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Sample records for alkyl thiolate monolayers

  1. Scanning probe microscopies for the creation and characterization of interfacial architectures: Studies of alkyl thiolate monolayers at gold

    SciTech Connect

    Green, John -Bruce

    1997-01-10

    Scanning probe microscopy (SPM) offers access to the structural and material properties of interfaces, and when combined with macroscopic characterization techniques results in a powerful interfacial development tool. However, the relative infancy of SPM techniques has dictated that initial investigations concentrate on model interfacial systems as benchmarks for testing the control and characterization capabilities of SPM. One such family of model interfacial systems results from the spontaneous adsorption of alkyl thiols to gold. This dissertation examines the application of SPM to the investigation of the interfacial properties of these alkyl thiolate monolayers. Structural investigations result in a proposed explanation for counterintuitive correlations between substrate roughness and heterogeneous electron transfer barrier properties. Frictional measurements are used for characterization of the surface free energy of a series of end-group functionalized monolayers, as well as for the material properties of monolayers composed of varying chain length alkyl thiols. Additional investigations used these characterization techniques to monitor the real-time evolution of chemical and electrochemical surface reactions. The results of these investigations demonstrates the value of SPM technology to the compositional mapping of surfaces, elucidation of interfacial defects, creation of molecularly sized chemically heterogeneous architectures, as well as to the monitoring of surface reactions. However, it is the future which will demonstrate the usefulness of SPM technology to the advancement of science and technology.

  2. Electrochemical Deposition Of Thiolate Monolayers On Metals

    NASA Technical Reports Server (NTRS)

    Porter, Marc D.; Weissharr, Duane E.

    1995-01-01

    Electrochemical method devised for coating metal (usually, gold) surfaces with adherent thiolate monolayers. Affords greater control over location and amount of material deposited and makes it easier to control chemical composition of deposits. One important potential use for this method lies in fabrication of chemically selective thin-film resonators for microwave oscillators used to detect pollutants: monolayer formulated to bind selectively pollutant chemical species of interest, causing increase in mass of monolayer and corresponding decrease in frequency of resonance. Another important potential use lies in selective chemical derivatization for purposes of improving adhesion, lubrication, protection against corrosion, electrocatalysis, and electroanalysis.

  3. Structure and function evolution of thiolate monolayers on gold

    SciTech Connect

    Edwards, Grant Alvin

    2006-01-01

    The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (infrared reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

  4. Structure and Function Evolution of Thiolate Monolayers on Gold

    SciTech Connect

    Edwards, Grant Alvin

    2006-01-01

    The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (inbred reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

  5. Thiolated cyclodextrin self-assembled monolayer-like characterized with secondary ion mass spectrometry

    NASA Astrophysics Data System (ADS)

    Rabara, L.; Aranyosiova, M.; Velic, D.

    2011-01-01

    In the work the focus is on the preparation of self-assembled monolayer-like films consisting of thiolated cyclodextrin on gold substrate and a characterization by using secondary ion mass spectrometry. The short (1 min) and long (1 h) time preparations of self-assembled monolayer-like films, resulting in submonolayer and monolayer regimes, are investigated, respectively. The observed species of thiolated cyclodextrin (M as molecular ion) self-assembled monolayer-like films are assigned to three groups: Au xH yS z clusters, fragments with origin in cyclodextrin molecule associated with Au, and molecular ions. The group of Au xH yS z ( x = 2-17, y = 0-2, z = 1-5) clusters have higher intensities than other species in the positive and even more in negative mass spectra. Interestingly, the dependence between the number of Au and S atoms shows that with the increasing size of Au xH yS z clusters up to 11 Au atoms, the number of associated S atoms is also increasing and then decreasing. Molecular species as (M-S+H)Na +, (M+H)Na +, AuMNa +, (M 2-S)Na +, and M 2Na + are determined, and also in cationized forms with K +. The intensities of thiolated cyclodextrin fragments at the long time preparation are approximately 10 times higher than the intensities of the same fragments observed at the short time. The largest observed ions in thiolated cyclodextrin self-assembled monolayer-like films are AuM 2 and Au 2M. The thiolated cyclodextrin molecular ions are compared with hexadecanethiol molecular ions in the form of Au xM w where the values of x and w are smaller for thiolated cyclodextrin than for hexadecanethiol. This result is supported with larger, more compact, and more stabile thiolated cyclodextrin molecule.

  6. Two-laser mass spectrometry of thiolate, disulfide, and sulfide self-assembled monolayers.

    SciTech Connect

    Trevor, J. L.; Lykke, K. R.; Chemistry; Univ. of Illinois at Chicago

    1998-03-31

    Self-assembled monolayers (SAMs) of thiolates, disulfides (RSSR+), and sulfides were studied on Au by N2 laser desorption followed by vacuum ultraviolet (VUV) (118-nm) photoionization of secondary neutrals in a time-of-flight mass spectrometer. Dimers (RSSR+) dominated the photoionization mass spectrum from all chain lengths of alkanethiolates and disulfides studied. Nonmethyl-terminated alkanethiolates with X = (OH and COOH) were detected as dimers without loss of the terminal group. Phenyl-SAMs with X = (H, OH, OCH3, Cl, and NO2) were detected as both monomers and dimers. Thiocholesterol SAMs were detected solely as monomers. The data suggest that dimerization occurs as a result of the recombination of surface thiolates during desorption. The alkane sulfides were detected intact, but with additional monomer and dimer species present in the spectra. The appearance of dimers is not a strong function of adsorbate structure or ordering and therefore cannot be taken as evidence for or against the recently proposed model of thiolate dimers on Au surfaces. Two receptor adsorbates, resorcin[4]arene tetrasulfide and {beta}-cyclodextrin sulfide were examined by two-laser mass spectrometry (L2MS), but only the former gave identifiable high mass peaks. Mixed thiolate and disulfide monolayers generated both pure and mixed dimers, providing information on nearest neighbor interactions. The mixed disulfide results indicate there is a common adsorption state for thiolates and disulfides. The laser desorption and VUV photoionization cross sections for these various organosulfur SAMs were found to be similar. L2MS with VUV photoionization was nonselective in its detection of these organosulfur species and produced mass spectra with little fragmentation.

  7. Chemical manipulation by X-rays of functionalized thiolate self-assembled monolayers on Au.

    PubMed

    Iqbal, P; Critchley, K; Attwood, D; Tunnicliffe, D; Evans, S D; Preece, J A

    2008-12-16

    The chemical modification caused by prolonged exposure to X-rays on a series of para-substituted phenyl moieties (-NO2, -CN, -CHO, -COOH, -CO2Me, and -CO2(1)Bu) at the surface of thiolate-Au self-assembled monolayers (SAMs) has been investigated by X-ray photoelectron spectroscopy (XPS). Furthermore, the influence that the phenyl group has on the chemical modification induced by the X-ray irradiation on the SAMs was investigated by comparing the XPS results obtained from irradiation on a NO2-aromatic-terminated SAM (6-(4-nitro-phenoxy)-hexane-1-thiolate (NPHT)) and NO2-aliphatic-terminated SAM (thioacetic acid S-(12-nitrododecyl) ester (TNDDE)). The NPHT and TNDDE SAMs have been shown to behave differently to X-ray exposure. The irradiation of the NPHT SAM led to the reduction of the nitro (-NO2) moiety to the amine (-NH2) moiety, as shown by the decrease in the intensity of the N 1s photoelectron peak for -NO2 (406 eV) in the XPS spectra with the concomitant increase in the N 1s photoelectron peak for -NH2 (399 eV). On the TNDDE SAM, XPS showed the -NO2 photoelectron peak again decreasing with prolonged X-ray irradiation whereas no peak was observed at 399 eV; therefore, the -NO2 moieties are selectively cleaved. No change was observed on the other functionalized monolayers apart from the -CO2(t)Bu-functionalized monolayer, where after 100 min of X-ray irradiation approximately 11% of the carbon content was lost. The S 2p and O 1s spectra remained unchanged during the irradiation suggesting the conversion of the -CO2(t)Bu to the -COOH moiety, although the conversion was not complete because the tertiary butyl moiety contributes 25% to the total carbon content of the SAM. Also, there was no evidence of the molecules desorbing from the substrate for any of the SAMs studied during the X-ray irradiation as shown by no change in the S 2p and C 1s XPS spectra taken during the X-ray irradiation.

  8. Clean thermal decomposition of tertiary-alkyl metal thiolates to metal sulfides: environmentally-benign, non-polar inks for solution-processed chalcopyrite solar cells

    NASA Astrophysics Data System (ADS)

    Heo, Jungwoo; Kim, Gi-Hwan; Jeong, Jaeki; Yoon, Yung Jin; Seo, Jung Hwa; Walker, Bright; Kim, Jin Young

    2016-11-01

    We report the preparation of Cu2S, In2S3, CuInS2 and Cu(In,Ga)S2 semiconducting films via the spin coating and annealing of soluble tertiary-alkyl thiolate complexes. The thiolate compounds are readily prepared via the reaction of metal bases and tertiary-alkyl thiols. The thiolate complexes are soluble in common organic solvents and can be solution processed by spin coating to yield thin films. Upon thermal annealing in the range of 200–400 °C, the tertiary-alkyl thiolates decompose cleanly to yield volatile dialkyl sulfides and metal sulfide films which are free of organic residue. Analysis of the reaction byproducts strongly suggests that the decomposition proceeds via an SN1 mechanism. The composition of the films can be controlled by adjusting the amount of each metal thiolate used in the precursor solution yielding bandgaps in the range of 1.2 to 3.3 eV. The films form functioning p-n junctions when deposited in contact with CdS films prepared by the same method. Functioning solar cells are observed when such p-n junctions are prepared on transparent conducting substrates and finished by depositing electrodes with appropriate work functions. This method enables the fabrication of metal chalcogenide films on a large scale via a simple and chemically clear process.

  9. Clean thermal decomposition of tertiary-alkyl metal thiolates to metal sulfides: environmentally-benign, non-polar inks for solution-processed chalcopyrite solar cells

    PubMed Central

    Heo, Jungwoo; Kim, Gi-Hwan; Jeong, Jaeki; Yoon, Yung Jin; Seo, Jung Hwa; Walker, Bright; Kim, Jin Young

    2016-01-01

    We report the preparation of Cu2S, In2S3, CuInS2 and Cu(In,Ga)S2 semiconducting films via the spin coating and annealing of soluble tertiary-alkyl thiolate complexes. The thiolate compounds are readily prepared via the reaction of metal bases and tertiary-alkyl thiols. The thiolate complexes are soluble in common organic solvents and can be solution processed by spin coating to yield thin films. Upon thermal annealing in the range of 200–400 °C, the tertiary-alkyl thiolates decompose cleanly to yield volatile dialkyl sulfides and metal sulfide films which are free of organic residue. Analysis of the reaction byproducts strongly suggests that the decomposition proceeds via an SN1 mechanism. The composition of the films can be controlled by adjusting the amount of each metal thiolate used in the precursor solution yielding bandgaps in the range of 1.2 to 3.3 eV. The films form functioning p-n junctions when deposited in contact with CdS films prepared by the same method. Functioning solar cells are observed when such p-n junctions are prepared on transparent conducting substrates and finished by depositing electrodes with appropriate work functions. This method enables the fabrication of metal chalcogenide films on a large scale via a simple and chemically clear process. PMID:27827402

  10. Clean thermal decomposition of tertiary-alkyl metal thiolates to metal sulfides: environmentally-benign, non-polar inks for solution-processed chalcopyrite solar cells.

    PubMed

    Heo, Jungwoo; Kim, Gi-Hwan; Jeong, Jaeki; Yoon, Yung Jin; Seo, Jung Hwa; Walker, Bright; Kim, Jin Young

    2016-11-09

    We report the preparation of Cu2S, In2S3, CuInS2 and Cu(In,Ga)S2 semiconducting films via the spin coating and annealing of soluble tertiary-alkyl thiolate complexes. The thiolate compounds are readily prepared via the reaction of metal bases and tertiary-alkyl thiols. The thiolate complexes are soluble in common organic solvents and can be solution processed by spin coating to yield thin films. Upon thermal annealing in the range of 200-400 °C, the tertiary-alkyl thiolates decompose cleanly to yield volatile dialkyl sulfides and metal sulfide films which are free of organic residue. Analysis of the reaction byproducts strongly suggests that the decomposition proceeds via an SN1 mechanism. The composition of the films can be controlled by adjusting the amount of each metal thiolate used in the precursor solution yielding bandgaps in the range of 1.2 to 3.3 eV. The films form functioning p-n junctions when deposited in contact with CdS films prepared by the same method. Functioning solar cells are observed when such p-n junctions are prepared on transparent conducting substrates and finished by depositing electrodes with appropriate work functions. This method enables the fabrication of metal chalcogenide films on a large scale via a simple and chemically clear process.

  11. Self-Assembled Monolayers of Perfluoroanthracenylaminoalkane Thiolates on Gold as Potential Electron Injection Layers.

    PubMed

    Zhang, Zibin; Wächter, Tobias; Kind, Martin; Schuster, Swen; Bats, Jan W; Nefedov, Alexei; Zharnikov, Michael; Terfort, Andreas

    2016-03-23

    As a material with relatively small band gap and low lying valence orbitals, perfluoroanthracene (PFA) is of interest for the modification of electrode surfaces, for example, as charge injection layers for n-type organic semiconductors. To covalently attach PFA in the form of self-assembled monolayers (SAMs), we developed a synthesis of derivatives with a sulfur termination, linked to the 2-position of the PFA moieties by an -NH- group and a short alkane chain with two and three methylene groups, respectively. Spectroscopic characterization of the SAMs reveals that the molecules adopt an almost upright orientation on the gold surface, with the packing density mostly determined by the steric demands of the PFA units. The number of the methylene groups in the -NH-alkyl linker has only a minor impact on the SAM structure because of the nonsymmetric attachment of the PFA units, which permits the compensation of the orientational constraints imposed by the bending potential. The investigated SAMs alter the work function of gold by +(0.59-0.64) eV, suggesting comparably strong depolarization effects, affecting the extent of the work function modification.

  12. Structure-property Relationships for Methyl-terminated Alkyl Self-assembled Monolayers

    SciTech Connect

    F DelRio; D Rampulla; C Jaye; G Stan; R Gates; D Fischer; R Cook

    2011-12-31

    Structure-property relationships for methyl-terminated alkyl self-assembled monolayers (SAMs) are developed using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and atomic force microscopy (AFM). NEXAFS C K-edge spectra are used to compute the dichroic ratio, which provides a quantitative measure of the molecular structure. AFM data are analyzed with an elastic adhesive contact model, modified by a first-order elastic perturbation method to include substrate effects, to extract the monolayer mechanical properties. Using this approach, the measured mechanical properties are not influenced by the substrate, which allows universal structure-property relationships to be developed for methyl-terminated alkyl SAMs.

  13. Photoinduced decomposition of alkyl monolayers using 172 nm vacuum ultraviolet light

    NASA Astrophysics Data System (ADS)

    Shirahata, Naoto; Oda, Kotaro; Asakura, Shuuichi; Fuwa, Akio; Yokogawa, Yoshiyuki; Kameyama, Tetsuya; Hozumi, Atsushi

    2004-07-01

    The photoinduced stability of two alkyl monolayers on Si has been investigated using a Xe2 excimer lamp radiating 172 nm vacuum ultraviolet (VUV) light. The photoinduced stability of 1-octadecene monolayer (ODM) was compared with that of alkylsilane monolayer. 1-octadecene was employed as a starting precursor of alkyl monolayer on Si. The alkylsilane monolayer was formed from otadecyltrimethoxysilane monoalyer (OTSM) onto the SiO2/Si substrate. The decomposition of ODM was investigated under VUV irradiation conducted at 10 and 105 Pa. The VUV light decomposed ODM at both 10 and 105 Pa. The photodecomposition rate at 105 Pa was smaller than that at 10 Pa. The decomposed methyl and ethyl groups from the alkyl chain formed carboxyl groups. The carboxyl coverage on the surface of Si increased with increasing VUV irradiation time ranging from 0 to 60 s at 10 Pa, and decreased after 60 s. In contrast, the Si-O component in x-ray photoelectron Si 2p spectrum drastically increased after the VUV irradiation time of 60 s. The Si-O component indicated complete covering of Si surface. Similar decomposition rates between ODM and OTSM were observed for the VUV irradiation time ranging from 0 to 45 s conducted at 10 Pa. After 45 s, the photodecomposition rate of ODM was smaller than that of OTSM. The effectiveness of VUV light for the micropatterning of ODM was also investigated. .

  14. Surface conductivity of InAs/GaSb superlattice infrared detectors treated with thiolated self assembled monolayers

    NASA Astrophysics Data System (ADS)

    Henry, Nathan C.; Brown, Alexander; Knorr, Daniel B.; Baril, Neil; Nallon, Eric; Lenhart, Joseph L.; Tidrow, Meimei; Bandara, Sumith

    2016-01-01

    The surface conductivity of InAs/GaSb based type II superlattice (T2SL) long wavelength infrared material following the deposition of thiolated self-assembled monolayers (SAMs) of cysteamine, octadecanethiol, dodecanethiol, and hexanethiol are reported. Quantitative mobility spectrum analysis (QMSA) was employed to study the mobility and to isolate and identify surface carriers following SAM treatments on planar samples. QMSA data collected following the deposition of the SAMs on InAs/GaSb material correlates well with dark current measurements, demonstrating the usefulness of QMSA as a tool for evaluating surface conductivity and predicting device performance. All samples displayed a reduction in surface conductivity and dark current density following thiol treatment. Dark current densities were reduced to 1.1 × 10-5, 1.3 × 10-5, 1.6 × 10-5, and 5 × 10-6 A/cm2 for hexanethiol, dodecanethiol, octadecanethiol, and cysteamine, respectively, from 5.7 × 10-4 A cm2 for unpassivated devices.

  15. Thermodynamic profiles at the solvated inorganic-organic interface: the case of gold-thiolate monolayers.

    PubMed

    Ravi, Venkataramanan; Binz, Jason M; Rioux, Robert M

    2013-09-11

    The thermodynamic adsorption profile at a solvated organic-inorganic interface is probed by following the binding and organization of carboxylic acid-terminated alkanethiols of varying chain lengths (C2, C3, and C6) to the surface of gold nanoparticles (NPs) (5.4 ± 0.7, 9.5 ± 0.6, and 19.4 ± 1.1 nm diameter) using isothermal titration calorimetry (ITC). We discuss the effect of alkyl chain length, temperature, and Au NP size on the energetics at an organic-inorganic interface. ITC allows for the quantification of the adsorption constant, enthalpy of adsorption, entropy of adsorption, and the binding stoichiometry in a single experiment. The thermodynamic parameters support a mechanism of stepwise adsorption of thiols to the surface of Au NPs and secondary ordering of the thiols at the organic-inorganic interface. The adsorption enthalpies are chain-length dependent; enthalpy becomes more exothermic as longer chains are confined, compensating for greater decreases in entropy with increasing chain length. We observe an apparent compensation effect: the negative ΔH is compensated by a negative ΔS as the thiols self-assemble on the Au NP surface. A comparison of the thermodynamic parameters indicates thiol-Au NP association is enthalpy-driven because of the large, exothermic enthalpies accompanied by an unfavorable entropic contribution associated with confinement of alkyl chains, reduced trans-gauche interconversion, and the apparent ordering of solvent molecules around the hydrophobic organic thiols (hydrophobic effect). Understanding the thermodynamics of adsorption at NP surfaces will provide critical insight into the role of ligands in directing size and shape during NP synthesis since thiols are a common ligand choice (i.e., Brust method). The ITC technique is applicable to a larger number of structure-directing ligands and solvent combinations and therefore should become an important tool for understanding reaction mechanisms in nanostructure synthesis.

  16. Chemical and physical passivation of type II strained-layer superlattice devices by means of thiolated self-assembled monolayers and polymer encapsulates

    NASA Astrophysics Data System (ADS)

    Henry, Nathan C.; Knorr, Daniel B.; Williams, Kristen S.; Baril, Neil; Nallon, Eric; Lenhart, Joseph L.; Andzelm, Jan W.; Pellegrino, Joseph; Tidrow, Meimei; Cleveland, Erin; Bandara, Sumith

    2015-05-01

    The efficacy of solution deposition of thiolated self-assembled monolayers (SAMs) has been explored for the purpose of passivating III-V type II superlattice (T2SL) photodetectors, more specifically a p-type heterojunction device. Sulfur passivation has previously been achieved on T2SL devices. However, degradation over time, temperature sensitivity and inconsistent reproducibility necessitate a physical encapsulate that can chemically bond to the chemical passivant. Thus, this research investigates two passivation methods, surface passivation with a thiol monolayer and passivation with a polymer encapsulant with a view toward future combination of these techniques. Analysis of the physical and chemical condition of the surface prior to deposition assisted in the development of ideal processes for optimized film quality. Successful deposition was facilitated by in situ oxide removal. Various commercially available functional (cysteamine) and non-functional (alkane) thiolated monolayers were investigated. Dark current was reduced by 3 orders of magnitude and achieved negligible surface leakage at low bias levels. The lowest dark current result, 7.69 × 10-6 A/cm2 at 50 mV, was achieved through passivation with cysteamine.

  17. NIR luminescence intensities increase linearly with proportion of polar thiolate ligands in protecting monolayers of Au38 and Au140 quantum dots.

    PubMed

    Wang, Gangli; Guo, Rui; Kalyuzhny, Gregory; Choi, Jai-Pil; Murray, Royce W

    2006-10-19

    The near-infrared photoluminescence of monolayer-protected Au38 and Au140 clusters (MPCs) is intensified with exchange of nonpolar ligands by more polar thiolate ligands. The effect is general and includes as more polar in-coming ligands: thiophenolates with a variety of p-substituents; alkanethiolates omega-terminated by alcohol, acid, or quaternary ammonium groups; and thio-amino acids. Remarkably, place exchanges of the initial phenylethanethiolates on Au38 MPCs by p-substituted thiophenolates and thio-amino acids and of hexanethiolates on Au140 MPCs by omega-quaternary ammonium terminated undecylthiolates result in increases in the near-infrared (NIR) luminescence intensities that are linear with the number of new polar ligands. The increased intensities are systematically larger for thiophenolate ligands having more electron-withdrawing substituents. Analogous effects on intensities are observed in the NIR emission of Au140 MPCs upon place exchange of alkanethiolates with thiolates having short connecting alkanethiolate chains to quaternary ammonium and to omega-carboxylic acid termini, and with oxidative charging of the Au cores. The observations are consistent with sensitivity of the luminescence mechanism to any factor that enhances the electronic polarization of the bonds between the Au core atoms and their thiolate ligands. The luminescence is discussed in terms of a surface electronic excitation, as opposed to a core volume excitation.

  18. Controlled oxidation, biofunctionalization, and patterning of alkyl monolayers on silicon and silicon nitride surfaces using plasma treatment.

    PubMed

    Rosso, Michel; Giesbers, Marcel; Schroën, Karin; Zuilhof, Han

    2010-01-19

    A new method is presented for the fast and reproducible functionalization of silicon and silicon nitride surfaces coated with covalently attached alkyl monolayers. After formation of a methyl-terminated 1-hexadecyl monolayer on H-terminated Si(100) and Si(111) surfaces, short plasma treatments (1-3 s) are sufficient to create oxidized functionalities without damaging the underlying oxide-free silicon. The new functional groups can, e.g., be derivatized using the reaction of surface aldehyde groups with primary amines to form imine bonds. In this way, plasma-treated monolayers on silicon or silicon nitride surfaces were successfully coated with nanoparticles, or proteins such as avidin. In addition, we demonstrate the possibility of micropatterning, using a soft contact mask during the plasma treatment. Using water contact angle measurements, ellipsometry, XPS, IRRAS, AFM, and reflectometry, proof of principle is demonstrated of a yet unexplored way to form patterned alkyl monolayers on oxide-free silicon surfaces.

  19. Tribology of monolayer films: comparison between n-alkanethiols on gold and n-alkyl trichlorosilanes on silicon.

    PubMed

    Booth, Brandon D; Vilt, Steven G; McCabe, Clare; Jennings, G Kane

    2009-09-01

    This Article presents a quantitative comparison of the frictional performance for monolayers derived from n-alkanethiolates on gold and n-alkyl trichlorosilanes on silicon. Monolayers were characterized by pin-on-disk tribometry, contact angle analysis, ellipsometry, and electrochemical impedance spectroscopy (EIS). Pin-on-disk microtribometry provided frictional analysis at applied normal loads from 10 to 1000 mN at a speed of 0.1 mm/s. At low loads (10 mN), methyl-terminated n-alkanethiolate self-assembled monolayers (SAMs) exhibited a 3-fold improvement in coefficient of friction over SAMs with hydroxyl- or carboxylic-acid-terminated surfaces. For monolayers prepared from both n-alkanethiols on gold and n-alkyl trichlorosilanes on silicon, a critical chain length of at least eight carbons is required for beneficial tribological performance at an applied load of 9.8 mN. Evidence for disruption of chemisorbed alkanethiolate SAMs with chain lengths n monolayers shows that monolayers prepared from n-octadecyl dimethylchlorosilane and n-octadecyl trichlorosilane withstood normal loads at least 30 times larger than those that damaged octadecanethiolate SAMs. Collectively, our results show that the tribological properties of monolayer films are dependent on their internal stabilities, which are influenced by cohesive chain interactions (van der Waals) and the adsorbate-substrate bond.

  20. Nanoseeding via dual surface modification of alkyl monolayer for site-controlled electroless metallization.

    PubMed

    Chen, Sung-Te; Chen, Giin-Shan

    2011-10-04

    In this work, an attempt to fabricate nanostructured metallization patterns on SiO(2) dielectric layers is made by using plasma-patterned self-assembled monolayers (SAMs), in conjunction with a novel aqueous seeding and electroless process. Taking octadecyltrichlorosilane (OTS) as a test material, the authors demonstrate that optimizing the N(2)-H(2) plasma conditions leads to the successive conversion of the topmost aliphatic chains of alkyl SAMs to carboxyl (COOH) and hydroxyl (C-OH) functional groups, which was previously found in alkyl SAMs only by exposure to "oxygen-based" plasma. Further modifying the plasma-exposed (either COOH or C-OH terminated) regions with an aqueous solution (SC-1) creates surface functionalities that are viable for site-controlled metallic seeding (e.g., Co or Ni) with an adsorption selectivity of greater than 1000:1. Neither the combination of costly PdCl(2) and complex additives nor the demerits of the associated aqueous chemistry (e.g., seed agglomeration and seed sparseness) are involved. Therefore, the seed particles are only 3 nm in size. Simultaneously, there are sufficient particle densities previously unattainable for electroless deposition to trigger highly resolved Cu metallization patterns with a film thickness of less than 10 nm. The formation of the seed-adsorbing sites is discussed, based on a plasma-dissociated, water-mediated chemical oxidation route.

  1. Structural, spectroscopic and redox properties of a mononuclear Co(II) thiolate complex--the reactivity toward S-alkylation: an experimental and theoretical study.

    PubMed

    Gennari, Marcello; Gerey, Bertrand; Hall, Nikita; Pécaut, Jacques; Vezin, Hervé; Collomb, Marie-Noëlle; Orio, Maylis; Duboc, Carole

    2012-10-28

    The structural, spectroscopic, redox properties and also the reactivity toward S-alkylation of a new mononuclear N2S2 dithiolate Co(II) complex [CoL] (1), with H(2)L = 2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1-diphenylethanethiol), have been investigated. The X-ray structure of 1 has revealed an unusual distorted square planar geometry for a Co(II) ion within a thiolate environment. The X-band EPR spectrum of displays a rhombic S = 1/2 signal consistent with a low spin configuration for the d(7) Co(II) ion with a large g-anisotropy (g(x) = 2.94, g(y) = 2.32 and g(z) = 2.01). By pulsed EPR experiments (HYSCORE), two weak hyperfine couplings (hfc) of 3.2 and 2.2 MHz have been measured and attributed respectively to protons and nitrogen nuclei of the bipyridine unit. In addition, another hyperfine coupling (hfc) of 7.5 MHz has been attributed to the cobalt ion. DFT calculations have successfully reproduced the (59)Co and (14)N hfc parameters. However, multiconfigurational ab initio calculations were required to predict the g-tensor of 1. The cyclic voltammogram (CV) displays two one-electron metal based processes: a quasi-reversible Co(III)/Co(II) oxidation wave at E(1/2) = -0.5 V vs. Fc(+)/Fc and a quasi-reversible Co(II)/Co(I) reduction wave at E(1/2) = -1.7 V. 1 reacts with CH(3)I, generating the mono S-methylated complex, [CoL(Me)I] (1(Me)). The X-band EPR spectrum of 1(Me) displays a typical signal of a high spin (S = 3/2) Co(II) species. An optimized structure of 1(Me), calculated by DFT, is consistent with its EPR and UV-visible spectra. Time dependent density functional theory (TD-DFT) calculations attribute the most prominent features observed in the electronic absorption spectra of 1 and 1(Me). The singly occupied MO (SOMO) of 1 shows a notable delocalization of the unpaired electron over the metal (85%) and the ligand, especially over the sulphur atoms (10.5%), indicating a certain degree of covalency for the Co-S bonds. In 1(Me), for two of the three SOMOs

  2. Model of vapor-induced resistivity changes in gold-thiolate monolayer-protected nanoparticle sensor films.

    PubMed

    Steinecker, William H; Rowe, Michael P; Zellers, Edward T

    2007-07-01

    An investigation of the modulation of charge transport through thin films of n-octanethiolate monolayer-protected gold nanoparticles (MPN) induced by the sorption of organic vapors is presented. A model is derived that allows predictions of MPN-coated chemiresistor (CR) responses from vapor-film partition coefficients, and analyte densities and dielectric constants. Calibrations with vapors of 28 compounds collected from an array of CRs and a parallel thickness-shear-mode resonator are used to verify assumptions inherent in the model and to assess its performance. Results afford insights into the nature of the vapor-MPN interactions, including systematic variations in apparent film swelling efficiencies, and show that the model can predict CR responses typically to within 24%. Using CRs of different dimensions, vapor sensitivities are found to be virtually independent of the MPN film volume over a range of 104 (device-area x MPN layer thickness). Sensitivities vary inversely with analyte vapor pressure similarly for the two sensor types, but the CR sensor affords significantly greater signal-to-noise ratios, yielding calculated detection limits in the low-part-per-billion concentration range for several of the analytes tested. The implications of these results for implementing MPN-coated CR arrays as detectors in microanalytical systems are considered.

  3. Self-Spreading of Lipid Bilayer on a Hydrophobic Surface Made by Self-Assembled Monolayer with Short Alkyl Chain.

    PubMed

    Omori, Yuya; Sakaue, Hiroyuki; Takahagi, Takayuki; Suzuki, Hitoshi

    2016-04-01

    Behaviors of self-spreading of lipid bilayer membrane on a glass surface modified with self-assembled monolayer (SAM) with short alkyl chain were observed with fluorescence microscopy. Hydrophobic surface made by SAM was found to hamper the self-spreading phenomenon but the lipid bilayer spread on a hydrophilic one where SAM was decomposed by oxidation. On a binary surface having a hydrophobic region and a hydrophilic one, the lipid bilayer spread on the hydrophilic region but it stopped at the boundary of the hydrophobic region.

  4. Thiol-terminated monolayers on oxide-free Si: assembly of semiconductor-alkyl-S-metal junctions.

    PubMed

    Böcking, Till; Salomon, Adi; Cahen, David; Gooding, J Justin

    2007-03-13

    Self-assembled monolayers formed by thermal hydrosilylation of a trifluoroacetyl-protected alkenylthiol on Si-H surfaces, followed by removal of the protecting groups, yield essentially oxide-free monolayers suitable for the formation of Si-C11H22-S-Hg and Si-C11H22-S-Au junctions in which the alkyl chains are chemically bound to the silicon surface (via Si-C bonds) and the metal electrode (via Hg-S or Au-S bonds). Two barriers to charge transport are present in the system: at low bias the current is temperature activated and hence limited by thermionic emission over the Schottky barrier in the silicon, whereas as at high bias transport is limited by tunneling through the organic monolayer. The thiol-terminated monolayer on oxide-free silicon provides a well-characterized system allowing a careful study of the importance of the interfacial bond to the metal electrode for current transport through saturated molecules.

  5. Water exclusion at the nanometer scale provides long-term passivation of silicon (111) grafted with alkyl monolayers.

    PubMed

    Gorostiza, P; Henry de Villeneuve, C; Sun, Q Y; Sanz, F; Wallart, X; Boukherroub, R; Allongue, P

    2006-03-23

    This work is a quantitative study of the conditions required for a long-term passivation of the interface silicon-alkyl monolayers prepared by thermal hydrosilyation of neat 1-alkenes on well-defined H-Si(111) surfaces. We present electrochemical capacitance measurements (C-U) in combination with ex situ atomic force microscopy (AFM) observations and X-ray photoelectron spectroscopy (XPS) measurements. Capacitance measurements as a function of the reaction time and XPS data reveal close correlations between the chemical composition at the interface and its electronic properties. A very low density of states is found if suboxide formation is carefully prevented. The monitoring of C-U plots and AFM imaging upon exposure of the sample in diverse conditions indicate that the initial electronic properties and structure of the interface are long-lasting only when the monolayer surface coverage is theta > 0.42. A model demonstrates that this threshold value corresponds to a monolayer with intermolecular channels narrower than approximately 2.82 A, which is equal to the diameter of a water molecule. Water exclusion from the monolayer promotes long-term passivation of the silicon surface against oxidation in air and water as well as perfect corrosion inhibition in 20% NH(4)F. We provide two criteria to assess when a sample is optimized: The first one is an effective dielectric constant <2.5, and the second one is a very characteristic energy diagram at open circuit potential.

  6. Site-selective electroless metallization on porous organosilica films by multisurface modification of alkyl monolayer and vacuum plasma.

    PubMed

    Chen, Giin-Shan; Chen, Sung-Te; Chen, Yenying W; Hsu, Yen-Che

    2013-01-15

    Taking plasma-enhanced chemical vapor deposited porous SiOCH (p-SiOCH) and octadecyltrichlorosilane (OTS) as model cases, this study elucidates the chemical reaction pathways for alkyl-based self-assembled monolayers (SAMs) on porous carbon-doped organosilica films under N(2)-H(2) vacuum plasma illumination. In contrast to previous findings that carboxylic groups are found in alkyl-based SAMs only by exposure to oxygen-based plasma, this study discovers that, upon exposure to reductive nitrogen-based vacuum plasma, surface carboxylic functional groups can be instantly formed on OTS-coated p-SiOCH films. Particular attention is given to developing a multisurface modification process, starting with the modification of p-SiOCH films by N(2)-H(2) plasma and continuing with SAM deposition and plasma patterning; this ultimately leads to site-selective seeding for the spatially controlled fabrication of Cu-wire metallization by electroless deposition. Plasma diagnosis and X-ray near-edge absorption and Fourier transform infrared spectroscopies show that, by adequately controlling the plasma parameters, the bulk of the p-SiOCH films are free from plasma damage (in terms of degradation in bonding structures and electrical properties); the formation of the seed-trapping carboxylic functional groups on the surface, the key factor for the validity of this new seeding process, is due to a water-mediated chemical oxygenation route.

  7. Effects of odd-even side chain length of alkyl-substituted diphenylbithiophenes on first monolayer thin film packing structure.

    PubMed

    Akkerman, Hylke B; Mannsfeld, Stefan C B; Kaushik, Ananth P; Verploegen, Eric; Burnier, Luc; Zoombelt, Arjan P; Saathoff, Jonathan D; Hong, Sanghyun; Atahan-Evrenk, Sule; Liu, Xueliang; Aspuru-Guzik, Alán; Toney, Michael F; Clancy, Paulette; Bao, Zhenan

    2013-07-31

    Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5'bis(4-alkylphenyl)-2,2'-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified SiO2 surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd-even effect in the strength of the intermolecular electronic coupling.

  8. Drug-Membrane Interactions Studied in Phospholipid Monolayers Adsorbed on Non-porous Alkylated Microspheres

    PubMed Central

    LUKACOVA, VIERA; PENG, MING; FANUCCI, GAIL; TANDLICH, ROMAN; HINDERLITER, ANNE; MAITY, BIKASH; MANIVANNAN, ETHIRAJAN; COOK, GREGORY R.; BALAZ, STEFAN

    2008-01-01

    Characterization of interactions with phospholipids is an integral part of the in vitro profiling of drug candidates because of the roles the interactions play in tissue accumulation and passive diffusion. Currently used test systems may inadequately emulate the bilayer core solvation properties (immobilized artificial membranes - IAM), suffer from potentially slow transport of some chemicals (liposomes in free or immobilized forms), and require a tedious separation (if used for free liposomes). Here we introduce a well-defined system overcoming these drawbacks: nonporous octadecylsilica particles coated with a self-assembled phospholipid monolayer. The coating mimics the structure of the headgroup region, as well as the thickness and properties of the hydrocarbon core more closely than IAM. The monolayer has a similar transition temperature pattern as the corresponding bilayer. The particles can be separated by filtration or a mild centrifugation. The partitioning equilibria of 81 tested chemicals were dissected into the headgroup and core contributions, the latter using the alkane/water partition coefficients. The deconvolution allowed a successful prediction of the bilayer/water partition coefficients with the standard deviation of 0.26 log units. The plate-friendly assay is suitable for high-throughput profiling of drug candidates without sacrificing the quality of analysis or details of the drug-phospholipid interactions. PMID:17218665

  9. Interactions of Gaseous HNO3 and Water with Individual and Mixed Alkyl Self-Assembled Monolayers at Room Temperature

    PubMed Central

    Nishino, Noriko; Hollingsworth, Scott A.; Stern, Abraham C.; Roeselová, Martina; Tobias, Douglas J.; Finlayson-Pitts, Barbara J.

    2014-01-01

    The major removal processes for gaseous nitric acid (HNO3) in the atmosphere are dry and wet deposition onto various surfaces. The surface in the boundary layer is often covered with organic films, but the interaction of gaseous HNO3 with them is not well understood. To better understand the factors controlling the uptake of gaseous nitric acid and its dissociation in organic films, studies were carried out using single component and mixtures of C8 and C18 alkyl self-assembled monolayers (SAMs) attached to a germanium (Ge) attenuated total reflectance (ATR) crystal upon which a thin layer of SiOx had been deposited. For comparison, diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) studies were also carried out using a C18 SAM attached to the native oxide layer on the surface of silicon powder. These studies show that the alkyl chain length and order/disorder of the SAMs does not significantly affect the uptake or dissociation/recombination of molecular HNO3. Thus, independent of the nature of the SAM, molecular HNO3 is observed up to 70–90 % relative humidity. After dissociation, molecular HNO3 is regenerated on all SAM surfaces when water is removed. Results of molecular dynamics simulations are consistent with experiments and show that defects and pores on the surfaces control the uptake, dissociation and recombination of molecular HNO3. Organic films on surfaces in the boundary layer will certainly be more irregular and less ordered than SAMs studied here, therefore undissociated HNO3 may be present on surfaces in the boundary layer to a greater extent than previously thought. The combination of this observation with the results of recent studies showing enhanced photolysis of nitric acid on surfaces suggests that renoxification of deposited nitric acid may need to be taken into account in atmospheric models. PMID:24352159

  10. Properties of Square-Pyramidal Alkyl-Thiolate FeIII-Complexes, Including an Analogue of the Unmodified Form of Nitrile Hydratase

    PubMed Central

    Lugo-Mas, Priscilla; Taylor, Wendy; Schweitzer, Dirk; Theisen, Roslyn M.; Xu, Liang; Shearer, Jason; Swartz, Rodney D.; Gleaves, Morgan C.; DiPasquale, Antonio; Kaminsky, Werner; Kovacs, Julie A.

    2009-01-01

    The syntheses and structures of three new coordinatively unsaturated, monomeric, square pyramidal thiolate-ligated Fe(III) complexes are described, [FeIII((tame—N3)S2Me2)]+ (1), [FeIII(Et—N2S2Me2)(py)]1- (3), and [FeIII((tame—N2S)S2Me2)]2- (15). The anionic bis-carboxamide, tris-thiolate N2S3 coordination sphere of 15 is potentially similar to that of the yet-to-be characterized unmodified form of NHase. Comparison of the magnetic and reactivity properties of these reveals how anionic charge build-up (from cationic 1 to anionic 3 and dianionic 15) and spin-state influence apical ligand affinity. For all of the ligand-field combinations examined, an intermediate S= 3/2 spin-state was shown to be favored by a strong N2S2 basal plane ligand-field, and this was found to reduce the affinity for apical ligands, even when they are built-in. This is in contrast to the post-translationaly modified NHase active site, which is low-spin, and displays a higher affinity for apical ligands. Cationic 1 and its reduced FeII precursor are shown to bind NO and CO, respectively, to afford [FeIII((tame-N3)S2Me(NO)]+ (18, νNO= 1865 cm-1), an analogue of NO-inactivated NHase, and [FeII((tame-N3)S2Me)(CO)] (16; νCO stretch (1895 cm-1). Anions (N3-, CN-) are shown to be unreactive towards 1, 3 and 15, and neutral ligands unreactive towards 3 and 15, even when present in 100-fold excess, and at low—temperatures. The curtailed reactivity of 15, an analogue of the unmodified form of NHase, and its apical-oxygenated S= 3/2 derivative [FeIII((tame—N2SO2)S2Me2)]2- (20) suggests that regioselective post—translational oxygenation of the basal plane NHase cysteinate sulfurs plays an important role in promoting substrate binding. This is supported by previously reported theoretical (DFT) calculations.1 PMID:18989922

  11. Half-flat vs. atomically flat: Alkyl monolayers on morphologically controlled Si(100) and Si(111) have very similar structure, density, and chemical stability

    NASA Astrophysics Data System (ADS)

    DeBenedetti, William J. I.; Li, Thomas L.; Hines, Melissa A.

    2017-02-01

    Chemists have long preferred the Si(111) surface for chemical functionalization, as a simple aqueous etch can be used to produce ideal, atomically flat H/Si(111) surfaces for subsequent reactions. In contrast, industry-standard etches produce rough H/Si(100) surfaces terminated by nanohillocks. The recent discovery of an aqueous etch that produces morphologically controlled H/Si(100) surfaces with a near atomically flat or "half-flat" morphology challenges the assumption that Si(111) is an inherently preferable starting point for chemical functionalization. This study shows that alkyl functionalization of morphologically controlled, "half-flat" Si(100) surfaces by terminal alkenes produces dense, tightly packed monolayers that are essentially identical to those on atomically flat Si(111). The striking similarity between the infrared spectra on these two surfaces — in terms of absolute absorbance, line shape and position, and polarization dependence — strongly suggests that alkyl monolayers on morphologically controlled Si(111) and Si(100) have essentially identical structures. The principle difference between the two surfaces is the amount of residual H at the Si/organic interface, a difference that is dictated by the structure of the Si(100) surface. Alkyl monolayers on morphologically controlled Si(111) and Si(100) surfaces were shown to be equally resistant to harsh oxidants. As a result, there appears to be no chemical reason to prefer one surface over the other, at least for functionalization with terminal alkenes.

  12. Half-flat vs. atomically flat: Alkyl monolayers on morphologically controlled Si(100) and Si(111) have very similar structure, density, and chemical stability.

    PubMed

    DeBenedetti, William J I; Li, Thomas L; Hines, Melissa A

    2017-02-07

    Chemists have long preferred the Si(111) surface for chemical functionalization, as a simple aqueous etch can be used to produce ideal, atomically flat H/Si(111) surfaces for subsequent reactions. In contrast, industry-standard etches produce rough H/Si(100) surfaces terminated by nanohillocks. The recent discovery of an aqueous etch that produces morphologically controlled H/Si(100) surfaces with a near atomically flat or "half-flat" morphology challenges the assumption that Si(111) is an inherently preferable starting point for chemical functionalization. This study shows that alkyl functionalization of morphologically controlled, "half-flat" Si(100) surfaces by terminal alkenes produces dense, tightly packed monolayers that are essentially identical to those on atomically flat Si(111). The striking similarity between the infrared spectra on these two surfaces - in terms of absolute absorbance, line shape and position, and polarization dependence - strongly suggests that alkyl monolayers on morphologically controlled Si(111) and Si(100) have essentially identical structures. The principle difference between the two surfaces is the amount of residual H at the Si/organic interface, a difference that is dictated by the structure of the Si(100) surface. Alkyl monolayers on morphologically controlled Si(111) and Si(100) surfaces were shown to be equally resistant to harsh oxidants. As a result, there appears to be no chemical reason to prefer one surface over the other, at least for functionalization with terminal alkenes.

  13. Molecular modeling of alkyl monolayers on the Si(100)-2 x 1 surface.

    PubMed

    Lee, Michael V; Guo, Dawei; Linford, Matthew R; Zuilhof, Han

    2004-10-12

    Molecular modeling was used to simulate various surfaces derived from the addition of 1-alkenes and 1-alkynes to Si=Si dimers on the Si(100)-2 x 1 surface. The primary aim was to better understand the interactions between adsorbates on the surface and distortions of the underlying silicon crystal due to functionalization. Random addition of ethylene and acetylene was used to determine how the addition of an adduct molecule affects subsequent additions for coverages up to one molecule per silicon dimer, that is, 100% coverage. Randomization subdues the effect that the relative positions of the adsorbates have on the enthalpy of the system. For ethylene and acetylene, the enthalpy of reaction changes less than 3 and 5 kcal/mol, respectively, from the first reacted species up to 100% coverage. As a result, a (near-)complete coverage is predicted, which is in line with experimental data. When 1-alkenes and 1-alkynes add by [2 + 2] addition, the hydrocarbon chains interact differently depending on the direction they project from the surface. These effects were investigated for four-carbon chains: 1-butene and 1-butyne. As expected, the chains that would otherwise intersect bend to avoid each other, raising the enthalpy of the system. For alkyl chains longer than four carbons, the chains are able to reorient themselves in a favorable manner, thus, resulting in a steady reduction in reaction enthalpy of about 2 kcal/mol for each additional methylene unit.

  14. The effect of poly(ethylene glycol) coating and monomer type on poly(alkyl cyanoacrylate) nanoparticle interactions with lipid monolayers and cells.

    PubMed

    Baghirov, Habib; Melikishvili, Sopio; Mørch, Yrr; Sulheim, Einar; Åslund, Andreas K O; Hianik, Tibor; de Lange Davies, Catharina

    2017-02-01

    The interaction of the promising drug carriers poly(alkyl cyanoacrylate) nanoparticles (PACA NPs) with lipid monolayers modeling the cell membrane and with RBE4 immortalized rat brain endothelial cells was compared to assess the relevance of lipid monolayer-based cell membrane models for PACA NP cellular uptake. NP properties such as size and charge of NPs and density of poly(ethylene glycol) coating (PEG) were kept in a narrow range to assess whether the type of PEG coating and the PACA monomer affected NP-monolayer and NP-cell interactions. The interaction with lipid monolayers was evaluated using surface pressure measurements and Brewster angle microscopy. NP association with and uptake by cells were assessed using flow cytometry and confocal laser scanning microscopy. The interaction between NPs and both lipid monolayers and the plasma membrane depended on the type of PEG. PEG density affected cellular uptake but not interaction with lipid monolayers. NP monomer, NPs size and charge had no effect on the interaction. This might be due to the fact that the size and charge distribution was kept rather narrow to study the effect of PACA monomer and PEG type. In conclusion, while modeling solely the passive aspect of NP-cell interactions, lipid monolayers nevertheless proved a valuable cell membrane model whose interaction with PACA NPs correlated well with NP-cell interaction. In addition, both NP-monolayer and NP-cell interactions were dependent on PEGylation type, which could be used in the design of NPs to either facilitate or hinder cellular uptake, depending on the intended purpose.

  15. Structure, interfacial properties, and dynamics of the sodium alkyl sulfate type surfactant monolayer at the water/trichloroethylene interface: a molecular dynamics simulation study.

    PubMed

    Shi, Wen-Xiong; Guo, Hong-Xia

    2010-05-20

    In this work, we perform a series of molecular dynamics (MD) simulations on the category of sodium alkyl sulfate (SDS-type) surfactant monolayers at the water/trichloroethylene (TCE) interface. Three separate tail-length SDS-type molecules are used. We investigate the conformation of surfactant chain (i.e., packing, orientation, and order), interfacial properties (i.e., interfacial thickness, interfacial tension, area compressibility, and bending modulus), their dependence on the chain length, and the average area per surfactant chain. We also examine the behavior of the surfactant monolayer in the metastable regime of negative surface tension with reference to collapse. The simulation has clearly shown that the very dilute monolayer is well described as a two-dimensional gas. With the increase of interfacial surfactant coverage, the monolayer is in the liquid-expanded (LE) phase. The surfactant tails at the interface become straighter, more ordered, and thicker at higher surfactant coverage. At the same time, interfacial tension of long-tail systems is always lower than that of short-tail systems. In the LE phase, the area compressibility modulus and the bending modulus increase with an increase in tail length. With a further decrease in molecular areas, the monolayer with large negative surface tension becomes unstable. Our simulations show that buckling of the monolayers is of dynamic nature as a response to mechanical instability. The further transformation pathway from buckling to bud can be controlled by the bending modulus, which depends crucially on the tail length and interfacial surfactant coverage. At a given area per molecule, the short tail chain makes the monolayer softer, and the budding process becomes more probable. For the supersaturated softer SDS monolayer, the collapse transition is initiated by the buckling of monolayers, followed primarily by budding and detachment of the nanoscale swollen micelle from the monolayer. Despite a number of

  16. Fabrication and tribological properties of self-assembled monolayer of n-alkyltrimethoxysilane on silicon: Effect of SAM alkyl chain length

    NASA Astrophysics Data System (ADS)

    Huo, Lixia; Du, Pengcheng; Zhou, Hui; Zhang, Kaifeng; Liu, Peng

    2017-02-01

    It is well known that the self-assembled organic molecules on a solid surface exhibit the friction-reducing performance. However, the effect of the molecular size of the self-assembled organic molecules has not been established. In the present work, self-assembled monolayers (SAMs) of n-alkyltrimethoxysilanes with different alkyl chain lengths (C6, C12, or C18) were fabricated on silicon substrate. The water contact angles of the SAMs increased from 26.8° of the hydroxylated silicon substrate to near 60° after self-assembly. The atomic force microscopy (AFM) analysis results showed that the mean roughness (Ra) of the SAMs decreased with increasing the alkyl chain length. The tribological properties of the SAMs sliding against Al2O3 ball were evaluated on an UMT-2 tribometer, and the worn surfaces of the samples were analyzed by means of Nano Scratch Tester and surface profilometry. It was found that lowest friction coefficient and smallest width of wear were achieved with the SAMs of C12 alkyl chain (C12-SAM). The superior friction reduction and wear resistance of the SAMs in comparison with the bare silicon substrate are attributed to good adhesion of the self-assembled films to the substrate, especially the C12-SAM with desirable alkyl chain length.

  17. Spectroscopic, electrochemical, and alkylation reactions: tert-butyl N-(2-mercaptoethyl)carbamate copper(II) and nickel(II) complexes as structural mimics for the active site of thiolate-alkylating enzymes.

    PubMed

    Ibrahim, Mohamed M; Mersal, Gaber A M; El-Shafai, Nagi; Ramadan, Abdel-Motaleb M; Youssef, Mohamed M

    2014-01-01

    Two new dithiolate copper(II) and nickel(II) complexes with the ligand tert-butyl N-(2-mercaptoethyl)-carbamate (Boc-SH) were prepared. Their structures were established to be [(Boc-S)2M], where M=Cu (1) and Ni (2) by using elemental analysis, thermal analysis, molar conductivity, FT-IR, Raman, UV/VIS, and ESR as well as EI-mass spectroscopic methods. The X-ray structure of the ligand Boc-SH was also determined. Spectral data showed that the carbamate ligand act as anioinic bidentate through one immine nitrogen and one thiolate sulfur donor atoms. The spectral techniques suggest that both complexes appear to have square planar geometries. The very low electrical conductance of the two complexes supports their neutral nature. The redox behaviors of the obtained complexes were also investigated by cyclic voltammetry. The monomeric nature of both complexes was assessed from their magnetic susceptibility values. The thermoanalytical data evidence that complex (2) is stable up to 165°C and undergo complete decomposition, resulting in NiO as a residual product. The TEM image of the obtained oxide residue showed its nanosize cluster, suggesting that complex (2) may be used as a precursor for the formation of nanooxide. The methylation reactions of the two dithiolate complexes (1) and (2) with methyl iodide appear to occur intramolecularly at the metal(II)-bound dithiolates, forming the metal(II)-bound dithioether complexes [M(Boc-SCH3)2]I2 with clean second-order constants of 7.95×10(-2) and 10.59×10(-2) M(-1) s(-1), respectively.

  18. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure study of water adsorption on pyridine-terminated thiolate self-assembled monolayers.

    PubMed

    Zubavichus, Yan; Zharnikov, Michael; Yang, Yongjie; Fuchs, Oliver; Umbach, Eberhard; Heske, Clemens; Ulman, Abraham; Grunze, Michael

    2004-12-07

    Adsorption of water on self-assembled monolayers (SAMs) of 4-(4-mercaptophenyl)pyridine on gold at low temperatures under ultrahigh vacuum conditions is studied by synchrotron radiation X-ray photoelectron and absorption spectroscopy. Water adsorption induces a strong modification of the chemical state of the pyridine N atoms at the SAM/ice interface, indicative for strong H bonding and partial proton transfer between water molecules and pyridine moieties. Additionally, the initial molecular orientation within the SAM is changed upon formation of an adsorbed water multilayer.

  19. Functionalized S 4Zn (II) complexes as structural modelling for the active site of thiolate-alkylating enzymes: The crystal structure of [TtiZn-SpyH] 2·HClO 4 [Tti = tris(thioimidazolyl)hydroborate and SpyH = pyridine-2-thiol

    NASA Astrophysics Data System (ADS)

    Ibrahim, Mohamed M.

    2009-11-01

    Two new functionalized S 3Zn-bound pyridinethiol complexes [TtiZn-SpyH] 2·HClO 41 and [TtiZn-Spy] 2 [Tti = tris(2-mercapto-1-xylyl-imidazolyl)hydroborate, SpyH = pyridine-2-thiol, and Spy = pyridine-4-thiol] were synthesized and characterized. Structural determination of complex 1 showed that the coordination geometry around zinc atom is ideally regular tetrahedral with three thione donors from the ligand Tti and one thiolate donor from the coligand pyridine-2-thiol. The average Zn(1)-S(thione) bond length is 2.349 Å and the Zn(1)-S(thiolate) bond length is 2.289 Å. The reactivity studies of both complexes 1 and 2 as models for the active sites of thiolate-alkylating enzymes toward methylation reactions showed that 1 is much less susceptible to methylation than that of complex 2. This decrease in the nucleophilicity of complex 1 could be explained by electronic effects of the pyridinum salts as well as the steric hindrance, which is provided by the perchlorate anion.

  20. Effects of perfluorinated alkyl acids on cellular responses of MCF-10A mammary epithelial cells in monolayers and on acini formation in vitro.

    PubMed

    Halsne, Ruth; Tandberg, Julia Isabel; Lobert, Viola Hélène; Østby, Gunn Charlotte; Thoen, Even; Ropstad, Erik; Verhaegen, Steven

    2016-09-30

    Perfluorinated alkyl acids (PFAAs) are stable chemicals detected in tissue and serum from various species, including humans, and have been linked to adverse health outcomes. Experimental PFAA exposure in rodents has been associated with changes in mammary gland development. The estrogen receptor (ER)-negative human breast epithelial cell line, MCF-10A, can be grown as monolayer, but also has the ability to form three-dimensional acini in vitro, reflecting aspects of mammary glandular morphogenesis. Cells were exposed to five different PFAAs, perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluoroundecanoic acid (PFUnDA), both in monolayer and acini cultures. In monolayer cultures only the higher concentrations of PFOS, PFNA and PFDA (400-500μM) caused a significant increase in cell death, whereas PFOA and PFUnDA had no effect. Normal acini maturation was negatively impacted by PFOS, PFNA and PFDA already at the lowest concentration tested (0.6μM). Observed effects included loss of organization of the cell clusters and absence of a hollow lumen. Overall, this study demonstrated that PFAAs can interfere with cellular events related to normal development of glandular breast tissue through ER-independent mechanisms. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  1. Thiolated 2-methacryloyloxyethyl phosphorylcholine for an antifouling biosensor platform.

    PubMed

    Goda, Tatsuro; Tabata, Miyuki; Sanjoh, Mai; Uchimura, Mai; Iwasaki, Yasuhiko; Miyahara, Yuji

    2013-10-07

    We developed a new building block for a protein- and cell-repellant self-assembled monolayer (SAM) from 2-methacryloyloxyethyl phosphorylcholine (MPC) via a simple Michael-type addition to one mercapto group in alkanedithiol. The thiolated MPC can enable functionalization of a noble metal electrode to minimize noise signal in biosensing.

  2. Mixed self-assembled monolayers (SAMs) consisting of methoxy-tri(ethylene glycol)-terminated and alkyl-terminated dimethylchlorosilanes control the non-specific adsorption of proteins at oxidic surfaces.

    PubMed

    Hoffmann, Christian; Tovar, Günter E M

    2006-03-15

    Monolayers from the newly synthesized compound methoxy-tri(ethylene glycol)-undecenyldimethylchlorosilane (CH3O(CH2CH2O)3(CH2)11Si(CH3)2Cl, MeO(EG)3C11DMS) and dodecyldimethylchlorosilane (DDMS), both pure and mixed, were prepared by self-assembly from organic solution in the presence of an organic base. The films obtained were characterized by advancing and receding contact angle measurements and ellipsometry to confirm the formation of self-assembled monolayers (SAMs). The resulting data on the covalently attached dimethylsilanes were compared to known oligo(ethylene glycol) (OEG)-terminated SAM systems based on terminal alkenes, thiolates or trihydrolyzable silanes. The composition of the mixed SAMs was found to depend directly and linearly on the composition of the silanization solution. Enhanced protein repellent properties were found for the SAMs using a variety of proteins, including the Ras Binding Domain (RBD), a protein with high relevance for cancer diagnostics. Roughly a RBD protein monolayer amount was adsorbed to silicon oxide surfaces silanized with DDMS or non-silanized silicon wafers, and in contrast, no RBD was adsorbed to surfaces silanized with MeO(EG)3C11DMS or to mixed monolayers consisting of DDMS and MeO(EG)3C11DMS if the content of OEG-silane overcame a critical content of X(EG) approximately 0.9.

  3. Influence of temperature and alkyl chain length on phase behavior in Langmuir monolayers of some oxyethylenated nonionic surfactants.

    PubMed

    Islam, Nazrul; Kato, Teiji

    2006-02-15

    We study the surface phase behavior in Langmuir monolayers of a series of nonionic surfactants of the general formula CnE1 with n=14, 16, and 18 by film balance and Brewster angle microscopy (BAM) over a wide range of temperatures. A cusp point followed by a pronounced plateau region in the pressure-area (pi-A) isotherms indicates a first-order phase transition in the coexisting state between a lower density liquid expanded (LE) phase and a higher density liquid condensed (LC) phase at the air-water interface. The formation of bright two-dimensional (2D) LC domains in a dark background visualized by BAM further confirms this observation. In addition to the cusp point at the onset of the LE-LC coexistence state, another cusp point followed by a small plateau is observed for the C14E1 and C18E1 monolayers, indicating a second phase transition between two condensed phases of different compressibility and tilt orientation of the molecules. This unusual two-step phase transition is explained by the Ostwald step rule. The C16E1 and C18E1 monolayers show a kink in their respective isotherms, after which the surface pressure increases steeply with only a little decrease in the molecular area, suggesting that the molecules undergo a transition from a tilted to an almost vertical orientation with respect to the water surface. The thermodynamic parameters for the condensation of the molecules in the LE-LC coexistence state were calculated by employing the 2D Clapeyron equation. The temperature coefficient of the critical surface pressure dpi(c)/dT values shows a decreasing trend from C14E1 to C18E1, suggesting that the condensation process becomes less and less prone to thermal perturbation as the chain length increases. For all the amphiphiles, the DeltaH values are found to be negative, suggesting an exothermic nature of condensation. The negative DeltaS values obtained from the relation DeltaH/T probably come from the restriction on the rotational and translational motion

  4. "Surface-Induced Dissociation of Acetone Cations from Self-Assembled Monolayer Surface of Flourinated Alkyl Thiol on Au (111) Substrate at Low Collision Energies"

    SciTech Connect

    Shukla, Anil K. ); Futrell, Jean H. )

    2003-08-15

    We have studied the dissociation of acetone molecular cations to acetyl cations following collision with a monolayer surface of fluorinated alkyl thiol (FC12) self-assembled on Au (111) substrate at 13, 25.2 and 49.6 eV kinetic energies. Three energetically distinct dissociation processes contribute to total dissociation in this energy range. At all energies there is a common dissociation pathway involving loss of nearly all of the parent ions kinetic energy in the collision process. Fragment ions resulting from this dissociation mechanism are scattered over a wide range of angles. The second pathway, observed at 25.2 and 49.6 eV kinetic energy is delayed dissociation of collisionally excited acetone cations after only a small fraction of the ions kinetic energy is lost in the collision process. Fragment ions resulting from this unique dynamics feature are scattered close to the surface parallel. These dissociations take place after the excited ions have passed through the collision region and the energy analyzer and prior to their entering the mass analyzer. At 49.6 eV kinetic energy, a small intensity fragment ion peak appears at intermediate kinetic energy spectra between the low energy loss and the highly inelastic scattering peaks.

  5. Enhancement of seeding for electroless Cu plating of metallic barrier layers by using alkyl self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Chen, Sung-Te; Chung, Yu-Cheng; Fang, Jau-Shiung; Cheng, Yi-Lung; Chen, Giin-Shan

    2017-05-01

    Tethering a self-assembled monolayer (SAM) on ultralow-k (porous) dielectric materials as a seed-trapping layer for electroless Cu plating has been extensively studied. By contrast, literature on direct electroless Cu plating of metallic barrier layers assisted by SAMs is scarce. Therefore, Ta, a crucial component of barrier materials for Cu interconnect metallization, was investigated as a model substrate for a new seeding (Ni catalyst formation) process of electroless Cu plating. Transmission and scanning electron microscopies indicated that catalytic particles formed on Ta films through Tasbnd OH groups tend to become aggregates with an average size of 14 nm and density of 2 × 1015 m-2. By contrast, Ta films with a plasma-functionalized SAM tightly bound catalytic particles without agglomeration, thus yielding a markedly smaller size (3 nm) and higher density (3 × 1016 m-2; one order greater than those formed by other novel methods). X-ray photoelectron spectroscopy clearly identified the types of material species and functional groups induced at each step of the seeding process. Moreover, the phase of the catalytic particles, either nickel alkoxide, Ni(OH)2, or metallic Ni, along with the seed-bonding mechanism, was also unambiguously distinguished. The enhancement of film-formation quality of Cu by the new seeding process was thus demonstrated.

  6. Preparation and wettability examinations of transparent SiO2 binder-added MgF2 nanoparticle coatings covered with fluoro-alkyl silane self-assembled monolayer.

    PubMed

    Murata, Tsuyoshi; Hieda, Junko; Saito, Nagahiro; Takai, Osamu

    2012-05-01

    SiO2-added MgF2 nanoparticle coatings with various surface roughness properties were formed on fused silica-glass substrates from autoclaved sols prepared at 100-180 °C. To give it hydrophobicity, we treated the samples with fluoro-alkyl silane (FAS) vapor to form self-assembled monolayers on the nanoparticle coating and we examined the wettability of the samples. The samples preserved good transparency even after the FAS treatment. The wettability examination revealed that higher autoclave temperatures produced a larger average MgF2 nanoparticle particle size, a larger surface roughness, and a higher contact angle and the roll-off angle.

  7. Preactivated thiolated glycogen as mucoadhesive polymer for drug delivery.

    PubMed

    Perrone, Mara; Lopalco, Antonio; Lopedota, Angela; Cutrignelli, Annalisa; Laquintana, Valentino; Douglas, Justin; Franco, Massimo; Liberati, Elisa; Russo, Vincenzo; Tongiani, Serena; Denora, Nunzio; Bernkop-Schnürch, Andreas

    2017-10-01

    The purpose of this study was to synthesize and characterize a novel thiolated glycogen, so-named S-preactivated thiolated glycogen, as a mucosal drug delivery systems and the assessment of its mucoadhesive properties. In this regard, glycogen-cysteine and glycogen-cysteine-2-mercaptonicotinic acid conjugates were synthesized. Glycogen was activated by an oxidative ring opening with sodium periodate resulting in reactive aldehyde groups to which cysteine was bound via reductive amination. The obtained thiolated polymer displayed 2203.09±200μmol thiol groups per gram polymer. In a second step, the thiol moieties of thiolated glycogen were protected by disulfide bond formation with the thiolated aromatic residue 2-mercaptonicotinic acid (2MNA). In vitro screening of mucoadhesive properties was performed on porcine intestinal mucosa using different methods. In particular, in terms of rheology investigations of mucus/polymer mixtures, the S-preactivated thiolated glycogen showed a 4.7-fold increase in dynamic viscosity over a time period of 5h, in comparison to mucus/Simulated Intestinal Fluid control. The S-preactivated polymer remained attached on freshly excised porcine mucosa for 45h. Analogous results were obtained with tensile studies demonstrating a 2.7-fold increase in maximum detachment force and 3.1- fold increase in total work of adhesion for the S-preactivated polymer compared to unmodified glycogen. Moreover, water-uptake studies showed an over 4h continuing weight gain for the S-preactivated polymer, whereas disintegration took place for the unmodified polymer within the first hour. Furthermore, even in the highest tested concentration of 2mg/ml the new conjugates did not show any cytotoxicity on Caco-2 cell monolayer using an MTT assay. According to these results, S-preactivated glycogen represents a promising type of mucoadhesive polymers useful for the development of various mucosal drug delivery systems. Copyright © 2017 Elsevier B.V. All rights

  8. Thiolated pyrimidine nucleotides may interfere thiol groups concentrated at lipid rafts of HIV-1 infected cells.

    PubMed

    Kanizsai, Szilvia; Ongrádi, Joseph; Aradi, János; Nagy, Károly

    2014-12-01

    Upon HIV infection, cells become activated and cell surface thiols are present in increased number. Earlier we demonstrated in vitro anti-HIV effect of thiolated pyrimidine nucleotide UD29, which interferes thiol function. To further analyse the redox processes required for HIV-1 entry and infection, toxicity assays were performed using HIV-1 infected monolayer HeLaCD4-LTR/ β-gal cells and suspension H9 T cells treated with several thiolated nucleotide derivatives of UD29. Selective cytotoxicity of thiolated pyrimidines on HIV-1 infected cells were observed. Results indicate that thiolated pyrimidine derivates may interfere with -SH (thiol) groups concentrated in lipid rafts of cell membrane and interacts HIV-1 infected (activated) cells resulting in a selective cytotoxicity of HIV-1 infected cells, and reducing HIV-1 entry.

  9. Characterization of Thiolate-Protected Gold Nanoparticles by Mass Spectrometry

    PubMed Central

    Harkness, Kellen M.; Cliffel, David E.; McLean, John A.

    2014-01-01

    Thiolate-protected gold nanoparticles (AuNPs) are a highly versatile nanomaterial, with wide-ranging physical properties dependent upon the protecting thiolate ligands and gold core size. These nanoparticles serve as a scaffold for a diverse and rapidly increasing number of applications, extending from molecular electronics to vaccine development. Key to the development of such applications is the ability to quickly and precisely characterize synthesized AuNPs. While a unique set of challenges have inhibited the potential of mass spectrometry in this area, recent improvements have made mass spectrometry a dominant technique in the characterization of small AuNPs, specifically those with discrete sizes and structures referred to as monolayer-protected gold clusters (MPCs). The unique ability of mass spectrometry to analyze the protecting monolayer of the AuNP may cause it to become a major technique in the characterization of larger AuNPs. The development of mass spectrometry techniques for AuNP characterization has begun to reveal interesting new areas of research. This report is a discussion of the historical challenges in this field, the emerging techniques which aim to meet those challenges, and the future role of mass spectrometry in the growing field of thiolate-protected AuNPs. PMID:20419232

  10. Synthesis of thiolated glycosaminoglycans and grafting to solid surfaces.

    PubMed

    Köwitsch, Alexander; Jurado Abreu, Mauricio; Chhalotre, Ankur; Hielscher, Martin; Fischer, Steffen; Mäder, Karsten; Groth, Thomas

    2014-12-19

    Glycosaminoglycans (GAGs) with varying degree of sulfation were chemically modified to obtain thiolated analogues (tGAGs) for subsequent surface grafting on vinyl-terminated self-assembled monolayers. Thiolation was achieved by the use of the disulfide containing crosslinker 3,3'-dithiobis(propanoic hydrazide) and subsequent reduction of the disulfide with dithiothreitol. Two different molar ratios of the crosslinker were used for conjugation. The tGAGs were characterized by (1)H-NMR, Raman and flow-field-flow-fractionation (A4F) to determine the chemical composition, structure and molecular weight of the products. Ellman's reagent was used to quantify the thiol concentration of tGAGs. The tGAGs were immobilized onto vinyl-terminated glass and silicon via thiol-ene reaction. This was achieved by homogeneous immobilization from solution as well as with microcontact printing and exposure to UV light. The results of water contact angle measurement (WCA), ellipsometry and confocal laser scanning microscopy (CLSM) demonstrated that the resulting surface coverage was dependent on the degree of thiolation of GAGs.

  11. Gold surfaces and nanoparticles are protected by Au(0)-thiyl species and are destroyed when Au(I)-thiolates form.

    PubMed

    Reimers, Jeffrey R; Ford, Michael J; Halder, Arnab; Ulstrup, Jens; Hush, Noel S

    2016-03-15

    The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)-thiyl, with Au(I)-thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)-thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s-d hybridization and charge polarization effects that perturbatively mix in some Au(I)-thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)-thiolate involvement. Predictions that Brust-Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)-thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established.

  12. Dithienylcyclopentene-functionalised subphthalocyaninatoboron complexes: photochromism, fluorescence modulation and formation of self-assembled monolayers on gold

    PubMed Central

    Weidner, Tobias; Baio, Joe E.; Seibel, Johannes

    2012-01-01

    Subphthalocyaninatoboron (SubPc) complexes bearing six peripheral n-dodecylthio substituents and an apical photochromic dithienylperfluorocyclopentene unit were prepared. The photoinduced isomerisation of the apical substitutent from the open to the ring-closed form significantly influences the photoluminescence of the covalently attached SubPc unit, which is more efficiently quenched by the ring-closed form. Films on gold were fabricated from these multifunctional conjugates and characterised by near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS). The results are in accord with the formation of self-assembled monolayers based on dome-shaped SubPc-based anchor groups. Their chemisorption is primarily due to the peripheral n-dodecylthio substituents, giving rise to covalently attached thiolate as well as coordinatively bound thioether units, whose alkyl chains are in an almost parallel orientation to the surface. PMID:22138955

  13. Monolayer coated aerogels and method of making

    DOEpatents

    Zemanian, Thomas Samuel; Fryxell, Glen; Ustyugov, Oleksiy A.

    2006-03-28

    Aerogels having a monolayer coating are described. The aerogel and a monolayer forming precursor are provided in a supercritical fluid, whereupon the aerogel and the monolayer forming precursor are reacted in said supercritical fluid to form a covalent bond between the aerogel and the monolayer forming precursor. Suitable aerogels are ceramic oxides such as silica, alumina, aluminosilicate, and combinations thereof. Suitable monolayer forming precursors include alkyl silanes, chlorosilanes, boranes, chloroboranes, germanes, and combinations thereof. The method may also include providing a surface preparation agent such as water, or hydroetching an aerogel to enhance the coating of the monolayer.

