned above.

STORAGE STABILITY OF PESTICIDES IN EXTRACT SOLVENTS AND SAMPLING MEDIA

EPA Science Inventory

Demonstrating that pesticides are stable in field media and their extracts over extended storage periods allows operational flexibility and cost efficiency. Stability of the 31 neutral pesticides and 2 acid herbicides of the Agricultural Health Study exposure pilot was evaluate...

Study of complex formation of 5,5'-(2 E, 2' E)-2,2'-(ethane-1,2-diylidene)bis(hydrazine-1-yl-2-ylidene)bis(4-amino-4H-1,2,4-triazole-3-thiol) (HYT) macrocyclic ligand with Cd2+ cation in non-aqueous solution by spectroscopic and conductometric methods

NASA Astrophysics Data System (ADS)

Mallaekeh, Hassan; Shams, Alireza; Shaker, Mohammad; Bahramzadeh, Ehsan; Arefi, Donya

2014-12-01

In this paper the complexation reaction of the 5,5'-(2 E,2' E)-2,2'-(ethane-1,2-diylidene)bis(hydrazine-1-yl-2-ylidene)bis(4-amino-4H-1,2,4-triazole-3-thiol) ligand (HYT) with Cd2+ education was studied in some binary mixtures of methanol (MeOH), n-propanol (PrOH) and dimethyl-formamide (DMF) at different temperatures using the conductometry and spectrophotometry. The stability constants of the complex was determined using a GENPLOT computer program. The conductance data and absorbance-mole ratio plots show that in all solvent systems, the stoichiometry of the complex formed between (HYT) and Cd2+ cation is 1: 1. The obtained results show that the stability of (HYT)-Cd complex is sensitive to the mixed solvents composition. The values of thermodynamic parameters (Δ G ∘, Δ H ∘, and Δ S ∘) for formation of (HYT)-Cd complex were obtained from temperature dependence of the stability constant using the van't Hoff plots. The results show that in most cases, the complex are enthalpy destabilized but entropy stabilized and the complex formation is affected by pH, time, temperature and the nature of the solvent.

Roles of the amino group of purine bases in the thermodynamic stability of DNA base pairing.

PubMed

Nakano, Shu-ichi; Sugimoto, Naoki

2014-08-05

The energetic aspects of hydrogen-bonded base-pair interactions are important for the design of functional nucleotide analogs and for practical applications of oligonucleotides. The present study investigated the contribution of the 2-amino group of DNA purine bases to the thermodynamic stability of oligonucleotide duplexes under different salt and solvent conditions, using 2'-deoxyriboinosine (I) and 2'-deoxyribo-2,6-diaminopurine (D) as non-canonical nucleotides. The stability of DNA duplexes was changed by substitution of a single base pair in the following order: G • C > D • T ≈ I • C > A • T > G • T > I • T. The apparent stabilization energy due to the presence of the 2-amino group of G and D varied depending on the salt concentration, and decreased in the water-ethanol mixed solvent. The effects of salt concentration on the thermodynamics of DNA duplexes were found to be partially sequence-dependent, and the 2-amino group of the purine bases might have an influence on the binding of ions to DNA through the formation of a stable base-paired structure. Our results also showed that physiological salt conditions were energetically favorable for complementary base recognition, and conversely, low salt concentration media and ethanol-containing solvents were effective for low stringency oligonucleotide hybridization, in the context of conditions employed in this study.

Investigation of Pu(IV)-acetohydroxamic acid complex by solvent extraction with di(2-ethylhexyl) phosphoric acid

NASA Astrophysics Data System (ADS)

Brown, M. Alex; Paulenova, Alena; Tkac, Peter

2010-03-01

The stability constant of the Pu(IV)-acetohydroxamic acid complex Pu(AHA)3+ at 1 M ionic strength (pH = 0) has been investigated by method of solvent extraction. Di(2-ethylhexyl) phosphoric acid (HDEHP) was used to extract Pu(IV) from perchloric and nitric acid media at various AHA concentrations. Distribution ratios over a range of ligand concentrations were used in conjunction with graphical methods to obtain logβ1 = 14.3 ± 0.03 in perchloric acid. The stability constant determined from solutions in nitric acid was excluded because of the uncertainty in plutonium speciation.

Study on the conformational equilibrium of the alanine dipeptide in water solution by using the averaged solvent electrostatic potential from molecular dynamics methodology.

PubMed

García-Prieto, Francisco F; Fdez Galván, Ignacio; Aguilar, Manuel A; Martín, M Elena

2011-11-21

The ASEP/MD method has been employed for studying the solvent effect on the conformational equilibrium of the alanine dipeptide in water solution. MP2 and density functional theory (DFT) levels of theory were used and results were compared. While in gas phase cyclic structures showing intramolecular hydrogen bonds were found to be the most stable, the stability order is reversed in water solution. Intermolecular interaction with the solvent causes the predominance of extended structures as the stabilizing contacts dipeptide-water are favoured. Free-energy differences in solution were calculated and PPII, α(R), and C5 conformers were identified as the most stable at MP2 level. Experimental data from Raman and IR techniques show discrepancies about the relative abundance of α(R) y C5, our results support the Raman data. The DFT level of theory agrees with MP2 in the location and stability of PPII and α(R) forms but fails in the location of C5. MP2 results suggest the possibility of finding traces of C7eq conformer in water solution, in agreement with recent experiments.

Behaviour of a solvent trapped in a physical molecular gel

NASA Astrophysics Data System (ADS)

Morfin, I.; Spagnoli, S.; Rambaud, C.; Longeville, S.; Plazanet, M.

2016-03-01

Physical gels formed by amphiphilic molecules, namely in this study Methyl-4,6-O-benzylidene-? -D-mannopyranoside, can be form either in polar and protic liquid-like water or in organic apolar solvent such as toluene. The solvent, that influences the supramolecular organization of the gelators, plays an important role in the stability and formation of the gel phase. Gelator-solvent interactions govern not only the assembly but also the solvent diffusion in the material. We present here measurements of neutron scattering (Time of Flight and Neutron Spin Echo) characterizing this microscopic behaviour. In addition, we show that transient grating spectroscopy provides valuable information through the characterization of the longitudinal acoustic wave propagating in the system. Opposite effects on the speed of sound in the gels are observed for the two solvents investigated, being relevant of the interactions between the gelators and the surrounding liquid.

Molecular basis of the osmolyte effect on protein stability: a lesson from the mechanical unfolding of lysozyme.

PubMed

Adamczak, Beata; Wieczór, Miłosz; Kogut, Mateusz; Stangret, Janusz; Czub, Jacek

2016-10-15

Osmolytes are a class of small organic molecules that shift the protein folding equilibrium. For this reason, they are accumulated by organisms under environmental stress and find applications in biotechnology where proteins need to be stabilized or dissolved. However, despite years of research, debate continues over the exact mechanisms underpinning the stabilizing and denaturing effect of osmolytes. Here, we simulated the mechanical denaturation of lysozyme in different solvent conditions to study the molecular mechanism by which two biologically relevant osmolytes, denaturing (urea) and stabilizing (betaine), affect the folding equilibrium. We found that urea interacts favorably with all types of residues via both hydrogen bonds and dispersion forces, and therefore accumulates in a diffuse solvation shell around the protein. This not only provides an enthalpic stabilization of the unfolded state, but also weakens the hydrophobic effect, as hydrophobic forces promote the association of urea with nonpolar residues, facilitating the unfolding. In contrast, we observed that betaine is excluded from the protein backbone and nonpolar side chains, but is accumulated near the basic residues, yielding a nonuniform distribution of betaine molecules at the protein surface. Spatially resolved solvent-protein interaction energies further suggested that betaine behaves in a ligand- rather than solvent-like manner and its exclusion from the protein surface arises mostly from the scarcity of favorable binding sites. Finally, we found that, in the presence of betaine, the reduced ability of water molecules to solvate the protein results in an additional enthalpic contribution to the betaine-induced stabilization. © 2016 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society.

Peptide-MHC Class I Tetramers Can Fail To Detect Relevant Functional T Cell Clonotypes and Underestimate Antigen-Reactive T Cell Populations.

PubMed

Rius, Cristina; Attaf, Meriem; Tungatt, Katie; Bianchi, Valentina; Legut, Mateusz; Bovay, Amandine; Donia, Marco; Thor Straten, Per; Peakman, Mark; Svane, Inge Marie; Ott, Sascha; Connor, Tom; Szomolay, Barbara; Dolton, Garry; Sewell, Andrew K

2018-04-01

Peptide-MHC (pMHC) multimers, usually used as streptavidin-based tetramers, have transformed the study of Ag-specific T cells by allowing direct detection, phenotyping, and enumeration within polyclonal T cell populations. These reagents are now a standard part of the immunology toolkit and have been used in many thousands of published studies. Unfortunately, the TCR-affinity threshold required for staining with standard pMHC multimer protocols is higher than that required for efficient T cell activation. This discrepancy makes it possible for pMHC multimer staining to miss fully functional T cells, especially where low-affinity TCRs predominate, such as in MHC class II-restricted responses or those directed against self-antigens. Several recent, somewhat alarming, reports indicate that pMHC staining might fail to detect the majority of functional T cells and have prompted suggestions that T cell immunology has become biased toward the type of cells amenable to detection with multimeric pMHC. We use several viral- and tumor-specific pMHC reagents to compare populations of human T cells stained by standard pMHC protocols and optimized protocols that we have developed. Our results confirm that optimized protocols recover greater populations of T cells that include fully functional T cell clonotypes that cannot be stained by regular pMHC-staining protocols. These results highlight the importance of using optimized procedures that include the use of protein kinase inhibitor and Ab cross-linking during staining to maximize the recovery of Ag-specific T cells and serve to further highlight that many previous quantifications of T cell responses with pMHC reagents are likely to have considerably underestimated the size of the relevant populations. Copyright © 2018 The Authors.

Plasmatic ADAMTS-13 metalloprotease and von Willebrand factor in children with cyanotic congenital heart disease

PubMed Central

Soares, R.P.S.; Bydlowski, S.P.; Nascimento, N.M.; Thomaz, A.M.; Bastos, E.N.M.; Lopes, A.A.

2013-01-01

Changes in plasma von Willebrand factor concentration (VWF:Ag) and ADAMTS-13 activity (the metalloprotease that cleaves VWF physiologically) have been reported in several cardiovascular disorders with prognostic implications. We therefore determined the level of these proteins in the plasma of children with cyanotic congenital heart disease (CCHD) undergoing surgical treatment. Forty-eight children were enrolled (age 0.83 to 7.58 years). Measurements were performed at baseline and 48 h after surgery. ELISA, collagen-binding assays and Western blotting were used to estimate antigenic and biological activities, and proteolysis of VWF multimers. Preoperatively, VWF:Ag and ADAMTS-13 activity were decreased (65 and 71% of normal levels considered as 113 (105-129) U/dL and 91 ± 24% respectively, P < 0.003) and correlated (r = 0.39, P = 0.0064). High molecular weight VWF multimers were not related, suggesting an interaction of VWF with cell membranes, followed by proteolytic cleavage. A low preoperative ADAMTS-13 activity, a longer activated partial thromboplastin time and the need for cardiopulmonary bypass correlated with postoperative bleeding (P < 0.05). Postoperatively, ADAMTS-13 activity increased but less extensively than VWF:Ag (respectively, 2.23 and 2.83 times baseline, P < 0.0001), resulting in an increased VWF:Ag/ADAMTS-13 activity ratio (1.20 to 1.54, respectively, pre- and postoperative median values, P = 0.0029). ADAMTS-13 consumption was further confirmed by decreased ADAMTS-13 antigenic concentration (0.91 ± 0.30 to 0.70 ± 0.25 µg/mL, P < 0.0001) and persistent proteolysis of VWF multimers. We conclude that, in pediatric CCHD, changes in circulating ADAMTS-13 suggest enzyme consumption, associated with abnormal structure and function of VWF. PMID:23558858

Dogs with heart diseases causing turbulent high-velocity blood flow have changes in platelet function and von Willebrand factor multimer distribution.

PubMed

Tarnow, Inge; Kristensen, Annemarie T; Olsen, Lisbeth H; Falk, Torkel; Haubro, Lotte; Pedersen, Lotte G; Pedersen, Henrik D

2005-01-01

The purpose of this prospective study was to investigate platelet function using in vitro tests based on both high and low shear rates and von Willebrand factor (vWf) multimeric composition in dogs with cardiac disease and turbulent high-velocity blood flow. Client-owned asymptomatic, untreated dogs were divided into 4 groups: 14 Cavalier King Charles Spaniels (Cavaliers) with mitral valve prolapse (MVP) and no or minimal mitral regurgitation (MR), 17 Cavaliers with MVP and moderate to severe MR, 14 control dogs, and 10 dogs with subaortic stenosis (SAS). Clinical examinations and echocardiography were performed in all dogs. PFA100 closure times (the ability of platelets to occlude a hole in a membrane at high shear rates), platelet activation markers (plasma thromboxane B2 concentration, platelet surface P-selectin expression), platelet aggregation (in whole blood and platelet-rich plasma with 3 different agonists), and vWf multimers were analyzed. Cavaliers with moderate to severe MR and dogs with SAS had longer closure times and a lower percentage of the largest vWf multimers than did controls. Maximal aggregation responses were unchanged in dogs with SAS but enhanced in Cavaliers with MVP (regardless of MR status) compared with control dogs. No significant difference in platelet activation markers was found among groups. The data suggest that a form of platelet dysfunction detected at high shear rates was present in dogs with MR and SAS, possibly associated with a qualitative vWf defect. Aggregation results suggest increased platelet reactivity in Cavaliers, but the platelets did not appear to circulate in a preactivated state in either disease.

Adiponectin complexes composition in Japanese-Brazilians regarding their glucose tolerance status.

PubMed

Crispim, Felipe; Vendramini, Marcio F; Moisés, Regina S

2013-04-09

Adiponectin circulates in different multimer complexes comprised of low molecular weight trimeric form (LMW), hexamer of middle molecular weight (MMW) and high molecular weight multimers (HMW). In Japanese-Brazilians, a population with high prevalence of glucose metabolism disturbances, we examined the associations of total adiponectin and its multimers with diabetes mellitus. Two study groups were examined: 26 patients with diabetes mellitus (DM,14 women and 12 men, aged 55.3 ± 8.6 years) and 27 age-matched control subjects with normal glucose tolerance (NGT,12 women and 15 men, aged 54.0 ± 9.2 years). We found no significant differences in total [NGT: 6.90 ug/ml (4.38-13.43); DM: 5.38 ug/ml (3.76-8.56), p = 0.35], MMW [NGT:2.34 ug/ml (1.38-3.25); DM: 1.80 ug/ml (1.18-2.84), p = 0.48] or LMW adiponectin [NGT: 2.07 ug/ml (1.45-3.48), DM: 2.93 ug/ml (1.78-3.99), p = 0.32] between groups. In contrast, HMW adiponectin levels were significantly lower in patients with DM [TGN: 2.39 ug/ml (1.20-4.75); DM: 1.04 ug/ml (0.42-1.60), p = 0.001]. A logistic regression analysis was done to identify independent associations with diabetes mellitus. The results showed that HOMA-IR and HMW adiponectin in women were independently associated with diabetes mellitus. The current investigation demonstrates that in Japanese-Brazilians HMW adiponectin is selectively reduced in individuals with type 2 diabetes, while no differences were found in MMW and LMW adiponectin isoforms.

Adiponectin complexes composition in Japanese-Brazilians regarding their glucose tolerance status

PubMed Central

2013-01-01

Background Adiponectin circulates in different multimer complexes comprised of low molecular weight trimeric form (LMW), hexamer of middle molecular weight (MMW) and high molecular weight multimers (HMW). In Japanese-Brazilians, a population with high prevalence of glucose metabolism disturbances, we examined the associations of total adiponectin and its multimers with diabetes mellitus. Methods Two study groups were examined: 26 patients with diabetes mellitus (DM,14 women and 12 men, aged 55.3 ± 8.6 years) and 27 age-matched control subjects with normal glucose tolerance (NGT,12 women and 15 men, aged 54.0 ± 9.2 years). Results We found no significant differences in total [NGT: 6.90 ug/ml (4.38-13.43); DM: 5.38 ug/ml (3.76-8.56), p = 0.35], MMW [NGT:2.34 ug/ml (1.38-3.25); DM: 1.80 ug/ml (1.18-2.84), p = 0.48] or LMW adiponectin [NGT: 2.07 ug/ml (1.45-3.48), DM: 2.93 ug/ml (1.78-3.99), p = 0.32] between groups. In contrast, HMW adiponectin levels were significantly lower in patients with DM [TGN: 2.39 ug/ml (1.20-4.75); DM: 1.04 ug/ml (0.42-1.60), p = 0.001]. A logistic regression analysis was done to identify independent associations with diabetes mellitus. The results showed that HOMA-IR and HMW adiponectin in women were independently associated with diabetes mellitus. Conclusion The current investigation demonstrates that in Japanese-Brazilians HMW adiponectin is selectively reduced in individuals with type 2 diabetes, while no differences were found in MMW and LMW adiponectin isoforms. PMID:23570346

Stabilization and activation of alpha-chymotrypsin in water-organic solvent systems by complex formation with oligoamines.

PubMed

Kudryashova, Elena V; Artemova, Tatiana M; Vinogradov, Alexei A; Gladilin, Alexander K; Mozhaev, Vadim V; Levashov, Andrey V

2003-04-01

Formation of enzyme-oligoamine complexes was suggested as an approach to obtain biocatalysts with enhanced resistance towards inactivation in water-organic media. Complex formation results in broadening (by 20-40% v/v ethanol) of the range of cosolvent concentrations where the enzyme retains its catalytic activity (stabilization effect). At moderate cosolvent concentrations (20-40% v/v) complex formation activates the enzyme (by 3-6 times). The magnitude of activation and stabilization effects increases with the number of possible electrostatic contacts between the protein surface and the molecules of oligoamines (OA). Circular dichroism spectra in the far-UV region show that complex formation stabilizes protein conformation and prevents aggregation in water-organic solvent mixtures. Two populations of the complexes with different thermodynamic stabilities were found in alpha-chymotrypsin (CT)-OA systems depending on the CT/OA ratio. The average dissociation constants and stoichiometries of both low- and high-affinity populations of the complexes were estimated. It appears that it is the low-affinity sites on the CT surface that are responsible for the activation effect.

Stabilization of gold nanoparticles by 6-mercaptopurine monolayers. Effects of the solvent properties.

PubMed

Viudez, Alfonso J; Madueño, Rafael; Pineda, Teresa; Blázquez, Manuel

2006-09-14

6-Mercaptopurine-coated gold nanoparticles (6MP-AuNPs) have been prepared by modification of the nanoparticle surface with 6MP upon displacement of the protective layer of citrate anions. The modification has been studied by UV-vis and FTIR spectroscopies. A study of the stability of these 6MP-AuNPs in aqueous solutions as a function of ionic strength and pH has shown the importance of the charges on the stabilization. The protonation of N9 of the 6MP molecules brings about a sudden flocculation phenomenon. However, the flocculation is reversible upon changing the pH to values where the molecules become newly charged. Evidence of the competence between the interaction of capping solvent molecules and the attractive forces between particles is also shown in this paper.

Comparison of Intermolecular Forces in Anhydrous Sorbitol and Solvent Cocrystals.

PubMed

Dierks, Teresa M; Korter, Timothy M

2017-08-03

The hygroscopicity of solid sorbitol is important for its utilization as a sweetener in the pharmaceutical and food industries. The molecular foundations of sorbitol hydration characteristics are explored here using two solvated cocrystals, sorbitol-water and sorbitol-pyridine. In this work, solid-state density functional theory and terahertz time-domain spectroscopy were used to evaluate the relative stabilities of these cocrystals as compared to anhydrous sorbitol in terms of conformational and cohesive energies. The modification of the hydrogen-bonding network in crystalline sorbitol by solvent molecules gives new insight into the origins of the notable stability of sorbitol-water as compared to similar solids such as mannitol-water. In particular, the energy analysis reveals that the relative instability of the mannitol hydrate is based primarily in the lack of water-water interactions which provide considerable stabilization in the sorbitol-water crystal.

Biocatalytic transformations in ionic liquids.

PubMed

van Rantwijk, Fred; Madeira Lau, Rute; Sheldon, Roger A

2003-03-01

Room temperature ionic liquids are non-volatile, thermally stable and highly polar; they are also moderately hydrophilic solvents. Here, we discuss their use as reaction media for biocatalysis. Enzymes of widely diverging types are catalytically active in ionic liquids or aqueous biphasic ionic liquid systems. Lipases, in particular, maintain their activity in anhydrous ionic liquid media; the (enantio)selectivity and operational stability are often better than in traditional media. The unconventional solvent properties of ionic liquids have been exploited in biocatalyst recycling and product recovery schemes that are not feasible with traditional solvent systems.

Superoxide Stabilization and a Universal KO2 Growth Mechanism in Potassium-Oxygen Batteries.

PubMed

Wang, Wanwan; Lai, Nien-Chu; Liang, Zhuojian; Wang, Yu; Lu, Yi-Chun

2018-04-23

Rechargeable potassium-oxygen (K-O 2 ) batteries promise to provide higher round-trip efficiency and cycle life than other alkali-oxygen batteries with satisfactory gravimetric energy density (935 Wh kg -1 ). Exploiting a strong electron-donating solvent, for example, dimethyl sulfoxide (DMSO) strongly stabilizes the discharge product (KO 2 ), resulting in significant improvement in electrode kinetics and chemical/electrochemical reversibility. The first DMSO-based K-O 2 battery demonstrates a much higher energy efficiency and stability than the glyme-based electrolyte. A universal KO 2 growth model is developed and it is demonstrated that the ideal solvent for K-O 2 batteries should strongly stabilize superoxide (strong donor ability) to obtain high electrode kinetics and reversibility while providing fast oxygen diffusion to achieve high discharge capacity. This work elucidates key electrolyte properties that control the efficiency and reversibility of K-O 2 batteries. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Networking Foundations for Collaborative Computing at Internet Scope

DTIC Science & Technology

2006-01-01

network-supported synchronous multime- dia groupwork at Internet scope and for large user groups. Contributions entail an novel classification for...multimedia resources in interactive groupwork , generalized to the domain of CSCW from the “right to speak” [26]. A floor control protocol mediates access to

Rapid acquisition of beta-sheet structure in the prion protein prior to multimer formation.

PubMed

Post, K; Pitschke, M; Schäfer, O; Wille, H; Appel, T R; Kirsch, D; Mehlhorn, I; Serban, H; Prusiner, S B; Riesner, D

1998-11-01

The N-terminally truncated form of the prion protein, PrP 27-30, and the corresponding recombinant protein, rPrP, were solubilized in 0.2% SDS, and the transitions induced by changing the conditions from 0.2% SDS to physiological conditions, i.e. removing SDS, were characterized with respect to solubility, resistance to proteolysis, secondary structure and multimerization. Circular dichroism, electron microscopy and fluorescence correlation spectroscopy were used to study the structural transitions of PrP. Within one minute the alpha-helical structure of PrP was transformed into one that was enriched in beta-sheets and consisted mainly of dimers. Larger oligomers were found after 20 minutes and larger multimers exhibiting resistance to proteolysis were found after several hours. It was concluded that the monomeric alpha-helical conformation was stable in SDS or when attached to the membrane; however, the state of lowest free energy in aqueous solution at neutral pH seems to be the multimeric, beta-sheet enriched conformation.

Optimized Li-Ion Electrolytes Containing Fluorinated Ester Co-Solvents

NASA Technical Reports Server (NTRS)

Prakash, G. K. Surya; Smart, Marshall; Smith, Kiah; Bugga, Ratnakumar

2010-01-01

A number of experimental lithium-ion cells, consisting of MCMB (meso-carbon microbeads) carbon anodes and LiNi(0.8)Co(0.2)O2 cathodes, have been fabricated with increased safety and expanded capability. These cells serve to verify and demonstrate the reversibility, low-temperature performance, and electrochemical aspects of each electrode as determined from a number of electrochemical characterization techniques. A number of Li-ion electrolytes possessing fluorinated ester co-solvents, namely trifluoroethyl butyrate (TFEB) and trifluoroethyl propionate (TFEP), were demonstrated to deliver good performance over a wide temperature range in experimental lithium-ion cells. The general approach taken in the development of these electrolyte formulations is to optimize the type and composition of the co-solvents in ternary and quaternary solutions, focusing upon adequate stability [i.e., EC (ethylene carbonate) content needed for anode passivation, and EMC (ethyl methyl carbonate) content needed for lowering the viscosity and widening the temperature range, while still providing good stability], enhancing the inherent safety characteristics (incorporation of fluorinated esters), and widening the temperature range of operation (the use of both fluorinated and non-fluorinated esters). Further - more, the use of electrolyte additives, such as VC (vinylene carbonate) [solid electrolyte interface (SEI) promoter] and DMAc (thermal stabilizing additive), provide enhanced high-temperature life characteristics. Multi-component electrolyte formulations enhance performance over a temperature range of -60 to +60 C. With the need for more safety with the use of these batteries, flammability was a consideration. One of the solvents investigated, TFEB, had the best performance with improved low-temperature capability and high-temperature resilience. This work optimized the use of TFEB as a co-solvent by developing the multi-component electrolytes, which also contain non-halogenated esters, film forming additives, thermal stabilizing additives, and flame retardant additives. Further optimization of these electrolyte formulations is anticipated to yield improved performance. It is also anticipated that much improved performance will be demonstrated once these electrolyte solutions are incorporated into hermetically sealed, large capacity prototype cells, especially if effort is devoted to ensure that all electrolyte components are highly pure.

Competing Intramolecular vs. Intermolecular Hydrogen Bonds in Solution

PubMed Central

Nagy, Peter I.

2014-01-01

A hydrogen bond for a local-minimum-energy structure can be identified according to the definition of the International Union of Pure and Applied Chemistry (IUPAC recommendation 2011) or by finding a special bond critical point on the density map of the structure in the framework of the atoms-in-molecules theory. Nonetheless, a given structural conformation may be simply favored by electrostatic interactions. The present review surveys the in-solution competition of the conformations with intramolecular vs. intermolecular hydrogen bonds for different types of small organic molecules. In their most stable gas-phase structure, an intramolecular hydrogen bond is possible. In a protic solution, the intramolecular hydrogen bond may disrupt in favor of two solute-solvent intermolecular hydrogen bonds. The balance of the increased internal energy and the stabilizing effect of the solute-solvent interactions regulates the new conformer composition in the liquid phase. The review additionally considers the solvent effects on the stability of simple dimeric systems as revealed from molecular dynamics simulations or on the basis of the calculated potential of mean force curves. Finally, studies of the solvent effects on the type of the intermolecular hydrogen bond (neutral or ionic) in acid-base complexes have been surveyed. PMID:25353178

High Performance of Perovskite Solar Cells via Catalytic Treatment in Two-Step Process: The Case of Solvent Engineering.

PubMed

Li, Wenzhe; Fan, Jiandong; Li, Jiangwei; Niu, Guangda; Mai, Yaohua; Wang, Liduo

2016-11-09

Currently, the potential mechanism of the solvent-assisted crystallization for mixed cations perovskite thin film (FA x MA 1-x PbI 3 ) prepared via two-step solution-process still remains obscure. Here, we clarified the molecular-competing-reacted process of NH 2 CH═NH 2 I (FAI) and CH 3 NH 3 I (MAI) with PbI 2 (DMSO) x complex in dimethyl sulfoxide (DMSO) and diethyl ether (DE) catalytic solvent system in the sequential two-step solution-process. The microscopic dynamics was characterized via the characterizations of in situ photoluminescence spectra. In addition, we found that the thermal stability of the perovskite films suffered from the residual solvent with high boiling point, for example, DMSO. The further DE treatment could promote the volatility process of DMSO and accelerate the crystallization process of perovskite films. The highest PCE over 19% with slight hysteresis effect was eventually obtained with a reproducible FA 0.88 MA 0.12 PbI 3 solar cell, which displayed a constant power output within 100 s upon light soaking and stable PCE output within 30 d in the thermal stability test.

Alginate as immobilization matrix and stabilizing agent in a two-phase liquid system: application in lipase-catalysed reactions.

PubMed

Hertzberg, S; Kvittingen, L; Anthonsen, T; Skjåk-Braek, G

1992-01-01

Alginate was evaluated as an immobilization matrix for enzyme-catalyzed reactions in organic solvents. In contrast to most hydrogels, calcium alginate was found to be stable in a range of organic solvents and to retain the enzyme inside the gel matrix. In hydrophobic solvents, the alginate gel (greater than 95% water) thus provided a stable, two-phase liquid system. The lipase from Candida cylindracea, after immobilization in alginate beads, catalysed esterification and transesterification in n-hexane under both batch and continuous-flow conditions. The operational stability of the lipase was markedly enhanced by alginate entrapment. In the esterification of butanoic acid with n-butanol, better results were obtained in the typical hydrophilic calcium alginate beads than in less hydrophilic matrices. The effects of substrate concentration, matrix area, and polarity of the substrate alcohols and of the organic solvent on the esterification activity were examined. The transesterification of octyl 2-bromopropanoate with ethanol was less efficient than that of ethyl 2-bromopropanoate with octanol. By using the hydrophilic alginate gel as an immobilization matrix in combination with a mobile hydrophobic phase, a two-phase liquid system was achieved with definite advantages for a continuous, enzyme-catalysed process.

Pilot plant studies of the CO{sub 2} capture performance of aqueous MEA and mixed MEA/MDEA solvents at the University of Regina CO{sub 2} capture technology development plant and the Boundary Dam CO{sub 2} capture demonstration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Idem, R.; Wilson, M.; Tontiwachwuthikul, P.

2006-04-12

Evaluations of the benefits of using a mixed MEA/MDEA solvent for CO{sub 2} capture in terms of the heat requirement for solvent regeneration, lean and rich loadings, CO{sub 2} production, and solvent stability were performed by comparing the performance of aqueous 5 kmol/m{sup 3} MEA with that of an aqueous 4:1 molar ratio MEA/MDEA blend of 5 kmol/ml total amine concentration as a function of the operating time. The tests were performed using two pilot CO{sub 2} capture plants of the International Test Centre for CO{sub 2} Capture (ITC), which provided two different sources and compositions of flue gas. Themore » University of Regina CO{sub 2} plant (UR unit) processes flue gas from the combustion of natural gas while the Boundary Dam CO{sub 2} plant (BD unit) processes flue gas from a coal-fired electric power station. The results show that a huge heat-duty reduction can be achieved by using a mixed MEA/MDEA solution instead of a single MEA solution in an industrial environment of a CO{sub 2} capture plant. However, this benefit is dependent on whether the chemical stability of the solvent can be maintained.« less

Effect of Solvents on the Behavior of Lithium and Superoxide Ions in Lithium-Oxygen Battery Electrolytes.

PubMed

Smirnov, Vladimir S; Kislenko, Sergey A

2018-01-05

The molecular life of intermediates, namely, O 2 - and Li + , produced during the discharge of aprotic Li-O 2 batteries was investigated by molecular dynamics simulation. This work is of potential interest in the development of new electrolytes for Li-air batteries. We present the results on the structure and stability of the Li + and O 2 - solvation shells and the thermodynamics and kinetics of the ion-association reaction in solvents such as dimethyl sulfoxide (DMSO), dimethoxyethane (DME), and acetonitrile (ACN). The residence time of solvent molecules in the Li + solvation shell increases with the solvent donor number and is 100 times larger in DMSO than in ACN. In DMSO and DME, the Li + ion diffuses with its solvation shell as a whole. On the contrary, in ACN it diffuses as a "bare" ion because of weak solvation. The rate constant for the association of the lithium ion with the superoxide anion in DMSO is two orders of magnitude slower than that in ACN due to fact that the free-energy barrier is 2.5 times larger in DMSO than in ACN. In addition, we show that despite the strong dependence of the Li + shell stability on donor number, the rate of association does not necessarily correlate with this solvent property. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

The influence of solvent on conformational properties of peptides with Aib residue-a DFT study.

PubMed

Wałęsa, Roksana; Broda, Małgorzata A

2017-11-21

The conformational propensities of the Aib residue on the example of two model peptides Ac-Aib-NHMe (1) and Ac-Aib-NMe 2 (2), were studied by B3LYP and M06-2X functionals, in the gas phase and in the polar solvents. To verify the reliability of selected functionals, we also performed MP2 calculations for the tested molecules in vacuum. Polarizable continuum models (PCM and SMD) were used to estimate the solvent effect. Ramachandran maps were calculated to find all energy minima. Noncovalent intramolecular interactions due to hydrogen-bonds and dipole attractions between carbonyl groups are responsible for the relative stabilities of the conformers. In order to verify the theoretical results, the available conformations of similar X-ray structures from the Cambridge Crystallographic Data Center (CCDC) were analyzed. The results of the calculations show that both derivatives with the Aib residue in the gas phase prefer structures stabilized by intramolecular N-H⋯O hydrogen bonds, i.e., C 5 and C 7 conformations, while polar solvent promotes helical conformation with φ, ψ values equal to +/-60°, +/-40°. In addition, in the case of molecule 2, the helical conformation is the only one available in the polar environment. This result is fully consistent with the X-ray data. Graphical abstract Effect of solvent on the Ramachandran maps of the model peptides with Aib residue.

Organic Solvent Effects in Biomass Conversion Reactions.

PubMed

Shuai, Li; Luterbacher, Jeremy

2016-01-01

Transforming lignocellulosic biomass into fuels and chemicals has been intensely studied in recent years. A large amount of work has been dedicated to finding suitable solvent systems, which can improve the transformation of biomass into value-added chemicals. These efforts have been undertaken based on numerous research results that have shown that organic solvents can improve both conversion and selectivity of biomass to platform molecules. We present an overview of these organic solvent effects, which are harnessed in biomass conversion processes, including conversion of biomass to sugars, conversion of sugars to furanic compounds, and production of lignin monomers. A special emphasis is placed on comparing the solvent effects on conversion and product selectivity in water with those in organic solvents while discussing the origins of the differences that arise. We have categorized results as benefiting from two major types of effects: solvent effects on solubility of biomass components including cellulose and lignin and solvent effects on chemical thermodynamics including those affecting reactants, intermediates, products, and/or catalysts. Finally, the challenges of using organic solvents in industrial processes are discussed from the perspective of solvent cost, solvent stability, and solvent safety. We suggest that a holistic view of solvent effects, the mechanistic elucidation of these effects, and the careful consideration of the challenges associated with solvent use could assist researchers in choosing and designing improved solvent systems for targeted biomass conversion processes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermal Stability of RNA Structures with Bulky Cations in Mixed Aqueous Solutions.

PubMed

Nakano, Shu-Ichi; Tanino, Yuichi; Hirayama, Hidenobu; Sugimoto, Naoki

2016-10-04

Bulky cations are used to develop nucleic-acid-based technologies for medical and technological applications in which nucleic acids function under nonaqueous conditions. In this study, the thermal stability of RNA structures was measured in the presence of various bulky cations in aqueous mixtures with organic solvents or polymer additives. The stability of oligonucleotide, transfer RNA, and polynucleotide structures was decreased in the presence of salts of tetrabutylammonium and tetrapentylammonium ions, and the stability and salt concentration dependences were dependent on cation sizes. The degree to which stability was dependent on salt concentration was correlated with reciprocals of the dielectric constants of mixed solutions, regardless of interactions between the cosolutes and RNA. Our results show that organic solvents affect the strength of electrostatic interactions between RNA and cations. Analysis of ion binding to RNA indicated greater enhancement of cation binding to RNA single strands than to duplexes in media with low dielectric constants. Furthermore, background bulky ions changed the dependence of RNA duplex stability on the concentration of metal ion salts. These unique properties of large tetraalkylammonium ions are useful for controlling the stability of RNA structures and its sensitivity to metal ion salts. Copyright © 2016 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Photophysics of Zinc Porphyrin Aggregates in Dilute Water-Ethanol Solutions.

PubMed

Stevens, Amy L; Joshi, Neeraj K; Paige, Matthew F; Steer, Ronald P

2017-12-14

Dimeric and multimeric aggregates of a model metalloporphyrin, zinc tetraphenylporphyrin (ZnTPP), have been produced in a controlled manner by incrementally increasing the water content of dilute aqueous ethanol solutions. Steady state absorption, fluorescence emission, and fluorescence excitation spectra have been measured to identify the aggregates present as a function of solvent composition. The dynamics of the excited states of the aggregates produced initially by excitation in the Soret region have been measured by ultrafast fluorescence upconversion techniques. Only the monomer produces measurable emission from S 2 with a picosecond lifetime; all Soret-excited aggregates, including the dimer, decay radiationlessly on a femtosecond time scale. The S 1 state is the only significant product of the radiationless decay of the S 2 state of the excited monomer, and the aggregates also produce substantial quantum yields of S 1 fluorescence when initially excited in the Soret region. The resulting fluorescent aggregates all decay on a subnanosecond time scale, likely by a mechanism that involves dissociation of the excited monomer from the excitonic multimer. The ZnTPP dimers excited at their ground state geometries in the Soret region exhibit a dynamic behavior that is quite different from those produced following noncoherent triplet-triplet annihilation under the same conditions. The important implications of these observations in determining the aggregation conditions promoting efficient photon upconversion by excitonic annihilation in a variety of media are thoroughly discussed.

Competitive lithium solvation of linear and cyclic carbonates from quantum chemistry

DOE PAGES

Kent, Paul R. C.; Ganesh, Panchapakesan; Borodin, Oleg; ...

2015-11-17

The composition of the lithium cation (Li+) solvation shell in mixed linear and cyclic carbonate-based electrolytes has been re-examined using Born–Oppenheimer molecular dynamics (BOMD) as a function of salt concentration and cluster calculations with ethylene carbonate:dimethyl carbonate (EC:DMC)–LiPF 6 as a model system. A coordination preference for EC over DMC to a Li+ was found at low salt concentrations, while a slightly higher preference for DMC over EC was found at high salt concentrations. Analysis of the relative binding energies of the (EC) n(DMC) m–Li+ and (EC) n(DMC) m–LiPF 6 solvates in the gas-phase and for an implicit solvent (asmore » a function of the solvent dielectric constant) indicated that the DMC-containing Li+ solvates were stabilized relative to (EC 4)–Li+ and (EC) 3–LiPF 6 by immersing them in the implicit solvent. Such stabilization was more pronounced in the implicit solvents with a high dielectric constant. Results from previous Raman and IR experiments were reanalyzed and reconciled by correcting them for changes of the Raman activities, IR intensities and band shifts for the solvents which occur upon Li+ coordination. After these correction factors were applied to the results of BOMD simulations, the composition of the Li+ solvation shell from the BOMD simulations was found to agree well with the solvation numbers extracted from Raman experiments. Finally, the mechanism of the Li+ diffusion in the dilute (EC:DMC)LiPF 6 mixed solvent electrolyte was studied using the BOMD simulations.« less

Improving the industrial production of 6-APA: enzymatic hydrolysis of penicillin G in the presence of organic solvents.

PubMed

Abian, Olga; Mateo, César; Fernández-Lorente, Gloria; Guisán, José M; Fernández-Lafuente, Roberto

2003-01-01

The hydrolysis of penicillin G in the presence of an organic solvent, used with the purpose of extracting it from the culture medium, may greatly simplify the industrial preparation of 6-APA. However, under these conditions, PGA immobilized onto Eupergit displays very low stability (half-life of 5 h in butanone-saturated water) and a significant degree of inhibition by the organic solvent (30%). The negative effect of the organic solvent strongly depended on the type of solvent utilized: water saturated with butanone (around 28% v/v) had a much more pronounced negative effect than that of methylisobutyl ketone (MIBK) (solubility in water was only 2%). These problems were sorted out by using a new penicillin G acylase derivative designed to work in the presence of organic solvents (with each enzyme molecule surrounded by an hydrophilic artificial environment) and a suitable organic solvent (MIBK). Using such solvent, this derivative kept its activity unaltered for 1 week at 32 degrees C. Moreover, the enzyme activity was hardly inhibited by the presence of the organic solvent. In this way, the new enzyme derivative thus prepared enables simplification of the industrial hydrolysis of penicillin G.

Green Aspects of Techniques for the Determination of Currently Used Pesticides in Environmental Samples

PubMed Central

Stocka, Jolanta; Tankiewicz, Maciej; Biziuk, Marek; Namieśnik, Jacek

2011-01-01

Pesticides are among the most dangerous environmental pollutants because of their stability, mobility and long-term effects on living organisms. Their presence in the environment is a particular danger. It is therefore crucial to monitor pesticide residues using all available analytical methods. The analysis of environmental samples for the presence of pesticides is very difficult: the processes involved in sample preparation are labor-intensive and time-consuming. To date, it has been standard practice to use large quantities of organic solvents in the sample preparation process; but as these solvents are themselves hazardous, solvent-less and solvent-minimized techniques are becoming popular. The application of Green Chemistry principles to sample preparation is primarily leading to the miniaturization of procedures and the use of solvent-less techniques, and these are discussed in the paper. PMID:22174632

Theoretical investigation on functional monomer and solvent selection for molecular imprinting of tramadol

NASA Astrophysics Data System (ADS)

Fonseca, Matheus C.; Nascimento, Clebio S.; Borges, Keyller B.

2016-02-01

The purpose of this Letter was to study for the first time the interaction process of tramadol (TRM) with distinct functional monomers (FM) in the formation of molecular imprinted polymer (MIP), using density functional theory (DFT) calculations at B3LYP/6-31G(d,p). As result we were able to establish that the best MIP synthesis conditions are obtained with acrylic acid as FM in 1:3 molar ratio and with chloroform as solvent. This condition presented the lowest stabilization energy for the pre-polymerization complexes. Besides, the intermolecular hydrogen bonds found between the template molecule and functional monomers play a primary role to the complex stability.

Effect of ionic liquid on activity, stability, and structure of enzymes: a review.

PubMed

Naushad, Mu; Alothman, Zied Abdullah; Khan, Abbul Bashar; Ali, Maroof

2012-11-01

Ionic liquids have shown their potential as a solvent media for many enzymatic reactions as well as protein preservation, because of their unusual characteristics. It is also observed that change in cation or anion alters the physiochemical properties of the ionic liquids, which in turn influence the enzymatic reactions by altering the structure, activity, enatioselectivity, and stability of the enzymes. Thus, it is utmost need of the researchers to have full understanding of these influences created by ionic liquids before choosing or developing an ionic liquid to serve as solvent media for enzymatic reaction or protein preservation. So, in the present review, we try to shed light on effects of ionic liquids chemistry on structure, stability, and activity of enzymes, which will be helpful for the researchers in various biocatalytic applications. Copyright © 2012. Published by Elsevier B.V.

Development of small-size tubular-flow continuous reactors for the analysis of operational stability of enzymes in low-water systems.

PubMed

Pirozzi, D; Halling, P J

2001-01-20

A very small-scale continuous flow reactor has been designed for use with enzymes in organic media, particularly for operational stability studies. It is constructed from fairly inexpensive components, and typically uses 5 mg of catalyst and flow rates of 1 to 5 mL/h, so only small quantities of feedstock need to be handled. The design allows control of the thermodynamic water activity of the feed, and works with temperatures up to at least 80 degrees C. The reactor has been operated with both nonpolar (octane) and polar (4-methyl-pentan-2-one) solvents, and with the more viscous solvent-free reactant mixture. It has been applied to studies of the operational stability of lipases from Chromobacterium viscosum (lyophilized powder or polypropylene-adsorbed) and Rhizomucor miehei (Lipozyme) in different experimental conditions. Transesterification of geraniol and ethylcaproate has been adopted as a model transformation.

Stability of anti-reflection coatings via the self-assembly encapsulation of silica nanoparticles by diazo-resins

NASA Astrophysics Data System (ADS)

Metzman, Jonathan S.; Ridley, Jason I.; Khalifa, Moataz B.; Heflin, James R.

2015-12-01

A modified silica nanoparticle (MSNP) solution was formed by the encapsulation of negatively charged silica nanoparticles by the UV-crosslinkable polycation oligomer diazo-resin (DAR). Appropriate DAR encapsulation concentrations were determined by use of zeta-potential and dynamic light scattering measurements. The MSNPs were used in conjunction with poly(styrene sulfonate) (PSS) to grow homogenous ionic self-assembled multilayer anti-reflection coatings. Stability was induced within the films by the exposure of UV-irradiation that allowed for crosslinking of the DAR and PSS. The films were characterized by UV/vis/IR spectroscopy and field emission scanning electron microscopy. The transmission and reflection levels were >98.5% and <0.05%, respectively. The refractive indices resided in the 1.25-1.26 range. The solvent stability was tested by sonication of the films in a ternary solvent (H2O/DMF/ZnCl2 3:5:2 w/w/w).

Synthesis of Co/MFe(2)O(4) (M = Fe, Mn) Core/Shell Nanocomposite Particles.

PubMed

Peng, Sheng; Xie, Jin; Sun, Shouheng

2008-01-01

Monodispersed cobalt nanoparticles (NPs) with controllable size (8-14 nm) have been synthesized using thermal decomposition of dicobaltoctacarbonyl in organic solvent. The as-synthesized high magnetic moment (125 emu/g) Co NPs are dispersible in various organic solvents, and can be easily transferred into aqueous phase by surface modification using phospholipids. However, the modified hydrophilic Co NPs are not stable as they are quickly oxidized, agglomerated in buffer. Co NPs are stabilized by coating the MFe(2)O(4) (M = Fe, Mn) ferrite shell. Core/shell structured bimagnetic Co/MFe(2)O(4) nanocomposites are prepared with tunable shell thickness (1-5 nm). The Co/MFe(2)O(4) nanocomposites retain the high magnetic moment density from the Co core, while gaining chemical and magnetic stability from the ferrite shell. Comparing to Co NPs, the nanocomposites show much enhanced stability in buffer solution at elevated temperatures, making them promising for biomedical applications.

Poly(ethylene glycol) stabilized Co nanoparticles as highly active and selective catalysts for the Pauson-Khand reaction.

PubMed

Muller, Jean-Luc; Klankermayer, Jürgen; Leitner, Walter

2007-05-21

PEG-stabilized cobalt nanoparticles were prepared by thermal decomoposition of [Co2(CO)8] in PEG and were shown to be highly active and selective catalysts, for intra- and intermolecular Pauson-Khand reactions (PKR), in organic solvents or aqueous media.

Polymer/Solvent and Polymer/Polymer Interaction Studies

DTIC Science & Technology

1980-09-01

temperatures up to 450 12 before serious degradation occurs. They have good hydrolytic stability, good solvent resistance, and excellent thermo- oxidative ...Concentration for Sorption in Glassy PVC 5 Temperature Dependence of the Flory-Huggins Interaction Parameters 115 6 Solubility of Dichloromethane in Polysulfone...116 7 Test of Applicability of the Langmuir Equation for Describing Sorption Data 117 8 Temperature Dependence of the Specific Volume of an Amorphous

Materials Research Center, University of Pittsburgh

DTIC Science & Technology

1994-04-29

porosities could be synthesized with active protein contained within the material. The incorporation of proteins into polyacrylates seres as a model system...enzyme with PEG and incorporate the modified enzyme into polyacrylates (Figure IV.D.3.1). The activity and stability of the functionalized enzyme have been... polyacrylate polymer. By varying the ratio of solvent (chloroform) and non-solvent (carbon tetrachloride) during the free-radical initiated

Thermodynamic Stability Analysis of Tolbutamide Polymorphs and Solubility in Organic Solvents.

