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1

Improved methods for calculating formation constants for nucleotide--cation complexes.  

PubMed

Two data reduction methods that can be used to calculate formation constants for nucleotide-cation complexes are described. Both methods are used to analyze data obtained by an anion-exchange resin method, and either method can improve the accuracy of the calculated formation constants by more than 50%. The key to this significant improvement in accuracy is the realization that the equation for the mathematical model describing such systems is always nonlinear in terms of the formation constants and, in the general case, is higher order in the cation concentration. There are two major reasons for the improved quality of the results associated with the new model. First, successive linear extrapolations are eliminated, and error propagation is reduced. Second, all of the data are used for the simultaneous calculation of all formation constants, and the uncertainty due to random experimental errors is minimized. PMID:6859527

Clary, L G; Voige, W H; Leary, J J

1983-02-15

2

Analysis of the association constants for charge-transfer complex formation  

NASA Astrophysics Data System (ADS)

The phenomenon of charge transfer (CT) complex formation has been of interest for more than 50 years and has led to the development of numerous applications. Even with the prolonged interest in these complexes the interactions responsible for complex formation have yet to be fully characterized and remain an area of sustained relevance. This report outlines the measurement of the association constants for CT complex formation of a series of methylated benzene donors with tetracyanoethylene, pyromellitic dianhydride, 2,3-dichloro-5,6-dicyano-p-benzoquinone, and 1,2,4,5-tetracyanobenzene acceptors in 1,2-dichloroethane solvent. The evaluation of the position of the CT absorption maximum and the magnitudes of the association constants within a theoretical model is described. The influence of solvent polarity on the magnitudes of the association constants was also discussed. These studies show that non-bonding interactions are important in most complexes while ion-pair interactions play a significant role in a select few of the complexes studied.

McKim, William D.; Ray, Jayanta; Arnold, Bradley R.

2013-02-01

3

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

NASA Astrophysics Data System (ADS)

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 ( ?M, ?x) needed for this extrapolation have been estimated from the Pitzer equations. The thermodynamic stability constants ( KMX) and activity coefficients of the various ion pairs ( ?MX) were determined from In ( solK MX?/? M? x) = In K mx+ In (? 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.

Millero, Frank J.

1992-08-01

4

Bacterial formate hydrogenlyase complex  

PubMed Central

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

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

2014-01-01

5

Dissociation of Bimolecular aIIbb3-Fibrinogen Complex under a Constant Tensile Force  

E-print Network

Dissociation of Bimolecular aIIbb3-Fibrinogen Complex under a Constant Tensile Force Rustem I the thermodynamics and kinetics of aIIbb3- fibrinogen bond formation and dissociation under constant unbinding forces

Barsegov, Valeri

6

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

ERIC Educational Resources Information Center

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)

Larsen, Erik; Eriksen, J.

1975-01-01

7

Measurements of Enthalpy Change of Reaction of Formation, Molar Heat Capacity and Constant-Volume Combustion Energy of Solid Complex Yb(Et 2dtc) 3 (phen)  

Microsoft Academic Search

A ternary solid complex Yb(Et2dtc)3(phen) was obtained from the reaction of hydrous ytterbium chloride with sodium diethyldithiocarbamate (NaEt2dtc), and 1, 10-phenanthroline (o-phen·H2O) in absolute ethanol. The bonding characteristics of the complex were characterized by IR. The result shows Yb3+ bands with two sulfur atoms in the Na(Et2dtc)3 and two nitrogen atoms in the o-phen. The enthalpy change of liquid-phase reaction

Weiming Song; Qilin Hu; Xuan Chang; Sanping Chen; Gang Xie; Shengli Gao

2006-01-01

8

Hydrolysis and formation constants at 25/sup 0/C  

SciTech Connect

A database consisting of hydrolysis and formation constants for about 20 metals associated with the disposal of nuclear waste is given. Complexing ligands for the various ionic species of these metals include OH, F, Cl, SO/sub 4/, PO/sub 4/ and CO/sub 3/. Table 1 consists of tabulated calculated and experimental values of log K/sub xy/, mainly at 25/sup 0/C and various ionic strengths together with references to the origin of the data. Table 2 consists of a column of recommended stability constants at 25/sup 0/C and zero ionic strength tabulated in the column headed log K/sub xy/(0); other columns contain coefficients for an extended Debye-Huckel equation to permit calculations of stability constants up to 3 ionic strength, and up to 0.7 ionic strength using the Davies equation. Selected stability constants calculated with these coefficients for various ionic strengths agree to an average of +- 2% when compared with published experimental and calculated values.

Phillips, S.L.

1982-05-01

9

The complex dielectric constant of snow at microwave frequencies  

Microsoft Academic Search

The complex dielectric constant of snow has been measured at microwave frequencies. New and old snow at different stages of metamorphosis have been studied. The results indicate that the complex dielectric constant is practically independent of the structure of snow. For dry snow, the dielectric constant is determined by the density. For wet snow, the imaginary part and the increase

M. Tiuri; A. Sihvola; E. Nyfors; M. Hallikaiken

1984-01-01

10

Determination of Complex Dielectric Constant of High-Loss Materials  

Microsoft Academic Search

A noncontacting measurement system for determining com-plex values of dielectric constant from measured values of complex reflection coefficient is described. A convenient graphical method for relating real and imaginary parts of dielectric constant to measured values and errors in the measured values of reflection coefficient is given.

G. C. Rose; R. J. Churchill; K. R. Cook

1972-01-01

11

Complex formation between benzene carboxylic acids and ?-cyclodextrin  

NASA Astrophysics Data System (ADS)

Complex formation between benzene carboxylic acids and ?-cyclodextrin in aqueous solutions at 290 300 K was studied using UV spectroscopy. The formation of 1:1 supramolecular inclusion compounds ?-cyclodextrin-benzene and ?-cyclodextrin-salicylic acid was found. Stability constants (Ks) of the complexes and thermodynamic parameters for formation of the inclusion compounds (?G, ?H, and ?S) were calculated.

Belyakova, L. A.; Lyashenko, D. Yu.

2008-05-01

12

Apparent Stability Constants of Magnesium and Calcium Complexes of Tricarboxylates  

Microsoft Academic Search

Arsenazo I was used as a metallochromic indicator for the spectrophotometric determination at 560 nm to 570 nm of apparent stability constants of magnesium and calcium complexes of tricarboxylates and ADP between pH 7.4 and pH 8.0. Average values of apparent stability constants (nM) in 0.14 M Tris-HCL at pH 8.0 obtained with this method are reported sequentially for the

Jerome L. Gabriel; Tadashi Aogaichi; Charles R. Dearolf; Gerhard W. E. Plaut

1983-01-01

13

Complexation of several fungicides with beta-cyclodextrin: determination of the association constants and isolation of the solid complexes.  

PubMed

The formation of inclusion complexes with beta-cyclodextrin was studied for several popular fungicides of different types: prochloraz, 2-phenylphenol, thiophanate methyl, 8-hydroxyquinoline, and benalaxyl. Phase solubility diagrams showed that in all cases complexation takes place, leading to an important increase of water solubility in prochloraz and benalaxyl. Equilibrium association constants could be determined from the phase solubility data and from NMR titrations in the case of 2-phenylphenol. Because of the low solubility of the complex formed between 8-hydroxyquinoline and beta-cyclodextrin, the corresponding association constant could not be determined. The solid complexes of fungicide-cyclodextrin were prepared and isolated by different methods. The isolation of real complexes and not physical mixtures was confirmed in the cases of prochloraz, 2-phenylphenol, and benalaxyl by differential scanning calorimetry. PMID:12903966

Lezcano, Minerva; Novo, Mercedes; Al-Soufi, Wajih; Rodríguez-Núñez, Eugenio; Tato, José Vázquez

2003-08-13

14

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

SciTech Connect

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.

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

1996-06-01

15

Stability constants of nickel(II)-nicotinamide complexes in aqueous-ethanol solutions  

NASA Astrophysics Data System (ADS)

The change in stability of 1: 1 and 1: 2 nicotinamide nickel(II) complexes in an aqueous ethanol with ethanol contents of 0 to 0.85 molar fractions is studied via potentiometry at 298.2 ± 0.1 K and a ionic strength of 0.25 (NaClO4). The constant of complex formation for the first step increases at concentrations of organic solvent lower than 0.5 molar fractions and decreases at a higher content of ethanol. The weakening of the solvation of the donor center in nicotinamide corresponds to the observed change in the stability of the complex. A linear interrelation between the change in the coordination equilibrium constant and the difference between the effect of solvent composition on the solvation of the complex ions and complexing agent is revealed.

Gamov, G. A.; Dushina, S. V.; Sharnin, V. A.

2014-05-01

16

Taurocholate and taurodeoxycholate: gel formation and protonation constants.  

PubMed

Taurocholate (TC) and taurodeoxycholate (TDC) in aqueous solutions, in the presence of sodium and hydrogen ions can give micellar products, even differently protonated. This phenomenon is investigated in this paper to explain whether the assumption of hydrogen ions is to attribute to the micellar aggregates, or to the protonation of taurocholate and taurodeoxycholate, respectively. In the course of this research, often the formation of gel occurred immediately after the mixture of the reagents (sodium, hydrogen ions and anions of bile acids) or after some time, depending on the concentrations of the reagents. No author mentions this evidence, but experiments carried out in the presence of gel are not reproducible because the investigated solutions cannot be considered in real equilibrium. The protonation study was performed by means of electromotive force measurements of a galvanic cell involving a glass electrode, at 25 degrees C and 1.00 mol dm(-3) NaCl, as ionic medium. The obtained protonation constants had the following values: log k1 = 0.07+/- 0.02 for TC and log k'1 = 1.60 +/- 0.03 for TDC. PMID:17822262

Antonilli, Marco; Bottari, Emilio; Festa, Maria Rosa

2007-01-01

17

Limitations on the determination of the stoichiometry and equilibrium constants of weak complexes by computer fitting methods: experimental verification  

Microsoft Academic Search

We present experimental evidence showing that computer fitting methods are inadequate for the study of weak complexations, whenever a certain equation relates the reaction parameters. In such cases, one must resort to direct (non-computational) methods for the determination of the stoichiometry of the interaction and the equilibrium constants. Our data refer to complex formation between cyclodextrins and diphenylpolyenes, and we

G. Pistolis; Angelos Malliaris

1999-01-01

18

New insights into formation of trivalent actinides complexes with DTPA.  

PubMed

Complexation of trivalent actinides with DTPA (diethylenetriamine pentaacetic acid) was studied as a function of pcH and temperature in (Na,H)Cl medium of 0.1 M ionic strength. Formation constants of both complexes AnHDTPA(-) and AnDTPA(2-) (where An stands for Am, Cm, and Cf) were determined by TRLFS, CE-ICP-MS, spectrophotometry, and solvent extraction. The values of formation constants obtained from the different techniques are coherent and consistent with reinterpreted literature data, showing a higher stability of Cf complexes than Am and Cm complexes. The effect of temperature indicates that formation constants of protonated and nonprotonated complexes are exothermic with a high positive entropic contribution. DFT calculations were also performed on the An/DTPA system. Geometry optimizations were conducted on AnDTPA(2-) and AnHDTPA(-) considering all possible protonation sites. For both complexes, one and two water molecules in the first coordination sphere of curium were also considered. DFT calculations indicate that the lowest energy structures correspond to protonation on oxygen that is not involved in An-DTPA bonds and that the structures with two water molecules are not stable. PMID:23152978

Leguay, Sébastien; Vercouter, Thomas; Topin, Sylvain; Aupiais, Jean; Guillaumont, Dominique; Miguirditchian, Manuel; Moisy, Philippe; Le Naour, Claire

2012-12-01

19

Stoichiometry and Formation Constant Determination by Linear Sweep Voltammetry.  

ERIC Educational Resources Information Center

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)

Schultz, Franklin A.

1979-01-01

20

Drop formation dynamics of constant low-viscosity, elastic fluids  

Microsoft Academic Search

The dynamics of drop formation under gravity has been investigated as a function of elasticity using a set of low-viscosity, ideal elastic fluids and an equivalent Newtonian glycerol–water solution. All solutions had the same shear viscosity, equilibrium surface tension, and density, but differed greatly in elasticity. The minimum drop radius in the early stages of drop formation (necking) was found

J. J. Cooper-White; J. E. Fagan; V. Tirtaatmadja; D. R. Lester; D. V. Boger

2002-01-01

21

Determination of thermodynamic values of acidic dissociation constants and complexation constants of profens and their utilization for optimization of separation conditions by Simul 5 Complex.  

PubMed

In this paper we determine acid dissociation constants, limiting ionic mobilities, complexation constants with ?-cyclodextrin or heptakis(2,3,6-tri-O-methyl)-?-cyclodextrin, and mobilities of resulting complexes of profens, using capillary zone electrophoresis and affinity capillary electrophoresis. Complexation parameters are determined for both neutral and fully charged forms of profens and further corrected for actual ionic strength and variable viscosity in order to obtain thermodynamic values of complexation constants. The accuracy of obtained complexation parameters is verified by multidimensional nonlinear regression of affinity capillary electrophoretic data, which provides the acid dissociation and complexation parameters within one set of measurements, and by NMR technique. A good agreement among all discussed methods was obtained. Determined complexation parameters were used as input parameters for simulations of electrophoretic separation of profens by Simul 5 Complex. An excellent agreement of experimental and simulated results was achieved in terms of positions, shapes, and amplitudes of analyte peaks, confirming the applicability of Simul 5 Complex to complex systems, and accuracy of obtained physical-chemical constants. Simultaneously, we were able to demonstrate the influence of electromigration dispersion on the separation efficiency, which is not possible using the common theoretical approaches, and predict the electromigration order reversals of profen peaks. We have shown that determined acid dissociation and complexation parameters in combination with tool Simul 5 Complex software can be used for optimization of separation conditions in capillary electrophoresis. PMID:25213298

Riesová, Martina; Svobodová, Jana; Ušelová, Kate?ina; Tošner, Zden?k; Zusková, Iva; Gaš, Bohuslav

2014-10-17

22

The equilibrium constant of beta-cyclodextrin-phenolphtalein complex; influence of temperature and tetrahydrofuran addition.  

PubMed

The temperature influence on creation of a supramolecular complex in which beta-cyclodextrin (beta-CD) is the host molecule and phenolphtalein (PP) is the guest has been studied in aqueous solution by UV-visible absorption spectroscopy. The decrease of temperature of beta-cyclodextrin-phenolphtalein system resulted in a decrease in absorbance of the UV-vis spectrum. Under favourable conditions (0.1 mM beta-CD, 30 microM PP) the termochromic effect is very significant (approximately =0.1 U of absorbance/10 degrees C). The formation constant of inclusion complex was determined at various temperatures (from 10 to 70 degrees C) using Scott's equation. The association constants (K11) for the binding in 0.02 M sodium carbonate (pH 10.5) at 10 and 70 degrees C are 7.44 and 0.26 x 10(4) M(-1) respectively. The stoichiometric ratio of investigated complex was found to be 1:1 on wide range of beta-cyclodextrin:phenolphtalein concentration ratio (from 0.8:1 to 427:1). Additionally, strong interaction between cyclodextrin and tetrahydrofuran (THF) was observed and the inhibitory effect of tetrahydrofurane on the association of beta-CD PP complex was studied. From linear Van't Hoff plots thermodynamic parameters such as: the change of enthalpy (deltaH(o)) and change of entropy (deltaS(o)) were estimated and interpreted. PMID:9863954

Zarzycki, P K; Lamparczyk, H

1998-10-01

23

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

Microsoft Academic Search

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) NaClOâ and (b) NaCl as the background electrolytes. The ionic

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

1995-01-01

24

Complex formation of p-boronophenylalanine with some monosaccharides.  

PubMed

To increase the solubility of p-boronophenylalanine (p-bpa) in neutral pH solution, the complex formation of p-bpa with some monosaccharides has been studied by 11B-NMR and UV spectroscopy. The complex formation constants (log K) obtained by the UV method in pH 7.4 solution are 2.43 (fructose), 2.19 (mannitol), 1.28 (galactose), 1.10 (mannose), and 0.85 (glucose), respectively. One hundred milligrams of p-bpa is able to dissolve in 3 ml of 0.3 M fructose solution at pH 7.98. Based on the results obtained, the behavior of p-bpa-monosaccharide complexes in vivo after injection of the complex solution is described. PMID:2508079

Mori, Y; Suzuki, A; Yoshino, K; Kakihana, H

1989-01-01

25

Stability constants: comparative study of fitting methods. Determination of second-order complexation constants by (23)Na and (7)Li NMR chemical shift titration.  

PubMed

NMR chemical shift titration has been widely used as a method for the determination of stability constants. Systems involving metal-ligand complexation have been investigated using a number of methodologies. There are significant differences in the values reported for stability constants obtained by different experimental methods, such as calorimetry and ion selective electrode (ISE) titrations; nor has NMR chemical shift titration always yielded consistent results. Different researchers have obtained different results for the same system with results differing by as much as an order of magnitude. The chemical shift data are generally plotted against the concentration ratio of the metal and ligand for a set of solutions. A nonlinear least squares fitting method using an analytical solution of the cubic equation for the equilibrium concentration of the free ligand is used in this study and compared with methods used in the literature. Second-order association constants for the LiClO(4):12-crown-4 system in acetonitrile and the NaClO(4):12-crown-4 system in methanol are reported. Formation of both 1:1 and 1:2 metal-ligand complexes are considered. The LiClO(4):12-crown-4 acetonitrile system had been investigated previously by NMR titration but only 1:1 complexation was considered in that study. This study provides convincing evidence that both 1:1 and 1:2 complexes are important, at least, in the lithium system. A Monte Carlo investigation of the propagation of errors from the chemical shifts to the stability constants shows that the choice of data analysis methods may, in part, contribute to discrepancies and that the nonlinear nature of the model can dramatically affect the error limits on the stability constants. PMID:16477684

Masiker, Marilyn C; Mayne, Charles L; Eyring, Edward M

2006-03-01

26

Determinacion de las constantes de hidrolisis y de los complejos con carbonatos del Praseodimio (III), en medio de fuerza ionica 2M de cloruro de sodio, a 303 K. (Determination of formation constants of hydroxo carbonate complexes of Pr(sup 3+) in 2M NaCl at 303 K).  

