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Sample records for complex formation constants

  1. Linear free energy relationship rate constants and basicities of N-substituted phenyl glycines in positronium-glycine complex formation

    NASA Astrophysics Data System (ADS)

    Chen, Rongti; Liang, Jiachang; Du, Youming; Cao, Chun; Yin, Dinzhen; Wang, Shuying; Zhang, Tianbao

    1987-06-01

    Complex formation between positronium and glycine derivatives in solution is discussed and the complex reaction rate constants obtained by means of a positron annihilation lifetime spectrometer with BaF 2 detectors. Rate constants mainly depend on the conjugation effect at the benzene ring and the induction effect of the substituents at the phenyl. There is a linear free energy relationship between rate constants and basicities of N-substituted phenyl glycines in orthopositronium-glycine complex formation.

  2. Studies on chalcone derivatives: Complex formation, thermal behavior, stability constant and antioxidant activity

    NASA Astrophysics Data System (ADS)

    El-Sayed, Yusif S.; Gaber, M.

    2015-02-01

    The chalcone 3-[4‧-dimethylaminophenyl]-1-(2-pyridyl) prop-2-en-1-one (DMAPP) and 3-(4‧-diethylaminophenyl)-1-(2-pyridinyl) prop-2-en-1-one abbreviated as DEAPP have been synthesized and characterized with IR, 1H NMR, 13C NMR spectroscopic techniques as described previously (El-Daly et al., 2008; Gaber et al., 2009; El-Sayed, 2013). By using UV visible spectroscopy method the mole fraction ratio for copper with DMAPP and DEAPP complexes were determined and it was found to be 1:1. The stability constants of this complex have been determined by Job's method. The stability constant (Kf) of copper with DMAPP and DEAPP complexes in universal buffer pH = 3.2 was determined to be 9.9 × 104 and 5.2 × 104 respectively. The effect of Cu(II) ion on the emission spectrum of the free chalcone is also assigned. Adherence to Beer's law and Ringbom optimum concentration ranges are determined. The thermal decomposition of the metal complexes is studied by TGA technique. The kinetic parameters like activation energy, pre-exponential factor and entropy of activation are estimated. The structure of complexes was energetically optimized through molecular mechanics applying MM+ force field coupled with molecular dynamics simulation. The bond lengths and bond angles have been calculated to confirm the geometry of the ligands and their Cu(II) complexes. The mode of interaction of the chalcone to copper nanoparticles was studied. The apparent association constants of the colloidal copper nanoparticles:chalcone complexes in solution were evaluated using the spectral method and compared with the formation constant of the Cu(II) chalcone complexes. Antioxidant activity of these chalcones was evaluated by using 1,1‧-diphenyl-2-picrylhydrazyl (DPPHrad) radicals scavenging method, which showed that the antioxidant activity of DMAPP has higher value than the DEAPP. Semi-empirical study results showed that DMAPP have higher dipole moment than DEAPP [1].

  3. Formation constants of copper(I) complexes with cysteine, penicillamine and glutathione: implications for copper speciation in the human eye.

    PubMed

    Königsberger, Lan-Chi; Königsberger, Erich; Hefter, Glenn; May, Peter M

    2015-12-21

    Protonation constants for the biologically-important thioamino acids cysteine (CSH), penicillamine (PSH) and glutathione (GSH), and the formation constants of their complexes with Cu(I), have been measured at 25 °C and an ionic strength of 1.00 mol dm(-3) (Na)Cl using glass electrode potentiometry. The first successful characterisation of binary Cu(I)-CSH and Cu(I)-GSH species over the whole pH range was achieved in this study by the addition of a second thioamino acid, which prevented the precipitation that normally occurs. Appropriate combinations of binary and ternary (mixed ligand) titration data were used to optimise the speciation models and formation constants for the binary species. The results obtained differ significantly from literature data with respect to the detection and quantification of protonated and polynuclear complexes. The present results are thought to be more reliable because of the exceptionally wide pH and concentration ranges employed, the excellent reproducibility of the data, the close agreement between the calculated and observed formation functions, and the low standard deviations and absence of numerical correlation in the constants. The present formation constants were incorporated into a large Cu speciation model which was used to predict, for the first time, metal-ligand equilibria in the biofluids of the human eye. This simulation provided an explanation for the precipitation of metallic copper in lens and cornea, which is known to occur as a consequence of Wilson's disease. PMID:26505238

  4. Determination of complex formation constants by phase sensitive alternating current polarography: Cadmium-polymethacrylic acid and cadmium-polygalacturonic acid.

    PubMed

    Garrigosa, Anna Maria; Gusmão, Rui; Ariño, Cristina; Díaz-Cruz, José Manuel; Esteban, Miquel

    2007-10-15

    The use of phase sensitive alternating current polarography (ACP) for the evaluation of complex formation constants of systems where electrodic adsorption is present has been proposed. The applicability of the technique implies the previous selection of the phase angle where contribution of capacitive current is minimized. This is made using Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) in the analysis of ACP measurements at different phase angles. The method is checked by the study of the complexation of Cd by polymethacrylic (PMA) and polygalacturonic (PGA) acids, and the optimal phase angles have been ca. -10 degrees for Cd-PMA and ca. -15 degrees for Cd-PGA systems. The goodness of phase sensitive ACP has been demonstrated comparing the determined complex formation constants with those obtained by reverse pulse polarography, a technique that minimizes the electrode adsorption effects on the measured currents. PMID:19073101

  5. Stability constants for the formation of rare earth-inorganic complexes as a function of ionic strength

    NASA Astrophysics Data System (ADS)

    Millero, Frank J.

    1992-08-01

    Recent studies have been made on the distribution of the rare earths (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in natural waters relative to their concentration in shales. These metals have also been used as models for the behavior of the trivalent actinides. The speciation of the rare earths in natural waters is modelled by using ionic interaction models which require reliable stability constants. In this paper the stability constants for the formation of lanthanide complexes ( k mx∗) with Cl -, NO 3-, SO 42-, OH -, HCO 3-, H 2PO 4-, HPO 42-, and CO 32- determined in NaClO 44 at various ionic strengths have been extrapolated to infinite dilution using the Pitzer interaction model. The activity coefficients for free ions ( γM, γx) needed for this extrapolation have been estimated from the Pitzer equations. The thermodynamic stability constants ( KMX) and activity coefficients of the various ion pairs ( γMX) were determined from In ( solK MX∗/γ Mγ x) = In K mx+ In (γ MX). The activity coefficients of the ion pairs have been used to determine Pitzer parameters ( BMX) for the rare earth complexes. The values of BMX were found to be the same for complexes of the same charge. These results make it possible to estimate the stability constants for the formation of rare earth complexes over a wide range of ionic strengths. The stability constants have been used to determine the speciation of the lanthanides in seawater and in brines. The carbonate complexes dominate for all natural waters where the carbonate alkalinity is greater than 0.001 eq/L at a pH near 8.

  6. Dynamic titration: determination of dissociation constants for noncovalent complexes in multiplexed format using HPLC-ESI-MS.

    PubMed

    Frycák, Petr; Schug, Kevin A

    2008-03-01

    With recent growth in fields such as life sciences and supramolecular chemistry, there has been an ever increasing need for high-throughput methods that would permit determination of binding affinities for noncovalent complexes of various host-guest systems. These are traditionally measured by titration experiments where concentration-dependent signals of species participating in solution-based binding equilibria are monitored by methods such as UV-vis spectrophotometry, calorimetry, or nuclear magnetic resonance spectrometry. Here we present a new titration technique that unifies and allows chromatographic separation of guests with determination of dissociation constants by electrospray mass spectrometry in a multiplexed format. A theoretical model has been derived that describes the complex formation for the guests eluted from a chromatographic column when hosts are admixed postcolumn. The model takes possible competition equilibria into account; i.e., it can deal with unresolved peaks of guests with the possible addition of multiple hosts in one experiment. This on-line workflow makes determination of binding affinities for large libraries of compounds possible. The potential of the method is demonstrated on the determination of dissociation constants for complexes of beta- and gamma-cyclodextrins with nonsteroidal antiinflammatory drugs ibuprofen, naproxen, and flurbiprofen. PMID:18237190

  7. Lattice constant variation and complex formation in zincblende gallium manganese arsenide

    NASA Astrophysics Data System (ADS)

    Schott, G. M.; Faschinger, W.; Molenkamp, L. W.

    2001-09-01

    We perform high resolution x-ray diffraction on GaMnAs mixed crystals as well as on GaMnAs/GaAs and GaAs/MnAs superlattices for samples grown by low-temperature molecular-beam epitaxy under different growth conditions. Although all samples are of high crystalline quality and show narrow rocking curve widths and pronounced finite thickness fringes, the lattice constant variation with increasing manganese concentration depends strongly on the growth conditions: For samples grown at substrate temperatures of 220 and 270 °C, the extrapolated relaxed lattice constant of Zincblende MnAs is 0.590 nm and 0.598 nm, respectively. This is in contrast to low-temperature GaAs, for which the lattice constant decreases with increasing substrate temperature.

  8. Determination of formation constants and structural characterization of cyclodextrin inclusion complexes with two phenolic isomers: carvacrol and thymol

    PubMed Central

    Kfoury, Miriana; Landy, David; Ruellan, Steven; Auezova, Lizette; Greige-Gerges, Hélène

    2016-01-01

    Summary Carvacrol and thymol have been widely studied for their ability to control food spoilage and to extend shelf-life of food products due to their antimicrobial and antioxidant activities. However, they suffer from poor aqueous solubility and pronounced flavoring ability that limit their application in food systems. These drawbacks could be surpassed by encapsulation in cyclodextrins (CDs). Applications of their inclusion complexes with CDs were reported without investigating the inclusion phenomenon in deep. In this study, inclusion complexes were characterized in terms of formation constants (K f), complexation efficiency (CE), CD:guest molar ratio and increase in bulk formulation by using an UV–visible competitive method, phase solubility studies as well as 1H and DOSY 1H NMR titration experiments. For the first time, a new algorithmic treatment that combines the chemical shifts and diffusion coefficients variations for all guest protons was applied to calculate K f. The position of the hydroxy group in carvacrol and thymol did not affect the stoichiometry of the inclusion complexes but led to a different binding stability with CDs. 2D ROESY NMR experiments were also performed to prove the encapsulation and illustrate the stable 3D conformation of the inclusion complexes. The structural investigation was accomplished with molecular modeling studies. Finally, the radical scavenging activity of carvacrol and thymol was evaluated by the ABTS radical scavenging assay. An improvement of this activity was observed upon encapsulation. Taken together, these results evidence that the encapsulation in CDs could be valuable for applications of carvacrol and thymol in food. PMID:26877806

  9. Determination of formation constants and structural characterization of cyclodextrin inclusion complexes with two phenolic isomers: carvacrol and thymol.

    PubMed

    Kfoury, Miriana; Landy, David; Ruellan, Steven; Auezova, Lizette; Greige-Gerges, Hélène; Fourmentin, Sophie

    2016-01-01

    Carvacrol and thymol have been widely studied for their ability to control food spoilage and to extend shelf-life of food products due to their antimicrobial and antioxidant activities. However, they suffer from poor aqueous solubility and pronounced flavoring ability that limit their application in food systems. These drawbacks could be surpassed by encapsulation in cyclodextrins (CDs). Applications of their inclusion complexes with CDs were reported without investigating the inclusion phenomenon in deep. In this study, inclusion complexes were characterized in terms of formation constants (K f), complexation efficiency (CE), CD:guest molar ratio and increase in bulk formulation by using an UV-visible competitive method, phase solubility studies as well as (1)H and DOSY (1)H NMR titration experiments. For the first time, a new algorithmic treatment that combines the chemical shifts and diffusion coefficients variations for all guest protons was applied to calculate K f. The position of the hydroxy group in carvacrol and thymol did not affect the stoichiometry of the inclusion complexes but led to a different binding stability with CDs. 2D ROESY NMR experiments were also performed to prove the encapsulation and illustrate the stable 3D conformation of the inclusion complexes. The structural investigation was accomplished with molecular modeling studies. Finally, the radical scavenging activity of carvacrol and thymol was evaluated by the ABTS radical scavenging assay. An improvement of this activity was observed upon encapsulation. Taken together, these results evidence that the encapsulation in CDs could be valuable for applications of carvacrol and thymol in food. PMID:26877806

  10. Complex dielectric constant well logging means and method for determining the water saturation and the water resistivity of an earth formation

    SciTech Connect

    Sims, J.C.; Cox, P.T.; Simpson, R.S.

    1988-09-27

    This patent describes a well logging system for determining the water saturation of an earth formation and the resistivity of the water comprising: means for transmitting electromagnetic energy at a frequency lying within a range of frequencies from 10 MHz to 200 MHz into the earth formation from a borehole traversing the earth formation, means for receiving electromagnetic energies at two locations in the borehole from the earth formation, means for deriving a complex dielectric constant from the received electromagnetic energies, and means for deriving the water resistivity and the water saturation of the earth formation in accordance with a predetermined porosity of the earth formation and with the real and imaginary parts of the derived complex dielectric constant.

  11. Stability constants for the formation of lead chloride complexes as a function of temperature and ionic strength

    NASA Astrophysics Data System (ADS)

    Luo, Yanxin; Millero, Frank J.

    2007-01-01

    The stability constants for the formation of lead (Pb 2+) with chloride Pb+nCl↔PbCln2-nβn(n=1,2,3) have been determined using a spectrophotometric method in NaClO 4 solutions as a function of ionic strength (0-6 m) and temperature (15-45 °C). The results have been fitted to the equations:

  12. Stability constants for the formation of lead chloride complexes as a function of temperature and ionic strength

    PubMed Central

    Luo, Yanxin; Millero, Frank J.

    2015-01-01

    The stability constants for the formation of lead (Pb2+) with chloride Pb2+=nCl−↔PbCln2−nβn(n=1,2,3) have been determined using a spectrophotometric method in NaClO4 solutions as a function of ionic strength (0–6 m) and temperature (15–45 °C). The results have been fitted to the equations: logβ1∗=logβ1+0.21I−8.61I0.5∕(1+1.2I0.5)+1927.40[I0.5∕(1+1.2I0.5)]∕Tlogβ2∗=logβ2+0.32I−4.67I0.5(1+1.2I0.5)+594.54[I0.5∕(1+1.2I0.5)]∕Tlogβ3∗=logβ3+0.40I−2.68I0.5(1+1.2I0.5)−43.98[I0.5∕(1+1.2I0.5)]∕T with standard errors of 0.05, 0.04 and 0.06, respectively. The thermodynamic values of log β1, logβ2 and logβ3 at 25.0 °C and the enthalpies of formation of PbCl+, PbCl20 and PbCl3− are in good agreement with literature values. We have combined our results with the earlier work of Seward (1984) to yield thermodynamic constants that are valid from 15 to 300 °C: logβ1=44.82+0.031T−21.21logTlogβ2=61.42+0.046T−29.51logTlogβ3=107.97+0.071T−51.46logT with standard errors of 0.05, 0.08 and 0.10, respectively. PMID:26937043

  13. Formation constants of ternary complexes of some heavy metal ions with N-(2-acetamido)iminodiacetic acid and aliphatic or aromatic acids

    SciTech Connect

    Hamed, M.M.A.; Mahmoud, M.R. . Dept. of Chemistry); Saleh, M.B.; Ahmed, I.T. . Dept. of Chemistry)

    1994-07-01

    N-(2-Acetamido)iminodiacetic acid (H[sub 2]ADA) is considered as one of the biologically important ligands. It is used as a complexing agent in the field of metal ion buffers working at the physiological pH range. Furthermore, it is widely used as an analytical chelating agent for the spectrophotometric determination of metal ions. Solution equilibria of the ternary systems involving La(III), Y(III), Ce(III), and UO[sub 2][sup 2+], N-(2-acetamido)iminodiacetic acid, and some aliphatic or aromatic acids have been investigated potentiometrically. The formation of 1:1:1 mixed ligand complexes is inferred from the potentiometric titration curves. Formation constants of the different binary and ternary complexes formed in such systems were determined at 25 [+-] 0.1 C and [mu] = 0.1 mol dm[sup [minus]3] (KNO[sub 3]). It is deduced that the mixed ligand complexes are more stable than the corresponding binary complexes containing the aliphatic or aromatic acidate moiety. The order of stability of the binary and ternary complexes is investigated and discussed in terms of the nature of both the metal ion and the secondary ligand (aliphatic or aromatic acid).

  14. Constant Communities in Complex Networks

    NASA Astrophysics Data System (ADS)

    Chakraborty, Tanmoy; Srinivasan, Sriram; Ganguly, Niloy; Bhowmick, Sanjukta; Mukherjee, Animesh

    2013-05-01

    Identifying community structure is a fundamental problem in network analysis. Most community detection algorithms are based on optimizing a combinatorial parameter, for example modularity. This optimization is generally NP-hard, thus merely changing the vertex order can alter their assignments to the community. However, there has been less study on how vertex ordering influences the results of the community detection algorithms. Here we identify and study the properties of invariant groups of vertices (constant communities) whose assignment to communities are, quite remarkably, not affected by vertex ordering. The percentage of constant communities can vary across different applications and based on empirical results we propose metrics to evaluate these communities. Using constant communities as a pre-processing step, one can significantly reduce the variation of the results. Finally, we present a case study on phoneme network and illustrate that constant communities, quite strikingly, form the core functional units of the larger communities.

  15. How the cosmological constant affects gravastar formation

    SciTech Connect

    Chan, R.; Silva, M.F.A. da; Rocha, P. E-mail: mfasnic@gmail.com

    2009-12-01

    Here we generalized a previous model of gravastar consisted of an internal de Sitter spacetime, a dynamical infinitely thin shell with an equation of state, but now we consider an external de Sitter-Schwarzschild spacetime. We have shown explicitly that the final output can be a black hole, a ''bounded excursion'' stable gravastar, a stable gravastar, or a de Sitter spacetime, depending on the total mass of the system, the cosmological constants, the equation of state of the thin shell and the initial position of the dynamical shell. We have found that the exterior cosmological constant imposes a limit to the gravastar formation, i.e., the exterior cosmological constant must be smaller than the interior cosmological constant. Besides, we have also shown that, in the particular case where the Schwarzschild mass vanishes, no stable gravastar can be formed, but we still have formation of black hole.

  16. Determination of formation constants of hydroxo and carbonate complexes of Pr(3+) in 2 M NaCl at 303 K.

    PubMed

    López-González, H; Jiménez-Reyes, M; Rojas-Hernández, A; Solache-Ríos, M

    1997-10-01

    The hydrolysis of praseodymium III in 2 M sodium chloride at 303 K was studied. Two methods were used: pH titration followed by a computational refinement and solvent extraction in the presence of a competitive ligand. The hydrolysis constants obtained by pH titration were: logbeta(1,H)=-7.68+/-0.07, logbeta(1,2H)=-15.10+/-0.03, and beta(1,3H)=-23.80+/-0.04. The stability constants of praseodymium carbonate complexes were determined by pH titration as well and were: logbeta(1,CO(2-)(3))=5.94+/-0.08 and logbeta(1,2CO(2-)(3))=11.15+/-0.15. Praseodymium carbonate species were taken into consideration for calculating the first hydrolysis constants by the solvent extraction method and the value obtained was: logbeta(1,H)=-7.69+/-0.27. The values for logbeta(1,H) attained by both methods are the same. The species-distribution diagram was obtained from the stability constants of praseodymium carbonate complexes and hydrolysis products in the conditions of the present work. PMID:18966931

  17. Bacterial formate hydrogenlyase complex

    PubMed Central

    McDowall, Jennifer S.; Murphy, Bonnie J.; Haumann, Michael; Palmer, Tracy; Armstrong, Fraser A.; Sargent, Frank

    2014-01-01

    Under anaerobic conditions, Escherichia coli can carry out a mixed-acid fermentation that ultimately produces molecular hydrogen. The enzyme directly responsible for hydrogen production is the membrane-bound formate hydrogenlyase (FHL) complex, which links formate oxidation to proton reduction and has evolutionary links to Complex I, the NADH:quinone oxidoreductase. Although the genetics, maturation, and some biochemistry of FHL are understood, the protein complex has never been isolated in an intact form to allow biochemical analysis. In this work, genetic tools are reported that allow the facile isolation of FHL in a single chromatographic step. The core complex is shown to comprise HycE (a [NiFe] hydrogenase component termed Hyd-3), FdhF (the molybdenum-dependent formate dehydrogenase-H), and three iron-sulfur proteins: HycB, HycF, and HycG. A proportion of this core complex remains associated with HycC and HycD, which are polytopic integral membrane proteins believed to anchor the core complex to the cytoplasmic side of the membrane. As isolated, the FHL complex retains formate hydrogenlyase activity in vitro. Protein film electrochemistry experiments on Hyd-3 demonstrate that it has a unique ability among [NiFe] hydrogenases to catalyze production of H2 even at high partial pressures of H2. Understanding and harnessing the activity of the FHL complex is critical to advancing future biohydrogen research efforts. PMID:25157147

  18. Thiocyanato Chromium (III) Complexes: Separation by Paper Electrophoresis and Estimate of Stability Constants

    ERIC Educational Resources Information Center

    Larsen, Erik; Eriksen, J.

    1975-01-01

    Describes an experiment wherein the student can demonstrate the existence of all the thiocyanato chromium complexes, estimate the stepwise formation constants, demonstrate the robustness of chromium III complexes, and show the principles of paper electrophoresis. (GS)

  19. A 1H NMR titration study on the binding constants for D- and L-tryptophan inclusion complexes with 6-O-α-D-glucosyl-β-cyclodextrin. Formation of 1:1 and 2:1 (host:guest) complexes

    NASA Astrophysics Data System (ADS)

    Akita, Tomoki; Matsui, Yoshihisa; Yamamoto, Tatsuyuki

    2014-02-01

    A 1H NMR titration study revealed that 6-O-α-D-glucosyl-β-cyclodextrin (G1-β-CD) forms 1:1 and 2:1 (host:guest) inclusion complexes with D- and L-tryptophan in alkaline D2O solutions (pD 11.0). The binding constants (K1's) for the 1:1 complexes of D-isomer at 298 K (59 mol-1 dm3) were virtually equal to that of L-isomer (54 mol-1 dm3). On the other hand, the K2 values for 2:1 complexes of D-isomer (42 mol-1 dm3) were larger than that of L-counterpart (12 mol-1 dm3). These facts suggest that the first CD molecule includes the indole ring moiety of tryptophan, followed by inclusion with the second CD molecule in the vicinity of chiral center, α-carbon of the guest, to result in the difference in K2's for two enantiomers. Two-dimensional NMR measurement (Rotating-frame nuclear Overhauser Effect SpectroscopY, ROESY) supported this interpretation.

  20. Density functional theory-based prediction of the formation constants of complexes of ammonia in aqueous solution: indications of the role of relativistic effects in the solution chemistry of gold(I).

    PubMed

    Hancock, Robert D; Bartolotti, Libero J

    2005-10-01

    A prediction of the formation constants (log K1) for complexes of metal ions with a single NH3 ligand in aqueous solution, using quantum mechanical calculations, is reported. DeltaG values at 298 K in the gas phase for eq 1 (DeltaG(DFT)) were calculated for 34 metal ions using density functional theory (DFT), with the expectation that these would correlate with the free energy of complex formation in aqueous solution (DeltaG(aq)). [M(H2O)6]n+(g) + NH(3)(g) = [M(H2O)5NH3]n+(g) + H2O(g) (eq 1). The DeltaG(aq) values include the effects of complex changes in solvation on complex formation, which are not included in eq 1. It was anticipated that such changes in solvation would be constant or vary systematically with changes in the log K(1) value for different metal ions; therefore, simple correlations between DeltaG(DFT) and DeltaG(aq) were sought. The bulk of the log K1(NH3) values used to calculate DeltaG(aq) were not experimental, but estimated previously (Hancock 1978, 1980) from a variety of empirical correlations. Separate linear correlations between DeltaG(DFT) and DeltaG(aq) for metal ions of different charges (M2+, M3+, and M4+) were found. In plots of DeltaG(DFT) versus DeltaG(aq), the slopes ranged from 2.201 for M2+ ions down to 1.076 for M4+ ions, with intercepts increasing from M2+ to M4+ ions. Two separate correlations occurred for the M3+ ions, which appeared to correspond to small metal ions with a coordination number (CN) of 6 and to large metal ions with a higher CN in the vicinity of 7-9. The good correlation coefficients (R) in the range of 0.97-0.99 for all these separate correlations suggest that the approach used here may be the basis for future predictions of aqueous phase chemistry that would otherwise be experimentally inaccessible. Thus, the log K1(NH3) value for the transuranic Lr3+, which has a half-life of 3.6 h in its most stable isotope, is predicted to be 1.46. These calculations should also lead to a greater insight into the factors

  1. Predicting Stability Constants for Uranyl Complexes Using Density Functional Theory

    SciTech Connect

    Vukovic, Sinisa; Hay, Benjamin P.; Bryantsev, Vyacheslav S.

    2015-04-02

    The ability to predict the equilibrium constants for the formation of 1:1 uranyl:ligand complexes (log K1 values) provides the essential foundation for the rational design of ligands with enhanced uranyl affinity and selectivity. We also use density functional theory (B3LYP) and the IEFPCM continuum solvation model to compute aqueous stability constants for UO22+ complexes with 18 donor ligands. Theoretical calculations permit reasonably good estimates of relative binding strengths, while the absolute log K1 values are significantly overestimated. Accurate predictions of the absolute log K1 values (root mean square deviation from experiment < 1.0 for log K1 values ranging from 0 to 16.8) can be obtained by fitting the experimental data for two groups of mono and divalent negative oxygen donor ligands. The utility of correlations is demonstrated for amidoxime and imide dioxime ligands, providing a useful means of screening for new ligands with strong chelate capability to uranyl.

  2. Predicting Stability Constants for Uranyl Complexes Using Density Functional Theory

    DOE PAGESBeta

    Vukovic, Sinisa; Hay, Benjamin P.; Bryantsev, Vyacheslav S.

    2015-04-02

    The ability to predict the equilibrium constants for the formation of 1:1 uranyl:ligand complexes (log K1 values) provides the essential foundation for the rational design of ligands with enhanced uranyl affinity and selectivity. We also use density functional theory (B3LYP) and the IEFPCM continuum solvation model to compute aqueous stability constants for UO22+ complexes with 18 donor ligands. Theoretical calculations permit reasonably good estimates of relative binding strengths, while the absolute log K1 values are significantly overestimated. Accurate predictions of the absolute log K1 values (root mean square deviation from experiment < 1.0 for log K1 values ranging from 0more » to 16.8) can be obtained by fitting the experimental data for two groups of mono and divalent negative oxygen donor ligands. The utility of correlations is demonstrated for amidoxime and imide dioxime ligands, providing a useful means of screening for new ligands with strong chelate capability to uranyl.« less

  3. Predicting stability constants for uranyl complexes using density functional theory.

    PubMed

    Vukovic, Sinisa; Hay, Benjamin P; Bryantsev, Vyacheslav S

    2015-04-20

    The ability to predict the equilibrium constants for the formation of 1:1 uranyl/ligand complexes (log K1 values) provides the essential foundation for the rational design of ligands with enhanced uranyl affinity and selectivity. We use density functional theory (B3LYP) and the integral equation formalism polarizable continuum model (IEF-PCM) to compute aqueous stability constants for UO2(2+) complexes with 18 donor ligands. Theoretical calculations permit reasonably good estimates of relative binding strengths, while the absolute log K1 values are significantly overestimated. Accurate predictions of the absolute log K1 values (root-mean-square deviation from experiment <1.0 for log K1 values ranging from 0 to 16.8) can be obtained by fitting the experimental data for two groups of mono- and divalent negative oxygen donor ligands. The utility of correlations is demonstrated for amidoxime and imide dioxime ligands, providing a useful means of screening for new ligands with strong chelating capability to uranyl. PMID:25835578

  4. Dissociation rate constant of the biotin-streptavidin complex.

    PubMed

    Piran, U; Riordan, W J

    1990-10-01

    We measured the dissociation rate constants of the biotin/streptavidin and biotin/egg avidin complexes by following the release of radiolabeled biotin from the preformed complexes in the presence of excess unlabeled biotin. For separation of bound and free labeled biotin we employed ultrafiltration with disposable microconcentrators. The dissociation rate constant for underivatized streptavidin was 2.4 x 10(-6) s-1, or approximately 30-fold higher than that observed for egg avidin 7.5 x 10(-8) s-1). The value for streptavidin was further increased after derivatization with an acridinium ester label. Both biotin binding proteins exhibited a faster initial phase, suggesting binding site heterogeneity due to partial subunit dissociation or denaturation. The convenience of the method and the relatively fast dissociation of biotin from streptavidin render the dissociation rate constant a practical experimental criterion for monitoring the integrity of the binding site during purification and derivatization procedures. PMID:2212686

  5. Variation of stability constants of thorium citrate complexes and of thorium hydrolysis constants with ionic strength

    SciTech Connect

    Choppin, G.R.; Erten, H.N.; Xia, Y.X.

    1995-09-01

    Citrate is among the organic anions that are expected to be present in the wastes planned for deposition in the Waste Isolation Pilot Plant repository. In this study, a solvent extraction method has been used to measure the stability constants of Thorium(IV)[Th(IV)] with citrate anions in aqueous solutions with (a) NaClO{sub 4} and (b) NaCl as the background electrolytes. The ionic strengths were varied up to 5 m (NaCl) and 14 m (NaClO{sub 4}). The data from the NaClO{sub 4} solutions at varying pH values were used to calculate the hydrolysis constants for formation of Th(OH){sup 3+} at the different ionic strengths.

  6. The formation constants of ionomycin with divalent cations in 80% methanol/water.

    PubMed

    Stiles, M K; Craig, M E; Gunnell, S L; Pfeiffer, D R; Taylor, R W

    1991-05-01

    The protonation constants and complex formation constants of ionomycin have been determined in 80% methanol/water (w/w) at 25.0 degrees C and mu = 0.050 (tetraethylammonium perchlorate). Potentiometric and spectrometric titration techniques give the following values for the mixed-mode protonation constants of ionomycin: log KH1 = 11.94 +/- 0.02 and log KH2 = 6.80 +/- 0.03. Comparison of these values with those for model compounds indicates that KH1 and KH2 refer to equilibria involving the beta-diketone and carboxylic acid moieties, respectively. Titrations of ionomycin with metal ion at fixed values of pH produced changes in the UV-visual absorbance spectra which were analyzed to give conditional complex formation constants, KMI'. The pH dependence of the values of KMI' indicated that 1:1 divalent metal ion-ionomycin (MI) complexes and protonated MHI+ complexes were formed in the pH range studied. The values of log KMI ranged from 5.30 +/- 0.11 for Sr2+ to 10.25 +/- 0.03 for Ni2+. The selectivity pattern and relative affinities (in parentheses) for the formation of the species MI are as follows: Ni2+ (2000) greater than Zn2+ (600) greater than CO2+ (440) greater than Mn2+ (47) greater than Mg2+ (1.00) greater than Ca2+ (0.21) greater than Sr2+ (0.022). Logarithmic values of KMHI, for the reaction MI + H+ in equilibrium MHI+, ranged from 5.9 (Ni2+) to 8.4 (Sr2+). Calculations using the values of the equilibrium constants determined indicate that an appreciable fraction of the complexed ionophore exists as the protonated complex, MHI+, in the pH range of 6.5-8.5. PMID:1850743

  7. Stability constants of europium complexes with a nitrogen heterocycle substituted methane-1,1-diphosphonic acid

    SciTech Connect

    Jensen, M.P.; Rickert, P.G.; Schmidt, M.A.; Nash, K.L.

    1996-06-01

    Even in moderately acidic solutions ([H{sup +}] > 0.01 M), N-piperidinomethane-1,1-diphosphonic acid (H{sub 4}PMDPA) is a strong complexant of trivalent lanthanide ions that shows enhanced complex solubility over previously studied 1,1-diphosphonic acids. The protonation constants of PMDPA in 2.0 M H/NaClO{sub 4} were determined by potentiometric and NMR titrations, and the stability constants for formation of complexes with Eu{sup 3+} were determined by solvent extraction. Difference in protonation equilibria induced by addition of the nitrogen heterocycle results in an increase in the complexation strength of PMDPA. In solutions containing 0.1 M H{sup +} and ligand concentrations greater than 0.02 M, PMDPA is the most effective 1,1-diphosphonic acid for europium complexation studied thus far.

  8. Spectrophotometric Determination of Iron(III)-Glycine Formation Constant in Aqueous Medium Using Competitive Ligand Binding

    ERIC Educational Resources Information Center

    Prasad, Rajendra; Prasad, Surendra

    2009-01-01

    The formation constant of iron(III) complex with glycine (Gly) ligand in aqueous acidic medium (0.2 M HNO[subscript 3], I = 0.2 M at 28 plus or minus 1 degree C) was determined spectrophotometrically in which a competing color reaction between Fe(III) and SCN[superscript -] was used as an indicator reaction. Under the specified conditions Fe(III)…

  9. Simulation of biomolecular diffusion and complex formation.

    PubMed Central

    Allison, S A; Northrup, S H; McCammon, J A

    1986-01-01

    Diffusion is a phenomenon of very widespread importance in molecular biophysics. Diffusion can determine the rates and character of the assembly of multisubunit structures, the binding of ligands to receptors, and the internal motions of molecules and assemblies that involve solvent surface displacements. Current computer simulation techniques provide much more detailed descriptions of diffusional processes than have been available in the past. Models can be constructed to include such realistic features as structural subunits at the submolecular level (domains, monomers, or atoms); detailed electrostatic charge distributions and corresponding solvent-screened inter- and intramolecular interactions; and hydrodynamic interactions. The trajectories can be analyzed either to provide direct information on biomolecular function (e.g., the bimolecular rate constant for formation of an electron-transfer complex between two proteins), or to provide or test models for the interpretation of experimental data (e.g., the time dependence of fluorescence depolarization for segments of DNA). Here, we first review the theory of diffusional simulations, with special emphasis on new techniques such as those for obtaining transport properties of flexible assemblies and rate constants of diffusion-controlled reactions. Then we survey a variety of recent applications, including studies of large-scale motion in DNA segments and substrate "steering" in enzyme-substrate binding. We conclude with a discussion of current work (e.g., formation of protein complexes) and possible areas for future work. PMID:3955168

  10. Constant-complexity stochastic simulation algorithm with optimal binning

    SciTech Connect

    Sanft, Kevin R.; Othmer, Hans G.

    2015-08-21

    At the molecular level, biochemical processes are governed by random interactions between reactant molecules, and the dynamics of such systems are inherently stochastic. When the copy numbers of reactants are large, a deterministic description is adequate, but when they are small, such systems are often modeled as continuous-time Markov jump processes that can be described by the chemical master equation. Gillespie’s Stochastic Simulation Algorithm (SSA) generates exact trajectories of these systems, but the amount of computational work required for each step of the original SSA is proportional to the number of reaction channels, leading to computational complexity that scales linearly with the problem size. The original SSA is therefore inefficient for large problems, which has prompted the development of several alternative formulations with improved scaling properties. We describe an exact SSA that uses a table data structure with event time binning to achieve constant computational complexity with respect to the number of reaction channels for weakly coupled reaction networks. We present a novel adaptive binning strategy and discuss optimal algorithm parameters. We compare the computational efficiency of the algorithm to existing methods and demonstrate excellent scaling for large problems. This method is well suited for generating exact trajectories of large weakly coupled models, including those that can be described by the reaction-diffusion master equation that arises from spatially discretized reaction-diffusion processes.

  11. Stoichiometry and Formation Constant Determination by Linear Sweep Voltammetry.

    ERIC Educational Resources Information Center

    Schultz, Franklin A.

    1979-01-01

    In this paper an experiment is described in which the equilibrium constants necessary for determining the composition and distribution of lead (II)-oxalate species may be measured by linear sweep voltammetry. (Author/BB)

  12. Theoretical studies on the first proton macroaffinity of Ni(II), Cu(II), Zn(II) and Cd(II) complexes of four triazacycloalkanes ([X]ane N3, X = 9-12): good correlations with the formation constants in solution.