PubMed

Svärd, Michael; Valavi, Masood; Khamar, Dikshitkumar; Kuhs, Manuel; Rasmuson, Åke C

2016-06-01

Melting temperatures and enthalpies of fusion have been determined by differential scanning calorimetry (DSC) for 2 polymorphs of the drug tolbutamide: FI(H) and FV. Heat capacities have been determined by temperature-modulated DSC for 4 polymorphs: FI(L), FI(H), FII, FV, and for the supercooled melt. The enthalpy of fusion of FII at its melting point has been estimated from the enthalpy of transition of FII into FI(H) through a thermodynamic cycle. Calorimetric data have been used to derive a quantitative polymorphic stability relationship between these 4 polymorphs, showing that FII is the stable polymorph below approximately 333 K, above which temperature FI(H) is the stable form up to its melting point. The relative stability of FV is well below the other polymorphs. The previously reported kinetic reversibility of the transformation between FI(L) and FI(H) has been verified using in situ Raman spectroscopy. The solid-liquid solubility of FII has been gravimetrically determined in 5 pure organic solvents (methanol, 1-propanol, ethyl acetate, acetonitrile, and toluene) over the temperature range 278 to 323 K. The ideal solubility has been estimated from calorimetric data, and solution activity coefficients at saturation in the 5 solvents determined. All solutions show positive deviation from Raoult's law, and all van't Hoff plots of solubility data are nonlinear. The solubility in toluene is well below that observed in the other investigated solvents. Solubility data have been correlated and extrapolated to the melting point using a semiempirical regression model. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Membrane formation in liquids by adding an antagonistic salt

NASA Astrophysics Data System (ADS)

Sadakane, Koichiro; Seto, Hideki

2018-03-01

Antagonistic salts are composed of hydrophilic and hydrophobic ions. In a binary mixture, such as water and organic solvent, these ion pairs preferentially dissolve to those phases, respectively, and there is a coupling between the charge density and the composition. The heterogeneous distribution of ions forms a large electric double layer at the interface between these solvents. This reduces the interfacial tension between water and organic solvent, and stabilizes an ordered structure, such as a membrane. These phenomena have been extensively studied from both theoretical and experimental point of view. In addition, the numerical simulations can reproduce such ordered structures.

Developing Modular and Adaptable Courseware Using TeachML.

ERIC Educational Resources Information Center

Wehner, Frank; Lorz, Alexander

This paper presents the use of an XML grammar for two complementary projects--CHAMELEON (Cooperative Hypermedia Adaptive MultimEdia Learning Objects) and EIT (Enabling Informal Teamwork). Areas of applications are modular courseware documents and the collaborative authoring process of didactical units. A number of requirements for a suitable…

Interfacing with a DMM.

ERIC Educational Resources Information Center

Beatty, Jim

1985-01-01

Suggests purchasing a digital multimer (DMM) with an IEEE-488 option to interface an instrument to a microcomputer, indicating that a DMM is well protected from overloads and is easy to connect. An example of its use in an experiment involving hydrolysis of tertiary butyl alcohol (with program listing) is given. (JN)

Ultrastable, highly luminescent quantum dot composites based on advanced surface manipulation strategy for flexible lighting-emitting.

PubMed

Kong, Lingqing; Zhang, Lin; Meng, Zhaohui; Xu, Chuan; Lin, Naibo; Liu, Xiang-Yang

2018-08-03

Although quantum dots (QDs) have remarkable potential application in flexible light emitting diodes (LED), the loss of solvent-protected QDs leads to low quantum yield (QY) and poor stability, severely restricting the development. Flexible QD LEDs (Q-LEDs) with three primary colors were fabricated by mixing CdS/ZnS, CdSe@ZnS/ZnS, and CdSe/CdS QDs with polydimethylsiloxane (PDMS) by in situ hydrosilylation based surface manipulation strategy, which endows the device with highly ultrastable and luminescent performance. The surface manipulation strategy mainly includes the control of solvent dosage, purification times of QDs, concentration of QDs in PDMS, and oxidation on the preparation process of the QDs and PDMS composites. The highest QY of CdSe@ZnS/ZnS-PDMS composite is 82.03%, higher than the QY (80%) of the QD solution. After UV bleaching, organic solvents (acetone, ethanol and water), and heating treatment, the QYs of the QDs and PDMS maintain a high value, manifesting their good stability. Q-LED hybrid light-emitting devices were further fabricated by a molding technique demonstrating satisfied current and thermal stability. Flexible Q-LEDs can be expended to other shapes, such as fibers and blocks, indicating the huge potential of QD-polymer composites for light sources and displays etc.

Electrostatic Solvation Energy for Two Oppositely Charged Ions in a Solvated Protein System: Salt Bridges Can Stabilize Proteins

PubMed Central

Gong, Haipeng; Freed, Karl F.

2010-01-01

Abstract Born-type electrostatic continuum methods have been an indispensable ingredient in a variety of implicit-solvent methods that reduce computational effort by orders of magnitude compared to explicit-solvent MD simulations and thus enable treatment using larger systems and/or longer times. An analysis of the limitations and failures of the Born approaches serves as a guide for fundamental improvements without diminishing the importance of prior works. One of the major limitations of the Born theory is the lack of a liquidlike description of the response of solvent dipoles to the electrostatic field of the solute and the changes therein, a feature contained in the continuum Langevin-Debye (LD) model applied here to investigate how Coulombic interactions depend on the location of charges relative to the protein/water boundary. This physically more realistic LD model is applied to study the stability of salt bridges. When compared head to head using the same (independently measurable) physical parameters (radii, dielectric constants, etc.), the LD model is in good agreement with observations, whereas the Born model is grossly in error. Our calculations also suggest that a salt bridge on the protein's surface can be stabilizing when the charge separation is ≤4 Å. PMID:20141761

Colloidal 2D nanosheets of MoS2 and other transition metal dichalcogenides through liquid-phase exfoliation.

PubMed

Grayfer, Ekaterina D; Kozlova, Mariia N; Fedorov, Vladimir E

2017-07-01

This review focuses on the exfoliation of transition metal dichalcogenides MQ 2 (TMD, M=Mo, W, etc., Q=S, Se, Te) in liquid media, leading to the formation of 2D nanosheets dispersed in colloids. Nowadays, colloidal dispersions of MoS 2 , MoSe 2 , WS 2 and other related materials are considered for a wide range of applications, including electronic and optoelectronic devices, energy storage and conversion, sensors for gases, catalysts and catalyst supports, biomedicine, etc. We address various methods developed so far for transferring these materials from bulk to nanoscale thickness, and discuss their stabilization and factors influencing it. Long-time known exfoliation through Li intercalation has received renewed attention in recent years, and is recognized as a method yielding highest dispersed concentrations of single-layer MoS 2 and related materials. Latest trends in the intercalation/exfoliation approach include electrochemical lithium intercalation, experimenting with various intercalating agents, multi-step intercalation, etc. On the other hand, direct sonication in solvents is a much simpler technique that allows one to avoid dangerous reagents, long reaction times and purifying steps. The influence of the solvent characteristics on the colloid formation was closely investigated in numerous recent studies. Moreover, it is being recognized that, besides solvent properties, sonication parameters and solvent transformations may affect the process in a crucial way. The latest data on the interaction of MoS 2 with solvents evidence that not only solution thermodynamics should be employed to understand the formation and stabilization of such colloids, but also general and organic chemistry. It appears that due to the sonolysis of the solvents and cutting of the MoS 2 layers in various directions, the reactive edges of the colloidal nanosheets may bear various functionalities, which participate in their stabilization in the colloidal state. In most cases, direct exfoliation of MQ 2 into colloidal nanosheets is conducted in organic solvents, while a small amount of works report low-concentrated colloids in pure water. To improve the dispersion abilities of transition metal dichalcogenides in water, various stabilizers are often introduced into the reaction media, and their interactions with nanosheets play an important role in the stabilization of the dispersions. Surfactants, polymers and biomolecules usually interact with transition metal dichalcogenide nanosheets through non-covalent mechanisms, similarly to the cases of graphene and carbon nanotubes. Finally, we survey covalent chemical modification of colloidal MQ 2 nanosheets, a special and different approach, consisting in the functionalization of MQ 2 surfaces with help of thiol chemistry, interaction with electrophiles, or formation of inorganic coordination complexes. The intentional design of surface chemistry of the nanosheets is a very promising way to control their solubility, compatibility with other moieties and incorporation into hybrid structures. Although the scope of the present review is limited to transition metal dichalcogenides, the dispersion in colloids of other chalcogenides (such as NbS 3 , VS 4 , Mo 2 S 3 , etc.) in many ways follows similar trends. We conclude the review by discussing current challenges in the area of exfoliation of MoS 2 and its related materials. Copyright © 2017 Elsevier B.V. All rights reserved.

Solubility behavior of lamivudine crystal forms in recrystallization solvents.

PubMed

Jozwiakowski, M J; Nguyen, N A; Sisco, J M; Spancake, C W

1996-02-01

Lamivudine can be obtained as acicular crystals (form I, 0.2 hydrate) from water or methanol and as bipyramidal crystals (form II, nonsolvated) from many nonaqueous solvents. Form II is thermodynamically favored in the solid state (higher melting point and greater density than form I) at ambient relative humidities. Solubility measurements on both forms versus solvent and temperature was used to determine whether entropy or enthalpy was the driving force for solubility. Solution calorimetry data indicated that form I is favored (less soluble) in all solvents studied on the basis of enthalpy alone. In higher alcohols and other organic solvents, form I has a larger entropy of solution than form II, which compensates for the enthalpic factors and results in physical stability for form II in these systems. The metastable crystal form solubility at 25 degrees C was estimated to be 1.2-2.3 times as high as the equilibrium solubility of the stable form, depending on the temperature, solvent, and crystal form. Binary solvent studies showed that > 18-20% water must be present in ethanol to convert the excess solid to form I at equilibrium.

An oxidant- and solvent-stable protease produced by Bacillus cereus SV1: application in the deproteinization of shrimp wastes and as a laundry detergent additive.

PubMed

Manni, Laila; Jellouli, Kemel; Ghorbel-Bellaaj, Olfa; Agrebi, Rym; Haddar, Anissa; Sellami-Kamoun, Alya; Nasri, Moncef

2010-04-01

The current increase in amount of shrimp wastes produced by the shrimp industry has led to the need in finding new methods for shrimp wastes disposal. In this study, an extracellular organic solvent- and oxidant-stable metalloprotease was produced by Bacillus cereus SV1. Maximum protease activity (5,900 U/mL) was obtained when the strain was grown in medium containing 40 g/L shrimp wastes powder as a sole carbon source. The optimum pH, optimum temperature, pH stability, and thermal stability of the crude enzyme preparation were pH 8.0, 60 degrees C, pH 6-9.5, and <55 degrees C, respectively. The crude protease was extremely stable toward several organic solvents. No loss of activity was observed even after 60 days of incubation at 30 degrees C in the presence of 50% (v/v) dimethyl sulfoxide and ethyl ether; the enzyme retained more than 70% of its original activity in the presence of ethanol and N,N-dimethylformamide. The protease showed high stability toward anionic (SDS) and non-ionic (Tween 80, Tween 20, and Triton X-100) surfactants. Interestingly, the activity of the enzyme was significantly enhanced by oxidizing agents. In addition, the enzyme showed excellent compatibility with some commercial liquid detergents. The protease of B. cereus SV1, produced under the optimal culture conditions, was tested for shrimp waste deproteinization in the preparation of chitin. The protein removal with a ratio E/S of 20 was about 88%. The novelties of the SV1 protease include its high stability to organic solvents and surfactants. These unique properties make it an ideal choice for application in detergent formulations and enzymatic peptide synthesis. In addition, the enzyme may find potential applications in the deproteinization of shrimp wastes to produce chitin.

FT-IR study and solvent-implicit and explicit effect on stepwise tautomerism of Guanylurea: M06-2X as a case of study.

PubMed

Karimzadeh, Morteza; Manouchehri, Neda; Saberi, Dariush; Niknam, Khodabakhsh

2018-06-15

All 66 conformers of guanylurea were optimized and frequency calculations were performed at M06-2X/6-311++G(d,p) level of theory. Theses conformers were categorized into five tautomers, and the most stable conformer of each tautomer were found. Geometrical parameters indicated that these tautomers have almost planar structure. Complete stepwise tautomerism were studied through both intramolecular proton transfer routs and internal rotations. Results indicated that the proton transfer routs involving four-membered heterocyclic structures were rate-determining steps. Also, intramolecular proton movement having six-membered transition state structures had very low energy barrier comparable to the transition states of internal rotation routs. Differentiation of studied tautomers could easily be done through their FT-IR spectra in the range of 3200 to 3900cm -1 by comparing absorption bands and intensity of peaks. Solvent-implicit effects on the stability of tautomers were also studied through re-optimization and frequency calculation in four solvents. Water, DMSO, acetone and toluene had stabilization effect on all considered tautomers, but the order of stabilization effect was as follows: water>DMSO>acetone>toluene. Finally, solvent-explicit, base-explicit and acid-explicit effect were also studied by taking place of studied tautomer nearside of acid, base or solvent and optimization of them. Frequency calculation for proton movement by contribution of explicit effect showed that formic acid had a very strong effect on proton transfer from tautomer A1 to tautomer D8 by lowering the energy barrier from 42.57 to 0.8kcal/mol. In addition, ammonia-explicit effect was found to lower the barrier from 42.57 to 22.46kcal/mol, but this effect is lower than that of water and methanol-explicit effect. Copyright © 2018 Elsevier B.V. All rights reserved.

Optimization of ultrasound-assisted extraction of pectinase enzyme from guava (Psidium guajava) peel: Enzyme recovery, specific activity, temperature, and storage stability.

PubMed

Amid, Mehrnoush; Murshid, Fara Syazana; Manap, Mohd Yazid; Islam Sarker, Zaidul

2016-01-01

This study aimed to investigate the effects of the ultrasound-assisted extraction conditions on the yield, specific activity, temperature, and storage stability of the pectinase enzyme from guava peel. The ultrasound variables studied were sonication time (10-30 min), ultrasound temperature (30-50 °C), pH (2.0-8.0), and solvent-to-sample ratio (2:1 mL/g to 6:1 mL/g). The main goal was to optimize the ultrasound-assisted extraction conditions to maximize the recovery of pectinase from guava peel with the most desirable enzyme-specific activity and stability. Under the optimum conditions, a high yield (96.2%), good specific activity (18.2 U/mg), temperature stability (88.3%), and storage stability (90.3%) of the extracted enzyme were achieved. The optimal conditions were 20 min sonication time, 40 °C temperature, at pH 5.0, using a 4:1 mL/g solvent-to-sample ratio. The study demonstrated that optimization of ultrasound-assisted process conditions for the enzyme extraction could improve the enzymatic characteristics and yield of the enzyme.

Modeling Insight into Battery Electrolyte Electrochemical Stability and Interfacial Structure.

PubMed

Borodin, Oleg; Ren, Xiaoming; Vatamanu, Jenel; von Wald Cresce, Arthur; Knap, Jaroslaw; Xu, Kang

2017-12-19

Electroactive interfaces distinguish electrochemistry from chemistry and enable electrochemical energy devices like batteries, fuel cells, and electric double layer capacitors. In batteries, electrolytes should be either thermodynamically stable at the electrode interfaces or kinetically stable by forming an electronically insulating but ionically conducting interphase. In addition to a traditional optimization of electrolytes by adding cosolvents and sacrificial additives to preferentially reduce or oxidize at the electrode surfaces, knowledge of the local electrolyte composition and structure within the double layer as a function of voltage constitutes the basis of manipulating an interphase and expanding the operating windows of electrochemical devices. In this work, we focus on how the molecular-scale insight into the solvent and ion partitioning in the electrolyte double layer as a function of applied potential could predict changes in electrolyte stability and its initial oxidation and reduction reactions. In molecular dynamics (MD) simulations, highly concentrated lithium aqueous and nonaqueous electrolytes were found to exclude the solvent molecules from directly interacting with the positive electrode surface, which provides an additional mechanism for extending the electrolyte oxidation stability in addition to the well-established simple elimination of "free" solvent at high salt concentrations. We demonstrate that depending on their chemical structures, the anions could be designed to preferentially adsorb or desorb from the positive electrode with increasing electrode potential. This provides additional leverage to dictate the order of anion oxidation and to effectively select a sacrificial anion for decomposition. The opposite electrosorption behaviors of bis(trifluoromethane)sulfonimide (TFSI) and trifluoromethanesulfonate (OTF) as predicted by MD simulation in highly concentrated aqueous electrolytes were confirmed by surface enhanced infrared spectroscopy. The proton transfer (H-transfer) reactions between solvent molecules on the cathode surface coupled with solvent oxidation were found to be ubiquitous for common Li-ion electrolyte components and dependent on the local molecular environment. Quantum chemistry (QC) calculations on the representative clusters showed that the majority of solvents such as carbonates, phosphates, sulfones, and ethers have significantly lower oxidation potential when oxidation is coupled with H-transfer, while without H-transfer their oxidation potentials reside well beyond battery operating potentials. Thus, screening of the solvent oxidation limits without considering H-transfer reactions is unlikely to be relevant, except for solvents containing unsaturated functionalities (such as C═C) that oxidize without H-transfer. On the anode, the F-transfer reaction and LiF formation during anion and fluorinated solvent reduction could be enhanced or diminished depending on salt and solvent partitioning in the double layer, again giving an additional tool to manipulate the order of reductive decompositions and interphase chemistry. Combined with experimental efforts, modeling results highlight the promise of interphasial compositional control by either bringing the desired components closer to the electrode surface to facilitate redox reaction or expelling them so that they are kinetically shielded from the potential of the electrode.

Method for producing metal oxide aerogels

DOEpatents

Tillotson, Thomas M.; Poco, John F.; Hrubesh, Lawrence W.; Thomas, Ian M.

1995-01-01

A two-step hydrolysis-condensation method was developed to form metal oxide aerogels of any density, including densities of less than 0.003g/cm.sup.3 and greater than 0.27g/cm.sup.3. High purity metal alkoxide is reacted with water, alcohol solvent, and an additive to form a partially condensed metal intermediate. All solvent and reaction-generated alcohol is removed, and the intermediate is diluted with a nonalcoholic solvent. The intermediate can be stored for future use to make aerogels of any density. The aerogels are formed by reacting the intermediate with water, nonalcoholic solvent, and a catalyst, and extracting the nonalcoholic solvent directly. The resulting monolithic aerogels are hydrophobic and stable under atmospheric conditions, and exhibit good optical transparency, high clarity, and homogeneity. The aerogels have high thermal insulation capacity, high porosity, mechanical strength and stability, and require shorter gelation times than aerogels formed by conventional methods.

Method for producing metal oxide aerogels

DOEpatents

Tillotson, T.M.; Poco, J.F.; Hrubesh, L.W.; Thomas, I.M.

1995-04-25

A two-step hydrolysis-condensation method was developed to form metal oxide aerogels of any density, including densities of less than 0.003g/cm{sup 3} and greater than 0.27g/cm{sup 3}. High purity metal alkoxide is reacted with water, alcohol solvent, and an additive to form a partially condensed metal intermediate. All solvent and reaction-generated alcohol is removed, and the intermediate is diluted with a nonalcoholic solvent. The intermediate can be stored for future use to make aerogels of any density. The aerogels are formed by reacting the intermediate with water, nonalcoholic solvent, and a catalyst, and extracting the nonalcoholic solvent directly. The resulting monolithic aerogels are hydrophobic and stable under atmospheric conditions, and exhibit good optical transparency, high clarity, and homogeneity. The aerogels have high thermal insulation capacity, high porosity, mechanical strength and stability, and require shorter gelation times than aerogels formed by conventional methods. 8 figs.

Effect of solvents on the electrochemical properties of binder-free sulfur cathode films in lithium–sulfur batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryu, Ho-Suk; Kim, Byeong-Wook; Park, Jin-Woo

Highlights: • The binder-free sulfur electrode with high sulfur contents of 75 wt.% was fabricated. • The binder-free sulfur electrode using NMP solvents showed 784 mAh g{sup −1} after 40 cycles. • The solvent affect the electrochemical properties of binder-free sulfur electrode films. - Abstract: The effects of solvents on the preparation of sulfur cathodes were investigated by fabricating binder-free sulfur electrode films using three different solvents: 1-methyl-2-pyrrolidinone (NMP), acetonitrile, and deionized water. These solvents are commonly employed to dissolve binders used to prepare sulfur cathodes for lithium–sulfur batteries. The sulfur electrode fabricated with NMP had a higher discharge capacitymore » and longer cycle life than the ones fabricated with acetonitrile and deionized water. Better adhesion between the current collector and the sulfur electrode accounted for the improved capacity and cycle life of the battery. In addition, the stability of the electrode in the electrolyte was a result of the solubility of sulfur in the solvent. We thus concluded that the solvents used in the fabrication of sulfur electrodes had a positive influence on the electrochemical properties of Li–S batteries.« less

Production of 10(S)-hydroxy-8(E)-octadecenoic and 7,10(S,S)-hydroxy-8(E)-octadecenoic ethyl esters by Novozym 435 in solvent-free media

USDA-ARS?s Scientific Manuscript database

Novozym 435, lipase B from Candida antarctica, was used in this study for the production of ethyl esters. For the first time, trans-hydroxy-fatty acid ethyl esters were synthesized in vitro in solvent-free media. We studied the effects of the substrate–ethanol molar ratio and enzyme synthetic stabil...

Ionic Liquids in Selective Oxidation: Catalysts and Solvents.

PubMed

Dai, Chengna; Zhang, Jie; Huang, Chongpin; Lei, Zhigang

2017-05-24

Selective oxidation has an important role in environmental and green chemistry (e.g., oxidative desulfurization of fuels and oxidative removal of mercury) as well as chemicals and intermediates chemistry to obtain high-value-added special products (e.g., organic sulfoxides and sulfones, aldehydes, ketones, carboxylic acids, epoxides, esters, and lactones). Due to their unique physical properties such as the nonvolatility, thermal stability, nonexplosion, high polarity, and temperature-dependent miscibility with water, ionic liquids (ILs) have attracted considerable attention as reaction solvents and media for selective oxidations and are considered as green alternatives to volatile organic solvents. Moreover, for easy separation and recyclable utilization, IL catalysts have attracted unprecedented attention as "biphasic catalyst" or "immobilized catalyst" by immobilizing metal- or nonmetal-containing ILs onto mineral or polymer supports to combine the unique properties of ILs (chemical and thermal stability, capacity for extraction of polar substrates and reaction products) with the extended surface of the supports. This review highlights the most recent outcomes on ILs in several important typical oxidation reactions. The contents are arranged in the series of oxidation of sulfides, oxidation of alcohols, epoxidation of alkenes, Baeyer-Villiger oxidation reaction, oxidation of alkanes, and oxidation of other compounds step by step involving ILs as solvents, catalysts, reagents, or their combinations.

High-performance dye-sensitized solar cells based on solvent-free electrolytes produced from eutectic melts.

PubMed

Bai, Yu; Cao, Yiming; Zhang, Jing; Wang, Mingkui; Li, Renzhi; Wang, Peng; Zakeeruddin, Shaik M; Grätzel, Michael

2008-08-01

Low-cost excitonic solar cells based on organic optoelectronic materials are receiving an ever-increasing amount of attention as potential alternatives to traditional inorganic photovoltaic devices. In this rapidly developing field, the dye-sensitized solar cell (DSC) has achieved so far the highest validated efficiency of 11.1% (ref. 2) and remarkable stability. However, the cells with the best performance use volatile solvents in their electrolytes, which may be prohibitive for outdoor solar panels in view of the need for robust encapsulation. Solvent-free room-temperature ionic liquids have been pursued as an attractive solution to this dilemma, and device efficiencies of over 7% were achieved by using some low-viscosity formulations containing 1-ethyl-3-methylimidazolium thiocyanate, selenocyanate, tricyanomethide or tetracyanoborate. Unfortunately, apart from tetracyanoborate, all of these low-viscosity melts proved to be unstable under prolonged thermal stress and light soaking. Here, we introduce the concept of using eutectic melts to produce solvent-free liquid redox electrolytes. Using a ternary melt in conjunction with a nanocrystalline titania film and the amphiphilic heteroleptic ruthenium complex Z907Na (ref. 10) as a sensitizer, we reach excellent stability and an unprecedented efficiency of 8.2% under air-mass 1.5 global illumination. Our results are of importance to realize large-scale outdoor applications of mesoscopic DSCs.

Effect of ethanol as a co-solvent on the aerosol performance and stability of spray-dried lysozyme.

PubMed

Ji, Shuying; Thulstrup, Peter Waaben; Mu, Huiling; Hansen, Steen Honoré; van de Weert, Marco; Rantanen, Jukka; Yang, Mingshi

2016-11-20

In the spray drying process, organic solvents can be added to facilitate drying, accommodate certain functional excipients, and modify the final particle characteristics. In this study, lysozyme was used as a model pharmaceutical protein to study the effect of ethanol as a co-solvent on the stability and aerosol performance of spray-dried protein. Lysozyme was dissolved in solutions with various ratios of ethanol and water, and subsequently spray-dried. A change from spherical particles into wrinkled and folded particles was observed upon increasing the ratio of ethanol in the feed. The aerosol performance of the spray-dried lysozyme from ethanol-water solution was improved compared to that from pure water. The conformation of lysozyme in the ethanol-water solution and spray dried powder was altered, but the native structure of lysozyme was restored upon reconstitution in water after the spray drying process. The enzymatic activities of the spray-dried lysozyme showed no significant impact of ethanol; however, the lysozyme enzymatic activity was ca. 25% lower compared to the starting material. In conclusion, the addition of ethanol as a co-solvent in the spray drying feed for lysozyme did not compromise the conformation of the protein after drying, while it improved the inhaled aerosol performance. Copyright © 2016 Elsevier B.V. All rights reserved.

Mechanistic Study of Electrolyte Additives to Stabilize High-Voltage Cathode-Electrolyte Interface in Lithium-Ion Batteries.

PubMed

Gao, Han; Maglia, Filippo; Lamp, Peter; Amine, Khalil; Chen, Zonghai

2017-12-27

Current developments of electrolyte additives to stabilize electrode-electrolyte interface in lithium-ion batteries highly rely on a trial-and-error search, which involves repetitive testing and intensive amount of resources. The lack of understandings on the fundamental protection mechanisms of the additives significantly increases the difficulty for the transformational development of new additives. In this study, we investigated two types of individual protection routes to build a robust cathode-electrolyte interphase at high potentials: (i) a direct reduction in the catalytic decomposition of the electrolyte solvent; and (ii) formation of a "corrosion inhibitor film" that prevents severely attack and passivation from protons that generated from the solvent oxidation, even the decomposition of solvent cannot be mitigated. Effect of two exemplary electrolyte additives, lithium difluoro(oxalato)borate (LiDFOB) and 3-hexylthiophene (3HT), on LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC 622) cathode were investigated to validate our hypothesis. It is demonstrated that understandings of both electrolyte additives and solvent are essential and careful balance between the cathode protection mechanism of additives and their side effects is critical to obtain optimum results. More importantly, this study opens up new directions of rational design of functional electrolyte additives for the next-generation high-energy-density lithium-ion chemistries.

Solvent Stability Study with Thermodynamic Analysis and Superior Biocatalytic Activity of Burkholderia cepacia Lipase Immobilized on Biocompatible Hybrid Matrix of Poly(vinyl alcohol) and Hypromellose.

PubMed

Badgujar, Kirtikumar C; Bhanage, Bhalchandra M

2014-12-26

In the present study, we have synthesized a biocompatible hybrid carrier of hypromellose (HY) and poly(vinyl alcohol) (PVA) for immobilization of Burkholderia cepacia lipase (BCL). The immobilized biocatalyst HY:PVA:BCL was subjected to determination of half-life time (τ) and deactivation rate constant (K(D)) in various organic solvents. Biocatalyst showed higher τ-value in a nonpolar solvent like cyclohexane (822 h) as compared to that of a polar solvent such as acetone (347 h), which signifies better compatibility of biocatalyst in the nonpolar solvents. Furthermore, the K(D)-value was found to be less in cyclohexane (0.843 × 10(-3)) as compared to acetone (1.997 × 10(-3)), indicating better stability in the nonpolar solvents. Immobilized-BCL (35 mg) was sufficient to achieve 99% conversion of phenethyl butyrate (natural constituent of essential oils and has wide industrial applications) using phenethyl alcohol (2 mmol) and vinyl butyrate (6 mmol) at 44 °C in 3 h. The activation energy (E(a)) was found to be lower for immobilized-BCL than crude-BCL, indicating better catalytic efficiency of immobilized lipase BCL. The immobilized-BCL reported 6-fold superior biocatalytic activity and 8 times recyclability as compared to crude-BCL. Improved catalytic activity of immobilized enzyme in nonpolar media was also supported by thermodynamic activation parameters such as enthalpy (ΔH(⧧)), entropy (ΔS(⧧)) and Gibb's free energy (ΔG(⧧)) study, which showed that phenethyl butyrate synthesis catalyzed by immobilized-BCL was feasible as compared to crude-BCL. The present work explains a thermodynamic investigation and superior biocatalytic activity for phenethyl butyrate synthesis using biocompatible immobilized HY:PVA:BCL in nonaqueous media for the first time.

Innovative aspects of protein stability in ionic liquid mixtures.

PubMed

Kumar, Awanish; Venkatesu, Pannuru

2018-06-01

Mixtures of ionic liquids (ILs) have attracted our attention because of their extraordinary performances in extraction technologies and in absorbing large amount of CO 2 gas. It has been observed that when two or more ILs are mixed in different proportions, a new solvent is obtained which is much better than that of each component of ILs from which the mixture is obtained. Within a mixture of ILs, several unidentified interactions occur among several ions which give rise to unique solvent properties to the mixture. Herein, in this review, we have highlighted the utilization of the advantageous properties of the IL mixtures in protein stability studies. This approach is exceptional and opens new directions to the use of ILs in biotechnology.

Solvent-based self-healing approaches for fiber-reinforced composites

NASA Astrophysics Data System (ADS)

Jones, Amanda R.

Damage in composite materials spans many length scales and is often difficult to detect or costly to repair. The incorporation of self-healing functionality in composite materials has the potential to greatly extend material lifetime and reliability. Although there has been remarkable progress in self-healing polymers over the past decade, self-repair in fiber-reinforced composite materials presents significant technical challenges due to stringent manufacturing and performance requirements. For high performance, fiber-reinforced composites, the self-healing components need to survive high temperature processing, reside in matrix interstitial regions to retain a high fiber volume fraction, and have minimal impact on the mechanical properties of the host material. This dissertation explores several microencapsulated solvent-based self-healing approaches for fiber-reinforced composites at the fiber/ matrix interface size scale as well as matrix cracking. Systems are initially developed for room temperature cured epoxies/ glass fiber interfaces and successfully transitioned to carbon fibers and high temperature-cured, thermoplastic-toughened matrices. Full recovery of interfacial bond strength after complete fiber/matrix debonding is achieved with a microencapsulated solvent-based healing chemistry. The surface of a glass fiber is functionalized with microcapsules containing varying concentrations of reactive epoxy resin and ethyl phenyl acetate (EPA) solvent. Microbond specimens consisting of a single fiber and a microdroplet of epoxy are cured at 35°C, tested, and the interfacial shear strengths (IFSS) during the initial (virgin) debonding and subsequent healing events are measured. Debonding of the fiber/matrix interface ruptures the capsules, releasing resin and solvent into the crack plane. The solvent swells the matrix, initiating transport of residual amine functionality for further curing with the epoxy resin delivered to the crack plane. Using a resin-solvent ratio of 3:97, a maximum of 100% IFSS recovery is achieved-- a significant enhancement over prior work that reported 44% average recovery of IFSS with microencapsulated dicyclopentadiene (DCPD) monomer and Grubbs' 1st Generation catalyst healing agents. The effects of capsule coverage, resin-solvent ratio, and capsule size on recovery of IFSS are also determined, providing guidelines for integration of this healing system into high fiber volume fraction structural composites. High healing efficiencies are achieved with capsules as small as 0.6 mum average diameter. The resin-solvent healing system is then extended to repair of a carbon fiber/epoxy interfacial bond. A binder is necessary to improve the retention of capsules on the carbon fiber surface. Two different methods for applying a binder to a carbon fiber surface are investigated. Healing efficiency is assessed by recovery of IFSS of a single functionalized fiber embedded in an epoxy microbond specimen. The two binder protocols produce comparable results, both yielding higher recovery of IFSS than samples prepared without a binder. A maximum of 91% recovery of IFSS is achieved. In the next study, the resin-solvent healing system is applied to both interfacial damage and matrix cracking in a model composite specimen, consisting of discrete fiber tows embedded in a room temperature cured epoxy. Glass fiber tows are precisely placed in a compact tension specimen for controlled crack growth. The progression of matrix cracking and fiber debonding is observed optically during testing. Healing potential is assessed by injection of the healing agents into reference specimens (no capsules). The area under the load-displacement curve recovered during the healing event serves as a metric for evaluation of healing performance. Though full recovery is achieved in neat epoxy specimens, healing efficiency in multi-tow specimens is limited to 50%, due to the larger crack separations and energy lost during fiber fracture. In the case of only a singular embedded fiber tow, healing efficiency increases to an average of 83% recovery with full recovery in several samples. Additionally, microcapsules are incorporated into the compact tension specimen and along the fiber tow interface to evaluate in situ healing. Several strategies to improve microcapsule thermal stability are investigated in order to transition solvent-based healing to high temperature cured material systems. A double shell wall technique is adopted for several different size scales of microcapsules. First, the effect of the inner polyurethane (PU) shell wall thickness on thermal stability is evaluated. Though high thermal stability at 180°C is achieved for large (ca. 150 mum in diameter) capsules, smaller capsules (> 2 mum in diameter) suffer from increased core loss. The addition of certain core thickeners improves thermal stability for small capsules (ca. 20% increase in core retention) when compared to capsules with solvent alone. However, an additional poly(dopamine) coating leads to the greatest improvement in thermal stability, with nearly full retention of the core solvent for all capsule size scales. Finally, a thermoplastic resin poly(bisphenol A-co-epichlorohydrin), PBAE, is blended with a high glass transition temperature (Tg) epoxy matrix to simultaneously toughen and act as a healing agent in combination with encapsulated solvents. Microcapsules are coated with poly(dopamine) to improve the thermal stability and retain the core solvent during a cure cycle at 180°C. The fracture toughness of the high Tg epoxy (EPON 828: diamino diphenyl sulfone) is doubled by the addition of 20 wt % PBAE alone and tripled by the addition of both microcapsules and the thermoplastic phase. Self-healing is achieved with up to 57% recovery of fracture toughness of the toughened epoxy. Healing performance and fracture toughness of the microcapsule containing material remain stable after aging 30 days. The relative amounts of thermoplastic phase and the presence of solvent-filled microcapsules influence the storage modulus, Tg, and healing performance of the polymer.

Influence of the composition of aqueous dimethylsulfoxide solvent on thermodynamics of complexing between 18-crown-6-ether and D,L-alanine

NASA Astrophysics Data System (ADS)

Usacheva, T. R.; Kuzmina, I. A.; Sharnin, V. A.; Chernov, I. V.; Matteoli, E.

2012-07-01

Standard thermodynamic parameters (log K o, Δr H o, TΔr S o) of complexing 18-crown-6 ether (18C6) with D,L-alanine (Ala) in mixed water-dimethysulfoxide (H2O-DMSO) solvents are calculated on the basis of calorimetric titration results. A rise in the DMSO concentration in mixed solvent is found to increase stability and increase the exothermicity of the formation of [Ala-18C6] molecular complex. Changes in the reaction energetic are shown to be determined by changes in the solvation state of 18C6 that is the characteristic of the reactions of molecular complex formation between 18C6 and D,L-alanine or glycine in water-organic solvents.

On the radiation stability of crown ethers in ionic liquids.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shkrob, I.; Marin, T.; Dietz, M.

2011-04-14

Crown ethers (CEs) are macrocyclic ionophores used for the separation of strontium-90 from acidic nuclear waste streams. Room temperature ionic liquids (ILs) are presently being considered as replacements for traditional molecular solvents employed in such separations. It is desirable that the extraction efficacy obtained with such solvents should not deteriorate in the strong radiation fields generated by decaying radionuclides. This deterioration will depend on the extent of radiation damage to both the IL solvent and the CE solute. While radiation damage to ILs has been extensively studied, the issue of the radiation stability of crown ethers, particularly in an ILmore » matrix, has not been adequately addressed. With this in mind, we have employed electron paramagnetic resonance (EPR) spectroscopy to study the formation of CE-related radicals in the radiolysis of selected CEs in ILs incorporating aromatic (imidazolium and pyridinium) cations. The crown ethers have been found to yield primarily hydrogen loss radicals, H atoms, and the formyl radical. In the low-dose regime, the relative yield of these radicals increases linearly with the mole fraction of the solute, suggesting negligible transfer of the excitation energy from the solvent to the solute; that is, the solvent has a 'radioprotective' effect. The damage to the CE in the loading region of practical interest is relatively low. Under such conditions, the main chemical pathway leading to decreased extraction performance is protonation of the macrocycle. At high radiation doses, sufficient to increase the acidity of the IL solvent significantly, such proton complexes compete with the solvent cations as electron traps. In this regime, the CEs will rapidly degrade as the result of H abstraction from the CE ring by the released H atoms. Thus, the radiation dose to which a CE/IL system is exposed must be maintained at a level sufficiently low to avoid this regime.« less

Formula for the Removal and Remediation of Polychlorinated Biphenyls in Painted Structures

NASA Technical Reports Server (NTRS)

Quinn, Jacqueline; Loftin, Kathleen; Geiger, Cherie

2010-01-01

An activated metal treatment system (AMTS) removes and destroys polychlorinated biphenyls (PCBs) found in painted structures or within the binding or caulking material on structures. It may be applied using a "paint-on and wipe-off" process that leaves the structure PCB-free and virtually unaltered in physical form. AMTS is used in conjunction with a solvent solution capable of donating hydrogen atoms. AMTS as a treatment technology has two functions: first, to extract PCBs from the material, and second, to degrade the extracted PCBs. The process for removing PCBs from structures is accomplished as an independent step to the degradation process. The goal is to extract the PCBs out of the paint, without destroying the paint, and to partition the PCBs into an environmentally friendly solvent. The research to date indicates this can be accomplished within the first 24 hours of AMTS contact with the paint. PCBs are extremely hydrophobic and prefer to be in the AMTS over the hardened paint or binder material. The solvent selected must be used to open, but not to destroy, the paint s polymeric lattice structure, allowing pathways for PCB movement out of the paint and into the solvent. A number of solvent systems were tested and are available for use within the AMTS. The second process of the AMTS is the degradation or dehalogenation of the PCBs. The solvent selection for this process is limited to solvents that are capable of donating a hydrogen atom to the PCB structure. Additional AMTS formulation properties that must be addressed for each site-specific application include viscosity and stability. The AMTS must be thick enough to remain where it is applied. Several thickening agents have been tested. Adding a stabilizing agent ensures that the AMTS will not evaporate and leave unprotected, activated metal exposed. During AMTS formulation testing, a number of reagents were evaluated to ensure the rate of dehalogenation was not inhibited by its addition to the system.

Influence of solvents on species crossover and capacity decay in non-aqueous vanadium redox flow batteries: Characterization of acetonitrile and 1, 3 dioxolane solvent mixture

NASA Astrophysics Data System (ADS)

Bamgbopa, Musbaudeen O.; Almheiri, Saif

2017-02-01

The importance of the choice of solvent in a non-aqueous redox flow battery (NARFB) cannot be overemphasized. Several studies demonstrated the influence of the solvent on electrolyte performance in terms of reaction rates, energy/power densities, and efficiencies. In this work, we investigate capacity decay as a direct consequence of varying reactant crossover rates through membranes in different solvent environments. Specifically, we demonstrate the superiority of an 84/16 vol% acetonitrile/1,3 dioxolane solvent mixture over pure acetonitrile in terms of energy efficiency (up to 89%) and capacity retention for vanadium NARFBs - while incorporating a Nafion 115 membrane. The permeability of Nafion to the vanadium acetylacetonate active species is an order of magnitude lower when pure acetonitrile is replaced by the solvent mixture. A method to estimate relative membrane permeability is formulated from numerical analysis of self-discharge experimental data. Furthermore, tests on a modified Nafion/SiO2 membrane, which generally offered low species permeability, also show that different solvents alter membrane permeability. Elemental and morphological analyses of cycled Nafion and NafionSi membranes in different solvent environments indicate that different crossover rates induced by the choice of solvent during cycling are due to changes in the membrane microstructure, intrinsic permeability, swelling rates, and chemical stability.

Model input and output files for the simulation of time of arrival of landfill leachate at the water table, Municipal Solid Waste Landfill Facility, U.S. Army Air Defense Artillery Center and Fort Bliss, El Paso County, Texas

USGS Publications Warehouse

Abeyta, Cynthia G.; Frenzel, Peter F.

1999-01-01

This report contains listings of model input and output files for the simulation of the time of arrival of landfill leachate at the water table from the Municipal Solid Waste Landfill Facility (MSWLF), about 10 miles northeast of downtown El Paso, Texas. This simulation was done by the U.S. Geological Survey in cooperation with the U.S. Department of the Army, U.S. Army Air Defense Artillery Center and Fort Bliss, El Paso, Texas. The U.S. Environmental Protection Agency-developed Hydrologic Evaluation of Landfill Performance (HELP) and Multimedia Exposure Assessment (MULTIMED) computer models were used to simulate the production of leachate by a landfill and transport of landfill leachate to the water table. Model input data files used with and output files generated by the HELP and MULTIMED models are provided in ASCII format on a 3.5-inch 1.44-megabyte IBM-PC compatible floppy disk.

Dynamic oligomeric conversions of the cytoplasmic RCK domains mediate MthK potassium channel activity.

PubMed

Kuo, Mario Meng-Chiang; Baker, Kent A; Wong, Lee; Choe, Senyon

2007-02-13

The crystal structure of the RCK-containing MthK provides a molecular framework for understanding the ligand gating mechanisms of K+ channels. Here we examined the macroscopic currents of MthK in enlarged Escherichia coli membrane by patch clamp and rapid perfusion techniques and showed that the channel undergoes desensitization in seconds after activation by Ca2+ or Cd2+. Additionally, MthK is inactivated by slightly acidic pH only from the cytoplasmic side. Examinations of isolated RCK domain by size-exclusion chromatography, static light scattering, analytical sedimentation, and stopped-flow spectroscopy show that Ca2+ rapidly converts isolated RCK monomers to multimers at alkaline pH. In contrast, the RCK domain at acidic pH remains firmly dimeric regardless of Ca2+ but restores predominantly to multimer or monomer at basic pH with or without Ca2+, respectively. These functional and biochemical analyses correlate the four functional states of the MthK channel with distinct oligomeric states of its RCK domains and indicate that the RCK domains undergo oligomeric conversions in modulating MthK activities.

Chemical synthesis and characterization of branched oligodeoxyribonucleotides (bDNA) for use as signal amplifiers in nucleic acid quantification assays.

PubMed

Horn, T; Chang, C A; Urdea, M S

1997-12-01

The divergent synthesis of bDNA structures is described. This new type of branched DNA contains one unique oligonucleotide, the primary sequence, covalently attached through a comb-like branching network to many identical copies of a different oligonucleotide, the secondary sequence. The bDNA comb molecules were assembled on a solid support using parameters optimized for bDNA synthesis. The chemistry was used to synthesize bDNA comb molecules containing 15 secondary sequences. The bDNA comb molecules were elaborated by enzymatic ligation into branched amplification multimers, large bDNA molecules (a total of 1068 nt) containing an average of 36 repeated DNA oligomer sequences, each capable of hybridizing specifically to an alkaline phosphatase-labeled oligonucleotide. The bDNA comb molecules were characterized by electrophoretic methods and by controlled cleavage at periodate-cleavable moieties incorporated during synthesis. The branched amplification multimers have been used as signal amplifiers in nucleic acid quantification assays for detection of viral infection. It is possible to detect as few as 50 molecules with bDNA technology.

Chemical synthesis and characterization of branched oligodeoxyribonucleotides (bDNA) for use as signal amplifiers in nucleic acid quantification assays.

PubMed Central

Horn, T; Chang, C A; Urdea, M S

1997-01-01

The divergent synthesis of bDNA structures is described. This new type of branched DNA contains one unique oligonucleotide, the primary sequence, covalently attached through a comb-like branching network to many identical copies of a different oligonucleotide, the secondary sequence. The bDNA comb molecules were assembled on a solid support using parameters optimized for bDNA synthesis. The chemistry was used to synthesize bDNA comb molecules containing 15 secondary sequences. The bDNA comb molecules were elaborated by enzymatic ligation into branched amplification multimers, large bDNA molecules (a total of 1068 nt) containing an average of 36 repeated DNA oligomer sequences, each capable of hybridizing specifically to an alkaline phosphatase-labeled oligonucleotide. The bDNA comb molecules were characterized by electrophoretic methods and by controlled cleavage at periodate-cleavable moieties incorporated during synthesis. The branched amplification multimers have been used as signal amplifiers in nucleic acid quantification assays for detection of viral infection. It is possible to detect as few as 50 molecules with bDNA technology. PMID:9365266

Dendronization-induced phase-transfer, stabilization and self-assembly of large colloidal Au nanoparticles

NASA Astrophysics Data System (ADS)

Malassis, Ludivine; Jishkariani, Davit; Murray, Christopher B.; Donnio, Bertrand

2016-07-01

The phase-transfer of CTAB-coated aqueous, spherical gold nanoparticles, with metallic core diameters ranging from ca. 27 to 54 nm, into organic solvents by exchanging the primitive polar bilayer with lipophilic, disulfide dendritic ligands is reported. The presence of such a thick nonpolar organic shell around these large nanoparticles enhances their stabilization against aggregation, in addition to enabling their transfer into a variety of solvents such as chloroform, toluene or tetrahydrofuran. Upon the slow evaporation of a chloroform suspension deposited on a solid support, the dendronized hybrids were found to self-assemble into ring structures of various diameters. Moreover, their self-assembly at the liquid-air interface affords the formation of fairly long-range ordered monolayers, over large areas, that can then be entirely transferred onto solid substrates.The phase-transfer of CTAB-coated aqueous, spherical gold nanoparticles, with metallic core diameters ranging from ca. 27 to 54 nm, into organic solvents by exchanging the primitive polar bilayer with lipophilic, disulfide dendritic ligands is reported. The presence of such a thick nonpolar organic shell around these large nanoparticles enhances their stabilization against aggregation, in addition to enabling their transfer into a variety of solvents such as chloroform, toluene or tetrahydrofuran. Upon the slow evaporation of a chloroform suspension deposited on a solid support, the dendronized hybrids were found to self-assemble into ring structures of various diameters. Moreover, their self-assembly at the liquid-air interface affords the formation of fairly long-range ordered monolayers, over large areas, that can then be entirely transferred onto solid substrates. Electronic supplementary information (ESI) available: TEM microscope images. See DOI: 10.1039/c6nr03404g

Energy storage devices having anodes containing Mg and electrolytes utilized therein

DOEpatents

Shao, Yuyan; Liu, Jun

2015-08-18

For a metal anode in a battery, the capacity fade is a significant consideration. In energy storage devices having an anode that includes Mg, the cycling stability can be improved by an electrolyte having a first salt, a second salt, and an organic solvent. Examples of the organic solvent include diglyme, triglyme, tetraglyme, or a combination thereof. The first salt can have a magnesium cation and be substantially soluble in the organic solvent. The second salt can enhance the solubility of the first salt and can have a magnesium cation or a lithium cation. The first salt, the second salt, or both have a BH.sub.4 anion.

High stable suspension of magnetite nanoparticles in ethanol by using sono-synthesized nanomagnetite in polyol medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bastami, Tahereh Rohani; Entezari, Mohammad H., E-mail: moh_entezari@yahoo.com

2013-09-01

Graphical abstract: - Highlights: • The sonochemical synthesis of magnetite nanoparticles was carried out in EG without any surfactant. • The nanoparticles with sizes ∼24 nm were composed of small building blocks with sizes ∼2 nm. • The hydrophilic magnetite nanoparticles were stable in ethanol even after 8 months. • Ultrasonic intensity showed a crucial role on the obtained high stable magnetite nanoparticles in ethanol. - Abstract: The sonochemical synthesis of magnetite nanoparticles was carried out at relatively low temperature (80 °C) in ethylene glycol (EG) as a polyol solvent. The particle size was determined by transmission electron microscopy (TEM).more » The magnetite nanoparticles with an average size of 24 nm were composed of small building blocks with an average size of 2–3 nm and the particles exhibited nearly spherical shape. The surface characterization was investigated by using Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The stability of magnetite nanoparticles was studied in ethanol as a polar solvent. The nanoparticles showed an enhanced stability in ethanol which is due to the hydrophilic surface of the particles. The colloidal stability of magnetite nanoparticles in ethanol was monitored by UV–visible spectrophotometer. According to the results, the nanoparticles synthesized in 30 min of sonication with intensity of 35 W/cm{sup 2} (50%) led to a maximum stability in ethanol as a polar solvent with respect to the other applied intensities. The obtained magnetite nanoparticles were stable for more than12 months.« less

Thin Metallic Films From Solvated Metal Atoms

NASA Astrophysics Data System (ADS)

Trivino, Galo C.; Klabunde, Kenneth J.; Dale, Brock

1988-02-01

Metals were evaporated under vacuum and the metal atoms solvated by excess organic solvents at low temperature. Upon warming stable colloidal metal particles were formed by controlled metal atom clustering. The particles were stabilized toward flocculation by solvation and electrostatic effects. Upon solvent removal the colloidal particles grew to form thin films that were metallic in appearance, but showed higher resistivities than pure metallic films. Gold, palladium, platinium, and especially indium are discussed.