National Technical Information Service (NTIS)

The hydrolysis of Praseodymium III in 2M 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 ...

H. D. G. Lopez

1996-01-01

27

The formation of bifurcated charge transfer complexes with molecular iodine  

NASA Astrophysics Data System (ADS)

I 2 complexes with triptycene and several di- and triaryl derivatives of methane and ethane were studied. For these complexes the values of ? CT are virtually identical to those reported for the complexes with the analogous monoaryl donors, while the values of ? for their blue shifted I 2 peaks are significantly lower than those for the monoaryl complexes. Both the equilibrium constants and - ?H 0 values for the formation of complexes from the components lead to the conclusion that the complexes with the di- and triaryl compounds are more stable than those with the monoaryl donors. For the diaryl donors, the ? S0298 values for complex formation are less favorable than those of the monoaryl donors. The dipole moment for I 2 in diphenylmethane is larger than the moment of I 2 in toluene. All of these observations can be explained by taking into account the transannular effect of one aromatic ring on another and viewing the complexes as bifurcated ones in which the I atom at one end of an I 2 molecule simultaneously interacts with two rings in the donor molecules.

Kulevsky, Norman; Pierce, Ken

1993-03-01

28

Determination of stability constants of aminoglycoside antibiotics with their metal complexes  

NASA Astrophysics Data System (ADS)

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-?-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.

Tiwow, Vanny M. A.

2014-03-01

29

Efficient quantum-classical method for computing thermal rate constant of recombination: Application to ozone formation  

E-print Network

: Application to ozone formation Mikhail V. Ivanov and Dmitri Babikov Citation: J. Chem. Phys. 136, 184304 (2012 for computing thermal rate constant of recombination: Application to ozone formation Mikhail V. Ivanov of ozone. Comparison of the predicted rate vs. experimental result is presented. � 2012 American Institute

Reid, Scott A.

30

Mechanisms of Benzene Formation: Rate Constant Theory from Soot to Jovian Atmospheres  

NASA Astrophysics Data System (ADS)

Benzene has been detected in the atmospheres of Jupiter and Saturn, and provides an initial species for forming larger condensable aromatics. Concentrations are sensitive to photolytic loss, the formation reaction, and the precursor reactant concentrations. Modelers have examined possible production kinetics, taken from soot combustion kinetics mechanisms. The candidate reactions 2C3H3 ? C6H6, C4H3 + C2H2 ? C6H4 + H, C4H5 + C2H2 ? C6H6 + H all proceed through a series of intermediates, and at various points alternative product channels are available. Since such chemical activation reaction systems are highly temperature and pressure dependent, the combustion and room temperature results must be extrapolated using kinetics rate theory to the low pressures and temperatures relevant to planetary atmospheres. Results of master equation calculations using parameters from established literature potential surfaces will be presented, as will probable production rates based on the recommended rate constants. Results from applying RRKM theory and master equation calculations to other small hydrocarbon reaction systems important to the formation of mid-size observable hydrocarbons will also be summarized. The C3H5 surface provides a particularly interesting and complex example. This work is supported by the NASA Outer Planets Research Program.

Smith, Gregory P.

2006-09-01

31

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

SciTech Connect

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).

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

1987-01-01

32

Simultaneous determination of stability constants of humate complexes with various metal ions using multitracer technique  

Microsoft Academic Search

Stability constants of humic acid complexes of 19 elements, Be, Ca, Sc, V, Cr, Mn, Fe, Co, Zn, Ga, Sr, Y, Ba, Ce, Eu, Gd, Tm, Yb, and Lu, were determined simultaneously using the multitracer technique. Since the results were obtained under an identical method, model, and sample, we could compare the stability constants of humate with various metal ions.

Yoshio Takahashi; Yoshitaka Minai; Shizuko Ambe; Yoshihiro Makide; Fumitoshi Ambe; Takeshi Tominaga

1997-01-01

33

Turbulent edge structure formation in complex configurations  

Microsoft Academic Search

Formation of nonlinear structures in drift-Alfvén turbulence is investigated in the often complex edge geometries of stellarator and tokamak configurations, by analysis of drift wave turbulence simulations using a model in which three-dimensional magnetic geometries are approximated. The structures of parallel mode extension, radially sheared zonal flows and perpendicular mode spectra are highlighted in particular for three-dimensional stellarator magnetic fields

A. Kendl; B. D. Scott; R. Ball; R. L. Dewar

2003-01-01

34

Complex dielectric constant of various biomolecules as a function of wavelength using surface plasmon resonance  

NASA Astrophysics Data System (ADS)

Present study focuses on determination of complex dielectric constant of biomolecules as function of frequency by means of surface plasmon resonance (SPR) technique without losing their biofunctionality. Surface plasmon modes have been excited in Kretschmann configuration at interface of ZnO-Au thin films. Various biomolecules (glucose oxidase, cholesterol oxidase, urease, and uricase) have been immobilized successfully on surface of ZnO thin film by electrostatic interaction. SPR reflectance curves for all biomolecules were recorded separately at different wavelengths (407-635 nm). Complex dielectric constant was determined by fitting the experimental SPR data with Fresnel's equations. Dielectric constant of all biomolecules shows frequency dispersion and attributed to ionic polarization.

Paliwal, Ayushi; Tomar, Monika; Gupta, Vinay

2014-07-01

35

Thermodynamics for complex formation between palladium(ii) and oxalate.  

PubMed

Complex formation between [Pd(H2O)4](2+) and oxalate (ox = C2O4(2-)) has been studied spectrophoto-metrically in aqueous solution at variable temperature, ionic strength and pH. Thermodynamic parameters at 298.2 K and 1.00 mol dm(-3) HClO4 ionic medium for the complex formation [Pd(H2O)4](2+) + H2ox ? [Pd(H2O)2(ox)] + 2H3O(+) with equilibrium constant K1,H (in mol dm(-3)) are log10K1,H = 3.38 ± 0.08, ?H = -33 ± 3 kJ mol(-1), and ?S = -48 ± 11 J K(-1) mol(-1), as determined from spectrophotometric equilibrium titrations at 15.0, 20.0, 25.0 and 31.0 °C. Thermodynamic overall stability constants ? (in (mol dm(-3))(-n), n = 1,2) for [Pd(H2O)2(ox)] and [Pd(ox)2](2-) at zero ionic strength and 298.2 K, defined as the equilibrium constants for the reaction Pd(2+) + nox(2-) ? [Pd(ox)n](2-2n) (water molecules omitted) are log10? = 9.04 ± 0.06 and log10? = 13.1 ± 0.3, respectively, calculated by use of Specific Ion Interaction Theory from spectrophotometric titrations with initial hydrogen ion concentrations of 1.00, 0.100 and 0.0100 mol dm(-3) and ionic strengths of 1.00, 2.00 or 3.00 mol dm(-3). The values derived together with literature data give estimated overall stability constants for Pd(ii) compounds such as [Pd(en)(ox)] and cis-[Pd(NH3)2Cl2], some of them analogs to Pt(ii) complexes used in cancer treatment. The palladium oxalato complexes are significantly more stable than palladium(ii) complexes with monodentate O-bonding ligands. A comparison between several different palladium complexes shows that different parameters contribute to the stability variations observed. These are discussed together with the so-called chelate effect. PMID:24912768

Pilný, Radomír; Lubal, P?emysl; Elding, Lars I

2014-08-28

36

Stability Constants of Np(V) Complexes with Fluoride and Sulfate at Variable Temperatures  

SciTech Connect

A solvent extraction method was used to determine the stability constants of Np(V) complexes with fluoride and sulfate in 1.0 M NaClO4 from 25 C to 60 C. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of fluoride and sulfate were increased. Stability constants of the 1:1 Np(V)-fluoride complexes and the 1:1 Np(V)-sulfate and 1:2 Np(V)-sulfate complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [F-] and [SO42-] 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.

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

2006-07-31

37

Measuring Dissociation Rate Constants of Protein Complexes through Subunit Exchange: Experimental Design and Theoretical Modeling  

SciTech Connect

Protein complexes are generally dynamic macromolecules that constantly disintegrate into, and simultaneously are assembled from, free subunits. Dissociation rate constants, koff, provide important structure and function information on protein complexes. However, because all existing methods for measuring koff require high-quality purification and specific modifications of protein complexes, dissociation kinetics has only been studied for a small set of model complexes. Here we propose a new method, called Metabolically-labeled Affinity-tagged Subunit Exchange (MASE) to measure koff using metabolic labeling, affinity purification and mass spectrometry. MASE is based on a subunit exchange process between an unlabeled affinity-tagged variant and a metabolically-labeled untagged variant of a complex. In this study, the subunit exchange process was modeled theoretically for a heterodimeric complex. The results showed that koff determines, and hence can be estimated from, the observed rate of subunit exchange. Future study will be needed to experimentally validate the new method.

Pan, Chongle [ORNL

2011-01-01

38

Complex formation between uranyl and various thiosemicarbazide derivatives  

SciTech Connect

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.

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

1987-01-01

39

Measurements of Complex Dielectric Constants of Paints and Primers for DSN Antennas: Part II  

NASA Astrophysics Data System (ADS)

In Part I of this article, complex dielectric constant values in the frequency range of 24 through 34 GHz were presented for paints and primers currently being used as well as for candidate replacements. Tables of complex dielectric constant values were given for (1) Triangle no. 6 white flat paint, (2) zinc chromate primer, (3) 18FHR6 white water-based paint, and (4) 283 water-based (Aquapoxy) primer. In this article, Part II, complex dielectric constants are presented for 500FHR6 acrylic urethane-based paint and Triangle no. 710 white glossy paint. In addition, this article gives plots of the real part of the complex dielectric constants and loss tangents of most of the above-mentioned paints and primers. These plots enable quick comparisons to be made of the dielectric properties of the paints and primers in the region of 32 GHz. A final part of the paint study, to be done in the near future, will be to use these complex dielectric constants to compute noise-temperature degradations that occur when various paints and primers are applied to antenna reflector surfaces.

Otoshi, T. Y.; Cirillo, R., Jr.; Sosnowski, J.

1999-07-01

40

Formation of scale inside the tubes of heat exchangers at a constant wall temperature  

NASA Astrophysics Data System (ADS)

A mathematical model for calculating scale formation inside tubes at a constant wall temperature is proposed. Expressions are obtained for calculating the surface density and thickness of a scale layer as applied to the operating conditions of steam turbine condensers. The calculation results are compared with experimental data.

Davidzon, M. I.

2007-09-01

41

Emission Time Constant of Exoelectron and Formative Delay Time Analyzed by Using Discharge Probability Distribution  

Microsoft Academic Search

A discharge probability model is proposed to analyze the stochastic distribution of the discharge delay time. The distribution is described as a hybrid function between the exponential and Gaussian distributions and their characteristic properties, such as the emission time constant of an exoelectron and the average and standard deviations of the formative delay time. The calculated results of the probability

Shirun Ho; Norihiro Uemura; Shunichiro Nobuki; Shunsuke Mori; Tatsuya Miyake; Keizo Suzuki; Yoshiro Mikami; Masatoshi Shiiki; Shoichi Kubo

2010-01-01

42

Steric Aspects of the Formation of Metal Chelate Complexes  

Microsoft Academic Search

The geometrical and thermodynamic aspects of the formation of complexes between metal cations and organic ligands are examined theoretically from the standpoint of conformational analysis. Particular attention has been devoted to the problem of the selectivity of the complex formation, which is of practical importance. It is shown that the selectivity of complex formation is largely determined by the steric

V G Dashevskii; A P Baranov; Martin I Kabachnik

1983-01-01

43

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

Microsoft Academic Search

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

Arup K. Basak; Arthur E. Martell

1988-01-01

44

Polychronous formation of mantle complexes in ophiolites  

NASA Astrophysics Data System (ADS)

The paper presents new determinations of the U-Pb zircon age of high-Al chromitite from dunite of the mantle section of the Voikar-Synya massif at the Kershor site in the boundary zone with rocks of the dunite-wehrlite-clinopyroxenite complex. The high-Cr chromitite from dunite in the central part of the same massif contains zircon dated at ca. 0.6 Ga [10]. It is suggested that Paleoproterozoic (2.0-1.9 Ga) zircons from chromitites of the mantle section near the petrological Moho boundary were formed in the course of partial melting of peridotites and/or their interaction with migrating MORB-type melts. The occurrence of Vendian and Paleoproterozoic zircons in chromitites from different parts of the mantle section, as well as previously published petrological, geochemical, and geological data [2, 11, 22] allow us to suggest a complex multistage evolution of the mantle section in ophiolites. The arguments stated below show that chromitites and host dunites could have been formed at different times and were probably related to different processes. Thus, not only various complexes of the pre-Paleozoic oceanic crust reworked in the suprasubduction setting differ in age, but also the mantle rock of similar petrography, vary in the time of their formation.

Savelieva, G. N.; Batanova, V. G.; Berezhnaya, N. A.; Presnyakov, S. L.; Sobolev, A. V.; Skublov, S. G.; Belousov, I. A.

2013-05-01

45

Vortex formation in a complex plasma  

NASA Astrophysics Data System (ADS)

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).

Ishihara, Osamu

46

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 ...

47

Determination of stability constants for complexes from catalytic linear scan voltammetric currents  

NASA Astrophysics Data System (ADS)

A linear scan voltammetric method for determining stability constants for complexes formed in the bulk solution between metal ions and ligands that catalyse their reduction is proposed. The method is based on the pure limiting kinetic current produced in the electrocatalytic process, which is recorded following preconcentration of ligands by convective transport on a hanging mercury drop electrode until surface excesses reach the values for adsorption equilibrium with the bulk solution. The stability constant for the Ni(o-phenylenediamine)2+ complex provided by the proposed method is reasonably consistent with reported values obtained from catalytic dc polarographic currents. Une méthode voltammétrique à balayage linéaire de potentiel a été développée pour la détermination des constants de stabilité des complexes des ions métalliques avec des ligands capables de catalyser leur réduction. La méthode utilise le courant limite cinétique produite par la réaction électrocatalytique. Cette courante est enregistrée après une période de préconcentration du ligand à la surface de l'électrode de goutte pendante de mercure jusqu'à la concentration superficiale atteint la valeur correspondante à l'équilibre d'adsorption avec la solution. La valeur de la constant de stabilité mesurée avec cette méthode pour le complexe Ni(o-phénylénédiamine) est d'accord avec les valeurs obtenues de la courant catalytique en polarographie de courant continu.

Muñiz Alvarez, J. L.; García Calzón, J. A.; López Fonseca, J. M.

1998-05-01

48

Factors affecting the threading of axle molecules through macrocycles: Binding constants for semirotaxane formation  

PubMed Central

The threading of more or less linear axle molecules through macrocyclic molecules, a fundamental process relating to the formation of interlocked molecular structures, has been investigated through the study in acetone of the equilibrium constants for the formation of pseudorotaxanes by NMR methods. The 30 new axle molecules have in common a secondary ammonium group, present as the thiocyanate salt, and an anthracen-9-ylmethyl group, but are rendered unique by the second amine substituent. All rotaxanes involve the well known polyether macrocycle, benzo[24]crown-8. The constants for the binding of axles having linear groups ranging from 2 to 18 carbon atoms show little variation in binding constant but are divided into two groups by their equilibration rates. Those with less than five methylene groups react rapidly on the NMR timescale, whereas those having more than five methylene groups are slow. Branching inhibits binding, but the effect decreases as the branch is moved away from the amine. Phenyl groups weaken binding when close to the amine but strengthen binding when more remote. Some functional groups decrease pseudorotaxane stability (alcohol functions), whereas others increase binding (carboxylic acid groups). PMID:11959934

Clifford, Thomas; Abushamleh, Ahmad; Busch, Daryle H.

2002-01-01

49

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

SciTech Connect

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).

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

2006-03-01

50

The Determination of Complex Dielectric Constants of Absorptive Liquids by Microwave Interferometry  

Microsoft Academic Search

This paper describes both a traveling-wave method and a standing-wave method for determining complex dielectric constants of liquids from measurements made at 10-cm wavelength with a traveling probe immersed in a dielectric-filled slotted line. An interferometric null technique was developed for improving the accuracy of the measurements, especially in highly absorptive media. In the traveling-wave method, absolute measurements of both

Franklin H. Branin

1952-01-01

51

Stability constants for the complexation of various metals with a rhamnolipid biosurfactant.  

PubMed

The presence of toxic metals in natural environments presents a potential health hazard for humans. Metal contaminants in these environments are usually tightly bound to colloidal particles and organic matter. This represents a major constraint to their removal using currently available in situ remediation technologies. One technique that has shown potential for facilitated metal removal from soil is treatment with an anionic microbial surfactant, rhamnolipid. Successful application of rhamnolipid in metal removal requires knowledge of the rhamnolipid-metal complexation reaction. Therefore, our objective was to evaluate the biosurfactant complexation affinity for the most common natural soil and water cations and for various metal contaminants. The conditional stability constant (log K) for each of these metals was determined using an ion-exchange resin technique. Results show the measured stability constants follow the order (from strongest to weakest): Al3+ > Cu2+ > Pb2+ > Cd2+ > Zn2+ > Fe3+ > Hg2+ > Ca2+ > Co2+ > Ni2+ > Mn2+ > Mg2+ > K+. These data indicate that rhamnolipid will preferentially complex metal contaminants such as lead, cadmium, and mercury in the presence of common soil or water cations. The measured rhamnolipid-metal stability constants were found in most cases to be similar or higher than conditional stability constants reported in the literature for metal complexation with acetic acid, oxalic acid, citric acid, and fulvic acids. These results help delineate the conditions under which rhamnolipid may be successfully applied as a remediation agent in the removal of metal contaminants from soil, as well as surface waters, ground water, and wastestreams. PMID:11285908

Ochoa-Loza, F J; Artiola, J F; Maier, R M

2001-01-01

52

QSPR Prediction of the Stability Constants of Gadolinium(III) Complexes for Magnetic Resonance Imaging.  