    PubMed

    Salehzadeh, Sadegh; Shooshtari, Amir; Bayat, Mehdi

    2009-04-21

    A theoretical study on the first protonation step of Ni(ii), Cu(ii), Zn(ii) and Cd(ii) complexes of some triazacycloalkanes with general formula [X]ane N(3) (X = 9-12) is reported. The calculations were performed at DFT (B3LYP) level of theory, using LanL2DZ basis set. The DFT calculations were performed again using DZVP2 basis set for Ni(ii), Cu(ii) and Zn(ii) complexes and DZVP for Cd(ii) complexes. Once again, two kinds of our recently published definitions for gas-phase proton affinities of polybasic ligands, proton microaffinity and proton macroaffinity, were extended to their metal complexes. Among the 16 investigated complexes the most stable complex has both the smallest proton macroaffinity and macrobasicity. The least stable complex has also both the greatest proton macroaffinity and macrobasicity. In the case of each metal ion there are good correlations between the calculated gas-phase proton macroaffinities as well as macrobasicities of the corresponding complexes with their formation constants in solution. PMID:19333512

  13. Laboratory measurement of the complex dielectric constant of soils

    NASA Technical Reports Server (NTRS)

    Wiebe, M. L.

    1971-01-01

    The dielectric constant of a material is an extremely important parameter when considering passive radiometric remote sensing applications. This is because the emitted energy measured by a microwave radiometer is dependent on the dielectric constant of the surface being scanned. Two techniques of measuring dielectric constants are described. The first method involves a dielectric located in air. The second method uses basically the same theoretical approach, but the dielectric under consideration is located inside a section of waveguide.

  14. Complexation Constants of Ubiquinone,0 and Ubiquinone,10 with Nucleosides and Nucleic Acid Bases

    NASA Astrophysics Data System (ADS)

    Rahawi, Kassim Y.; Shanshal, Muthana

    2008-02-01

    UV spectrophotometric measurements were done on mixtures of the ubiquinones Ub,0 and Ub,10 in their monomeric form (c < 10-5 mol/l) with the nucleosides; adenosine, cytidine, 2'-desoxyadenosine, 2'-desoxy-quanosine, guanosine and thymidine, as well as the nucleic acid bases; adenine, cytosine, hypoxanthine, thymine and uracil. Applying the Liptay method, it was found that both ubiquinones form 1 : 1 interaction complexes with the nucleic acid components. The complexation constants were found in the order of 105 mol-1. The calculated ΔG values were negative (˜-7.0 kcal/mol), suggesting a favoured hydrogen bridge formation. This is confirmed by the positive change of the entropy ΔS. The complexation enthalpies ΔH for all complexes are negative, suggesting exothermal interactions.

  15. Stability constants of Ni(II)- and Cu(II)-N-heterocycle complexes according to spectrophotometric data

    NASA Astrophysics Data System (ADS)

    Badhe, Samata; Tekade, Pradip; Bajaj, Sonal; Thakare, Shrikant

    2015-12-01

    The interaction of Ni(II) and Cu(II) with ethyl 4-(4-hydroxyphenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine- 5-carboxylate [Ligand 1], 4-(1H-benzimidazol-2-yl)phenol [Ligand 2], and 2-(3-phenylamino- 4,5-dihydro-1,2-oxazol-5-yl)phenol [Ligand 3] have been studied by spectrophotometric technique at 0.01 M ionic strength and 28°C in 70% dioxane—water mixture. The data obtained were used to estimate the stability constant of these ligands. Spectrophotometric investigation of Ni(II) and Cu(II) complexes with these ligands shows 1: 1 complex formation. The formation of complexes has been studied by Job's variation method. The values of conditional stability constants of Cu(II) complexes are greater than the corresponding Ni(II) complexes. The greater value of stability constant of Cu(II) complexes may be due to the fact of more stable nature of Cu(II). The value of stability constant of Cu(II)—Ligand 2 complex is greater than that of Cu(II)-Ligand 1 and Cu(II)-Ligand 3. The same of Ni(II)-Ligand 3 complex is greater than that of Ni(II)-Ligand 1 and Ni(II)-Ligand 2.

  16. The potentiometric determination of stability constants for zinc acetate complexes in aqueous solutions to 295C

    SciTech Connect

    Giordano, T.H. ); Drummond, S.E. )

    1991-09-01

    A potentiometric method was used to determine the formation quotients of zinc acetate complexes in aqueous solutions from 50 to 295C at ionic strengths of 0.03, 0.3, and 1.0 m. The potentiometric titrations were carried out in an externally heated, Teflon-lined concentration cell fitted with hydrogen electrodes. Formal sodium acetate concentrations of the experimental solutions ranged from 0.001 to 0.1 m with acetic acid to sodium acetate ratios ranging from 30 to 300. Sodium trifluoromethanesulfonate (F{sub 3}CSO{sub 3}Na) was used as a supporting electrolyte. Stoichiometries and formation quotients for the complexes ZnCH{sub 3}COO{sup +}, Zn(CH{sub 3}COO){sub 2}, and Zn(CH{sub 3}COO){sub 3}{sup {minus}} were derived from the titration data by regression analysis. Stability constants at infinite dilution (K{sub n}) and other relevant thermodynamic quantities were calculated for these three complexes. Calculations of zinc speciation in acetate-chloride solutions show that zinc acetate complexes should have an importance similar to zinc chloride complexes in high acetate waters where chloride to acetate molal ratios are less than about 10.

  17. Laser complex for investigation of semiconductor nonlinear constants

    NASA Astrophysics Data System (ADS)

    Grabovski, Vitaly V.; Fekeshgazi, Ishtvan V.; May, Konstantin V.; Prokhorenko, Valentin I.; Yatskiv, Dmytro Y.

    1995-11-01

    The laser complex for the investigations of nonlinear properties of semiconductors has been designed. The results of the two-photon absorption coefficient of the chalcohenide glass As2S3 measurements are presented. The measurements accuracy and threshold sensitivity of the complex are estimated.

  18. Studies on chemical kinetics of positronium complex formation

    NASA Astrophysics Data System (ADS)

    Du, Youming; Zhang, Tianbao; Cao, Chun; Chen, Yun-Ti; Liang, Jiachang

    1993-09-01

    The complex formation between ortho-positronium and N-( p-substituted-phenyl) glycine ( p-RPhG, G=NHCH 2COOH; R=NO 2, Cl, H, CH 3, CH 3O) or N-( m-substituted-phenyl) glycine ( m-RPhG, R=NO 2, Cl) in solutions of 30% (v/v) ethanol—water and 20% (v/v) dioxane—water is discussed. The application of a BaF 2 scintillation counter to a positron annihilation lifetime spectrometer is described. By means of this new type of spectrometer, the complex formation reaction rate constants of ortho-positronium with the glycine derivatives in solutions are determined. The results indicate that the rate constants mainly depend on the conjugation effect at the benzene ring, the induction effects of the substitutes on the phenyl and solvents. There exists a linear free-energy relationship between rate constants and the basicities of N-substituted phenyl glycines in ortho-positronium—glycine complex formation. It means that the transient complex formation of ortho-positronium with molecules is like a general chemical reaction and obeys classical rules.

  19. Competitive counterion complexation allows the true host : guest binding constants from a single titration by ionic receptors.

    PubMed

    Pessêgo, Márcia; Basílio, Nuno; Muñiz, M Carmen; García-Río, Luis

    2016-07-01

    Counterion competitive complexation is a background process currently ignored by using ionic hosts. Consequently, guest binding constants are strongly affected by the design of the titration experiments in such a way that the results are dependent on the guest concentration and on the presence of added salts, usually buffers. In the present manuscript we show that these experimental difficulties can be overcome by just considering the counterion competitive complexation. Moreover a single titration allows us to obtain not only the true binding constants but also the stoichiometry of the complex showing the formation of 1 : 1 : 1 (host : guest : counterion) complexes. The detection of high stoichiometry complexes is not restricted to a single titration experiment but also to a displacement assay where both competitive and competitive-cooperative complexation models are taken into consideration. PMID:27278457

  20. Dynamics of plasma flow formation in a pulsed accelerator operating at a constant pressure

    NASA Astrophysics Data System (ADS)

    Baimbetov, F. B.; Zhukeshov, A. M.; Amrenova, A. U.

    2007-01-01

    Features in the dynamics of plasma flow formation at a constant pressure in a pulsed coaxial accelerator have been studied. The temperature and density of electrons in a plasma bunch have been determined using a probe technique.

  1. Determination of stability constants of aminoglycoside antibiotics with their metal complexes

    NASA Astrophysics Data System (ADS)

    Tiwow, Vanny M. A.

    2014-03-01

    One group of aminoglycoside antibiotics contains aminosugars. The aminosugar neomycin B with its derivate product neamine (2-Deoxy-4-0-(2,6-diamino-2,6-dideoxy-α-D-glucopyranosyl)-D-Streptamine) was identified as a free ligands and metal complexes. In particular, the stability constants of metal complexes by potentiometric titration techniques were investigated. Our previous study had determined the acid dissociation constants of these aminosugars with few metal complexes in fair depth. In this work, the complexation of two pyridine-containing amino alcohols and an amino sugar (neamine) have been measured potentiometrically. For instance, the stability constant of copper(II) complexation were determine and the model system generated an excellent fit. Stability constants with several metals have been determined and will be reported.

  2. Correlation between stabilities of uranyl ion complexes with various monocarboxylic acids and Hammett-Taft substituent constants

    SciTech Connect

    Poluektov, N.S.; Perfil'ev, V.A.; Meshkova, S.B.; Mishchenko, V.T.

    1987-01-01

    A correlation has been observed between the stabilities of uranyl ion complexes (1:1 composition) and the substituent inductive constants in formic and acetic acid derivatives. For substituents which are not directly involved in couples formation the parameters of the Hammett-Taft equation log K/sub 1/ = A + B have the following values: A = 1.311, B = -2.360. For substituents which form a coordination bond with the uranyl ion, A = 7.0077 and B = - 17.321. In the case of complexes formed between the uranyl ion and salicylic acid and its derivatives, there is a correlation between complex stability and sigma/sub m/ and sigma/sub p/ substituent constants for the meta- and para-positions, respectively (A = 12.72, B = -4.41).

  3. Dissociation of bimolecular αIIbβ3-fibrinogen complex under a constant tensile force.

    PubMed

    Litvinov, Rustem I; Barsegov, Valeri; Schissler, Andrew J; Fisher, Andrew R; Bennett, Joel S; Weisel, John W; Shuman, Henry

    2011-01-01

    The regulated ability of integrin αIIbβ3 to bind fibrinogen plays a crucial role in platelet aggregation, adhesion, and hemostasis. Employing an optical-trap-based electronic force clamp, we studied the thermodynamics and kinetics of αIIbβ3-fibrinogen bond formation and dissociation under constant unbinding forces, mimicking the forces of physiologic blood shear on a thrombus. The distribution of bond lifetimes was bimodal, indicating that the αIIbβ3-fibrinogen complex exists in two bound states with different mechanical stability. The αIIbβ3 antagonist, abciximab, inhibited binding without affecting the unbinding kinetics, whereas Mn²(+) biased the αIIbβ3-fibrinogen complex to the strong bound state with reduced off-rate. The average bond lifetimes decreased exponentially with increasing pulling force from ∼5 pN to 50 pN, suggesting that in this force range the αIIbβ3-fibrinogen interactions are classical slip bonds. We found no evidence for catch bonds, which is consistent with the known lack of shear-enhanced platelet adhesion on fibrinogen-coated surfaces. Taken together, these data provide important quantitative and qualitative characteristics of αIIbβ3-fibrinogen binding and unbinding that underlie the dynamics of platelet adhesion and aggregation in blood flow. PMID:21190668

  4. Complex organic molecules and star formation

    NASA Astrophysics Data System (ADS)

    Bacmann, A.; Faure, A.

    2014-12-01

    Star forming regions are characterised by the presence of a wealth of chemical species. For the past two to three decades, ever more complex organic species have been detected in the hot cores of protostars. The evolution of these molecules in the course of the star forming process is still uncertain, but it is likely that they are partially incorporated into protoplanetary disks and then into planetesimals and the small bodies of planetary systems. The complex organic molecules seen in star forming regions are particularly interesting since they probably make up building blocks for prebiotic chemistry. Recently we showed that these species were also present in the cold gas in prestellar cores, which represent the very first stages of star formation. These detections question the models which were until now accepted to account for the presence of complex organic molecules in star forming regions. In this article, we shortly review our current understanding of complex organic molecule formation in the early stages of star formation, in hot and cold cores alike and present new results on the formation of their likely precursor radicals.

  5. The thermodynamic characteristics of complex formation between calcium ions and L-leucine in aqueous solution

    NASA Astrophysics Data System (ADS)

    Kurochkin, V. Yu.; Chernikov, V. V.; Orlova, T. D.

    2011-04-01

    Complex formation of L-leucine with calcium ions in aqueous solution was studied by potentiometric titration at 298.15 K and ionic strength values I = 0.5, 1.0, and 1.5 (KNO3). The formation of the CaL+ and CaHL2+ complex particles was established and their stability constants were determined. The enthalpies of protolytic equilibria of leucine and formation of calcium ion complexes with leucine were determined calorimetrically at 298.15 K and I = 0.5 (KNO3). The thermodynamic characteristics of complex formation between calcium ions and L-leucine were calculated.

  6. Stability Constants of Np(V) Complexes with Phosphate at Variable Temperatures

    SciTech Connect

    Xia, Yuanxian; Friese, Judah I.; Moore, Dean A.; Rao, Linfeng

    2006-05-04

    A solvent extraction method was used to determine the stability constants of Np(V) complexes with phosphate in 1.0 M NaClO4 from 25o C to 55o C. A morpholine-4-ethanesulfonic acid buffer was used to maintain pH at about 5 in the Np(V)-H2PO4- system. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of phosphate were increased. Stability constants of the 1:1 Np(V)-H2PO4- complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [H2PO4-] on the distribution ratio. The enthalpy and entropy of complexation were calculated from the stability constants at different temperatures by using the Van’t Hoff equation.

  7. Binding constant determination of uranyl-citrate complex by ACE using a multi-injection method.

    PubMed

    Zhang, Yiding; Li, Linnan; Huang, Hexiang; Xu, Linnan; Li, Ze; Bai, Yu; Liu, Huwei

    2015-04-01

    The binding constant determination of uranyl with small-molecule ligands such as citric acid could provide fundamental knowledge for a better understanding of the study of uranyl complexation, which is of considerable importance for multiple purposes. In this work, the binding constant of uranyl-citrate complex was determined by ACE. Besides the common single-injection method, a multi-injection method to measure the electrophoretic mobility was also applied. The BGEs used contained HClO4 and NaClO4 , with a pH of 1.98 ± 0.02 and ionic strength of 0.050 mol/L, then citric acid was added to reach different concentrations. The electrophoretic mobilities of the uranyl-citrate complex measured by both of the two methods were consistent, and then the binding constant was calculated by nonlinear fitting assuming that the reaction had a 1:1 stoichiometry and the complex was [(UO2 )(Cit)](-) . The binding constant obtained by the multi-injection method was log K = 9.68 ± 0.07, and that obtained by the single-injection method was log K = 9.73 ± 0.02. The results provided additional knowledge of the uranyl-citrate system, and they demonstrated that compared with other methods, ACE using the multi-injection method could be an efficient, fast, and simple way to determine electrophoretic mobilities and to calculate binding constants. PMID:25598434

  8. Equilibrium constant for carbamate formation from monoethanolamine and its relationship with temperature

    SciTech Connect

    Aroua, M.K.; Benamor, A.; Haji-Sulaiman, M.Z.

    1999-09-01

    Removal of acid gases such as CO{sub 2} and H{sub 2}S using aqueous solutions of alkanolamines is an industrially important process. The equilibrium constant for the formation of carbamate from monoethanolamine was evaluated at various temperatures of 298, 308, 318, and 328 K and ionic strengths up to 1.7 M. From the plot of log{sub 10} K versus I{sup 0.5}, the variation of the thermodynamical constant with temperature follows the relationship log{sub 10} K{sub 1} = {minus}0.934 + (0.671 {times} 10{sup 3})K/T.

  9. Determination of stability constants and acute toxicity of potential hepatotropic gadolinium complexes.

    PubMed

    Mikiciuk-Olasik, Elzbieta; Wojewoda, Emilia; Bilichowski, Ireneusz; Witczak, Małgorzata; Karwowski, Bolesław; Wagrowska-Danilewicz, Małgorzata; Stasikowska, Olga

    2010-01-01

    Due to their high specificity for the hepatobiliary system, iminodiacetic acid derivatives are known to form a class of hepatobiliary agents. In this paper we present new hepatotropic gadolinium complexes to be used as potential MRI contrast agents. Derivatives of N-(2-phenylamine-2-oxoethyl) iminodiacetic acid are introduced as ligands into such complexes. In this way, we hope to achieve a valuable diagnostic tool for investigating of pathological changes in the liver. Stability constants of complexes were determined by potentiometric titration in 0.1 mol L(-1) NaNO3 solution at 20.0 +/- 0.1 degrees C. Stability and selectivity constants were also determined for endogenous metal ions such as Cu2+, Ca2+, and Zn2+ with the use of SUPERQUAD computer program. Acute toxicity of new gadolinium complexes was assessed in mice and histopathology examinations were carried out. PMID:20369788

  10. J(Si,H) Coupling Constants in Nonclassical Transition-Metal Silane Complexes.

    PubMed

    Scherer, Wolfgang; Meixner, Petra; Batke, Kilian; Barquera-Lozada, José E; Ruhland, Klaus; Fischer, Andreas; Eickerling, Georg; Eichele, Klaus

    2016-09-12

    We will outline that the sign and magnitude of J(Si,H) coupling constants provide a highly sensitive tool to measure the extent of Si-H bond activation in nonclassical silane complexes. Up to now, this structure-property relationship was obscured by erroneous J(Si,H) sign determinations in the literature. These new findings also help to identify the salient control parameters of the Si-H bond activation process in nonclassical silane complexes. PMID:27503583

  11. Hydrolysis of oxaliplatin-evaluation of the acid dissociation constant for the oxalato monodentate complex.

    PubMed

    Jerremalm, Elin; Eksborg, Staffan; Ehrsson, Hans

    2003-02-01

    Alkaline hydrolysis of the platinum anticancer drug oxaliplatin gives the oxalato monodentate complex and the dihydrated oxaliplatin complex in two consecutive steps. The acid dissociation constant for the oxalato monodentate intermediate was determined by a kinetic approach. The pK(a) value was estimated as 7.23. The monodentate intermediate is assumed to rapidly react with endogenous compounds, resulting in a continuous conversion of oxaliplatin via the monodentate form. PMID:12532393

  12. DISSOCIATION OF ARSENITE-PEPTIDE COMPLEXES: TRIPHASIC NATURE, RATE CONSTANTS, HALF LIVES AND BIOLOGICAL IMPORTANCE

    EPA Science Inventory

    We determined the number and the dissociation rate constants of different complexes formed from arsenite and two peptides containing either one (RV AVGNDYASGYHYGV for peptide 20) or three cysteines (LE AWQGK VEGTEHLYSMK K for peptide 10) via radioactive 73As labeled arsenite and ...

  13. Determination of complex permittivity from propagation constant measurement with planar transmission lines

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A new two-standard calibration procedure is outlined for determining the complex permittivity of materials from the propagation constant measured with planar transmission lines. Once calibrated, a closed-form expression for the material permittivity is obtained. The effects of radiation and conducto...

  14. Quantum theory of the complex dielectric constant of free carriers in polar semiconductors

    SciTech Connect

    Jensen, B.

    1982-09-01

    The optical constants and reflectivity of a semiconductor are known as functions of the real and imaginary parts of the complex dielectric constant. The imaginary part of the complex dielectric constant e/sub 2/ is proportional to the optical conductivity, which has recently been calculated from the quantum density matrix equation of motion. The expression obtained for e/sub 2/ reduces to the Drude result, as obtained from the quasi-classical Boltzmann transport equation, in the limit of low frequencies and elastic scattering mechanisms, and to the quantum result found using time dependent perturbation theory in the limit of high frequencies. This paper derives the real part of the complex dielectric constant e/sub 1/ for a III-V or II-VI semiconductor with the band structure of the Kane theory, using the quantum density matrix method. The relation of e/sub 1/ to the second order perturbation energy of the system is shown, and the reflectivity is a minimum when the second order perturbation energy vanishes. The quantum calculation for e/sub 1/ gives approximately the same result as the Drude theory, except near the fundamental absorption edge, and reduces to the Drude result at low frequencies. Using the complex dielectric constant, the real and imaginary parts of the complex refractive index, the skin depth, and surface impedance, and the reflectivity are found. The plasma resonance is examined. The surface impedance and the skin depth are shown to reduce to the usual classical result in the limit that e/sub 1/ = 0 and w tau << 1, where w is the angular frequency of the applied field and tau is the electron scattering time.

  15. Multiparametric curve fitting-IX Simultaneous regression estimation of stoichiometry and stability constants of complexes.

    PubMed

    Havel, J; Meloun, M

    1986-05-01

    A chemical model (i.e., the number of complexes, their stoichiometry and stability constants with molar absorptivities) in solution equilibria may be established by (i) the trial-and-error method in which stability constants are estimated for an assumed set of complexes in the mixture and a fitness test is used to resolve a choice of plausible models to find the true one; (ii) the simultaneous estimation of the stoichiometry and stability constants for species divided into "certain" species for which the parameters beta(pqr), (p, q, r) are known and held constant, and "uncertain" species with unknown parameters which are determined by regression analysis. The interdependence of stability constants and particular sets of stoichiometric indices requires that the computational strategy should be chosen carefully for each particular case. The benefits and limitations of both approaches are compared by means of examples of potentiometric titration data analysis by the POLET(84) program and of spectrophotometric data analysis by the SQUAD(84) program. A strategy for efficient computation is suggested. PMID:18964117

  16. Complex formation between uranyl and various thiosemicarbazide derivatives

    SciTech Connect

    Chuguryan, D.G.; Dzyubenko, V.I.

    1987-01-01

    Complex formation between hexavalent uranium and salicylaldehyde thiosemicarbazone (H/sub 2/L), salicylaldehyde S-methyl-isothiosemicarbazone (H/sub 2/Q), S-methyl-N/sub 1/,N/sub 4/-bis(salicylidene)isothiosemicarbazide(H/sub 2/Z), and thiosemicarbazidodiacetic acid (H/sub 2/R) has been studied spectrophotometrically in solution. Stability constants for complexes having the composition UO/sub 2/A have been calculated. Solid uranyl derivatives having the composition UO/sub 2/L x 2H/sub 2/O, UO/sub 2/Q x 2H/sub 2/O, UO/sub 2/Z x 2H/sub 2/O, and UO/sub 2/R x 2H/sub 2/O have been obtained. These derivatives were isolated and their IR spectroscopic behavior and thermal properties were investigated.

  17. Stability constants important to the understanding of plutonium in environmental waters, hydroxy and carbonate complexation of PuO{sub 2}{sup +}

    SciTech Connect

    Bennett, D A

    1990-04-20

    The formation constants for the reactions PuO{sub 2}{sup +} + H{sub 2}O = PuO{sub 2}(OH) + H{sup +} and PuO{sub 2}{sup +} + CO{sub 3}{sup 2} = PuO{sub 2}(CO{sub 3}){sup {minus}} were determined in aqueous sodium perchlorate solutions by laser-induced photoacoustic spectroscopy. The molar absorptivity of the PuO{sub 2}{sup +} band at 569 nm decreased with increasing hydroxide concentration. Similarly, spectral changes occurred between 540 and 580 nm as the carbonate concentration was increased. The absorption data were analyzed by the non-linear least-squares program SQUAD to yield complexation constants. Using the specific ion interaction theory, both complexation constants were extrapolated to zero ionic strength. These thermodynamic complexation constants were combined with the oxidation-reduction potentials of Pu to obtain Eh versus pH diagrams. 120 refs., 35 figs., 12 tabs.

  18. The stability constants of copper(II) complexes with some alpha-amino acids in dioxan-water mixtures.

    PubMed

    Doğan, A; Köseoğlu, F; Kiliç, E

    2001-08-15

    In this study, the overall stability constants of copper(II) complexes with some alpha-amino acids (glycine, dl-alanine, dl-valine, l-leucine, l-asparagine, l-glutamine) were determined by potentiometric titration in water, 25% dioxan-75% water, 35% dioxan-65% water, 50% dioxan-50% water, and 60% dioxan-40% water. The titrations were performed at 25 degrees C, under nitrogen atmosphere, and the ionic strength of the medium was maintained at 0.10 M by using sodium perchlorate. The formation curves of their complexes (n-p[L]) were obtained by means of the titration data. Then the stability constants were determined in relation to these curves. The mol ratio of copper(II) to alpha-amino acid was also determined and it was found that the complexes were CuL(2) type. Another important result obtained was that the tendency of amino acids to form complexes with copper(II) was greater in dioxan-water mixtures compared to water. PMID:11488627

  19. Temperature dependency of the equilibrium constant for the formation of carbamate from diethanolamine

    SciTech Connect

    Aroua, M.K.; Amor, A.B.; Haji-Sulaiman, M.Z.

    1997-07-01

    Aqueous alkanolamine solutions are frequently used to remove acidic components such as H{sub 2}S and CO{sub 2} from process gas streams. The equilibrium constant for the formation of diethanolamine carbamate was determined experimentally at (303, 313, 323, and 331) K for ionic strengths up to 1.8 mol/dm{sup 3}, the inert electrolyte being NaClO{sub 4}. A linear relationship was found to hole between log K and I{sup 0.5}. The thermodynamical constant has been determined and expressed by the equation log K{sub 1} = {minus}5.12 + 1.781 {times} 10{sup 3} K/T.

  20. Vortex formation in a complex plasma

    NASA Astrophysics Data System (ADS)

    Ishihara, Osamu

    Complex plasma experiments in ground-based laboratories as well as in microgravity conditions have shown the formation of vortex structures in various conditions (e.g., 1,2,3,4). The vortex structures formed in a complex plasma are visible by naked eyes with the help of irradiating laser and the individual dust particles in the structure give us the opportunity to study detailed physics of the commonly observed natural phenomena known such as tornadoes, typhoons, hurricanes and dust devils. Based on the Navier-Stokes equation with proper complex plasma conditions we analyze as much as possible in a universal way the vortex structure and clarifies the role of the controlling parameters like flow velocity and external magnetic field. 1. G. E. Morfill,H. M. Thomas, U. Konopka,H. Rothermel, M. Zuzic, A. Ivlev, and J. Goree, Phys,. Rev. Lett. 83, 1598 (1999). 2. E. Nebbat and R. Annou, Phys. Plasmas 17, 093702 (2010). 3. Y. Saitou and O. Ishihara, Phys. Rev. Lett. 111, 185003 (2013). 4. V. N. Tsytovich and N. G. Gusein-zade, Plasma Phys. Rep. 39, 515 (2013).

  1. Stability Constants of Technetium (IV) Oxalate Complexes as a Function of Ionic Strength

    SciTech Connect

    Xia, Yuanxian; Hess, Nancy J.; Felmy, Andrew R.

    2006-03-01

    Solvent extraction methods were used to determine the stability constants of Tc(IV) with oxalate anions in NaCl solutions ranging in concentration from 0.5 M to 2.0 M. All experiments were conducted in an atmosphere-controlled chamber under Ar atmosphere (< 1.0ppm O2). A reducing agent (hydrazine) was used during extractions to maintain technetium in the tetravalent oxidation state. Independent tests confirmed that the oxidation state of technetium did not change during extractions. The distribution ratio of Tc(IV) between the organic and aqueous phases was found to decrease as the concentration of oxalic acid increased. At the oxalic acid concentrations used in these experiments, the complexes TcO(Ox) and TcO(Ox)22- were found to be the dominant aqueous species. Based on these data, the thermodynamic stability constants of Tc(IV) with oxalate complexes were calculated by the Specific Ion Interaction Theory (SIT).

  2. Association constants and enthalpies of formation of heteroassociates of anions of cresol red and thymol blue

    NASA Astrophysics Data System (ADS)

    Shapovalov, S. A.

    2011-01-01

    The tendency of anions of sulfophthaleine dyes to heteroassociation was studied in aqueous solutions of phenol red, cresol red, thymol blue, and non-substituted phenol red. It was spectrophotometrically determined that single (HAn-) and doubly charged anions (An2-) of sulfophthaleines can form stable heteroassociates of the composition Ct+ · HAn- and (Ct+)2 · An2- with cations (Ct+) of polymethine dyes, pinacyanol, and quinaldine red. The values of enthalpy formation of ions of dyes and heteroassociates were calculated semi-empirically and compared with experimentally determined values of the equilibrium association constants.

  3. Complex dielectric constants for selected near-millimeter-wave materials at 245 GHz

    NASA Technical Reports Server (NTRS)

    Dutta, J. M.; Jones, C. R.; Dave, H.

    1986-01-01

    A double-beam instrument developed in this laboratory has been used to measure the complex dielectric constant of selected materials at 245 GHz. It is reported here the results for crystalline quartz, fused silica (Spectrosil WF and Dynasil 4000), beryllia (iso-pressed), boron nitride (hot-pressed), and a nickel ferrite (Trans-Tech 2-111). Results are compared with the data obtained by other researchers.

  4. Variation of stability constants of thorium and uranium oxalate complexes with ionic strength

    SciTech Connect

    Erten, H.N; Mohammed, A.K.; Choppin, G.R.

    1993-12-31

    Extraction of Th(IV) and UO{sub 2}{sup 2+} by a solution of TTA and HDEHP, respectively, in toluene was used to obtain stability constants of their oxalate complexes in 1, 3, 5, 7 and 9 M ionic strength (NaClO{sub 2}) solutions. The complexes formed were the MOx, MHOx, MOx{sub 2} and M(HOx){sub 2} (M = Th, UO{sub 2}) species. The values were analyzed by the Specific Interaction Theory and agreed to I {le} 3 M but required an additional term for fitting at I > 3 M.

  5. Complex trajectories sans isochrones: quantum barrier scattering with rectilinear constant velocity trajectories.

    PubMed

    Rowland, Brad A; Wyatt, Robert E

    2007-10-28

    One of the major obstacles in employing complex-valued trajectory methods for quantum barrier scattering calculations is the search for isochrones. In this study, complex-valued derivative propagation method trajectories in the arbitrary Lagrangian-Eulerian frame are employed to solve the complex Hamilton-Jacobi equation for quantum barrier scattering problems employing constant velocity trajectories moving along rectilinear paths whose initial points can be in the complex plane or even along the real axis. It is shown that this effectively removes the need for isochrones for barrier transmission problems. Model problems tested include the Eckart, Gaussian, and metastable quadratic+cubic potentials over a variety of wave packet energies. For comparison, the "exact" solution is computed from the time-dependent Schrodinger equation via pseudospectral methods. PMID:17979316

  6. QSPR prediction of the stability constants of gadolinium(III) complexes for magnetic resonance imaging.

    PubMed

    Dioury, Fabienne; Duprat, Arthur; Dreyfus, Gérard; Ferroud, Clotilde; Cossy, Janine

    2014-10-27

    Gadolinium(III) complexes constitute the largest class of compounds used as contrast agents for Magnetic Resonance Imaging (MRI). A quantitative structure-property relationship (QSPR) machine-learning based method is applied to predict the thermodynamic stability constants of these complexes (log KGdL), a property commonly associated with the toxicity of such organometallic pharmaceuticals. In this approach, the log KGdL value of each complex is predicted by a graph machine, a combination of parametrized functions that encodes the 2D structure of the ligand. The efficiency of the predictive model is estimated on an independent test set; in addition, the method is shown to be effective (i) for estimating the stability constants of uncharacterized, newly synthesized polyamino-polycarboxylic compounds and (ii) for providing independent log KGdL estimations for complexants for which conflicting or questionable experimental data were reported. The exhaustive database of log KGdL values for 158 complexants, reported for potential application as contrast agents for MRI and used in the present study, is available in the Supporting Information (122 primary literature sources). PMID:25181704

  7. Potentiometric determination of the dissociation constants of an asymmetric sorbent containing l-proline, and the stability constants of its Cu(II) complexes.

    PubMed

    Zolotarev, Y A; Kurganov, A A; Davankov, V A

    1978-09-01

    The dissociation constants of the carboxyl groups (pK(a1) = 2.2, n = 1.8) and amino groups (pK(a2) = 9.5, n(2) = 1.6) of a sorbent prepared by reacting l-proline with a cross-linked chloromethylated styrene polymer have been determined by potentiometric titration. The potentiometrically measured stability constants of the Cu(II) complexes of the resin (logbeta(1) = 6.9 and log beta(2) = 12.4) were found to be close to the values for the Cu(II) complexes of N-benzyl-l-proline. For complexed resins of alpha-amino-acid type the pH-values of decomplexation do not appear to be directly correlated with the stability constants. PMID:18962307

  8. Estimating the acidity of transition metal hydride and dihydrogen complexes by adding ligand acidity constants.

    PubMed

    Morris, Robert H

    2014-02-01

    A simple equation (pKa(THF) = ∑AL + Ccharge + Cnd + Cd6) can be used to obtain an estimate of the pKa of diamagnetic transition metal hydride and dihydrogen complexes in tetrahydrofuran, and, by use of conversion equations, in other solvents. It involves adding acidity constants AL for each of the ligands in the 5-, 6-, 7-, or 8-coordinate conjugate base complex of the hydride or dihydrogen complex along with a correction for the charge (Ccharge = -15, 0 or 30 for x = +1, 0 or -1 charge, respectively) and the periodic row of the transition metal (Cnd = 0 for 3d or 4d metal, 2 for 5d metal) as well as a correction for d(6) octahedral acids (Cd6 = 6 for d(6) metal ion in the acid, 0 for others) that are not dihydrogen complexes. Constants AL are provided for 13 commonly occurring ligand types; of these, nine neutral ligands are correlated with Lever's electrochemical ligand parameters EL. This method gives good estimates of the over 170 literature pKa values that range from less than zero to 50 with a standard deviation of 3 pKa units for complexes of the metals chromium to nickel, molybdenum, ruthenium to palladium, and tungsten to platinum in the periodic table. This approach allows a quick assessment of the acidity of hydride complexes found in nature (e.g., hydrogenases) and in industry (e.g., catalysis and hydrogen energy applications). The pKa values calculated for acids that have bulky or large bite angle chelating ligands deviate the most from this correlation. The method also provides an estimate of the base strength of the deprotonated form of the complex. PMID:24410025

  9. Stability constants determination of successive metal complexes by hyphenated CE-ICPMS.

    PubMed

    Petit, Jeremy; Aupiais, Jean; Topin, Sylvain; Geertsen, Valérie; Beaucaire, Catherine; Stambouli, Moncef

    2010-01-01

    The study of radionuclides speciation requires accurate evaluation of stability constants, which can be achieved by CE-ICPMS. We have previously described a method for 1:1 metal complexes stability constants determination. In this paper, we present its extension to the case of successive complexations and its application to uranyl-oxalate and lanthanum-oxalate systems. Several significant steps are discussed: analytical conditions choice, mathematical treatment by non-linear regression, ligand concentration and ionic strength corrections. The following values were obtained: at infinite dilution, log(beta(1) degrees (UO(2)Oxa))=6.93+/-0.05, log(beta(2) degrees (UO(2)(Oxa)(2) (2-)))=11.92+/-0.43 and log(beta(3) degrees (UO(2)(Oxa)(3) (4-)))=15.11+/-0.12; log(beta(1) degrees (LaOxa(+)))=5.90+/-0.07, log(beta(2) degrees (La(Oxa)(2) (-)))=9.18+/-0.19 and log(beta(3) degrees (La(Oxa)(3) (3-)))=9.81+/-0.33. These values are in good agreement with the literature data, even though we suggest the existence of a new lanthanum-oxalate complex: La(Oxa)(3) (3-). This study confirms the suitability of CE-ICPMS for complexation studies. PMID:20084632

  10. Experimental study of the complex resistivity and dielectric constant of chrome-contaminated soil

    NASA Astrophysics Data System (ADS)

    Liu, Haorui; Yang, Heli; Yi, Fengyan

    2016-08-01

    Heavy metals such as arsenic and chromium often contaminate soils near industrialized areas. Soil samples, made with different water content and chromate pollutant concentrations, are often needed to test soil quality. Because complex resistivity and complex dielectric characteristics of these samples need to be measured, the relationship between these measurement results and chromium concentration as well as water content was studied. Based on soil sample observations, the amplitude of the sample complex resistivity decreased with an increase of contamination concentration and water content. The phase of complex resistivity takes on a tendency of initially decrease, and then increase with the increasing of contamination concentration and water content. For a soil sample with the same resistivity, the higher the amplitude of complex resistivity, the lower the water content and the higher the contamination concentration. The real and imaginary parts of the complex dielectric constant increase with an increase in contamination concentration and water content. Note that resistivity and complex resistivity methods are necessary to adequately evaluate pollution at various sites.