Application of liquid-liquid interactions with single-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Wang, Randy Kai-Wei

This study covers three important research topics related to the application of liquid-liquid interaction with single-walled carbon nanotubes (SWNTs). The first topic describes the removal of SWNT bundles from liquid suspensions of nanotubes. The key to this work includes the use of liquid-liquid interfaces to trap the SWNT bundles due to the free energy change of the system during the process. SWNTs pack into crystalline ropes that form bundles due to strong van der Waals attraction. Bundling diminishes mechanical and electronic properties because it could interrupt the electronic structure of the nanotubes. Also, the electronic devices based on as-grown nanotubes, which contains a mixture of individual nanotubes and nanotube bundles, make the electrical response unpredictable. We developed a new simple process to remove bundles by liquid-liquid interaction. SWNTs bundles are trapped at the interface because bundles stabilize the emulsions. Eliminating the use of ultracentrifugation to remove SWNT bundles enables large-scale production with reduced production costs and time savings. The second topic presented the swelling effect of the surfactant layer surrounding SWNTs with nonpolar solvents. Solvatochromic shifts in the absorbance and fluorescence spectra are observed when surfactant-stabilized aqueous SWNT suspensions are mixed with immiscible organic solvents. When aqueous surfactant-suspended SWNTs are mixed with certain solvents, the spectra closely match the peaks for SWNTs dispersed in only that solvent. These spectral changes suggest the hydrophobic region of the micelle surrounding SWNTs swells with the organic solvent when mixed. The solvatochromic shifts of the aqueous SWNT suspensions are reversible once the solvent evaporates. However, some surfactant-solvent systems show permanent changes to the fluorescence emission intensity after exposure to the organic solvent. The intensity of some large diameter SWNT (n, m) types increase by more than 175%. These differences are attributed to surfactant reorganization, which can improve nanotube coverage, resulting in decreased exposure to quenching mechanisms from the aqueous phase. The third topic describes the further study of the solvatochromism of the SWNTs. Since SWNTs are encapsulated with microenvironments of nonpolar solvents, it provides a new method to measure the photophysical properties of nanotubes in environments with known properties. Fluorescence and absorbance spectra of SWNTs show solvatochromic shifts in 16 nonpolar solvents, which are proportional to the solvent induction polarization. The photophysical properties of SWNTs were used to determine the relationship between the longitudinal polarizability and other nanotube properties, alpha11,|| ∝ 1/(R2E11 3). (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)

How Methylation Modifies the Photophysics of the Native All- trans-Retinal Protonated Schiff Base: A CASPT2/MD Study in Gas Phase and in Methanol.

PubMed

Barata-Morgado, Rute; Sánchez, M Luz; Muñoz-Losa, Aurora; Martín, M Elena; Olivares Del Valle, Francisco J; Aguilar, Manuel A

2018-03-22

A comparison between the free-energy surfaces of the all- trans-retinal protonated Schiff base (RPSB) and its 10-methylated derivative in gas phase and methanol solution is performed at CASSCF//CASSCF and CASPT2//CASSCF levels. Solvent effects were included using the average solvent electrostatic potential from molecular dynamics method. This is a QM/MM (quantum mechanics/molecular mechanics) method that makes use of the mean field approximation. It is found that the methyl group bonded to C10 produces noticeable changes in the solution free-energy profile of the S 1 excited state, mainly in the relative stability of the minimum energy conical intersections (MECIs) with respect to the Franck-Condon (FC) point. The conical intersections yielding the 9- cis and 11- cis isomers are stabilized while that yielding the 13- cis isomer is destabilized; in fact, it becomes inaccessible by excitation to S 1 . Furthermore, the planar S 1 minimum is not present in the methylated compound. The solvent notably stabilizes the S 2 excited state at the FC geometry. Therefore, if the S 2 state has an effect on the photoisomerization dynamics, it must be because it permits the RPSB population to branch around the FC point. All these changes combine to speed up the photoisomerization in the 10-methylated compound with respect to the native compound.

Influence of solvent evaporation rate and formulation factors on solid dispersion physical stability.

PubMed

Wu, Jian X; Yang, Mingshi; Berg, Frans van den; Pajander, Jari; Rades, Thomas; Rantanen, Jukka

2011-12-18

New chemical entities (NCEs) often show poor water solubility necessitating solid dispersion formulation. The aim of the current study is to employ design of experiments in investigating the influence of one critical process factor (solvent evaporation rate) and two formulation factors (PVP:piroxicam ratio (PVP:PRX) and PVP molecular weight (P(MW))) on the physical stability of PRX solid dispersion prepared by the solvent evaporation method. The results showed the rank order of an increase in factors contributing to a decrease in the extent of PRX nucleation being evaporation rate>PVP:PRX>P(MW). The same rank order was found for the decrease in the extent of PRX crystal growth in PVP matrices from day 0 up to day 12. However, after 12days the rank became PVP:PRX>evaporation rate>P(MW). The effects of an increase in evaporation rate and PVP:PRX ratio in stabilizing PRX were of the same order of magnitude, while the effect from P(MW) was much smaller. The findings were confirmed by XRPD. FT-IR showed that PRX recrystallization in the PVP matrix followed Ostwald's step rule, and an increase in the three factors all led to increased hydrogen bonding interaction between PRX and PVP. The present study showed the applicability of the Quality by Design approach in solid dispersion research, and highlights the need for multifactorial analysis. Copyright © 2011 Elsevier B.V. All rights reserved.

Unscrambling the effect of C-terminal tail deletion on the stability of a cold-adapted, organic solvent stable lipase from Staphylococcus epidermidis AT2.

PubMed

Kamarudin, Nor Hafizah Ahmad; Rahman, Raja Noor Zaliha Raja Abd; Ali, Mohd Shukuri Mohamad; Leow, Thean Chor; Basri, Mahiran; Salleh, Abu Bakar

2014-08-01

Terminal moieties of most proteins are long known to be disordered and flexible. To unravel the functional role of these regions on the structural stability and biochemical properties of AT2 lipase, four C-terminal end residues, (Ile-Thr-Arg-Lys) which formed a flexible, short tail-like random-coil segment were targeted for mutation. Swapping of the tail-like region had resulted in an improved crystallizability and anti-aggregation property along with a slight shift of the thermostability profile. The lipolytic activity of mutant (M386) retained by 43 % compared to its wild-type with 18 % of the remaining activity at 45 °C. In silico analysis conducted at 25 and 45 °C was found to be in accordance to the experimental findings in which the RMSD values of M386 were more stable throughout the total trajectory in comparison to its wild-type. Terminal moieties were also observed to exhibit large movement and flexibility as denoted by high RMSF values at both dynamics. Variation in organic solvent stability property was detected in M386 where the lipolytic activity was stimulated in the presence of 25 % (v/v) of DMSO, isopropanol, and diethyl ether. This may be worth due to changes in the surface charge residues at the mutation point which probably involve in protein-solvent interaction.

Characterization and Storage Stability Study of Bixin Extracted from Bixa orellana Using Organic Solvent

NASA Astrophysics Data System (ADS)

Husa, N. N.; Hamzah, F.; Said, H. M.

2018-05-01

Colorant is one of the additives to give a better appearance or improve the colour of the product. Synthetic colorant has been widely used in industrial due to its readiness in the market and its colour stability. However the arising issues related to the safety, nutrition and also the therapeutic effect has encouraged users to become more concern about the colouring component. Thus, the present research was conducted in order to produce natural colorant called bixin from Bixa orellana or also known as annatto seeds. The study was focusing on the effect of the solvent on the characteristic and concentration of the extracted bixin. While stability of the bixin during different storage condition was determined to further validate the effectiveness of the solvent. The result indicated that methanol and acetone gave darker of the bixin colour as compared to the water. However, the deterioration rate of the bixin in acetone and methanol were faster as compared to the water. The extracted bixin was analysed using Fourier-transform infrared spectroscopy (FTIR) and spectrophotometer analysis. The strong band for the bixin was observed at absorbance range of 1704 – 1740cm-1. The study indicates that the concentration of the extracted bixin was the highest in methanol which gave 817.7 ppm of bixin. Meanwhile, bixin concentration in acetone and water was 602.9 ppm and 477.19 ppm respectively.

Extraction, stability, and separation of betalains from Opuntia joconostle cv. using response surface methodology.

PubMed

Sanchez-Gonzalez, Noe; Jaime-Fonseca, Monica R; San Martin-Martinez, Eduardo; Zepeda, L Gerardo

2013-12-11

Betalains were extracted and analyzed from Opuntia joconostle (the prickly pear known as xoconostle in Mexico). For the extraction, two solvent systems were used, methanol/water and ethanol/water. A three-variable Box-Behnken statistical design was used for extraction: solvent concentration (0-80%, v/v), temperature (5-30 °C), and treatment time (10-30 min). The extraction and stability of betalains from xoconostle were studied using response surface methodology (RSM). Techniques such as UV-vis, column chromatography, and HPLC were employed for the separation and analysis of the main pigments present in the extracts. Maximum pigment concentration (92 mg/100 g of fruit) was obtained at a temperature of 15 °C and a time of 10 min for methanol/water (20:80), whereas maximum stability of the pigment was observed at pH 5 and a temperature of 25 °C. HPLC chromatograms showed the main betalains of the xoconostle characterized were betalain, betanidin, and isobetalain.

Stability of Polymer Ultrathin Films (<7 nm) Made by a Top-Down Approach.

PubMed

Bal, Jayanta Kumar; Beuvier, Thomas; Unni, Aparna Beena; Chavez Panduro, Elvia Anabela; Vignaud, Guillaume; Delorme, Nicolas; Chebil, Mohamed Souheib; Grohens, Yves; Gibaud, Alain

2015-08-25

In polymer physics, the dewetting of spin-coated polystyrene ultrathin films on silicon remains mysterious. By adopting a simple top-down method based on good solvent rinsing, we are able to prepare flat polystyrene films with a controlled thickness ranging from 1.3 to 7.0 nm. Their stability was scrutinized after a classical annealing procedure above the glass transition temperature. Films were found to be stable on oxide-free silicon irrespective of film thickness, while they were unstable (<2.9 nm) and metastable (>2.9 nm) on 2 nm oxide-covered silicon substrates. The Lifshitz-van der Waals intermolecular theory that predicts the domains of stability as a function of the film thickness and of the substrate nature is now fully reconciled with our experimental observations. We surmise that this reconciliation is due to the good solvent rinsing procedure that removes the residual stress and/or the density variation of the polystyrene films inhibiting thermodynamically the dewetting on oxide-free silicon.

Theoretical study on substituent and solvent effects for nanocubes formed with gear-shaped amphiphile molecules.

PubMed

Mashiko, T; Hiraoka, S; Nagashima, U; Tachikawa, M

2017-01-04

Gear-shaped amphiphile molecules (1) recently synthesized by Hiraoka et al. self-assemble into a hexameric structure, nanocubes (1 6 ), in 25% aqueous methanol due to a solvophobic effect. Here we have carried out molecular dynamic simulations to elucidate the stability of these hexameric capsules (1 6 and 2 6 ) in water, 25% aqueous methanol, and methanol. In all solvents, the 1 6 nanocubes are maintained for all trajectories. On the other hand, 2 6 was found to collapse for one trajectory in water and seven trajectories in 25% aqueous methanol. In a pure methanol solvent, 2 6 was found to collapse for all trajectories. The number of collapsed trajectories of 2 6 increased with the amount of methanol in the solvent. We therefore focused on the structure of the π-π stacking between pyridyl groups and the CH-π interactions between the methyl and pyridyl groups within the nanocube. Our study clearly shows the role played by the methanol solvent molecules in the assembly of the nanocube in terms of the substituent and solvent effects at the molecular level, and that these substituent and solvent effects are important for the self-assembly of the nanocubes.

Influence of Polar Organic Solvents in an Ionic Liquid Containing Lithium Bis(fluorosulfonyl)amide: Effect on the Cation-Anion Interaction, Lithium Ion Battery Performance, and Solid Electrolyte Interphase.

PubMed

Lahiri, Abhishek; Li, Guozhu; Olschewski, Mark; Endres, Frank

2016-12-14

Ionic liquid-organic solvent mixtures have recently been investigated as potential battery electrolytes. However, contradictory results with these mixtures have been shown for battery performance. In this manuscript, we studied the influence of the addition of polar organic solvents into the ionic liquid electrolyte 1 M lithium bis(fluorosulfonyl)amide (LiFSI)-1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide ([Py 1,4 ]FSI) and tested it for lithium ion battery applications. From infrared and Raman spectroscopy, clear changes in the lithium solvation and cation-anion interactions in the ionic liquid were observed on addition of organic solvents. From the lithiation/delithiation studies on electrodeposited Ge, the storage capacity for the ionic liquid-highly polar organic solvent (acetonitrile) mixture was found to be the highest at low C-rates (0.425 C) compared to using an ionic liquid alone and ionic liquid-less polar solvent (dimethyl carbonate) mixtures. Furthermore, XPS and AFM were used to evaluate the solid electrolyte interphase (SEI) and to correlate its stability with Li storage capacity.

Constitutive expression of active microbial transglutaminase in Escherichia coli and comparative characterization to a known variant.

PubMed

Javitt, Gabe; Ben-Barak-Zelas, Zohar; Jerabek-Willemsen, Moran; Fishman, Ayelet

2017-02-28

Microbial transglutaminase (mTG) is a robust enzyme catalyzing the formation of an isopeptide bond between glutamine and lysine residues. It has found use in food applications, pharmaceuticals, textiles, and biomedicine. Overexpression of soluble and active mTG in E. coli has been limited due to improper protein folding and requirement for proteolytic cleavage of the pro-domain. Furthermore, to integrate mTG more fully industrially and academically, thermostable and solvent-stable variants may be imperative. A novel expression system constitutively producing active mTG was designed. Wild-type (WT) mTG and a S2P variant had similar expression levels, comparable to previous studies. Kinetic constants were determined by a glutamate dehydrogenase-coupled assay, and the S2P variant showed an increased affinity and a doubled enzyme efficiency towards Z-Gln-Gly. The melting temperature (T m ) of the WT was determined by intrinsic fluorescence measurements to be 55.8 ± 0.1 °C and of the S2P variant to be 56.3 ± 0.4 °C and 45.5 ± 0.1 °C, showing a moderately different thermostability profile. Stability in water miscible organic solvents was determined for both the WT and S2P variant. Of the solvents tested, incubation of mTG in isopropanol for 24 h at 4 °C showed the strongest stabilizing effect with mTG retaining 61 and 72% activity for WT and S2P respectively in 70% isopropanol. Both enzymes also showed an increased initial activity in the presence of organic solvents with the highest activity increase in 40% DMSO. Nevertheless, both enzymes were inactivated in 70% of all organic solvents tested. A constitutive expression system of active mTG in E. coli without downstream proteolytic cleavage processing was used for overexpression and characterization. High throughput techniques for testing thermostability and kinetics were useful in streamlining analysis and could be used in the future for quickly identifying beneficial mutants. Hitherto untested thermostability and stability of mTG in organic solvents was evaluated, which can pave the way for use of the enzyme in novel applications and processes.

Solvent-induced chirality control in the enantioseparation of 1-phenylethylamine via diastereomeric salt formation.

PubMed

Kodama, Koichi; Kimura, Yuria; Shitara, Hiroaki; Yasutake, Mikio; Sakurai, Rumiko; Hirose, Takuji

2011-04-01

Solvent-induced chirality control in the enantioseparation of 1-phenylethylamine 1 by N-(p-toluenesulfonyl)-(S)-phenylalanine 2 via diastereomeric salt formation was studied. (S)-1·(S)-2 was preferentially crystallized as a less-soluble salt from aqueous alcohol, while (R)-1·(S)-2 salt was mainly obtained by addition of solvents with a six-membered ring such as dioxane, cyclohexane, tetrahydropyran, and cyclohexene to 2-propanol. Further investigations were carried out from the viewpoints of molecular structures, optical rotation measurement, and X-ray crystallographic analyses. Crystallographic analyses have revealed that incorporation of the six-membered ring solvent molecule in (R)-1·(S)-2 without hydrogen bonds changed the molecular conformation of (S)-2 to stabilize the salt, which changed the selectivity of 1 in the enantioseparation. Copyright © 2010 Wiley-Liss, Inc.

Random copolymers that protect proteins

NASA Astrophysics Data System (ADS)

Alexander-Katz, Alfredo; Van Lehn, Reid C.

2018-03-01

Scientists have tried and in some limited cases succeeded to harness proteins to do chemistry (1) or use them in functional materials. However, most proteins only function correctly if they fold into specific conformations, which typically occurs with the assistance of other proteins (such as chaperones, translocons, or transporters) that mediate structure formation, membrane insertion, and intracellular trafficking (2, 3). Several methods have been used to improve protein stability in nonbiological environments—including micelle encapsulation, polymer conjugation, and sol-gel trapping (4)—but for most intended applications, they suffer from low levels of functionality, difficult chemical postfunctionalization, or the requirement of very specific solvent environments. On page 1239 of this issue, Panganiban et al. (5) introduce an approach for stabilizing proteins in disparate solvent environments that does not suffer from these drawbacks.

Thermal behavior of glassy phase stabilized ammonium nitrate (PSAN) thin films

DOE PAGES

Yeager, J. D.; Chellappa, R.; Singh, S.; ...

2015-06-01

Ammonium nitrate (AN) is a high interest material because of its wide usage in propellants and explosives but can be difficult to handle from a formulation standpoint. It is soluble in many common solvents and has complex phase behavior. Here, we formulate phase stabilized AN (PSAN) films in a polymer matrix and characterize thermal and phase behavior using neutron reflectometry and ellipsometry. Our PSAN films are generally stable up to 160 °C, though we observe small material loss between 60 and 100 °C, which we attribute to solvent interactions with the PSAN. Crystallization of AN from supersaturated polymer is mostmore » common at thicker regions of the film, suggesting a critical nucleation thickness for the AN which can be avoided by making very thin films.« less

Comparison of extraction methods for quantifying vitamin E from animal tissues.

PubMed

Xu, Zhimin

2008-12-01

Four extraction methods: (1) solvent (SOL), (2) ultrasound assisted solvent (UA), (3) saponification and solvent (SP), and (4) saponification and ultrasound assisted solvent (SP-UA), were used in sample preparation for quantifying vitamin E (tocopherols) in chicken liver and plasma samples. The extraction yields of SOL, UA, SP, and SP-UA methods obtained by adding delta-tocopherol as internal reference were 95%, 104%, 65%, and 62% for liver and 98%, 103%, 97%, and 94% for plasma, respectively. The methods with saponification significantly affected the stabilities of tocopherols in liver samples. The measured values of alpha- and gamma-tocopherols using the solvent only extraction (SOL) method were much lower than that using any of the other extraction methods. This indicated that less of the tocopherols in those samples were in a form that could be extracted directly by solvent. The measured value of alpha-tocopherol in the liver sample using the ultrasound assisted solvent (UA) method was 1.5-2.5 times of that obtained from the saponification and solvent (SP) method. The differences in measured values of tocopherols in the plasma samples by using the two methods were not significant. However, the measured value of the saponification and ultrasound assisted solvent (SP-UA) method was lower than either the saponification and solvent (SP) or the ultrasound assisted solvent (UA) method. Also, the reproducibility of the ultrasound assisted solvent (UA) method was greater than any of the saponification methods. Compared with the traditional saponification method, the ultrasound assisted solvent method could effectively extract tocopherols from sample matrix without any chemical degradation reactions, especially for complex animal tissue such as liver.

Electric current-producing device having sulfone-based electrolyte

DOEpatents

Angell, Charles Austen; Sun, Xiao-Guang

2010-11-16

Electrolytic solvents and applications of such solvents including electric current-producing devices. For example, a solvent can include a sulfone compound of R1--SO2--R2, with R1 being an alkyl group and R2 a partially oxygenated alkyl group, to exhibit high chemical and thermal stability and high oxidation resistance. For another example, a battery can include, between an anode and a cathode, an electrolyte which includes ionic electrolyte salts and a non-aqueous electrolyte solvent which includes a non-symmetrical, non-cyclic sulfone. The sulfone has a formula of R1--SO2--R2, wherein R1 is a linear or branched alkyl or partially or fully fluorinated linear or branched alkyl group having 1 to 7 carbon atoms, and R2 is a linear or branched or partially or fully fluorinated linear or branched oxygen containing alkyl group having 1 to 7 carbon atoms. The electrolyte can include an electrolyte co-solvent and an electrolyte additive for protective layer formation.

Phase Behavior of a Single Structured Ionomer Chain in Solution

DOE PAGES

Aryal, Dipak; Etampawala, Thusitha; Perahia, Dvora; ...

2014-08-14

Structured polymers offer a means to tailor transport pathways within mechanically stable manifolds. Here we examine the building block of such a membrane, namely a single large pentablock co-polymer that consist of a center block of a randomly sulfonated polystyrene, designed for transport, tethered to poly-ethylene-r-propylene and end-capped by poly-t-butyl styrene, for mechanical stability,using molecular dynamics simulations. The polymer structure in a cyclohexane-heptane mixture, a technologically viable solvent, and in water, a poor solvent for all segments and a ubiquitous substance is extracted. In all solvents the pentablock collapsed into nearly spherical aggregates where the ionic block is segregated. Inmore » hydrophobic solvents, the ionic block resides in the center, surrounded by swollen intermix of flexible and end blocks. In water all blocks are collapsed with the sulfonated block residing on the surface. Our results demonstrate that solvents drive different local nano-segregation, providing a gateway to assemble membranes with controlled topology.« less

Improved solubility of DNA in recyclable and reusable bio-based deep eutectic solvents with long-term structural and chemical stability.

PubMed

Mondal, Dibyendu; Sharma, Mukesh; Mukesh, Chandrakant; Gupta, Vishal; Prasad, Kamalesh

2013-10-25

The solubility of DNA in bio-based deep eutectic solvents (DESs) consisting of mixtures of choline chloride with levulinic acid, glycerol, ethylene glycol, sorbitol and resorcinol was investigated. The macromolecule was found to be soluble and chemically and structurally stable in DESs consisting of mixtures containing glycerol and ethylene glycol. Furthermore recyclability of the DESs was demonstrated over three consecutive reuses in DNA dissolution.

Molecular Dynamics Simulation Study of Solvent and State of Charge Effects on Solid-Phase Structure and Counterion Binding in a Nitroxide Radical Containing Polymer Energy Storage Material

DOE PAGES

Kemper, Travis W.; Gennett, Thomas; Larsen, Ross E.

2016-10-19

Here we performed molecular dynamics simulations to understand the effects of solvent swelling and state of charge (SOC) on the redox active, organic radical cathode material poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA). We show that the polar solvent acetonitrile primarily solvates the nitroxide radical without disrupting the packing of the (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) pendant groups of PTMA. We also simulated bulk PTMA in different SOC, 25%, 50%, 75%, and 100%, by converting the appropriate number of TEMPO groups to the cation charge state and adding BF 4 - counterions to the simulation. At each SOC the packing of PTMA, the solvent, and the counterionsmore » were examined. The binding of the anion to the nitroxide cation site was examined using the potential of mean force and found to be on the order of tens of meV, with a binding energy that decreased with increasing SOC. Additionally, we found that the cation state is stabilized by the presence of a nearby anion by more than 1 eV, and the implications of this stabilization on charge transport are discussed. Finally, we describe the implications of our results for how the SOC of an organic electrode affects electron and anion charge transport during the charging and discharging processes.« less

Mechanistic Study of Electrolyte Additives to Stabilize High-Voltage Cathode–Electrolyte Interface in Lithium-Ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Han; Maglia, Filippo; Lamp, Peter

Current developments of electrolyte additives to stabilize electrode-electrolyte interface in Li-ion batteries highly rely on a trial-and-error search, which involves repetitive testing and intensive amount of resources. The lack of understandings on the fundamental protection mechanisms of the additives significantly increases the difficulty for the transformational development of new additives. In this study, we investigated two types of individual protection routes to build a robust cathode-electrolyte interphase at high potentials: (i) a direct reduction in the catalytic decomposition of the electrolyte solvent; and (ii) formation of a “corrosion inhibitor film” that prevents severely attack and passivation from protons that generatedmore » from the solvent oxidation, even the decomposition of solvent cannot not mitigated. Effect of three exemplary electrolyte additives: (i) lithium difluoro(oxalato)borate (LiDFOB); (ii) 3-hexylthiophene (3HT); and (iii) tris(hexafluoro-iso-propyl)phosphate (HFiP), on LiNi0.6Mn0.2Co0.2O2 (NMC 622) cathode were investigated to validate our hypothesis. It is demonstrated that understandings of both electrolyte additives and solvent are essential and careful balance between the cathode protection mechanism of additives and their side effects is critical to obtain optimum results. More importantly, this study opens up new directions of rational design of functional electrolyte additives for the next generation high-energy density lithium-ion chemistries.« less

Long-chain amine-templated synthesis of gallium sulfide and gallium selenide nanotubes

NASA Astrophysics Data System (ADS)

Seral-Ascaso, A.; Metel, S.; Pokle, A.; Backes, C.; Zhang, C. J.; Nerl, H. C.; Rode, K.; Berner, N. C.; Downing, C.; McEvoy, N.; Muñoz, E.; Harvey, A.; Gholamvand, Z.; Duesberg, G. S.; Coleman, J. N.; Nicolosi, V.

2016-06-01

We describe the soft chemistry synthesis of amine-templated gallium chalcogenide nanotubes through the reaction of gallium(iii) acetylacetonate and the chalcogen (sulfur, selenium) using a mixture of long-chain amines (hexadecylamine and dodecylamine) as a solvent. Beyond their role as solvent, the amines also act as a template, directing the growth of discrete units with a one-dimensional multilayer tubular nanostructure. These new materials, which broaden the family of amine-stabilized gallium chalcogenides, can be tentatively classified as direct large band gap semiconductors. Their preliminary performance as active material for electrodes in lithium ion batteries has also been tested, demonstrating great potential in energy storage field even without optimization.We describe the soft chemistry synthesis of amine-templated gallium chalcogenide nanotubes through the reaction of gallium(iii) acetylacetonate and the chalcogen (sulfur, selenium) using a mixture of long-chain amines (hexadecylamine and dodecylamine) as a solvent. Beyond their role as solvent, the amines also act as a template, directing the growth of discrete units with a one-dimensional multilayer tubular nanostructure. These new materials, which broaden the family of amine-stabilized gallium chalcogenides, can be tentatively classified as direct large band gap semiconductors. Their preliminary performance as active material for electrodes in lithium ion batteries has also been tested, demonstrating great potential in energy storage field even without optimization. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01663d

Protein immobilization on epoxy-activated thin polymer films: effect of surface wettability and enzyme loading.

PubMed

Chen, Bo; Pernodet, Nadine; Rafailovich, Miriam H; Bakhtina, Asya; Gross, Richard A

2008-12-02

A series of epoxy-activated polymer films composed of poly(glycidyl methacrylate/butyl methacrylate/hydroxyethyl methacrylate) were prepared. Variation in comonomer composition allowed exploration of relationships between surface wettability and Candida antartica lipase B (CALB) binding to surfaces. By changing solvents and polymer concentrations, suitable conditions were developed for preparation by spin-coating of uniform thin films. Film roughness determined by AFM after incubation in PBS buffer for 2 days was less than 1 nm. The occurrence of single CALB molecules and CALB aggregates at surfaces was determined by AFM imaging and measurements of volume. Absolute numbers of protein monomers and multimers at surfaces were used to determine values of CALB specific activity. Increased film wettability, as the water contact angle of films increased from 420 to 550, resulted in a decreased total number of immobilized CALB molecules. With further increases in the water contact angle of films from 55 degrees to 63 degrees, there was an increased tendency of CALB molecules to form aggregates on surfaces. On all flat surfaces, two height populations, differing by more than 30%, were observed from height distribution curves. They are attributed to changes in protein conformation and/or orientation caused by protein-surface and protein-protein interactions. The fraction of molecules in these populations changed as a function of film water contact angle. The enzyme activity of immobilized films was determined by measuring CALB-catalyzed hydrolysis of p-nitrophenyl butyrate. Total enzyme specific activity decreased by decreasing film hydrophobicity.

Flexible Graphene Composites for Human Space Flight Applications

NASA Technical Reports Server (NTRS)

Sosa, Edward D.

2013-01-01

Graphene oxide allows for better dispersion stability in aqueous and organic solvents. Stabilizers provide dispersion of pristine graphene. Roll coating provide the best coverage of polyurethane sheets. Graphene and GO coated polyurethane used to fabricate flexible laminate composite. Permeation testing indicates that pristine graphene acts as a better gas barrier material. Continuous graphene films are expected to provide even better gas barrier properties.

Liquid permeation and chemical stability of anodic alumina membranes

PubMed Central

Buldakov, Dmitrii A; Tishkin, Alexey A; Lukashin, Alexey V; Eliseev, Andrei A

2017-01-01

A study on the chemical stability of anodic alumina membranes and their performance in long-term water and organic solvent permeation experiments is reported. Anodic alumina possesses high stability for both protonic and aprotonic organic solvents. However, serious degradation of the membrane occurs in pure water, leading to a drastic decrease of permeance (over 20% of the initial value after the passing of 0.250 m3/m2 of pure water). The drying of the membrane induces further permeance drop-off. The rate of membrane degradation strongly depends on the pH of the penetrant solution and increases in basic media. According to 27Al NMR and thermogravimetry results, the degradation of the membranes is associated with the dissolution of water-soluble [Al13O4(OH)24(H2O)12]7+ polyhydroxocomplexes and their further redeposition in the form of [Al(OH)4]−, resulting in channels blocking. This process intensifies in basic pH due to the high positive charge of the anodic alumina surface. An approach for improving anodic aluminum oxide stability towards dissolution in water by carbon CVD coating of the membrane walls is suggested. PMID:28382245

Stability of polymer encapsulated quantum dots in cell culture media

NASA Astrophysics Data System (ADS)

Ojea-Jiménez, I.; Piella, J.; Nguyen, T.-L.; Bestetti, A.; Ryan, A. D.; Puntes, V.

2013-04-01

The unique optical properties of Quantum Dots have attracted a great interest to use these nanomaterials in diverse biological applications. The synthesis of QDs by methods from the literature permits one to obtain nanocrystals coated by hydrophobic alkyl coordinating ligands and soluble in most of the cases in organic solvents. The ideal biocompatible QD must be homogeneously dispersed and colloidally stable in aqueous solvents, exhibit pH and salt stability, show low levels of nonspecific binding to biological components, maintain a high quantum yield, and have a small hydrodynamic diameter. Polymer encapsulation represents an excellent scaffold on which to build additional biological function, allowing for a wide range of grafting approaches for biological ligands. As these QD are functionalized with poly(ethylene)glycol (PEG) derivatives on their surface, they show long term stability without any significant change in the optical properties, and they are also highly stable in the most common buffer solutions such as Phosphate Buffer Saline (PBS) or borate. However, as biological studies are normally done in more complex biological media which contain a mixture of amino acids, salts, glucose and vitamins, it is essential to determine the stability of our synthesized QDs under these conditions before tackling biological studies.

Extraction of organic compounds with room temperature ionic liquids.

PubMed

Poole, Colin F; Poole, Salwa K

2010-04-16

Room temperature ionic liquids are novel solvents with a rather specific blend of physical and solution properties that makes them of interest for applications in separation science. They are good solvents for a wide range of compounds in which they behave as polar solvents. Their physical properties of note that distinguish them from conventional organic solvents are a negligible vapor pressure, high thermal stability, and relatively high viscosity. They can form biphasic systems with water or low polarity organic solvents and gases suitable for use in liquid-liquid and gas-liquid partition systems. An analysis of partition coefficients for varied compounds in these systems allows characterization of solvent selectivity using the solvation parameter model, which together with spectroscopic studies of solvent effects on probe substances, results in a detailed picture of solvent behavior. These studies indicate that the solution properties of ionic liquids are similar to those of polar organic solvents. Practical applications of ionic liquids in sample preparation include extractive distillation, aqueous biphasic systems, liquid-liquid extraction, liquid-phase microextraction, supported liquid membrane extraction, matrix solvents for headspace analysis, and micellar extraction. The specific advantages and limitations of ionic liquids in these studies is discussed with a view to defining future uses and the need not to neglect the identification of new room temperature ionic liquids with physical and solution properties tailored to the needs of specific sample preparation techniques. The defining feature of the special nature of ionic liquids is not their solution or physical properties viewed separately but their unique combinations when taken together compared with traditional organic solvents. Copyright 2009 Elsevier B.V. All rights reserved.

From micelle supramolecular assemblies in selective solvents to isoporous membranes.

PubMed

Nunes, Suzana P; Karunakaran, Madhavan; Pradeep, Neelakanda; Behzad, Ali Reza; Hooghan, Bobby; Sougrat, Rachid; He, Haoze; Peinemann, Klaus-Viktor

2011-08-16

The supramolecular assembly of PS-b-P4VP copolymer micelles induced by selective solvent mixtures was used to manufacture isoporous membranes. Micelle order in solution was confirmed by cryo-scanning electron microscopy in casting solutions, leading to ordered pore morphology. When dioxane, a solvent that interacts poorly with the micelle corona, was added to the solution, polymer-polymer segment contact was preferential, increasing the intermicelle contact. Immersion in water gave rise to asymmetric porous membranes with exceptional pore uniformity and high porosity. The introduction of a small number of carbon nanotubes to the casting solution improved the membrane stability and the reversibility of the gate response in the presence of different pH values.

Method for applying a photoresist layer to a substrate having a preexisting topology

DOEpatents

Morales, Alfredo M.; Gonzales, Marcela

2004-01-20

The present invention describes a method for preventing a photoresist layer from delaminating, peeling, away from the surface of a substrate that already contains an etched three dimensional structure such as a hole or a trench. The process comprises establishing a saturated vapor phase of the solvent media used to formulate the photoresist layer, above the surface of the coated substrate as the applied photoresist is heated in order to "cure" or drive off the retained solvent constituent within the layer. By controlling the rate and manner in which solvent is removed from the photoresist layer the layer is stabilized and kept from differentially shrinking and peeling away from the substrate.

The role of stabilization centers in protein thermal stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Magyar, Csaba; Gromiha, M. Michael; Sávoly, Zoltán

2016-02-26

The definition of stabilization centers was introduced almost two decades ago. They are centers of noncovalent long range interaction clusters, believed to have a role in maintaining the three-dimensional structure of proteins by preventing their decay due to their cooperative long range interactions. Here, this hypothesis is investigated from the viewpoint of thermal stability for the first time, using a large protein thermodynamics database. The positions of amino acids belonging to stabilization centers are correlated with available experimental thermodynamic data on protein thermal stability. Our analysis suggests that stabilization centers, especially solvent exposed ones, do contribute to the thermal stabilizationmore » of proteins. - Highlights: • Stabilization centers contribute to thermal stabilization of protein structures. • Stabilization center content correlates with melting temperature of proteins. • Exposed stabilization center content correlates with stability even in hyperthermophiles. • Stability changing mutations are frequently found at stabilization centers.« less

Differential geometry based solvation model I: Eulerian formulation

NASA Astrophysics Data System (ADS)

Chen, Zhan; Baker, Nathan A.; Wei, G. W.

2010-11-01

This paper presents a differential geometry based model for the analysis and computation of the equilibrium property of solvation. Differential geometry theory of surfaces is utilized to define and construct smooth interfaces with good stability and differentiability for use in characterizing the solvent-solute boundaries and in generating continuous dielectric functions across the computational domain. A total free energy functional is constructed to couple polar and nonpolar contributions to the solvation process. Geometric measure theory is employed to rigorously convert a Lagrangian formulation of the surface energy into an Eulerian formulation so as to bring all energy terms into an equal footing. By optimizing the total free energy functional, we derive coupled generalized Poisson-Boltzmann equation (GPBE) and generalized geometric flow equation (GGFE) for the electrostatic potential and the construction of realistic solvent-solute boundaries, respectively. By solving the coupled GPBE and GGFE, we obtain the electrostatic potential, the solvent-solute boundary profile, and the smooth dielectric function, and thereby improve the accuracy and stability of implicit solvation calculations. We also design efficient second-order numerical schemes for the solution of the GPBE and GGFE. Matrix resulted from the discretization of the GPBE is accelerated with appropriate preconditioners. An alternative direct implicit (ADI) scheme is designed to improve the stability of solving the GGFE. Two iterative approaches are designed to solve the coupled system of nonlinear partial differential equations. Extensive numerical experiments are designed to validate the present theoretical model, test computational methods, and optimize numerical algorithms. Example solvation analysis of both small compounds and proteins are carried out to further demonstrate the accuracy, stability, efficiency and robustness of the present new model and numerical approaches. Comparison is given to both experimental and theoretical results in the literature.

Differential geometry based solvation model I: Eulerian formulation

PubMed Central

Chen, Zhan; Baker, Nathan A.; Wei, G. W.

2010-01-01

This paper presents a differential geometry based model for the analysis and computation of the equilibrium property of solvation. Differential geometry theory of surfaces is utilized to define and construct smooth interfaces with good stability and differentiability for use in characterizing the solvent-solute boundaries and in generating continuous dielectric functions across the computational domain. A total free energy functional is constructed to couple polar and nonpolar contributions to the salvation process. Geometric measure theory is employed to rigorously convert a Lagrangian formulation of the surface energy into an Eulerian formulation so as to bring all energy terms into an equal footing. By minimizing the total free energy functional, we derive coupled generalized Poisson-Boltzmann equation (GPBE) and generalized geometric flow equation (GGFE) for the electrostatic potential and the construction of realistic solvent-solute boundaries, respectively. By solving the coupled GPBE and GGFE, we obtain the electrostatic potential, the solvent-solute boundary profile, and the smooth dielectric function, and thereby improve the accuracy and stability of implicit solvation calculations. We also design efficient second order numerical schemes for the solution of the GPBE and GGFE. Matrix resulted from the discretization of the GPBE is accelerated with appropriate preconditioners. An alternative direct implicit (ADI) scheme is designed to improve the stability of solving the GGFE. Two iterative approaches are designed to solve the coupled system of nonlinear partial differential equations. Extensive numerical experiments are designed to validate the present theoretical model, test computational methods, and optimize numerical algorithms. Example solvation analysis of both small compounds and proteins are carried out to further demonstrate the accuracy, stability, efficiency and robustness of the present new model and numerical approaches. Comparison is given to both experimental and theoretical results in the literature. PMID:20938489

Toward a Molecular Understanding of Energetics in Li–S Batteries Using Nonaqueous Electrolytes: A High-Level Quantum Chemical Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Assary, Rajeev S.; Curtiss, Larry A.; Moore, Jeffrey S.

2014-06-05

The Li-S battery (secondary cell or redox flow) technology is a promising future alternative to the present lithium intercalation-based energy storage and, therefore, a molecular level understanding of the chemical processes and properties such as stability of intermediates, reactivity of polysulfides and reactivity towards the non-aqueous electrolytes in the Li-S batteries is of great interest. In this paper, quantum chemical methods (G4MP2, MP2, and B3LYP) were utilized to compute reduction potentials of lithium polysulfides and polysulfide molecular clusters, energetics of disproportionation and association reactions of likely intermediates, and their reactions with ether-based electrolytes. Based on the computed reaction energetics inmore » solution, a probable mechanism during the discharge process for polysulfide anions and lithium polysulfides in solution is proposed and likely intermediates such as S42-,S32-, S22-, and S31- radical were identified. Additionally, the stability and reactivity of propylene carbonate and tetraglyme solvent molecules were assessed against the above-mentioned intermediates and other reactive species by computing the reaction energetics required to initiate the solvent decomposition reactions in solution. Calculations suggest that the propylene carbonate molecule is unstable against the polysulfide anions such as S22-, S32-, and S42- (ΔH† < 0.8 eV) and highly reactive towards Li2S2 and Li2S3. Even though the tetraglyme solvent molecule exhibits increased stability towards polysulfide anions compared to propylene carbonate, this molecule too is vulnerable to nucleophilic attack from Li2S2 and Li2S3 species in solutions. Hence, a long- term stability of the ether molecules is unlikely if high concentration of these reactive intermediates present in the Li-S energy storage systems.« less

Synthesis, NMR, FT-IR, X-ray structural characterization, DFT analysis and isomerism aspects of 5-(2,6-dichlorobenzylidene)pyrimidine-2,4,6(1H,3H,5H)-trione.

PubMed

Barakat, Assem; Al-Najjar, Hany J; Al-Majid, Abdullah Mohammed; Soliman, Saied M; Mabkhot, Yahia Nasser; Shaik, Mohammed Rafi; Ghabbour, Hazem A; Fun, Hoong-Kun

2015-08-05

The synthesis and spectral characterization of the 5-(2,6-dichlorobenzylidene)pyrimidine-2,4,6(1H,3H,5H)-trione;3 was reported. The solid state molecular structure of 3 was studied using X-ray crystallography. The relative stabilities of the seven possible isomers of 3 were calculated by DFT/B3LYP method using 6-311 G(d,p) basis set. The calculated total energies and thermodynamic parameters were used to predict the relative stabilities of these isomers. The effect of solvent polarity on the relative stability of these isomers was studied at the same level of theory using PCM. It was found that the keto form, (T0), is the most stable isomer both in the gaseous state and solution. In solution, the calculated total energies of all isomers are decreased indicating that all isomers are stabilized by the solvent effect. The vibrational spectra of the most stable isomer, 3(T0) are calculated using the same level of theory and the results are compared with the experimentally measured FTIR spectra. Good correlation was obtained between the experimental and calculated vibrational frequencies (R(2)=0.9992). The electronic spectra of 3(T0) in gas phase as well as in solutions were calculated using the TD-DFT method. All the predicted electronic transitions showed very little spectral shifts and increase in the intensity of absorption due to solvent effect. Also the (1)H- and (13)C-NMR chemical shifts of the stable isomer were calculated and the results were correlated with the experimental data. Good correlations between the experimental and calculated chemical shifts were obtained. Copyright © 2015 Elsevier B.V. All rights reserved.

Molecular basis for competitive solvation of the Burkholderia cepacia lipase by sorbitol and urea.

PubMed

Oliveira, Ivan P; Martínez, Leandro

2016-08-21

Increasing the stability of proteins is important for their application in industrial processes. In the intracellular environment many small molecules, called osmolytes, contribute to protein stabilization under physical or chemical stress. Understanding the nature of the interactions of these osmolytes with proteins can help the design of solvents and mutations to increase protein stability in extracellular media. One of the most common stabilizing osmolyes is sorbitol and one of the most common chemical denaturants is urea. In this work, we use molecular dynamics simulations to obtain a detailed picture of the solvation of the Burkholderia cepacia lipase (BCL) in the presence of the protecting osmolyte sorbitol and of the urea denaturant. We show that both sorbitol and urea compete with water for interactions with the protein surface. Overall, sorbitol promotes the organization of water in the first solvation shell and displaces water from the second solvation shell, while urea causes opposite effects. These effects are, however, highly heterogeneous among residue types. For instance, the depletion of water from the first protein solvation shell by urea can be traced down essentially to the side chain of negatively charged residues. The organization of water in the first solvation shell promoted by sorbitol occurs at polar (but not charged) residues, where the urea effect is minor. By contrast, sorbitol depletes water from the second solvation shell of polar residues, while urea promotes water organization at the same distances. The interactions of urea with negatively charged residues are insensitive to the presence of sorbitol. This osmolyte removes water and urea particularly from the second solvation shell of polar and non-polar residues. In summary, we provide a comprehensive description of the diversity of protein-solvent interactions, which can guide further investigations on the stability of proteins in non-conventional media, and assist solvent and protein design.

Removal of PCB and Other Halogenated Organic Contaminants found in Ex Situ Structures

NASA Technical Reports Server (NTRS)

Quinn, Jacqueline (Inventor); Clausen, Christian (Inventor); Geiger, Cherie L. (Inventor); Coon, Christina (Inventor); Berger, Cristina M. (Inventor); Filipek, Laura B. (Inventor); Milum, Kristen M. (Inventor)

2007-01-01

Emulsified systems or a surfactant-stabilized, biodegradable water-in-solvent emulsion with bimetallic particles contained with the emulsion droplets are useful at removing PCBs from ex situ structures. The hydrophobic emulsion system draws PCBs through the solvent/surfactant membrane. Once inside the membrane, the PCBs diffuse into the bimetallic particles and undergo degradation. The PCBs continue to enter, diffuse, degrade, and biphenyl will exit the particle maintaining a concentration gradient across the membrane and maintaining a driving force of the reaction.

Removal of PCB and other halogenated organic contaminants found in ex situ structures

NASA Technical Reports Server (NTRS)

Quinn, Jacqueline (Inventor); Clausen, Christian (Inventor); Geiger, Cherie L. (Inventor); Coon, Christina (Inventor); Berger, Cristina M. (Inventor); Filipek, Laura B. (Inventor); Milum, Kristen M. (Inventor)

2007-01-01

Emulsified systems of a surfactant-stabilized, biodegradable water-in-solvent emulsion with bimetallic particles contained with the emulsion droplets are useful at removing PCBs from ex situ structures. The hydrophobic emulsion system draws PCBs through the solvent/surfactant membrane. Once inside the membrane, the PCBs diffuse into the bimetallic particles and undergo degradation. The PCBs continue to enter, diffuse, degrade, and biphenyl will exit the particle maintaining a concentration gradient across the membrane and maintaining a driving force of the reaction.

Thixotropic Low-Solvent, Non-Hap Wheel Well Cleaner

DTIC Science & Technology

1999-09-28

cleaning composition for cleaning aircraft wheel wells. The cleaning composition broadly comprises from about 0.1 to about 15% of a D- limonene composition...broadly comprises from about 0.1 to about 15% of a D- limonene composition, containing less than 0.5% of a stabilizing anti-oxidant acting as a solvent...well as effective from a cleaning 2Q ß ;s a further object of the present invention to provide a standpoint. D- limonene , a by-product of the

Long-term stability enhancement of Brillouin measurement in polymer optical fibers using amorphous fluoropolymer

NASA Astrophysics Data System (ADS)

Matsutani, Natsuki; Lee, Heeyoung; Mizuno, Yosuke; Nakamura, Kentaro

2018-01-01

For Brillouin-sensing applications, we develop a method for mitigating the Fresnel reflection at the perfluorinated-polymer-optical-fiber ends by covering them with an amorphous fluoropolymer (CYTOP, fiber core material) dissolved in a volatile solvent. Unlike the conventional method using water, even after solvent evaporation, the CYTOP layer remains, resulting in long-term Fresnel reduction. In addition, the high viscosity of the CYTOP solution is a practical advantage. The effectiveness of this method is experimentally proved by Brillouin measurement.

Removal of PCB and other halogenated organic contaminants found in ex situ structures

NASA Technical Reports Server (NTRS)

Clausen, Christian A. (Inventor); Milum, Kristen M. (Inventor); Quinn, Jacqueline W. (Inventor); Berger, Cristina M. (Inventor); Geiger, Cherie L. (Inventor); Filipek, Laura B. (Inventor); Coon, Christina (Inventor)

2009-01-01

Emulsified systems of a surfactant-stabilized, biodegradable water-in-solvent emulsion with bimetallic particles contained with the emulsion droplets are useful at removing PCBs from ex situ structures. The hydrophobic emulsion system draws PCBs through the solvent/surfactant membrane. Once inside the membrane, the PCBs diffuse into the bimetallic particles and undergo degradation. The PCBs continue to enter, diffuse, degrade, and biphenyl will exit the particle maintaining a concentration gradient across the membrane and maintaining a driving force of the reaction.