PubMed

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

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

2014-10-27

53

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

NASA Astrophysics Data System (ADS)

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.

Shapovalov, S. A.

2011-01-01

54

Spectrophotometric studies of molecular complex formation between water-soluble cobalt(II) Schiff base complex and nucleotides in mixed solvent systems  

NASA Astrophysics Data System (ADS)

The formation constants for 1:1 molecular complex formation between water-soluble cobalt(II) tetradentate Schiff base complex, disodium[{bis(4-methoxy-5-sulfo-salicylaldehyde)-4,5-dimethyl-o-phenylenediiminato}cobalt(II)], Na 2[Co(SO 3-4-meosal-4,5-dmophen)], and nucleotides, adenosine-5'-triphosphate (ATP) and cytidine-5'-triphosphate (CTP), in mixed solvent systems of ethanol and water with different volume fractions of ethanol and water have been determined spectrophotometrically at constant ionic strength ( I = 0.2 mol dm -3 NaClO 4) and temperature 278 K. Trends in the values of formation constants according to the volume fractions of ethanol and water in ethanol and water mixed solvent systems, suggest that the trend of molecular complex formation increases with increasing the volume fraction of ethanol in mixed solvent systems.

Boghaei, Davar M.; Gharagozlou, Mehrnaz

2005-10-01

55

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

PubMed

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

Morris, Robert H

2014-02-01

56

Potentiometric studies of complex formation between methylmercury(II) and EDTA.  

PubMed

The protonation of EDTA (ethylenediaminetetra-acetic acid) and its complex formation with methylmercury(II) ions was studied by a potentiometric method at 25 degrees in 1.0M NaNO(3). The protonation constants of EDTA and the equilibrium constants for the complexation reactions between methylmercuric ions and EDTA were evaluated by analysing the experimental data with the ETITR version of the general error-minimizing program LETAGROP. The results were used to develop an analytical method, based on complexometric titration and ion-exchange separation, for the determination of inorganic and organic mercury in the presence of one another. PMID:18962242

Jawaid, M

1978-04-01

57

Estimation of the initial equilibrium constants in the formation of tetragonal lysozyme nuclei  

NASA Astrophysics Data System (ADS)

Knowledge of the solution aggregate composition in both undersaturated (pre-nucleated) and oversaturated (nucleated and crystal growing) solutions is important to the eventual understanding of the (protein) crystal nucleation and growth process. Using relative light scattering intensity measurements at 90?, estimates of the initial equilibrium constants in the formation of tetragonal lysozyme nuclei have been made. While the aggregation pathway is not known, it is assumed that the first step is dimer formation ( K 1 = [P 2]/[P 1] 2). Experiments at 3.0% NaCl, 0.1M acetate buffer, pH 4.0, 22°C indicate K 1 values of (1-3) × 10 4 L mol -1. Estimation of subsequent equilibrium constants will be dependent upon the aggregation model chosen or determined. For a 1 ? 2 ? 4 pathway, K 2 values are estimated to be (2-4) × 10 3 L mol -1, while for a 1 ? 2 ? 3 pathway, values of (10-20) × 1 0 3 L mol -1 are estimated. Equilibrium values of this magnitude essentially "fix" the monomer concentration by the saturation concentration point, with only the higher order aggregates showing appreciable concentration increase with increasing total protein concentration. This strongly suggests that tetragonal lysozyme crystal growth is by addition of aggregates preformed in the bulk solution, not by monomer addition. This is independent of a screw dislocation or surface nucleation type mechanism.

Pusey, Marc Lee

1991-03-01

58

The formation of voids in a universe with cold dark matter and a cosmological constant  

E-print Network

A spherical Lagrangian hydrodynamical code has been written to study the formation of cosmological structures in the early Universe. In this code we take into account the presence of collisionless non-baryonic cold dark matter (CDM), the cosmological constant and a series of physical processes present during and after the recombination era, such as photon drag resulting from the cosmic background radiation and hydrogen molecular production. We follow the evolution of the structure since the recombination era until the present epoch. As an application of this code we study the formation of voids starting from negative density perturbations which evolved during and after the recombination era. We analyse a set of COBE-normalized models, using different spectra to see their influence on the formation of voids. Our results show that large voids with diameters ranging from 10h^{-1} Mpc up to 50h^{-1} Mpc can be formed in a universe model dominated by the cosmological constant (\\Omega_\\Lambda ~ 0.8). This particular scenario is capable of forming large and deep empty regions (with density contrasts \\delta < -0.6). Our results also show that the physical processes acting on the baryonic matter produce a transition region where the radius of the dark matter component is greater than the baryonic void radius. The thickness of this transition region ranges from about tens of kiloparsecs up to a few megaparsecs, depending on the spectrum considered. Putative objects formed near voids and within the transition region would have a different amount of baryonic/dark matter when compared with \\Omega_b/\\Omega_d. If one were to use these galaxies to determine, by dynamical effects or other techniques, the quantity of dark matter present in the Universe, the result obtained would be only local and not representative of the Universe as a whole.

O. D. Miranda; J. C. N. de Araujo

2001-05-18

59

Predicting the stability constants of metal-ion complexes from first principles.  

PubMed

The most important experimental quantity describing the thermodynamics of metal-ion binding with various (in)organic ligands, or biomolecules, is the stability constant of the complex (?). In principle, it can be calculated as the free-energy change associated with the metal-ion complexation, i.e., its uptake from the solution under standard conditions. Because this process is associated with the interactions of charged species, large values of interaction and solvation energies are in general involved. Using the standard thermodynamic cycle (in vacuo complexation and solvation/desolvation of the reference state and of the resulting complexes), one usually subtracts values of several hundreds of kilocalories per mole to obtain final results on the order of units or tens of kilocalories per mole. In this work, we use density functional theory and Møller-Plesset second-order perturbation theory calculations together with the conductor-like screening model for realistic solvation to calculate the stability constants of selected complexes--[M(NH3)4](2+), [M(NH3)4(H2O)2](2+), [M(Imi)(H2O)5](2+), [M(H2O)3(His)](+), [M(H2O)4(Cys)], [M(H2O)3(Cys)], [M(CH3COO)(H2O)3](+), [M(CH3COO)(H2O)5](+), [M(SCH2COO)2](2-)--with eight divalent metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+)). Using the currently available computational protocols, we show that it is possible to achieve a relative accuracy of 2-4 kcal·mol(-1) (1-3 orders of magnitude in ?). However, because most of the computed values are affected by metal- and ligand-dependent systematic shifts, the accuracy of the "absolute" (uncorrected) values is generally lower. For metal-dependent systematic shifts, we propose the specific values to be used for the given metal ion and current protocol. At the same time, we argue that ligand-dependent shifts (which cannot be easily removed) do not influence the metal-ion selectivity of the particular site, and therefore it can be computed to within 2 kcal·mol(-1) average accuracy. Finally, a critical discussion is presented that aims at potential caveats that one may encounter in theoretical predictions of the stability constants and highlights the perspective that theoretical calculations may become both competitive and complementary tools to experimental measurements. PMID:24000817

Gutten, Ondrej; Rulíšek, Lubomír

2013-09-16

60

Variation of lattice constant and cluster formation in GaAsBi  

SciTech Connect

We investigate the structural properties of GaAsBi layers grown by molecular beam epitaxy on GaAs at substrate temperatures between 220–315 °C. Irrespective of the growth temperature, the structures exhibited similar Bi compositions, and good overall crystal quality as deduced from X-Ray diffraction measurements. After thermal annealing at temperatures as low as 500 °C, the GaAsBi layers grown at the lowest temperatures exhibited a significant reduction of the lattice constant. The lattice variation was significantly larger for Bi-containing samples than for Bi-free low-temperature GaAs samples grown as a reference. Rutherford backscattering spectrometry gave no evidence of Bi diffusing out of the layer during annealing. However, dark-field and Z-contrast transmission electron microscopy analyses revealed the formation of GaAsBi clusters with a Bi content higher than in the surrounding matrix, as well as the presence of metallic As clusters. The apparent reduction of the lattice constant can be explained by a two-fold process: the diffusion of the excess As incorporated within As{sub Ga} antisites to As clusters, and the reduction of the Bi content in the GaAs matrix due to diffusion of Bi to GaAsBi clusters. Diffusion of both As and Bi are believed to be assisted by the native point defects, which are present in the low-temperature as-grown material.

Puustinen, J.; Schramm, A.; Guina, M. [Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland)] [Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere (Finland); Wu, M.; Luna, E. [Paul-Drude Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)] [Paul-Drude Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Laukkanen, P. [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland)] [Department of Physics and Astronomy, University of Turku, FI-20014 Turku (Finland); Laitinen, M.; Sajavaara, T. [Department of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä (Finland)] [Department of Physics, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä (Finland)

2013-12-28

61

Pathway of Actin Filament Branch Formation by Arp2/3 Complex*S  

E-print Network

Pathway of Actin Filament Branch Formation by Arp2/3 Complex*S Received for publication,July 18/3 complex revealed that the complex binds to and disso- ciates from actin filaments extremely slowly and actin monomers with high affinity. These two ligands have only modest impacts on the interaction

62

Lead(II) Complex Formation with Glutathione  

PubMed Central

A structural investigation of complexes formed between the Pb2+ ion and glutathione (GSH, denoted AH3 in its triprotonated form) the most abundant non2protein thiol in biological systems, was carried out for a series of aqueous solutions at pH 8.5 and CPb2+ = 10 mM, and in the solid state. The Pb LIII-edge EXAFS oscillation for a solid compound with the empirical formula [Pb(AH2)]ClO4 was modeled with one Pb-S and two short Pb-O bond distances at 2.64 ± 0.04 Å 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 Pb2+ ions. In aqueous solution at the mole ratio GSH / Pb(II) = 2.0 (CPb2+ = 10 mM, pH 8.5), lead(II) complexes with two thiolate ligands form, characterized by a ligand-to-metal charge transfer band (LMCT) S- ? Pb2+ at 317 nm in the UV-vis spectrum and mean Pb-S and Pb-(N/O) bond distances of 2.65 ± 0.04 Å and 2.51 ± 0.04 Å, respectively, from a Pb LIII-edge EXAFS spectrum. For solutions with higher mole ratios, GSH / Pb(II) ? 3.0, ESI-MS spectra identified a trisglutathionyl lead(II) complex, for which Pb LIII-edge EXAFS spectroscopy shows a mean Pb-S distance of 2.65 ± 0.04 Å in PbS3 coordination, 207Pb NMR spectroscopy displays a chemical shift of 2793 ppm, and in the UV-vis spectrum an S- ? Pb2+ LMCT band appears at 335 nm. The complex persists at high excess of glutathione, and also at ~25 K in frozen glycerol (33%) / water glasses for GSH / Pb(II) mole ratios from 4.0 to 10 (CPb2+ = 10 mM) measured by Pb LIII-edge EXAFS spectroscopy. PMID:22594853

Mah, Vicky

2012-01-01

63

Polyaniline–transition metal salt complexes: insight into formation mechanisms  

Microsoft Academic Search

Two basic morphologies of emeraldine base of polyaniline–transition metal salt complex films cast from N-methylpyrrolidinone solutions are described. The first morphology consists of grains and the other consists of loose aggregates, respectively. The correlation of the film morphology with formation of precipitate in the complex solution, kinetics of solvent evaporation from the cast film, amount of solvent entrapped in the

O. P. Dimitriev; P. S. Smertenko; B. Stiller; L. Brehmer

2005-01-01

64

Rovibrational energies and spectroscopic constants for H2O-Ng complexes.  

PubMed

In this work, rovibrational energies and spectroscopic constants for the water -Ng complexes (Ng = He, Ne, Ar, Kr and Xe) were calculated through two different approaches (by solving the Nuclear Schrödinger equation and by applying the Dunham's method) and using two different potential energy curves (PEC). These PEC were determined using potential parameters obtained through molecular beam scattering experiments and accurate theoretical calculation, respectively. It was found that the theoretical rovibrational energies are in a good agreement (only for the lowest numbers of vibrational states) with those obtained through experimental PEC. Another important conclusions was regarding the calculated first two rovibrational energies for the H 2 O-Ar system, that are in a good agreement with the experimental data. PMID:25425286

da Cunha, Wiliam F; de Oliveira, Rhuiago Mendes; Roncaratti, Luiz F; Martins, João B L; E Silva, Geraldo M; Gargano, Ricardo

2014-12-01

65

Novel Characterization Method of Ions in Liquid Crystal Materials by Complex Dielectric Constant Measurements  

NASA Astrophysics Data System (ADS)

The frequency dependence of the complex dielectric constant of liquid crystal materials doped with tetra-n-butylammonium iodide (TBAI) is investigated in the low-frequency region, and the experimental results are analyzed in terms of space charge polarization. The contribution from an electric double layer is also taken into consideration in the analysis. By means of curve fitting utilizing theoretical expressions of the space charge polarization, five sets of diffusion coefficient and density values are obtained for mobile ions. It is confirmed by experiments on the temperature dependence that five kinds of ions follow Walden's rule, and verified from the viewpoint of ion radii that two of the five kinds of ions are TBA+ and I-. The frequency-dependent dielectric properties, which are characteristic of the behaviors of ions, can be well explained by this study and the analytical method introduced here is considered to be powerful for the evaluation of the attributes of mobile ions.

Sawada, Atsushi; Tarumi, Kazuaki; Naemura, Shohei

1999-03-01

66

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

PubMed Central

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

Liu, Guangliang; Cai, Yong

2010-01-01

67

Spectrofluorometric determination of certain quinolone through charge transfer complex formation  

Microsoft Academic Search

A spectrofluorimetric method was developed for the determination of three fluoroquinolones antibacterials, namely, ofloxacin (OFL), levofloxacin (LEV), lomefloxacin (LOM), and pipemidic acid (PIP) through charge transfer (CT) complex formation with 7,7,8,8-tetracyanoquinodimethane (TCNQ). TCNQ was found to react with these drugs to produce stable complexes and the fluorescence intensity of the complexes was enhanced in 15–90 times higher than that of

Li Ming Du; Ya Qin Yang; Qing Mei Wang

2004-01-01

68

Spectrophotometric determination of the formation constant of triiodide ions in aqueous-organic solvent or polymer mixed media both in absence and presence of a surfactant  

NASA Astrophysics Data System (ADS)

The formation constant of triiodide ions from iodine-iodide equilibrium in aqueous-organic solvent or polymer mixed media have been determined spectrophotometrically at three different temperatures 20, 30 and 40 °C. The organic solvents chosen for the study are ethylene glycol, 2-methoxy ethanol, and 2-ethoxy ethanol while the polymers include polyethylene glycol (PEG), hydroxypropyl cellulose (HPC) or polyethylene oxide (PEO). Effect of a surfactant on the formation of triiodide ions in the mixed media has also been investigated. Though presence of the organic solvents led to an increase in the triiodide formation except for 2-ethoxy ethanol mixed media at low percentage, the increase in presence of PEG or the other polymer mixed media even at very low percentage was much higher as compared to those in ethylene glycol or its homologues. The increase in the formation constant has been discussed in terms of changes in its solvation properties and the hydrophobic character of the mixed media besides the solvent dielectric effects. The sharp increase in triiodide formation in presence of the polymer under study suggests the possibility of iodine being present as triiodide or other higher polyiodides in the inclusion complexes of iodine with other polymers like starch or PVA. The decrease in the triiodide formation in presence of surfactant micelles may, however, be attributed to solubilization of iodine by the micelles. Iodine was found to be better solubilized in TX-100 micelles as compared to SDS micelles.

Naorem, Homendra; Devi, Seram Dushila

2013-01-01

69

Polarographic determination of lead hydroxide formation constants at low ionic strength  

USGS Publications Warehouse

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.

Lind, C.J.

1978-01-01

70

Determination of stability constants of Cu(I), Cd(II) & Zn(II) complexes with thiols using fluorescent probes.  