  11. Cadmium(II) complex formation with glutathione.

    PubMed

    Mah, Vicky; Jalilehvand, Farideh

    2010-03-01

    Complex formation between heavy metal ions and glutathione (GSH) is considered as the initial step in many detoxification processes in living organisms. In this study the structure and coordination between the cadmium(II) ion and GSH were investigated in aqueous solutions (pH 7.5 and 11.0) and in the solid state, using a combination of spectroscopic techniques. The similarity of the Cd K-edge and L(3)-edge X-ray absorption spectra of the solid compound [Cd(GS)(GSH)]ClO(4).3H(2)O, precipitating at pH 3.0, with the previously studied cysteine compound {Cd(HCys)(2).H(2)O}(2).H(3)O(+).ClO(4) (-) corresponds to Cd(S-GS)(3)O (dominating) and Cd(S-GS)(4) four-coordination within oligomeric complexes with mean bond distances of 2.51 +/- 0.02 A for Cd-S and 2.24 +/- 0.04 A for Cd-O. For cadmium(II) solutions (C (Cd(II)) approximately 0.05 M) at pH 7.5 with moderate excess of GSH (C (GSH)/C (Cd(II)) = 3.0-5.0), a mix of Cd(S-GS)(3)O (dominating) and Cd(S-GS)(4) species is consistent with the broad (113)Cd NMR resonances in the range 632-658 ppm. In alkaline solutions (pH 11.0 and C (GSH)/C (Cd(II)) = 2.0 or 3.0), two distinct peaks at 322 and 674 ppm are obtained. The first peak indicates six-coordinated mononuclear and dinuclear complexes with CdS(2)N(2)(N/O)(2) and CdSN(3)O(2) coordination in fast exchange, whereas the second corresponds to Cd(S-GS)(4) sites. At high ligand excess the tetrathiolate complex, Cd(S-GS)(4), characterized by a sharp delta((113)Cd) NMR signal at 677 ppm, predominates. The average Cd-S distance, obtained from the X-ray absorption spectra, varied within a narrow range, 2.49-2.53 A, for all solutions (pH 7.5 and 11.0) regardless of the coordination geometry. PMID:20035360

  12. Use of laser induced photoacoustic spectroscopy (LIPAS) to determine equilibrium constants of cation-cation complexes

    SciTech Connect

    Hannink, N.J.; Hoffman, D.C.; Silva, R.J.; Russo, R.E.

    1993-12-31

    Laser Induced PhotoAcoustic Spectroscopy (LIPAS) is a relatively new, photothermal technique to examine solutions. Studies in the past have shown it to be more sensitive than conventional absorption spectroscopy, while, yielding the same information thus allowing lower concentrations to be used. This study is using LIPAS to examine solutions to determine the equilibrium constants of cation-cation complexes. It has been found that actinyl(V) cations form cation-cation complexes with a variety of cations, including actinyl(VI) cations. The radioactive nature of the actinide elements requires special handling techniques and also require limits be placed on the amount of material that can be used. The sensitivity of some oxidation states of the actinides to oxygen also presents a problem. Preliminary results will be presented for actinyl(V)-actinyl(VI) cation-cation complexes that were studied using a remote LIPAS system incorporating fiber optics for transmission of laser signals.

  13. Constant Electric and Magnetic Fields Effect on the Structuring and Thermomechanical and Thermophysical Properties of Nanocomposites Formed from Pectin-Cu2+-Polyethyleneimine Interpolyelectrolyte-Metal Complexes

    NASA Astrophysics Data System (ADS)

    Demchenko, V.; Shtompel', V.; Riabov, S.; Lysenkov, E.

    2015-12-01

    Applying wide-angle X-ray scattering method, thermomechanical analysis, and differential scanning calorimetry, the structural organization and properties of nanocomposites formed by chemical reduction of Cu2+ cations in the interpolyelectrolyte-metal complex (pectin-Cu2+-polyethyleneimine) under the influence of a constant magnetic and electric fields have been studied. It has been found that the chemical reduction of Cu2+ cations in the interpolyelectrolyte-metal complex bulk under constant electric and magnetic fields leads to formation of nanocomposite consisting of interpolyelectrolyte complex, including pectin-polyethyleneimine and nanoparticles of the metal Cu phase, whereas nanocomposite with Cu/Cu2O nanoparticles is formed in original state (without any field). It was observed that, under constant field, nanocomposites obtained have higher structural glass-transition temperatures and thermal stability.

  14. Constant Electric and Magnetic Fields Effect on the Structuring and Thermomechanical and Thermophysical Properties of Nanocomposites Formed from Pectin-Cu(2+)-Polyethyleneimine Interpolyelectrolyte-Metal Complexes.

    PubMed

    Demchenko, V; Shtompel', V; Riabov, S; Lysenkov, E

    2015-12-01

    Applying wide-angle X-ray scattering method, thermomechanical analysis, and differential scanning calorimetry, the structural organization and properties of nanocomposites formed by chemical reduction of Сu(2+) cations in the interpolyelectrolyte-metal complex (pectin-Cu(2+)-polyethyleneimine) under the influence of a constant magnetic and electric fields have been studied. It has been found that the chemical reduction of Cu(2+) cations in the interpolyelectrolyte-metal complex bulk under constant electric and magnetic fields leads to formation of nanocomposite consisting of interpolyelectrolyte complex, including pectin-polyethyleneimine and nanoparticles of the metal Cu phase, whereas nanocomposite with Cu/Cu2O nanoparticles is formed in original state (without any field). It was observed that, under constant field, nanocomposites obtained have higher structural glass-transition temperatures and thermal stability. PMID:26659610

  15. Cyclodextrins in pharmaceutical formulations II: solubilization, binding constant, and complexation efficiency.

    PubMed

    Jambhekar, Sunil S; Breen, Philip

    2016-02-01

    Cyclodextrins are cyclic oligosaccharides that have been recognized as pharmaceutical adjuvants for the past 20 years. The molecular structure of these glucose derivatives, which approximates a truncated cone, bucket, or torus, generates a hydrophilic exterior surface and a nonpolar interior cavity. Cyclodextrins can interact with appropriately sized drug molecules to yield an inclusion complex. These noncovalent inclusion complexes offer a variety of advantages over noncomplexed forms of a drug. Cyclodextrins are carbohydrates that are primarily used to enhance the aqueous solubility, physical chemical stability, and bioavailability of drugs. Their other applications include preventing drug-drug interactions, converting liquid drugs into microcrystalline powders, minimizing gastrointestinal and ocular irritation, and reducing or eliminating unpleasant taste and smell. Here, we focus on the solubilization of drugs by complexation, and discuss the determination and significance of binding constants for cyclodextrin complexes, and the determination of complexation efficiency and factors that influence it. We also make some general observations on cyclodextrin complexation and the use of cyclodextrins in solid, as well as parenteral, dosage forms. PMID:26687191

  16. The potentiometric determination of stability constants for zinc acetate complexes in aqueous solutions to 295°C

    NASA Astrophysics Data System (ADS)

    Glordano, Thomas H.; Drummond, S. E.

    1991-09-01

    A potentiometric method was used to determine the formation quotients of zinc acetate complexes in aqueous solutions from 50 to 295°C at ionic strengths of 0.03,0.3, and 1.0 m. The potentiometric titrations were carried out in an externally heated, Teflon-lined concentration cell fitted with hydrogen electrodes. Formal sodium acetate concentrations of the experimental solutions ranged from 0.001 to 0. 1 m with acetic acid to sodium acetate ratios ranging from 30 to 300. Sodium trifluoromethanesulfonate (F3CSO3Na) was used as a supporting electrolyte. Stoichiometries and formation quotients for the complexes ZnCH3COO+, Zn(CH3COO)2, and Zn(CH3COO)-3 were derived from the titration data by regression analysis. Stability constants at infinite dilution (Kn) and other relevant thermodynamic quantities were calculated for these three complexes. Logarithms for the formation constants of the general reaction Zn2+ + nCH3COO- = Zn(CH3COO)n2-n are n = 1-(1.9 ± 0.2, 50°C), (2.3 ± 0.1, 100°C), (2.8 ± 0.1, 150°C), (3.5 ± 0.1, 200°C), (4.3 ± 0.2, 250°C), (5.3 ± 0.3, 300°C); n = 2-(3.4 ± 0.1, 50°C), (4.0 ± 0.1, 100°C), (4.83 ± 0.09, 150°C), (5.9 ± 0.1, 200°C), (7.1 ± 0.1, 250°C), (8.7 ± 0.2, 300°C); n = 3-(4.1 ± 0.3, 50°C), (4.7 ± 0.3, 100°C), (5.5 ± 0.3, 150°C), (6.6 ± 0.3, 200°C), (7.9 ± 0.3, 250°C), (9.4 ± 0.3, 300°C). Calculations of zinc speciation in acetate-chloride solutions show that zinc acetate complexes should have an importance similar to zinc chloride complexes in high acetate waters where chloride to acetate molal ratios are less than about 10.

  17. Stability Constants of Mixed Ligand Complexes of Nickel(II) with Adenine and Some Amino Acids

    PubMed Central

    Türkel, Naciye

    2015-01-01

    Nickel is one of the essential trace elements found in biological systems. It is mostly found in nickel-based enzymes as an essential cofactor. It forms coordination complexes with amino acids within enzymes. Nickel is also present in nucleic acids, though its function in DNA or RNA is still not clearly understood. In this study, complex formation tendencies of Ni(II) with adenine and certain L-amino acids such as aspartic acid, glutamic acid, asparagine, leucine, phenylalanine, and tryptophan were investigated in an aqueous medium. Potentiometric equilibrium measurements showed that both binary and ternary complexes of Ni(II) form with adenine and the above-mentioned L-amino acids. Ternary complexes of Ni(II)-adenine-L-amino acids are formed by stepwise mechanisms. Relative stabilities of the ternary complexes are compared with those of the corresponding binary complexes in terms of Δlog10⁡K, log10⁡X, and % RS values. It was shown that the most stable ternary complex is Ni(II):Ade:L-Asn while the weakest one is Ni(II):Ade:L-Phe in aqueous solution used in this research. In addition, results of this research clearly show that various binary and ternary type Ni(II) complexes are formed in different concentrations as a function of pH in aqueous solution. PMID:26843852

  18. The Influence of Kinetics on the Formation of Complexes Between Mercury and Dissolved Organic Matter

    NASA Astrophysics Data System (ADS)

    Miller, C. L.; Gu, B.; Brooks, S.; Southworth, G.

    2008-12-01

    Strong complexes between mercury (Hg) and dissolved organic matter (DOM) dominate the speciation of Hg(II) in most oxygenated aquatic systems but the rate of formation of these complexes has not be thoroughly investigated. Kinetic experiments were used to measure the formation rate of strong Hg(II)-DOM complexes in water collected from the Upper East Fork Poplar Creek (UEFPC) in Oak Ridge, TN and in solution prepared using various DOM isolates. The loss of reactive mercury (HgR), defined as the amount of Hg reducible by stannous chloride (SnCl2), was used to examine the formation rates of strong Hg-DOM complexes which are nonreactive with SnCl2. We found that the formation of nonreactive Hg complexes followed first-order reaction kinetics, and the rate constant for the formation these complexes is similar both in creek water and solutions containing unfractionated DOM isolates ( ~4.8 day-1 ). C-18 Solid phase extractions were also used to examine the association of Hg(II) with different fractions of DOM as the mercury transformed from reactive, inorganic complexes to strong Hg-DOM complexes. In both the UEFPC and in laboratory solutions containing Hg and an unfractionated DOM isolate, the complexation of Hg shifted from hydrophilic to hydrophobic complexes as the strong Hg-DOM complexes were formed. This study concludes that, while equilibrium models suggest that strong Hg-DOM complexes dominate the speciation of Hg under equilibrium conditions, the formation of these complexes is kinetically limited. The slow formation of strong Hg-DOM complexes may have important implications in understanding the cycling, transport and bioavailability of Hg in systems such as the UEFPC with varying input sources of organic and inorganic Hg complexes.

  19. Potentiometric estimation of the stability constants of ion-lonophore complexes in ion-selective membranes by the sandwich membrane method: theory, advantages, and limitations.

    PubMed

    Shultz, Mikhail M; Stefanova, Olga K; Mokrov, Sergey B; Mikhelson, Konstantin N

    2002-02-01

    Segmented sandwich membrane method of studying stoichiometry and stability constants of ion-ionophore complexes in ion-selective membranes is considered in detail. The experimental data (reported earlier in Russian) concerning complexes of various ions with valinomycin, with H+-selective neutral ionophore hexabutyltriamidophosphate, and with anion-binding neutral ionophore p-hexyl trifluoroacetylbenzoate is presented in a compact form. Advantages of titration technique in the sandwich membrane method (the presence of an internal criterion of reliability, and the possibility of direct determination of complex stoichiometry coefficients) are specially addressed. Biases of the estimates of the constants caused by ion-pair formation in real membranes and by diffusion potential are analyzed by means of computer simulations. The possibility of revealing two coexisting complexes with different compositions is also discussed. PMID:11838668

  20. Diffusion impregnation of alloys under conditions of complex formation

    SciTech Connect

    Pavlina, V.S.; Matychak, Y.S.

    1985-05-01

    In most cases, diffusion impregnation of alloys with elements for the purpose of improving their service properties occurs with chemical interaction with the constituents of the base. Such processes are described within the limits of the model of reaction diffusion, assuming the formation and growth of new continuous layers by the Fick equation. At the same time, instantaneous reaction of the elements is assumed, as the result of which the rate of the whole process is limited by diffusion. Together with this, diffusion processes and chemical transformations occur simultaneously, as the result of which continuous phases are not formed (internal oxidation, nitriding, etc.). The purpose of this work was an analytical investigation of diffusion impregnation by element A from a constant source of a flat specimen initially uniformly alloyed with a mobile impurity B. The model presented makes it possible to investigate the initial stage of homogeneous formation of complexes and to reveal their influence on the kinetics of redistribution of the diffusing elements.

  1. The evolution of galaxies at constant number density: a less biased view of star formation, quenching, and structural formation

    NASA Astrophysics Data System (ADS)

    Ownsworth, Jamie R.; Conselice, Christopher J.; Mundy, Carl J.; Mortlock, Alice; Hartley, William G.; Duncan, Kenneth; Almaini, Omar

    2016-09-01

    Due to significant galaxy contamination and impurity in stellar mass selected samples (up to 95 per cent from z = 0-3), we examine the star formation history, quenching time-scales, and structural evolution of galaxies using a constant number density selection with data from the United Kingdom Infra-Red Deep Sky Survey Ultra-Deep Survey field. Using this methodology, we investigate the evolution of galaxies at a variety of number densities from z = 0-3. We find that samples chosen at number densities ranging from 3 × 10-4 to 10-5 galaxies Mpc-3 (corresponding to z ˜ 0.5 stellar masses of M* = 1010.95-11.6 M0) have a star-forming blue fraction of ˜50 per cent at z ˜ 2.5, which evolves to a nearly 100 per cent quenched red and dead population by z ˜ 1. We also see evidence for number density downsizing, such that the galaxies selected at the lowest densities (highest masses) become a homogeneous red population before those at higher number densities. Examining the evolution of the colours for these systems furthermore shows that the formation redshift of galaxies selected at these number densities is zform > 3. The structural evolution through size and Sérsic index fits reveal that while there remains evolution in terms of galaxies becoming larger and more concentrated in stellar mass at lower redshifts, the magnitude of the change is significantly smaller than for a mass-selected sample. We also find that changes in size and structure continues at z < 1, and is coupled strongly to passivity evolution. We conclude that galaxy structure is driving the quenching of galaxies, such that galaxies become concentrated before they become passive.

  2. Measurements of the complex dielectric constant of sand and dust particles at 11 GHz

    NASA Astrophysics Data System (ADS)

    Al-Rizzo, Hussain M.; Al-Hafid, Hafid T.

    1988-03-01

    Measurements are reported of the refractive index (Delta-n) and loss tangent (tan delta) of dust particles in a laboratory-simulated model of dust storms, carried out at 11 GHz utilizing a confocal microwave open-cavity resonator. Four samples were used namely, sandy, silty, clayey silt, and clayey, for concentrations varying from 10-4 to 4 x 10-3 g/cu cm. The particle-size distribution (PSD) of each sample was measured by seiving along with the hydrometer technique. Dielectric-constant measurements were also conducted at bulk concentrations using the standing-wave technique for the dry samples and as a function of volumetric moisture content for up to 0.5 cu cm/cu cm. The complex dielectric constant of the dust particle material was evaluated by two approaches. In one the data for permittivities obtained over the whole range of measured concentrations were extrapolated to the particle densities of the samples. In the other a mixing formula was utilized for the determination of epsilon(s) from permittivities measured at bulk concentrations.

  3. Spectrophotometric study of complex formation between oxovanadium (IV) and antiamebic drugs.

    PubMed

    Abu-Eittah, R; El-Nasr, M S

    1976-09-01

    Complex formation between oxovanadium(IV) and the antiamebic drugs 5, 7-dibromo-8-quinolinol and 5, 7-dichloro-8-quinolinol was studied in the pH 1.5-2.0 range, using ethanol, dioxane-water, and dimethylformamide as solvents. The composition of the formed complexes was determined by more than one procedure. In ethanol and dioxane-water, the 1:1 and 1:2 complexes were formed; in dimethylformamide, the 1:1, 1:2 and 1:3 complexes were formed. The stability constants were computed using two procedures: the molar ratio method and the extrapolation method. The reproducibility or results in satisfactory. PMID:966156

  4. FAST TRACK COMMUNICATION: SUSY transformations with complex factorization constants: application to spectral singularities

    NASA Astrophysics Data System (ADS)

    Samsonov, Boris F.

    2010-10-01

    Supersymmetric (SUSY) transformation operators with complex factorization constants are analyzed as operators acting in the Hilbert space of functions square integrable on the positive semiaxis. The obtained results are applied to Hamiltonians possessing spectral singularities which are non-Hermitian SUSY partners of self-adjoint operators. A new regularization procedure for the resolution of the identity operator in terms of a continuous biorthonormal set of the non-Hermitian Hamiltonian eigenfunctions is proposed. It is also argued that if the binorm of continuous spectrum eigenfunctions is interpreted in the same way as the norm of similar functions in the usual Hermitian case, then one can state that the function corresponding to a spectral singularity has zero binorm.

  5. The shock-induced star formation sequence resulting from a constant spiral pattern speed

    SciTech Connect

    Martínez-García, Eric E.; Puerari, Ivânio E-mail: puerari@inaoep.mx

    2014-08-01

    We utilize a suite of multiwavelength data of nine nearby spirals to analyze the shock-induced star formation sequence that may result from a constant spiral pattern speed. The sequence involves tracers as the H I, CO 24 μm, and FUV, where the spiral arms were analyzed with Fourier techniques in order to obtain their azimuthal phases as a function of radius. It was found that only two of the objects, NGC 628 and NGC 5194, present coherent phases resembling the theoretical expectations, as indicated by the phase shifts of CO- 24 μm. The evidence is more clear for NGC 5194 and moderate for NGC 628. It was also found that the phase shifts are different for the two spiral arms. With the exception on NGC 3627, a two-dimensional Fourier analysis showed that the rest of the objects do not exhibit bi-symmetric spiral structures of stellar mass, i.e., grand-design spirals. A phase order inversion indicates a corotation radius of ∼89'' for NGC 628 and ∼202'' for NGC 5194. For these two objects, the CO-Hα phase shifts corroborate the CO-24 μm azimuthal offsets. Also for NGC 5194, the CO-70 μm, CO-140 μm, and CO-250 μm phase shifts indicate a corotation region.

  6. Polarographic determination of lead hydroxide formation constants at low ionic strength

    USGS Publications Warehouse

    Lind, Carol J.

    1978-01-01

    Values of formation constants for lead hydroxide at 25 ??C were calculated from normal pulse polarographic measurements of 10-6 M lead in 0.01 M sodium perchlorate. The low concentrations simulate those found in many freshwaters, permitting direct application of the values when considering distributions of lead species. The precise evaluation of species distribution in waters at other ionic strengths requires activity coefficient corrections. As opposed to much of the previously published work done at high ionic strength, the values reported here were obtained at low ionic strength, permitting use of smaller and better defined activity coefficient corrections. These values were further confirmed by differential-pulse polarography and differential-pulse anodic stripping voltammetry data. The logs of the values for ??1??? ??2???, and ??3??? were calculated to be 6.59, 10.80, and 13.63, respectively. When corrected to zero ionic strength these values were calculated to be 6.77, 11.07, and 13.89, respectively.

  7. Dielectric constant enhancement of epoxy thermosets via formation of polyelectrolyte nanophases.

    PubMed

    Cong, Houluo; Li, Jingang; Li, Lei; Zheng, Sixun

    2014-12-18

    Poly(ethylene oxide)-block-poly(sodium p-styrenesulfonate) (PEO-b-PSSNa) diblock copolymer was synthesized and then incorporated into epoxy to obtain the nanostructured epoxy thermosets containing polyelectrolyte nanophases. This PEO-b-PSSNa diblock copolymer was synthesized via the radical polymerization of p-styrenesulfonate mediated with 4-cyano-4-(thiobenzoylthio)valeric ester-terminated poly(ethylene oxide). The formation of polyelectrolyte (i.e., PSSNa) nanophases in epoxy followed a self-assembly mechanism. The precursors of epoxy acted as the selective solvent of the diblock copolymer, and thus, the self-assembled nanostructures were formed. The self-organized nanophases were fixed through the subsequent curing reaction. By means of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), the morphologies of the nanostructured epoxy thermosets containing PSSNa nanophases were investigated. In the glassy state, the epoxy matrixes were significantly reinforced by the spherical PSSNa nanodomains, as evidenced by dynamic mechanical analysis. The measurement of dielectric properties showed that, with the incorporation of PSSNa nanophases, the dielectric constants of the epoxy thermoset were significantly increased. Compared to the control epoxy, the dielectric loss of the nanostructured thermosets still remained at quite a low level, although the values of dielectric loss were slightly increased with inclusion of PSSNa nanophases. PMID:25482332

  8. Complexation of Arsenite with Dissolved Organic Matter: Conditional Distribution Coefficients and Apparent Stability Constants

    PubMed Central

    Liu, Guangliang; Cai, Yong

    2010-01-01

    The complexation of arsenic (As) with dissolved organic matter (DOM), although playing an important role in regulating As mobility and transformation, is poorly characterized, as evidenced by scarce reporting of fundamental parameters of As-DOM complexes. The complexation of arsenite (AsIII) with Aldrich humic acid (HA) at different pHs was characterized using a recently developed analytical technique to measure both free and DOM-bound As. Conditional distribution coefficient (KD), describing capacity of DOM in binding AsIII from the mass perspective, and apparent stability constant (Ks), describing stability of resulting AsIII-DOM complexes, were calculated to characterize AsIII-DOM complexation. Log KD of AsIII ranged from 3.7 to 2.2 (decreasing with increase of As/DOM ratio) at pH 5.2, from 3.6 to 2.6 at pH 7, and from 4.3 to 3.2 at pH = 9.3, respectively. Two-site ligand binding models can capture the heterogeneity of binding sites and be used to calculate Ks by classifying the binding sites into strong (S1) and weak (S2) groups. Log Ks for S1 sites are 7.0, 6.5, and 5.9 for pH 5.2, 7, and 9.3, respectively, which are approximately 1–2 orders of magnitude higher than for weak S2 sites. The results suggest that AsIII complexation with DOM increases with pH, as evidenced by significant spikes in concentrations of DOM-bound AsIII and in KD values at pH 9.3. In contrary to KD, log Ks decreased with pH, in particular for S1 sites, probably due to the presence of negatively charged H2AsO3− and the involvement of metal-bridged AsIII-DOM complexation at pH 9.3. PMID:20801484

  9. Coordination of lanthanides by two polyamino polycarboxylic macrocycles: formation of highly stable lanthanide complexes

    SciTech Connect

    Loncin, M.F.; Desreux, J.F.; Merciny, E.

    1986-07-16

    The formation constants of a few lanthanide complexes with DOTA (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) and TETA (1,4,8,11-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid) have been measured by potentiometric and competition methods. The ligand DOTA forms the most stable lanthanide chelates known so far (log K/sub ML/ = 28.2-29.2) while the stability of the TETA compounds at 80 /sup 0/C (log K/sub ML/ = 14.5-16.5) is comparable to the stability of the EDTA complexes. A competition method with the oxalate anion as a probe had to be used for determining the formation constants of the DOTA lanthanide chelates because of the high stability of these compounds. The relative stability of the DOTA and TETA complexes in accounted for by steric factors with reference to known solution- and solid-state structures. 20 references, 2 tables.

  10. Formation of β-cyclodextrin complexes in an anhydrous environment.

    PubMed

    Sifaoui, Hocine; Modarressi, Ali; Magri, Pierre; Stachowicz-Kuśnierz, Anna; Korchowiec, Jacek; Rogalski, Marek

    2016-09-01

    The formation of inclusion complexes of β-cyclodextrin was studied at the melting temperature of guest compounds by differential scanning calorimetry. The complexes of long-chain n-alkanes, polyaromatics, and organic acids were investigated by calorimetry and IR spectroscopy. The complexation ratio of β-cyclodextrin was compared with results obtained in an aqueous environment. The stability and structure of inclusion complexes with various stoichiometries were estimated by quantum chemistry and molecular dynamics calculations. Comparison of experimental and theoretical results confirmed the possible formation of multiple inclusion complexes with guest molecules capable of forming hydrogen bonds. This finding gives new insight into the mechanism of formation of host-guest complexes and shows that hydrophobic interactions play a secondary role in this case. Graphical abstract The formation of complexes of β-cyclodextrin with selected n-alkanes, polyaromatics, and organic acids in an anhydrous environment is studied by differential scanning calorimetry, IR spectroscopy, and molecular modeling. The results obtained confirm the possible formation of multiple inclusion complexes with guest molecules capable of forming hydrogen bonds and give a new perspective on the mechanism of formation of host-guest complexes. PMID:27518085

  11. Studies of formation of bivalent copper complexes with native and denatured DNA.

    PubMed

    Sorokin, V A; Blagoi, Y P; Valeev, V A; Kornilova, S V; Gladchenko, G O; Reva, I D; Sokhan, V I

    1987-06-01

    The formation of Cu2+ complexes with native and denatured DNA is studied by the methods of differential UV spectroscopy, CD spectroscopy, and viscometry. On ion binding to the bases of native DNA the latter transforms into a new conformation. This transition is accompanied with a sharp increase in UV absorption and a decrease in the intrinsic viscosity though the high degree of helicity persists. Possible sites of Cu2+ ion binding on DNA of various conformations are found along with corresponding constants of complex formation. PMID:3598574

  12. Thermodynamic functions of formation of n-alkane complexes with crystalline urea

    SciTech Connect

    Tolmachev, V.V.; Semenov, L.V.; Gaile, A.A.; Proskuryakov, V.A.

    1987-07-10

    For optimization of the conditions of deparaffination of petroleum fractions with the aid of urea, with the composition of the feedstock taken into account, it is important to know the equilibrium constants of formation of complexes of urea with n-alkanes differing in the number of carbon atoms in their molecules, as functions of temperature. In this investigation they obtained experimental data necessary for calculating the thermodynamic functions of formation of n-alkane complexes with crystalline urea up to the decomposition temperature, using Kirchhoff's equations.

  13. Multiparametric curve fitting-XI: POLET computer program for estimation of formation constants and stoichiometric indices from normalized potentiometric data.

    PubMed

    Havel, J; Meloun, M

    1986-06-01

    The FORTRAN computer program POLET(84) analyses a set of normalized potentiometric titration curves to find a chemical model, i.e., the number of species present and their stoichiometry, and to determine the corresponding stability constants log beta(pqrs) and unknown stoichiometric indices p, q, r, and s of up to quaternary M(p)L(q)Y(r)H(s) complexes. The program belongs to the ABLET family, based on the LETAG subroutine, and can use an algorithmic and/or heuristic minimization strategy, or a beneficial combination of both. The data, a set of potentiometric titration curves plotted as volume and potential, are converted into normalized variables (formation function, pH) and then a computer-assisted search for a chemical model by POLET(84) is applied. The procedure for efficient application of POLET(84) in an equilibrium analysis is described and the program is validated by use of literature and simulated data. The reliability of the chemical model and its parameters is established by the degree-of-fit achieved, and the closeness of the stoichiometric indices to integral values. PMID:18964133

  14. Determination of the complexation constants of Pb(II) and Cd(II) with thymol blue using spectrophotometry, SQUAD and the HSAB principle

    NASA Astrophysics Data System (ADS)

    Balderas-Hernández, P.; Rojas-Hernández, A.; Galván, M.; Romo, M. Romero; Palomar-Pardavé, M.; Ramírez-Silva, M. T.

    2007-01-01

    This paper presents the results concerning the determination of the formation constants of the complexes between thymol blue, TB, and the metal ions Pb(II) or Cd(II). The experimental procedure was carried out in the presence of a nitrogen atmosphere at 25 °C. The spectrophotometry data obtained were processed through the software SQUAD to calculate the complexation constants of the metal-indicator and to establish an adequate base of the models which considered the structure of the indicator, and the actual metal species in the aqueous solutions. For the Pb(II)-TB-H 2O system the log K value calculated for the PbTB complex was 5.591 ± 0.057 while for the Cd(II)-TB-H 2O system, the log K value of the CdTB complex was 5.099 ± 0.008. Also, supporting theoretical chemistry results on the chemical hardness of TB molecule were performed to enable establishment of a relative prediction scale of the TB complexation constants ranking in the framework of the Principle of Hard and Soft Acids and Bases or HSAB Principle.

  15. Determination of the complexation constants of Pb(II) and Cd(II) with thymol blue using spectrophotometry, SQUAD and the HSAB principle.

    PubMed

    Balderas-Hernández, P; Rojas-Hernández, A; Galván, M; Romo, M Romero; Palomar-Pardavé, M; Ramírez-Silva, M T

    2007-01-01

    This paper presents the results concerning the determination of the formation constants of the complexes between thymol blue, TB, and the metal ions Pb(II) or Cd(II). The experimental procedure was carried out in the presence of a nitrogen atmosphere at 25 degrees C. The spectrophotometry data obtained were processed through the software SQUAD to calculate the complexation constants of the metal-indicator and to establish an adequate base of the models which considered the structure of the indicator, and the actual metal species in the aqueous solutions. For the Pb(II)-TB-H2O system the logK value calculated for the PbTB complex was 5.591+/-0.057 while for the Cd(II)-TB-H2O system, the logK value of the CdTB complex was 5.099+/-0.008. Also, supporting theoretical chemistry results on the chemical hardness of TB molecule were performed to enable establishment of a relative prediction scale of the TB complexation constants ranking in the framework of the Principle of Hard and Soft Acids and Bases or HSAB Principle. PMID:16829173

  16. Complex formation of alkaline-earth cations with crown ethers and cryptands in methanol solutions

    SciTech Connect

    Buschman, H.J.

    1986-06-01

    The complexation of alkaline-earth cations by different crown ethers, azacrown ethers, and cryptands has been studied in methanol solutions by means of calorimetric and potentiometric titrations. The smallest monocyclic ligands examined from 2:1 complexes (ratio of ligand to cation) with cations which are too large to fit into the ligand cavity. With the smallest cryptand, only Sr/sup 2 +/ and Ba/sup 2 +/ ions are able to form exclusive complexes. In the case of the reaction of cryptand (211) with Ca/sup 2 +/, a separate estimation of stability constants for the formation of exclusive and inclusive complexes was possible for the first time. Higher values for stability constants are found for the reaction of alkaline-earth cations with cryptands compared to the reaction with alkali ions. This increase is only caused by favorable entropic contributions.

  17. Bow shock formation in a complex plasma.

    PubMed

    Saitou, Y; Nakamura, Y; Kamimura, T; Ishihara, O

    2012-02-10

    A bow shock is observed in a two-dimensional supersonic flow of charged microparticles in a complex plasma. A thin conducting needle is used to make a potential barrier as an obstacle for the particle flow in the complex plasma. The flow is generated and the flow velocity is controlled by changing a tilt angle of the device under the gravitational force. A void, microparticle-free region, is formed around the potential barrier surrounding the obstacle. The flow is bent around the leading edge of the void and forms an arcuate structure when the flow is supersonic. The structure is characterized by the bow shock as confirmed by a polytropic hydrodynamic theory as well as numerical simulation. PMID:22401079

  18. Formation, structure, and reactivity of palladium superoxo complexes

    SciTech Connect

    Talsi, E.P.; Babenko, V.P.; Shubin, A.A.; Chinakov, V.D.; Nekipelov, V.M.; Zamaraev, K.I.

    1987-11-18

    The mechanism of formation of palladium superoxo complexes, their structure, and their reactivity are discussed. The formation of the palladium superoxo complexes in the reaction of palladium(II) acetate, propionate, trifluororacetate, and bis(acetylacetonate) and palladium(0) tetrakis(triphenylphosphine) with hydrogen peroxide and potassium superoxide has been detected in solution by electron proton resonance. The oxidation of olefins and carbon monoxide by these complexes is considered. Reaction mechanisms and reaction kinetics for these oxidations are reported using the palladium superoxo complexes. 44 references, 8 figures, 2 tables.

  19. Lead(II) complex formation with glutathione.

    PubMed

    Mah, Vicky; Jalilehvand, Farideh

    2012-06-01

    A structural investigation of complexes formed between the Pb(2+) ion and glutathione (GSH, denoted AH(3) in its triprotonated form), the most abundant nonprotein thiol in biological systems, was carried out for a series of aqueous solutions at pH 8.5 and C(Pb(2+)) = 10 mM and in the solid state. The Pb L(III)-edge extended X-ray absorption fine structure (EXAFS) oscillation for a solid compound with the empirical formula [Pb(AH(2))]ClO(4) was modeled with one Pb-S and two short Pb-O bond distances at 2.64 ± 0.04 and 2.28 ± 0.04 Å, respectively. In addition, Pb···Pb interactions at 4.15 ± 0.05 Å indicate dimeric species in a network where the thiolate group forms an asymmetrical bridge between two Pb(2+) ions. In aqueous solution at the mole ratio GSH/Pb(II) = 2.0 (C(Pb(2+)) = 10 mM, pH 8.5), lead(II) complexes with two thiolate ligands form, characterized by a ligand-to-metal charge-transfer band (LMCT) S(-) → Pb(2+) at 317 nm in the UV-vis spectrum and mean Pb-S and Pb-(N/O) bond distances of 2.65 ± 0.04 and 2.51 ± 0.04 Å, respectively, from a Pb L(III)-edge EXAFS spectrum. For solutions with higher mole ratios, GSH/Pb(II) ≥ 3.0, electrospray ionization mass spectroscopy spectra identified a triglutathionyllead(II) complex, for which Pb L(III)-edge EXAFS spectroscopy shows a mean Pb-S distance of 2.65 ± 0.04 Å in PbS(3) coordination, (207)Pb NMR spectroscopy displays a chemical shift of 2793 ppm, and in the UV-vis spectrum, an S(-) → Pb(2+) LMCT band appears at 335 nm. The complex persists at high excess of GSH and also at ∼25 K in frozen glycerol (33%)/water glasses for GSH/Pb(II) mole ratios from 4.0 to 10 (C(Pb(2+)) = 10 mM) measured by Pb L(III)-edge EXAFS spectroscopy. PMID:22594853

  20. Direct computer simulation of ferredoxin and FNR complex formation in solution

    NASA Astrophysics Data System (ADS)

    Kovalenko, I. B.; Diakonova, A. N.; Abaturova, A. M.; Riznichenko, G. Yu; Rubin, A. B.