Long life lithium batteries with stabilized electrodes

DOEpatents

Amine, Khalil [Downers Grove, IL; Liu, Jun [Naperville, IL; Vissers, Donald R [Naperville, IL; Lu, Wenquan [Darien, IL

2009-03-24

The present invention relates to non-aqueous electrolytes having electrode stabilizing additives, stabilized electrodes, and electrochemical devices containing the same. Thus the present invention provides electrolytes containing an alkali metal salt, a polar aprotic solvent, and an electrode stabilizing additive. In some embodiments the additives include a substituted or unsubstituted cyclic or spirocyclic hydrocarbon containing at least one oxygen atom and at least one alkenyl or alkynyl group. When used in electrochemical devices with, e.g., lithium manganese oxide spinel electrodes or olivine or carbon-coated olivine electrodes, the new electrolytes provide batteries with improved calendar and cycle life.

Realizing Full Coverage of Stable Perovskite Film by Modified Anti-Solvent Process

NASA Astrophysics Data System (ADS)

Ji, Long; Zhang, Ting; Wang, Yafei; Zhang, Peng; Liu, Detao; Chen, Zhi; Li, Shibin

2017-05-01

Lead-free solution-processed solid-state photovoltaic devices based on formamidinium tin triiodide (FASnI3) and cesium tin triiodide (CsSnI3) perovskite semiconductor as the light harvester are reported. In this letter, we used solvent engineering and anti-solvent dripping method to fabricate perovskite films. SnCl2 was used as an inhibitor of Sn4+ in FASnI3 precursor solution. We obtained the best films under the function of toluene or chlorobenzene in anti-solvent dripping method and monitored the oxidation of FASnI3 films in air. We chose SnF2 as an additive of CsSnI3 precursor solution to prevent the oxidation of the Sn2+, improving the stability of CsSnI3. The experimental results we obtained can pave the way for lead-free tin-based perovskite solar cells (PSCs).

Solvent screening for a hard-to-dissolve molecular crystal.

PubMed

Maiti, A; Pagoria, P F; Gash, A E; Han, T Y; Orme, C A; Gee, R H; Fried, L E

2008-09-01

Materials with a high-degree of inter- and intra-molecular hydrogen bonding generally have limited solubility in conventional organic solvents. This presents a problem for the dissolution, manipulation and purification of these materials. Using a state-of-the-art density-functional-theory based quantum chemical solvation model we systematically evaluated solvents for a known hydrogen-bonded molecular crystal. This, coupled with direct solubility measurements, uncovered a class of ionic liquids involving fluoride anions that possess more than two orders of magnitude higher solvation power as compared with the best conventional solvents. The crystal structure of one such ionic liquid, determined by X-ray diffraction spectroscopy, indicates that F- ions are stabilized through H-bonded chains with water. The presence of coordinating water in such ionic liquids seems to facilitate the dissolution process by keeping the chemical activity of the F- ions in check.

Feasibility study for a secondary Na/S battery

NASA Technical Reports Server (NTRS)

Abraham, K. M.; Schiff, R.; Brummer, S. B.

1979-01-01

The feasibility of a moderate temperature Na battery was studied. This battery is to operate at a temperature in the range of 100-150 C. Two kinds of cathode were investigated: (1) a soluble S cathode consisting of a solution of Na2Sn in an organic solvent and (2) an insoluble S cathode consisting of a transition metal dichalcogenide in contact with a Na(+)ion conducting electrolyte. Four amide solvents, dimethyl acetamide, diethyl acetamide, N-methyl acetamide and acetamide, were investigated as possible solvents for the soluble S cathode. Results of stability and electrochemical studies using these solvents are presented. The dialkyl substituted amides were found to be superior. Although the alcohol 1,3-cyclohexanediol was found to be stable in the presence of Na2Sn at 130 C, its Na2Sn solutions did not appear to have suitable electrochemical properties.

Spongy Gels by a Top-Down Approach from Polymer Fibrous Sponges.

PubMed

Jiang, Shaohua; Duan, Gaigai; Kuhn, Ute; Mörl, Michaela; Altstädt, Volker; Yarin, Alexander L; Greiner, Andreas

2017-03-13

Ultralight cellular sponges offer a unique set of properties. We show here that solvent uptake by these sponges results in new gel-like materials, which we term spongy gels. The appearance of the spongy gels is very similar to classic organogels. Usually, organogels are formed by a bottom-up process. In contrast, the spongy gels are formed by a top-down approach that offers numerous advantages for the design of their properties, reproducibility, and stability. The sponges themselves represent the scaffold of a gel that could be filled with a solvent, and thereby form a mechanically stable gel-like material. The spongy gels are independent of a time-consuming or otherwise demanding in situ scaffold formation. As solvent evaporation from gels is a concern for various applications, we also studied solvent evaporation of wetting and non-wetting liquids dispersed in the sponge. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Structure and dynamics of human vimentin intermediate filament dimer and tetramer in explicit and implicit solvent models.

PubMed

Qin, Zhao; Buehler, Markus J

2011-01-01

Intermediate filaments, in addition to microtubules and microfilaments, are one of the three major components of the cytoskeleton in eukaryotic cells, and play an important role in mechanotransduction as well as in providing mechanical stability to cells at large stretch. The molecular structures, mechanical and dynamical properties of the intermediate filament basic building blocks, the dimer and the tetramer, however, have remained elusive due to persistent experimental challenges owing to the large size and fibrillar geometry of this protein. We have recently reported an atomistic-level model of the human vimentin dimer and tetramer, obtained through a bottom-up approach based on structural optimization via molecular simulation based on an implicit solvent model (Qin et al. in PLoS ONE 2009 4(10):e7294, 9). Here we present extensive simulations and structural analyses of the model based on ultra large-scale atomistic-level simulations in an explicit solvent model, with system sizes exceeding 500,000 atoms and simulations carried out at 20 ns time-scales. We report a detailed comparison of the structural and dynamical behavior of this large biomolecular model with implicit and explicit solvent models. Our simulations confirm the stability of the molecular model and provide insight into the dynamical properties of the dimer and tetramer. Specifically, our simulations reveal a heterogeneous distribution of the bending stiffness along the molecular axis with the formation of rather soft and highly flexible hinge-like regions defined by non-alpha-helical linker domains. We report a comparison of Ramachandran maps and the solvent accessible surface area between implicit and explicit solvent models, and compute the persistence length of the dimer and tetramer structure of vimentin intermediate filaments for various subdomains of the protein. Our simulations provide detailed insight into the dynamical properties of the vimentin dimer and tetramer intermediate filament building blocks, which may guide the development of novel coarse-grained models of intermediate filaments, and could also help in understanding assembly mechanisms.

Role of solvent-mediated carbodiimide cross-linking in fabrication of electrospun gelatin nanofibrous membranes as ophthalmic biomaterials.

PubMed

Chou, Shih-Feng; Luo, Li-Jyuan; Lai, Jui-Yang; Ma, David Hui-Kang

2017-02-01

Due to their ability to mimic the structure of extracellular matrix, electrospun gelatin nanofibers are promising cell scaffolding materials for tissue engineering applications. However, the hydrophilic gelatin molecules usually need stabilization before use in aqueous physiological environment. Considering that biomaterials cross-linked via film immersion technique may have a more homogeneous cross-linked structure than vapor phase cross-linking, this work aims to investigate the chemical modification of electrospun gelatin nanofibrous membranes by liquid phase carbodiimide in the presence of ethanol/water co-solvents with varying ethanol concentrations ranging from 80 to 99.5vol%. The results of characterization showed that increasing water content in the binary reaction solvent system increases the extent of cross-linking of gelatin nanofibers, but simultaneously promotes the effect of biopolymer swelling and distortion in fiber mat structure. As compared to non-cross-linked counterparts, carbodiimide treated gelatin nanofibrous mats exhibited better thermal and biological stability where the shrinkage temperature and resistance to enzymatic degradation varied in response to ethanol/water solvent composition-mediated generation of cross-links. Irrespective of their cross-linking density, all studied membrane samples did not induce any responses in ocular epithelial cell cultures derived from cornea, lens, and retina. Unlike many other cross-linking agents and/or methods (e.g., excessive vapor phase cross-linking) that may pose a risk of toxicity, our study demonstrated that these nanofibrous materials are well tolerated by anterior segment tissues. These findings also indicate the safety of using ethanol/water co-solvents for chemical cross-linking of gelatin to engineer nanofibrous materials with negligible biological effects. In summary, the present results suggest the importance of solvent-mediated carbodiimide cross-linking in modulating structure-property relationship without compromising in vitro and in vivo biocompatibility of electrospun gelatin nanofibers for future ophthalmic applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Supercritical antisolvent co-precipitation of rifampicin and ethyl cellulose.

PubMed

Djerafi, Rania; Swanepoel, Andri; Crampon, Christelle; Kalombo, Lonji; Labuschagne, Philip; Badens, Elisabeth; Masmoudi, Yasmine

2017-05-01

Rifampicin-loaded submicron-sized particles were prepared through supercritical anti-solvent process using ethyl cellulose as polymeric encapsulating excipient. Ethyl acetate and a mixture of ethyl acetate/dimethyl sulfoxide (70/30 and 85/15) were used as solvents for both drug and polymeric excipient. When ethyl acetate was used, rifampicin was crystallized separately without being embedded within the ethyl cellulose matrix while by using the ethyl acetate/dimethyl sulfoxide mixture, reduced crystallinity of the active ingredient was observed and a simultaneous precipitation of ethyl cellulose and drug was achieved. The effect of solvent/CO 2 molar ratio and polymer/drug mass ratio on the co-precipitates morphology and drug loading was investigated. Using the solvent mixture, co-precipitates with particle sizes ranging between 190 and 230nm were obtained with drug loading and drug precipitation yield from respectively 8.5 to 38.5 and 42.4 to 77.2% when decreasing the ethyl cellulose/rifampicin ratio. Results show that the solvent nature and the initial drug concentrations affect morphology and drug precipitation yield of the formulations. In vitro dissolution studies revealed that the release profile of rifampicin was sustained when co-precipitation was carried out with the solvent mixture. It was demonstrated that the drug to polymer ratio influenced amorphous content of the SAS co-precipitates. Differential scanning calorimetry thermograms and infrared spectra revealed that there is neither interaction between rifampicin and the polymer nor degradation of rifampicin during co-precipitation. In addition, stability stress tests on SAS co-precipitates were carried out at 75% relative humidity and room temperature in order to evaluate their physical stability. SAS co-precipitates were X-ray amorphous and remained stable after 6months of storage. The SAS co-precipitation process using a mixture of ethyl acetate/dimethyl sulfoxide demonstrates that this strategy can be successful for controlling rifampicin delivery. Copyright © 2017 Elsevier B.V. All rights reserved.

Micron-sized columnar grains of CH3NH3PbI3 grown by solvent-vapor assisted low-temperature (75 °C) solid-state reaction: The role of non-coordinating solvent-vapor

NASA Astrophysics Data System (ADS)

Zheng, Huifeng; Liu, Yangqiao; Sun, Jing

2018-04-01

The preparation of hybrid perovskite films with large columnar grains via low-temperature solid-state reaction remains a big challenge. Conventional solvent annealing using DMF, DMSO and ethanol, etc. fails to work effectively at low temperature (<100 °C). Here, we comprehensively investigated the effects of non-coordinating solvent vapor on the properties of perovskite film, and obtained micron-sized columnar grains (with an average grain size of 1.4 μm) of CH3NH3PbI3 even at a low temperature of 75 °C when annealed with benzyl alcohol vapor. The perovskite solar cells based on benzyl-alcohol-vapor annealing (75 °C), delivered much higher photovoltaic performance, better stability and smaller hysteresis than those based on conventional thermal annealing. Additionally, a champion power conversion efficiency (PCE) of 15.1% was obtained and the average PCE reached 12.2% with a tiny deviation. Finally, the mechanism of solvent annealing with non-coordinating solvent was discussed. Moreover, we revealed that high polarity and high boiling point of the solvent used for generating vapor, was critical to grow micron-sized columnar grains at such a low temperature (75 °C). This work will contribute to understanding the mechanism of grain growth in solvent annealing and improving its facility and effectiveness.

Lipase-catalyzed synthesis of xylitol monoesters: solvent engineering approach.

PubMed

Castillo, E; Pezzotti, F; Navarro, A; López-Munguía, A

2003-05-08

A solvent engineering strategy was applied to the lipase-catalyzed synthesis of xylitol-oleic acid monoesters. The different esterification degrees for this polyhydroxylated molecule were examined in different organic solvent mixtures. In this context, conditions for high selectivity towards monooleoyl xylitol synthesis were enhanced from 6 mol% in pure n-hexane to 73 mol% in 2-methyl-2-propanol/dimethylsulfoxide (DMSO) 80:20 (v/v). On the contrary, the highest production of di- and trioleoyl xylitol, corresponding to 94 mol%, was achieved in n-hexane. Changes in polarity of the reaction medium and in the molecular interactions between solvents and reactants were correlated with the activity coefficients of products. Based on experimental results and calculated thermodynamic activities, the effect of different binary mixtures of solvents on the selective production of xylitol esters is reported. From this analysis, it is concluded that in the more polar conditions (100% dimethylsulfoxide (DMSO)), the synthesis of xylitol monoesters is favored. However, these conditions are unfavorable in terms of enzyme stability. As an alternative, binary mixtures of solvents were proposed. Each mixture of solvents was characterized in terms of the quantitative polarity parameter E(T)(30) and related with the activity coefficients of xylitol esters. To our knowledge, the characterization of solvent mixtures in terms of this polarity parameter and its relationship with the selectivity of the process has not been previously reported.

Low operational stability of enzymes in dry organic solvents: changes in the active site might affect catalysis.

PubMed

Bansal, Vibha; Delgado, Yamixa; Legault, Marc; Barletta, Gabriel

2012-02-14

The potential of enzyme catalysis in organic solvents for synthetic applications has been overshadowed by the fact that their catalytic properties are affected by organic solvents. In addition, it has recently been shown that an enzyme's initial activity diminishes considerably after prolonged exposure to organic media. Studies geared towards understanding this last drawback have yielded unclear results. In the present work we decided to use electron paramagnetic resonance spectroscopy (EPR) to study the motion of an active site spin label (a nitroxide free radical) during 96 h of exposure of the serine protease subtilisin Carlsberg to four different organic solvents. Our EPR data shows a typical two component spectra that was quantified by the ratio of the anisotropic and isotropic signals. The isotropic component, associated with a mobile nitroxide free radical, increases during prolonged exposure to all solvents used in the study. The maximum increase (of 43%) was observed in 1,4-dioxane. Based on these and previous studies we suggest that prolonged exposure of the enzyme to these solvents provokes a cascade of events that could induce substrates to adopt different binding conformations. This is the first EPR study of the motion of an active-site spin label during prolonged exposure of an enzyme to organic solvents ever reported.

Fabrication of Janus particles composed of poly (lactic-co-glycolic) acid and hard fat using a solvent evaporation method.

PubMed

Matsumoto, Akihiro; Murao, Satoshi; Matsumoto, Michiko; Watanabe, Chie; Murakami, Masahiro

The feasibility of fabricating Janus particles based on phase separation between a hard fat and a biocompatible polymer was investigated. The solvent evaporation method used involved preparing an oil-in-water (o/w) emulsion with a mixture of poly (lactic-co-glycolic) acid (PLGA), hard fat, and an organic solvent as the oil phase and a polyvinyl alcohol aqueous solution as the water phase. The Janus particles were formed when the solvent was evaporated to obtain certain concentrations of PLGA and hard fat in the oil phase, at which phase separation was estimated to occur based on the phase diagram analysis. The hard fat hemisphere was proven to be the oil phase using a lipophilic dye Oil Red O. When the solvent evaporation process was performed maintaining a specific volume during the emulsification process; Janus particles were formed within 1.5 h. However, the formed Janus particles were destroyed by stirring for over 6 h. In contrast, a few Janus particles were formed when enough water to dissolve the oil phase solvent was added to the emulsion immediately after the emulsification process. The optimized volume of the solvent evaporation medium dominantly formed Janus particles and maintained the conformation for over 6 h with stirring. These results indicate that the formation and stability of Janus particles depend on the rate of solvent evaporation. Therefore, optimization of the solvent evaporation rate is critical to obtaining stable PLGA and hard fat Janus particles.

Synthesis of polyaniline (PANI) and functionalized polyaniline (F-PANI) nanoparticles with controlled size by solvent displacement method. Application in fluorescence detection and bacteria killing by photothermal effect.

PubMed

Abel, Silvestre Bongiovanni; Yslas, Edith I; Rivarola, Claudia R; Barbero, Cesar A

2018-03-23

Polyaniline nanoparticles (PANI-NPs) were easily obtained applying the solvent displacement method by using N-methylpyrrolidone (NMP) as good solvent and water as poor solvent. Different polymers such as polyvinylpyrrolidone (PVP), chondroitin sulfate (ChS), polyvinyl alcohol (PVA), and polyacrylic acid (PAA) were used as stabilizers. Dynamic light scattering and scanning electron microscopy corroborated the size and morphology of the formed NPs. It was demonstrated that the size of nanoparticles could be controlled by setting the concentration of PANI in NMP, the NMP to water ratio, and the stabilizer's nature. The functionalization and fluorescence of NPs were checked by spectroscopic techniques. Since polyaniline show only weak intrinsic luminescence, fluorescent groups were linked to the polyaniline chains prior to the nanoparticle formation using a linker. Polyaniline chains were functionalized by nucleophilic addition of cysteamine trough the thiol group thereby incorporating pendant primary aliphatic amine groups to the polyaniline backbone. Then, dansyl chloride (DNS-Cl), which could act as an extrinsic chromophore, was conjugated to the amine pendant groups. Later, the functionalized polyaniline was used to produce nanoparticles by solvent displacement. The optical and functional properties of fluorescent nanoparticles (F-PANI-NPs) were determined. F-PANI-NPs in the conductive state (pH < 4) are able to absorb near infrared radiation (NIR) creating a photothermal effect in an aqueous medium. Thus, multifunctional nanoparticles are obtained. The application of NIR on a F-PANI-NPs dispersion in contact with Pseudomonas aeruginosa causes bacterial death. Therefore, the F-PANI-NPs could be tracked and applied to inhibit different diseases caused by pathogenic microorganisms and resistant to antibiotics as well as a new disinfection method to surgical materials.

Investigation of solvent polarity effect on molecular structure and vibrational spectrum of xanthine with the aid of quantum chemical computations.

PubMed

Polat, Turgay; Yıldırım, Gurcan

2014-04-05

The main scope of this study is to determine the effects of 8 solvents on the geometric structure and vibrational spectra of the title compound, xanthine, by means of the DFT/B3LYP level of theory in the combination with the polarizable conductor continuum model (CPCM) for the first time. After determination of the most-steady state (favored structure) of the xanthine molecule, the role of the solvent polarity on the SCF energy (for the molecule stability), atomic charges (for charge distribution) and dipole moments (for molecular charge transfer) belonging to tautomer is discussed in detail. The results obtained indicate not only the presence of the hydrogen bonding and strong intra-molecular charge transfer (ICT) in the compound but the increment of the molecule stability with the solvent polarity, as well. Moreover, it is noted that the optimized geometric parameters and the theoretical vibrational frequencies are in good agreement with the available experimental results found in the literature. In fact, the correlations between the experimental and theoretical findings for the molecular structures improve with the enhancement of the solvent polarity. At the same time, the dimer forms of the xanthine compound are simulated to describe the effect of intermolecular hydrogen bonding on the molecular geometry and vibrational frequencies. It is found that the CO and NH stretching vibrations shift regularly to lower frequency value with higher IR intensity as the dielectric medium enhances systematically due to the intermolecular NH⋯O hydrogen bonds. Theoretical vibrational spectra are also assigned based on the potential energy distribution (PED) using the VEDA 4 program. Copyright © 2013 Elsevier B.V. All rights reserved.

On the chemical stabilities of ionic liquids.

PubMed

Sowmiah, Subbiah; Srinivasadesikan, Venkatesan; Tseng, Ming-Chung; Chu, Yen-Ho

2009-09-25

Ionic liquids are novel solvents of interest as greener alternatives to conventional organic solvents aimed at facilitating sustainable chemistry. As a consequence of their unusual physical properties, reusability, and eco-friendly nature, ionic liquids have attracted the attention of organic chemists. Numerous reports have revealed that many catalysts and reagents were supported in the ionic liquid phase, resulting in enhanced reactivity and selectivity in various important reaction transformations. However, synthetic chemists cannot ignore the stability data and intermolecular interactions, or even reactions that are directly applicable to organic reactions in ionic liquids. It is becoming evident from the increasing number of reports on use of ionic liquids as solvents, catalysts, and reagents in organic synthesis that they are not totally inert under many reaction conditions. While in some cases, their unexpected reactivity has proven fortuitously advantageous in others is has been a problem, it is imperative that when selecting an ionic liquid for a particular synthetic application, attention be paid to its compatibility with the reaction conditions. Even though, more than 200 room temperature ionic liquids are known, only a few reports have commented their effects on reaction mechanisms or rate/stability. Therefore, rather than attempting to give a comprehensive overview of ionic liquid chemistry, this review focuses on the non-innocent nature of ionic liquids, with a decided emphasis to clearly illuminate the ability of ionic liquids to affect the mechanistic aspects of some organic reactions thereby affecting and promoting the yield and selectivity.

Self-assembly of resins and asphaltenes facilitates asphaltene dissolution by an organic acid.

PubMed

Hashmi, Sara M; Firoozabadi, Abbas

2013-03-15

Asphaltene precipitation occurs in petroleum fluids under certain unfavorable conditions, but can be controlled by tuning composition. Aromatic solvents in large quantities can prevent precipitation entirely and can dissolve already precipitated asphaltenes. Some polymeric surfactants can dissolve asphaltenes when added at much lower concentrations than required by aromatic solvents. Other dispersants can truncate asphaltene precipitation at the sub-micron length scale, creating stable colloidal asphaltene dispersants. One particular asphaltene dispersant, dodecylbenzene sulfonic acid (DBSA), can do both, namely: (1) stabilize asphaltene colloids and (2) dissolve asphaltenes to the molecular scale. Acid-base interactions are responsible for the efficiency of DBSA in dissolving asphaltenes compared to aromatic solvents. However, many details remain to be quantified regarding the action of DBSA on asphaltenes, including the effect of petroleum fluid composition. For instance, resins, naturally amphiphilic components of petroleum fluids, can associate with asphaltenes, but it is unknown whether they cooperate or compete with DBSA. Similarly, the presence of metals is known to hinder asphaltene dissolution by DBSA, but its effect on colloidal asphaltene stabilization has yet to be considered. We introduce the concepts of cooperativity and competition between petroleum fluid components and DBSA in stabilizing and dissolving asphaltenes. Notably, we find that resins cooperatively interact with DBSA in dissolving asphaltenes. We use UV-vis spectroscopy to investigate the interactions responsible for the phase transitions between unstable suspensions, stable suspensions, and molecular solutions of asphaltenes. Copyright © 2012 Elsevier Inc. All rights reserved.

Synthesis of CO2/N2-triggered reversible stability-controllable poly(2-(diethylamino)ethyl methacrylate)-grafted-AuNPs by surface-initiated atom transfer radical polymerization.

PubMed

Kitayama, Yukiya; Takeuchi, Toshifumi

2014-10-28

CO2/N2-triggered stability-controllable gold nanoparticles (AuNPs) grafted with poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) layers (PDEAEMA-g-AuNPs) were synthesized by the surface-initiated atom transfer radical polymerization of DEAEMA with AuNPs bearing the bis[2-(2-bromoisobutyryloxy)undecyl] layer (grafting from method). Extension of the PDEAEMA chain length increased the stability of the PDEAEMA-g-AuNPs in CO2-bubbled water because of the electrosteric repulsion of the protonated PDEAEMA layer. The chain-length-dependent stability of PDEAEMA-g-AuNPs was confirmed by DLS and UV-vis spectra by using the localized surface plasmon resonance property of the AuNPs, where the extinction wavelength was shifted toward shorter wavelength with increasing PDEAEMA chain length. The reversible stability change with the gas stimuli of CO2/N2 was also successfully demonstrated. Finally, the transfer across the immiscible interface between water and organic solvent was successfully demonstrated by N2-triggered insolubilization of PDEAEMA layer on AuNPs in the aqueous phase, leading to the successful collection of AuNPs using organic solvent from the aqueous phase. Our "grafting from" method of reversible stability-controllable AuNPs can be applied to develop advanced materials such as reusable optical AuNP-based nanosensors because the molecular recognition layer can be constructed by two-step polymerization.

Molecular Level Structure and Dynamics of Electrolytes Using 17O Nuclear Magnetic Resonance Spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murugesan, Vijayakumar; Han, Kee Sung; Hu, Jianzhi

2017-03-19

Electrolytes help harness the energy from electrochemical processes by serving as solvents and transport media for redox-active ions. Molecular-level interactions between ionic solutes and solvent molecules – commonly referred to as solvation phenomena – give rise to many functional properties of electrolytes such as ionic conductivity, viscosity, and stability. It is critical to understand the evolution of solvation phenomena as a function of competing counterions and solvent mixtures to predict and design the optimal electrolyte for a target application. Probing oxygen environments is of great interest as oxygens are located at strategic molecular sites in battery solvents and are directlymore » involved in inter- and intramolecular solvation interactions. NMR signals from 17O nuclei in battery electrolytes offer nondestructive bulk measurements of isotropic shielding, electric field gradient tensors, and transverse and longitudinal relaxation rates, which are excellent means for probing structure, bonding, and dynamics of both solute and solvent molecules. This article describes the use of 17O NMR spectroscopy in probing the solvation structures of various electrolyte systems ranging from transition metal ions in aqueous solution to lithium cations in organic solvent mixtures.« less

Chemical probes and engineered constructs reveal a detailed unfolding mechanism for a solvent-free multi-domain protein

PubMed Central

Eschweiler, Joseph D.; Martini, Rachel M.; Ruotolo, Brandon T.

2017-01-01

Despite the growing application of gas-phase measurements in structural biology and drug discovery, the factors that govern protein stabilities and structures in a solvent-free environment are still poorly understood. Here, we examine the solvent-free unfolding pathway for a group of homologous serum albumins. Utilizing a combination of chemical probes and non-covalent reconstructions, we draw new specific conclusions regarding the unfolding of albumins in the gas-phase, as well as more-general inferences regarding the sensitivity of collision induced unfolding to changes in protein primary and tertiary structure. Our findings suggest that the general unfolding pathway of low charge state albumin ions is largely unaffected by changes in primary structure; however, the stabilities of intermediates along these pathways vary widely as sequences diverge. Additionally, we find that human albumin follows a domain associated unfolding pathway, and are able to assign each unfolded form observed in our gas-phase dataset to the disruption of specific domains within the protein. The totality of our data informs the first detailed mechanism for multi-domain protein unfolding in the gas phase, and highlights key similarities and differences from the known the solution-phase pathway. PMID:27959526

Antimicrobial nanocapsules: from new solvent-free process to in vitro efficiency

PubMed Central

Steelandt, Julie; Salmon, Damien; Gilbert, Elodie; Almouazen, Eyad; Renaud, François NR; Roussel, Laurène; Haftek, Marek; Pirot, Fabrice

2014-01-01

Skin and mucosal infections constitute recurrent pathologies resulting from either inappropriate antiseptic procedures or a lack of efficacy of antimicrobial products. In this field, nanomaterials offer interesting antimicrobial properties (eg, long-lasting activity; intracellular and tissular penetration) as compared to conventional products. The aim of this work was to produce, by a new solvent-free process, a stable and easily freeze-dryable chlorhexidine-loaded polymeric nanocapsule (CHX-NC) suspension, and then to assess the antimicrobial properties of nanomaterials. The relevance of the process and the physicochemical properties of the CHX-NCs were examined by the assessment of encapsulation efficiency, stability of the nanomaterial suspension after 1 month of storage, and by analysis of granulometry and surface electric charge of nanocapsules. In vitro antimicrobial activities of the CHX-NCs and chlorhexidine digluconate solution were compared by measuring the inhibition diameters of two bacterial strains (Escherichia coli and Staphylococcus aureus) and one fungal strain (Candida albicans) cultured onto appropriate media. Based on the findings of this study, we report a new solvent-free process for the production of nanomaterials exhibiting antimicrobial activity, suitable stability, and easily incorporable as a new ingredient in various pharmaceutical products. PMID:25278751

Enzyme stability, thermodynamics and secondary structures of α-amylase as probed by the CD spectroscopy.

PubMed

Kikani, B A; Singh, S P

2015-11-01

An amylase of a thermophilic bacterium, Bacillus sp. TSSC-3 (GenBank Number, EU710557) isolated from the Tulsi Shyam hot spring reservoir (Gujarat, India) was purified to the homogeneity in a single step on phenyl sepharose 6FF. The molecular weight of the enzyme was 25kD, while the temperature and pH optima for the enzyme catalysis were 80°C and 7, respectively. The purified enzyme was highly thermostable with broad pH stability and displayed remarkable resistance against surfactants, chelators, urea, guanidine HCl and various solvents as well. The stability and changes in the secondary structure of the enzyme under various extreme conditions were determined by the circular dichroism (CD) spectroscopy. The stability trends and the changes in the α-helices and β-sheets were analyzed by Mean Residual Ellipticity (MRE) and K2D3. The CD data confirmed the structural stability of the enzyme under various harsh conditions, yet it indicated reduced α-helix content and increased β-sheets upon denaturation. The thermodynamic parameters; deactivation rate constant, half-life, changes in entropy, enthalpy, activation energy and Gibb's free energy indicated that the enzyme-substrate reactions were highly stable. The overall profile of the enzyme: high thermostability, alkalitolerance, calcium independent nature, dextrose equivalent values and resistance against chemical denaturants, solvents and surfactants suggest its commercial applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Water-in-oil Pickering emulsions stabilized by stearoylated microcrystalline cellulose.

PubMed

Pang, Bo; Liu, Huan; Liu, Peiwen; Peng, Xinwen; Zhang, Kai

2018-03-01

Hydrophobic particles with static water contact angles larger than 90° are more like to stabilize W/O Pickering emulsions. In particular, high internal phase Pickering emulsions (HIPEs) are of great interest for diverse applications. However, W/O HIPEs have rarely been realized using sustainable biopolymers. Herein, we used stearoylated microcrystalline cellulose (SMCC) to stabilize W/O Pickering emulsions and especially, W/O HIPEs. Moreover, these W/O HIPEs can be further used as platforms for the preparation of porous materials, such as porous foams. Stearoylated microcrystalline cellulose (SMCC) was prepared by modifying MCC with stearoyl chloride under heterogeneous conditions. Using SMCC as emulsifiers, W/O medium and high internal phase Pickering emulsions (MIPEs and HIPEs) with various organic solvents as continuous phases were prepared using one-step and two-step methods, respectively. Polystyrene (PS) foams were prepared after polymerization of oil phase using HIPEs as templates and their oil/water separation capacity were studied. SMCC could efficiently stabilize W/O Pickering emulsions and HIPEs could only be prepared via the two-step method. The internal phase volume fraction of the SMCC-stabilized HIPEs reached as high as 89%. Diverse internal phase volume fractions led to distinct inner structures of foams with closed or open cells. These macroporous polystyrene (PS) foams demonstrated great potential for the effective absorption of organic solvents from underwater. Copyright © 2017 Elsevier Inc. All rights reserved.

Temperature Dependence and Energetics of Single Ions at the Aqueous Liquid-Vapor Interface

PubMed Central

Ou, Shuching; Patel, Sandeep

2014-01-01

We investigate temperature-dependence of free energetics with two single halide anions, I− and Cl−, crossing the aqueous liquid-vapor interface through molecular dynamics simulations. The result shows that I− has a modest surface stability of 0.5 kcal/mol at 300 K and the stability decreases as the temperature increases, indicating the surface adsorption process for the anion is entropically disfavored. In contrast, Cl− shows no such surface state at all temperatures. Decomposition of free energetics reveals that water-water interactions provide a favorable enthalpic contribution, while the desolvation of ion induces an increase in free energy. Calculations of surface fluctuations demonstrate that I− generates significantly greater interfacial fluctuations compared to Cl−. The fluctuation is attributed to the malleability of the solvation shells, which allows for more long-ranged perturbations and solvent density redistribution induced by I− as the anion approaches the liquid-vapor interface. The increase in temperature of the solvent enhances the inherent thermally-excited fluctuations and consequently reduces the relative contribution from anion to surface fluctuations, which is consistent with the decrease in surface-stability of I−. Our results indicate a strong correlation with induced interfacial fluctuations and anion surface stability; moreover, resulting temperature dependent behavior of induced fluctuations suggests the possibility of a critical level of induced fluctuations associated with surface stability. PMID:23537166

Development of a process for the extraction of {sup 137}Cs from acidic HLLW based on crown-calix extractant use of di-alkylamide modifier

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alexova, J.; Sirova, M.; Rais, J.

2008-07-01

Within the framework of the ARTIST project of total fuel retreatment with ecological mixtures of solvents and extractants containing only C, H, O, and N atoms, a process segment of extraction of {sup 137}Cs from acidic stream was developed. The process with 25,27-Bis(1-octyloxy)calix[4]arene-crown- 6, DOC[4]C6, dissolved at its 0.01 M concentration in a mixture of 90 vol % 1-octanol and 10% dihexyl octanamide, DHOA was proposed as a viable variant due to its good multicycle performance, even with irradiated solvent, and due to the good chemical stability of the chosen combination of solvent mixture. (authors)

Lithium-Air and ionic Liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kellar, Michael

2015-09-01

The final portion of this project was accomplished at Sandia National Labs, Livermore, with the overall goal being to optimize lithium-air cells with an ionic liquid electrolyte. Both of these are potential future routes for lithium-ion technology. Lithiumair presents the advantage of higher gravimetric energy density, and ionic liquids present the advantage of greater hydrophobicity and much lower volatility, along with a larger window of electrochemical stability. Ionic liquids however have several drawbacks for the battery industry. Currently they are not as cost effective as many organic solvents. Additionally, because of the added viscosity of ionic interactions compared to themore » typical dipole interactions of a solvent, the ionic conductivity is lower than for common organic solvents.« less

Analyzing the molecular basis of enzyme stability in ethanol/water mixtures using molecular dynamics simulations.

PubMed

Lousa, Diana; Baptista, António M; Soares, Cláudio M

2012-02-27

One of the drawbacks of nonaqueous enzymology is the fact that enzymes tend to be less stable in organic solvents than in water. There are, however, some enzymes that display very high stabilities in nonaqueous media. In order to take full advantage of the use of nonaqueous solvents in enzyme catalysis, it is essential to elucidate the molecular basis of enzyme stability in these media. Toward this end, we performed μs-long molecular dynamics simulations using two homologous proteases, pseudolysin, and thermolysin, which are known to have considerably different stabilities in solutions containing ethanol. The analysis of the simulations indicates that pseudolysin is more stable than thermolysin in ethanol/water mixtures and that the disulfide bridge between C30 and C58 is important for the stability of the former enzyme, which is consistent with previous experimental observations. Our results indicate that thermolysin has a higher tendency to interact with ethanol molecules (especially through van der Waals contacts) than pseudolysin, which can lead to the disruption of intraprotein hydrophobic interactions and ultimately result in protein unfolding. In the absence of the C30-C58 disulfide bridge, pseudolysin undergoes larger conformational changes, becoming more open and more permeable to ethanol molecules which accumulate in its interior and form hydrophobic interactions with the enzyme, destroying its structure. Our observations are not only in good agreement with several previous experimental findings on the stability of the enzymes studied in ethanol/water mixtures but also give an insight on the molecular determinants of this stability. Our findings may, therefore, be useful in the rational development of enzymes with increased stability in these media.

Amino Acid Side Chain Interactions in the Presence of Salts

PubMed Central

Hassan, Sergio A.

2005-01-01

The effects of salt on the intermolecular interactions between polar/charged amino acids are investigated through molecular dynamics simulations. The mean forces and associated potentials are calculated for NaCl salt in the 0–2 M concentration range at 298 K. It is found that the addition of salt may stabilize or destabilize the interactions, depending on the nature of the interacting molecules. The degree of (de)stabilization is quantified, and the origin of the salt-dependent modulation is discussed based upon an analysis of solvent density profiles. To gain insight into the molecular origin of the salt modulation, spatial distribution functions (sdf’s) are calculated, revealing a high degree of solvent structuredness in all cases. The peaks in the sdf’s are consistent with long-range hydrogen-bonding networks connecting the solute hydrophilic groups, and that contribute to their intermolecular solvent-induced forces. The restructuring of water around the solutes as they dissociate from close contact is analyzed. This analysis offers clues on how the solvent structure modulates the effective intermolecular interactions in complex solutes. This modulation results from a critical balance between bulk electrostatic forces and those exerted by (i) the water molecules in the structured region between the monomers, which is disrupted by ions that transiently enter the hydration shells, and (ii) the ions in the hydration shells in direct interactions with the solutes. The implications of these findings in protein/ligand (noncovalent) association/dissociation mechanisms are briefly discussed. PMID:16479276

Molecular simulation of CO chemisorption on Co(0001) in presence of supercritical fluid solvent: A potential of mean force study

NASA Astrophysics Data System (ADS)

Asiaee, Alireza; Benjamin, Kenneth M.

2016-08-01

For several decades, heterogeneous catalytic processes have been improved through utilizing supercritical fluids (SCFs) as solvents. While numerous experimental studies have been established across a range of chemistries, such as oxidation, pyrolysis, amination, and Fischer-Tropsch synthesis, still there is little fundamental, molecular-level information regarding the role of the SCF on elementary heterogeneous catalytic steps. In this study, the influence of hexane solvent on the adsorption of carbon monoxide on Co(0001), as the first step in the reaction mechanism of many processes involving syngas conversion, is probed. Simulations are performed at various bulk hexane densities, ranging from ideal gas conditions (no SCF hexane) to various near- and super-critical hexane densities. For this purpose, both density functional theory and molecular dynamics simulations are employed to determine the adsorption energy and free energy change during CO chemisorption. Potential of mean force calculations, utilizing umbrella sampling and the weighted histogram analysis method, provide the first commentary on SCF solvent effects on the energetic aspects of the chemisorption process. Simulation results indicate an enhanced stability of CO adsorption on the catalyst surface in the presence of supercritical hexane within the reduced pressure range of 1.0-1.5 at a constant temperature of 523 K. Furthermore, it is shown that the maximum stability of CO in the adsorbed state as a function of supercritical hexane density at 523 K nearly coincides with the maximum isothermal compressibility of bulk hexane at this temperature.

EFFECT OF DEUTERIUM OXIDE ON LOCAL ANESTHETIC ACTIVITY OF PROCAINE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Susina, S.V.; Hiter, F.D.; Siegel, F.P.

1962-12-01

Since it appears that D/sub 2/O is toxic in animals only when the concentration in the body fluids reaches high levels (> 20%), and since D/sub 2/O resembles the common solvent protium oxide more closely than any other, possible pharmaceutical applications of this solvent were explored. In studies in mice, D/ sub 2/O was used as a solvent for procaine and the effect on the stability and local anesthetic activity was noted. The ED/sub 50/ was determined by the method using corneal sensitivity, and comparison was made with procaine solutions in H/ sub 2/O. In H/sub 2/O the ED/sub 50/more » was 1.8% while in D/sub 2/O it was 1.0%. The LD/sub 50/was determined by intraperitoneal injection in mice. There appeared to be no significant difference in the toxicity of procaine in either solvent. Stability studies indicate that procaine is more stable in D/sub 2/O than H/sub 2/O at apparent pH values of 8.0, 8.5, and 9.0. Hence, the increased local anesthetic activity of procaine in D/sub 2/O may be accounted for by the fact that procaine free base is more stable in D/sub 2/O solutions, or that at the same apparent pH a D/sub 2/O solution of procaine will contain more free base than in the corresponding aqueous solution. (H.H.D.)« less

Conformational analysis of some 4‧-substituted 2-(phenylselanyl)- 2-(methoxy)- acetophenones

NASA Astrophysics Data System (ADS)

Traesel, Henrique J.; Olivato, Paulo R.; Valença, J.; Rodrigues, Daniel N. S.; Zukerman-Schpector, Julio; Colle, Maurizio Dal

2018-04-01

A conformational study of some 4‧-substituited 2-(phenylselanyl)-2-(methoxy)-acetophenones (OMe 1, H 2, and Cl 3) was performed using IR carbonyl stretching band analysis supported by NBO and PCM calculations at the B3LYP/6-31 + G (d,p) level for 1-3 and using X-ray diffraction for 1 and 2. The computational results indicated the existence of three stable conformers for the series (c2, c3, and c1 in order of decreasing stability), whose relative abundance changes with solvent permittivity. The experimental trend observed for the components of the triplet carbonyl band in all solvents matches well with computational results and thus allows for their assignment to distinct conformers. The relative population of the c1 conformer increases in more polar solvents, becoming the most stable conformer in the highest permittivity solvent, acetonitrile, as indicated by IR spectra and PCM calculations. These findings are related to the quasi parallel geometry assumed by the Cδ+ = Oδ- and Cδ+-Oδ- dipoles, which favour stronger solvation. NBO analysis shows that the sum of the energies (ΣE) of the relevant orbital interactions stabilizes the c3 conformer of 1-3 slightly, likely due to the minor contribution of the LPO5→σ*C3sbnd Se10 interaction. However, only the c1 conformer is significantly destabilized by the Oδ-(1)CO … Oδ-(5)OMe short contact electrostatic repulsion, which is also responsible for its highest νCO frequency. In addition, the LPO5→ σ*C2sbnd C3 orbital interaction accounts for the lowest νCO frequency of c3 conformer. X-ray single crystal analysis of compounds 1 and 2 indicates that in the solid state they assume the least stable c1 conformation found in the gas phase. Molecules of these compounds are stabilized in the crystal through a series of Csbnd H⋯O and Csbnd H … π intermolecular interactions.

Selection of an anti-solvent for efficient and stable cesium-containing triple cation planar perovskite solar cells.

PubMed

Xiao, Meng; Zhao, Li; Geng, Min; Li, Yanyan; Dong, Binghai; Xu, Zuxun; Wan, Li; Li, Wenlu; Wang, Shimin

2018-06-19

The perovskite layer is a crucial component influencing high-performance perovskite solar cells (PSCs). In the one-step solution method, anti-solvents are important for obtaining smooth and uniform perovskite active layers. This work explored the effect of various anti-solvents on the preparation of triple cation perovskite active layers. In general, anti-solvents with low dielectric constants, low polarity, and low boiling point are suitable for the preparation of perovskite films. Microstructural and elemental analyses of the perovskite films were systematically conducted by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The photoelectric properties, carrier transfer, and recombination process in the PSCs were investigated using photocurrent-voltage characteristic curves and electrochemical impedance spectroscopy. Optimum performance was obtained when the anti-solvent was diethyl ether (DEE) and the ratio of the optimum amount of DEE to the volume of the precursor was 1 : 10. Meanwhile, we found that the partial replacement of formamidinium/methylammonium by cesium could increase the stability of the PSCs and enhance the power conversion efficiency from 15.49% to over 17.38%.

An investigative study of polymer adsorption onto montmorillonite clay

NASA Astrophysics Data System (ADS)

McConnell Boykin, Cheri Lynn

For colloidal systems with adsorbed polymer, the mechanisms governing stabilization and flocculation are defined by the critical overlap concentration, c*. Below c*, steric stabilization or bridging flocculation are viable mechanisms of adsorption, while above c* associative thickening stabilization, depletion stabilization or depletion flocculation may occur. While these types of systems have been described by their mechanism of interaction, few studies have been geared towards evaluating and actually defining these interactions. This research focuses on elucidating the mechanisms of interaction for a series of polyacrylamide copolymers adsorbed onto montmorillonite clay. The well-defined copolymers synthesized and characterized for these studies include: nonionic polyacrylamide, (PAm); cationic poly(acrylamide-co-[3-(methacryloylamino) propyl] trimethylammonium chloride), (PAmMaap Quat); nonionic/anionic poly(acrylamide-co-acrylic acid), (PAmAA); and anionic poly(acrylamide-co-[2-acrylamido-2-methylpropane sulfonic acid]), (PAmAmps). By combining the results from the following experiments it was possible to determine the mechanisms of interaction for each of the clay/polymer systems at pH 3, 7 and 10. The adsorption capacity of each of the copolymers was determined from constructing adsorption isotherms while the polymer conformation was determined from 13C NMR line-broadening experiments. FTIR spectroscopy verified which surface of the clay was involved in adsorption along with the polymer moiety bound to the surface. Finally, the stabilization behavior was evaluated from statistically designed phase diagrams as a function of polymer and clay concentrations. By evaluating the phase behavior as well as c* for the polymer/solvent systems, it was determined that there was no direct correlation between c* for a polymer/solvent system and the mechanism of interaction for colloid/polymer/solvent systems previously defined by Vincent, Sato and Napper. In general, the nonionic polymers act as H-bond acceptors (amide and acid moieties) and donators (acid groups) which result in associatively stabilized homogeneous montmorillonite clay dispersions. The cationic copolymers exhibit strong, irreversible interactions with the clay resulting in heterogeneous bridging flocculation, which was shown to be dependent on the charge density of the copolymer. Furthermore, the anionic copolymers show no signs of adsorption, but create a network of repulsive forces with the montmorillonite clay, which ultimately results in depletion stabilization with some degree of depletion flocculation.

A simple model for solvation in mixed solvents. Applications to the stabilization and destabilization of macromolecular structures.

PubMed

Schellman, J A

1990-08-31

The properties of a simple model for solvation in mixed solvents are explored in this paper. The model is based on the supposition that solvent replacement is a simple one-for-one substitution reaction at macromolecular sites which are independent of one another. This leads to a new form for the binding polynomial in which all terms are associated with ligand interchange rather than ligand addition. The principal solvent acts as one of the ligands. Thermodynamic analysis then shows that thermodynamic binding (i.e., selective interaction) depends on the properties of K'-1, whereas stoichiometric binding (site occupation) depends on K'. K' is a 'practical' interchange equilibrium constant given by (f3/f1)K, where K is the true equilibrium constant for the interchange of components 3 and 1 on the site and f3 and f4 denote their respective activity coefficients on the mole fraction scale. Values of K' less than unity lead to negative selective interaction. It is selective interaction and not occupation number which determines the thermodynamic effects of solvation. When K' greater than 100 on the mole fraction scale or K' greater than 2 on the molality scale (in water), the differences between stoichiometric binding and selective interaction become less than 1%. The theory of this paper is therefore necessary only for very weak binding constants. When K'-1 is small, large concentrations of the added solvent component are required to produce a thermodynamic effect. Under these circumstances the isotherms for the selective interaction and for the excess (or transfer) free energy are strongly dependent on the behavior of the activity coefficients of both solvent components. Two classes of behavior are described depending on whether the components display positive or negative deviations from Raoult's law. Examples which are discussed are aqueous solutions of urea and guanidinium chloride for positive deviations and of sucrose and glucose for negative deviations. Examination of the few studies which have been reported in the literature shows that most of the qualitative features of the stabilization of proteins by sugars and their destabilization by urea and guanidinium chloride are faithfully represented with the model. This includes maxima in the free energy of stabilization and destabilization, decreased and zero selective interaction at high concentrations, etc. These phenomena had no prior explanation. Deficiencies in the model as a representation of solvation in aqueous solution are discussed in the appendix.

Development of a Topical Resveratrol Formulation for Commercial Applications Using Dendrimer Nanotechnology.