  14. Modeling the photosensitizing properties of thiolate-protected gold nanoclusters.

    PubMed

    Azarias, Cloé; Adamo, Carlo; Perrier, Aurélie

    2016-03-21

    An accurate computational strategy for studying the structural, redox and optical properties of thiolated gold nanoclusters (GNCs) using (Time-Dependent) Density Functional Theory is proposed. The influence of the pseudopotential/basis set, solvent description and the choice of the functional has been investigated to model the structural and electronic properties of the Au25(SR)18(-) system, with R being an organic ligand. This study aims to describe with a comparable precision both the GNC and the organic ligands and rationalize the effect of coating on different GNC properties. Two differently coated GNCs have been considered: the system with R = CH2CH2Ph and the GNC coated with 17 alkyl chains (C6H13) and functionalized by one fluorophore pyrene derivative (CH2CH2(NH)(CO)Py). The computational protocol we propose should then be used to design more efficient metal cluster-sensitized solar cells.

  15. Understanding the Phase Diagram of Self-Assembled Monolayers of Alkanethiolates on Gold

    PubMed Central

    2016-01-01

    Alkanethiolate monolayers on gold are important both for applications in nanoscience as well as fundamental studies of adsorption and self-assembly at metal surfaces. While considerable experimental effort has been put into understanding the phase diagram of these systems, theoretical work based on density functional theory (DFT) has long been hampered by the inability of conventional exchange-correlation functionals to describe dispersive interactions. In this work, we combine dispersion-corrected DFT calculations using the new vdW-DF-CX functional with the ab initio thermodynamics method to study the stability of dense standing-up and low-coverage lying-down phases on Au(111). We demonstrate that the lying-down phase has a thermodynamic region of stability starting from thiolates with alkyl chains consisting of n ≈ 3 methylene units. This phase emerges as a consequence of a competition between dispersive chain–chain and chain–substrate interactions, where the strength of the latter varies more strongly with n. A phase diagram is derived under ultrahigh-vacuum conditions, detailing the phase transition temperatures of the system as a function of the chain length. The present work illustrates that accurate ab initio modeling of dispersive interactions is both feasible and essential for describing self-assembled monolayers. PMID:27313813

  16. Gold surfaces and nanoparticles are protected by Au(0)–thiyl species and are destroyed when Au(I)–thiolates form

    PubMed Central

    Reimers, Jeffrey R.; Ford, Michael J.; Halder, Arnab; Ulstrup, Jens; Hush, Noel S.

    2016-01-01

    The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)–thiyl, with Au(I)–thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)–thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s–d hybridization and charge polarization effects that perturbatively mix in some Au(I)–thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)–thiolate involvement. Predictions that Brust–Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)–thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established. PMID:26929334

  17. Characterization of Functionalized Self-Assembled Monolayers and Surface-Attached Interlocking Molecules Using Near-Edge X-ray Absorption Fine Structure Spectroscopy

    SciTech Connect

    Willey, Trevor M.

    2004-04-01

    Quantitative knowledge of the fundamental structure and substrate binding, as well as the direct measurement of conformational changes, are essential to the development of self-assembled monolayers (SAMs) and surface-attached interlocking molecules, catenanes and rotaxanes. These monolayers are vital to development of nano-mechanical, molecular electronic, and biological/chemical sensor applications. This dissertation investigates properties of functionalized SAMs in sulfur-gold based adsorbed molecular monolayers using quantitative spectroscopic techniques including near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and x-ray photoelectron spectroscopy (XPS). The stability of the gold-thiolate interface is addressed. A simple model SAM consisting of dodecanethiol adsorbed on Au(111) degrades significantly in less than 24 hours under ambient laboratory air. S 2p and O 1s XPS show the gold-bound thiolates oxidize to sulfinates and sulfonates. A reduction of organic material on the surface and a decrease in order are observed as the layer degrades. The effect of the carboxyl vs. carboxylate functionalization on SAM structure is investigated. Carboxyl-terminated layers consisting of long alkyl-chain thiols vs. thioctic acid with short, sterically separated, alkyl groups are compared and contrasted. NEXAFS shows a conformational change, or chemical switchability, with carboxyl groups tilted over and carboxylate endgroups more upright. Surface-attached loops and simple surface-attached rotaxanes are quantitatively characterized, and preparation conditions that lead to desired films are outlined. A dithiol is often insufficient to form a molecular species bound at each end to the substrate, while a structurally related disulfide-containing polymer yields surface-attached loops. Similarly, spectroscopic techniques show the successful production of a simple, surface-attached rotaxane that requires a ''molecular riveting'' step to hold the mechanically attached

  18. Dynamics of decanethiol self-assembled monolayers on Au(111) studied by time-resolved scanning tunneling microscopy.

    PubMed

    Wu, Hairong; Sotthewes, Kai; Kumar, Avijit; Vancso, G Julius; Schön, Peter M; Zandvliet, Harold J W

    2013-02-19

    We investigated the dynamics of decanethiol self-assembled monolayers on Au(111) surfaces using time-resolved scanning tunneling microscopy at room temperature. The expected ordered phases (β, δ, χ*, and φ) and a disordered phase (ε) were observed. Current-time traces with the feedback loop disabled were recorded at different locations on the surface. The sulfur end group of the decanethiolate molecule exhibits a stochastic two-level switching process when the molecule is adsorbed in a (local) β phase registry. This two-level process is attributed to the diffusion of the Au-thiolate complex between two adjacent adsorption sites. The irregular current jumps in the current-time traces recorded on the tails of decanethiolate molecules in the ordered β, δ, and χ* phases are ascribed to wagging of the alkyl tails. Finally, the disordered phase is characterized by even larger current jumps, which indicates that the tail of the decanethiolate flips up occasionally and makes contact with the tip. Our experiments reveal that the massive dynamics of the self-assembled monolayer is due to diffusion of decanethiol-Au complexes, rather than the diffusion of decanethiolate molecules.

  19. Use of thiolated oligonucleotides as anti-fouling diluents in electrochemical peptide-based sensors.

    PubMed

    McQuistan, Adam; Zaitouna, Anita J; Echeverria, Elena; Lai, Rebecca Y

    2014-05-11

    We incorporated short thiolated oligonucleotides as passivating diluents in the fabrication of electrochemical peptide-based (E-PB) sensors, with the goal of creating a negatively charged layer capable of resisting non-specific adsorption of matrix contaminants. The E-PB HIV sensors fabricated using these diluents were found to be more specific and selective, while retaining attributes similar to the sensor fabricated without these diluents. Overall, these results highlight the advantages of using oligonucleotides as anti-fouling diluents in self-assembled monolayer-based sensors.

  20. HEC-cysteamine conjugates: influence of degree of thiolation on efflux pump inhibitory and permeation enhancing properties.

    PubMed

    Rahmat, Deni; Sakloetsakun, Duangkamon; Shahnaz, Gul; Sarti, Federica; Laffleur, Flavia; Schnürch, Andreas Bernkop

    2012-01-17

    Within the present study hydroxyethyl cellulose-cysteamine conjugates are investigated regarding biocompatibility, in situ gelling, permeation enhancing and efflux pump inhibitory properties. For this purpose, a series of concentrations of sodium periodate was prepared to oxidize HEC leading to ring opening of glucose subunits. The resulting polymers showing varying degrees of oxidation (DO) were then conjugated with cysteamine stabilized via reductive amination. Consequently, HEC-cysteamine conjugates with increasing degree in thiolation were obtained. Since the conjugates are positively charged, potency of cytotoxicity was tested by resazurin assay. In situ gelling properties of the conjugates were studied to investigate change of their viscosity due to inter- and/or intramolecular crosslinking via disulfide bonds. The influence of the presence of the conjugates on transport of rhodamine 123 and fluoresceinisothiocyanate-dextran 4 (FD4) representing model compounds for P-glycoprotein (P-gp) inhibition and permeation enhancing studies, respectively, across Caco-2 cell monolayers was determined. The conjugates showed a degree of thiolation in the range of 316-2158 μmol/g. Within 30 min, dynamic viscosity of the conjugate with the lowest degree of thiolation 0.5% (m/v) increased up to 300-fold. The conjugates showed a degree of thiolation-dependent increase in cytotoxicity but they all were found comparatively low cytotoxic. The addition of the conjugate with thiol group content of 1670 μmol/g resulted in the highest improvement in the transport of both rhodamine 123 and FD4 as compared to buffer control. Accordingly, the degree of thiolation strongly influences the properties of the conjugates and the modulation of the degree of thiolation could be exploited for development of various drug delivery systems.

  1. Superatomic S(2) silver clusters stabilized by a thiolate-phosphine monolayer: insight into electronic and optical properties of Ag14(SC6H3F2)12(PPh3)8 and Ag16(SC6H3F2)14(DPPE)4.

    PubMed

    Gell, Lars; Lehtovaara, Lauri; Häkkinen, Hannu

    2014-09-18

    The electronic structure of two recently crystallographically solved, thiolate-phosphine protected silver clusters Ag14 and Ag16 are analyzed via density functional theory (DFT) and their optical excitations are analyzed from time-dependent DFT perturbation theory. Both clusters can be characterized as having the S(2) free-electron configuration in the metal core, which is the first time such a configuration is confirmed for structurally known ligand-protected noble metal clusters. However, their different core shapes and ligand layer induce significantly different optical spectra. Performance of gradient-corrected DFT functionals is discussed and it is shown that the asymptotically correct Leeuwen-Baerends LB94 functional reproduces the optical spectrum of Ag14 in a good agreement with experiment. Choice of the functional becomes important for clusters where the optical transitions are dominated by the electron-rich ligand layer.

  2. Adsorption of self-assembled monolayer on Cu(111): First-principles study

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Cheng, Jiang-Tao; Ma, Shang-Yi; Wang, Hong-De

    2017-08-01

    The density function theory is used to explore the structures of alkyl-thiolate (RS, R=CH3, CF3) monolayer on the Cu(111) surface. By performing the total energy calculations for RS at three possible adsorption sites (fcc, hcp, bridge) with five different coverages (1/12, 1/9, 1/6, 1/4, 1/3), we obtained the stable adsorption configurations of the Cu-RS system. Especially, the effect of Van der Waals interaction on the adsorption configurations was studied by the DFT-D2 method. The work functions for Cu-RS (R=CH3, CF3) systems were calculated, we find that the CH3S adsorbed on the Cu(111) surface decreases the metal work function remarkably, and the work functions strongly depend on the coverage. In the case of the Cu-CF3S system, the results are just the opposite. Thus, controlling the kind and coverage of the surface adsorbates would be an effective technique to tune the work function of the metal.

  3. Thiolated polymers as mucoadhesive drug delivery systems.

    PubMed

    Duggan, Sarah; Cummins, Wayne; O' Donovan, Orla; Hughes, Helen; Owens, Eleanor

    2017-03-30

    Mucoadhesion is the process of binding a material to the mucosal layer of the body. Utilising both natural and synthetic polymers, mucoadhesive drug delivery is a method of controlled drug release which allows for intimate contact between the polymer and a target tissue. It has the potential to increase bioavailability, decrease potential side effects and offer protection to more sensitive drugs such as proteins and peptide based drugs. The thiolation of polymers has, in the last number of years, come to the fore of mucoadhesive drug delivery, markedly improving mucoadhesion due to the introduction of free thiol groups onto the polymer backbone while also offering a more cohesive polymeric matrix for the slower and more controlled release of drug. This review explores the concept of mucoadhesion and the recent advances in both the polymers and the methods of thiolation used in the synthesis of mucoadhesive drug delivery devices.

  4. The halogen analogs of thiolated gold nanoclusters

    SciTech Connect

    Jiang, Deen; Walter, Michael

    2012-01-01

    Is it possible to replace all the thiolates in a thiolated gold nanocluster with halogens while still maintaining the geometry and the electronic structure? In this work, we show from density functional theory that such halogen analogs of thiolated gold nanoclusters are highly likely. Using Au{sub 25}X{sub 18}{sup -} as an example, where X = F, Cl, Br, or I replaces -SR, we find that Au{sub 25}Cl{sub 18}{sup -} demonstrates a high similarity to Au{sub 25}(SR){sub 18}{sup -} by showing Au-Cl distances, Cl-Au-Cl angles, band gap, and frontier orbitals similar to those in Au{sub 25}(SR){sub 18}{sup -}. DFT-based global minimization also indicates the energetic preference of staple formation for the Au{sub 25}Cl{sub 18}{sup -} cluster. The similarity between Au{sub m}(SR){sub n} and Au{sub m}X{sub n} could be exploited to make viable Au{sub m}X{sub n} clusters and to predict structures for Au{sub m}(SR){sub n}.

  5. Synthesis and characterisation of mucoadhesive thiolated polymers.

    PubMed

    Bernkop-Schnürch, A; Steininger, S

    2000-01-25

    This study examined various factors influencing the mucoadhesive properties of thiolated polymers (thiomers), which are capable of forming covalent bonds with thiol sub-structures of the mucus glycoprotein. Mediated by a carbodiimide, L-cysteine was therefore covalently bound to polycarbophil (PCP) and to carboxymethylcellulose (CMC). The resulting polymer conjugates displayed 12.3 and 22.3 micromol thiol groups per gram, respectively. Whereas the swelling behaviour of tablets based on CMC was not markedly influenced by the immobilisation of cysteine, it was improved significantly (P<0.05) in case of PCP. Tensile studies carried out with the unmodified and thiolated polymers of pH 3, 5 and 7, respectively, revealed that only if the polymer displays a pH-value of 5, the total work of adhesion can be improved significantly due to the covalent attachment of thiol groups. These results were in good agreement with a new mucoadhesion test system described here taking also the cohesiveness of the delivery system into account. The results represent helpful basic information in order to improve the mucoadhesive properties of thiolated polymers.

  6. The Smallest Thiolated Gold Superatom Complexes

    SciTech Connect

    Jiang, Deen; Whetten, Robert L; Luo, Weidong; Dai, Sheng

    2009-01-01

    The superatom concept of metallic cluster valence is based on the electron-shell model as first proposed to explain the special stability of certain metal-atom clusters generated in the gas phase. It accounts for the magic-number series 2, 8, 18, 34, 58,... by shell-closing of the superatom orbitals 1S, 1P, 1D,.... Recently, the superatom-complex concept has been introduced to explain the compositions of high-yield gold-cluster compounds, especially Au{sub 25}(SR){sub 18}{sup -} and Au{sub 102}(SR){sub 44} (with -SR being a thiolate group), corresponding to the magic numbers of 8 and 58, respectively. Surprisingly, no thiolated gold cluster accounting for the first closing (electron count 2) has yet been determined. Structure-bonding considerations lead us to propose Au{sub 12}(SR){sub 9}{sup +} as the superior candidate for the smallest thiolated gold superatom. This cluster features an octahedron core covered by three RS(AuSR){sub 2} motifs. It has a unique C{sub 3} axis, is chiral, and possesses ideal aurophilic interactions and, therefore, should exist in nature. The folding of thiol-rich biomolecules may help us to realize this complex, which may also be prepared from available phosphine-ligated gold clusters.

  7. Alkylating agents stronger than alkyl triflates.

    PubMed

    Kato, Tsuyoshi; Stoyanov, Evgenii; Geier, Jens; Grützmacher, Hansjörg; Reed, Christopher A

    2004-10-06

    A new class of potent electrophilic "R(+)" alkylating agents has been developed using weakly nucleophilic carborane anions as leaving groups. These reagents, R(CHB(11)Me(5)X(6)) (R = Me, Et, and i-Pr; X = Cl, Br), are prepared via metathesis reactions with conventional alkylating agents such as alkyl triflates, using the high oxophilicity of silylium ion-like species, Et(3)Si(carborane), as the driving force to obtain increased alkyl electrophilicity. The crystal structure of the isopropyl reagent, i-Pr(CHB(11)Me(5)Br(6)), has been determined, revealing covalence in the alkyl-carborane bonding. This contrasts with the free i-Pr(+) carbocation observed when the anion is less coordinating (e.g. Sb(2)F(11)(-)) or with tertiary alkyl centers, as in [tert-butyl][carborane] salts. In solution, the reagents exist as equilibrating isomers with the alkyl group at the 7-11 or 12 halide positions of the CB(11) icosahedral carborane anion. These alkylating agents are so electrophilic that they (a) react with alkanes at or below room temperature via hydride extraction to produce carbenium ions, (b) alkylate benzene without a Friedel-Crafts catalyst to give arenium ions, and (c) alkylate electron-deficient phosphorus compounds that are otherwise inert to conventional alkylating agents such as methyl triflate.

  8. Chirality in thiolate-protected gold clusters.

    PubMed

    Knoppe, Stefan; Bürgi, Thomas

    2014-04-15

    Over recent years, research on thiolate-protected gold clusters Au(m)(SR)n has gained significant interest. Milestones were the successful determination of a series of crystal structures (Au102(SR)44, Au25(SR)18, Au38(SR)24, Au36(SR)24, and Au28(SR)20). For Au102(SR)44, Au38(SR)24, and Au28(SR)20, intrinsic chirality was found. Strong Cotton effects (circular dichroism, CD) of gold clusters protected by chiral ligands have been reported a long time ago, indicating the transfer of chiral information from the ligand into the cluster core. Our lab has done extensive studies on chiral thiolate-protected gold clusters, including those protected with chiral ligands. We demonstrated that vibrational circular dichroism can serve as a useful tool for the determination of conformation of the ligand on the surface of the cluster. The first reports on crystal structures of Au102(SR)44 and Au38(SR)24 revealed the intrinsic chirality of these clusters. Their chirality mainly arises from the arrangement of the ligands on the surface of the cluster cores. As achiral ligands are used to stabilize the clusters, racemic mixtures are obtained. However, the separation of the enantiomers by HPLC was demonstrated which enabled the measurement of their CD spectra. Thermally induced inversion allows determination of the activation parameters for their racemization. The inversion demonstrates that the gold-thiolate interface is anything but fixed; in contrast, it is rather flexible. This result is of fundamental interest and needs to be considered in future applications. A second line of our research is the selective introduction of chiral, bidentate ligands into the ligand layer of intrinsically chiral gold clusters. The ligand exchange reaction is highly diastereoselective. The bidentate ligand connects two of the protecting units on the cluster surface and thus effectively stabilizes the cluster against thermally induced inversion. A minor (but significant) influence of chiral ligands to

  9. Syntheses and Structure Determinations of Calcium Thiolates.

    PubMed

    Chadwick, Scott; Englich, Ulrich; Noll, Bruce; Ruhlandt-Senge, Karin

    1998-09-07

    The exploration of synthetic methodologies toward heavy alkaline-earth chalcogenolates resulted in the preparation and structural characterization of a family of calcium thiolates, including [Ca(SC(6)F(5))(2)(py)(4)], 1 (py = pyridine), the separated ion-triple [Ca(18-crown-6)(NH(3))(3))][SMes](2).2THF, 2 (Mes = 2,4,6-tBu(3)C(6)H(2)), and the contact triple [Ca(18-crown-6)(SMes)(2)].THF, 3. Compound 1 was prepared by treating [Ca(N(SiMe(3))(2))(2)](2) with 4 equiv of HSC(6)F(5) under addition of pyridine. The thiolates 2 and 3 were synthesized by treatment of calcium metal dissolved in dry, liquid NH(3) under addition of 2 equiv of HSMes and crown ether or, alternatively, by the reduction of MesSSMes with calcium metal in dry, liquid ammonia. We also report two reaction products isolated during attempted calcium thiolate syntheses: [CaBr(4)(THF)(2)(&mgr;(2)-Li)(2)(THF)(4)], 4, isolated as the product of a salt elimination reaction between CaBr(2) and 2 equiv of [Li(THF)(n)()S-2,4,6-(i)()Pr(3)C(6)H(2)](m)(). [(NH(4))(py)(SC(6)F(5))], 5, was obtained as the sole product in the reaction of metallic calcium with HSC(6)F(5) in liquid ammonia under addition of pyridine. All compounds were characterized by single-crystal X-ray crystallography in addition to IR and NMR spectroscopy.

  10. Transthiocarbamoylation of Proteins by Thiolated Isothiocyanates*

    PubMed Central

    Shibata, Takahiro; Kimura, Yuuki; Mukai, Akihiro; Mori, Hitoshi; Ito, Sohei; Asaka, Yukio; Oe, Sho; Tanaka, Hiroshi; Takahashi, Takashi; Uchida, Koji

    2011-01-01

    Isothiocyanates, membrane-permeable electrophiles that form adducts with thiols, have been suggested to have important medical benefits. Here we shed light on isothiocyanate-thiol conjugates and studied their electrophilic potential transferring an isothiocyanate moiety to cellular proteins. When we examined the effect of sulfhydryl molecules on cellular response induced by 6-methylsulfinylhexyl isothiocyanate (6-HITC), an analog of sulforaphane isolated from broccoli, we observed significant induction of heme oxygenase-1 by 6-HITC even in the presence of N-acetyl-l-cysteine or glutathione (GSH). In addition, the authentic 6-HITC-β-mercaptoethanol (6-HITC-ME) conjugate markedly up-regulated the enzyme expression, suggesting the electrophilic potential of thiolated isothiocyanates. To gain a chemical insight into the cellular response induced by thiolated isothiocyanates, we studied the occurrence of transthiocarbamoylation of sulfhydryl molecules by 6-HITC-ME and observed that, upon incubation of 6-HITC-ME with GSH, a single product corresponding to the GSH conjugate of 6-HITC was generated. To test the functional ability of thiolated isothiocyanates to thiocarbamoylate proteins in living cells, we designed a novel probe, combining an isothiocyanate-reactive group and an alkyne functionality, and revealed that the transthiocarbamoylation of proteins occurred in the cells upon exposure to 6-HITC-ME. The target of thiocarbamoylation included heat shock protein 90 β (Hsp90β), a chaperone ATPase of the Hsp90 family implicated in protein maturation and targeting. To identify the sites of the Hsp90β modification, we utilized nano-LC/MALDI-TOF MS/MS and suggested that a thiol group on the peptide containing Cys-521 reacted with 6-HITC, resulting in a covalent adduct in a 6-HITC-treated recombinant Hsp90β in vitro. The site-selective binding to Cys-521 was supported by in silico modeling. Further study on the thiocarbamoylation of Hsp90β suggested that the formation

  11. True Nature of an Archetypal Self-Assembly System: Mobile Au-Thiolate Species on Au(111)

    NASA Astrophysics Data System (ADS)

    Yu, Miao; Bovet, N.; Satterley, Christopher J.; Bengió, S.; Lovelock, Kevin R. J.; Milligan, P. K.; Jones, Robert G.; Woodruff, D. P.; Dhanak, V.

    2006-10-01

    Alkanethiol self-assembled monolayer (SAM) phases on Au(111) have been assumed to involve direct S head group bonding to the substrate. Using x-ray standing wave experiments, we show the thiolate actually bonds to gold adatoms; self-organization in these archetypal SAM systems must therefore be governed by the movement of these Au-S-R moieties on the surface between two distinct local hollow sites on the surface. The results of recent ab initio total energy calculations provide strong support for this description, and a rationale for the implied significant molecular mobility in these systems.

  12. True nature of an archetypal self-assembly system: mobile Au-thiolate species on Au(111).

    PubMed

    Yu, Miao; Bovet, N; Satterley, Christopher J; Bengió, S; Lovelock, Kevin R J; Milligan, P K; Jones, Robert G; Woodruff, D P; Dhanak, V

    2006-10-20

    Alkanethiol self-assembled monolayer (SAM) phases on Au(111) have been assumed to involve direct S head group bonding to the substrate. Using x-ray standing wave experiments, we show the thiolate actually bonds to gold adatoms; self-organization in these archetypal SAM systems must therefore be governed by the movement of these Au-S-R moieties on the surface between two distinct local hollow sites on the surface. The results of recent ab initio total energy calculations provide strong support for this description, and a rationale for the implied significant molecular mobility in these systems.

  13. From Ultrafine Thiolate-Capped Copper Nanoclusters toward Copper Sulfide Nanodiscs: A Thermally Activated Evolution Route

    SciTech Connect

    Mott, Derrick; Yin, Jun; Engelhard, Mark H.; Loukrakpam, Rameshwori; Chang, Paul; Miller, George; Bae, In-Tae; Das, N. C.; Wang, Chong M.; Luo, Jin; Zhong, Chuan-Jian

    2010-01-12

    In this report we show that the size, shape, and composition of pre-synthesized metal nanoparticles can be engineered through exploiting concurrent interparticle coalescence and interfacial copper-thiolate cleavage under a thermally-activated evolution process. This concept is demonstrated by thermally-activated processing of ultrafine (~0.5 nm) copper nanoparticles encapsulated with thiolate monolayer (Cun(SR)m) toward copper sulfide nanodiscs with controllable sizes and shapes. It involved a thermally-activated coalescence of Cun(SR)m nanoclusters accompanied by interfacial Cu-S cleavage towards the formation of Cu2S nanocrystals with well-defined nanodisc shapes with an average diameter and thickness ranging from 10.7 ±1.4 nm and 5.5 ±0.5 nm (aspect ratio ~2) to 31.2 ±4.3 nm and 3.9 ±0.4 nm (aspect ratio ~7) depending on the thermal processing parameters. These nanodiscs are stable and display remarkable ordering upon self-assembly. The abilities to create the ultrafine copper nanoclusters and to enable them to undergo a thermally-activated coalescence and a concurrent Cu-S bond cleavage toward the formation of Cu2S nanodiscs is entirely new. The viability of fine tuning the size and shape of the Cu2S nanocrystals by controlling the relative binding strength of thiolates, the C-S cleavage reactivity, and the interparticle coalescence activity, and their potential applications in electronic, sensing and photochemical devices are also discussed.

  14. Synthesis and In Vitro Evaluation of Thiolated Carrageenan.

    PubMed

    Suchaoin, Wongsakorn; Bonengel, Sonja; Hussain, Shah; Huck, Christian W; Ma, Benjamin N; Bernkop-Schnürch, Andreas

    2015-08-01

    The aim of this study was to generate and characterize a thiolated carrageenan. Thiolated carrageenan (carrageenan-SH) was synthesized from kappa (κ)- and iota (ι)-carrageenan by bromine replacement of the hydroxyl moieties followed by substitution to thiol groups using thiourea. Thiolated κ- and ι-carrageenan exhibited 176.57 ± 20.11 and 109.51 ± 18.26 μmol thiol groups per gram polymer, respectively. The resazurin test in Caco-2 cells revealed no toxic effect of both thiolated carrageenans at a concentration below 0.1% (w/v). Regarding efflux pump inhibitory effect, cellular accumulation of multidrug-resistance protein 2 substrate, sulforhodamine 101, was 1.38- and 1.35-fold increased in cells treated with thiolated κ- and ι-carrageenan, respectively. Modification of κ- and ι-carrageenan led to 3.9- and 2.0-fold increase in dynamic viscosity of mucus-thiolated carrageenan mixture within 4 h. Furthermore, residence time of κ- and ι-carrageenan-SH on porcine intestinal mucosa was 6.4- and 1.8-fold prolonged, respectively, as demonstrated by rotating cylinder method, indicating improved mucoadhesive properties. Hence, thiolation of carrageenans led to novel pharmaceutical excipients for various applications.

  15. Development of controlled drug release systems based on thiolated polymers.

    PubMed

    Bernkop-Schnürch, A; Scholler, S; Biebel, R G

    2000-05-03

    The purpose of the present study was to generate mucoadhesive matrix-tablets based on thiolated polymers. Mediated by a carbodiimide, L-cysteine was thereby covalently linked to polycarbophil (PCP) and sodium carboxymethylcellulose (CMC). The resulting thiolated polymers displayed 100+/-8 and 1280+/-84 micromol thiol groups per gram, respectively (means+/-S.D.; n=6-8). In aqueous solutions these modified polymers were capable of forming inter- and/or intramolecular disulfide bonds. The velocity of this process augmented with increase of the polymer- and decrease of the proton-concentration. The oxidation proceeded more rapidly within thiolated PCP than within thiolated CMC. Due to the formation of disulfide bonds within thiol-containing polymers, the stability of matrix-tablets based on such polymers could be strongly improved. Whereas tablets based on the corresponding unmodified polymer disintegrated within 2 h, the swollen carrier matrix of thiolated CMC and PCP remained stable for 6.2 h (mean, n=4) and more than 48 h, respectively. Release studies of the model drug rifampicin demonstrated that a controlled release can be provided by thiolated polymer tablets. The combination of high stability, controlled drug release and mucoadhesive properties renders matrix-tablets based on thiolated polymers useful as novel drug delivery systems.

  16. Perforated monolayers

    SciTech Connect

    Regen, S.L.

    1992-01-01

    Our research over this past grant period has focused on (1) developing methods for making in situ permeation measurements at the air-water interface, (2) defining the structural and conformational behavior of selected calix(4)arenes, (3) defining the metal complexation properties of certain upper-rim functionalized calix(4)arenes, and (4) synthesizing a broad series of polymerizable calixarenes, to be used for constructing perforated monolayers and multilayers.

  17. Well-ordered self-assembled monolayers created via vapor-phase reactions on a monolayer template.

    PubMed

    Ferguson, Melinda K; Low, Emily R; Morris, John R

    2004-04-13

    The reaction of vapor-phase alkyl isocyanates (O=C=N-(CH2)n-1CH3) with OH-terminated alkanethiol template monolayers on Au produces well-organized self-assembled monolayers, containing intrachain carbamate linkages (Au/S(CH2)16O(C=O)NH(CH2)n-1CH3, where n = 1-8, 11, and 12). X-ray photoelectron spectroscopy, contact angle goniometry, and reflection absorption infrared spectroscopy suggest that the template surface completely reacts with the isocyanates yielding a monolayer that contains an interchain hydrogen-bonded carbamate network. Spectroscopic data indicates that the alkyl underlayer remains well ordered following reaction with the isocyanates. The order of the overlayer and the hydrogen-bonding interactions between adjacent chains increase as a function of the alkyl isocyanate chain length, n. The overlayer appears to be well ordered for n > or = 5.

  18. The striped phases of ethylthiolate monolayers on the Au(111) surface: a scanning tunneling microscopy study.

    PubMed

    Li, Fangsen; Tang, Lin; Voznyy, Oleksandr; Gao, Jianzhi; Guo, Quanmin

    2013-05-21

    Striped phases of ethylthiolate monolayers, corresponding to surface coverage in between 0.2 ML and 0.27 ML, were studied using high-resolution scanning tunneling microscopy. Striped phases consist of rows of Au-adatom-diethythiolate (AAD) aligned along the [112] direction. In the perpendicular [110] direction, the AAD rows adjust their spacing according to the surface coverage. A (5√3 × √3)-R30° striped phase with 0.27 ML thiolate and a (6√3 × √3)-R30° striped phase with 0.23 ML thiolate, both with long-range order, are found. A localized (5 × √3)-rect. phase is also found as a minority phase embedded in the 5√3 × √3)-R30° phase. This (5 × √3)-rect. phase can be constructed using di-Au-adatom-tri-thiolate species.

  19. Assembly of designed protein scaffolds into monolayers for nanoparticle patterning.

    PubMed

    Mejias, Sara H; Couleaud, Pierre; Casado, Santiago; Granados, Daniel; Garcia, Miguel Angel; Abad, Jose M; Cortajarena, Aitziber L

    2016-05-01

    The controlled assembly of building blocks to achieve new nanostructured materials with defined properties at different length scales through rational design is the basis and future of bottom-up nanofabrication. This work describes the assembly of the idealized protein building block, the consensus tetratricopeptide repeat (CTPR), into monolayers by oriented immobilization of the blocks. The selectivity of thiol-gold interaction for an oriented immobilization has been verified by comparing a non-thiolated protein building block. The physical properties of the CTPR protein thin biomolecular films including topography, thickness, and viscoelasticity, are characterized. Finally, the ability of these scaffolds to act as templates for inorganic nanostructures has been demonstrated by the formation of well-packed gold nanoparticles (GNPs) monolayer patterned by the CTPR monolayer. Copyright © 2016 Elsevier B.V. All rights reserved.

  20. Partial Crystallinity in Alkyl Side Chain Polymers.

    NASA Astrophysics Data System (ADS)

    Sahni, Vasav; Prasad, Shishir; Villate, Johanna; Jiang, Zhang; Sinha, Sunil; Dhinojwala, Ali

    2009-03-01

    Surface freezing is the formation of a crystalline monolayer at the free surface of a melt at a temperature Ts, a few degrees above the bulk freezing temperature, Tb. This effect, i.e. Ts> Tb, common to many chain molecules, is in marked contrast with the surface melting effect, i.e. Ts<=Tb, shown by almost all other materials. Various theoretical and experimental studies have been done to characterize the monolayer formed when the surface freezes before the bulk. We have studied the structure of a novel crystalline surface monolayer on top of a disordered melt of the same material (poly(n-alkyl acrylate)s) using grazing incidence x-ray diffraction. The grazing incidence x-ray diffraction, surface tension, and bulk latent heat results show that there is partial side-chain crystallinity. Also, the surface tension results explain the trend of the difference between the surface order-to-disorder transition temperature and the bulk melting temperature (δT) as a function of side chain length. The behavior of the crystal length, crystal spacing and tilt with varying alkyl chain length and temperature was also studied.

  1. Thiolated graphene oxide as promising mucoadhesive carrier for hydrophobic drugs.

    PubMed

    Pereira de Sousa, Irene; Buttenhauser, Katrin; Suchaoin, Wongsakorn; Partenhauser, Alexandra; Perrone, Mara; Matuszczak, Barbara; Bernkop-Schnürch, Andreas

    2016-07-25

    The aim of this study was to improve the mucoadhesive properties of graphene by conjugating thiol ligands, in order to formulate an oral delivery system for hydrophobic drugs showing long mucus residence time. Graphene oxide was obtained by oxidation of graphite and then was thiolated following two synthetic paths. On the one hand, the hydroxyl groups were conjugated with thiourea passing through the formation of a brominated intermediate. On the other hand, the carboxylic acid groups were conjugated with cysteamine via carbodiimide chemistry. The mucoadhesive properties of thiolated graphene were evaluated by rheological measurements and by residence time assay. Then, valsartan was loaded on thiolated graphene and the release profile was evaluated in simulated intestinal fluid. Following both synthetic paths it was possible to obtain thiolated graphene bearing 215-302μmol SH/g product. Both products induced after 1h incubation an increase of mucus viscosity of about 22-33-fold compared to unmodified graphite. The residence time assay confirmed that 60% of thiolated graphene could be retained on intestinal mucosa after 4h incubation, whereas just 20% of unmodified graphite could be retained. Valsartan could be loaded with a drug loading of about 31±0.3% and a sustained release profile was observed for both formulations. According to the presented data, the thiolation of graphene could improve its mucoadhesive properties. Therefore, thiolated graphene represents a promising platform for oral delivery of hydrophobic drugs, possessing a long residence time on intestinal mucosa which allows the release of the loaded drug close to the adsorptive epithelium. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. Determining cysteine oxidation status using differential alkylation

    NASA Astrophysics Data System (ADS)

    Schilling, Birgit; Yoo, Chris B.; Collins, Christopher J.; Gibson, Bradford W.

    2004-08-01

    Oxidative damage to proteins plays a major role in aging and in the pathology of many degenerative diseases. Under conditions of oxidative stress, reactive oxygen and nitrogen species can modify key redox sensitive amino acid side chains leading to altered biological activities or structures of the targeted proteins. This in turn can affect signaling or regulatory control pathways as well as protein turnover and degradation efficiency in the proteasome. Cysteine residues are particularly susceptible to oxidation, primarily through reversible modifications (e.g., thiolation and nitrosylation), although irreversible oxidation can lead to products that cannot be repaired in vivo such as sulfonic acid. This report describes a strategy to determine the overall level of reversible cysteine oxidation using a stable isotope differential alkylation approach in combination with mass spectrometric analysis. This method employs 13C-labeled alkylating reagents, such as N-ethyl-[1,4-13C2]-maleimide, bromo-[1,2-13C2]-acetic acid and their non-labeled counterparts to quantitatively assess the level of cysteine oxidation at specific sites in oxidized proteins. The differential alkylation protocol was evaluated using standard peptides and proteins, and then applied to monitor and determine the level of oxidative damage induced by diamide, a mild oxidant. The formation and mass spectrometric analysis of irreversible cysteine acid modification will also be discussed as several such modifications have been identified in subunits of the mitochondrial electron transport chain complexes. This strategy will hopefully contribute to our understanding of the role that cysteine oxidation plays in such chronic diseases such as Parkinson's disease, where studies in animal and cell models have shown oxidative damage to mitochondrial Complex I to be a specific and early target.

  3. Properties of the gold-sulphur interface: from self-assembled monolayers to clusters

    NASA Astrophysics Data System (ADS)

    Bürgi, Thomas

    2015-09-01

    The gold-sulphur interface of self-assembled monolayers (SAMs) was extensively studied some time ago. More recently tremendous progress has been made in the preparation and characterization of thiolate-protected gold clusters. In this feature article we address different properties of the two systems such as their structure, the mobility of the thiolates on the surface and other dynamical aspects, the chirality of the structures and characteristics related to it and their vibrational properties. SAMs and clusters are in the focus of different communities that typically use different experimental approaches to study the respective systems. However, it seems that the nature of the Au-S interfaces in the two cases is quite similar. Recent single crystal X-ray structures of thiolate-protected gold clusters reveal staple motifs characterized by gold ad-atoms sandwiched between two sulphur atoms. This finding contradicts older work on SAMs. However, newer studies on SAMs also reveal ad-atoms. Whether this finding can be generalized remains to be shown. In any case, more and more studies highlight the dynamic nature of the Au-S interface, both on flat surfaces and in clusters. At temperatures slightly above ambient thiolates migrate on the gold surface and on clusters. Evidence for desorption of thiolates at room temperature, at least under certain conditions, has been demonstrated for both systems. The adsorbed thiolate can lead to chirality at different lengths scales, which has been shown both on surfaces and for clusters. Chirality emerges from the organization of the thiolates as well as locally at the molecular level. Chirality can also be transferred from a chiral surface to an adsorbate, as evidenced by vibrational spectroscopy.

  4. Properties of the gold-sulphur interface: from self-assembled monolayers to clusters.

    PubMed

    Bürgi, Thomas

    2015-10-14

    The gold-sulphur interface of self-assembled monolayers (SAMs) was extensively studied some time ago. More recently tremendous progress has been made in the preparation and characterization of thiolate-protected gold clusters. In this feature article we address different properties of the two systems such as their structure, the mobility of the thiolates on the surface and other dynamical aspects, the chirality of the structures and characteristics related to it and their vibrational properties. SAMs and clusters are in the focus of different communities that typically use different experimental approaches to study the respective systems. However, it seems that the nature of the Au-S interfaces in the two cases is quite similar. Recent single crystal X-ray structures of thiolate-protected gold clusters reveal staple motifs characterized by gold ad-atoms sandwiched between two sulphur atoms. This finding contradicts older work on SAMs. However, newer studies on SAMs also reveal ad-atoms. Whether this finding can be generalized remains to be shown. In any case, more and more studies highlight the dynamic nature of the Au-S interface, both on flat surfaces and in clusters. At temperatures slightly above ambient thiolates migrate on the gold surface and on clusters. Evidence for desorption of thiolates at room temperature, at least under certain conditions, has been demonstrated for both systems. The adsorbed thiolate can lead to chirality at different lengths scales, which has been shown both on surfaces and for clusters. Chirality emerges from the organization of the thiolates as well as locally at the molecular level. Chirality can also be transferred from a chiral surface to an adsorbate, as evidenced by vibrational spectroscopy.

  5. Enhanced oral delivery of docetaxel using thiolated chitosan nanoparticles: preparation, in vitro and in vivo studies.

    PubMed

    Saremi, Shahrooz; Dinarvand, Rassoul; Kebriaeezadeh, Abbas; Ostad, Seyed Nasser; Atyabi, Fatemeh

    2013-01-01

    The aim of this study was to evaluate a nanoparticulate system with mucoadhesion properties composed of a core of polymethyl methacrylate surrounded by a shell of thiolated chitosan (Ch-GSH-pMMA) for enhancing oral bioavailability of docetaxel (DTX), an anticancer drug. DTX-loaded nanoparticles were prepared by emulsion polymerization method using cerium ammonium nitrate as an initiator. Physicochemical properties of the nanoparticles such as particle size, size distribution, morphology, drug loading, and entrapment efficiency were characterized. The pharmacokinetic study was carried out in vivo using wistar rats. The half-life of DTX-loaded NPs was about 9 times longer than oral DTX used as positive control. The oral bioavailability of DTX was increased to 68.9% for DTX-loaded nanoparticles compared to 6.5% for positive control. The nanoparticles showed stronger effect on the reduction of the transepithelial electrical resistance (TEER) of Caco-2 cell monolayer by opening the tight junctions. According to apparent permeability coefficient (P(app)) results, the DTX-loaded NPs showed more specific permeation across the Caco-2 cell monolayer in comparison to the DTX. In conclusion, the nanoparticles prepared in this study showed promising results for the development of an oral drug delivery system for anticancer drugs.

  6. Enhanced Oral Delivery of Docetaxel Using Thiolated Chitosan Nanoparticles: Preparation, In Vitro and In Vivo Studies

    PubMed Central

    Saremi, Shahrooz; Kebriaeezadeh, Abbas; Ostad, Seyed Nasser; Atyabi, Fatemeh

    2013-01-01

    The aim of this study was to evaluate a nanoparticulate system with mucoadhesion properties composed of a core of polymethyl methacrylate surrounded by a shell of thiolated chitosan (Ch-GSH-pMMA) for enhancing oral bioavailability of docetaxel (DTX), an anticancer drug. DTX-loaded nanoparticles were prepared by emulsion polymerization method using cerium ammonium nitrate as an initiator. Physicochemical properties of the nanoparticles such as particle size, size distribution, morphology, drug loading, and entrapment efficiency were characterized. The pharmacokinetic study was carried out in vivo using wistar rats. The half-life of DTX-loaded NPs was about 9 times longer than oral DTX used as positive control. The oral bioavailability of DTX was increased to 68.9% for DTX-loaded nanoparticles compared to 6.5% for positive control. The nanoparticles showed stronger effect on the reduction of the transepithelial electrical resistance (TEER) of Caco-2 cell monolayer by opening the tight junctions. According to apparent permeability coefficient (Papp) results, the DTX-loaded NPs showed more specific permeation across the Caco-2 cell monolayer in comparison to the DTX. In conclusion, the nanoparticles prepared in this study showed promising results for the development of an oral drug delivery system for anticancer drugs. PMID:23971023

  7. Perforated monolayers

    SciTech Connect

    Regen, S.L.

    1992-12-01

    Goal of this research program is to create ultrathin organic membranes that possess uniform and adjustable pores ( < 7[angstrom] diameter). Such membranes are expected to possess high permeation selectivity (permselectivity) and high permeability, and to provide the basis for energy-efficient methods of molecular separation. Work carried out has demonstrated feasibility of using perforated monolayer''-based composites as molecular sieve membranes. Specifically, composite membranes derived from Langmuir-Blodgett multilayers of the calix[6]arene-based surfactant shown below plus poly[l-(trimethylsilyl)-l-propyne] (PTMSP) were found to exhibit sieving behavior towards He, N[sub 2] and SF[sub 6]. Results of derivative studies that have also been completed are also described in this report.

  8. The expanding universe of thiolated gold nanoclusters and beyond.

    PubMed

    Jiang, De-en

    2013-08-21

    Thiolated gold nanoclusters form a universe of their own. Researchers in this field are constantly pushing the boundary of this universe by identifying new compositions and in a few "lucky" cases, solving their structures. Such solved structures, even if there are only few, provide important hints for predicting the many identified compositions that are yet to be crystallized or structure determined. Structure prediction is the most pressing issue for a computational chemist in this field. The success of the density functional theory method in gauging the energetic ordering of isomers for thiolated gold clusters has been truly remarkable, but to predict the most stable structure for a given composition remains a great challenge. In this feature article from a computational chemist's point of view, the author shows how one understands and predicts structures for thiolated gold nanoclusters based on his old and new results. To further entertain the reader, the author also offers several "imaginative" structures, claims, and challenges for this field.

  9. Better alkylation control

    SciTech Connect

    Ryskamp, C.J.; McGee, N.F.; Badavas, P.C.

    1986-11-01

    The control strategies presented provide effective advanced regulatory control of the reactors and the distillation towers associated with HF and sulfuric acid alkylation units. Reactor isobutane/olefin ration, thruput and temperature are the major control variables in the reactor section. While alkylate Reid vapor pressure and product compositions are desired control variables for the fractionation towers. Feed impurities and variable operating conditions in a refinery alkylation unit produce many undesirable side reactions. Most of the side products such as acid-soluble oil (polymer) and heavy alkylate are detrimental to the alkylate product quality and the unit operation. Polymerication is very harmful because it not only produces the tar that spends the catalyst, but also reduces the yield of valuable products. Improved control of the reactor's total feed composition and operating conditions can provide economic benefits such as improved quality and yield of alkylate, and reduced acid consumption. Improved control in the distillation section of the unit can assure Reid vapor pressure (RVP) control of the alkylate product, reduce the propane and normal butane diluents in the reactor recycle streams, reduce isobutane losses in the unit product streams, and reduce unit utility costs.

  10. The characterization of organic monolayers at gold surfaces using scanning tunneling microscopy and atomic force microscopy correlation with macrostructural properties

    SciTech Connect

    Alves, C.A.

    1992-09-09

    Monolayer films formed by self-assembly of organothiols at epitaxially grown Au(111) films at mica were examined in air using scanning tunneling (STM) and atomic force microscopies (AFM). n-Alkanethiolate monolayers exhibit a hexagonal packing arrangement with nearest-neighbor and next-nearest-neighbor spacings of 0.50 and 0.87 nm. This arrangement is consistent with the ({radical}3 {times} {radical}3)R30{degrees} adlayer structure at Au(111). STM reveals the structure of the Au-bound sulfur, while AFM details the structure at the monolayer/air interface, revealing that the order at the Au-S interface is retained up to the monolayer/air interface. The investigation of the self-assembled CF{sub 3}(CF{sub 2})7(CH{sub 2}){sub 2}SH monolayer at Au(lll) by AFM reveals a (2 {times} 2) adlayer structure, with nearest-neighbor and next-nearest-neighbor spacings of 0.58 {plus_minus} 0.02 nm and 1.0 {plus_minus} 0.02 nm, respectively. This is consistent with the larger van der Waals diameter of the fluorinated chain. Coverage of this fluorinated thiolate monolayer is (6.3{plus_minus}0.8) {times} 10{sup {minus}10} mol/cm{sup 2}, consistent with the expected 0.25 monolayer coverage of the (2 {times} 2) adlayer structure at Au(l11). Infrared reflection spectroscopy also confirm this. Upon prolonged exposure to air, the thiolate species is oxidized to elemental sulfur in the forms of cyclooctasulfur (cyclo-S{sub 8}) and other allotropes. STM reveals square structures on aged thiolate monolayers. Dimensions of these squares (0.40--0.50 rum per side) are close to those of cyclo-S{sub 8}. Electrochemical reductive desorption experiments also reveal a change in the surface species with time, with a second desorption wave.

  11. The characterization of organic monolayers at gold surfaces using scanning tunneling microscopy and atomic force microscopy correlation with macrostructural properties

    NASA Astrophysics Data System (ADS)

    Alves, C. A.

    1992-09-01

    Monolayer films formed by self-assembly of organothiols at epitaxially grown Au(111) films at mica were examined in air using scanning tunneling (STM) and atomic force microscopies (AFM). n-Alkanethiolate monolayers exhibit a hexagonal packing arrangement with nearest-neighbor and next-nearest-neighbor spacings of 0.50 and 0.87 nm. This arrangement is consistent with (the square root of 3 x the square root of 3)R30 deg adlayer structure at Au(111). STM reveals the structure of the Au-bound sulfur, while AFM details the structure at the monolayer/air interface, revealing that the order at the Au-S interface is retained up to the monolayer/air interface. The investigation of the self-assembled (CF3CF2)7(CH2)2SH monolayer at Au(111) by AFM reveals a (2 x 2) adlayer structure, with nearest-neighbor and next-nearest-neighbor spacings of 0.58 plus or minus 0.02 nm and 1.0 plus or minus 0.02 nm, respectively. This is consistent with the larger van der Waals diameter of the fluorinated chain. Coverage of this fluorinated thiolate monolayer is (6.3 plus or minus 0.8) x 10(exp -10) mol/cm(sup 2), consistent with the expected 0.25 monolayer coverage of the (2 x 2) adlayer structure at Au(111). Infrared reflection spectroscopy also confirmed this. Upon prolonged exposure to air, the thiolate species is oxidized to elemental sulfur in the forms of cyclooctasulfur (cyclo-S8) and other allotropes. STM reveals square structures on aged thiolate monolayers. Dimensions of these squares (0.40-0.50 nm per side) are close to those of cyclo-S8. Electrochemical reductive desorption experiments also reveal a change in the surface species with time, with a second desorption wave.

  12. The characterization of organic monolayers at gold surfaces using scanning tunneling microscopy and atomic force microscopy correlation with macrostructural properties

    SciTech Connect

    Alves, C.A.

    1992-09-09

    Monolayer films formed by self-assembly of organothiols at epitaxially grown Au(111) films at mica were examined in air using scanning tunneling (STM) and atomic force microscopies (AFM). n-Alkanethiolate monolayers exhibit a hexagonal packing arrangement with nearest-neighbor and next-nearest-neighbor spacings of 0.50 and 0.87 nm. This arrangement is consistent with the ([radical]3 [times] [radical]3)R30[degrees] adlayer structure at Au(111). STM reveals the structure of the Au-bound sulfur, while AFM details the structure at the monolayer/air interface, revealing that the order at the Au-S interface is retained up to the monolayer/air interface. The investigation of the self-assembled CF[sub 3](CF[sub 2])7(CH[sub 2])[sub 2]SH monolayer at Au(lll) by AFM reveals a (2 [times] 2) adlayer structure, with nearest-neighbor and next-nearest-neighbor spacings of 0.58 [plus minus] 0.02 nm and 1.0 [plus minus] 0.02 nm, respectively. This is consistent with the larger van der Waals diameter of the fluorinated chain. Coverage of this fluorinated thiolate monolayer is (6.3[plus minus]0.8) [times] 10[sup [minus]10] mol/cm[sup 2], consistent with the expected 0.25 monolayer coverage of the (2 [times] 2) adlayer structure at Au(l11). Infrared reflection spectroscopy also confirm this. Upon prolonged exposure to air, the thiolate species is oxidized to elemental sulfur in the forms of cyclooctasulfur (cyclo-S[sub 8]) and other allotropes. STM reveals square structures on aged thiolate monolayers. Dimensions of these squares (0.40--0.50 rum per side) are close to those of cyclo-S[sub 8]. Electrochemical reductive desorption experiments also reveal a change in the surface species with time, with a second desorption wave.

  13. Effect of Thiolated Ligands in Au Nanowire Synthesis.

    PubMed

    Wang, Yawen; He, Jiating; Yu, Suzhu; Chen, Hongyu

    2017-08-30

    Thiolated ligands are seldom used as morphology-directing reagent in the synthesis of Au nanostructures due to their low selectivity toward the different facets. Recently, we developed a thiolated ligands-induced synthesis of nanowires where the selective Au deposition only occurs at the ligand-deficient Au-substrate interface. Herein, the structural effect of thiolated ligands in this active surface growth is systematically investigated. It is revealed that their ability of rendering surface is closely related to the molecular structure. Ligands with aromatic backbones are capable of inducing nanowire formation, whereas those with aliphatic backbones cannot, likely because the former can pack better at short time scale of the rapid growth. The substituents of the ligands are critical for the colloidal stability of the final structure. It is further demonstrated that aromatic and aliphatic ligands could be mixed to turn on the continual lateral growth, leading to nanowires with tapered ends. The ligand generality in this growth mode also allows the creation of superhydrophobic surface, with the nanowire forest providing the nanoscale surface roughness and the hydrophobic ligand offering the surface property. These applications of the thiolated ligands in the nanosynthesis open a new approach for controlled synthesis of Au-based nanostructures with various morphologies and properties. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. The Scope of Direct Alkylation of Gold Surface with Solutions of C1–C4n-Alkylstannanes

    PubMed Central

    2015-01-01

    Treatment of cleaned gold surfaces with dilute tetrahydrofuran or chloroform solutions of tetraalkylstannanes (alkyl = methyl, ethyl, n-propyl, n-butyl) or di-n-butylmethylstannyl tosylate under ambient conditions causes a self-limited growth of disordered monolayers consisting of alkyls and tin oxide. Extensive use of deuterium labeling showed that the alkyls originate from the stannane and not from ambient impurities, and that trialkylstannyl groups are absent in the monolayers, contrary to previous proposals. Methyl groups attached to the Sn atom are not transferred to the surface. Ethyl groups are transferred slowly, and propyl and butyl rapidly. In all cases, tin oxide is codeposited in submonolayer amounts. The monolayers were characterized by ellipsometry, contact angle goniometry, polarization modulated IR reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy with ferrocyanide/ferricyanide, which revealed a very low charge-transfer resistance. The thermal stability of the monolayers and their resistance to solvents are comparable with those of an n-octadecanethiol monolayer. A preliminary examination of the kinetics of monolayer deposition from a THF solution of tetra-n-butylstannane revealed an approximately half-order dependence on the bulk solution concentration of the stannane, hinting that more than one alkyl can be transferred from a single stannane molecule. A detailed structure of the attachment of the alkyl groups is not known, and it is proposed that it involves direct single or multiple bonding of one or more C atoms to one or more Au atoms. PMID:26327466

  15. Theoretical examination of solvent and R group dependence in gold thiolate nanoparticle synthesis.

    PubMed

    Neidhart, Suzanne M; Barngrover, Brian M; Aikens, Christine M

    2015-03-28

    The growth of gold thiolate nanoparticles can be affected by the solvent and the R group on the ligand. In this work, the difference between methanol and benzene solvents as well as the effect of alkyl (methyl) and aromatic (phenyl) thiols on the reaction energies and barrier heights is investigated theoretically. Density functional theory (DFT) calculations using the BP86 functional and a triple ζ polarized basis set show that the overall reaction favors methylthiol over phenylthiol with reaction energies of -0.54 and -0.39 eV in methanol, respectively. At the same level of theory, the methanol solvent is favored over the benzene solvent for reactions forming ions; in benzene, the overall reaction energies for methylthiol and phenylthiol reacting with AuCl4(-) to form Au(HSR)2(+) are 0.37 eV and 0.44 eV, respectively. Methylthiol in methanol also has the lowest barrier heights at about 0.3 eV, whereas phenylthiol has barrier heights around 0.4 eV. Barrier heights in benzene are significantly larger than those in methanol.

  16. Facile one-pot synthesis of luminescent-thiolated Au nanocluster and Au(I)-thiolate complexes as highly selective Cu2+ probes

    NASA Astrophysics Data System (ADS)

    Pal, Nabin Kumar; Kryschi, Carola

    2015-05-01

    Here in this paper, we reported of a facile photo-induced one-step method for synthesizing highly luminescent Au(I)-thiolate complexes (size 2-3 nm) and thiolated Au nanocluster (AuNC, size 1.6 nm). The hydrophilic thiol being 3-mercaptopropanoic acid (3-MPA) was used as stabilizing agent. The as-prepared Au(I)-thiolate complexes exhibit bright red photoluminescence (PL) and were used as an efficient sensor for the selective detection of Cu2+ ions. We also observed the formation of thiol-stabilized Au nanoparticles through continuous electron beam irradiation of Au(I)-thiolated complexes. The Au(I)-thiolate complexes show a PL lifetime on the μs time scale, whereas the PL lifetime of the thiolated AuNC is on the ns time scales. The photo-physical, electronic, structural and morphological properties of the thiolated AuNC and Au(I)-thiolate complexes were examined upon performing UV-Vis absorption spectroscopy, stationary and time-resolved PL spectroscopy, X-ray photoelectron spectroscopy, femtosecond transient absorption spectroscopy and transmission electron microscopy experiments.

  17. Synthesis Of Alkyl Hydroperoxides Via Alkylation Of gem-Dihydroperoxides

    PubMed Central

    Kyasa, ShivaKumar; Puffer, Benjamin W.

    2013-01-01

    Two-fold alkylation of 1,1-dihydroperoxides, followed by hydrolysis of the resulting bisperoxyacetals, provides a convenient method for synthesis of primary and secondary alkyl hydroperoxides. PMID:23469994

  18. An oral oligonucleotide delivery system based on a thiolated polymer: Development and in vitro evaluation.

    PubMed

    Martien, Ronny; Hoyer, Herbert; Perera, Glen; Schnürch, Andreas Bernkop

    2011-08-01

    The purpose of this study was to develop and evaluate an oral oligonucleotide delivery system based on a thiolated polymer/reduced glutathione (GSH) system providing a protective effect toward nucleases and permeation enhancement. A polycarbophil-cysteine conjugate (PCP-Cys) was synthesized. Enzymatic degradation of a model oligonucleotide by DNase I and within freshly collected intestinal fluid was investigated in the absence and presence of PCP-Cys. Permeation studies with PCP-Cys/GSH versus control were performed in vitro on Caco-2 cell monolayers and ex vivo on rat intestinal mucosa. PCP-Cys displayed 223 ± 13.8 μmol thiol groups per gram polymer. After 4h, 61% of the free oligonucleotides were degraded by DNase I and 80% within intestinal fluid. In contrast, less than 41% (DNase I) and 60% (intestinal fluid) were degraded in the presence of 0.02% (m/v) PCP-Cys. Permeation studies revealed an 8-fold (Caco-2) and 10-fold (intestinal mucosa) increase in apparent permeability compared to buffer control. Hence, this PCP-Cys/GSH system might be a promising tool for the oral administration of oligonucleotides as it allows a significant protection toward degrading enzymes and facilitates their transport across intestinal membranes.

  19. Directly thiolated modification onto the surface of detonation nanodiamonds.

    PubMed

    Hsu, Ming-Hua; Chuang, Hong; Cheng, Fong-Yu; Huang, Ying-Pei; Han, Chien-Chung; Chen, Jiun-Yu; Huang, Su-Chin; Chen, Jen-Kun; Wu, Dian-Syue; Chu, Hsueh-Liang; Chang, Chia-Ching

    2014-05-28

    An efficient method for modifying the surface of detonation nanodiamonds (5 and 100 nm) with thiol groups (-SH) by using an organic chemistry strategy is presented herein. Thiolated nanodiamonds were characterized by spectroscopic techniques, and the atomic percentage of sulfur was analyzed by elemental analysis and X-ray photoelectron spectroscopy. The conjugation between thiolated nanodiamonds and gold nanoparticles was elucidated by transmission electron microscopy and UV-vis spectrometry. Moreover, the material did not show significant cytotoxicity to the human lung carcinoma cell line and may prospectively be applied in bioconjugated technology. The new method that we elucidated may significantly improve the approach to surface modification of detonation nanodiamonds and build up a new platform for the application of nanodiamonds.

  20. Investigation of a thiolated polymer in gene delivery

    NASA Astrophysics Data System (ADS)

    Bacalocostantis, Irene

    Thiol-containing bioreducible polymers show significant potential as delivery vectors in gene therapy, a rapidly growing field which seeks to treat genetic-based disorders by delivering functional synthetic genes to diseased cells. Studies have shown that thiolated polymers exhibit improved biodegradability and prolonged in vivo circulation times over non-thiolated polymers. However, the extent to which thiol concentrations impact the carrier's delivery potential has not been well explored. The aim of this dissertation is to investigate how relative concentrations of free thiols and disulfide crosslinks impact a polymeric carriers delivery performance with respect to DNA packaging, complex stability, cargo protection, gene release, internalization efficiency and cytotoxicity. To accomplish this goal, several fluorescent polymers containing varying concentrations of thiol groups were synthesized by conjugating thiol-pendant chains onto the primary amines of cationic poly(allylamine). In vitro delivery assays and characterization techniques were employed to assess the effect of thiols in gene delivery.

  1. Allicin-inspired thiolated fluoroquinolones as antibacterials against ESKAPE pathogens.

    PubMed

    Sheppard, Jordan G; Long, Timothy E

    2016-11-15

    Thiolated fluoroquinolones were synthesized from ciprofloxacin and evaluated for antimicrobial activity against a panel of pathogenic bacteria. Gram-positive species including methicillin-resistant Staphylococcus aureus (MRSA) exhibited the highest level of increased sensitivity toward ciprofloxacin bound with a N-propylthio substituent. Evidence was found that the antibiotics form disulfides with low molecular weight thiols in bacteria and potentiate generation of cytosolic reactive oxygen species (ROS). In final analysis, the enhanced anti-MRSA activity of thiolated fluoroquinolones was attributed to increased cell permeability and reaction with cytosolic thiols that yields an inactive disulfide metabolite and the parent drug ciprofloxacin as an inhibitor of DNA synthesis. Copyright © 2016 Elsevier Ltd. All rights reserved.

  2. Metal thiolate clusters in cobalt(II)-metallothionein.

    PubMed

    Vasák, M; Kägi, J H

    1981-11-01

    Rabbit liver metallothionein-1 in which all seven metal-binding sites are occupied by cobalt(II) exhibits spectral features typical of tetrathiolate coordination with approximate Td microsymmetry [Vasák, M. (1980) J. Am. Chem. Soc. 102, 3953-3955]. With a total of 20 cysteine residues per molecule, this mode of metal binding implies that some of the thiolate ligands are shared by neighboring Co(II) ions, resulting in clustered structures. In this study, evidence for the existence of thiolate-linked Co(II) clusters is presented and their mode of formation is explored by comparing the optical and magnetic properties of forms of Co(II)-metallothionein containing 1-7 equivalents of Co(II). Preparations with up to 4 Co(II) equivalents display electronic spectra in the d-d and charge-transfer regions that resemble those of isolated tetrahedral Co(II)-tetrathiolate complexes. Upon binding of more than four Co(II) ions, however, the spectrum changes progressively and approaches in the fully saturated Co(II)-metallothionein an absorption profile similar to that of crystallographically defined model (Co)II-tetrathiolate clusters [Dance, I. G. (1979) J. Am. Chem. Soc. 101, 6264-6273]. These effects are closely paralleled by changes in the ESR spectrum. Above 4 Co(II) equivalents per thionein, the ESR signal at gx approximately 5.9 measured at 4 K decreases progressively in intensity, until in the fully occupied protein the complex is nearly diamagnetic. These changes, which were confirmed by measurements of paramagnetic susceptibility, establish the existence of Co(II) thiolate clusters in Co(II)-metallothionein. The loss of paramagnetism reflects most likely antiferromagnetic coupling of neighboring Co(II) ions brought about by a superexchange mechanism via the thiolate bridging ligands.

  3. Metal thiolate clusters in cobalt(II)-metallothionein.

    PubMed Central

    Vasák, M; Kägi, J H

    1981-01-01

    Rabbit liver metallothionein-1 in which all seven metal-binding sites are occupied by cobalt(II) exhibits spectral features typical of tetrathiolate coordination with approximate Td microsymmetry [Vasák, M. (1980) J. Am. Chem. Soc. 102, 3953-3955]. With a total of 20 cysteine residues per molecule, this mode of metal binding implies that some of the thiolate ligands are shared by neighboring Co(II) ions, resulting in clustered structures. In this study, evidence for the existence of thiolate-linked Co(II) clusters is presented and their mode of formation is explored by comparing the optical and magnetic properties of forms of Co(II)-metallothionein containing 1-7 equivalents of Co(II). Preparations with up to 4 Co(II) equivalents display electronic spectra in the d-d and charge-transfer regions that resemble those of isolated tetrahedral Co(II)-tetrathiolate complexes. Upon binding of more than four Co(II) ions, however, the spectrum changes progressively and approaches in the fully saturated Co(II)-metallothionein an absorption profile similar to that of crystallographically defined model (Co)II-tetrathiolate clusters [Dance, I. G. (1979) J. Am. Chem. Soc. 101, 6264-6273]. These effects are closely paralleled by changes in the ESR spectrum. Above 4 Co(II) equivalents per thionein, the ESR signal at gx approximately 5.9 measured at 4 K decreases progressively in intensity, until in the fully occupied protein the complex is nearly diamagnetic. These changes, which were confirmed by measurements of paramagnetic susceptibility, establish the existence of Co(II) thiolate clusters in Co(II)-metallothionein. The loss of paramagnetism reflects most likely antiferromagnetic coupling of neighboring Co(II) ions brought about by a superexchange mechanism via the thiolate bridging ligands. PMID:6273885

  4. Barium thiolates and selenolates: syntheses and structural principles.

    PubMed

    Ruhlandt-Senge, K; Englich, U

    2000-11-17

    The synthesis and structural characterization of a family of barium thiolates and selenolates is described. The thiolates were synthesized by metallation of thiols, the selenolates by reductive insertion of the metal into the selenium-selenium bond of diorganodiselenides. Both reaction sequences were carried out by using barium metal dissolved in ammonia; this afforded barium thiolates and selenolates in good yield and purity. The structural principles displayed in the target compounds span a wide range of solid-state formulations, including monomeric and dimeric species, and separated ion triples, namely [Ba(thf)4(SMes*)2] (1; Mes* = 2,4,6-tBU3C6H2), [Ba(thf)4(SeMes*)2] (2), [Ba([18]crown-6)(hmpa)2][(SeMes*)2] (3), the dimeric [(Ba(py)3(thf)(SeTrip)2)2] (4; py = pyridine, Trip = 2,4.6-iPr3C6H2), and [Ba([18]crown-6)(SeTrip)2] (5). The full range of association modes is completed by [Ba([18]crown-6)(hmpa)SMes*][SMes*] (6) communicated earlier by this group. In the solid state, this compound displays an intermediate ion coordination mode: one anion is bound to the metal, while the second one is unassociated. Together these compounds provide structural information about all three different association modes for alkaline earth metal derivatives. This collection of structural data allows important conclusions about the influence of solvation and ligation on structural trends.

  5. Heterogeneous electron-transfer kinetics for PQQ covalently attached to aminoalkanethiol monolayers on gold.

    PubMed

    Park, Wonchoul; Ahmed, Jalal; Kim, Sunghyun

    2009-01-01

    Pyrroloquinoline quinone (PQQ) was covalently attached to a gold electrode surface via the self-assembled monolayers of aminoalkanethiols (NH2)(CH2)nSH) with different alkyl chain lengths (n=2, 6, 8, and 11). The voltammetric behaviors of PQQ-SAMs both at full and at partial monolayers were examined. It was found that the redox response of PQQ became more reversible with increasing dilution by alkanethiols owing to the less lateral interaction between PQQ heads. Voltammograms were transformed from quasi-reversibility to irreversibility as the alkyl chain spacer became longer. The electron tunneling barrier constant (beta) and distance dependence of the long range electron-transfer parameters have been studied in acidic solution using cyclic voltammetry. A logarithmic dependence of the heterogeneous electron-transfer rate constant on the alkyl chain length was found for full and partial PQQ monolayers. The beta value was close to 1.0 per CH2 unit regardless of dilution effect.

  6. Photoemission core-level shifts reveal the thiolate-Au(111) interface

    SciTech Connect

    Groenbeck, Henrik; Odelius, Michael

    2010-08-15

    The nature of the thiolate/Au(111) interface is a long-standing puzzle. It has been suggested that thiolates drive surface reconstruction, however, a consensus regarding the adsorption configuration is missing. Herein, the density-functional theory is used to evaluate surface core-level shifts (SCLSs) for methyl thiolates on Au(111) assuming a representative set of different surface reconstructions. The SCLSs are found to provide sensitive fingerprints of the anchoring configuration, and it is only thiolate adsorption in the form of MeS-Au-SMe complexes that can be reconciled with experimental data.

  7. Discontinuum between a thiolate and a thiol ligand.

    PubMed

    McGuire, Danny G; Khan, Masood A; Ashby, Michael T

    2002-04-22

    The effect of H-bond donation to the thiolate ligand of (eta(5)-C(5)H(5))Fe(CO)(2)SR (1) to give H-bond adducts (1 small middle dotHX) and eventually protonation to give [(eta(5)-C(5)H(5))Fe(CO)(2)(HSR)](+) (1H(+)()) has been investigated experimentally and computationally. The electronic structures of 1(R = Me), several derivatives of 1(R = Me) small middle dotHX, and 1(R = Me)H(+)() have been investigated using DFT (density functional theory) computational methods. As previously suggested, these calculations indicate the HOMO of 1 is Fedpi-Sppi antibonding and largely sulfur in character. The calculations indicate the electronic structure of 1 is not altered markedly by H-bond donation to the S center, but protonation results in a reorganization of the electronic structure of 1H(+)() and a HOMO that is largely metal in character. The reduction of Fe-S distances upon protonation of 1(R = Ph) to give 1(R = Ph)H(+)() small middle dotBF(4)()(-)() (2.282(2) and 2.258(2) A, respectively), as determined by single-crystal X-ray crystallography, also indicates diminished Fedpi-Sppi antibonding. Using the carbonyl stretching frequencies as a gauge of the donor ability of the thiolate ligand, we conclude that H-bonding has a continuous effect on the donor properties of the thiolate ligand of 1 (i.e., is a function of the pK(a) of the H-bond donor). A discontinuous effect results when the pK(b) of 1 is reached and the complex is protonated. For our study of 1, the maximal effect of H-bonding is about 30% of protonation. Because the position of acid-base equilibrium depends on the relative basicities of the thiolate ligand and the conjugate base of the H-bond donor (and the relative heats of solvation of the acids and their conjugate bases), a true continuum of effects can be anticipated only for systems that are pK-matched in their given environments. Thus, when the conjugate base of the H-bond donor is a stronger base than the thiolate ligand (as in the present case), H

  8. Electron transport across the alkanethiol self-assembled monolayer/Au(111) interface: role of the chemical anchor.

    PubMed

    Lindstrom, C D; Muntwiler, M; Zhu, X-Y

    2005-11-24

    Alkanethiol self-assembled monolayers (SAMs) on Au(111) are model systems for molecular electronics. We probe the role of the chemisorption bond on electron dynamics at the SAM/Au interface using time-resolved two-photon photoemission. Formation of the Au-S bond is evidenced by a localized sigma resonance, which broadens and shifts upward in energy when the lying-down chemisorbed molecules stand up. The localized chemisorption bond does not affect the electronic coupling between delocalized image resonances and the metal substrate. Instead, lifetimes of image resonances are decreased due to scattering with S atoms within the thiol or thiolate monolayer.

  9. Differential alkylation-based redox proteomics--Lessons learnt.

    PubMed

    Wojdyla, Katarzyna; Rogowska-Wrzesinska, Adelina

    2015-12-01

    Cysteine is one of the most reactive amino acids. This is due to the electronegativity of sulphur atom in the side chain of thiolate group. It results in cysteine being present in several distinct redox forms inside the cell. Amongst these, reversible oxidations, S-nitrosylation and S-sulfenylation are crucial mediators of intracellular redox signalling, with known associations to health and disease. Study of their functionalities has intensified thanks to the development of various analytical strategies, with particular contribution from differential alkylation-based proteomics methods. Presented here is a critical evaluation of differential alkylation-based strategies for the analysis of S-nitrosylation and S-sulfenylation. The aim is to assess the current status and to provide insights for future directions in the dynamically evolving field of redox proteomics. To achieve that we collected 35 original research articles published since 2010 and analysed them considering the following parameters, (i) resolution of modification site, (ii) quantitative information, including correction of modification levels by protein abundance changes and determination of modification site occupancy, (iii) throughput, including the amount of starting material required for analysis. The results of this meta-analysis are the core of this review, complemented by issues related to biological models and sample preparation in redox proteomics, including conditions for free thiol blocking and labelling of target cysteine oxoforms.