PubMed

Fluorometric competing-ligand titrations were used to measure stability constants of Zn(II), Cd(II) and Cu(I) complexes of cysteine and glutathione (GSH). Cu(I)-stability constants were also determined for the dipeptides Arg-Cys and Gln-Cys which are produced by a marine alga under copper stress. The fluorescent ion indicators FluoZin-1 and BTC (Invitrogen) were used as competing ligands in titrations involving Zn(II) and Cd(II). Phen Green SK (Invitrogen) was likewise used in Cu(I) titrations. Conditional and cumulative general stability constants were determined using a least squares fit of the titration data to speciation models. The measured stability constants of Cd(II) and Zn(II) complexes were consistent with previous work, validating our method and assumptions. Our results also include the first general stability constants for Cu(I)-cysteine complexes and an alternative set for Cu(I)-GSH complexes. While these stability constants indicate that Cu(I) forms strong complexes with thiols, they are not strong enough to effectively buffer Cu(I) in seawater. PMID:23954481

Walsh, Michael J; Ahner, Beth A

2013-11-01

71

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

PubMed

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 NaNO(3)) using a potentiometric technique. The order of -?G(0) and -?H(0) was found to obey Co(2+) < Ni(2+) < Cu(2+) > Zn(2+), 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 ?log K. PMID:23226992

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

2012-01-01

72

Spectrophotometric determination of the formation constants of some transition metal cations with a new synthetic Schiff base in dichloromethane and chloroform using rank annihilation factor analysis  

NASA Astrophysics Data System (ADS)

The complex formation between a new synthesized Schiff base and the cations Ni 2+, Co 2+, Cu 2+, Zn 2+ in dichloromethane (DCM) and chloroform solutions was investigated spectrophotometrically using rank annihilation factor analysis (RAFA). The results of mole ratio plots and continuous variation data show the stoichiometry of complexation were found to be 1:1, and 2:1 metal ion to ligand. The stoichiometry was obtained as 1:1 metal ion to ligand ratio for Co 2+, Ni 2+ and Zn 2+ in chloroform and 2:1 for Cu 2+. In DCM the stoichiometry was obtained as 1:1 for Co 2+ and 2:1 for Ni 2+ and Zn 2+ and a consecutive 2:1 metal ion to ligand ratio was obtained for Cu 2+. Formation constants of these complexes were estimated by application of RAFA on spectrophotometric data. In this process the contribution of ligand was removed from the absorbance data matrix when the complex stability constant acts as an optimizing object and simply combined with the pure spectrum of the ligand, the rank of the original data matrix can be reduced by one by annihilating the information of the ligand from the original data matrix.

Afkhami, Abbas; Madrakian, Tayyebeh; Keypour, Hassan; Soltanbeygi, Saeid; Khajavi, Farzad; Rezaeivala, Majid

2011-01-01

73

Tungsten speciation in sulfidic waters: Determination of thiotungstate formation constants and modeling their distribution in natural waters  

NASA Astrophysics Data System (ADS)

Using UV/VIS spectrophotometry the equilibrium constants for the formation of monothiotungstate, WO3S2- (WO42-+H2S?WO3S+H2O; log K01 = 3.08 ± 0.11), dithiotungstate, WO2S22- (WO3S+H2S?WO2S22-+H2O; log K12 = 3.22 ± 0.22), trithiotungstate, WOS32- (WO2S22-+H2S?WO3S+H2O; log K23 = 2.76 ± 0.10), and tetrathiotungstate, WS42- (WO3S+H2S?WS42-+H2O; log K34 ?2.36) were determined. The equilibrium constants describing the formation of thiotungstates are approximately two orders of magnitude less than the equilibrium constants for the formation of the analogous thiomolybdates. These equilibrium constants for thiotungstates were used to model tungstate speciation in sulfidic waters. The model predicts that thiotungstate species are negligible in most natural waters, but are likely to be important in circum-neutral, anoxic waters with ?0.1 mM S(-II) concentrations. Natural waters that are conducive to thiotungstate formation include the Black Sea, Tyro and Bannock Basins, and porewaters with high rates of sulfate reduction such as those common in salt marshes. Preliminary field investigations indicate that thiotungstate formation may lead to increased W solubility.

Mohajerin, T. Jade; Helz, George R.; White, Christopher D.; Johannesson, Karen H.

2014-11-01

74

Complexation of Al(III) with gluconate in alkaline to hyperalkaline solutions: formation, stability and structure.  

PubMed

Contrary to suggestions in the literature, it has been proven that Al(III) forms a 1?:?1 complex with gluconate (hereafter Gluc(-)) in strongly alkaline (pH > 12) aqueous solutions. The complex formation was proven via(27)Al and (1)H NMR, freezing-point depression, polarimetric measurements as well as potentiometric and conductometric titrations. This complexation is a pH independent process, i.e., a condensation reaction takes place. The stability constant of the complex formed was derived from (1)H NMR and polarimetric measurements, and was found to be log K = 2.4 ± 0.4. In the complex formed, Al(III) has a tetrahedral geometry, and the Al(OH)4(-) is most probably statistically distributed between the alcoholate groups of the Gluc(-). PMID:23897548

Pallagi, Attila; Tasi, Ágost Gyula; Peintler, Gábor; Forgo, Péter; Pálinkó, István; Sipos, Pál

2013-10-01

75

Thermodynamics of cationic lipid-DNA complex formation as studied by isothermal titration calorimetry.  

PubMed Central

The detailed analysis of the cationic lipid-DNA complex formation by means of isothermal titration calorimetry is presented. Most experiments were done using 1,2-dioleyl-sn-glycero-3-ethylphosphocholine (EDOPC), but basic titrations were also done using DOTAP, DOTAP:DOPC, and DOTAP:DOPE mixtures. Complex formation was endothermic with less than 1 kcal absorbed per mole of lipid or DNA charge. This enthalpy change was attributed to DNA-DNA mutual repulsion within the lamellar complex. The exception was DOTAP:DOPE-containing lipoplex for which the enthalpy of formation was exothermic, presumably because of DOPE amine group protonation. Experimental conditions, namely, direction and titration increment as well as concentration of titrant, which dictate the structure of resulting lipoplex (whether lamellar complex or DNA-coated vesicle), were found to affect the apparent thermodynamics of complex formation. The structure, in turn, influences the biological properties of the lipoplex. If the titration of lipid into DNA was carried out in large increments, the DeltaH was larger than when the injection increments were smaller, a finding that is consistent with increased vesicle disruption under large increments and which is expected theoretically. Cationic lipid-DNA binding was weak in high ionic strength solutions, however, the effective binding constant is within micromolar range because of macromolecular nature of the interaction. PMID:12080142

Pozharski, Edwin; MacDonald, Robert C

2002-01-01

76

Universal reaction mechanism of boronic acids with diols in aqueous solution: kinetics and the basic concept of a conditional formation constant.  

PubMed

To establish a detailed reaction mechanism for the condensation between a boronic acid, RB(OH)2, and a diol, H2L, in aqueous solution, the acid dissociation constants (Ka(BL)) of boronic acid diol esters (HBLs) were determined based on the well-established concept of conditional formation constants of metal complexes. The pKa values of HBLs were 2.30, 2.77, and 2.00 for the reaction systems, 2,4-difluorophenylboronic acid and chromotropic acid, 3-nitrophenylboronic acid and alizarin red?S, and phenylboronic acid and alizarin red?S, respectively. A general and precise reaction mechanism of RB(OH)2 with H2L in aqueous solution, which can serve as a universal reaction mechanism for RB(OH)2 and H2L, was proposed on the basis of (a)?the relative kinetic reactivities of the RB(OH)2 and its conjugate base, that is, the boronate ion, toward H2L, and (b)?the determined pKa values of HBLs. The use of the conditional formation constant, K', based on the main reaction: RB(OH)2 + H2L (K1)? RB(L)(OH)(-) + H3O(+) instead of the binding constant has been proposed for the general reaction of uncomplexed boronic acid species (B') with uncomplexed diol species (L') to form boronic acid diol complex species (esters, BL') in aqueous solution at pH?5-11: B' + L' (K')? BL'. The proposed reaction mechanism explains perfectly the formation of boronic acid diol ester in aqueous solution. PMID:25169423

Furikado, Yuki; Nagahata, Tomomi; Okamoto, Takuya; Sugaya, Tomoaki; Iwatsuki, Satoshi; Inamo, Masahiko; Takagi, Hideo D; Odani, Akira; Ishihara, Koji

2014-10-01

77

A tethering complex dimer catalyzes trans-SNARE complex formation in intracellular membrane fusion  

PubMed Central

SNARE complexes mediate membrane fusion in the endomembrane system. They consist of coiled-coil bundles of four helices designated as Qa, Qb, Qc and R. A critical intermediate in the fusion pathway is the trans-SNARE complex generated by the assembly of SNAREs residing in opposing membranes. Mechanistic details of trans-SNARE complex formation and topology in a physiological system remain largely unresolved. Our studies on native yeast vacuoles revealed that SNAREs alone are insufficient to form trans-SNARE complexes and that additional factors, potentially tethering complexes and Rab GTPases, are required for the process. Here we report a novel finding that a HOPS tethering complex dimer catalyzes Rab GTPase-dependent formation of a topologically preferred QbQcR-Qa trans-SNARE complex. PMID:22754631

Kulkarni, Aditya; Alpadi, Kannan; Namjoshi, Sarita; Peters, Christopher

2012-01-01

78

Formation and characterization of OH–Al–humate–montmorillonite complexes  

Microsoft Academic Search

We studied the formation of OH–Al–humate–montmorillonite complexes as affected by the nature of the humic acid and the sequence of addition of montmorillonite, humic acid and hydrolytic species of Al. Complexes were prepared at pH 7.0 by different addition sequences of montmorillonite, 3 or 6 mmol Al and 5, 10 or 20 mg of humic acid per g of clay.

A Violante; M Arienzo; F Sannino; C Colombo; A Piccolo; L Gianfreda

1999-01-01

79

Complex formation and decay in ion-molecule reactions  

NASA Astrophysics Data System (ADS)

The potential energy surfaces for ion-molecule reactions typically have several minima that lie lower in energy than the asymptotes for the reactant and product channels. Such complexes can be covalently bound, hydrogen bonded or electrostatically bound. The nature of these complexes can have dramatic effects on the outcome of the reaction. We review three experimental studies that show three different cases of such influence. The reaction of acetylene cation with methane shows channels that proceed via a long-lived, covalently bound complex, and one channel that proceeds by a short-lived, weakly bound encounter complex. Specific reactant vibrations strongly influence both total reactivity and branching between the product channels, and the effect is related to the mode-specific coupling of vibration to the reaction coordinate. The reaction of phenol cation with ammonia is a case involving both electrostatically bound and hydrogen-bonded complexes, with ring-coordination complexes acting as precursors to the formation of the hydrogen-bonded complexes where reaction can occur. Again, vibration has a significant effect, related to the isomerization between coordination and hydrogen-bonded geometries. Finally, the reaction of ammonia cation with methanol involves competition between formation of different hydrogen-bonded intermediates, and the complex that forms largely determines the outcome of the reaction.

Green, Richard J.; Anderson, Scott L.

80

The Binding Constant for Complexation of Bilirubin to Bovine Serum Albumin. An Experiment for the Biophysical Chemistry Laboratory  

NASA Astrophysics Data System (ADS)

Students use fluorescence spectroscopy to measure the binding constant for bilirubin-bovine serum albumin complexation by the Method of Continuous Variations. The experiment applies fundamental concepts of physical chemistry to a commercially available system of biological interest. The experiment is easily completed in a single laboratory period, and students obtain binding constants on the order of 10 7, in good agreement with literature values.

Williams, Kathryn R.; Adhyaru, Bhavin; Pierce, Russell E.; Schulman, Stephen G.

2002-01-01

81

Complex-anisotropy-induced pattern formation in bistable media.  

PubMed

A construct of anisotropy in bistable media is adopted to characterize the effects of anisotropy on pattern formation by means of anisotropic line tension. A velocity curvature relation is further derived to account for the anisotropic wave propagations. Stability analysis of transverse perturbations indicates that a sufficiently strong complex anisotropy can induce dynamical instabilities and even lead to a breakup of the wave patterns. Numerical simulations show that complex anisotropy can induce rich spatiotemporal behaviors in bistable media. The results of analysis and simulations demonstrate that this method successfully incorporates complex anisotropy into the reaction diffusion model and has general significance. PMID:19391804

He, Zhi Zhu; Liu, Jing

2009-02-01

82

Pattern formation in oscillatory complex networks consisting of excitable nodes  

E-print Network

Oscillatory dynamics of complex networks has recently attracted great attention. In this paper we study pattern formation in oscillatory complex networks consisting of excitable nodes. We find that there exist a few center nodes and small skeletons for most oscillations. Complicated and seemingly random oscillatory patterns can be viewed as well-organized target waves propagating from center nodes along the shortest paths, and the shortest loops passing through both the center nodes and their driver nodes play the role of oscillation sources. Analyzing simple skeletons we are able to understand and predict various essential properties of the oscillations and effectively modulate the oscillations. These methods and results will give insights into pattern formation in complex networks, and provide suggestive ideas for studying and controlling oscillations in neural networks.

Liao Xuhong; Xia Qinzhi; Qian Yu; Zhang Lisheng; Hu Gang; Mi Yuanyuan

2010-09-11

83

Equilibrium and Formation/Dissociation Kinetics of some Lanthanide(III)-PCTA complexes  

PubMed Central

The protonation constants (KiH) of 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9,-triacetic acid (PCTA) and stability constants of complexes formed between this pyridine containing macrocycle and several different metal ions have been determined in 1.0 M KCl, 25°C and compared to previous literature values. The first protonation constant was found to be 0.5-0.6 log units higher than the value reported previously and a total five protonation steps were detected (log KiH = 11.36, 7.35, 3.83, 2.12 and 1.29). The stability constants of complexes formed between PCTA and Mg2+, Ca2+, Cu2+ and Zn2+ were also somewhat higher than those previously reported but this difference could be largely attributed to the higher first protonation constant of the ligand. Stability constants of complexes formed between PCTA and the Ln3+ series of ions and Y3+ were determined by using an “out-of-cell” potentiometric method. These values ranged from log K = 18.15 for Ce(PCTA) to log K = 20.63 for Yb(PCTA), increasing along the lanthanide series in proportion to decreasing Ln3+ cation size. The rates of complex formation for Ce(PCTA), Eu(PCTA), Y(PCTA) and Yb(PCTA) were followed by conventional UV-VIS spectroscopy in the pH range pH=3.5 - 4.4. First order rate constants (saturation kinetics) obtained for different ligand / metal ion ratios were consistent with rapid formation of a diprotonated intermediate, Ln(H2PCTA)2+. The stabilities of the intermediates as determined from the kinetic data were 2.81, 3.12, 2.97 and 2.69 log K units for Ce(H2PCTA), Eu(H2PCTA), Y(H2PCTA) and Yb(H2PCTA), respectively. Rearrangement of these intermediates to the fully chelated complexes was the rate determining step and the rate constant (kr) for this process was found to be inversely proportional to the proton concentration. The formation rates (kOH) increased with a decrease in lanthanide ion size (9.68×107 M-1s-1, 1.74×108 M-1s-1, 1.13×108 M-1s-1 and 1.11×109 M-1s-1 for Ce(PCTA), Eu(PCTA), Y(PCTA) and Yb(PCTA), respectively). These data indicate that the Ln(PCTA) complexes exhibit the fastest formation rates among all lanthanide macrocyclic ligand complexes studied to date. The acid catalyzed dissociation rates (k1) varied with cation from 9.61×10-4 M-1s-1, 5.08×10-4 M-1s-1, 1.07×10-3 M-1s-1 and 2.80×10-4 M-1s-1 for Ce(PCTA), Eu(PCTA), Y(PCTA) and Yb(PCTA), respectively. PMID:17083226

Tircso, Gyula; Kovacs, Zoltan; Sherry, A. Dean

2008-01-01

84

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

SciTech Connect

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.

Rustad, J.R.; Felmy, A.R.; Hay, B.P. [Pacific Northwest National Lab., Richland, WA (United States)] [Pacific Northwest National Lab., Richland, WA (United States)

1996-05-01

85

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

SciTech Connect

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.

Mumper, R.J.; Jay, M. [Univ. of Kentucky, Lexington, KY (United States)

1992-10-15

86

Complex formation in rare-earth metal-propionic acid-diamagnetic salt systems by 1 H NMR spectroscopy  

Microsoft Academic Search

Complex formation of propionic acid with ions of rare-earth metals of the yttrium subgroup (D2O, 5.0 M NaNO3) in the absence and presence of diamagnetic Mg2+ cations was studied by 1H NMR spectroscopy in combination with mathematic simulation of complicated equilibria. Stability constants for monopropionate\\u000a complexes of rare-earth ions decrease when the rare-earth cation and Mg2+ are present in the

I. V. Sukhno; V. Yu. Buz’ko; V. T. Panyushkin

2006-01-01

87

Estimation of the initial equilibrium constants in the formation of tetragonal lysozyme nuclei  

NASA Technical Reports Server (NTRS)

Results are presented from a study of the equilibria, kinetic rates, and the aggregation pathway which leads from a lysozyme monomer crystal to a tetragonal crystal, using dialyzed and recrystallized commercial hen eggwhite lysozyme. Relative light scattering intensity measurements were used to estimate the initial equilibrium constants for undersaturated lysozyme solutions in the tetragonal regime. The K1 value was estimated to be (1-3) x 10 exp 4 L/mol. Estimates of subsequent equilibrium constants depend on the crystal aggregation model chosen or determined. Experimental data suggest that tetragonal lysozyme crystal grows by addition of aggregates preformed in the bulk solution, rather than by monomer addition.

Pusey, Marc L.

1991-01-01

88

Complex formation of native and hydroxypropylated cyclodextrins with benzoic acid in aqueous solution: Volumetric and 1H NMR study  

NASA Astrophysics Data System (ADS)

Novel data on complexation of benzoic acid by parent and hydroxypropylated cyclodextrins were obtained by densimetry and 1H NMR. Formation of 1:1 inclusion complexes was detected in most cases with the exception of hydroxypropyl-?-cyclodextrin, which is able to form 1:2 complexes. The data demonstrated penetration of carboxylic group of benzoic acid inside macrocyclic cavity, its insertion into ?-cyclodextrin cavity being deeper. Binding constants and volumes of transfer were calculated and analyzed in terms of influence of cyclodextrin structure on binding mode and driving forces of interaction as well as on the complex stability.

Terekhova, Irina; Ko?bia?, Malgorzata; Kumeev, Roman; Gierycz, Pawe?