PubMed

Pentek, Tyler; Newenhouse, Eric; O'Brien, Brennin; Chauhan, Abhay Singh

2017-01-14

Resveratrol (RSV) is well known for its anti-oxidant and anti-aging properties. However, resveratrol is insoluble in water and has stability issues. Recently, efforts were placed to prepare a resveratrol-based advanced anti-aging topical product but it contains harsh organic solvents and oils that could be harmful to the human body and the environment. Hence, we propose the use of a multifunctional dendrimer to solve the solubility and stability issues of resveratrol. A dendrimer-resveratrol complex was prepared, optimized and tested for solubility enhancement, stability in solution and cream dosage forms. We have also developed a high performance liquid chromatography method to measure the resveratrol within the final product. PAMAM dendrimers increased the solubility and stability of resveratrol in water and semisolid dosage forms. Therefore, this product would be water based 'green' formulation devoid of harsh organic solvents and oils and can be safely applied to the skin. Additionally, we have shown that the dendrimer helped to increase overall RSV loading and skin penetration of resveratrol. The dendrimer-RSV formulation was successfully scaled up towards commercialization. Dendrimer with RSV has led to an innovation in anti-aging cream and solutions that could be commercially marketed. Dendrimer-RSV complex could also be added to other product forms for additional purposes and applications.

Boosting protein stability with the computational design of β-sheet surfaces.

PubMed

Kim, Doo Nam; Jacobs, Timothy M; Kuhlman, Brian

2016-03-01

β-sheets often have one face packed against the core of the protein and the other facing solvent. Mutational studies have indicated that the solvent-facing residues can contribute significantly to protein stability, and that the preferred amino acid at each sequence position is dependent on the precise structure of the protein backbone and the identity of the neighboring amino acids. This suggests that the most advantageous methods for designing β-sheet surfaces will be approaches that take into account the multiple energetic factors at play including side chain rotamer preferences, van der Waals forces, electrostatics, and desolvation effects. Here, we show that the protein design software Rosetta, which models these energetic factors, can be used to dramatically increase protein stability by optimizing interactions on the surfaces of small β-sheet proteins. Two design variants of the β-sandwich protein from tenascin were made with 7 and 14 mutations respectively on its β-sheet surfaces. These changes raised the thermal midpoint for unfolding from 45°C to 64°C and 74°C. Additionally, we tested an empirical approach based on increasing the number of potential salt bridges on the surfaces of the β-sheets. This was not a robust strategy for increasing stability, as three of the four variants tested were unfolded. © 2016 The Protein Society.

Interplay of Electrostatics and Hydrophobic Effects in the Metamorphic Protein Human Lymphotactin.

PubMed

Korkmaz, Elif Nihal; Volkman, Brian F; Cui, Qiang

2015-07-30

The human lymphotactin (hLtn) is a protein that features two native states both of which are physiologically relevant: it is a monomer (hLtn10) at 10 °C with 200 mM salt and a dimer (hLtn40) at 40 °C and without salt. Here we focus on the networks of electrostatic and hydrophobic interactions that display substantial changes upon the conversion from hLtn10 to hLtn40 since they are expected to modulate the relative stability of the two folds. In addition to the Arg 23-Arg 43 interaction discussed in previous work, we find several other like-charge pairs that are likely important to the stability of hLtn10. Free energy perturbation calculations are carried out to explicitly evaluate the contribution of the Arg 23-Arg 43 interaction to the hLtn10 stability. hLtn40 features a larger number of salt bridges, and a set of hydrophobic residues undergo major changes in the solvent accessible surface area between hLtn10 and hLtn40, pointing to their importance to the relative stability of the two folds. We also discuss the use of explicit and implicit solvent simulations for characterizing the conformational ensembles under different solution conditions.

Thermal Stability of Oil Palm Empty Fruit Bunch (OPEFB) Nanocrystalline Cellulose: Effects of post-treatment of oven drying and solvent exchange techniques

NASA Astrophysics Data System (ADS)

Indarti, E.; Marwan; Wanrosli, W. D.

2015-06-01

Nanocrystallinecellulose (NCC) from biomass is a promising material with huge potentials in various applications. A big challenge in its utilization is the agglomeration of the NCC's during processing due to hydrogen bonding among the cellulose chains when in close proximity to each other. Obtaining NCC's in a non-agglomerated and non-aqueous condition is challenging. In the present work NCC's was isolated from oil palm empty fruit bunch (OPEFB) using TEMPO-oxidation reaction method. To obtain non-agglomerated and non-aqueous products, the NCC's underwent post-treatment using oven drying (OD) and solvent exchanged (SE) techniques. The thermal stability of all samples was determined from TGA and DTG profiles whilst FTIR was used to analyzethe chemical modifications that occurred under these conditions. NCC-SE has better thermal stability than the NCC-OD and its on-set degradation temperature and residue are also higher. FTIR analysis shows that NCC-SE has a slightly different chemical composition whereby the absorption band at 1300 cm-1 (due to C-O symmetric stretching) is absent as compared to NCC-OD indicating that in NCC-SE the carboxylate group is in acid form which contribute to its thermal stability

Using mass spectrometry and small molecule reagents to detect distinctive structural features of different prion conformations (strains)

USDA-ARS?s Scientific Manuscript database

A prion (PrPSc) is a conformer of a normal cellular prion protein (PrPC). Although they are isosequential, PrPSc is an infectious protein able to convert PrPC into the prion conformation and thereby propagate an infection. PrPC is monomeric while PrPSc is a multimer. PrPSc can adopt more than one co...

Recombinant PrPSc shares structural features with brain-derived PrPSc suggesting that they have a similar architecture: Insights from limited proteolysis

USDA-ARS?s Scientific Manuscript database

An extensive body of experimental and spectroscopic evidence supports the hypothesis that PrPSc is a multimer of 4-rung ß-solenoids, and that individual PrPSc solenoids stack to form amyloid fibers. We recently used limited proteolysis to map the ß-strands and connecting loops that make up the PrPSc...

Molecular Mechanisms of ZnO Nanoparticle Dispersion in Solution: Modeling of Surfactant Association, Electrostatic Shielding and Counter Ion Dynamics.

PubMed

Duchstein, Patrick; Milek, Theodor; Zahn, Dirk

2015-01-01

Molecular models of 5 nm sized ZnO/Zn(OH)2 core-shell nanoparticles in ethanolic solution were derived as scale-up models (based on an earlier model created from ion-by-ion aggregation and self-organization) and subjected to mechanistic analyses of surface stabilization by block-copolymers. The latter comprise a poly-methacrylate chain accounting for strong surfactant association to the nanoparticle by hydrogen bonding and salt-bridges. While dangling poly-ethylene oxide chains provide only a limited degree of sterical hindering to nanoparticle agglomeration, the key mechanism of surface stabilization is electrostatic shielding arising from the acrylates and a halo of Na+ counter ions associated to the nanoparticle. Molecular dynamics simulations reveal different solvent shells and distance-dependent mobility of ions and solvent molecules. From this, we provide a molecular rationale of effective particle size, net charge and polarizability of the nanoparticles in solution.

Molecular Mechanisms of ZnO Nanoparticle Dispersion in Solution: Modeling of Surfactant Association, Electrostatic Shielding and Counter Ion Dynamics

PubMed Central

Duchstein, Patrick; Milek, Theodor; Zahn, Dirk

2015-01-01

Molecular models of 5 nm sized ZnO/Zn(OH)2 core-shell nanoparticles in ethanolic solution were derived as scale-up models (based on an earlier model created from ion-by-ion aggregation and self-organization) and subjected to mechanistic analyses of surface stabilization by block-copolymers. The latter comprise a poly-methacrylate chain accounting for strong surfactant association to the nanoparticle by hydrogen bonding and salt-bridges. While dangling poly-ethylene oxide chains provide only a limited degree of sterical hindering to nanoparticle agglomeration, the key mechanism of surface stabilization is electrostatic shielding arising from the acrylates and a halo of Na+ counter ions associated to the nanoparticle. Molecular dynamics simulations reveal different solvent shells and distance-dependent mobility of ions and solvent molecules. From this, we provide a molecular rationale of effective particle size, net charge and polarizability of the nanoparticles in solution. PMID:25962096

Refractometric sensitivity and thermal stabilization of fluorescent core microcapillary sensors: theory and experiment.

PubMed

Lane, S; Marsiglio, F; Zhi, Y; Meldrum, A

2015-02-20

Fluorescent-core microcapillaries (FCMs) present a robust basis for the application of optical whispering gallery modes toward refractometric sensing. An important question concerns whether these devices can be rendered insensitive to local temperature fluctuations, which may otherwise limit their refractometric detection limits, mainly as a result of thermorefractive effects. Here, we first use a standard cylindrical cavity formalism to develop the refractometric and thermally limited detection limits for the FCM structure. We then measure the thermal response of a real device with different analytes in the channel and compare the result to the theory. Good stability against temperature fluctuations was obtained for an ethanol solvent, with a near-zero observed thermal shift for the transverse magnetic modes. Similarly good results could in principle be obtained for any other solvent (e.g., water), if the thickness of the fluorescent layer can be sufficiently well controlled.

Liquid exfoliation of solvent-stabilized few-layer black phosphorus for applications beyond electronics

PubMed Central

Hanlon, Damien; Backes, Claudia; Doherty, Evie; Cucinotta, Clotilde S.; Berner, Nina C.; Boland, Conor; Lee, Kangho; Harvey, Andrew; Lynch, Peter; Gholamvand, Zahra; Zhang, Saifeng; Wang, Kangpeng; Moynihan, Glenn; Pokle, Anuj; Ramasse, Quentin M.; McEvoy, Niall; Blau, Werner J.; Wang, Jun; Abellan, Gonzalo; Hauke, Frank; Hirsch, Andreas; Sanvito, Stefano; O'Regan, David D.; Duesberg, Georg S.; Nicolosi, Valeria; Coleman, Jonathan N.

2015-01-01

Few-layer black phosphorus (BP) is a new two-dimensional material which is of great interest for applications, mainly in electronics. However, its lack of environmental stability severely limits its synthesis and processing. Here we demonstrate that high-quality, few-layer BP nanosheets, with controllable size and observable photoluminescence, can be produced in large quantities by liquid phase exfoliation under ambient conditions in solvents such as N-cyclohexyl-2-pyrrolidone (CHP). Nanosheets are surprisingly stable in CHP, probably due to the solvation shell protecting the nanosheets from reacting with water or oxygen. Experiments, supported by simulations, show reactions to occur only at the nanosheet edge, with the rate and extent of the reaction dependent on the water/oxygen content. We demonstrate that liquid-exfoliated BP nanosheets are potentially useful in a range of applications from ultrafast saturable absorbers to gas sensors to fillers for composite reinforcement. PMID:26469634

Physicochemical and mechanical properties of paracetamol cocrystal with 5-nitroisophthalic acid.

PubMed

Hiendrawan, Stevanus; Veriansyah, Bambang; Widjojokusumo, Edward; Soewandhi, Sundani Nurono; Wikarsa, Saleh; Tjandrawinata, Raymond R

2016-01-30

We report novel pharmaceutical cocrystal of a popular antipyretic drug paracetamol (PCA) with coformer 5-nitroisophhthalic acid (5NIP) to improve its tabletability. The cocrystal (PCA-5NIP at molar ratio of 1:1) was synthesized by solvent evaporation technique using methanol as solvent. The physicochemical properties of cocrystal were characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), fourier transform infrared spectroscopy (FTIR), hot stage polarized microscopy (HSPM) and scanning electron microscopy (SEM). Stability of the cocrystal was assessed by storing them at 40°C/75% RH for one month. Compared to PCA, the cocrystal displayed superior tableting performance. PCA-5NIP cocrystal showed a similar dissolution profile as compared to PCA and exhibited good stability. This study showed the utility of PCA-5NIP cocrystal for improving mechanical properties of PCA. Copyright © 2015 Elsevier B.V. All rights reserved.

On the Stability of NaO2 in Na-O2 Batteries.

PubMed

Liu, Chenjuan; Carboni, Marco; Brant, William R; Pan, Ruijun; Hedman, Jonas; Zhu, Jiefang; Gustafsson, Torbjörn; Younesi, Reza

2018-04-25

Na-O 2 batteries are regarded as promising candidates for energy storage. They have higher energy efficiency, rate capability, and chemical reversibility than Li-O 2 batteries; in addition, sodium is cheaper and more abundant compared to lithium. However, inconsistent observations and instability of discharge products have inhibited the understanding of the working mechanism of this technology. In this work, we have investigated a number of factors that influence the stability of the discharge products. By means of in operando powder X-ray diffraction study, the influence of oxygen, sodium anode, salt, solvent, and carbon cathode were investigated. The Na metal anode and an ether-based solvent are the main factors that lead to the instability and decomposition of NaO 2 in the cell environment. This fundamental insight brings new information on the working mechanism of Na-O 2 batteries.

Stabilized Alumina/Ethanol Colloidal Dispersion for Seeding High Temperature Air Flows

NASA Technical Reports Server (NTRS)

Wernet, Judith H.; Wernet, Mark P.

1994-01-01

Seeding air flows with particles to enable measurements of gas velocities via laser anemometry and/or particle image velocimetry techniques can be quite exasperating. The seeding requirements are compounded when high temperature environments are encountered and special care must be used in selecting a refractory seed material. The pH stabilization techniques commonly employed in ceramic processing are used to obtain stable dispersions for generating aerosols of refractory seed material. By adding submicron alumina particles to a preadjusted pH solution of ethanol, a stable dispersion is obtained which when atomized produces a high quality aerosol. Commercial grade alumina powder is used with a moderate size distribution. The technique is not limited to alumina/ethanol and is also demonstrated with an alumina/H2O system. Other ceramic powders in various polar solvents could also be used once the point of zero charge (pH(sub pzc)) of the powder in the solvent has been determined.

Selective dissolution of halide perovskites as a step towards recycling solar cells

NASA Astrophysics Data System (ADS)

Kim, Byeong Jo; Kim, Dong Hoe; Kwon, Seung Lee; Park, So Yeon; Li, Zhen; Zhu, Kai; Jung, Hyun Suk

2016-05-01

Most research on perovskite solar cells has focused on improving power-conversion efficiency and stability. However, if one could refurbish perovskite solar cells, their stability might not be a critical issue. From the perspective of cost effectiveness, if failed, perovskite solar cells could be collected and recycled; reuse of their gold electrodes and transparent conducting glasses could reduce the price per watt of perovskite photovoltaic modules. Herein, we present a simple and effective method for removing the perovskite layer and reusing the mesoporous TiO2-coated transparent conducting glass substrate via selective dissolution. We find that the perovskite layer can be easily decomposed in polar aprotic solvents because of the reaction between polar aprotic solvents and Pb2+ cations. After 10 cycles of recycling, a mesoporous TiO2-coated transparent conducting glass substrate-based perovskite solar cell still shows a constant power-conversion efficiency, thereby demonstrating the possibility of recycling perovskite solar cells.

Selective dissolution of halide perovskites as a step towards recycling solar cells.

PubMed

Kim, Byeong Jo; Kim, Dong Hoe; Kwon, Seung Lee; Park, So Yeon; Li, Zhen; Zhu, Kai; Jung, Hyun Suk

2016-05-23

Most research on perovskite solar cells has focused on improving power-conversion efficiency and stability. However, if one could refurbish perovskite solar cells, their stability might not be a critical issue. From the perspective of cost effectiveness, if failed, perovskite solar cells could be collected and recycled; reuse of their gold electrodes and transparent conducting glasses could reduce the price per watt of perovskite photovoltaic modules. Herein, we present a simple and effective method for removing the perovskite layer and reusing the mesoporous TiO2-coated transparent conducting glass substrate via selective dissolution. We find that the perovskite layer can be easily decomposed in polar aprotic solvents because of the reaction between polar aprotic solvents and Pb(2+) cations. After 10 cycles of recycling, a mesoporous TiO2-coated transparent conducting glass substrate-based perovskite solar cell still shows a constant power-conversion efficiency, thereby demonstrating the possibility of recycling perovskite solar cells.

Solvent effect on the self-assembly of salt solvates of an antihypertensive drug azilsartan and 2-methylimidazole

NASA Astrophysics Data System (ADS)

Zhang, Xian-Rui; Zhang, Lei

2017-06-01

Three salt solvates of azilsartan (AZ) with 2-methylimidazole (2MI) (namely AZ-2MI-H2O, AZ-2MI-ACE and AZ-2MI-THF) and one azilsartan solvate (AZ-DIO, ACE = acetone, THF = tetrahydrofuran, and DIO = 1,4-dioxane) were manufactured by solvent-controlled self-assembly in aqueous-organic solutions. The experimental result of AZ-DIO shows that AZ is high affinity to DIO molecule, which has a unique ability to prevent salt formation between AZ and 2MI. Thermal studies of three salt solvates exhibit poor thermodynamic stability in environmental conditions. Solubility experiments show that AZ-2MI-ACE and AZ-2MI-THF are unstable and convert to AZ-2MI-H2O in aqueous solution, and that AZ-2MI-H2O exhibits increased solubility and retention stability in an aqueous medium compared with the commercial AZ-A crystalline form.

Solvent extraction of gold using ionic liquid based process

NASA Astrophysics Data System (ADS)

Makertihartha, I. G. B. N.; Zunita, Megawati; Rizki, Z.; Dharmawijaya, P. T.

2017-01-01

In decades, many research and mineral processing industries are using solvent extraction technology for metal ions separation. Solvent extraction technique has been used for the purification of precious metals such as Au and Pd, and base metals such as Cu, Zn and Cd. This process uses organic compounds as solvent. Organic solvents have some undesired properties i.e. toxic, volatile, excessive used, flammable, difficult to recycle, low reusability, low Au recovery, together with the problems related to the disposal of spent extractants and diluents, even the costs associated with these processes are relatively expensive. Therefore, a lot of research have boosted into the development of safe and environmentally friendly process for Au separation. Ionic liquids (ILs) are the potential alternative for gold extraction because they possess several desirable properties, such as a the ability to expanse temperature process up to 300°C, good solvent properties for a wide range of metal ions, high selectivity, low vapor pressures, stability up to 200°C, easy preparation, environmentally friendly (commonly called as "green solvent"), and relatively low cost. This review paper is focused in investigate of some ILs that have the potentials as solvent in extraction of Au from mineral/metal alloy at various conditions (pH, temperature, and pressure). Performances of ILs extraction of Au are studied in depth, i.e. structural relationship of ILs with capability to separate Au from metal ions aggregate. Optimal extraction conditon in order to gain high percent of Au in mineral processing is also investigated.

Identification and characterization of the elusive mutation causing the historical von Willebrand Disease type IIC Miami.

PubMed

Obser, T; Ledford-Kraemer, M; Oyen, F; Brehm, M A; Denis, C V; Marschalek, R; Montgomery, R R; Sadler, J E; Schneppenheim, S; Budde, U; Schneppenheim, R

2016-09-01

Essentials Von Willebrand disease IIC Miami features high von Willebrand factor (VWF) with reduced function. We aimed to identify and characterize the elusive underlying mutation in the original family. An inframe duplication of VWF exons 9-10 was identified and characterized. The mutation causes a defect in VWF multimerization and decreased VWF clearance from the circulation. Background A variant of von Willebrand disease (VWD) type 2A, phenotype IIC (VWD2AIIC), is characterized by recessive inheritance, low von Willebrand factor antigen (VWF:Ag), lack of VWF high-molecular-weight multimers, absence of VWF proteolytic fragments and mutations in the VWF propeptide. A family with dominantly inherited VWD2AIIC but markedly elevated VWF:Ag of > 2 U L(-1) was described as VWD type IIC Miami (VWD2AIIC-Miami) in 1993; however, the molecular defect remained elusive. Objectives To identify the molecular mechanism underlying the phenotype of the original VWD2AIIC-Miami. Patients and Methods We studied the original family with VWD2AIIC-Miami phenotypically and by genotyping. The identified mutation was recombinantly expressed and characterized by standard techniques, confocal imaging and in a mouse model, respectively. Results By Multiplex ligation-dependent probe amplification we identified an in-frame duplication of VWF exons 9-10 (c.998_1156dup; p.Glu333_385dup) in all patients. Recombinant mutant (rm)VWF only presented as a dimer. Co-expressed with wild-type VWF, the multimer pattern was indistinguishable from patients' plasma VWF. Immunofluorescence studies indicated retention of rmVWF in unusually large intracellular granules in the endoplasmic reticulum. ADAMTS-13 proteolysis of rmVWF under denaturing conditions was normal; however, an aberrant proteolytic fragment was apparent. A decreased ratio of VWF propeptide to VWF:Ag and a 1-desamino-8-d-arginine vasopressin (DDAVP) test in one patient indicated delayed VWF clearance, which was supported by clearance data after infusion of rmVWF into VWF(-/-) mice. Conclusion The unique phenotype of VWD2 type IIC-Miami results from dominant impairment of multimer assembly, an aberrant structure of mutant mature VWF and reduced clearance in vivo. © 2016 International Society on Thrombosis and Haemostasis.

Experiment on the treatment of waste extraction solvent from the molybdenum-99 process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsien-Ming Hsiao; Chang-Liang Hu; Kuang-Li Chien

2013-07-01

In the Mo-99 (Molybdenum-99) isotope extraction test process for radiopharmaceutical applications, organic solvent is used to extract Mo-99 from an irradiated UO{sub 2} dissolution. The extraction solvent was stored when the test work was stopped. A total of about 120 liters of waste solvent was stored at INER (Institute of Nuclear Energy Research, Taiwan). The extraction solvent consisted of 5% di-(2-ethylhexyl)-phosphoric acid (D2EHPA) and kerosene. The radionuclides found in the waste solvent include Cs-137, Am-241, Tc-99, and Sr-90, which give off gross alpha and beta radioactivity of 1898 and 471 Bq/ml, respectively. This study aims to remove radionuclides from themore » waste solvent using sodium carbonate and sodium hydroxide solutions in different concentrations. After mixing the waste solvent with the alkaline solution followed by settling, a third phase other than organic and aqueous phase appeared which is expected due to the saponification reaction. The experimental results showed that increasing the number of washing and the alkaline solution concentration could enhance the radionuclides removal rate. An optimal removal method was proposed using 2 M Na{sub 2}CO{sub 3} solution twice followed by 1 M NaOH solution one time for the third phase generated early in the mixing stages. The remaining gross alpha and beta radioactivity of the treated organic solvent was 2 and 3 Bq/ml, respectively. The treated solvent could be stabilized by ashing at 500 deg. C and then immobilized. The alkaline solution would be neutralized by hydrochloric or nitric acid and then treated using a variety of adsorbents or bone char via adsorption to remove nuclides to meet the wastewater discharge limitation. (authors)« less

Pilot-Scale Silicone Process for Low-Cost Carbon Dioxide Capture Preliminary Techno-Economic Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Surinder; Spiry, Irina; Wood, Benjamin

This report presents system and economic analysis for a carbon-capture unit which uses an aminosilicone-based solvent for CO{sub 2} capture in a pulverized coal (PC) boiler. The aminosilicone solvent is a 60/40 wt/wt mixture of 3-aminopropyl end-capped polydimethylsiloxane (GAP-1m) with tri-ethylene glycol (TEG) as a co-solvent. For comparison purposes, the report also shows results for a carbon-capture unit based on a conventional approach using mono-ethanol amine (MEA). The first year removal cost of CO{sub 2} for the aminosilicone-based carbon-capture process ismore » $46.04/ton of CO2 as compared to $$60.25/ton of CO{sub 2} when MEA is used. The aminosilicone-based process has <77% of the CAPEX of a system using MEA solvent. The lower CAPEX is due to several factors, including the higher working capacity of the aminosilicone solvent compared the MEA, which reduces the solvent flow rate required, reducing equipment sizes. If it is determined that carbon steel can be used in the rich-lean heat exchanger in the carbon capture unit, the first year removal cost of CO{sub 2} decreases to $$44.12/ton. The aminosilicone-based solvent has a higher thermal stability than MEA, allowing desorption to be conducted at higher temperatures and pressures, decreasing the number of compressor stages needed. The aminosilicone-based solvent also has a lower vapor pressure, allowing the desorption to be conducted in a continuous-stirred tank reactor versus a more expensive packed column. The aminosilicone-based solvent has a lower heat capacity, which decreases the heat load on the desorber. In summary, the amino-silicone solvent has significant advantages over conventional systems using MEA.« less

Pilot-Scale Silicone Process for Low-Cost Carbon Dioxide Capture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Surinder; Spiry, Irina; Wood, Benjamin

This report presents system and economicanalysis for a carbon-capture unit which uses an aminosilicone-based solvent for CO₂ capture in a pulverized coal (PC) boiler. The aminosilicone solvent is a 60/40 wt/wt mixture of 3-aminopropyl end-capped polydimethylsiloxane (GAP-1m) with tri-ethylene glycol (TEG) as a co-solvent. Forcomparison purposes, the report also shows results for a carbon-capture unit based on a conventional approach using mono-ethanol amine (MEA). The first year removal cost of CO₂ for the aminosilicone-based carbon-capture process is $46.04/ton of CO₂ as compared to $60.25/ton of CO₂ when MEA is used. The aminosilicone- based process has <77% of the CAPEX ofmore » a system using MEA solvent. The lower CAPEX is due to several factors, including the higher working capacity of the aminosilicone solvent compared the MEA, which reduces the solvent flow rate required, reducing equipment sizes. If it is determined that carbon steel can be used in the rich-lean heat exchanger in the carbon capture unit, the first year removal cost of CO₂ decreases to $44.12/ton. The aminosilicone-based solvent has a higherthermal stability than MEA, allowing desorption to be conducted at higher temperatures and pressures, decreasing the number of compressor stages needed. The aminosilicone-based solvent also has a lowervapor pressure, allowing the desorption to be conducted in a continuous-stirred tank reactor versus a more expensive packed column. The aminosilicone-based solvent has a lowerheat capacity, which decreases the heat load on the desorber. In summary, the amino-silicone solvent has significant advantages overconventional systems using MEA.« less

Trip report. Eurochemic company assistance: Hanford Atomic Products Operation spent fuel processing technology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shank, E.M.

1959-06-23

Information obtained from HAPO during visit by M.K. Twichell, UCNC, and E.M. Shank, ORNL, is given. Included are the tentative procedures for obtaining and transmitting information to the Eurochemic company. Discussions are given on pulsed columns, corrosion, puse generators, centrifuges, valves, in-line instrumentation, evaporators, resin column design, off-gas processing, solvent recovery, liquid-waste handling, process control, equipment decontamination, criticality, radiation protection, diluent, and solvent stability, backmixing in a pulsed column, and use of 40% TBP in the purex flowsheet.

Thermodynamics of the complex formation of copper(II) with L-phenylalanine in aqueous ethanol solutions

NASA Astrophysics Data System (ADS)

Burov, D. M.; Ledenkov, S. F.; Vandyshev, V. N.

2013-05-01

Constants of the acid dissociation and complexation of L-phenylalanine (HPhe) with copper(II) ions are determined by potentiometry in aqueous ethanol solutions containing 0 to 0.7 molar fraction of alcohol. Changes in the Gibbs energy for the transfer from water to a binary solvent of L-phenylalanine, Phe- anion, and [CuPhe]+ complex are calculated. It is found that the weakening of solvation of the ligand donor groups in solvents with high ethanol contents is accompanied by an increase in the stability of [CuPhe]+ complex.

Electrolytes For Electrooptic Devices Comprising Ionic Liqu Ids

DOEpatents

Warner, Benjamin P.; McCleskey, T. Mark; Agrawal, Anoop; Cronin, John P.; Tonazzi, Juan C. L.; Burrell, Anthony K.

2005-02-08

Electrolyte solutions of soluble bifunctional redox dyes in molten salt solvent may be used to prepare electrooptic devices with enhanced stability toward ultraviolet radiation. The solvents include lithium or quaternary ammonium cations, and perfluorinated sulfonylimide anions selected from trifluoromethylsulfonate (CF.sub.3 SO.sub.3.sup.-), bis(trifluoromethylsulfonyl)imide ((CF.sub.3 SO.sub.2).sub.2 N.sup.-), bis(perfluoroethylsulfonyl)imide ((CF.sub.3 CF.sub.2 SO.sub.2).sub.2 N.sup.-) and tris(trifluoromethylsulfonyl)methide ((CF.sub.3 SO.sub.2).sub.3 C.sup.-).

Salt Bridge Rearrangement (SaBRe) Explains the Dissociation Behavior of Noncovalent Complexes

NASA Astrophysics Data System (ADS)

Loo, Rachel R. Ogorzalek; Loo, Joseph A.

2016-06-01

Native electrospray ionization-mass spectrometry, with gas-phase activation and solution compositions that partially release subcomplexes, can elucidate topologies of macromolecular assemblies. That so much complexity can be preserved in gas-phase assemblies is remarkable, although a long-standing conundrum has been the differences between their gas- and solution-phase decompositions. Collision-induced dissociation of multimeric noncovalent complexes typically distributes products asymmetrically (i.e., by ejecting a single subunit bearing a large percentage of the excess charge). That unexpected behavior has been rationalized as one subunit "unfolding" to depart with more charge. We present an alternative explanation based on heterolytic ion-pair scission and rearrangement, a mechanism that inherently partitions charge asymmetrically. Excessive barriers to dissociation are circumvented in this manner, when local charge rearrangements access a lower-barrier surface. An implication of this ion pair consideration is that stability differences between high- and low-charge state ions usually attributed to Coulomb repulsion may, alternatively, be conveyed by attractive forces from ion pairs (salt bridges) stabilizing low-charge state ions. Should the number of ion pairs be roughly inversely related to charge, symmetric dissociations would be favored from highly charged complexes, as observed. Correlations between a gas-phase protein's size and charge reflect the quantity of restraining ion pairs. Collisionally-facilitated salt bridge rearrangement (SaBRe) may explain unusual size "contractions" seen for some activated, low charge state complexes. That some low-charged multimers preferentially cleave covalent bonds or shed small ions to disrupting noncovalent associations is also explained by greater ion pairing in low charge state complexes.

Salt Bridge Rearrangement (SaBRe) Explains the Dissociation Behavior of Noncovalent Complexes.

PubMed

Loo, Rachel R Ogorzalek; Loo, Joseph A

2016-06-01

Native electrospray ionization-mass spectrometry, with gas-phase activation and solution compositions that partially release subcomplexes, can elucidate topologies of macromolecular assemblies. That so much complexity can be preserved in gas-phase assemblies is remarkable, although a long-standing conundrum has been the differences between their gas- and solution-phase decompositions. Collision-induced dissociation of multimeric noncovalent complexes typically distributes products asymmetrically (i.e., by ejecting a single subunit bearing a large percentage of the excess charge). That unexpected behavior has been rationalized as one subunit "unfolding" to depart with more charge. We present an alternative explanation based on heterolytic ion-pair scission and rearrangement, a mechanism that inherently partitions charge asymmetrically. Excessive barriers to dissociation are circumvented in this manner, when local charge rearrangements access a lower-barrier surface. An implication of this ion pair consideration is that stability differences between high- and low-charge state ions usually attributed to Coulomb repulsion may, alternatively, be conveyed by attractive forces from ion pairs (salt bridges) stabilizing low-charge state ions. Should the number of ion pairs be roughly inversely related to charge, symmetric dissociations would be favored from highly charged complexes, as observed. Correlations between a gas-phase protein's size and charge reflect the quantity of restraining ion pairs. Collisionally-facilitated salt bridge rearrangement (SaBRe) may explain unusual size "contractions" seen for some activated, low charge state complexes. That some low-charged multimers preferentially cleave covalent bonds or shed small ions to disrupting noncovalent associations is also explained by greater ion pairing in low charge state complexes. Graphical Abstract ᅟ.

Tunable solvation effects on the size-selective fractionation of metal nanoparticles in CO2 gas-expanded solvents.

PubMed

Anand, Madhu; McLeod, M Chandler; Bell, Philip W; Roberts, Christopher B

2005-12-08

This paper presents an environmentally friendly, inexpensive, rapid, and efficient process for size-selective fractionation of polydisperse metal nanoparticle dispersions into multiple narrow size populations. The dispersibility of ligand-stabilized silver and gold nanoparticles is controlled by altering the ligand tails-solvent interaction (solvation) by the addition of carbon dioxide (CO2) gas as an antisolvent, thereby tailoring the bulk solvent strength. This is accomplished by adjusting the CO2 pressure over the liquid, resulting in a simple means to tune the nanoparticle precipitation by size. This study also details the influence of various factors on the size-separation process, such as the types of metal, ligand, and solvent, as well as the use of recursive fractionation and the time allowed for settling during each fractionation step. The pressure range required for the precipitation process is the same for both the silver and gold particles capped with dodecanethiol ligands. A change in ligand or solvent length has an effect on the interaction between the solvent and the ligand tails and therefore the pressure range required for precipitation. Stronger interactions between solvent and ligand tails require greater CO2 pressure to precipitate the particles. Temperature is another variable that impacts the dispersibility of the nanoparticles through changes in the density and the mole fraction of CO2 in the gas-expanded liquids. Recursive fractionation for a given system within a particular pressure range (solvent strength) further reduces the polydispersity of the fraction obtained within that pressure range. Specifically, this work utilizes the highly tunable solvent properties of organic/CO2 solvent mixtures to selectively size-separate dispersions of polydisperse nanoparticles (2 to 12 nm) into more monodisperse fractions (+/-2 nm). In addition to providing efficient separation of the particles, this process also allows all of the solvent and antisolvent to be recovered, thereby rendering it a green solvent process.

Measurement of water-soluble B vitamins in infant formula by liquid chromatography/tandem mass spectrometry.

PubMed

Huang, Min; Winters, Doug; Crowley, Richard; Sullivan, Darryl

2009-01-01

A method has been developed for the simultaneous measurement of multiple B vitamins (i.e., B1, B2, B3, B5, and B6) in infant formulas by LC-MSIMS. The vitamins were extracted with acidic solvent, followed by protein precipitation at a pH range of 4.5 to 5.5, and filtered. This simplified procedure eliminates many of the potential sources of laboratory error and facilitates rapid and efficient analysis. As is common in most cases, isotope internal standards were added to account for variations in sample preparation, as well as changes in MS measurement. In this method, isotope-labeled internal standards of B1, B3, B5, and B6 were used. The factors affecting analytical performance were investigated and optimized. In addition, the stability of these vitamins in the extraction solution was investigated. An acidic condition (5 mM HCl) was applied to successfully stabilize B1, which had shown a decrease in signal when other solvents were used. The quantitative extraction and good stability allowed isotope standards to be added to the filtered sample solution, instead of to the extraction solvent. The addition of the isotope to the small portion of the filtered sample solution significantly reduces cost. A comprehensive evaluation of the analysis of the standard reference material and good spike recovery of the vitamins (100 +/- 6%) demonstrates the accuracy of the method. The results for commercially available infant formula samples were also compared with those obtained using the current microbiological method.

One-step production of multiple emulsions: microfluidic, polymer-stabilized and particle-stabilized approaches.

PubMed

Clegg, Paul S; Tavacoli, Joe W; Wilde, Pete J

2016-01-28

Multiple emulsions have great potential for application in food science as a means to reduce fat content or for controlled encapsulation and release of actives. However, neither production nor stability is straightforward. Typically, multiple emulsions are prepared via two emulsification steps and a variety of approaches have been deployed to give long-term stability. It is well known that multiple emulsions can be prepared in a single step by harnessing emulsion inversion, although the resulting emulsions are usually short lived. Recently, several contrasting methods have been demonstrated which give rise to stable multiple emulsions via one-step production processes. Here we review the current state of microfluidic, polymer-stabilized and particle-stabilized approaches; these rely on phase separation, the role of electrolyte and the trapping of solvent with particles respectively.

Surface area generation and droplet size control in solvent extraction systems utilizing high intensity electric fields

DOEpatents

Scott, Timothy C.; Wham, Robert M.

1988-01-01

A method and system for solvent extraction where droplets are shattered by a high intensity electric field. These shattered droplets form a plurality of smaller droplets which have a greater combined surface area than the original droplet. Dispersion, coalescence and phase separation are accomplished in one vessel through the use of the single pulsing high intensity electric field. Electric field conditions are chosen so that simultaneous dispersion and coalescence are taking place in the emulsion formed in the electric field. The electric field creates a large amount of interfacial surface area for solvent extraction when the droplet is disintegrated and is capable of controlling droplet size and thus droplet stability. These operations take place in the presence of a counter current flow of the continuous phase.

Dispersions of Goethite Nanorods in Aprotic Polar Solvents

PubMed Central

Coursault, Delphine; Dozov, Ivan; Nobili, Maurizio; Dupont, Laurent; Chanéac, Corinne

2017-01-01

Colloidal suspensions of anisotropic nanoparticles can spontaneously self-organize in liquid-crystalline phases beyond some concentration threshold. These phases often respond to electric and magnetic fields. At lower concentrations, usual isotropic liquids are observed but they can display very strong Kerr and Cotton-Mouton effects (i.e., field-induced particle orientation). For many examples of these colloidal suspensions, the solvent is water, which hinders most electro-optic applications. Here, for goethite (α-FeOOH) nanorod dispersions, we show that water can be replaced by polar aprotic solvents, such as N-methyl-2-pyrrolidone (NMP) and dimethylsulfoxide (DMSO), without loss of colloidal stability. By polarized-light microscopy, small-angle X-ray scattering and electro-optic measurements, we found that the nematic phase, with its field-response properties, is retained. Moreover, a strong Kerr effect was also observed with isotropic goethite suspensions in these polar aprotic solvents. Furthermore, we found no significant difference in the behavior of both the nematic and isotropic phases between the aqueous and non-aqueous dispersions. Our work shows that goethite nanorod suspensions in polar aprotic solvents, suitable for electro-optic applications, can easily be produced and that they keep all their outstanding properties. It also suggests that this solvent replacement method could be extended to the aqueous colloidal suspensions of other kinds of charged anisotropic nanoparticles. PMID:29039797

Organic solvent-free sugar-based transparency nanopatterning material derived from biomass for eco-friendly optical biochips using green lithography

NASA Astrophysics Data System (ADS)

Takei, Satoshi; Oshima, Akihiro; Oyama, Tomoko G.; Ito, Kenta; Sugahara, Kigenn; Kashiwakura, Miki; Kozawa, Takahiro; Tagawa, Seiichi

2014-05-01

An organic solvent-free sugar-based transparency nanopatterning material which had specific desired properties such as nanostructures of subwavelength grating and moth-eye antireflection, acceptable thermal stability of 160 °C, and low imaginary refractive index of less than 0.005 at 350-800 nm was proposed using electron beam lithography. The organic solvent-free sugar-based transparency nanopatterning material is expected for non-petroleum resources, environmental affair, safety, easiness of handling, and health of the working people, instead of the common developable process of tetramethylammonium hydroxide. 120 nm moth-eye antireflection nanopatterns images with exposure dose of 10 μC/cm2 were provided by specific process conditions of electron beam lithography. The developed sugar derivatives with hydroxyl groups and EB sensitive groups in the organic solvent-free sugar-based transparency nanopatterning material were applicable to future development of optical interface films of biology and electronics as a novel chemical design.

Development of solvent-free offset ink using vegetable oil esters and high molecular-weight resin.

PubMed

Park, Jung Min; Kim, Young Han; Kim, Sung Bin

2013-01-01

In the development of solvent-free offset ink, the roles of resin molecular weight and used solvent on the ink performance were evaluated by examining the relationship between the various properties of resin and solvent and print quality. To find the best performing resin, the soy-oil fatty acid methyl ester (FAME) was applied to the five modified-phenolic resins having different molecular weights. It is found from the experimental results that the ink made of higher molecular weight and better solubility resin gives better printability and print quality. It is because larger molecular weight resin with better solubility gives higher rate of ink transfer. From the ink application of different esters to high molecular weight resin, the best printing performance was yielded from the soy-oil fatty acid butyl ester (FABE). It is due to its high kinematic viscosity resulting in the smallest change of ink transfer weight upon multiple number of printing, which improves the stability of ink quality.

Reversal in solvatochromism in some novel styrylpyridinium dyes having a hydrophobic cleft.

PubMed

Panigrahi, Mallika; Dash, Sukalyan; Patel, Sabita; Behera, P K; Mishra, B K

2007-11-01

The influence of solvent polarity on the electronic transition of four different N-hexadecyl styrylpyridinium dyes has been investigated in 15 solvents. The E(T)(30) scale has been used to propose a quantitative approach towards the relative stability of the electronic ground and excited state species. The extents of contribution of dipolar aprotic solvents towards the solvation of the excited species have been determined to be 42-48% for some of the dyes. Instead of a steady solvatochromism, all the dyes suffer a reversal in solvatochromism. The transitions of the solvatochromism, referred to as solvatochromic switches, are found to be at E(T)(30) values of approximately 50 for methyl and N,N-dimethylamino substituted dyes while at 37.6 for hydroxyl substituted dye and approximately 45 for 4-(1-methyl-2-phenylethenyl) pyridinium dye. A reversal in the trend of solvent effect in the later dye corresponding to 4-(4-methyl styryl)pyridinium dye has been attributed to an analogy of series and parallel electron flow.

Influence of grafting solvents on the properties of polymer electrolyte membranes prepared by γ-ray preirradiation method

NASA Astrophysics Data System (ADS)

Kimura, Yosuke; Asano, Masaharu; Chen, Jinhua; Maekawa, Yasunari; Katakai, Ryoichi; Yoshida, Masaru

2008-07-01

The effect of grafting solvents, such as isopropanol (iPrOH), tetrachloroethane (TCE), tetrahydrofuran (THF), and toluene, on the preparation of poly(ethylene- co-tetrafluoroethylene)-graft-poly(styrene sulfonic acid) (ETFE-g-PSSA) electrolyte membranes by the γ-ray preirradiation grafting method was investigated. It was found that the iPrOH can drastically accelerate the grafting, resulting in a higher degree of grafting. However, for an appropriate degree of grafting of about 50%, the sulfonic acid groups in the ETFE-g-PSSA membrane prepared with the iPrOH were mainly distributed near the membrane surface, as shown by low proton conductivity in the membrane thickness direction. In contrast to this result, the ETFE-g-PSSA membranes prepared with the THF, toluene and TCE exhibited uniform distribution of the sulfonic acid groups in the membrane. Especially, in the case of the TCE grafting solvent, the chemical stability of the resultant electrolyte membrane was clearly higher than those prepared with the other grafting solvents.

Enzymatic hybridization of α-lipoic acid with bioactive compounds in ionic solvents.

PubMed

Papadopoulou, Athena A; Katsoura, Maria H; Chatzikonstantinou, Alexandra; Kyriakou, Eleni; Polydera, Angeliki C; Tzakos, Andreas G; Stamatis, Haralambos

2013-05-01

The lipase-catalyzed molecular hybridization of α-lipoic acid (LA) with bioactive compounds pyridoxine, tyrosol and tyramine was performed in ionic solvents and deep eutectic solvents. The biocatalytic reactions were catalyzed by Candida antarctica lipase B immobilized onto various functionalized multi-walled carbon nanotubes (f-CNTs-CaLB), as well as by commercial Novozym 435. The use of f-CNTs-CaLB leads, in most cases, to higher conversion yields as compared to Novozym 435. The nature and ion composition of ionic solvents affect the performance of the biocatalytic process. The highest conversion yield was observed in (mtoa)NTf2. The high enzyme stability and the relatively low solubility of substrates in specific media account for the improved biocatalytic synthesis of molecular hybrids of LA. Principal component analysis was used to screen for potential lipoxygenase inhibitors. In vitro studies showed that the synthesized compounds exhibit up to 10-fold increased inhibitory activity on lipoxygenase mediated lipid peroxidation as compared to parent molecules. Copyright © 2013 Elsevier Ltd. All rights reserved.

The High-Resolution Structure of Activated Opsin Reveals a Conserved Solvent Network in the Transmembrane Region Essential for Activation.

PubMed

Blankenship, Elise; Vahedi-Faridi, Ardeschir; Lodowski, David T

2015-12-01

Rhodopsin, a light-activated G protein coupled receptor (GPCR), has been the subject of numerous biochemical and structural investigations, serving as a model receptor for GPCRs and their activation. We present the 2.3-Å resolution structure of native source rhodopsin stabilized in a conformation competent for G protein binding. An extensive water-mediated hydrogen bond network linking the chromophore binding site to the site of G protein binding is observed, providing connections to conserved motifs essential for GPCR activation. Comparison of this extensive solvent-mediated hydrogen-bonding network with the positions of ordered solvent in earlier crystallographic structures of rhodopsin photointermediates reveals both static structural and dynamic functional water-protein interactions present during the activation process. When considered along with observations that solvent occupies similar positions in the structures of other GPCRs, these analyses strongly support an integral role for this dynamic ordered water network in both rhodopsin and GPCR activation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Spectrophotometric and spectroscopic studies of charge transfer complex of 1-Naphthylamine as an electron donor with picric acid as an electron acceptor in different polar solvents

NASA Astrophysics Data System (ADS)

Singh, Neeti; Ahmad, Afaq

2010-08-01

The charge transfer complex of 1-Naphthylamine as a donor with π-acceptor picric acid has been studied spectrophotometrically in different solvents at room temperature. The results indicate that the formation of charge transfer complex is high in less polar solvent. The stoichiometry of the complex was found to be 1:1 by straight line method. The data are analysed in terms of formation constant ( KCT), molar extinction coefficient ( ɛCT), standard free energy (Δ G o), oscillator strength ( ƒ), transition dipole moment ( μ EN), resonance energy ( R N) and ionization potential ( I D). It is concluded that the formation constant ( KCT) of the complex is found to be depends upon the nature of both electron acceptor and donor and also on the polarity of solvents. Further the charge transfer molecular complex between picric acid and 1-Naphthylamine is stabilized by hydrogen bonding.

Equilibrium swelling of elastomeric materials in solvent environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Green, P.F.

1990-03-01

The equilibrium swelling of silicones, fluorosilicones, VITON and ethylene-propylene-diene (EPDM) elastomers in an environment of the jet fuel JP4 was investigated. The volume of silicone and DPDM elastomers increased by approximately 100% when they were placed in a saturated environment of JP4. Conversely, the volume of the fluorosilicone elastomer increased by approximately 15% and that of VITON less than 1%. In acetone, a commonly used solvent, the equilibrium swelling of VITON and the fluorosilicone elastomer was excessive, on the order of 100%, wheras the silicone and EPDM elastomers exhibited small changes in dimensions. Reasons for these observations are discussed inmore » detail. We also present a simple scheme by which one may, qualitatively, determine the dimensional stability of these elastomers in different solvents if the cohesive energy density of the solvent, which is readily available in a number of handbooks, is known. We also evaluated the vulnerability of some commonly used engineering thermoplastics to JP4. The results are tabulated. 13 refs., 6 figs., 3 tab.« less

Mechanisms of protein stabilization and prevention of protein aggregation by glycerol.

PubMed

Vagenende, Vincent; Yap, Miranda G S; Trout, Bernhardt L

2009-11-24

The stability of proteins in aqueous solution is routinely enhanced by cosolvents such as glycerol. Glycerol is known to shift the native protein ensemble to more compact states. Glycerol also inhibits protein aggregation during the refolding of many proteins. However, mechanistic insight into protein stabilization and prevention of protein aggregation by glycerol is still lacking. In this study, we derive mechanisms of glycerol-induced protein stabilization by combining the thermodynamic framework of preferential interactions with molecular-level insight into solvent-protein interactions gained from molecular simulations. Contrary to the common conception that preferential hydration of proteins in polyol/water mixtures is determined by the molecular size of the polyol and the surface area of the protein, we present evidence that preferential hydration of proteins in glycerol/water mixtures mainly originates from electrostatic interactions that induce orientations of glycerol molecules at the protein surface such that glycerol is further excluded. These interactions shift the native protein toward more compact conformations. Moreover, glycerol preferentially interacts with large patches of contiguous hydrophobicity where glycerol acts as an amphiphilic interface between the hydrophobic surface and the polar solvent. Accordingly, we propose that glycerol prevents protein aggregation by inhibiting protein unfolding and by stabilizing aggregation-prone intermediates through preferential interactions with hydrophobic surface regions that favor amphiphilic interface orientations of glycerol. These mechanisms agree well with experimental data available in the literature, and we discuss the extent to which these mechanisms apply to other cosolvents, including polyols, arginine, and urea.

Essential roles of protein-solvent many-body correlation in solvent-entropy effect on protein folding and denaturation: comparison between hard-sphere solvent and water.