  10. Formation mechanism and biological activity of novel thiolated human-like collagen iron complex.

    PubMed

    Zhu, Chenhui; Liu, Lingyun; Deng, Jianjun; Ma, Xiaoxuan; Hui, Junfeng; Fan, Daidi

    2016-03-01

    To develop an iron supplement that is effectively absorbed and utilized, thiolated human-like collagen was created to improve the iron binding capacity of human-like collagen. A thiolated human-like collagen-iron complex was prepared in a phosphate buffer, and one mole of thiolated human-like collagen-iron possessed approximately 28.83 moles of iron. The characteristics of thiolated human-like collagen-iron were investigated by ultraviolet-visible absorption spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and differential scanning calorimetry. The results showed that the thiolated human-like collagen-iron complex retained the secondary structure of human-like collagen and had greater thermodynamic stability than human-like collagen, although interactions between iron ions and human-like collagen occurred during the formation of the complex. In addition, to evaluate the bioavailability of thiolated human-like collagen-iron, an in vitro Caco-2 cell model and an in vivo iron deficiency anemia mouse model were employed. The data demonstrated that the thiolated human-like collagen-iron complex exhibited greater bioavailability and was more easily utilized than FeSO4, ferric ammonium citrate, or ferrous glycinate. These results indicated that the thiolated human-like collagen-iron complex is a potential iron supplement in the biomedical field.

  11. Mucus permeating thiolated self-emulsifying drug delivery systems.

    PubMed

    Rohrer, Julia; Partenhauser, Alexandra; Hauptstein, Sabine; Gallati, Caroline Marie; Matuszczak, Barbara; Abdulkarim, Muthanna; Gumbleton, Mark; Bernkop-Schnürch, Andreas

    2016-01-01

    Mucus represents a critical obstacle for self-emulsifying drug delivery systems (SEDDS) targeting the epithelial membrane site. The aim of the study was the development of a novel SEDDS to overcome the mucus barrier. Two novel conjugates N-dodecyl-4-mercaptobutanimidamide (thiobutylamidine-dodecylamine, TBA-D) and 2-mercapto-N-octylacetamide (thioglycolicacid-octylamine, TGA-O) were synthesized, incorporated into SEDDS and analyzed for stability, cytotoxicity and physico-chemical characteristics using dynamic light scattering. Mucus interaction studies were performed using in vitro assays based on multiple particle tracking, rotational silicone tubes and rheology. TBA-D was synthesized using dodecylamine and iminothiolane as thiol precursor (yield=55 ± 5%). TGA-O was obtained via crosslinking of octylamine with SATA ((2,5-dioxopyrrolidin-1-yl) 2-acetylsulfanylacetate) (yield=70 ± 6%). The chemical structure of target compounds was confirmed via NMR analysis. The thiol-conjugates were incorporated in an amount of 3% (m/m) into SEDDS (Cremophor EL 30%, Capmul MCM 30%, Captex 355 30% and propylene glycol 10%), namely thiolated SEDDS leading to a droplet size around 50 nm and zeta potential close to 0 mV. Thiolated SEDDS with an effective diffusion coefficient 〈Deff〉 of up to 0.871 ± 0.122 cm(2) s(-1) × 10(-9) were obtained. Rotational silicone studies show increased permeation of the thiolated SEDDS A in comparison with unthiolated control. Rheological studies confirmed the mucolytic activity of the thiol-conjugates which differed only by 3% from DTT (dithiothreitol) serving as positive control. Low molecular weight thiol-conjugates were identified to improve the mucus permeation, leading to highly efficient mucus permeating SEDDS, which were superior to conventional SEDDS and might thus be a new carrier for lipophilic drug delivery. Copyright © 2015 Elsevier B.V. All rights reserved.

  12. Modulation of the gelation efficiency of fibrillar and spherical aggregates by means of thiolation.

    PubMed

    Munialo, Claire D; de Jongh, Harmen H J; Broersen, Kerensa; van der Linden, Erik; Martin, Anneke H

    2013-11-27

    Fibrillar and spherical aggregates were prepared from whey protein isolate (WPI). These aggregates were thiolated to a substantial degree to observe any impact on functionality. Sulfur-containing groups were introduced on these aggregates which could be converted to thiol groups by deblocking. Changes on a molecular and microstructural level were studied using tryptophan fluorescence, transmission electron microscopy, and particle size analysis. The average size (nm) of spherical aggregates increased from 38 to 68 nm (blocked variant) and 106 nm (deblocked variant) after thiolation, whereas the structure of fibrillar aggregates was not affected. Subsequently, gels containing these different aggregates were prepared. Rheological measurements showed that thiolation decreased the gelation concentration and increased gel strength for both WPI fibrillar and spherical aggregates. This effect was more pronounced upon thiolation of preformed fibrillar aggregates. The findings suggest that thiolation at a protein aggregate level is a promising strategy to increase gelation efficiency.

  13. Method of making alkyl esters

    DOEpatents

    Elliott, Brian

    2010-09-14

    Methods of making alkyl esters are described herein. The methods are capable of using raw, unprocessed, low-cost feedstocks and waste grease. Generally, the method involves converting a glyceride source to a fatty acid composition and esterifying the fatty acid composition to make alkyl esters. In an embodiment, a method of making alkyl esters comprises providing a glyceride source. The method further comprises converting the glyceride source to a fatty acid composition comprising free fatty acids and less than about 1% glyceride by mass. Moreover, the method comprises esterifying the fatty acid composition in the presence of a solid acid catalyst at a temperature ranging firm about 70.degree. C. to about 120.degree. C. to produce alkyl esters, such that at least 85% of the free fatty acids are converted to alkyl esters. The method also incorporates the use of packed bed reactors for glyceride conversion and/or fatty acid esterification to make alkyl esters.

  14. Thiolated chitosan nanoparticles for the nasal administration of leuprolide: bioavailability and pharmacokinetic characterization.

    PubMed

    Shahnaz, Gul; Vetter, Anja; Barthelmes, Jan; Rahmat, Deni; Laffleur, Flavia; Iqbal, Javed; Perera, Glen; Schlocker, Wolfgang; Dünnhaput, Sarah; Augustijns, Patrick; Bernkop-Schnürch, Andreas

    2012-05-30

    The purpose of this study was to develop thiolated nanoparticles to enhance the bioavailability for the nasal application of leuprolide. Thiolated chitosan-thioglycolic acid (chitosan-TGA) and unmodified chitosan nanoparticles (NPs) were developed via ionic gelation with tripolyphosphate (TPP). Leuprolide was incorporated during the formulation process of NPs. The thiolated (chitosan-TGA) NPs had a mean size of 252 ± 82 nm, a zeta potential of +10.9 ± 4 mV, and payload of leuprolide was 12 ± 2.8. Sustained release of leuprolide from thiolated NPs was demonstrated over 6h, which might be attributed to inter- and/or intramolecular disulfide formation within the NPs network. Ciliary beat frequency (CBF) study demonstrated that thiolated NPs can be considered as suitable additives for nasal drug delivery systems. Compared to leuprolide solution, unmodified NPs and thiolated NPs provoked increased leuprolide transport through porcine nasal mucosa by 2.0 and 5.2 folds, respectively. The results of a pharmacokinetic study in male Sprague-Dawley rats showed improved transport of leuprolide from thiolated NPs as compared to leuprolide solution. Thiolated NPs had a 6.9-fold increase in area under the curve, more than 4-fold increase in elimination half-life, and a ∼3.8-fold increase in maximum plasma concentration compared to nasal solution alone. The relative nasal bioavailability (versus s.c. injection) of leuprolide thiolated NPs calculated on the basis of AUC((0-6)) was about 19.6% as compared to leuprolide solution 2.8%. The enhanced bioavailability of leuprolide is likely due to facilitated transport by thiolated NPs rather than improved release. Copyright © 2012. Published by Elsevier B.V.

  15. Grafted silane monolayers: reconsideration of growth mechanisms

    NASA Astrophysics Data System (ADS)

    Ivanov, D. A.; Nysten, B.; Jonas, A. M.; Legras, R.

    1998-03-01

    Chemical force microscopy is a new technique devised to image chemical heterogeneities on surfaces. It requires the chemical modification of Atomic Force Microscopy (AFM) tips in order to create chemical probes. In this respect, self-assembled monolayers (SAM) of alkylchlorosilanes are particularly interesting as modifying agents for AFM tips. We report here our results on the kinetics of silanization and on the structure of such SAM's grafted on model surfaces (hydroxylated Si(100) wafers). AFM, contact angle measurements, X-ray reflectivity and X-ray photoelectron spectroscopy were used to characterize SAM's of octadecyltrichlorosilane (OTS) and octadecyldimethylchlorosilane (ODMS) grown from hexadecane and toluene solutions. The mechanism of grafting of OTS follows two stages. The first rapid stage corresponds to the nucleation and growth of island-like monolayer domains. The second slower stage is related to the densification of the monolayer. SAM's of ODMS were found to form thinner layers as compared to OTS, due to their lower grafting density probably resulting in a more disordered state of grafted alkyl chains. We also address the problems concerning the relationships between the quality of final SAM structures and the water content as well as the nature of the solvent used for silanization.

  16. Interfacial thermal conductance of thiolate-protected gold nanospheres

    NASA Astrophysics Data System (ADS)

    Stocker, Kelsey M.; Neidhart, Suzanne M.; Gezelter, J. Daniel

    2016-01-01

    Molecular dynamics simulations of thiolate-protected and solvated gold nanoparticles were carried out in the presence of a non-equilibrium heat flux between the solvent and the core of the particle. The interfacial thermal conductance (G) was computed for these interfaces, and the behavior of the thermal conductance was studied as a function of particle size, ligand flexibility, and ligand chain length. In all cases, thermal conductance of the ligand-protected particles was higher than the bare metal-solvent interface. A number of mechanisms for the enhanced conductance were investigated, including thiolate-driven corrugation of the metal surface, solvent ordering at the interface, solvent-ligand interpenetration, and ligand ordering relative to the particle surface. Only the smallest particles exhibited significant corrugation. All ligands permitted substantial solvent-ligand interpenetration, and ligand chain length has a significant influence on the orientational ordering of interfacial solvent. Solvent-ligand vibrational overlap, particularly in the low frequency range (<80 cm-1), was significantly altered by ligand rigidity, and had direct influence on the interfacial thermal conductance.

  17. Thiolated silicone oil: synthesis, gelling and mucoadhesive properties.

    PubMed

    Partenhauser, Alexandra; Laffleur, Flavia; Rohrer, Julia; Bernkop-Schnürch, Andreas

    2015-04-01

    The aim of this study was the development of novel thiolated silicone oils and their evaluation with regard to gelling and mucoadhesive properties. A thiol coupling of 220 ± 14 and 127 ± 33 μmol/g polymer for 3-mercaptopropionic acid (MPA)- and cysteine-coupled silicone oil was determined, respectively. The dynamic viscosity of MPA-silicone raised significantly (p<0.000001) after oxidation with iodine to a maximum of 523-fold within 1h. During tensile studies, MPA-silicone showed both the highest results for total work of adhesion (TWA) and maximum detachment force (MDF) with a 3.8- and 3.4-fold increase, respectively, compared to the control. As far as the residence time on small intestinal mucosa is concerned, both silicone conjugates were detectable in almost the same quantities for up to 8h with 56.9 ± 3.3 and 47.8 ± 8.9% of the initially applied conjugated silicone oil. Thiolated silicone oils can be regarded superior in comparison to commonly used silicone oils due to a prolonged retention time in the small intestine as site of action. Gelling and mucoadhesive features are advantageous for antiflatulent as well as mucoprotective biomaterials. Thus, these novel thiomers seem promising for an upgrade of currently available products for the treatment of dyspepsia, reflux oesophagitis and even inflammatory bowel diseases such as ulcerative colitis or Crohn's disease.

  18. Thoughts on thiolate tethering. Tribute and thanks to a teacher.

    PubMed

    Ullrich, V

    2003-01-01

    A unique feature of P450 enzymes is in the presence of a thiolate ligand heme but its exact function in catalysis is a matter of debate. For P450 dependent monooxygenases the "active oxygen" complex seems to exist only as a transition state in which the thiolate ligand provides electron density in order to prevent pi-backbonding of the oxygen to the iron (-S-Fe-O(z.rad;)). The corresponding ground state (Compound I) would be a ferryl species (Fe(IV)z.dbnd6;O) with an electron hole either at the porphyrin or at the sulfur. Apart from this role we postulate that a second function is related to the electronic structure of Compound II as an electron acceptor and this property is shared among monooxygenases, thromboxane synthase, prostacyclin synthase, allene oxide synthase, P450(NOR(-)) and chloroperoxidase. As a common step in all P450 enzymes an extremely rapid electron uptake by Compound II allows that the primary substrate radicals are oxidized to cations which immediately combine with a neighbouring nucleophile. Thus "electron transfer" may substitute for "oxygen rebound" as the final step leading to product formation. The same principle also applies methane monooxygenases in which the role of the thiyl sulfur is replaced by a ferryl-oxyl entity.

  19. 40 CFR 721.9595 - Alkyl benzene sulfonic acids and alkyl sulfates, amine salts (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alkyl benzene sulfonic acids and alkyl... Significant New Uses for Specific Chemical Substances § 721.9595 Alkyl benzene sulfonic acids and alkyl...) The chemical substances identified generically as alkyl benzene sulfonic acids and alkyl...

  20. 40 CFR 721.9595 - Alkyl benzene sulfonic acids and alkyl sulfates, amine salts (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Alkyl benzene sulfonic acids and alkyl... Significant New Uses for Specific Chemical Substances § 721.9595 Alkyl benzene sulfonic acids and alkyl...) The chemical substances identified generically as alkyl benzene sulfonic acids and alkyl...

  1. 40 CFR 721.9595 - Alkyl benzene sulfonic acids and alkyl sulfates, amine salts (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Alkyl benzene sulfonic acids and alkyl... Significant New Uses for Specific Chemical Substances § 721.9595 Alkyl benzene sulfonic acids and alkyl...) The chemical substances identified generically as alkyl benzene sulfonic acids and alkyl...

  2. 40 CFR 721.9595 - Alkyl benzene sulfonic acids and alkyl sulfates, amine salts (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Alkyl benzene sulfonic acids and alkyl... Significant New Uses for Specific Chemical Substances § 721.9595 Alkyl benzene sulfonic acids and alkyl...) The chemical substances identified generically as alkyl benzene sulfonic acids and alkyl...

  3. 40 CFR 721.9595 - Alkyl benzene sulfonic acids and alkyl sulfates, amine salts (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Alkyl benzene sulfonic acids and alkyl... Significant New Uses for Specific Chemical Substances § 721.9595 Alkyl benzene sulfonic acids and alkyl...) The chemical substances identified generically as alkyl benzene sulfonic acids and alkyl sulfates...

  4. The Structure of Self-Assembled Monolayers of Alkylsiloxanes on Silicon: A Comparison of Results from Ellipsometry and Low-Angle X-Ray Reflectivity

    DTIC Science & Technology

    1989-05-01

    Thicknesses measured by the two methods differ by 2.2 (rlms) for alkyl chains of 10 - 18 carbon atoms and have a maximum difference of 4.2 e Ellipsometry...the approximate area projected by each alkyl group in the plane of the monolayer is 0,, 1’ ) # . Preliminary studies indicate that the use of this...projected by each alkyl group in the plane of the monolayer is - 21 ± 3 A2 . Preliminary studies indicate that this technique can be used to follow the

  5. Methods of making monolayers

    DOEpatents

    Alford, Kentin L [Pasco, WA; Simmons, Kevin L [Kennewick, WA; Samuels, William D [Richland, WA; Zemanian, Thomas S [Richland, WA; Liu, Jun [Albuquerque, NM; Shin, Yongsoon [Richland, WA; Fryxell, Glen E [Kennewick, WA

    2009-12-08

    The invention pertains to methods of forming monolayers on various surfaces. The surfaces can be selected from a wide array of materials, including, for example, aluminum dioxide, silicon dioxide, carbon and SiC. The substrates can be planar or porous. The monolayer is formed under enhanced pressure conditions. The monolayer contains functionalized molecules, and accordingly functionalizes a surface of the substrate. The properties of the functionalized substrate can enhance the substrate's applicability for numerous purposes including, for example, utilization in extracting contaminants, or incorporation into a polymeric matrix.

  6. Methods of making monolayers

    DOEpatents

    Alford, Kentin L [Pasco, WA; Simmons, Kevin L [Kennewick, WA; Samuels, William D [Richland, WA; Zemanian, Thomas S [Richland, WA; Liu, Jun [Albuquerque, NM; Shin, Yongsoon [Richland, WA; Fryxell, Glen E [Kennewick, WA

    2009-09-15

    The invention pertains to methods of forming monolayers on various surfaces. The surfaces can be selected from a wide array of materials, including, for example, aluminum dioxide, silicon dioxide, carbon and SiC. The substrates can be planar or porous. The monolayer is formed under enhanced pressure conditions. The monolayer contains functionalized molecules, and accordingly functionalizes a surface of the substrate. The properties of the functionalized substrate can enhance the substrate's applicability for numerous purposes including, for example, utilization in extracting contaminants, or incorporation into a polymeric matrix.

  7. Highly covalent ferric-thiolate bonds exhibit surprisingly low mechanical stability.

    PubMed

    Zheng, Peng; Li, Hongbin

    2011-05-04

    Depending on their nature, different chemical bonds show vastly different stability with covalent bonds being the most stable ones that rupture at forces above nanonewton. Studies have revealed that ferric-thiolate bonds are highly covalent and are conceived to be of high mechanical stability. Here, we used single molecule force spectroscopy techniques to directly determine the mechanical strength of such highly covalent ferric-thiolate bonds in rubredoxin. We observed that the ferric-thiolate bond ruptures at surprisingly low forces of ∼200 pN, significantly lower than that of typical covalent bonds, such as C-Si, S-S, and Au-thiolate bonds, which typically ruptures at >1.5 nN. And the mechanical strength of Fe-thiolate bonds is observed to correlate with the covalency of the bonds. Our results indicated that highly covalent Fe-thiolate bonds are mechanically labile and display features that clearly distinguish themselves from typical covalent bonds. Our study not only opens new avenues to investigating this important class of chemical bonds, but may also shed new lights on our understanding of the chemical nature of these metal thiolate bonds.

  8. Self-organization of surfactant molecules on solid surface: an STM study of sodium alkyl sulfonates [rapid communication

    NASA Astrophysics Data System (ADS)

    Yin, Xiu-Li; Wan, Li-Jun; Yang, Zheng-Yu; Yu, Jia-Yong

    2005-02-01

    Adsorption and self-organization of sodium alkyl sulfonates (STS and SHS) on HOPG have been studied by using in situ scanning tunneling microscopy (STM). Both SHS and STS molecules adsorb on HOPG surface and form long-range well-ordered monolayers. The molecular rows and the axes of alkyl chain of the molecules cross each other at angles of 60° and 90° in the STS and SHS layers, respectively. Molecular details such as sulfonate functional group (head) and alkyl chain are clearly imaged. The neighboring molecules in different rows form a "head to head" configuration. Structural models for the molecular arrangement of the two adlayers are proposed.

  9. Effect of the Metal on Disulfide/Thiolate Interconversion: Manganese versus Cobalt.

    PubMed

    Gennari, Marcello; Brazzolotto, Deborah; Yu, Shengying; Pécaut, Jacques; Philouze, Christian; Rouzières, Mathieu; Clérac, Rodolphe; Orio, Maylis; Duboc, Carole

    2015-12-14

    It has recently been proposed that disulfide/thiolate interconversion supported by transition-metal ions is involved in several relevant biological processes. In this context, the present contribution represents a unique investigation of the effect of the coordinated metal (M) on the M(n+)-disulfide/M((n+1)+)-thiolate switch properties. Like its isostructural Co(II)-based parent compound, Co(II)2SS (Angew. Chem. Int. Ed.- 2014, 53, 5318), the new dinuclear disulfide-bridged Mn(II) complex Mn(II)2SS can undergo an M(II)-disulfide/M(III)-thiolate interconversion, which leads to the first disulfide/thiolate switch based on Mn. The coordination of iodide to the metal ion stabilizes the oxidized form, as the disulfide is reduced to the thiolate. The reverse process, which involves the reduction of M(III) to M(II) with the concomitant oxidation of the thiolates, requires the release of iodide. The Mn(II)2SS complex slowly reacts with Bu4NI in CH2Cl2 to afford the mononuclear Mn(III)-thiolate complex Mn(III)I. The process is much slower (ca. 16 h) and much less efficient (ca. 30% yield) with respect to the instantaneous and quantitative conversion of Co(II)2SS into Co(III)I under similar conditions. This distinctive behavior can be rationalized by considering the different electrochemical properties of the involved Co and Mn complexes and the DFT-calculated driving force of the disulfide/thiolate conversion. For both Mn and Co systems, M(II)-disulfide/M(III)-thiolate interconversion is reversible. However, when the iodide is removed with Ag(+), the M(II)2SS complexes are regenerated, albeit much slower for Mn than for Co systems.

  10. Polyimides with pendant alkyl groups

    NASA Technical Reports Server (NTRS)

    Jensen, B. J.; Young, P. R.

    1982-01-01

    The effect on selected polyimide properties when pendant alkyl groups were attached to the polymer backbone was investigated. A series of polymers were prepared using benzophenone tetracarboxylic acid dianhydride (BTDA) and seven different p-alkyl-m,p'-diaminobenzophenone monomers. The alkyl groups varied in length from C(1) (methyl) to C(9) (nonyl). The polyimide prepared from BTDA and m,p'-diaminobenzophenone was included as a control. All polymers were characterized by various chromatographic, spectroscopic, thermal, and mechanical techniques. Increasing the length of the pendant alkyl group resulted in a systematic decrease in glass transition temperature (Tg) for vacuum cured films. A 70 C decrease in Tg to 193 C was observed for the nonyl polymer compared to the Tg for the control. A corresponding systematic increase in Tg indicative of crosslinking, was observed for air cured films. Thermogravimetric analysis revealed a slight sacrifice in thermal stability with increasing alkyl length. No improvement in film toughness was observed.

  11. Effect of a strong interfacial electric field on the orientation of the dipole moment of thiolated aib-oligopeptides tethered to mercury on either the N- or C-terminus.

    PubMed

    Becucci, Lucia; Guryanov, Ivan; Maran, Flavio; Guidelli, Rolando

    2010-05-05

    Four oligopeptides consisting of a sequence of alpha-aminoisobutyric acid (Aib) residues, thiolated at either the N- or C-terminus by means of a -(CH(2))(2)-SH anchor, were self-assembled on mercury, which is a substrate known to impart a high fluidity to self-assembled monolayers (SAMs). The surface dipole potential of these peptide SAMs was estimated in 0.1 M KCl aqueous solution at a negatively charged electrode, where the interfacial electric field is directed toward the metal. To the best of our knowledge, this is the first estimate of the surface dipole potential of peptide SAMs in aqueous solution. The procedure adopted consisted in measuring the charge involved in the gradual expansion of a peptide-coated mercury drop and then combining the resulting information with an estimate of the charge density experienced by diffuse layer ions. The dipole moment of the tethered thiolated peptides was found to be directed toward the metal, independent of whether they were thiolated at the C- or N-terminus. This result was confirmed by the effect of these SAMs on the kinetics and thermodynamics of the Eu(III)/Eu(II) redox couple. The combined outcome of these studies indicates that a strong interfacial electric field orients the dipole moment of peptide SAMs tethered to mercury, even against their "natural" dipole moment.

  12. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli; Fabbri, Jason D.; Melosh, Nicholas A.; Hussain, Zahid; Shen, Zhi-Xun

    2013-10-29

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  13. Diamondoid monolayers as electron emitters

    DOEpatents

    Yang, Wanli [El Cerrito, CA; Fabbri, Jason D [San Francisco, CA; Melosh, Nicholas A [Menlo Park, CA; Hussain, Zahid [Orinda, CA; Shen, Zhi-Xun [Stanford, CA

    2012-04-10

    Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

  14. Janus Gold Nanoparticles from Nanodroplets of Alkyl Thiols: A Molecular Dynamics Study.

    PubMed

    Bhandary, Debdip; Valechi, Vasumathi; Cordeiro, Maria Natália D S; Singh, Jayant K

    2017-03-28

    Janus particles provide an asymmetry in structure, which can impart diverse functionalities leading to immense importance in various applications, ranging from targeted delivery to interfacial phenomena, including catalysis, electronics, and optics. In this work, we present results of a molecular dynamics study of the growth mechanism of coating on gold nanoparticles (AuNPs) from droplets of n-alkyl thiols with different chain lengths (C5 and C11) and terminal groups (CH3 and COOH). The effect of chain lengths and functional groups on the formation of a monolayer of alkyl thiols on AuNPs is investigated. A two-step mechanism, initiated by the binding of the droplet to the nanoparticle surface with a time constant on the order of ∼1 ns, followed by the diffusion-driven growth with a larger time constant (on the order of 100 ns), is shown to capture the growth dynamics of the monolayer. It is observed that the time required for complete wetting increases with an increase in the chain length. Moreover, the monolayer formation is slowed down in the presence of carboxyl groups because of strong hydrogen bonding. The kinetics of the n-alkyl thiols coating on the nanoparticles is found to be independent of the droplet size but carboxyl-terminated thiols spread more with increasing droplet size. Furthermore, different time constants for different chains and functional groups yield Janus coating when two droplets of alkyl thiols with different terminal groups are allowed to form monolayers on the nanoparticle. The Janus balance (β) for different combinations of alkyl thiols and nanoparticle sizes varies in the range of 0.42-0.71.

  15. Monolayer to Bilayer Structural Transition in Confined Pyrrolidinium-Based Ionic Liquids.

    PubMed

    Smith, Alexander M; Lovelock, Kevin R J; Gosvami, Nitya Nand; Licence, Peter; Dolan, Andrew; Welton, Tom; Perkin, Susan

    2013-02-07

    Ionic liquids can be intricately nanostructured in the bulk and at interfaces resulting from a delicate interplay between interionic and surface forces. Here we report the structuring of a series of dialkylpyrrolidinium-based ionic liquids induced by confinement. The ionic liquids containing cations with shorter alkyl chain substituents form alternating cation-anion monolayer structures on confinement to a thin film, whereas a cation with a longer alkyl chain substituent leads to bilayer formation. The crossover from monolayer to bilayer structure occurs between chain lengths of n = 8 and 10 for these pyrrolidinium-based ionic liquids. The bilayer structure for n = 10 involves full interdigitation of the alkyl chains; this is in contrast with previous observations for imidazolium-based ionic liquids. The results are pertinent to these liquids' application as electrolytes, where the electrolyte is confined inside the pores of a nanoporous electrode, for example, in devices such as supercapacitors or batteries.

  16. Improving oral bioavailability of acyclovir using nanoparticulates of thiolated xyloglucan.

    PubMed

    Madgulkar, Ashwini; Bhalekar, Mangesh R; Dikpati, Amrita A

    2016-08-01

    Acyclovir a BCS class III drug exhibits poor bioavailability due to limited permeability. The intention of this research work was to formulate and characterize thiolated xyloglucan polysaccharide nanoparticles (TH-NPs) of acyclovir with the purpose of increasing its oral bioavailability. Acyclovir-loaded TH-NPs were prepared using a cross-linking agent. Interactions of formulation excipients were reconnoitered using Fourier transform infrared spectroscopy (FT-IR). The formulated nanoparticles were lyophilised by the addition of a cryoprotectant and characterized for its particle size, morphology and stability and optimized using Box Behnken Design.The optimized TH-NP formulation exhibited particle size of 474.4±2.01 and an entrapment efficiency of 81.57%. A marked enhancement in the mucoadhesion was also observed. In-vivo study in a rat model proved that relative bioavailability of acyclovir TH-NPs is ∼2.575 fold greater than that of the marketed acyclovir drug suspension.

  17. Luminescence of Au(I)-thiolate complex affected by solvent

    NASA Astrophysics Data System (ADS)

    Yang, Lina; Cao, Yuanjie; Chen, Juan; Sun, Zhihu; Yao, Tao; Jiang, Yong; Wei, Shiqiang

    2017-08-01

    This work presents a study on the correlation between luminescence property of Au(I)-SR (SR: thiolate) complexes and solvent polarity. Luminescent [Au15(SR)14-16]+ complexes were synthesized in the weakly polar solvent of toluene, while the non-luminescent [Au7(SR)6]+ species were obtained by the same synthesis method in the polar solvent of ethanol. The dependence of luminescence intensity on the mixed solvent with various toluene/ethanol ratios was also explored. It is proposed that the luminescence of Au(I)-SR complexes originates from the aggregation of the bilayer supramolecular structures induced by the weakly polar solvent. This aggregation strengthens the intra and intercomplex aurophilic Au(I)···Au(I) interactions and subsequently enhances the luminescence intensity of the complexes.

  18. Rapid Degradation of Alkanethiol-Based Self-Assembled Monolayers on Gold in Ambient Laboratory Conditions

    SciTech Connect

    Willey, T M; Vance, A L; van Buuren, T; Bostedt, C; Terminello, L J; Fadley, C S

    2004-07-21

    Self-assembled monolayers (SAMs) consisting of alkanethiols and similar sulfur-containing molecules on noble metal substrates are extensively used and explored for various chemical and biological surface-functionalization in the scientific community. SAMs consisting of thiol- or disulfide-containing molecules adsorbed on gold are commonly used due to their ease of preparation and stability. However, the gold-thiolate bond is easily and rapidly oxidized under ambient conditions, adversely affecting SAM quality and structure. Here, the oxidation of dodecanethiol on gold is explored for various 12-hour exposures to ambient laboratory air and light. SAM samples are freshly prepared, air-exposed, and stored in small, capped vials. X-ray photoelectron spectroscopy (XPS) reveals nearly complete oxidation of the thiolate in air-exposed samples, and a decrease in carbon signal on the surface. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) at the Carbon K-edge shows a loss of upright orientational order upon air-exposure. Alternatively, the oxidation of the thiolate is minor when SAMs are stored in limited-air-containing small 15 ml vials. Thus, care must be taken to avoid SAM degradation by ensuring alkanethiolates on gold have sufficient durability for each intended environment and application.

  19. The Dispersion Properties of Precipitated Calcium Carbonate Suspensions Adsorbed with Alkyl Polyglycoside in Aqueous Medium.

    PubMed

    Song, Myung-Geun; Kim, Jong-Yun; Kim, Jong-Duk

    2000-06-01

    The zeta potentials and dispersion properties of precipitated calcium carbonate suspensions adsorbed with alkyl polyglycosides in aqueous medium were investigated. Within the investigated pH ranges, the adsorption curves of alkyl polyglycosides on calcium carbonates show sigmoidal shapes, and the zeta potential decreases as the amount of adsorption increases. At positively charged surfaces of low pH, the adsorption amounts were greater than those at negatively charged surfaces, indicating that alkyl polyglycosides were negatively charged in aqueous solutions. At low concentrations of alkyl polyglycosides, the dispersion stabilities of suspensions were very poor and showed no linearity with zeta potentials over the entire range of pHs, which may be attributed to the onset of hydrophobic interaction between particles due to the adsorption of surfactant molecules. This destabilization continued until monolayer coverage by the surfactant layer was complete. Based on the classical DLVO theory, there may be a strong hydrophobic interaction between particles. Beyond monolayer adsorption, the dispersion stability increases, probably by the formation of hemimicelle or admicelle. Therefore, it is believed that ionization of alkyl polyglycosides and admicelles of surfactants on particle surface plays a key role in the stability of dispersions and the abrupt increase in adsorption. Copyright 2000 Academic Press.

  20. Thiolated silicone oil: Synthesis, gelling and mucoadhesive properties

    PubMed Central

    Partenhauser, Alexandra; Laffleur, Flavia; Rohrer, Julia; Bernkop-Schnürch, Andreas

    2015-01-01

    The aim of this study was the development of novel thiolated silicone oils and their evaluation with regard to gelling and mucoadhesive properties. A thiol coupling of 220 ± 14 and 127 ± 33 μmol/g polymer for 3-mercaptopropionic acid (MPA)- and cysteine-coupled silicone oil was determined, respectively. The dynamic viscosity of MPA–silicone raised significantly (p < 0.000001) after oxidation with iodine to a maximum of 523-fold within 1 h. During tensile studies, MPA–silicone showed both the highest results for total work of adhesion (TWA) and maximum detachment force (MDF) with a 3.8- and 3.4-fold increase, respectively, compared to the control. As far as the residence time on small intestinal mucosa is concerned, both silicone conjugates were detectable in almost the same quantities for up to 8 h with 56.9 ± 3.3 and 47.8 ± 8.9% of the initially applied conjugated silicone oil. Thiolated silicone oils can be regarded superior in comparison to commonly used silicone oils due to a prolonged retention time in the small intestine as site of action. Gelling and mucoadhesive features are advantageous for antiflatulent as well as mucoprotective biomaterials. Thus, these novel thiomers seem promising for an upgrade of currently available products for the treatment of dyspepsia, reflux oesophagitis and even inflammatory bowel diseases such as ulcerative colitis or Crohn’s disease. PMID:25660565

  1. A thiolate-ligated nonheme oxoiron(IV) complex relevant to cytochrome P450.

    PubMed

    Bukowski, Michael R; Koehntop, Kevin D; Stubna, Audria; Bominaar, Emile L; Halfen, Jason A; Münck, Eckard; Nam, Wonwoo; Que, Lawrence

    2005-11-11

    Thiolate-ligated oxoiron(IV) centers are postulated to be the key oxidants in the catalytic cycles of oxygen-activating cytochrome P450 and related enzymes. Despite considerable synthetic efforts, chemists have not succeeded in preparing an appropriate model complex. Here we report the synthesis and spectroscopic characterization of [FeIV(O)(TMCS)]+ where TMCS is a pentadentate ligand that provides a square pyramidal N4(SR)apical, where SR is thiolate, ligand environment about the iron center, which is similar to that of cytochrome P450. The rigidity of the ligand framework stabilizes the thiolate in an oxidizing environment. Reactivity studies suggest that thiolate coordination favors hydrogen-atom abstraction chemistry over oxygen-atom transfer pathways in the presence of reducing substrates.

  2. Effect of Immobilized Thiolated Glycosaminoglycans on Fibronectin Adsorption and Behavior of Fibroblasts.

    PubMed

    Köwitsch, Alexander; Niepel, Marcus S; Michanetzis, Georgios P A; Missirlis, Yannis F; Groth, Thomas

    2016-03-01

    Glycosaminoglycans (GAGs) chondroitin sulfate, heparin, hyaluronan, and sulfated hyaluronan are lower and higher thiolated to enable a one-step covalent modification of gold or vinyl-terminated surfaces. Measurements of water contact angle and zeta potentials reveal that sulfated GAG-modified surfaces are more wettable and possess a negative surface potential. Additionally, higher thiolated GAGs (tGAGs) exhibit increased wettability and higher surface roughness. Fibronectin (FN) adsorption increases with sulfation degree of tGAGs. The tGAG-functionalized surfaces with higher degree of sulfation promote fibroblast adhesion most under serum-free conditions. The preadsorption of FN allows for more cell adhesion on tGAG surfaces. Metabolic activity measurements show that cell growth is enhanced for tGAGs up to a certain thiolation degree. Overall, thiolation of GAGs does not hamper their bioactivity toward proteins and cells, which make them highly interesting for biomimetic surface modification of implants and tissue engineering scaffolds.

  3. Simultaneous optimization of monolayer formation factors, including temperature, to significantly improve nucleic acid hybridization efficiency on gold substrates.

    PubMed

    Pris, Andrew D; Ostrowski, Sara G; Garaas, Sarah D

    2010-04-20

    Past literature investigations have optimized various single factors used in the formation of thiolated, single stranded DNA (ss-DNA) monolayers on gold. In this study a more comprehensive approach is taken, where a design of experiment (DOE) is employed to simultaneously optimize all of the factors involved in construction of the capture monolayer used in a fluorescence-based hybridization assay. Statistical analysis of the fluorescent intensities resulting from the DOE provides empirical evidence for the importance and the optimal levels of traditional and novel factors included in this investigation. We report on the statistical importance of a novel factor, temperature of the system during monolayer formation of the capture molecule and lateral spacer molecule, and how proper usage of this temperature factor increased the hybridization signal 50%. An initial theory of how the physical factor of heat is mechanistically supplementing the function of the lateral spacer molecule is provided.

  4. S-protected thiolated hydroxyethyl cellulose (HEC): Novel mucoadhesive excipient with improved stability.

    PubMed

    Leonaviciute, Gintare; Bonengel, Sonja; Mahmood, Arshad; Ahmad Idrees, Muneeb; Bernkop-Schnürch, Andreas

    2016-06-25

    The aim of this study was the design of novel S-protected thiolated hydroxyethyl cellulose (HEC) and the assessment of its mucoadhesive properties and biodegradability compared to the corresponding unmodified polymer. Thiolated HEC was S-protected via disulfide bond formation between 6-mercaptonicotinamide (6-MNA) and the thiol substructures of the polymer. In vitro screening of mucoadhesive properties was accomplished using two different methods: rotating cylinder studies and viscosity measurements. Moreover, biodegradability of these polymers by cellulase, xylanase and lysozyme was evaluated. MTT and LDH assays were performed on Caco-2 cells to determine the cytotoxicity of S-protected thiolated HEC. Thiolated HEC displayed 280.09±1.70μmol of free thiol groups per gram polymer. S-protected thiolated HEC exhibiting 270.8±21.11μmol immobilized 6-MNA ligands per gram of polymer was shown being 2.4-fold more mucoadhesive compared to thiolated HEC. No mucoadhesion was observed in case of unmodified HEC. Results were in a good agreement with rheological studies. The presence of free thiol moieties likely caused lower degree of hydrolysis by xylanase, whereas the degradation by both enzymes cellulase and xylanase was more hampered when 6-MNA was introduced as ligand for thiol group's protection. Findings in cell viability revealed that all three conjugates were non-toxic. S-protection of thiolated hydroxyethyl cellulose improved mucoadhesive properties and provided pronounced stability towards enzymatic attack, that makes this excipient superior for non-invasive drug administration over thiolated and unmodified forms.

  5. Thiolated chitosan nanoparticles: transfection study in the Caco-2 differentiated cell culture.

    PubMed

    Martien, Ronny; Loretz, Brigitta; Sandbichler, Adolf Michael; Schnürch, Andreas Bernkop

    2008-01-30

    The aim of this study was to monitor the expression of secreted protein in differentiated Caco-2 cells after transfection with nanoparticles, in order to improve gene delivery. Based on unmodified chitosan and thiolated chitosan conjugates, nanoparticles with the gene reporter pSEAP (recombinant Secreted Alkaline Phosphatase) were generated at pH 4.0. Transfection studies of thiolated chitosan in Caco-2 cells during the exponential growth phase and differentiation growth phase of the cells led to a 5.0-fold and 2.0-fold increase in protein expression when compared to unmodified chitosan nanoparticles. The mean particle size for both unmodified chitosan and cross-linked thiolated chitosan nanoparticles is 212.2 ± 86 and 113.6 ± 40 nm, respectively. The zeta potential of nanoparticles was determined to be 7.9 ± 0.38 mV for unmodified chitosan nanoparticles and 4.3 ± 0.74 mV for cross-linked thiolated chitosan nanoparticles. Red blood cell lysis evaluation was used to evaluate the membrane damaging properties of unmodified and thiolated chitosan nanoparticles and led to 4.61 ± 0.36% and 2.29 ± 0.25% lysis, respectively. Additionally, cross-linked thiolated chitosan nanoparticles were found to exhibit higher stability toward degradation in gastric juices. Furthermore the reversible effect of thiolated chitosan on barrier properties was monitored by measuring the transepithelial electrical resistance (TEER) and is supported by immunohistochemical staining for the tight junction protein claudin. According to these results cross-linked thiolated chitosan nanoparticles have the potential to be used as a non-viral vector system for gene therapy.

  6. Thiolated chitosan nanoparticles: transfection study in the Caco-2 differentiated cell culture

    NASA Astrophysics Data System (ADS)

    Martien, Ronny; Loretz, Brigitta; Sandbichler, Adolf Michael; Bernkop Schnürch, Andreas

    2008-01-01

    The aim of this study was to monitor the expression of secreted protein in differentiated Caco-2 cells after transfection with nanoparticles, in order to improve gene delivery. Based on unmodified chitosan and thiolated chitosan conjugates, nanoparticles with the gene reporter pSEAP (recombinant Secreted Alkaline Phosphatase) were generated at pH 4.0. Transfection studies of thiolated chitosan in Caco-2 cells during the exponential growth phase and differentiation growth phase of the cells led to a 5.0-fold and 2.0-fold increase in protein expression when compared to unmodified chitosan nanoparticles. The mean particle size for both unmodified chitosan and cross-linked thiolated chitosan nanoparticles is 212.2 ± 86 and 113.6 ± 40 nm, respectively. The zeta potential of nanoparticles was determined to be 7.9 ± 0.38 mV for unmodified chitosan nanoparticles and 4.3 ± 0.74 mV for cross-linked thiolated chitosan nanoparticles. Red blood cell lysis evaluation was used to evaluate the membrane damaging properties of unmodified and thiolated chitosan nanoparticles and led to 4.61 ± 0.36% and 2.29 ± 0.25% lysis, respectively. Additionally, cross-linked thiolated chitosan nanoparticles were found to exhibit higher stability toward degradation in gastric juices. Furthermore the reversible effect of thiolated chitosan on barrier properties was monitored by measuring the transepithelial electrical resistance (TEER) and is supported by immunohistochemical staining for the tight junction protein claudin. According to these results cross-linked thiolated chitosan nanoparticles have the potential to be used as a non-viral vector system for gene therapy.

  7. Thiolated chitosan-modified PLA-PCL-TPGS nanoparticles for oral chemotherapy of lung cancer

    NASA Astrophysics Data System (ADS)

    Jiang, Liqin; Li, Xuemin; Liu, Lingrong; Zhang, Qiqing

    2013-02-01

    Oral chemotherapy is a key step towards `chemotherapy at home', a dream of cancer patients, which will radically change the clinical practice of chemotherapy and greatly improve the quality of life of the patients. In this research, three types of nanoparticle formulation from commercial PCL and self-synthesized d-α-tocopheryl polyethylene glycol 1000 succinate (PLA-PCL-TPGS) random copolymer were prepared in this research for oral delivery of antitumor agents, including thiolated chitosan-modified PCL nanoparticles, unmodified PLA-PCL-TPGS nanoparticles, and thiolated chitosan-modified PLA-PCL-TPGS nanoparticles. Firstly, the PLA-PCL-TPGS random copolymer was synthesized and characterized. Thiolated chitosan greatly increases its mucoadhesiveness and permeation properties, thus increasing the chances of nanoparticle uptake by the gastrointestinal mucosa and improving drug absorption. The PLA-PCL-TPGS nanoparticles were found by FESEM that they are of spherical shape and around 200 nm in diameter. The surface charge of PLA-PCL-TPGS nanoparticles was reversed from anionic to cationic after thiolated chitosan modification. The thiolated chitosan-modified PLA-PCL-TPGS nanoparticles have significantly higher level of the cell uptake than that of thiolated chitosan-modified PLGA nanoparticles and unmodified PLA-PCL-TPGS nanoparticles. In vitro cell viability studies showed advantages of the thiolated chitosan-modified PLA-PCL-TPGS nanoparticles over Taxol® in terms of cytotoxicity against A549 cells. It seems that the mucoadhesive nanoparticles can increase paclitaxel transport by opening tight junctions and bypassing the efflux pump of P-glycoprotein. In conclusion, PLA-PCL-TPGS nanoparticles modified by thiolated chitosan could enhance the cellular uptake and cytotoxicity, which revealed a potential application for oral chemotherapy of lung cancer.

  8. Thiolated chitosan-modified PLA-PCL-TPGS nanoparticles for oral chemotherapy of lung cancer.

    PubMed

    Jiang, Liqin; Li, Xuemin; Liu, Lingrong; Zhang, Qiqing

    2013-02-09

    Oral chemotherapy is a key step towards 'chemotherapy at home', a dream of cancer patients, which will radically change the clinical practice of chemotherapy and greatly improve the quality of life of the patients. In this research, three types of nanoparticle formulation from commercial PCL and self-synthesized d-α-tocopheryl polyethylene glycol 1000 succinate (PLA-PCL-TPGS) random copolymer were prepared in this research for oral delivery of antitumor agents, including thiolated chitosan-modified PCL nanoparticles, unmodified PLA-PCL-TPGS nanoparticles, and thiolated chitosan-modified PLA-PCL-TPGS nanoparticles. Firstly, the PLA-PCL-TPGS random copolymer was synthesized and characterized. Thiolated chitosan greatly increases its mucoadhesiveness and permeation properties, thus increasing the chances of nanoparticle uptake by the gastrointestinal mucosa and improving drug absorption. The PLA-PCL-TPGS nanoparticles were found by FESEM that they are of spherical shape and around 200 nm in diameter. The surface charge of PLA-PCL-TPGS nanoparticles was reversed from anionic to cationic after thiolated chitosan modification. The thiolated chitosan-modified PLA-PCL-TPGS nanoparticles have significantly higher level of the cell uptake than that of thiolated chitosan-modified PLGA nanoparticles and unmodified PLA-PCL-TPGS nanoparticles. In vitro cell viability studies showed advantages of the thiolated chitosan-modified PLA-PCL-TPGS nanoparticles over Taxol® in terms of cytotoxicity against A549 cells. It seems that the mucoadhesive nanoparticles can increase paclitaxel transport by opening tight junctions and bypassing the efflux pump of P-glycoprotein. In conclusion, PLA-PCL-TPGS nanoparticles modified by thiolated chitosan could enhance the cellular uptake and cytotoxicity, which revealed a potential application for oral chemotherapy of lung cancer.

  9. Monolayer and bilayer structures in ionic liquids and their mixtures confined to nano-films.

    PubMed

    Smith, Alexander M; Lovelock, Kevin R J; Perkin, Susan

    2013-01-01

    The confinement of liquids to thin films can lead to dramatic changes in their structural arrangement and dynamic properties. Ionic liquids display nano-structures in the bulk of the liquid, consisting of polar and non-polar domains, whereas a solid surface can induce layered structures in the near-surface liquid. Here we compare and contrast the layer structures in a series of imidazolium and pyrrolidinium-based ionic liquids upon confinement of the liquids to films of approximately 0-20 nm between two negatively charged mica surfaces. Using a surface force balance (SFB) we measured the force between the two atomically smooth mica surfaces with ionic liquid between, directly revealing the ion packing and dimensions of layered structures for each liquid. The ionic liquids with shorter alkyl chain substituents form alternating cation-anion monolayer structures on confinement, whilst a longer alkyl chain leads to alignment of the cations in bilayer formation. The crossover from monolayers to bilayers, however, occurs at different alkyl chain lengths for imidazolium- and pyrrolidinium-based ionic liquids with a common anion. In addition, we find that imidazolium cation bilayers are arranged in toe-to-toe orientation, whereas pyrrolidinium cations form bilayers consisting of fully interdigitated alkyl chains. Results for a mixture of monolayer-preferring (i.e. short alkyl chain) and bilayer-preferring (i.e. long alkyl chain) liquids indicate alkyl chain segregation and bilayer-like structures. We discuss the driving forces for these self-assembly effects, and the contrasting behaviour of the imidazolium and pyrrolidinium-type ionic liquids.

  10. Characterization and reactivity of organic monolayers on gold and platinum surfaces

    SciTech Connect

    Wu, Chien-Ching

    1995-12-06

    Purpose is to understand how the mobilization, dielectric, orientation, composition, coverage, and structure of self-assembled organic monolayers on metal surfaces affects the surface reactivities and properties of these films in order to facilitate the construction of desired films. Two model systems were used: tiols at Au and aromatic acids at Pt. Surface analysis methods, including contact angle, electrochemistry, ellipsometry, infrared reflection absorption spectroscopy (IRRAS), and x-ray photospectroscopy, were used to study the self-assembled organic monolayers on Au and Pt. IRRAS, contact angle, and electrochemistry were used to determine the surface pKa of phenylcarboxylic acids and pyridylcarboxylic acids monolayers on Pt. These techniques were also used to determine the orientation of polymethylene chain axis and the carboxylic follow the structural evolution of the chains and end group of the thiolate monolayers during formation. IRRAS was also used to assess the carboxylic acid group in terms of its possible existence as the non-hydrogen-bonded species, the hydrogen-bonded dimeric group, and the hydrogen-bonded polymeric group. These different forms of the end group were also followed vs coverage, as well as the reactivity vs solution pH. IRRAS and contact angle were used to calculate the rate constant of the esterification of carboxylic acid-terminated monolayers on Au.

  11. Self assembled monolayers on silicon for molecular electronics.

    PubMed

    Aswal, D K; Lenfant, S; Guerin, D; Yakhmi, J V; Vuillaume, D

    2006-05-24

    We present an overview of various aspects of the self-assembly of organic monolayers on silicon substrates for molecular electronics applications. Different chemical strategies employed for grafting the self-assembled monolayers (SAMs) of alkanes having different chain lengths on native oxide of Si or on bare Si have been reviewed. The utility of different characterization techniques in determination of the thickness, molecular ordering and orientation, surface coverage, growth kinetics and chemical composition of the SAMs has been discussed by choosing appropriate examples. The metal counterelectrodes are an integral part of SAMs for measuring their electrical properties as well as using them for molecular electronic devices. A brief discussion on the variety of options available for the deposition of metal counterelectrodes, that is, soft metal contacts, vapor deposition and soft lithography, has been presented. Various theoretical models, namely, tunneling (direct and Fowler-Nordheim), thermionic emission, Poole-Frenkel emission and hopping conduction, used for explaining the electronic transport in dielectric SAMs have been outlined and, some experimental data on alkane SAMs have been analyzed using these models. It has been found that short alkyl chains show excellent agreement with tunneling models; while more experimental data on long alkyl chains are required to understand their transport mechanism(s). Finally, the concepts and realization of various molecular electronic components, that is, diodes, resonant tunnel diodes, memories and transistors, based on appropriate architecture of SAMs comprising of alkyl chains (sigma- molecule) and conjugated molecules (pi-molecule) have been presented.

  12. Surface-segregated monolayers: a new type of ordered monolayer for surface modification of organic semiconductors.

    PubMed

    Wei, Qingshuo; Tajima, Keisuke; Tong, Yujin; Ye, Shen; Hashimoto, Kazuhito

    2009-12-09

    We report a new type of ordered monolayer for the surface modification of organic semiconductors. Fullerene derivatives with fluorocarbon chains ([6,6]-phenyl-C(61)-buryric acid 1H,1H-perfluoro-1-alkyl ester or FC(n)) spontaneously segregated as a monolayer on the surface of a [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) film during a spin-coating process from the mixture solutions, as confirmed by X-ray photoelectron spectroscopy (XPS). Ultraviolet photoelectron spectroscopy (UPS) showed the shift of ionization potentials (IPs) depending on the fluorocarbon chain length, indicating the formation of surface dipole moments. Surface-sensitive vibrational spectroscopy, sum frequency generation (SFG) revealed the ordered molecular orientations of the C(60) moiety in the surface FC(n) layers. The intensity of the SFG signals from FC(n) on the surface showed a clear odd-even effect when the length of the fluorocarbon chain was changed. This new concept of the surface-segregated monolayer provides a facile and versatile approach to modifying the surface of organic semiconductors and is applicable to various organic optoelectronic devices.

  13. 40 CFR 721.1875 - Boric acid, alkyl and substituted alkyl esters (generic name).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Boric acid, alkyl and substituted... Significant New Uses for Specific Chemical Substances § 721.1875 Boric acid, alkyl and substituted alkyl... chemical substance boric acid, alkyl and substituted alkyl esters (PMN P-86-1252) is subject to reporting...

  14. 40 CFR 721.1875 - Boric acid, alkyl and substituted alkyl esters (generic name).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Boric acid, alkyl and substituted... Significant New Uses for Specific Chemical Substances § 721.1875 Boric acid, alkyl and substituted alkyl... chemical substance boric acid, alkyl and substituted alkyl esters (PMN P-86-1252) is subject to reporting...

  15. 40 CFR 721.1875 - Boric acid, alkyl and substituted alkyl esters (generic name).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Boric acid, alkyl and substituted... Significant New Uses for Specific Chemical Substances § 721.1875 Boric acid, alkyl and substituted alkyl... chemical substance boric acid, alkyl and substituted alkyl esters (PMN P-86-1252) is subject to reporting...

  16. Nanoscale Phase Segregation of Mixed Thiolates on Gold Nanoparticles

    PubMed Central

    Harkness, Kellen M.; Balinski, Andrzej

    2012-01-01

    Phase segregation and domain formation is observed within the protecting monolayer of gold nanoparticles (AuNPs) using ion mobility-mass spectrometry, a two-dimensional gas-phase separation technique. Experimental data is compared to a theoretical model that represents a randomly distributed ligand mixture. Deviations from this model provide evidence for nanophase separation resulting in anisotropic AuNPs. PMID:21882306

  17. How do the thiolate ligand and its relative position control the oxygen activation in the cysteine dioxygenase model?

    PubMed

    Che, Xin; Gao, Jun; Zhang, Dongju; Liu, Chengbu

    2012-06-07

    In the iron(II)-thiolate models of cysteine dioxygenase, the thiolate ligand is a key factor in the oxygen activation. In this contribution, four model compounds have been theoretically investigated. This comparative study reveals that the thiolate ligand itself and its relative position are both important for the activation of O(2). Before the O(2) binding, the thiolate ligand must transfer charge to Fe(II), and the effective nuclear charges of Fe(II) is decreased, which results in a lower redox potential of compounds. In other words, the thiolate ligand provides a prerequisite for the O(2) activation. Furthermore, the relative position of the thiolate ligand is discovered to determine the reaction path of O(2) activation. The amount of charge transfer is crucial for these reactions; the more charge it transfers, the lower the related redox potentials. This work really helps think deeper into the O(2) activation process of mononuclear nonheme iron enzymes.

  18. Interfacial assignment of branched-alkyl benzene sulfonates: A molecular simulation

    NASA Astrophysics Data System (ADS)

    Liu, Zi-Yu; Wei, Ning; Wang, Ce; Zhou, He; Zhang, Lei; Liao, Qi; Zhang, Lu

    2015-11-01

    A molecular dynamics simulation was conducted to analyze orientations of sodium branched-alkyl benzene sulfonates molecules at nonane/water interface, which is helpful to design optimal surfactant structures to achieve ultralow interfacial tension (IFT). Through the two dimensional density profiles, monolayer collapses are found when surfactant concentration continues to increase. Thus the precise scope of monolayer is certain and orientation can be analyzed. Based on the simulated results, we verdict the interfacial assignment of branched-alkyl benzene sulfonates at the oil-water interface, and discuss the effect of hydrophobic tail structure on surfactant assignment. Bigger hydrophobic size can slow the change rate of surfactant occupied area as steric hindrance, and surfactant meta hydrophobic tails have a stronger tendency to stretch to the oil phase below the collapsed concentration. Furthermore, an interfacial model with reference to collapse, increasing steric hindrance and charge repulsive force between interfacial surfactant molecules, responsible for effecting of surfactant concentration and structure has been supposed.

  19. Molecular and electronic structure of electroactive self-assembled monolayers

    NASA Astrophysics Data System (ADS)

    Méndez De Leo, Lucila P.; de la Llave, Ezequiel; Scherlis, Damián; Williams, Federico J.

    2013-03-01

    Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAM-induced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30° tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. We found for the first time that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at -1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.

  20. Molecular and electronic structure of electroactive self-assembled monolayers.

    PubMed

    Méndez De Leo, Lucila P; de la Llave, Ezequiel; Scherlis, Damián; Williams, Federico J

    2013-03-21

    Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAM-induced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30° tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. We found for the first time that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at -1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.

  1. Mild Catalytic methods for Alkyl-Alkyl Bond Formation

    SciTech Connect

    Vicic, David A

    2009-08-10

    Overview of Research Goals and Accomplishments for the Period 07/01/06 – 06/30/07: Our overall research goal is to transform the rapidly emerging synthetic chemistry involving alkyl-alkyl cross-couplings into more of a mechanism-based field so that that new, rationally-designed catalysts can be performed under energy efficient conditions. Our specific objectives for the previous year were 1) to obtain a proper electronic description of an active catalyst for alkyl-alkyl cross-coupling reactions and 2) to determine the effect of ligand structure on the rate, scope, selectivity, and functional group compatibility of C(sp3)-C(sp3) cross-coupling catalysis. We have completed both of these initial objectives and established a firm base for further studies. The specific significant achievements of the current grant period include: 1) we have performed magnetic and computational studies on (terpyridine)NiMe, an active catalyst for alkyl-alkyl cross couplings, and have discovered that the unpaired electron resides heavily on the terpyridine ligand and that the proper electronic description of this nickel complex is a Ni(II)-methyl cation bound to a reduced terpyridine ligand; 2) we have for the first time shown that alkyl halide reduction by terpyridyl nickel catalysts is substantially ligand based; 3) we have shown by isotopic labeling studies that the active catalyst (terpyridine)NiMe is not produced via a mechanism that involves the formation of methyl radicals when (TMEDA)NiMe2 is used as the catalyst precursor; 4) we have performed an extensive ligand survey for the alkyl-alkyl cross-coupling reactions and have found that electronic factors only moderately influence reactivity in the terpyridine-based catalysis and that the most dramatic effects arise from steric and solubility factors; 5) we have found that the use of bis(dialkylphosphino)methanes as ligands for nickel does not produce active catalysts for cross-coupling but rather leads to bridging hydride

  2. Preparation of thiolated polymeric nanocomposite for sensitive electroanalysis of dopamine.

    PubMed

    Su, Zhaohong; Liu, Ying; Xie, Qingji; Chen, Li; Zhang, Yi; Meng, Yue; Li, Yan; Fu, Yingchun; Ma, Ming; Yao, Shouzhuo

    2012-01-01

    We report on the thiol-ene chemistry guided preparation of novel thiolated polymeric nanocomposite films of abundant anionic carboxylic groups for electrostatic enrichment and sensitive electroanalysis of cationic dopamine (DA) in neutral solution. Briefly, the thiol-ene nucleophilic reaction of a carboxylated thiol with oxidized polypyrrole (PPy), which was electrosynthesized on an Au electrode in the presence of solution-dispersed acidified multiwalled carbon nanotubes (MWCNTs), produced an a PPy-thiol-MWCNTs/Au electrode, and the PPy can be electrochemically overoxidized (OPPy) to form an OPPy-thiol-MWCNTs/Au electrode. The carboxylic groups of the polymeric nanocomposite film originate from the acidified MWCNTs, PPy-tethered carboxylated thiol, and OPPy. The carboxylated thiols examined are mercaptosuccinic acid (MSA) and thioglycolic acid, with β-mercaptoethanol as a control. Electrochemical quartz crystal microbalance, scanning electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy were used for film characterization and process monitoring. Under the optimized condition, the differential pulse voltammetry peak current of DA oxidation at OPPy-MSA-MWCNTs/Au electrode is linear with DA concentration from 1.00×10(-9) to 2.87×10(-6) mol L(-1), with a limit of detection of 0.4 nmol L(-1), good anti-interferent ability and stability.

  3. Thermochromic luminescent nest-like silver thiolate cluster.

    PubMed

    Li, Bo; Huang, Ren-Wu; Qin, Jian-Hua; Zang, Shuang-Quan; Gao, Guang-Gang; Hou, Hong-Wei; Mak, Thomas C W

    2014-09-22

    A novel discrete open high-nuclearity nest-like silver thiolate cluster complex, [Ag33 S3 (StBu)16 (CF3 COO)9 (NO3 )(CH3 CN)2 ](NO3 ) (1), has been isolated with nitrate and S(2-) anions acting as structure-directing templates. Its similar nest-like structure has been assembled into an extended layer [Ag31 S3 (StBu)16 (NO3 )9 ]n (2) by adjustment of auxiliary ligand. More interestingly, both complexes exhibit temperature-dependent luminescence of high sensitivity with a large fluorescence enhancement (12-fold for 1, 21-fold for 2), which can be easily recognized by the naked-eye (dramatic red-shift Δ=104 nm for 1, larger Δ=113 nm for 2 at 77 K compared to those at 298 K). The correlation between luminescent thermochromism and temperature-dependent variation of the coordination modes of template NO3 (-) anion, Ag⋅⋅⋅S and Ag⋅⋅⋅Ag distances are also elucidated through variable-temperature single-crystal X-ray crystal structure (VT-SCXRD) analyses. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Thiolated arsenicals in arsenic metabolism: Occurrence, formation, and biological implications.

    PubMed

    Sun, Yuzhen; Liu, Guangliang; Cai, Yong

    2016-11-01

    Arsenic (As) is a notoriously toxic pollutant of health concern worldwide with potential risk of cancer induction, but meanwhile it is used as medicines for the treatment of different conditions including hematological cancers. Arsenic can undergo extensive metabolism in biological systems, and both toxicological and therapeutic effects of arsenic compounds are closely related to their metabolism. Recent studies have identified methylated thioarsenicals as a new class of arsenic metabolites in biological systems after exposure of inorganic and organic arsenicals, including arsenite, dimethylarsinic acid (DMA(V)), dimethylarsinous glutathione (DMA(III)GS), and arsenosugars. The increasing detection of thiolated arsenicals, including monomethylmonothioarsonic acid (MMMTA(V)), dimethylmonothioarsinic acid (DMMTA(V)) and its glutathione conjugate (DMMTA(V)GS), and dimethyldithioarsinic acid (DMDTA(V)) suggests that thioarsenicals may be important metabolites and play important roles in arsenic toxicity and therapeutic effects. Here we summarized the reported occurrence of thioarsenicals in biological systems, the possible formation pathways of thioarsenicals, and their toxicity, and discussed the biological implications of thioarsenicals on arsenic metabolism, toxicity, and therapeutic effects. Copyright © 2016. Published by Elsevier B.V.

  5. Fluorinated and Charged Hydrogenated Alkanethiolates Grafted on Gold: Expanding the Diversity of Mixed-Monolayer Nanoparticles for Biological Applications.

    PubMed

    Bidoggia, Silvia; Milocco, Francesca; Polizzi, Stefano; Canton, Patrizia; Saccani, Alessandra; Sanavio, Barbara; Krol, Silke; Stellacci, Francesco; Pengo, Paolo; Pasquato, Lucia

    2017-01-18

    Low intrinsic toxicity, high solubility, and stability are important and necessary features of gold nanoparticles to be used in the biomedical field. In this context, charged nanoparticles proved to be very versatile, and among them charged mixed-monolayer gold nanoparticles, displaying monolayers with well-defined morphologies, represent a paradigm. By using mixtures of hydrogenated and fluorinated thiols, the formation of monolayer domains may be brought to an extreme because of the immiscibility of fluorinated and hydrogenated chains. Following this rationale, mixed monolayer gold nanoparticles featuring ammonium, sulfonate, or carboxylic groups on their surface were prepared by using amphiphilic hydrogenated thiols and 1H,1H,2H,2H-perfluoro-alkanethiols. The toxicity of these systems was assessed in HeLa cells and was found to be, in general, low even for the cationic nanoparticles which usually show a high cytotoxicity and is comparable to that of homoligand gold nanoparticles displaying amphiphilic-charge neutral-hydrogenated or fluorinated thiolates in their monolayer. These properties make the mixed ligand monolayer gold nanoparticles an interesting new candidate for medical application.

  6. Method of making gold thiolate and photochemically functionalized microcantilevers

    DOEpatents

    Boiadjiev, Vassil I [Knoxville, TN; Brown, Gilbert M [Knoxville, TN; Pinnaduwage, Lal A [Knoxville, TN; Thundat, Thomas G [Knoxville, TN; Bonnesen, Peter V [Knoxville, TN; Goretzki, Gudrun [Nottingham, GB

    2009-08-25

    Highly sensitive sensor platforms for the detection of specific reagents, such as chromate, gasoline and biological species, using microcantilevers and other microelectromechanical systems (MEMS) whose surfaces have been modified with photochemically attached organic monolayers, such as self-assembled monolayers (SAM), or gold-thiol surface linkage are taught. The microcantilever sensors use photochemical hydrosilylation to modify silicon surfaces and gold-thiol chemistry to modify metallic surfaces thereby enabling individual microcantilevers in multicantilever array chips to be modified separately. Terminal vinyl substituted hydrocarbons with a variety of molecular recognition sites can be attached to the surface of silicon via the photochemical hydrosilylation process. By focusing the activating UV light sequentially on selected silicon or silicon nitride hydrogen terminated surfaces and soaking or spotting selected metallic surfaces with organic thiols, sulfides, or disulfides, the microcantilevers are functionalized. The device and photochemical method are intended to be integrated into systems for detecting specific agents including chromate groundwater contamination, gasoline, and biological species.

  7. Pseudorotational epitaxy of self-assembled octadecyltrichlorosilane monolayers on sapphire (0001)

    DOE PAGES

    Steinrück, H. -G.; Magerl, A.; Deutsch, M.; ...

    2014-10-06

    The structure of octadecyltrichlorosilane self-assembled monolayers (SAMs) on sapphire (0001) was studied by Å-resolution surface-specific x-ray scattering methods. The monolayer was found to consist of three sublayers where the outermost layer corresponds to vertically oriented, closely packed alkyl tails. Laterally, the monolayer is hexagonally packed and exhibits pseudorotational epitaxy to the sapphire, manifested by a broad scattering peak at zero relative azimuthal rotation, with long powderlike tails. The lattice mismatch of ~1% – 3% to the sapphire’s and the different length scale introduced by the lateral Si-O-Si bonding prohibit positional epitaxy. However, the substrate induces an intriguing increase in themore » crystalline coherence length of the SAM’s powderlike crystallites when rotationally aligned with the sapphire’s lattice. As a result, the increase correlates well with the rotational dependence of the separation of corresponding substrate-monolayer lattice sites.« less

  8. Fluorinated alkyne-derived monolayers on oxide-free silicon nanowires via one-step hydrosilylation

    NASA Astrophysics Data System (ADS)

    Nguyen Minh, Quyen; Pujari, Sidharam P.; Wang, Bin; Wang, Zhanhua; Haick, Hossam; Zuilhof, Han; van Rijn, Cees J. M.

    2016-11-01

    Passivation of oxide-free silicon nanowires (Si NWs) by the formation of high-quality fluorinated 1-hexadecyne-derived monolayers with varying fluorine content has been investigated. Alkyl chain monolayers (C16H30-xFx) with a varying number of fluorine substituents (x = 0, 1, 3, 9, 17) were attached onto hydrogen-terminated silicon (Sisbnd H) surfaces with an effective one-step hydrosilylation. This surface chemistry gives well-defined monolayers on nanowires that have a cylindrical core-shell structure, as characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and static contact angle (SCA) analysis. The monolayers were stable under acidic and basic conditions, as well as under extreme conditions (such as UV exposure), and provide excellent surface passivation, which opens up applications in the fields of field effect transistors, optoelectronics and especially for disease diagnosis.

  9. Pseudorotational epitaxy of self-assembled octadecyltrichlorosilane monolayers on sapphire (0001)

    SciTech Connect

    Steinrück, H. -G.; Magerl, A.; Deutsch, M.; Ocko, B. M.

    2014-10-06

    The structure of octadecyltrichlorosilane self-assembled monolayers (SAMs) on sapphire (0001) was studied by Å-resolution surface-specific x-ray scattering methods. The monolayer was found to consist of three sublayers where the outermost layer corresponds to vertically oriented, closely packed alkyl tails. Laterally, the monolayer is hexagonally packed and exhibits pseudorotational epitaxy to the sapphire, manifested by a broad scattering peak at zero relative azimuthal rotation, with long powderlike tails. The lattice mismatch of ~1% – 3% to the sapphire’s and the different length scale introduced by the lateral Si-O-Si bonding prohibit positional epitaxy. However, the substrate induces an intriguing increase in the crystalline coherence length of the SAM’s powderlike crystallites when rotationally aligned with the sapphire’s lattice. As a result, the increase correlates well with the rotational dependence of the separation of corresponding substrate-monolayer lattice sites.

  10. Nanometer-scale organic thin film transistors from self-assembled monolayers.

    PubMed

    Vuillaume, Dominique

    2002-01-01

    A survey of the most interesting results on nanometer-scale organic thin film transistors (nano-OTFT) is presented. Additionally, we discuss our recent results on the properties of end-group functionalized organic self-assembled monolayers and on their use in the fabrication of nanometer-scale field-effect transistors. Nanometer-scale organic transistors (channel length 30 nm) were fabricated, with a self-assembled monolayer as gate insulator. The carrier transport in these transistors, as a function of the channel length, was investigated, and a transition from a dispersive to a ballistic transport at a channel length of 200 nm was observed. On a molecular scale, alkyl monolayers functionalized at their omega-ends by aromatic moieties were prepared. A high anisotropic conductivity in molecular insulator/semiconductor heterostructures of monolayer thickness was observed. These molecular architectures provide a basis for the building blocks of molecular transistors.

  11. Transfection efficiency of chitosan and thiolated chitosan in retinal pigment epithelium cells: A comparative study

    PubMed Central

    Oliveira, Ana V.; Silva, Andreia P.; Bitoque, Diogo B.; Silva, Gabriela A.; Rosa da Costa, Ana M.

    2013-01-01

    OBJECTIVE: Gene therapy relies on efficient vector for a therapeutic effect. Efficient non-viral vectors are sought as an alternative to viral vectors. Chitosan, a cationic polymer, has been studied for its gene delivery potential. In this work, disulfide bond containing groups were covalently added to chitosan to improve the transfection efficiency. These bonds can be cleaved by cytoplasmic glutathione, thus, releasing the DNA load more efficiently. MATERIALS AND METHODS: Chitosan and thiolated chitosan nanoparticles (NPs) were prepared in order to obtain a NH3+:PO4− ratio of 5:1 and characterized for plasmid DNA complexation and release efficiency. Cytotoxicity and gene delivery studies were carried out on retinal pigment epithelial cells. RESULTS: In this work, we show that chitosan was effectively modified to incorporate a disulfide bond. The transfection efficiency of chitosan and thiolated chitosan varied according to the cell line used, however, thiolation did not seem to significantly improve transfection efficiency. CONCLUSION: The apparent lack of improvement in transfection efficiency of the thiolated chitosan NPs is most likely due to its size increase and charge inversion relatively to chitosan. Therefore, for retinal cells, thiolated chitosan does not seem to constitute an efficient strategy for gene delivery. PMID:23833516

  12. Thiolated tRNAs of Trypanosoma brucei Are Imported into Mitochondria and Dethiolated after Import*

    PubMed Central

    Bruske, Ellen Inga; Sendfeld, Franziska; Schneider, André

    2009-01-01

    All mitochondrial tRNAs in Trypanosoma brucei derive from cytosolic tRNAs that are in part imported into mitochondria. Some trypanosomal tRNAs are thiolated in a compartment-specific manner. We have identified three proteins required for the thio modification of cytosolic tRNAGln, tRNAGlu, and tRNALys. RNA interference-mediated ablation of these proteins results in the cytosolic accumulation non-thio-modified tRNAs but does not increase their import. Moreover, in vitro import experiments showed that both thio-modified and non-thio-modified tRNAGlu can efficiently be imported into mitochondria. These results indicate that unlike previously suggested the cytosol-specific thio modifications do not function as antideterminants for mitochondrial tRNA import. Consistent with these results we showed by using inducible expression of a tagged tRNAGlu that it is mainly the thiolated form that is imported in vivo. Unexpectedly, the imported tRNA becomes dethiolated after import, which explains why the non-thiolated form is enriched in mitochondria. Finally, we have identified two genes required for thiolation of imported tRNATrp whose wobble nucleotide is subject to mitochondrial C to U editing. Interestingly, down-regulation of thiolation resulted in an increase of edited tRNATrp but did not affect growth. PMID:19875444

  13. Formulation and In Vitro Characterization of Thiolated Buccoadhesive Film of Fluconazole.

    PubMed

    Naz, Kiran; Shahnaz, Gul; Ahmed, Naveed; Qureshi, Naveeda Akhtar; Sarwar, Hafiz Shoaib; Imran, Muhammad; Khan, Gul Majid

    2016-08-10

    The present work is focused on the development of thiolated film for fluconazole buccal delivery. To this end, unmodified polymers chitosan and sodium carboxymethylcellulose (NaCMC) backbone was covalently modified by thioglycolic acid (TGA) and cysteine, respectively. The thiolated buccoadhesive film was evaluated in terms of thickness, weight uniformity, water-uptake capacity, drug content, and release patterns. Moreover, mucoadhesion profile was investigated on buccal mucosa. The resulting chitosan-TGA and NaCMC-cysteine conjugates displayed 171 ± 13 and 380 ± 19 μmol thiol groups per gram of polymer (mean ± SD; n = 3), respectively. The water binding capacity of the thiolated film was significantly ∼2-fold higher (p < 0.05) as compared to unmodified film. The obtained thiolated film displayed 5.8-fold higher mucoadhesive properties compared with corresponding film. Controlled release of drugs from film was observed over 8 h. The transport of fluconazole across excised buccal mucosa was enhanced up to 17-fold in comparison with fluconazole applied in buffer. Based on these findings, thiolated film seems to be promising for fluconazole buccal delivery.