2011-10-01

89

Constant-Pressure Molecular Dynamics Techniques Applied to Complex Molecular Systems and Solvated Proteins  

Microsoft Academic Search

To assess the feasibility of high-pressure simulation of biomolecular systems, we discuss some practical aspects of molecular dynamics simulation techniques at constant pressure and temperature. We compare the extended Lagrangian (EL) method, initially developed by Andersen1 for sampling from well-defined statistical mechanical ensembles, with the method by Berendsen et al.,2 where temperature and\\/or pressure are kept constant by weakly coupling

Emanuele Paci; Massimo Marchi

1996-01-01

90

Single-stranded nucleic acids promote SAMHD1 complex formation.  

PubMed

SAM domain and HD domain-containing protein 1 (SAMHD1) is a dGTP-dependent triphosphohydrolase that degrades deoxyribonucleoside triphosphates (dNTPs) thereby limiting the intracellular dNTP pool. Mutations in SAMHD1 cause Aicardi-Goutières syndrome (AGS), an inflammatory encephalopathy that mimics congenital viral infection and that phenotypically overlaps with the autoimmune disease systemic lupus erythematosus. Both disorders are characterized by activation of the antiviral cytokine interferon-? initiated by immune recognition of self nucleic acids. Here we provide first direct evidence that SAMHD1 associates with endogenous nucleic acids in situ. Using fluorescence cross-correlation spectroscopy, we demonstrate that SAMHD1 specifically interacts with ssRNA and ssDNA and establish that nucleic acid-binding and formation of SAMHD1 complexes are mutually dependent. Interaction with nucleic acids and complex formation do not require the SAM domain, but are dependent on the HD domain and the C-terminal region of SAMHD1. We finally demonstrate that mutations associated with AGS exhibit both impaired nucleic acid-binding and complex formation implicating that interaction with nucleic acids is an integral aspect of SAMHD1 function. PMID:23371319

Tüngler, Victoria; Staroske, Wolfgang; Kind, Barbara; Dobrick, Manuela; Kretschmer, Stefanie; Schmidt, Franziska; Krug, Claudia; Lorenz, Mike; Chara, Osvaldo; Schwille, Petra; Lee-Kirsch, Min Ae

2013-06-01

91

Demixing-stimulated lane formation in binary complex plasma  

SciTech Connect

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.

Du, C.-R.; Jiang, K.; Suetterlin, K. R.; Ivlev, A. V.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85748, Garching (Germany)

2011-11-29

92

Energy Transfer between Ln(III) Ions in Aqueous Solutions Upon Formation of Labile Binuclear Fluoride and Nitrate Complexes of These Ions  

NASA Astrophysics Data System (ADS)

The influence of anions on nonradiative electronic energy transfer between lanthanide ions in aqueous solutions is studied. The rate constant k t of energy transfer was found to increase by three orders of magnitude upon addition of salts of hydrofluoric acid to the solution. This effect is caused by the formation of bridge labile binuclear complexes, an excited energy donor-fluorine anion-acceptor, which increase the encounter time between a donor and an acceptor, resulting in the increase in the probability of energy transfer. The independence of k t of the Förster overlap integral in the bridge complex containing F- was explained by the fact that energy transfer occurs in each event of the binuclear complex formation, the maximum rate constant of energy transfer being equal to the rate constant of the binuclear complex association. Bridge complexes formed via the NO{3/-} anion are also considered. These binuclear complexes are unstable, and k t for them is proportional to the Förster overlap integral. In this case, energy transfer occurs not during each event of the complex formation. This allows us to estimate the lower limit of the dissociation constant of the binuclear complex and its stability constant. Thus, the study of influence of various anions on energy transfer represents a new efficient luminescent method for analysis of properties of labile binuclear complexes in solutions.

Sveshnikova, E. B.; Dudar', S. S.; Ermolaev, V. L.

2000-06-01

93

Determination of the dissociation constants for recombinant c-Myc, Max, and DNA complexes: The inhibitory effect of linoleic acid on the DNA-binding step  

SciTech Connect

c-Myc, the protein product of protooncogene c-myc, functions in cell proliferation, differentiation, and neoplastic disease. In this study, recombinant c-Myc and Max proteins, encompassing DNA binding (basic region) and dimerization (helix-loop-helix/leucine zipper) domain of human origin, were expressed in bacteria as Myc87 and Max85. Myc87 was purified under denatured conditions and was renatured again. The dissociation constant for the protein dimers and for dimer/DNA complexes were not detectable by isothermal titration calorimetry because of the low degree of solubility of Myc87 and Max85. Therefore, we set up equations which were used to determine the dissociation constants from the proportion of protein-DNA complexes. The dimer dissociation constants in TBS were 5.90({+-}0.54) x 10{sup -7} M for Max85/Max85 homodimer, 6.85({+-}0.25) x 10{sup -3} M for Myc87/Myc87 homodimer, and 2.55({+-}0.29) x 10{sup -8} M for Myc87/Max85 heterodimer, and the DNA-binding dissociation constants in TBS were 1.33({+-}0.21) x 10{sup -9} M for Max85/Max85/DNA, 2.27({+-}0.08) x 10{sup -12} M for Myc87/Myc87/DNA, and 4.43({+-}0.37) x 10{sup -10} M for Myc87/Max85/DNA. In addition, we revealed that linoleic acid which is known as an inhibitor for the formation of Max/Max/DNA complex reduced the affinity of Max homodimer for DNA. This result indicates that linoleic acid may bind to the DNA-binding region of Max homodimer.

Jung, Kyung Chae [Department of Chemistry, Seoul National University, Seoul (Korea, Republic of); Rhee, Ho Sung [Department of Chemistry, Seoul National University, Seoul (Korea, Republic of); Park, Chi Hoon [Department of Chemistry, Seoul National University, Seoul (Korea, Republic of); Yang, Chul-Hak [Department of Chemistry, Seoul National University, Seoul (Korea, Republic of)]. E-mail: chulyang@plaza.snu.ac.kr

2005-08-19

94

Suspended microstrip patch resonator sensor for determination of complex dielectric constant of liquid and paste  

Microsoft Academic Search

We report a new accurate suspended microstrip patch resonator to determine dielectric constant and loss tangent of petrol, kerosene, Vaseline and wax. Our results shows good agreement with available results. No calibration liquid is used and its use will further improve accuracy.

A. K. Verma; Nasimuddin; R. K. Garg; A. S. Omar

2003-01-01

95

Determination of the binding constant of indomethacin-beta-cyclodextrin complex by capillary electrophoresis: experimental optimization and temperature study.  

PubMed

The apparent electrophoretic mobilities of indomethacin in beta-cyclodextrin at a range of concentrations were measured directly by capillary electrophoresis. Three different linear plots and a non linear plot are proposed for the apparent binding constant calculations, based on the fact that the molar ratio of the inclusion complex was 1:1. K values obtained at 298 K were 421 M(-1) (double reciprocal fit), 488 M(-1) (x-reciprocal fit), 428 M(-1) (y-reciprocal fit) and 490 M(-1) (non linear fit). The corresponding K values at 313 K were 380 M(-1) (double reciprocal fit), 355 M(-1) (x-reciprocal fit), 366 M(-1) (y-reciprocal fit) and 339 M(-1) (non linear fit). Using the proposed methods, the binding constant of the indomethacin-beta-cyclodextrin inclusion complex can be obtained easily. The methods have been applied to obtain the values of the constant K under different experimental conditions. Under optimized conditions the K constant is temperature dependent and non-arrhenian behaviour was observed. PMID:18065101

Acosta, G; Linares, D; Olsina, R; Martínez, L D; Gomez, M R

2007-11-01

96

Magnetic resonance for downhole complex-lithology earth formation evaluation  

NASA Astrophysics Data System (ADS)

Many petroleum-bearing reservoirs are known as complex-lithology, complex-mineralogy earth formations where the existing nuclear magnetic resonance (NMR) analysis models require modification and extension to work properly. This paper discusses the effects of mineralogy variation in complex-lithology formation rocks that will cause NMR response variations. In particular, the existence of iron-rich authigenic clays and the nonquartz grains in siliciclastics affect the surface relaxivity and the internal field inhomogeneity. Using a simplified pore-lining clay model, we estimated that the magnitude of the internal gradient in siliciclastics is comparable with or greater than that of the instrument-generated field gradient common to the currently used NMR logging tools. To account for these effects for reservoir fluid identification and quantification from NMR data, an inversion model is created, which includes the mean susceptibility of the grain minerals, the correlation between pore size and the relaxation time of the wetting-phase fluid in the pores and the geometric restriction to the fluid molecular diffusion.

Chen, Songhua; Li, Lilong; Zhang, Gigi; Chen, Jason

2011-08-01

97

Complex Interactions between Formative Assessment, Technology, and Classroom Practices  

NSDL National Science Digital Library

Interactive engagement (IE) methods provide instructors with evidence of student thinking that can guide instructional decisions across a range of timescales: facilitating an activity, determining the flow of activities, or modifying the curriculum. Thus, from the instructor's perspective, IE activities can function as formative assessments. As a practical matter, the ability to utilize this potential depends on how the activities are implemented. This paper describes different tools for small group problem solving, including whiteboards, Tablet PCs, digital cameras, and photo-sharing websites. These tools provide the instructor with varying levels of access to student work during and after class, and therefore provide a range of support for formative assessment. Furthermore, the tools differ in physical size, ease of use, and the roles for students and instructor. These differences lead to complex, often surprising interactions with classroom practices.

Price, Edward

2012-05-15

98

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

PubMed

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)Lmol(-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 100nm, in agreement with scrambled eggs multi-association between various polyelectrolyte chains. PMID:25256478

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

2014-11-26

99

Low temperature elastic constants and nonlinear acoustic response in rocks and complex materials  

SciTech Connect

The 'P-M Space' model of Guyer and McCall has some success in describing the large nonlinear effects ('slow dynamics') observed by Johnson et al. in rocks. The model uses elements which couple classical nonlinear elasticity with hysteretic components. The actual processes and scales corresponding to the model elements are not yet defined, however it is reasonable to seek energy scales by studying the low-temperature dependence of the elastic constants. We have measured qualitative elastic properties of basalt and Berea sandstone from room temperature down to 4 K using Resonant Ultrasound Spectroscopy (RUS). A simple elastic solid should show a monotonic increase in the elastic constants as temperature decreases. The basalt samples show this gross behavior but the sandstone shows a very unexpected anomalous regime between 40 K and 200 K where the elastic constants decrease with decreasing temperature. Both rocks show temperature-dependent structure in both the modulus and internal friction, and also significant hysteresis, indicating history and rate-dependent properties. This data provides insight into the time and energy scales of dynamical effects observed in sandstones.

Darling, T. W. (Timothy W.); Ulrich, T. J. (Timothy J.); Johnson, P. A. (Paul A.); Tencate, J. A. (James A.)

2001-01-01

100

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

PubMed

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

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

2012-01-01

101

Ion wake formation with dust charge fluctuation in complex plasma  

SciTech Connect

In complex plasma, the interaction mechanism among dust grains near the plasma sheath is significantly influenced by the downward ion flow towards the sheath and dust charge fluctuation over grain surface. Asymmetric ion flow towards the sheath gives rise to well known attractive wake potential in addition to repulsive Yukawa type of potential. The present work shows that the charging dynamics play a significant role in modification of plasma dielectric response function and hence the interaction mechanism among test dust particulates. The effective Debye length is found to be a characteristic of dust size and background plasma response towards the grain along with ion flow speed. The potentials thus obtained show a damping in strength of interaction in the presence of dynamical charging of dust as compared to that of constant charge dust grains. The result also shows decrease in focal length of ion lensing with increase in grain size.

Bhattacharjee, Saurav; Das, Nilakshi [Department of Physics, Tezpur University, Tezpur, Assam, 784 028 (India)] [Department of Physics, Tezpur University, Tezpur, Assam, 784 028 (India)

2013-11-15

102

Protein-free parallel triple-stranded DNA complex formation  

PubMed Central

A 14 nt DNA sequence 5?-AGAATGTGGCAAAG-3? from the zinc finger repeat of the human KRAB zinc finger protein gene ZNF91 bearing the intercalator 2-methoxy,6-chloro,9-amino acridine (Acr) attached to the sugar–phosphate backbone in various positions has been shown to form a specific triple helix (triplex) with a 16 bp hairpin (intramolecular) or a two-stranded (intermolecular) duplex having the identical sequence in the same (parallel) orientation. Intramolecular targets with the identical sequence in the antiparallel orientation and a non-specific target sequence were tested as controls. Apparent binding constants for formation of the triplex were determined by quantitating electrophoretic band shifts. Binding of the single-stranded oligonucleotide probe sequence to the target led to an increase in the fluorescence anisotropy of acridine. The parallel orientation of the two identical sequence segments was confirmed by measurement of fluorescence resonance energy transfer between the acridine on the 5?-end of the probe strand as donor and BODIPY-Texas Red on the 3?-amino group of either strand of the target duplex as acceptor. There was full protection from OsO4-bipyridine modification of thymines in the probe strand of the triplex, in accordance with the presumed triplex formation, which excluded displacement of the homologous duplex strand by the probe–intercalator conjugate. The implications of these results for the existence of protein-independent parallel triplexes are discussed. PMID:11160932

Shchyolkina, A. K.; Timofeev, E. N.; Lysov, Yu. P.; Florentiev, V. L.; Jovin, T. M.; Arndt-Jovin, D. J.

2001-01-01

103

Multiphasic Kinetics of Myoglobin/Sodium Dodecyl Sulfate Complex Formation  

PubMed Central

We have carried out a kinetic analysis of the conformational changes that myoglobin (Mb) undergoes in the presence of the anionic surfactant sodium dodecyl sulfate (SDS). The time-resolved results have been combined with steady-state circular dichroism (CD) and resonance Raman (RR) spectroscopy. Time-resolved absorption spectra indicate that SDS induces changes in the heme coordination with the formation of three different Mb species, depending on SDS concentration. The formation of the Mb/SDS complex involves three or four phases, depending on surfactant concentration. The kinetic data are analyzed assuming two modes of interaction according to whether SDS is monomeric or micellar. The two pathways are separated but interconnected through free Mb. At the lowest concentrations a six-coordinated, low-spin form dominates. Two distinct five-coordinated species are formed at higher SDS concentrations: one is a protein-free heme and the other reequilibrates slowly with the six-coordinated, low-spin form. The resulting complexes have been characterized by CD and RR. In addition, CD spectra show that the local changes in the heme environment are coupled to changes in the protein structure. PMID:17369406

Feis, Alessandro; Tofani, Luca; De Sanctis, Giampiero; Coletta, Massimo; Smulevich, Giulietta

2007-01-01

104

Incipient species formation in salamanders of the Ensatina complex  

PubMed Central

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

Wake, David B.

1997-01-01

105

Determination of third order elastic constants in a complex solid applying coda wave interferometry  

Microsoft Academic Search

In this letter we describe the development of coda wave interferometry to determine acoustoelastically derived third order nonlinear coefficients of a highly complex material, concrete. Concrete, a structurally heterogeneous and volumetrically mechanically damaged material, is an example of a class of materials that exhibit strong multiple scattering as well as significant elastic nonlinear response. We show that intense scattering can

C. Payan; V. Garnier; J. Moysan; P. A. Johnson

2009-01-01

106

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

ERIC Educational Resources Information Center

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)

Marin, Dolores; Mendicuti, Francisco

1988-01-01

107

Schrodinger-Newton equation with complex Newton constant and induced gravity  

E-print Network

In the reversible Schrodinger-Newton equation a complex Newton coupling G*exp(-i*alpha) is proposed in place of G. The equation becomes irreversible and all initial one-body states are expected to converge to solitonic stationary states. This feature is verified numerically. For two-body solutions we point out that an effective Newtonian interaction is induced by the imaginary mean-fields as if they were real. The effective strength of such induced gravity depends on the local wave functions of the participating distant bodies.

Lajos Diósi; Tibor Norbert Papp

2009-06-08

108

Physical volcanology of the Gubisa Formation, Kone Volcanic Complex, Ethiopia  

NASA Astrophysics Data System (ADS)

Despite their significance for understanding the potential environmental factors involved in hominin evolution in Ethiopia, very few modern volcanologic studies have been carried out on the Quaternary calderas and associated silicic tephra deposits of the Ethiopian Rift. We present here the second of a set of papers reporting the findings of fieldwork and laboratory analyses of one of the largest of these structures, Kone Caldera, located within the Kone Volcanic Complex in the northern Main Ethiopian Rift. The most recent major episode of explosive eruptive activity at Kone Caldera was apparently associated with formation of part of the overall 8-km-diameter collapse area, and deposited a widely-dispersed alkali rhyolite tephra that reaches a thickness of up to 60 m in vent-proximal deposits. We report here the physical characteristics of this unit in order to constrain eruptive conditions. The pumice fall deposit suggests that an abrupt decrease in magma discharge rate occurred part way through the eruption.

Rampey, Michael L.; Oppenheimer, Clive; Pyle, David M.; Yirgu, Gezahegn

2014-08-01

109

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

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

110

Micelle Formation of Coenzyme Q10 with Dipotassium Glycyrrhizate Using Inclusion Complex of Coenzyme Q10 with ?-Cyclodextrin.  