    2010-06-01

    Ferredoxin reduced by Photosystem I in light serves as an electron donor for the reduction of NADP+ to NADPH, and this reaction is catalyzed by enzyme ferredoxin:NADP+-reductase (FNR). Kinetics and mechanisms of this reaction have been extensively studied experimentally by site-specific mutagenesis, laser flash photolysis and stopped-flow methods. We have applied a method of multiparticle computer simulation to study the effects of electrostatic interactions upon the reaction rate of Fd-FNR complex formation. Using the model we calculated rate constants of Fd-FNR complex formation for the wild-type proteins and some mutant forms of FNR at different values of ionic strength. Simulation revealed that electrostatic interactions play an important role in Fd-FNR complex formation and define its specificity.

  1. Direct computer simulation of ferredoxin and FNR complex formation in solution.

    PubMed

    Kovalenko, I B; Diakonova, A N; Abaturova, A M; Riznichenko, G Yu; Rubin, A B

    2010-01-01

    Ferredoxin reduced by Photosystem I in light serves as an electron donor for the reduction of NADP(+) to NADPH, and this reaction is catalyzed by enzyme ferredoxin:NADP(+)-reductase (FNR). Kinetics and mechanisms of this reaction have been extensively studied experimentally by site-specific mutagenesis, laser flash photolysis and stopped-flow methods. We have applied a method of multiparticle computer simulation to study the effects of electrostatic interactions upon the reaction rate of Fd-FNR complex formation. Using the model we calculated rate constants of Fd-FNR complex formation for the wild-type proteins and some mutant forms of FNR at different values of ionic strength. Simulation revealed that electrostatic interactions play an important role in Fd-FNR complex formation and define its specificity. PMID:20453296

  2. Formation of a Bridging Phosphinidene Thorium Complex.

    PubMed

    Behrle, Andrew C; Castro, Ludovic; Maron, Laurent; Walensky, Justin R

    2015-12-01

    The synthesis and structural determination of the first thorium phosphinidene complex are reported. The reaction of 2 equiv of (C5Me5)2Th(CH3)2 with H2P(2,4,6-(i)Pr3C6H2) at 95 °C produces [(C5Me5)2Th]2(μ2-P[(2,6-CH2CHCH3)2-4-(i)PrC6H2] as well as 4 equiv of methane, 2 equiv from deprotonation of the phosphine and 2 equiv from C-H bond activation of one methyl group of each of the isopropyl groups at the 2- and 6-positions. Transition state calculations indicate that the steps in the mechanism are P-H, C-H, C-H, and then P-H bond activation to form the phosphinidene. PMID:26575219

  3. Direct electronic probing of biological complexes formation

    NASA Astrophysics Data System (ADS)

    Macchia, Eleonora; Magliulo, Maria; Manoli, Kyriaki; Giordano, Francesco; Palazzo, Gerardo; Torsi, Luisa

    2014-10-01

    Functional bio-interlayer organic field - effect transistors (FBI-OFET), embedding streptavidin, avidin and neutravidin as bio-recognition element, have been studied to probe the electronic properties of protein complexes. The threshold voltage control has been achieved modifying the SiO2 gate diaelectric surface by means of the deposition of an interlayer of bio-recognition elements. A threshold voltage shift with respect to the unmodified dielectric surface toward more negative potential values has been found for the three different proteins, in agreement with their isoelectric points. The relative responses in terms of source - drain current, mobility and threshold voltage upon exposure to biotin of the FBI-OFET devices have been compared for the three bio-recognition elements.

  4. Estimated rate constants for hydrogen abstraction from N-heterocyclic carbene-borane complexes by an alkyl radical.

    PubMed

    Solovyev, Andrey; Ueng, Shau-Hua; Monot, Julien; Fensterbank, Louis; Malacria, Max; Lacôte, Emmanuel; Curran, Dennis P

    2010-07-01

    Rate constants for hydrogen abstraction by a nonyl radical from 20 complexes of N-heterocyclic carbenes and boranes (NHC-boranes) have been determined by the pyridine-2-thioneoxycarbonyl (PTOC) competition kinetic method at a single concentration point. The rate constants range from <1 x 10(4) to 8 x 10(4) M(-1) s(-1). They show little dependence on the electronic properties of the carbene core, but there is a trend for increasing rate constants with decreasing size of the carbene N-substituents. Two promising new reagents with small N-substituents (R = Me) have been identified. PMID:20536158

  5. A bilogarithmic method for the spectrophotometric evaluation of stability constants of 1:1 weak complexes from mole ratio data.

    PubMed

    Boccio, Maravillas; Sayago, Ana; Asuero, Agustín G

    2006-08-01

    The absorbance changes that occur when the mole ratio of the components of ligand complex equilibria is varied while the concentration of one component is kept constant (mole ratio method) allow evaluating stability constants in favourable conditions. Values of the corresponding stability (association) constants are normally assigned on the basis of spectrophotometric analysis. Determination of stability constants can be performed by a number of linear procedures, but most of these, suffer from theoretical and practical drawbacks, e.g., linear transformation of the rectangular hyperbola type of binding constants, is valid only when one of the two species is present in a large excess. A rigorous treatment of the experimental mole ratio data for 1:1 weak complexes is carried out in this paper with the aim of eliminating some of the assumptions involved in the other methods usually applied for evaluating stability constants. Orthogonal regression is required in order to take into account the error in both axes. The method has been applied to literature data for the iron(III)-thiocyanate and nickel(II)-selenocyanate systems, as well as to a number of host-guest cyclodextrin complexes. PMID:16647826

  6. Complex formation of Am(III) and Am(IV) with phosphate ions in acetonitrile solutions

    SciTech Connect

    Perevalov, S.A.; Lebedev, I.A.; Myasoedov, B.F.

    1988-05-01

    The first dissociation constant of H/sub 3/PO/sub 4/ in acetonitrile solution (K/sub 1//sup 0/ = 1.75/centered dot/10/sup /minus/13/) and the constant of formation of H(H/sub 2/PO/sub 4/)/sub 2//sup /minus// dimers (K/sub d//sup 0/ = 8/centered dot/10/sup 2/) were determined by the method of pH-potentiometry. The complex formation of Am(III) in acetonitrile solutions containing 0.05-2.0 M H/sub 3/PO/sub 4/ was investigated by a spectrophotometric method; the stability constants of the complexes AmH/sub 2/PO/sub 4//sup 2+/ (/beta//sub 1//sup III/ = 1.0/centered dot/10/sup 12/) and Am(H/sub 2/PO/sub 4/)/sub 2//sup +/ (/beta//sub 2//sup III/ = 4.3/centered dot/10/sup 24/) were determined. The formal potentials of the couple Am/sup (IV)//Am/sup (III)/ in 0.3-1.9 M solutions of H/sub 3/PO/sub 4/ in acetonitrile were measured, and the stability constant of the phosphate complex of tetravalent americium Am(H/sub 2/PO/sub 4/)/sub 3//sup +/ (/beta//sub 3//sup IV/ = 2.5/centered dot/10/sup 46/) was calculated according to the value of the shift of the potential relative to the standard.

  7. Determination of Equilibrium Constants of Some Novel Antioxidant Compounds and Study on their Complexes with Some Divalent Metal ions in Ethanol-water Mixed.

    PubMed

    Atabey, Hasan; Findik, Esra; Sari, Hayati; Ceylan, Mustafa

    2012-12-01

    This study aims to investigate the nature and type of complexes formed in solution, between novel antioxidant compounds [P1(4-(1-(3-hydroxy-4-methoxyphenyl)propyl)benzene-1,2-diol) and P2(4-(1-(3-hydroxy-4-methoxyphenyl)propyl)benzene-1,3-diol)] and the ions Cu2+, Ni2+, Zn2+ and Co2+. Potentiometric titration technique was used to follow the formation of complexes during the course of coordination. The stability of the complexes formed was controlled through the determination of stability constants in aqueous ethanol solution at 25 ± 0.1 C° and ionic strength of 0.1 M NaCl. Basicity of the ligand was also assessed by the determination of the dissociation constants of the ligand. All the constants were computed by computer refinement of pH-volume data using the SUPERQUAD program. The species distribution diagram of each type of complex has been obtained after computer calculation process. PMID:24061367

  8. Dynamics of Lane Formation in Driven Binary Complex Plasmas

    SciTech Connect

    Suetterlin, K. R.; Ivlev, A. V.; Raeth, C.; Thomas, H. M.; Rubin-Zuzic, M.; Morfill, G. E.; Wysocki, A.; Loewen, H.; Goedheer, W. J.; Fortov, V. E.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F.

    2009-02-27

    The dynamical onset of lane formation is studied in experiments with binary complex plasmas under microgravity conditions. Small microparticles are driven and penetrate into a cloud of big particles, revealing a strong tendency towards lane formation. The observed time-resolved lane-formation process is in good agreement with computer simulations of a binary Yukawa model with Langevin dynamics. The laning is quantified in terms of the anisotropic scaling index, leading to a universal order parameter for driven systems.

  9. Complex formation between neptunium(V) and various thiosemicarbazide derivatives in aqueous solution

    SciTech Connect

    Chuguryan, D.G.; Dzyubenko, V.I.; Gerbeleu, N.V.

    1987-01-01

    Complex formation between neptunium(V) and various thiosemicarbazide derivatives in solution has been studied spectrophotometrically in the pH range 4-10. Stepwise formation of three types of complexes, with composition NpO/sub 2/HA, NpO/sub 2/A/sup -/, and NpOHA/sup 2 -/, has been demonstrated with salicylaldehyde thiosemicarbazone (H/sub 2/L) and salicylaldehyde S-methyl-isothiosemicarbazone (H/sub 2/Q) at t = 25 +/- 1/sup 0/C and ..mu.. = 0.05. The logarithmic stability constants of the first two complexes are 5.14 +/- 0.06, 11.85 +/- 0.04 and 8.42 +/- 0.09, 13.33 +/- 0.015 for H/sub 2/L and H/sub 2/Q, respectively; equilibrium constants for the formation of hydroxo complexes of the form NpO/sub 2/OHL/sup 2 -/ and NpO/sub 2/OHQ/sup 2 -/ were also determined, and found to be equal to (2.23 +/-0.37) x 10/sup -5/ and (5.02 +/- 0.9) x 10/sup -5/, respectively. In the case of S-methyl-N/sub 1/,N/sub 4/-bis(salicylidene)isothiosemicarbazide (H/sub 2/Z), only one type of complex is formed under these experimental conditions, namely, NpO/sub 2/Z/sup -/, with a logarithmic stability constant of 4.78 +/- 0.03. Dissociation constants for H/sub 2/Q and H/sub 2/Z were also determined.

  10. Complex molecule formation around massive young stellar objects

    NASA Astrophysics Data System (ADS)

    Öberg, Karin I.; Fayolle, Edith C.; Reiter, John B.; Cyganowski, Claudia

    2014-02-01

    Interstellar complex organic molecules were first identified in the hot inner regions of massive young stellar objects (MYSOs), but have more recently been found in many colder sources, indicating that complex molecules can form at a range of temperatures. However, individually these observations provide limited constraints on how complex molecules form, and whether the same formation pathways dominate in cold, warm and hot environments. To address these questions, we use spatially resolved observations from the Submillimeter Array of three MYSOs together with mostly unresolved literature data to explore how molecular ratios depend on environmental parameters, especially temperature. Towards the three MYSOs, we find multiple complex organic emission peaks characterized by different molecular compositions and temperatures. In particular, CH3CCH and CH3CN seem to always trace a lukewarm (T ≈ 60 K) and a hot (T > 100 K) complex chemistry, respectively. These spatial trends are consistent with abundance-temperature correlations of four representative complex organics - CH3CCH, CH3CN, CH3OCH3 and CH3CHO - in a large sample of complex molecule hosts mined from the literature. Together, these results indicate a general chemical evolution with temperature, i.e. that new complex molecule formation pathways are activated as a MYSO heats up. This is qualitatively consistent with model predictions. Furthermore, these results suggest that ratios of complex molecules may be developed into a powerful probe of the evolutionary stage of a MYSO, and may provide information about its formation history.

  11. Complex molecule formation around massive young stellar objects.

    PubMed

    Oberg, Karin I; Fayolle, Edith C; Reiter, John B; Cyganowski, Claudia

    2014-01-01

    Interstellar complex organic molecules were first identified in the hot inner regions of massive young stellar objects (MYSOs), but have more recently been found in many colder sources, indicating that complex molecules can form at a range of temperatures. However, individually these observations provide limited constraints on how complex molecules form, and whether the same formation pathways dominate in cold, warm and hot environments. To address these questions, we use spatially resolved observations from the Submillimeter Array of three MYSOs together with mostly unresolved literature data to explore how molecular ratios depend on environmental parameters, especially temperature. Towards the three MYSOs, we find multiple complex organic emission peaks characterized by different molecular compositions and temperatures. In particular, CH3CCH and CH3CN seem to always trace a lukewarm (T = 60 K) and a hot (T > 100 K) complex chemistry, respectively. These spatial trends are consistent with abundance-temperature correlations of four representative complex organics--CH3CCH, CH3CN, CH3OCH3 and CH3CHO--in a large sample of complex molecule hosts mined from the literature. Together, these results indicate a general chemical evolution with temperature, i.e. that new complex molecule formation pathways are activated as a MYSO heats up. This is qualitatively consistent with model predictions. Furthermore, these results suggest that ratios of complex molecules may be developed into a powerful probe of the evolutionary stage of a MYSO, and may provide information about its formation history. PMID:25302375

  12. Molecular statics calculations of proton binding to goethite surfaces: A new approach to estimation of stability constants for multisite surface complexation models

    NASA Astrophysics Data System (ADS)

    Rustad, James R.; Felmy, Andrew R.; Hay, Benjamin P.

    1996-05-01

    A new approach to estimating stability constants for proton binding in multisite surface complexation models is presented. The method is based on molecular statics computation of energies for the formation of proton vacancies and interstitials in ideal periodic slabs representing the (100), (110), (010), (001), and (021) surfaces of goethite. Gas-phase energies of clusters representing the hydrolysis products of ferric iron are calculated using the same potential energy functions used for the surface. These energies are linearly related to the hydrolysis constants for ferric iron in aqueous solution. Stability constants for proton binding at goethite surfaces are estimated by assuming the same log K- Δ E relationship for goethite surface protonation reactions. These stability constants predict a pH of zero charge of 8.9, in adequate agreement with measurements on CO 2-free goethite. The estimated stability constants differ significantly from previous estimations based on Pauling bond strength. We find that nearly all the surface oxide ions are reactive; nineteen of the twenty-six surface sites investigated have log Kint between 7.7 and 9.4. This implies a site density between fifteen and sixteen reactive sites/nm for crystals dominated by (110) and (021) crystal faces.

  13. Molecular statics calculations of proton binding to goethite surfaces: A new approach to estimation of stability constants for multisite surface complexation models

    SciTech Connect

    Rustad, J.R.; Felmy, A.R.; Hay, B.P.

    1996-05-01

    A new approach to estimating stability constants for proton binding in multisite surface complexation models is presented. The method is based on molecular statics computation of energies for the formation of proton vacancies and interstitials in ideal periodic slabs representing the (100), (110), (010), (001), and (021) surfaces of goethite. Gas-phase energies of clusters representing the hydrolysis products of ferric iron are calculated using the same potential energy functions used for the surface. These energies are linearly related to the hydrolysis constants for ferric iron in aqueous solution. Stability constants for proton binding at goethite surfaces are estimated by assuming the same log K-{Delta}E relationship for goethite surface protonation reactions. These stability constants predict a pH of zero charge of 8.9, in adequate agreement with measurements on CO{sub 2}-free goethite. The estimated stability constants differ significantly from previous estimations based on Pauling bond strength. We find that nearly all the surface oxide ions are reactive; nineteen of the twenty-six surface sites investigated have log K{sup int} between 7.7 and 9.4. This implies a site density between fifteen and sixteen reactive sites/nm for crystals dominated by (110) and (021) crystal faces. 39 refs., 8 figs., 4 tabs.

  14. A two force-constant model for complexes B⋯M-X (B is a Lewis base and MX is any diatomic molecule): Intermolecular stretching force constants from centrifugal distortion constants DJ or ΔJ

    NASA Astrophysics Data System (ADS)

    Bittner, Dror M.; Walker, Nicholas R.; Legon, Anthony C.

    2016-02-01

    A two force-constant model is proposed for complexes of the type B⋯MX, in which B is a simple Lewis base of at least C2v symmetry and MX is any diatomic molecule lying along a Cn axis (n ≥ 2) of B. The model assumes a rigid subunit B and that force constants beyond quadratic are negligible. It leads to expressions that allow, in principle, the determination of three quadratic force constants F11, F12, and F22 associated with the r(B⋯M) = r2 and r(M-X) = r1 internal coordinates from the equilibrium centrifugal distortion constants DJ e or ΔJ e , the equilibrium principal axis coordinates a1 and a2, and equilibrium principal moments of inertia. The model can be applied generally to complexes containing different types of intermolecular bond. For example, the intermolecular bond of B⋯MX can be a hydrogen bond if MX is a hydrogen halide, a halogen-bond if MX is a dihalogen molecule, or a stronger, coinage-metal bond if MX is a coinage metal halide. The equations were tested for BrCN, for which accurate equilibrium spectroscopic constants and a complete force field are available. In practice, equilibrium values of DJ e or ΔJ e for B⋯MX are not available and zero-point quantities must be used instead. The effect of doing so has been tested for BrCN. The zero-point centrifugal distortion constants DJ 0 or ΔJ 0 for all B⋯MX investigated so far are of insufficient accuracy to allow F11 and F22 to be determined simultaneously, even under the assumption F12 = 0 which is shown to be reasonable for BrCN. The calculation of F22 at a series of fixed values of F11 reveals, however, that in cases for which F11 is sufficiently larger than F22, a good approximation to F22 is obtained. Plots of F22 versus F11 have been provided for Kr⋯CuCl, Xe⋯CuCl, OC⋯CuCl, and C2H2⋯AgCl as examples. Even in cases where F22 ˜ F11 (e.g., OC⋯CuCl), such plots will yield either F22 or F11 if the other becomes available.

  15. A two force-constant model for complexes B⋯M-X (B is a Lewis base and MX is any diatomic molecule): Intermolecular stretching force constants from centrifugal distortion constants D(J) or Δ(J).

    PubMed

    Bittner, Dror M; Walker, Nicholas R; Legon, Anthony C

    2016-02-21

    A two force-constant model is proposed for complexes of the type B⋯MX, in which B is a simple Lewis base of at least C2v symmetry and MX is any diatomic molecule lying along a Cn axis (n ≥ 2) of B. The model assumes a rigid subunit B and that force constants beyond quadratic are negligible. It leads to expressions that allow, in principle, the determination of three quadratic force constants F11, F12, and F22 associated with the r(B⋯M) = r2 and r(M-X) = r1 internal coordinates from the equilibrium centrifugal distortion constants DJ (e) or ΔJ (e), the equilibrium principal axis coordinates a1 and a2, and equilibrium principal moments of inertia. The model can be applied generally to complexes containing different types of intermolecular bond. For example, the intermolecular bond of B⋯MX can be a hydrogen bond if MX is a hydrogen halide, a halogen-bond if MX is a dihalogen molecule, or a stronger, coinage-metal bond if MX is a coinage metal halide. The equations were tested for BrCN, for which accurate equilibrium spectroscopic constants and a complete force field are available. In practice, equilibrium values of DJ (e) or ΔJ (e) for B⋯MX are not available and zero-point quantities must be used instead. The effect of doing so has been tested for BrCN. The zero-point centrifugal distortion constants DJ (0) or ΔJ (0) for all B⋯MX investigated so far are of insufficient accuracy to allow F11 and F22 to be determined simultaneously, even under the assumption F12 = 0 which is shown to be reasonable for BrCN. The calculation of F22 at a series of fixed values of F11 reveals, however, that in cases for which F11 is sufficiently larger than F22, a good approximation to F22 is obtained. Plots of F22 versus F11 have been provided for Kr⋯CuCl, Xe⋯CuCl, OC⋯CuCl, and C2H2⋯AgCl as examples. Even in cases where F22 ∼ F11 (e.g., OC⋯CuCl), such plots will yield either F22 or F11 if the other becomes available. PMID:26896987

  16. Study of ground state EDA complex formation between [70]fullerene and a series of polynuclear aromatic hydrocarbons

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Sumanta; Nayak, Sandip K.; Chattopadhyay, Subrata; Banerjee, Manas; Mukherjee, Asok K.

    2002-01-01

    [70]fullerene has been shown to form 1:1 EDA complex with anthracene, naphthalene, phenanthrene, pyrene and acenaphthene in CCl 4 medium. Charge transfer (CT) bands have been detected in all the cases. Isosbestic points have been observed in the cases of phenanthrene and acenaphthene complexes. Ionisation potentials of the donors and CT transition energies have been found to correlate in accordance with Mulliken equation and from this correlation the electron affinity of C 70 has been found to be 2.59 eV. Enthalpies and entropies of formation of the complexes have been estimated from the formation constants of the complexes determined spectrophotometrically at three different temperatures.

  17. Rate constant for formation of chlorine nitrate by the reaction ClO + NO2 + M

    NASA Technical Reports Server (NTRS)

    Leu, M. T.; Lin, C. L.; Demore, W. B.

    1977-01-01

    The pseudo-first-order decay of ClO in a large excess of NO2 was monitored in a discharge flow/mass-spectrometer apparatus in order to measure the rate constant of the reaction ClO + NO2 + M yields ClONO2 + M for M = He, Ar, and N2 over the temperature range from 248 to 417 K. Numerical results are given for He at 248, 299, 360, and 417 K (1 to 9 torr); for Ar at 298 K (1 to 4 torr); and for N2 at 299, 360, and 417 K (1 to 6 torr). Systematic errors are estimated, and identification of the reaction product is discussed. The results obtained are shown to be in excellent agreement with other recent measurements of the same rate constant.

  18. Structure of tetracarbonylethyleneosmium: ethylene structure changes upon complex formation.

    PubMed

    Karunatilaka, Chandana; Tackett, Brandon S; Washington, John; Kukolich, Stephen G

    2007-08-29

    Rotational spectra of seven isotopomers of tetracarbonylethyleneosmium, Os(CO)4(eta2-C2H4), were measured in the 4-12 GHz range using a Flygare-Balle-type pulsed-beam Fourier transform microwave spectrometer system. Olefin-transition metal complexes of this type occur extensively in recent organic syntheses and serve as important models for transition states in the metal-mediated transformations of alkenes. Three osmium ((192)Os, (190)Os, and (188)Os) and three unique 13C isotopomers (13C in ethylene, axial, and equatorial positions) were observed in natural abundance. Additional spectra were measured for a perdeuterated sample, Os(CO)4(eta2-C2D4). The measured rotational constants for the main osmium isotopomer ((192)Os) are A = 929.3256(6), B = 755.1707(3), and C = 752.7446(3) MHz, indicating a near-prolate asymmetric top molecule. The approximately 140 assigned b-type transitions were fit using a Watson S-reduced Hamiltonian including A, B, C, and five centrifugal distortion constants. A near-complete r0 gas-phase structure has been determined from a least-squares structural fit using eight adjustable structural parameters to fit the 21 measured rotational constants. Changes in the structure of ethylene on coordination to Os(CO)4 are large and well-determined. For the complex, the experimental ethylene C-C bond length is 1.432(5) A, which falls between the free ethylene value of 1.3391(13) A and the ethane value of 1.534(2) A. The angle between the plane of the CH2 group and the extended ethylene C-C bond ( angleout-of-plane) is 26.0(3) degrees , indicating that this complex is better described as a metallacyclopropane than as a pi-bonded olefin-metal complex. The Os-C-C-H dihedral angle is 106.7(2) degrees , indicating that the ethylene carbon atoms have near sp3 character in the complex. Kraitchman analysis of the available rotational constants gave principal axis coordinates for the carbon and hydrogen atoms in excellent agreement with the least-squares fit

  19. Flexible Acyclic Polyol-Chloride Anion Complexes and Their Characterization by Photoelectron Spectroscopy and Variable Temperature Binding Constant Determinations.

    PubMed

    Shokri, Alireza; Wang, Xue-Bin; Wang, Yanping; O'Doherty, George A; Kass, Steven R

    2016-03-17

    Flexible acyclic alcohols with one to five hydroxyl groups were bound to a chloride anion and these complexes were interrogated by negative ion photoelectron spectroscopy and companion density functional theory computations. The resulting vertical detachment energies are reproduced on average to 0.10 eV by M06-2X/aug-cc-pVTZ predictions and range from 4.45-5.96 eV. These values are 0.84-2.35 eV larger than the adiabatic detachment energy of Cl(-) as a result of the larger hydrogen bond networks in the bigger polyols. Adiabatic detachment energies of the alcohol-Cl(-) clusters are more difficult to determine both experimentally and computationally. This is due to the large geometry changes that occur upon photodetachment and the large bond dissociation energy of H-Cl which enables the resulting chlorine atom to abstract a hydrogen from any of the methylene (CH2) or methine (CH) positions. Both ionic and nonionic hydrogen bonds (i.e., OH···Cl(-) and OH···OH···Cl(-)) form in the larger polyols complexes and are found to be energetically comparable. Subtle structural differences, consequently can lead to the formation of different types of hydrogen bonds, and maximizing the ionic ones is not always preferred. Solution equilibrium binding constants between the alcohols and tetrabutylammonium chloride (TBACl) in acetonitrile at -24.2, +22.0, and +53.6 °C were also determined. The free energies of association are nearly identical for all of the substrates (i.e., ΔG° = -2.8 ± 0.7 kcal mol(-1)). Compensating enthalpy and entropy values reveal, contrary to expectation and the intrinsic gas-phase preferences, that the bigger systems with more hydroxyl groups are entropically favored and enthalpically disfavored relative to the smaller species. This suggests that more solvent molecules are released upon binding TBACl to alcohols with more hydroxyl groups and is consistent with the measured negative heat capacities. These quantities increase with molecular

  20. Contours of constant pseudo-Brewster angle in the complex ? plane and an analytical method for the determination of optical constants.

    PubMed

    Azzam, R M; Ugbo, E E

    1989-12-15

    The locus of all points in the complex plane of the dielectric function ?[?(r) + j?(i) = |?| exp(jtheta)], that represent all possible interfaces characterized by the same pseudo-Brewster angle theta(p)B of minimum p reflectance, is derived in the polar form: |?| = l cos(zeta/3), where l = 2(tan(2)Phi(p)B)k, zeta = arccos(- costheta cos(2)Phi(p)B/k(3)), and k = (1 - 2/3 sin(2)Phi(p)B)(1/2). Families of iso-Phi(p)B contours for (I) 0 degrees 80 degrees ) is the iso-Phi(p)B contour accurately approximated as a circle. We find that |?| < 1 for Phi(p)B < 37.23 degrees , and |?| > 1 for Phi(p)B > 45 degrees . The optical constants n,k (where n + jk = ?((1/2)) is the complex refractive index) are determined from the normal incidence reflectance R(0) and Phi(p)B graphically and analytically. Nomograms that consist of iso-R(0) and iso-Phi(p)B families of contours in the nk plane are presented. Equations that permit the reader to produce his own version of the same nomogram are also given. Valid multiple solutions (n,k) for a given measurement set (R(0),phi(p)B) are possible in the domain of fractional optical constants. An analytical solution of the (R(0),Phi(p)B) ? (n,k) inversion problem is developed that involves an exact (noniterative) solution of a quartic equation in |?|. Finally, a graphic representation is developed for the determination of complex ? from two pseudo-Brewster angles measured in two different media of incidence. PMID:20556031

  1. Does slow energy transfer limit the observed time constant for radical pair formation in photosystem II reaction centers?

    PubMed

    Rech, T; Durrant, J R; Joseph, D M; Barber, J; Porter, G; Klug, D R

    1994-12-13

    We have used spectrally photoselective femtosecond transient absorption spectroscopy on photosystem II reaction centers to show that there are at least two pools of chlorin molecules/states which can transfer excitation energy to P680, the primary electron donor in photosystem II. It has previously been shown that one chlorin pool equilibrates with P680 in 100 fs [Durrant et al. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 11632-11636], and we report here the observation of energy transfer from a second more weakly coupled chlorin pool. The effect of the weakly coupled pool is to increase the apparent time constant for radical pair formation from 21 ps when P680 is selectively excited to 27 ps when the accessory chlorins are excited. We conclude that it is possible to observe both radical pair formation somewhat slowed by an energy transfer step and radical pair formation not limited by this slow energy transfer, depending upon which chromophores are initially excited. These observations provide evidence that when using photoselective excitation of P680, the observed 21 ps time constant for radical pair formation is not limited by a slow energy transfer step. PMID:7993905

  2. Quantitative assessment of complex formation of nuclear-receptor accessory proteins.

    PubMed

    Graumann, K; Jungbauer, A

    2000-02-01

    Like other nuclear receptors, steroid hormone receptors form large protein hetero-complexes in their inactive, ligand-friendly state. Several heat-shock proteins, immunophilins and others have been identified as members of these highly dynamic complexes. The interaction kinetics and dynamics of hsp90, hsp70, p60 (Hop), FKBP52, FKBP51, p48 (Hip) and p23 have been assessed by a biosensor approach measuring the complex formation in real time. A core chaperone complex has been reconstituted from p60, hsp90 and hsp70. p60 forms a molecular bridge between hsp90 and hsp70 with an affinity in the range of 10(5) M(-1). Dynamics of hsp90-p60 complex formation is modulated by ATP through changes in the co-operativity of interaction. At low protein concentrations ATP stabilizes the complex. Binding of p23 to hsp90 did not change the affinity of the hsp90-p60 complex and the stabilizing effect of ATP. Saturation of the p48-hsp70 interaction could not be achieved, suggesting multiple binding sites. A picture of the protein complex, including stoichiometric coefficients, co-operativity of interaction and equilibrium-binding constants, has been formed. PMID:10642522

  3. Sub-THz complex dielectric constants of smectite clay thin samples with Na+/Ca++ ions

    NASA Astrophysics Data System (ADS)

    Rahman, Rezwanur; McCarty, Douglas K.; Prasad, Manika

    2015-09-01

    We implement a technique to characterize the electromagnetic properties at frequencies 100 to 165 GHz (3 cm-1 to 4.95 cm-1) of oriented smectite samples using an open cavity resonator connected to a submillimeter wave VNA (Vector Network Analyzer). We measured dielectric constants perpendicular to the bedding plane on oriented Na+ ion and Ca++ ion stabilized smectite samples deposited on a glass slide at ambient laboratory conditions (room temperature and room light). The clay layer is much thinner (˜30 μm) than the glass substrate (˜2.18 mm). The real part of dielectric constant, ɛre, is essentially constant over this frequency range but is larger in Na+ ion than in Ca++ ion infused clay. The total electrical conductivity (associated with the imaginary part of dielectric constant, ɛim) of both samples increases monotonically at lower frequencies (<110 GHz) but shows rapid increase for Na+ ions in the regime > 110 GHz. The dispersion of the samples display a dependence on the ionic strength in the clay interlayers, i.e., ζ potential in the Stern layers.

  4. Geology of the Biwabik Iron Formation and Duluth Complex.

    PubMed

    Jirsa, Mark A; Miller, James D; Morey, G B

    2008-10-01

    The Biwabik Iron Formation is a approximately 1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by approximately 1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact. PMID:17997209

  5. Geology of the Biwabik Iron Formation and Duluth Complex

    USGS Publications Warehouse

    Jirsa, M.A.; Miller, J.D., Jr.; Morey, G.B.

    2008-01-01

    The Biwabik Iron Formation is a ???1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by ???1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact. ?? 2007 Elsevier Inc. All rights reserved.

  6. Formation of copper complexes in landfill leachate and their toxicity to zebrafish embryos

    SciTech Connect

    Fraser, J.K.; Butler, C.A.; Timperley, M.H.; Evans, C.W.

    2000-05-01

    Toxic metal organic complexes have not been found in natural waters, although some organic acids form bioavailable lipophilic and metabolite-type metal complexes. Landfill leachates usually contain organic acids and in the urban environment these leachates, when mixed with storm waters containing Cu, could be a source of toxic Cu organic complexes in streams and estuaries. The authors investigated the formation of Cu complexes in the leachate from an active urban landfill and found that some of the complexes formed were toxic to zebrafish embryos. High and low nominal molecular weight (NMWT) fractions; >5,000 Da and <700 Da, of leachate both formed Cu complexes with almost identical Cu complexing characteristics but the toxicity was due solely to the low NMWT complexes formed in the <700 Da fraction. Chemical equilibrium modeling with MINTEQA2 and H and Cu complex conditional association constants and ligand concentrations obtained from pH and Cu titrations with a Cu ion-selective electrode and van den Berg-Ruzic analyses of the titration data was used to calculate the copper speciation in the embryo test solutions. This calculated speciation, which was confirmed by measurements of Cu{sup 2+} in the test solutions, enabled the toxicity due to the free Cu ion and to the Cu complexes to be distinguished.

  7. Surface-Guided Formation of an Organocobalt Complex.

    PubMed

    Weber, Peter B; Hellwig, Raphael; Paintner, Tobias; Lattelais, Marie; Paszkiewicz, Mateusz; Casado Aguilar, Pablo; Deimel, Peter S; Guo, Yuanyuan; Zhang, Yi-Qi; Allegretti, Francesco; Papageorgiou, Anthoula C; Reichert, Joachim; Klyatskaya, Svetlana; Ruben, Mario; Barth, Johannes V; Bocquet, Marie-Laure; Klappenberger, Florian

    2016-05-01

    Organocobalt complexes represent a versatile tool in organic synthesis as they are important intermediates in Pauson-Khand, Friedel-Crafts, and Nicholas reactions. Herein, a single-molecule-level investigation addressing the formation of an organocobalt complex at a solid-vacuum interface is reported. Deposition of 4,4'-(ethyne-1,2-diyl)dibenzonitrile and Co atoms on the Ag(111) surface followed by annealing resulted in genuine complexes in which single Co atoms laterally coordinated to two carbonitrile groups undergo organometallic bonding with the internal alkyne moiety of adjacent molecules. Alternative complexation scenarios involving fragmentation of the precursor were ruled out by complementary X-ray photoelectron spectroscopy. According to density functional theory analysis, the complexation with the alkyne moiety follows the Dewar-Chatt-Duncanson model for a two-electron-donor ligand where an alkyne-to-Co donation occurs together with a strong metal-to-alkyne back-donation. PMID:27059261

  8. Formation of complex bacterial colonies via self-generated vortices

    NASA Astrophysics Data System (ADS)

    Czirók, András; Ben-Jacob, Eshel; Cohen, Inon; Vicsek, Tamás

    1996-08-01

    Depending on the environmental conditions bacterial colonies growing on agar surfaces can exhibit complex colony formation and various types of collective motion. Experimental results are presented concerning the hydrodynamics (vortices, migration of bacteria in clusters) and colony formation of a morphotype of Bacillus subtilis. Some of these features are not specific to this morphotype but also have been observed in several other bacterial strains, suggesting the presence of universal effects. A simple model of self-propelled particles is proposed, which is capable of describing the hydrodynamics on the intermediate level, including the experimentally observed rotating disks of bacteria. The colony formation is captured by a complex generic model taking into account nutrient diffusion, reproduction, and sporulation of bacteria, extracellular slime deposition, chemoregulation, and inhomogeneous population. Our model also sheds light on some possible biological benefits of this ``multicellular behavior.''