  14. Direct synthesis of thiolate-protected gold nanoparticles using Bunte salts as ligand precursors: investigations of ligand shell formation and core growth

    NASA Astrophysics Data System (ADS)

    Lohse, Samuel E.

    2011-12-01

    Applications of ligand-protected nanoparticles have increased markedly in recent years, yet their controlled synthesis remains an under-developed field. Nanoparticle syntheses are highly specialized in their execution and often possess significant limitations. For example, the synthesis of thiol-stabilized gold nanoparticles (AuNPs) with core diameters greater than 5.0 nm is difficult to achieve using existing methods. This dissertation describes the development of a synthetic strategy for thiolate-stabilized AuNPs over a wide range of core sizes using alkyl thiosulfates (Bunte salts) as ligand precursors. The use of Bunte salts permits the synthesis of larger AuNPs than can be achieved using thiols by allowing the AuNP cores to grow to larger diameters before the formation of the thiolate ligand shell. Chapter II details the development of a direct synthesis strategy using Bunte salts as ligand precursors that produces AuNPs with diameters up to 20 nm. Chapter III describes an investigation of the ligand shell formation that occurs during these syntheses. The ligand shell formation involves the adsorption of the Bunte salt to the AuNP surface, where it is converted to the thiolate. This conversion requires an excess of sodium borohydride in the synthesis of >5 nm AuNPs, but not for the synthesis of smaller AuNPs. This synthetic strategy was adapted for use in flow reactors to attain simultaneous AuNP synthesis and characterization. Chapter IV demonstrates that thiol-stabilized AuNPs can be synthesized in a microfluidic device with product monitoring provided by UV-vis absorbance spectroscopy. The development of a capillary flow reactor that permits the incorporation of new monitoring techniques is presented in Chapter V. The incorporation of Small-Angle X-ray Scattering (SAXS) analysis provides quantitative in situ determinations of AuNP diameter. The combination of synthetic control and monitoring makes capillary flow reactors powerful tools for optimization of

  15. Redox regulation by reversible protein S-thiolation in bacteria

    PubMed Central

    Loi, Vu Van; Rossius, Martina; Antelmann, Haike

    2015-01-01

    Low molecular weight (LMW) thiols function as thiol-redox buffers to maintain the reduced state of the cytoplasm. The best studied LMW thiol is the tripeptide glutathione (GSH) present in all eukaryotes and Gram-negative bacteria. Firmicutes bacteria, including Bacillus and Staphylococcus species utilize the redox buffer bacillithiol (BSH) while Actinomycetes produce the related redox buffer mycothiol (MSH). In eukaryotes, proteins are post-translationally modified to S-glutathionylated proteins under conditions of oxidative stress. S-glutathionylation has emerged as major redox-regulatory mechanism in eukaryotes and protects active site cysteine residues against overoxidation to sulfonic acids. First studies identified S-glutathionylated proteins also in Gram-negative bacteria. Advances in mass spectrometry have further facilitated the identification of protein S-bacillithiolations and S-mycothiolation as BSH- and MSH-mixed protein disulfides formed under oxidative stress in Firmicutes and Actinomycetes, respectively. In Bacillus subtilis, protein S-bacillithiolation controls the activities of the redox-sensing OhrR repressor and the methionine synthase MetE in vivo. In Corynebacterium glutamicum, protein S-mycothiolation was more widespread and affected the functions of the maltodextrin phosphorylase MalP and thiol peroxidase (Tpx). In addition, novel bacilliredoxins (Brx) and mycoredoxins (Mrx1) were shown to function similar to glutaredoxins in the reduction of BSH- and MSH-mixed protein disulfides. Here we review the current knowledge about the functions of the bacterial thiol-redox buffers glutathione, bacillithiol, and mycothiol and the role of protein S-thiolation in redox regulation and thiol protection in model and pathogenic bacteria. PMID:25852656

  16. Design and synthesis of a novel cationic thiolated polymer.

    PubMed

    Rahmat, Deni; Sakloetsakun, Duangkamon; Shahnaz, Gul; Perera, Glen; Kaindl, Reinhard; Bernkop-Schnürch, Andreas

    2011-06-15

    The purpose of this study was to design and characterize a novel cationic thiolated polymer. In this regard a hydroxyethylcellulose-cysteamine conjugate (HEC-cysteamine) was synthesized. Oxidative ring opening with periodate and reductive amination with cysteamine were performed in order to immobilize free thiol groups to HEC. The resulting HEC-cysteamine displayed 2035 ± 162 μmol immobilized free thiol groups and 185 ± 64 μmol disulfide bonds per gram of polymer being soluble in both acidic and basic conditions. Unlike the unmodified HEC, in case of HEC-cysteamine, a three-fold increase in the viscosity was observed when equal volumes of the polymer were mixed with mucin solution. Tablets based on HEC-cysteamine remained attached on freshly excised porcine mucosa for 8 0h and displayed increased disintegration time of 2h. Swelling behavior of HEC-cysteamine tablets in 0.1M phosphate buffer pH 6.8 indicated swelling ratio of 19 within 8h. In contrast, tablets comprising unmodified HEC detached from the mucosa within few seconds and immediately disintegrated. In addition, they did not exhibit swelling behavior. The transport of rhodamine 123 across freshly excised rat intestine enhanced by a value of approximately 1.6-fold (p-value = 0.0024) in the presence of 0.5% (m/v) HEC-cysteamine as compared to buffer control. Result from cytotoxicity test of HEC-cysteamine applied to Caco-2 cells in concentration of 0.5% (m/v) revealed 82.4 ± 4.60% cell viability. According to these results, HEC-cysteamine seems to be a promising polymer for various pharmaceutical applications especially for intestinal drug delivery.

  17. Thermal stability and molecular ordering of organic semiconductor monolayers: effect of an anchor group.

    PubMed

    Jones, Andrew O F; Knauer, Philipp; Resel, Roland; Ringk, Andreas; Strohriegl, Peter; Werzer, Oliver; Sferrazza, Michele

    2015-06-08

    The thermal stability and molecular order in monolayers of two organic semiconductors, PBI-PA and PBI-alkyl, based on perylene derivatives with an identical molecular structure except for an anchor group for attachment to the substrate in PBI-PA, are reported. In situ X-ray reflectivity measurements are used to follow the stability of these monolayers in terms of order and thickness as temperature is increased. Films have thicknesses corresponding approximately to the length of one molecule; molecules stand upright on the substrate with a defined structure. PBI-PA monolayers have a high degree of order at room temperature and a stable film exists up to 250 °C, but decomposes rapidly above 300 °C. In contrast, stable physisorbed PBI-alkyl monolayers only exist up to 100 °C. Above the bulk melting point at 200 °C no more order exists. The results encourage using anchor groups in monolayers for various applications as it allows enhanced stability at the interface with the substrate. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Outlook for the U. S. alkylation industry

    SciTech Connect

    Felten, J.R.; Bradshaw, T.; McCarthy, K. )

    1994-01-01

    Alkylation has long been recognized in the refining industry as one of the best options to convert refinery olefins into valuable, clean, high octane blending components. In fact, refinery alkylation is a preferred source of blending stocks for reformulated gasoline. However, the hydrofluoric acid (HF) alkylation process and, to a lesser extent, the sulfuric acid (SA) process have come under increasing pressure in the US due to safety and environmental concerns. This paper examines the current outlook for the US alkylation industry including: key trends and driving forces in the industry, the impact of environmental issues on both HF and SA alkylation, US alkylation supply/demand forecast including the outlook for oxygenates, how US refines will respond to the increased demand and restricted supply for alkylates, and the outlook for new solid acid alkylation (SAC) technology.

  19. Total synthesis of alkyl citrate natural products.

    PubMed

    Rizzacasa, Mark A; Sturgess, Dayna

    2014-03-07

    This review highlights the synthesis of members of the alkyl citrate family of natural products. The focus is on the stereoselective construction of the alkyl citrate moiety common to these compounds.

  20. Possible mechanism of generation of nitrite and non-thiolate nitroso compounds in blood plasma during inflammatory processes.

    PubMed

    Titov, V Yu; Boldyrikhin, V S; Ivanova, A V; Osipov, A N

    2014-08-01

    Generation of nitrite (NO2¯) and non-thiolate nitroso compounds in human blood during leukocyte activation mainly occurred due to destruction of NO donors in the plasma, but not due to intensification of NO synthesis. We proposed a mechanism of production of nitrite and non-thiolate nitroso compounds in the blood during inflammation.

  1. Electronic structure of thiolate-covered gold nanoparticles: Au102(MBA)44.

    PubMed

    Li, Yan; Galli, Giulia; Gygi, François

    2008-09-23

    We present first principles, density functional theory (DFT) calculations of the structural and electronic properties of thiolate-protected gold nanoparticles [Au(102)(MBA)(44) ] that have been recently crystallized and measured by X-ray diffraction. Our calculations yield structural properties in very good agreement with experiment and reveal the impact of thiolate adsorption on both the surface geometry and the electronic structure of the gold core; in particular, within DFT we observe the emergence of an energy gap of about 0.5 eV, upon MBA adsorption. Using a localized orbital analysis, we characterize the electron distribution in the nanoparticle and provide insight into the bonding of thiolates on curved gold surfaces.

  2. Synthesis of mucoadhesive thiolated gelatin using a two-step reaction process.

    PubMed

    Duggan, Sarah; O'Donovan, Orla; Owens, Eleanor; Cummins, Wayne; Hughes, Helen

    2015-04-01

    Using a novel two-step approach, the thiolation of gelatin for mucoadhesive drug delivery has been achieved. The initial step involved the amination of native gelatin via an amine to carboxylic acid coupling reaction with ethylene diamine, followed by thiolation with Traut's reagent. The resulting thiolated product showed an increase in thiol content of up to 10-fold in comparison with control gelatin samples. Improved cohesion and mucoadhesion in comparison with unmodified and control gelatin samples was also observed. This reaction process was observed to be influenced by both the temperature and the pH of the amination reaction, affecting both amine content and product yield. Swelling ability, cohesion and mucoadhesion were all observed to be strongly dependent on the thiol content of the samples but also, importantly, the molecular weight (MW) of the gelatin used. Gelatin with a MW of 20-25 kDa proved to be optimal in creating this novel mucoadhesive gelatin material.

  3. Chichibabin-type direct alkylation of pyridyl alcohols with alkyl lithium reagents.

    PubMed

    Jeffrey, Jenna L; Sarpong, Richmond

    2012-11-02

    Direct C(6) alkylation of pyridyl alcohols can be achieved following an initial deprotonation of the hydroxy group. This transformation, which is believed to occur by a Chichibabin-type alkylation, avoids lateral deprotonation prior to pyridine ring alkylation and gives increased regioselectivity for C(6) over C(4) alkylation.

  4. Refiners discuss HF alkylation process and issues

    SciTech Connect

    Not Available

    1992-04-06

    Safety and oxygenate operations made HF alkylation a hot topic of discussion at the most recent National Petroleum Refiners Association annual question and answer session on refining and petrochemical technology. This paper provides answers to a variety of questions regarding the mechanical, process, and safety aspects of the HF alkylation process. Among the issues discussed were mitigation techniques, removal of oxygenates from alkylation unit feed, and amylene alkylation.

  5. 40 CFR 721.9892 - Alkylated urea.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Alkylated urea. 721.9892 Section 721... Alkylated urea. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as an alkylated urea (PMN P-93-1649) is subject to reporting under this...

  6. 40 CFR 721.9892 - Alkylated urea.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alkylated urea. 721.9892 Section 721... Alkylated urea. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as an alkylated urea (PMN P-93-1649) is subject to reporting under this...

  7. 40 CFR 721.9892 - Alkylated urea.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Alkylated urea. 721.9892 Section 721... Alkylated urea. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as an alkylated urea (PMN P-93-1649) is subject to reporting under this...

  8. 40 CFR 721.9892 - Alkylated urea.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Alkylated urea. 721.9892 Section 721... Alkylated urea. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as an alkylated urea (PMN P-93-1649) is subject to reporting under this...

  9. 40 CFR 721.9892 - Alkylated urea.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Alkylated urea. 721.9892 Section 721... Alkylated urea. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as an alkylated urea (PMN P-93-1649) is subject to reporting under this...

  10. Staple Fitness: A Concept to Understand and Predict the Structures of Thiolated Gold Nanoclusters

    SciTech Connect

    Jiang, Deen

    2011-01-01

    A profound connection has been found between the structures of thiolated gold clusters and the combinatorial problem of pairing up dots on a surface. The bridge is the concept of staple fitness: the fittest combination corresponds to the experimental structure. This connection has been demonstrated for both Au{sub 25}(SR){sub 18} and Au{sub 38}(SR){sub 24} (-SR being a thiolate group) and applied to predict a promising structure for the recently synthesized Au{sub 19}(SR){sub 13}.

  11. The effect of thiolated phospholipids on formation of supported lipid bilayers on gold substrates investigated by surface-sensitive methods.

    PubMed

    Kılıç, Abdulhalim; Fazeli Jadidi, M; Özer, Hakan Özgür; Kök, Fatma Neşe

    2017-09-08

    Most of the model lipid membrane studies on gold involve the usage of various surface-modification strategies to rupture liposomes and induce lipid bilayer formation since liposomes with polar surfaces do not interact with bare, hydrophobic gold. In this study, a thiol-modified phospholipid, 1,2-Dipalmitoyl-sn-Glycero-3-Phosphothioethanol (DPPTE) was incorporated into phosphatidylcholine (PC) based liposomes to form supported lipid bilayer (SLB) on gold surfaces without further modification. The binding kinetics of liposomes with different DPPTE ratio (0.01 to 100%mol/mol) and diameters were monitored by Quartz Crystal Microbalance with Dissipation (QCM-D). The dissipation change per frequency change, i.e. acoustic ratio, which is evaluated as a degree of the viscoelasticity, considerably decreased with the presence of DPPTE (from 162.3GHz(-1) for flattened PC liposomes to ca. 89.5GHz(-1) for 100% DPPTE liposomes) when compared to the results of two reference rigid monolayers and two viscoelastic layers. To assess the quality of SLB platform, the interpretation of QCM-D data was also complemented with Surface Plasmon Resonance. The optimum thiolated-lipid ratio (1%, lower thiol ratio and higher rigidity) was then used to determine the dry-lipid mass deposition, the water content and the thickness values of the SLB via viscoelastic modelling. Further surface characterization studies were performed by Atomic Force Microscopy with high spatial resolution. The results suggested that model membrane was almost continuous with minimum defects but showed more dissipative/soft nature compared to an ideal bilayer due to partially fused liposomes/overlapped lipid bilayers/multilayer islands. These local elevations distorted the planarity and led the increase of overall membrane thickness to ∼7.0nm. Copyright © 2017 Elsevier B.V. All rights reserved.

  12. Attaching Thiolated Superconductor Grains on Gold Surfaces for Nanoelectronics Applications

    NASA Astrophysics Data System (ADS)

    De Los Santos Valladares, Luis; Bustamante Dominguez, Angel; Llandro, Justin; Suzuki, Seiichi; Mitrelias, Thanos; Bellido Quispe, Richard; Barnes, Crispin H. W.; Majima, Yutaka

    2010-09-01

    We report that the high critical temperature superconductor (HTCS) LaCaBaCu3O7 in the form of nanograins can be linked to Au(111) surfaces through self assembled monolayers (SAMs) of HS-C8H16-HS [octane (di)thiol]. We show that La1113 particles (100 nm mean diameter) can be functionalized by octane (di)thiol without affecting their superconducting critical temperature (TC=80 K). X-ray photoemission spectroscopy (XPS) analysis reveals that the thiol functional heads link the superconducting grain surfaces creating sulfonates and we deduce that bonding between the S atoms and Cu(1) atoms of the La1113 structure would be formed. We suggest a design for a superconducting transistor fabricated by immobilized La1113 nanograins in between two gold electrodes which could be controlled by an external magnetic field gate.

  13. Recycle of tin thiolate compounds relevant to ammonia-borane regeneration.

    PubMed

    Sutton, Andrew D; Davis, Benjamin L; Bhattacharyya, Koyel X; Ellis, Bobby D; Gordon, John C; Power, Philip P

    2010-01-07

    The use of benzenedithiol as a digestant for ammonia-borane spent fuel has been shown to result in tin thiolate compounds which we demonstrate can be recycled, yielding Bu(3)SnH and ortho-benzenedithiol for reintroduction to the ammonia-borane regeneration scheme.

  14. Thiolated polycarbophil as an adjuvant for permeation enhancement in nasal delivery of antisense oligonucleotides.

    PubMed

    Vetter, A; Martien, R; Bernkop-Schnürch, A

    2010-03-01

    The purpose of this study was to investigate the effect of thiolated polycarbophil as an adjuvant to enhance the permeation and improve the stability of a phosphorothioate antisense oligonucleotide (PTO-ODN) on the nasal mucosa. Polycarbophil-cysteine (PCP-Cys) was synthesized by the covalent attachment of L-cysteine to the polymeric backbone. Cytotoxicity tests were examined on human nasal epithelial cells from surgery of nasal polyps confirmed by histological studies. Deoxyribonuclease I activity in respiratory region of the porcine nasal cavity was analyzed by an enzymatic assay. The enzymatic degradation of PTO-ODNs on freshly excised porcine nasal mucosa was analyzed and protection of PCP-cysteine toward DNase I degradation was evaluated. Permeation studies were performed in Ussing-type diffusion chambers. PCP-Cys/GSH did not arise a remarkable mortal effect. Porcine respiratory mucosa was shown to possess nuclease activity corresponding to 0.69 Kunitz units/mL. PTO-ODNs were degraded by incubation with nasal mucosa. In the presence of 0.45% thiolated polycarbophil and 0.5% glutathione (GSH), this degradation process could be lowered. In the presence of thiolated polycarbophil and GSH the uptake of PTO-ODNs from the nasal mucosa was 1.7-fold improved. According to these results thiolated polycarbophil/GSH might be a promising excipient for nasal administration of PTO-ODNs.

  15. Development and evaluation of buccoadhesive tablet for selegiline hydrochloride based on thiolated polycarbophil.

    PubMed

    Wasnik, Mangesh N; Godse, Rutika D; Nair, Hema A

    2014-05-01

    Selegiline hydrochloride (SHCl), a monoamine oxidase B inhibitor, is used as an adjunct in the therapy of Parkinson's disease. This study is concerned with the preparation and evaluation of mucoadhesive buccal tablet for controlled systemic delivery of SHCl. Buccal absorption of selegiline can bypass its first-pass metabolism and improve bioavailability accompanied by greatly reduced metabolite formation, which is potentially of enhanced therapeutic value in patients with Parkinson's disease. Polycarbophil-cysteine (PCP-cys) conjugate, which is a thiolated derivative of the mucoadhesive polymer polycarbophil, was synthesized by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride-mediated amide bond coupling. Tablets of SHCl based on native and thiolated polycarbophil were prepared. The prepared tablets were evaluated for drug content, swelling behavior, mucoadhesive strength, in vitro drug release, ex vivo permeation and in vitro cytotoxicity. PCP-cys tablets showed enhanced mucoadhesion and retarded drug release compared to polycarbophil tablets. Permeation data of SHCl from matrices prepared using the PCP-cys polymer revealed a significantly higher value of apparent permeability in comparison to polycarbophil, which supported the information in literature that thiolation imparts permeation enhancing properties to mucoadhesive polymers. In vitro cytotoxicity studies on PCP-cys using L-929 mouse fibroblast cell line indicated that conjugation with cysteine does not impart any apparent toxicity to polycarbophil. The results from the study indicate that the buccal delivery of SHCl using thiolated polycarbophil tablet could provide a way for improved therapy of Parkinson's disease.

  16. Effect of a thiolated polymer on oral paclitaxel absorption and tumor growth in rats.

    PubMed

    Föger, Florian; Malaivijitnond, Suchinda; Wannaprasert, Thanakul; Huck, Christian; Bernkop-Schnürch, Andreas; Werle, Martin

    2008-02-01

    The anticancer agent paclitaxel is currently commercially available only as an infusion due to its low oral bioavailability. An oral formulation would be highly beneficial for patients. Besides the low solubility, the main reason for the limited oral bioavailability of paclitaxel is that it is a substrate of the efflux pump P-glycoprotein (P-gp). Recently, it has been demonstrated that P-gp can be inhibited by thiolated polymers. In this study, an oral paclitaxel formulation based on thiolated polycarbophil was evaluated in vivo in wild-type rats and in mammary cancer-induced rats. The paclitaxel plasma level after a single administration of paclitaxel was observed for 12 h in healthy rats. Moreover, cancer-induced rats were treated weekly for 5 weeks with the novel formulation. It was demonstrated that (1) co-administration of thiolated polycarbophil significantly improved paclitaxel plasma levels, (2) a more constant pharmacokinetic profile could be achieved and (3) the tumor growth was reduced. These effects can most likely be attributed to P-gp inhibition. According to the achieved results, thiolated polymers are believed to be interesting tools for the delivery of P-gp substrates such as paclitaxel.

  17. A complex thiolate switch regulates the Bacillus subtilis organic peroxide sensor OhrR.

    PubMed

    Lee, Jin-Won; Soonsanga, Sumarin; Helmann, John D

    2007-05-22

    Oxidation of protein thiolates is central to numerous redox-regulated processes. Bacillus subtilis OhrR is an organic peroxide sensor that represses expression of an inducible peroxiredoxin, OhrA. Here, we present evidence that oxidation of the sole cysteine residue in OhrR leads to a sulfenic acid-containing intermediate that retains DNA-binding activity: further reaction to generate either a mixed disulfide (S-thiolation) or a protein sulfenamide (sulfenyl-amide) derivative is essential for derepression. Protein S-thiolation protects OhrR from overoxidation and provides for a facile regeneration of active OhrR by thiol-disulfide exchange reactions. The sulfenamide can also be reduced by thiol-disulfide exchange reactions, although this process is much slower than for mixed disulfides. Recovery of oxidized OhrR from B. subtilis identifies three distinct S-thiolated species, including mixed disulfides with a novel 398-Da thiol, cysteine, and CoASH. Evidence for in vivo formation of the sulfenamide derivative is also presented.

  18. In vivo evaluation of thiolated chitosan tablets for oral insulin delivery.

    PubMed

    Millotti, Gioconda; Laffleur, Flavia; Perera, Glen; Vigl, Claudia; Pickl, Karin; Sinner, Frank; Bernkop-Schnürch, Andreas

    2014-10-01

    Chitosan-6-mercaptonicotinic acid (chitosan-6-MNA) is a thiolated chitosan with strong mucoadhesive properties and a pH-independent reactivity. This study aimed to evaluate the in vivo potential for the oral delivery of insulin. The comparison of the nonconjugated chitosan and chitosan-6-MNA was performed on several studies such as mucoadhesion, release, and in vivo studies. Thiolated chitosan formulations were both about 80-fold more mucoadhesive compared with unmodified ones. The thiolated chitosan tablets showed a sustained release for 5 h for the polymer of 20 kDa and 8 h for the polymer of 400 kDa. Human insulin was quantified in rats' plasma by means of ELISA specific for human insulin with no cross-reactivity with the endogenous insulin. In vivo results showed thiolation having a tremendous impact on the absorption of insulin. The absolute bioavailabilities were 0.73% for chitosan-6-MNA of 20 kDa and 0.62% for chitosan-6-MNA 400 kDa. The areas under the concentration-time curves (AUC) of chitosan-6-MNA formulations compared with unmodified chitosan were 4.8-fold improved for the polymer of 20 kDa and 21.02-fold improved for the polymer of 400 kDa. The improvement in the AUC with regard to the most promising aliphatic thiomer was up to 6.8-fold. Therefore, chitosan-6-MNA represents a promising excipient for the oral delivery of insulin.

  19. From thioether substituted porphyrins to sulfur linked porphyrin dimers: an unusual SNAr via thiolate displacement?

    PubMed

    Ryan, Aoife A; Plunkett, Shane; Casey, Aoife; McCabe, Thomas; Senge, Mathias O

    2014-01-11

    Treatment of meso 2-ethylhexyl-3-mercaptopropionate substituted porphyrins with base at room temperature generated a porphyrin thiolate anion which in situ reacted in a nucleophilic aromatic substitution (SNAr) reaction with remaining thioether derivative. This reaction yielded S-linked bisporphyrins in good yields, with mechanistic insight obtained via displacement reactions. Additionally, SNAr of the thioether chain was achieved using S- and organolithium nucleophiles.

  20. Development and optimization of thiolated dendrimer as a viable mucoadhesive excipient for the controlled drug delivery: an acyclovir model formulation.

    PubMed

    Yandrapu, Sarath K; Kanujia, Parijat; Chalasani, Kishore B; Mangamoori, Lakshminarasu; Kolapalli, Ramanamurthy V; Chauhan, Abhay

    2013-05-01

    In the present study we report the development of novel thiolated dendrimers for mucoadhesive drug delivery. The thiolated dendrimers were synthesized by conjugating PAMAM dendrimer (G3.5)with cysteamine at two different molar ratios, i.e. 1:30 (DCys1) and 1:60 (DCys2). The thiolated dendrimers were further encapsulated with acyclovir (DCys1Ac and DCys2Ac) and the conjugates were characterized for thiol content, drug loading, drug release, and mucoadhesive behavior. The thiolated dendrimer conjugates showed thiol content of 10.56 ± 0.34 and 68.21 ± 1.84 μM/mg of the conjugate for DCys1 and DCys2, respectively. The acyclovir loading was observed to be highest in dendrimer drug conjugate (DAc) compared to other DCys1Ac and DCys2Ac conjugates. The thiolated dendrimers showed sustained release of acyclovir and showed higher mucoadhesion. The in vitro mucoadhesive activity of DCys2Ac was 1.53 and 2.89 fold higher mucoadhesion compared to DCys1Ac and DAc, respectively. These results demonstrated the usefulness of thiolated dendrimers as a mucoadhesive carrier and represent a novel platform for drug delivery. This study demonstrates the utility of thiolated dendrimers as mucoadhesive carriers as reported in an acyclovir delivery model system. Copyright © 2013 Elsevier Inc. All rights reserved.

  1. Unraveling a generic growth pattern in structure evolution of thiolate-protected gold nanoclusters

    NASA Astrophysics Data System (ADS)

    Xu, Wen Wu; Li, Yadong; Gao, Yi; Zeng, Xiao Cheng

    2016-03-01

    Precise control of the growth of thiolate-protected gold nanoclusters is a prerequisite for their applications in catalysis and bioengineering. Here, we bring to bear a new series of thiolate-protected nanoclusters with a unique growth pattern, i.e., Au20(SR)16, Au28(SR)20, Au36(SR)24, Au44(SR)28, and Au52(SR)32. These nanoclusters can be viewed as resulting from the stepwise addition of a common structural motif [Au8(SR)4]. The highly negative values of the nucleus-independent chemical shift (NICS) in the center of the tetrahedral Au4 units suggest that the overall stabilities of these clusters stem from the local stability of each tetrahedral Au4 unit. Generalization of this growth-pattern rule to large-sized nanoclusters allows us to identify the structures of three new thiolate-protected nanoclusters, namely, Au60(SR)36, Au68(SR)40, and Au76(SR)44. Remarkably, all three large-sized nanoclusters possess relatively large HOMO-LUMO gaps and negative NICS values, suggesting their high chemical stability. Further extension of the growth-pattern rule to the infinitely long nanowire limit results in a one-dimensional (1D) thiolate-protected gold nanowire (RS-AuNW) with a band gap of 0.78 eV. Such a unique growth-pattern rule offers a guide for precise synthesis of a new class of large-sized thiolate-protected gold nanoclusters or even RS-AuNW which, to our knowledge, has not been reported in the literature.Precise control of the growth of thiolate-protected gold nanoclusters is a prerequisite for their applications in catalysis and bioengineering. Here, we bring to bear a new series of thiolate-protected nanoclusters with a unique growth pattern, i.e., Au20(SR)16, Au28(SR)20, Au36(SR)24, Au44(SR)28, and Au52(SR)32. These nanoclusters can be viewed as resulting from the stepwise addition of a common structural motif [Au8(SR)4]. The highly negative values of the nucleus-independent chemical shift (NICS) in the center of the tetrahedral Au4 units suggest that the overall

  2. Methods of making alkyl esters

    DOEpatents

    Elliott, Brian

    2010-08-03

    A method comprising contacting an alcohol, a feed comprising one or more glycerides and equal to or greater than 2 wt % of one or more free fatty acids, and a solid acid catalyst, a nanostructured polymer catalyst, or a sulfated zirconia catalyst in one or more reactors, and recovering from the one or more reactors an effluent comprising equal to or greater than about 75 wt % alkyl ester and equal to or less than about 5 wt % glyceride.

  3. Au₂₅(SEt)₁₈, a nearly naked thiolate-protected Au₂₅ cluster: structural analysis by single crystal X-ray crystallography and electron nuclear double resonance.

    PubMed

    Dainese, Tiziano; Antonello, Sabrina; Gascón, José A; Pan, Fangfang; Perera, Neranjan V; Ruzzi, Marco; Venzo, Alfonso; Zoleo, Alfonso; Rissanen, Kari; Maran, Flavio

    2014-04-22

    X-ray crystallography has been fundamental in discovering fine structural features of ultrasmall gold clusters capped by thiolated ligands. For still unknown structures, however, new tools capable of providing relevant structural information are sought. We prepared a 25-gold atom nanocluster protected by the smallest ligand ever used, ethanethiol. This cluster displays the electrochemistry, mass spectrometry, and UV-vis absorption spectroscopy features of similar Au25 clusters protected by 18 thiolated ligands. The anionic and the neutral form of Au25(SEt)18 were fully characterized by (1)H and (13)C NMR spectroscopy, which confirmed the monolayer's properties and the paramagnetism of neutral Au25(SEt)18(0). X-ray crystallography analysis of the latter provided the first known structure of a gold cluster protected by a simple, linear alkanethiolate. Here, we also report the direct observation by electron nuclear double resonance (ENDOR) of hyperfine interactions between a surface-delocalized unpaired electron and the gold atoms of a nanocluster. The advantages of knowing the exact molecular structure and having used such a small ligand allowed us to compare the experimental values of hyperfine couplings with DFT calculations unaffected by structure's approximations or omissions.

  4. Cell line-dependent cytotoxicity of poly(isobutylcyanoacrylate) nanoparticles coated with chitosan and thiolated chitosan: Insights from cultured human epithelial HeLa, Caco2/TC7 and HT-29/MTX cells.

    PubMed

    Pradines, Bénédicte; Lievin-Le Moal, Vanessa; Vauthier, Christine; Ponchel, Gilles; Loiseau, Philippe M; Bouchemal, Kawthar

    2015-08-01

    Nanoparticles composed of poly(isobutylcyanoacrylate) core coated with a mixture of chitosan and thiolated chitosan have already shown promising results in terms of mucoadhesion and permeation enhancement properties of pharmaceutical active drugs delivered via mucosal routes. In the present work, the cytotoxicity of these nanoparticles was first investigated using direct contact assay on undifferentiated human cervix epithelial HeLa cells. The results showed strong toxicity in HeLa cells for the two investigated concentrations 25 and 50 μg/mL. The cytotoxic effect was mainly attributed to the poly(isobutylcyanoacrylate) core since no significant differences in nanoparticle cytotoxicity were reported when nanoparticle shell composition was modified by adding chitosan or thiolated chitosan. In contrast, lower nanoparticle toxicity was reported using human fully-differentiated enterocyte-like Caco-2/TC7, and fully-differentiated mucus-secreting HT-29/MTX cells forming monolayer in culture mimicking an intestinal epithelial barrier. This study demonstrated that the toxicity of poly(isobutylcyanoacrylate) nanoparticles is highly cell line-dependent.

  5. PREPARATION OF ALKYL PYROPHOSPHATE EXTRACTANTS

    DOEpatents

    Levine, C.A.; Skiens, W.E.; Moore, G.R.

    1960-08-01

    A process for providing superior solvent extractants for metal recovery processes is given wherein the extractant comprises an alkyl pyrophosphoric acid ester dissolved in an organic solvent diluent. Finely divided solid P/sub 2/O/ sub 5/ is slurried in an organic solvent-diluent selected from organic solvents such as kerosene, benzene, chlorobenzene, toluene, etc. An alcohol selected from the higher alcohols having 4 to 17 carbon atoms. e.g.. hexanol-1. heptanol-3, octanol-1. 2.6-dimethyl-heptanol-4, and decanol-1, is rapidly added to the P/sub 2/O/sub 5/ slurry in the amount of about 2 moles of alcohol to 1 mole of P/sub 2/ O/sub 5/. The temperature is maintained below about 110 deg C during the course of the P/sub 2/O/sub 5/-alcohol reaction. An alkyl pyrophosphate extractant compound is formed as a consequence of the reaction process. The alkyl pyrophosphate solvent-diluent extractant phase is useful in solvent extraction metal recovery processes.

  6. Iron-Catalyzed Decarboxylative Alkyl Etherification of Vinylarenes with Aliphatic Acids as the Alkyl Source.

    PubMed

    Jian, Wujun; Ge, Liang; Jiao, Yihang; Qian, Bo; Bao, Hongli

    2017-03-20

    Because of the lack of effective alkylating reagents, alkyl etherification of olefins with general alkyl groups has not been previously reported. In this work, a variety of alkyl diacyl peroxides and peresters generated from aliphatic acids have been found to enable the first iron-catalyzed alkyl etherification of olefins with general alkyl groups. Primary, secondary and tertiary aliphatic acids are suitable for this reaction, delivering products with yields up to 97 %. Primary and secondary alcohols react well, affording products in up to 91 % yield.

  7. tRNA thiolation links translation to stress responses in Saccharomyces cerevisiae.

    PubMed

    Damon, Jadyn R; Pincus, David; Ploegh, Hidde L

    2015-01-15

    Although tRNA modifications have been well catalogued, the precise functions of many modifications and their roles in mediating gene expression are still being elucidated. Whereas tRNA modifications were long assumed to be constitutive, it is now apparent that the modification status of tRNAs changes in response to different environmental conditions. The URM1 pathway is required for thiolation of the cytoplasmic tRNAs tGlu(UUC), tGln(UUG), and tLys(UUU) in Saccharomyces cerevisiae. We demonstrate that URM1 pathway mutants have impaired translation, which results in increased basal activation of the Hsf1-mediated heat shock response; we also find that tRNA thiolation levels in wild-type cells decrease when cells are grown at elevated temperature. We show that defects in tRNA thiolation can be conditionally advantageous, conferring resistance to endoplasmic reticulum stress. URM1 pathway proteins are unstable and hence are more sensitive to changes in the translational capacity of cells, which is decreased in cells experiencing stresses. We propose a model in which a stress-induced decrease in translation results in decreased levels of URM1 pathway components, which results in decreased tRNA thiolation levels, which further serves to decrease translation. This mechanism ensures that tRNA thiolation and translation are tightly coupled and coregulated according to need. © 2015 Damon et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

  8. Thiolated polymers: synthesis and in vitro evaluation of polymer-cysteamine conjugates.

    PubMed

    Bernkop-Schnürch, A; Clausen, A E; Hnatyszyn, M

    2001-09-11

    The purpose of the present study was to synthesize and characterize novel thiolated polymers. Mediated by a carbodiimide cysteamine was covalently linked to sodium carboxymethylcellulose (CMC) and polycarbophil (PCP). The resulting CMC-cysteamine conjugates displayed 77.9+/-6.7 and 365.1+/-8.7 micromol thiol groups per gram of polymer, whereas the PCP-cysteamine conjugates showed 26.3+/-1.9 and 122.7+/-3.8 micromol thiol groups per gram of polymer (mean+/-S.D.; n=3). In aqueous solutions above pH 5.0 both modified polymers were capable of forming inter- and/or intra-molecular disulfide bonds. The reaction velocity of this oxidation process was accelerated with a decrease in the proton concentration. The oxidation proceeded more rapidly within thiolated CMC than within thiolated PCP. Permeation studies carried out in Ussing-type chambers with freshly excised intestinal mucosa from guinea pigs utilizing sodium fluorescein as model drug for the paracellular uptake revealed an enhancement ratio (R=P(app) (conjugate)/P(app) (control)) of 1.15 and 1.41 (mean+/-S.D.; n=3) for the higher thiolated CMC-cysteamine (0.5%; m/v) and PCP-cysteamine conjugate (1.0%; m/v), respectively. The decrease in the transepithelial electrical resistance values was in good correlation with the enhancement ratios. Due to a high crosslinking tendency by the formation of disulfide bonds stabilizing drug carrier systems based on thiolated polymers and a permeation enhancing effect, CMC- and PCP-cysteamine conjugates represent promising excipients for the development of novel drug delivery systems.

  9. Stretching of BDT-gold molecular junctions: thiol or thiolate termination?

    NASA Astrophysics Data System (ADS)

    Souza, Amaury De Melo; Rungger, Ivan; Pontes, Renato Borges; Rocha, Alexandre Reily; da Silva, Antônio José Roque; Schwingenschlöegl, Udo; Sanvito, Stefano

    2014-11-01

    It is often assumed that the hydrogen atoms in the thiol groups of a benzene-1,4-dithiol dissociate when Au-benzene-1,4-dithiol-Au junctions are formed. We demonstrate, by stability and transport property calculations, that this assumption cannot be made. We show that the dissociative adsorption of methanethiol and benzene-1,4-dithiol molecules on a flat Au(111) surface is energetically unfavorable and that the activation barrier for this reaction is as high as 1 eV. For the molecule in the junction, our results show, for all electrode geometries studied, that the thiol junctions are energetically more stable than their thiolate counterparts. Due to the fact that density functional theory (DFT) within the local density approximation (LDA) underestimates the energy difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital by several electron-volts, and that it does not capture the renormalization of the energy levels due to the image charge effect, the conductance of the Au-benzene-1,4-dithiol-Au junctions is overestimated. After taking into account corrections due to image charge effects by means of constrained-DFT calculations and electrostatic classical models, we apply a scissor operator to correct the DFT energy level positions, and calculate the transport properties of the thiol and thiolate molecular junctions as a function of the electrode separation. For the thiol junctions, we show that the conductance decreases as the electrode separation increases, whereas the opposite trend is found for the thiolate junctions. Both behaviors have been observed in experiments, therefore pointing to the possible coexistence of both thiol and thiolate junctions. Moreover, the corrected conductance values, for both thiol and thiolate, are up to two orders of magnitude smaller than those calculated with DFT-LDA. This brings the theoretical results in quantitatively good agreement with experimental data.

  10. Approaching the intrinsic photoluminescence linewidth in transition metal dichalcogenide monolayers

    NASA Astrophysics Data System (ADS)

    Ajayi, Obafunso A.; Ardelean, Jenny V.; Shepard, Gabriella D.; Wang, Jue; Antony, Abhinandan; Taniguchi, Takeshi; Watanabe, Kenji; Heinz, Tony F.; Strauf, Stefan; Zhu, X.-Y.; Hone, James C.

    2017-09-01

    Excitonic states in monolayer transition metal dichalcogenides (TMDCs) have been the subject of extensive recent interest. Their intrinsic properties can, however, be obscured due to the influence of inhomogeneity in the external environment. Here we report methods for fabricating high quality TMDC monolayers with narrow photoluminescence (PL) linewidth approaching the intrinsic limit. We find that encapsulation in hexagonal boron nitride (h-BN) sharply reduces the PL linewidth, and that passivation of the oxide substrate by an alkyl monolayer further decreases the linewidth and also minimizes the charged exciton (trion) peak. The combination of these sample preparation methods results in much reduced spatial variation in the PL emission, with a full-width-at-half-maximum as low as 1.7 meV. Analysis of the PL line shape yields a homogeneous width of 1.43  ±  0.08 meV and inhomogeneous broadening of 1.1  ±  0.3 meV.

  11. Approaching the intrinsic photoluminescence linewidth in transition metal dichalcogenide monolayers

    DOE PAGES

    Ajayi, Obafunso A.; Ardelean, Jenny V.; Shepard, Gabriella D.; ...

    2017-07-24

    Excitonic states in monolayer transition metal dichalcogenides (TMDCs) have been the subject of extensive recent interest. Their intrinsic properties can, however, be obscured due to the influence of inhomogeneity in the external environment. Here we report methods for fabricating high quality TMDC monolayers with narrow photoluminescence (PL) linewidth approaching the intrinsic limit. We find that encapsulation in hexagonal boron nitride (h-BN) sharply reduces the PL linewidth, and that passivation of the oxide substrate by an alkyl monolayer further decreases the linewidth and also minimizes the charged exciton (trion) peak. The combination of these sample preparation methods results in much reducedmore » spatial variation in the PL emission, with a full-width-at-half-maximum as low as 1.7 meV. Furthermore, analysis of the PL line shape yields a homogeneous width of 1.43 ± 0.08 meV and inhomogeneous broadening of 1.1 ± 0.3 meV.« less

  12. Thiol-ene immobilisation of carbohydrates onto glass slides as a simple alternative to gold-thiol monolayers, amines or lipid binding.

    PubMed

    Biggs, Caroline I; Edmondson, Steve; Gibson, Matthew I

    2015-01-01

    Carbohydrate arrays are a vital tool in studying infection, probing the mechanisms of bacterial, viral and toxin adhesion and the development of new treatments, by mimicking the structure of the glycocalyx. Current methods rely on the formation of monolayers of carbohydrates that have been chemically modified with a linker to enable interaction with a functionalised surface. This includes amines, biotin, lipids or thiols. Thiol-addition to gold to form self-assembled monolayers is perhaps the simplest method for immobilisation as thiolated glycans are readily accessible from reducing carbohydrates in a single step, but are limited to gold surfaces. Here we have developed a quick and versatile methodology which enables the use of thiolated carbohydrates to be immobilised as monolayers directly onto acrylate-functional glass slides via a 'thiol-ene'/Michael-type reaction. By combining the ease of thiol chemistry with glass slides, which are compatible with microarray scanners this offers a cost effective, but also useful method to assemble arrays.

  13. Comparative study of decyl thiocyanate and decanethiol self-assembled monolayers on gold substrates

    NASA Astrophysics Data System (ADS)

    Dreesen, L.; Volcke, C.; Sartenaer, Y.; Peremans, A.; Thiry, P. A.; Humbert, C.; Grugier, J.; Marchand-Brynaert, J.

    2006-09-01

    In a recent paper Ciszek et al. [J.W. Ciszek, M.P. Stewart, J.M. Tour, J. Am. Chem. Soc. 126 (2004) 13172] showed that organic thiocyanates may be an interesting alternative to the use of thiols for thiolate assemblies. We use scanning tunnelling microscopy (STM), infrared reflection absorption and sum-frequency generation spectroscopies (IRRAS and SFG) in order to study the adsorption properties of decyl thiocyanates (DTCN) and compare them to the decanethiol (DT) ones. Firstly, IRRAS measurements show that DTCN molecules form self-assembled monolayers (SAMs) on gold via a thiolate link with the metallic substrate. Secondly, the DTCN SAM on gold is less ordered than the DT one as highlighted by SFG spectroscopy. Indeed, the intensities of the methyl vibration modes vanish while the methylene ones increase when DTCN molecules are adsorbed on the substrate instead of DT. We explain the differences in SAMs quality on the basis of STM measurements which reveal differences in molecular order and packing.

  14. Homogeneously Mixed Monolayers: Emergence of Compositionally Conflicted Interfaces.

    PubMed

    Marquez, Maria D; Zenasni, Oussama; Jamison, Andrew C; Lee, T Randall

    2017-06-13

    The ability to manipulate interfaces at the nanoscale via a variety of thin-film technologies offers a plethora of avenues for advancing surface applications. These include surfaces with remarkable antibiofouling properties as well as those with tunable physical and electronic properties. Molecular self-assembly is one notably attractive method used to decorate and modify surfaces. Of particular interest to surface scientists has been the thiolate-gold system, which serves as a reliable method for generating model thin-film monolayers that transform the interfacial properties of gold surfaces. Despite widespread interest, efforts to tune the interfacial properties using mixed adsorbate systems have frequently led to phase-separated domains of molecules on the surface with random sizes and shapes depending on the structure and chemical composition of the adsorbates. This feature article highlights newly emerging methods for generating mixed thin-film interfaces, not only to enhance the aforementioned properties of organic thin films, but also to give rise to interfacial compositions never before observed in nature. An example would be the development of monolayers formed from bidentate adsorbates and other unique headgroup architectures that provide the surface bonding stability necessary to allow the assembly of interfaces that expose mixtures of chains that are fundamentally different in character (i.e., either phase-incompatible or structurally dissimilar), producing compositionally "conflicted" interfaces. By also exploring the prior efforts to produce such homogeneously blended interfaces, this feature article seeks to convey the relationships between the methods of film formation and the overall properties of the resulting interfaces.

  15. Organic surfaces exposed by self-assembled organothiol monolayers: Preparation, characterization, and application

    NASA Astrophysics Data System (ADS)

    Kind, Martin; Wöll, Christof

    2009-07-01

    Organic surfaces play a major role in materials science. Most surfaces that we touch in our daily lives are made from organic materials, e.g., vegetables, fruit, skin, wood, and textiles made from natural fibers. In the context of biology, organic surfaces play a prominent role too, proteins docking onto cell surfaces are a good example. To better understand the characteristics of organic surfaces, including physico-chemical properties like wettability or chemical reactivities and physical properties like friction and lubrication, a structurally well-defined model system that can be investigated with numerous analytical techniques is desirable. In the last two decades, one particular system, self-assembled monolayers or SAMs, have demonstrated their suitability for this purpose. In particular, organothiols consisting of an organic molecule with an attached SH-group are well suited to fabricating structurally well-defined adlayers of monolayer thickness on gold substrates using a simple preparation procedure. These ultrathin monolayers expose an organic surface with properties that can be tailored by varying the type of organothiol employed. After a short introduction into the preparation of SAMs, this article provides an overview of the possibilities and limitations of organic surfaces exposed by Au-thiolate SAMs. Applications are as diverse as the metallization of organic surfaces, a fundamental problem in materials science, and the fabrication of surfaces that resist the adsorption of proteins. In addition to a number of different case studies, we will also discuss the most powerful analytical techniques needed to characterize these important model systems.

  16. Ternary surface monolayers for ultrasensitive (zeptomole) amperometric detection of nucleic acid hybridization without signal amplification.

    PubMed

    Wu, Jie; Campuzano, Susana; Halford, Colin; Haake, David A; Wang, Joseph

    2010-11-01

    A ternary surface monolayer, consisting of coassembled thiolated capture probe, mercaptohexanol and dithiothreitol, is shown to offer dramatic improvements in the signal-to-noise characteristics of electrochemical DNA hybridization biosensors based on common self-assembled monolayers. Remarkably low detection limits down to 40 zmol (in 4 μL samples) as well as only 1 CFU Escherichia coli per sensor are thus obtained without any additional amplification step in connection to the commonly used horseradish peroxidase/3,3',5,5'-tetramethylbenzidine system. Such dramatic improvements in the detection limits (compared to those of common binary alkanethiol interfaces and to those of most electrochemical DNA sensing strategies without target or signal amplification) are attributed primarily to the remarkably higher resistance to nonspecific adsorption. This reflects the highly compact layer (with lower pinhole density) produced by the coupling of the cyclic- and linear-configuration "backfillers" that leads to a remarkably low background noise even in the presence of complex sample matrixes. A wide range of surface compositions have been investigated, and the ternary mixed monolayer has been systematically optimized. Detailed impedance spectroscopy and cyclic voltammetric studies shed useful insights into the surface coverage. The impressive sensitivity and high specificity of the simple developed methodology indicate great promise for a wide range of nucleic acid testing, including clinical diagnostics, biothreat detection, food safety, and forensic analysis.

  17. Modulating Electrical Properties of InAs Nanowires via Molecular Monolayers.

    PubMed

    Cheung, Ho-Yuen; Yip, SenPo; Han, Ning; Dong, Goufa; Fang, Ming; Yang, Zai-xing; Wang, Fengyun; Lin, Hao; Wong, Chun-Yuen; Ho, Johnny C

    2015-07-28

    In recent years, InAs nanowires have been demonstrated with the excellent electron mobility as well as highly efficient near-infrared and visible photoresponse at room temperature. However, due to the presence of a large amount of surface states that originate from the unstable native oxide, the fabricated nanowire transistors are always operated in the depletion mode with degraded electron mobility, which is not energy-efficient. In this work, instead of the conventional inorganic sulfur or alkanethiol surface passivation, we employ aromatic thiolate (ArS(-))-based molecular monolayers with controllable molecular design and electron density for the surface modification of InAs nanowires (i.e., device channels) by simple wet chemistry. More importantly, besides reliably improving the device performances by enhancing the electron mobility and the current on-off ratio through surface state passivation, the device threshold voltage (VTh) can also be modulated by varying the para-substituent of the monolayers such that the molecule bearing electron-withdrawing groups would significantly shift the VTh towards the positive region for the enhancement mode device operation, in which the effect has been quantified by density functional theory calculations. These findings reveal explicitly the efficient modulation of the InAs nanowires' electronic transport properties via ArS(-)-based molecular monolayers, which further elucidates the technological potency of this ArS(-) surface treatment for future nanoelectronic device fabrication and circuit integration.

  18. Phase behaviour in binary mixed Langmuir Blodgett monolayers of triglycerides

    NASA Astrophysics Data System (ADS)

    Zdravkova, Aneliya N.; van der Eerden, J. P. J. M.

    2007-09-01

    Binary mixed monolayers of the triglycerides (TAGs)-tripalmitin (PPP), tristearin (SSS) and triarachidin (AAA) at the air-water interface are investigated with the Langmuir method. Langmuir-Blodgett (LB) layers obtained by deposition on mica are investigated by Atomic Force Microscopy. Combining Langmuir and AFM results the relation between the phase behaviour of binary mixed TAGs and their chain length is established. TAG mixtures form monolayers with molecules in trident conformation at the air-water interface, like pure TAGs. The area Acond=63 Å 2 and the pressure πcond=8-10 mN/m that separate "gas" and "condensed" film structures are the same for all mixtures and pure systems. In the π- A isotherms the sharpness of the transition from "gas" to "condensed" phase decreases with the average chain length for all systems. Using AFM data the monolayer thicknesses for mixtures and pure systems is found to be linearly dependent on the average chain length of the TAG molecules. A linear relation between film thickness and applied AFM force is established. The corresponding coefficient K˜ is higher for mixed monolayers ( K˜=0.08±0.01 nN) than for pure systems ( K˜=0.07±0.01 nN). AFM images show phase separation in the systems PPP-SSS and PPP-AAA. The solubility of the shorter PPP molecules in the "long" (SSS- and AAA-rich) phase is significant. For the mixture SSS-AAA, phase separation is not observed. In that mixture the monolayer thickness varies linearly with composition, supporting the conclusion that SSS and AAA mix almost ideally. The main driving force for phase separation is the difference in the alkyl chain length. Indeed PPP-AAA (length difference 4 C atoms) shows the most clear phase separation. The relatively weak phase separation in PPP-SSS and the absence of phase separation in SSS-AAA show that the influence of chain length difference decreases with increasing average chain length. In air PPP-SSS and PPP-AAA mixed monolayers are unstable and

  19. Glycosylated Self-Assembled Monolayers for Arrays and Surface Analysis

    PubMed Central

    Cheng, Fang; Ratner, Daniel M.

    2013-01-01

    Over the past few decades, carbohydrates (glycans) have received growing attention for their many roles in biological systems, including pathogenesis, receptor-ligand interactions, and cell signaling. To unravel the biology of this important category of biomolecules, a host of new tools have been developed for glycomics investigation. At the forefront is the carbohydrate microarray, developed to immobilize functional glycans on a solid substrate to rapidly screen a variety of potential binding partners (carbohydrates, proteins, nucleic acids, cells, and viruses). The essential role played by surface modification on glycan microarray performance requires new methods to rigorously characterize glycan surface chemistries. Due to their highly reproducible nature and well-studied properties, self-assembled monolayers (SAMs) on gold are powerful models for presenting glycans on a solid substrate, engineering biomimetic microenvironments and exploring the bioactivity of immobilized carbohydrates via surface plasmon resonance (SPR). However, it can be challenging to prepare high quality glycosylated SAMs (glyco-SAMs) that retain their biological function following surface immobilization. Herein, a selection of versatile methods for the preparation of glyco-SAMs using natural and chemically modified glycans is described. This chapter will highlight the following three immobilization techniques: (1) direct self assembly using thiolated glycosides onto gold, (2) tethering aminated glycosides onto amine-reactive SAMs, and (3) conjugating natural glycan onto divinyl sulfone-activated SAMs. PMID:22057519

  20. Ordering and defects in self-assembled monolayers on nanoporous gold

    NASA Astrophysics Data System (ADS)

    Patel, Dipna A.; Weller, Andrew M.; Chevalier, Robert B.; Karos, Constantine A.; Landis, Elizabeth C.

    2016-11-01

    Self-assembled monolayers are commonly used to tailor nanoporous structures for applications, and they also provide a model system for determining the effects of nanoscale structure on self-assembly. We have investigated the ordering and defects in alkanethiol self-assembled monolayers on nanoporous gold, a high surface area mesoporous material. Infrared reflection absorption spectroscopy was used to characterize the effects of alkyl chain length and nanoporous gold pore size on molecular layer ordering. Cyclic voltammetry was used to characterize the monolayer density and ordering, with ferrocenylalkylthiolates used to quantify and characterize defect sites. We find that dense and well-ordered molecular layers form quickly with low defect levels. However, we do not observe differences in molecular layer ordering or defects with changes in pore size.

  1. Monolayer patterning using ketone dipoles.

    PubMed

    Kim, Min Kyoung; Xue, Yi; Pašková, Tereza; Zimmt, Matthew B

    2013-08-14

    The self-assembly of multi-component monolayers with designed patterns requires molecular recognition among components. Dipolar interactions have been found to influence morphologies of self-assembled monolayers and can affect molecular recognition functions. Ketone groups have large dipole moments (2.6 D) and are easily incorporated into molecules. The potential of ketone groups for dipolar patterning has been evaluated through synthesis of two 1,5-disubstituted anthracenes bearing mono-ketone side chains, STM characterization of monolayers self-assembled from their single and two component solutions and molecular mechanics simulations to determine their self-assembly energetics. The results reveal that (i) anthracenes bearing self-repulsive mono-ketone side chains assemble in an atypical monolayer morphology that establishes dipolar attraction, instead of repulsion, between ketones in adjacent side chains; (ii) pairs of anthracene molecules whose self-repulsive ketone side chains are dipolar complementary spontaneously assemble compositionally patterned monolayers, in which the two components segregate into neighboring, single component columns, driven by side chain dipolar interactions; (iii) compositionally patterned monolayers also assemble from dipolar complementary anthracene pairs that employ different dipolar groups (ketones or CF2 groups) in their side chains; (iv) the ketone group, with its larger dipole moment and size, provides comparable driving force for patterned monolayer formation to that of the smaller dipole, and smaller size, CF2 group.

  2. Luminescent Organic Semiconducting Langmuir Monolayers.

    PubMed

    Agina, Elena V; Mannanov, Artur A; Sizov, Alexey S; Vechter, Olga; Borshchev, Oleg V; Bakirov, Artem V; Shcherbina, Maxim A; Chvalun, Sergei N; Konstantinov, Vladislav G; Bruevich, Vladimir V; Kozlov, Oleg V; Pshenichnikov, Maxim S; Paraschuk, Dmitry Yu; Ponomarenko, Sergei A

    2017-05-31

    In recent years, monolayer organic field-effect devices such as transistors and sensors have demonstrated their high potential. In contrast, monolayer electroluminescent organic field-effect devices are still in their infancy. One of the key challenges here is to create an organic material that self-organizes in a monolayer and combines efficient charge transport with luminescence. Herein, we report a novel organosilicon derivative of oligothiophene-phenylene dimer D2-Und-PTTP-TMS (D2, tetramethyldisiloxane; Und, undecylenic spacer; P, 1,4-phenylene; T, 2,5-thiophene; TMS, trimethylsilyl) that meets these requirements. The self-assembled Langmuir monolayers of the dimer were investigated by steady-state and time-resolved photoluminescence spectroscopy, atomic force microscopy, X-ray reflectometry, and grazing-incidence X-ray diffraction, and their semiconducting properties were evaluated in organic field-effect transistors. We found that the best uniform, fully covered, highly ordered monolayers were semiconducting. Thus, the ordered two-dimensional (2D) packing of conjugated organic molecules in the semiconducting Langmuir monolayer is compatible with its high-yield luminescence, so that 2D molecular aggregation per se does not preclude highly luminescent properties. Our findings pave the way to the rational design of functional materials for monolayer organic light-emitting transistors and other optoelectronic devices.

  3. Bimetallic oxidative addition involving radical intermediates in nickel-catalyzed alkyl-alkyl Kumada coupling reactions.

    PubMed

    Breitenfeld, Jan; Ruiz, Jesus; Wodrich, Matthew D; Hu, Xile

    2013-08-14

    Many nickel-based catalysts have been reported for cross-coupling reactions of nonactivated alkyl halides. The mechanistic understanding of these reactions is still primitive. Here we report a mechanistic study of alkyl-alkyl Kumada coupling catalyzed by a preformed nickel(II) pincer complex ([(N2N)Ni-Cl]). The coupling proceeds through a radical process, involving two nickel centers for the oxidative addition of alkyl halide. The catalysis is second-order in Grignard reagent, first-order in catalyst, and zero-order in alkyl halide. A transient species, [(N2N)Ni-alkyl(2)](alkyl(2)-MgCl), is identified as the key intermediate responsible for the activation of alkyl halide, the formation of which is the turnover-determining step of the catalysis.

  4. Controlling liquid crystal alignment using photocleavable cyanobiphenyl self-assembled monolayers.

    PubMed

    Prompinit, Panida; Achalkumar, Ammathnadu S; Bramble, Jonathan P; Bushby, Richard J; Wälti, Christoph; Evans, Stephen D

    2010-12-01

    We report on the development of novel cyano-biphenyl-based thiolate self-assembled monolayers designed to promote homeotropic alignment of calamitic liquid crystals. The molecules developed contain an ortho-nitrobenzyl protected carboxylic acid group that on irradiation by soft UV (365 nm) is cleaved to yield carboxylic acid groups exposed at the surface that promote planar alignment. Using a combination of wetting, X-ray photoelectron spectroscopy, Fourier transform-infrared reflection absorption spectroscopy, and ellipsometry we show that high photolysis yields (>90%) can be achieved and that the patterned SAMs are suitable for the controlled alignment of calamitic liquid crystals. This study further shows that such photo-patterned SAMs can be used to control the formation of focal conic domains (FCDs) in the smectic-A phase in terms of positioning and size confinement on surfaces.

  5. Inkjet printed electrode arrays for potential modulation of DNA self-assembled monolayers on gold.

    PubMed

    Li, Yunchao; Li, Paul C H; Parameswaran, M Ash; Yu, Hua-Zhong

    2008-11-15

    In this paper, we report a novel and cost-effective fabrication technique to produce electrode arrays that can be used for monitoring and electrical manipulation of the molecular orientation of DNA self-assembled monolayers (SAMs) on gold. The electrode arrays were prepared from gold coated glass sides or compact discs (CD-Rs) by using standard office inkjet printers without any hardware or software modifications. In this method, electrode arrays of varied shape and size (from submillimeter to centimeter) can be rapidly fabricated and are suitable for standard electrochemical measurements. We were able to use a dual-channel potentiostat to control the electrodes individually and a fluorescence (FL) scanner to image the electrode array simultaneously. With such an integrated modulation setup, the structural switching behavior (from "lying" to "standing" position) and the enhanced hybridization reactivity of thiolate DNA SAMs on gold under potential control have been successfully demonstrated.

  6. Self-assembled monolayers of polythiophene conductive polymers improve biocompatibility and electrical impedance of neural electrodes.

    PubMed

    Widge, Alik S; Jeffries-El, Malika; Cui, Xinyan; Lagenaur, Carl F; Matsuoka, Yoky

    2007-03-15

    There is continued interest in the development of conductive polymer coatings to improve the electrical properties and biocompatibility of electrodes for neural prostheses. We present here a new type of coating, based on mixed self-assembled monolayers (SAMs) of thiolated poly(alkylthiophene)s and functionalized alkanethiols. When assembled as a SAM on electrodes designed for in vitro electrophysiology, these polymers are able to significantly lower electrode impedance at 1 kHz. The same mixed formulation is able to promote the outgrowth of neurites from primary mouse cortical neurons when the alkanethiol component is functionalized with a neural cell adhesion molecule (NCAM) binding antibody. Atomic force microscopy of the SAMs shows that they exert their effect through the well-known mechanism of increasing electrode surface area. These new covalently bound films have the potential to be more robust and are more controllable in their composition than existing electrodeposited conductive polymer coatings.

  7. The structure and dynamics of Nano Particles encapsulated by the SDS monolayer collapse at the water/TCE interface

    PubMed Central

    Shi, Wenxiong

    2016-01-01

    The super-saturated surfactant monolayer collapses with the nanoparticles (NPs) at the water/trichloroethylene (TCE) interface are investigated using molecular dynamics (MD) simulations. The results show that sodium alkyl sulfate (SDS) monolayer collapse is initiated by buckling and followed primarily by budding and the bud encapsulating the NPs and oil molecules. The developed bud detaches from the monolayer into a water phase and forms the swollen micelle emulsion with NPs and oil molecules. We investigate the wavelength of the initial budding and the theoretical description of the budding process. The wavelength of the monolayer increases with bending modulus. The energy barrier of the budding can be easily overcome by thermal fluctuation energy, which indicates that budding process proceeds rapidly. PMID:27853312

  8. The structure and dynamics of Nano Particles encapsulated by the SDS monolayer collapse at the water/TCE interface

    NASA Astrophysics Data System (ADS)

    Shi, Wenxiong

    2016-11-01

    The super-saturated surfactant monolayer collapses with the nanoparticles (NPs) at the water/trichloroethylene (TCE) interface are investigated using molecular dynamics (MD) simulations. The results show that sodium alkyl sulfate (SDS) monolayer collapse is initiated by buckling and followed primarily by budding and the bud encapsulating the NPs and oil molecules. The developed bud detaches from the monolayer into a water phase and forms the swollen micelle emulsion with NPs and oil molecules. We investigate the wavelength of the initial budding and the theoretical description of the budding process. The wavelength of the monolayer increases with bending modulus. The energy barrier of the budding can be easily overcome by thermal fluctuation energy, which indicates that budding process proceeds rapidly.

  9. Reactions of Tributylstannyl Anioniods with Alkyl Bromides.

    DTIC Science & Technology

    1981-09-28

    g (12 mmol) of cesium tert-butoxide was added to the reaction vessel before the addition of n-butyllithium. Alkylation of Tributylstannyl Anionoids...Dry reaction vessels were purged with argon. The desired alkyl halide (1.0 mmol unless noted) and any desired additive were added to the reaction ...OFFICE OF NAVAL RESEARCH Contract N00014-79-C-0584 Task No. NR 053-714 TECHNICAL REPORT No. 2 Reactions of Tributylstannyl Anionoids with Alkyl

  10. Measuring binding kinetics of aromatic thiolated molecules with nanoparticles via surface-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Devetter, Brent M.; Mukherjee, Prabuddha; Murphy, Catherine J.; Bhargava, Rohit

    2015-05-01

    Colloidal plasmonic nanomaterials, consisting of metals such as gold and silver, are excellent candidates for advanced optical probes and devices, but precise control over surface chemistry is essential for realizing their full potential. Coupling thiolated (R-SH) molecules to nanoprobe surfaces is a convenient and established route to tailor surface properties. The ability to dynamically probe and monitor the surface chemistry of nanoparticles in solution is essential for rapidly manufacturing spectroscopically tunable nanoparticles. In this study, we report the development of surface-enhanced Raman spectroscopy (SERS) as a method to monitor the kinetics of gold-thiolate bond formation on colloidal gold nanoparticles. A theoretical model combining SERS enhancement with the Beer-Lambert law is proposed to explain ensemble scattering and absorption effects in colloids during chemisorption. In order to maximize biological relevance and signal reproducibility, experiments used to validate the model focused on maintaining nanoparticle stability after the addition of water-soluble aromatic thiolated molecules. Our results indicate that ligand exchange on gold nanoparticles follow a first-order Langmuir adsorption model with rate constants on the order of 0.01 min-1. This study demonstrates an experimental spectroscopic method and theoretical model for monitoring binding kinetics that may prove useful for designing novel probes.Colloidal plasmonic nanomaterials, consisting of metals such as gold and silver, are excellent candidates for advanced optical probes and devices, but precise control over surface chemistry is essential for realizing their full potential. Coupling thiolated (R-SH) molecules to nanoprobe surfaces is a convenient and established route to tailor surface properties. The ability to dynamically probe and monitor the surface chemistry of nanoparticles in solution is essential for rapidly manufacturing spectroscopically tunable nanoparticles. In this

  11. Reversible dissociation of thiolate ligands from molybdenum in an enzyme of the dimethyl sulfoxide reductase family.

    PubMed

    Bray, R C; Adams, B; Smith, A T; Bennett, B; Bailey, S

    2000-09-19

    Much is unknown concerning the role of thiolate ligands of molybdenum in molybdopterin enzymes. It has been suggested that thiolate dissociation from molybdenum is part of the catalytic mechanism of bis-molybdopterin enzymes of the dimethyl sulfoxide reductase (DMSOR) family. For DMSOR from Rhodobacter capsulatus, thiolate dissociation has therefore been investigated crystallographically, by UV/visible spectroscopy, and by enzyme assays. When crystallized from sodium citrate, all four thiolates of DMSOR are within bonding distance of Mo, but after extended exposure to Na(+)-Hepes, a pair of thiolates dissociates, a mixture of structures being indicated after shorter exposures to this buffer. DMSOR is stable in sodium citrate and other buffers but unstable aerobically although not anaerobically in Na(+)-Hepes. Aerobically in Na(+)-Hepes, a first-order reaction (k = 0.032 hr(-)(1) at 37 degrees C) leads to loss of activity in the backward but not the forward (dimethyl sulfoxide reduction) assay and loss of absorption at lambda > approximately 450 nm. This reaction can be reversed by a cycle of reduction and reoxidation ("redox-cycling"). Slower irreversible loss of activity in the forward assay and cofactor dissociation follow. Spectral analogy with a mono-molybdopterin enzyme supports the conclusion that in the Hepes-modified DMSOR form, only two cofactor dithiolene sulfur atoms are coordinated to molybdenum. Loss of activity provides the first clear evidence that sulfur ligand dissociation is an artifact, not part of the catalytic cycle. Clearly, structural data on DMSOR samples extensively exposed to Hepes is not directly relevant to the native enzyme. The nature of the oxygen ligands detected crystallographically is discussed, as is the specificity of Hepes and the mechanism whereby its effects are achieved. DMSOR forms complexes with Na(+)-Hepes and other buffer ions. For DMSOR crystallized from Hepes, electron density in the substrate binding channel suggests

  12. Thiolated polymers: self-crosslinking properties of thiolated 450 kDa poly(acrylic acid) and their influence on mucoadhesion.

    PubMed

    Marschütz, Michaela K; Bernkop-Schnürch, Andreas

    2002-05-01

    This study examined the rheological and mucoadhesive properties of a self-crosslinking anionic thiolated polymer in vitro. Mediated by a carbodiimide, L-cysteine was covalently bound to poly(acrylic acid) of 450 kDa molecular mass. The resulting thiolated polymers (conjugates I and II) contained 90.5+/-15.8 and 511.6+/-52 micromol thiol groups per gram polymer, respectively (mean+/-S.D., n=3). The amount of covalently attached cysteine was therefore dependent on the concentration of carbodiimide used for the coupling reaction. Both conjugates (3%, m/v) were capable of forming inter- and/or intramolecular disulfide bonds in 100 mM phosphate buffer pH 6.8. Consequently, the apparent viscosity of conjugates I and II increased 12- and 10-fold, respectively, within 24 h of incubation at 37 degrees C. Further, rheological synergy was observed by mixing equal volumes of polymer (unmodified as well as modified) with a mucin solution. A six-fold increase in viscosity immediately after mixing could be observed for the conjugate II/mucin mixture. This clearly indicates the high interaction potential of self-crosslinking thiomers with the mucus gel layer. Mucoadhesion studies confirmed the rheological results. Tablets based on conjugate II remained attached on freshly excised porcine mucosa for about 25 times longer than the corresponding controls, which is the longest time of mucoadhesion ever found among anionic thiomers. Due to the results of the present study, self-crosslinking thiolated poly(acrylates) of 450 kDa represent very promising excipients for the development of various mucoadhesive drug delivery systems.

  13. 40 CFR 721.1875 - Boric acid, alkyl and substituted alkyl esters (generic name).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... alkyl esters (generic name). 721.1875 Section 721.1875 Protection of Environment ENVIRONMENTAL... esters (generic name). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance boric acid, alkyl and substituted alkyl esters (PMN P-86-1252) is subject to reporting...

  14. 40 CFR 721.1875 - Boric acid, alkyl and substituted alkyl esters (generic name).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... alkyl esters (generic name). 721.1875 Section 721.1875 Protection of Environment ENVIRONMENTAL... esters (generic name). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance boric acid, alkyl and substituted alkyl esters (PMN P-86-1252) is subject to reporting...

  15. New insight into the structure of thiolated gold clusters: a structural prediction of the Au187(SR)68 cluster.

    PubMed

    Tlahuice-Flores, A

    2015-02-28

    The structure of the thiolated Au187 cluster has been elucidated by density functional theory calculations. The structural model comprises a Marks-decahedral Au153 core protected with 34 monomer motifs. The predicted structure accomplished in this study is in good agreement with the experimental X-ray diffraction pattern. It is noteworthy that the used methodology represents an advance in the prediction of the molecular structure of thiolated gold clusters constituted by hundreds of gold atoms.

  16. Comparing Surfaces and Engineered Interfaces using Self-Assembled Monolayers (SAMs) and Injected SAMs Silanes

    SciTech Connect

    Morris, Mark J.; Simmons, Kevin L.