PubMed

Oshima, Hiraku; Kinoshita, Masahiro

2015-04-14

In earlier works, we showed that the entropic effect originating from the translational displacement of water molecules plays the pivotal role in protein folding and denaturation. The two different solvent models, hard-sphere solvent and model water, were employed in theoretical methods wherein the entropic effect was treated as an essential factor. However, there were similarities and differences in the results obtained from the two solvent models. In the present work, to unveil the physical origins of the similarities and differences, we simultaneously consider structural transition, cold denaturation, and pressure denaturation for the same protein by employing the two solvent models and considering three different thermodynamic states for each solvent model. The solvent-entropy change upon protein folding/unfolding is decomposed into the protein-solvent pair (PA) and many-body (MB) correlation components using the integral equation theories. Each component is further decomposed into the excluded-volume (EV) and solvent-accessible surface (SAS) terms by applying the morphometric approach. The four physically insightful constituents, (PA, EV), (PA, SAS), (MB, EV), and (MB, SAS), are thus obtained. Moreover, (MB, SAS) is discussed by dividing it into two factors. This all-inclusive investigation leads to the following results: (1) the protein-water many-body correlation always plays critical roles in a variety of folding/unfolding processes; (2) the hard-sphere solvent model fails when it does not correctly reproduce the protein-water many-body correlation; (3) the hard-sphere solvent model becomes problematic when the dependence of the many-body correlation on the solvent number density and temperature is essential: it is not quite suited to studies on cold and pressure denaturating of a protein; (4) when the temperature and solvent number density are limited to the ambient values, the hard-sphere solvent model is usually successful; and (5) even at the ambient values, however, the many-body correlation plays significant roles in the β-sheet formation and argument of relative stabilities of very similar structures of a protein. These results are argued in detail with respect to the four physically insightful constituents and the two factors mentioned above. The relevance to the absence or presence of hydrogen-bonding properties in the solvent is also discussed in detail.

Essential roles of protein-solvent many-body correlation in solvent-entropy effect on protein folding and denaturation: Comparison between hard-sphere solvent and water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oshima, Hiraku; Kinoshita, Masahiro, E-mail: kinoshit@iae.kyoto-u.ac.jp

In earlier works, we showed that the entropic effect originating from the translational displacement of water molecules plays the pivotal role in protein folding and denaturation. The two different solvent models, hard-sphere solvent and model water, were employed in theoretical methods wherein the entropic effect was treated as an essential factor. However, there were similarities and differences in the results obtained from the two solvent models. In the present work, to unveil the physical origins of the similarities and differences, we simultaneously consider structural transition, cold denaturation, and pressure denaturation for the same protein by employing the two solvent modelsmore » and considering three different thermodynamic states for each solvent model. The solvent-entropy change upon protein folding/unfolding is decomposed into the protein-solvent pair (PA) and many-body (MB) correlation components using the integral equation theories. Each component is further decomposed into the excluded-volume (EV) and solvent-accessible surface (SAS) terms by applying the morphometric approach. The four physically insightful constituents, (PA, EV), (PA, SAS), (MB, EV), and (MB, SAS), are thus obtained. Moreover, (MB, SAS) is discussed by dividing it into two factors. This all-inclusive investigation leads to the following results: (1) the protein-water many-body correlation always plays critical roles in a variety of folding/unfolding processes; (2) the hard-sphere solvent model fails when it does not correctly reproduce the protein-water many-body correlation; (3) the hard-sphere solvent model becomes problematic when the dependence of the many-body correlation on the solvent number density and temperature is essential: it is not quite suited to studies on cold and pressure denaturating of a protein; (4) when the temperature and solvent number density are limited to the ambient values, the hard-sphere solvent model is usually successful; and (5) even at the ambient values, however, the many-body correlation plays significant roles in the β-sheet formation and argument of relative stabilities of very similar structures of a protein. These results are argued in detail with respect to the four physically insightful constituents and the two factors mentioned above. The relevance to the absence or presence of hydrogen-bonding properties in the solvent is also discussed in detail.« less

Enhanced Production and Characterization of a Solvent Stable Amylase from Solvent Tolerant Bacillus tequilensis RG-01: Thermostable and Surfactant Resistant

PubMed Central

Tiwari, Soni; Shukla, Neha; Mishra, Pooja; Gaur, Rajeeva

2014-01-01

Ten bacterial strains isolated from the soil samples in the presence of cyclohexane were screened for amylase production. Among them, culture RG-01 was adjudged as the best amylase producer and was identified as Bacillus tequilensis from MTCC, Chandigarh. The isolate showed maximum amylase production (8100 U/mL) in the presence of starch, peptone, and Ca2+ ions at 55°C pH 7.0 within 24 h of incubation. The enzyme was stable in the presence of n-dodecane, isooctane, n-decane, xylene, toluene, n-hexane, n-butanol, and cyclohexane, respectively. The presence of benzene, methanol, and ethanol marginally reduced the amylase stability, respectively. The enzyme was showed it 100% activity at 55°C and pH 7.0 with 119% and 127% stability at 55°C and pH 7.0, respectively. The enzyme was also stable in the presence of SDS, Tween-40, Tween-60, and Tween-80 (1%) and was found stimulatory effect, respectively. Only Triton-X-100 showed a moderate inhibitory effect (5%) on amylase activity. This isolate (Bacillus tequilensis RG-01) may be useful in several industrial applications owing to its thermotolerant and organic solvents and surfactants resistance characteristics. PMID:25401163

A three-dimensional graphene aerogel containing solvent-free polyaniline fluid for high performance supercapacitors.

PubMed

Gao, Zhaodongfang; Yang, Junwei; Huang, Jing; Xiong, Chuanxi; Yang, Quanling

2017-11-23

Conducting polymer based supercapacitors usually suffer from the difficulty of achieving high specific capacitance and good long-term stability simultaneously. In this communication, a long-chain protonic acid doped solvent-free self-suspended polyaniline (S-PANI) fluid and reduced graphene oxide (RGO) were used to fabricate a three-dimensional RGO/S-PANI aerogel via a simple self-assembled hydrothermal method, which was then applied as a supercapacitor electrode. This 3D RGO/S-PANI composite exhibited a high specific capacitance of up to 480 F g -1 at a current density of 1 A g -1 and 334 F g -1 even at a high discharge rate of 40 A g -1 . An outstanding cycling performance, with 96.14% of the initial capacitance remaining after 10 000 charging/discharging cycles at a rate of 10 A g -1 , was also achieved. Compared with the conventional conducting polymer materials, the 3D RGO/S-PANI composite presented more reliable rate capability and cycling stability. Moreover, S-PANI possesses excellent processability, thereby revealing its enormous potential in large scale production. We anticipate that the solvent-free fluid technique is also applicable to the preparation of other 3D graphene/polymer materials for energy storage.

The interaction between ketamine and some crown ethers in common organic solvents studied by NMR: The effect of donating atoms and ligand structure

NASA Astrophysics Data System (ADS)

Chekin, Fereshteh; Bordbar, Maryam; Fathollahi, Yaghoub; Alizadeh, Naader

2006-02-01

1H NMR spectroscopy was used to investigate the stoichiometry and stability of the drug ketamine cation complexes with some crown ethers, such as 15-crown-5 (15C5), aza-15-crown-5 (A15C5), 18-crown-6 (18C6), aza-18-crown-6 (A18C6), diaza-18-crown-6 (DA18C6), dibenzyl-diaza-18-crown-6 (DBzDA18C6) and cryptant [2,2,2] (C222) in acetonitrile (AN), dimethylsulfoxide (DMSO) and methanol (MeOH) at 27 °C. In order to evaluate the formation constants of the ketamine cation complexes, the CH 3 protons chemical shift (on the nitrogen atom of ketamine) was measured as function of ligand/ketamine mole ratio. The formation constant of resulting complexes were calculated by the computer fitting of chemical shift versus mole ratio data to appropriate equations. A significant chemical shift variation was not observed for 15C5 and 18C6. The stoichiometry of the mono aza and diaza ligands are 1:1 and 1:2 (ligand/ketamine), respectively. In all of the solvents studied, DA18C6 formed more stable complexes than other ligands. The solvent effect on the stability of these complexes is discussed.

Traceable atomic force microscopy of high-quality solvent-free crystals of [6,6]-phenyl-C61-butyric acid methyl ester

NASA Astrophysics Data System (ADS)

Lazzerini, Giovanni Mattia; Paternò, Giuseppe Maria; Tregnago, Giulia; Treat, Neil; Stingelin, Natalie; Yacoot, Andrew; Cacialli, Franco

2016-02-01

We report high-resolution, traceable atomic force microscopy measurements of high-quality, solvent-free single crystals of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). These were grown by drop-casting PCBM solutions onto the spectrosil substrates and by removing the residual solvent in a vacuum. A home-built atomic force microscope featuring a plane mirror differential optical interferometer, fiber-fed from a frequency-stabilized laser (emitting at 632.8 nm), was used to measure the crystals' height. The optical interferometer together with the stabilized laser provides traceability (via the laser wavelength) of the vertical measurements made with the atomic force microscope. We find that the crystals can conform to the surface topography, thanks to their height being significantly smaller compared to their lateral dimensions (namely, heights between about 50 nm and 140 nm, for the crystals analysed, vs. several tens of microns lateral dimensions). The vast majority of the crystals are flat, but an isolated, non-flat crystal provides insights into the growth mechanism and allows identification of "molecular terraces" whose height corresponds to one of the lattice constants of the single PCBM crystal (1.4 nm) as measured with X-ray diffraction.

Hydrogen Bonding Stabilized Self-Assembly of Inorganic Nanoparticles: Mechanism and Collective Properties.

PubMed

Yue, Mingli; Li, Yanchun; Hou, Ying; Cao, Wenxin; Zhu, Jiaqi; Han, Jiecai; Lu, Zhongyuan; Yang, Ming

2015-06-23

Developing a simple and efficient method to organize nanoscale building blocks into ordered superstructures, understanding the mechanism for self-assembly and revealing the essential collective properties are crucial steps toward the practical use of nanostructures in nanotechnology-based applications. In this study, we showed that the high-yield formation of ZnO nanoparticle chains with micrometer length can be readily achieved by the variation of solvents from methanol to water. Spectroscopic studies confirmed the solvent effect on the surface properties of ZnO nanoparticles, which were found to be critical for the formation of anisotropic assemblies. Quantum mechanical calculations and all atom molecular dynamic simulations indicated the contribution of hydrogen bonding for stabilizing the structure in water. Dissipative particle dynamics further revealed the importance of solvent-nanoparticle interactions for promoting one-dimensional self-assembly. The branching of chains was found upon aging, resulting in the size increase of the ensembles and network formation. Steady-state and time-resolved luminescent spectroscopes, which probed the variation of defect-related emission, revealed stronger Forster resonance energy transfer (FRET) between nanoparticles when the chain networks were formed. The high efficiency of FRET quenching can be ascribed to the presence of multiple energy transfer channels, as well as the short internanoparticle distances and the dipole alignment.

Free energy landscape of a minimalist salt bridge model.

PubMed

Li, Xubin; Lv, Chao; Corbett, Karen M; Zheng, Lianqing; Wu, Dongsheng; Yang, Wei

2016-01-01

Salt bridges are essential to protein stability and dynamics. Despite the importance, there has been scarce of detailed discussion on how salt bridge partners interact with each other in distinct solvent exposed environments. In this study, employing a recent generalized orthogonal space tempering (gOST) method, we enabled efficient molecular dynamics simulation of repetitive breaking and reforming of salt bridge structures within a minimalist salt-bridge model, the Asp-Arg dipeptide and thereby were able to map its detailed free energy landscape in aqueous solution. Free energy surface analysis shows that although individually-solvated states are more favorable, salt-bridge states still occupy a noticeable portion of the overall population. Notably, the competing forces, e.g. intercharge attractions that drive the formation of salt bridges and solvation forces that pull the charged groups away from each other, are energetically comparable. As the result, the salt bridge stability is highly tunable by local environments; for instance when local water molecules are perturbed to interact more strongly with each other, the population of the salt-bridge states is likely to increase. Our results reveal the critical role of local solvent structures in modulating salt-bridge partner interactions and imply the importance of water fluctuations on conformational dynamics that involves solvent accessible salt bridge formations. © 2015 The Protein Society.

Traceable atomic force microscopy of high-quality solvent-free crystals of [6,6]-phenyl-C{sub 61}-butyric acid methyl ester

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lazzerini, Giovanni Mattia; Yacoot, Andrew; Paternò, Giuseppe Maria

2016-02-01

We report high-resolution, traceable atomic force microscopy measurements of high-quality, solvent-free single crystals of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). These were grown by drop-casting PCBM solutions onto the spectrosil substrates and by removing the residual solvent in a vacuum. A home-built atomic force microscope featuring a plane mirror differential optical interferometer, fiber-fed from a frequency-stabilized laser (emitting at 632.8 nm), was used to measure the crystals' height. The optical interferometer together with the stabilized laser provides traceability (via the laser wavelength) of the vertical measurements made with the atomic force microscope. We find that the crystals can conform to the surfacemore » topography, thanks to their height being significantly smaller compared to their lateral dimensions (namely, heights between about 50 nm and 140 nm, for the crystals analysed, vs. several tens of microns lateral dimensions). The vast majority of the crystals are flat, but an isolated, non-flat crystal provides insights into the growth mechanism and allows identification of “molecular terraces” whose height corresponds to one of the lattice constants of the single PCBM crystal (1.4 nm) as measured with X-ray diffraction.« less

Prediction of protein mutant stability using classification and regression tool.

PubMed

Huang, Liang-Tsung; Saraboji, K; Ho, Shinn-Ying; Hwang, Shiow-Fen; Ponnuswamy, M N; Gromiha, M Michael

2007-02-01

Prediction of protein stability upon amino acid substitutions is an important problem in molecular biology and the solving of which would help for designing stable mutants. In this work, we have analyzed the stability of protein mutants using two different datasets of 1396 and 2204 mutants obtained from ProTherm database, respectively for free energy change due to thermal (DeltaDeltaG) and denaturant denaturations (DeltaDeltaG(H(2)O)). We have used a set of 48 physical, chemical energetic and conformational properties of amino acid residues and computed the difference of amino acid properties for each mutant in both sets of data. These differences in amino acid properties have been related to protein stability (DeltaDeltaG and DeltaDeltaG(H(2)O)) and are used to train with classification and regression tool for predicting the stability of protein mutants. Further, we have tested the method with 4 fold, 5 fold and 10 fold cross validation procedures. We found that the physical properties, shape and flexibility are important determinants of protein stability. The classification of mutants based on secondary structure (helix, strand, turn and coil) and solvent accessibility (buried, partially buried, partially exposed and exposed) distinguished the stabilizing/destabilizing mutants at an average accuracy of 81% and 80%, respectively for DeltaDeltaG and DeltaDeltaG(H(2)O). The correlation between the experimental and predicted stability change is 0.61 for DeltaDeltaG and 0.44 for DeltaDeltaG(H(2)O). Further, the free energy change due to the replacement of amino acid residue has been predicted within an average error of 1.08 kcal/mol and 1.37 kcal/mol for thermal and chemical denaturation, respectively. The relative importance of secondary structure and solvent accessibility, and the influence of the dataset on prediction of protein mutant stability have been discussed.

Feasibility of electrospray deposition for rapid screening of the cocrystal formation and single step, continuous production of pharmaceutical nanococrystals.

PubMed

Emami, Shahram; Siahi-Shadbad, Mohammadreza; Barzegar-Jalali, Mohammad; Adibkia, Khosro

2018-06-01

This study employed electrospray deposition (ESD) for simultaneous synthesis and particle engineering of cocrystals. Exploring new methods for the efficient production of cocrystals with desired particle properties is an essential demand. The possibility of cocrystal formation by ESD was examined for indomethacin-saccharin, indomethacin-nicotinamide, naproxen-nicotinamide, and naproxen-iso-nicotinamide cocrystals. Solutions of the drug and coformer at stoichiometric ratios were sprayed to a high electric field which caused rapid evaporation of the solvent and the formation of fine particles. The phase purity, size, and morphology of products were compared with reference cocrystals. Experiments were performed to evaluate the effects of stoichiometric ratio, concentration and solvent type on the cocrystal formation. Physical stability and dissolution properties of the electrosprayed cocrystals were also compared with reference cocrystals. ESD was found to be an efficient and rapid method to produce cocrystals for all studied systems other than indomethacin-nicotinamide. Pure cocrystals only formed at a specific drug:coformer ratio. The solvent type has a weak effect on the cocrystal formation and morphology. Electrosprayed cocrystals exhibited nano to micrometer sizes with distinct morphologies with comparable physical stability with reference cocrystals. Nanococrystals of indomethacin-saccharin with a mean size of 219 nm displayed a threefold higher dissolution rate than solvent evaporated cocrystal. ESD successfully was utilized to produce pure cocrystals of poorly soluble drugs with different morphologies and sizes ranging from nano to micrometer sizes in one step. This study highlighted the usefulness of ESD for simultaneous preparation and particle engineering of pharmaceutical cocrystals.

Molecular simulation of CO chemisorption on Co(0001) in presence of supercritical fluid solvent: A potential of mean force study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asiaee, Alireza; Benjamin, Kenneth M., E-mail: kenneth.benjamin@sdsmt.edu

2016-08-28

For several decades, heterogeneous catalytic processes have been improved through utilizing supercritical fluids (SCFs) as solvents. While numerous experimental studies have been established across a range of chemistries, such as oxidation, pyrolysis, amination, and Fischer-Tropsch synthesis, still there is little fundamental, molecular-level information regarding the role of the SCF on elementary heterogeneous catalytic steps. In this study, the influence of hexane solvent on the adsorption of carbon monoxide on Co(0001), as the first step in the reaction mechanism of many processes involving syngas conversion, is probed. Simulations are performed at various bulk hexane densities, ranging from ideal gas conditions (nomore » SCF hexane) to various near- and super-critical hexane densities. For this purpose, both density functional theory and molecular dynamics simulations are employed to determine the adsorption energy and free energy change during CO chemisorption. Potential of mean force calculations, utilizing umbrella sampling and the weighted histogram analysis method, provide the first commentary on SCF solvent effects on the energetic aspects of the chemisorption process. Simulation results indicate an enhanced stability of CO adsorption on the catalyst surface in the presence of supercritical hexane within the reduced pressure range of 1.0–1.5 at a constant temperature of 523 K. Furthermore, it is shown that the maximum stability of CO in the adsorbed state as a function of supercritical hexane density at 523 K nearly coincides with the maximum isothermal compressibility of bulk hexane at this temperature.« less

Molecular dynamics investigation of the ionic liquid/enzyme interface: application to engineering enzyme surface charge.

PubMed

Burney, Patrick R; Nordwald, Erik M; Hickman, Katie; Kaar, Joel L; Pfaendtner, Jim

2015-04-01

Molecular simulations of the enzymes Candida rugosa lipase and Bos taurus α-chymotrypsin in aqueous ionic liquids 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium ethyl sulfate were used to study the change in enzyme-solvent interactions induced by modification of the enzyme surface charge. The enzymes were altered by randomly mutating lysine surface residues to glutamate, effectively decreasing the net surface charge by two for each mutation. These mutations resemble succinylation of the enzyme by chemical modification, which has been shown to enhance the stability of both enzymes in ILs. After establishing that the enzymes were stable on the simulated time scales, we focused the analysis on the organization of the ionic liquid substituents about the enzyme surface. Calculated solvent charge densities show that for both enzymes and in both solvents that changing positively charged residues to negative charge does indeed increase the charge density of the solvent near the enzyme surface. The radial distribution of IL constituents with respect to the enzyme reveals decreased interactions with the anion are prevalent in the modified systems when compared to the wild type, which is largely accompanied by an increase in cation contact. Additionally, the radial dependence of the charge density and ion distribution indicates that the effect of altering enzyme charge is confined to short range (≤1 nm) ordering of the IL. Ultimately, these results, which are consistent with that from prior experiments, provide molecular insight into the effect of enzyme surface charge on enzyme stability in ILs. © 2015 Wiley Periodicals, Inc.

Dramatically stabilizing multiprotein complex structure in the absence of bulk water using tuned Hofmeister salts.

PubMed

Han, Linjie; Hyung, Suk-Joon; Ruotolo, Brandon T

2013-01-01

The role that water plays in the salt-based stabilization of proteins is central to our understanding of protein biophysics. Ion hydration and the ability of ions to alter water surface tension are typically invoked, along with direct ion-protein binding, to describe Hofmeister stabilization phenomena observed for proteins experimentally, but the relative influence of these forces has been extraordinarily difficult to measure directly. Recently, we have used gas-phase measurements of proteins and large multiprotein complexes, using a combination of innovative ion mobility (IM) and mass spectrometry (MS) techniques, to assess the ability of bound cations and anions to stabilize protein ions in the absence of the solvation forces described above. Our previous work has studied a broad set of 12 anions bound to a range of proteins and protein complexes, and while primarily motivated by the analytical challenges surrounding the gas-phase measurement of solution-phase relevant protein structures, our work has also lead to a detailed physical mechanism of anion-protein complex stabilization in the absence of bulk solvent. Our more-recent work has screened a similarly-broad set of cations for their ability to stabilize gas-phase protein structure, and we have discovered surprising differences between the operative mechanisms for cations and anions in gas-phase protein stabilization. In both cases, cations and anions affect protein stabilization in the absence of solvent in a manner that is generally reversed relative to their ability to stabilize the same proteins in solution. In addition, our evidence suggests that the relative solution-phase binding affinity of the anions and cations studied here is preserved in our gas-phase measurements, allowing us to study the influence of such interactions in detail. In this report, we collect and summarize such gas-phase measurements to distill a generalized picture of salt-based protein stabilization in the absence of bulk water. Further, we communicate our most recent efforts to study the combined effects of stabilizing cations and anions on gas-phase proteins, and identify those salts that bear anion/cation pairs having the strongest stabilizing influence on protein structures

Crystal growth, differential gas adsorption, high thermal stability, and reversible coordination of two new barium-organic frameworks, Ba(SBA)(DMF){sub 4} and Ba{sub 2}(BTEC)(H{sub 2}O)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halake, Shobha; Ok, Kang Min, E-mail: kmok@cau.ac.kr

2015-11-15

Single crystals of two barium-organic framework materials, Ba(SBA)(DMF){sub 4} (CAUMOF-15) and Ba{sub 2}(BTEC)(H{sub 2}O) (CAUMOF-16), have been grown through solvothermal reactions (H{sub 2}SBA=4,4′-sulfonyldibenzoic acid and H{sub 4}BTEC=1,2,4,5-benzenetetracarboxylic acid). The crystal structures of the reported frameworks have been determined by single-crystal X-ray diffraction. The materials have been fully characterized by powder X-ray diffraction (PXRD), elemental analyses, Infrared (IR) spectroscopy, and thermogravimetric analyses (TGA). CAUMOF-15 reveals a three-dimensional open-framework that comprises of an inorganic motif with one-dimensional chains and the SBA linkers. CAUMOF-16 shows another three-dimensional backbone consisting of layers of edge-shared BaO{sub 9} and BaO{sub 10} polyhedra, and BTEC pillars. Bothmore » of the 3D frameworks exhibit relatively high thermal stabilities. The PXRD and IR spectral data confirm that CAUMOF-15 and CAUMOF-16 reveal reversible coordinations of the respective solvent molecules, DMF and H{sub 2}O. Gas adsorption properties towards nitrogen, hydrogen, and carbon dioxide have been also investigated. - Graphical abstract: Crystals of two new barium-organic frameworks, Ba(SBA)(DMF){sub 4} and Ba{sub 2}(BTEC)(H{sub 2}O), exhibiting a differential gas adsorption, a high thermal stability, and a reversible coordination of solvent molecules have been grown. - Highlights: • Crystals of two new 3D Ba-MOFs are grown. • The two Ba-MOFs reveal very high thermal stabilities up to ca. 400 °C. • Ba(SBA)(DMF){sub 4} exhibits differential gas adsorption properties. • The two Ba-MOFs show reversible coordination of the solvent molecules.« less

The Use of Solar Heating and Heat Cured Polymers for Lunar Surface Stabilization

NASA Technical Reports Server (NTRS)

Hintze, Paul; Curran, Jerry; Back, Reddy

2008-01-01

Dust ejecta can affect visibility during a lunar landing, erode nearby coated surfaces and get into mechanical assemblies of in-place infrastructure. Regolith erosion was observed at many of the Apollo landing sites. This problem needs to be addressed at the beginning of the lunar base missions, as the amount of infrastructure susceptible to problems will increase with each landing. Protecting infrastructure from dust and debris is a crucial step in its long term functionality. A proposed way to mitigate these hazards is to build a lunar launch pad. Other areas of a lunar habitat will also need surface stabilization methods to help mitigate dust hazards. Roads would prevent dust from being lifted during movement and dust free zones might be required for certain areas critical to crew safety or to critical science missions. Work at NASA Kennedy Space Center (KSC) is investigating methods of stabilizing the lunar regolith including: sintering the regolith into a solid and using heat or UV cured polymers to stabilize the surface. Sintering, a method in which powders are heated until fusing into solids, has been proposed as one way of building a Lunar launch/landing pad. A solar concentrator has been built and used in the field to sinter JSC-1 Lunar stimulant. Polymer palliatives are used by the military to build helicopter landing pads and roads in dusty and sandy areas. Those polymers are dispersed in a solvent (water), making them unsuitable for lunar use. Commercially available, solvent free, polymer powders are being investigated to determine their viability to work in the same way as the solvent borne terrestrial analog. This presentation will describe the ongoing work at KSC in this field. Results from field testing will be presented. Physical testing results, including compression and abrasion, of field and laboratory prepared samples will be presented.

Laboratory diagnosis of von Willebrand's disease.

PubMed

Rick, M E

1994-12-01

The diagnosis of von Willebrand's disease is becoming complex as more is understood about the disease. Clinical information and laboratory data are necessary for the diagnosis because of the overlap of normal and abnormal laboratory values. A complete evaluation including von Willebrand factor multimers, ristocetin-induced platelet aggregation, factor VIII activity level, and a template bleeding time is necessary to correctly classify the patient so that optimal treatment may be given.

Purification and characterization of a heteromultimeric glycoprotein from Artocarpus heterophyllus latex with an inhibitory effect on human blood coagulation.

PubMed

Siritapetawee, Jaruwan; Thammasirirak, Sompong

2011-01-01

Plant latex has many health benefits and has been used in folk medicine. In this study, the biological effect of Artocarpus heterophyllus (jackfruit) latex on human blood coagulation was investigated. By a combination of heat precipitation and ion-exchange chromatography, a heat stable heteromultimeric glycoprotein (HSGPL1) was purified from jackfruit milky latex. The apparent molecular masses of the monomeric proteins on SDS/PAGE were 33, 31 and 29 kDa. The isoelectric points (pIs) of the monomers were 6.63, 6.63 and 6.93, respectively. Glycosylation and deglycosylation tests confirmed that each subunit of HSGPL1 formed the native multimer by sugar-based interaction. Moreover, the multimer of HSGPL1 also resisted 2-mercaptoethanol action. Peptide mass fingerprint analysis indicated that HSGPL1 was a complex protein related to Hsps/chaperones. HSGPL1 has an effect on intrinsic pathways of the human blood coagulation system by significantly prolonging the activated partial thrombin time (APTT). In contrast, it has no effect on the human extrinsic blood coagulation system using the prothrombin time (PT) test. The prolonged APTT resulted from the serine protease inhibitor property of HSGPL1, since it reduced activity of human blood coagulation factors XI(a) and α-XII(a).

Circular trimers of gelatinase B/matrix metalloproteinase-9 constitute a distinct population of functional enzyme molecules differentially regulated by tissue inhibitor of metalloproteinases-1

PubMed Central

Vandooren, Jennifer; Born, Benjamin; Solomonov, Inna; Zajac, Ewa; Saldova, Radka; Senske, Michael; Ugarte-Berzal, Estefanía; Martens, Erik; Van den Steen, Philippe E.; Van Damme, Jo; Garcia-Pardo, Angeles; Froeyen, Matheus; Deryugina, Elena I.; Quigley, James P.; Moestrup, Søren K.; Rudd, Pauline M.; Sagi, Irit; Opdenakker, Ghislain

2015-01-01

Gelatinase B/matrix metalloproteinase-9 (MMP-9) (EC 3.4.24.35) cleaves many substrates and is produced by most cell types as a zymogen, proMMP-9, in complex with the tissue inhibitor of metalloproteinases-1 (TIMP-1). Natural proMMP-9 occurs as monomers, homomultimers, and heterocomplexes, but our knowledge about the overall structure of proMMP-9 monomers and multimers is limited. We investigated biochemical, biophysical, and functional characteristics of zymogen and activated forms of MMP-9 monomers and multimers. In contrast to a conventional notion of a dimeric nature of MMP-9 homomultimers, we demonstrate that these are reduction-sensitive trimers. Based on the information from electrophoresis, atomic force microscopy (AFM) and transmission electron microscopy (TEM), we generated a 3Dstructure model of the proMMP-9 trimer. Remarkably, the proMMP-9 trimers possessed a 50-fold higher affinity for TIMP-1 than the monomers. In vivo, this finding was reflected in a higher extent of TIMP-1 inhibition of angiogenesis induced by trimers versus monomers. Our results show that proMMP-9 trimers constitute a novel structural and functional entity that is differentially regulated by TIMP-1. PMID:25360794

Method for determining the composition and orientation of III-V {001} semiconductor surfaces

NASA Astrophysics Data System (ADS)

Sung, M. M.; Kim, C.; Rabalais, J. W.

1996-09-01

A method for determining the composition and orientation of III-V {001} semiconductor surfaces is presented and applications are described. The information is obtained from the techniques of time-of-flight scattering and recoiling spectrometry (TOF-SARS), using the composition from azimuth-specific elemental accessibilities (CASEA) method, and low energy electron diffraction (LEED). The azimuth-specific elemental accessibilities (ASEA) are measured experimentally and calculated from the number of accessible atoms in the unit cell and from three-dimensional trajectory simulations using the SARIC program. The in situ analyses identify the 1st-layer elemental species and determine the orientation of the reconstructed surface symmetry elements with respect to the bulk crystallographic directions. This is demonstrated for the III-V {001} compound semiconductor surfaces of GaAs and InAs in the (4 × 2) and (4 × 2) phases and InP in the (4 × 2) phase. The analyses confirm the missing-row-dimer (MRD) structure for GaAs and InAs in which the missing row direction is parallel to the direction of the 1st-layer multimers (dimers) and the missing-row-trimer-dimer (MRTD) structure for InP in which the missing row direction is perpendicular to the direction of the 1st-layer multimers (trimers).

IN-SITU OXIDATION OF 1,4-DIOXANE (LABORATORY RESULTS)

EPA Science Inventory

Interest in the solvent stabilizer, 1,4-dioxane, is increasing because analytical detection limits have decreased indicating its presence at chlorinated volatile organic compound contaminated sites. The most common method for removing 1,4-dioxane from contaminated water is advanc...

Role of the parCBA Operon of the Broad-Host-Range Plasmid RK2 in Stable Plasmid Maintenance

PubMed Central

Easter, Carla L.; Schwab, Helmut; Helinski, Donald R.

1998-01-01

The par region of the stably maintained broad-host-range plasmid RK2 is organized as two divergent operons, parCBA and parDE, and a cis-acting site. parDE encodes a postsegregational killing system, and parCBA encodes a resolvase (ParA), a nuclease (ParB), and a protein of unknown function (ParC). The present study was undertaken to further delineate the role of the parCBA region in the stable maintenance of RK2 by first introducing precise deletions in the three genes and then assessing the abilities of the different constructs to stabilize RK2 in three strains of Escherichia coli and two strains of Pseudomonas aeruginosa. The intact parCBA operon was effective in stabilizing a conjugation-defective RK2 derivative in E. coli MC1061K and RR1 but was relatively ineffective in E. coli MV10Δlac. In the two strains in which the parCBA operon was effective, deletions in parB, parC, or both parB and parC caused an approximately twofold reduction in the stabilizing ability of the operon, while a deletion in the parA gene resulted in a much greater loss of parCBA activity. For P. aeruginosa PAO1161Rifr, the parCBA operon provided little if any plasmid stability, but for P. aeruginosa PAC452Rifr, the RK2 plasmid was stabilized to a substantial extent by parCBA. With this latter strain, parA and res alone were sufficient for stabilization. The cer resolvase system of plasmid ColE1 and the loxP/Cre system of plasmid P1 were tested in comparison with the parCBA operon. We found that, not unlike what was previously observed with MC1061K, cer failed to stabilize the RK2 plasmid with par deletions in strain MV10Δlac, but this multimer resolution system was effective in stabilizing the plasmid in strain RR1. The loxP/Cre system, on the other hand, was very effective in stabilizing the plasmid in all three E. coli strains. These observations indicate that the parA gene, along with its res site, exhibits a significant level of plasmid stabilization in the absence of the parC and parB genes but that in at least one E. coli strain, all three genes are required for maximum stabilization. It cannot be determined from these results whether or not the stabilization effects seen with parCBA or the cer and loxP/Cre systems are strictly due to a reduction in the level of RK2 dimers and an increase in the number of plasmid monomer units or if these systems play a role in a more complex process of plasmid stabilization that requires as an essential step the resolution of plasmid dimers. PMID:9811663

Conductivity and electrochemical stability of concentrated aqueous choline chloride solutions

NASA Astrophysics Data System (ADS)

Grishina, E. P.; Kudryakova, N. O.

2017-10-01

The conductivity and electrochemical stability of choline chloride (ChCl) solutions with water contents ranging from 20 to 39 wt % are studied. Exposing ChCl to moist ambient air yields a highly concentrated aqueous solution that, as an electrolyte, exhibits the properties and variations in conductivity with temperature and concentration characteristic of other similar systems. Its electrochemical stability window, determined by cyclic voltammetry, is comparable to that of ChCl-based deep eutectic solvents (DESs). Products of the electrolysis of ChCl‒H2O mixtures seem to be less toxic than those of Reline, Ethaline, and Maline.

Selective Solvent-Induced Stabilization of Polar Oxide Surfaces in an Electrochemical Environment

NASA Astrophysics Data System (ADS)

Yoo, Su-Hyun; Todorova, Mira; Neugebauer, Jörg

2018-02-01

The impact of an electrochemical environment on the thermodynamic stability of polar oxide surfaces is investigated for the example of ZnO(0001) surfaces immersed in water using density functional theory calculations. We show that solvation effects are highly selective: They have little effect on surfaces showing a metallic character, but largely stabilize semiconducting structures, particularly those that have a high electrostatic penalty in vacuum. The high selectivity is shown to have direct consequences for the surface phase diagram and explains, e.g., why certain surface structures could be observed only in an electrochemical environment.

The effects of certain glycols, substituted glycols and related organic solvents on the thermal stability of soluble collagen

PubMed Central

Hart, G. J.; Russell, A. E.; Cooper, D. R.

1971-01-01

The effects of a number of related diols, substituted diols and glycerol on the thermal stability of acid-soluble calf skin collagen were investigated. Thermal transition temperatures were determined by optical rotation measurement. Short-chain diols with terminal hydroxyl groups, i.e. ethylene glycol and propane-1,3-diol, stabilized the protein at all accessible concentrations. Stabilization was also observed with glycerol and diethylene glycol. Higher homologues in the diol series produced various effects, as did hydroxyl-group positional isomerism. Monoalkyl substitution of diols progressively lowered the denaturation temperature of collagen. Results are discussed in relation to possible mechanisms of perturbant action. PMID:5169191

Nitrile functionalized disiloxanes with dissolved LiTFSI as lithium ion electrolytes with high thermal and electrochemical stability

NASA Astrophysics Data System (ADS)

Pohl, Benjamin; Hiller, Martin M.; Seidel, Sarah M.; Grünebaum, Mariano; Wiemhöfer, Hans-Dieter

2015-01-01

Liquid disiloxanes functionalized with terminal nitrile groups are introduced as alternative non-volatile solvents for lithium-ion battery electrolytes in combination with LiTFSI as lithium salt. Two series of disiloxanes were investigated differing with respect to the attachment of the nitrile containing side group to silicon, i.e. via a Si-C or a Si-O bond. Total conductivities up to 1 mS cm-1 at 30 °C were measured by impedance spectroscopy. Electrochemical characterization was done on half cells using LiFePO4 cathodes by cyclic voltammetry and constant current cycling. Attractive issues and advantages of the investigated LiTFSI containing disiloxanes in comparison to current electrolyte solvents are: a) In spite of the presence of LiTFSI, the aluminum pitting corrosion is suppressed, b) the electrochemical stability window is extended on the cathode side up to 5.6 V vs. Li/Li+, for a LiTFSI concentration of 0.7 mol kg-1, c) the reported nitrile functionalized disiloxanes show excellent thermal stability with a boiling point up to 106 °C (0.1 mbar), a rather low glass transition temperature of -107 °C, while no melting/crystallization was observed.

Wheel-like Ln18 Cluster Organic Frameworks for Magnetic Refrigeration and Conversion of CO2.

PubMed

Song, Tian-Qun; Dong, Jie; Yang, An-Fei; Che, Xue-Jing; Gao, Hong-Ling; Cui, Jian-Zhong; Zhao, Bin

2018-03-19

Two isostructural 2D MOFs ([Ln 7 (CDA) 6 (HCOO) 3 (μ 3 -OH) 6 (H 2 O) 8 ] n , abbreviated as 1-Gd and 2-Dy) were successfully synthesized under solvothermal conditions. The self-assembly of lanthanide(III) nitrate and 1,1'-cyclopropane-dicarboxylic acid (H 2 CDA) resulted in wheel-like Ln 18 cluster second building units (SBU), which are further linked to six neighboring wheels to generate a 2D ordered honeycomb array. Both 1-Gd and 2-Dy exhibit high thermal stability and decompose above 330 °C. Moreover, they have good solvent stability in ten common solvents and pH stability with pH values from 1 to 13. Magnetic studies reveal that 1-Gd exhibits weak antiferromagnetic coupling between adjacent Gd 3+ ions and has a large magnetocaloric effect of 47.30 J kg -1 K -1 (Δ H = 7.0 T at 2 K), while 2-Dy shows ferromagnetic interaction between adjacent Dy 3+ ions. Interestingly, 1-Gd and 2-Dy can catalyze the cycloaddition of CO 2 to epoxides under mild conditions and can be reused at least five rounds with negligible loss of catalytic performance.

Optical Degradation of Colloidal Eu-Complex Embedded in Silica Glass Film Using Reprecipitation and Sol-Gel Methods.

PubMed

Fukuda, Takeshi; Kurabayashi, Tomokazu; Yamaki, Tatsuki

2016-04-01

A reprecipitation method has been investigated for fabricating colloidal nanoparticles using Eu-complex. Herein, we investigated optical degradation characteristics of (1,10-phenanthroline)tris [4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]europium(III) colloidal nanoparticles, which were embedded into a silica glass film fabricated by a conventional sol-gel process. At first, we tried several types of good solvents for the reprecipitation method, and dimethyl sulfoxide (DMSO) is found to be a suitable solvent for realizing the small diameter and the high long-term stability against the ultraviolet irradiation even though the boing point of DMSO is higher than that of water used as a poor solvent. By optimizing the good solvent and the concentration of Eu-complex, the relative photoluminescence intensity of 0.96 was achieved even though the ultraviolet light was continuously irradiated for 90 min. In addition, the average diameter of 106 nm was achieved when DMSO was used as a good solvent, resulting in the high transmittance at a visible wavelength region. Therefore, we can achieve the transparent emissive thin film with a center wavelength of 612 nm, and the optical degradation was drastically reduced by forming nanoparticles.

Dispersing surface-modified imogolite nanotubes in polar and non-polar solvents

NASA Astrophysics Data System (ADS)

Li, Ming; Brant, Jonathan A.

2018-02-01

Furthering the development of nanocomposite structures, namely membranes for water treatment applications, requires that methods be developed to ensure nanoparticle dispersion in polar and non-polar solvents, as both are widely used in associated synthesis techniques. Here, we report on a two-step method to graft polyvinylpyrrolidone (PVP), and a one-step method for octadecylphosphonic acid (OPA), onto the outer surfaces of imogolite nanotubes. The goal of these approaches was to improve and maintain nanotube dispersion in polymer compatible polar and non-polar solvents. The PVP coating modified the imogolite surface charge from positive to weakly negative at pH ≤ 9; the OPA made it weakly positive at acidic pH values to negative at pH ≥ 7. The PVP surface coating stabilized the nanotubes through steric hindrance in polar protic, dipolar aprotic, and chloroform. In difference to the PVP, the OPA surface coating allowed the nanotubes to be dispersed in n-hexane and chloroform, but not in the polar solvents. The lack of miscibility in the polar solvents, as well as the better dispersion in n-hexane, was attributed to the stronger hydrophobicity of the OPA polymer relative to the PVP. [Figure not available: see fulltext.

Dephasing dynamics in confined myoglobin

NASA Astrophysics Data System (ADS)

Goj, Anne; Loring, Roger F.

2007-11-01

Confinement of a solution can slow solvent dynamics and in turn influence the reactivity and structure of the solute. Encapsulating a protein in an aqueous pore affects its binding properties, stability to degradation, interconversion between conformational states, and energy relaxation. We perform molecular dynamics simulations of H64V-CO mutant myoglobin solvated by varying amounts of liquid water, and in turn enclosed by a matrix of immobilized solvent, to mimic differing degrees of confinement of H64V-CO in a glass. We calculate the three-pulse vibrational echo signal of the CO ligand from the autocorrelation function of fluctuations in the CO vibrational frequency. When the first solvation layer alone is free to relax, the correlation function displays only fast relaxation reminiscent of the case of a protein in a fixed, immobilized solvent matrix. However the vibrational echo signal in this case decays significantly more rapidly than for a static solvent. With two solvation layers mobile, the correlation function displays long time relaxation characteristic of the unconfined protein and the echo signal decays rapidly. The echo signal of the protein with two mobile solvation layers is nearly identical to that of the unconfined protein, despite the substantially constrained solvent dynamics in the confined case.

Capping agents in nanoparticle synthesis: Surfactant and solvent system

NASA Astrophysics Data System (ADS)

Gulati, Shivani; Sachdeva, M.; Bhasin, K. K.

2018-05-01

The preparation of nanomaterials by organometallic precursors require a capping agent, which primarily acts as stabilizing agent and provide colloidal stability along with preventing agglomeration and stopping uncontrolled growth. Final morphology of nanocrystal largely depends on the type of capping agent which is adsorbed on the surface of nanocrystal. Thus capping agents are the keys to obtain the small-sized nanoparticles and are very frequently used in colloidal synthesis of nanoparticles to avoid its overgrowth.

Clusters of isoleucine, leucine, and valine side chains define cores of stability in high-energy states of globular proteins: Sequence determinants of structure and stability.

PubMed

Kathuria, Sagar V; Chan, Yvonne H; Nobrega, R Paul; Özen, Ayşegül; Matthews, C Robert

2016-03-01

Measurements of protection against exchange of main chain amide hydrogens (NH) with solvent hydrogens in globular proteins have provided remarkable insights into the structures of rare high-energy states that populate their folding free-energy surfaces. Lacking, however, has been a unifying theory that rationalizes these high-energy states in terms of the structures and sequences of their resident proteins. The Branched Aliphatic Side Chain (BASiC) hypothesis has been developed to explain the observed patterns of protection in a pair of TIM barrel proteins. This hypothesis supposes that the side chains of isoleucine, leucine, and valine (ILV) residues often form large hydrophobic clusters that very effectively impede the penetration of water to their underlying hydrogen bond networks and, thereby, enhance the protection against solvent exchange. The linkage between the secondary and tertiary structures enables these ILV clusters to serve as cores of stability in high-energy partially folded states. Statistically significant correlations between the locations of large ILV clusters in native conformations and strong protection against exchange for a variety of motifs reported in the literature support the generality of the BASiC hypothesis. The results also illustrate the necessity to elaborate this simple hypothesis to account for the roles of adjacent hydrocarbon moieties in defining stability cores of partially folded states along folding reaction coordinates. © 2015 The Protein Society.

Probing Contaminant Transport to and from Clay Surfaces in Organic Solvents and Water Using Solution Calorimetry.

PubMed

Pourmohammadbagher, Amin; Shaw, John M

2015-09-15

Clays, in tailings, are a significant ongoing environmental concern in the mining and oilsands production industries, and clay rehabilitation following contamination poses challenges episodically. Understanding the fundamentals of clay behavior can lead to better environmental impact mitigation strategies. Systematic calorimetric measurements are shown to provide a framework for parsing the synergistic and antagonistic impacts of trace (i.e., parts per million level) components on the surface compositions of clays. The enthalpy of solution of as-received and "contaminated" clays, in as-received and "contaminated" organic solvents and water, at 60 °C and atmospheric pressure, provides important illustrative examples. Clay contamination included pre-saturation of clays with water and organic liquids. Solvent contamination included the addition of trace water to organic solvents and trace organic liquids to water. Enthalpy of solution outcomes are interpreted using a quantitative mass and energy balance modeling framework that isolates terms for solvent and trace contaminant sorption/desorption and surface energy effects. Underlying surface energies are shown to dominate the energetics of the solvent-clay interaction, and organic liquids as solvents or as trace contaminants are shown to displace water from as-received clay surfaces. This approach can be readily extended to include pH, salts, or other effects and is expected to provide mechanistic and quantitative insights underlying the stability of clays in tailings ponds and the behaviors of clays in diverse industrial and natural environments.

Sorting of Semiconducting Single-Walled Carbon Nanotubes in Polar Solvents with an Amphiphilic Conjugated Polymer Provides General Guidelines for Enrichment.

PubMed

Ouyang, Jianying; Ding, Jianfu; Lefebvre, Jacques; Li, Zhao; Guo, Chang; Kell, Arnold J; Malenfant, Patrick R L

2018-02-27

Conjugated polymer extraction (CPE) has been shown to be a highly effective method to isolate high-purity semiconducting single-walled carbon nanotubes (sc-SWCNTs). In both literature reports and industrial manufacturing, this method has enabled enrichment of sc-SWCNTs with high purity (≥99.9%). High selectivity is typically obtained in nonpolar aromatic solvents, yet polar solvents may provide process improvements in terms of yield, purity and efficiency. Using an amphiphilic fluorene-alt-pyridine conjugated copolymer with hydrophilic side chains, we have investigated the enrichment of sc-SWCNTs in polar solvents. Various conditions such as polymer/SWCNT ratio, solvent polarity, solvent dielectric constant as well as polymer solubility and SWCNT dispersibility were explored in order to optimize the purity and yield of the enriched product. Herein, we provide insights on CPE by demonstrating that a conjugated polymer having a hydrophobic backbone and hydrophilic oligo(ethylene oxide) side chains provides near full recovery (95%) of sc-SWCNTs using a multiextraction protocol. High purity is also obtained, and differences in chiral selectivity compared to analogous hydrophobic systems were confirmed by optical absorption and Raman spectroscopy as well as photoluminescence excitation mapping. Taking into consideration the solvent dielectric constant, polarity index as well as polymer solubility and SWCNT dispersibility provides a better understanding of structure-property effects on sc-SWCNT enrichment. The resulting hydrophilic SWCNT dispersions demonstrate long-term colloidal stability, making them suitable for ink formulation and high-performance thin-film transistors fabrication.

Theoretical analysis of co-solvent effect on the proton transfer reaction of glycine in a water-acetonitrile mixture

NASA Astrophysics Data System (ADS)

Kasai, Yukako; Yoshida, Norio; Nakano, Haruyuki

2015-05-01

The co-solvent effect on the proton transfer reaction of glycine in a water-acetonitrile mixture was examined using the reference interaction-site model self-consistent field theory. The free energy profiles of the proton transfer reaction of glycine between the carboxyl oxygen and amino nitrogen were computed in a water-acetonitrile mixture solvent at various molar fractions. Two types of reactions, the intramolecular proton transfer and water-mediated proton transfer, were considered. In both types of the reactions, a similar tendency was observed. In the pure water solvent, the zwitterionic form, where the carboxyl oxygen is deprotonated while the amino nitrogen is protonated, is more stable than the neutral form. The reaction free energy is -10.6 kcal mol-1. On the other hand, in the pure acetonitrile solvent, glycine takes only the neutral form. The reaction free energy from the neutral to zwitterionic form gradually increases with increasing acetonitrile concentration, and in an equally mixed solvent, the zwitterionic and neutral forms are almost isoenergetic, with a difference of only 0.3 kcal mol-1. The free energy component analysis based on the thermodynamic cycle of the reaction also revealed that the free energy change of the neutral form is insensitive to the change of solvent environment but the zwitterionic form shows drastic changes. In particular, the excess chemical potential, one of the components of the solvation free energy, is dominant and contributes to the stabilization of the zwitterionic form.