PubMed

Micelles can be formed from coenzyme Q10 (CoQ10) and dipotassium glycyrrhizate (GZK2) by using an inclusion complex of CoQ10 with ?-cyclodextrin (?-CD). The mechanism of micelle formation was kinetically investigated. Adding GZK2 to a supersaturated solution of the CoQ10/?-CD inclusion complex led to a linear increase in the solubility of CoQ10 due to the formation of micelles of CoQ10 when the molar ratio of GZK2/?-CD increased to ?1.6, after which the concentration remained constant. The equilibrium constant K for micelle formation was 0.68 (-) and the ratio of GZK2 to CoQ10 was 1. These results suggest that the formation of CoQ10 micelles with GZK2 might proceed via the displacement of CoQ10 by GZK2 in the ?-CD cavity followed by the formation of CoQ10 micelles. PMID:25187379

Uekaji, Yukiko; Onishi, Mayu; Nakata, Daisuke; Terao, Keiji; Paananen, Arja; Partanen, Riitta; Yoshii, Hidefumi

2014-10-01

111

Deciphering complex soil/site formation in sands  

NASA Astrophysics Data System (ADS)

This paper summarizes aspects of the geoarchaeological research at two adjacent multi-component archaeological sites, 13JP86 and 13JP87, along Indian Creek in central Iowa, USA. The sites, both recently salvaged but now destroyed, formed in late Pleistocene sands reworked from glacial sediments that emanated from the wasting Des Moines Lobe glacier some 13,000-14,000 years ago. The soils contained shallowly dispersed and mixed artifacts that span the Paleoindian-to-historic cultural spectrum. In open areas, as at Indian Creek, site formation processes equate to natural soil genetic processes, plus human imprints. Cultural materials, once deposited, become part of the soil and subject to dynamic soil processes. These soils had reasonably well expressed Ap, A, and E horizons that collectively formed thick one-layered biomantles, underlain by well expressed argillic Bt horizons. The biomantles had been well bioturbated, deeply in some pedons, but still exhibited organized A and E horizons. The Bt horizons were also bioturbated, though less so, and consisted of multiple thin to thick sandy clay bands, termed illuvial clay lamellae (icl's). The icl's contained modest to appreciable amounts of illuvial clay as bridges between grains, and as diffuse splotches and blebs separated by less clayey, E horizon-like interlamellar sandy zones. Deeper and less bioturbated E-like sandy zones had accumulated so much clay that they had coalesced with icl's into thick, complexly banded argillic Bt horizons. The process histories of the sandy pedons were obviously extremely complex. The geoarchaeological aspects of the project, which were mainly complex pedologic ones, were largely interpreted by drawing on the genetic principles of dynamic denudation to explain soil/site evolution. Many questions were raised, and most were answered under these principles. New concepts and perspectives were gained in this study, and the resulting interpretive scenarios carry explanatory implications for sandy soils everywhere, whether charged with cultural materials or not.

Johnson, D. L.; Johnson, D. N.; Benn, D. W.; Bettis, E. A., III

2008-10-01

112

Determination of stability constants of metal-humic acid complexes by potentiometric titration and ion-selective electrodes. [Cu, Pb, Cd  

Microsoft Academic Search

A new technique based on the combined use of potentiometric titration and ion-selective electrodes is proposed for determining apparent stability constants (successive stability constants and overall stability constants) of divalent metal cation (Cu\\/sup 2 +\\/, Pb\\/sup 2 +\\/, and Cd\\/sup 2 +\\/) complexes with humic acids. Fourteen humic acids from diverse sources, including humified rice straw, were examined. The stability

T. Takamatsu; T. Yoshida

1978-01-01

113

Flow partitioning in the lithosphere during core complex formation: An interactive evolutionary computation  

E-print Network

Flow partitioning in the lithosphere during core complex formation: An interactive evolutionary the dynamics of core complex formation in a three-layer model of the lithosphere. In this method a mathematical largely by lower crustal flow. Introduction Metamorphic core complexes form when continental lithosphere

Boschetti, Fabio

114

Star Formation in the Northern Cloud Complex of NGC 2264  

NASA Astrophysics Data System (ADS)

We have made continuum and spectral line observations of several outflow sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope (HHT) and ARO 12 m millimeter-wave telescope. This study explores the kinematics and outflow energetics of the young stellar systems observed and assesses the impact star formation is having on the surrounding cloud environment. Our data set incorporates 12CO (3-2),13CO (3-2), and 12CO (1-0) observations of outflows associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS 25 and 27, respectively, in the northern cloud complex. Complementary 870 ?m continuum maps were made with the HHT 19 channel bolometer array. Our results indicate there is a weak <=0.5% coupling between outflow kinetic energy and turbulent energy of the cloud. An analysis of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining their dynamical integrity except where outflowing material directly interacts with the core, such as along the outflow axes.

Hedden, Abigail S.; Walker, Christopher K.; Groppi, Christopher E.; Butner, Harold M.

2006-07-01

115

Adhesion and formation of microbial biofilms in complex microfluidic devices  

SciTech Connect

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.

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

2012-01-01

116

Integrin activation and focal complex formation in cardiac hypertrophy  

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

117

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

SciTech Connect

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.

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

1988-06-01

118

Energy Transfer between Ln(III) Ions in Aqueous Solutions Upon Formation of Labile Binuclear Fluoride and Nitrate Complexes of These Ions  

Microsoft Academic Search

The influence of anions on nonradiative electronic energy transfer between lanthanide ions in aqueous solutions is studied. The rate constant k t of energy transfer was found to increase by three orders of magnitude upon addition of salts of hydrofluoric acid to the solution. This effect is caused by the formation of bridge labile binuclear complexes, an excited energy donor-fluorine

E. B. Sveshnikova; S. S. Dudar; V. L. Ermolaev

2000-01-01

119

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

ERIC Educational Resources Information Center

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)

Busby, David C.; And Others

1981-01-01

120

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)

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.

Saha, Avijit; Mukherjee, Asok K.

2004-07-01

121

Force Spectroscopy with a Small Dithering of AFM Tip: A Method of Direct and Continuous Measurement of the Spring Constant of Single Molecules and Molecular Complexes  

PubMed Central

A new method of direct and continuous measurement of the spring constant of single molecule or molecular complex is elaborated. To that end the standard force spectroscopy technique with functionalized tips and samples is combined with a small dithering of the tip. The change of the dithering amplitude as a function of the pulling force is measured to extract the spring constant of the complex. The potentialities of this method are illustrated for the experiments with single bovine serum albumin—its polyclonal antibody (Ab-BSA) and fibrinogen—fibrinogen complexes. PMID:14747352

Chtcheglova, Lilia A.; Shubeita, George T.; Sekatskii, Sergey K.; Dietler, Giovanni

2004-01-01

122

Analysis of diatomic bond dissociation and formation in terms of the reaction force and the position-dependent reaction force constant  

Microsoft Academic Search

Bond dissociation and formation in diatomic molecules are analyzed in terms of the reaction force F(R) and the reaction force constant ?(R). These were determined for a group of 13 molecules from their extended-Rydberg potential energy functions V(R), which are of near-experimental quality. From F(R) and ?(R) comes a two-stage description of dissociation\\/formation. In dissociation, the first stage involves stretching

Jane S. Murray; Alejandro Toro-Labbé; Tim Clark; Peter Politzer

2009-01-01

123

Formation and use of poly-L-histidine-catalase complexes  

Microsoft Academic Search

Insoluble complexes of poly-L-histidine (polyhistidine) and catalase were prepared by mixing the two reactants together in solution at pH 5.5 and subsequently elevating the pH to approximately 7.0, at which point they precipitated. Complexes formed at optimal ratios of polyhistidine to catalase contained essentially all of the catalase present in the original solution. The catalase present in such complexes contained

Douglas Gibbs; James Varani; Isaac Ginsburg

1989-01-01

124

Supercoiled pseudocircular domains in single-twisted DNAs under tension: Elastic constants and unwinding dynamics in complexes with topo I.  

PubMed

Extension versus twist data of Koster et al. (Nature 2005, 434, 671-674) are analyzed to obtain C for the main-chain segments and the twist energy parameter (ET ) for the supercoiled pseudocircular (sp) domain(s) from which C is estimated via simulations. The torsional rigidity in the tension-free sp domain(s) (C?=?163 fJ fm) is typical of the unstrained DNA and is less than half the value in the main-chain segments under tension (C?=?350-410 fJ fm). Tension is suggested to induce a structural transition to a torsionally stiffer state. Data of Koster et al. for the rate of extension owing to unwinding of a covalent complex of DNA with human Topoisomerase Ib (H Topo I) are analyzed to determine the torque and rate of rotation from which an effective friction coefficient is obtained. A Langevin equation for the unwinding motion in a supercoiled DNA:H Topo I complex is solved to obtain the temporal trajectory of the average winding angle and the time-dependent distribution of winding angles. The mean rate constant for the religation reaction is estimated from the measured probability of reaction per turn. We predict that unwinding proceeds rather far during a single-cleavage and religation cycle, and is effectively completely equilibrated during the 3.2 cleavage and religation cycles that occur during each noncovalent binding and dissociation event. H Topo I is predicted to be completely processive as in accord with observations on calf-thymus Topo I (Brewood et al., Biochemistry 2010, 49, 3367-3380). © 2013 Wiley Periodicals, Inc. Biopolymers 99: 1046-1069, 2013. PMID:23640759

Schurr, J Michael; Fujimoto, Bryant S

2013-12-01

125

The competition for graphene formation on Re(0001): A complex interplay between carbon  

E-print Network

) structure. In the range 500­700 K, the formation of a high-quality single-layer of graphene is strongly conditions, the formation of a long-range ordered graphene layer on Re(0001) without carbon bulk saturationThe competition for graphene formation on Re(0001): A complex interplay between carbon segregation

Alfè, Dario

126

Determination of binding constants of labile ligands in metal–ligand complexes containing carboxylic groups bound polymer by using breakthrough technique  

Microsoft Academic Search

This study was conducted to confirm the possibilities of determining the binding constants of ligands in metal–ligand complexes containing carboxylic groups bound polymer by using breakthrough technique. Aniline and o-anisidine were selected as model ligands. A mini column apparatus was used to study sorption of ligands onto ligand exchange resin. The experiments were conducted in a constant temperature at 25°C.

Ahmet Ayar; A. Ihsan Pekacar; Bedrettin Mercimek

2003-01-01

127

Topology and Complexity of Formations Abubakr Muhammad1  

E-print Network

, animal herds, bacterial colonies, schools of fish, formations of flying birds, and so on. These group colonies and fish schools provide a lot of insight into the study and design of artificial multi

Egerstedt, Magnus

128

Mathematical Constants  

NSDL National Science Digital Library

This website features supplementary materials for a book called Mathematical Constants by Stephen Finch, a Clay Mathematics Institute Book Fellow. The book is a collection of stories about 136 mathematical constants that, according to one reviewer, "will startle us, intrigue us and nurture our quest of mysterious patterns amongst numbers and structures." On this website, the author has errata and addenda to the book as well as some sample essays on integer compositions, optimal stopping and Reuleaux triangles. Supplementary materials are organized by topic, which include Number Theory and Combinatorics, Geometry and Topology, Probability and Stochastic Processes, Real and Complex Analysis, and Inequalities and Approximation. The website also includes links to the book publisher and companies selling the book as well as some of the author's favorite websites.

129

Electrochemistry and metal complex formation of organic diselenides  

Microsoft Academic Search

This review article is devoted to electrochemical investigations of symmetric organic diselenides and to their specific interactions with metals. Diselenides, as well as their metal complexes, are interesting from the biological, pharmacological and synthetic points of view. Special attention has been paid to their electroreduction on mercury electrodes in protic and aprotic solutions where mercury-assisted reactions proceed. Recent investigations of

Ji?í Ludvík; Bengt Nygård

1997-01-01

130

A cyclic voltammetry investigation of the complex formation between Cu 2+ and some Schiff bases in binary acetonitrile/dimethylformamide mixtures  

NASA Astrophysics Data System (ADS)

The complex formation between Cu 2+ ions and some Schiff base ligands was studied in binary solvent mixtures of acetonitrile (AN)/dimethylformamide (DMF) systems at 25 °C using the cyclic voltammetric technique. The stoichiometry and stability of the complexes were determined by monitoring the shift in the half-wave potential of the CV peaks of the copper against the ligands concentration. The stoichiometry of all the complexes was found to be 1:1 and the complexation constants increased with decreasing amounts of dimethylformamide in these binary systems. In all cases, the variation of the stability constant with composition of the solvents was monotonic and showed good correlation with the inherent solvation ability of the neat solvents which form the mixture.

Rahimi-Nasrabadi, M.; Ganjali, M. R.; Gholivand, M. B.; Ahmadi, F.; Norouzi, P.; Salavati-Niasari, M.

2008-08-01

131

Formation of complex structures in dusty plasmas under temperature gradients  

Microsoft Academic Search

Thermophoretic effects on dust structures under temperature gradients in glow and radio-frequency discharge plasmas are studied\\u000a experimentally. The geometry of dust structures consisting of micrometer-sized polydisperse grains depends on heat release\\u000a in the plasma. Thermophoretic forces associated with heat release can control the formation of dust structures of different\\u000a geometries. A theoretical model is proposed to describe dust separation with

L. M. Vasilyak; S. P. Vetchinin; D. N. Polyakov; V. E. Fortov

2005-01-01

132

Relation between State-Selected or State-Averaged Cross Sections of Endothermic Reactions and Rate Constants of Exothermic Reactions. Application of Bimolecular Microcanonical Activated Complex Theory  

Microsoft Academic Search

An expression is derived relating state-selected or state-averaged molecular beam reaction cross sections of endothermic reactions to observed rate constants for the inverse (exothermic) reactions. An approximation of Anlauf, Maylotte, Polanyi, and Bernstein is used, together with bimolecular microcanonical activated complex theory [R. A. Marcus, J. Chem. Phys. 45, 2138 (1966)].

R. A. Marcus

1970-01-01

133

C-NH2 bond formation mediated by iridium complexes.  

PubMed

In the presence of phosphanes (PR3 ), the amido-bridged trinuclear complex [{Ir(?-NH2 )(tfbb)}3 ] (tfbb=tetrafluorobenzobarrelene) transforms into mononuclear discrete compounds [Ir(1,2-?(2) -4-?-C12 H8 F4 N)(PR3 )3 ], which are the products of the C?N coupling between the amido moiety and a vinylic carbon of the diolefin. An alternative synthetic approach to these species involves the reaction of the 18?e(-) complex [Ir(Cl)(tfbb)(PMePh2 )2 ] with gaseous ammonia and additional phosphane. DFT studies show that both transformations occur through nucleophilic attack. In the first case the amido moiety attacks a diolefin coordinated to a neighboring molecule following a bimolecular mechanism induced by the highly basic NH2 moiety; the second pathway involves a direct nucleophilic attack of ammonia to a coordinated tfbb molecule. PMID:25044533

Mena, Inmaculada; Casado, Miguel A; Polo, Víctor; García-Orduña, Pilar; Lahoz, Fernando J; Oro, Luis A

2014-09-01

134

Structural basis for cooperativity of CRM1 export complex formation  

PubMed Central

In eukaryotes, the nucleocytoplasmic transport of macromolecules is mainly mediated by soluble nuclear transport receptors of the karyopherin-? superfamily termed importins and exportins. The highly versatile exportin chromosome region maintenance 1 (CRM1) is essential for nuclear depletion of numerous structurally and functionally unrelated protein and ribonucleoprotein cargoes. CRM1 has been shown to adopt a toroidal structure in several functional transport complexes and was thought to maintain this conformation throughout the entire nucleocytoplasmic transport cycle. We solved crystal structures of free CRM1 from the thermophilic eukaryote Chaetomium thermophilum. Surprisingly, unbound CRM1 exhibits an overall extended and pitched superhelical conformation. The two regulatory regions, namely the acidic loop and the C-terminal ?-helix, are dramatically repositioned in free CRM1 in comparison with the ternary CRM1–Ran–Snurportin1 export complex. Single-particle EM analysis demonstrates that, in a noncrystalline environment, free CRM1 exists in equilibrium between extended, superhelical and compact, ring-like conformations. Molecular dynamics simulations show that the C-terminal helix plays an important role in regulating the transition from an extended to a compact conformation and reveal how the binding site for nuclear export signals of cargoes is modulated by different CRM1 conformations. Combining these results, we propose a model for the cooperativity of CRM1 export complex assembly involving the long-range allosteric communication between the distant binding sites of GTP-bound Ran and cargo. PMID:23277578

Monecke, Thomas; Haselbach, David; Voß, Béla; Russek, Andreas; Neumann, Piotr; Thomson, Emma; Hurt, Ed; Zachariae, Ulrich; Stark, Holger; Grubmüller, Helmut; Dickmanns, Achim; Ficner, Ralf

2013-01-01

135

Decay of activity complexes and the formation of coronal holes  

NASA Astrophysics Data System (ADS)

Analysis of long-term measurements of solar magnetic fields and the flux of UV radiation from the Sun indicates a cause-effect relationship between activity complexs, their residual magnetic fields, and coronal holes. A comparison of the background magnetic fields of the Sun and the evolution of former activity complexes reveals unipolar magnetic regions that form after the decay of these complexes. The latitude and time evolution of unipolar magnetic regions in solar cycles 21-24 is studied. A North-South asymmetry in solar activity is manifest in the distribution of unipolar regions migrating toward higher latitudes. It is shown that, when residual magnetic fields of the opposite polarity reach the polar regions, this leads to a sign change of the polar magnetic field and a decrease in the area of polar coronal holes, or even their complete disappearance. These interactions can explain the triple sign change of the polar magnetic field of the Sun in cycle 21 and the short-term polarity reversals observed in 2010 and 2011.

Mordvinov, A. V.; Yazev, S. A.

2013-06-01

136

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

NASA Astrophysics Data System (ADS)

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.

El-Shall, M. S.

2010-04-01

137

Contributions to the Sudbury Igneous Complex and the Depth of Excavation: Evidence from Onaping Formation Zircon  

NASA Astrophysics Data System (ADS)

U-Pb data for zircon preserved in the crater-fill sequence (Onaping Formation) of the Sudbury impact structure reveal a previously unrecognized but significant contributor to the Sudbury Igneous Complex.

Petrus, J. A.; Ayer, J. A.; Long, D. G. F.; Lightfoot, P. C.; Kamber, B. S.