    2003-11-01

    The objective of this study was to show a comparison between property changes by formation of a self-assembled monolayer on the surface of PPG synthetic precipitated silica, which is a technique developed at PNNL, and by adding the SAMs silane chemical directly into the mixing bowl. These coatings have the potential to greatly increase the bond strength and enhance other properties between the particle and the rubber matrix of a rubber compound. Tensile testing measured peak stress and elongation at break. The increase in tensile strength shows how well the polymer-filler interfacial adhesion is doing. The study used five different SAM systems with a sulfur cured styrene butadiene rubber (SBR) tire rubber formulation. The three propylsilanes were propyl triethoxysilane, allyl triethoxysilane and 3-mercaptopropyl triethoxysilane. Five combinations of silanes were used in this study. The application of the silanes were 100% propyl triethoxy silane (100% Alkyl); a 10/90 mixture of allyl and propyl triethoxy silanes (10% vinyl/90% alkyl); a 50/50 mixture of the allyl and propyl (50% vinyl/50% alkyl); a 10/90mixture of 3-mercaptopropyl trimethoxysilane and propyl trimethoxysilane (10% mercaptan/90% alkyl) and lastly a 50/50 3-mercaptopropyl and propylsilanes (50% mercaptan/alkyl). The data not only shows improvement with SAMs, the peak stress data (ultimate strength) shows that the by changing the amount of silane content can change the physical properties

  17. Nanoscale Surface Curvature Effects on Ligand-Nanoparticle Interactions: A Plasmon-Enhanced Spectroscopic Study of Thiolated Ligand Adsorption, Desorption, and Exchange on Gold Nanoparticles.

    PubMed

    Villarreal, Esteban; Li, Guangfang Grace; Zhang, Qingfeng; Fu, Xiaoqi; Wang, Hui

    2017-07-12

    The interfacial adsorption, desorption, and exchange behaviors of thiolated ligands on nanotextured Au nanoparticle surfaces exhibit phenomenal site-to-site variations essentially dictated by the local surface curvatures, resulting in heterogeneous thermodynamic and kinetic profiles remarkably more sophisticated than those associated with the self-assembly of organothiol ligand monolayers on atomically flat Au surfaces. Here we use plasmon-enhanced Raman scattering as a spectroscopic tool combining time-resolving and molecular fingerprinting capabilities to quantitatively correlate the ligand dynamics with detailed molecular structures in real time under a diverse set of ligand adsorption, desorption, and exchange conditions at both equilibrium and nonequilibrium states, which enables us to delineate the effects of nanoscale surface curvature on the binding affinity, cooperativity, structural ordering, and the adsorption/desorption/exchange kinetics of organothiol ligands on colloidal Au nanoparticles. This work provides mechanistic insights on the key thermodynamic, kinetic, and geometric factors underpinning the surface curvature-dependent interfacial ligand behaviors, which serve as a central knowledge framework guiding the site-selective incorporation of desired surface functionalities into individual metallic nanoparticles for specific applications.

  18. Trivalent lanthanide compounds with fluorinated thiolate ligands: Ln-F dative interactions vary with Ln and solvent.

    PubMed

    Melman, Jonathan H; Rohde, Christa; Emge, Thomas J; Brennan, John G

    2002-01-14

    The fluorinated tris-thiolate compounds Ln(SC(6)F(5))(3) can be isolated as THF, pyridine, or DME coordination complexes. In THF, the larger Ce forms dimeric [(THF)(3)Ce(SC(6)F(5))(3)](2) (1) with bridging thiolate ligands, while the smaller lanthanides (Ln = Ho (2), Er (3)) form monometallic (THF)(3)Ln(SC(6)F(5))(3) compounds. There is a tendency for fluoride to coordinate to Ln throughout the lanthanide series (Ce-Er). The cerium compound 1 contains a pair of bridging thiolates connecting two eight-coordinate Ce(III) ions. Of the two terminal thiolates, only one exhibits a distinct Ce-F bond. In contrast, the Ho derivative (THF)(3)Ho(SC(6)F(5))(3) is a molecular compound in the solid state, with two monodentate thiolates and one thiolate that again coordinates through both S and F atoms. Incorporation of a stronger Lewis base reduces but does not necessarily eliminate the tendency to form Ln-F bonds. Structural characterization of the eight-coordinate (pyridine)(4)Sm(SC(6)F(5))(3) (4) reveals a single, clearly defined Ln-F interaction, while in (pyridine)(4)Yb(SC(6)F(5))(3) (5) there are no Yb-F bonds. In the structure of (DME)(2)Er(SC(6)F(5))(3) (6) the DME ligands completely displace F from the Er coordination sphere.

  19. Sum-frequency spectroscopic study of Langmuir monolayers of lipids having oppositely charged headgroups.

    PubMed

    Sung, Woongmo; Seok, Sangjun; Kim, Doseok; Tian, C S; Shen, Y R

    2010-12-07

    Sum-frequency vibrational spectroscopy, with the help of surface pressure-area (π-A) isotherm, was used to study lipid Langmuir monolayers composed of molecules with positively and negatively charged headgroups as well as a 1:1 neutral mixture of the two. The spectral profiles of the CH(x) stretch vibrations are similar for all monolayers in the liquid-condensed (LC) phase. They suggest a monolayer structure of closely packed alkyl chains that are nearly all-trans and well oriented along the surface normal. In the liquid-expanded (LE) phase, the spectra of all monolayers appear characteristic of loosely packed chains with significant gauche defects. The OH stretch spectra of interfacial water for both positively and negatively charged monolayers are significantly enhanced in comparison with a neutral water interface, but the phase measurement of SFVS indicates that OH in the two cases points toward the bulk and the interface, respectively. The enhancement results mainly from surface-field-induced polar ordering of interfacial water molecules. For a charge-neutral monolayer composed of an equal number of positively and negatively charged lipid molecules, no such enhancement is observed. This mixed monolayer exhibits a wide range of LC/LE coexistence region extended to very low surface pressure and its CH(x) spectral profile in the coexistence region resembles that of the LC phase. This result suggests that in the LC/LE coexistence region, the mixed monolayer consists of coexisting LC and LE patches in which oppositely charged lipid molecules are homogeneously mixed and dispersed.

  20. Phenomenological Modeling for Langmuir Monolayers

    NASA Astrophysics Data System (ADS)

    Baptiste, Dimitri; Kelly, David; Safford, Twymun; Prayaga, Chandra; Varney, Christopher N.; Wade, Aaron

    Experimentally, Langmuir monolayers have applications in molecular optical, electronic, and sensor devices. Traditionally, Langmuir monolayers are described by a rigid rod model where the rods interact via a Leonard-Jones potential. Here, we propose effective phenomenological models and utilize Monte Carlo simulations to analyze the phase behavior and compare with experimental isotherms. Research reported in this abstract was supported by UWF NIH MARC U-STAR 1T34GM110517-01.

  1. Sulphur adsorption on gold monolayer

    NASA Astrophysics Data System (ADS)

    Kaur, Damanpreet; Kaur, Sumandeep; Srivastava, Sunita

    2017-05-01

    We use Density Functional Theory to study the electronic and magnetic properties of two dimensional gold monolayer and investigate the effect of adsorption of sulphur atom on it. Of all the possible adsorption sites, hollow site was found to be the most favorable one for adsorption. On-top and bridge adsorption sites are found to exhibit net magnetic moment of adsorbed gold monolayer. This feature of small but non zero magnetic moment could find applications in building small molecular magnetic devices.

  2. A Unified AMBER-Compatible Molecular Mechanics Force Field for Thiolate-Protected Gold Nanoclusters.

    PubMed

    Pohjolainen, Emmi; Chen, Xi; Malola, Sami; Groenhof, Gerrit; Häkkinen, Hannu

    2016-03-08

    We present transferable AMBER-compatible force field parameters for thiolate-protected gold nanoclusters. Five different sized clusters containing both organo-soluble and water-soluble thiolate ligands served as test systems in MD simulations, and parameters were validated against DFT and experimental results. The cluster geometries remain intact during the MD simulations in various solvents, and structural fluctuations and energetics showed agreement with DFT calculations. Experimental diffusion coefficients and crystal structures were also reproduced with sufficient accuracy. The presented parameter set contains the minimum number of cluster-specific parameters enabling the use of these parameters for several different gold nanoclusters. The parameterization of ligands can also be extended to different types of ligands.

  3. Optical signatures of thiolate/Cu(110) and S/Cu(110) surface structures

    NASA Astrophysics Data System (ADS)

    Martin, D. S.; Lane, P. D.; Isted, G. E.; Cole, R. J.; Blanchard, N. P.

    2010-08-01

    The optical properties of thiolate/Cu(110) and S/Cu(110) surfaces created by the adsorption of methanethiol and L-cysteine are investigated using reflection anisotropy spectroscopy (RAS). We find that characteristic optical signatures are obtained from these systems. The experimental RAS profiles are simulated using a four-phase model consisting of vacuum, anisotropic overlayer, anisotropic surface, and isotropic substrate. The results of the simulations suggest that a broad optical transition at 3.8 eV is associated with the thiolate/Cu(110) interface, consistent with recent first-principles calculations [S. D’Agostino , Phys. Rev. B 75, 195444 (2007)10.1103/PhysRevB.75.195444].

  4. Structural Order in Ultrathin Films of the Monolayer Protected Clusters Based Upon 4-nm Gold Nanocrystals: An Experimental and Theoretical Study

    PubMed Central

    Bhattarai, Nabraj; Khanal, Subarna; Bahena, Daniel; Olmos-Asar, Jimena A.; Ponce, Arturo; Whetten, Robert L.; Mariscal, Marcelo M.; Jose-Yacaman, Miguel

    2014-01-01

    The structural order in ultrathin films of monolayer protected clusters (MPCs) is important in a number of application areas but can be difficult to demonstrate by conventional methods, particularly when the metallic core dimension, d, is in the intermediate size-range, 1.5 < d < 5.0 nm. Here, improved techniques for the synthesis of monodisperse thiolate-protected gold nanoparticles have made possible the production of dodecane-thiolate saturated ~ 4 ± 0.5 nm Au clusters with single-crystal core structure and morphology. An ultrathin ordered film or superlattice of these nanocrystal-core MPCs is prepared and investigated using aberration corrected scanning/transmission electron microscopy (STEM) which allowed imaging of long-range hexagonally ordered superlattices of the nanocrystals, separated by the thiolate groups. The lattice constants determined by direct imaging are in good agreement with those determined by small-angle electron diffraction. The STEM image revealed the characteristic grain boundary (GB) with sigma (Σ) 13 in the interface between two crystals. The formation and structures found are interpreted on the basis of theoretical calculations employing molecular dynamics (MD) simulations and coarse-grained (CG) approach. PMID:24875295

  5. Synthesis and photochromic properties of thiolated N-salicylidene-anilines on silver nanoparticles

    NASA Astrophysics Data System (ADS)

    Mahmoodi, Nosrat O.; Aghajani, Nafiseh; Ghavidast, Atefeh

    2017-01-01

    Here, we synthesized the salicylidene-aniline (anil) photochromes with thiol group (thiolated Schiff base) to modify silver nanoparticles (AgNPs) surface and their photochromic properties were described. A photochromic response related to the light induced tautomerization of the anils functionality along with bathochromic shift in the absorption band is observed in AgNPs surfaces. We have also examined that enol→keto photoisomerization rate by UV light for functionalized AgNPs are clearly faster than free anils.

  6. Replacement of the proximal heme thiolate ligand in chloroperoxidase with a histidine residue

    PubMed Central

    Yi, Xianwen; Mroczko, Mark; Manoj, Kelath M.; Wang, Xiaotang; Hager, Lowell P.

    1999-01-01

    Chloroperoxidase is a versatile heme enzyme which can cross over the catalytic boundaries of other oxidative hemoproteins and perform multiple functions. Chloroperoxidase, in addition to catalyzing classical peroxidative reactions, also acts as a P450 cytochrome and a potent catalase. The multiple functions of chloroperoxidase must be derived from its unique active site structure. Chloroperoxidase possesses a proximal cysteine thiolate heme iron ligand analogous to the P450 cytochromes; however, unlike the P450 enzymes, chloroperoxidase possesses a very polar environment distal to its heme prosthetic group and contains a glutamic acid residue in close proximity to the heme iron. The presence of a thiolate ligand in chloroperoxidase has long been thought to play an essential role in its chlorination and epoxidation activities; however, the research reported in this paper proves that hypothesis to be invalid. To explore the role of Cys-29, the amino acid residue supplying the thiolate ligand in chloroperoxidase, Cys-29 has been replaced with a histidine residue. Mutant clones of the chloroperoxidase genome have been expressed in a Caldariomyces fumago expression system by using gene replacement rather than gene insertion technology. C. fumago produces wild-type chloroperoxidase, thus requiring gene replacement of the wild type by the mutant gene. To the best of our knowledge, this is the first time that gene replacement has been reported for this type of fungus. The recombinant histidine mutants retain most of their chlorination, peroxidation, epoxidation, and catalase activities. These results downplay the importance of a thiolate ligand in chloroperoxidase and suggest that the distal environment of the heme active site plays the major role in maintaining the diverse activities of this enzyme. PMID:10535936

  7. Electrochemical method of controlling thiolate coverage on a conductive substrate such as gold

    DOEpatents

    Porter, Marc D.; Weisshaar, Duane E.

    1998-10-27

    An electrochemical method for forming a partial monomolecular layer of a predetermined extent of coverage of a thiolate of the formula, XRS--, therein R can be a linear or branched chain hydrocarbon or an aromatic or the like and X can be any compatible end group, e.g., OH, COOH, CH.sub.3 or the like, upon a substrate such as gold, which involves applying in an electrochemical system a constant voltage preselected to yield the desired predetermined extent of coverage.

  8. Electrochemical method of controlling thiolate coverage on a conductive substrate such as gold

    NASA Technical Reports Server (NTRS)

    Porter, Marc D. (Inventor); Weisshaar, Duane E. (Inventor)

    1998-01-01

    An electrochemical method for forming a partial monomolecular layer of a predetermined extent of coverage of a thiolate of the formula, XRS--, therein R can be a linear or branched chain hydrocarbon or an aromatic or the like and X can be any compatible end group, e.g., OH, COOH, CH.sub.3 or the like, upon a substrate such as gold, which involves applying in an electrochemical system a constant voltage preselected to yield the desired predetermined extent of coverage.

  9. Occupational asthma due to alkyl cyanoacrylate

    SciTech Connect

    Nakazawa, T. )

    1990-08-01

    A case of bronchial asthma induced by occupational exposure to alkyl cyanoacrylate, an adhesive, occurred in an assembly operation. Provocative exposure testing induced immediate and delayed asthmatic responses. Alkyl cyanoacrylate seemed to act as an allergen or as an irritant, resulting in the development of asthma.

  10. S-alkylation of soft scorpionates.

    PubMed

    Rajasekharan-Nair, Rajeev; Moore, Dean; Chalmers, Kirsten; Wallace, Dawn; Diamond, Louise M; Darby, Lisa; Armstrong, David R; Reglinski, John; Spicer, Mark D

    2013-02-11

    The alkylation reactions of soft scorpionates are reported. The hydrotris(S-alkyl-methimazolyl)borate dications (alkyl = methyl, allyl, benzyl), which were prepared by the reaction of Tm(Me) anion and primary alkyl halides, have been isolated and structurally characterised. The reaction is, however, not universally successful. DFT analysis of these alkylation reactions (C=S versus B-H alkylation) indicates that the observed outcome is driven by kinetic factors. Extending the study to incorporate alternative imine thiones (mercaptobenzothiazole, bz; thiazoline, tz) led to the structural characterisation of di[aquo-μ-aquohydrotris(mercaptobenzothiazolyl)boratosodium], which contains sodium atoms in the κ(3)-S,S,S coordination mode. Alkylation of Na[Tbz] and Na[tzTtz] leads to decomposition resulting in the formation of the simple S-alkylated heterocycles. The analysis of the species involved in these reactions shows an inherent weakness in the B-N bond in soft scorpionates, which has implications for their use in more advanced chemistry.

  11. Alkylation of phenol: a mechanistic view.

    PubMed

    Ma, Qisheng; Chakraborty, Deb; Faglioni, Francesco; Muller, Rick P; Goddard, William A; Harris, Thomas; Campbell, Curt; Tang, Yongchun

    2006-02-16

    The current work utilizes the ab initio density functional theory (DFT) to develop a molecular level of the mechanistic understanding on the phenol alkylation in the presence of a cation-exchange resin catalyst, Amberlyst-15. The catalyst is modeled with the benzene sulfonic acid, and the effect of this acid on olefins such as isopropene (i-Pr) and tributene (t-Bu) in a phenol solution mimics the experimental condition. A neutral-pathway mechanism is established to account for early-stage high concentration of the phenolic ether observed in experiments. The mechanism involves an exothermic reaction between olefin and the benzene sulfonic acid to form ester followed by three reaction pathways leading to direct O-alkylation, o-C-alkylation, and p-C-alkylation. Our calculations conclude that O-alkylation to form the phenolic ether is the most energetically favorable in the neutral condition. An ionic rearrangement mechanism describes intramolecular migrations of the alkyl group from the phenolic ether to form C-alkylphenols, while the positively charged protonation significantly lowers transition barriers for these migrations. The ionic rearrangement mechanism accounts for high yields of o-C-alkylphenol and p-C-alkylphenol. Competition between the H atom and the alkyl R group at the substitutive site of the protonated ortho configuration is found to be the determining factor to the ortho/para ratio of C-alkylation products.

  12. Synthesis, structural characterization, photophysical properties and theoretical analysis of gold(I) thiolate-phosphine complexes.

    PubMed

    Koshevoy, Igor O; Smirnova, Ekaterina S; Haukka, Matti; Laguna, Antonio; Chueca, Jessica Camara; Pakkanen, Tapani A; Tunik, Sergey P; Ospino, Isaura; Crespo, Olga

    2011-07-28

    A series of luminescent dinuclear neutral complexes of stoichiometry [(AuSPh)(2)(PPh(2)-(C(6)H(4))(n)-PPh(2))] (n = 1, 2, 3) as well as their tetranuclear cationic derivatives [(Au(2)SPh)(2)(PPh(2)-(C(6)H(4))(n)-PPh(2))(2)](PF(6))(2) are reported. Their crystal structures have been elucidated by X-ray studies. These studies indicate that, for the dinuclear species, only when n = 1 the molecules exhibit intermolecular aurophilic interactions. None of the tetranuclear species crystallizes in their molecular form, due to the formation of aggregates through Au···Au interactions. The origin of the luminescence has been analyzed by computational studies indicating that the presence or absence of aurophilic interactions does not affect the luminescent behavior and that intraligand charge transfer processes which involve the thiolate and the diphosphine are responsible for the emissions. The result is in contrast with the thiolate-gold charge transfer processes which dominate the photophysics of gold-thiolate compounds and reveals the influence of the phenylene spacers in the emissive behavior of these compounds. This journal is © The Royal Society of Chemistry 2011

  13. Sandwich electrochemical immunoassay for the detection of Staphylococcal enterotoxin B based on immobilized thiolated antibodies.

    PubMed

    Chatrathi, Madhu Prakash; Wang, Joseph; Collins, Greg E

    2007-06-15

    A new approach for the sensitive detection of Staphylococcal enterotoxin B (SEB) is presented based upon an electrochemical enzymatic immunoassay that utilizes thiolated antibodies immobilized on a gold surface. This method relies on the use of amine- or sulfhydryl-reactive heterobifunctional cross-linkers for the introduction of 2-pyridyl-disulfide groups to the antibody. The disulfide-containing linkages are subsequently cleaved with a suitable reducing agent, such as dithiothreitol (DTT), and the thiolated antibody-gold bond is covalently formed on a gold working electrode. Various cross-linking agents for immobilization of the capture antibody onto the gold electrode were investigated and compared. Factors influencing the thiolation and immobilization were investigated and optimized. The feasibility of such antibody immobilization and the subsequent sandwich enzyme immunoassay is demonstrated for the sensitive detection of SEB. The detection limit estimated from a representative dose-response curve is 1 ng/mL, corresponding to 5 pg in a 5-microL sample. Coupling the specificity of immunoassays with the sensitivity and low detection limits of electrochemical detection shows real promise for future sensing technology in enabling the development of single-use disposable devices.

  14. Sulfide ions as modulators of metal-thiolate cluster size in a plant metallothionein.

    PubMed

    Huber, Tamara; Freisinger, Eva

    2013-06-28

    Metallothioneins are small cysteine-rich proteins coordinating various transition metal ions preferably with the electron configuration d(10). They are ubiquitously present in all phyla, and next to phytochelatins they represent a successful molecular concept for high-capacity metal ion binding. Recent studies showed the incorporation of sulfide ions into the metal-thiolate cluster of metallothionein 2 from the plant Cicer arietinum (cicMT2) increasing the cadmium binding capacity and stability of the cluster. In the present work, the sulfide-induced structural changes accompanying the cluster formation and the sulfide-modulated increase in cluster size are analyzed in detail with a variety of analytical and spectroscopic techniques. Evaluation of the mechanism of sulfide containing Cd(II)-thiolate cluster formation in cicMT2 reveals a strong dependence on the sequence of metal and sulfide additions for successful sulfide incorporation. To probe the general ability of metallothioneins to form sulfide containing larger metal-thiolate clusters, analogous experiments were performed with a mammalian metallothionein. The observation that the cadmium binding ability of rabbit liver MT2A was only slightly increased led to the development of a hypothesis in which the long cysteine-free linker regions present in certain plant metallothioneins may contribute to the accommodation of the respective larger cluster assemblies.

  15. Thiolated silicone oils as adhesive skin protectants for improved barrier function.

    PubMed

    Partenhauser, A; Zupančič, O; Rohrer, J; Bonengel, S; Bernkop-Schnürch, A

    2016-06-01

    The purpose of this study was the evaluation of thiolated silicone oil as novel skin protectant exhibiting prolonged residence time, enhanced barrier function and reinforced occlusivity. Two silicone conjugates were synthesized with mercaptopropionic acid (MPA) and thioglycolic acid (TGA) as thiol ligands. Adhesion, protection against artificial urine and water vapour permeability with both a Payne cup set-up and transepidermal water loss (TEWL) measurements on porcine skin were assessed. Silicone thiomers showed pronounced substantivity on skin with 22.1 ± 6.3% and 39.2 ± 6.7% remaining silicone after 8 h for silicone-TGA and silicone-MPA, respectively, whereas unmodified silicone oil and dimethicone were no longer detectable. In particular, silicone-MPA provided a protective shield against artificial urine penetration with less than 25% leakage within 6 h. An up to 2.5-fold improved water vapour impermeability for silicone-MPA in comparison with unmodified control was discovered with the Payne cup model. In addition, for silicone-MPA a reduced TEWL by two-thirds corresponding to non-thiolated control was determined for up to 8 h. Thiolation of silicone oil leads to enhanced skin adhesiveness and barrier function, which is a major advantage compared to commonly used silicones and might thus be a promising treatment modality for various topical applications. © 2015 Society of Cosmetic Scientists and the Société Française de Cosmétologie.

  16. Derivatives of the thiolate-protected gold cluster Au25(SR)18 -1

    NASA Astrophysics Data System (ADS)

    Lopez-Acevedo, O.; Häkkinen, H.

    2011-07-01

    Loss of small fragments (like AuL, Au2L3, Au4L4) have been found systematically in several MALDI and FAB experiments on thiolate-protected gold clusters of different sizes. When using the cluster Au25L18 -1 as parent cluster, the fragmented cluster Au21L14 -1 has been reported to be obtained in high proportion (L = SCH2CH2Ph). Here we analyse a few possible fragmentation patterns of the well-known parent cluster Au25L18 -1 (L = SCH3). Using DFT calculations we study the different atomic configurations obtained after a AuL fragment is lost from Au25L18 -1. We found energetically favourable configurations that can be written as Au13 [Au2L3]6- z [AuL2] z -1, where the modification can be described as a replacement of the long protecting unit by a short one (Au2L3 → AuL2). A full replacement ( z = 6) gives rise to a protected Au19L12 -1 cluster. This mechanism does not modify the super-atomic electronic structure of the gold core, i.e., all these fragments remain an 8 electron super-atom clusters exactly like the parent Au25L18 -1. We suggest that the Au19L12 -1 cluster could be realized by using a bulky thiolate, such as the tert-butyl thiolate SC(CH3)3.

  17. Measuring binding kinetics of aromatic thiolated molecules with nanoparticles via surface-enhanced Raman spectroscopy

    PubMed Central

    DeVetter, Brent M.; Mukherjee, Prabuddha; Murphy, Catherine J.; Bhargava, Rohit

    2015-01-01

    Colloidal plasmonic nanomaterials, consisting of metals such as gold and silver, are excellent candidates for advanced optical probes and devices, but precise control over surface chemistry is essential for realizing their full potential. Coupling thiolated (R-SH) molecules to nanoprobe surfaces is a convenient and established route to tailor surface properties. The ability to dynamically probe and monitor the surface chemistry of nanoparticles in solution is essential for rapidly manufacturing spectroscopically tunable nanoparticles. In this study, we report the development of surface-enhanced Raman spectroscopy (SERS) as a method to monitor the kinetics of gold-thiolate bond formation on colloidal gold nanoparticles. A theoretical model combining SERS enhancement with the Beer-Lambert law is proposed to explain ensemble scattering and absorption effects in colloids during chemisorption. In order to maximize biological relevance and signal reproducibility, experiments used to validate the model focused on maintaining nanoparticle stability after the addition of water-soluble aromatic thiolated molecules. Our results indicate that ligand exchange on gold nanoparticles follow a first-order Langmuir adsorption model with rate constants on the order of 0.01 min 1. This study demonstrates an experimental spectroscopic method and theoretical model for monitoring binding kinetics that may prove useful for designing novel probes. PMID:25905515

  18. Preparation and comparison of chitosan nanoparticles with different degrees of glutathione thiolation

    PubMed Central

    Yousefpour, P.; Atyabi, F.; Dinarvand, R.; Vasheghani-Farahani, E.

    2011-01-01

    Background Chitosan has gained considerable attentions as a biocompatible carrier to improve delivery of active agents. Application of this vehicle in the form of nanoparticle could profit advantages of nanotechnology to increase efficacy of active agents. The purpose of this study was to provide detailed information about chitosan–glutathione (Cht-GSH)nanoparticles which are gaining popularity because of their high mucoadhesive and extended drug release properties. Methods Depolymerization of chitosan was carried out using sodium nitrite method.Glutathione was covalently attached to chitosan and the solubility of the resulting conjugates was evaluated. Nanoparticles were prepared by ionic gelation method and then the effect of glutathione immobilization on properties of nanoparticles was investigated. Results Thiolation efficiency was higher in lower molecular weight chitosan polymers compared to unmodified chitosan nanoparticles. Cht-GSH conjugates of the same molecular weight but with different degrees of thiolation had the same hydrodynamic diameter (995± nm) and surface charge (102± mV) as unmodified chitosan, but comprised of a denser network structure and lower concentration. Cht-GSH nanoparticles also exhibited greater mucoadhesive strength which was less affected by ionic strength and pH of the environment. Conclusion Thiolation improves the solubility of chitosan without any significant changes in size and charge of nanoparticles, but affects the nanogel structure. PMID:22615683

  19. Atomic-force and fluorescence microscopy of Langmuir-Blodgett monolayers of [ital L]-[alpha]-dimyristoylphosphatidic acid

    SciTech Connect

    Mikrut, J.M. ); Dutta, P.; Ketterson, J.B. ); MacDonald, R.C. )

    1993-11-15

    We have obtained fluorescence and atomic-force-microscopy images of the liquid and solid phases of Langmuir-Blodgett monolayers of [ital L]-[alpha]-dimyristoylphosphatidic acid, some containing [similar to]1 mol % of [ital L]-[alpha]-phosphatidylethanolamine-[ital N]-4-nitrobenzo-2-oxa-1,3-diazole. The fluorescence microscopy images are similar to those of monolayers at the air-water interface, but slight differences indicate that changes occur in the monolayers as a result of the deposition process. The atomic-force-microscopy images show the clean glass substrates to be very much rougher than when the monolayers are deposited on them. We propose that a water layer provides a smooth surface on which the Langmuir-Blodgett monolayers rest. We measured a [similar to]25-A height difference between the liquid and solid phase region, one explanation being that the alkyl chains of the molecule are standing up in the solid phase and lying down in the liquid phase. This result is consistent with the fluorescence and atomic-force-microscopy images which show an increase in the amount of solid phase domains as a result of the deposition process. Further, the atomic-force-microscopy images of the monolayers show features which have not been described before and which could not be attributed to the presence of the dye. Finally, we showed that if the Langmuir-Blodgett monolayers are not stored in a humid environment, they begin to collapse into multilayers.

  20. Cyclic Oxonitriles: Stereodivergent Grignard Addition-Alkylations

    PubMed Central

    Fleming, Fraser F.; Wei, Guoqing; Zhang, Zhiyu; Steward, Omar W.

    2008-01-01

    Sequential carbonyl addition-conjugate addition of Grignard reagents to cyclic 5–7–membered oxoalkenenitriles efficiently generates cyclic magnesiated nitriles. Alkylations of these magnesiated nitriles exhibit diastereoselectivities that depend intimately on the size of the carbocyclic ring: 5-membered oxonitriles generate magnesiated nitriles whose alkylations are controlled by steric constraints whereas 6- and 7-membered oxonitriles generate internally coordinated, C-magnesiated nitriles whose alkylations are controlled by stereoelectronic effects. Reversing the alkylation selectivity of 6-membered C-magnesiated nitriles is achieved by conversion to an N-metalated nitrile in which steric, rather than electronic, effects direct the electrophile trajectory. Collectively, the conjugate addition-alkylation generates highly substituted, cyclic 5–7-membered nitriles containing three new stereocenters with selective access to diastereomers at the quaternary nitrile-bearing carbon. PMID:17567075

  1. Unraveling the dynamics and structure of functionalized self-assembled monolayers on gold using 2D IR spectroscopy and MD simulations

    PubMed Central

    Yan, Chang; Yuan, Rongfeng; Pfalzgraff, William C.; Nishida, Jun; Wang, Lu; Markland, Thomas E.; Fayer, Michael D.

    2016-01-01

    Functionalized self-assembled monolayers (SAMs) are the focus of ongoing investigations because they can be chemically tuned to control their structure and dynamics for a wide variety of applications, including electrochemistry, catalysis, and as models of biological interfaces. Here we combine reflection 2D infrared vibrational echo spectroscopy (R-2D IR) and molecular dynamics simulations to determine the relationship between the structures of functionalized alkanethiol SAMs on gold surfaces and their underlying molecular motions on timescales of tens to hundreds of picoseconds. We find that at higher head group density, the monolayers have more disorder in the alkyl chain packing and faster dynamics. The dynamics of alkanethiol SAMs on gold are much slower than the dynamics of alkylsiloxane SAMs on silica. Using the simulations, we assess how the different molecular motions of the alkyl chain monolayers give rise to the dynamics observed in the experiments. PMID:27044113

  2. Calculation of monolayer structures of hydrocarbon chains on transition metal dichalcogenides: Dotriacontane on MoSe2

    NASA Astrophysics Data System (ADS)

    Cincotti, S.; Burda, J.; Hentschke, R.; Rabe, J. P.

    1995-03-01

    In situ scanning tunneling microscopy at the interface between atomically flat solid surfaces and solutions containing alkyl chains or alkyl derivatives show that the solute molecules often adsorb from solution to form dense crystalline monolayers at the liquid-solid interface. The structure of these layers depends on the nature of the substrate, and thus cannot be predicted from simple packing considerations alone. As an example of a theoretical approach to this problem on the atomic level, we present a calculation of the monolayer structure of dotriacontane on MoSe2. We carry out energy minimizations of periodic clusters of dotriacontane on MoSe2, where the potential energy is based on ab initio second-order Mo/ller-Plesset perturbation calculations of the adsorbate-substrate interactions combined with a phenomenological force field description of the intra-adsorbate interactions. The resulting adsorbate structure is in excellent agreement with the experimentally observed structure.

  3. Alkylation of organic aromatic compounds

    DOEpatents

    Smith, L.A. Jr.; Arganbright, R.P.; Hearn, D.

    1993-01-05

    Aromatic compounds are alkylated in a combination reactor/distillation column comprising a vessel suitable for operating between 70 C and 500 C and from 0.5 to 20 atmospheres pressure; an inert distillation packing in the lower one-third of said vessel; solid acidic catalytic material such as zeolites or an acidic cation exchange resin supported in the middle one-third of said vessel; and inert distillation packing in the upper one-third of said vessel. A benzene inlet is located near the upper end of the vessel; an olefin inlet is juxtaposed with said solid acidic catalytic material; a bottoms outlet is positioned near the bottom of said vessel for removing said cumene and ethyl benzene; and an overhead outlet is placed at the top of said vessel for removing any unreacted benzene and olefin.

  4. Alkylation of organic aromatic compounds

    DOEpatents

    Smith, Jr., Lawrence A.; Arganbright, Robert P.; Hearn, Dennis

    1993-01-01

    Aromatic compounds are alkylated in a catalytic distillation, wherein the catalyst structure also serves as a distillation component by contacting the aromatic compound with a C.sub.2 to C.sub.10 olefin in the catalyst bed under 0.25 to 50 atmospheres of pressure and at temperatures in the range of 80.degree. C. to 500.degree. C., using as the catalyst a mole sieve characterized as acidic or an acidic cation exchange resin. For example, ethyl benzene is produced by feeding ethylene to about the mid point of the catalyst bed while benzene is conveniently added through the reflux in molar excess to that required to react with ethylene, thereby reacting substantially all of the ethylene and recovering benzene as the principal overhead and ethyl benzene in the bottoms.

  5. Alkylation of organic aromatic compounds

    DOEpatents

    Smith, L.A. Jr.; Arganbright, R.P.; Hearn, D.

    1994-06-14

    Aromatic compounds are alkylated in a catalytic distillation, wherein the catalyst structure also serves as a distillation component by contacting the aromatic compound with a C[sub 2] to C[sub 10] olefin in the catalyst bed under 0.25 to 50 atmospheres of pressure and at temperatures in the range of 80 C to 500 C, using as the catalyst a molecular sieve characterized as acidic or an acidic cation exchange resin. For example, ethyl benzene is produced by feeding ethylene below the catalyst bed while benzene is conveniently added through the reflux in molar excess to that required to react with ethylene, thereby reacting substantially all of the ethylene and recovering benzene as the principal overhead and ethyl benzene in the bottoms. 1 fig.

  6. Alkylation of organic aromatic compounds

    DOEpatents

    Smith, L.A. Jr.; Arganbright, R.P.; Hearn, D.

    1993-09-07

    Aromatic compounds are alkylated in a catalytic distillation, wherein the catalyst structure also serves as a distillation component by contacting the aromatic compound with a C[sub 2] to C[sub 10] olefin in the catalyst bed under 0.25 to 50 atmospheres of pressure and at temperatures in the range of 80 C to 500 C, using as the catalyst a molecular sieve characterized as acidic or an acidic cation exchange resin. For example, ethyl benzene is produced by feeding ethylene to about the mid point of the catalyst bed while benzene is conveniently added through the reflux in molar excess to that required to react with ethylene, thereby reacting substantially all of the ethylene and recovering benzene as the principal overhead and ethyl benzene in the bottoms. 1 figures.

  7. Alkylation of organic aromatic compounds

    DOEpatents

    Smith, Jr., Lawrence A.

    1989-01-01

    Aromatic compounds are alkylated in a catalytic distillation, wherein the catalyst structure also serves as a distillation component by contacting the aromatic compound with a C.sub.2 to C.sub.10 olefin in the catalyst bed under 0.25 to 50 atmospheres of pressure and at temperatures in the range of 80.degree. C. to 500.degree. C., using as the catalyst a mole sieve characterized as acidic or an acidic cation exchange resin. For example, ethyl benzene is produced by feeding ethylene below the catalyst bed while benzene is conveniently added through the reflux in molar excess to that required to react with ethylene, thereby reacting substantially all of the ethylene and recovering benzene as the principal overhead and ethyl benzene in the bottoms.

  8. Alkylation of organic aromatic compounds

    DOEpatents

    Smith, L.A. Jr.

    1989-07-18

    Aromatic compounds are alkylated in a catalytic distillation, wherein the catalyst structure also serves as a distillation component by contacting the aromatic compound with a C[sub 2] to C[sub 10] olefin in the catalyst bed under 0.25 to 50 atmospheres of pressure and at temperatures in the range of 80 C to 500 C, using as the catalyst a mole sieve characterized as acidic or an acidic cation exchange resin. For example, ethyl benzene is produced by feeding ethylene below the catalyst bed while benzene is conveniently added through the reflux in molar excess to that required to react with ethylene, thereby reacting substantially all of the ethylene and recovering benzene as the principal overhead and ethyl benzene in the bottoms. 1 fig.

  9. Alkylation of organic aromatic compounds

    DOEpatents

    Smith, Jr., Lawrence A.; Arganbright, Robert P.; Hearn, Dennis

    1994-01-01

    Aromatic compounds are alkylated in a catalytic distillation, wherein the catalyst structure also serves as a distillation component by contacting the aromatic compound with a C.sub.2 to C.sub.10 olefin in the catalyst bed under 0.25 to 50 atmospheres of pressure and at temperatures in the range of 80.degree. C. to 500.degree. C., using as the catalyst a mole sieve characterized as acidic or an acidic cation exchange resin. For example, ethyl benzene is produced by feeding ethylene below the catalyst bed while benzene is conveniently added through the reflux in molar excess to that required to react with ethylene, thereby reacting substantially all of the ethylene and recovering benzene as the principal overhead and ethyl benzene in the bottoms.

  10. Alkylation of organic aromatic compounds

    DOEpatents

    Smith, Jr., Lawrence A.; Arganbright, Robert P.; Hearn, Dennis

    1993-01-01

    Aromatic compounds are alkylated in a combination reactor/distillation column comprising a vessel suitable for operating between 70.degree. C. and 500.degree. C. and from 0.5 to 20 atmospheres pressure; an inert distillation packing in the lower one-third of said vessel; solid acidic catalytic material such as zeolites or an acidic cation exchange resin supported in the middle one-third of said vessel; and inert distillation packing in the upper one-third of said vessel. A benzene inlet is located near the upper end of the vessel; an olefin inlet is juxtaposed with said solid acidic catalytic material; a bottoms outlet is positioned near the bottom of said vessel for removing said cumene and ethyl benzene; and an overhead outlet is placed at the top of said vessel for removing any unreacted benzene and olefin.

  11. Matrix tablets based on thiolated poly(acrylic acid): pH-dependent variation in disintegration and mucoadhesion.

    PubMed

    Guggi, Davide; Marschütz, Michaela K; Bernkop-Schnürch, Andreas

    2004-04-15

    This study examined the influence of the pH on the mucoadhesive and cohesive properties of polyarcylic acid (PAA) and thiolated PAA. The pH of PAA (molecular mass: 450 kDa) and of a corresponding PAA-cysteine conjugate was adjusted to 3, 4, 5, 6, 7 and 8. The amount of immobilised thiol groups and disulfide bonds was determined via Ellman's reagent. Tablets were compressed out of each pH-batch of both thiolated and unmodified PAA and the swelling behaviour, the disintegration time and the mucoadhesiveness were evaluated. The amount of thiol/disulfide groups per gram thiolated PAA of pH 3 and pH 8 was determined to be 332 +/- 94 micromol and 162 +/- 46 micromol, respectively. The thiolated PAA tablets displayed a minimum four-fold higher water uptake compared to unmodified PAA tablets. A faster and higher water uptake of both polymer types was observed above pH 5. Thiolated polymer tablets showed a 3-20-fold more prolonged disintegration time than unmodified PAA tablets. The cohesiveness of PAA-cysteine conjugate increased at higher pH, whereas the unmodified PAA behaved inversely. A 3-7-fold stronger mucoadhesiveness was observed for the PAA-cysteine conjugate tablets compared to unmodified PAA tablets. For both thiolated and unmodified polymer the mucoadhesiveness was 2-4-fold enhanced below pH 5. The difference in mucoadhesion between the two polymer types was most pronounced at these lower pH values. In this study substantial information regarding the pH-dependence of mucoadhesion and cohesion of unmodified polyacrylates and of thiolated polyacrylates is provided, representing helpful basic information for an ameliorated deployment of these polymers.

  12. The Role of Tris(2-carboxyethyl)phosphine Reducing Agent in the Controlled Formation of α,ω-Alkanedithiols Monolayers on Au(111) with Monocoordinated and Bicoordinated Configurations.

    PubMed

    Euti, Esteban M; Vélez-Romero, Patricio; Leiva, Ezequiel P M; Macagno, Vicente A; Paredes-Olivera, Patricia A; Patrito, E Martín; Cometto, Fernando P

    2016-09-20

    The addition of the reducing agent tris(2-carboxyethyl) phosphine (TCEP) during the formation of α,ω-alkanedithiols monolayers on Au(111) using the immersion method produces the assembly of monolayers with bicoordinated molecules (both S-terminal groups bound to the surface) that have a reductive desorption potential that is more positive than for monolayers with monocoordinated molecules in a standing up configuration. We show that the use of TCEP either during formation of the monolayer or as a post treatment procedure allows the controlled formation of monolayers with bicoordinated or monocoordinated configurations. Density functional theory (DFT) calculations were performed to elucidate the role of TCEP in the formation of the bicoordinated configuration. We investigated the TCEP-dithiol interaction in ethanol solvent as well as the coadsorption of trimethylphosphine with 1,2-ethanedithiol on Au(111). The Brønsted base character of the phosphine facilitates the H exchange from the -SH groups of the dithiol to the phosphorus atom of TCEP with very low activation energy barriers, thus allowing the thiolate groups to bind to the Au(111) surface, thus yielding the bicoordinated configuration. Dithiol lifting mechanisms such as H exchange between S atoms and the formation of intra/inter layer disulfide bonds have much higher energy barriers.

  13. Alkylated graphene nanosheet composites with polyaniline nanofibers.

    PubMed

    Grinou, Ali; Yun, Young Soo; Cho, Se Youn; Jin, Hyoung-Joon

    2011-07-01

    We demonstrate a simple method to prepare alkylated graphene/polyaniline composites (a-GR/PANI) using solution mixing of exfoliated alkyl Iodododecane treated graphene oxide sheets with polyaniline nanofiber; polyaniline nanofibers (PANI) prepared by using rapid mixing polymerization significantly improve the processibility of polyaniline and its performance in many conventional applications. Also, polyaniline nanofibers exhibit excellent water dispersibility due to their uniform nanofiber morphology. Morphological study using SEM and TEM analysis showed that the fibrous PANI in the composites a-GR/PANI mainly adsorbed onto the surface or intercalated between the graphene sheets, due especially to the good interfacial interaction between the alkylated gaphene and the polyaniline nanofibers. The existence of polyaniline nanofibers on the surface of the garphene and the alkylated graphene sheets was confirmed by using FT-IR, FT-Raman and X-ray diffraction analysis. Due to the good interfacial interaction between the alkylated graphene and the polyanilines nanofibers, the composite (a-GR/PANI) exhibited excellent dispersion stability in DMF compared to the same composite (GR/PANI) without alkylation. The electrical conductivity of the (GR/PANI) composite was 9% higher than that of pure PANI and the same weight percent for the composite after alkylation was 13% higher than that of pure PANI nanofibers.

  14. Chemical and Electrical Passivation of Single-Crystal Silicon(100) Surfaces Through a Two-Step Chlorination/Alkylation Process

    SciTech Connect

    Nemanick,E.; Hurley, P.; Webb, L.; Knapp, D.; Michalak, D.; Brunschwig, B.; Lewis, N.

    2006-01-01

    Single-crystal Si(100) surfaces have been functionalized by using a two-step radical chlorination-Grignard (R= MgCl, R = CH{sub 3}, C{sub 2}H{sub 5}, C{sub 4}H{sub 9}, C{sub 6}H{sub 5}, or CH{sub 2}C{sub 6}H{sub 5}) alkylation method. After alkylation, no chlorine was detectable on the surface by X-ray photoelectron spectroscopy (XPS), and the C 1s region showed a silicon-induced peak shift indicative of a Si-C bond. The relative intensity of this peak decreased, as expected, as the steric bulk of the alkyl increased. Despite the lack of full alkyl termination of the atop sites of the Si(100) surface, functionalization significantly reduced the rate of surface oxidation in air compared to that of the H-terminated Si(100) surface, with alkylated surfaces forming less than half a monolayer of oxide after over one month of exposure to air. Studies of the charge-carrier lifetime with rf photoconductivity decay methods indicated a surface recombination velocity of <30 cm s{sup -1} for methylated surfaces, and <60 cm s-1 for Si surfaces functionalized with the other alkyl groups evaluated. Soft X-ray photoelectron spectroscopic data indicated that the H-Si(100) surfaces were terminated by SiH, SiH{sub 2}, and SiH{sub 3} species, whereas Cl-Si(100) surfaces were predominantly terminated by monochloro (SiCl and SiHCl) and dichloro (SiCl{sub 2} and SiHCl{sub 2}) Si species. Methylation produced signals consistent with termination by Si-alkyl bonding arising from SiH(CH{sub 3})-, SiH{sub 2}(CH{sub 3})-, and Si(CH{sub 3}){sub 2}-type species.

  15. Regioselectivity of Birch reductive alkylation of biaryls.

    PubMed

    Lebeuf, Raphaël; Robert, Frédéric; Landais, Yannick

    2005-10-13

    [reaction: see text] The regioselectivity of the Birch reductive alkylation of polysubstituted biaryls has been investigated. Results indicate that regioselectivity is affected by the electronic nature of substituents on both aromatic rings. The electron-rich 3,5-dimethoxyphenyl moiety is selectively reduced and then alkylated, while phenols and aniline are not dearomatized under these conditions. Biaryls possessing a phenol moiety are alkylated on the second ring, providing that the acidic proton has been removed prior to the Li/NH3 reduction.

  16. Characterizing the mechanics of cultured cell monolayers

    PubMed Central

    Peter, Loic; Bellis, Julien; Baum, Buzz; Kabla, Alexandre J.; Charras, Guillaume T.

    2012-01-01

    One-cell-thick monolayers are the simplest tissues in multicellular organisms, yet they fulfill critical roles in development and normal physiology. In early development, embryonic morphogenesis results largely from monolayer rearrangement and deformation due to internally generated forces. Later, monolayers act as physical barriers separating the internal environment from the exterior and must withstand externally applied forces. Though resisting and generating mechanical forces is an essential part of monolayer function, simple experimental methods to characterize monolayer mechanical properties are lacking. Here, we describe a system for tensile testing of freely suspended cultured monolayers that enables the examination of their mechanical behavior at multi-, uni-, and subcellular scales. Using this system, we provide measurements of monolayer elasticity and show that this is two orders of magnitude larger than the elasticity of their isolated cellular components. Monolayers could withstand more than a doubling in length before failing through rupture of intercellular junctions. Measurement of stress at fracture enabled a first estimation of the average force needed to separate cells within truly mature monolayers, approximately ninefold larger than measured in pairs of isolated cells. As in single cells, monolayer mechanical properties were strongly dependent on the integrity of the actin cytoskeleton, myosin, and intercellular adhesions interfacing adjacent cells. High magnification imaging revealed that keratin filaments became progressively stretched during extension, suggesting they participate in monolayer mechanics. This multiscale study of monolayer response to deformation enabled by our device provides the first quantitative investigation of the link between monolayer biology and mechanics. PMID:22991459

  17. Electroactive Self-Assembled Monolayers Detect Micelle Formation.

    PubMed

    Dionne, Eric R; Badia, Antonella

    2017-02-15

    The interfacial electrochemistry of self-assembled monolayers (SAMs) of ferrocenyldodecanethiolate on gold (FcC12SAu) electrodes is applied to detect the micellization of some common anionic surfactants, sodium n-alkyl sulfates, sodium n-alkyl sulfonates, sodium diamyl sulfosuccinate, and sodium dodecanoate, in aqueous solution by cyclic voltammetry. The apparent formal redox potential (E°'SAM) of the FcC12SAu SAM is used to track changes in the concentration of the unaggregated surfactant anions and determine the critical micelle concentration (cmc). The effect of added salt (NaF) on the sodium alkyl sulfate concentration dependence of E°'SAM is also investigated. Weakly hydrated anions, such as ClO4(-), pair with the electrogenerated SAM-bound ferroceniums to neutralize the excess positive charge created at the SAM/electrolyte solution interface and stabilize the oxidized cations. E°'SAM exhibits a Nernstian-type dependence on the anion activity in solution. Aggregation of the surfactant anions into micelles above the cmc causes the free surfactant anion activity to deviate from the molar concentration of added surfactant, resulting in a break in the plot of E°'SAM versus the logarithm of the concentration of anionic surfactant. The concentration at which this deviation occurs is in good agreement with literature or experimentally determined values of the cmc. The effects of Ohmic potential drop, liquid junction potential, and surfactant adsorption behavior on E°'SAM are addressed. Ultimately, the E°'SAM response as a function of the anionic surfactant concentration exhibits the same features reported using potentiometry and surfactant ion-selective electrodes, which provide a direct measure of the free surfactant anion activity, thus making FcC12SAu SAM electrodes useful for the detection of surfactant aggregation and micelle formation.

  18. Electromelting of confined monolayer ice.

    PubMed

    Qiu, Hu; Guo, Wanlin

    2013-05-10

    In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under a perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to the field-induced disruption of the water-wall interaction induced well-ordered network of the hydrogen bond. This electromelting process should add an important new ingredient to the physics of water.

  19. 21 CFR 176.120 - Alkyl ketene dimers.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 3 2011-04-01 2011-04-01 false Alkyl ketene dimers. 176.120 Section 176.120 Food... Use Only as Components of Paper and Paperboard § 176.120 Alkyl ketene dimers. Alkyl ketene dimers may... section. (a) The alkyl ketene dimers are manufactured by the dehydrohalogenation of the acyl...

  20. 21 CFR 176.120 - Alkyl ketene dimers.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 3 2010-04-01 2009-04-01 true Alkyl ketene dimers. 176.120 Section 176.120 Food... Use Only as Components of Paper and Paperboard § 176.120 Alkyl ketene dimers. Alkyl ketene dimers may... section. (a) The alkyl ketene dimers are manufactured by the dehydrohalogenation of the acyl...

  1. Ruthenium-catalyzed meta/ortho-selective C-H alkylation of azoarenes using alkyl bromides.

    PubMed

    Li, Gang; Ma, Xingxing; Jia, Chunqi; Han, Qingqing; Wang, Ya; Wang, Junjie; Yu, Liuyang; Yang, Suling

    2017-01-19

    meta/ortho-Selective CAr-H (di)alkylation reactions of azoarenes have been achieved via [Ru(p-cymene)Cl2]2 catalyzed ortho-metalation using various types of alkyl bromides. Particularly, dual meta-alkylation of azoarene and reduction offer an attractive strategy for the synthesis of meta-alkylanilines, which are difficult to access via traditional aniline functionalization methods.

  2. MIES investigation of alkanethiol monolayers self-assembled on Au(111) and Ag(111) surfaces

    NASA Astrophysics Data System (ADS)

    Heinz, Bertram; Morgner, Harald

    1997-02-01

    Self-assembled monolayers of alkanethiols (SH(CH 2) mCH 3, m=7,8,9,11,15,17) have been prepared to study their electronic properties by means of metastable induced electron spectroscopy (MIES). The thermal metastable helium atoms used as projectiles in this technique interact exclusively with molecular orbitals exposed at the top of the film, which makes the method perfectly surface sensitive. Access of metastable helium atoms to the methyl group or to the CH 2-groups of the alkyl chain depends strongly on the orientation of the molecular axis. The MIE-spectrum of nonanethiol on Au(111) and the MIE-spectrum of hexadecane physisorbed on graphite served as references for upright aligned and flat lying alkyl chains. Both MIE-spectra can be related to the electronic bandstructure of polyethylene. Electron emission originating from the upright methyl groups and flat lying CH 2-groups is distinguished by characteristic intensities in the MIE-spectra. On this basis, a quantity R has been introduced as a measure for the molecular orientation of the alkyl chain at the top surface of the films. The evolution of R with respect to different molecular assemblies of the alkyl chains is consistent with XPS, LEED and UPS results. Within the series of dense and ordered alkanethiol films on gold and silver R decreases monotonously upon increasing the alkyl chain length. This behaviour indicates either the emergence of CH 2-groups at the cost of methyl groups at the top surface or a decreasing degree of orientational order of the methyl groups or both in the case of longer alkyl chains.

  3. Molecular Understanding on the Underwater Oleophobicity of Self-Assembled Monolayers: Zwitterionic versus Nonionic.

    PubMed

    Cheng, Gang; Liao, Mingrui; Zhao, Daohui; Zhou, Jian

    2017-02-21

    Molecular dynamics simulations are conducted to investigate the underwater oleophobicity of self-assembled monolayers (SAMs) with different head groups. Simulation results show that the order of underwater oleophobicity of SAMs is methyl < amide < oligo(ethylene glycol) (OEG) < ethanolamine (ETA) < hydroxyl < mixed-charged zwitterionic. The underwater-oil contact angles (OCAs) are <133° for all nonionic hydrophilic SAMs, while the mixed-charged zwitterionic SAMs are underwater superoleophobic (OCA can reach 180°). It appears that surfaces with stronger underwater oleophobicity have better antifouling performance. Further study on the effect of different alkyl ammonium ions on mixed-charged SAMs reveals that the underwater OCAs are >143.6° for all SAMs; mixed-charged SAMs containing primary alkyl ammonium ion are likely to possess the best underwater oleophobicity for its strong hydration capacity. It seems that alkyl sulfonate anion (SO3(-)) is more hydrophilic than alkyl trimethylammonium ion (NC3(+)) for the hydrophobic methyl groups on nitrogen atoms and that the hydration of SO3(-) in mixed-charged SAMs can be seriously blocked by NC3(+). The monomer of SO3(-) should be slightly longer than that of NC3(+) to obtain better underwater oleophobicity in NC3(+)-/SO3(-)-SAMs. In addition, the underwater oleophobicity of SAMs might become worse at low grafting densities. This work systematically proves that a zwitterionic surface is more underwater oleophobic than a nonionic surface. These results will help for the design and development of superoleophobic surfaces.

  4. N-Alkylation by Hydrogen Autotransfer Reactions.

    PubMed

    Ma, Xiantao; Su, Chenliang; Xu, Qing

    2016-06-01

    Owing to the importance of amine/amide derivatives in all fields of chemistry, and also the green and environmentally benign features of using alcohols as alkylating reagents, the relatively high atom economic dehydrative N-alkylation reactions of amines/amides with alcohols through hydrogen autotransfer processes have received much attention and have developed rapidly in recent decades. Various efficient homogeneous and heterogeneous transition metal catalysts, nano materials, electrochemical methods, biomimetic methods, asymmetric N-alkylation reactions, aerobic oxidative methods, and even certain transition metal-free, catalyst-free, or autocatalyzed methods, have also been developed in recent years. With a brief introduction to the background and developments in this area of research, this chapter focuses mainly on recent progress and technical and conceptual advances contributing to the development of this research in the last decade. In addition to mainstream research on homogeneous and heterogeneous transition metal-catalyzed reactions, possible mechanistic routes for hydrogen transfer and alcohol activation, which are key processes in N-alkylation reactions but seldom discussed in the past, the recent reports on computational mechanistic studies of the N-alkylation reactions, and the newly emerged N-alkylation methods based on novel alcohol activation protocols such as air-promoted reactions and transition metal-free methods, are also reviewed in this chapter. Problems and bottlenecks that remained to be solved in the field, and promising new research that deserves greater future attention and effort, are also reviewed and discussed.

  5. Crystalline self-assembly into monolayers of folded oligomers at the air-water interface

    PubMed

    Lederer; Godt; Howes; Kjaer; Als-Nielsen; Lahav; Wegner; Leiserowitz; Weissbuch

    2000-06-16

    Insertion of the 1,3-bis(ethynylene)benzene unit as a rigid spacer into a linear alkyl chain, thus separating the two resulting stems by 9 A. induces chain folding at the air-water interface. These folded molecules self-assemble into crystalline monolayers at this interface, with the plane of the folding unit almost perpendicular to the water surface, as determined by synchrotron grazing-incidence X-ray diffraction. Three distinct molecular shapes, of the types U, inverted U, and M, were obtained in the two-dimensional crystalline state, depending upon the number of spacer units, and the number and position of the hydrophilic groups in the molecule. The molecules form ribbons with a higher crystal coherence in the direction of stacking between the molecular ribbons, and a lower coherence along the ribbon direction. A similar molecule, but with a spacer unit that imposes a 5 A separation between alkyl chains, yields the conventional herringbone arrangement.

  6. Synthesis of Thiolated Alginate and Evaluation of Mucoadhesiveness, Cytotoxicity and Release Retardant Properties

    PubMed Central

    Jindal, A. B.; Wasnik, M. N.; Nair, Hema A.

    2010-01-01

    Modification of polymers by covalent attachment of thiol bearing pendant groups is reported to impart many beneficial properties to them. Hence in the present study, sodium alginate–cysteine conjugate was synthesized by carbodiimide mediated coupling under varying reaction conditions and the derivatives characterized for thiol content. The thiolated alginate species synthesized had bound thiol content ranging from 247.8±11.03–324.54±10.107 ΅mol/g of polymer depending on the reaction conditions. Matrix tablets based on sodium alginate-cysteine conjugate and native sodium alginate containing tramadol hydrochloride as a model drug were prepared and mucoadhesive strength and in vitro drug release from the tablets were compared. Tablets containing 75 mg sodium alginate-cysteine conjugate could sustain release of 10 mg of model drug for 3 h, whereas 90% of the drug was released within 1 h from corresponding tablets prepared using native sodium alginate. An approximately 2-fold increase in the minimal detachment force of the tablets from an artificial mucin film was observed for sodium alginate–cysteine conjugate as compared to native sodium alginate. In vitro cytotoxicity studies in L-929 mouse fibroblast cells studied using an MTT assay revealed that at low concentrations of polymer, sodium alginate–cysteine conjugate was less toxic to L-929 mouse fibroblast cell line when compared to native sodium alginate. Hence, thiolation is found to be a simple route to improving polymer performance. The combination of improved controlled drug release and mucoadhesive properties coupled with the low toxicity of these new excipients builds up immense scope for the use of thiolated polymers in mucoadhesive drug delivery systems. PMID:21969750

  7. REACTIONS OF ELECTROPHILES WITH NUCLEOPHILIC THIOLATE SITES: RELEVANCE TO PATHOPHYSIOLOGICAL MECHANISMS AND REMEDIATION

    PubMed Central

    LoPachin, Richard M.; Gavin, Terrence

    2016-01-01

    Electrophiles are electron deficient species that form covalent bonds with electron rich nucleophiles. In biological systems, reversible electrophile-nucleophile interactions mediate basal cytophysiological functions (e.g., enzyme regulation through S-nitrosylation), whereas irreversible electrophilic adduction of cellular macromolecules is involved in pathogenic processes that underlie many disease and injury states. The nucleophiles most often targeted by electrophiles are side chains on protein amino acids (e.g., Cys, His and Lys) and aromatic nitrogen sites on DNA bases (e.g., guanine N7). The sulfhydryl thiol (RSH) side-chain of cysteine residues is a weak nucleophile that can be ionized in specific conditions to a more reactive nucleophilic thiolate (RS−). This review will focus on electrophile interactions with cysteine thiolates and the pathophysiological consequences that result from irreversible electrophile modification of this anionic sulfur. According to the Hard and Soft, Acids and Bases (HSAB) theory of Pearson, electrophiles and nucleophiles can be classified as either soft or hard depending on their relative polarizability. HSAB theory suggests that electrophiles will preferentially and more rapidly form covalent adducts with nucleophiles of comparable softness or hardness. Application of HSAB principles, in conjunction with in vitro and proteomic studies, have indicated that soft electrophiles of broad chemical classes selectively form covalent Michael-type adducts with soft, highly reactive cysteine thiolate nucleophiles. Therefore, these electrophiles exhibit a common mechanism of cytotoxicity. As we will discuss, this level of detailed mechanistic understanding is a necessary prerequisite for the rational development of effective prevention and treatment strategies for electrophile-based pathogenic states. PMID:26559119

  8. Reactions of electrophiles with nucleophilic thiolate sites: relevance to pathophysiological mechanisms and remediation.

    PubMed

    LoPachin, Richard M; Gavin, Terrence

    2016-01-01

    Electrophiles are electron-deficient species that form covalent bonds with electron-rich nucleophiles. In biological systems, reversible electrophile-nucleophile interactions mediate basal cytophysiological functions (e.g. enzyme regulation through S-nitrosylation), whereas irreversible electrophilic adduction of cellular macromolecules is involved in pathogenic processes that underlie many disease and injury states. The nucleophiles most often targeted by electrophiles are side chains on protein amino acids (e.g. Cys, His, and Lys) and aromatic nitrogen sites on DNA bases (e.g. guanine N7). The sulfhydryl thiol (RSH) side chain of cysteine residues is a weak nucleophile that can be ionized in specific conditions to a more reactive nucleophilic thiolate (RS(-)). This review will focus on electrophile interactions with cysteine thiolates and the pathophysiological consequences that result from irreversible electrophile modification of this anionic sulfur. According to the Hard and Soft, Acids and Bases (HSAB) theory of Pearson, electrophiles and nucleophiles can be classified as either soft or hard depending on their relative polarizability. HSAB theory suggests that electrophiles will preferentially and more rapidly form covalent adducts with nucleophiles of comparable softness or hardness. Application of HSAB principles, in conjunction with in vitro and proteomic studies, have indicated that soft electrophiles of broad chemical classes selectively form covalent Michael-type adducts with soft, highly reactive cysteine thiolate nucleophiles. Therefore, these electrophiles exhibit a common mechanism of cytotoxicity. As we will discuss, this level of detailed mechanistic understanding is a necessary prerequisite for the rational development of effective prevention and treatment strategies for electrophile-based pathogenic states.

  9. Enhancing the efficiency of thiomers: Utilizing a highly mucoadhesive polymer as backbone for thiolation and preactivation.

    PubMed

    Prüfert, Felix; Bonengel, Sonja; Menzel, Claudia; Bernkop-Schnürch, Andreas

    2017-01-01

    The objective of this study was to develop a novel thiomer with enhanced mucoadhesive properties using a highly mucoadhesive polymeric backbone. Fixomer™ A-30 (poly(methacrylic acid-co-sodium acrylamidomethyl propane sulfonate)), exhibiting a mucoadhesive strength superior to that of all other polymers, was thiolated by conjugation with l-cysteine and furthermore preactivated with 2-mercaptonicotinic acid (MNA). The resulting derivatives Fix-SH and Fix-S-MNA exhibited coupling rates of 755μmol thiol groups and 304μmol MNA per gram polymer, respectively. The mucoadhesive profile was evaluated with three different methods: tensile studies, rotating cylinder and rheological synergism. In tensile studies, a total work of adhesion of above 500μJ was determined for the unmodified polymer that increased to around 750μJ after thiolation and around 1500μJ after preactivation. The adhesion time of Fix-SH on the rotating cylinder was 3.7-fold and that of Fix-S-MNA 6.8-fold longer compared to the unmodified polymer. A rheological synergism was observed for the unmodified polymer as well as the derivatives with a non-significant difference for Fix-SH but a 5.44-fold improvement for Fix-S-MNA. Fix-S-MNA showed a significantly improved swelling behavior with a water-uptake up to the 30-fold of its initial weight over >50h whereas thiolation showed only slight improvements. Derivatization had no significant influence on cell viability. According to the results, Fix-S-MNA seems to be a suitable polymer for mucoadhesive drug delivery systems. Copyright © 2016. Published by Elsevier B.V.

  10. The Structure and Phase Diagram of Chiral Alkyl-Serine Monolayers on Mercury

    SciTech Connect

    L Tamam; D Medina; T Menahem; Y Mastai; E Sloutskin; S Yefet; M Deutsch

    2011-12-31

    The structure of liquid-mercury-supported Langmuir films (LFs) of chiral serine-modified fatty acid molecules was studied as a function of length, n = 8-22 carbons, temperature, T = 5-25 C, and surface coverage, A {approx} 40-200 {angstrom}{sup 2} per molecule, for both homochiral and heterochiral compounds. Using surface pressure {pi}-area A isotherms and surface-specific synchrotron X-ray diffraction methods the phase diagram was determined in detail. No lateral order was found for phases comprising surface-parallel molecules, in contrast with unmodified fatty acid LFs on mercury. For phases comprising standing-up molecules, long range lateral order was found for n {>=} 12, but no order for n = 8. The molecules in the ordered phases are extended, and tilt rigidly by {approx}40{sup o} from the surface normal. The homochiral LFs pack in an oblique, single-molecule, unit cell. The heterochiral LFs pack in a body-centered rectangular unit cell, containing two molecules. Unlike unmodified fatty acid LFs, the structure of the standing-up phase does not vary with n, T or A. The interactions underlying these characteristics, and the role of chirality, are discussed.

  11. Acid-Base-Triggered Structural Transformation of a Polyoxometalate Core Inside a Dodecahedrane-like Silver Thiolate Shell.

    PubMed

    Liu, Hong; Song, Chao-Yu; Huang, Ren-Wu; Zhang, Yu; Xu, Hong; Li, Mei-Jia; Zang, Shuang-Quan; Gao, Guang-Gang

    2016-03-07

    Self-assembly of metavanadate and organosilver(I) salts leads to a novel dodecahedrane-like [Ag30 ((t) BuS)20 ](10+) silver(I) thiolate nanocage that tightly wraps an unusual C2h polyoxovanadate anion. The polyoxovanadate core undergoes transformation to a D3d configuration upon acidification, and reverts back to its original C2h structure upon addition of base. Chromism was observed for the silver(I) thiolate cluster during the configurational change of the central polyoxovanadate core; the color of the solution changes reversibly from green to dark yellow. This work represents the first reported example of chromic polyoxometalate-templated silver(I) thiolate shells that respond to external acid-base stimuli. It also represents an important advance in providing crystallographic proof that structural transformations occur in a nanoscale core-shell cluster. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Composition driven monolayer to bilayer transformation in a surfactant intercalated Mg-Al layered double hydroxide.

    PubMed

    Naik, Vikrant V; Chalasani, Rajesh; Vasudevan, S

    2011-03-15

    The structure and organization of dodecyl sulfate (DDS) surfactant chains intercalated in an Mg-Al layered double hydroxide (LDH), Mg(1-x)Alx(OH)2, with differing Al/Mg ratios has been investigated. The Mg-Al LDHs can be prepared over a range of compositions with x varying from 0.167 to 0.37 and therefore provides a simple system to study how the organization of the alkyl chains of the intercalated DDS anions change with packing density; the Al/Mg ratio or x providing a convenient handle to do so. Powder X-ray diffraction measurements showed that at high packing densities (x ≥ 0.3) the alkyl chains of the intercalated dodecyl sulfate ions are anchored on opposing LDH sheets and arranged as bilayers with an interlayer spacing of ∼27 Å. At lower packing densities (x < 0.2) the surfactant chains form a monolayer with the alkyl chains oriented flat in the galleries with an interlayer spacing of ∼8 Å. For the in between compositions, 0.2 ≤ x < 0.3, the material is biphasic. MD simulations were performed to understand how the anchoring density of the intercalated surfactant chains in the Mg-Al LDH-DDS affects the organization of the chains and the interlayer spacing. The simulations are able to reproduce the composition driven monolayer to bilayer transformation in the arrangement of the intercalated surfactant chains and in addition provide insights into the factors that decide the arrangement of the surfactant chains in the two situations. In the bilayer arrangement, it is the dispersive van der Waals interactions between chains in opposing layers of the anchored bilayer that is responsible for the cohesive energy of the solid whereas at lower packing densities, where a monolayer arrangement is favored, Coulomb interactions between the positively charged Mg-Al LDH sheets and the negatively charged headgroup of the DDS anion dominate.

  13. Rectifying enhancement induced by conjugation breaking in thiolated arylethynylene single-molecular diodes

    NASA Astrophysics Data System (ADS)

    Zuo, Xi; Chu, Lei; Zhang, Guang-Ping; Wang, Chuan-Kui

    2016-10-01

    Rectifying properties of three cyano side group substituted arylethynylene thiolate molecules are theoretically investigated based on abinitio calculations. The current-voltage curves show that rectifying performance of the junctions correlates negatively with conjugation of the molecules, which reveals a much more pronounced rectification behavior for that with broken-conjugated dihydroanthracene core (sAH) than the counterpart with linearly-conjugated anthracene core (sAC) or cross-conjugated anthraquinone core (sAQ). It is demonstrated that the conjugation breaking induced localization of molecular orbital and asymmetric evolution of its spatial distribution under positive and negative biases play the key role for the rectification enhancement in sAH.

  14. Electrochemical method of controlling thiolate coverage on a conductive substrate such as gold

    DOEpatents

    Porter, M.D.; Weisshaar, D.E.

    1998-10-27

    An electrochemical method is described for forming a partial monomolecular layer of a predetermined extent of coverage of a thiolate of the formula, XRS-, therein R can be a linear or branched chain hydrocarbon or an aromatic or the like and X can be any compatible end group, e.g., OH, COOH, CH{sub 3} or the like, upon a substrate such as gold, which involves applying in an electrochemical system a constant voltage preselected to yield the desired predetermined extent of coverage. 13 figs.

  15. Electrochemical method of controlling thiolate coverage on a conductive substrate such as gold

    DOEpatents

    Porter, Marc D.; Weisshaar, Duane E.

    1997-06-03

    An electrochemical method for forming a partial monomolecular layer of a predetermined extent of coverage of a thiolate of the formula, XRS.sup.-, wherein R can be a linear or branched chain hydrocarbon or an aromatic or the like and X can be any compatible end group, e.g., OH, COOH, CH.sub.3 or the like, upon a substrate such as gold, which involves applying in an electrochemical system a constant voltage preselected to yield the desired predetermined extent of coverage.

  16. X-Ray Absorption Spectroscopy of Cuprous-Thiolate Clusters in Saccharomyces Cerevisiae Metallothionein

    SciTech Connect

    Zhang, L.; Pickering, I.J.; Winge, D.R.; George, G.N.

    2009-05-28

    Copper (Cu) metallothioneins are cuprous-thiolate proteins that contain multimetallic clusters, and are thought to have dual functions of Cu storage and Cu detoxification. We have used a combination of X-ray absorption spectroscopy (XAS) and density-functional theory (DFT) to investigate the nature of Cu binding to Saccharomyces cerevisiae metallothionein. We found that the XAS of metallothionein prepared, containing a full complement of Cu, was quantitatively consistent with the crystal structure, and that reconstitution of the apo-metallothionein with stoichiometric Cu results in the formation of a tetracopper cluster, indicating cooperative binding of the Cu ions by the metallothionein.

  17. Inkjet deposition of alkanethiolate monolayers and DNA oligonucleotides on gold: evaluation of spot uniformity by wet etching.

    PubMed

    Bietsch, Alexander; Hegner, Martin; Lang, Hans Peter; Gerber, Christoph

    2004-06-08

    Inkjet printing allows localized, contact-free deposition of liquids onto arbitrary substrates. In this article we demonstrate the fast formation of high-quality self-assembled monolayers (SAMs) on gold surfaces. Using a selective etch process, we verify the uniformity of the deposited spots. A direct comparison with microcontact-printed SAMs on Au revealed similar resist quality as inkjet-deposited alkanethiolate SAMs. Likewise, inkjet printing of thiol-functionalized and non-thiolated single-stranded DNA oligomers formed molecular layers protecting Au from etchants. For all compounds used, we achieved etched patterns that were homogeneous and free of defects. These results indicate that an inkjet is a convenient tool for surface functionalization and the direct writing of molecular films and resists.