  9. Impact of electric-field dependent dielectric constants on two-dimensional electron gases in complex oxides

    SciTech Connect

    Peelaers, H.; Gordon, L.; Steiauf, D.; Janotti, A.; Van de Walle, C. G.; Krishnaswamy, K.; Sarwe, A.

    2015-11-02

    High-density two-dimensional electron gas (2DEG) can be formed at complex oxide interfaces such as SrTiO{sub 3}/GdTiO{sub 3} and SrTiO{sub 3}/LaAlO{sub 3}. The electric field in the vicinity of the interface depends on the dielectric properties of the material as well as on the electron distribution. However, it is known that electric fields can strongly modify the dielectric constant of SrTiO{sub 3} as well as other complex oxides. Solving the electrostatic problem thus requires a self-consistent approach in which the dielectric constant varies according to the local magnitude of the field. We have implemented the field dependence of the dielectric constant in a Schrödinger-Poisson solver in order to study its effect on the electron distribution in a 2DEG. Using the SrTiO{sub 3}/GdTiO{sub 3} interface as an example, we demonstrate that including the field dependence results in the 2DEG being confined closer to the interface compared to assuming a single field-independent value for the dielectric constant. Our conclusions also apply to SrTiO{sub 3}/LaAlO{sub 3} as well as other similar interfaces.

  10. Stability constants of copper(II) mixed complexes with some 4-quinolone antibiotics and (N-N) donors.

    PubMed

    Mendoza-Díaz, G; Perez-Alonso, R; Moreno-Esparza, R

    1996-11-15

    Studies of complexation equilibria of the antibiotic anions nalidixate and cinoxacinate with [Cu(phen)]2+ and [Cu(bipy)]2+ are reported. These studies indicate that the stability of this type of complex is strongly related to the metal environment. A correlation between the stability constants, determined here, with the sigma donation character of the ligand is proposed. This study shows that the stability constant for the reaction between the quinolones and the moiety [Cu(N-N)]2+ is dependent on the coordinate diamine to the metal ion. This is in agreement with previous studies where other physical properties as their electronic absorption spectra in the visible region, display similar behavior. These results suggest that inside the living cells, a possible interaction with some metal ion will be strongly controlled by the type of ligand bound to the cation. PMID:8893520

  11. Seeking the constant in what is transient: Karl Ernst von Baer's vision of organic formation.

    PubMed

    Vienne, Florence

    2015-03-01

    A well-established narrative in the history of science has it that the years around 1800 saw the end of a purely descriptive, classificatory and static natural history. The emergence of a temporal understanding of nature and the new developmental-history approach, it is thought, permitted the formation of modern biology. This paper questions that historical narrative by closely analysing the concepts of development, history and time set out in Karl Ernst von Baer's study of the mammalian egg (1827). I show that Baer's research on embryogenesis aimed not simply to explain temporal changes, but to inscribe the formation of new individual organisms into a continuous, unending organic process. I confront Baer's views with other explanations of embryogenesis arising in the 1820s and 1830s, especially those of Jean-Baptiste Dumas and Jean-Louis Prévost and of Theodor Schwann. By highlighting divergences between these scientists, especially as to their view of the role of gender differences in reproduction, I argue that biology evolved not from a homogeneous concept of developmental history but out of various, even opposing, views and research programmes. Thus, the birth of biology did not imply the end of all natural history's thought models. PMID:26013434

  12. Bacterial cadherin domains as carbohydrate binding modules: determination of affinity constants to insoluble complex polysaccharides.

    PubMed

    Fraiberg, Milana; Borovok, Ilya; Weiner, Ronald M; Lamed, Raphael; Bayer, Edward A

    2012-01-01

    Cadherin (CA) and cadherin-like (CADG) doublet domains from the complex polysaccharide-degrading marine bacterium, Saccharophagus degradans 2-40, demonstrated reversible calcium-dependent binding to different complex polysaccharides, which serve as growth substrates for the bacterium. Here we describe a procedure based on adsorption of CA and CADG doublet domains to different insoluble complex polysaccharides, followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) for visualizing and quantifying the distribution of cadherins between the bound and unbound fractions. Scatchard plots were employed to determine the kinetics of interactions of CA and CADG with several complex carbohydrates. On the basis of these binding studies, the CA and CADG doublet domains are proposed to form a new family of carbohydrate-binding module (CBM). PMID:22843394

  13. Formation and stability of lanthanide complexes and their encapsulation into polymeric microspheres

    SciTech Connect

    Mumper, R.J.; Jay, M.

    1992-10-15

    The complexation of lanthanides (Ln) with dicarbonyl compounds (acetylacetone, acac; ethyl acetoacetate; 3-ethyl-2,4-pentanedione; 2,4-hexanedione; 3-methyl-2,4-pentanedione; and diethyl malonate) was investigated using a potentiometric titration technique. The ability of a dicarbonyl compound to complex with the lanthanide elements was greatly dependent on its pK{sub a} and on the pH of the titrated solution. Selected lanthanide complexes (Ln complexes) were incorporated into spherical poly(L-lactic acid)(PLA) matrices and irradiated in a nuclear reactor with neutrons to produce short-lived high-energy {Beta}-particle-emitting radioisotopes. The lanthanides investigated (Ho, Dy, Sm, and La) were chosen on the basis of their physical and nuclear properties. A transition element (Re) was also studied. The small decrease in the ionic radii of the lanthanides with increasing atomic number led to (a) greater ability to extract and complex from an aqueous solution with complexing agents, (b) larger formation and stability constants for the Ln complexes, (c) increased solubility of the Ln complexes in chloroform, and (d) increase in the maximum percent incorporation of the stable lanthanides in PLA spheres. Ho(aca) was found to be the most promising candidate of the complexes studied on the basis of the above observations and due to the favorable physical properties of {sup 165}Ho and nuclear properties of {sup 166}Ho. 21 refs., 5 figs., 4 tabs.

  14. Positronium formation studies in crystalline molecular complexes: Triphenylphosphine oxide - Acetanilide

    NASA Astrophysics Data System (ADS)

    Oliveira, F. C.; Denadai, A. M. L.; Guerra, L. D. L.; Fulgêncio, F. H.; Windmöller, D.; Santos, G. C.; Fernandes, N. G.; Yoshida, M. I.; Donnici, C. L.; Magalhães, W. F.; Machado, J. C.

    2013-04-01

    Hydrogen bond formation in the triphenylphosphine oxide (TPPO), acetanilide (ACN) supramolecular heterosynton system, named [TPPO0.5·ACN0.5], has been studied by Positron Annihilation Lifetime Spectroscopy (PALS) and supported by several analytical techniques. In toluene solution, Isothermal Titration Calorimetry (ITC) presented a 1:1 stoichiometry and indicated that the complexation process is driven by entropy, with low enthalpy contribution. X-ray structure determination showed the existence of a three-dimensional network of hydrogen bonds, allowing also the confirmation of the existence of a 1:1 crystalline molecular complex in solid state. The results of thermal analysis (TGA, DTA and DSC) and FTIR spectroscopy showed that the interactions in the complex are relatively weaker than those found in pure precursors, leading to a higher positronium formation probability at [TPPO0.5·ACN0.5]. These weak interactions in the complex enhance the possibility of the n- and π-electrons to interact with positrons and consequently, the probability of positronium formation is higher. Through the present work is shown that PALS is a sensible powerful tool to investigate intermolecular interactions in solid heterosynton supramolecular systems.

  15. Formation of Complex Molecules via radiative association reactions

    NASA Astrophysics Data System (ADS)

    Acharyya, Kinsuk; Herbst, Eric

    2016-07-01

    The detection of increasing numbers of complex organic molecules in the various phases of star formation plays a key role since they follow the same chemical rules of carbon-based chemistry that are observed in our planet Earth. Many of these molecules are believed to be formed on the surfaces of grains, and can then be released to the gas phase when these grains are heated. This is evident when we observe a rich chemistry in hot core regions. However, recently complex organic molecules have also been observed in cold clouds. Therefore, it is necessary to re-examine various pathways for the formation of these molecules in the gas phase. In this presentation, I will discuss role of radiative association reactions in the formation of complex molecules in the gas phase and at low temperature. We will compare abundance of assorted molecules with and without new radiative association reactions and will show that the abundance of a few complex molecules such as HCOOCH3, CH3OCH3 etc. can go up due to introduction of these reactions, which can help to explain their observed abundances.

  16. Accelerating procelain formation by incorporating a complex additive

    SciTech Connect

    Maslennikova, G.N.; Dubovitskii, S.A.; Moroz, I.K.

    1986-05-01

    The authors studied the influence of a complex additive consisting of oxides of calcium, zinc, and magnesium on the formaton of porcelain. In order to achieve a more uniform distribution of the complex additive in the porcelain body it was incorporated in the form of water soluble salts-nitrates, which ensured comparability of results and excluded the effect of the different types of anions. The study of the main parameters of sintering (porosity, shrinkage, and mechanical strength) for the test bodies showed that they sinter at lower temperatures and attain zero porosity, maximum shrinkage, and mechanical strength. The most typical bodies indentified in this way were investigated by methods of complex differential thermal analysis and x-ray diffraction. Thus, the introduction of complex additives consisting of calcium, zinc, and magnesium oxides contributes to the earlier formation of porcelain. With the reduction of firing temperatures by 100/sup 0/C the authors observe an improvement in the basic properties of porcelain.

  17. Hydrolysis, formation and ionization constants at 25/sup 0/C, and at high temperature-high ionic strength

    SciTech Connect

    Phillips, S.L.; Phillips, C.A.; Skeen, J.

    1985-02-01

    Thermochemical data for nuclear waste disposal are compiled. The resulting computerized database consists of critically evaluated data on Gibbs energy of formation, enthalpy of formation, entropy and heat capacity of selected substances for about 16 elements at 25/sup 0/C and zero ionic strength. Elements covered are Am, As, Br, C, Cl, F, I, Mo, Np, N, O, P, Pu, Si, Sr, S, and U. Values of these thermodynamic properties were used to calculate equilibrium quotients for hydrolysis, complexation and ionization reactions up to 300/sup 0/C and 3 ionic strength, for selected chemical reactions.

  18. Star Formation in Giant Complexes: the Cat's Paw Nebula

    NASA Astrophysics Data System (ADS)

    Ascenso, Joana; Wolk, Scott; Lombardi, Marco; Alves, João; Rathborne, Jill; Forbrich, Jan; Leibundgut, Bruno; Hilker, Michael

    2013-07-01

    NGC 6334, the Cat's Paw Nebula, is a 106 M⊙ molecular cloud, one of the most massive known clouds in the Galaxy. It hosts the youngest massive cluster complex within 2 kpc of the Sun, and is therefore an ideal laboratory to investigate the onset and early evolution of star formation in an environment comparable to that of massive, extra-galactic complexes. Using multi-wavelength data, we are conducting the most sensitive and most complete characterization of this unique region to date.

  19. Polarographic Determination of Composition and Thermodynamic Stability Constant of a Complex Metal Ion.

    ERIC Educational Resources Information Center

    Marin, Dolores; Mendicuti, Francisco

    1988-01-01

    Describes a laboratory experiment designed to encourage laboratory cooperation among individual undergraduate students or groups. Notes each student contributes results individually and the exchange of data is essential to obtain final results. Uses the polarographic method for determining complex metal ions. (MVL)

  20. Constant Modulus Algorithm with Reduced Complexity Employing DFT Domain Fast Filtering

    NASA Astrophysics Data System (ADS)

    Yang, Yoon Gi; Lee, Chang Su; Yang, Soo Mi

    In this paper, a novel CMA (constant modulus algorithm) algorithm employing fast convolution in the DFT (discrete Fourier transform) domain is proposed. We propose a non-linear adaptation algorithm that minimizes CMA cost function in the DFT domain. The proposed algorithm is completely new one as compared to the recently introduced similar DFT domain CMA algorithm in that, the original CMA cost function has not been changed to develop DFT domain algorithm, resulting improved convergence properties. Using the proposed approach, we can reduce the number of multiplications to O(N log 2 N), whereas the conventional CMA has the computation order of O(N2). Simulation results show that the proposed algorithm provides a comparable performance to the conventional CMA.

  1. The role of plasma proteins in formation of obstructive protamine complexes

    SciTech Connect

    De Paulis, R.; Mohammad, S.F.; Chiariello, L.; Morea, M.; Olsen, D.B. )

    1991-06-01

    Formation of complexes between heparin and protamine (in saline), or heparin, plasma proteins, and protamine (in plasma) was assessed by measurements of light transmission through different test solutions. To examine the formation of these complexes, 125I-labeled protamine was used. Addition of 125I-protamine to plasma or blood resulted in the sedimentation of 125I-protamine in the form of insoluble complexes. This complex formation was not affected by the presence of heparin, suggesting that protamine-plasma protein interaction may be primarily responsible for precipitation of 125I-protamine. To assess the capability of these complexes to obstruct the pulmonary circulation, an in vitro experimental model was developed. Citrated serum, plasma, blood, or saline were allowed to flow through a glass bead column with the help of a peristaltic pump. A pressure transducer positioned before the column allowed pressure measurements at a constant flow rate during the experiment. Mixing of protamine with plasma or blood prior to their passage through the glass bead column resulted in a significant increase in pressure suggesting that the column was being clogged with insoluble complexes. The increase in pressure occurred both in the presence and absence of heparin in plasma or blood. Under identical experimental conditions, the increase in pressure was insignificant when protamine was added to saline or serum regardless of whether heparin was present or absent. This was further confirmed by the use of 125I-protamine. These observations suggest that protamine forms insoluble complexes with certain plasma proteins. Based on these observations, it is hypothesized that following intravenous administration, protamine immediately forms complexes in circulating blood.

  2. Demixing-stimulated lane formation in binary complex plasma

    SciTech Connect

    Du, C.-R.; Jiang, K.; Suetterlin, K. R.; Ivlev, A. V.; Morfill, G. E.

    2011-11-29

    Recently lane formation and phase separation have been reported for experiments with binary complex plasmas in the PK3-Plus laboratory onboard the International Space Station (ISS). Positive non-additivity of particle interactions is known to stimulate phase separation (demixing), but its effect on lane formation is unknown. In this work, we used Langevin dynamics (LD) simulation to probe the role of non-additivity interactions on lane formation. The competition between laning and demixing leads to thicker lanes. Analysis based on anisotropic scaling indices reveals a crossover from normal laning mode to a demixing-stimulated laning mode. Extensive numerical simulations enabled us to identify a critical value of the non-additivity parameter {Delta} for the crossover.

  3. The Dynamics of Coalition Formation on Complex Networks

    PubMed Central

    Auer, S.; Heitzig, J.; Kornek, U.; Schöll, E.; Kurths, J.

    2015-01-01

    Complex networks describe the structure of many socio-economic systems. However, in studies of decision-making processes the evolution of the underlying social relations are disregarded. In this report, we aim to understand the formation of self-organizing domains of cooperation (“coalitions”) on an acquaintance network. We include both the network’s influence on the formation of coalitions and vice versa how the network adapts to the current coalition structure, thus forming a social feedback loop. We increase complexity from simple opinion adaptation processes studied in earlier research to more complex decision-making determined by costs and benefits, and from bilateral to multilateral cooperation. We show how phase transitions emerge from such coevolutionary dynamics, which can be interpreted as processes of great transformations. If the network adaptation rate is high, the social dynamics prevent the formation of a grand coalition and therefore full cooperation. We find some empirical support for our main results: Our model develops a bimodal coalition size distribution over time similar to those found in social structures. Our detection and distinguishing of phase transitions may be exemplary for other models of socio-economic systems with low agent numbers and therefore strong finite-size effects. PMID:26303622

  4. The Dynamics of Coalition Formation on Complex Networks.

    PubMed

    Auer, S; Heitzig, J; Kornek, U; Schöll, E; Kurths, J

    2015-01-01

    Complex networks describe the structure of many socio-economic systems. However, in studies of decision-making processes the evolution of the underlying social relations are disregarded. In this report, we aim to understand the formation of self-organizing domains of cooperation ("coalitions") on an acquaintance network. We include both the network's influence on the formation of coalitions and vice versa how the network adapts to the current coalition structure, thus forming a social feedback loop. We increase complexity from simple opinion adaptation processes studied in earlier research to more complex decision-making determined by costs and benefits, and from bilateral to multilateral cooperation. We show how phase transitions emerge from such coevolutionary dynamics, which can be interpreted as processes of great transformations. If the network adaptation rate is high, the social dynamics prevent the formation of a grand coalition and therefore full cooperation. We find some empirical support for our main results: Our model develops a bimodal coalition size distribution over time similar to those found in social structures. Our detection and distinguishing of phase transitions may be exemplary for other models of socio-economic systems with low agent numbers and therefore strong finite-size effects. PMID:26303622

  5. Correlations between Community Structure and Link Formation in Complex Networks

    PubMed Central

    Liu, Zhen; He, Jia-Lin; Kapoor, Komal; Srivastava, Jaideep

    2013-01-01

    Background Links in complex networks commonly represent specific ties between pairs of nodes, such as protein-protein interactions in biological networks or friendships in social networks. However, understanding the mechanism of link formation in complex networks is a long standing challenge for network analysis and data mining. Methodology/Principal Findings Links in complex networks have a tendency to cluster locally and form so-called communities. This widely existed phenomenon reflects some underlying mechanism of link formation. To study the correlations between community structure and link formation, we present a general computational framework including a theory for network partitioning and link probability estimation. Our approach enables us to accurately identify missing links in partially observed networks in an efficient way. The links having high connection likelihoods in the communities reveal that links are formed preferentially to create cliques and accordingly promote the clustering level of the communities. The experimental results verify that such a mechanism can be well captured by our approach. Conclusions/Significance Our findings provide a new insight into understanding how links are created in the communities. The computational framework opens a wide range of possibilities to develop new approaches and applications, such as community detection and missing link prediction. PMID:24039818

  6. The Dynamics of Coalition Formation on Complex Networks

    NASA Astrophysics Data System (ADS)

    Auer, S.; Heitzig, J.; Kornek, U.; Schöll, E.; Kurths, J.

    2015-08-01

    Complex networks describe the structure of many socio-economic systems. However, in studies of decision-making processes the evolution of the underlying social relations are disregarded. In this report, we aim to understand the formation of self-organizing domains of cooperation (“coalitions”) on an acquaintance network. We include both the network’s influence on the formation of coalitions and vice versa how the network adapts to the current coalition structure, thus forming a social feedback loop. We increase complexity from simple opinion adaptation processes studied in earlier research to more complex decision-making determined by costs and benefits, and from bilateral to multilateral cooperation. We show how phase transitions emerge from such coevolutionary dynamics, which can be interpreted as processes of great transformations. If the network adaptation rate is high, the social dynamics prevent the formation of a grand coalition and therefore full cooperation. We find some empirical support for our main results: Our model develops a bimodal coalition size distribution over time similar to those found in social structures. Our detection and distinguishing of phase transitions may be exemplary for other models of socio-economic systems with low agent numbers and therefore strong finite-size effects.

  7. The catalytic role of uranyl in formation of polycatechol complexes

    PubMed Central

    2011-01-01

    To better understand the association of contaminant uranium with natural organic matter (NOM) and the fate of uranium in ground water, spectroscopic studies of uranium complexation with catechol were conducted. Catechol provides a model for ubiquitous functional groups present in NOM. Liquid samples were analyzed using Raman, FTIR, and UV-Vis spectroscopy. Catechol was found to polymerize in presence of uranyl ions. Polymerization in presence of uranyl was compared to reactions in the presence of molybdate, another oxyion, and self polymerization of catechol at high pH. The effect of time and dissolved oxygen were also studied. It was found that oxygen was required for self-polymerization at elevated pH. The potential formation of phenoxy radicals as well as quinones was monitored. The benzene ring was found to be intact after polymerization. No evidence for formation of ether bonds was found, suggesting polymerization was due to formation of C-C bonds between catechol ligands. Uranyl was found to form outer sphere complexes with catechol at initial stages but over time (six months) polycatechol complexes were formed and precipitated from solution (forming humic-like material) while uranyl ions remained in solution. Our studies show that uranyl acts as a catalyst in catechol-polymerization. PMID:21396112

  8. Complex formation between polyelectrolytes and oppositely charged oligoelectrolytes.

    PubMed

    Zhou, Jiajia; Barz, Matthias; Schmid, Friederike

    2016-04-28

    We study the complex formation between one long polyanion chain and many short oligocation chains by computer simulations. We employ a coarse-grained bead-spring model for the polyelectrolyte chains and model explicitly the small salt ions. We systematically vary the concentration and the length of the oligocation and examine how the oligocations affects the chain conformation, the static structure factor, the radial and axial distribution of various charged species, and the number of bound ions in the complex. At low oligocation concentration, the polyanion has an extended structure. Upon increasing the oligocation concentration, the polyanion chain collapses and forms a compact globule, but the complex still carries a net negative charge. Once the total charge of the oligocations is equal to that of the polyanion, the collapse stops and is replaced by a slow expansion. In this regime, the net charge on the complexes is positive or neutral, depending on the microion concentration in solution. The expansion can be explained by the reduction of the oligocation bridging. We find that the behavior and the structure of the complex are largely independent of the length of oligocations, and very similar to that observed when replacing the oligocations by multivalent salt cations, and conclude that the main driving force keeping the complex together is the release of monovalent counterions and coions. We speculate on the implications of this finding for the problem of controlled oligolyte release and oligolyte substitution. PMID:27131564

  9. Complex formation between polyelectrolytes and oppositely charged oligoelectrolytes

    NASA Astrophysics Data System (ADS)

    Zhou, Jiajia; Barz, Matthias; Schmid, Friederike

    2016-04-01

    We study the complex formation between one long polyanion chain and many short oligocation chains by computer simulations. We employ a coarse-grained bead-spring model for the polyelectrolyte chains and model explicitly the small salt ions. We systematically vary the concentration and the length of the oligocation and examine how the oligocations affects the chain conformation, the static structure factor, the radial and axial distribution of various charged species, and the number of bound ions in the complex. At low oligocation concentration, the polyanion has an extended structure. Upon increasing the oligocation concentration, the polyanion chain collapses and forms a compact globule, but the complex still carries a net negative charge. Once the total charge of the oligocations is equal to that of the polyanion, the collapse stops and is replaced by a slow expansion. In this regime, the net charge on the complexes is positive or neutral, depending on the microion concentration in solution. The expansion can be explained by the reduction of the oligocation bridging. We find that the behavior and the structure of the complex are largely independent of the length of oligocations, and very similar to that observed when replacing the oligocations by multivalent salt cations, and conclude that the main driving force keeping the complex together is the release of monovalent counterions and coions. We speculate on the implications of this finding for the problem of controlled oligolyte release and oligolyte substitution.

  10. Temperature and salt effects on the formation of preinitiation complexes between RNA polymerase and phage DNA.

    PubMed

    Escarmis, C; Domingo, E; Warner, R C

    1975-08-21

    The influence of temperature and KCl concentration on the formation of rifampicin-resistant preinitiation complexes by holo RNA polymerase has been compared for T4 DNA and Azotobacter phage A21 DNA. The sharp transition with respect to temperature between an inactive complex of polymerase and DNA and a preinitiation complex reflects an equilibrium between the two complexes, the position of which depends on the temperature and the salt concentration. The transition is shifted to higher temperatures by increasing the KCl concentration. The position of this transition is characteristically different for T4 and A21 DNA. The midpoint for A21 DNA is about 15 degrees C above that for T4 at 0.006 M KCl. At 0.15 M KCl the transition for A21 DNA cannot be observed below 37 degrees C. This difference is responsible for the apparent inhibition of a21 dna transcription by KCl and for the low template activity of A21 DNA under the conditions of the standard assay. Both holo and core RNA polymerases are able to form complexes with A21 DNA that are resistant to attack by rifampicin. The second-order rate constant for the inactivation of the complex with the core enxyme is three times greater than that for the complex with the holoenzyme. PMID:1100115

  11. Titanium complex formation of organic ligands in titania gels.

    PubMed

    Nishikiori, Hiromasa; Todoroki, Kenta; Setiawan, Rudi Agus; Teshima, Katsuya; Fujii, Tsuneo; Satozono, Hiroshi

    2015-01-27

    Thin films of organic ligand-dispersing titania gels were prepared from titanium alkoxide sols containing ligand molecules by steam treatment without heating. The formation of the ligand-titanium complex and the photoinduced electron transfer process in the systems were investigated by photoelectrochemical measurements. The complex was formed between the 8-hydroxyquinoline (HQ) and titanium species, such as the titanium ion, on the titania nanoparticle surface through the oxygen and nitrogen atoms of the quinolate. A photocurrent was observed in the electrodes containing the complex due to the electron injection from the LUMO of the complex into the titania conduction band. A bidentate ligand, 2,3-dihydroxynaphthalene (DHN), formed the complex on the titania surface through dehydration between its two hydroxyl groups of DHN and two TiOH groups of the titania. The electron injection from the HOMO of DHN to the titania conduction band was observed during light irradiation. This direct electron injection was more effective than the two-step electron injection. PMID:25535798

  12. Formation of a Ternary Complex for Selenocysteine Biosynthesis in Bacteria.

    PubMed

    Silva, Ivan R; Serrão, Vitor H B; Manzine, Livia R; Faim, Lívia M; da Silva, Marco T A; Makki, Raphaela; Saidemberg, Daniel M; Cornélio, Marinônio L; Palma, Mário S; Thiemann, Otavio H

    2015-12-01

    The synthesis of selenocysteine-containing proteins (selenoproteins) involves the interaction of selenocysteine synthase (SelA), tRNA (tRNA(Sec)), selenophosphate synthetase (SelD, SPS), a specific elongation factor (SelB), and a specific mRNA sequence known as selenocysteine insertion sequence (SECIS). Because selenium compounds are highly toxic in the cellular environment, the association of selenium with proteins throughout its metabolism is essential for cell survival. In this study, we demonstrate the interaction of SPS with the SelA-tRNA(Sec) complex, resulting in a 1.3-MDa ternary complex of 27.0 ± 0.5 nm in diameter and 4.02 ± 0.05 nm in height. To assemble the ternary complex, SPS undergoes a conformational change. We demonstrated that the glycine-rich N-terminal region of SPS is crucial for the SelA-tRNA(Sec)-SPS interaction and selenoprotein biosynthesis, as revealed by functional complementation experiments. Taken together, our results provide new insights into selenoprotein biosynthesis, demonstrating for the first time the formation of the functional ternary SelA-tRNA(Sec)-SPS complex. We propose that this complex is necessary for proper selenocysteine synthesis and may be involved in avoiding the cellular toxicity of selenium compounds. PMID:26378233

  13. Dynamics of electrical double layer formation in room-temperature ionic liquids under constant-current charging conditions.

    PubMed

    Jiang, Xikai; Huang, Jingsong; Zhao, Hui; Sumpter, Bobby G; Qiao, Rui

    2014-07-16

    We report detailed simulation results on the formation dynamics of an electrical double layer (EDL) inside an electrochemical cell featuring room-temperature ionic liquids (RTILs) enclosed between two planar electrodes. Under relatively small charging currents, the evolution of cell potential from molecular dynamics (MD) simulations during charging can be suitably predicted by the Landau-Ginzburg-type continuum model proposed recently (Bazant et al 2011 Phys. Rev. Lett. 106 046102). Under very large charging currents, the cell potential from MD simulations shows pronounced oscillation during the initial stage of charging, a feature not captured by the continuum model. Such oscillation originates from the sequential growth of the ionic space charge layers near the electrode surface. This allows the evolution of EDLs in RTILs with time, an atomistic process difficult to visualize experimentally, to be studied by analyzing the cell potential under constant-current charging conditions. While the continuum model cannot predict the potential oscillation under such far-from-equilibrium charging conditions, it can nevertheless qualitatively capture the growth of cell potential during the later stage of charging. Improving the continuum model by introducing frequency-dependent dielectric constant and density-dependent ion diffusion coefficients may help to further extend the applicability of the model. The evolution of ion density profiles is also compared between the MD and the continuum model, showing good agreement. PMID:24919471

  14. Dynamics of electrical double layer formation in room-temperature ionic liquids under constant-current charging conditions

    SciTech Connect

    Jiang, Xikai; Huang, Jingsong; Zhao, Hui; Sumpter, Bobby G; Qiao, Rui

    2014-01-01

    We report detailed simulation results on the formation dynamics of an electrical double layer (EDL) inside an electrochemical cell featuring room-temperature ionic liquids (RTILs) enclosed between two planar electrodes. Under relatively small charging currents, the evolution of cell potential during charging can be suitably predicted by the Landau-Ginzburg-type continuum model proposed recently (M. Z. Bazant, B. D. Storey, and A. A. Kornyshev, Phys. Rev. Lett., 106, 046102, 2011). Under very large charging currents, the cell potential shows pronounced oscillation during the initial stage of charging, a feature not captured by the continuum model. Such oscillation originates from the sequential growth of the ionic space charge layers near the electrode surface, allowing the evolution of EDLs in RTILs with time, an atomistic process difficult to visualize experimentally, to be studied by analyzing the cell potential under constant current charging conditions. While the continuum model cannot predict the potential oscillation under such far-from-equilibrium charging conditions, it can nevertheless qualitatively capture the growth of cell potential during the later stage of charging. Improving the continuum model by introducing frequency-dependent dielectric constant and density-dependent ion diffusion coefficients may help to further extend the applicability of the model. Keywords: ionic

  15. Formation of polyelectrolyte complexes with diethylaminoethyl dextran: charge ratio and molar mass effect.

    PubMed

    Le Cerf, Didier; Pepin, Anne Sophie; Niang, Pape Momar; Cristea, Mariana; Karakasyan-Dia, Carole; Picton, Luc

    2014-11-26

    The formation of polyelectrolyte complexes (PECs) between carboxymethyl pullulan and DEAE Dextran, was investigated, in dilute solution, with emphasis on the effect of charge density (molar ratio or pH) and molar masses. Electrophoretic mobility measurements have evidenced that insoluble PECs (neutral electrophoretic mobility) occurs for charge ratio between 0.6 (excess of polycation) and 1 (stoichiometry usual value) according to the pH. This atypical result is explained by the inaccessibility of some permanent cationic charge when screened by pH dependant cationic ones (due to the Hoffman alkylation). Isothermal titration calorimetry (ITC) indicates an endothermic formation of PEC with a binding constant around 10(5) L mol(-1). Finally asymmetrical flow field flow fractionation coupled on line with static multi angle light scattering (AF4/MALS) evidences soluble PECs with very large average molar masses and size around 100 nm, in agreement with scrambled eggs multi-association between various polyelectrolyte chains. PMID:25256478

  16. GABAergic complex basket formations in the human neocortex.

    PubMed

    Blazquez-Llorca, Lidia; García-Marín, Virginia; DeFelipe, Javier

    2010-12-15

    Certain GABAergic interneurons in the cerebral cortex, basket cells, establish multiple connections with cell bodies that typically outline the somata and proximal dendrites of pyramidal cells. During studies into the distribution of the vesicular GABA transporter (VGAT) in the human cerebral cortex, we were struck by the presence of a very dense, pericellular arrangement of multiple VGAT-immunoreactive (-ir) terminals in certain cortical areas. We called these terminals "Complex basket formations" (Cbk-formations) to distinguish them from the simpler and more typical pericellular GABAergic innervations of most cortical neurons. Here we examined the distribution of these VGAT-ir Cbk-formations in various cortical areas, including the somatosensory (area 3b), visual (areas 17 and 18), motor (area 4), associative frontal (dorsolateral areas 9, 10, 45, 46, and orbital areas 11, 12, 13, 14, 47), associative temporal (areas 20, 21, 22, and 38), and limbic cingulate areas (areas 24, 32). Furthermore, we used dual or triple staining techniques to study the chemical nature of the innervated cells. We found that VGAT-ir Cbk-formations were most frequently found in area 4 followed by areas 3b, 13, and 18. In addition, they were mostly observed in layer III, except in area 17, where they were most dense in layer IV. We also found that 70% of the innervated neurons were pyramidal cells, while the remaining 30% were multipolar cells. Most of these multipolar cells expressed the calcium-binding protein parvalbumin and the lectin Vicia villosa agglutinin. PMID:21031559

  17. The ribosome-associated complex antagonizes prion formation in yeast

    PubMed Central

    Amor, Alvaro J; Castanzo, Dominic T; Delany, Sean P; Selechnik, Daniel M; van Ooy, Alex; Cameron, Dale M

    2015-01-01

    Abstract The number of known fungal proteins capable of switching between alternative stable conformations is steadily increasing, suggesting that a prion-like mechanism may be broadly utilized as a means to propagate altered cellular states. To gain insight into the mechanisms by which cells regulate prion formation and toxicity we examined the role of the yeast ribosome-associated complex (RAC) in modulating both the formation of the [PSI+] prion – an alternative conformer of Sup35 protein – and the toxicity of aggregation-prone polypeptides. The Hsp40 RAC chaperone Zuo1 anchors the RAC to ribosomes and stimulates the ATPase activity of the Hsp70 chaperone Ssb. We found that cells lacking Zuo1 are sensitive to over-expression of some aggregation-prone proteins, including the Sup35 prion domain, suggesting that co-translational protein misfolding increases in Δzuo1 strains. Consistent with this finding, Δzuo1 cells exhibit higher frequencies of spontaneous and induced prion formation. Cells expressing mutant forms of Zuo1 lacking either a C-terminal charged region required for ribosome association, or the J-domain responsible for Ssb ATPase stimulation, exhibit similarly high frequencies of prion formation. Our findings are consistent with a role for the RAC in chaperoning nascent Sup35 to regulate folding of the N-terminal prion domain as it emerges from the ribosome. PMID:25739058

  18. Formation and Redox Interconversion of Niobium Methylidene and Methylidyne Complexes.

    PubMed

    Searles, Keith; Smith, Kyle T; Kurogi, Takashi; Chen, Chun-Hsing; Carroll, Patrick J; Mindiola, Daniel J

    2016-06-01

    The niobium methylidene [{(Ar'O)2 Nb}2 (μ2 -Cl)2 (μ2 -CH2 )] (2) can be cleanly prepared via thermolysis or photolysis of [(Ar'O)2 Nb(CH3 )2 Cl] (1) (OAr'=2,6-bis(diphenylmethyl)-4-tert-butylphenoxide). Reduction of 2 with two equivalents of KC8 results in formation of the first niobium methylidyne [K][{(Ar'O)2 Nb}2 (μ2 -CH)(μ2 -H)(μ2 -Cl)] (3) via a binuclear α-hydrogen elimination. Oxidation of 3 with two equiv of ClCPh3 reforms 2. In addition to solid state X-ray analysis, all these complexes were elucidated via multinuclear NMR experiments and isotopic labelling studies, including a crossover experiment, support the notion for a radical mechanism as well as a binuclear α-hydrogen abstraction pathway being operative in the formation of 2 from 1. PMID:27110689

  19. Formation of glutathionyl dinitrosyl iron complexes protects against iron genotoxicity.

    PubMed

    Lewandowska, Hanna; Sadło, Jarosław; Męczyńska, Sylwia; Stępkowski, Tomasz M; Wójciuk, Grzegorz; Kruszewski, Marcin

    2015-07-28

    Dinitrosyl iron(i) complexes (DNICs), intracellular NO donors, are important factors in nitric oxide-dependent regulation of cellular metabolism and signal transduction. It has been shown that NO diminishes the toxicity of iron ions and vice versa. To gain insight into the possible role of DNIC in this phenomenon, we examined the effect of GS-DNIC formation on the ability of iron ions to mediate DNA damage, by treatment of the pUC19 plasmid with physiologically relevant concentrations of GS-DNIC. It was shown that GS-DNIC formation protects against the genotoxic effect of iron ions alone and iron ions in the presence of a naturally abundant antioxidant, GSH. This sheds new light on the iron-related protective effect of NO under the circumstances of oxidative stress. PMID:26079708

  20. Constant speed control for complex cross-section welding using robot based on angle self-test

    NASA Astrophysics Data System (ADS)

    Xue, Long; Zou, Yong; Huang, Jiqiang; Huang, Junfen; Tao, Xinghua; Hu, Yanfeng

    2014-03-01

    Expandable profile liner(EPL) is a promising new oil well casing cementing technique, and welding is a major EPLs connection technology. Connection of EPL is still in the stage of manual welding so far, automatic welding technology is a hotspot of EPL which is one of the key technologies to be solved. A robot for automatic welding of "8" type EPL is studied. Four quadrants of mathematical equations of the 8-shaped cross-section track of EPL, consisting of multiple arcs, are established. Mechanism program for complex cross-section welding of EPL based on angle detection is proposed according to characteristics of small size, small valleys, and large forming errors, etc. A welding velocity vector control model is established by linkage control of a welding vehicle, a small driven actuator, and a height tracking mechanism. A constant speed control model based on an angle and symmetrical analysis model of rectangular coordinate system for EPL is built. Constraint conditions of constant speed control between each section are analyzed with 4 sections in first quadrant as an example, and cooperation work mechanism of the welding vehicle and the small tracking actuator is established based on pressure detection. The constant speed control model using angle self-test can be used to avoid the need for a precise mathematical model for tracking control and to adapt manufacture and installation deviation of EPL workpiece. The model is able to solve constant speed and trajectory tracking problems of EPL cross-section welding. EPL seams welded by the studied robot are good in appearance, and non-destructive testing(NDT) shows the seams are good in quality with no welding defects. Bulge tests show that the maximum pressure of welded EPL is 35 MPa, which can fulfill expansion performance requirements.