2013-08-01

138

Complex Formation between Bovine Serum Albumin and Strong Polyelectrolytes: Effect of Polymer Charge Density  

E-print Network

Complex Formation between Bovine Serum Albumin and Strong Polyelectrolytes: Effect of Polymer serum albumin (BSA) to poly- (diallyldimethylammonium chloride) (PDADMAC), poly Form: February 25, 1998 Light scattering and pH titration were used to examine the binding of bovine

Dubin, Paul D.

139

The morpho-anatomy and histology of the pineal complex in a major Indian carp, Catla catla: identification of the pineal photoreceptor cells and their responsiveness to constant light and constant darkness during different phases of the annual reproductive cycle.  

PubMed

In contrast to mammals in which the pineal gland is a discrete structure situated dorsally in the brain, the "pineal gland" in teleost fishes is composed of a number of separate but connected constituent parts, collectively described as the "pineal complex." In this paper, we have described the pineal complex in a common Indian carp, Catla catla, which exhibits an annual reproductive cycle. Attempts have been made to (a) provide an in-depth description of the structure of the pineal complex; and (b) identify the photoreceptor cells of the pineal, by exposing the animals to constant light (LL) and constant darkness (DD). Furthermore, we examined any possible influence of the reproductive status of the fish on the responsiveness of the pineal photoreceptor cells in C. catla following exposure to LL and DD. To this end, a total of four experiments were carried out during the four different phases of the annual reproductive cycle that is characteristic of this species. Each of these four experiments was carried out for a period of 30 days after which the fishes were sacrificed, different parts of the pineal complex were dissected out, and processed for histological and karyometric studies. Our results showed that the pineal complex in this species is composed of three separate but connected parts, (a) an end vesicle (EV); (b) a dorsal sac (DS); and (c) a long and thin pineal stalk (PS) that attaches the EV to the DS. Detailed karyometric and histo-morphologic studies following exposure of the animals to DD and LL showed that constant darkness led to a stimulatory effect on the pineal photoreceptor cells of the EV as evident from a significant increase in the nuclear diameter. In contrast, the nuclear diameter of the photoreceptor cells in animals subjected to constant light showed a significant reduction. Furthermore, the observed cellular changes in the EV of fish exposed either to LL or DD were independent of the stage of the gonadal cycle. The apparent lack of any cellular responses either in the PS, or in the DS, following exposure to LL and DD, suggests that in C. catla the photoreceptor cells are located only within the epithelial lining of the EV and that these cells respond in a manner similar to mammalian pinealocytes when subjected to comparable photoperiod-induced experimental conditions. PMID:14682472

Dey, R; Bhattacharya, S; Maitra, S K; Banerji, T K

2003-11-01

140

Study of cadmium-humic interactions and determination of stability constants of cadmium-humate complexes from their diffusion coefficients obtained by scanned stripping voltammetry and dynamic light scattering techniques.  

PubMed

Diffusion coefficients of Cd-humate complexes are dependent on pH and [Cd]/[Humic] Acid (HA)] ratio in a Cd-HA system. These two factors mainly control the mass transport and complexation kinetics of Cd that may influence bioavailability and toxicity of Cd species in environmental systems. Determination of diffusion coefficients of Cd-HA systems by Scanned stripping voltammetry and dynamic light scattering techniques can provide a better understanding of the systems and can be very useful for extracting other speciation parameters of the systems. This study revealed that Cd(2+) ion along with small dynamic Cd complexes was predominantly present in a Cd-HA system at pH 5 with high diffusion coefficients. HA molecules were in aggregated form at pH 5. However, HA molecules were in disaggregated form at pH 6 and concentrations of Cd(2+) ion and small Cd-dynamic complexes decreased with a decrease in diffusion coefficients of Cd complexes at this pH due to formation of Cd-humate complexes. No further decrease in the hydrodynamic radii of HA was observed with the increase of pH from 6 to 7. The Cd-humate system partially lost its lability at pH 7. Conditional stability constants were calculated for Cd-humate complexes by combining the diffusion coefficient data obtained by two techniques. The log K values calculated in this study are in good agreement with the data available from the literature. PMID:20103116

Chakraborty, Parthasarathi

2010-02-01

141

Dynamic Membrane Formation Mechanisms of a Combined Coagulation Dynamic Membrane Process in Treating Polluted River Water at a Constant Pressure  

Microsoft Academic Search

The dynamic membrane formation mechanisms and filtration mechanisms were investigated at 4 cm and 8 cm water head drop (WHD). Flux variation, resistance plot curve shape, the relationship t\\/V - t and t\\/V - V were investigated to study the dynamic membrane formation and filtration. And effluent turbidity and particles size distribution were also used to demonstrate the effluent particles

Chunhua Xu; Baoyu Gao; Baichuan Cao; Weifeng Liu; Yang Song; Dandan Cheng

2009-01-01

142

Ultrasonic absorption associated with tertiary butanol complex formation in normal-hexane solutions  

E-print Network

ULTRASONIC ABSORPTION ASSOCIATED WITH TERTIARY BUTANOL COMPLEX FORMATION IN NORMAL-HEXANE SOLUTIONS A Thesis by SALIM MICHEL BUCARAM Submitted to the Graduate School of the Agricultural and Mechanical College of Texas in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE May 196l Major Subject; Physics ULTRASONIC ABSORPTION ASSOCIATED WITH TERTIARY BUTANOL COMPLEX FORMATION IN NORMAL-HEXANE SOLUTIONS A Thesis by SALIM MICHEL BUCARAM Approved as to style and content by...

Bucaram, Salim Michel

2012-06-07

143

Module Based Complexity Formation: Periodic Patterning in Feathers and Hairs  

PubMed Central

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

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

2012-01-01

144

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

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.

Vail, III, William Banning (Bothell, WA)

2000-01-01

145

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

SciTech Connect

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 consistent with the formation of dimeric Hg(II)-GSH complexes proposed in a recent EXAFS study.

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

2012-08-23

146

Real-time live imaging of T-cell signaling complex formation.  

PubMed

Protection against infectious diseases is mediated by the immune system (1,2). T lymphocytes are the master coordinators of the immune system, regulating the activation and responses of multiple immune cells (3,4). T-cell activation is dependent on the recognition of specific antigens displayed by antigen presenting cells (APCs). The T-cell antigen receptor (TCR) is specific to each T-cell clone and determines antigen specificity (5). The binding of the TCR to the antigen induces the phosphorylation of components of the TCR complex. In order to promote T-cell activation, this signal must be transduced from the membrane to the cytoplasm and the nucleus, initiating various crucial responses such as recruitment of signaling proteins to the TCR;APC site (the immune synapse), their molecular activation, cytoskeletal rearrangement, elevation of intracellular calcium concentration, and changes in gene expression (6,7). The correct initiation and termination of activating signals is crucial for appropriate T-cell responses. The activity of signaling proteins is dependent on the formation and termination of protein-protein interactions, post translational modifications such as protein phosphorylation, formation of protein complexes, protein ubiquitylation and the recruitment of proteins to various cellular sites (8). Understanding the inner workings of the T-cell activation process is crucial for both immunological research and clinical applications. Various assays have been developed in order to investigate protein-protein interactions; however, biochemical assays, such as the widely used co-immunoprecipitation method, do not allow protein location to be discerned, thus precluding the observation of valuable insights into the dynamics of cellular mechanisms. Additionally, these bulk assays usually combine proteins from many different cells that might be at different stages of the investigated cellular process. This can have a detrimental effect on temporal resolution. The use of 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

Noy, Elad; Pauker, Maor H; Barda-Saad, Mira

2013-01-01

147

Orientation of the Central Pair Complex During Flagellar Bend Formation in  

E-print Network

Orientation of the Central Pair Complex During Flagellar Bend Formation in Chlamydomonas David R Thin section electron micrographs of rapidly fixed Chlamydomonas cells were used to establish a relationship between flagellar bends and orientation of the central pair microtubule complex. Using conditions

Mitchell, David

148

Formation of an Intrapolymer Complex from Human Serum Albumin and Poly(ethylene glycol)  

E-print Network

Formation of an Intrapolymer Complex from Human Serum Albumin and Poly(ethylene glycol) Shinji Form: October 13, 1998 Complexation between human serum albumin (HSA) and poly(ethylene glycol) (PEG, it has been demonstrated that poly(dial- lyldimethylammonium chloride) and bovine serum albu- min give

Dubin, Paul D.

149

Energy transfer between Ln(III) ions in aqueous solutions upon formation of labile binuclear fluoride and nitrate complexes of these ions  

Microsoft Academic Search

The influence of anions on nonradiative electronic energy transfer between lanthanide ions in aqueous solutions is studied.\\u000a The rate constant k\\u000a \\u000a t\\u000a of energy transfer was found to increase by three orders of magnitude upon addition of salts of hydrofluoric acid to the\\u000a solution. This effect is caused by the formation of bridge labile binuclear complexes, an excited energy donor-fluorine

E. B. Sveshnikova; S. S. Dudar’; V. L. Ermolaev

2000-01-01

150

Carbon-heteroatom bond formation catalysed by organometallic complexes  

PubMed Central

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

Hartwig, John F.

2010-01-01

151

A selective spectrofluorimetric method for carbendazim determination in oranges involving inclusion-complex formation with cucurbit[7]uril.  

PubMed

The increase in fluorescence intensity with respect to carbendazim that occurs as a result of supramolecular-complex formation between carbendazim and cucurbit[7]uril has been studied. This host-guest interaction has been employed to develop a sensitive and selective method for benzoimidazole-type pesticide determination in fruit samples. The association constant and stoichiometry of the complex formed are reported herein, and the influence of experimental variables, such as the pH or ionic strength of the solution, on complex formation and the presence of interfering substances is also discussed. Under the optimal conditions found, the developed method allows the detection of carbendazim at a 5.0x10(-9)M level. To test the method, matrix solid phase dispersion was employed as a sample preparation method for carbendazim determination in orange samples with an RSD (%) (n=3) value of 5%. The LOD and LOQ values calculated for real samples were 0.10 and 0.52mg/kg, respectively, thus showing that the proposed method is sensitive enough to meet legal requirements. PMID:20441936

del Pozo, M; Hernández, L; Quintana, C

2010-06-15

152

Complex Formation History of Highly Evolved Basaltic Shergottite, Zagami  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

153

The ORC/Cdc6/MCM2-7 complex facilitates MCM2-7 dimerization during prereplicative complex formation.  

PubMed

The replicative mini-chromosome-maintenance 2-7 (MCM2-7) helicase is loaded in Saccharomyces cerevisiae and other eukaryotes as a head-to-head double-hexamer around origin DNA. At first, ORC/Cdc6 recruits with the help of Cdt1 a single MCM2-7 hexamer to form an 'initial' ORC/Cdc6/Cdt1/MCM2-7 complex. Then, on ATP hydrolysis and Cdt1 release, the 'initial' complex is transformed into an ORC/Cdc6/MCM2-7 (OCM) complex. However, it remains unclear how the OCM is subsequently converted into a MCM2-7 double-hexamer. Through analysis of MCM2-7 hexamer-interface mutants we discovered a complex competent for MCM2-7 dimerization. We demonstrate that these MCM2-7 mutants arrest during prereplicative complex (pre-RC) assembly after OCM formation, but before MCM2-7 double-hexamer assembly. Remarkably, only the OCM complex, but not the 'initial' ORC/Cdc6/Cdt1/MCM2-7 complex, is competent for MCM2-7 dimerization. The MCM2-7 dimer, in contrast to the MCM2-7 double-hexamer, interacts with ORC/Cdc6 and is salt-sensitive, classifying the arrested complex as a helicase-loading intermediate. Accordingly, we found that overexpression of the mutants cause cell-cycle arrest and dominant lethality. Our work identifies the OCM complex as competent for MCM2-7 dimerization, reveals MCM2-7 dimerization as a limiting step during pre-RC formation and defines critical mechanisms that explain how origins are licensed. PMID:24234446

Evrin, Cecile; Fernández-Cid, Alejandra; Riera, Alberto; Zech, Juergen; Clarke, Pippa; Herrera, M Carmen; Tognetti, Silvia; Lurz, Rudi; Speck, Christian

2014-02-01

154

Factors leading to the formation of arc cloud complexes  

NASA Technical Reports Server (NTRS)

A total of 12 mesoscale convective systems (MCSs) were investigated. The duration of the gust front, produced by each MCS, was used to classify the MCSs. Category 1 MCSs were defined as ones that produced a gust front and the gust front lasted for more than 6 h. There were 7 category 1 MCSs in the sample. Category 2 MCSs were defined as ones that produced a gust front and the gust front lasted for 6 h or less. There were 4 category 2 MCSs. The MCS of Case 12 was not categorized because the precipitation characteristics were similar to a squall line, rather than an MCS. All of the category 1 MCSs produced arc cloud complexes (ACCs), while only one of the category 2 MCSs produced an ACC. To determine if there were any differences in the characteristics between the MCSs of the two categories, composite analyses were accomplished. The analyses showed that there were significant differences in the characteristics of category 1 and 2 MCSs. Category 1 MCSs, on average, had higher thunderstorm heights, greater precipitation intensities, colder cloud top temperatures and produced larger magnitudes of surface divergence than category 2 MCSs.

Welshinger, Mark John; Brundidge, Kenneth C.

1987-01-01

155

Interferogram formation in the presence of complex and large deformation  

USGS Publications Warehouse

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.

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

2007-01-01

156

Estimation of Stability Constants of Cadmium(II) bis-Complexes with Amino Acids by Model Based on 3?v Connectivity Index.  

PubMed

Linear model for estimation of the second, K2, and overall, ?2, stability constant of cadmium(II) binary and ternary bis-complexes with five aliphatic ?-amino acids based on valence connectivity index of the 3rd order (3?v) was developed. Set of amino acids included glycine, alanine, 2-aminobutanoic, 2-aminopentanoic (norvaline) and 2-aminohexanoic acid (norleucine), which by bonding to the cadmium(II) gave 25 K2 and 15 ?2 values. For estimation of log ?2, the model gave r = 0.940, and the S.E.cv = 0.10, and for the two subsets of log K2 constants the model yielded r = 0.936 and 0.842, and S.E.cv = 0.09. The complex CdGG was excluded from all regressions. PMID:24061889

Mili?evi?, Ante; Raos, Nenad

2010-12-01

157

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

PubMed

Stoichiometry and apparent stability constant (K(C)) 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 K(C) in methanol is greater than in the binary solutions. The effects of changing solvent composition on K(C) data were explained by linear solvation free energy relationships using the solvatochromic parameter of Kamlet and Taft (?, ? and ?(*)). Multiple linear regression analysis indicates that the hydrogen bond donating ability (?) of the solvent and non-specific interactions (?(*)) play an important role in the degree of occurrence of the reaction. The effect of temperature on K(C) 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. PMID:22609565

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

2012-09-01

158

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

NASA Astrophysics Data System (ADS)

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 (?, ? and ?*). Multiple linear regression analysis indicates that the hydrogen bond donating ability (?) of the solvent and non-specific interactions (?*) 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.

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

2012-09-01

159

Cleavage and formation of molecular dinitrogen in a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine.  

PubMed

The N?N bond of molecular dinitrogen bridging two molybdenum atoms in the pentamethylcyclopentadienyl molybdenum complexes that bear ferrocenyldiphosphine as an auxiliary ligand is homolytically cleaved under visible light irradiation at room temperature to afford two molar molybdenum nitride complexes. Conversely, the bridging molecular dinitrogen is reformed by the oxidation of the molybdenum nitride complex at room temperature. This result provides a successful example of the cleavage and formation of molecular dinitrogen induced by a pair of two different external stimuli using a single system assisted by molybdenum complexes bearing ferrocenyldiphosphine under ambient conditions. PMID:25214300

Miyazaki, Takamasa; Tanaka, Hiromasa; Tanabe, Yoshiaki; Yuki, Masahiro; Nakajima, Kazunari; Yoshizawa, Kazunari; Nishibayashi, Yoshiaki

2014-10-20

160

The effect of polyion complex formation on in vitro/in vivo correlation of hydrophilic matrix tablets.  

PubMed

The aim of this study was to investigate the effects of polyion complex formation on in vivo performance of hydrophilic matrix tablets. Three kinds of controlled release theophylline tablets were prepared by direct compression using carboxymethyldextran (CMD), a mixture of CMD and [2-(diethylamino)ethyl]dextran (EA), and a mixture of dextran sulfate (DS) and EA. According to a conventional dissolution test, in vitro drug release profiles of these tablets were similar to each other. In vivo absorption profiles of theophylline after oral administration to beagle dogs, however, were quite different and were not consistent with in vitro release profiles. Thus, we applied a modified in vitro release test considering destructive forces. An excellent in vitro/in vivo correlation was obtained in the cases of CMD/EA- and DS/EA-tablets. The results suggested that the drug was released constantly in the overall gastrointestinal tract, and even in the colon. Then, hydrophilic matrices were characterized by swelling rate, matrix density and strength in a wet state. DS/EA-tablets showed limited swelling, higher density and a larger value of wet strength than the others. These findings indicated that polyion complex formation in gel layer contributes to prevent over-swelling and strengthen the wetted matrices. PMID:12932710

Miyazaki, Yasunori; Yakou, Shigeru; Nagai, Tsuneji; Takayama, Kozo

2003-09-01

161

Complex formation processes in 3d metal hexacyanoferrate(II) gelatin-immobilised matrices  

NASA Astrophysics Data System (ADS)

Data on nontraditional complex formation reactions in iron(II, III), cobalt(II), cobalt(III), nickel(II), and copper(II) hexacyanoferrate(II) gelatin-immobilised matrixes with fixation of the immobilised substances by intermolecular forces are surveyed and described systematically. Such reactions proceed when the matrices come into contact with aqueous solutions of nitrogen-, oxygen-, and sulfur-containing polydentate ligands. The practical possibilities for complex formation reactions in metal hexacyanoferrate(II) gelatin-immobilised matrixes are demonstrated. The bibliography includes 147 references.