  18. A General Method for Solvent Exchange of Plasmonic Nanoparticles and Self-Assembly into SERS-Active Monolayers

    PubMed Central

    2015-01-01

    We present a general route for the transfer of Au and Ag nanoparticles of different shapes and sizes, from water into various organic solvents. The experimental conditions for each type of nanoparticles were optimized by using a combination of thiolated poly(ethylene glycol) and a hydrophobic capping agent, such as dodecanethiol. The functionalized nanoparticles were readily transferred into organic dispersions with long-term stability (months). Such organic dispersions efficiently spread out on water, leading to self-assembly at the air/liquid interface into extended nanoparticle arrays which could in turn be transferred onto solid substrates. The dense close packing in the obtained nanoparticle monolayers results in extensive plasmon coupling, rendering them efficient substrates for surface-enhanced Raman scattering spectroscopy. PMID:26258732

  19. Contact-line friction of liquid drops on self-assembled monolayers: chain-length effects.

    PubMed

    Voué, M; Rioboo, R; Adao, M H; Conti, J; Bondar, A I; Ivanov, D A; Blake, T D; De Coninck, J

    2007-04-24

    The static and dynamic wetting properties of self-assembled alkanethiol monolayers of increasing chain length were studied. The molecular-kinetic theory of wetting was used to interpret the dynamic contact angle data and evaluate the contact-line friction on the microscopic scale. Although the surfaces had a similar static wettability, the coefficient of contact-line friction zeta0 increased linearly with alkyl chain length. This result supports the hypothesis of energy dissipation due to a local deformation of the nanometer-thick layer at the contact line.

  20. Copper-catalyzed thiolation annulations of 1,4-dihalides with sulfides leading to 2-trifluoromethyl benzothiophenes and benzothiazoles.

    PubMed

    Li, Chun-Lin; Zhang, Xing-Guo; Tang, Ri-Yuan; Zhong, Ping; Li, Jin-Heng

    2010-10-15

    Copper-catalyzed double thiolation reaction of 1,4-dihalides with sulfides has been developed for selectively synthesizing 2-trifluoromethyl benzothiophenes and benzothiazoles. In the presence of CuI, a variety of 2-halo-1-(2-haloaryl)-3,3,3-trifluoropropylenes smoothly underwent the thiolation annulation with Na(2)S to afford 2-trifluoromethyl benzothiophenes in moderate to good yields. Moreover, the conditions are compatible with N-(2-haloaryl)trifluoroacetimidoyl chlorides in the presence of NaHS and K(3)PO(4), leading to 2-trifluoromethyl benzothiazoles.

  1. Synthesis and characterization of thiolate-Ag(I) complexes by solid-state and solution NMR and their antimicrobial activity

    NASA Astrophysics Data System (ADS)

    Isab, Anvarhusein A.; Wazeer, Mohammed I. M.

    2007-02-01

    Silver(I) complexes of several thiolates have been prepared. These complexes have been characterized by elemental analysis and 13C NMR spectroscopy. All the Ag(I)-thiolate complexes are polymeric in nature. Therefore, 13C CP MAS NMR is being used extensively to analyze the binding site of the ligand and the nature of complexation. A significant shift difference was observed for S binding site whereas smaller shift was observed for carboxylate binding site. The antimicrobial activities for Ag(I)-glutathione complex was measured and compared with Ag(I)-captopril complex.

  2. Conformation, orientation and interaction in molecular monolayers: A surface second harmonic and sum frequency generation study

    SciTech Connect

    Superfine, R.; Huang, J.Y.; Shen, Y.R.

    1988-12-01

    We have used sum frequency generation (SFG) to study the order in a silane monolayer before and after the deposition of a coadsorbed liquid crystal monolayer. We observe an increase in the order of the chain of the silane molecule induced by the interpenetration of the liquid crystal molecules. By using second harmonic generation (SHG) and SFG, we have studied the orientation and conformation of the liquid crystal molecule on clean and silane coated glass surfaces. On both surfaces, the biphenyl group is tilted by 70{degree} with the alkyl chain end pointing away from the surface. The shift in the C-H stretch frequencies in the coadsorbed system indicates a significant interaction between molecules. 9 refs., 3 figs.

  3. Ligand-Accelerated ortho-C–H Alkylation of Arylcarboxylic Acids Using Alkyl Boron Reagents

    PubMed Central

    Thuy-Boun, Peter S.; Villa, Giorgio; Dang, Devin; Richardson, Paul; Su, Shun; Yu, Jin-Quan

    2013-01-01

    A protocol for the Pd(II)-catalyzed ortho-C–H alkylation of phenylacetic and benzoic acids using alkylboron reagents is disclosed. Mono-protected amino acid ligands (MPAA) were found to significantly promote reactivity. Both potassium alkyltrifluoroborates and alkylboronic acids were compatible coupling partners. The possibility of a radical alkyl transfer to Pd(II) was also investigated. PMID:24124892

  4. Palladium-Catalyzed Arylation of Alkyl Sulfenate Anions.

    PubMed

    Jia, Tiezheng; Zhang, Mengnan; Jiang, Hui; Wang, Carol Y; Walsh, Patrick J

    2015-11-04

    A unique palladium-catalyzed arylation of alkyl sulfenate anions is introduced that affords aryl alkyl sulfoxides in high yields. Due to the base sensitivity of the starting sulfoxides, sulfenate anion intermediates, and alkyl aryl sulfoxide products, the use of a mild method to generate alkyl sulfenate anions was crucial to the success of this process. Thus, a fluoride triggered elimination strategy was employed with alkyl 2-(trimethylsilyl)ethyl sulfoxides to liberate the requisite alkyl sulfenate anion intermediates. In the presence of palladium catalysts with bulky monodentate phosphines (SPhos and Cy-CarPhos) and aryl bromides or chlorides, alkyl sulfenate anions were readily arylated. Moreover, the thermal fragmentation and the base promoted elimination of alkyl sulfoxides was overridden. The alkyl sulfenate anion arylation exhibited excellent chemoselectivity in the presence of functional groups, such as anilines and phenols, which are also known to undergo palladium catalyzed arylation reactions.

  5. Alkylation of isobutane with light olefins: Yields of alkylates for different olefins

    SciTech Connect

    Albright, L.F.; Kranz, K.E.; Masters, K.R.

    1993-12-01

    For alkylation of isobutane with C{sub 3}-C{sub 5} olefins using sulfuric acid as the catalyst, the yields of alkylates with different olefins are compared as the operating conditions are changed. The results of recent pilot plant experiments with propylene, C{sub 4} olefins, and C{sub 5} olefins permit such comparisons. The yields expressed as weight of alkylate produced per 100 wt of olefin consumed varied from about 201:100 to 220:100. Weight ratios of the isobutane consumed per olefin consumed vary from about 101:100 to 120:100. differences of yield values are explained by the changes in the overall chemistry. The procedure employed to calculate yields with good accuracy is based on the analysis of the alkylate and the amount of conjunct polymers produced. Based on literature data, yields are also reported for alkylations using HF as the catalyst.

  6. Ultra-high vacuum scanning tunneling microscopy and theoretical studies of 1-halohexane monolayers on graphite

    PubMed Central

    Müller, Thomas; Werblowsky, Tova L.; Florio, Gina M.; Berne, Bruce J.; Flynn, George W.

    2005-01-01

    A simple model system for the 2D self-assembly of functionalized organic molecules on surfaces was examined in a concerted experimental and theoretical effort. Monolayers of 1-halohexanes were formed through vapor deposition onto graphite surfaces in ultrahigh vacuum. Low-temperature scanning tunneling microscopy allowed the molecular conformation, orientation, and monolayer crystallographic parameters to be determined. Essentially identical noncommensurate monolayer structures were found for all 1-halohexanes, with differences in image contrast ascribed mainly to electronic factors. Energy minimizations and molecular dynamics simulations reproduced structural parameters of 1-bromohexane monolayers quantitatively. An analysis of interactions driving the self-assembly process revealed the crucial role played by small but anisotropic electrostatic forces associated with the halogen substituent. While alkyl chain dispersion interactions drive the formation of a close-packed adsorbate monolayer, electrostatic headgroup forces are found to compete successfully in the control of both the angle between lamella and backbone axes and the angle between surface and backbone planes. This competition is consistent with energetic tradeoffs apparent in adsorption energies measured in earlier temperature-programmed desorption studies. In accordance with the higher degree of disorder observed in scanning tunneling microscopy images of 1-fluorohexane, theoretical simulations show that electrostatic forces associated with the fluorine substituent are sufficiently strong to upset the delicate balance of interactions required for the formation of an ordered monolayer. The detailed dissection of the driving forces for self-assembly of these simple model systems is expected to aid in the understanding of the more complex self-assembly processes taking place in the presence of solvent. PMID:15758073

  7. Effect of chirality on monoacylglycerol ester monolayer characteristics: 3-monostearoyl-sn-glycerol.

    PubMed

    Vollhardt, D; Brezesinski, G

    2017-03-08

    The effect of chirality on the thermodynamic behavior, the morphological features, and the 2D lattice structures of 3-monostearoyl-sn-glycerol monolayers is studied. The present study focusses on the influence of the alkyl chain length on the chiral discrimination. Surface pressure-area (π-A) isotherms, Brewster angle microscopy (BAM), and particularly, grazing incidence X-ray diffraction (GIXD) are the experimental basis of the presented results. The π-A isotherms of the enantiomeric 3-monostearoyl-sn-glycerol monolayers measured between 25 and 38 °C resemble those of the racemic 1-monostearoyl-rac-glycerol monolayers, thus indicating small energetic differences between the enantiomeric and the racemic forms. The absolute ΔS values increase as the temperature decreases and thus, the ordering of the condensed phase increases at lower temperatures. The extrapolation to zero ΔS provides a critical temperature Tc of 42.1 °C (315.3 K), above which the monolayer cannot be compressed into the condensed state. Despite the great tendency of the 3-monostearoyl-sn-glycerol domains to develop irregular deviations in shape and inner texture, regular domains similar to those of the racemic monoacylglycerol esters are also formed. GIXD measurements performed over a large range of lateral pressures at four different temperatures (5, 10, 15 and 20 °C) indicate the dominance of the chiral nature. Contour plots with three clearly separated diffraction signals are observable in a large pressure range which is shifted to higher lateral pressures with increasing temperature. The comparison with the contour plots of the homologous 3-monopalmitoyl-sn-glycerol monolayers reveals the stronger dominance of the chiral nature with increasing alkyl chain length and thus, demonstrates the stronger influence of the lattice symmetry. The lattice data obtained by fitting the contour plots with 3 or 2 peaks demonstrate the resemblance to orthorhombic structures with NN tilted molecules at

  8. Structure and DNA Hybridization Properties of Mixed Nucleic Acid/Maleimide-ethylene glycol Monolayers

    PubMed Central

    Lee, Chi-Ying; Nguyen, Phuong-Cac T.; Grainger, David W.; Gamble, Lara J.; Castner, David G.

    2008-01-01

    The surface structure and DNA hybridization performance of thiolated single-strand DNA (HS-ssDNA) covalently attached to a maleimide-ethylene glycol disulfide (MEG) monolayer on gold have been investigated. Monolayer immobilization chemistry and surface coverage of reactive ssDNA probes were studied by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Orientation of the ssDNA probes was determined by near edge X-ray absorption fine structure (NEXAFS). Target DNA hybridization on the DNA-MEG probe surfaces was measured by surface plasmon resonance (SPR) to demonstrate the utility of these probe surfaces for detection of DNA targets from both purified target DNA samples and complex biological mixtures such as blood serum. Data from complementary techniques showed that immobilized ssDNA density is strongly dependent on the spotted bulk DNA concentration and buffer ionic strength. Variation of the immobilized ssDNA density had a profound influence on the DNA probe orientation at the surface and subsequent target hybridization efficiency. With increasing surface probe density, NEXAFS polarization dependence results (followed by monitoring the N 1s → π* transition) indicate that the immobilized ssDNA molecules reorient towards a more upright position on the MEG monolayer. SPR assays of DNA targets from buffer and serum showed that DNA hybridization efficiency increased with decreasing surface probe density. However, target detection in serum was better on the “high density” probe surface than on the “high efficiency” probe surface. The amount of target detected for both ssDNA surfaces were several orders of magnitude poorer in serum than in purified DNA samples due to non-specific serum protein adsorption onto the sensing surface. PMID:17492838

  9. Significance of the amide functionality on DOPA-based monolayers on gold.

    PubMed

    Rībena, Dina; Alekseev, Alexander; van Asselen, Otto; Mannie, Gilbère J A; Hendrix, Marco M R M; van der Ven, Leendert G J; Sommerdijk, Nico A J M; de With, Gijsbertus

    2012-12-11

    The adhesive proteins secreted by marine mussels contain an unusual amino acid, 3,4-dihydroxyphenylalanine (DOPA), that is responsible for the cohesive and adhesive strength of this natural glue and gives mussels the ability to attach themselves to rocks, metals, and plastics. Here we report a detailed structural and spectroscopic investigation of the interface between N-stearoyldopamine and a single-crystalline Au(111) model surface and an amide-absent molecule, 4-stearylcatechol, also on Au(111), with the aim of understanding the role of the amide functionality in the packing, orientation, and fundamental interaction between the substrate and the monolayer formed from an aqueous environment by the Langmuir-Blodgett technique. The organization of monolayers on gold was observed directly and studied in detail by X-ray photoelectron spectroscopy (XPS), contact angle measurements (CA), surface-enhanced Raman spectroscopy (SERS), infrared reflection-absorption spectroscopy (IRRAS), and atomic force microscopy (AFM). Our study shows that within the monolayer the catecholic oxygen atoms are coordinated to the gold surface, having a more perpendicular orientation with respect to the aromatic ring and the apparently tilted alkyl chains, whereas the amide functionality stabilizes the monolayer that is formed.

  10. Synthesis of core-shell gold coated magnetic nanoparticles and their interaction with thiolated DNA.

    PubMed

    Robinson, Ian; Tung, Le D; Maenosono, Shinya; Wälti, Christoph; Thanh, Nguyen T K

    2010-12-01

    Core-shell magnetic nanoparticles have received significant attention recently and are actively investigated owing to their large potential for a variety of applications. Here, the synthesis and characterization of bimetallic nanoparticles containing a magnetic core and a gold shell are discussed. The gold shell facilitates, for example, the conjugation of thiolated biological molecules to the surface of the nanoparticles. The composite nanoparticles were produced by the reduction of a gold salt on the surface of pre-formed cobalt or magnetite nanoparticles. The synthesized nanoparticles were characterized using ultraviolet-visible absorption spectroscopy, transmission electron microscopy, energy dispersion X-ray spectroscopy, X-ray diffraction and super-conducting quantum interference device magnetometry. The spectrographic data revealed the simultaneous presence of cobalt and gold in 5.6±0.8 nm alloy nanoparticles, and demonstrated the presence of distinct magnetite and gold phases in 9.2±1.3 nm core-shell magnetic nanoparticles. The cobalt-gold nanoparticles were of similar size to the cobalt seed, while the magnetite-gold nanoparticles were significantly larger than the magnetic seeds, indicating that different processes are responsible for the addition of the gold shell. The effect on the magnetic properties by adding a layer of gold to the cobalt and magnetite nanoparticles was studied. The functionalization of the magnetic nanoparticles is demonstrated through the conjugation of thiolated DNA to the gold shell.

  11. The axial ligand effect of oxo-iron porphyrin catalysts. How does chloride compare to thiolate?

    PubMed

    de Visser, Sam P

    2006-03-01

    We have performed density functional theory calculations on an oxo-iron porphyrin catalyst with chloride as an axial ligand and tested its reactivity toward propene. The reactions proceed via multistate reactivity on competing doublet and quartet spin surfaces. Close-lying epoxidation and hydroxylation mechanisms are identified, whereby in the gas phase the epoxidation reaction is dominant, while in environments with a large dielectric constant the hydroxylation pathways become competitive. By contrast to reactions with thiolate as an axial ligand all low-lying pathways have small ring-closure and rebound barriers, so it is expected that side products and rearrangements will be unlikely with Fe=O(porphyrin)Cl, whereas with Fe=O(porphyrin)SH some side products were predicted. The major differences in the electronic configurations of Fe=O(porphyrin)Cl and Fe=O(porphyrin)SH are due to strong mixing of thiolate orbitals with iron 3d orbitals, a mixing which is much less with chloride as an axial ligand. Predictions of the reactivity of ethylbenzene-h (12) versus ethylbenzene-d (12) are made.

  12. What Protects the Core When the Thiolated Gold Cluster is Extremely Small?

    SciTech Connect

    Jiang, Deen; Chen, Wei; Whetten, Robert L; Chen, Zhongfang

    2009-01-01

    The title question is motivated by the fact that extremely small thiolated-gold clusters such as Au{sub 20}(SR){sub 16} have been isolated, but their undetermined structures cannot be fully rationalized by the present knowledge derived from single-crystal structures of larger clusters. One needs to go beyond the linear monomer (RSAuSR) and V-shaped dimer (RSAuSRAuSR) motifs that were found to protect larger clusters. We hypothesize that the U-shaped trimer motif (RSAuSRAuSRAuSR) is required to protect the core of some extremely small thiolated-gold clusters, which have about 20 or fewer Au atoms. We test this hypothesis by proposing structural models for Au{sub 10}(SR){sub 8} based on two trimer motifs protecting a tetrahedral Au{sub 4} core and for Au{sub 20}(SR){sub 16} based on four trimer motifs protecting an Au{sub 8} core.

  13. Mucoadhesion mechanism of chitosan and thiolated chitosan-poly(isobutyl cyanoacrylate) core-shell nanoparticles.

    PubMed

    Bravo-Osuna, Irene; Vauthier, Christine; Farabollini, Alessandra; Palmieri, Giovanni Filippo; Ponchel, Gilles

    2007-04-01

    The study is focused on the evaluation of the potential bioadhesive behaviour of chitosan and thiolated chitosan (chitosan-TBA)-coated poly(isobutyl cyanoacrylates) (PIBCA) nanoparticles. Nanoparticles were obtained by radical emulsion polymerisation with chitosan of different molecular weight and with different proportions of chitosan/chitosan-TBA. Mucoadhesion was ex vivo evaluated under static conditions by applying nanoparticle suspensions on rat intestinal mucosal surfaces and evaluating the amount of nanoparticles remaining attached to the mucosa after incubation. The analysis of the results obtained demonstrated that the presence of either chitosan or thiolated chitosan on the PIBCA nanoparticle surface clearly enhanced the mucoadhesion behaviour thanks to non-covalent interactions (ionic interaction and hydrogen bonds) with mucus chains. Both, the molecular weight of chitosan and the proportion of chitosan-TBA in the formulation influenced the nanoparticle hydrodynamic diameter and hence their transport through the mucus layer. Improved interpenetration ability with the mucus chain during the attachment process was suggested for the chitosan of high molecular weight, enhancing the bioadhesiveness of the system. The presence of thiol groups on the nanoparticle surface at high concentration (200 x 10(-6) micromol SH/cm2) increased the mucoadhesion capacity of nanoparticles by forming covalent bonds with the cysteine residues of the mucus glycoproteins.

  14. Evaluating the mucoadhesive properties of drug delivery systems based on hydrated thiolated alginate.

    PubMed

    Davidovich-Pinhas, Maya; Harari, Offer; Bianco-Peled, Havazelet

    2009-05-21

    Mucoadhesive polymers have been proposed as drug delivery carriers due to their ability to adhere to the mucus layer. A relatively new class of mucoadhesive polymers, termed thiomers, was suggested as an improved carrier capable of creating disulfide covalent bond with the mucus. Since the wet physiological environment is likely to cause any delivery system to adsorb water and arrive hydrated to its target, studying the performance of mucoadhesive systems in their hydrated form is of major importance. Model thiomer, alginate-thiol, were synthesized and characterized the product using Nuclear Magnetic Resonance (NMR), Fourier Transform Infra Red spectroscopy (FTIR). The swelling behavior was determined gravimetrically and found to be affected from the thiolation. Interactions between the alginate-thiol and mucin glycoproteins, which are believed to be an outcome of disulfide bonds, were verified using rheology experiments. Adhesion of hydrated tablets with different cross linking densities to porcine's fresh small intestine tissue were characterized using a Lloyd Tensile Machine. It was shown that the thiolation did not improve the adhesion properties of hydrated tablets. It appears that the benefit achieved by adding thiol group to the polymer in dry tablet form was flawed in hydrated form due to formation of inter-molecular disulfide junctions.

  15. Transformation of thiolated chitosan-templated gold nanoparticles to huge microcubes

    SciTech Connect

    Sun, Yudie; Liu, Honglin; Yang, Liangbao; Sun, Bai; Liu, Jinhuai

    2014-05-01

    Graphical abstract: - Highlights: • Mercapto groups were grafted to chitosan molecule by a reactive amine reduction. • Functional polymer with well-defined monomer units controls AuNPs assembly. • Assembled morphologies depend on the ratio of AuNPs to thiolate groups. • Microcubes with side length of ∼20 μm was synthesized through a dialysis step. • A edge-to-middle growth mechanism of gold microcubes was observed. - Abstract: The L-cysteine molecules were successfully grafted to the 2-amino group of chitosan by a reactive amine reduction, and the as-synthesized thiolated chitosan (TC) molecules were used as the templates to direct the self-assembly of gold nanoparticles and induce the transformation of these assemblies to gold microcubes through a deep-going dialysis. We found that the ratio of gold nanoparticles to TC molecules could greatly affect the shape of the assembled clusters. Different stages of these clusters and microstructures during the dialysis process were characterized by scanning electron microscope (SEM), and the microcubes with average side length of about 20 μm were successfully synthesized. According to the morphology evolution of the assembly, it could be concluded that the microcubes were formed from external to internal. The SERS area mapping images of microcubes and some clusters were also collected to study the formation mechanism of gold microcubes. Our work demonstrates a simple and highly effective way to assemble gold nanoparticles into microcubes with unique properties.

  16. Fungal unspecific peroxygenases: heme-thiolate proteins that combine peroxidase and cytochrome p450 properties.

    PubMed

    Hofrichter, Martin; Kellner, Harald; Pecyna, Marek J; Ullrich, René

    2015-01-01

    Eleven years ago, a secreted heme-thiolate peroxidase with promiscuity for oxygen transfer reactions was discovered in the basidiomycetous fungus, Agrocybe aegerita. The enzyme turned out to be a functional mono-peroxygenase that transferred an oxygen atom from hydrogen peroxide to diverse organic substrates (aromatics, heterocycles, linear and cyclic alkanes/alkenes, fatty acids, etc.). Later similar enzymes were found in other mushroom genera such as Coprinellus and Marasmius. Approximately one thousand putative peroxygenase sequences that form two large clusters can be found in genetic databases and fungal genomes, indicating the widespread occurrence of such enzymes in the whole fungal kingdom including all phyla of true fungi (Eumycota) and certain fungus-like heterokonts (Oomycota). This new enzyme type was classified as unspecific peroxygenase (UPO, EC 1.11.2.1) and placed in a separate peroxidase subclass. Furthermore, UPOs and related heme-thiolate peroxidases such as well-studied chloroperoxidase (CPO) represent a separate superfamily of heme proteins on the phylogenetic level. The reactions catalyzed by UPOs include hydroxylation, epoxidation, O- and N-dealkylation, aromatization, sulfoxidation, N-oxygenation, dechlorination and halide oxidation. In many cases, the product patterns of UPOs resemble those of human cytochrome P450 (P450) monooxygenases and, in fact, combine the catalytic cycle of heme peroxidases with the "peroxide shunt" of P450s. Here, an overview on UPOs is provided with focus on their molecular and catalytic properties.

  17. Thiolated human serum albumin cross-linked dextran hydrogels as a macroscale delivery system.

    PubMed

    Gao, Yue; Kieltyka, Roxanne E; Jesse, Wim; Norder, Ben; Korobko, Alexander V; Kros, Alexander

    2014-07-21

    Hydrogels play an important role in macroscale delivery systems by enabling the transport of cells and molecules. Here we present a facile and benign method to prepare a dextran-based hydrogel (Dex-sHSA) using human serum albumin (HSA) as a simultaneous drug carrier and covalent cross-linker. Drug binding affinity of the albumin protein was conserved in the thiolation step using 2-iminothiolane and subsequently, in the in situ gelation step. Oscillation rheometry studies confirmed the formation of a three-dimensional viscoelastic network upon reaction of dextran and the HSA protein. The mechanical properties of Dex-sHSA hydrogel can be tuned by the protein concentration, and the degree of thiolation of sHSA. Sustained release of hydrophobic drugs, such as ibuprofen, paclitaxel and dexamethasone, from the Dex-sHSA network was shown over one week. Hence, this albumin-based dextran hydrogel system demonstrates its potential as a macroscale delivery system of hydrophobic therapeutics for a wide range of biomedical applications.

  18. In situ gelable interpenetrating double network hydrogel formulated from binary components: thiolated chitosan and oxidized dextran.

    PubMed

    Zhang, Hanwei; Qadeer, Aisha; Chen, Weiliam

    2011-05-09

    In situ gelable interpenetrating double-network hydrogels composed of thiolated chitosan (Chitosan-NAC) and oxidized dextran (Odex), completely devoid of potentially cytotoxic small molecule cross-linkers and that do not require complex maneuvers or catalysis, have been formulated. The interpenetrating network structure is created by Schiff base formations and disulfide bond inter-cross-linkings through exploiting the disparity of their reaction times. Compared with the autogelable thiolated chitosan hydrogels that typically require a relatively long time span for gelation to occur, the Odex/Chitosan-NAC composition solidifies rapidly and forms a well-developed 3D network in a short time span. Compared with typical hydrogels derived from natural materials, the Odex/Chitosan-NAC hydrogels are mechanically strong and resist degradation. The cytotoxicity potential of the hydrogels was determined by an in vitro viability assay using fibroblast as a model cell, and the results reveal that the hydrogels are noncytotoxic. In parallel, in vivo results from subdermal implantation in mice models demonstrate that this hydrogel is not only highly resistant to degradation but also induces very mild tissue response.

  19. A bio-inspired switch based on cobalt(II) disulfide/cobalt(III) thiolate interconversion.

    PubMed

    Gennari, Marcello; Gerey, Bertrand; Hall, Nikita; Pécaut, Jacques; Collomb, Marie-Noëlle; Rouzières, Mathieu; Clérac, Rodolphe; Orio, Maylis; Duboc, Carole

    2014-05-19

    Disulfide/thiolate interconversion supported by transition-metal ions is proposed to be implicated in fundamental biological processes, such as the transport of metal ions or the regulation of the production of reactive oxygen species. We report herein a mononuclear dithiolate Co(III) complex, [Co(III)LS(Cl)] (1; LS=sulfur containing ligand), that undergoes a clean, fast, quantitative and reversible Co(II) disulfide/Co(III) thiolate interconversion mediated by a chloride anion. The removal of Cl(-) from the Co(III) complex leads to the formation of a bis(μ-thiolato) μ-disulfido dicobalt(II) complex, [Co2(II,II)LSSL](2+) (2(2+)). The structures of both complexes have been resolved by single-crystal X-ray diffraction; their magnetic, spectroscopic, and redox properties investigated together with DFT calculations. This system is a unique example of metal-based switchable M(n)2-RSSR/2 M((n+1))-SR (M=metal ion, n=oxidation state) system that does not contain copper, acts under aerobic conditions, and involves systems with different nuclearities.

  20. In situ Gelable Interpenetrating Double Network Hydrogel Formulated from Binary Components: Thiolated Chitosan and Oxidized Dextran

    PubMed Central

    Zhang, Hanwei; Qadeer, Aisha; Chen, Weiliam

    2011-01-01

    In situ gelable interpenetrating double network hydrogels composed of thiolated chitosan (Chitosan-NAC) and oxidized dextran (Odex), completely devoid of potentially cytotoxic small molecule crosslinkers and do not require complex maneuvers or catalysis, have been formulated. The interpenetrating network structure is created by Schiff base formations and disulfide bond inter-crosslinkings through exploiting the disparity of their reaction times. Compare to the auto-gelable thiolated chitosan hydrogels that typically require a relatively long time span for gelation to occur, the Odex/Chitosan-NAC composition solidifies rapidly and forms a well-developed three-dimensional network in a short time span. Compare to typical hydrogels derived from natural materials, the Odex/Chitosan-NAC hydrogels are mechanically strong and resist degradation. The cytotoxicity potential of the hydrogels was determined by an in vitro viability assay using fibroblast as a model cell and the results reveal that the hydrogels are non-cytotoxic. In parallel, in vivo results from subdermal implantation in mice models demonstrate that this hydrogel is not only highly resistant to degradation but also induces very mild tissue response. PMID:21410248

  1. Thiolated chitosan nanoparticles for enhancing oral absorption of docetaxel: preparation, in vitro and ex vivo evaluation.

    PubMed

    Saremi, Shahrooz; Atyabi, Fatemeh; Akhlaghi, Seyedeh Parinaz; Ostad, Seyed Nasser; Dinarvand, Rassoul

    2011-01-12

    The aim of this study was to prepare and evaluate mucoadhesive core-shell nanoparticles based on copolymerization of thiolated chitosan coated on poly methyl methacrylate cores as a carrier for oral delivery of docetaxel. Docetaxel-loaded nanoparticles with various concentrations were prepared via a radical emulsion polymerization method using cerium ammonium nitrate as an initiator. The physicochemical properties of the obtained nanoparticles were characterized by: dynamic light-scattering analysis for their mean size, size distribution, and zeta potential; scanning electron microscopy and transmission electron microscopy for surface morphology; and differential scanning calorimetry analysis for confirmation of molecular dispersity of docetaxel in the nanoparticles. Nanoparticles were spherical with mean diameter below 200 nm, polydispersity of below 0.15, and positive zeta potential values. The entrapment efficiency of the nanoparticles was approximately 90%. In vitro release studies showed a sustained release characteristic for 10 days after a burst release at the beginning. Ex vivo studies showed a significant increase in the transportation of docetaxel from intestinal membrane of rat when formulated as nanoparticles. Cellular uptake of nanoparticles was investigated using fluoresceinamine-loaded nanoparticles. Docetaxel nanoparticles showed a high cytotoxicity effect in the Caco-2 and MCF-7 cell lines after 72 hours. It can be concluded that by combining the advantages of both thiolated polymers and colloidal particles, these nanoparticles can be proposed as a drug carrier system for mucosal delivery of hydrophobic drugs.

  2. Heme-thiolate ferryl of aromatic peroxygenase is basic and reactive

    PubMed Central

    Wang, Xiaoshi; Ullrich, René; Hofrichter, Martin; Groves, John T.

    2015-01-01

    A kinetic and spectroscopic characterization of the ferryl intermediate (APO-II) from APO, the heme-thiolate peroxygenase from Agrocybe aegerita, is described. APO-II was generated by reaction of the ferric enzyme with metachloroperoxybenzoic acid in the presence of nitroxyl radicals and detected with the use of rapid-mixing stopped-flow UV-visible (UV-vis) spectroscopy. The nitroxyl radicals served as selective reductants of APO-I, reacting only slowly with APO-II. APO-II displayed a split Soret UV-vis spectrum (370 nm and 428 nm) characteristic of thiolate ligation. Rapid-mixing, pH-jump spectrophotometry revealed a basic pKa of 10.0 for the FeIV−O−H of APO-II, indicating that APO-II is protonated under typical turnover conditions. Kinetic characterization showed that APO-II is unusually reactive toward a panel of benzylic C−H and phenolic substrates, with second-order rate constants for C−H and O−H bond scission in the range of 10–107 M−1⋅s−1. Our results demonstrate the important role of the axial cysteine ligand in increasing the proton affinity of the ferryl oxygen of APO intermediates, thus providing additional driving force for C−H and O−H bond scission. PMID:25759437

  3. Stabilizing subnanometer Ag(0) nanoclusters by thiolate and diphosphine ligands and their crystal structures

    NASA Astrophysics Data System (ADS)

    Yang, Huayan; Wang, Yu; Zheng, Nanfeng

    2013-03-01

    The combined use of thiolate and diphosphine as surface ligands helps to stabilize subnanometer Ag(0) nanoclusters, resulting in the successful crystallization of two Ag(0)-containing nanoclusters (Ag16 and Ag32) for X-ray single crystal analysis. Both clusters have core-shell structures with Ag86+ and Ag2212+ as their cores, which are not simply either fragments of face-centered cubic metals or their five-fold twinned counterparts. The clusters display UV-Vis absorption spectra consisting of molecule-like optical transitions.The combined use of thiolate and diphosphine as surface ligands helps to stabilize subnanometer Ag(0) nanoclusters, resulting in the successful crystallization of two Ag(0)-containing nanoclusters (Ag16 and Ag32) for X-ray single crystal analysis. Both clusters have core-shell structures with Ag86+ and Ag2212+ as their cores, which are not simply either fragments of face-centered cubic metals or their five-fold twinned counterparts. The clusters display UV-Vis absorption spectra consisting of molecule-like optical transitions. Electronic supplementary information (ESI) available: Experimental details, more pictures of the structure and XPS spectra of the clusters. CCDC 916463 and 916464. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3nr34328f

  4. Synthesis and In Vitro Antiproliferative Activity of Novel Phenyl Ring-Substituted 5-Alkyl-12(H)-quino[3,4-b][1,4]benzothiazine Derivatives.

    PubMed

    Zięba, Andrzej; Latocha, Małgorzata; Sochanik, Aleksander; Nycz, Anna; Kuśmierz, Dariusz

    2016-11-04

    A novel series of tetracyclic quinobenzothiazine derivatives was synthetized. Compounds containing a substituent (hydroxyl, methyl, phenyl, piperidyl, or piperazinyl) in positions 9 and 11 were obtained by cyclization of suitable 4-aminoquinolinium-3-thiolates. Quinobenzothiazine 10-O-substituted derivatives were obtained by alkylating the hydroxyl group in position 10 of the parent (quinobenzothiazine) system. Antiproliferative activity of the synthesized compounds was studied using cultured neoplastic cells (MDA-MB-231, SNB-19, and C-32 cell lines). Four selected compounds were investigated in more detail for cytotoxicity and antiproliferative effect. Transcriptional activity of genes regulating cell cycle (TP53), apoptosis (BAX, BCL-2), as well as proliferation (H3) were assessed. Finally, the ability of the selected compounds to bind DNA was checked in the presence of ethidium bromide.

  5. Characterization of self-assembled monolayers (SAMs) on silicon substrate comparative with polymer substrate for Escherichia coli O157:H7 detection

    NASA Astrophysics Data System (ADS)

    Moldovan, Carmen; Mihailescu, Carmen; Stan, Dana; Ruta, Lavinia; Iosub, Rodica; Gavrila, Raluca; Purica, Munizer; Vasilica, Schiopu

    2009-08-01

    This article presents the characterization of two substrates, silicon and polymer coated with gold, that are functionalized by mixed self-assembled monolayers (SAMs) in order to efficiently immobilize the anti- Escherichia coli O157:H7 polyclonal purified antibody. A biosurface functionalized by SAMs (self-assembled monolayers) technique has been developed. Immobilization of goat anti- E. coli O157:H7 antibody was performed by covalently bonding of thiolate mixed self-assembled monolayers (SAMs) realized on two substrates: polymer coated with gold and silicon coated with gold. The F(ab') 2 fragments of the antibodies have been used for eliminating nonspecific bindings between the Fc portions of antibodies and the Fc receptor on cells. The properties of the monolayers and the biofilm formatted with attached antibody molecules were analyzed at each step using infrared spectroscopy (FTIR-ATR), atomic force microscopy (AFM), scanning electron microscopy (SEM) and cyclic voltammetry (CV). In our study the gold-coated silicon substrates approach yielded the best results. These experimental results revealed the necessity to investigate each stage of the immobilization process taking into account in the same time the factors that influence the chemistry of the surface and the further interactions as well and also provide a solid basis for further studies aiming at elaborating sensitive and specific immunosensor or a microarray for the detection of E. coli O157:H7.

  6. On the inclusion of alkanes into the monolayer of aliphatic alcohols at the water/alkane vapor interface: a quantum chemical approach.

    PubMed

    Vysotsky, Yuri B; Fomina, Elena S; Belyaeva, Elena A; Fainerman, Valentin B; Vollhardt, Dieter

    2013-02-14

    In the framework of the quantum chemical semiempirical PM3 method thermodynamic and structural parameters of the formation and clusterization of aliphatic alcohols C(n)H(2n+1)OH (n(OH) = 8-16) at 298 K at the water/alkane vapor C(n)H(2n+2), (n(CH(3)) = 6-16) interface were calculated. The dependencies of enthalpy, entropy and Gibbs' energy of clusterization per one monomer molecule of 2D films on the alkyl chain length of corresponding alcohols and alkanes, the molar fraction of alkanes in the monolayers and the immersion degree of alcohol molecules into the water phase were shown to be linear or stepwise. The threshold of spontaneous clusterization of aliphatic alcohols at the water/alkane vapor interface was 10-11 carbon atoms at 298 K which is in line with experimental data at the air/water interface. It is shown that the presence of alkane vapor does not influence the process of alcohol monolayer formation. The structure of these monolayers is analogous to those obtained at the air/water interface in agreement with experimental data. The inclusion of alkane molecules into the amphiphilic monolayer at the water/alkane vapor interface is possible for amphiphiles with the spontaneous clusterization threshold at the air/water interface (n(s)(0)) of at least 16 methylene units in the alkyl chain, and it does not depend on the molar fraction of alkanes in the corresponding monolayer. The inclusion of alkanes from the vapor phase into the amphiphilic monolayer also requires that the difference between the alkyl chain lengths of alcohols and alkanes is not larger than n(s)(0) - 15 and n(s)(0) - 14 for the 2D film 1 and 2D film 2, respectively.

  7. Alkyl phosphonic acids and sulfonic acids in the Murchison meteorite

    NASA Technical Reports Server (NTRS)

    Cooper, George W.; Onwo, Wilfred M.; Cronin, John R.

    1992-01-01

    Homologous series of alkyl phosphonic acids and alkyl sulfonic acids, along with inorganic orthophosphate and sulfate, are identified in water extracts of the Murchison meteorite after conversion to their t-butyl dimethylsilyl derivatives. The methyl, ethyl, propyl, and butyl compounds are observed in both series. Five of the eight possible alkyl phosphonic acids and seven of the eight possible alkyl sulfonic acids through C4 are identified. Abundances decrease with increasing carbon number as observed of other homologous series indigenous to Murchison. Concentrations range downward from approximately 380 nmol/gram in the alkyl sulfonic acid series, and from 9 nmol/gram in the alkyl phosphonic acid series.

  8. Chiral Alkyl Halides: Underexplored Motifs in Medicine

    PubMed Central

    Gál, Bálint; Bucher, Cyril; Burns, Noah Z.

    2016-01-01

    While alkyl halides are valuable intermediates in synthetic organic chemistry, their use as bioactive motifs in drug discovery and medicinal chemistry is rare in comparison. This is likely attributable to the common misconception that these compounds are merely non-specific alkylators in biological systems. A number of chlorinated compounds in the pharmaceutical and food industries, as well as a growing number of halogenated marine natural products showing unique bioactivity, illustrate the role that chiral alkyl halides can play in drug discovery. Through a series of case studies, we demonstrate in this review that these motifs can indeed be stable under physiological conditions, and that halogenation can enhance bioactivity through both steric and electronic effects. Our hope is that, by placing such compounds in the minds of the chemical community, they may gain more traction in drug discovery and inspire more synthetic chemists to develop methods for selective halogenation. PMID:27827902

  9. The effect of the antioxidant on the properties of thiolated poly(aspartic acid) polymers in aqueous ocular formulations.

    PubMed

    Budai-Szűcs, Mária; Horvát, Gabriella; Gyarmati, Benjámin; Szilágyi, Barnabás Áron; Szilágyi, András; Berkó, Szilvia; Ambrus, Rita; Szabó-Révész, Piroska; Sandri, Giuseppina; Bonferoni, Maria Cristina; Caramella, Carla; Csányi, Erzsébet

    2017-04-01

    Thiolated polymers are a promising new group of excipients, but their stability against atmospheric oxidation has not been investigated in detail, and only a few efforts have been made to improve their stability. The oxidation of the thiol groups in solutions of thiolated polymers may result in a decrease of mucoadhesion and unpredictable in situ gelation. The aims of our work were to study the stability of aqueous solutions of thiolated polymers and the effects of stabilizing agents. We investigated thiolated poly(aspartic acid) polymers stabilized with dithiothreitol, glutathione or acetylcysteine. The effects of these antioxidants on the gel structure, mucoadhesion and drug release were determined by means of scanning electron microscopy, swelling, rheology, adhesion and drug release tests. It was concluded that the stability of polymer solutions containing antioxidants is sufficient for one day. Polymers stabilized with dithiotreitol demonstrated fast swelling and drug release, but weaker mucoadhesion as compared with the other samples. Polymers stabilized with glutathione displayed the weakest cohesive properties, resulting in fast and uncontrolled drug release and moderate mucoadhesion. Acetylcysteine-stabilized polymers exhibited an optimum cross-linked structure, with free thiol groups ensuring polymer-mucin interactions, resulting in the best mucoadhesive properties.

  10. Improvement of Thiolate/Disulfide Mediated Dye-Sensitized Solar Cells through Supramolecular Lithium Cation Assembling of Crown Ether

    PubMed Central

    Liu, Linfeng; Li, Xiong; Chen, Jiangzhao; Rong, Yaoguang; Ku, Zhiliang; Han, Hongwei

    2013-01-01

    A supramolecular lithium cation assemblies of crown ether, [Li⊂12-crown-4]+, has been used to replace conventional tetraalkylammonium counterion in thiolate/disulfide (ET−/BET) mediated dye-sensitized solar cells (DSCs), which exhibit high stability and efficiency of 6.61% under 100 mW·cm−2 simulated sunlight illumination. PMID:23933601

  11. Monohalogenated acetamide-induced cellular stress and genotoxicity are related to electrophilic softness and thiol/thiolate reactivity.

    PubMed

    Pals, Justin A; Wagner, Elizabeth D; Plewa, Michael J; Xia, Menghang; Attene-Ramos, Matias S

    2017-08-01

    Haloacetamides (HAMs) are cytotoxic, genotoxic, and mutagenic byproducts of drinking water disinfection. They are soft electrophilic compounds that form covalent bonds with the free thiol/thiolate in cysteine residues through an SN2 reaction mechanism. Toxicity of the monohalogenated HAMs (iodoacetamide, IAM; bromoacetamide, BAM; or chloroacetamide, CAM) varied depending on the halogen substituent. The aim of this research was to investigate how the halogen atom affects the reactivity and toxicological properties of HAMs, measured as induction of oxidative/electrophilic stress response and genotoxicity. Additionally, we wanted to determine how well in silico estimates of electrophilic softness matched thiol/thiolate reactivity and in vitro toxicological endpoints. Each of the HAMs significantly induced nuclear Rad51 accumulation and ARE signaling activity compared to a negative control. The rank order of effect was IAM>BAM>CAM for Rad51, and BAM≈IAM>CAM for ARE. In general, electrophilic softness and in chemico thiol/thiolate reactivity provided a qualitative indicator of toxicity, as the softer electrophiles IAM and BAM were more thiol/thiolate reactive and were more toxic than CAM. Copyright © 2017. Published by Elsevier B.V.

  12. Nickel-catalyzed thiolation of unactivated aryl C-H bonds: efficient access to diverse aryl sulfides.

    PubMed

    Yan, Sheng-Yi; Liu, Yue-Jin; Liu, Bin; Liu, Yan-Hua; Shi, Bing-Feng

    2015-03-07

    A nickel-catalyzed thiolation of unactivated C(sp(2))-H bonds with disulfides employing the PIP directing group was described. This process uses a catalytic nickel catalyst and no metallic oxidants or cocatalysts are required. The reaction tolerates various important functional groups and heteroarenes, providing an efficient synthetic pathway to access diverse diaryl sulfides.

  13. Alkyl ferulates in wound healing potato tubers.

    PubMed

    Bernards, M A; Lewis, N G

    1992-10-01

    Seven ferulic acid esters of 1-alkanols ranging in carbon length from C16 to C28 were synthesized and an HPLC protocol for their separation developed. Extracts prepared from wound healing potato (Solanum tuberosum) tubers and analysed by HPLC indicated that alkyl ferulate esters begin to accumulate 3-7 days after wound treatment. Of the nine esters identified by EIMS, (including two esters of odd chain length alkanols) hexadecyl and octadecyl ferulates were predominant. Alkyl ferulate esters were restricted to the wound periderm.

  14. Transition metal-free decarboxylative alkylation reactions.

    PubMed

    Liu, Ping; Zhang, Guanghui; Sun, Peipei

    2016-11-22

    This review summarizes advances in the decarboxylative alkylation of carboxylic acids and their derivatives under transition metal-free conditions in recent years. Unlike most transition metal-catalyzed decarboxylative coupling reactions which tend to undergo catalytic cycles, the mechanisms of reactions under metal-free conditions are usually diverse and even ambiguous in some cases. This article offers an overview of reaction types and their corresponding mechanisms, highlights some of the advantages and limitations, and focuses on introducing UV and visible light-induced, organocatalyst and peroxide promoted radical processes for decarboxylative alkylation and the formation of C-C bonds.

  15. Modeling Stimuli-Responsive Nanoparticle Monolayer

    NASA Astrophysics Data System (ADS)

    Yong, Xin

    2015-03-01

    Using dissipative particle dynamics (DPD), we model a monolayer formed at the water-oil interface, which comprises stimuli-responsive nanoparticles. The solid core of the nanoparticle encompasses beads arranged in an fcc lattice structure and its surface is uniformly grafted with stimuli-responsive polymer chains. The surface-active nanoparticles adsorb to the interface from the suspension to minimize total energy of the system and create a monolayer covering the interface. We investigate the monolayer formation by characterizing the detailed adsorption kinetics. We explore the microstructure of the monolayer at different surface coverage, including the particle crowding and ordering, and elucidate the response of monolayer to external stimuli. The collective behavior of the particles within the monolayer is demonstrated quantitatively by vector-vector autocorrelation functions. This study provides a fundamental understanding of the interfacial behavior of stimuli-responsive nanoparticles.

  16. Plasma protein thiolation index (PTI) as a biomarker of thiol-specific oxidative stress in haemodialyzed patients.

    PubMed

    Colombo, Graziano; Reggiani, Francesco; Podestà, Manuel A; Garavaglia, Maria Lisa; Portinaro, Nicola M; Milzani, Aldo; Badalamenti, Salvatore; Dalle-Donne, Isabella

    2015-12-01

    The role of oxidative stress in patients with end stage renal disease (ESRD), which occurs at significantly higher levels than in the general population, is often underestimated in clinical practice. Emerging evidence highlights the strong correlation of oxidative stress with chronic inflammation and cardiovascular disease, which are highly prevalent in most patients on maintenance haemodialysis (HD) and are a major risk factor for mortality in this population. In this study, total plasma thiols and plasma S-thiolated proteins were measured in patients with ESRD, before and after a regular HD session, and compared to age-matched healthy subjects. We found a significant decrease in the level of total plasma thiols and, conversely, a significant increase in the level of S-thiolated proteins in these patients. In most patients, post-HD plasma level of total thiols did not differ from the one in healthy subjects, whereas plasma level of S-thiolated proteins was lower in HD patients than in age-matched healthy controls. This suggests that a single HD session restores plasma thiol redox status and re-establishes the antioxidant capacity of plasma thiols. Additionally, we determined protein thiolation index (PTI), i.e., the molar ratio between the sum of all low molecular mass thiols bound to S-thiolated plasma proteins and protein free cysteinyl residues. Patients with ESRD had a significantly higher PTI compared to age-matched healthy subjects and HD was associated with a decrease in PTI to normal, or lower than normal, levels. Although this study is limited in size, our results suggest that PTI is a useful indicator of thiol-specific oxidative stress in patients with ESRD on maintenance HD. This study also emphasizes that PTI determination is a cheap and simple tool suitable for large-scale clinical studies that could be used for routine screening of thiol-specific oxidative stress.

  17. Preparation and characterization of laminated thiolated chitosan-based freeze-dried wafers for potential buccal delivery of macromolecules.

    PubMed

    Boateng, Joshua S; Ayensu, Isaac

    2014-05-01

    This study involves the development and functional characterization of a thiolated chitosan (CS) system for potential buccal delivery of proteins. Thiolated CS was synthesized by conjugating pure CS with thioglycolic acid and dialyzed to remove excess acid. Amount of thiol groups immobilized on CS was determined using L-cysteine calibration curve. The weight average molecular weights of CS and thiolated CS were monitored using gel permeation chromatography. Laminated wafers were obtained by pouring gels (containing bovine serum albumin; BSA, different amounts of glutathione as enzyme inhibitor and mucin to mimic salivary conditions) of the thiolated CS into moulds previously lined with impervious ethylcellulose (EC) films and freeze-dried. The resulting formulations were analyzed using attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy, circular dichroism (CD) and scanning electron microscopy (SEM). The formulations were further characterized for functional buccal mucosa performance using hydration, swelling, mucoadhesion and in vitro drug dissolution studies. FTIR showed successful thiolation of CS's amine functionality, CD confirmed that BSA conformation remained unchanged throughout the gel formulation and freeze-drying process, whilst SEM showed a porous microstructure of the wafers and a uniform EC film laminate with no visible pores or cracks. The functional characterization studies showed that glutathione had significant effects on hydration, mucoadhesion and subsequently drug dissolution and release characteristics, whilst mucin affected the mucoadhesive properties of the wafers. It was concluded that BSA-loaded wafers containing 10% w/w glutathione as enzyme inhibitor was the formulation choice for potential buccal delivery and should be selected for further investigations.

  18. Metal-Assisted Oxo Atom Addition to an Fe(III) Thiolate.

    PubMed

    Villar-Acevedo, Gloria; Lugo-Mas, Priscilla; Blakely, Maike N; Rees, Julian A; Ganas, Abbie S; Hanada, Erin M; Kaminsky, Werner; Kovacs, Julie A

    2017-01-11

    Cysteinate oxygenation is intimately tied to the function of both cysteine dioxygenases (CDOs) and nitrile hydratases (NHases), and yet the mechanisms by which sulfurs are oxidized by these enzymes are unknown, in part because intermediates have yet to be observed. Herein, we report a five-coordinate bis-thiolate ligated Fe(III) complex, [Fe(III)(S2(Me2)N3(Pr,Pr))](+) (2), that reacts with oxo atom donors (PhIO, IBX-ester, and H2O2) to afford a rare example of a singly oxygenated sulfenate, [Fe(III)(η(2)-S(Me2)O)(S(Me2))N3(Pr,Pr)](+) (5), resembling both a proposed intermediate in the CDO catalytic cycle and the essential NHase Fe-S(O)(Cys114) proposed to be intimately involved in nitrile hydrolysis. Comparison of the reactivity of 2 with that of a more electron-rich, crystallographically characterized derivative, [Fe(III)S2(Me2)N(Me)N2(amide)(Pr,Pr)](-) (8), shows that oxo atom donor reactivity correlates with the metal ion's ability to bind exogenous ligands. Density functional theory calculations suggest that the mechanism of S-oxygenation does not proceed via direct attack at the thiolate sulfurs; the average spin-density on the thiolate sulfurs is approximately the same for 2 and 8, and Mulliken charges on the sulfurs of 8 are roughly twice those of 2, implying that 8 should be more susceptible to sulfur oxidation. Carboxamide-ligated 8 is shown to be unreactive towards oxo atom donors, in contrast to imine-ligated 2. Azide (N3(-)) is shown to inhibit sulfur oxidation with 2, and a green intermediate is observed, which then slowly converts to sulfenate-ligated 5. This suggests that the mechanism of sulfur oxidation involves initial coordination of the oxo atom donor to the metal ion. Whether the green intermediate is an oxo atom donor adduct, Fe-O═I-Ph, or an Fe(V)═O remains to be determined.

  19. Thiolation of arabinoxylan and its application in the fabrication of controlled release mucoadhesive oral films.

    PubMed

    Hanif, Muhammad; Zaman, Muhammad

    2017-03-20

    Mucoadhesion is an important property that helps oral drug delivery system to remain attached with buccal mucosa and hence to improve the delivery of the drug. The current study was designed to achieve the thiol modification of Arabinoxylan (ARX) and to develop a mucoadhesive oral film for the improved delivery of tizanidine hydrochloride (TZN HCl). Synthesis of thiolated arabinoxylan (TARX) was accomplished by esterification of ARX with thioglycolic acid (TGA). TARX was further used for the development of mucoadhesive oral films which were prepared by using a solvent casting technique. Formulation of the films was designed and optimized by using central composite design (CCRD), selecting TARX (X1) and glycerol (X2) as variables. Prepared film formulations were evaluated for mechanical strength, ex-vivo mucoadhesion, in-vitro drug release, ex-vivo drug permeation, surface morphology and drug contents. Thiolation of ARX was confirmed by fourier transform infra-red spectroscopy (FTIR) as a peak related to thiol group appeared at 2516 cm(-1). The claim of successful thiolation of ARX was strengthened by the presence of 2809.003 ± 1.03 μmoles of thiol contents per gram of the polymer, which was determined by Ellman's reagent method. From the results, it was observed that the films were of satisfactory mechanical strength and mucoadhesiveness with folding endurance greater than 300 and mucoadhesive strength 11.53 ± 0.17 N, respectively. Reasonable drug retention was observed during in-vitro dissolution (85.03% cumulative drug release) and ex-vivo permeation (78.90% cumulative amount of permeated drug) studies conducted for 8 h. Effects of varying concentrations of both polymer and plasticizer on prepared mucoadhesive oral films were evaluated by ANOVA and it was observed that glycerol can enhanced the dissolution as well as permeation of the drug while TARX has opposite impact on these parameters. In nutshell, TARX in combination with glycerolwas found to

  20. Enhancement of alkylation catalysts for improved supercritical fluid regeneration

    DOEpatents

    Ginosar, Daniel M.; Petkovic, Lucia

    2009-09-22

    A method of modifying an alkylation catalyst to reduce the formation of condensed hydrocarbon species thereon. The method comprises providing an alkylation catalyst comprising a plurality of active sites. The plurality of active sites on the alkylation catalyst may include a plurality of weakly acidic active sites, intermediate acidity active sites, and strongly acidic active sites. A base is adsorbed to a portion of the plurality of active sites, such as the strongly acidic active sites, selectively poisoning the strongly acidic active sites. A method of modifying the alkylation catalyst by providing an alkylation catalyst comprising a pore size distribution that sterically constrains formation of the condensed hydrocarbon species on the alkylation catalyst or by synthesizing the alkylation catalyst to comprise a decreased number of strongly acidic active sites is also disclosed, as is a method of improving a regeneration efficiency of the alkylation catalyst.

  1. Enhancement of alkylation catalysts for improved supercritical fluid regeneration

    DOEpatents

    Ginosar, Daniel M.; Petkovic, Lucia M.

    2010-12-28

    A method of modifying an alkylation catalyst to reduce the formation of condensed hydrocarbon species thereon. The method comprises providing an alkylation catalyst comprising a plurality of active sites. The plurality of active sites on the alkylation catalyst may include a plurality of weakly acidic active sites, intermediate acidity active sites, and strongly acidic active sites. A base is adsorbed to a portion of the plurality of active sites, such as the strongly acidic active sites, selectively poisoning the strongly acidic active sites. A method of modifying the alkylation catalyst by providing an alkylation catalyst comprising a pore size distribution that sterically constrains formation of the condensed hydrocarbon species on the alkylation catalyst or by synthesizing the alkylation catalyst to comprise a decreased number of strongly acidic active sites is also disclosed, as is a method of improving a regeneration efficiency of the alkylation catalyst.

  2. Self-assembly of an unprecedented polyoxomolybdate anion [Mo20O66]12- in a giant peanut-like 62-core silver-thiolate nanocluster.

    PubMed

    Huang, Ren-Wu; Xu, Qing-Qing; Lu, Hong-Lin; Guo, Xiao-Kang; Zang, Shuang-Quan; Gao, Guang-Gang; Tang, Ming-Sheng; Mak, Thomas C W

    2015-04-28

    A polyoxometalate-templated silver thiolate nanocluster, [Ag62(S(t)Bu)40(Mo20O66)(Mo6O19)3(CH3CN)2]·(CF3SO3)4 (1), has been isolated, in which a giant peanut-like silver(i)-thiolate cluster [Ag62(S(t)Bu)40](22+) encapsulates an unprecedented [Mo20O66](12-) polyoxoanion core. It opens a new approach for the synthesis of both elusive polyoxometalates and high-nuclearity silver(i)-thiolate nanoclusters.

  3. Hematite nanoparticle monolayers on mica electrokinetic characteristics.

    PubMed

    Morga, Maria; Adamczyk, Zbigniew; Oćwieja, Magdalena

    2012-11-15

    Electrokinetic properties of α-Fe(2)O(3) (hematite) nanoparticle monolayers on mica were thoroughly characterized using the streaming potential method. Hematite suspensions were obtained by acidic hydrolysis of ferric chloride. The average size of particles (hydrodynamic diameter), determined by dynamic light scattering (DLS) and AFM, was 22 nm (pH=5.5, I=10(-2)M). The hematite monolayers on mica were produced under diffusion-controlled transport from the suspensions of various bulk concentration. The monolayer coverage, quantitatively determined by AFM and SEM, was regulated within broad limits by adjusting the nanoparticle deposition time. This allowed one to uniquely express zeta potential of hematite monolayers, determined by the streaming potential measurements, in terms of the particle coverage. Such dependencies, obtained for various pH, were successfully interpreted in terms of the three-dimensional electrokinetic model. A universal calibrating graph was produced enabling one to determine hematite monolayer coverage from the measured value of the streaming potential. The influence of the ionic strength, varied between 10(-4) and 10(-2)M, on the zeta potential of hematite monolayers was also studied. Additionally, the stability of monolayers (desorption kinetics) was determined under in situ conditions using the streaming potential method. Our experimental data prove that it is feasible to produce uniform and stable hematite particle monolayers of well-controlled coverage. Such monolayers may find practical applications as universal substrates for protein immobilization (biosensors) and in electrocatalytic applications. Copyright © 2012 Elsevier Inc. All rights reserved.

  4. Structure and shear response of lipid monolayers

    SciTech Connect

    Dutta, P.; Ketterson, J.B.

    1990-02-01

    Organic monolayers and multilayers are both scientifically fascinating and technologically promising; they are, however, both complex systems and relatively inaccessible to experimental probes. In this Progress Report, we describe our X-ray diffraction studies, which have given us substantial new information about the structures and phase transitions in monolayers on the surface of water; our use of these monolayers as a unique probe of the dynamics of wetting and spreading; and our studies of monolayer mechanical properties using a simple but effective technique available to anyone using the Wilhelmy method to measure surface tension.

  5. Equilibrating Nanoparticle Monolayers Using Wetting Films

    SciTech Connect

    Pontoni, D.; Alvine, K; Checco, A; Gang, O; Ocko, B; Pershan, P

    2009-01-01

    Monolayers of bimodal gold nanoparticles on silicon are investigated by a combination of microscopy (dry monolayers) and x-ray diffraction (dry and wet monolayers). In the presence of an excess of small particles, the nanoscale packing structure closely resembles the small-particle-rich scenario of the structural crossover transition that has been predicted and also observed with micron-scale hard-sphere colloids. Structural morphology is monitored in situ during monolayer dissolution and reassembly within the thin liquid wetting film. This approach allows investigation of size and solvent effects on nanoparticles in quasi-two-dimensional confinement.

  6. Sensitive methods for estimating the anchoring strength of nematic liquid crystals on Langmuir-Blodgett monolayers of fatty acids

    SciTech Connect

    Fazio, Valentina S. U.; Nannelli, Francesca; Komitov, Lachezar

    2001-06-01

    The anchoring of the nematic liquid crystal N-(p-methoxybenzylidene)-p-butylaniline (MBBA) on Langmuir-Blodgett monolayers of fatty acids (COOHC{sub n}H{sub 2n+1}) was studied as a function of the length of the fatty acid alkyl chain n (n=15,17,19,21). The monolayers were deposited onto glass plates coated with indium tin oxide, which were used to assemble sandwich cells of various thicknesses that were filled with MBBA in the nematic phase. The mechanism of relaxation from the flow-induced quasiplanar to the surface-induced homeotropic alignment was studied for the four aligning monolayers. It was found that the speed of the relaxation decreases linearly with increasing length of the alkyl chain n, which suggests that the Langmuir-Blodgett film plays a role in the phenomenon. This fact was confirmed by a sensitive estimation of the anchoring strength of MBBA on the fatty acid monolayers after anchoring breaking, which takes place at the transition between two electric-field-induced turbulent states, denoted as DSM1 and DSM2 (where DSM indicates dynamic scattering mode). It was found that the threshold electric field for the anchoring breaking, which can be considered as a measure of the anchoring strength, also decreases linearly as n increases. Both methods thus possess a high sensitivity in resolving small differences in anchoring strength. In cells coated with mixed Langmuir-Blodgett monolayers of two fatty acids (n=15 and n=17) a maximum of the relaxation speed was observed when the two acids were present in equal amounts. This observation suggests an efficient method for controlling the anchoring strength in homeotropic cells by changing the ratio between the components of the surfactant film.

  7. IONIC LIQUID-CATALYZED ALKYLATION OF ISOBUTANE WITH 2-BUTENE

    EPA Science Inventory

    A detailed study of the alkylation of isobutane with 2-butene in ionic liquid media has been conducted using 1-alkyl-3-methylimidazolium halides?aluminum chloride encompassing various alkyl groups (butyl-, hexyl-, and octyl-) and halides (Cl, Br, and I) on its cations and anions,...

  8. 40 CFR 721.2825 - Alkyl ester (generic name).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Alkyl ester (generic name). 721.2825... Substances § 721.2825 Alkyl ester (generic name). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance alkyl ester (PMN P-84-968) is subject to reporting under this section...

  9. 40 CFR 721.2825 - Alkyl ester (generic name).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alkyl ester (generic name). 721.2825... Substances § 721.2825 Alkyl ester (generic name). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance alkyl ester (PMN P-84-968) is subject to reporting under this section...

  10. 40 CFR 721.2420 - Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ..., alkyl sulfate salt. 721.2420 Section 721.2420 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2420 Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt. (a... generically as an alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt (PMN P-91-288) is subject...

  11. 40 CFR 721.2410 - Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ..., alkyl sulfate salts. 721.2410 Section 721.2410 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2410 Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts. (a... generically as alkoxylated dialkyldiethylenetriamine, alkyl sulfate salts (PMN P-94-325, 326, and 327)...

  12. 40 CFR 721.2410 - Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ..., alkyl sulfate salts. 721.2410 Section 721.2410 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2410 Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts. (a... generically as alkoxylated dialkyldiethylenetriamine, alkyl sulfate salts (PMN P-94-325, 326, and 327)...

  13. 40 CFR 721.2420 - Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ..., alkyl sulfate salt. 721.2420 Section 721.2420 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2420 Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt. (a... generically as an alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt (PMN P-91-288) is subject...

  14. 40 CFR 721.2410 - Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ..., alkyl sulfate salts. 721.2410 Section 721.2410 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2410 Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts. (a... generically as alkoxylated dialkyldiethylenetriamine, alkyl sulfate salts (PMN P-94-325, 326, and 327)...

  15. 40 CFR 721.2410 - Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ..., alkyl sulfate salts. 721.2410 Section 721.2410 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2410 Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts. (a... generically as alkoxylated dialkyldiethylenetriamine, alkyl sulfate salts (PMN P-94-325, 326, and 327)...

  16. 40 CFR 721.2420 - Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ..., alkyl sulfate salt. 721.2420 Section 721.2420 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2420 Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt. (a... generically as an alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt (PMN P-91-288) is subject...

  17. 40 CFR 721.2420 - Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ..., alkyl sulfate salt. 721.2420 Section 721.2420 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2420 Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt. (a... generically as an alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt (PMN P-91-288) is subject...

  18. 40 CFR 721.2410 - Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ..., alkyl sulfate salts. 721.2410 Section 721.2410 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2410 Alkoxylated alkyldiethylenetriamine, alkyl sulfate salts. (a... generically as alkoxylated dialkyldiethylenetriamine, alkyl sulfate salts (PMN P-94-325, 326, and 327)...

  19. 40 CFR 721.2420 - Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ..., alkyl sulfate salt. 721.2420 Section 721.2420 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Specific Chemical Substances § 721.2420 Alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt. (a... generically as an alkoxylated dialkyldiethylenetriamine, alkyl sulfate salt (PMN P-91-288) is subject...

  20. 40 CFR 721.10233 - Linear alkyl epoxide (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Linear alkyl epoxide (generic). 721... Substances § 721.10233 Linear alkyl epoxide (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as linear alkyl epoxide (PMN...

  1. 40 CFR 721.10233 - Linear alkyl epoxide (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Linear alkyl epoxide (generic). 721... Substances § 721.10233 Linear alkyl epoxide (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as linear alkyl epoxide (PMN...

  2. 40 CFR 721.10233 - Linear alkyl epoxide (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Linear alkyl epoxide (generic). 721... Substances § 721.10233 Linear alkyl epoxide (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified generically as linear alkyl epoxide (PMN...

  3. 40 CFR 721.4136 - Alkyl heteropolycyclic-aniline (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alkyl heteropolycyclic-aniline... Specific Chemical Substances § 721.4136 Alkyl heteropolycyclic-aniline (generic). (a) Chemical substance... alkyl heteropolycyclic-aniline (PMN P-00-0067) is subject to reporting under this section for...

  4. 40 CFR 721.5769 - Mixture of nitrated alkylated phenols.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Mixture of nitrated alkylated phenols... Substances § 721.5769 Mixture of nitrated alkylated phenols. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as a mixture of nitrated alkylated...

  5. 40 CFR 721.5769 - Mixture of nitrated alkylated phenols.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Mixture of nitrated alkylated phenols... Substances § 721.5769 Mixture of nitrated alkylated phenols. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as a mixture of nitrated alkylated...

  6. 40 CFR 721.5769 - Mixture of nitrated alkylated phenols.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Mixture of nitrated alkylated phenols... Substances § 721.5769 Mixture of nitrated alkylated phenols. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as a mixture of nitrated alkylated...

  7. 40 CFR 721.5769 - Mixture of nitrated alkylated phenols.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Mixture of nitrated alkylated phenols... Substances § 721.5769 Mixture of nitrated alkylated phenols. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as a mixture of nitrated alkylated...

  8. 40 CFR 721.5769 - Mixture of nitrated alkylated phenols.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Mixture of nitrated alkylated phenols... Substances § 721.5769 Mixture of nitrated alkylated phenols. (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance identified as a mixture of nitrated alkylated...

  9. IONIC LIQUID-CATALYZED ALKYLATION OF ISOBUTANE WITH 2-BUTENE

    EPA Science Inventory

    A detailed study of the alkylation of isobutane with 2-butene in ionic liquid media has been conducted using 1-alkyl-3-methylimidazolium halides?aluminum chloride encompassing various alkyl groups (butyl-, hexyl-, and octyl-) and halides (Cl, Br, and I) on its cations and anions,...

  10. 40 CFR 721.555 - Alkyl amino nitriles (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alkyl amino nitriles (generic). 721... Substances § 721.555 Alkyl amino nitriles (generic). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substances identified generically as alkyl amino nitriles (PMNs P-96...

  11. 40 CFR 721.4136 - Alkyl heteropolycyclic-aniline (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Alkyl heteropolycyclic-aniline... Specific Chemical Substances § 721.4136 Alkyl heteropolycyclic-aniline (generic). (a) Chemical substance... alkyl heteropolycyclic-aniline (PMN P-00-0067) is subject to reporting under this section for the...

  12. 40 CFR 721.4136 - Alkyl heteropolycyclic-aniline (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Alkyl heteropolycyclic-aniline... Specific Chemical Substances § 721.4136 Alkyl heteropolycyclic-aniline (generic). (a) Chemical substance... alkyl heteropolycyclic-aniline (PMN P-00-0067) is subject to reporting under this section for the...

  13. 40 CFR 721.4136 - Alkyl heteropolycyclic-aniline (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Alkyl heteropolycyclic-aniline... Specific Chemical Substances § 721.4136 Alkyl heteropolycyclic-aniline (generic). (a) Chemical substance... alkyl heteropolycyclic-aniline (PMN P-00-0067) is subject to reporting under this section for the...

  14. 40 CFR 721.4136 - Alkyl heteropolycyclic-aniline (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Alkyl heteropolycyclic-aniline... Specific Chemical Substances § 721.4136 Alkyl heteropolycyclic-aniline (generic). (a) Chemical substance... alkyl heteropolycyclic-aniline (PMN P-00-0067) is subject to reporting under this section for the...

  15. Copper-catalyzed radical carbooxygenation: alkylation and alkoxylation of styrenes.

    PubMed

    Liao, Zhixiong; Yi, Hong; Li, Zheng; Fan, Chao; Zhang, Xu; Liu, Jie; Deng, Zixin; Lei, Aiwen

    2015-01-01

    A simple copper-catalyzed direct radical carbooxygenation of styrenes is developed utilizing alkyl bromides as radical resources. This catalytic radical difunctionalization accomplishes both alkylation and alkoxylation of styrenes in one pot. A broad range of styrenes and alcohols are well tolerated in this transformation. The EPR experiment shows that alkyl halides could oxidize Cu(I) to Cu(II) in this transformation.

  16. 40 CFR 721.10699 - Polyfluorinated alkyl thio acrylamide (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Polyfluorinated alkyl thio acrylamide... Specific Chemical Substances § 721.10699 Polyfluorinated alkyl thio acrylamide (generic). (a) Chemical... as polyfluorinated alkyl thio acrylamide (PMN P-11-529) is subject to reporting under this...

  17. 40 CFR 721.2825 - Alkyl ester (generic name).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Alkyl ester (generic name). 721.2825... Substances § 721.2825 Alkyl ester (generic name). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance alkyl ester (PMN P-84-968) is subject to reporting under this...

  18. 40 CFR 721.2825 - Alkyl ester (generic name).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Alkyl ester (generic name). 721.2825... Substances § 721.2825 Alkyl ester (generic name). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance alkyl ester (PMN P-84-968) is subject to reporting under this...

  19. 40 CFR 721.2825 - Alkyl ester (generic name).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Alkyl ester (generic name). 721.2825... Substances § 721.2825 Alkyl ester (generic name). (a) Chemical substance and significant new uses subject to reporting. (1) The chemical substance alkyl ester (PMN P-84-968) is subject to reporting under this...

  20. 40 CFR 721.10087 - Substituted alkyl phosphine oxide (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Substituted alkyl phosphine oxide... Specific Chemical Substances § 721.10087 Substituted alkyl phosphine oxide (generic). (a) Chemical... as substituted alkyl phosphine oxide (PMN P-06-332) is subject to reporting under this section for...

  1. 40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 32 2012-07-01 2012-07-01 false Alkali metal alkyl borohydride... Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a) Chemical substance... alkali metal alkyl borohydride (PMN P-00-1089) is subject to reporting under this section for...

  2. 40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 32 2013-07-01 2013-07-01 false Alkali metal alkyl borohydride... Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a) Chemical substance... alkali metal alkyl borohydride (PMN P-00-1089) is subject to reporting under this section for...

  3. 40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Alkali metal alkyl borohydride... Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a) Chemical substance... alkali metal alkyl borohydride (PMN P-00-1089) is subject to reporting under this section for...

  4. 40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 31 2014-07-01 2014-07-01 false Alkali metal alkyl borohydride... Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a) Chemical substance... alkali metal alkyl borohydride (PMN P-00-1089) is subject to reporting under this section for...

  5. 40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 31 2011-07-01 2011-07-01 false Alkali metal alkyl borohydride... Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic). (a) Chemical substance... alkali metal alkyl borohydride (PMN P-00-1089) is subject to reporting under this section for...

  6. In vitro testing of thiolated poly(aspartic acid) from ophthalmic formulation aspects.

    PubMed

    Budai-Szű Cs, Mária; Horvát, Gabriella; Gyarmati, Benjámin; Szilágyi, Barnabás Áron; Szilágyi, András; Csihi, Tímea; Berkó, Szilvia; Szabó-Révész, Piroska; Mori, Michela; Sandri, Giuseppina; Bonferoni, Maria Cristina; Caramella, Carla; Csányi, Erzsébet

    2016-08-01

    Ocular drug delivery formulations must meet anatomical, biopharmaceutical, patient-driven and regulatory requirements. Mucoadhesive polymers can serve as a better alternative to currently available ophthalmic formulations by providing improved bioavailability. If all requirements are addressed, a polymeric formulation resembling the tear film of the eye might be the best solution. The optimum formulation must not have high osmotic activity, should provide appropriate surface tension, pH and refractive index, must be non-toxic and should be transparent and mucoadhesive. We would like to highlight the importance of in vitro polymer testing from a pharmaceutical aspect. We, therefore, carried out physical-chemical investigations to verify the suitability of certain systems for ophthalmic formulations. In this work, in situ gelling, mucoadhesive thiolated poly(aspartic acid)s were tested from ophthalmic formulation aspects. The results of preformulation measurements indicate that these polymers can be used as potential carriers in ophthalmic drug delivery.