  1. Formation of gold mineralization in ultramafic alkalic magmatic complexes

    NASA Astrophysics Data System (ADS)

    Ryabchikov, I. D.; Kogarko, L. N.; Sazonov, A. M.; Kononkova, N. N.

    2016-06-01

    Study of mineral inclusions within alluvial gold particles of the Guli Complex (East Siberia) and findings of lode gold in rocks of the same intrusion have demonstrated that gold mineralization occurs in interstitions of both early high-magnesium rocks (dunite) and later alkalic and carbonatite rocks. In dunite the native gold occurs in association with Fe-Ni sulfides (monosulfide solid solution, pentlandite, and heazlewoodite). Formation of the gold-bearing alloys took place under a low oxygen potential over a broad range of temperatures: from those close to 600°C down to below 400°C.

  2. Redox reactions and complex formation of transplutonium elements in solutions

    SciTech Connect

    Krot, N.N.; Myasoedov, B.F.

    1986-01-01

    This paper gives a brief analysis of the kinetics and mechanism of a number of redox processes and the complex formation of transplutonium elements in unusual oxidation states. The composition and strength of complexes of TPE with various addends have been determined. The new experimental data on the oxidation potentials of americium and berkelium ions in solutions are cited in abbreviated form. It follows from the data that in phosphoric acid solutions, when the H/sub 3/PO/sub 4/ concentration is increased from 10 to 15 M, the oxidation potential of the couple Am(IV)-Am(III) decreases. The oxidation potentials of the couples Am(VI)-Am(V), Cm(V)-Cm(IV), and Bk(IV)Bk(III) are also presented.

  3. Nucleation-dependent tau filament formation: the importance of dimerization and an estimation of elementary rate constants.

    PubMed

    Congdon, Erin E; Kim, Sohee; Bonchak, Jonathan; Songrug, Tanakorn; Matzavinos, Anastasios; Kuret, Jeff

    2008-05-16

    Filamentous inclusions composed of the microtubule-associated protein tau are found in Alzheimer disease and other tauopathic neurodegenerative diseases, but the mechanisms underlying their formation from full-length protein monomer under physiological conditions are unclear. To address this issue, the fibrillization of recombinant full-length four-repeat human tau was examined in vitro as a function of time and submicromolar tau concentrations using electron microscopy assay methods and a small-molecule inducer of aggregation, thiazine red. Data were then fit to a simple homogeneous nucleation model with rate constant constraints established from filament dissociation rate, critical concentration, and mass-per-unit length measurements. The model was then tested by comparing the predicted time-dependent evolution of length distributions to experimental data. Results indicated that once assembly-competent conformations were attained, the rate-limiting step in the fibrillization pathway was tau dimer formation. Filament elongation then proceeded by addition of tau monomers to nascent filament ends. Filaments isolated at reaction plateau contained approximately 2 tau protomers/beta-strand spacing on the basis of mass-per-unit length measurements. The model suggests four key steps in the aggregation pathway that must be surmounted for tau filaments to form in disease. PMID:18359772

  4. Characterization of Hydrogen Complex Formation in III-V Semiconductors

    SciTech Connect

    Williams, Michael D

    2006-09-28

    Atomic hydrogen has been found to react with some impurity species in semiconductors. Hydrogenation is a methodology for the introduction of atomic hydrogen into the semiconductor for the express purpose of forming complexes within the material. Efforts to develop hydrogenation as an isolation technique for AlGaAs and Si based devices failed to demonstrate its commercial viability. This was due in large measure to the low activation energies of the formed complexes. Recent studies of dopant passivation in long wavelength (0.98 - 1.55m) materials suggested that for the appropriate choice of dopants much higher activation energies can be obtained. This effort studied the formation of these complexes in InP, This material is extensively used in optoelectronics, i.e., lasers, modulators and detectors. The experimental techniques were general to the extent that the results can be applied to other areas such as sensor technology, photovoltaics and to other material systems. The activation energies for the complexes have been determined and are reported in the scientific literature. The hydrogenation process has been shown by us to have a profound effect on the electronic structure of the materials and was thoroughly investigated. The information obtained will be useful in assessing the long term reliability of device structures fabricated using this phenomenon and in determining new device functionalities.

  5. DFT calculations of 15N NMR shielding constants, chemical shifts and complexation shifts in complexes of rhodium(II) tetraformate with some nitrogenous organic ligands

    NASA Astrophysics Data System (ADS)

    Leniak, Arkadiusz; Jaźwiński, Jarosław

    2015-03-01

    Benchmark calculations of 15N NMR shielding constants for a set of model complexes of rhodium(II) tetraformate with nine organic ligands using the Density Functional Theory (DFT) methods have been carried out. The calculations were performed by means of several methods: the non-relativistic, relativistic scalar ZORA, and spin-orbit ZORA approaches at the CGA-PBE/QZ4P theory level, and the GIAO NMR method using the B3PW91 functional with the 6-311++G(2d,p) basis set for C, H, N, O atoms and the Stuttgart basis set for the Rh atom. The geometry of compounds was optimised either by the same basis set as for the NMR calculations or applying the B3LYP functional with the 6-31G(2d) basis set for C, H, N, O atoms and LANL2DZ for the Rh atom. Computed 15N NMR shielding constants σ were compatible with experimental 15N chemical shifts δ of complexes exhibiting similar structure and fulfil the linear equation δ = aσ + b. The a and b parameters for all data sets have been estimated by means of linear regression analysis. In contrast to the correlation method giving "scaled" chemical shifts, the conversion of shielding constants to chemical shifts with respect to the reference shielding of CH3NO2 provided very inaccurate "raw" δ values. The application of the former to the calculation of complexation shifts Δδ (Δδ = δcompl - δlig) reproduced experimental values qualitatively or semi-quantitatively. The non-relativistic B3PW91/[6-311++G(2d,p), Stuttgart] theory level reproduced the NMR parameters as good as the more expensive relativistic CGA-PBE//QZ4P ZORA approaches.

  6. Interference-mediated synaptonemal complex formation with embedded crossover designation

    PubMed Central

    Zhang, Liangran; Espagne, Eric; de Muyt, Arnaud; Zickler, Denise; Kleckner, Nancy E.

    2014-01-01

    Biological systems exhibit complex patterns at length scales ranging from the molecular to the organismic. Along chromosomes, events often occur stochastically at different positions in different nuclei but nonetheless tend to be relatively evenly spaced. Examples include replication origin firings, formation of chromatin loops along chromosome axes and, during meiosis, localization of crossover recombination sites (“crossover interference”). We present evidence in the fungus Sordaria macrospora that crossover interference is part of a broader pattern that includes synaptonemal complex (SC) nucleation. This pattern comprises relatively evenly spaced SC nucleation sites, among which a subset are crossover sites that show a classical interference distribution. This pattern ensures that SC forms regularly along the entire length of the chromosome as required for the maintenance of homolog pairing while concomitantly having crossover interactions locally embedded within the SC structure as required for both DNA recombination and structural events of chiasma formation. This pattern can be explained by a threshold-based designation and spreading interference process. This model can be generalized to give diverse types of related and/or partially overlapping patterns, in two or more dimensions, for any type of object. PMID:25380597

  7. Method for rapidly determining the swelling-clay content in shales and shaly sandstone formations by high-frequency dielectric constant measurements

    SciTech Connect

    Kroeger, M.K.; Longo, J.M.; Steiger, R.P.; Leung, P.K.

    1989-10-24

    This patent describes a method for measuring the swelling-clay content of earth formations by dielectric measurements. It comprises: grinding a sample of the earth formation to a size suitable for testing; washing the sample with a fluid having a water activity substantially less than that of water; packing the washed sample into a sample cell suitable for dielectric measurement; measuring the dielectric constant of the washed sample at a preselected frequency; and comparing the measured dielectric constant of the rock sample to a calibration curve, to determine the swelling-clay content of the earth formation.

  8. Incipient species formation in salamanders of the Ensatina complex

    PubMed Central

    Wake, David B.

    1997-01-01

    The Ensatina eschscholtzii complex of plethodontid salamanders, a well-known “ring species,” is thought to illustrate stages in the speciation process. Early research, based on morphology and coloration, has been extended by the incorporation of studies of protein variation and mitochondrial DNA sequences. The new data show that the complex includes a number of geographically and genetically distinct components that are at or near the species level. The complex is old and apparently has undergone instances of range contraction, isolation, differentiation, and then expansion and secondary contact. While the hypothesis that speciation is retarded by gene flow around the ring is not supported by molecular data, the general biogeographical hypothesis is supported. There is evidence of a north to south range expansion along two axes, with secondary contact and completion of the ring in southern California. Current research targets regions once thought to show primary intergradation, but which molecular markers reveal to be zones of secondary contact. Here emphasis is on the subspecies E. e. xanthoptica, which is involved in four distinct secondary contacts in central California. There is evidence of renewed genetic interactions upon recontact, with greater genetic differentiation within xanthoptica than between it and some of the interacting populations. The complex presents a full array of intermediate conditions between well-marked species and geographically variable populations. Geographically differentiated segments represent a diversity of depths of time of isolation and admixture, reflecting the complicated geomorphological history of California. Ensatina illustrates the continuing difficulty in making taxonomic assignments in complexes studied during species formation. PMID:9223261

  9. Effect of acidity on the equilibria of formation of mixed Co2+ complexes with heparin and arginine in aqueous solutions at 37°C

    NASA Astrophysics Data System (ADS)

    Feofanova, M. A.; Frantseva, Yu. V.; Semenov, A. N.; Baranova, N. V.; Zhuravlev, E. V.

    2014-02-01

    Results from studying interactions in the heparin-Co2+ ion-arginine system are presented. The constants of formation of mixed Co2+ complexes with heparin and arginine in aqueous solutions in a broad pH range at 37°C are determined potentiometrically. The chemical equilibria in the system are simulated and the stoichiometry of formation of the complex forms is determined.

  10. The thermodynamic characteristics of complex formation of Cd2+ with N,N-Bis(carboxymethyl)aspartic acid in aqueous solutions at 298.15 K

    NASA Astrophysics Data System (ADS)

    Lytkin, A. I.; Chernyavskaya, N. V.; Litvinenko, V. E.

    2011-01-01

    The equilibrium constants and heats of formation of complexes of N,N-bis(carboxymethyl)aspartic acid (H4Y) with Cd2+ ions at 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO3) were determined by potentiometric titration and calorimetrically. The thermodynamic characteristics of formation of the CdY2- complex at fixed and zero ionic strength values were calculated. The values obtained were interpreted.

  11. Factor Xa dimerization competes with prothrombinase complex formation on platelet-like membrane surfaces.

    PubMed

    Koklic, Tilen; Chattopadhyay, Rima; Majumder, Rinku; Lentz, Barry R

    2015-04-01

    Exposure of phosphatidylserine (PS) molecules on activated platelet membrane surface is a crucial event in blood coagulation. Binding of PS to specific sites on factor Xa (fXa) and factor Va (fVa) promotes their assembly into a complex that enhances proteolysis of prothrombin by approximately 10⁵. Recent studies demonstrate that both soluble PS and PS-containing model membranes promote formation of inactive fXa dimers at 5 mM Ca²⁺. In the present study, we show how competition between fXa dimerization and prothrombinase formation depends on Ca²⁺ and lipid membrane concentrations. We used homo-FRET measurements between fluorescein-E-G-R-chloromethylketone (CK)-Xa [fXa irreversibly inactivated by alkylation of the active site histidine residue with FEGR (FEGR-fXa)] and prothrombinase activity measurements to reveal the balance between fXa dimer formation and fXa-fVa complex formation. Changes in FEGR-fXa dimer homo-FRET with addition of fVa to model-membrane-bound FEGR-fXa unambiguously demonstrated that formation of the FEGR-fXa-fVa complex dissociated the dimer. Quantitative global analysis according to a model for protein interaction equilibria on a surface provided an estimate of a surface constant for fXa dimer dissociation (K(fXa×fXa)(d, σ)) approximately 10-fold lower than K(fXa×fVa)(d,σ) for fXa-fVa complex. Experiments performed using activated platelet-derived microparticles (MPs) showed that competition between fXa dimerization and fXa-fVa complex formation was even more prominent on MPs. In summary, at Ca²⁺ concentrations found in the maturing platelet plug (2-5 mM), fVa can compete fXa off of inactive fXa dimers to significantly amplify thrombin production, both because it releases dimer inhibition and because of its well-known cofactor activity. This suggests a hitherto unanticipated mechanism by which PS-exposing platelet membranes can regulate amplification and propagation of blood coagulation. PMID:25572019

  12. Influence of structural features of carrageenan on the formation of polyelectrolyte complexes with chitosan.

    PubMed

    Volod'ko, A V; Davydova, V N; Glazunov, V P; Likhatskaya, G N; Yermak, I M

    2016-03-01

    The polyelectrolyte complexes (PEC) of carrageenans (CG)-κ-, κ/β-, λ-and x-CG with chitosan were obtained. The formation of PEC was detected by Fourier-transform infrared (FTIR) spectroscopy and by centrifugation in a Percoll gradient. The influence of the structural peculiarities of CG on its interaction with chitosan was studied. The results of centrifugation showed that x-CG with a high degree of sulphation (SD) was completely bound to chitosan, unlike low SD κ-CG and κ/β-CG. Binding constant values showed there was a high affinity of CG for chitosan. CG with flexible macromolecule conformation and high SD exhibited the greatest binding affinity for chitosan. The full-atomic 3D-structures of the PEC κ-CG: chitosan in solution have been obtained by the experiments in silico for the first time. The amino groups of chitosan make the largest contribution to the energy of the complex formation by means of hydrogen and ionic bonds. The most probable complexes have stoichiometries of 1:1 and 1:1.5. PMID:26712704

  13. Cadmium(II) Complex Formation with Cysteine and Penicillamine

    PubMed Central

    Jalilehvand, Farideh; Leung, Bonnie O.; Mah, Vicky

    2009-01-01

    The complex formation between cadmium(II) and the ligands cysteine (H2Cys) or penicillamine (H2Pen = 3, 3′-dimethylcysteine) in aqueous solutions, containing CCd(II) ∼ 0.1 mol dm-3 and CH2L = 0.2 – 2 mol dm-3, was studied at pH = 7.5 and 11.0 by means of 113Cd-NMR and Cd K- and L3-edge X-ray absorption spectroscopy. For all cadmium(II)-cysteine mole ratios the mean Cd-S and Cd-(N/O) bond distances were found in the ranges 2.52 – 2.54 Å and 2.27 – 2.35 Å, respectively. The corresponding cadmium(II)-penicillamine complexes showed slightly shorter Cd-S bonds, 2.50 – 2.53 Å, but with the Cd-(N/O) bond distances in a similar wide range, 2.28 – 2.33 Å. For the mole ratio CH2L / CCd(II) = 2, the 113Cd chemical shifts, in the range 509 – 527 ppm at both pH values, indicated complexes with distorted tetrahedral CdS2N(N/O) coordination geometry. With a large excess of cysteine (mole ratios CH2Cys / CCd(II) ≥ 10) complexes with CdS4 coordination geometry dominate, consistent with the 113Cd NMR chemical shifts, δ ∼ 680 ppm at pH 7.5 and 636 - 658 ppm at pH 11.0, and their mean Cd-S distances of 2.53 ± 0.02 Å. At pH 7.5, the complexes are almost exclusively sulfur-coordinated as [Cd(S-cysteinate)4]n-, while at higher pH the deprotonation of the amine groups promotes chelate formation, and at pH 11.0 a minor amount of the [Cd(Cys)3]4- complex with CdS3N coordination is formed. For the corresponding penicillamine solutions with mole ratios CH2Pen / CCd(II) ≥ 10, the 113Cd-NMR chemical shifts, δ ∼ 600 ppm at pH 7.5 and 578 ppm at pH 11.0, together with the average bond distances Cd-S 2.53 ± 0.02 Å and Cd-O 2.30 – 2.33 Å, indicate that [Cd(penicillaminate)3]n- complexes with chelating CdS3(N/O) coordination dominate already at pH 7.5, and become mixed with CdS2N(N/O) complexes at pH 11.0. The present study reveals differences between cysteine and penicillamine as ligands to the cadmium(II) ion that can explain why cysteine-rich metallothionines

  14. Cadmium(II) complex formation with cysteine and penicillamine.

    PubMed

    Jalilehvand, Farideh; Leung, Bonnie O; Mah, Vicky

    2009-07-01

    The complex formation between cadmium(II) and the ligands cysteine (H(2)Cys) and penicillamine (H(2)Pen = 3,3'-dimethylcysteine) in aqueous solutions, having C(Cd(II)) approximately 0.1 mol dm(-3) and C(H(2)L) = 0.2-2 mol dm(-3), was studied at pH = 7.5 and 11.0 by means of (113)Cd NMR and Cd K- and L(3)-edge X-ray absorption spectroscopy. For all cadmium(II)-cysteine molar ratios, the mean Cd-S and Cd-(N/O) bond distances were found in the ranges 2.52-2.54 and 2.27-2.35 A, respectively. The corresponding cadmium(II)-penicillamine complexes showed slightly shorter Cd-S bonds, 2.50-2.53 A, but with the Cd-(N/O) bond distances in a similar wide range, 2.28-2.33 A. For the molar ratio C(H(2)L)/C(Cd(II)) = 2, the (113)Cd chemical shifts, in the range 509-527 ppm at both pH values, indicated complexes with distorted tetrahedral CdS(2)N(N/O) coordination geometry. With a large excess of cysteine (molar ratios C(H(2)Cys)/C(Cd(II)) >or= 10), complexes with CdS(4) coordination geometry dominate, consistent with the (113)Cd NMR chemical shifts, delta approximately 680 ppm at pH 7.5 and 636-658 ppm at pH 11.0, and their mean Cd-S distances were 2.53 +/- 0.02 A. At pH 7.5, the complexes are almost exclusively sulfur-coordinated as [Cd(S-cysteinate)(4)](n-), while at higher pH, the deprotonation of the amine groups promotes chelate formation. At pH 11.0, a minor amount of the [Cd(Cys)(3)](4-) complex with CdS(3)N coordination is formed. For the corresponding penicillamine solutions with molar ratios C(H(2)Pen)/C(Cd(II)) >or= 10, the (113)Cd NMR chemical shifts, delta approximately 600 ppm at pH 7.5 and 578 ppm at pH 11.0, together with the average bond distances, Cd-S 2.53 +/- 0.02 A and Cd-(N/O) 2.30-2.33 A, indicate that [Cd(penicillaminate)(3)](n-) complexes with chelating CdS(3)(N/O) coordination dominate already at pH 7.5 and become mixed with CdS(2)N(N/O) complexes at pH 11.0. The present study reveals differences between cysteine and penicillamine as ligands to the

  15. A spectroscopic study on the formation of Cm(III) acetate complexes at elevated temperatures.

    PubMed

    Fröhlich, Daniel R; Skerencak-Frech, Andrej; Panak, Petra J

    2014-03-14

    The complexation of Cm(III) with acetate is studied by time resolved laser fluorescence spectroscopy (TRLFS) as a function of ionic strength, ligand concentration, temperature and background electrolyte (NaClO4, NaCl and CaCl2 solution). The speciation of Cm(III) is determined by peak deconvolution of the emission spectra. To obtain the thermodynamic stability constants (log K) for the formation of [Cm(Ac)n](3-n) (n = 1-3), the experimental data are extrapolated to zero ionic strength according to the specific ion interaction theory (SIT). The results show a continuous increase of the stability constants with increasing temperature (20-90 °C). The standard reaction enthalpies and entropies (ΔrH, ΔrS) of the respective reactions are derived from the integrated Van't Hoff equation. The results show that all complexation steps are endothermic and thus entropy driven (ΔrH and ΔrS > 0). PMID:24448229

  16. Image formation in the eye: very specified complexity

    NASA Astrophysics Data System (ADS)

    Stoltzmann, David E.

    2005-08-01

    The formation of an image, and its correct interpretation by sighted living creatures, is a unique example of specified complexity unlike anything else in nature. While many of the functional aspects of living organisms are extremely complex, only an image requires a unique mapping process by the eye-brain system to be useful to the organism. The transfer of light from an object scene to a visual detection system (eye + brain) conveys an enormous amount of information. But unless that information is correctly organized into a useful image, the exchange of information is degraded and of questionable use. This paper examines the "connections" necessary for images to be interpreted correctly, as well as addressing the additional complexity requirement of dual-image mapping for stereovision capabilities. Statistics are presented for "simple eyes" consisting of a few pixels to illustrate the daunting task that random chance has to produce any form of a functional eye. For example, a 12-pixel eye (or camera) has 12! (479,001,600) possible pixel-to-brain (computer) wiring combinations, which can then be compared to the 126 million rods/cones of the actual human eye. If one tries to "connect the wires" (correctly interpret the information contained) in a 12-pixel image by random processes, by the time 6 pixels become correctly connected, over 99.9% of all the trials are incorrect, producing "noise" rather than a recognizable image. Higher numbers of pixels quickly make the problem astronomically worse for achieving any kind of useful image. This paper concludes that random-chance purposeless undirected processes cannot account for how images are perceived by living organisms.

  17. Cyclodextrins in pharmaceutical formulations I: structure and physicochemical properties, formation of complexes, and types of complex.

    PubMed

    Jambhekar, Sunil S; Breen, Philip

    2016-02-01

    Cyclodextrins are cyclic oligosaccharides that have been recognized as pharmaceutical adjuvants for the past 20 years. The molecular structure of these glucose derivatives, which approximates a truncated cone, bucket, or torus, generates a hydrophilic exterior surface and a nonpolar interior cavity. Cyclodextrins can interact with appropriately sized drug molecules to yield an inclusion complex. These noncovalent inclusion complexes offer a variety of advantages over the noncomplexed form of a drug. Cyclodextrins are primarily used to enhance the aqueous solubility, physical chemical stability, and bioavailability of drugs. Their other applications include preventing drug-drug interactions, converting liquid drugs into microcrystalline powders, minimizing gastrointestinal and ocular irritation, and reducing or eliminating unpleasant taste and smell. Here, we discuss the physical chemical properties of various cyclodextrins, including the effects of substitutions on these properties. Additionally, we report on the regulatory status of their use, commercial products containing cyclodextrins, toxicological considerations, and the forces involved in complex formation. We also highlight the types of complex formed and discuss the methods used to determine the types of complex present. PMID:26686054

  18. Thermodynamic Investigation and Mixed Ligand Complex Formation of 1,4-Bis-(3-aminopropyl)-piperazine and Biorelevant Ligands

    PubMed Central

    El-Sherif, Ahmed A.; Shehata, Mohamed R.; Shoukry, Mohamed M.; Barakat, Mohammad H.

    2012-01-01

    Thermodynamic parameters for protonation of 1,4-bis(3-aminopropyl)-piperazine (BAPP) and its metal complexation with some divalent metal ions were determined in aqueous solution at constant ionic strength (0.1 M NaNO3) using a potentiometric technique. The order of –ΔG0 and –ΔH0 was found to obey Co2+ < Ni2+ < Cu2+ > Zn2+, in accordance with the Irving-Williams order. The formation equilibria of zinc (II) complexes and the ternary complexes Zn(BAPP)L, where L = amino acid, amides, or DNA constituents), have been investigated. Ternary complexes are formed by a simultaneous mechanism. The concentration distribution of the complexes in solution was evaluated as a function of pH. Stoichiometry and stability constants for the complexes formed are reported and discussed. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameter Δlog K. PMID:23226992

  19. Formation of complexes of antimicrobial agent norfloxacin with antitumor antibiotics of anthracycline series

    NASA Astrophysics Data System (ADS)

    Evstigneev, M. P.; Rybakova, K. A.; Davies, D. B.

    2007-05-01

    The formation of complexes in solutions of the norfloxacin antimicrobial agent (NOR) with daunomycin (DAU) and nogalamycin (NOG), antitumor anthracycline antibiotics, was studied using 1H NMR spectroscopy. Based on the concentration and temperature dependences of the chemical shifts of the protons of interacting molecules, the equilibrium constants and thermodynamic parameters (enthalpy and entropy) of heteroassociation of the antibiotics were calculated. It was shown that NOR interacts with DAU (NOG) in aqueous solutions forming stacked heterocomplexes with parallel orientation of the molecular chromophores. The conclusion was drawn that such interactions should be taken into account when anthracyclines and quinolones are jointly administered during combined chemotherapy, since they can contribute to the medico-biological synergistic effect of these antibiotics.

  20. Phase Transition in Postsynaptic Densities Underlies Formation of Synaptic Complexes and Synaptic Plasticity.

    PubMed

    Zeng, Menglong; Shang, Yuan; Araki, Yoichi; Guo, Tingfeng; Huganir, Richard L; Zhang, Mingjie

    2016-08-25

    Postsynaptic densities (PSDs) are membrane semi-enclosed, submicron protein-enriched cellular compartments beneath postsynaptic membranes, which constantly exchange their components with bulk aqueous cytoplasm in synaptic spines. Formation and activity-dependent modulation of PSDs is considered as one of the most basic molecular events governing synaptic plasticity in the nervous system. In this study, we discover that SynGAP, one of the most abundant PSD proteins and a Ras/Rap GTPase activator, forms a homo-trimer and binds to multiple copies of PSD-95. Binding of SynGAP to PSD-95 induces phase separation of the complex, forming highly concentrated liquid-like droplets reminiscent of the PSD. The multivalent nature of the SynGAP/PSD-95 complex is critical for the phase separation to occur and for proper activity-dependent SynGAP dispersions from the PSD. In addition to revealing a dynamic anchoring mechanism of SynGAP at the PSD, our results also suggest a model for phase-transition-mediated formation of PSD. PMID:27565345

  1. Variation in DNA binding constants with a change in geometry of ternary copper(II) complexes with N2O donor Schiff base and cyanate or dicyanamide

    NASA Astrophysics Data System (ADS)

    Jana, Subrata; Santra, Ramesh Chandra; Das, Saurabh; Chattopadhyay, Shouvik

    2014-09-01

    Two new copper(II) complexes, [Cu(L)(OCN)] (1) and [CuL(dca)]n (2), where HL = 2-(-(2-(diethylamino)ethylimino)methyl)naphthalen-1-ol, dca = N(CN)2-, have been synthesized and characterized by elemental analysis, IR, UV-VIS spectroscopy and single crystal X-ray diffraction studies. Complex 1 has square planar and complex 2 square pyramidal geometries in solid state around metal centre. Interactions of the complexes with calf thymus DNA (CT DNA) were studied by UV-VIS spectroscopy. Binding constant and site size of interaction were determined. Binding site size and intrinsic binding constant K revealed complex 1 interacted with calf thymus DNA better than complex 2.

  2. Probing the Formation of Complex Organic Molecules in Interstellar Ices - Beyond the FTIR - RGA Limitation

    NASA Astrophysics Data System (ADS)

    Kaiser, Ralf I.

    2015-08-01

    An understanding of the formation of key classes of complex organic molecules (COMs) within interstellar ices is of core value to the laboratory astrophysics community with structural isomers - molecules with the same molecular formula but different connectivities of atoms - serving as a molecular clock and tracers in defining the evolutionary stage of cold molecular clouds and star forming regions. Here, the lack of data on products, branching ratios, and rate constants of their formation and how they depend on the ice temperature and composition limits the understanding how COMs are synthesized. Classically, infrared spectroscopy combined with mass spectrometry of the irradiated and subliming ices have been exploited for the last decades, but the usefulness of these methods has reached the limits when it comes to the identification of CMS in those ices. Here, infrared spectroscopy can only untangle the functional groups of COMs; mass spectrometry coupled with electron impact ionization cannot discriminate structural isomers and suffers from extensive fragmentation. This talk presents a novel approach to elucidate the formation of COMs by exploiting - besides classical infrared, Raman, and ultraviolet-visual spectroscopy - reflectron time-of-flight mass spectrometry (ReTOF) coupled with tunable vacuum ultraviolet (VUV) soft photoionization (ReTOF-PI). This technique has the unique power to identify the molecules based on a cross correlation of their mass-to-charge ratios, their ionization energies (IE), and their sublimation temperatures ultimately unraveling an inventory of individual COMs molecules formed upon interaction of ionizing radiation with interstellar analog ices.

  3. Determination of Effective Stability Constants of Ion-Carrier Complexes in Ion Selective Nanospheres with Charged Solvatochromic Dyes.

    PubMed

    Xie, Xiaojiang; Bakker, Eric

    2015-11-17

    Ionophores are widely used ion carriers in ion selective sensors. The effective stability constant (β) is a key physical parameter providing valuable guidelines to the design of ionophores and carrier-based ion selective sensors. The β value of ion-carrier complex in plasticized poly(vinyl chloride) (PVC) membranes and solutions have been determined in the past by various techniques, but most of them are difficult to implement at the nanoscale owing to the ultrasmall sample volume. A new methodology based on charged solvatochromic dyes is introduced here for the first time to determine β values directly within ion selective nanospheres. Four ionophores with different selectivities toward Na(+), K(+), Ca(2+), and H(+), respectively, are successfully characterized in nanospheres composed of triblock copolymer Pluronic F-127 and bis(2-ethylhexyl) sebacate. The values determined in the nanospheres are smaller compared with those in plasticized PVC membranes, indicating a more polar nanosphere microenvironment and possible uneven distribution of the sensing components in the interfacial region. PMID:26502342

  4. Determination of plasma frequency, damping constant, and size distribution from the complex dielectric function of noble metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Mendoza Herrera, Luis J.; Arboleda, David Muñetón; Schinca, Daniel C.; Scaffardi, Lucía B.

    2014-12-01

    This paper develops a novel method for simultaneously determining the plasma frequency ωP and the damping constant γfr e e in the bulk damped oscillator Drude model, based on experimentally measured real and imaginary parts of the metal refractive index in the IR wavelength range, lifting the usual approximation that restricts frequency values to the UV-deep UV region. Our method was applied to gold, silver, and copper, improving the relative uncertainties in the final values for ωp (0.5%-1.6%) and for γfr e e (3%-8%), which are smaller than those reported in the literature. These small uncertainties in ωp and γfr e e determination yield a much better fit of the experimental complex dielectric function. For the case of nanoparticles (Nps), a series expansion of the Drude expression (which includes ωp and γfr e e determined using our method) enables size-dependent dielectric function to be written as the sum of three terms: the experimental bulk dielectric function plus two size corrective terms, one for free electron, and the other for bound-electron contributions. Finally, size distribution of nanometric and subnanometric gold Nps in colloidal suspension was determined through fitting its experimental optical extinction spectrum using Mie theory based on the previously determined dielectric function. Results are compared with size histogram obtained from Transmission Electron Microscopy (TEM).

  5. Determination of plasma frequency, damping constant, and size distribution from the complex dielectric function of noble metal nanoparticles

    SciTech Connect

    Mendoza Herrera, Luis J.; Arboleda, David Muñetón; Schinca, Daniel C.; Scaffardi, Lucía B.

    2014-12-21

    This paper develops a novel method for simultaneously determining the plasma frequency ω{sub P}   and the damping constant γ{sub free} in the bulk damped oscillator Drude model, based on experimentally measured real and imaginary parts of the metal refractive index in the IR wavelength range, lifting the usual approximation that restricts frequency values to the UV-deep UV region. Our method was applied to gold, silver, and copper, improving the relative uncertainties in the final values for ω{sub p} (0.5%–1.6%) and for γ{sub free} (3%–8%), which are smaller than those reported in the literature. These small uncertainties in ω{sub p} and γ{sub free} determination yield a much better fit of the experimental complex dielectric function. For the case of nanoparticles (Nps), a series expansion of the Drude expression (which includes ω{sub p} and γ{sub free} determined using our method) enables size-dependent dielectric function to be written as the sum of three terms: the experimental bulk dielectric function plus two size corrective terms, one for free electron, and the other for bound-electron contributions. Finally, size distribution of nanometric and subnanometric gold Nps in colloidal suspension was determined through fitting its experimental optical extinction spectrum using Mie theory based on the previously determined dielectric function. Results are compared with size histogram obtained from Transmission Electron Microscopy (TEM)

  6. Stability constants and thermodynamic data for complexes of 12-crown-4 with alkali metal and alkaline-earth cations in methanol solutions

    SciTech Connect

    Buschmann, H.

    1987-03-01

    The formation of 1:1- and 2:1-complexes of the crown ether 12C4 with mono- and bivalent cations was studied in methanol solutions by calorimetric, potentiometric and conductometric titrations. It is shown that not all donor atoms of the ligand 12C4 take part in complex formation. The accuracy of the three experimental methods are checked by comparing the results for the complexation of alkali ions with crown ether 18C6.

  7. Integrin activation and focal complex formation in cardiac hypertrophy

    NASA Technical Reports Server (NTRS)

    Laser, M.; Willey, C. D.; Jiang, W.; Cooper, G. 4th; Menick, D. R.; Zile, M. R.; Kuppuswamy, D.

    2000-01-01

    Cardiac hypertrophy is characterized by both remodeling of the extracellular matrix (ECM) and hypertrophic growth of the cardiocytes. Here we show increased expression and cytoskeletal association of the ECM proteins fibronectin and vitronectin in pressure-overloaded feline myocardium. These changes are accompanied by cytoskeletal binding and phosphorylation of focal adhesion kinase (FAK) at Tyr-397 and Tyr-925, c-Src at Tyr-416, recruitment of the adapter proteins p130(Cas), Shc, and Nck, and activation of the extracellular-regulated kinases ERK1/2. A synthetic peptide containing the Arg-Gly-Asp (RGD) motif of fibronectin and vitronectin was used to stimulate adult feline cardiomyocytes cultured on laminin or within a type-I collagen matrix. Whereas cardiocytes under both conditions showed RGD-stimulated ERK1/2 activation, only collagen-embedded cells exhibited cytoskeletal assembly of FAK, c-Src, Nck, and Shc. In RGD-stimulated collagen-embedded cells, FAK was phosphorylated only at Tyr-397 and c-Src association occurred without Tyr-416 phosphorylation and p130(Cas) association. Therefore, c-Src activation is not required for its cytoskeletal binding but may be important for additional phosphorylation of FAK. Overall, our study suggests that multiple signaling pathways originate in pressure-overloaded heart following integrin engagement with ECM proteins, including focal complex formation and ERK1/2 activation, and many of these pathways can be activated in cardiomyocytes via RGD-stimulated integrin activation.