A new ether-based electrolyte for dendrite-free lithium-metal based rechargeable batteries

PubMed Central

Miao, Rongrong; Yang, Jun; Xu, Zhixin; Wang, Jiulin; Nuli, Yanna; Sun, Limin

2016-01-01

A new ether-based electrolyte to match lithium metal electrode is prepared by introducing 1, 4-dioxane as co-solvent into lithium bis(fluorosulfonyl)imide/1,2-dimethoxyethane solution. Under the synergetic effect of solvents and salt, this simple liquid electrolyte presents stable Li cycling with dendrite-free Li deposition even at relatively high current rate, high coulombic efficiency of ca. 98%, and good anodic stability up to ~4.87 V vs Li RE. Its excellent performance will open up a new possibility for high energy-density rechargeable Li metal battery system. PMID:26878890

PMR polyimide prepreg with improved tack characteristics

NASA Technical Reports Server (NTRS)

Serafini, T. T.; Delvigs, P.

1976-01-01

Current PMR Polyimide prepreg technology utilizes methanol or ethanol solvents for preparation of the PMR prepreg solutions. The volatility of these solvents limits the tack and drape retention characteristics of unprotected prepreg exposed to ambient conditions. Studies conducted to achieve PMR 15 Polyimide prepreg with improved tack and drape characteristics were described. Improved tack and drape retention were obtained by incorporation of an additional monomer. The effects of various levels of the added monomer on the thermo-oxidative stability and mechanical properties of graphite fiber reinforced PMR 15 composites exposed and tested at 316 C (600 F) were discussed.

Durable electrooptic devices comprising ionic liquids

DOEpatents

Agrawal, Anoop; Cronin, John P.; Tonazzi, Juan C. L.; Warner, Benjamin P.; McCleskey, T. Mark; Burrell, Anthony K.

2005-11-01

Electrolyte solutions for electrochromic devices such as rear view mirrors and displays with low leakage currents are prepared using inexpensive, low conductivity conductors. Preferred electrolytes include bifunctional redox dyes and molten salt solvents with enhanced stability toward ultraviolet radiation. The solvents include lithium or quaternary ammonium cations, and perfluorinated sulfonylimide anions selected from trifluoromethylsulfonate (CF3SO3-), bis(trifluoromethylsulfonyl)imide ((CF3SO2)2N-), bis(perfluoroethylsulfonyl)imide ((CF3CF2SO2)2N-) and tris(trifluoromethylsulfonyl)methide ((CF3SO2)3C-). Electroluminescent, electrochromic and photoelectrochromic devices with nanostructured electrodes include ionic liquids with bifunctional redox dyes.

Influence of Mixed Solvent on the Electrochemical Property of Hybrid Capacitor.

PubMed

Lee, Byunggwan; Yoon, J R

2015-11-01

The hybrid capacitors (2245 size, cylindrical type) were prepared by using activated carbon cathode and Li4Ti5O12 anode. In order to improve the cell operation at high temperature range, propylene carbonate (PC) was used in combination with acetonitrile (AN) with volume ratio of 7:3, 5:5, and 3:7, respectively. We investigated the electrochemical behavior of the hybrid capacitors that enabled cell operation with stability at high temperature. The organic electrolyte of hybrid capacitor containing PC and AN with a volume ratio 7:3 intended to exhibit highly reversible cycle performance with good capacity retention at 60 degrees C after 2200 cycles. From this study, it has been found that the very strong influence of the solvent nature on the characteristics of hybrid capacitor, and the difference in performance associated with the two solvents.

Substituent and Solvent Effects on Excited State Charge Transfer Behavior of Highly Fluorescent Dyes Containing Thiophenylimidazole-Based Aldehydes

NASA Technical Reports Server (NTRS)

Santos, Javier; Bu, Xiu R.; Mintz, Eric A.

2001-01-01

The excited state charge transfer for a series of highly fluorescent dyes containing thiophenylimidazole moiety was investigated. These systems follow the Twisted Intramolecular Charge Transfer (TICT) model. Dual fluorescence was observed for each substituted dye. X-ray structures analysis reveals a twisted ground state geometry for the donor substituted aryl on the 4 and 5 position at the imidazole ring. The excited state charge transfer was modeled by a linear solvation energy relationship using Taft's pi and Dimroth's E(sub T)(30) as solvent parameters. There is linear relation between the energy of the fluorescence transition and solvent polarity. The degree of stabilization of the excited state charge transfer was found to be consistent with the intramolecular molecular charge transfer. Excited dipole moment was studied by utilizing the solvatochromic shift method.

SOLVENT NANOFILTRATION USING LOW-COST INORGANIC MEMBRANE MODULES - PHASE I

EPA Science Inventory

This Phase I project addresses: (1) development of fully inorganic nanofiltration (NF) membrane modules that have the attributes of low-cost, excellent chemical resistance in aggressive organic and aqueous media and high thermal stability; and (2) demonstration of the perfo...

Protein Engineering by Random Mutagenesis and Structure-Guided Consensus of Geobacillus stearothermophilus Lipase T6 for Enhanced Stability in Methanol

PubMed Central

Dror, Adi; Shemesh, Einav; Dayan, Natali

2014-01-01

The abilities of enzymes to catalyze reactions in nonnatural environments of organic solvents have opened new opportunities for enzyme-based industrial processes. However, the main drawback of such processes is that most enzymes have a limited stability in polar organic solvents. In this study, we employed protein engineering methods to generate a lipase for enhanced stability in methanol, which is important for biodiesel production. Two protein engineering approaches, random mutagenesis (error-prone PCR) and structure-guided consensus, were applied in parallel on an unexplored lipase gene from Geobacillus stearothermophilus T6. A high-throughput colorimetric screening assay was used to evaluate lipase activity after an incubation period in high methanol concentrations. Both protein engineering approaches were successful in producing variants with elevated half-life values in 70% methanol. The best variant of the random mutagenesis library, Q185L, exhibited 23-fold-improved stability, yet its methanolysis activity was decreased by one-half compared to the wild type. The best variant from the consensus library, H86Y/A269T, exhibited 66-fold-improved stability in methanol along with elevated thermostability (+4.3°C) and a 2-fold-higher fatty acid methyl ester yield from soybean oil. Based on in silico modeling, we suggest that the Q185L substitution facilitates a closed lid conformation that limits access for both the methanol and substrate excess into the active site. The enhanced stability of H86Y/A269T was a result of formation of new hydrogen bonds. These improved characteristics make this variant a potential biocatalyst for biodiesel production. PMID:24362426

Stabilization of AuNPs by monofunctional triazole linked to ferrocene, ferricenium, or coumarin and applications to synthesis, sensing, and catalysis.

PubMed

Li, Na; Zhao, Pengxiang; Igartua, María E; Rapakousiou, Amalia; Salmon, Lionel; Moya, Sergio; Ruiz, Jaime; Astruc, Didier

2014-11-03

Monofunctional triazoles linked to ferrocene, ferricenium, or coumarin (Cou), easily synthesized by copper-catalyzed azide alkyne (CuAAC) "click" reactions between the corresponding functional azides and (trimethylsilyl)acetylene followed by silyl group deprotection, provide a variety of convenient neutral ligands for the stabilization of functional gold nanoparticles (AuNPs) in polar organic solvents. These triazole (trz)-AuNPs are very useful toward a variety of applications to synthesis, sensing, and catalysis. Both ferrocenyl (Fc) and isostructural ferricenium linked triazoles give rise to AuNP stabilization, although by different synthetic routes. Indeed, the first direct synthesis and stabilization of AuNPs by ferricenium are obtained by the reduction of HAuCl4 upon reaction with a ferrocene derivative, AuNP stabilization resulting from a synergy between electrostatic and coordination effects. The ferricenium/ferrocene trz-AuNP redox couple is fully reversible, as shown by cyclic voltammograms that were recorded with both redox forms. These trz-AuNPs are stable for weeks in various polar solvents, but at the same time, the advantage of trz-AuNPs is the easy substitution of neutral trz ligands by thiols and other ligands, giving rise to applications. Indeed, this ligand substitution of trz at the AuNP surface yields a stable Fc-terminated nanogold-cored dendrimer upon reaction with a Fc-terminated thiol dendron, substitution of Cou-linked trz with cysteine, homocysteine, and glutathione provides remarkably efficient biothiol sensing, and a ferricenium-linked trz-AuNP catalyst is effective for NaBH4 reduction of 4-nitrophenol to 4-aminophenol. In this catalytic example, the additional electrostatic AuNP stabilization modulates the reaction rate and induction time.

Preparation and Characterization of the Solid Spherical HMX/F2602 by the Suspension Spray-Drying Method

NASA Astrophysics Data System (ADS)

Ji, Wei; Li, Xiaodong; Wang, Jingyu; Ye, Baoyun; Wang, Cailing

2016-10-01

Solid spherical octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine/fluororubber2602 (HMX/F2602) was prepared by the suspension spray-drying method as follows: firstly, thinning octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) was obtained by a solvent-anti-solvent method. Secondly, thinning HMX suspended in ethyl acetate solvent in a solution of a binder-F2602-was made into a suspension. Finally, the samples were prepared by spray drying. The samples were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), and Fourier transform infrared (FTIR), and its thermal stability as well as mechanical and spark sensitivities were measured. The results of SEM showed that the grain of HMX/F2602 was solid spherical and the particle distribution was homogeneous. The results of XPS indicated that F2602 can be successfully coated on the surface of HMX crystals. Compared to raw HMX, th characteristic drop height was increased from 19.60 to 40.37 cm, an increase of 79.10%. The friction sensitivities of HMX reduced from 100 to 28% and the spark sensitivity of HMX/F2602 increased. The critical explosion temperatures of raw HMX and HMX/F2602 were 275.43 and 274.30°C, respectively. The amount of gas evolution of raw HMX and HMX/F2602 was 0.15 and 0.12 ml.(5 g)-1, respectively. The results of DSC and vacuum stability tests (VSTs) indicate that the thermal stability of HMX/F2602 was equal to that of raw HMX and HMX and F2602 had good compatibility.

Stereochemical inversion of a cyano-stabilized grignard reagent: remarkable effects of the ethereal solvent structure and concentration.

PubMed

Gao, Ming; Patwardhan, Neeraj N; Carlier, Paul R

2013-09-25

Chiral organometallic reagents are useful in asymmetric synthesis, and configurational stability of these species is critical to success. In this study we followed the epimerization of a chiral Grignard reagent, prepared by Mg/Br exchange of bromonitrile trans-2b. This compound underwent highly retentive Mg/Br exchange in Et2O; less retention was observed in 2-MeTHF and THF. Epimerization rate constants k(tc) were determined at 195 K by measuring the diastereomer ratio of deuteration product d1-3b as a function of the delay time before quench. Studies were also performed at varying concentrations of Et2O in toluene. Remarkable dynamic range in k(tc) was seen: relative to reaction at 0.12 M Et2O in toluene, epimerization was 26-, 800-, and 1300-fold faster in Et2O, 2-MeTHF, and THF, respectively. Thus, the identity and concentration of an ethereal solvent can dramatically affect configurational stability. Reaction stoichiometry experiments suggested that, in Et2O, the Grignard reagent derived from trans-2b exists as an i-PrMgCl heterodimer; the invariance of k(tc) over a 20-fold range in [Mg]total ruled out mandatory deaggregation (or aggregation) on the epimerization path. Analysis of the dependency of k(tc) on [Et2O] and temperature in Et2O/toluene solution at 195, 212, and 231 K indicated fast incremental solvation before rate-limiting ion-pair separation and provided an estimate of the entropic cost of capturing a solvent ligand (-13 ± 3 eu). Calculations at the MP2/6-31G*(PCM)//B3LYP/6-31G* level provide support for these conclusions and map out a possible "ionogenic conducted tour" pathway for epimerization.

Understanding the colloidal dispersion stability of 1D and 2D materials: Perspectives from molecular simulations and theoretical modeling.

PubMed

Lin, Shangchao; Shih, Chih-Jen; Sresht, Vishnu; Govind Rajan, Ananth; Strano, Michael S; Blankschtein, Daniel

2017-06-01

The colloidal dispersion stability of 1D and 2D materials in the liquid phase is critical for scalable nano-manufacturing, chemical modification, composites production, and deployment as conductive inks or nanofluids. Here, we review recent computational and theoretical studies carried out by our group to model the dispersion stability of 1D and 2D materials, including single-walled carbon nanotubes, graphene, and graphene oxide in aqueous surfactant solutions or organic solvents. All-atomistic (AA) molecular dynamics (MD) simulations can probe the molecular level details of the adsorption morphology of surfactants and solvents around these materials, as well as quantify the interaction energy between the nanomaterials mediated by surfactants or solvents. Utilizing concepts from reaction kinetics and diffusion, one can directly predict the rate constants for the aggregation kinetics and dispersion life times using MD outputs. Furthermore, the use of coarse-grained (CG) MD simulations allows quantitative prediction of surfactant adsorption isotherms. Combined with the Poisson-Boltzmann equation, the Langmuir isotherm, and the DLVO theory, one can directly use CGMD outputs to: (i) predict electrostatic potentials around the nanomaterial, (ii) correlate surfactant surface coverages with surfactant concentrations in the bulk dispersion medium, and (iii) determine energy barriers against coagulation. Finally, we discuss challenges associated with studying emerging 2D materials, such as, hexagonal boron nitride (h-BN), phosphorene, and transition metal dichalcogenides (TMDCs), including molybdenum disulfide (MoS 2 ). An outlook is provided to address these challenges with plans to develop force-field parameters for MD simulations to enable predictive modeling of emerging 2D materials in the liquid phase. Copyright © 2016 Elsevier B.V. All rights reserved.

Unfolding of a model protein on ion exchange and mixed mode chromatography surfaces.

PubMed

Gospodarek, Adrian M; Hiser, Diana E; O'Connell, John P; Fernandez, Erik J

2014-08-15

Recent studies with proteins indicate that conformational changes and aggregation can occur during ion exchange chromatography (IEC). Such behavior is not usually expected, but could lead to decreased yield and product degradation from both IEC and multi mode chromatography (MMC) that has ligands of both hydrophobic and charged functionalities. In this study, we used hydrogen exchange mass spectrometry to investigate unfolding of the model protein BSA on IEC and MMC surfaces under different solution conditions at 25°C. Increased solvent exposure, indicating greater unfolding relative to that in solution, was found for protein adsorbed on cationic IEC and MMC surfaces in the pH range of 3.0 to 4.5, where BSA has decreased stability in solution. There was no effect of anionic surfaces at pH values in the range from 6.0 to 9.0. Differences of solvent exposure of whole molecules when adsorbed and in solution suggest that adsorbed BSA unfolds at lower pH values and may show aggregation, depending upon pH and the surface type. Measurements on digested peptides showed that classifications of stability can be made for various regions; these are generally retained as pH is changed. When salt was added to MMC systems, where electrostatic interactions would be minimized, less solvent exposure was seen, implying that it is the cationic moieties, rather than the hydrophobic ligands, which cause greater surface unfolding at low salt concentrations. These results suggest that proteins of lower stability may exhibit unfolding and aggregation during IEC and MMC separations, as they can with hydrophobic interaction chromatography. Copyright © 2014 Elsevier B.V. All rights reserved.

Modeling the chelation of As(III) in lewisite by dithiols using density functional theory and solvent-assisted proton exchange.

PubMed

Harper, Lenora K; Bayse, Craig A

2015-12-01

Dithiols such as British anti-lewisite (BAL, rac-2,3-dimercaptopropanol) are an important class of antidotes for the blister agent lewisite (trans-2-chlorovinyldichloroarsine) and, more generally, are chelating agents for arsenic and other toxic metals. The reaction of the vicinal thiols of BAL with lewisite through the chelation of the As(III) center has been modeled using density functional theory (DFT) and solvent-assisted proton exchange (SAPE), a microsolvation method that uses a network of water molecules to mimic the role of bulk solvent in models of aqueous phase chemical reactions. The small activation barriers for the stepwise SN2-type nucleophilic attack of BAL on lewisite (0.7-4.9kcal/mol) are consistent with the favorable leaving group properties of the chloride and the affinity of As(III) for soft sulfur nucleophiles. Small, but insignificant, differences in activation barriers were found for the initial attack of the primary versus secondary thiol of BAL and the R vs S enantiomer. An examination of the relative stability of various dithiol-lewisite complexes shows that ethanedithiols like BAL form the most favorable chelation complexes because the angles formed in five-membered ring are most consistent with the hybridization of As(III). More obtuse S-As-S angles are required for larger chelate rings, but internal As⋯N or As⋯O interactions can enhance the stability of moderate-sized rings. The low barriers for lewisite detoxification by BAL and the greater stability of the chelation complexes of small dithiols are consistent with the rapid reversal of toxicity demonstrated in previously reported animal models. Copyright © 2015 Elsevier Inc. All rights reserved.

A toxic organic solvent-free technology for the preparation of PEGylated paclitaxel nanosuspension based on human serum albumin for effective cancer therapy

PubMed Central

Yin, Tingjie; Dong, Lihui; Cui, Bei; Wang, Lei; Yin, Lifang; Zhou, Jianping; Huo, Meirong

2015-01-01

Clinically, paclitaxel (PTX) is one of most commonly prescribed therapies against a wide range of solid neoplasms. Despite its success, the clinical applicability of PTX (Taxol®) is severely hampered by systemic toxicities induced by Cremophor EL. While attempts to bypass the need for Cremophor EL have been developed through platforms such as Abraxane™, nab™ relies heavily on the use of organic solvents, namely, chloroform. The toxicity introduced by residual chloroform poses a potential risk to patient health. To mitigate the toxicities of toxic organic solvent-based manufacture methods, we have designed a method for the formulation of PTX nanosuspensions (PTX-PEG [polyethylene glycol]-HSA [human serum albumin]) that eliminates the dependence on toxic organic solvents. Coined the solid-dispersion technology, this technique permits the dispersion of PTX into PEG skeleton without the use of organic solvents or Cremophor EL as a solubilizer. Once the PTX-PEG dispersion is complete, the dispersion can be formulated with HSA into nanosuspensions suitable for intravenous administration. Additionally, the incorporation of PEG permits the prolonged circulation through the steric stabilization effect. Finally, HSA-mediated targeting permits active receptor-mediated endocytosis for enhanced tumor uptake and reduced side effects. By eliminating the need for both Cremophor EL and organic solvents while simultaneously increasing antitumor efficacy, this method provides a superior alternative to currently accepted methods for PTX delivery. PMID:26715846

Physical and Chemical Toeholds for Exoplanet Bioastronomy

NASA Technical Reports Server (NTRS)

Hoehler, Tori

2013-01-01

If a search for exoplanet life were mounted today, the likely focus would be to detect oxygen (or ozone) in the atmosphere of a water-bearing rocky planet orbiting roughly 1AU from a G-type star. This appropriately conservative and practical default is necessary in large part because biological input on the question of where and how to look for life has progressed little beyond a purely empirical reliance on the example of terrestrial biology. However, fundamental physical and chemical considerations may impose significant yet universal constraints on biological potential. The liquid water + oxygen paradigm will be considered as an example, with a focus on the question, is liquid water a prerequisite for life? . Life requires a solvent to mediate interactions among biological molecules. A key class of these interactions is molecular recognition with high specificity, which is essential for high fidelity catalysis and (especially) information processing. For example, to correctly reproduce a string consisting of 600,000 units of information (e.g., 600 kilobases, equivalent to the genome of the smallest free living terrestrial organisms) with a 90% success rate requires specificity greater than 10(exp 7):1 for the target molecule vs. incorrect alternatives. Such specificity requires (i) that the correct molecular association is energetically stabilized by at least 40 kJ/mol relative to alternatives, and (ii) that the system is able to sample among possible states (alternative molecular associations) rapidly enough to allow the system to fall under thermodynamic control and express the energetic stabilization. We argue that electrostatic interactions are required to confer the necessary energetic stabilization vs. a large library of molecular alternatives, and that a solvent with polarity and dielectric properties comparable to water is required for the system to sample among possible states and express thermodynamic control. Electrostatic associations can be made in non-polar solvents, but the resulting complexes are too stable to be "unmade" with sufficient frequency to confer thermodynamic control on the system. Such considerations suggest that water, or a solvent with properties very like water, is necessary to support high-fidelity information processing a feature that must be common to all biology and can therefore be considered a critical prerequisite for life.

Improved delivery of the OVA-CD4 peptide to T helper cells by polymeric surface display on Salmonella

PubMed Central

2014-01-01

Background Autotransporter proteins represent a treasure trove for molecular engineers who modify Gram-negative bacteria for the export or secretion of foreign proteins across two membrane barriers. A particularly promising direction is the development of autotransporters as antigen display or secretion systems. Immunologists have been using ovalbumin as a reporter antigen for years and have developed sophisticated tools to detect specific T cells that respond to ovalbumin. Although ovalbumin-expressing bacteria are being used to trace T cell responses to colonizing or invading pathogens, current constructs for ovalbumin presentation have not been optimized. Results The activation of T helper cells in response to ovalbumin was improved by displaying the OVA-CD4 reporter epitope as a multimer on the surface of Salmonella and fused to the autotransporter MisL. Expression was optimized by including tandem in vivo promoters and two post-segregational killing systems for plasmid stabilization. Conclusions The use of an autotransporter protein to present relevant epitope repeats on the surface of bacteria, combined with additional techniques favoring stable and efficient in vivo transcription, optimizes antigen presentation to T cells. The technique of multimeric epitope surface display should also benefit the development of new Salmonella or other enterobacterial vaccines. PMID:24898796

Allostery and the dynamic oligomerization of porphobilinogen synthase

PubMed Central

Jaffe, Eileen K.; Lawrence, Sarah H.

2011-01-01

The structural basis for allosteric regulation of porphobilinogen synthase (PBGS) is modulation of a quaternary structure equilibrium between octamer and hexamer (via dimers), which is represented schematically as 8mer ⇔ 2mer ⇔ 2mer* ⇔ 6mer*. The “*” represents a reorientation between two domains of each subunit that occurs in the dissociated state because it is sterically forbidden in the larger multimers. Allosteric effectors of PBGS are both intrinsic and extrinsic and are phylogenetically variable. In some species this equilibrium is modulated intrinsically by magnesium which binds at a site specific to the 8mer. In other species this equilibrium is modulated intrinsically by pH; the guanidinium group of an arginine being spatially equivalent to the allosteric magnesium ion. In humans, disease associated variants all shift the equilibrium toward the 6mer* relative to wild type. The 6mer* has a surface cavity that is not present in the 8mer and is proposed as a small molecule allosteric binding site. In silico and in vitro approaches have revealed species-specific allosteric PBGS inhibitors that stabilize the 6mer*. Some of these inhibitors are drugs in clinical use leading to the hypothesis that extrinsic allosteric inhibition of human PBGS could be a mechanism for drug side effects. PMID:22037356

Biodiesel production from ethanolysis of palm oil using deep eutectic solvent (DES) as co-solvent

NASA Astrophysics Data System (ADS)

Manurung, R.; Winarta, A.; Taslim; Indra, L.

2017-06-01

Biodiesel produced from ethanolysis is more renewable and have better properties (higher oxidation stability, lower cloud and pour point) compared to methanolysis, but it has a disadvantage such as complicated purification. To improve ethanolysis process, deep eutectic solvent (DES) can be prepared from choline chloride and glycerol and used as co-solvent in ethanolysis. The deep eutectic solvent is formed from a quaternary ammonium salt (choline chloride) and a hydrogen bond donor (Glycerol), it is a non-toxic, biodegradable solvent compared to a conventional volatile organic solvent such as hexane. The deep eutectic solvent is prepared by mixing choline chloride and glycerol with molar ratio 1:2 at temperature 80 °C, stirring speed 300 rpm for 1 hour. The DES is characterized by its density and viscosity. The ethanolysis is performed at a reaction temperature of 70 °C, ethanol to oil molar ratio of 9:1, potassium hydroxide as catalyst concentration of 1.2 wt. DES as co-solvent with concentration 0.5 to 3 wt. stirring speed 400 rpm, and a reaction time 1 hour. The obtained biodiesel is then characterized by its density, viscosity, and ester content. The oil - ethanol phase condition is observed in the reaction tube. The oil - ethanol phase with DES tends to form meniscus compared to without DES, showed that oil and ethanol become more slightly miscible, which favors the reaction. Using DES as co-solvent in ethanolysis showed increasing in yield and easier purification. The esters properties meet the international standards ASTM D6751, with the highest yield achieved 83,67 with 99,77 conversion at DES concentration 2 . Increasing DES concentration above 2 in ethanolysis decrease the conversion and yield, because of the excessive glycerol in the systems makes the reaction equilibrium moves to the reactant side.

Effect of preparation methods on dispersion stability and electrochemical performance of graphene sheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Li, E-mail: chenli1981@lut.cn; Li, Na; Zhang, Mingxia

Chemical exfoliation is one of the most important strategies for preparing graphene. The aggregation of graphene sheets severely prevents graphene from exhibiting excellent properties. However, there are no attempts to investigate the effect of preparation methods on the dispersity of graphene sheets. In this study, three chemical exfoliation methods, including Hummers method, modified Hummers method, and improved method, were used to prepare graphene sheets. The influence of preparation methods on the structure, dispersion stability in organic solvents, and electrochemical properties of graphene sheets were investigated. Fourier transform infrared microscopy, Raman spectra, transmission electron microscopy, and UV–vis spectrophotometry were employed tomore » analyze the structure of the as-prepared graphene sheets. The results showed that graphene prepared by improved method exhibits excellent dispersity and stability in organic solvents without any additional stabilizer or modifier, which is attributed to the completely exfoliation and regular structure. Moreover, cyclic voltammetric and electrochemical impedance spectroscopy measurements showed that graphene prepared by improved method exhibits superior electrochemical properties than that prepared by the other two methods. - Graphical abstract: Graphene oxides with different oxidation degree were obtained via three methods, and then graphene with different crystal structures were created by chemical reduction of exfoliated graphene oxides. - Highlights: • Graphene oxides with different oxidation degree were obtained via three oxidation methods. • The influence of oxidation methods on microstructure of graphene was investigated. • The effect of oxidation methods on dispersion stability of graphene was investigated. • The effect of oxidation methods on electrochemical properties of graphene was discussed.« less

Selective dissolution of halide perovskites as a step towards recycling solar cells

PubMed Central

Kim, Byeong Jo; Kim, Dong Hoe; Kwon, Seung Lee; Park, So Yeon; Li, Zhen; Zhu, Kai; Jung, Hyun Suk

2016-01-01

Most research on perovskite solar cells has focused on improving power-conversion efficiency and stability. However, if one could refurbish perovskite solar cells, their stability might not be a critical issue. From the perspective of cost effectiveness, if failed, perovskite solar cells could be collected and recycled; reuse of their gold electrodes and transparent conducting glasses could reduce the price per watt of perovskite photovoltaic modules. Herein, we present a simple and effective method for removing the perovskite layer and reusing the mesoporous TiO2-coated transparent conducting glass substrate via selective dissolution. We find that the perovskite layer can be easily decomposed in polar aprotic solvents because of the reaction between polar aprotic solvents and Pb2+ cations. After 10 cycles of recycling, a mesoporous TiO2-coated transparent conducting glass substrate-based perovskite solar cell still shows a constant power-conversion efficiency, thereby demonstrating the possibility of recycling perovskite solar cells. PMID:27211006

Demonstration of a stabilized alumina/ethanol colloidal dispersion technique for seeding high temperature air flows

NASA Technical Reports Server (NTRS)

Wernet, Mark P.; Skoch, Gary J.; Wernet, Judith H.

1995-01-01

Laser anemometry enables the measurement of complex flow fields via the light scattered from small particles entrained in the flow. In the study of turbomachinery, refractory seed materials are required for seeding the flow due to the high temperatures encountered. In this work we present a pH stabilization technique commonly employed in ceramic processing to obtain stable dispersions for generating aerosols of refractory seed material. By adding submicron alumina particles to a preadjusted pH solution of ethanol, a stable dispersion is obtained which when atomized, produces a high quality aerosol. Commercial grade alumina powder is used with a moderate size distribution. Other metal oxide powders in various polar solvents could also be used once the point of zero charge (pH(pzc)) of the powder in the solvent has been determined. Laser anemometry measurements obtained using the new seeding technique are compared to measurements obtained using Polystyrene Latex (PSL) spheres as the seed material.

Electrochemical Properties and Speciation in Mg(HMDS)2-Based Electrolytes for Magnesium Batteries as a Function of Ethereal Solvent Type and Temperature.

PubMed

Merrill, Laura C; Schaefer, Jennifer L

2017-09-19

Magnesium batteries are a promising alternative to lithium-ion batteries due to the widespread abundance of magnesium and its high specific volumetric energy capacity. Ethereal solvents such as tetrahydrofuran (THF) are commonly used for magnesium-ion electrolytes due to their chemical compatibility with magnesium metal, but the volatile nature of THF is a concern for practical application. Herein, we investigate magnesium bis(hexamethyldisilazide) plus aluminum chloride (Mg(HMDS) 2 -AlCl 3 ) electrolytes in THF, diglyme, and tetraglyme at varying temperature. We find that, despite the higher thermal stability of the glyme-based electrolytes, THF-based electrolytes have better reversibility at room temperature. Deposition/stripping efficiency is found to be a strong function of temperature. Diglyme-based Mg(HMDS) 2 -AlCl 3 electrolytes are found to not exchange as quickly as THF and tetraglyme, stabilizing AlCl 2 + and facilitating undesired aluminum deposition. Raman spectroscopy, 27 Al NMR, and mass spectrometry are used to identify solution speciation.

Competitive cesium-133 NMR spectroscopic study of complexation of different metal ions with dibenzo-21-crown-7 in acetonitrile-dimethylsulfoxide and nitromethane-dimethylsulfoxide mixtures.

PubMed

Sahmsipur, Mojtaba; Dastjerdi, Leila Shafiee; Alizadeh, Nader; Bijanzadeh, Hamid Reza

2008-04-01

(133)Cs NMR spectroscopy was used to determine the stoichiometry and stability of the Cs(+) ion complex with dibenzo-21-crown-7 (DB21C7) in acetonitrile-dimethylsulfoxide (96.5:3.5, w/w) and nitromethane-dimethylsulfoxide (96.5:3.5, w/w) mixtures. A competitive (133)Cs NMR technique was also employed to probe the complexation of Na(+), K(+), Rb(+), Ag(+), Tl(+), NH(4)(+), Mg(2+), Ba(2+), Hg(2+), Pb(2+) and UO(2)(2+) ions with DB21C7 in the same solvent systems. All the resulting 1:1 complexes in nitromethane-dimethylsulfoxide were more stable than those in acetonitrile-dimethylsulfoxide solution. In both solvent systems, the stability of the resulting complexes was found to vary in the order Rb(+)>K(+) approximately Ba(2+)>Tl(+)>Cs(+)>NH(4)(+) approximately Pb(2+)>Ag(+)>UO(2)(2+)>Hg(2+)>Mg(2+)>Na(+).

A thermostable variant of fructose bisphosphate aldolase constructed by directed evolution also shows increased stability in organic solvents.

PubMed

Hao, Jijun; Berry, Alan

2004-09-01

Thermostable variants of the Class II fructose bisphosphate aldolase have been isolated following four rounds of directed evolution using DNA shuffling of the fda genes from Escherichia coli and Edwardsiella ictaluri. Variants from all four generations of evolution have been purified and characterized. The variants show increased thermostability with no loss of catalytic function at room temperature. The temperature at which 50% of the initial enzyme activity is lost after incubation for 10 min (T50) of the most stable variant, 4-43D6, is increased by 11-12 degrees C over the wild-type enzymes and the half-life of activity at 53 degrees C is increased approximately 190-fold. In addition, variant 4-43D6 shows increased stability to treatment with organic solvents. DNA sequencing of the evolved variants has identified the mutations which have been introduced and which lead to increased thermostability, and the role of the mutations introduced is discussed.

Selective dissolution of halide perovskites as a step towards recycling solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Byeong Jo; Kim, Dong Hoe; Kwon, Seung Lee

Most research on perovskite solar cells has focused on improving power-conversion efficiency and stability. However, if one could refurbish perovskite solar cells, their stability might not be a critical issue. From the perspective of cost effectiveness, if failed, perovskite solar cells could be collected and recycled; reuse of their gold electrodes and transparent conducting glasses could reduce the price per watt of perovskite photovoltaic modules. Here, we present a simple and effective method for removing the perovskite layer and reusing the mesoporous TiO 2-coated transparent conducting glass substrate via selective dissolution. We find that the perovskite layer can be easilymore » decomposed in polar aprotic solvents because of the reaction between polar aprotic solvents and Pb 2+ cations. After 10 cycles of recycling, a mesoporous TiO 2-coated transparent conducting glass substrate-based perovskite solar cell still shows a constant power-conversion efficiency, thereby demonstrating the possibility of recycling perovskite solar cells.« less

Selective dissolution of halide perovskites as a step towards recycling solar cells

DOE PAGES

Kim, Byeong Jo; Kim, Dong Hoe; Kwon, Seung Lee; ...

2016-05-23

Most research on perovskite solar cells has focused on improving power-conversion efficiency and stability. However, if one could refurbish perovskite solar cells, their stability might not be a critical issue. From the perspective of cost effectiveness, if failed, perovskite solar cells could be collected and recycled; reuse of their gold electrodes and transparent conducting glasses could reduce the price per watt of perovskite photovoltaic modules. Here, we present a simple and effective method for removing the perovskite layer and reusing the mesoporous TiO 2-coated transparent conducting glass substrate via selective dissolution. We find that the perovskite layer can be easilymore » decomposed in polar aprotic solvents because of the reaction between polar aprotic solvents and Pb 2+ cations. After 10 cycles of recycling, a mesoporous TiO 2-coated transparent conducting glass substrate-based perovskite solar cell still shows a constant power-conversion efficiency, thereby demonstrating the possibility of recycling perovskite solar cells.« less

High-yield synthesis of brookite TiO.sub.2 nanoparticles

DOEpatents

Huber, Dale L [Albuquerque, NM; Monson, Todd C [Albuquerque, NM

2011-05-17

A method for forming non-agglomerated brookite TiO.sub.2 nanoparticles without the use of expensive organic surfactants or high temperature processing. Embodiments of this invention use titanium isopropoxide as the titanium precursor and isopropanol as both the solvent and ligand for ligand-stabilized brookite-phase titania. Isopropanol molecules serve as the ligands interacting with the titania surfaces that stabilize the titania nanoparticles. The isopropanol ligands can be exchanged with other alcohols and other ligands during or after the nanoparticle formation reaction.

Slipstream pilot-scale demonstration of a novel amine-based post-combustion technology for carbon dioxide capture from coal-fired power plant flue gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krishnamurthy, Krish R.

Post-combustion CO 2 capture (PCC) technology offers flexibility to treat the flue gas from both existing and new coal-fired power plants and can be applied to treat all or a portion of the flue gas. Solvent-based technologies are today the leading option for PCC from commercial coal-fired power plants as they have been applied in large-scale in other applications. Linde and BASF have been working together to develop and further improve a PCC process incorporating BASF’s novel aqueous amine-based solvent technology. This technology offers significant benefits compared to other solvent-based processes as it aims to reduce the regeneration energy requirementsmore » using novel solvents that are very stable under the coal-fired power plant feed gas conditions. BASF has developed the desired solvent based on the evaluation of a large number of candidates. In addition, long-term small pilot-scale testing of the BASF solvent has been performed on a lignite-fired flue gas. In coordination with BASF, Linde has evaluated a number of options for capital cost reduction in large engineered systems for solvent-based PCC technology. This report provides a summary of the work performed and results from a project supported by the US DOE (DE-FE0007453) for the pilot-scale demonstration of a Linde-BASF PCC technology using coal-fired power plant flue gas at a 1-1.5 MWe scale in Wilsonville, AL at the National Carbon Capture Center (NCCC). Following a project kick-off meeting in November 2011 and the conclusion of pilot plant design and engineering in February 2013, mechanical completion of the pilot plant was achieved in July 2014, and final commissioning activities were completed to enable start-up of operations in January 2015. Parametric tests were performed from January to December 2015 to determine optimal test conditions and evaluate process performance over a variety of operation parameters. A long-duration 1500-hour continuous test campaign was performed from May to August 2016 at a selected process condition to evaluate process performance and solvent stability over a longer period similar to how the process would operate as a continuously running large-scale PCC plant. The pilot plant integrated a number of unique features of the Linde-BASF technology aimed at lowering overall energy consumption and capital costs. During the overall test period including startup, parametric testing and long-duration testing, the pilot plant was operated for a total of 6,764 hours out of which testing with flue gas was performed for 4,109 hours. The pilot plant testing demonstrated all of the performance targets including CO 2 capture rate exceeding 90%, CO 2 purity exceeding 99.9 mol% (dry), flue gas processing capacity up to 15,500 lbs/hr (equivalent to 1.5 MWe capacity slipstream), regeneration energy as low as 2.7 GJ/tonne CO 2, and regenerator operating pressure up to 3.4 bara. Excellent solvent stability performance data was measured and verified by Linde and BASF during both test campaigns. In addition to process data, significant operational learnings were gained from pilot tests that will contribute greatly to the commercial success of PCC. Based on a thorough techno-economic assessment (TEA) of the Linde-BASF PCC process integrated with a 550 MWe supercritical coal-fired power plant, the net efficiency of the integrated power plant with CO 2 capture is increased from 28.4% with the DOE/NETL Case 12 reference to 30.9% with the Linde-BASF PCC plant previously presented utilizing the BASF OASE® blue solvent [Ref. 4], and is further increased to 31.4% using a Linde-BASF PCC plant with BASF OASE® blue solvent and an advanced stripper interstage heater (SIH) configuration. The Linde-BASF PCC plant incorporating the BASF OASE® blue solvent also results in significantly lower overall capital costs, thereby reducing the cost of electricity (COE) and cost of CO 2 captured from $147.25/MWh and $56.49/MT CO 2, respectively, for the reference DOE/NETL Case 12 plant, to $128.49/MWh and $41.85/MT CO2 for process case LB1, respectively, and $126.65/MWh and $40.66/MT CO 2 for process case SIH, respectively. With additional innovative Linde-BASF PCC process configuration improvements, the COE and cost of CO 2 captured can be further reduced to $125.51/MWh and $39.90/MT CO 2 for a further optimized PCC process defined as LB1-CREB. Most notably, the Linde-BASF process options assessed have already demonstrated the potential to lower the cost of CO 2 captured below the DOE target of $40/MT CO 2 at the 550 MWe scale for second generation PCC technologies. Project organization, structure, goals, tasks, accomplishments, process criteria and milestones will be presented in this report along with highlights and key results from parametric and long-duration testing of the Linde-BASF PCC pilot. The parametric and long-duration testing campaigns were aimed at validating the performance of the PCC technology against targets determined from a preliminary techno-economic assessment. The stability of the solvent with extended operation in a realistic power plant setting was measured with performance verified. Additionally, general solvent classification information, process operating conditions, normalized solvent performance data, solvent stability test results, flue gas conditions data, CO 2 purity data in the gaseous product stream, steam requirements and process flow diagrams, and updated process economic data for a scaled-up 550 MWe supercritical power plant with CO 2 capture are presented and discussed in this report.« less

A deeper insight into an intriguing acetonitrile-water binary mixture: synergistic effect, dynamic Stokes shift, fluorescence correlation spectroscopy, and NMR studies.

PubMed

Koley, Somnath; Ghosh, Subhadip

2016-11-30

An insight study reveals the strong synergistic solvation behaviours from reporter dye molecules within the acetonitrile (ACN)-water (WT) binary mixture. Synergism of a binary mixture refers to some unique changes of the physical and thermodynamic properties of the solvent mixture, originating from the interactions among its cosolvents, which are absent within the pure cosolvents. Synergistic solvation of a binary mixture is likely to be fundamental for greater stabilization of an excited state solute dipole; at least to some extent greater as compared to one stabilized by any of its cosolvents alone. A dynamic Stokes shift due to the solvation of an excited dipole in the ACN-WT binary mixture is found to be highly relevant to the ground state physical properties of the solute molecule (polarity, hydrophilicity, acidity, etc.). Largely different solvation times in the ACN-WT mixture are observed from different dye molecules with widely varying polarities. However, earlier study shows that dye molecules, irrespective of their varying polarities, exhibit very similar solvation times within a pure solvent (J. Phys. Chem. B, 2014, 118, 7577-7785). On further study with fluorescence correlation spectroscopy (FCS) we observed that, unlike the translational diffusion coefficient (D t ) of a dye molecule within a pure solvent, which remains the same irrespective of the location of the dye molecule inside the solvent, a broad distribution among the D t values of a dye molecule is obtained from different locations within the ACN-WT binary mixture. Lastly our 1 H NMR study in the ACN-WT binary mixture shows the existence of strong hydrogen bond interactions among the cosolvents in the ACN-WT mixture.

Structural elucidation and molecular characterization of Marinobacter sp. α-amylase.

PubMed

Kumar, Sumit; Khan, Rizwan Hasan; Khare, S K

2016-01-01

Halophiles have been perceived as potential source of novel enzymes in recent years. The interest emanates from their ability to catalyze efficiently under high salt and organic solvents. Marinobacter sp. EMB8 α-amylase was found to be active and stable in salt and organic solvents. A study was carried out using circular dichroism (CD), fluorescence spectroscopy, and bioinformatics analysis of similar protein sequence to ascertain molecular basis of salt and solvent adaptability of α-amylase. Structural changes recorded in the presence of varying amounts of NaCl exhibited an increase in negative ellipticity as a function of salt, confirming that salt stabilizes the protein and increases the secondary structure, making it catalytically functional. The data of intrinsic and extrinsic fluorescence (using 1-anilinonaphthalene 8-sulfonate [ANS] as probe) further confirmed the role of salt. The α-amylase was active in the presence of nonpolar solvents, namely, hexane and decane, but inactivated by ethanol. The decrease in the activity was correlated with the loss of tertiary structure in the presence of ethanol. Guanidine hydrochloride and pH denaturation indicated the molten globule state at pH 4.0. Partial N-terminal amino acid sequence of the purified α-amylase revealed the relatedness to Pseudoalteromonas sp. α-amylase. "FVHLFEW" was found as the N-terminal signature sequence. Bioinformatics analysis was done using M. algicola α-amylase protein having the same N-terminal signature sequence. The three-dimensional structure of Marinobacter α-amylase was deduced using the I-TASSER server, which reflected the enrichment of acidic amino acids on the surface, imparting the stability in the presence of salt. Our study clearly indicate that salt is necessary for maintaining the secondary and tertiary structure of halophilic protein, which is a necessary prerequisite for catalysis.

Conformational Changes of the Alanine Dipeptide in Water-Ethanol Binary Mixtures.

PubMed

Almeida, Glauco G; Cordeiro, João M M; Martín, M Elena; Aguilar, Manuel A

2016-04-12

Experimental work developed in the last years has evidenced the capacity of alcohols and polyalcohols to modify the energy landscape of peptides and proteins. However, the mechanism underlying this effect is not clear. Taking as a model system the alanine dipeptide (AD) we perform a QM/MM study in water, ethanol, and a 40-60% in volume water-ethanol mixture. The AD molecule was described at the MP2/aug-cc-pVDZ level. In polar solution, only αR and PPII conformers contribute in an appreciable way to the conformational equilibrium. The final in solution αR-PPII free energy difference is determined from the interplay between the internal energy of the dipeptide and the solute-solvent interaction free energy. Internal energy favors the formation of PPII, whereas, on the contrary, solute-solvent interaction is favorable to αR, so any factor that decreases the solute-solvent interaction free energy will increase the PPII population. The addition of ethanol increases the stability of the PPII conformer. Our results point to the presence of preferential solvation in this system, the composition of the first solvation shell in the binary mixture being dominated by water molecules. Remarkably, this fact does not affect the differential conformational stability that is controlled by long-range interactions. From the analysis of solvent density maps it is concluded that, in the water-ethanol mixture, ethanol molecules are more likely found around the alanine side chain and the carbonyl group, but while in PPII ethanol molecules interact mainly with the carbonyl group of the N-terminal end, in C5 the interaction is with the carbonyl group of the C-terminal end. In αR, ethanol interacts with both carbonyl groups.

Temperature Responses of Soil Organic Matter Components With Varying Recalcitrance

NASA Astrophysics Data System (ADS)

Simpson, M. J.; Feng, X.

2007-12-01

The response of soil organic matter (SOM) to global warming remains unclear partly due to the chemical heterogeneity of SOM composition. In this study, the decomposition of SOM from two grassland soils was investigated in a one-year laboratory incubation at six different temperatures. SOM was separated into solvent- extractable compounds, suberin- and cutin-derived compounds, and lignin monomers by solvent extraction, base hydrolysis, and CuO oxidation, respectively. These SOM components had distinct chemical structures and recalcitrance, and their decomposition was fitted by a two-pool exponential decay model. The stability of SOM components was assessed using geochemical parameters and kinetic parameters derived from model fitting. Lignin monomers exhibited much lower decay rates than solvent-extractable compounds and a relatively low percentage of lignin monomers partitioned into the labile SOM pool, which confirmed the generally accepted recalcitrance of lignin compounds. Suberin- and cutin-derived compounds had a poor fitting for the exponential decay model, and their recalcitrance was shown by the geochemical degradation parameter which stabilized during the incubation. The aliphatic components of suberin degraded faster than cutin-derived compounds, suggesting that cutin-derived compounds in the soil may be at a higher stage of degradation than suberin- derived compounds. The temperature sensitivity of decomposition, expressed as Q10, was derived from the relationship between temperature and SOM decay rates. SOM components exhibited varying temperature responses and the decomposition of the recalcitrant lignin monomers had much higher Q10 values than soil respiration or the solvent-extractable compounds decomposition. Our study shows that the decomposition of recalcitrant SOM is highly sensitive to temperature, more so than bulk soil mineralization. This observation suggests a potential acceleration in the degradation of the recalcitrant SOM pool with global warming.

Probing the free energy landscape of the FBP28WW domain using multiple techniques.

PubMed

Periole, Xavier; Allen, Lucy R; Tamiola, Kamil; Mark, Alan E; Paci, Emanuele

2009-05-01

The free-energy landscape of a small protein, the FBP 28 WW domain, has been explored using molecular dynamics (MD) simulations with alternative descriptions of the molecule. The molecular models used range from coarse-grained to all-atom with either an implicit or explicit treatment of the solvent. Sampling of conformation space was performed using both conventional and temperature-replica exchange MD simulations. Experimental chemical shifts and NOEs were used to validate the simulations, and experimental phi values both for validation and as restraints. This combination of different approaches has provided insight into the free energy landscape and barriers encountered by the protein during folding and enabled the characterization of native, denatured and transition states which are compatible with the available experimental data. All the molecular models used stabilize well defined native and denatured basins; however, the degree of agreement with the available experimental data varies. While the most detailed, explicit solvent model predicts the data reasonably accurately, it does not fold despite a simulation time 10 times that of the experimental folding time. The less detailed models performed poorly relative to the explicit solvent model: an implicit solvent model stabilizes a ground state which differs from the experimental native state, and a structure-based model underestimates the size of the barrier between the two states. The use of experimental phi values both as restraints, and to extract structures from unfolding simulations, result in conformations which, although not necessarily true transition states, appear to share the geometrical characteristics of transition state structures. In addition to characterizing the native, transition and denatured states of this particular system in this work, the advantages and limitations of using varying levels of representation are discussed. 2008 Wiley Periodicals, Inc.