  7. Self-assembly of thiolated cyanine aggregates on Au(111) and Au nanoparticle surfaces

    NASA Astrophysics Data System (ADS)

    Menéndez, Guillermo O.; Cortés, Emiliano; Grumelli, Doris; Méndez de Leo, Lucila P.; Williams, Federico J.; Tognalli, Nicolás G.; Fainstein, Alejandro; Vela, María Elena; Jares-Erijman, Elizabeth A.; Salvarezza, Roberto C.

    2012-01-01

    Heptamethinecyanine J-aggregates display sharp, intense fluorescence emission making them attractive candidates for developing a variety of chem-bio-sensing applications. They have been immobilized on planar thiol-covered Au surfaces and thiol-capped Au nanoparticles by weak molecular interactions. In this work the self-assembly of novel thiolated cyanine (CNN) on Au(111) and citrate-capped AuNPs from solutions containing monomers and J-aggregates has been studied by using STM, XPS, PM-IRRAS, electrochemical techniques and Raman spectroscopy. Data show that CNN species adsorb on the Au surfaces by forming thiolate-Au bonds. We found that the J-aggregates are preferentially adsorbed on the Au(111) surface directly from the solution while adsorbed CNN monomers cannot organize into aggregates on the substrate surface. These results indicate that the CNN-Au interaction is not able to disorganize the large J-aggregates stabilized by π-π stacking to optimize the S-Au binding site but it is strong enough to hinder the π-π stacking when CNNs are chemisorbed as monomers. The optical properties of the J-aggregates remain active after adsorption. The possibility of covalently bonding CNN J-aggregates to Au planar surfaces and Au nanoparticles controlling the J-aggregate/Au distance opens a new path regarding their improved stability and the wide range of biological applications of both CNN and AuNP biocompatible systems.Heptamethinecyanine J-aggregates display sharp, intense fluorescence emission making them attractive candidates for developing a variety of chem-bio-sensing applications. They have been immobilized on planar thiol-covered Au surfaces and thiol-capped Au nanoparticles by weak molecular interactions. In this work the self-assembly of novel thiolated cyanine (CNN) on Au(111) and citrate-capped AuNPs from solutions containing monomers and J-aggregates has been studied by using STM, XPS, PM-IRRAS, electrochemical techniques and Raman spectroscopy. Data show

  8. Thiolated gold nanoparticle solvation in near-critical fluids: The role of density, temperature, and topology

    NASA Astrophysics Data System (ADS)

    Yadav, Hari O. S.; Chakravarty, Charusita

    2017-05-01

    We employ molecular dynamics simulations to study the structure and solvation thermodynamics of thiolated gold nanoparticles of size 1.2 and 1.6 nm with ligand of chain length 8-16 carbons in ethane and propane over a wide range of densities close to the critical isotherm. The Helmholtz free energy is estimated by explicitly calculating the change in entropy and internal energy of solvation, and the effect of density and temperature on fluctuation-driven inherent anisotropy in the ligand corona is characterized. Since the topological variation further accentuates this instantaneous asymmetry in the ligand cloud, the anisotropy with varying surface coverage and chain length is also studied including the solvent contributions to the entropic and energetic metrics. Our results are consistent with the experiment, suggesting a route of obtaining structural insights into solvation thermodynamics that could be useful for understanding the stability of nanoparticle dispersions.

  9. Incorporation of sulfide ions into the cadmium(II) thiolate cluster of Cicer arietinum metallothionein2.

    PubMed

    Wan, Xiaoqiong; Freisinger, Eva

    2013-01-18

    The plant metallothionein2 from Cicer arietinum (chickpea), cic-MT2, is known to coordinate five divalent metal ions such as Zn(II) or Cd(II), which are arranged in a single metal thiolate cluster. When the Zn(II) form of the protein is titrated with Cd(II) ions in the presence of sulfide ions, an increased Cd(II) binding capacity and concomitant incorporation of sulfide ions into the cluster are observed. The exact stoichiometry of this novel cluster, its spectroscopic properties, and the significantly increased pH stability are analyzed with different techniques, including UV and circular dichroism spectroscopy and colorimetric assays. Limited proteolytic digestion provides information about the spacial arrangement of the cluster within the protein. Increasing the Cd(II) scavenging properties of a metallothionein by additionally recruiting sulfide ions might be an economic and very efficient detoxification strategy for plants.

  10. A Biological Approach for the Synthesis of Bismuth Nanoparticles: Using Thiolated M13 Phage as Scaffold.

    PubMed

    Vera-Robles, L Irais; Escobar-Alarcón, Luis; Picquart, Michel; Hernández-Pozos, J Luis; Haro-Poniatowski, Emmanuel

    2016-04-05

    We report the synthesis of Bi nanoparticles (Bi NPs) using the M13 phage as scaffold. The p8 protein of the phage is functionalized with thiol groups of different lengths, and these thiolated regions act as nucleation centers for Bi(3+) ions. The size distribution, shape, and resilience to oxidation of the Bi NPs depend on the length of the thiol group used. The NPs are characterized by high resolution transmission electron microscopy, Raman, and IR spectroscopies, matrix assisted laser desorption/ionization, and optical absorption. These results show that the nanoparticles are crystalline and have a typical diameter of ∼3.0 nm. The method of preparation presented here is reproducible and implies "greener" conditions than those reported elsewhere. To the best of our knowledge, this is the first report of bismuth nanoparticles synthesized by a biomineralization method.

  11. Thiolated gold nanoparticle solvation in near-critical fluids: The role of density, temperature, and topology.

    PubMed

    Yadav, Hari O S; Chakravarty, Charusita

    2017-05-07

    We employ molecular dynamics simulations to study the structure and solvation thermodynamics of thiolated gold nanoparticles of size 1.2 and 1.6 nm with ligand of chain length 8-16 carbons in ethane and propane over a wide range of densities close to the critical isotherm. The Helmholtz free energy is estimated by explicitly calculating the change in entropy and internal energy of solvation, and the effect of density and temperature on fluctuation-driven inherent anisotropy in the ligand corona is characterized. Since the topological variation further accentuates this instantaneous asymmetry in the ligand cloud, the anisotropy with varying surface coverage and chain length is also studied including the solvent contributions to the entropic and energetic metrics. Our results are consistent with the experiment, suggesting a route of obtaining structural insights into solvation thermodynamics that could be useful for understanding the stability of nanoparticle dispersions.

  12. Synthesis of core-shell gold coated magnetic nanoparticles and their interaction with thiolated DNA

    NASA Astrophysics Data System (ADS)

    Robinson, Ian; Tung, Le D.; Maenosono, Shinya; Wälti, Christoph; Thanh, Nguyen T. K.

    2010-12-01

    Core-shell magnetic nanoparticles have received significant attention recently and are actively investigated owing to their large potential for a variety of applications. Here, the synthesis and characterization of bimetallic nanoparticles containing a magnetic core and a gold shell are discussed. The gold shell facilitates, for example, the conjugation of thiolated biological molecules to the surface of the nanoparticles. The composite nanoparticles were produced by the reduction of a gold salt on the surface of pre-formed cobalt or magnetite nanoparticles. The synthesized nanoparticles were characterized using ultraviolet-visible absorption spectroscopy, transmission electron microscopy, energy dispersion X-ray spectroscopy, X-ray diffraction and super-conducting quantum interference device magnetometry. The spectrographic data revealed the simultaneous presence of cobalt and gold in 5.6 +/- 0.8 nm alloy nanoparticles, and demonstrated the presence of distinct magnetite and gold phases in 9.2 +/- 1.3 nm core-shell magnetic nanoparticles. The cobalt-gold nanoparticles were of similar size to the cobalt seed, while the magnetite-gold nanoparticles were significantly larger than the magnetic seeds, indicating that different processes are responsible for the addition of the gold shell. The effect on the magnetic properties by adding a layer of gold to the cobalt and magnetite nanoparticles was studied. The functionalization of the magnetic nanoparticles is demonstrated through the conjugation of thiolated DNA to the gold shell.Core-shell magnetic nanoparticles have received significant attention recently and are actively investigated owing to their large potential for a variety of applications. Here, the synthesis and characterization of bimetallic nanoparticles containing a magnetic core and a gold shell are discussed. The gold shell facilitates, for example, the conjugation of thiolated biological molecules to the surface of the nanoparticles. The composite

  13. Dewetting of a solid monolayer.

    PubMed

    Pierre-Louis, O; Chame, Anna; Saito, Yukio

    2007-09-28

    We report on the dewetting of a monolayer on a solid substrate, where mass transport occurs via surface diffusion. For a wide range of parameters, a labyrinthine pattern of bilayer islands is formed. An irreversible regime and a thermodynamic regime are identified. In both regimes, the velocity of a dewetting front, the wavelength of the bilayer island pattern, and the rate of nucleation of dewetted zones are obtained. We also point out the existence of a scaling behavior, which is analyzed by means of a geometrical model.

  14. Palladium-Catalyzed Alkylation with Alkyl Halides by C(sp(3) )-H Activation.

    PubMed

    Wu, Zhuo; Ma, Ding; Zhou, Bo; Ji, Xiaoming; Ma, Xiaotian; Wang, Xiaoling; Zhang, Yanghui

    2017-09-25

    Utilizing halogens as traceless directing goups represents an attractive strategy for C-H functionalization. A two C-H alkylation system, initiated by the oxidative addition of organohalides to Pd(0) , has been developed. The first reaction involves an intermolecular alkylation of palladacycles to form C(sp(3) )-C(sp(2) ) bonds followed by C(sp(2) )-H activation/cyclization to deliver alkylated benzocyclobutenes as the final products. In the second reaction, two C-C bonds are formed by the reaction of palladacycles with CH2 Br2 , and provides a facile and efficient method for the synthesis of indanes. The alkylated benzocyclobutene products can be transformed into tricyclic hyrocarbons, and the indane derivatives are essential structural motifs in bioactive and odorant molecules. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  15. Poly(ethyleneoxide) functionalization through alkylation

    DOEpatents

    Sivanandan, Kulandaivelu; Eitouni, Hany Basam; Li, Yan; Pratt, Russell Clayton

    2015-04-21

    A new and efficient method of functionalizing high molecular weight polymers through alkylation using a metal amide base is described. This novel procedure can also be used to synthesize polymer-based macro-initiators containing radical initiating groups at the chain-ends for synthesis of block copolymers.

  16. Synthesis and characterization of chitosan alkyl urea.

    PubMed

    Wang, Jing; Jiang, Ji-Zhou; Chen, Wei; Bai, Zheng-Wu

    2016-07-10

    Chitosan is a versatile material employed for various purposes in many fields including the development of chiral stationary phases for enantioseparation. Chitosan alkyl urea is a kind of intermediate used to prepare enantioseparation materials. In order to synthesize the intermediates, in the present work, a new way to prepare chitosan alkyl urea has been established: chitosan was first reacted with methyl chloroformate yielding N-methoxyformylated chitosan, which was then converted to chitosan alkyl urea through amine-ester exchange reaction. With a large excess of methyl chloroformate and primary amine of low stereohindrance, the amino group in chitosan could be almost completely converted to ureido group. The as-prepared chitosan alkyl urea derivatives were characterized by IR, (1)H NMR, (13)C NMR,(1)H-(1)H COSY and (1)H-(13)C HSQC NMR spectra. The chemical shifts of hydrogen and carbon atoms of glucose unit were assigned. It was found that the degree of substitution was obviously lower if cyclopropyl amine, aniline, tert-butyl amine and diethyl amine were used as reactants for the amine-ester exchange reaction. The reason was explained with the aid of theoretical calculations. Copyright © 2016 Elsevier Ltd. All rights reserved.

  17. Development and evaluation of mucoadhesive nanoparticles based on thiolated Eudragit for oral delivery of protein drugs

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Yang, Zhijie; Hu, Xi; Zhang, Ling; Li, Feng; Li, Meimei; Tang, Xing; Xiao, Wei

    2015-02-01

    The objective of this study was to develop pH-sensitive Eudragit L100-cysteine/reduced glutathione (Eul-cys/GSH) nanoparticles (NPs), which provided the mucoadhesion and protection for protein drugs against enzymatic degradation. Insulin was chosen as a model biomolecule for testing this system. The Eul-cys conjugate, which was obtained by grafting cysteine onto the carboxy group of Eudragit L100, was analyzed by HNMR and SEM, and the swelling degree (SD), cation binding, and enzymatic inhibition were also determined. The results obtained showed that the Eul-cys conjugate represent a pH-sensitive delivery system which effectively protected the insulin from being degraded by the proteases, and this is related to the mechanism of Ca2+ binding. Insulin-loaded Eul-cys/GSH NPs were prepared by a diffusion method involving an electrostatic interaction between the network structure of the polymer and the embedded proteins, including insulin and GSH. TEM images indicated that Eul-cys/GSH existed as smooth and spherical NPs in aqueous solution with particle sizes of 260 ± 20 nm. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) findings showed the presence of amorphous insulin in thiolated NPs and higher free thiol oxidation than the result obtained by Ellman's reagent method. In addition, thiolated NPs showed excellent binding efficiency to the mucin in rat intestine, indicating that Eul-cys/GSH NPs have great potential to be applied as safe carriers for the oral administration of protein drugs.

  18. Time-dependent density functional theory study of the luminescence properties of gold phosphine thiolate complexes.

    PubMed

    Guidez, Emilie B; Aikens, Christine M

    2015-04-09

    The origin of the emission of the gold phosphine thiolate complex (TPA)AuSCH(CH3)2 (TPA = 1,3,5-triaza-7-phosphaadamantanetriylphosphine) is investigated using time-dependent density functional theory (TDDFT). This system absorbs light at 3.6 eV, which corresponds mostly to a ligand-to-metal transition with some interligand character. The P-Au-S angle decreases upon relaxation in the S1 and T1 states. Our calculations show that these two states are strongly spin-orbit coupled at the ground state geometry. Ligand effects on the optical properties of this complex are also discussed by looking at the simple AuP(CH3)3SCH3 complex. The excitation energies differ by several tenths of an electronvolt. Excited state optimizations show that the excited singlet and triplet of the (TPA)AuSCH(CH3)2 complex are bent. On the other hand, the Au-S bond breaks in the excited state for the simple complex, and TDDFT is no longer an adequate method. The excited state energy landscape of gold phosphine thiolate systems is very complex, with several state crossings. This study also shows that the formation of the [(TPA)AuSCH(CH3)2]2 dimer is favorable in the ground state. The inclusion of dispersion interactions in the calculations affects the optimized geometries of both ground and excited states. Upon excitation, the formation of a Au-Au bond occurs, which results in an increase in energy of the low energy excited states in comparison to the monomer. The experimentally observed emission of the (TPA)AuSCH(CH3)2 complex at 1.86 eV cannot be unambiguously assigned and may originate from several excited states.

  19. Thiolated chitosan nanoparticles enhance anti-inflammatory effects of intranasally delivered theophylline

    PubMed Central

    Lee, Dong-Won; Shirley, Shawna A; Lockey, Richard F; Mohapatra, Shyam S

    2006-01-01

    Background Chitosan, a polymer derived from chitin, has been used for nasal drug delivery because of its biocompatibility, biodegradability and bioadhesiveness. Theophylline is a drug that reduces the inflammatory effects of allergic asthma but is difficult to administer at an appropriate dosage without causing adverse side effects. It was hypothesized that adsorption of theophylline to chitosan nanoparticles modified by the addition of thiol groups would improve theophylline absorption by the bronchial epithelium and enhance its anti-inflammatory effects. Objectives We sought to develop an improved drug-delivery matrix for theophylline based on thiolated chitosan, and to investigate whether thiolated chitosan nanoparticles (TCNs) can enhance theophylline's capacity to alleviate allergic asthma. Methods A mouse model of allergic asthma was used to test the effects of theophylline in vivo. BALB/c mice were sensitized to ovalbumin (OVA) and OVA-challenged to produce an inflammatory allergic condition. They were then treated intranasally with theophylline alone, chitosan nanoparticles alone or theophylline adsorbed to TCNs. The effects of theophylline on cellular infiltration in bronchoalveolar lavage (BAL) fluid, histopathology of lung sections, and apoptosis of lung cells were investigated to determine the effectiveness of TCNs as a drug-delivery vehicle for theophylline. Results Theophylline alone exerts a moderate anti-inflammatory effect, as evidenced by the decrease in eosinophils in BAL fluid, the reduction of bronchial damage, inhibition of mucus hypersecretion and increased apoptosis of lung cells. The effects of theophylline were significantly enhanced when the drug was delivered by TCNs. Conclusion Intranasal delivery of theophylline complexed with TCNs augmented the anti-inflammatory effects of the drug compared to theophylline administered alone in a mouse model of allergic asthma. The beneficial effects of theophylline in treating asthma may be enhanced

  20. Non-thiolate ligation of nickel by nucleotide-free UreG of Klebsiella aerogenes.

    PubMed

    Martin-Diaconescu, Vlad; Joseph, Crisjoe A; Boer, Jodi L; Mulrooney, Scott B; Hausinger, Robert P; Maroney, Michael J

    2017-06-01

    Nickel-dependent ureases are activated by a multiprotein complex that includes the GTPase UreG. Prior studies showed that nucleotide-free UreG from Klebsiella aerogenes is monomeric and binds one nickel or zinc ion with near-equivalent affinity using an undefined binding site, whereas nucleotide-free UreG from Helicobacter pylori selectively binds one zinc ion per dimer via a universally conserved Cys-Pro-His motif in each protomer. Iodoacetamide-treated K. aerogenes UreG was nearly unaffected in nickel binding compared to non-treated sample, suggesting the absence of thiolate ligands to the metal. X-ray absorption spectroscopy of nickel-bound UreG showed the metal possessed four-coordinate geometry with all O/N donor ligands including one imidazole, thus confirming the absence of thiolate ligation. The nickel site in Strep-tag II-modified protein possessed six-coordinate geometry, again with all O/N donor ligands, but now including two or three imidazoles. An identical site was noted for the Strep-tag II-modified H74A variant, substituted in the Cys-Pro-His motif, ruling out coordination by this His residue. These results are consistent with metal binding to both His6 and a His residue of the fusion peptide in Strep-tagged K. aerogenes UreG. We conclude that the nickel- and zinc-binding site in nucleotide-free K. aerogenes UreG is distinct from that of nucleotide-free H. pylori UreG and does not involve the Cys-Pro-His motif. Further, we show the Strep-tag II can perturb metal coordination of this protein.

  1. Periodic trends within a series of five-coordinate thiolate-ligated [MII(SMe2N4(tren))]+ (M = Mn, Fe, Co, Ni, Cu, Zn) complexes, including a rare example of a stable CuII-thiolate.

    PubMed

    Brines, Lisa M; Shearer, Jason; Fender, Jessica K; Schweitzer, Dirk; Shoner, Steven C; Barnhart, David; Kaminsky, Werner; Lovell, Scott; Kovacs, Julie A

    2007-10-29

    A series of five-coordinate thiolate-ligated complexes [M(II)(tren)N4S(Me2)]+ (M = Mn, Fe, Co, Ni, Cu, Zn; tren = tris(2-aminoethyl)amine) are reported, and their structural, electronic, and magnetic properties are compared. Isolation of dimeric [Ni(II)(SN4(tren)-RS(dang))]2 ("dang"= dangling, uncoordinated thiolate supported by H bonds), using the less bulky [(tren)N4S](1-) ligand, pointed to the need for gem-dimethyls adjacent to the sulfur to sterically prevent dimerization. All of the gem-dimethyl derivatized complexes are monomeric and, with the exception of [Ni(II)(S(Me2)N4(tren)]+, are isostructural and adopt a tetragonally distorted trigonal bipyramidal geometry favored by ligand constraints. The nickel complex uniquely adopts an approximately ideal square pyramidal geometry and resembles the active site of Ni-superoxide dismutase (Ni-SOD). Even in coordinating solvents such as MeCN, only five-coordinate structures are observed. The MII-S thiolate bonds systematically decrease in length across the series (Mn-S > Fe-S > Co-S > Ni-S approximately Cu-S < Zn-S) with exceptions occurring upon the occupation of sigma* orbitals. The copper complex, [Cu(II)(S(Me2)N4(tren)]+, represents a rare example of a stable CuII-thiolate, and models the perturbed "green" copper site of nitrite reductase. In contrast to the intensely colored, low-spin Fe(III)-thiolates, the M(II)-thiolates described herein are colorless to moderately colored and high-spin (in cases where more than one spin-state is possible), reflecting the poorer energy match between the metal d- and sulfur orbitals upon reduction of the metal ion. As the d-orbitals drop in energy proceeding across the across the series M(2+) (M= Mn, Fe, Co, Ni, Cu), the sulfur-to-metal charge-transfer transition moves into the visible region, and the redox potentials cathodically shift. The reduced M(+1) oxidation state is only accessible with copper, and the more oxidized M(+4) oxidation state is only accessible for

  2. X-ray specular reflection studies of silicon coated by organic monolayers (alkylsiloxanes)

    NASA Astrophysics Data System (ADS)

    Tidswell, I. M.; Ocko, B. M.; Pershan, P. S.; Wasserman, S. R.; Whitesides, G. M.; Axe, J. D.

    1990-01-01

    X-ray specular reflectivity has been used to characterize the structure of silicon-silicon-oxide surfaces coated with chemisorbed hydrocarbon monolayer films (alkylsiloxanes). Using synchrotron radiation the reflectivity was followed over 9 orders of magnitude, from grazing incidence to an incident angle of φ~=6.5°, or q=(4π/λ)sin(φ)=0.8 Å-1, allowing a spatial resolution of features approximately π/0.8~=4.0 Å along the surface normal. Analysis was performed by fitting the data to reflectivities calculated from models of the surface electron density and by calculating Patterson functions directly from the data. Although the measured reflectivities could be equally well described by different sets of model parameters, the electron densities calculated from these different parameters were remarkably alike. Inspection of the electron densities allowed identification of a layer of SiO2 (~=17-Å thick), a layer of head-group region where the alkylsiloxane adsorbs to the SiO2, and the hydrocarbon layer. Fitting the data also required that the various interfaces have different widths. The fact that the same local hydrocarbon density of 0.85 g/cm3 was observed for both fully formed and partially formed monolayers with alkane chains of varying length excluded a model in which the partially formed monolayer was made up of separated islands of well-formed monolayers. Measurements before and after chemical reaction of a monolayer in which the alkyl chain was terminated by an olefinic group demonstrated the ability to use x-ray reflectivity to characterize chemical changes. The effects of radiation damage on these types of measurements are described.

  3. Binding of methylene blue onto Langmuir monolayers representing cell membranes may explain its efficiency as photosensitizer in photodynamic therapy.

    PubMed

    Schmidt, Thaís F; Caseli, Luciano; Oliveira, Osvaldo N; Itri, Rosangela

    2015-04-14

    We provide evidence for the electrostatic interactions between the cationic photosensitizer methylene blue (MB) and cell membrane models represented by neat and mixed Langmuir monolayers of dioleylphosphatidylcholine (DOPC) and 1,1',2,2'-tetraoleoylcardiolipin (CL). From surface pressure measurements, MB was found to adsorb strongly and expand CL-containing monolayers, while it caused an apparent decreasing in molecular area on neat DOPC monolayer. The binding site of MB could be inferred from data with the surface-specific polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) technique, where changes induced by MB were observed in the vibrational modes of the phosphate groups of both CL and DOPC. The incorporation of MB also affected the carbonyl groups and the packing of the alkyl chains, thus indicating that MB binding site favors singlet oxygen generation close to the double bonds in the alkyl chains, an important requirement for photodynamic efficiency. Significantly, the data presented here demonstrate that MB may act in membranes composed by PCs, such as mammalian plasma membranes, and in those containing CL, as in bacterial and inner mitochondrial membranes.

  4. Effects of alkyl chain length on properties of 1-alkyl-3-methylimidazolium fluorohydrogenate ionic liquid crystals.

    PubMed

    Xu, Fei; Matsumoto, Kazuhiko; Hagiwara, Rika

    2010-11-15

    A series of 1-alkyl-3-methylimidazolium fluorohydrogenate salts (C(x)MIm(FH)(2)F, x=8, 10, 12, 14, 16, and 18) have been characterized by thermal analysis, polarized optical microscopy, IR spectroscopy, X-ray diffraction, and anisotropic ionic conductivity measurements. Liquid crystalline mesophases with a smectic A interdigitated bilayer structure are observed from C(10) to C(18), showing a fan-like or focal conic texture. The temperature range of the mesophase increases with the increase in the alkyl chain length (from 10.1 °C for C(10)MIm(FH)(2)F to 123.1 °C for C(18)MIm(FH)(2)F). The distance between the two layers in the smectic structure gradually increases with increasing alkyl chain length and decreases with increasing temperature. Conductivity parallel to the smectic layers is around 10 mS cm(-1) regardless of the alkyl chain length, whereas that perpendicular to the smectic layers decreases with increasing alkyl chain length because of the thicker insulating sheet with the longer alkyl chain.

  5. Improvements in the characterization of the crystalline structure of acid-terminated alkanethiol self-assembled monolayers on Au(111).

    PubMed

    Mendoza, Sandra M; Arfaoui, Imad; Zanarini, Simone; Paolucci, Francesco; Rudolf, Petra

    2007-01-16

    We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and contact angle techniques were used for characterization, and the results were compared with those obtained from n-alkanethiols of similar chain length, providing a detailed description of the two-dimensional crystalline structure. Molecular resolution STM images show that 11-MUA forms a dense-packed monolayer arranged in a (square root 3 x square root 3)R30 degrees structure with a c(2 x 4) superlattice, where the simple hexagonal phase, the c(2 x 4) superlattice, and nonordered areas coexist. 16-MHDA assembles in a uniform monolayer with similar morphology to that of 11-MUA, but molecular resolution could not be reached in STM due to both the hydrophilicity of the acid groups and the poor conductivity of the thick monolayer. Nevertheless, the monolayer thicknesses estimated by XPS and electrochemistry and the highly blocking character of the film observed by electrochemistry as well as the low water contact angle are consistent with 16-MHDA molecules forming a compact monolayer on the Au(111) substrate with fully extended alkyl chains and acid groups pointing away from the surface. The results obtained for 16-MHDA were reproducible under different preparation conditions such as the addition or omission of acetic acid to the ethanolic solution. Contrary to other reports, we demonstrate that ordered acid-terminated self-assembled monolayers are obtained with the same preparation conditions as those of the methyl-terminated ones, without any additional treatment.

  6. Multifunctional self-assembled monolayers

    SciTech Connect

    Zawodzinski, T.; Bar, G.; Rubin, S.; Uribe, F.; Ferrais, J.

    1996-06-01

    This is the final report of at three year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The specific goals of this research project were threefold: to develop multifunctional self-assembled monolayers, to understand the role of monolayer structure on the functioning of such systems, and to apply this knowledge to the development of electrochemical enzyme sensors. An array of molecules that can be used to attach electrochemically active biomolecules to gold surfaces has been synthesized. Several members of a class of electroactive compounds have been characterized and the factors controlling surface modification are beginning to be characterized. Enzymes have been attached to self-assembled molecules arranged on the gold surface, a critical step toward the ultimate goal of this project. Several alternative enzyme attachment strategies to achieve robust enzyme- modified surfaces have been explored. Several means of juxtaposing enzymes and mediators, electroactive compounds through which the enzyme can exchange electrons with the electrode surface, have also been investigated. Finally, the development of sensitive biosensors based on films loaded with nanoscale-supported gold particles that have surface modified with the self-assembled enzyme and mediator have been explored.

  7. Domain Relaxation in Polymer Monolayers

    NASA Astrophysics Data System (ADS)

    Bernoff, Andrew J.; Alexander, James C.; Mann, J. R.; Mann, Elizabeth K.

    2004-11-01

    We report on an experimental and theoretical study of a polymer monolayer on the surface of a subfluid. When stretched (by a transient applied flow), the monolayer takes the form of a bola consisting of two roughly circular reservoirs connected by a thin tether. This shape relaxes to the minimum energy configuration of a circular domain. The tether is never observed to rupture, even when it is more than a hundred times as long as it is thin. We model these experiments by taking previous descriptions of the hydrodynamics (primarily those of Stone & McConnell and Lubensky & Goldstein ), identifying the dominant effects, and reducing the system to a more tractable form. The result is a free boundary problem where motion is driven by the line tension of the domain and damped by the viscosity of the subfluid. Using this model we derive relaxation rates for perturbations of a uniform strip and a circular patch. Lubrication theory for the tether evolution yields the thin film equation HT = -(H^2H_XXX)_X. This evolution equation appears not to manifest rupture, in agreement with the experiments. Finally, we speculate on which physical properties of the system (such as line tension) can be deduced by comparison of theory to experiment.

  8. Electrochemical and vibrational spectroscopic studies of coadsorption: Formation of mixed monolayers of methylene blue and long-chain dithioethers at sulfur-modified polycrystalline gold surfaces

    SciTech Connect

    Barner, B.J.; Corn, R.M. )

    1990-05-01

    Molecular conformation and order within mixed monolayers of methylene blue, sulfide, and the long-chain dithioether C{sub 14}H{sub 29}SC{sub 2}H{sub 4}SC{sub 14}H{sub 29} adsorbed onto polycrystalline evaporated gold films are studied by using electrochemical methods and ex situ vibrational spectroscopy. The methylene blue dye molecules directly chemisorb onto the sulfur-modified gold surface and do not significantly partition into the alkyl portions of the monolayer. However, upon reduction to leucomethylene blue, the dye molecules do partition into the alkyl subphase. Repeated electrochemical reduction and oxidation of the chemisorbed methylene blue result in an ordering of the adsorbed alkyl chains from a liquid-like structure to a close-packed configuration. The presence of a partial dithioether monolayer also leads to the formation of a stabilized leucomethylene blue film. The variations of the molecular structure observed in these mixed systems arise from the competing processes of chemisorption, aggregation, and hydrophobic solubilization occurring within the thin film.

  9. Corrosion abatement in sulfuric acid alkylation unit horizontal contactors

    SciTech Connect

    Schutt, H.U.

    1997-09-01

    The need to increase throughput in alkylation plants has resulted in higher operating temperatures and higher water levels in alkylation acids than projected by design. Combined with higher flow rates, the more severe process environment causes carbon steel to corrode at increased rates. Carbon steel is the main material of construction for horizontal contactors (Stratco reactors). A leak to the atmosphere in the hydraulic end cone of one contactor and the realization that basic corrosion data are not available for high throughput process conditions in alkylation units prompted a laboratory study to develop the lacking expertise. Corrosion in alkylation unit horizontal contactors is successfully mitigated by saturating fresh alkylation acid with ferrous sulfate.

  10. Formation of Thiolated Nucleosides Present in tRNA from Salmonella enterica serovar Typhimurium Occurs in Two Principally Distinct Pathways

    PubMed Central

    Leipuviene, Ramune; Qian, Qiang; Björk, Glenn R.

    2004-01-01

    tRNA from Salmonella enterica serovar Typhimurium contains five thiolated nucleosides, 2-thiocytidine (s2C), 4-thiouridine (s4U), 5-methylaminomethyl-2-thiouridine (mnm5s2U), 5-carboxymethylaminomethyl-2-thiouridine (cmnm5s2U), and N-6-(4-hydroxyisopentenyl)-2-methylthioadenosine (ms2io6A). The levels of all of them are significantly reduced in cells with a mutated iscS gene, which encodes the cysteine desulfurase IscS, a member of the ISC machinery that is responsible for [Fe-S] cluster formation in proteins. A mutant (iscU52) was isolated that carried an amino acid substitution (S107T) in the IscU protein, which functions as a major scaffold in the formation of [Fe-S] clusters. In contrast to the iscS mutant, the iscU52 mutant showed reduced levels of only two of the thiolated nucleosides, ms2io6A (10-fold) and s2C (more than 2-fold). Deletions of the iscU, hscA, or fdx genes from the isc operon lead to a similar tRNA thiolation pattern to that seen for the iscU52 mutant. Unexpectedly, deletion of the iscA gene, coding for an alternative scaffold protein for the [Fe-S] clusters, showed a novel tRNA thiolation pattern, where the synthesis of only one thiolated nucleoside, ms2io6A, was decreased twofold. Based on our results, we suggest two principal distinct routes for thiolation of tRNA: (i) a direct sulfur transfer from IscS to the tRNA modifying enzymes ThiI and MnmA, which form s4U and the s2U moiety of (c)mnm5s2U, respectively; and (ii) an involvement of [Fe-S] proteins (an unidentified enzyme in the synthesis of s2C and MiaB in the synthesis of ms2io6A) in the transfer of sulfur to the tRNA. PMID:14729702

  11. Stilling Waves with Ordered Molecular Monolayers

    ERIC Educational Resources Information Center

    Vitz, Ed

    2008-01-01

    A demonstration of the damping effect of an oil monolayer on water waves is described. The history of this remarkable demonstration--with a 2000 (or more) year span--and a brief explanation in terms of the properties of water and the monolayer are presented. If a layer of olive oil, one molecule thick (about one-ten millionth of a centimeter), is…

  12. Stilling Waves with Ordered Molecular Monolayers

    ERIC Educational Resources Information Center

    Vitz, Ed

    2008-01-01

    A demonstration of the damping effect of an oil monolayer on water waves is described. The history of this remarkable demonstration--with a 2000 (or more) year span--and a brief explanation in terms of the properties of water and the monolayer are presented. If a layer of olive oil, one molecule thick (about one-ten millionth of a centimeter), is…

  13. Searches for new alkylation catalysts, processes forge ahead

    SciTech Connect

    Rhodes, A.

    1994-08-22

    As a result of the hazardous properties of hydrofluoric acid (HF), HF alkylation has been the subject of much recent controversy. The safety and environmental requirements associated with the HF alkylation processes continue to drive industry to develop new alkylation technologies. In fact, several major process licensors are well on their ways to bringing these new technologies to market. The new alkylation processes under development center around new, less-harmful catalysts. Although this work is progressing rapidly, an update of the status of some of these new processes will keep refiners abreast of the new options they may soon have for building new alkylation units or retrofitting existing ones. The process development and economics are described for a Topsoe/Kellogg fixed bed alkylation process and the Kerr-McGee homogeneous alkylation technology process.

  14. Nonlinear light scattering by a dipole monolayer

    NASA Astrophysics Data System (ADS)

    Averbukh, B. B.; Averbukh, I. B.

    2013-08-01

    Scattering of a strong p-polarized monochromatic field by a dipole monolayer is considered. It is shown that a triplet should be observed at incident angles (between the wave vector of the incident wave and the normal to the monolayer surface) not too close to π/2 in the spectrum of the scattered radiation. For grazing incidence of a strong field on the monolayer, waves with frequencies of the strong field and the high-frequency component of the triplet scatter forward and backward. In this case, radiation with frequency of the low-frequency component of the triplet propagates in the form of two inhomogeneous waves along the monolayer on both sides of it, exponentially decaying with distance from the monolayer.

  15. Tuning the self-assembled monolayer formation on nanoparticle surfaces with different curvatures: Investigations on spherical silica particles and plane-crystal-shaped zirconia particles

    PubMed Central

    Feichtenschlager, Bernhard; Lomoschitz, Christoph J.; Kickelbick, Guido

    2011-01-01

    The ordering of dodecyl-chain self-assembled monolayers (SAM) on different nanoscopic surfaces was investigated by FT-IR studies. As model systems plane-crystal-shaped ZrO2 nanoparticles and spherical SiO2 nanoparticles were examined. The type of capping agent was chosen dependent on the substrate, therefore dodecylphosphonic acid and octadecylphosphonic acid were used for ZrO2 and dodecyltrimethoxysilane for SiO2 samples. The plane ZrO2 nanocrystals yielded more ordered alkyl-chain structures whereas spherical SiO2 nanoparticles showed significantly lower alkyl-chain ordering. Submicron-sized silica spheres revealed a significantly higher alkyl chain ordering, comparable to an analogously prepared SAM on a non-curved plane oxidized Si-wafer. In the case of ZrO2 nanocrystals an intense alkyl-chain alignment could be disturbed by decreasing the grafting density from the maximum of 2.1 molecules/nm2 through the variation of coupling agent concentration to lower values. Furthermore, the co-adsorption of a different coupling agent, such as phenylphosphonic acid for ZrO2 and phenyltrimethoxysilane for SiO2, resulted in a significantly lower alkyl-chain ordering for ZrO2 plane crystals and for large SiO2 spherical particles at high grafting density. An increasing amount of order-disturbing molecules leads to a gradual decrease in alkyl-chain alignment on the surface of the inorganic nanoparticles. In the case of the ZrO2 nanoparticle system it is shown via dynamic light scattering (DLS) that the mixed monolayer formation on the particle surface impacts the dispersion quality in organic solvents such as n-hexane. PMID:21549385

  16. Self-assembly of an unprecedented polyoxomolybdate anion [Mo20O66]12- in a giant peanut-like 62-core silver-thiolate nanocluster

    NASA Astrophysics Data System (ADS)

    Huang, Ren-Wu; Xu, Qing-Qing; Lu, Hong-Lin; Guo, Xiao-Kang; Zang, Shuang-Quan; Gao, Guang-Gang; Tang, Ming-Sheng; Mak, Thomas C. W.

    2015-04-01

    A polyoxometalate-templated silver thiolate nanocluster, [Ag62(StBu)40(Mo20O66)(Mo6O19)3(CH3CN)2].(CF3SO3)4 (1), has been isolated, in which a giant peanut-like silver(i)-thiolate cluster [Ag62(StBu)40]22+ encapsulates an unprecedented [Mo20O66]12- polyoxoanion core. It opens a new approach for the synthesis of both elusive polyoxometalates and high-nuclearity silver(i)-thiolate nanoclusters.A polyoxometalate-templated silver thiolate nanocluster, [Ag62(StBu)40(Mo20O66)(Mo6O19)3(CH3CN)2].(CF3SO3)4 (1), has been isolated, in which a giant peanut-like silver(i)-thiolate cluster [Ag62(StBu)40]22+ encapsulates an unprecedented [Mo20O66]12- polyoxoanion core. It opens a new approach for the synthesis of both elusive polyoxometalates and high-nuclearity silver(i)-thiolate nanoclusters. Electronic supplementary information (ESI) available: Details of measurements, experimental and theoretical calculated details, additional structural figure and characterization data. See DOI: 10.1039/c5nr00171d

  17. Synthesis and Monolayer Behaviors of Succinic Acid-Type Gemini Surfactants Containing Semifluoroalkyl Groups.

    PubMed

    Kawase, Tokuzo; Nagase, Youhei; Oida, Tatsuo

    2016-01-01

    In this work, novel succinic acid-type gemini surfactants containing semifluoroalkyl groups, dl- and meso-2,3-bis[Rf-(CH2)n]-succinic acids (Rf = C4F9, C6F13, C8F17; n = 2, 9), were successfully synthesized, and the effects of Rf, methylene chain length (n), and stereochemistry on their monolayer behaviors were studied. Critical micelle concentrations (CMC) of dl- and meso-2,3-bis[C4F9(CH2)9]-succinic acids were one order of magnitude smaller than that of the corresponding 1+1 type surfactant, C4F9(CH2)9COOH. From surface pressure-area (π-A) measurements, the lift-off areas of the geminis were found to decrease in the order C4F9 ≥ C6F13 > C8F17, regardless of methylene chain length and stereochemistry. The zero-pressure molecular areas of the geminis were twice those of the corresponding 1+1 type surfactants. Based on Gibbs compression modulus analysis, it was clarified that 2,3-bis[C8F17(CH2)n]-succinic gemini with short methylene chains (n = 2) would form more rigid monolayers than those having long methylene chains (n = 9). Unlike for 2,3-bis(alkyl)-succinic acids, the effects of stereochemistry on the monolayer behavior of semifluoroalkylated geminis were small.

  18. Stability of silanols and grafted alkylsilane monolayers on plasma-activated mica surfaces.

    PubMed

    Liberelle, Benoît; Banquy, Xavier; Giasson, Suzanne

    2008-04-01

    We investigated the effect of physical and chemical modifications of mica surfaces induced by water vapor-based plasma treatments on the stability of silanols and grafted alkylsilane monolayers. The plasma-activated substrates were characterized using XPS, TOF-SIMS, and contact angle measurements. They revealed a large surface coverage of silanol groups (Si-OH) and a loss of aluminum atoms compared to freshly cleaved mica surfaces. The stability of plasma-induced silanol groups was investigated by contact angle measurements using ethylene glycol as a probe liquid. The Si-OH surface coverage decreased rapidly under vacuum or thermal treatment to give rise to hydrophobic dehydrated surfaces. The stability of end-grafted monofunctionalized n-alkylsilanes was investigated in different solvents and at different pH using water contact angle measurements. The degrafting of alkylsilanes from the activated mica was promoted in acidic aqueous solutions. This detachment was associated with the hydrolysis of covalent bonds between the alkylsilanes and the mica surface. The monolayer stability was enhanced by increasing the length of the alkyl chains that probably act as a hydrophobic protective layer against hydrolysis reactions. Stable alkylsilane monolayers in water with pH greater than 5.5 were obtained on mica surfaces activated at low plasma pressure. We attributed this stability to the loss of surface Al atoms induced by the plasma treatment.

  19. Preparation and in vitro evaluation of mucoadhesion and permeation enhancement of thiolated chitosan-pHEMA core-shell nanoparticles.

    PubMed

    Moghaddam, Firooze Aghaei; Atyabi, Fatemeh; Dinarvand, Rassoul

    2009-06-01

    The aim of the present work was to evaluate the in vitro mucoadhesion and permeation enhancement properties of thiolated chitosan (chitosan-glutathione) coated poly(hydroxyl ethyl methacrylate) nanoparticles. Core-shell nanoparticles were prepared by radical emulsion polymerization method initiated by cerium(IV) ammonium nitrate. Different molecular weights of chitosan were utilized for nanoparticles preparation. The physicochemical properties of nanoparticles were characterized by size, zeta potential, and thiol content. Incorporation of fluorescein isothiocyanate dextran (FD4, MW 4400 Da), which was used as the model macromolecule, was achieved by incubation method. The intestinal mucoadhesion and penetration enhancement properties of nanoparticles were investigated using excised rat jejunum. All nanoparticle systems showed mucoadhesion and improved apparent permeation coefficient (P(app)) of FD4. Nanoparticles prepared by thiolated chitosan with medium molecular weight revealed the most mucoadhesion and penetration enhancement properties.

  20. The effects of self-assembled monolayers on organic thin film transistors

    NASA Astrophysics Data System (ADS)

    Dhagat, Parul

    This thesis presents an approach to the problem of designing high-mobility organic thin film transistors. The influence of two critical surfaces, the dielectric and the electrode surface on the microstructure and carrier mobility of organic semiconductors, is explored. Modifying the organic/dielectric and the organic/contact interface with self-assembled monolayers enhances the carrier mobility in the channel which is related to measured changes in organic thin film microstructure. In order to passivate the dangling hydroxyl bonds on silicon dioxide (SiO2) dielectric surface, self-assembled monolayers (SAM) have been employed. Ordered and disordered octadecyltrichlorosilane (OTS) SAM treatments were applied, an n-type organic semiconductor 3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (PTCBI) is deposited. A change in the unit cell orientation of PTCBI from (001) to (011) is observed between the two OTS treated and the control untreated SiO2 surfaces, respectively. The observed field effect mobility is surface treatment dependent, with the ordered OTS resulting the largest carrier mobility, followed by the disordered OTS and the untreated SiO 2. Thiolated (-SH) SAMs modify the work function of gold contacts to reduce the electron injection barrier. Two types of SAMs were used: alkanethiols SAMs with different hydrocarbon chain lengths varying from eight to eighteen methylene groups and a perfluorobenzenethiol (PFBT) SAM. The objective of this study was to match the work function of the contacts to the lowest unoccupied molecular orbital of the channel material, PTCBI. PTCBI deposited on top of the ordered and long chain alkanethiols exhibit (001) and (011) orientations. The short chain and disordered alkanethiols, PFBT and untreated gold exhibit a unit cell orientation of (112¯). To the resolution of these experiments no significant difference in mobility was observed.

  1. Synthesis, electronic properties and self-assembly on Au{111} of thiolated (oligo)phenothiazines

    PubMed Central

    Franz, Adam W; Stoycheva, Svetlana; Himmelhaus, Michael

    2010-01-01

    Summary (Oligo)phenothiazinyl thioacetates, synthesized by a one-pot sequence, are electrochemically oxidizable and highly fluorescent. SAMs can be readily formed from thiols prepared by in situ deprotection of the thioacetates in the presence of a gold-coated silicon wafer. Monolayer formation is confirmed by ellipsometry and the results compared to those obtained by force field and DFT calculations. PMID:20703376

  2. Coulomb excitations of monolayer germanene

    NASA Astrophysics Data System (ADS)

    Shih, Po-Hsin; Chiu, Yu-Huang; Wu, Jhao-Ying; Shyu, Feng-Lin; Lin, Ming-Fa

    2017-01-01

    The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbit coupling and the buckled structure. The collective and single-particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e–h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e–h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes.

  3. Thermoelectric transport in monolayer phosphorene

    NASA Astrophysics Data System (ADS)

    Zare, Moslem; Rameshti, Babak Zare; Ghamsari, Farnood G.; Asgari, Reza

    2017-01-01

    We apply the generalized Boltzmann theory to describe thermoelectric transport properties of monolayer phosphorene in the presence of short- and long-range charged impurity interactions. First, we propose a low-energy Hamiltonian to explore the accurate electronic band structure of phosphorene in comparison with those results obtained by density-functional simulations. We explain the effect of the coupling between the conduction and valence bands on the thermoelectric properties. We show that the electric conductivity of phosphorene is highly anisotropic, while the Seebeck coefficient and figure of merit, without being influenced via either the presence or absence of the coupling term, are nearly isotropic. Furthermore, we demonstrate that the conductivity for the n type of doping is more influenced by the coupling term than that of the p type. Along with thermopower sign change, profound thermoelectric effects can be achieved.

  4. Coulomb excitations of monolayer germanene

    PubMed Central

    Shih, Po-Hsin; Chiu, Yu-Huang; Wu, Jhao-Ying; Shyu, Feng-Lin; Lin, Ming-Fa

    2017-01-01

    The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbit coupling and the buckled structure. The collective and single-particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e–h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e–h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes. PMID:28091555

  5. PROCESS FOR PRODUCING ALKYL ORTHOPHOSPHORIC ACID EXTRACTANTS

    DOEpatents

    Grinstead, R.R.

    1962-01-23

    A process is given for producing superior alkyl orthophosphoric acid extractants for use in solvent extraction methods to recover and purify various metals such as uranium and vanadium. The process comprises slurrying P/sub 2/O/ sub 5/ in a solvent diluent such as kerosene, benzene, isopropyl ether, and the like. An alipbatic alcohol having from nine to seventeen carbon atoms, and w- hcrein ihc OH group is situated inward of the terminal carbon atoms, is added to the slurry while the reaction temperature is mainiained below 60 deg C. The alcohol is added in the mole ratio of about 2 to l, alcohol to P/sub 2/O/sub 5/. A pyrophosphate reaotion product is formed in the slurry-alcohol mixture. Subsequently, the pyrophosphate reaction product is hydrolyzed with dilute mineral acid to produce the desired alkyl orthophosphoric aeid extractant. The extraetant may then be separated and utilized in metal-recovery, solvent- extraction processes. (AEC)

  6. Engineering Chemically Active Defects in Monolayer MoS2 Transistors via Ion-Beam Irradiation and Their Healing via Vapor Deposition of Alkanethiols.

    PubMed

    Bertolazzi, Simone; Bonacchi, Sara; Nan, Guangjun; Pershin, Anton; Beljonne, David; Samorì, Paolo

    2017-03-01

    Irradiation of 2D sheets of transition metal dichalcogenides with ion beams has emerged as an effective approach to engineer chemically active defects in 2D materials. In this context, argon-ion bombardment has been utilized to introduce sulfur vacancies in monolayer molybdenum disulfide (MoS2 ). However, a detailed understanding of the effects of generated defects on the functional properties of 2D MoS2 is still lacking. In this work, the correlation between critical electronic device parameters and the density of sulfur vacancies is systematically investigated through the fabrication and characterization of back-gated monolayer MoS2 field-effect transistors (FETs) exposed to a variable fluence of low-energy argon ions. The electrical properties of pristine and ion-irradiated FETs can be largely improved/recovered by exposing the devices to vapors of short linear thiolated molecules. Such a solvent-free chemical treatment-carried out strictly under inert atmosphere-rules out secondary healing effects induced by oxygen or oxygen-containing molecules. The results provide a guideline to design monolayer MoS2 optoelectronic devices with a controlled density of sulfur vacancies, which can be further exploited to introduce ad hoc molecular functionalities by means of thiol chemistry approaches.

  7. Confirmation of a de novo structure prediction for an atomically precise monolayer-coated silver nanoparticle

    PubMed Central

    Conn, Brian E.; Atnagulov, Aydar; Yoon, Bokwon; Barnett, Robert N.; Landman, Uzi; Bigioni, Terry P.

    2016-01-01

    Fathoming the principles underpinning the structures of monolayer-coated molecular metal nanoparticles remains an enduring challenge. Notwithstanding recent x-ray determinations, coveted veritable de novo structural predictions are scarce. Building on recent syntheses and de novo structure predictions of M3AuxAg17−x(TBBT)12, where M is a countercation, x = 0 or 1, and TBBT is 4-tert-butylbenzenethiol, we report an x-ray–determined structure that authenticates an a priori prediction and, in conjunction with first-principles theoretical analysis, lends force to the underlying forecasting methodology. The predicted and verified Ag(SR)3 monomer, together with the recently discovered Ag2(SR)5 dimer and Ag3(SR)6 trimer, establishes a family of unique mount motifs for silver thiolate nanoparticles, expanding knowledge beyond the earlier-known Au-S staples in thiol-capped gold nanoclusters. These findings demonstrate key principles underlying ligand-shell anchoring to the metal core, as well as unique T-like benzene dimer and cyclic benzene trimer ligand bundling configurations, opening vistas for rational design of metal and alloy nanoparticles. PMID:28138537

  8. Dual-chemiresistor GC detector employing monolayer-protected metal nanocluster interfaces.

    PubMed

    Cai, Qing-Yun; Zellers, Edward T

    2002-07-15

    The synthesis and testing of two gold-thiolate monolayer-protected (nano)clusters as interfacial layers on a dual-chemiresistor vapor sensor array are described. Responses (changes in dc resistance) to each of 11 organic solvent vapors are rapid, reversible, and linear with concentration at low vapor concentrations, becoming sublinear at higher concentrations. Limits of detection (LODs) range from 0.1 to 24 parts per million and vary inversely with solvent vapor pressure. When configured as a GC detector and used to analyze 0.5-L preconcentrated samples of the 11-vapor mixture, the array provides LODs of < or = 700 parts per trillion for most vapors, comparing favorably with those from an integrated array of polymer-coated surface acoustic wave sensors configured and tested similarly. This first report on the use of such an array as a GC detector shows that the combination of response patterns and GC retention times improves capabilities for vapor recognition compared to the sensor array alone or to single-detector GC systems. Spray-coated nanocluster thin films can be deposited reproducibly and exhibit response stability in air that ranges from fair to excellent for up to several months. Scaling the active device area down by a factor of 16 has no significant effect on sensitivity. Implications of these results for portable vapor sensing systems are discussed.

  9. Alkyl-functionalized oxide-free silicon nanoparticles: synthesis and optical properties.

    PubMed

    Rosso-Vasic, Milena; Spruijt, Evan; van Lagen, Barend; De Cola, Luisa; Zuilhof, Han

    2008-10-01

    Highly monodisperse silicon nanoparticles (1.57 +/- 0.21 nm) are synthesized with a covalently attached alkyl monolayer on a gram scale. Infrared spectroscopy shows that these silicon nanoparticles contain only a few oxygen atoms per nanoparticle. XPS spectra clearly show the presence of unoxidized Si and attached alkyl chains. Owing to the relatively efficient synthesis (yields approximately 100-fold higher than of those previously reported) the molar extinction coefficient epsilon can be measured: epsilon(max) = 1.7 x 10(-4) M(-1)cm(-1), only a factor of 4 lower than that of CdS and CdSe nanoparticles of that size. The quantum yield of emission ranges from 0.12 (C(10)H(21)-capping) to 0.23 (C(16)H(33)-capping). UV/Vis absorption and emission spectroscopy show clear vibrational progressions (974 +/- 14 cm(-1); up to five vibrational bands visible at room temperature), resembling bulk SiC phonons, which support the monodispersity observed by TEM. This was also confirmed by time-resolved fluorescence anisotropy measurements, which display a strictly monoexponential decay that can only be indicative of monodisperse, ball-shaped nanoparticles.

  10. Studies on Mixed Monolayers and Langmuir-Blodgett Films of Schiff-Base Complex Cu(SBC(18))(2) and Calix

    PubMed

    Pang, Shufeng; Ye, Zhifeng; Li, Chun; Liang, Yingqiu

    2001-08-15

    Mixed monolayers of Schiff-base complex Cu(SBC(18))(2) with an octadecyl hydrocarbon chain and Calix[4]arene without a long alkyl chain at an air/water interface were studied in ultrapure water at different temperatures. Interface behavior and thermodynamic estimation of the mixed monolayer indicate that a strong intermolecular interaction exists between the mixed components (Cu(SBC(18))(2) and calix[4]arene) and the two-dimensional miscibility decreases with the molar fraction of Cu(SBC(18))(2). It is noticeable that the calix[4]arene monolayer can be transferred successfully onto solid substrates due to the introduction of Cu(SBC(18))(2). FTIR transmission and UV-Vis absorption spectra of mixed LB films provide further evidence of molecular interaction between the headgroups. Copyright 2001 Academic Press.

  11. In pursuit of homoleptic actinide alkyl complexes.

    PubMed

    Seaman, Lani A; Walensky, Justin R; Wu, Guang; Hayton, Trevor W

    2013-04-01

    This Forum Article describes the pursuit of isolable homoleptic actinide alkyl complexes, starting with the pioneering work of Gilman during the Manhattan project. The initial reports in this area suggested that homoleptic uranium alkyls were too unstable to be isolated, but Wilkinson demonstrated that tractable uranium alkyls could be generated by purposeful "ate" complex formation, which serves to saturate the uranium coordination sphere and provide the complexes with greater kinetic stability. More recently, we reported the solid-state molecular structures of several homoleptic uranium alkyl complexes, including [Li(THF)4][U(CH2(t)Bu)5], [Li(TMEDA)]2[UMe6], [K(THF)]3[K(THF)2][U(CH2Ph)6]2, and [Li(THF)4][U(CH2SiMe3)6], by employing Wilkinson's strategy. Herein, we describe our attempts to extend this chemistry to thorium. The treatment of ThCl4(DME)2 with 5 equiv of LiCH2(t)Bu or LiCH2SiMe3 at -25 °C in THF affords [Th(CH2(t)Bu)5] (1) and [Li(DME)2][Th(CH2SiMe3)5 (2), respectively, in moderate yields. Similarly, the treatment of ThCl4(DME)2 with 6 equiv of K(CH2Ph) produces [K(THF)]2[Th(CH2Ph)6] (3), in good yield. Complexes 1-3 have been fully characterized, while the structures of 1 and 3 were confirmed by X-ray crystallography. Additionally, the electronic properties of 1 and 3 were explored by density functional theory.

  12. ALKYL PYROPHOSPHATE METAL SOLVENT EXTRACTANTS AND PROCESS

    DOEpatents

    Long, R.L.

    1958-09-30

    A process is presented for the recovery of uranium from aqueous mineral acidic solutions by solvent extraction. The extractant is a synmmetrical dialkyl pyrophosphate in which the alkyl substituents have a chain length of from 4 to 17 carbon atoms. Mentioned as a preferred extractant is dioctyl pyrophosphate. The uranium is precipitated irom the organic extractant phase with an agent such as HF, fluoride salts. alcohol, or ammonia.

  13. Soluble Alkyl Substituted Polygermanes. Thermochromic Behavior.

    DTIC Science & Technology

    1986-07-17

    are strongly thermochromic . The effect is attributed to conformational locking of the backbone which is caused by the crystallization of the side groups...are strongly thermochromic . The effect is attributed to the conformational locking of the backbone which is caused by the crystallization of the side...SYMBOL. 02 &m A -- .- h.. .. .. . . . . . . . . ... . . . .. RJ 5008 (52258) 1/24/86 Chemis try SOLUBLE ALKYL SUBSTITUTED POLYGERMANES: THERMOCHROMIC

  14. Protein S-thiolation targets glycolysis and protein synthesis in response to oxidative stress in the yeast Saccharomyces cerevisiae.

    PubMed Central

    Shenton, Daniel; Grant, Chris M

    2003-01-01

    The irreversible oxidation of cysteine residues can be prevented by protein S-thiolation, a process by which protein SH groups form mixed disulphides with low-molecular-mass thiols such as glutathione. We report here the target proteins which are modified in yeast cells in response to H(2)O(2). In particular, a range of glycolytic and related enzymes (Tdh3, Eno2, Adh1, Tpi1, Ald6 and Fba1), as well as translation factors (Tef2, Tef5, Nip1 and Rps5) are identified. The oxidative stress conditions used to induce S-thiolation are shown to inhibit GAPDH (glyceraldehyde-3-phosphate dehydrogenase), enolase and alcohol dehydrogenase activities, whereas they have no effect on aldolase, triose phosphate isomerase or aldehyde dehydrogenase activities. The inhibition of GAPDH, enolase and alcohol dehydrogenase is readily reversible once the oxidant is removed. In addition, we show that peroxide stress has little or no effect on glucose-6-phosphate dehydrogenase or 6-phosphogluconate dehydrogenase, the enzymes that catalyse NADPH production via the pentose phosphate pathway. Thus the inhibition of glycolytic flux is proposed to result in glucose equivalents entering the pentose phosphate pathway for the generation of NADPH. Radiolabelling is used to confirm that peroxide stress results in a rapid and reversible inhibition of protein synthesis. Furthermore, we show that glycolytic enzyme activities and protein synthesis are irreversibly inhibited in a mutant that lacks glutathione, and hence cannot modify proteins by S-thiolation. In summary, protein S-thiolation appears to serve an adaptive function during exposure to an oxidative stress by reprogramming metabolism and protecting protein synthesis against irreversible oxidation. PMID:12755685

  15. Sequential oxidations of thiolates and the cobalt metallocenter in a synthetic metallopeptide: Implications for the biosynthesis of nitrile hydratase

    PubMed Central

    Dutta, Arnab; Flores, Marco; Roy, Souvik; Schmitt, Jennifer C.; Hamilton, G. Alexander; Hartnett, Hilairy E.; Shearer, Jason; Jones, Anne K.

    2013-01-01

    Cobalt nitrile hydratases (Co-NHase) contain a catalytic cobalt (III) ion coordinated in an N2S3 first coordination sphere comprised of two amidate nitrogens and three cysteine-derived sulfur donors: a thiolate (-SR), a sulfenate (-S(R)O−), and a sulfinate (-S(R)O2−). The sequence of biosynthetic reactions that leads to the post-translational oxidations of the metal and the sulfur ligands is unknown, but the process is believed to be initiated directly by oxygen. Herein we utilize cobalt bound in an N2S2 first coordination sphere by a seven amino acid peptide known as SODA (ACDLPCG) to model this oxidation process. Upon exposure to oxygen, Co-SODA is oxidized in two steps. In the first fast step (seconds), magnetic susceptibility measurements demonstrated that the metallocenter remains paramagnetic, i.e. Co2+, and sulfur K-edge X-ray absorption spectroscopy (XAS) is used to show that one of the thiolates is oxidized to sulfinate. In a second process on a longer timescale (hours), magnetic susceptibility measurements and Co K-edge XAS show that the metal is oxidized to Co3+. Unlike other model complexes, additional slow oxidation of the second thiolate in Co-SODA is not observed, and a catalytically active complex is never formed. The likely reason is the absence of the axial thiolate ligand. In essence, the reactivity of Co-SODA can be described as intermediate between previously described models which either quickly convert to final product or are stable in air, and it offers a first glimpse into a possible oxidation pathway for nitrile hydratase biosynthesis. PMID:23587023

  16. The Scarlet Letter of Alkylation: A Mini Review of Selective Alkylating Agents

    PubMed Central

    Oronsky, Bryan T; Reid, Tony; Knox, Susan J; Scicinski, Jan J

    2012-01-01

    If there were a stigma scale for chemotherapy, alkylating agents would be ranked at the top of the list. The chemical term alkylation is associated with nonselective toxicity, an association that dates back to the use of nitrogen mustards during World War I as chemical warfare agents. That this stigma persists and extends to compounds that, through selectivity, attempt to “tame” the indiscriminate destructive potential of alkylation is the subject of this review. Selective alkylation, as it is referred to herein, constitutes an extremely nascent and dynamic field in oncology. The pharmacodynamic response to this selective strategy depends on a delicate kinetic balance between specificity and the rate and extent of binding. Three representative compounds are presented: RRx-001, 3-bromopyruvate, and TH-302. The main impetus for the development of these compounds has been the avoidance of the serious complications of traditional alkylating agents; therefore, it is the thesis of this review that they should not experience stigma by association. PMID:22937173

  17. Tetrahydrofurfuryloxide derivatives of alkyl aluminum species.

    SciTech Connect

    Boyle, Timothy J.; Avilucea, Gabriel; Bunge, Scott D.; Alam, Todd Michael; Rodriguez, Mark Andrew; Cherry, Brian Ray; Tissot, Ralph George, Jr.; Segall, Judith M.

    2004-12-01

    Tetrahydrofurfuryl alcohol (H-OTHF) was successfully reacted with a series of aluminum alkyls (AlR{sub 3}) to yield compounds of the general formula [R{sub 2}Al({mu}-OTHF)]{sub 2} where R = CH{sub 3} (1), CH{sub 2}CH{sub 3} (2), and CH{sub 2}CH(CH{sub 3}){sub 2} (3). Further, reactivity studies showed that the alkyls for 1 were easily exchanged, forming compounds of the general formula [Me(OR)Al({mu}-OTHF)]{sub 2} where OR = OC{sub 6}H{sub 3}(Me){sub 2}-2,6 (4), OC{sub 6}H{sub 3}(CMe{sub 3}){sub 2}-2,6 (5a), and OSi(C{sub 6}H5){sub 3} (6). For 5a, reflux temperatures were required to get the full exchange; otherwise the asymmetric derivative [Me(OR)Al({mu}-OTHF){sub 2}AlMe{sub 2}] (5b) was isolated. The bulk powders of 1-6 were found to be in agreement with the crystal structures on the basis of elemental analyses and multinuclear solid state NMR studies. Multinuclear solution state NMR studies indicate that the alkyl OTHF derivatives have cis/trans isomers due to the chiral proton on the OTHF ligand.

  18. Influence of bidisperse self-assembled monolayer structure on the slip boundary condition of thin polymer films.

    PubMed

    McGraw, Joshua D; Klos, Mischa; Bridet, Antoine; Hähl, Hendrik; Paulus, Michael; Castillo, Juan Manuel; Horsch, Martin; Jacobs, Karin

    2017-05-28

    Alkylsilane self-assembled monolayers (SAMs) are often used as model substrates for their ease of preparation and hydrophobic properties. We have observed that these atomically smooth monolayers also provide a slip boundary condition for dewetting films composed of unentangled polymers. This slip length, an indirect measure of the friction between a given liquid and different solids, is switchable and can be increased [R. Fetzer et al., Phys. Rev. Lett. 95, 127801 (2005); O. Bäumchen et al., J. Phys.: Condens. Matter 24, 325102 (2012)] if the alkyl chain length is changed from 18 to 12 backbone carbons, for example. Typically, this change in boundary condition is affected in a quantized way, using one or the other alkyl chain length, thus obtaining one or the other slip length. Here, we present results in which this SAM structure is changed in a continuous way. We prepare bidisperse mixed SAMs of alkyl silanes, with the composition as a control parameter. We find that all the mixed SAMs investigated show an enhanced slip boundary condition as compared to the single-component SAMs. The slip boundary condition is accessed using optical and atomic force microscopy, and we describe these observations in the context of X-ray reflectivity measurements. The slip length, varying over nearly two orders of magnitude, of identical polymer melts on chemically similar SAMs is found to correlate with the density of exposed alkyl chains. Our results demonstrate the importance of a well characterized solid/liquid pair, down to the angstrom level, when discussing the friction between a liquid and a solid.

  19. Influence of bidisperse self-assembled monolayer structure on the slip boundary condition of thin polymer films

    NASA Astrophysics Data System (ADS)

    McGraw, Joshua D.; Klos, Mischa; Bridet, Antoine; Hähl, Hendrik; Paulus, Michael; Castillo, Juan Manuel; Horsch, Martin; Jacobs, Karin

    2017-05-01

    Alkylsilane self-assembled monolayers (SAMs) are often used as model substrates for their ease of preparation and hydrophobic properties. We have observed that these atomically smooth monolayers also provide a slip boundary condition for dewetting films composed of unentangled polymers. This slip length, an indirect measure of the friction between a given liquid and different solids, is switchable and can be increased [R. Fetzer et al., Phys. Rev. Lett. 95, 127801 (2005); O. Bäumchen et al., J. Phys.: Condens. Matter 24, 325102 (2012)] if the alkyl chain length is changed from 18 to 12 backbone carbons, for example. Typically, this change in boundary condition is affected in a quantized way, using one or the other alkyl chain length, thus obtaining one or the other slip length. Here, we present results in which this SAM structure is changed in a continuous way. We prepare bidisperse mixed SAMs of alkyl silanes, with the composition as a control parameter. We find that all the mixed SAMs investigated show an enhanced slip boundary condition as compared to the single-component SAMs. The slip boundary condition is accessed using optical and atomic force microscopy, and we describe these observations in the context of X-ray reflectivity measurements. The slip length, varying over nearly two orders of magnitude, of identical polymer melts on chemically similar SAMs is found to correlate with the density of exposed alkyl chains. Our results demonstrate the importance of a well characterized solid/liquid pair, down to the angstrom level, when discussing the friction between a liquid and a solid.

  20. Modulating release of ranibizumab and aflibercept from thiolated chitosan-based hydrogels for potential treatment of ocular neovascularization.

    PubMed

    Moreno, Miguel; Pow, Poh Yih; Tabitha, Tan Su Teng; Nirmal, Sonali; Larsson, Andreas; Radhakrishnan, Krishna; Nirmal, Jayabalan; Quah, Soo Tng; Geifman Shochat, Susana; Agrawal, Rupesh; Venkatraman, Subbu

    2017-08-01

    This paper describes the synthesis of thiolated chitosan-based hydrogels with varying degrees of crosslinking that has been utilized to modulate release kinetics of two clinically relevant FDA-approved anti-VEGF protein drugs, ranibizumab and aflibercept. These hydrogels have been fabricated into disc shaped structures for potential use as patches on ocular surface. Protein conformational changes and aggregation after loading and release was evaluated by circular dichroism (CD), steady-state tryptophan fluorescence spectroscopy, electrophoresis and size-exclusion chromatography (SEC). Finally, the capacity of both released proteins to bind to VEGF was tested by ELISA and surface plasmon resonance (SPR) technology. The study demonstrates the versatility of thiolated chitosan-based hydrogels for delivering proteins. The effect of various parameters of the hydrogel on protein release kinetics and mechanism of protein release was studied using the Korsmeyer-Peppas release model. Furthermore, we have studied the stability of released proteins in detail while comparing it with non-entrapped proteins under physiological conditions to understand the effect of formulation conditions on protein stability. The disc-shaped thiolated chitosan-based hydrogels provide a potentially useful platform to deliver ranibizumab and aflibercept for the treatments of ocular diseases such as wet AMD, DME and corneal neovascularization.

  1. A novel thiolated human-like collage zinc complex as a promising zinc supplement: physicochemical characteristics and biocompatibility.

    PubMed

    Zhu, Chenhui; Ma, Xiaoxuan; Wang, Yonghui; Mi, Yu; Fan, Daidi; Deng, Jianjun; Xue, Wenjiao

    2014-11-01

    To improve zinc binding ability to human-like collagen (HLC) and stability of metal complex, HLC was thiolated by mercaptosuccinylation reaction with S-acetylmercaptosuccinic anhydride (S-AMSA) at pH8.0. One mole of thiolated HLC-Zn (SHLC-Zn) complex possessed 24.3mol zinc ions when pH was 8.0 and zinc concentration was 15 mM. The physicochemical properties and biocompatibility of thiolated HLC-Zn (SHLC-Zn) complex were investigated by UV-vis, CD, electrophoresis analysis, differential scanning calorimetry (DSC) and cell viability assay, respectively. The results showed that SHLC-Zn complex(1) exhibited higher zinc ions than that of native HLC and still maintained the secondary structure of HLC though interaction occurred between SHLC and zinc ions, (2) increased the apparent molecular weight when compared with native HLC, (3) exhibited greater thermal stability than native HLC, and (4) presented toxicity free for BHK cells. This study suggests that the SHLC-Zn complex is a potential nutrition as well as zinc supplement in the medical application. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. Surface-Enhanced Raman Scattering from Self-Assembled Film of Thiolated Peg-Modified Gold Nanoparticles

    NASA Astrophysics Data System (ADS)

    Chen, Q.; Wu, Q.; Zhang, Q.; Hu, J.

    2017-07-01

    Self-assembly of thiolated polyethylene glycol (PEG)-modifi ed Au nanoparticles (NPs) into a closely packed particle film at a water-air interface for the production of reproducible, highly active surface-enhanced Raman scattering (SERS) was developed. Upon modifi cation with thiolated PEG, the Au NPs can sustain severe conditions (e.g., 3 M NaCl solution), and after separation from colloids and drying, they can be redispersed into water, forming colloids again. We found that the thiolated PEG-modifi ed Au NPs, from their concentrated colloids, can spontaneously selfassemble into a two-dimensional (2D) closely packed particle film at the water-air interface. With abundant hot spots created and exposed, the 2D particle film produces large, reproducible SERS signal for 4-mercaptobenzoic acid (probe molecule), reaching a detection limit of 1 × 10-11 M. These results offer a useful way for the storage of Au NPs and the fabrication of highly reproducible and active SERS substrate.

  3. Total Structure and Electronic Structure Analysis of Doped Thiolated Silver [MAg24(SR)18](2-) (M = Pd, Pt) Clusters.

    PubMed

    Yan, Juanzhu; Su, Haifeng; Yang, Huayan; Malola, Sami; Lin, Shuichao; Häkkinen, Hannu; Zheng, Nanfeng

    2015-09-23

    With the incorporation of Pd or Pt atoms, thiolated Ag-rich 25-metal-atom nanoclusters were successfully prepared and structurally characterized for the first time. With a composition of [PdAg24(SR)18](2-) or [PtAg24(SR)18](2-), the obtained 25-metal-atom nanoclusters have a metal framework structure similar to that of widely investigated Au25(SR)18. In both clusters, a M@Ag12 (M = Pd, Pt) core is capped by six distorted dimeric -RS-Ag-SR-Ag-SR- units. However, the silver-thiolate overlayer gives rise to a geometric chirality at variance to Au25(SR)18. The effect of doping on the electronic structure was studied through measured optical absorption spectra and ab initio analysis. This work demonstrates that modulating electronic structures by transition-metal doping is expected to provide effective means to manipulate electronic, optical, chemical, and catalytic properties of thiolated noble metal nanoclusters.