  8. Lipogenic Enzymes Complexes and Cytoplasmic Lipid Droplet Formation During Adipogenesis.

    PubMed

    Padilla-Benavides, Teresita; Velez-delValle, Cristina; Marsch-Moreno, Meytha; Castro-Muñozledo, Federico; Kuri-Harcuch, Walid

    2016-10-01

    Lipid droplets are dynamic organelles that store triglycerides and participate in their mobilization in adipose cells. These organelles require the reorganization of some structural components, the cytoskeleton, and the activation of lipogenic enzymes. Using confocal microscopy, we analyzed the participation of cytoskeletal components and two lipogenic enzymes, fatty acid synthase and glycerophosphate dehydrogenase, during lipid droplet biogenesis in differentiating 3T3-F442A cells into adipocytes. We show that subcortical actin microfilaments are extended at the basal side of the cells in parallel arrangement to the culture dish substrate, and that the microtubule network traverses the cytoplasm as a scaffold that supports the round shape of the mature adipocyte. By immunoprecipitation, we show that vimentin and perilipin1a associate during the early stages of the differentiation process for lipid droplet formation. We also report that the antibody against perilipin1 detected a band that might correspond to a modified form of the molecule. Finally, the cytosolic distribution and punctate organization of lipogenic enzymes and their co-localization in the proximity of lipid droplets suggest the existence of dynamic protein complexes involved in synthesis and storage of triglycerides. J. Cell. Biochem. 117: 2315-2326, 2016. © 2016 Wiley Periodicals, Inc. PMID:26928794

  9. Adhesion and formation of microbial biofilms in complex microfluidic devices

    SciTech Connect

    Kumar, Aloke; Karig, David K; Neethirajan, Suresh; Suresh, Anil K; Srijanto, Bernadeta R; Mukherjee, Partha P; Retterer, Scott T; Doktycz, Mitchel John

    2012-01-01

    Shewanella oneidensis is a metal reducing bacterium, which is of interest for bioremediation and clean energy applications. S. oneidensis biofilms play a critical role in several situations such as in microbial energy harvesting devices. Here, we use a microfluidic device to quantify the effects of hydrodynamics on the biofilm morphology of S. oneidensis. For different rates of fluid flow through a complex microfluidic device, we studied the spatiotemporal dynamics of biofilms, and we quantified several morphological features such as spatial distribution, cluster formation and surface coverage. We found that hydrodynamics resulted in significant differences in biofilm dynamics. The baffles in the device created regions of low and high flow in the same device. At higher flow rates, a nonuniform biofilm develops, due to unequal advection in different regions of the microchannel. However, at lower flow rates, a more uniform biofilm evolved. This depicts competition between adhesion events, growth and fluid advection. Atomic force microscopy (AFM) revealed that higher production of extra-cellular polymeric substances (EPS) occurred at higher flow velocities.

  10. Structural basis of complement membrane attack complex formation.

    PubMed

    Serna, Marina; Giles, Joanna L; Morgan, B Paul; Bubeck, Doryen

    2016-01-01

    In response to complement activation, the membrane attack complex (MAC) assembles from fluid-phase proteins to form pores in lipid bilayers. MAC directly lyses pathogens by a 'multi-hit' mechanism; however, sublytic MAC pores on host cells activate signalling pathways. Previous studies have described the structures of individual MAC components and subcomplexes; however, the molecular details of its assembly and mechanism of action remain unresolved. Here we report the electron cryo-microscopy structure of human MAC at subnanometre resolution. Structural analyses define the stoichiometry of the complete pore and identify a network of interaction interfaces that determine its assembly mechanism. MAC adopts a 'split-washer' configuration, in contrast to the predicted closed ring observed for perforin and cholesterol-dependent cytolysins. Assembly precursors partially penetrate the lipid bilayer, resulting in an irregular β-barrel pore. Our results demonstrate how differences in symmetric and asymmetric components of the MAC underpin a molecular basis for pore formation and suggest a mechanism of action that extends beyond membrane penetration. PMID:26841837

  11. Structural basis of complement membrane attack complex formation

    PubMed Central

    Serna, Marina; Giles, Joanna L.; Morgan, B. Paul; Bubeck, Doryen

    2016-01-01

    In response to complement activation, the membrane attack complex (MAC) assembles from fluid-phase proteins to form pores in lipid bilayers. MAC directly lyses pathogens by a ‘multi-hit' mechanism; however, sublytic MAC pores on host cells activate signalling pathways. Previous studies have described the structures of individual MAC components and subcomplexes; however, the molecular details of its assembly and mechanism of action remain unresolved. Here we report the electron cryo-microscopy structure of human MAC at subnanometre resolution. Structural analyses define the stoichiometry of the complete pore and identify a network of interaction interfaces that determine its assembly mechanism. MAC adopts a ‘split-washer' configuration, in contrast to the predicted closed ring observed for perforin and cholesterol-dependent cytolysins. Assembly precursors partially penetrate the lipid bilayer, resulting in an irregular β-barrel pore. Our results demonstrate how differences in symmetric and asymmetric components of the MAC underpin a molecular basis for pore formation and suggest a mechanism of action that extends beyond membrane penetration. PMID:26841837

  12. Structural basis of complement membrane attack complex formation

    NASA Astrophysics Data System (ADS)

    Serna, Marina; Giles, Joanna L.; Morgan, B. Paul; Bubeck, Doryen

    2016-02-01

    In response to complement activation, the membrane attack complex (MAC) assembles from fluid-phase proteins to form pores in lipid bilayers. MAC directly lyses pathogens by a `multi-hit' mechanism; however, sublytic MAC pores on host cells activate signalling pathways. Previous studies have described the structures of individual MAC components and subcomplexes; however, the molecular details of its assembly and mechanism of action remain unresolved. Here we report the electron cryo-microscopy structure of human MAC at subnanometre resolution. Structural analyses define the stoichiometry of the complete pore and identify a network of interaction interfaces that determine its assembly mechanism. MAC adopts a `split-washer' configuration, in contrast to the predicted closed ring observed for perforin and cholesterol-dependent cytolysins. Assembly precursors partially penetrate the lipid bilayer, resulting in an irregular β-barrel pore. Our results demonstrate how differences in symmetric and asymmetric components of the MAC underpin a molecular basis for pore formation and suggest a mechanism of action that extends beyond membrane penetration.

  13. Synthesis of crystalline americium hydroxide, Am(OH){sub 3}, and determination of its enthalpy of formation; estimation of the solubility-product constants of actinide(III) hydroxides

    SciTech Connect

    Morss, L.R.; Williams, C.W.

    1993-12-31

    This paper reports a new synthesis of pure, microcrystalline Am(OH){sub 3}, its characterization by x-ray powder diffraction and infrared spectroscopy, and the calorimetric determination of its enthalpy of solution in dilute hydrochloric acid. From the enthalpy of solution the enthalpy of formation of Am(OH){sub 3} has been calculated to be {minus}1371.2{plus_minus}7.9 kj{center_dot}mol{sup {minus}1}, which represents the first experimental determination of an enthalpy of formation of any actinide hydroxide. The free energy of formation and solubility product constant of Am(OH){sub 3} (K{sub sp} = 7 {times} 10{sup {minus}31}) have been calculated from our enthalpy of formation and entropy estimates and are compared with literature measurements under near-equilibrium conditions. Since many properties of the tripositive lanthanide and actinide ions (e.g., hydrolysis, complex-ion formation, and thermochemistry) change in a regular manner, these properties can be interpreted systematically in terms of ionic size. This paper compares the thermochemistry of Am(OH){sub 3} with thermochemical studies of lanthanide hydroxides. A combined structural and acid-base model is used to explain the systematic differences in enthalpies of solution between the oxides and hydroxides of the 4f{sup n} and 5f{sup n} subgroups and to predict solubility-product constants for the actinide(III) hydroxides of Pu through Cf.

  14. Reactions of dioxygen complexes. Oxidative dehydrogenation of 1,6-bis(2-pyridyl)-2,5-diazahexane through cobalt dioxygen complex formation

    SciTech Connect

    Basak, A.K.; Martell, A.E.

    1988-06-01

    The formation constants and oxygenation constants of the cobalt(II) complexes of 1,6-bis(2-pyridyl)-2,5-diazahexane (PYEN) have been determined by potentiometric equilibrium measurements under nitrogen and oxygen. The kinetics of the oxidative degradation of the coordinated ligand in the cobalt dioxygen complex have been measured spectrophotometrically, and the rate constants of two parallel degradation reactions have been determined. Both reactions were found to be second order, first order with respect to the concentration of the dioxygen complex and first order with respect to the hydroxide ion concentration. Kinetics and product analysis reveal that one of the terminal aminomethyl residues of the ligand PYEN undergoes two-electron oxidation to form the corresponding imine, which under the reaction conditions employed is converted to pyridine-2-carboxyaldehyde, identified semiquantitatively as the (2,6-dinitrophenyl)hydrazone. Comparisons of these results with those of systems investigated previously, and the large kinetic deuterium isotope effect for the dehydrogenation reaction, are employed as the basis of a proposed reaction mechanism, which involves deprotonation of an aliphatic amino group in a preequilibrium step. Reaction mechanisms are suggested. 30 references, 10 figures, 3 tables.

  15. Reactions of a Dinitrogen Complex of Molybdenum: Formation of a Carbon-Nitrogen Bond.

    ERIC Educational Resources Information Center

    Busby, David C.; And Others

    1981-01-01

    Reports a procedure for the formation of alkyldiazenido complexes of molybdenum in the absence of dioxygen, suitable for inclusion in an advanced inorganic chemistry laboratory. Includes background information and experimental procedures for two complexes. (SK)

  16. Absorption spectrometric study of charge transfer complex formation between 4-acetamidophenol (paracetamol) and a series of quinones including vitamin K3.

    PubMed

    Saha, Avijit; Mukherjee, Asok K

    2004-07-01

    The formation of charge transfer (CT) complexes of 4-acetamidophenol (commonly called 'paracetamol') and a series of quinones (including Vitamin K3) has been studied spectrophotometrically in ethanol medium. The vertical ionisation potential of paracetamol and the degrees of charge transfer of the complexes in their ground state has been estimated from the trends in the charge transfer bands. The oscillator and transition dipole strengths of the complexes have been determined from the CT absorption spectra at 298 K. The complexes have been found by Job's method of continuous variation to have the uncommon 2:1 (paracetamol:quinone) stoichiometry in each case. The enthalpies and entropies of formation of the complexes have been obtained by determining their formation constants at five different temperatures. PMID:15248945

  17. Absorption spectrometric study of charge transfer complex formation between 4-acetamidophenol (paracetamol) and a series of quinones including Vitamin K 3

    NASA Astrophysics Data System (ADS)

    Saha, Avijit; Mukherjee, Asok K.

    2004-07-01

    The formation of charge transfer (CT) complexes of 4-acetamidophenol (commonly called 'paracetamol') and a series of quinones (including Vitamin K 3) has been studied spectrophotometrically in ethanol medium. The vertical ionisation potential of paracetamol and the degrees of charge transfer of the complexes in their ground state has been estimated from the trends in the charge transfer bands. The oscillator and transition dipole strengths of the complexes have been determined from the CT absorption spectra at 298 K. The complexes have been found by Job's method of continuous variation to have the uncommon 2:1 (paracetamol:quinone) stoichiometry in each case. The enthalpies and entropies of formation of the complexes have been obtained by determining their formation constants at five different temperatures.

  18. Selective determination of rate constants of reactions of atomic hydrogen with various functional groups of a complex molecule

    NASA Astrophysics Data System (ADS)

    Brauer, G. B.; Pugachev, D. V.; Azatyan, V. V.

    2016-05-01

    The possibility of determining absolute values of the rate constants of reactions of active intermediate species with different functional groups of molecules is demonstrated by measuring macrokinetic combustion characteristics. The Arrhenius parameters of the rate constant of the reaction between atomic hydrogen with the methylene group of ethanol and molecular oxygen within the temperature range of 830-970 K are determined. The reasons for the differences between the rate constants of reactions with the methylene and methyl groups of an ethanol molecule are discussed using thermochemical data. It is found that the obtained values of activation energies and preexponential factors of rate constants are in good agreement with the literature data on the region of lower temperatures.

  19. Estimation of free acid content in lanthanide salt solutions used for potentiometric determination of stability constant of lanthanide complexes with organic ligands

    SciTech Connect

    Zheltvai, T.I.; Tishchenko, M.A.

    1985-08-20

    This paper studies the possibility of alkalimetric titration of free acid after binding the metal ions by the disodium salt of ethylenediaminetetraacetic (complexone III). The proposed method of free acid determination in lanthanide salt solutions is very simple and helps to avoid gross methodical errors in works involving determination of stability constants of lanthanide complexes.

  20. Ethanol oxidation by imidorhenium(V) complexes: formation of amidorhenium(III) complexes.

    PubMed

    Suing, A L; Dewan, C R; White, P S; Thorp, H H

    2000-12-25

    The reaction of Re(NC6H4R)Cl3(PPh3)2 (R = H, 4-Cl, 4-OMe) with 1,2-bis(diphenylphosphino)ethane (dppe) is investigated in refluxing ethanol. The reaction produces two major products, Re(NC6H4R)Cl(dppe)(2)2+ (R = H, 1-H; R = Cl, 1-Cl; R = OMe, 1-OMe) and the rhenium(III) species Re(NHC6H4R)Cl(dppe)2+ (R = H, 2-H; R = Cl, 2-Cl). Complexes 1-H (orthorhombic, Pcab, a = 22.3075(10) A, b = 23.1271(10) A, c = 23.3584(10) A, Z = 8), 1-Cl (triclinic, P1, a = 11.9403(6) A, b = 14.6673(8) A, c = 17.2664(9) A, alpha = 92.019(1) degrees, beta = 97.379(1) degrees, gamma = 90.134(1) degrees, Z = 2), and 1-OMe (triclinic, P1, a = 11.340(3) A, b = 13.134(4) A, c = 13.3796(25) A, alpha = 102.370(20) degrees, beta = 107.688(17) degrees, gamma = 114.408(20) degrees, Z = 1) are crystallographically characterized and show an average Re-N bond length (1.71 A) typical of imidorhenium(V) complexes. There is a small systematic decrease in the Re-N bond length on going from Cl to H to OMe. Complex 2-Cl (monoclinic, Cc, a = 24.2381(11) A, b = 13.4504(6) A, c = 17.466(8) A, beta = 97.06900(0) degrees, Z = 4) is also crystallographically characterized and shows a Re-N bond length (1.98 A) suggestive of amidorhenium(III). The rhenium(III) complexes exhibit unusual proton NMR spectra where all of the resonances are found at expected locations except those for the amido protons, which are at 37.8 ppm for 2-Cl and 37.3 ppm for 1-H. The phosphorus resonances are also unremarkable, but the 13C spectrum of 2-Cl shows a significantly shifted resonance at 177.3 ppm, which is assigned to the ipso carbon of the phenylamido ligand. The extraordinary shifts of the amido hydrogen and ipso carbon are attributed to second-order magnetism that is strongly focused along the axially compressed amido axis. The reducing equivalents for the formation of the Re(III) product are provided by oxidation of the ethanol solvent, which produces acetal and acetaldehyde in amounts as much as 30 equiv based on the quantity of

  1. Salting Constants of Small Organic Molecules in Aerosol-Relevant Salts and Application to Aerosol Formation in the Southeastern United States

    NASA Astrophysics Data System (ADS)

    Waxman, E.; Carlton, A. M. G.; Ziemann, P. J.; Volkamer, R. M.

    2014-12-01

    Secondary organic aerosol (SOA) formation from small water-soluble molecules such as glyoxal and methyl glyoxal is a topic of emerging interest. Results from recent field campaigns, e.g. Waxman et al. (2013, GRL) and Knote et al. (2014, ACP), show that these molecules can form significant SOA mass as a result of 'salting-in'. Salting-in happens when a molecule's solubility increases with salt concentration and salting-out is the reverse. Salting effects modify the solubility exponentially with increasing salt concentration, and thus the effective Henry's law constant can strongly modify partitioning, and multiphase chemical reaction rates in aerosol water. Moreover, the solubility in aerosol water cannot easily inferred based on the solubility in cloud water, as the salting effects could change the solubility by a factor of 104 or more. In this work, we have devised and applied a novel experimental setup to measure salting constants using an ion trap mass spectrometer. We focus on small, water soluble molecules like methyl glyoxal and similar compounds and measure salting constants for aerosol-relevant salts including ammonium sulfate, ammonium nitrate, and sodium chloride. The Setschenow salting-constant values are then used to parameterize the effects of salting in CMAQ. We present a series of sensitivity studies of the effects that inorganic aerosols have on the SOA formation from small soluble molecules in the southeastern United States.

  2. On the formation of dynamic structures in the form of rotating rings and vortices in a thin layer of a magnetodielectric colloid subjected to a constant electric field

    NASA Astrophysics Data System (ADS)

    Danilov, M. I.; Yastrebov, S. S.

    2012-04-01

    Experimental data on the electrical and optical properties of a thin layer of a magnetodielectric colloid obtained by Kozhevnikov et al. (Tech. Phys. 51 (7), 946 (2006)), are analyzed. Using a three-layer hierarchical model, the possible structure and properties of near-electrode layers are determined, the formation mechanisms of dynamic structures are described, and the variation of the electrical properties of the magnetodielectric colloid layer with time and constant electric field strength are discussed.

  3. Double layer formation at the interface of complex plasmas

    SciTech Connect

    Yaroshenko, V. V.; Thoma, M. H.; Thomas, H. M.; Morfill, G. E.

    2008-08-15

    Necessary conditions are formulated for the generation of a double layer at the interface of a complex plasma and a particle-free electron-ion plasma in a weakly collisional discharge. Examples are calculated for realistic observed complex plasmas, and it is shown that situations of both ''smooth'' transitions and 'sharp' transitions can exist. The model can explain the abrupt boundaries observed.

  4. Determining resistivity of a formation adjacent to a borehole having casing by generating constant current flow in portion of casing and using at least two voltage measurement electrodes

    DOEpatents

    Vail, III, William Banning

    2000-01-01

    Methods of operation of different types of multiple electrode apparatus vertically disposed in a cased well to measure information related to the resistivity of adjacent geological formations from within the cased well are described. The multiple electrode apparatus has a minimum of two spaced apart voltage measurement electrodes that electrically engage a first portion of the interior of the cased well and that provide at least first voltage information. Current control means are used to control the magnitude of any selected current that flows along a second portion of the interior of the casing to be equal to a predetermined selected constant. The first portion of the interior of the cased well is spaced apart from the second portion of the interior of the cased well. The first voltage information and the predetermined selected constant value of any selected current flowing along the casing are used in part to determine a magnitude related to the formation resistivity adjacent to the first portion of the interior of the cased well. Methods and apparatus having a plurality of voltage measurement electrodes are disclosed that provide voltage related information in the presence of constant currents flowing along the casing which is used to provide formation resistivity.

  5. Coexistence facilitates interspecific biofilm formation in complex microbial communities.

    PubMed

    Madsen, Jonas S; Røder, Henriette L; Russel, Jakob; Sørensen, Helle; Burmølle, Mette; Sørensen, Søren J

    2016-09-01

    Social interactions in which bacteria respond to one another by modifying their phenotype are central determinants of microbial communities. It is known that interspecific interactions influence the biofilm phenotype of bacteria; a phenotype that is central to the fitness of bacteria. However, the underlying role of fundamental ecological factors, specifically coexistence and phylogenetic history, in biofilm formation remains unclear. This study examines how social interactions affect biofilm formation in multi-species co-cultures from five diverse environments. We found prevalence of increased biofilm formation among co-cultured bacteria that have coexisted in their original environment. Conversely, when randomly co-culturing bacteria across these five consortia, we found less biofilm induction and a prevalence of biofilm reduction. Reduction in biofilm formation was even more predominant when co-culturing bacteria from environments where long-term coexistence was unlikely to have occurred. Phylogenetic diversity was not found to be a strong underlying factor but a relation between biofilm induction and phylogenetic history was found. The data indicates that biofilm reduction is typically correlated with an increase in planktonic cell numbers, thus implying a behavioral response rather than mere growth competition. Our findings suggest that an increase in biofilm formation is a common adaptive response to long-term coexistence. PMID:27119650

  6. Quantifying the association constant and stoichiometry of the complexation between colloidal polyacrylate-coated gold nanoparticles and chymotrypsin.

    PubMed

    Hou, Jie; Szaflarski, Diane M; Simon, John D

    2013-04-25

    Qualitative and quantitative insights into the capacity and association constant for the binding of chymotrypsin to polyacrylate-coated gold nanoparticles is determined using fluorescence quenching, optical absorption and circular dichroism spectroscopy, isothermal calorimetry, and gel electrophoresis. The collective data reveal a binding capacity and constant for this particular system of ~7 and ~2 × 10(6) M(-1), respectively. These values vary among the individual techniques, and not all techniques are able to provide quantitative information. The present study demonstrates that accurately quantifying the association between nanoparticles and biological materials requires using multiple approaches to ensure consistency among the binding parameters determined. PMID:23305403

  7. Crystal structures of complexes of NAD{sup +}-dependent formate dehydrogenase from methylotrophic bacterium Pseudomonas sp. 101 with formate

    SciTech Connect

    Filippova, E. V. Polyakov, K. M.; Tikhonova, T. V.; Stekhanova, T. N.; Boiko, K. M.; Sadykhov, I. G.; Tishkov, V. I.; Popov, V. O.; Labru, N.

    2006-07-15

    Formate dehydrogenase (FDH) from the methylotrophic bacterium Pseudomonas sp. 101 catalyzes oxidation of formate to NI{sub 2} with the coupled reduction of nicotinamide adenine dinucleotide (NAD{sup +}). The three-dimensional structures of the apo form (the free enzyme) and the holo form (the ternary FDH-NAD{sup +}-azide complex) of FDH have been established earlier. In the present study, the structures of FDH complexes with formate are solved at 2.19 and 2.28 A resolution by the molecular replacement method and refined to the R factors of 22.3 and 20.5%, respectively. Both crystal structures contain four protein molecules per asymmetric unit. These molecules form two dimers identical to the dimer of the apo form of FDH. Two possible formatebinding sites are found in the active site of the FDH structure. In the complexes the sulfur atom of residue Cys354 exists in the oxidized state.

  8. The Effect of Complex Formation upon the Redox Potentials of Metallic Ions. Cyclic Voltammetry Experiments.

    ERIC Educational Resources Information Center

    Ibanez, Jorge G.; And Others

    1988-01-01

    Describes experiments in which students prepare in situ soluble complexes of metal ions with different ligands and observe and estimate the change in formal potential that the ion undergoes upon complexation. Discusses student formation and analysis of soluble complexes of two different metal ions with the same ligand. (CW)

  9. An Efficient Format for Nearly Constant-Time Access to Arbitrary Time Intervals in Large Trace Files

    DOE PAGESBeta

    Chan, Anthony; Gropp, William; Lusk, Ewing

    2008-01-01

    A powerful method to aid in understanding the performance of parallel applications uses log or trace files containing time-stamped events and states (pairs of events). These trace files can be very large, often hundreds or even thousands of megabytes. Because of the cost of accessing and displaying such files, other methods are often used that reduce the size of the tracefiles at the cost of sacrificing detail or other information. This paper describes a hierarchical trace file format that provides for display of an arbitrary time window in a time independent of the total size of the file andmore » roughly proportional to the number of events within the time window. This format eliminates the need to sacrifice data to achieve a smaller trace file size (since storage is inexpensive, it is necessary only to make efficient use of bandwidth to that storage). The format can be used to organize a trace file or to create a separate file of annotations that may be used with conventional trace files. We present an analysis of the time to access all of the events relevant to an interval of time and we describe experiments demonstrating the performance of this file format.« less

  10. Economy of operon formation: cotranscription minimizes shortfall in protein complexes.

    PubMed

    Sneppen, Kim; Pedersen, Steen; Krishna, Sandeep; Dodd, Ian; Semsey, Szabolcs

    2010-01-01

    Genes of prokaryotes and Archaea are often organized in cotranscribed groups, or operons. In contrast, eukaryotic genes are generally transcribed independently. Here we show that there is a substantial economic gain for the cell to cotranscribe genes encoding protein complexes because it synchronizes the fluctuations, or noise, in the levels of the different components. This correlation substantially reduces the shortfall in production of the complex. This benefit is relatively large in small cells such as bacterial cells, in which there are few mRNAs and proteins per cell, and is diminished in larger cells such as eukaryotic cells. PMID:20877578

  11. Interaction between mosquito-larvicidal Lysinibacillus sphaericus binary toxin components: analysis of complex formation.

    PubMed

    Kale, Avinash; Hire, Ramesh S; Hadapad, Ashok B; D'Souza, Stanislaus F; Kumar, Vinay

    2013-11-01

    The two components (BinA and BinB) of Lysinibacillus sphaericus binary toxin together are highly toxic to Culex and Anopheles mosquito larvae, and have been employed world-wide to control mosquito borne diseases. Upon binding to the membrane receptor an oligomeric form (BinA2.BinB2) of the binary toxin is expected to play role in pore formation. It is not clear if these two proteins interact in solution as well, in the absence of receptor. The interactions between active forms of BinA and BinB polypeptides were probed in solution using size-exclusion chromatography, pull-down assay, surface plasmon resonance, circular dichroism, and by chemically crosslinking BinA and BinB components. We demonstrate that the two proteins interact weakly with first association and dissociation rate constants of 4.5×10(3) M(-1) s(-1) and 0.8 s(-1), resulting in conformational change, most likely, in toxic BinA protein that could kinetically favor membrane translocation of the active oligomer. The weak interactions between the two toxin components could be stabilized by glutaraldehyde crosslinking. The cross-linked complex, interestingly, showed maximal Culex larvicidal activity (LC50 value of 1.59 ng mL(-1)) reported so far for combination of BinA/BinB components, and thus is an attractive option for development of new bio-pesticides for control of mosquito borne vector diseases. PMID:23974012

  12. Structural Basis of Clostridium perfringens Toxin Complex Formation

    SciTech Connect

    Adams,J.; Gregg, K.; Bayer, E.; Boraston, A.; Smith, S.

    2008-01-01

    The virulent properties of the common human and livestock pathogen Clostridium perfringens are attributable to a formidable battery of toxins. Among these are a number of large and highly modular carbohydrate-active enzymes, including the {mu}-toxin and sialidases, whose catalytic properties are consistent with degradation of the mucosal layer of the human gut, glycosaminoglycans, and other cellular glycans found throughout the body. The conservation of noncatalytic ancillary modules among these enzymes suggests they make significant contributions to the overall functionality of the toxins. Here, we describe the structural basis of an ultra-tight interaction (Ka = 1.44 x 1011 M-1) between the X82 and dockerin modules, which are found throughout numerous C. perfringens carbohydrate-active enzymes. Extensive hydrogen-bonding and van der Waals contacts between the X82 and dockerin modules give rise to the observed high affinity. The {mu}-toxin dockerin module in this complex is positioned {approx}180 relative to the orientation of the dockerin modules on the cohesin module surface within cellulolytic complexes. These observations represent a unique property of these clostridial toxins whereby they can associate into large, noncovalent multitoxin complexes that allow potentiation of the activities of the individual toxins by combining complementary toxin specificities.

  13. DNA and buffers: the hidden danger of complex formation.

    PubMed

    Stellwagen, N C; Gelfi, C; Righetti, P G

    2000-08-01

    The free solution electrophoretic mobility of DNA differs significantly in different buffers, suggesting that DNA-buffer interactions are present in certain buffer systems. Here, capillary and gel electrophoresis data are combined to show that the Tris ions in Tris-acetate-EDTA (TAE) buffers are associated with the DNA helix to approximately the same extent as sodium ions. The borate ions in Tris-borate-EDTA (TBE) buffers interact with DNA to form highly charged DNA-borate complexes, which are stable both in free solution and in polyacrylamide gels. DNA-borate complexes are not observed in agarose gels, because of the competition of the agarose gel fibers for the borate residues. The resulting agarose-borate complexes increase the negative charge of the agarose gel fibers, leading to an increased electroendosmotic flow of the solvent in agarose-TBE gels. The combined results indicate that the buffers in which DNA is studied cannot automatically be assumed to be innocuous. PMID:10861374

  14. Enhanced inhibition of bacterial biofilm formation and reduced leukocyte toxicity by chloramphenicol:β-cyclodextrin:N-acetylcysteine complex.

    PubMed

    Aiassa, Virginia; Zoppi, Ariana; Becerra, M Cecilia; Albesa, Inés; Longhi, Marcela R

    2016-11-01

    The purpose of this study was to improve the physicochemical and biological properties of chloramphenicol (CP) by multicomponent complexation with β-cyclodextrin (β-CD) and N-acetylcysteine (NAC). The present work describes the ability of solid multicomponent complex (MC) to decrease biomass and cellular activity of Staphylococcus by crystal violet and XTT assay, and leukocyte toxicity, measuring the increase of reactive oxygen species by chemiluminescence, and using 123-dihydrorhodamine. In addition, MC was prepared by the freeze-drying or physical mixture methods, and then characterized by scanning electron microscopy and powder X-ray diffraction. Nuclear magnetic resonance and phase solubility studies provided information at the molecular level on the structure of the MC and its association binding constants, respectively. The results obtained allowed us to conclude that MC formation is an effective pharmaceutical strategy that can reduce CP toxicity against leukocytes, while enhancing its solubility and antibiofilm activity. PMID:27516318

  15. Structural and spectroscopic study of Al(III)-3-hydroxyflavone complex: Determination of the stability constants in water-methanol mixtures

    NASA Astrophysics Data System (ADS)

    Davila, Y. A.; Sancho, M. I.; Almandoz, M. C.; Blanco, S. E.

    2012-09-01

    Stoichiometry and apparent stability constant (KC) of the complex formed between Al(III) and 3-hydroxyflavone were determined in methanol and water-methanol mixtures (% water w/w: 3.11; 6.15; 10.4; 15.2; 19.9 and 25.3) by UV-vis spectroscopy at 25.0 °C and constant ionic strength (0.05 M, sodium chloride). Stoichiometry of the complex (1:2, metal:ligand) is not modified with an increase in water percentage in the analyzed interval. The value of KC in methanol is greater than in the binary solutions. The effects of changing solvent composition on KC data were explained by linear solvation free energy relationships using the solvatochromic parameter of Kamlet and Taft (α, β and π*). Multiple linear regression analysis indicates that the hydrogen bond donating ability (α) of the solvent and non-specific interactions (π*) play an important role in the degree of occurrence of the reaction. The effect of temperature on KC was also analyzed by assessing standard entropy and enthalpy variations of the reaction in methanol. Finally, the structure of the complex was investigated using FTIR spectroscopy and DFT calculations. The ligand exhibits small structural changes upon complexation, localized on the chelating site. The calculated vibrational frequencies of the complex were successfully compared against the experimental values.

  16. Effect of Solvent Dielectric Constant on the Formation of Large Flat Bilayer Stacks in a Lecithin/Hexadecanol Hydrogel.

    PubMed

    Nakagawa, Yasuharu; Nakazawa, Hiromitsu; Kato, Satoru

    2016-07-12

    We investigated the effect of dielectric properties of the aqueous medium on the novel type of hydrogel composed of a crude lecithin mixture (PC70) and hexadecanol (HD), in which charged sheet-like bilayers are kept far apart due to interbilayer repulsive interaction. We used dipropylene glycol (DPG) as a modifier of the dielectric properties and examined its effect on the hydrogel by synchrotron X-ray diffraction, differential scanning calorimetry (DSC), polarized optical microscopy, and freeze-fracture electron microscopy. We found that at a DPG weight fraction in the aqueous medium WDPG ≈ 0.4, the bilayer organization is transformed into unusually large flat bilayer stacks with a regular lamellar spacing of 6.25 nm and consequently disintegration of the hydrogel takes place. Semiquantitative calculation of the interbilayer interaction energy based on the Deyaguin-Landau-Verwey-Overbeek (DLVO) theory suggested that the reduction of the aqueous medium dielectric constant ε by DPG may lower the energy barrier preventing flat bilayers from coming closer together. We inferred that the size of the bilayer sheet increases because the reduction of ε promotes protonation of acidic lipids that work as edge-capping molecules. PMID:27322136

  17. Laboratory Measurement of the Gas-Phase Rate Constant for Formation of Nitric Acid from the Reaction of OH and NO2

    NASA Astrophysics Data System (ADS)

    Mollner, A. K.; Feng, L.; Sprague, M. K.; Okumura, M.; Vallavudasan, S.; Sander, S. P.; Martien, P. T.; Harley, R. A.; McCoy, A. B.

    2007-12-01

    The rate constant for the reaction OH + NO2 + M → HONO2 + M is among the most influential parameters affecting air pollution levels. There remains significant uncertainty about this rate, due to lack of laboratory data at 1 atm and to the unknown yield of a secondary channel forming peroxynitrous acid (HOONO). New experimental measurements of both the kinetics and HOONO/HONO2 branching ratios at 760 Torr are presented. The results are compared with current recommendations; when incorporated in models, the new parameters lead to significantly higher modeled ozone levels and reduced formation of nitric acid.

  18. Formation rates of complex organics in UV irradiated CH_3OH-rich ices. I. Experiments

    NASA Astrophysics Data System (ADS)

    Öberg, K. I.; Garrod, R. T.; van Dishoeck, E. F.; Linnartz, H.

    2009-09-01

    Context: Gas-phase complex organic molecules are commonly detected in the warm inner regions of protostellar envelopes, so-called hot cores. Recent models show that photochemistry in ices followed by desorption may explain the observed abundances. There is, however, a general lack of quantitative data on UV-induced complex chemistry in ices. Aims: This study aims to experimentally quantify the UV-induced production rates of complex organics in CH3OH-rich ices under a variety of astrophysically relevant conditions. Methods: The ices are irradiated with a broad-band UV hydrogen microwave-discharge lamp under ultra-high vacuum conditions, at 20-70 K, and then heated to 200 K. The reaction products are identified by reflection-absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD), through comparison with RAIRS and TPD curves of pure complex species, and through the observed effects of isotopic substitution and enhancement of specific functional groups, such as CH3, in the ice. Results: Complex organics are readily formed in all experiments, both during irradiation and during the slow warm-up of the ices after the UV lamp is turned off. The relative abundances of photoproducts depend on the UV fluence, the ice temperature, and whether pure CH3OH ice or CH3OH:CH4/CO ice mixtures are used. C2H6, CH3CHO, CH3CH2OH, CH3OCH3, HCOOCH3, HOCH2CHO and (CH2OH)2 are all detected in at least one experiment. Varying the ice thickness and the UV flux does not affect the chemistry. The derived product-formation yields and their dependences on different experimental parameters, such as the initial ice composition, are used to estimate the CH3OH photodissociation branching ratios in ice and the relative diffusion barriers of the formed radicals. At 20 K, the pure CH3OH photodesorption yield is 2.1(±1.0)×10-3 per incident UV photon, the photo-destruction cross section 2.6(±0.9)×10-18 cm^2. Conclusions: Photochemistry in CH3OH ices is efficient enough to

  19. Biological pattern formation: from basic mechanisms to complex structures

    SciTech Connect

    Koch, A.J.; Meinhardt, H. )

    1994-10-01

    The reliable development of highly complex organisms is an intriguing and fascinating problem. The genetic material is, as a rule, the same in each cell of an organism. How then do cells, under the influence of their common genes, produce spatial patterns Simple models are discussed that describe the generation of patterns out of an initially nearly homogeneous state. They are based on nonlinear interactions of at least two chemicals and on their diffusion. The concepts of local autocatalysis and of long-range inhibition play a fundamental role. Numerical simulations show that the models account for many basic biological observations such as the regeneration of a pattern after excision of tissue or the production of regular (or nearly regular) arrays of organs during (or after) completion of growth. Very complex patterns can be generated in a reproducible way by hierarchical coupling of several such elementary reactions. Applications to animal coats and to the generation of polygonally shaped patterns are provided. It is further shown how to generate a strictly periodic pattern of units that themselves exhibit a complex and polar fine structure. This is illustrated by two examples: the assembly of photoreceptor cells in the eye of [ital Drosophila] and the positioning of leaves and axillary buds in a growing shoot. In both cases, the substructures have to achieve an internal polarity under the influence of some primary pattern-forming system existing in the fly's eye or in the plant. The fact that similar models can describe essential steps in organisms as distantly related as animals and plants suggests that they reveal some universal mechanisms.