Roles of molecular hydrogen and a hydrogen donor solvent in the cracking of moal model compounds with dispersed catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, Toshimitsu; Ikenaga, Na-oki; Sakota, Takahiro

1994-12-31

It is of great importance to evaluate quantitative hydrogen transfer process by using coal model compounds with a hydrogen-donor solvent. Cronauer el al. showed that in the cracking of benzyl phenyl ether the hydrogen required to stabilize free radicals comes from a donor solvent or intramolecular rearrangement and not from gaseous hydrogen in the absence of a catalyst. Korobkov et al. and Schlosberg et al. showed that the thermolysis of benzyl phenyl ether and dibenzyl ether were accomplished by intramolecular rearrangements. Yokokawa et al. reported that tetralin retarded the catalyzed hydrocracking of coal model compounds containing C-C and C-O bonds.more » However, few studies dealt with quantitative discussion in the hydrogen transfer process from a hydrogen-donor solvent or molecular hydrogen to free radicals derived from a model compound except a series of studies by Nicole and co-workers. On the other hand, it is well known that the amount of naphthalene produced from tetralin decreases after the liquefaction of coal in tetralin with catalyst as compared to the liquefaction in the absence of catalysts. To account for this, two mechanisms are proposed. One is that the catalyst hydrogenates naphthalene produced from tetralin, and the other is that the catalyst promotes the direct hydrogen transfer from molecular hydrogen to free radicals. The purpose of this work is to elucidate the role of catalyst and tetralin by means of the quantitative treatment of the hydrogen transfer reaction stabilizing thermally decomposed free radicals. Cracking of benzyl phenyl ether (BPE), dibenzyl ether (DBE), 1,2-diphenylethane, and 1,3-diphenylpropane was studied in tetralin in the presence of highly disposed catalyst.« less

Synthesis, structure and stability of a chiral imine-based Schiff-based ligand derived from L-glutamic acid and its [Cu4] complex

NASA Astrophysics Data System (ADS)

Muche, Simon; Levacheva, Irina; Samsonova, Olga; Biernasiuk, Anna; Malm, Anna; Lonsdale, Richard; Popiołek, Łukasz; Bakowsky, Udo; Hołyńska, Małgorzata

2017-01-01

Studies of the stability of a ligand derived from L-glutamic acid and ortho-vanillin and its new [Cu4] complex are presented. The [Cu4] complex contains a heterocubane [CuII4O4] core and pendant carboxylic groups increasing its solubility in water, also under basic conditions. The stability of the complex in different solvents is confirmed with ESI-MS studies and such experiments as successful recrystallization. The complex is stable also under physiological conditions whereas the ligand is partly decomposed to L-glutamic acid and ortho-vanillin.

Comparative evaluation of the stability of seven-transmembrane microbial rhodopsins to various physicochemical stimuli

NASA Astrophysics Data System (ADS)

Honda, Naoya; Tsukamoto, Takashi; Sudo, Yuki

2017-08-01

Rhodopsins are seven-transmembrane proteins that function as photoreceptors for a variety of biological processes. Their characteristic visible colors make rhodopsins a good model for membrane-embedded proteins. In this study, by utilizing their color changes, we performed comparative studies on the stability of five microbial rhodopsins using the same instruments, procedures and media. As denaturants, we employed four physicochemical stimuli: (i) thermal perturbation, (ii) the water-soluble reagent hydroxylamine, (iii) the detergent sodium dodecyl sulfate, and (iv) the organic solvent ethanol. On the basis of the results, models for stabilization mechanisms in rhodopsins against each stimulus is proposed.

Picosecond flash spectroscopic studies on ultraviolet stabilizers and stabilized polymers

NASA Technical Reports Server (NTRS)

Scott, G. W.

1982-01-01

Spectroscopic and excited state decay kinetics are reported for monomeric and polymeric forms of ultraviolet stabilizers in the 2-(2'-hydroxyphenyl)-benzotriazole and 2-hydroxybenzophenone classes. For some of these molecules in various solvents at room temperature, (1) ground state absorption spectra, (2) emission spectra, (3) picosecond time-resolved transient absorption spectra, (4) ground state absorption recovery kinetics, (5) emission kinetics, and (6) transient absorption kinetics are reported. In the solid state at low temperatures, emission spectra and their temperature dependent kinetics up to approximately 200K as well as, in one case, the 12K excitation spectra of the observed dual emission are also reported.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woltornist, Steven J.; Carrillo, Jan-Michael Y.; Xu, Thomas O.

The unique electrical, thermal, and mechanical properties of graphene make it a perfect candidate for applications in graphene/graphite based polymer composites, yet challenges due to the lack of solubility of pristine graphene/graphite in water and common organic solvents have limited its practical utilization. In this paper, we report a scalable and environmentally friendly technique to form water-in-oil type emulsions stabilized by overlapping pristine graphene sheets, enabling the synthesis of open cell foams containing a continuous graphitic network. Our approach utilizes the insolubility of graphene/graphite in both water and organic solvents and so does not require oxidation, reduction, surfactants, high boilingmore » solvents, chemical functionalization, or the input of large amounts of mechanical energy or heat. At the heart of our technique is the strong attraction of graphene to high-energy oil and water interfaces. This allows for the creation of stable water-in-oil emulsions with controlled droplet size and overlapping graphene sheets playing the role of surfactant by covering the droplet surface and stabilizing the interfaces with a thin graphitic skin. Finally, these emulsions are used as templates for the synthesis of open cell foams with densities below 0.35 g/cm 3 that exhibit remarkable mechanical and electrical properties including compressive moduli up to ~100 MPa, compressive strengths of over 8.3 MPa (1200 psi), and bulk conductivities approaching 7 S/m.« less

Microencapsulation, Chemical Characterization, and Antimicrobial Activity of Mexican (Lippia graveolens H.B.K.) and European (Origanum vulgare L.) Oregano Essential Oils

PubMed Central

Regalado-González, Carlos; Vázquez-Landaverde, Pedro; Guerrero-Legarreta, Isabel; García-Almendárez, Blanca E.

2014-01-01

The effect of solvent polarity (methanol and pentane) on the chemical composition of hydrodistilled essential oils (EO's) of Lippia graveolens H.B.K. (MXO) and Origanum vulgare L. (EUO) was studied by GC-MS. Composition of modified starch microencapsulated EO's was conducted by headspace-solid-phase microextraction (HS-SPME). The antimicrobial activity of free and microencapsulated EO's was evaluated. They were tested against Salmonella sp., Brochothrix thermosphacta, Pseudomonas fragi, Lactobacillus plantarum, and Micrococcus luteus. Thymol and carvacrol were among the main components of EO's and their free and microencapsulated inhibitory activity was tested against M. luteus, showing an additive combined effect. Chemical composition of EO's varied according to the solvent used for GC analysis and to volatile fraction as evaluated by HS-SPME. Thymol (both solvents) was the main component in essential oil of MXO, while carvacrol was the main component of the volatile fraction. EUO showed α-pinene (methanol) and γ-terpinene (pentane) as major constituents, the latter being the main component of the volatile fraction. EO's showed good stability after 3 months storage at 4°C, where antimicrobial activity of microencapsulated EO's remained the same, while free EO's decreased 41% (MXO) and 67% (EUO) from initial activity. Microencapsulation retains most antimicrobial activity and improves stability of EO's from oregano. PMID:25177730

Thermodynamics of formation for the 18-crown-6-triglycine molecular complex in water-dimethylsulfoxide solvents

NASA Astrophysics Data System (ADS)

Usacheva, T. R.; Lan, Pham Thi; Sharnin, V. A.

2014-06-01

The effect of a water-dimethylsulfoxide (DMSO) solvent on the formation of a molecular complex of 18-crown-6 (18C6) with triglycine (diglycylglycine, 3Gly) is studied via calorimetric titration. It is found that switching from water to an H2O-DMSO mixture with DMSO mole fraction of 0.30 is accompanied by a monotonic increase in the stability of [3Gly18C6] complex, from log K ∘ = 1.10 to log K ∘ = 2.44, and an increase in the exothermicity of the reaction of its formation, from -5.9 to -16.9 kJ/mol. It is shown that the [3Gly18C6] complex exhibits enthalpy stabilization with negative values of enthalpy and entropy over the investigated range of H2O-DMSO solvents. Analysis of the reagents' solvation characteristics reveals that the increase in the reaction's exothermicity of transfer is due to differences in the solvation of [3Gly18C6] and 18C6 with a small solvation contribution from 3Gly. It is concluded that the change in the Gibbs energy of the reaction 3Glysolv + 18C6solv ↔ [3Gly18C6]solv is due to differences in the change in the solvation state of the complex and the peptide (Δtr G ∘([3Gly18C6])-Δtr G ∘(3Gly)).

Theoretical Insight into the Influences of Molecular Ratios on Stabilities and Mechanical Properties, Solvent Effect of HMX/FOX-7 Cocrystal Explosive

NASA Astrophysics Data System (ADS)

Wei, Yan-Ju; Ren, Fu-De; Shi, Wen-Jing; Zhao, Qi

2016-10-01

A molecular dynamics method was employed to study the binding energies of the selected crystal planes of the 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane/1,1-diamino-2,2-dinitroethylene (HMX/FOX-7) cocrystal in different molecular molar ratios. Mechanical properties, densities, and detonation velocities of the cocrystals in different ratios were estimated. The intermolecular interactions and bond dissociation energies (BDEs) of the N-NO2 bond in the HMX:FOX-7 (1:1) complex were calculated using the B3LYP and MP2(full) methods at the 6-311++G (d,p) and 6-311++G(2df,2p) basis sets. Solvent effects on stability are discussed. The results indicate that HMX/FOX-7 cocrystals prefer cocrystalizing in a 1:1 molar ratio, which has good mechanical properties. The N-NO2 bond becomes strong upon the formation of a complex and the sensitivity of HMX might decrease in cocrystals. The sensitivity change of HMX/FOX-7 originates from not only the formation of intermolecular interaction but also the increment in the N-NO2 BDE. HMX/FOX-7 cocrystals exhibit good detonation performance and meet the requirements of high-density energetic materials. Solvents with low dielectric constants may be chosen to obtain stable HMX/FOX-7 cocrystals.

Comprehensive Insights into the Reactivity of Electrolytes Based on Sodium Ions.

PubMed

Eshetu, Gebrekidan Gebresilassie; Grugeon, Sylvie; Kim, Huikyong; Jeong, Sangsik; Wu, Liming; Gachot, Gregory; Laruelle, Stephane; Armand, Michel; Passerini, Stefano

2016-03-08

We report a systematic investigation of Na-based electrolytes that comprise various NaX [X=hexafluorophosphate (PF6 ), perchlorate (ClO4 ), bis(trifluoromethanesulfonyl)imide (TFSI), fluorosulfonyl-(trifluoromethanesulfonyl)imide (FTFSI), and bis(fluorosulfonyl)imide (FSI)] salts and solvent mixtures [ethylene carbonate (EC)/dimethyl carbonate (DMC), EC/diethyl carbonate (DEC), and EC/propylene carbonate (PC)] with respect to the Al current collector stability, formation of soluble degradation compounds, reactivity towards sodiated hard carbon (Nax -HC), and solid-electrolyte interphase (SEI) layer formation. Cyclic voltammetry demonstrates that the stability of Al is highly influenced by the nature of the anions, solvents, and additives. GC-MS analysis reveals that the formation of SEI telltales depends on the nature of the linear alkyl carbonates and the battery chemistry (Li(+) vs. Na(+) ). FTIR spectroscopy shows that double alkyl carbonates are the main components of the SEI layer on Nax -HC. In the presence of Na salts, EC/DMC and EC/DEC presented a higher reactivity towards Nax -HC than EC/PC. For a fixed solvent mixture, the onset temperature follows the sequence NaClO4

Development of eco-friendly submicron emulsions stabilized by a bio-derived gum.

PubMed

Pérez-Mosqueda, Luis María; Ramírez, Pablo; Trujillo-Cayado, Luis Alfonso; Santos, Jenifer; Muñoz, José

2014-11-01

Many traditional organic solvents are being gradually replaced by ecofriendly alternatives. D-Limonene is a terpenic (bio)-solvent that fulfils the requirements to be considered a green solvent. D-Limonene sub-micron emulsions suffer from Ostwald ripening destabilization. In this study, we examined the influence of the addition of a natural gum (rosin gum) to D-limonene in order to prevent Ostwald ripening. This contribution deals with the study of emulsions formulated with a mixture of D-limonene and rosin gum as dispersed phase and Pluronic PE9400 as emulsifier. The procedure followed for the development of these formulations was based on the application of product design principles. This led to the optimum ratio rosin gum/D-limonene and subsequently to the optimum surfactant concentration. The combination of different techniques (rheology, laser diffraction and multiple light scattering) was demonstrated to be a powerful tool to assist in the prediction of the emulsions destabilization process. Not only did the addition of rosin gum highly increase the stability of these emulsions by inhibiting the Ostwald ripening, but it also reduced the emulsions droplet size. Thus, we found that stable sub-micron D-limonene-in-water emulsions have been obtained in the range 3-6 wt% Pluronic PE-9400 by means of a single-step rotor/stator homogenizing process. Copyright © 2014 Elsevier B.V. All rights reserved.

Polymer/Pristine graphene based composites: from emulsions to strong, electrically conducting foams

DOE PAGES

Woltornist, Steven J.; Carrillo, Jan-Michael Y.; Xu, Thomas O.; ...

2015-01-21

The unique electrical, thermal, and mechanical properties of graphene make it a perfect candidate for applications in graphene/graphite based polymer composites, yet challenges due to the lack of solubility of pristine graphene/graphite in water and common organic solvents have limited its practical utilization. In this paper, we report a scalable and environmentally friendly technique to form water-in-oil type emulsions stabilized by overlapping pristine graphene sheets, enabling the synthesis of open cell foams containing a continuous graphitic network. Our approach utilizes the insolubility of graphene/graphite in both water and organic solvents and so does not require oxidation, reduction, surfactants, high boilingmore » solvents, chemical functionalization, or the input of large amounts of mechanical energy or heat. At the heart of our technique is the strong attraction of graphene to high-energy oil and water interfaces. This allows for the creation of stable water-in-oil emulsions with controlled droplet size and overlapping graphene sheets playing the role of surfactant by covering the droplet surface and stabilizing the interfaces with a thin graphitic skin. Finally, these emulsions are used as templates for the synthesis of open cell foams with densities below 0.35 g/cm 3 that exhibit remarkable mechanical and electrical properties including compressive moduli up to ~100 MPa, compressive strengths of over 8.3 MPa (1200 psi), and bulk conductivities approaching 7 S/m.« less

Synthesis, crystal structure and properties of a new 3D supramolecular unsymmetrical tetradentate Schiff bases copper (II) framework with stable tunnels

NASA Astrophysics Data System (ADS)

Al-Noaimi, Mousa; Awwadi, Firas F.; Al-Razagg, Raiid; Esmadi, Fatima T.

2016-12-01

Flexible unsymmetrical Schiff base ligand (L) which is derived from the half unit Y = C6H5COCH2C(Ndbnd CH2C6H4NH2)CH3 (obtained from the reaction of benzoylacetone and 2-aminobenzylamine) and 2- quinolinecarboxaldehyde have been successfully co-assembled with Cu(ClO4)2 to give out the [Cu(L)]ClO4 complex. The complex crystallizes in two different space groups; P21/n and P-1. The crystal structure of the P-1 phase indicates the presence of tunnels; the volume of these tunnels is 157 Å3 which is big enough to accommodate solvent molecules. The X-ray data indicates that these tunnels are most probably filled by highly disordered solvent molecules or solvent molecules with partial occupancy. The tunneled structure is stabilized via π-π stacking interactions to give a supramolecular MOF with 1D rhomboidal tunnels array. The copper(II) atom assumes a distorted-square pyrimidal coordination geometry where the perchlorate is located on the apex of the pyramide. In addition, this work presents and discusses the spectroscopic (IR, UV/vis), electro-chemical (cyclic voltammetry) behavior of the Cu(II) complexes. The Cu(II) oxidation state is stabilized by the novel tetradentate ligands, showing Cu(I/II) couple around 0.1 vs. Cp2Fe/Cp2Fe+.

Microencapsulation, chemical characterization, and antimicrobial activity of Mexican (Lippia graveolens H.B.K.) and European (Origanum vulgare L.) oregano essential oils.

PubMed

Hernández-Hernández, Elvia; Regalado-González, Carlos; Vázquez-Landaverde, Pedro; Guerrero-Legarreta, Isabel; García-Almendárez, Blanca E

2014-01-01

The effect of solvent polarity (methanol and pentane) on the chemical composition of hydrodistilled essential oils (EO's) of Lippia graveolens H.B.K. (MXO) and Origanum vulgare L. (EUO) was studied by GC-MS. Composition of modified starch microencapsulated EO's was conducted by headspace-solid-phase microextraction (HS-SPME). The antimicrobial activity of free and microencapsulated EO's was evaluated. They were tested against Salmonella sp., Brochothrix thermosphacta, Pseudomonas fragi, Lactobacillus plantarum, and Micrococcus luteus. Thymol and carvacrol were among the main components of EO's and their free and microencapsulated inhibitory activity was tested against M. luteus, showing an additive combined effect. Chemical composition of EO's varied according to the solvent used for GC analysis and to volatile fraction as evaluated by HS-SPME. Thymol (both solvents) was the main component in essential oil of MXO, while carvacrol was the main component of the volatile fraction. EUO showed α-pinene (methanol) and γ-terpinene (pentane) as major constituents, the latter being the main component of the volatile fraction. EO's showed good stability after 3 months storage at 4°C, where antimicrobial activity of microencapsulated EO's remained the same, while free EO's decreased 41% (MXO) and 67% (EUO) from initial activity. Microencapsulation retains most antimicrobial activity and improves stability of EO's from oregano.

Surface morphology control of cross-linked polymer particles via dispersion polymerization.

PubMed

Peng, Bo; Imhof, Arnout

2015-05-14

Cross-linked polymer colloids (poly(methyl methacrylate) and polystyrene) with diverse shapes were prepared in polar solvents (ethanol, methanol and water) via dispersion polymerization, in which a linear addition of the cross-linker was used during reaction. Apart from spherical particles we found dented spheres or particles covered with nodules, or a combination of both. A comprehensive investigation was carried out, mainly concentrating on the effect of the experimental conditions (e.g., the addition start time and total addition time, cross-linker density and the solvency of the solvents) on particle morphologies. Consequently, we suggest a number of effective ways for the synthesis of regular (spherical) colloidal particles through maintaining a relatively low concentration of the cross-linker during the entire reaction, or forcing the co-polymerization (of monomer and cross-linker) locus to the continuous medium, or using a high quality or quantity of the stabilizer. Moreover, the size of the particles was also precisely manipulated by varying the polarity of the solvents, the concentration of the cross-linker, and the amount and average molecular weight of the stabilizer. In addition, the formation of the heavily dented particles with a very rough surface prepared under a pure or oxygen-'contaminated' nitrogen environment was monitored over time. The results accumulated in this article are of use for a better understanding of the mechanism of the polymerization and control over the structure and property of polymer particles.

Elucidating the Solvation Structure and Dynamics of Lithium Polysulfides Resulting from Competitive Salt and Solvent Interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajput, Nav Nidhi; Murugesan, Vijayakumar; Shin, Yongwoo

2017-04-10

Fundamental molecular level understanding of functional properties of liquid solutions provides an important basis for designing optimized electrolytes for numerous applica-tions. In particular, exhaustive knowledge of solvation structure, stability and transport properties is critical for developing stable electrolytes for fast charging and high energy density next-generation energy storage systems. Here we report the correlation between solubility, solvation structure and translational dynamics of a lithium salt (Li-TFSI) and polysulfides species using well-benchmarked classical molecular dynamics simulations combined with nuclear magnetic resonance (NMR). It is observed that the polysulfide chain length has a significant effect on the ion-ion and ion-solvent interaction asmore » well as on the diffusion coefficient of the ionic species in solution. In particular, extensive cluster formation is observed in lower order poly-sulfides (Sx2-; x≤4), whereas the longer polysulfides (Sx2-; x>4) show high solubility and slow dynamics in the solu-tion. It is observed that optimal solvent/salt ratio is essen-tial to control the solubility and conductivity as the addi-tion of Li salt increases the solubility but decreases the mo-bility of the ionic species. This work provides a coupled theoretical and experimental study of bulk solvation struc-ture and transport properties of multi-component electro-lyte systems, yielding design metrics for developing optimal electrolytes with improved stability and solubility.« less

Kinetics and mechanical stability of the fibril state control fibril formation time of polypeptide chains: A computational study

NASA Astrophysics Data System (ADS)

Kouza, Maksim; Co, Nguyen Truong; Li, Mai Suan; Kmiecik, Sebastian; Kolinski, Andrzej; Kloczkowski, Andrzej; Buhimschi, Irina Alexandra

2018-06-01

Fibril formation resulting from protein misfolding and aggregation is a hallmark of several neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Despite much progress in the understanding of the protein aggregation process, the factors governing fibril formation rates and fibril stability have not been fully understood. Using lattice models, we have shown that the fibril formation time is controlled by the kinetic stability of the fibril state but not by its energy. Having performed all-atom explicit solvent molecular dynamics simulations with the GROMOS43a1 force field for full-length amyloid beta peptides Aβ40 and Aβ42 and truncated peptides, we demonstrated that kinetic stability can be accessed via mechanical stability in such a way that the higher the mechanical stability or the kinetic stability, the faster the fibril formation. This result opens up a new way for predicting fibril formation rates based on mechanical stability that may be easily estimated by steered molecular dynamics.

Factors influencing the stability and type of hydroxyapatite stabilized Pickering emulsion.

PubMed

Zhang, Ming; Wang, Ai-Juan; Li, Jun-Ming; Song, Na; Song, Yang; He, Rui

2017-01-01

Hydroxyapatite (HAp) nanoparticle stabilized Pickering emulsion was fabricated with poly(l-lactic acid) dissolved in dichloromethane (CH 2 Cl 2 ) solution as oil phase and HAp aqueous dispersion as aqueous phase. Pickering emulsion was cured via in situ solvent evaporation method. Effect of PLLA concentrations, pH value, HAp concentrations, oil-water ratio, emulsification rates and times were studied on emulsion stability and emulsion type, etc. The results indicated emulsion stability increased with the increase of HAp concentration, emulsification rate and time; it is very stable when pH value of aqueous phase was adjusted to 10. Stable W/O and O/W emulsions were fabricated successfully using as-received HAp particles as stabilizer by adjusting the fabricating parameters. The interaction between HAp and PLLA played an important role to stabilize Pickering emulsions. SEM results indicated that both microsphere and porous materials were fabricated using emulsion stabilized by unmodified HAp nanoparticles, implying that both W/O and O/W emulsion type were obtained. Copyright © 2016 Elsevier B.V. All rights reserved.

Membrane binding of human immunodeficiency virus type 1 matrix protein in vivo supports a conformational myristyl switch mechanism.

PubMed Central

Spearman, P; Horton, R; Ratner, L; Kuli-Zade, I

1997-01-01

The interaction of the human immunodeficiency virus (HIV) Gag protein with the plasma membrane of a cell is a critical event in the assembly of HIV particles. The matrix protein region (MA) of HIV type 1 (HIV-1) Pr55Gag has previously been demonstrated to confer membrane-binding properties on the precursor polyprotein. Both the myristic acid moiety and additional determinants within MA are essential for plasma membrane binding and subsequent particle formation. In this study, we demonstrated the myristylation-dependent membrane interaction of MA in an in vivo membrane-binding assay. When expressed within mammalian cells, MA was found both in association with cellular membranes and in a membrane-free form. In contrast, the intact precursor Pr55Gag molecule analyzed in an identical manner was found almost exclusively bound to membranes. Both membrane-bound and membrane-free forms of MA were myristylated and phosphorylated. Differential membrane binding was not due to the formation of multimers, as dimeric and trimeric forms of MA were also found in both membrane-bound and membrane-free fractions. To define the requirements for membrane binding of MA, we analyzed the membrane binding of a series of MA deletion mutants. Surprisingly, deletions within alpha-helical regions forming the globular head of MA led to a dramatic increase in overall membrane binding. The stability of the MA-membrane interaction was not affected by these deletions, and no deletion eliminated membrane binding of the molecule. These results establish that myristic acid is a primary determinant of the stability of the Gag protein-membrane interaction and provide support for the hypothesis that a significant proportion of HIV-1 MA molecules may adopt a conformation in which myristic acid is hidden and unavailable for membrane interaction. PMID:9261380

Left Ventricular Assist Device Design Reduces von Willebrand Factor Degradation: A Comparative Study Between the HeartMate II and the EVAHEART Left Ventricular Assist System.

PubMed

Bartoli, Carlo R; Kang, Jooeun; Zhang, David; Howard, Jessica; Acker, Michael; Atluri, Pavan; Motomura, Tadashi

2017-04-01

Supraphysiologic shear stress from continuous-flow left ventricular assist devices (LVADs) accelerates von Willebrand factor (vWF) degradation and predisposes patients to nonsurgical bleeding. It is unknown whether unique design characteristics of LVADs differentially affect vWF degradation. We tested the hypothesis that the centrifugal-flow EVAHEART (Evaheart, Houston, TX) left ventricular assist system (LVAS), which was designed to minimize shear stress (low operational revolutions per minute [rpm], larger flow gaps, low shear stress, flat H-Q curve), reduced vWF degradation versus the axial-flow HeartMate II (Thoratec, Pleasanton, CA) LVAD. Whole human blood was obtained from volunteer donors (n = 22). Blood was circulated for 12 hours in mock circulatory loops through a HeartMate II (n = 10; 11,400 rpm, 6.3 ± 0.8 L/min, 76 ± 2 mm Hg) or an EVAHEART LVAS (n = 12; 2,300 rpm, 5.7 ± 0.1 L/min, 80 ± 1 mm Hg). vWF degradation was characterized with electrophoresis and immunoblotting for large vWF multimers and 11 vWF degradation fragments. The HeartMate II eliminated large vWF multimers and significantly (p < 0.05) increased 10 of 11 vWF degradation fragments at 6 and 12 hours. The increase was approximately 2.0-fold at 6 hours and 2.2-fold at 12 hours. In contrast, the EVAHEART LVAS modestly reduced large vWF multimers and significantly increased 5 of 11 and 8 of 11 vWF degradation fragments at 6 and 12 hours, respectively. The increase was approximately 1.5-fold at 6 hours and 1.7-fold at 12 hours. The EVAHEART LVAS caused significantly less degradation (p < 0.01) than the HeartMate II of the 140 kDa vWF fragment (cleavage product of ADAMTS-13, the vWF protease). The EVAHEART LVAS caused significantly less vWF degradation than the HeartMate II in a mock circulatory loop with whole human blood. LVAD design features may minimize vWF degradation. These data may inform the design and operation of next-generation LVADs to minimize blood trauma. Copyright © 2017 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.

Functionalization of graphene using deep eutectic solvents

NASA Astrophysics Data System (ADS)

Hayyan, Maan; Abo-Hamad, Ali; AlSaadi, Mohammed AbdulHakim; Hashim, Mohd Ali

2015-08-01

Deep eutectic solvents (DESs) have received attention in various applications because of their distinctive properties. In this work, DESs were used as functionalizing agents for graphene due to their potential to introduce new functional groups and cause other surface modifications. Eighteen different types of ammonium- and phosphonium-salt-based DESs were prepared and characterized by FTIR. The graphene was characterized by FTIR, STA, Raman spectroscopy, XRD, SEM, and TEM. Additional experiments were performed to study the dispersion behavior of the functionalized graphene in different solvents. The DESs exhibited both reduction and functionalization effects on DES-treated graphene. Dispersion stability was investigated and then characterized by UV-vis spectroscopy and zeta potential. DES-modified graphene can be used in many applications, such as drug delivery, wastewater treatment, catalysts, composite materials, nanofluids, and biosensors. To the best of our knowledge, this is the first investigation on the use of DESs for graphene functionalization.

Functionalization of graphene using deep eutectic solvents.

PubMed

Hayyan, Maan; Abo-Hamad, Ali; AlSaadi, Mohammed AbdulHakim; Hashim, Mohd Ali

2015-12-01

Deep eutectic solvents (DESs) have received attention in various applications because of their distinctive properties. In this work, DESs were used as functionalizing agents for graphene due to their potential to introduce new functional groups and cause other surface modifications. Eighteen different types of ammonium- and phosphonium-salt-based DESs were prepared and characterized by FTIR. The graphene was characterized by FTIR, STA, Raman spectroscopy, XRD, SEM, and TEM. Additional experiments were performed to study the dispersion behavior of the functionalized graphene in different solvents. The DESs exhibited both reduction and functionalization effects on DES-treated graphene. Dispersion stability was investigated and then characterized by UV-vis spectroscopy and zeta potential. DES-modified graphene can be used in many applications, such as drug delivery, wastewater treatment, catalysts, composite materials, nanofluids, and biosensors. To the best of our knowledge, this is the first investigation on the use of DESs for graphene functionalization.

Non-aqueous homogenous biocatalytic conversion of polysaccharides in ionic liquids using chemically modified glucosidase.

PubMed

Brogan, Alex P S; Bui-Le, Liem; Hallett, Jason P

2018-06-25

The increasing requirement to produce platform chemicals and fuels from renewable sources means advances in biocatalysis are rapidly becoming a necessity. Biomass is widely used in nature as a source of energy and as chemical building blocks. However, recalcitrance towards traditional chemical processes and solvents provides a significant barrier to widespread utility. Here, by optimizing enzyme solubility in ionic liquids, we have discovered solvent-induced substrate promiscuity of glucosidase, demonstrating an unprecedented example of homogeneous enzyme bioprocessing of cellulose. Specifically, chemical modification of glucosidase for solubilization in ionic liquids can increase thermal stability to up to 137 °C, allowing for enzymatic activity 30 times greater than is possible in aqueous media. These results establish that through a synergistic combination of chemical biology (enzyme modification) and reaction engineering (solvent choice), the biocatalytic capability of enzymes can be intensified: a key step towards the full-scale deployment of industrial biocatalysis.

Modeling the thermal unfolding 2DIR spectra of a β-hairpin peptide based on the implicit solvent MD simulation.

PubMed

Wu, Tianmin; Yang, Lijiang; Zhang, Ruiting; Shao, Qiang; Zhuang, Wei

2013-07-25

We simulated the equilibrium isotope-edited FTIR and 2DIR spectra of a β-hairpin peptide trpzip2 at a series of temperatures. The simulation was based on the configuration distributions generated using the GB(OBC) implicit solvent model and the integrated tempering sampling (ITS) technique. A soaking procedure was adapted to generate the peptide in explicit solvent configurations for the spectroscopy calculations. The nonlinear exciton propagation (NEP) method was then used to calculate the spectra. Agreeing with the experiments, the intensities and ellipticities of the isotope-shifted peaks in our simulated signals have the site-specific temperature dependences, which suggest the inhomogeneous local thermal stabilities along the peptide chain. Our simulation thus proposes a cost-effective means to understand a peptide's conformational change and related IR spectra across its thermal unfolding transition.

Hydrophobic potential of mean force as a solvation function for protein structure prediction.

PubMed

Lin, Matthew S; Fawzi, Nicolas Lux; Head-Gordon, Teresa

2007-06-01

We have developed a solvation function that combines a Generalized Born model for polarization of protein charge by the high dielectric solvent, with a hydrophobic potential of mean force (HPMF) as a model for hydrophobic interaction, to aid in the discrimination of native structures from other misfolded states in protein structure prediction. We find that our energy function outperforms other reported scoring functions in terms of correct native ranking for 91% of proteins and low Z scores for a variety of decoy sets, including the challenging Rosetta decoys. This work shows that the stabilizing effect of hydrophobic exposure to aqueous solvent that defines the HPMF hydration physics is an apparent improvement over solvent-accessible surface area models that penalize hydrophobic exposure. Decoys generated by thermal sampling around the native-state basin reveal a potentially important role for side-chain entropy in the future development of even more accurate free energy surfaces.

An ambient stable core-substituted perylene bisimide dianion: isolation and single crystal structure analysis† †Electronic supplementary information (ESI) available: Synthesis, spectroelectrochemistry, UV-vis, electrochemistry, X-ray diffraction, NMR and mass spectra. CCDC 1032959. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4sc03671a Click here for additional data file. Click here for additional data file.

PubMed Central

Seifert, Sabine; Schmidt, David

2015-01-01

Here we report the first example of an isolable, ambient stable perylene bisimide (PBI) dianion which was synthesized by catalytic reduction of a highly electron deficient PBI derivative. The remarkable stability of this unprecedented dianion in air for months facilitated its complete characterization by different methods, including single crystal X-ray analysis. Furthermore, solvent dependent cyclic and square wave voltammetry studies revealed that the formation of PBI dianions is preferred in more polar solvents, whereas the generation of PBI radical anions should be favoured in less polar solvents. PMID:28717450

Biosynthesis of glycerol carbonate from glycerol by lipase in dimethyl carbonate as the solvent.

PubMed

Lee, Kyung Hwa; Park, Chang-Ho; Lee, Eun Yeol

2010-11-01

Glycerol carbonate was synthesized from renewable glycerol and dimethyl carbonate using lipase in solvent-free reaction system in which excess dimethyl carbonate played as the reaction medium. A variety of lipases have been tested for their abilities to catalyze transesterification reaction, and Candida antartica lipase B and Novozyme 435 exhibited higher catalytic activities. The silica-coated glycerol with a 1:1 ratio was supplied to prevent two-phase formation between hydrophobic dimethyl carbonate and hydrophilic glycerol. Glycerol carbonate was successfully synthesized with more than 90% conversion from dimethyl carbonate and glycerol with a molar ratio of 10 using Novozyme 435-catalyzed transesterification at 70 °C. The Novozyme 435 [5% (w/w) and 20% (w/w)] and silica gel were more than four times recycled with good stability in a repeated batch operation for the solvent-free synthesis of glycerol carbonate.

Opening Furan for Tailoring Properties of Bio-based Poly(Furfuryl Alcohol) Thermoset.

PubMed

Falco, Guillaume; Guigo, Nathanael; Vincent, Luc; Sbirrazzuoli, Nicolas

2018-06-11

This work shows how furan ring-opening reactions were controlled by polymerization conditions to tune the cross-link density in bio-based poly(furfuryl alcohol) (PFA). The influence of water and isopropyl alcohol (IPA) on the polymerization of furfuryl alcohol, and particularly on furan ring-opening, was investigated by means of 13 C NMR and FT-IR spectroscopy. Results indicated that formation of open structures were favored in the presence of solvents, thus leading to modification of the thermo-mechanical properties compared to PFA cross-linked without solvent. Dynamic mechanical analyses showed that when slightly more open structures were present in PFA it resulted in an important decrease of the cross-link density. Despite lower glass-transition temperature and lower elastic modulus for PFA polymerized with solvent, the thermal stability remains very high (>350 °C) even with more open structures in PFA. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spectral characteristics of ortho, meta and para dihydroxy benzenes in different solvents, pH and beta-cyclodextrin.

PubMed

Stalin, T; Devi, R Anitha; Rajendiran, N

2005-09-01

Spectral characteristics of ortho, meta and para dihydroxy benzenes (DHB's) have been studied in different solvents, pH and beta-cyclodextrin. Solvent study shows that: (i) the interaction of OH group with the aromatic ring is less than that of amino group both in the ground and excited states, (ii) in absorption, the charge transfer interaction of OH group in para position is larger than ortho and meta positions. pH studies reveals that DHB's are more acidic than phenol. The higher pK(a) value of oDHB (monoanion-dianion) indicates that the formed monoanion is more stabilized by intramolecular hydrogen bonding. DHB's forms a 1:1 inclusion complex with beta-CD. In beta-CD medium, absorption spectra of DHB's mono and dianions shows unusual blue shifts, whereas in the excited state, the spectral characteristics of DHB's follow the same trend in both aqueous and beta-CD medium.

Solvent-free fabrication of biodegradable hot-film flow sensor for noninvasive respiratory monitoring

NASA Astrophysics Data System (ADS)

Dinh, Toan; Phan, Hoang-Phuong; Nguyen, Tuan-Khoa; Qamar, Afzaal; Woodfield, Peter; Zhu, Yong; Nguyen, Nam-Trung; Viet Dao, Dzung

2017-06-01

In this paper, we report on a low-cost, environment-friendly and wearable thermal flow sensor, which can be manufactured in-house using pencil graphite as a sensing hot film and biodegradable printing paper as a substrate, without using any toxic solvents or cleanroom facilities. The hot film flow sensor offers excellent performance such as high signal-to-noise ratio (≥slant 40 for an air flow velocity of 1 m s-1), high sensitivity to airflow (53.7 mV(m s-1)-0.8) and outstanding long-term stability (almost no drift in 24 h). The sensor can be comfortably affixed to the philtrum of patients and measures human respiration in realtime. The results indicate that the wearable thermal flow sensors fabricated by this solvent-free and user-friendly method could be employed in human respiratory monitoring.

An insight into non-emissive excited states in conjugated polymers

NASA Astrophysics Data System (ADS)

Hu, Zhongjian; Willard, Adam P.; Ono, Robert J.; Bielawski, Christopher W.; Rossky, Peter J.; vanden Bout, David A.

2015-09-01

Conjugated polymers in the solid state usually exhibit low fluorescence quantum yields, which limit their applications in many areas such as light-emitting diodes. Despite considerable research efforts, the underlying mechanism still remains controversial and elusive. Here, the nature and properties of excited states in the archetypal polythiophene are investigated via aggregates suspended in solvents with different dielectric constants (ε). In relatively polar solvents (ε>~ 3), the aggregates exhibit a low fluorescence quantum yield (QY) of 2-5%, similar to bulk films, however, in relatively nonpolar solvents (ε<~ 3) they demonstrate much higher fluorescence QY up to 20-30%. A series of mixed quantum-classical atomistic simulations illustrate that dielectric induced stabilization of nonradiative charge-transfer (CT) type states can lead to similar drastic reduction in fluorescence QY as seen experimentally. Fluorescence lifetime measurement reveals that the CT-type states exist as a competitive channel of the formation of emissive exciton-type states.

European Science Notes Information Bulletin Reports on Current European/Middle Eastern Science,

DTIC Science & Technology

1988-02-01

monosaccharides and stated that genetic stability of certain for the preparation of isotopically la- recombinant microoraanisms is one of the beled sugars...hydrocarbons and polyethylene glycol (PEG)/ polysaccharide hydrocarbon derivatives) in the aqueous and PEG/salt. The polysaccharide may be phase. The solvent

SBIR reports on the chemistry of lithium battery technology

NASA Astrophysics Data System (ADS)

Kilroy, W. P.

1989-11-01

The following contents are included: Identification of an Improved Mixed Solvent Electrolyte for a Lithium Secondary Battery; Catalyzed Cathodes for Lithium-Thionyl Chloride Batteries; Improved Lithium/Thionyl Chloride Cells Using New Electrolyte Salts; Development of Calcium Primary Cells With Improved Anode Stability and Energy Density.

Theoretical analysis of co-solvent effect on the proton transfer reaction of glycine in a water–acetonitrile mixture

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kasai, Yukako; Yoshida, Norio, E-mail: noriwo@chem.kyushu-univ.jp; Nakano, Haruyuki

2015-05-28

The co-solvent effect on the proton transfer reaction of glycine in a water–acetonitrile mixture was examined using the reference interaction-site model self-consistent field theory. The free energy profiles of the proton transfer reaction of glycine between the carboxyl oxygen and amino nitrogen were computed in a water–acetonitrile mixture solvent at various molar fractions. Two types of reactions, the intramolecular proton transfer and water-mediated proton transfer, were considered. In both types of the reactions, a similar tendency was observed. In the pure water solvent, the zwitterionic form, where the carboxyl oxygen is deprotonated while the amino nitrogen is protonated, is moremore » stable than the neutral form. The reaction free energy is −10.6 kcal mol{sup −1}. On the other hand, in the pure acetonitrile solvent, glycine takes only the neutral form. The reaction free energy from the neutral to zwitterionic form gradually increases with increasing acetonitrile concentration, and in an equally mixed solvent, the zwitterionic and neutral forms are almost isoenergetic, with a difference of only 0.3 kcal mol{sup −1}. The free energy component analysis based on the thermodynamic cycle of the reaction also revealed that the free energy change of the neutral form is insensitive to the change of solvent environment but the zwitterionic form shows drastic changes. In particular, the excess chemical potential, one of the components of the solvation free energy, is dominant and contributes to the stabilization of the zwitterionic form.« less

Additive effect on reductive decomposition and binding of carbonate-based solvent toward solid electrolyte interphase formation in lithium-ion battery.

PubMed

Ushirogata, Keisuke; Sodeyama, Keitaro; Okuno, Yukihiro; Tateyama, Yoshitaka

2013-08-14

The solid-electrolyte interphase (SEI) formed through the reductive decomposition of solvent molecules plays a crucial role in the stability and capability of a lithium-ion battery (LIB). Here we investigated the effects of adding vinylene carbonate (VC) to ethylene carbonate (EC) solvent, a typical electrolyte in LIBs, on the reductive decomposition. We focused on both thermodynamics and kinetics of the possible processes and used density functional theory-based molecular dynamics with explicit solvent and Blue-moon ensemble technique for the free energy change. We considered Li(+) in only EC solvent (EC system) and in EC solvent with a VC additive (EC/VC system) to elucidate the additive effects. In addition to clarifying the equilibrium properties, we evaluated the free energy changes along several EC or VC decomposition pathways under one-electron (1e) reduction condition. Two-electron (2e) reduction and attacks of anion radicals to intact molecules were also examined. The present results completely reproduce the gaseous products observed in the experiments. We also found a new mechanism involving the VC additive: the VC additive preferentially reacts with the EC anion radical to suppress the 2e reduction of EC and enhance the initial SEI formation, contrary to the conventional scenario in which VC additive is sacrificially reduced and its radical oligomerization becomes the source of SEI. Because our mechanism needs only 1e reduction, the irreversible capacity at the SEI formation will decrease, which is also consistent with the experimental observations. These results reveal the primary role of VC additive in the EC solvent.

Influence of OH⋯N and NH⋯O inter- and intramolecular hydrogen bonds in the conformational equilibrium of some 1,3-disubstituted cyclohexanes through NMR spectroscopy and theoretical calculations

NASA Astrophysics Data System (ADS)

de Oliveira, Paulo R.; Viesser, Renan V.; Guerrero, Palimécio G., Jr.; Rittner, Roberto

2011-05-01

The analysis of concentration effects in the 1H NMR data of cis-3-aminocyclohexanol ( ACOL) showed that its diequatorial conformer changes from 60% at 0.01 mol L -1 to 70% at 0.40 mol L -1 in acetone-d 6. A similar increase was also observed for the diequatorial conformer of cis-3-N-methylaminocyclohexanol ( MCOL), from 32% (CDCl 3 0.01 mol L -1) to 55% (CDCl 3 0.40 mol L -1). The increase in solvent basicity leads to a large stabilization effect for the diequatorial conformer of both compounds too. For ACOL, it changes from 47% (Δ Geqeq- axax = 0.06 kcal mol -1) in CCl 4 to 93% (Δ Geqeq- axax = -1.53 kcal mol -1) in DMSO, while for MCOL it goes from 7% (Δ Geqeq- axax = 1.54 kcal mol -1) in CCl 4 to 82% (Δ Geqeq- axax = -0.88 kcal mol -1) in pyridine-d 6. These results indicate that the intr amolecular hydrogen bonds (IAHB) OH⋯N and NH⋯O stabilize the diaxial conformers of these compounds in a non-polar solvent. For cis-3-amino-1-methoxycyclohexane ( ACNE) and cis-3-N-methylamino-1-methoxy-cyclohexane ( MCNE) no changes were observed in equilibrium with the variation of solvent polarity. These results indicate for the first time that the IAHB NH⋯O is not strong enough to stabilize the diaxial conformer of these compounds and that the conformation equilibria of the cis isomers of compounds ACOL and MCOL are influenced only by the IAHB OH⋯N. Moreover, the presence of a secondary amino group (93% of diaxial conformer in CCl 4) leads to an IAHB OH⋯N stronger than in primary and tertiary amino-derivatives (53 and 54% of diaxial conformer, respectively) for 1,3-disubstituted cyclohexanes. Values obtained from the theoretical data through the B3LYP functional are in agreement with the experimental results and indicate that the IAHB strength that influences the conformational equilibrium of these compounds is the IAHB OH⋯N. Thus, the IAHB NH⋯O do not stabilize the diaxial conformer of the cis isomer of compounds ACNE and MCNE showing that the diequatorial conformer will always be more stable than the diaxial conformer, independent of concentration or solvent.

Effect of the deletion of the C region on the structure and hydration of insulin-like growth factor 1: a molecular dynamics investigation

NASA Astrophysics Data System (ADS)

Degreve, Leo; Silva, Luciene B.

The structure and hydration of insulin-like growth factor 1 and an inactive mutant lacking the C region have been investigated in aqueous solution by molecular dynamics simulation. The overall structures of the two polypeptide resemble those determined by NMR spectroscopy. The deletion of the C region in the wild polypeptide introduces structural stability in the mutant, leading to a better definition of the secondary structure elements. A detailed hydration analysis was performed using the radial distribution functions and energy distributions. The backbone of the mutant is in general more solvent accessible than the wild polypeptide backbone. The structural rearrangements induced in the mutant led to changes in the solvent exposition of Tyr24 and Tyr60, which are residues important for ligand-receptor complex formation. Tyr24 exhibited a similar degree of solvent exposition in both IGF-1 and in the mutant; however, its hydroxyl group in the wild polypeptide is better solvated than in the mutant. Tyr60 was found to be solvent exposed in the wild protein, while in the mutant the involvement of its hydroxyl group in intramolecular hydrogen bonds led to it being buried away from the solvent.

Unveiling the mechanism of the promising two-dimensional photoswitch - Hemithioindigo

NASA Astrophysics Data System (ADS)

Li, Donglin; Yang, Yonggang; Li, Chaozheng; Liu, Yufang

2018-07-01

The control of internal molecular motions by outside stimuli is a decisive task in the construction of functional molecules and molecular machines. Light-induced intramolecular rotations of photoswitches have attracted increasing research interests because of the high stability and high reversibility of photoswitches. Recently, Henry et al. reported an unprecedented two-dimensional controlled photoswitch, the hemithioindigo (HTI) derivative Z1, whose single bond rotation in dimethyl sulphoxide (DMSO) solvent and double bond rotation in cyclohexane solvent can be induced by visible light (J. Am. Chem. Soc. 2016, 138, 12,219). Here we investigate the intramolecular rotations of the HTI and Z1 in different polar solvents by time-dependent density functional theory (TDDFT) and Nonadiabatic dynamic simulations. Due to the steric hindrance between methyl and thioindigo fragment, the rotations of Z1 in the excited state are obstructed. Interestingly, the HTI exhibits two distinct rotation paths in DMSO and cyclohexane solvents at about 50 fs. The intermolecular hydrogen bonds between HTI and DMSO play an important role in the rotation of HTI in DMSO solvent. Therefore, the HTI is a more promising two-dimensional photoswitch compared with the Z1. Our finding is thus of fundamental importance to understand the mechanisms of this class of photoswitches and design complex molecular behavior.

Polymorphs and solvatomorphs of azilsartan medoxomil: Elucidation of solvent-induced construction and conformational diversity

NASA Astrophysics Data System (ADS)

Zhang, Xian-Rui; He, Sai-Fei; Zhang, Shuo; Li, Jing; Li, Shan; Liu, Jin-Song; Zhang, Lei

2017-02-01

Two polymorphs (AM-A and AM-B) of azilsartan medoxomil (AM) and four AM solvatomorphs with toluene (AM-TOL), 1,4-dioxane (AM-DIO), chloroform (AM-TCM) and N,N-dimethylacetamide (AM-DMA) have been prepared by the hydrolysis of azilsartan medoxomil potassium in aqueous-organic solutions. In the crystal structures of two polymorphs and three solvatomorphs (AM-TOL, AM-DIO and AM-TCM), two asymmetric AM molecules form the dimeric cycle-like structures via intermolecular Nsbnd H⋯N hydrogen bonds in R22 (26) ring, while AM-DMA shows intramolecular Nsbnd H⋯O hydrogen bond between AM and DMA molecules. The hydrogen bonds (Csbnd H⋯O or Csbnd H⋯N) and π···π (or Csbnd H···π) interactions are helpful to stabilize the conformational diversity of AM. The solvent-induced experiment shows that solvent molecules have great influence on the solvatomorph formation and DIO can form the most steady solvatomorph than other solvents. The thermal study demonstrates that toluene molecules in three solvatomorphs (AM-TOL, AM-DIO and AM-TCM) are the most difficult to remove from the cage. Our results illustrate that the solvent plays significant role in tuning the size of the cage and producing the conformational diversity of AM molecules.