  4. Thiolated DNA-based chemistry and control in the structure and optical properties of plasmonic nanoparticles with ultrasmall interior nanogap.

    PubMed

    Oh, Jeong-Wook; Lim, Dong-Kwon; Kim, Gyeong-Hwan; Suh, Yung Doug; Nam, Jwa-Min

    2014-10-08

    The design, synthesis and control of plasmonic nanostructures, especially with ultrasmall plasmonically coupled nanogap (∼1 nm or smaller), are of significant interest and importance in chemistry, nanoscience, materials science, optics and nanobiotechnology. Here, we studied and established the thiolated DNA-based synthetic principles and methods in forming and controlling Au core-nanogap-Au shell structures [Au-nanobridged nanogap particles (Au-NNPs)] with various interior nanogap and Au shell structures. We found that differences in the binding affinities and modes among four different bases to Au core, DNA sequence, DNA grafting density and chemical reagents alter Au shell growth mechanism and interior nanogap-forming process on thiolated DNA-modified Au core. Importantly, poly A or poly C sequence creates a wider interior nanogap with a smoother Au shell, while poly T sequence results in a narrower interstitial interior gap with rougher Au shell, and on the basis of the electromagnetic field calculation and experimental results, we unraveled the relationships between the width of the interior plasmonic nanogap, Au shell structure, electromagnetic field and surface-enhanced Raman scattering. These principles and findings shown in this paper offer the fundamental basis for the thiolated DNA-based chemistry in forming and controlling metal nanostructures with ∼1 nm plasmonic gap and insight in the optical properties of the plasmonic NNPs, and these plasmonic nanogap structures are useful as strong and controllable optical signal-generating nanoprobes.

  5. Highly doped silicon nanowires by monolayer doping.

    PubMed

    Veerbeek, Janneke; Ye, Liang; Vijselaar, Wouter; Kudernac, Tibor; van der Wiel, Wilfred G; Huskens, Jurriaan

    2017-02-23

    Controlling the doping concentration of silicon nanostructures is challenging. Here, we investigated three different monolayer doping techniques to obtain silicon nanowires with a high doping dose. These routes were based on conventional monolayer doping, starting from covalently bound dopant-containing molecules, or on monolayer contact doping, in which a source substrate coated with a monolayer of a carborane silane was the dopant source. As a third route, both techniques were combined to retain the benefits of conformal monolayer formation and the use of an external capping layer. These routes were used for doping fragile porous nanowires fabricated by metal-assisted chemical etching. Differences in porosity were used to tune the total doping dose inside the nanowires, as measured by X-ray photoelectron spectroscopy and secondary ion mass spectrometry measurements. The higher the porosity, the higher was the surface available for dopant-containing molecules, which in turn led to a higher doping dose. Slightly porous nanowires could be doped via all three routes, which resulted in highly doped nanowires with (projected areal) doping doses of 10(14)-10(15) boron atoms per cm(2) compared to 10(12) atoms per cm(2) for a non-porous planar sample. Highly porous nanowires were not compatible with the conventional monolayer doping technique, but monolayer contact doping and the combined route resulted for these highly porous nanowires in tremendously high doping doses up to 10(17) boron atoms per cm(2).

  6. Electrical conductivity in Langmuir-Blodgett films of n-alkyl cyanobiphenyls using current sensing atomic force microscope

    SciTech Connect

    Gayathri, H. N.; Suresh, K. A.

    2015-06-28

    We report our studies on the nanoscale electrical conductivity in monolayers of n-alkyl cyanobiphenyl materials deposited on solid surface. Initially, the 8CB, 9CB, and 10CB monolayer films were prepared by the Langmuir technique at air-water interface and characterized by surface manometry and Brewster angle microscopy. The monolayer films were transferred on to solid substrates by the Langmuir-Blodgett (L-B) technique. The 8CB, 9CB, and 10CB monolayer L-B films were deposited on freshly cleaved mica and studied by atomic force microscope (AFM), thereby measuring the film thickness as ∼1.5 nm. The electrical conductivity measurements were carried out on 9CB and 10CB monolayer L-B films deposited onto highly ordered pyrolytic graphite using current sensing AFM. The nanoscale current-voltage (I-V) measurements show a non-linear variation. The nature of the curve indicates electron tunneling to be the mechanism for electrical conduction. Furthermore, analysis of the I-V curve reveals a transition in the electron conduction mechanism from direct tunneling to injection tunneling. From the transition voltage, we have estimated the values of barrier height for 9CB and 10CB to be 0.71 eV and 0.37 eV, respectively. For both 9CB and 10CB, the effective mass of electron was calculated to be 0.021 m{sub e} and 0.065 m{sub e}, respectively. These parameters are important in the design of molecular electronic devices.

  7. Electrical conductivity in Langmuir-Blodgett films of n-alkyl cyanobiphenyls using current sensing atomic force microscope

    NASA Astrophysics Data System (ADS)

    Gayathri, H. N.; Suresh, K. A.

    2015-06-01

    We report our studies on the nanoscale electrical conductivity in monolayers of n-alkyl cyanobiphenyl materials deposited on solid surface. Initially, the 8CB, 9CB, and 10CB monolayer films were prepared by the Langmuir technique at air-water interface and characterized by surface manometry and Brewster angle microscopy. The monolayer films were transferred on to solid substrates by the Langmuir-Blodgett (L-B) technique. The 8CB, 9CB, and 10CB monolayer L-B films were deposited on freshly cleaved mica and studied by atomic force microscope (AFM), thereby measuring the film thickness as ˜1.5 nm. The electrical conductivity measurements were carried out on 9CB and 10CB monolayer L-B films deposited onto highly ordered pyrolytic graphite using current sensing AFM. The nanoscale current-voltage (I-V) measurements show a non-linear variation. The nature of the curve indicates electron tunneling to be the mechanism for electrical conduction. Furthermore, analysis of the I-V curve reveals a transition in the electron conduction mechanism from direct tunneling to injection tunneling. From the transition voltage, we have estimated the values of barrier height for 9CB and 10CB to be 0.71 eV and 0.37 eV, respectively. For both 9CB and 10CB, the effective mass of electron was calculated to be 0.021 me and 0.065 me, respectively. These parameters are important in the design of molecular electronic devices.

  8. A pH-Sensitive Supramolecular Switch Based on Mixed Carboxylic Acid Terminated Self-Assembled Monolayers on Au(111).

    PubMed

    Jacquelín, Daniela K; Pérez, Manuel A; Euti, Esteban M; Arisnabarreta, Nicolás; Cometto, Fernando P; Paredes-Olivera, Patricia; Patrito, E Martín

    2016-02-02

    We show that homogeneously mixed self-assembled monolayers (SAMs) of mercaptoalkanoic acids of different chain lengths can be used to build up a pH-sensitive supramolecular switch. The acids with short and long alkyl chains interact via the strong hydrogen bond between carboxylic acid groups. The pH acts as a trigger by breaking or restoring the hydrogen bond interaction in basic or acidic solutions, respectively. The corresponding changes in the monolayer structure were determined by ellipsometry, surface-enhanced Raman spectroscopy, and contact angle measurements. Density functional theory (DFT) calculations were performed to elucidate the structures of interacting molecules compatible with the surface coverage obtained from electrochemical reductive desorption experiments. The simplicity of the preparation procedure assures a high reproducibility whereas the stability of the homogeneous mixed SAM guarantees the reversibility of the switching process.

  9. Alkyl-thiol Langmuir films on the surface of liquid mercury.

    PubMed

    Kraack, H; Tamam, L; Sloutskin, E; Deutsch, M; Ocko, B M

    2007-07-03

    The coverage dependent phase behavior of monolayers of alkyl thiols (CH3(CH2)(n-1)SH, denoted as CnSH) on mercury was studied for chain lengths 9 monolayer of standing-up molecules is formed, exhibiting well-ordered phases, the structure of which is n- and coverage-dependent. The molecular chains pack in a centered rectangular unit cell, with an approximately 27 degrees tilt from the surface normal toward nearest neighbors. The strong sulfur-mercury bond induces a noncentered unit cell for the headgroups, incorporating one mercury atom per two thiol molecules. The small but significant differences in structure of these films on gold and on mercury are discussed and assigned to the different structure of the subphase: long-range-ordered crystal for gold and short-range-ordered liquid for mercury.

  10. Monolayer coated gold nanoparticles for delivery applications

    PubMed Central

    Rana, Subinoy; Bajaj, Avinash; Mout, Rubul; Rotello, Vincent M.

    2011-01-01

    Gold nanoparticles (AuNPs) provide attractive vehicles for delivery of drugs, genetic materials, proteins, and small molecules. AuNPs feature low core toxicity coupled with the ability to parametrically control particle size and surface properties. In this review, we focus on engineering of the AuNP surface monolayer, highlighting recent advances in tuning monolayer structures for efficient delivery of drugs and biomolecules. This review covers two broad categories of particle functionalization, organic monolayers and biomolecule coatings, and discusses their applications in drug, DNA/RNA, protein and small molecule delivery. PMID:21925556

  11. DNA-directed alkylating ligands as potential antitumor agents: sequence specificity of alkylation by intercalating aniline mustards.

    PubMed

    Prakash, A S; Denny, W A; Gourdie, T A; Valu, K K; Woodgate, P D; Wakelin, L P

    1990-10-23

    The sequence preferences for alkylation of a series of novel parasubstituted aniline mustards linked to the DNA-intercalating chromophore 9-aminoacridine by an alkyl chain of variable length were studied by using procedures analogous to Maxam-Gilbert reactions. The compounds alkylate DNA at both guanine and adenine sites. For mustards linked to the acridine by a short alkyl chain through a para O- or S-link group, 5'-GT sequences are the most preferred sites at which N7-guanine alkylation occurs. For analogues with longer chain lengths, the preference of 5'-GT sequences diminishes in favor of N7-adenine alkylation at the complementary 5'-AC sequence. Magnesium ions are shown to selectively inhibit alkylation at the N7 of adenine (in the major groove) by these compounds but not the alkylation at the N3 of adenine (in the minor groove) by the antitumor antibiotic CC-1065. Effects of chromophore variation were also studied by using aniline mustards linked to quinazoline and sterically hindered tert-butyl-9-aminoacridine chromophores. The results demonstrate that in this series of DNA-directed mustards the noncovalent interactions of the carrier chromophores with DNA significantly modify the sequence selectivity of alkylation by the mustard. Relationships between the DNA alkylation patterns of these compounds and their biological activities are discussed.

  12. Enhanced nonlinear spectroscopy for monolayers and thin films in near-Brewster's angle reflection pump-probe geometry

    NASA Astrophysics Data System (ADS)

    Nishida, Jun; Yan, Chang; Fayer, Michael D.

    2017-03-01

    We experimentally demonstrate and theoretically explicate a method that greatly enhances the detection of third-order nonlinear signals from monolayers and thin films on dielectric substrates. Nonlinear infrared signals, including two dimensional infrared (2D IR) vibrational echo signals, were detected from a functionalized alkyl chain monolayer on a dielectric SiO2 surface in a near-Brewster's angle reflection pump-probe geometry. We observed a tremendous enhancement of the signal-to-noise (S/N) ratio in this geometry compared with a conventional transmission pump-probe geometry signal. The S/N enhancement is achieved by the greatly increased modulation of the local oscillator (LO) field that is induced by the nonlinear signal field. By reducing the LO field without loss of the signal field, the modulation amplitude acquired in this geometry was enhanced by more than a factor of 50. The incident angle dependence of the enhancement was measured and the result agreed remarkably well with theoretical calculations. We combined this geometry with a germanium acousto-optic modulator pulse shaping system to apply 2D IR spectroscopy to the monolayer. The enhanced and phase-stable 2D IR spectra gave detailed dynamical information for the functionalized alkyl chain monolayer. The application of the method to films with finite thickness was described theoretically. The range of film thicknesses over which the method is applicable is delineated, and we demonstrate that accurate dynamical information from thin films can be obtained in spite of dispersive contributions that increase with the film thickness. While we focus on infrared experiments in this article, the method and the theory are applicable to visible and ultraviolet experiments as well.

  13. Surface organization of a DPPC monolayer on concentrated SrCl2 and ZnCl2 solutions.

    PubMed

    Adams, Ellen M; Verreault, Dominique; Jayarathne, Thilina; Cochran, Richard E; Stone, Elizabeth A; Allen, Heather C

    2016-11-30

    Transition metals are known to be enriched in organic-coated marine aerosols, but the impact these cations have on their surface properties is not well understood. Here the effect of Zn(2+) enrichment on the surface properties of a dipalmitoylphosphatidylcholine (DPPC) monolayer was investigated and compared to that of the alkaline earth metal Sr(2+), an ion not enriched in aerosols. Phase behavior of the DPPC film on concentrated aqueous solutions was probed with surface pressure-area isotherms while domain morphology was monitored with Brewster angle microscopy (BAM). Infrared reflection-absorption spectroscopy (IRRAS) and vibrational sum frequency generation (VSFG) spectroscopy were used to assess the impact of cations on the conformation and orientation of alkyl chains as well as the hydration state of the carbonyl and phosphatidylcholine (PC) moieties. Results of compression isotherms and BAM show that Zn(2+) strongly interacts with DPPC molecules, and induces condensation of the monolayer while Sr(2+) only weakly interacts with the monolayer in expanded phases. Conformational order and orientation of alkyl chains in the condensed phase are not significantly altered by either cation. IRRAS indicates that Sr(2+) has weak interactions with the PC headgroup. Zn(2+) ions cause dehydration of carbonyl groups and binds to the phosphate group in a 2 : 1 bridging complex. Findings here suggest that Sr(2+) is not enriched in aerosols because it behaves similar to a monovalent ion and only weakly interacts with the monolayer, while enrichment of Zn(2+) is due to strong binding to the lipid film.

  14. Cobalt Cystathionine β-Synthase: A Cobalt-Substituted Heme Protein with a Unique Thiolate Ligation Motif

    PubMed Central

    Smith, Aaron T.; Majtan, Tomas; Freeman, Katherine M.; Su, Yang; Kraus, Jan P.; Burstyn, Judith N.

    2012-01-01

    Human cystathionine β-synthase (hCBS), a key enzyme in the transsulfuration pathway, catalyzes the condensation of serine with homocysteine to produce cystathionine. CBS from higher organisms is unique in that it is the only known protein that binds pyridoxal-5′-phosphate (PLP) and heme. Intriguingly, the function of the heme in hCBS has yet to be elucidated. Herein we describe characterization of a cobalt-substituted variant of hCBS (Co hCBS) in which CoPPIX replaces FePPIX (heme). Co(III) hCBS is a unique Co-substituted heme protein: the Co(III) ion is 6-coordinate, low-spin, diamagnetic, and bears a cysteine(thiolate) as one of its axial ligands. The peak positions and intensities of the electronic absorption and MCD spectra of Co(III) hCBS are distinct from those of previously Co-substituted heme proteins; TD-DFT calculations reveal that the unique features arise from the 6-coordinate Co bound axially by cysteine(thiolate) and a neutral donor, presumably histidine. Reactivity of Co(III) hCBS with HgCl2 is consistent with loss of the cysteine(thiolate) ligand. Co(III) hCBS is slowly reduced to Co(II) hCBS, which contains a 5-coordinate, low-spin, S = ½ Co-porphyrin that does not retain the cysteine(thiolate) ligand; this form of Co(II) hCBS binds NO(g) but not CO(g). Co(II) hCBS is reoxidized in air to form a new Co(III) form, which does not contain a cysteine(thiolate) ligand. Canonical and alternative CBS assays suggest that maintaining the native heme ligation motif of wild-type Fe hCBS (Cys/His) is essential to maintain maximal activity in Co hCBS. Correlation between the coordination structures and enzyme activity in both native Fe and Co-substituted proteins implicates a structural role for the heme in CBS. PMID:21480614

  15. Synthesis of functionalized epoxides by copper-catalyzed alkylative epoxidation of allylic alcohols with alkyl nitriles.

    PubMed

    Bunescu, Ala; Wang, Qian; Zhu, Jieping

    2015-04-17

    A copper-catalyzed oxyalkylation of allylic alcohols using nonactivated alkyl nitriles as reaction partners was developed. A sequence involving generation of an alkyl nitrile radical followed by its addition to a double bond and a copper-mediated formation of C(sp(3))-O bond was proposed to account for the reaction outcome. The protocol provided an efficient route to functionalized tri- and tetrasubstituted epoxides via formation of a C(sp(3))-C(sp(3)) and a C(sp(3))-O bond with moderate to excellent diastereoselectivity.

  16. Effects of alkyl parabens on plant pathogenic fungi.

    PubMed

    Ito, Shinsaku; Yazawa, Satoru; Nakagawa, Yasutaka; Sasaki, Yasuyuki; Yajima, Shunsuke

    2015-04-15

    Alkyl parabens are used as antimicrobial preservatives in cosmetics, food, and pharmaceutical products. However, the mode of action of these chemicals has not been assessed thoroughly. In this study, we determined the effects of alkyl parabens on plant pathogenic fungi. All the fungi tested, were susceptible to parabens. The effect of linear alkyl parabens on plant pathogenic fungi was related to the length of the alkyl chain. In addition, the antifungal activity was correlated with the paraben-induced inhibition of oxygen consumption. The antifungal activity of linear alkyl parabens likely originates, at least in part, from their ability to inhibit the membrane respiratory chain, especially mitochondrial complex II. Additionally, we determined that some alkyl parabens inhibit Alternaria brassicicola infection of cabbage. Copyright © 2015 Elsevier Ltd. All rights reserved.

  17. Alkylation damage by lipid electrophiles targets functional protein systems.

    PubMed

    Codreanu, Simona G; Ullery, Jody C; Zhu, Jing; Tallman, Keri A; Beavers, William N; Porter, Ned A; Marnett, Lawrence J; Zhang, Bing; Liebler, Daniel C

    2014-03-01

    Protein alkylation by reactive electrophiles contributes to chemical toxicities and oxidative stress, but the functional impact of alkylation damage across proteomes is poorly understood. We used Click chemistry and shotgun proteomics to profile the accumulation of proteome damage in human cells treated with lipid electrophile probes. Protein target profiles revealed three damage susceptibility classes, as well as proteins that were highly resistant to alkylation. Damage occurred selectively across functional protein interaction networks, with the most highly alkylation-susceptible proteins mapping to networks involved in cytoskeletal regulation. Proteins with lower damage susceptibility mapped to networks involved in protein synthesis and turnover and were alkylated only at electrophile concentrations that caused significant toxicity. Hierarchical susceptibility of proteome systems to alkylation may allow cells to survive sublethal damage while protecting critical cell functions.

  18. Alkylation Damage by Lipid Electrophiles Targets Functional Protein Systems*

    PubMed Central

    Codreanu, Simona G.; Ullery, Jody C.; Zhu, Jing; Tallman, Keri A.; Beavers, William N.; Porter, Ned A.; Marnett, Lawrence J.; Zhang, Bing; Liebler, Daniel C.

    2014-01-01

    Protein alkylation by reactive electrophiles contributes to chemical toxicities and oxidative stress, but the functional impact of alkylation damage across proteomes is poorly understood. We used Click chemistry and shotgun proteomics to profile the accumulation of proteome damage in human cells treated with lipid electrophile probes. Protein target profiles revealed three damage susceptibility classes, as well as proteins that were highly resistant to alkylation. Damage occurred selectively across functional protein interaction networks, with the most highly alkylation-susceptible proteins mapping to networks involved in cytoskeletal regulation. Proteins with lower damage susceptibility mapped to networks involved in protein synthesis and turnover and were alkylated only at electrophile concentrations that caused significant toxicity. Hierarchical susceptibility of proteome systems to alkylation may allow cells to survive sublethal damage while protecting critical cell functions. PMID:24429493

  19. Structural Alterations of the Cysteine Desulfurase IscS of Salmonella enterica Serovar Typhimurium Reveal Substrate Specificity of IscS in tRNA Thiolation

    PubMed Central

    Lundgren, Hans K.; Björk, Glenn R.

    2006-01-01

    The cysteine desulfurase IscS in Salmonella enterica serovar Typhimurium is required for the formation of all four thiolated nucleosides in tRNA, which is thought to occur via two principally different biosynthetic pathways. The synthesis of 4-thiouridine (s4U) and 5-methylaminomethyl-2-thiouridine (mnm5s2U) occurs by a transfer of sulfur from IscS via various proteins to the target nucleoside in the tRNA, and no iron-sulfur cluster protein participates, whereas the synthesis of 2-thiocytidine (s2C) and N6-(4-hydroxyisopentenyl)-2-methylthioadenosine (ms2io6A) is dependent on iron-sulfur cluster proteins, whose formation and maintenance depend on IscS. Accordingly, inactivation of IscS should result in decreased synthesis of all thiolated nucleosides. We selected mutants defective either in the synthesis of a thiolated nucleoside (mnm5s2U) specific for the iron-sulfur protein-independent pathway or in the synthesis of a thiolated nucleoside (ms2io6A) specific for the iron-sulfur protein-dependent pathway. Although we found altered forms of IscS that influenced the synthesis of all thiolated nucleosides, consistent with the model, we also found mutants defective in subsets of thiolated nucleosides. Alterations in the C-terminal region of IscS reduced the level of only ms2io6A, suggesting that the synthesis of this nucleoside is especially sensitive to minor aberrations in iron-sulfur cluster transfer activity. Our results suggest that IscS has an intrinsic substrate specificity in how it mediates sulfur mobilization and/or iron-sulfur cluster formation and maintenance required for thiolation of tRNA. PMID:16585765

  20. The Abiotic Chemistry of Thiolated Acetate Derivatives and the Origin of Life.

    PubMed

    Chandru, Kuhan; Gilbert, Alexis; Butch, Christopher; Aono, Masashi; Cleaves, H James

    2016-07-21

    Thioesters and thioacetic acid (TAA) have been invoked as key reagents for the origin of life as activated forms of acetate analogous to acetyl-CoA. These species could have served as high-energy group-transfer reagents and allowed carbon insertions to form higher molecular weight compounds such as pyruvate. The apparent antiquity of the Wood-Ljungdahl CO2 fixation pathway and its presence in organisms which inhabit hydrothermal (HT) environments has also led to suggestions that there may be a connection between the abiotic chemistry of compounds similar to TAA and the origins of metabolism. These compounds' apparent chemical simplicity has made their prebiotic availability assumed, however, although the kinetic behavior and thermochemical properties of TAA and analogous esters have been preliminarily explored in other contexts, the geochemical relevance of these compounds merits further evaluation. Therefore, the chemical behavior of the simplest thiolated acetic acid derivatives, TAA and methylthioacetate (MTA) were explored here. Using laboratory measurements, literature data, and thermochemical models, we examine the plausibility of the accumulation of these compounds in various geological settings. Due to the high free energy change of their hydrolysis and corresponding low equilibrium constants, it is unlikely that these species could have accumulated abiotically to any significant extant.

  1. Tamoxifen-loaded thiolated alginate-albumin nanoparticles as antitumoral drug delivery systems.

    PubMed

    Martínez, A; Benito-Miguel, M; Iglesias, I; Teijón, J M; Blanco, M D

    2012-06-01

    Nanoparticles based on disulfide bond reduced bovine serum albumin and thiolated alginate (alginate-cysteine conjugate) have been prepared by coacervation method and have been loaded with tamoxifen (TMX). The TMX load into the nanoparticles was optimized (4-6 μg/mg NP) by freeze-drying the systems before the loading procedure. Maximum TMX release (45-52%) took place between 2 and 25 h. Cytotoxicity of unloaded nanoparticles in MCF-7 and HeLa cells was not observed, although a small decrease in viability took place at very high concentration. Cell uptake of nanoparticles occurred in both cell types and the presence of polysaccharide in the nanoparticle composition allowed a better interaction with cells. The administration of 10 μM TMX by TMX-nanoparticles was effective in both cellular lines, and the effect of the drug-loaded systems on MCF-7 cell cycle showed the efficacy of the TMX-loaded nanoparticles. Copyright © 2012 Wiley Periodicals, Inc.

  2. Synthesis of thiolated chitosan and preparation nanoparticles with sodium alginate for ocular drug delivery

    PubMed Central

    Su, Meiqin; Tang, Shaoheng; Wang, Lingsong; Liang, Xinfang; Meng, Feihong; Hong, Ying; Xu, Zhiran

    2012-01-01

    Purpose The goal of the present study was to synthesize mucoadhesive polymer – thiolated chitosan (TCS) from chitosan (CS), then prepared CS/TCS-sodium alginate nanoparticles (CS/TCS-SA NPs), determined which was more potential for ocular drug delivery. Methods A new method for preparing TCS was developed, and the characteristics were determined using Fourier transform infrared spectroscopy and the degree of thiol immobilized was measured by Ellman’s reagent. Human corneal epithelium (HCE) cells were incubated with different concentrations of TCS for 48 h to determine the cell viabilities. CS/TCS-SA NPs were prepared and optimized by a modified ionic gelation method. The particle sizes, zeta potentials, Scanning electron microscopy images, mucoadhesion, in vitro cell uptake and in vivo studies of the two types of NP were compared. Results The new method enabled a high degree of thiol substitution of TCS, up to 1,411.01±4.02 μmol/g. In vitro cytocompatibility results suggest that TCS is nontoxic. Compared to CS-SA NPs, TCS-SA NPs were more stable, with higher mucoadhesive properties and could deliver greater amounts of drugs into HCE cells in vitro and cornea in vivo. Conclusions TCS-SA NPs have better delivery capability, suggesting they have good potential for ocular drug delivery applications. PMID:22876124

  3. Mucoadhesive effect of thiolated PEG stearate and its modified NLC for ocular drug delivery.

    PubMed

    Shen, Jie; Wang, Yu; Ping, Qineng; Xiao, Yanyu; Huang, Xin

    2009-08-04

    This study was to develop a thiolated non-ionic surfactant, cysteine-polyethylene glycol stearate (Cys-PEG-SA), for the assembling of nanoparticulate ocular drug delivery system with mucoadhesive property. Cys-PEG-SA was synthesized in two steps reaction involving a new derivative intermediate formation of p-nitrophenylcarbonyl-PEG-SA (pNP-PEG-SA). Up to 369.43+/-25.54 mumol free thiol groups per gram of the conjugates was reached. The nanostructured lipid carrier (NLC) loaded cyclosporine A (CyA) was prepared by melt-emulsification method. The mucoadhesive NLC (Cys-NLC) was obtained by incubating NLC emulsion with Cys-PEG-SA. The mucoadhesive properties of these nanocarriers were examined by using mucin particles method. The particle size or zeta potential of the porcine mucin particles were changed with the added concentration of Cys-PEG-SA, and the disulphide bond breaker cysteine significantly reduced the adhesion of Cys-NLC to mucin particles (P<0.05), whereas PEG-SA and NLC did not alternate the properties of the mucin particles. When Cys-NLC was administered topically to the rabbit eye, the encapsulated cyclosporine was found to remain on the ocular surface in the cul-de-sac for up to 6 h, both precorneal retention time and concentration were dramatically increased (P<0.05), compared with the NLC without thiomer modification.

  4. Drug permeability and mucoadhesion properties of thiolated trimethyl chitosan nanoparticles in oral insulin delivery.

    PubMed

    Yin, Lichen; Ding, Jieying; He, Chunbai; Cui, Liming; Tang, Cui; Yin, Chunhua

    2009-10-01

    Trimethyl chitosan-cysteine conjugate (TMC-Cys) was synthesized in an attempt to combine the mucoadhesion and the permeation enhancing effects of TMC and thiolated polymers related to different mechanisms for oral absorption. TMC-Cys with various molecular weights (30, 200, and 500 kDa) and quaternization degrees (15 and 30%) was allowed to form polyelectrolyte nanoparticles with insulin through self-assembly, which demonstrated particle size of 100-200 nm, zeta potential of +12 to +18 mV, and high encapsulation efficiency. TMC-Cys/insulin nanoparticles (TMC-Cys NP) showed a 2.1-4.7-fold increase in mucoadhesion compared to TMC/insulin nanoparticles (TMC NP), which might be partly attributed to disulfide formation between TMC-Cys and mucin as evidenced by DSC measurement. Compared to insulin solution and TMC NP, TMC-Cys NP induced increased insulin transport through rat intestine by 3.3-11.7 and 1.7-2.6 folds, promoted Caco-2 cell internalization by 7.5-12.7 and 1.7-3.0 folds, and augmented uptake in Peyer's patches by 14.7-20.9 and 1.7-5.0 folds, respectively. Such results were further confirmed by in vivo experiment with the optimal TMC-Cys NP. Biocompatibility assessment revealed lack of toxicity of TMC-Cys NP. Therefore, self-assembled nanoparticles between TMC-Cys and protein drugs could be an effective and safe oral delivery system.

  5. Ligand effects on the optical and chiroptical properties of the thiolated Au18 cluster.

    PubMed

    Tlahuice-Flores, Alfredo

    2016-10-12

    The effect of chiral and achiral ligands protecting the inner Au9 core of the Au18(SR)14 cluster is studied based on density functional theory (DFT) and its corrected long-range interaction (DFT-D) approach. It was found that the electronic properties (energy levels) depend on the specific ligands, which induce distinct distortions on the Au-S framework. However, the substitution of S-c-C6H11 as SCH3 ligands may be considered to be correct given the obtained resemblance to the displayed bonding, optical and chiroptical properties. A further comparison of the CD and UV spectra displayed by the Au18 cluster protected by chiral and achiral ligands attests that more intense profiles are featured by ligands including phenyl rings and/or oxygen atoms such that the Au18 cluster protected by either achiral meta-mercaptobenzoic acid (m-MBA) or achiral SPh ligands displays more intense UV and CD signals. These results provide new insight into the effect of ligands on thiolated gold clusters.

  6. Protein degradation and dynamic tRNA thiolation fine-tune translation at elevated temperatures.

    PubMed

    Tyagi, Kshitiz; Pedrioli, Patrick G A

    2015-05-19

    Maintenance of protein quality control has implications in various processes such as neurodegeneration and ageing. To investigate how environmental insults affect this process, we analysed the proteome of yeast continuously exposed to mild heat stress. In agreement with previous transcriptomics studies, amongst the most marked changes, we found up-regulation of cytoprotective factors; a shift from oxidative phosphorylation to fermentation; and down-regulation of translation. Importantly, we also identified a novel, post-translationally controlled, component of the heat shock response. The abundance of Ncs2p and Ncs6p, two members of the URM1 pathway responsible for the thiolation of wobble uridines in cytoplasmic tRNAs tK(UUU), tQ(UUG) and tE(UUC), is down-regulated in a proteasomal dependent fashion. Using random forests we show that this results in differential translation of transcripts with a biased content for the corresponding codons. We propose that the role of this pathway in promoting catabolic and inhibiting anabolic processes, affords cells with additional time and resources needed to attain proper protein folding under periods of stress. © The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.

  7. Thiolated methylated dimethylaminobenzyl chitosan: A novel chitosan derivative as a potential delivery vehicle.

    PubMed

    Hakimi, Shirin; Mortazavian, Elaheh; Mohammadi, Zohreh; Samadi, Fatemeh Yazdi; Samadikhah, Hamidreza; Taheritarigh, Sadegh; Tehrani, Niyousha Rafiee; Rafiee-Tehrani, Morteza

    2017-02-01

    Chitosan is a natural mucoadhesive, biodegradable, biocompatible and nontoxic polymer which has been used in pharmaceutical industry for a lot of purposes such as dissolution enhancing, absorption enhancing, sustained releasing and protein, gene or drug delivery. Two major disadvantages of chitosan are poor solubility in physiological pH and low efficiency for protein and gene delivery. In this study thiolated methylated N-(4-N,N-dimethylaminobenzyl) chitosan was prepared for the first time in order to improve the solubility and delivery properties of chitosan. This novel chitosan derivative was characterized using (1)H NMR, Ellman test, TGA and Zetasizer. Cell toxicity studies were performed on Human Embryonic Kidney 293 (Hek293) cell line using XTT method, to investigate the potential effect of this new derivative on cell viability. (1)H NMR results showed that all substitution reactions were successfully carried out. Zeta potential of new derivative at acidic and physiological pHs was greater than chitosan and it revealed an increase in solubility of the derivative. Furthermore, it had no significant cytotoxicity against Hek293 cell line in comparison to chitosan. These findings confirm that this new derivative can be introduced as a suitable compound for biomedical purposes. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. In situ thiolated alginate hydrogel: Instant formation and its application in hemostasis.

    PubMed

    Xu, Guanzhe; Cheng, Liang; Zhang, Qintong; Sun, Yunlong; Chen, Changlin; Xu, Heng; Chai, Yimin; Lang, Meidong

    2016-11-01

    An in situ formed hydrogel was synthesized by sodium alginate and cysteine methyl ester, which turned the sodium alginate into thiolated alginate (SA-SH). SA-SH can in situ formed into hydrogel (SA-SS-SA) with a large amount of water through covalent bond in less than 20 s. The structure characterization showed that the mechanism of SA-SH gelation was thiol-disulfide transformation. The rheology and cytotoxicity experiments of SA-SS-SA hydrogel were also investigated, which indicated that SA-SS-SA hydrogel had an appropriate mechanical strength as well as an excellent biocompatibility. The SA-SS-SA hydrogel would degrade under certain conditions after a few days and its mechanism was disulfide alkaline reduction. Finally, the hemostatic property of SA-SH was tested by rat tail amputation experiment. The time to hemostasis of rat reduced from 8.26 min to 3.24 min, which proved that SA-SH had an excellent hemostatic property.

  9. A functional [NiFe]-hydrogenase model compound that undergoes biologically relevant reversible thiolate protonation.

    PubMed

    Weber, Katharina; Krämer, Tobias; Shafaat, Hannah S; Weyhermüller, Thomas; Bill, Eckhard; van Gastel, Maurice; Neese, Frank; Lubitz, Wolfgang

    2012-12-26

    Two model compounds of the active site of [NiFe]-hydrogenases with an unusual {S(2)Ni(μ-S)(μ-CO)Fe(CO)(2)S}-coordination environment around the metals are reported. The neutral compound [Ni(xbsms)(μ-CO)(μ-S)Fe(CO)(2)('S')], (1) (H(2)xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene) is converted to [1H][BF(4)] by reversible protonation using HBF(4)·Et(2)O. The protonation takes place at the terminal thiolate sulfur atom that is coordinated to nickel. Catalytic intermediates with a protonated terminal cysteinate were suggested for the native protein but have not yet been confirmed experimentally. [1H][BF(4)] is the first dinuclear [NiFe] model compound for such a species. Both complexes have been synthesized and characterized by X-ray crystallography, NMR-, FTIR-, and (57)Fe-Mössbauer spectroscopy as well as by electronic absorption and resonance Raman spectroscopy. The experimental results clearly show that the protonation has a significant impact on the electronic structure of the iron center, although it takes place at the nickel site. DFT calculations support the interpretation of the spectroscopic data and indicate the presence of a bonding interaction between the metal ions, which is relevant for the enzyme as well. Electrochemical experiments show that both 1 and [1H][BF(4)] are active for electrocatalytic proton reduction in aprotic solvents.

  10. Thiolated poly(aspartic acid) as potential in situ gelling, ocular mucoadhesive drug delivery system.

    PubMed

    Horvát, Gabriella; Gyarmati, Benjámin; Berkó, Szilvia; Szabó-Révész, Piroska; Szilágyi, Barnabás Áron; Szilágyi, András; Soós, Judit; Sandri, Giuseppina; Bonferoni, Maria Cristina; Rossi, Silvia; Ferrari, Franca; Caramella, Carla; Csányi, Erzsébet; Budai-Szűcs, Mária

    2015-01-25

    The ophthalmic formulations on the market suffer from poor bioavailability, and it would therefore be useful to design a new formulation which is able to prolong the residence time and reduce the administration frequency. Polymer matrices which exhibit strong mucoadhesion are promising platforms in ocular drug delivery from the aspect of improved bioavailability. In the present study, an in situ gelling, mucoadhesive drug delivery system was fabricated from thiolated poly(aspartic acid) (ThioPASP). The thiol groups of ThioPASP are able to form disulphide linkages with the mucin glycoproteins and prolong the residence time on the eye. The effects of the thiol groups on the structure, swelling behaviour and mucoadhesive character of the gel and on the drug release profile were determined. The gel structure was characterized by means of rheology. The ThioPASP gel was demonstrated by rheology, tensile test and 'wash away' measurements to display strong mucoadhesion. The drug release from the ThioPASP gel was studied on a vertical Franz diffusion cell: a burst release of sodium diclofenac occurred in the first hour, followed by sustained release of the encapsulated drug for up to 24h. The results proved the importance of the presence of the thiol groups and suggested that a ThioPASP formulation can be useful as an in situ gelling, ocular dosage form. Copyright © 2014 Elsevier B.V. All rights reserved.

  11. Thiolate and phosphorothioate functionalized fluoresceins and their use as fluorescent labels.

    PubMed

    Bieniarz, C; Young, D F; Cornwell, M J

    1994-01-01

    We report the syntheses of two new fluorescein derivatives, 3',6'-dihydroxy-3-oxo-2-[(phosphonothio)-acetyl]spiro[isobenzof uran- 1(3H),9'-9H-xanthene]-6-carboxylic acid hydrazide, disodium salt, a phosphorothioate fluorescein, and 3',6'-dihydroxy-3-oxo-2-(mercaptoacetyl)spiro[isobenzofuran-1(3H), 9'-9H- xanthene]-6-carboxylic acid hydrazide, a mercaptoacetyl fluorescein. The latter is derived from the first compound by hydrolysis of the phosphate. Direct nonenzymatic labeling of the maleimide-derivatized IgG molecule by the novel mercaptoacetyl fluorescein is discussed. We also present a new method of bioconjugating phosphorothioate-functionalized fluorophores to a maleimide-derivatized protein, based on the alkaline phosphatase-catalyzed hydrolysis of the S-P bond of the phosphorothioate and the concomitant liberation of the fluorophore thiolate. This last species reacts in situ with the maleimide on the protein. A high degree of conjugation control is achieved in that modulation of the stoichiometry of the label and enzyme results in incorporation from seven to eight fluorophores per protein, depending on the ratio of the phosphorothioate fluorescein to alkaline phosphatase. The quantum yield of the mercaptoacetyl fluorescein relative to 6-carboxyfluorescein is 0.22 and lambda exc = 494 nm and lambda em = 517 nm.

  12. Thiolated-2-methacryloyloxyethyl phosphorylcholine protected silver nanoparticles as novel photo-induced cell-killing agents.

    PubMed

    Sangsuwan, Arunee; Kawasaki, Hideya; Iwasaki, Yasuhiko

    2016-04-01

    Silver nanoparticles (AgNPs) have several medical applications as antimicrobial agents such as in drug delivery and cancer therapy. However, AgNPs are of limited use because of their toxicity, which may damage the surrounding healthy tissue. In this study, thiolated-2-methacryloyloxyethyl phosphorylcholine (MPC-SH) protected silver nanoparticles (MPC-AgNPs) are prepared as cell-killing agents under UV irradiation. MPC-AgNPs are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-visible spectrophotometry. The surface plasmon resonance (SPR) band of MPC-AgNPs is observed at 404 nm, and the average diameter of the particles is determined at 13.4 ± 2.2 nm through transmission electron microscopy (TEM) and at 18.4 nm (PDI=0.18) through dynamic light scattering (DLS). Cell viability in contact with MPC-AgNPs is relatively high, and MPC-AgNPs also exhibit a cell-killing effect under UV irradiation.

  13. 3D cell entrapment in crosslinked thiolated gelatin-poly(ethylene glycol) diacrylate hydrogels

    PubMed Central

    Fu, Yao; Xu, Kedi; Zheng, Xiaoxiang; Giacomin, A. Jeffrey; Mix, Adam W.; Kao, Weiyuan John

    2012-01-01

    The combined use of natural ECM components and synthetic materials offers an attractive alternative to fabricate hydrogel-based tissue engineering scaffolds to study cell-matrix interactions in three-dimensions (3D). A facile method was developed to modify gelatin with cysteine via a bifunctional PEG linker, thus introducing free thiol groups to gelatin chains. A covalently crosslinked gelatin hydrogel was fabricated using thiolated gelatin and poly(ethylene glycol) diacrylate (PEGdA) via thiol-ene reaction. Unmodified gelatin was physically incorporated in a PEGdA-only matrix for comparison. We sought to understand the effect of crosslinking modality on hydrogel physicochemical properties and the impact on 3D cell entrapment. Compared to physically incorporated gelatin hydrogels, covalently crosslinked gelatin hydrogels displayed higher maximum weight swelling ratio (Qmax), higher water content, significantly lower cumulative gelatin dissolution up to 7 days, and lower gel stiffness. Furthermore, fibroblasts encapsulated within covalently crosslinked gelatin hydrogels showed extensive cytoplasmic spreading and the formation of cellular networks over 28 days. In contrast, fibroblasts encapsulated in the physically incorporated gelatin hydrogels remained spheroidal. Hence, crosslinking ECM protein with synthetic matrix creates a stable scaffold with tunable mechanical properties and with long-term cell anchorage points, thus supporting cell attachment and growth in the 3D environment. PMID:21955690

  14. Methylated and thiolated arsenic species for environmental and health research - A review on synthesis and characterization.

    PubMed

    Cullen, William R; Liu, Qingqing; Lu, Xiufen; McKnight-Whitford, Anthony; Peng, Hanyong; Popowich, Aleksandra; Yan, Xiaowen; Zhang, Qi; Fricke, Michael; Sun, Hongsui; Le, X Chris

    2016-11-01

    Hundreds of millions of people around the world are exposed to elevated concentrations of inorganic and organic arsenic compounds, increasing the risk of a wide range of health effects. Studies of the environmental fate and human health effects of arsenic require authentic arsenic compounds. We summarize here the synthesis and characterization of more than a dozen methylated and thiolated arsenic compounds that are not commercially available. We discuss the methods of synthesis for the following 14 trivalent (III) and pentavalent (V) arsenic compounds: monomethylarsonous acid (MMA(III)), dicysteinylmethyldithioarsenite (MMA(III)(Cys)2), monomethylarsonic acid (MMA(V)), monomethylmonothioarsonic acid (MMMTA(V)) or monothio-MMA(V), monomethyldithioarsonic acid (MMDTA(V)) or dithio-MMA(V), monomethyltrithioarsonate (MMTTA(V)) or trithio-MMA(V), dimethylarsinous acid (DMA(III)), dimethylarsino-glutathione (DMA(III)(SG)), dimethylarsinic acid (DMA(V)), dimethylmonothioarsinic acid (DMMTA(V)) or monothio-DMA(V), dimethyldithioarsinic acid (DMDTA(V)) or dithio-DMA(V), trimethylarsine oxide (TMAO(V)), arsenobetaine (AsB), and an arsenicin-A model compound. We have reviewed and compared the available methods, synthesized the arsenic compounds in our laboratories, and provided characterization information. On the basis of reaction yield, ease of synthesis and purification of product, safety considerations, and our experience, we recommend a method for the synthesis of each of these arsenic compounds. Copyright © 2016. Published by Elsevier B.V.

  15. Mucoadhesive thiolated chitosans as platforms for oral controlled drug delivery: synthesis and in vitro evaluation.

    PubMed

    Roldo, Marta; Hornof, Margit; Caliceti, Paolo; Bernkop-Schnürch, Andreas

    2004-01-01

    The aim of the present study was to evaluate the influence of the degree of modification and the polymer chain length on the mucoadhesive properties and the swelling behavior of thiolated chitosan derivatives obtained via a simple one-step reaction between the polymer and 2-iminothiolane. The conjugates differing in molecular mass of the polymer backbone and in the amount of immobilized thiol groups were compressed into tablets. They were investigated for their mucoadhesive properties on freshly excised porcine mucosa via tensile studies and the rotating cylinder method. Moreover, the swelling behavior of these tablets in aqueous solutions was studied by a simple gravimetric method. The obtained results demonstrated that the total work of adhesion of chitosan-TBA (=4-thio-butyl-amidine) conjugates can be improved by an increasing number of covalently attached thiol groups; a 100-fold increase compared to unmodified chitosan was observed for a medium molecular mass chitosan-TBA conjugate exhibiting 264 microM thiol groups per gram polymer. Also, the polymer chain length had an influence on the mucoadhesive properties of the polymer. The medium molecular mass polymer displayed a fourfold improved adhesion on the rotating cylinder compared to the derivative of low molecular mass. These results contribute to the development of new delivery systems exhibiting improved mucoadhesive properties.

  16. Thiolated Carboxymethyl-Hyaluronic-Acid-Based Biomaterials Enhance Wound Healing in Rats, Dogs, and Horses

    PubMed Central

    Yang, Guanghui; Prestwich, Glenn D.; Mann, Brenda K.

    2011-01-01

    The progression of wound healing is a complicated but well-known process involving many factors, yet there are few products on the market that enhance and accelerate wound healing. This is particularly problematic in veterinary medicine where multiple species must be treated and large animals heal slower, oftentimes with complicating factors such as the development of exuberant granulation tissue. In this study a crosslinked-hyaluronic-acid (HA-) based biomaterial was used to treat wounds on multiple species: rats, dogs, and horses. The base molecule, thiolated carboxymethyl HA, was first found to increase keratinocyte proliferation in vitro. Crosslinked gels and films were then both found to enhance the rate of wound healing in rats and resulted in thicker epidermis than untreated controls. Crosslinked films were used to treat wounds on forelimbs of dogs and horses. Although wounds healed slower compared to rats, the films again enhanced wound healing compared to untreated controls, both in terms of wound closure and quality of tissue. This study indicates that these crosslinked HA-based biomaterials enhance wound healing across multiple species and therefore may prove particularly useful in veterinary medicine. Reduced wound closure times and better quality of healed tissue would decrease risk of infection and pain associated with open wounds. PMID:23738117

  17. A novel thermo-sensitive hydrogel based on thiolated chitosan/hydroxyapatite/beta-glycerophosphate.

    PubMed

    Liu, Xujie; Chen, Yan; Huang, Qianli; He, Wei; Feng, Qingling; Yu, Bo

    2014-09-22

    In order to get a water-soluble in situ gel-forming system, a thiolated chitosan, chitosan-4-thio-butylamidine (CS-TBA) conjugate was synthesized and used to replace the unmodified chitosan in the application of the in situ gel-forming system. A novel thermo-sensitive hydrogel was prepared based on CS-TBA/hydroxyapatite (HA)/beta-glycerophosphate disodium (β-GP). The gel formation, rheological properties, morphology, degradation, cytotoxicity, as well as protein release process of the novel gel system were investigated in this study. The CS-TBA/HA/β-GP gel showed a higher storage modulus (G') and loss modulus (G″) and a decreased bovine serum albumin (BSA) release rate which was maintained the protein release for a longer time compared with the unmodified chitosan (CS)/HA/β-GP gel, due to the existence of thiol groups and/or disulfide bonds. The CS-TBA/HA/β-GP gel has a porous structure with a uniform distribution of nano-hydroxyapatite, an appropriate degradation rate and low cytotoxicity, showing potential applications in drug delivery and tissue engineering.

  18. Ammonia formation by a thiolate-bridged diiron amide complex as a nitrogenase mimic

    NASA Astrophysics Data System (ADS)

    Li, Yang; Li, Ying; Wang, Baomin; Luo, Yi; Yang, Dawei; Tong, Peng; Zhao, Jinfeng; Luo, Lun; Zhou, Yuhan; Chen, Si; Cheng, Fang; Qu, Jingping

    2013-04-01

    Although nitrogenase enzymes routinely convert molecular nitrogen into ammonia under ambient temperature and pressure, this reaction is currently carried out industrially using the Haber-Bosch process, which requires extreme temperatures and pressures to activate dinitrogen. Biological fixation occurs through dinitrogen and reduced NxHy species at multi-iron centres of compounds bearing sulfur ligands, but it is difficult to elucidate the mechanistic details and to obtain stable model intermediate complexes for further investigation. Metal-based synthetic models have been applied to reveal partial details, although most models involve a mononuclear system. Here, we report a diiron complex bridged by a bidentate thiolate ligand that can accommodate HN=NH. Following reductions and protonations, HN=NH is converted to NH3 through pivotal intermediate complexes bridged by N2H3- and NH2- species. Notably, the final ammonia release was effected with water as the proton source. Density functional theory calculations were carried out, and a pathway of biological nitrogen fixation is proposed.

  19. Ultrabright Luminescence from Gold Nanoclusters: Rigidifying the Au(I)-Thiolate Shell.

    PubMed

    Pyo, Kyunglim; Thanthirige, Viraj Dhanushka; Kwak, Kyuju; Pandurangan, Prabhu; Ramakrishna, Guda; Lee, Dongil

    2015-07-01

    Luminescent nanomaterials have captured the imagination of scientists for a long time and offer great promise for applications in organic/inorganic light-emitting displays, optoelectronics, optical sensors, biomedical imaging, and diagnostics. Atomically precise gold clusters with well-defined core-shell structures present bright prospects to achieve high photoluminescence efficiencies. In this study, gold clusters with a luminescence quantum yield greater than 60% were synthesized based on the Au22(SG)18 cluster, where SG is glutathione, by rigidifying its gold shell with tetraoctylammonium (TOA) cations. Time-resolved and temperature-dependent optical measurements on Au22(SG)18 have shown the presence of high quantum yield visible luminescence below freezing, indicating that shell rigidity enhances the luminescence quantum efficiency. To achieve high rigidity of the gold shell, Au22(SG)18 was bound to bulky TOA that resulted in greater than 60% quantum yield luminescence at room temperature. Optical measurements have confirmed that the rigidity of gold shell was responsible for the luminescence enhancement. This work presents an effective strategy to enhance the photoluminescence efficiencies of gold clusters by rigidifying the Au(I)-thiolate shell.

  20. The Abiotic Chemistry of Thiolated Acetate Derivatives and the Origin of Life

    PubMed Central

    Chandru, Kuhan; Gilbert, Alexis; Butch, Christopher; Aono, Masashi; Cleaves, H. James

    2016-01-01

    Thioesters and thioacetic acid (TAA) have been invoked as key reagents for the origin of life as activated forms of acetate analogous to acetyl-CoA. These species could have served as high-energy group-transfer reagents and allowed carbon insertions to form higher molecular weight compounds such as pyruvate. The apparent antiquity of the Wood-Ljungdahl CO2 fixation pathway and its presence in organisms which inhabit hydrothermal (HT) environments has also led to suggestions that there may be a connection between the abiotic chemistry of compounds similar to TAA and the origins of metabolism. These compounds’ apparent chemical simplicity has made their prebiotic availability assumed, however, although the kinetic behavior and thermochemical properties of TAA and analogous esters have been preliminarily explored in other contexts, the geochemical relevance of these compounds merits further evaluation. Therefore, the chemical behavior of the simplest thiolated acetic acid derivatives, TAA and methylthioacetate (MTA) were explored here. Using laboratory measurements, literature data, and thermochemical models, we examine the plausibility of the accumulation of these compounds in various geological settings. Due to the high free energy change of their hydrolysis and corresponding low equilibrium constants, it is unlikely that these species could have accumulated abiotically to any significant extant. PMID:27443234

  1. The Abiotic Chemistry of Thiolated Acetate Derivatives and the Origin of Life

    NASA Astrophysics Data System (ADS)

    Chandru, Kuhan; Gilbert, Alexis; Butch, Christopher; Aono, Masashi; Cleaves, H. James

    2016-07-01

    Thioesters and thioacetic acid (TAA) have been invoked as key reagents for the origin of life as activated forms of acetate analogous to acetyl-CoA. These species could have served as high-energy group-transfer reagents and allowed carbon insertions to form higher molecular weight compounds such as pyruvate. The apparent antiquity of the Wood-Ljungdahl CO2 fixation pathway and its presence in organisms which inhabit hydrothermal (HT) environments has also led to suggestions that there may be a connection between the abiotic chemistry of compounds similar to TAA and the origins of metabolism. These compounds’ apparent chemical simplicity has made their prebiotic availability assumed, however, although the kinetic behavior and thermochemical properties of TAA and analogous esters have been preliminarily explored in other contexts, the geochemical relevance of these compounds merits further evaluation. Therefore, the chemical behavior of the simplest thiolated acetic acid derivatives, TAA and methylthioacetate (MTA) were explored here. Using laboratory measurements, literature data, and thermochemical models, we examine the plausibility of the accumulation of these compounds in various geological settings. Due to the high free energy change of their hydrolysis and corresponding low equilibrium constants, it is unlikely that these species could have accumulated abiotically to any significant extant.

  2. Electrochemical Biosensor: Multistep functionalization of thiolated ssDNA on gold-coated microcantilever

    NASA Astrophysics Data System (ADS)

    Dulanto Carbajal, Jorge

    Bio-chemical sensors are an emerging and vibrant area of research. The use of micromechanical cantilevers is relatively new as biomechanical recognition detectors. Reactions on a gold coated and chemically functionalized surface produce a mechanical deflection of the cantilever which is used as the input signal of the detector. Within the area of biosensors, DNA-sensors have a wide range of applications such as DNA hybridization detectors, DNA mismatch sequence detectors and protein detectors. We designed and built a microcantilever sensor system which allows for control and characterization of surface conditions. This includes controlled functionalization which can be a dominant factor in signal generation and reproducibility in these systems. Additionally, we developed a multistep functionalization protocol which consists of a sequence of short incubations and characterizations of thiolated ssDNA on a gold-coated cantilever. Multistep functionalization is a new protocol that is used to control the ssDNA surface density on a gold-coated cantilever. Repeatable responses and feasible biosensors are obtained using this protocol.

  3. Hierarchy of bond stiffnesses within icosahedral-based gold clusters protected by thiolates

    PubMed Central

    Yamazoe, Seiji; Takano, Shinjiro; Kurashige, Wataru; Yokoyama, Toshihiko; Nitta, Kiyofumi; Negishi, Yuichi; Tsukuda, Tatsuya

    2016-01-01

    Unique thermal properties of metal clusters are believed to originate from the hierarchy of the bonding. However, an atomic-level understanding of how the bond stiffnesses are affected by the atomic packing of a metal cluster and the interfacial structure with the surrounding environment has not been attained to date. Here we elucidate the hierarchy in the bond stiffness in thiolate-protected, icosahedral-based gold clusters Au25(SC2H4Ph)18, Au38(SC2H4Ph)24 and Au144(SC2H4Ph)60 by analysing Au L3-edge extended X-ray absorption fine structure data. The Au–Au bonds have different stiffnesses depending on their lengths. The long Au–Au bonds, which are more flexible than those in the bulk metal, are located at the icosahedral-based gold core surface. The short Au–Au bonds, which are stiffer than those in the bulk metal, are mainly distributed along the radial direction and form a cyclic structural backbone with the rigid Au–SR oligomers. PMID:26778685

  4. Cationic Thiolated Poly(aspartamide) Polymer as a Potential Excipient for Artificial Tear Formulations.

    PubMed

    Budai-Szűcs, Mária; Horvát, Gabriella; Szilágyi, Barnabás Áron; Gyarmati, Benjámin; Szilágyi, András; Berkó, Szilvia; Szabó-Révész, Piroska; Sandri, Giuseppina; Bonferoni, Maria Cristina; Caramella, Carla; Soós, Judit; Facskó, Andrea; Csányi, Erzsébet

    2016-01-01

    Dry eye disease is a relatively common ocular problem, which causes eye discomfort and visual disorders leading to a decrease in the quality of life. The aim of this study was to find a possible excipient for eye drop formulations, which is able to stabilize the tear film. A cationic thiolated polyaspartamide polymer, poly[(N-mercaptoethylaspartamide)-co-(N-(N',N'-dimethylaminoethyl)aspartamide)] (ThioPASP-DME), was used as a potential vehicle. Besides satisfying the basic requirements, the chemical structure of ThioPASP-DME is similar to those of ocular mucins as it is a protein-like polymer bearing a considerable number of thiol groups. The solution of the polymer is therefore able to mimic the physiological properties of the mucins and it can interact with the mucus layer via disulphide bond formation. The resultant mucoadhesion provides a prolonged residence time and ensures protective effect for the corneal/conjunctival epithelium. ThioPASP-DME also has an antioxidant effect due to the presence of the thiol groups. The applicability of ThioPASP-DME as a potential excipient in eye drops was determined by means of ocular compatibility tests and through examinations of the interactions with the mucosal surface. The results indicate that ThioPASP-DME can serve as a potential eye drop excipient for the therapy of dry eye disease.

  5. Cationic Thiolated Poly(aspartamide) Polymer as a Potential Excipient for Artificial Tear Formulations

    PubMed Central

    Budai-Szűcs, Mária; Horvát, Gabriella; Szilágyi, Barnabás Áron; Gyarmati, Benjámin; Szilágyi, András; Berkó, Szilvia; Szabó-Révész, Piroska; Sandri, Giuseppina; Bonferoni, Maria Cristina; Caramella, Carla; Soós, Judit; Facskó, Andrea; Csányi, Erzsébet

    2016-01-01

    Dry eye disease is a relatively common ocular problem, which causes eye discomfort and visual disorders leading to a decrease in the quality of life. The aim of this study was to find a possible excipient for eye drop formulations, which is able to stabilize the tear film. A cationic thiolated polyaspartamide polymer, poly[(N-mercaptoethylaspartamide)-co-(N-(N′,N′-dimethylaminoethyl)aspartamide)] (ThioPASP-DME), was used as a potential vehicle. Besides satisfying the basic requirements, the chemical structure of ThioPASP-DME is similar to those of ocular mucins as it is a protein-like polymer bearing a considerable number of thiol groups. The solution of the polymer is therefore able to mimic the physiological properties of the mucins and it can interact with the mucus layer via disulphide bond formation. The resultant mucoadhesion provides a prolonged residence time and ensures protective effect for the corneal/conjunctival epithelium. ThioPASP-DME also has an antioxidant effect due to the presence of the thiol groups. The applicability of ThioPASP-DME as a potential excipient in eye drops was determined by means of ocular compatibility tests and through examinations of the interactions with the mucosal surface. The results indicate that ThioPASP-DME can serve as a potential eye drop excipient for the therapy of dry eye disease. PMID:27313866

  6. Accurate Molecular Dimensions from Stearic Acid Monolayers.

    ERIC Educational Resources Information Center

    Lane, Charles A.; And Others

    1984-01-01

    Discusses modifications in the fatty acid monolayer experiment to reduce the inaccurate moleculary data students usually obtain. Copies of the experimental procedure used and a Pascal computer program to work up the data are available from the authors. (JN)

  7. Accurate Molecular Dimensions from Stearic Acid Monolayers.

    ERIC Educational Resources Information Center

    Lane, Charles A.; And Others

    1984-01-01

    Discusses modifications in the fatty acid monolayer experiment to reduce the inaccurate moleculary data students usually obtain. Copies of the experimental procedure used and a Pascal computer program to work up the data are available from the authors. (JN)

  8. Multicellular density fluctuations in epithelial monolayers

    NASA Astrophysics Data System (ADS)

    Zehnder, Steven M.; Wiatt, Marina K.; Uruena, Juan M.; Dunn, Alison C.; Sawyer, W. Gregory; Angelini, Thomas E.

    2015-09-01

    Changes in cell size often accompany multicellular motion in tissue, and cell number density is known to strongly influence collective migration in monolayers. Density fluctuations in other forms of active matter have been explored extensively, but not the potential role of density fluctuations in collective cell migration. Here we investigate collective motion in cell monolayers, focusing on the divergent component of the migration velocity field to probe density fluctuations. We find spatial patterns of diverging and converging cell groups throughout the monolayers, which oscillate in time with a period of approximately 3-4 h. Simultaneous fluorescence measurements of a cytosol dye within the cells show that fluid passes between groups of cells, facilitating these oscillations in cell density. Our findings reveal that cell-cell interactions in monolayers may be mediated by intercellular fluid flow.

  9. Method to synthesize metal chalcogenide monolayer nanomaterials

    SciTech Connect

    Hernandez-Sanchez, Bernadette A.; Boyle, Timothy J.

    2016-12-13

    Metal chalcogenide monolayer nanomaterials can be synthesized from metal alkoxide precursors by solution precipitation or solvothermal processing. The synthesis routes are more scalable, less complex and easier to implement than other synthesis routes.

  10. Photochemical Production of Alkyl Nitrates in the Tropical Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Dahl, E. E.; Yvon-Lewis, S. A.; Saltzman, E. S.

    2005-12-01

    Alkyl nitrates are important to the tropospheric NOx/ozone cycle because they represent a significant fraction of the reactive nitrogen (NOy). Previous work has shown that there is an oceanic source of alkyl nitrates. A photochemical mechanism for the formation of alkyl nitrates in seawater has been proposed. This mechanism involves the reaction of ROO and NO, where ROO is an alkyl peroxy radical. ROO and NO radicals in seawater are derived from the photolysis of DOM and nitrite, respectively. In this study, the photochemical production of low molecular weight alkyl nitrates (C1-C3) was observed in shipboard incubation experiments in the tropical Pacific during the PHASE 1 cruise. Seawater samples from several regions, including high and low-chlorophyll areas, were collected and incubated. Alkyl nitrate production rates as high as 2 nM/hour were observed. The production rate of alkyl nitrates was clearly dependent upon the initial concentration of nitrite, most likely as the source for NO radicals. While the magnitude of production varied between sample locations, the ratios of the production rates of the various alkyl nitrates remained relatively constant. The observed production ratios of methyl, ethyl, isopropyl, and n-propyl nitrate were 5.9:1.0:0.1:0.2. These ratios presumably reflect the speciation of peroxy radicals formed in seawater, and the yield of alkyl nitrates from the ROO+NO reaction. The observed production rate ratios are similar to the concentration ratios of alkyl nitrates observed in ambient seawater and the overlying atmosphere during the study. A comparison of the measured production rates and the observed concentrations, suggests that photochemically produced alkyl nitrates are a major source of atmospheric alkyl nitrates in the surface ocean and marine atmosphere.

  11. Lithium perchlorate-nitromethane-promoted alkylation of anilines with arylmethanols.

    PubMed

    Zhou, Jun; Mao, Hai-Feng; Wang, Lu; Zou, Jian-Ping; Zhang, Wei

    2011-11-01

    A new application of lithium perchlorate-nitromethane (LPNM) for the formation of aromatic C-N and C-C bonds is introduced. LPNM-promoted reactions of anilines with diarylmethanols selectively generate N-alkylated anilines or mono and double Friedel-Crafts alkylation products under different conditions by changing the reaction time, reaction temperature, and the ratio of the reactants. This method does not require the use of transition metal catalysts to prepare alkylated aniline derivatives.

  12. Corrosion abatement in sulfuric acid alkylation unit horizontal contactors

    SciTech Connect

    Schutt, H.U.

    1999-03-01

    A leak to the atmosphere in the hydraulic end cone of a horizontal contactor and the realization that basic corrosion data are not available for high-throughput process conditions in alkylation units prompted a laboratory study to develop the lacking expertise. Corrosion in the horizontal contractor of an alkylation unit was mitigated successfully by saturating fresh alkylation acid with ferrous sulfate (FeSO{sub 4}).

  13. A kinetic approach to the alkylating potential of carcinogenic lactones.

    PubMed

    Manso, José A; Pérez-Prior, M Teresa; García-Santos, M del Pilar; Calle, Emilio; Casado, Julio

    2005-07-01

    The alkylating potential of beta-propiolactone (BPL), beta-butyrolactone (BBL), gamma-butyrolactone, and delta-valerolactone, which can be formed by the in vivo nitrosation of primary amino acids, was investigated kinetically. The nucleophile NBP, 4-(p-nitrobenzyl)pyridine, a trap for alkylating agents, was used as an alkylation substrate. The alkylation reactions were performed under mimicked cellular conditions at neutral pH in water/dioxane solvent mixtures. To gain insight into the effect of the hydrolysis of lactones on their alkylating efficiency, alkylation and competing hydrolysis were studied in parallel. Conclusions were drawn as follows: (i) gamma-Butyrolactone and delta-valerolactone afford neither appreciable NBP alkylation nor hydrolysis reactions; (ii) the alkylating potential of BPL is 10-fold higher than that of BBL, the reactivity of both being essentially enthalpy-controlled; (iii) a correlation was found between the alkylating potential of lactones and their carcinogenicity; (iv) the hydrolysis of lactones is not sufficiently effective to prevent alkylation; (v) the efficiency of alkylation, expressed as the alkylation rate/hydrolysis rate ratio, decreases strongly with increasing amounts of dioxane in the reaction media; (vi) the absorption coefficients of the NBP-lactone adducts are as follows: epsilon(NBP-BPL) = 5101 +/- 111 M(-1) cm(-1) (lambda = 584 nm) and epsilon(NBP-BBL) = 462 +/- 19 M(-1) cm(-1) (lambda = 586 nm), the pronounced difference between these values being rationalized in terms of the adducts' structure; and (vii) linear correlations exist between the adducts' absorption coefficients and the water/dioxane ratio in the reaction media.

  14. Surface modification of silicon oxide with trialkoxysilanes toward close-packed monolayer formation.

    PubMed

    Tanaka, Mutsuo; Sawaguchi, Takahiro; Kuwahara, Masashi; Niwa, Osamu

    2013-05-28

    In order to scrutinize potential of trialkoxysilanes to form close-packed monolayer, surface modification of silicon oxide was carried out with the trialkoxysilanes bearing a ferrocene moiety for analysis by electrochemical methods. As it was found that hydrogen-terminated silicon reacts with trialkoxysilane through natural oxidation in organic solvents, where the silicon oxide layer is thin enough to afford conductivity for electrochemical analysis, hydrogen-terminated silicon wafer was immersed in trialkoxysilane solution for surface modification without oxidation treatment. Cyclic voltammetry measurements to determine surface concentrations of the immobilized ferrocene-silane on silicon surface were carried out with various temperature, concentration, solvent, and molecular structure, while the blocking effect in the cyclic voltammogram was investigated to obtain insight into density leading to the close-packed layer. The results suggested that a monolayer modification tended to occur under milder conditions when the ferrocene-silane had a longer alkyl chain, and formation of a close-packed layer to show significant blocking effect was observed. However, the surface modification proceeded even when surface concentration of the immobilized ferrocene-silane was greater than that expected for the monolayer. On the basis of these tendencies, the surface of silicon oxide modified with trialkoxysilane is considered to be a partial multilayer rather than monolayer although a close-packed layer is formed. This result is supported by the comparison with carbon surface modified with ferrocene-diazonium, in which a significant blocking effect was observed when surface concentrations of the immobilized ferrocene moiety are lower than that for silicon oxide modified with ferrocene-silane.

  15. C60 fullerene promotes lung monolayer collapse

    PubMed Central

    Barnoud, Jonathan; Urbini, Laura; Monticelli, Luca

    2015-01-01

    Airborne nanometre-sized pollutants are responsible for various respiratory diseases. Such pollutants can reach the gas-exchange surface in the alveoli, which is lined with a monolayer of lung surfactant. The relationship between physiological effects of pollutants and molecular-level interactions is largely unknown. Here, we determine the effects of carbon nanoparticles on the properties of a model of lung monolayer using molecular simulations. We simulate phase-separated lipid monolayers in the presence of a model pollutant nanoparticle, C60 fullerene. In the absence of nanoparticles, the monolayers collapse only at very low surface tensions (around 0 mN m−1). In the presence of nanoparticles, instead, monolayer collapse is observed at significantly higher surface tensions (up to ca 10 mN m−1). Collapse at higher tensions is related to lower mechanical rigidity of the monolayer. It is possible that similar mechanisms operate on lung surfactant in vivo, which suggests that health effects of airborne carbon nanoparticles may be mediated by alterations of the mechanical properties of lung surfactant. PMID:25589571

  16. Alkyl Chlorides as Hydrogen Bond Acceptors

    SciTech Connect

    Nadas, Janos I; Vukovic, Sinisa; Hay, Benjamin

    2012-01-01

    To gain an understanding of the role of an alkyl chloride as a hydrogen bond acceptor, geometries and interaction energies were calculated at the MP2/aug-cc-pVDZ level of theory for complexes between ethyl chloride and representative hydrogen donor groups. The results establish that these donors, which include hydrogen cyanide, methanol, nitrobenzene, pyrrole, acetamide, and N-methylurea, form X-H {hor_ellipsis} Cl hydrogen bonds (X = C, N, O) of weak to moderate strength, with {Delta}E values ranging from -2.8 to -5.3 kcal/mol.

  17. Characterisation of phase transition in adsorbed monolayers at the air/water interface.

    PubMed

    Vollhardt, D; Fainerman, V B

    2010-02-26

    Recent work has provided experimental and theoretical evidence that a first order fluid/condensed (LE/LC) phase transition can occur in adsorbed monolayers of amphiphiles and surfactants which are dissolved in aqueous solution. Similar to Langmuir monolayers, also in the case of adsorbed monolayers, the existence of a G/LE phase transition, as assumed by several authors, is a matter of question. Representative studies, at first performed with a tailored amphiphile and later with numerous other amphiphiles, also with n-dodecanol, provide insight into the main characteristics of the adsorbed monolayer during the adsorption kinetics. The general conditions necessary for the formation of a two-phase coexistence in adsorbed monolayers can be optimally studied using dynamic surface pressure measurements, Brewster angle microscopy (BAM) and synchrotron X-ray diffraction at grazing incidence (GIXD). A characteristic break point in the time dependence of the adsorption kinetics curves indicates the phase transition which is largely affected by the concentration of the amphiphile in the aqueous solution and on the temperature. Formation and growth of condensed phase domains after the phase transition point are visualised by BAM. As demonstrated by a tailored amphiphile, various types of morphological textures of the condensed phase can occur in different temperature regions. Lattice structure and tilt angle of the alkyl chains in the condensed phase of the adsorbed monolayer are determined using GIXD. The main growth directions of the condensed phase textures are correlated with the two-dimensional lattice structure. The results, obtained for the characteristics of the condensed phase after a first order main transition, are supported by experimental bridging to the Langmuir monolayers. Phase transition of adsorbing trace impurities in model surfactants can strongly affect the characteristics of the main component. Dodecanol present as minor component in aqueous sodium

  18. Determination of reaction rate constants for alkylation of 4-(p-nitrobenzyl) pyridine by different alkylating agents.

    PubMed

    Walles, S A

    1980-02-01

    The rate constants have been determined for the reaction between some different alkylating agents and 4-(p-nitrobenzyl) pyridine (NBP) in methanol. These constants have been compared with those for alkylation of aniline in water. All the constants were lower in methanol than in water but in different degrees. The rate constants of the different alkylating agents have been calculated at a nucleophilic strength n=2. The genetic risk defined as the degree of alkylation of a nucleophile (n=2) is equivalent to the rate constant kn=2 and the target dose. The dependence of the genetic risk on the rate constant (kn=2) is discussed.

  19. 40 CFR 721.10218 - 2-Propenoic acid, 2-mehtyl-, C12-15-branched and linear alkyl esters, telomers with alkyl 2...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...-branched and linear alkyl esters, telomers with alkyl 2- thio]-2-alkanoate, aminoalkyl methacrylate and alkyl methacrylate, tert-Bu 2-ethylhexanoperoxoate-initiated (generic). 721.10218 Section 721.10218...-alkanoate, aminoalkyl methacrylate and alkyl methacrylate, tert-Bu 2-ethylhexanoperoxoate-initiated...

  20. 40 CFR 721.10218 - 2-Propenoic acid, 2-mehtyl-, C12-15-branched and linear alkyl esters, telomers with alkyl 2...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...-branched and linear alkyl esters, telomers with alkyl 2- thio]-2-alkanoate, aminoalkyl methacrylate and alkyl methacrylate, tert-Bu 2-ethylhexanoperoxoate-initiated (generic). 721.10218 Section 721.10218...-alkanoate, aminoalkyl methacrylate and alkyl methacrylate, tert-Bu 2-ethylhexanoperoxoate-initiated...