  20. Module Based Complexity Formation: Periodic Patterning in Feathers and Hairs

    PubMed Central

    Chuong, Cheng-Ming; Yeh, Chao-Yuan; Jiang, Ting-Xin; Widelitz, Randall

    2012-01-01

    Patterns describe order which emerges from homogeneity. Complex patterns on the integument are striking because of their visibility throughout an organism's lifespan. Periodic patterning is an effective design because the ensemble of hair or feather follicles (modules) allows the generation of complexity, including regional variations and cyclic regeneration, giving the skin appendages a new lease on life. Spatial patterns include the arrangements of feathers and hairs in specified number, size, and spacing. We explore how a field of equivalent progenitor cells can generate periodically arranged modules based on genetic information, physical-chemical rules and developmental timing. Reconstitution experiments suggest a competitive equilibrium regulated by activators / inhibitors involving Turing reaction-diffusion. Temporal patterns result from oscillating stem cell activities within each module (micro-environment regulation), reflected as growth (anagen) and resting (telogen) phases during the cycling of feather and hair follicles. Stimulating modules with activators initiates the spread of regenerative hair waves, while global inhibitors outside each module (macro-environment) prevent this. Different wave patterns can be simulated by Cellular Automata principles. Hormonal status and seasonal changes can modulate appendage phenotypes, leading to “organ metamorphosis”, with multiple ectodermal organ phenotypes generated from the same precursors. We discuss potential evolutionary novel steps using this module based complexity in several amniote integument organs, exemplified by the spectacular peacock feather pattern. We thus explore the application of the acquired knowledge of patterning in tissue engineering. New hair follicles can be generated after wounding. Hairs and feathers can be reconstituted through self-organization of dissociated progenitor cells. PMID:23539312

  1. The formation and study of titanium, zirconium, and hafnium complexes

    NASA Technical Reports Server (NTRS)

    Wilson, Bobby; Sarin, Sam; Smith, Laverne; Wilson, Melanie

    1989-01-01

    Research involves the preparation and characterization of a series of Ti, Zr, Hf, TiO, and HfO complexes using the poly(pyrazole) borates as ligands. The study will provide increased understanding of the decomposition of these coordination compounds which may lead to the production of molecular oxygen on the Moon from lunar materials such as ilmenite and rutile. The model compounds are investigated under reducing conditions of molecular hydrogen by use of a high temperature/pressure stainless steel autoclave reactor and by thermogravimetric analysis.

  2. Ganymede and Callisto - Complex crater formation and planetary crusts

    NASA Technical Reports Server (NTRS)

    Schenk, Paul M.

    1991-01-01

    Results are presented on measurements of crater depths and other morphological parameters (such as central peak and terrace frequency) of fresh craters on Ganymede and Callisto, two geophysically very similar but geologically divergent large icy satellites of Jupiter. These data were used to investigate the crater mechanics on icy satellites and the intersatellite crater scaling and crustal properties. The morphological transition diameters of and complex crater depths on Ganymede and Callisto were found to be similar, indicating that the crusts of both satellites are dominated by water ice with only a minor rocky component.

  3. New Pathways for the Formation of Complex Organics and Prebiotic Synthesis in the Gas Phase

    NASA Astrophysics Data System (ADS)

    El-Shall, M. S.

    2010-04-01

    We study the formation mechanisms of complex organics that are present in interstellar clouds. The reaction of acetylene ion with water produces vinyl alcohol while the reaction of benzene ion with acetylene produces naphthalene-type ion.

  4. Determination of the Physical Constants of Ferric and Ferrous Complexes of Phytic Acid by Proton Nuclear Magnetic Resonance and Resistance of Complexes to Enzymatic Dephosphoralation by Aspergillus ficcum

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Understanding the fate and transport of organic forms of phosphate requires in the case of myo-inositol hex kis phosphate (phytate) knowledge charge speciation as a function of pH and affinity of mineral cations such as soluble iron for phytate. Twelve acidity constants exist for phytic acid becau...

  5. The complex interplay between semantics and grammar in impression formation.

    PubMed

    Shreves, Wyley B; Hart, William; Adams, John M; Guadagno, Rosanna E; Eno, Cassie A

    2014-09-01

    We sought to bridge findings showing that (a) describing a person's behavior with the perfective verb aspect (did), compared to the imperfective aspect (was doing), increases processing of semantic knowledge unrelated to the target's action such as stereotypes and (b) an increased recognition of stereotypical thoughts often promotes a judgment correction for the stereotypes. We hypothesized an interplay between grammar (verb conjugation) and semantic information (gender) in impression-formation. Participants read a resume, attributed to a male or female, for a traditionally masculine job. When the resume was written in the imperfective, people rated a male (vs. female) more positively. When the resume was in the perfective, this pattern reversed. Only these latter effects of gender were influenced by cognitive load. Further, people more quickly indicated the applicant's gender in the perfective condition, suggesting an enhanced focus on gender during processing. PMID:24950389

  6. Constant Rate or Stepwise Injection of Cold Fluid into a Geologic Formation: A Hydro-Thermo-Mechanical Analysis

    NASA Astrophysics Data System (ADS)

    Kim, S.; Hosseini, S. A.

    2015-12-01

    Operations such as CO2 geologic storage, enhanced geothermal systems, and wastewater injection are rendering fluid injection as important as fluid extraction. In particular, injecting fluid colder than the original fluid causes thermal contraction and ensuing decreases in stresses, which yield an effect opposite of what volume expansion driven by the fluid injection imposes. In this study, we conduct numerical simulations to investigate pore-pressure buildup, thermal diffusion, and stress changes for two conditions: (1) constant rate, and (2) stepwise injection of cold fluid. The numerical-simulation method—which combines fluid flow, poroelasticity, thermal diffusion, and thermal stress—is based on the single-phase flow condition to simplify a computation model and thus facilitate a focus on mechanical responses. We also examine temporal evolutions of stress states and mobilized friction angles across base, injection-zone, and caprock layers for two different stress regimes: normal-faulting and reverse-faulting. Under the normal-faulting stress regime, the maximum mobilized friction angle occurs inside of the injection zone, which may act to improve the stability of the caprock. Special attention is required, however, because the location of the maximum mobilized friction angle is close to interfaces with the caprock and base layers. The hypothetical stepwise injection of cold fluid is shown to improve the stability of the injection zone to some extent. Under the reverse-faulting stress regime, the maximum mobilized friction angle occurs near the middle of the injection zone; stability in the injection zone is enhanced while that in the caprock/base is aggravated with time. The hypothetical stepwise injection not only helps improve the stability of the injection zone but also delays the moment when the maximum friction angle is mobilized. Finally, we suggest using dimensionless parameters to determine a prevalence of the thermal-stress effect in the injection

  7. Subcellular location for the formation of the retinol/retinol-binding protein complex in rat liver

    SciTech Connect

    Crumbaugh, L.M.; Green, E.L.; Smith, J.E.

    1986-03-01

    Retinol complexes with retinol-binding protein (RBP) within the hepatocyte, however the subcellular location where complex formation occurs has not previously been identified. A model similar to that of lipoproteins formation has been hypothesized. The authors have identified the initial site of retinol/RBP complex formation. Furthermore, the authors have elucidated the progression of the complex through the subcellular organelles. Intravenous injections of /sup 3/H-retinol suspended in Tween 40 were administered to vitamin A depleted rats. After intervals of 2, 3, 4, 5, 10, 15, 20, and 30 minutes the rat livers were removed and fractions enriched in rough and smooth microsomes and Golgi apparatus were prepared. Extracts of these subcellular fractions were chromatographed on Sephadex G-100. Simultaneous elution of /sup 3/H-retinol and immunoreactive RBP indicated the presence of the complex. The retinol/RBP complex was observed in rough microsomes 2 minute after the injection of /sup 3/H-retinal. The complex appeared subsequently in smooth microsomes and Golgi apparatus. The complex was first detected serum around 10 minutes after injection. Based on the data, they believe that the retinol/RBP complex formation occurs in rough microsomes.

  8. {sup 13}C and {sup 17}O NMR binding constant studies of uranyl carbonate complexes in near-neutral aqueous solution. Yucca Mountain Project Milestone Report 3351

    SciTech Connect

    Clark, D.L.; Newton, T.W.; Palmer, P.D.; Zwick, B.D.

    1995-01-01

    Valuable structural information, much of it unavailable by other methods, can be obtained about complexes in solution through NMR spectroscopy. From chemical shift and intensity measurements of complexed species, NMR can serve as a species-specific structural probe for molecules in solution and can be used to validate thermodynamic constants used in geochemical modeling. Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy has been employed to study the speciation of uranium(VI) ions in aqueous carbonate solutions as a function of pH, ionic strength, carbonate concentration, uranium concentration, and temperature. Carbon-13 and oxygen-17 NMR spectroscopy were used to monitor the fractions, and hence thermodynamic binding constants of two different uranyl species U0{sub 2}(CO{sub 3}){sub 3}{sup 4{minus}} and (UO{sub 2}){sub 3}(CO{sub 3}){sub 6}{sup 6{minus}} in aqueous solution. Synthetic buffer solutions were prepared under the ionic strength conditions used in the NMR studies in order to obtain an accurate measure of the hydrogen ion concentration, and a discussion of pH = {minus}log(a{sub H}{sup +}) versus p[H] = {minus}log[H+] is provided. It is shown that for quantitative studies, the quantity p[H] needs to be used. Fourteen uranium(VI) binding constants recommended by the OECD NEA literature review were corrected to the ionic strengths employed in the NMR study using specific ion interaction theory (SIT), and the predicted species distributions were compared with the actual species observed by multinuclear NMR. Agreement between observed and predicted stability fields is excellent. This establishes the utility of multinuclear NMR as a species-specific tool for the study of the actinide carbonate complexation constants, and serves as a means for validating the recommendations provided by the OECD NEA.

  9. Use of the ion exchange method for the determination of stability constants of trivalent metal complexes with humic and fulvic acids--part I: Eu3+ and Am3+ complexes in weakly acidic conditions.

    PubMed

    Wenming, Dong; Hongxia, Zhang; Meide, Huang; Zuyi, Tao

    2002-06-01

    The conditional stability constants for tracer concentrations of Eu(III) and Am(III) with a red earth humic acid (REHA), a red earth fulvic acid (REFA) and a fulvic acid from weathered coal (WFA) were determined at pH 5.2-6.4 (such values are similar to those in non-calcareous soils) in the presence of HAc/NaAc or NaNO3 by using the cation exchange method. It was found that 1:1 complexes were predominately formed in weakly acidic conditions. The total exchangeable proton capacities and the degrees of dissociation of these humic substances were determined by using a potentiometric titration method. The key parameters necessary for the experimental determination of the conditional stability constants of metal ions with humic substances in weakly acidic conditions by using the cation exchange method were discussed. The conditional stability constants of 1:1 complexes obtained in this paper were compared with the literature data of Am(III) determined by using the ion exchange method and the solvent extraction method and with the stability constants of 1:1 complexes of UO2(2+) and Th4+ with the same soil humic substances. These results indicate the great stability of bivalent UO2(2+), trivalent Eu3+, Am3+ and tetravalent Th4+ complexes with humic and fulvic acids in weakly acidic conditions. PMID:12102358

  10. Enhancing the Reduction Potential of Quinones via Complex Formation.

    PubMed

    Nepal, Binod; Scheiner, Steve

    2016-05-20

    Quantum calculations are used to study the manner in which quinones interact with proton-donating molecules. For neutral donors, a stacked geometry is favored over a H-bond structure. The former is stabilized by charge transfers from the N or O lone pairs to the quinone's π* orbitals. Following the addition of an electron to the quinone, the radical anion forms strong H-bonded complexes with the various donors. The presence of the donor enhances the electron affinity of the quinone. This enhancement is on the order of 15 kcal/mol for neutral donors, but up to as much as 85 kcal/mol for a cationic donor. The increase in electron affinity is larger for electron-rich quinones than for their electron-deficient counterparts, containing halogen substituents. Similar trends are in evidence when the systems are immersed in aqueous solvent. PMID:27135719

  11. Carbon–heteroatom bond formation catalysed by organometallic complexes

    PubMed Central

    Hartwig, John F.

    2010-01-01

    At one time the synthetic chemist’s last resort, reactions catalysed by transition metals are now the preferred method for synthesizing many types of organic molecule. A recent success in this type of catalysis is the discovery of reactions that form bonds between carbon and heteroatoms (such as nitrogen, oxygen, sulphur, silicon and boron) via complexes of transition metals with amides, alkoxides, thiolates, silyl groups or boryl groups. The development of these catalytic processes has been supported by the discovery of new elementary reactions that occur at metal–heteroatom bonds and by the identification of factors that control these reactions. Together, these findings have led to new synthetic processes that are in daily use and have formed a foundation for the development of processes that are likely to be central to synthetic chemistry in the future. PMID:18800130

  12. Glutathione Complex Formation With Mercury(Ii) in Aqueous Solution at Physiological Ph

    SciTech Connect

    Mah, V.; Jalilehvand, F.; /SLAC

    2012-08-23

    The mercury(II) complexes formed in neutral aqueous solution with glutathione (GSH, here denoted AH{sub 3} in its triprotonated form) were studied using Hg L{sub III}-edge extended X-ray absorption fine structure (EXAFS) and {sup 199}Hg NMR spectroscopy, complemented with electrospray ionization mass spectrometric (ESI-MS) analyses. The [Hg(AH){sub 2}]{sup 2-} complex, with the Hg-S bond distances at 2.325 {+-} 0.01 {angstrom} in linear S-Hg-S coordination, and the {sup 199}Hg NMR chemical shift at -984 ppm, dominates except at high excess of glutathione. In a series of solutions with C{sub Hg(II)} {approx} 17 mM and GSH/Hg(II) mole ratios rising from 2.4 to 11.8, the gradually increasing mean Hg-S bond distance corresponds to an increasing amount of the [Hg(AH){sub 3}]{sup 4-} complex. ESI-MS peaks appear at -m/z values of 1208 and 1230 corresponding to the [Na{sub 4}Hg(AH){sub 2}(A)]{sup -} and [Na{sub 5}Hg(AH)(A){sub 2}]{sup -} species, respectively. In another series of solutions at pH 7.0 with CHg(II) 50 mM and GSH/Hg(II) ratios from 2.0 to 10.0, the Hg L{sub III}-edge EXAFS and {sup 199}Hg NMR spectra show that at high excess of glutathione (0.35 M) about 70% of the total mercury(II) concentration is present as the [Hg(AH){sub 3}]4- complex, with the average Hg-S bond distance 2.42 {+-} 0.02 {angstrom} in trigonal HgS{sub 3} coordination. The proportions of HgSn species, n = 2, 3, and 4, quantified by fitting linear combinations of model EXAFS oscillations to the experimental EXAFS data in our present and previous studies were used to obtain stability constants for the [Hg(AH){sub 3}]{sup 4-} complex and also for the [Hg(A){sub 4}]{sup 10-} complex that is present at high pH. For Hg(II) in low concentration at physiological conditions (pH 7.4, C{sub GSH} = 2.2 mM), the relative amounts of the HgS{sub 2} species [Hg(AH){sub 2}]{sup 2-}, [Hg(AH)(A)]{sup 3-}, and the HgS{sub 3} complex [Hg(AH){sub 3}]{sup 4-} were calculated to be 95:2:3. Our results are not

  13. Formation, Migration, and Reactivity of Au CO Complexes on Gold Surfaces

    DOE PAGESBeta

    Wang, Jun; McEntee, Monica; Tang, Wenjie; Neurock, Matthew; Baddorf, Arthur P.; Maksymovych, Petro; Yates, Jr, John T.

    2016-01-12

    Here, we report experimental as well as theoretical evidence that suggests Au CO complex formation upon the exposure of CO to active sites (step edges and threading dislocations) on a Au(111) surface. Room-temperature scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, transmission infrared spectroscopy, and density functional theory calculations point to Au CO complex formation and migration. Room-temperature STM of the Au(111) surface at CO pressures in the range from 10^ 8 to 10^ 4 Torr (dosage up to 10^6 langmuir) indicates Au atom extraction from dislocation sites of the herringbone reconstruction, mobile Au CO complex formation and diffusion, and Aumore » adatom cluster formation on both elbows and step edges on the Au surface. The formation and mobility of the Au CO complex result from the reduced Au Au bonding at elbows and step edges leading to stronger Au CO bonding and to the formation of a more positively charged CO (CO +) on Au. These studies indicate that the mobile Au CO complex is involved in the Au nanoparticle formation and reactivity, and that the positive charge on CO increases due to the stronger adsorption of CO at Au sites with lower coordination numbers.« less

  14. Formation, Migration, and Reactivity of Au-CO Complexes on Gold Surfaces.

    PubMed

    Wang, Jun; McEntee, Monica; Tang, Wenjie; Neurock, Matthew; Baddorf, Arthur P; Maksymovych, Petro; Yates, John T

    2016-02-10

    We report experimental as well as theoretical evidence that suggests Au-CO complex formation upon the exposure of CO to active sites (step edges and threading dislocations) on a Au(111) surface. Room-temperature scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, transmission infrared spectroscopy, and density functional theory calculations point to Au-CO complex formation and migration. Room-temperature STM of the Au(111) surface at CO pressures in the range from 10(-8) to 10(-4) Torr (dosage up to 10(6) langmuir) indicates Au atom extraction from dislocation sites of the herringbone reconstruction, mobile Au-CO complex formation and diffusion, and Au adatom cluster formation on both elbows and step edges on the Au surface. The formation and mobility of the Au-CO complex result from the reduced Au-Au bonding at elbows and step edges leading to stronger Au-CO bonding and to the formation of a more positively charged CO (CO(δ+)) on Au. Our studies indicate that the mobile Au-CO complex is involved in the Au nanoparticle formation and reactivity, and that the positive charge on CO increases due to the stronger adsorption of CO at Au sites with lower coordination numbers. PMID:26754257

  15. Real-time Live Imaging of T-cell Signaling Complex Formation

    PubMed Central

    Barda-Saad, Mira

    2013-01-01

    real-time imaging of live cells allows both the spatial tracking of proteins and the ability to temporally distinguish between signaling events, thus shedding light on the dynamics of the process 9,10. We present a method of real-time imaging of signaling-complex formation during T-cell activation. Primary T-cells or T-cell lines, such as Jurkat, are transfected with plasmids encoding for proteins of interest fused to monomeric fluorescent proteins, preventing non-physiological oligomerization 11. Live T cells are dropped over a coverslip pre-coated with T-cell activating antibody 8,9, which binds to the CD3/TCR complex, inducing T-cell activation while overcoming the need for specific activating antigens. Activated cells are constantly imaged with the use of confocal microscopy. Imaging data are analyzed to yield quantitative results, such as the colocalization coefficient of the signaling proteins. PMID:23851483

  16. Substrate Binding Promotes Formation of the Skp1-Cul1-Fbxl3 (SCFFbxl3) Protein Complex*

    PubMed Central

    Yumimoto, Kanae; Muneoka, Tetsuya; Tsuboi, Tomohiro; Nakayama, Keiichi I.

    2013-01-01

    The Skp1–Cul1–F-box protein (SCF) complex is one of the most well characterized types of ubiquitin ligase (E3), with the E3 activity of the complex being regulated in part at the level of complex formation. Fbxl3 is an F-box protein that is responsible for the ubiquitylation and consequent degradation of cryptochromes (Crys) and thus regulates oscillation of the circadian clock. Here we show that formation of the SCFFbxl3 complex is regulated by substrate binding in vivo. Fbxl3 did not associate with Skp1 and Cul1 to a substantial extent in transfected mammalian cells. Unexpectedly, however, formation of the SCFFbxl3 complex was markedly promoted by forced expression of its substrate Cry1 in these cells. A mutant form of Fbxl3 that does not bind to Cry1 was unable to form an SCF complex, suggesting that interaction of Cry1 with Fbxl3 is essential for formation of SCFFbxl3. In contrast, recombinant Fbxl3 associated with recombinant Skp1 and Cul1 in vitro even in the absence of recombinant Cry1. Domain-swap analysis revealed that the COOH-terminal leucine-rich repeat domain of Fbxl3 attenuates the interaction of Skp1, suggesting that a yet unknown protein associated with the COOH-terminal domain of Fbxl3 and inhibited SCF complex formation. Our results thus provide important insight into the regulation of both SCF ubiquitin ligase activity and circadian rhythmicity. PMID:24085301

  17. Complex Formation History of Highly Evolved Basaltic Shergottite, Zagami

    NASA Technical Reports Server (NTRS)

    Niihara, T.; Misawa, K.; Mikouchi, T.; Nyquist, L. E.; Park, J.; Hirata, D.

    2012-01-01

    Zagami, a basaltic shergottite, contains several kinds of lithologies such as Normal Zagami consisting of Fine-grained (FG) and Coarse-grained (CG), Dark Mottled lithology (DML), and Olivine-rich late-stage melt pocket (DN). Treiman and Sutton concluded that Zagami (Normal Zagami) is a fractional crystallization product from a single magma. It has been suggested that there were two igneous stages (deep magma chamber and shallow magma chamber or surface lava flow) on the basis of chemical zoning features of pyroxenes which have homogeneous Mg-rich cores and FeO, CaO zoning at the rims. Nyquist et al. reported that FG has a different initial Sr isotopic ratio than CG and DML, and suggested the possibility of magma mixing on Mars. Here we report new results of petrology and mineralogy for DML and the Olivine-rich lithology (we do not use DN here), the most evolved lithology in this rock, to understand the relationship among lithologies and reveal Zagami s formation history

  18. Direct measurement via phage titre of the dissociation constants in solution of fusion phage-substrate complexes.

    PubMed Central

    Dyson, M R; Germaschewski, V; Murray, K

    1995-01-01

    Studies of interactions between filamentous fusion phage particles and protein or nucleic acid molecules have gained increasing importance with recent successes of screening techniques based upon random phage display libraries (biopanning). Since a number of different phage are usually obtained by biopanning, it is useful to compare quantitatively the binding affinities of individual phage for the substrate used for selection. A procedure is described for determination of relative dissociation constants (KdRel) between filamentous phage carrying peptide fusions to the coat protein gpIII and substrates in solution. This novel method is based on the measurement of phage titres. Phage selected from a random fusion phage library for binding to a monoclonal antibody or a viral structural protein exhibited KdRel values in the nanomolar and micromolar ranges for their respective substrates, thus validating the method over a wide range of binding affinities. PMID:7784206

  19. The imidazole role in strontium beta-diketonate complexes formation.

    PubMed

    Marchetti, Fabio; Pettinari, Claudio; Pettinari, Riccardo; Cingolani, Augusto; Gobetto, Roberto; Chierotti, Michele R; Drozdov, Andrei; Troyanov, Sergey I

    2006-04-01

    A selection of new strontium beta-diketonate derivatives (imH2)2[Sr2(beta-dike)6] [where imH = imidazole and beta-dike = tfac (tfacH = 1,1,1-trifluoro-2,4-pentanedione), tfbz (tfbzH = 1,1,1-trifluoro-4-phenyl-2,4-butanedione), or hfac (hfacH = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione)], [Sr2(tfac)4(Meim)2(H2O)2], (MeimH)2[Sr(beta-dike)4] (where Meim = 1-methylimidazole and beta-dike = tfbz or hfac), [Sr2(thd)4(imH)2(EtOH)], and [Sr2(thd)4(Meim)2(EtOH)] (where thdH = 2,2,6,6-tetramethyl-3,5-heptanedione) have been synthesized and fully characterized. (imH2)2[Sr2(beta-dike)6] and (MeimH)2[Sr(beta-dike)4] are di- and mononuclear Sr anionic complexes, respectively, while [Sr2(tfac)4(Meim)2(H2O)2], [Sr2(thd)4(imH)2(EtOH)], and [Sr2(thd)4(Meim)2(EtOH)] are neutral dinuclear molecular derivatives. The derivative (imH2)2[Sr2(hfac)6] slowly decomposes in solution under aerobic conditions, giving (imH2)2[Sr(H2O)2(tfa)3](tfa) (tfaH = trifluoroacetic acid), which is an ionic compound containing polynuclear anionic chains composed of Sr(H2O)2(tfa)3 units. When a deficiency of imH is employed, the thdH proligand forms not only the dinuclear derivative [Sr2(thd)4(imH)2(EtOH)] but also an additional product with the formula [Sr(thd)2(H2O)2(EtOH)], in which the Sr atom is seven-coordinated. A complete solid-state characterization has been accomplished by comparing X-ray and solid-state 13C NMR data. Elucidation of the H-bond interaction between the heterocyclic rings and metal complexes by cross-polarization magic-angle-spinning 15N NMR is also reported. PMID:16562964

  20. Oxidative peptide /and amide/ formation from Schiff base complexes

    NASA Technical Reports Server (NTRS)

    Strehler, B. L.; Li, M. P.; Martin, K.; Fliss, H.; Schmid, P.

    1982-01-01

    One hypothesis of the origin of pre-modern forms of life is that the original replicating molecules were specific polypeptides which acted as templates for the assembly of poly-Schiff bases complementary to the template, and that these polymers were then oxidized to peptide linkages, probably by photo-produced oxidants. A double cycle of such anti-parallel complementary replication would yield the original peptide polymer. If this model were valid, the Schiff base between an N-acyl alpha mino aldehyde and an amino acid should yield a dipeptide in aqueous solution in the presence of an appropriate oxidant. In the present study it is shown that the substituted dipeptide, N-acetyl-tyrosyl-tyrosine, is produced in high yield in aqueous solution at pH 9 through the action of H2O2 on the Schiff-base complex between N-acetyl-tyrosinal and tyrosine and that a great variety of N-acyl amino acids are formed from amino acids and aliphatic aldehydes under similar conditions.

  1. Interferogram formation in the presence of complex and large deformation

    NASA Astrophysics Data System (ADS)

    Yun, Sang-Ho; Zebker, Howard; Segall, Paul; Hooper, Andrew; Poland, Michael

    2007-06-01

    Sierra Negra volcano in Isabela island, Galápagos, erupted from October 22 to October 30 in 2005. During the 8 days of eruption, the center of Sierra Negra's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the huge subsidence and the earthquake, it is difficult to form an interferogram inside the caldera that spans the eruption. The deformation is so large and spatially variable that the approximations used in existing InSAR software (ROI, ROI_PAC, DORIS, GAMMA) cannot properly coregister SAR image pairs spanning the eruption. We have developed here a two-step algorithm that can form intra-caldera interferograms from these data. The first step involves a ``rubber-sheeting'' SAR image coregistration. In the second step we use range offset estimates to mitigate the steep phase gradient. Using this new algorithm, we retrieve an interferogram with the best coverage to date inside the caldera of Sierra Negra.

  2. An illustration of the complexity of continent formation

    NASA Technical Reports Server (NTRS)

    Burke, Kevin

    1988-01-01

    It was pointed out that a consensus may be emerging in crustal growth models, considering the clustering of most growth curves and their uncertainties. Curves most distant from this clustering represent models involving extensive recycling of continental material back into the mantle, but the author wondered if geochemical signatures for this would be recognizable considering the lack of evidence from seismic tomography for discrete mantle reservoirs, and the likelihood of core-mantle interaction based on recent high pressure experiments. Unreactivated Archean rocks represent only 2 percent of present continental area, and the author was uncomfortable about basing inferences on what the early Earth was like on such a small amount of information. He feels that the hypothesis of continental assembly that needs testing is that of banging together of island arcs, such as in Indonesia today. As an example of how complex this process can be, the author described the geology of the Caribbean arc system, which shows evidence for reversals of subduction polarity, numerous collisional events, and substantial strike-slip movements. It seemed unlikely to the author that Archean examples would have been less complicated.

  3. Interferogram formation in the presence of complex and large deformation

    USGS Publications Warehouse

    Yun, S.-H.; Zebker, H.; Segall, P.; Hooper, A.; Poland, M.

    2007-01-01

    Sierra Negra volcano in Isabela island, Gala??pagos, erupted from October 22 to October 30 in 2005. During the 8 days of eruption, the center of Sierra Negra's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the huge subsidence and the earthquake, it is difficult to form an interferogram inside the caldera that spans the eruption. The deformation is so large and spatially variable that the approximations used in existing InSAR software (ROI, ROI_PAC, DORIS, GAMMA) cannot properly coregister SAR image pairs spanning the eruption. We have developed here a two-step algorithm that can form intra-caldera interferograms from these data. The first step involves a "rubber-sheeting" SAR image coregistration. In the second step we use range offset estimates to mitigate the steep phase gradient. Using this new algorithm, we retrieve an interferogram with the best coverage to date inside the caldera of Sierra Negra. Copyright 2007 by the American Geophysical Union.

  4. The adenylate cyclase receptor complex and aqueous humor formation.

    PubMed Central

    Caprioli, J.; Sears, M.

    1984-01-01

    The secretory tissue of the eye, the ciliary processes, contains an enzyme receptor complex, composed of membrane proteins, the catalytic moiety of the enzyme adenylate cyclase, a guanyl nucleotide regulatory protein (or N protein), and other features. The enzyme can be activated by well-known neurohumoral or humoral agents, catecholamines, glycoprotein hormones produced by the hypothalamic pituitary axis, and other related compounds, including placental gonadotropin, organic fluorides, and forskolin, a diterpene. These compounds cause the ciliary epithelia to produce cyclic AMP at an accelerated rate. Cyclic AMP, as a second messenger, causes, either directly or indirectly, a decrease in the net rate of aqueous humor inflow that may be modulated by cofactors. Clinical syndromes fit the experimental data so that an integrated explanation can be given for the reduced intraocular pressure witnessed under certain central nervous system and adrenergic influences. The molecular biology of this concept provides important leads for future investigations that bear directly both upon the regulation of intraocular pressure and upon glaucoma. Images FIG. 11 PMID:6093393

  5. Polyphenol-Aluminum Complex Formation: Implications for Aluminum Tolerance in Plants.

    PubMed

    Zhang, Liangliang; Liu, Ruiqiang; Gung, Benjamin W; Tindall, Steven; Gonzalez, Javier M; Halvorson, Jonathan J; Hagerman, Ann E

    2016-04-20

    Natural polyphenols may play an important role in aluminum detoxification in some plants. We examined the interaction between Al(3+) and the purified high molecular weight polyphenols pentagalloyl glucose (940 Da) and oenothein B (1568 Da), and the related compound methyl gallate (184 Da) at pH 4 and 6. We used spectrophotometric titration and chemometric modeling to determine stability constants and stoichiometries for the aluminum-phenol (AlL) complexes. The structures and spectral features of aluminum-methyl gallate complexes were evaluated with quantum chemical calculations. The high molecular weight polyphenols formed Al3L2 complexes with conditional stability constants (β) ∼ 1 × 10(23) at pH 6 and AlL complexes with β ∼ 1 × 10(5) at pH 4. Methyl gallate formed AlL complexes with β = 1 × 10(6) at pH 6 but did not complex aluminum at pH 4. At intermediate metal-to-polyphenol ratios, high molecular weight polyphenols formed insoluble Al complexes but methyl gallate complexes were soluble. The high molecular weight polyphenols have high affinities and solubility features that are favorable for a role in aluminum detoxification in the environment. PMID:27022835

  6. Structure of soybean serine acetyltransferase and formation of the cysteine regulatory complex as a molecular chaperone

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Serine acetyltransferase (SAT) catalyzes the limiting reaction in plant and microbial biosynthesis of cysteine. In addition to its enzymatic function, SAT forms a macromolecular complex with O-acetylserine sulfhydrylase (OASS). Formation of the cysteine regulatory complex (CRC) is a critical biochem...

  7. Phosphorylation-dependent formation of a quaternary complex at the c-fos SRE.

    PubMed Central

    Gille, H; Kortenjann, M; Strahl, T; Shaw, P E

    1996-01-01

    The rapid and transient induction of the human proto-oncogene c-fos in response to a variety of stimuli depends on the serum responses element (SRE). In vivo footprinting experiments show that this promoter element is bound by a multicomponent complex including the serum response factor (SRF) and a ternary complex factor such as Elk-1. SRF is thought to recruit a ternary complex factor monomer into an asymmetric complex. In this report, we describe a quaternary complex over the SRE which, in addition to an SRF dimer, contains two Elk-1 molecules. Its formation at the SRE is strictly dependent on phosphorylation of S-383 in the Elk-1 regulatory domain and appears to involve a weak intermolecular association between the two Elk-1 molecules. The influence of mutations in Elk-1 on quaternary complex formation in vitro correlates with their effect on the induction of c-fos reporter expression in response to mitogenic stimuli in vivo. PMID:8622654

  8. MICROCALORIMETRIC STUDIES ON THE FORMATION OF MAGNESIUM COMPLEXES OF ADENINE NUCLEOTIDES

    PubMed Central

    Belaich, J. P.; Sari, J. C.

    1969-01-01

    Values for the thermodynamic quantities (ΔF, ΔH, ΔS) in reactions in which complexes of adenine nucleotides with magnesium ion (ATPMg--, ADPMg-, AMPMg) are formed have been obtained by a microcalorimetric technique by using an isothermic Calvet's apparatus. Experimental values measured at ionic strength μ = 0.2 indicate that complex formation reactions are driven by the entropic factor and that stability of complexes increases with length of the phosphate chain. PMID:5261047

  9. Evidence of iron(III)-oxalato complex formation in aqueous solution from x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Magini, Mauro

    1981-02-01

    An aqueous solution of ferric ammonium oxalate has been examined to provide direct experimental evidence of complex formation between iron(III) and a typical organic complexing ligand. The radial distribution function as well as analysis of the structure function lead to the conclusion that the dominant species present in solution is the trioxalato-iron(III) complex in which each oxalate ion occupies two corners of a distorted octahedron around the Fe 3+ ions.

  10. HC[triple bond]P and H3C-C[triple bond]P as proton acceptors in protonated complexes containing two phosphorus bases: structures, binding energies, and spin-spin coupling constants.

    PubMed

    Alkorta, Ibon; Elguero, José; Bene, Janet E Del

    2007-10-01

    Ab initio calculations at the MP2/aug'-cc-pVTZ level have been carried out to investigate the structures and binding energies of cationic complexes involving protonated sp, sp2, and sp3 phosphorus bases as proton donor ions and the sp-hybridized phosphorus bases H-C[triple bond]P and H3C-C[triple bond]P as proton acceptors. These proton-bound complexes exhibit a variety of structural motifs, but all are stabilized by interactions that occur through the pi cloud of the acceptor base. The binding energies of these complexes range from 6 to 15 kcal/mol. Corresponding complexes with H3C-C[triple bond]P as the proton acceptor are more stable than those with H-C[triple bond]P as the acceptor, a reflection of the greater basicity of H3C-C[triple bond]P. In most complexes with sp2- or sp3-hybridized P-H donor ions, the P-H bond lengthens and the P-H stretching frequency is red-shifted relative to the corresponding monomers. Complex formation also leads to a lengthening of the C[triple bond]P bond and a red shift of the C[triple bond]P stretching vibration. The two-bond coupling constants 2pihJ(P-P) and 2pihJ(P-C) are significantly smaller than 2hJ(P-P) and 2hJ(P-C) for complexes in which hydrogen bonding occurs through lone pairs of electrons on P or C. This reflects the absence of significant s electron density in the hydrogen-bonding regions of these pi complexes. PMID:17760429