Mikhailov, Oleg V.

1995-07-01

162

{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

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.

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

1995-01-01

163

Generating functional analysis of complex formation and dissociation in large protein interaction networks  

NASA Astrophysics Data System (ADS)

We analyze large systems of interacting proteins, using techniques from the non-equilibrium statistical mechanics of disordered many-particle systems. Apart from protein production and removal, the most relevant microscopic processes in the proteome are complex formation and dissociation, and the microscopic degrees of freedom are the evolving concentrations of unbound proteins (in multiple post-translational states) and of protein complexes. Here we only include dimer-complexes, for mathematical simplicity, and we draw the network that describes which proteins are reaction partners from an ensemble of random graphs with an arbitrary degree distribution. We show how generating functional analysis methods can be used successfully to derive closed equations for dynamical order parameters, representing an exact macroscopic description of the complex formation and dissociation dynamics in the infinite system limit. We end this paper with a discussion of the possible routes towards solving the nontrivial order parameter equations, either exactly (in specific limits) or approximately.

Coolen, A. C. C.; Rabello, S.

2009-12-01

164

Polynucleotides. XXVI1) Complex formation of polynucleotides derived from formycin and laurusin with cyclonucleoside oligonucleotides  

PubMed Central

Poly(formycin phosphate) and poly(laurusin phosphate) were synthesized by polymerizing formycin and laurusin 5?-diphosphate by means of E. coli polynucleotide phosphorylase. The complex formation of these polynucleotides with cyclonucleoside polynucleotides were investigated. While poly(formycin phosphate) did not form the complex with an octanucleotide of 6,2?-anhydro-6-oxy-1-?-D-arabinofuranosyluracil, poly(laurusin phosphate) did form a 1: 1 complex with octanucleotide of 8,2?-anhydro-8-mercapto-9-?-D-arabinofuranosyladenine in the presence of 0.15M Na ion at neutrality and 3o. CD spectrum of this complex showed a couple of a trough at 286 nm and a peak at 262 nm. This fact suggests that the complex has a left-handed helical conformation, which is opposite to the natural double helical polynucleotides. The cause of this phenomenon was discussed in connection with the complex of cyclonucleoside oligonucleotides. PMID:10793723

Ikehara, Morio; Tezuka, Toru

1974-01-01

165

Effects of amylose chain length and heat treatment on amylose-glycerol monocaprate complex formation.  

PubMed

Aqueous mixtures of amylose with different chain lengths (DP 23-849), which had been enzymatically synthesized or isolated from potato and maize starches, and glycerol monocaprate (GMC, 5:1 weight ratio) were analyzed by using a differential scanning calorimeter (DSC). The mixtures were thermally treated (first DSC scan: 20-140 °C, 5 °C/min and prolonged heat treatment: 100 °C for 24 h) and its effect on the amylose-GMC complex formation was analyzed by DSC and X-ray diffractometer. The amylose, especially short ones, readily associated in the dispersion forming the amylose-amylose crystals but the presence of GMC inhibited the crystal formation. The longer amylose had the greater possibility for the complex formation with GMC, and the prolonged heat treatment facilitated the amylose-GMC complex formation. Both type I and type II complexes were formed during quenching after the initial DSC heating. However, only the type II complexes were formed after the prolonged heat treatment with improved crystallinity and thermostability. PMID:23618264

Zhou, Xing; Wang, Ren; Zhang, Yuxian; Yoo, Sang-Ho; Lim, Seung-Taik

2013-06-01

166

Formation of P450oP450 Complexes and Their Effect on P450 Function  

PubMed Central

Cytochromes P450 (P450) are membrane-bound enzymes that catalyze the monooxygenation of a diverse array of xenobiotic and endogenous compounds. The P450s responsible for foreign compound metabolism generally are localized in the endoplasmic reticulum of the liver, lung and small intestine. P450 enzymes do not act alone but require an interaction with other electron transfer proteins such as NADPH-cytochrome P450 reductase (CPR) and cytochrome b5. Because P450s are localized in the endoplasmic reticulum with these and other ER-resident proteins, there is a potential for protein-protein interactions to influence P450 function. There has been increasing evidence that P450 enzymes form complexes in the ER, with compelling support that formation of P450•P450 complexes can significantly influence their function. Our goal is to review the research supporting the formation of P450•P450 complexes, their specificity, and how drug metabolism may be affected. This review describes the potential mechanisms by which P450s may interact, and provides evidence to support each of the possible mechanisms. Additionally, evidence for the formation of both heteromeric and homomeric P450 complexes are reviewed. Finally, direct physical evidence for P450 complex formation in solution and in membranes is summarized, and questions directing the future research of functional P450 interactions are discussed with respect to their potential impact on drug metabolism. PMID:22155419

Reed, James R.; Backes, Wayne L.

2011-01-01

167

Complex formation between alkylpyridines and Na 3 PO 4 under gas chromatography conditions  

Microsoft Academic Search

1.The specific retention volumes, the differential molar free energies, enthalpies, and entropies of sorption for twelve pyridine bases have been determined by gas chromatography on columns containing equimolar amounts of the salts sodium orthophosphate and potassium fluoride, with hydrogenated Apiezon L as the stationary phase.2.Alkylpyridines form donor-acceptor complexes with sodium orthophosphate and the thermodynamic characteristics of complex formation have been

R. V. Golovnya; I. L. Zhuravleva; B. M. Polanuer

1984-01-01

168

Characterisation of the electron transfer and complex formation between flavodoxin from D. vulgaris and the haem domain of cytochrome P450 BM3 from B. megaterium.  

PubMed

Investigation of the complex formation and electron transfer kinetics between P450 BMP and flavodoxin was carried out following the suggested involvement of flavodoxin in modulating the electron transfer to BMP in artificial redox chains bound to an electrode surface. While electron transfer measurements show the formation of a tightly bound complex, the NMR data indicate the formation of shortly lived complexes. The measured k(obs) ranged from 24.2 s(-1) to 44.1 s(-1) with k(on) ranging from 0.07 x 10(6) to 1.1 x 10(6) s(-1) M(-1) and K(d) ranging from 300 microM to 24 microM in buffers of different ionic strength. This apparent contradiction is due to the existence of two events in the complex formation prior to electron transfer. A stable complex is initially formed. Within such tightly bound complex, flavodoxin rocks rapidly between different positions. The rocking of the bound flavodoxin between several different orientations gives rise to the transient complexes in fast exchange as observed in the NMR experiments. Docking simulations with two different approaches support the theory that there is no highly specific orientation in the complex, but instead one side of the flavodoxin binds the P450 with high overall affinity but with a number of different orientations. The level of functionality of each orientation is dependent on the distance between cofactors, which can vary between 8 and 25 A, with some of the transient complexes showing distances compatible with the measured electron transfer rate constants. PMID:19366612

Fantuzzi, Andrea; Meharenna, Yergalem T; Briscoe, Paul B; Guerlesquin, Francoise; Sadeghi, Sheila J; Gilardi, Gianfranco

2009-04-01

169

Phosphonato complexes of platinum(II): kinetics of formation and phosphorus-31 NMR characterization studies  

Microsoft Academic Search

Reactions of cis-diamminedichloroplatinum(II) with phosphonoformic acid (PFA), phosphonoacetic acid (PAA), and methylenediphosphonic acid (MDP) yield various phosphonatoplatinum(II) chelates which were characterized by phosphorus-31 NMR spectroscopy. The P-31 resonances for the chelates appear at 6-12 ppm downfield as compared to the uncomplexed ligands. All complexes exhibit monoprotic acidic behavior in the pH range 2-10. The chemical shift-pH profiles yielded acidity constants,

L. L. Slavin; R. N. Bose

1990-01-01

170

Low temperature rate constants for the N(4S) + CH(X2{\\Pi}r) reaction. Implications for N2 formation cycles in dense interstellar clouds  

E-print Network

Rate constants for the potentially important interstellar N(4S) + CH(X2{\\Pi}r) reaction have been measured in a continuous supersonic flow reactor over the range 56 K molecules. In parallel, quantum dynamics calculations of the title reaction have been performed based on accurate global potential energy surfaces for the 13A' and 13A" states of HCN and HNC, brought about through a hierarchical construction scheme. Both adiabatic potential energy surfaces are barrierless, each one having two deep potential wells suggesting that this reaction is dominated by a complex-forming mechanism. The experimental and theoretical work are inexcellent agreement, predicti...

Daranlot, Julien; Xie, Changjian; Loison, Jean-Christophe; Caubet, Philippe; Costes, Michel; Wakelam, Valentine; Xie, Daiqian; Guod, Hua; Hickson, Kevin M

2013-01-01

171

Conformational heterogeneity in antibody-protein antigen recognition: implications for high affinity protein complex formation.  

PubMed

Specific, high affinity protein-protein interactions lie at the heart of many essential biological processes, including the recognition of an apparently limitless range of foreign proteins by natural antibodies, which has been exploited to develop therapeutic antibodies. To mediate biological processes, high affinity protein complexes need to form on appropriate, relatively rapid timescales, which presents a challenge for the productive engagement of complexes with large and complex contact surfaces (?600-1800 ?(2)). We have obtained comprehensive backbone NMR assignments for two distinct, high affinity antibody fragments (single chain variable and antigen-binding (Fab) fragments), which recognize the structurally diverse cytokines interleukin-1? (IL-1?, ?-sheet) and interleukin-6 (IL-6, ?-helical). NMR studies have revealed that the hearts of the antigen binding sites in both free anti-IL-1? Fab and anti-IL-6 single chain variable exist in multiple conformations, which interconvert on a timescale comparable with the rates of antibody-antigen complex formation. In addition, we have identified a conserved antigen binding-induced change in the orientation of the two variable domains. The observed conformational heterogeneity and slow dynamics at protein antigen binding sites appears to be a conserved feature of many high affinity protein-protein interfaces structurally characterized by NMR, suggesting an essential role in protein complex formation. We propose that this behavior may reflect a soft capture, protein-protein docking mechanism, facilitating formation of high affinity protein complexes on a timescale consistent with biological processes. PMID:24436329

Addis, Philip W; Hall, Catherine J; Bruton, Shaun; Veverka, Vaclav; Wilkinson, Ian C; Muskett, Frederick W; Renshaw, Philip S; Prosser, Christine E; Carrington, Bruce; Lawson, Alastair D G; Griffin, Robert; Taylor, Richard J; Waters, Lorna C; Henry, Alistair J; Carr, Mark D

2014-03-01

172

Equilibrium investigation of complex formation reactions involving copper(II), nitrilo-tris(methyl phosphonic acid) and amino acids, peptides or DNA constitutents. The kinetics, mechanism and correlation of rates with complex stability for metal ion promoted hydrolysis of glycine methyl ester  

Microsoft Academic Search

The complex formation reactions of [Cu(NTP)(OH2)] (NTP?=?nitrilo-tris(methyl phosphonic acid)) with some selected bio-relevant ligands containing different functional groups, are investigated. Stoichiometry and stability constants for the complexes formed are reported. The results show that the ternary complexes are formed in a stepwise mechanism whereby NTP binds to copper(II), followed by coordination of amino acid, peptide or DNA. Copper(II) is found

Ahmed A. El-Sherif; Mohamed M. Shoukry

2006-01-01

173

Phosphonato complexes of platinum(II): kinetics of formation and phosphorus-31 NMR characterization studies  

SciTech Connect

Reactions of cis-diamminedichloroplatinum(II) with phosphonoformic acid (PFA), phosphonoacetic acid (PAA), and methylenediphosphonic acid (MDP) yield various phosphonatoplatinum(II) chelates which were characterized by phosphorus-31 NMR spectroscopy. The P-31 resonances for the chelates appear at 6-12 ppm downfield as compared to the uncomplexed ligands. All complexes exhibit monoprotic acidic behavior in the pH range 2-10. The chemical shift-pH profiles yielded acidity constants, 1.0 x 10(-4), 1.5 x 10(-4), and 1.3 x 10(-6) M-1, for the PFA, PAA, and MDP chelates. In addition to the monomeric chelate, MDP formed a bridged diplatinum(II,II) complex when it reacted with cis-Pt (NH3)2(H2O)2(2)+. The P-31 resonance for this binuclear complex appears at 22 ppm downfield from the unreacted ligand. Rate data for the complexation reactions of the phosphonate ligands with the dichloroplatinum complex are consistent with a mechanism in which a monodentate complex is formed initially through rate-limiting aquation process of the platinum complex, followed by a rapid chelation. For the PFA and PAA complexes, initial binding sites are the carboxylato oxygens. Implications of the various binding modes of the phosphonates in relationship to their antiviral activities are discussed.

Slavin, L.L.; Bose, R.N. (Chemistry Department, Kent State University, OH (USA))

1990-12-01

174

Phosphonato complexes of platinum(II): kinetics of formation and phosphorus-31 NMR characterization studies.  

PubMed

Reactions of cis-diamminedichloroplatinum(II) with phosphonoformic acid (PFA), phosphonoacetic acid (PAA), and methylenediphosphonic acid (MDP) yield various phosphonatoplatinum(II) chelates which were characterized by phosphorus-31 NMR spectroscopy. The P-31 resonances for the chelates appear at 6-12 ppm downfield as compared to the uncomplexed ligands. All complexes exhibit monoprotic acidic behavior in the pH range 2-10. The chemical shift-pH profiles yielded acidity constants, 1.0 x 10(-4), 1.5 x 10(-4), and 1.3 x 10(-6) M-1, for the PFA, PAA, and MDP chelates. In addition to the monomeric chelate, MDP formed a bridged diplatinum(II,II) complex when it reacted with cis-Pt (NH3)2(H2O)2(2)+. The P-31 resonance for this binuclear complex appears at 22 ppm downfield from the unreacted ligand. Rate data for the complexation reactions of the phosphonate ligands with the dichloroplatinum complex are consistent with a mechanism in which a monodentate complex is formed initially through rate-limiting aquation process of the platinum complex, followed by a rapid chelation. For the PFA and PAA complexes, initial binding sites are the carboxylato oxygens. Implications of the various binding modes of the phosphonates in relationship to their antiviral activities are discussed. PMID:2150856

Slavin, L L; Bose, R N

1990-12-01

175

A Tide Coming in 'faster than a galloping horse': Tax Haven Islands and Rapid Complex Constant Change  

Microsoft Academic Search

Many islands have hosted tax havens and offshore finance centres (OFCs) since the early twentieth century. However, from around 1998 they faced an overwhelming tide of complex and wide-ranging initiatives from organisations including the OECD, the IMF, the G7's Financial Action Task Force (FATF) and Financial Stability Forum, and the EU. In addition, national governments including the US and UK

Mark P. Hampton

176

Structural, electronic properties and heat of formation of Mg2FeH6 complex hydride: an ab initio study  

NASA Astrophysics Data System (ADS)

In this work, the structural, energetic and electronic properties of Mg2FeH6 complex hydride have been studied using two different methods based on the density functional theory (DFT): the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) and the pseudo-potentials plane waves (PP-PW) methods. Based on the calculated results, the ground state of Mg2FeH6 is found to be paramagnetic (PM), which is in agreement with experimental results, and also, the optimized structural parameters including lattice constants and atomic positions are very close to the experimental and other theoretical works. For a detailed study, electronic structure calculations including those of the energy band, density of states (DOS) and charge density distribution have been performed. It is found that Mg2FeH6 hydride is a semiconductor with a direct energy gap at the X-point of about 1.87 and 2.25 eV for the FP-LAPW + lo and PW-PP methods, respectively, and the Mg atom acts as a donor to form a cation ion and the negatively charged FeH6 complex results in a mainly ionic bonding between the Mg and FeH6 complex. Other physical and energetic properties such as bulk modulus, cohesive energy and formation enthalpy of Mg2FeH6 are in good agreement with the theoretically and experimentally determined values.

Zareii, S. M.; Sarhaddi, R.

2012-07-01

177

Communication: Structure, formation, and equilibration of ensembles of Ag-S complexes on an Ag surface  

SciTech Connect

We have utilized conditions of very low temperature (4.7 K) and very low sulfur coverage to isolate and identify Ag-S complexes that exist on the Ag(111) surface. The experimental conditions are such that the complexes form at temperatures above the temperature of observation. These complexes can be regarded as polymeric chains of varying length, with an Ag4S pyramid at the core of each monomeric unit. Steps may catalyze the formation of the chains and this mechanism may be reflected in the chain length distribution.

Russell, Selena M. [Ames Laboratory; Kim, Yousoo [RIKEN Advanced Science Institute; Liu, Da-Jiang [Ames Laboratory; Evans, J. W. [Ames Laboratory; Thiel, P. A. [Ames Laboratory

2013-02-15

178

Three-Coordinate Terminal Imidoiron(III) Complexes: Structure, Spectroscopy, and Mechanism of Formation  

PubMed Central

Reaction of 1-adamantyl azide with iron(I) diketiminate precursors gives metastable but isolable imidoiron(III) complexes LFe=NAd (L = bulky ?-diketiminate ligand; Ad = 1-adamantyl). This paper addresses: (1) the spectroscopic and structural characterization of the Fe=N multiple bond in these interesting three-coordinate iron imido complexes, and (2) the mechanism through which the imido complexes form. The iron(III) imido complexes have been examined by 1H NMR and EPR spectroscopies and temperature-dependent magnetic susceptibility (SQUID), and structurally characterized by crystallography and/or X-ray absorption (EXAFS) measurements. These data show that the imido complexes have quartet ground states and short (1.68 ± 0.01 Å) iron-nitrogen bonds. The formation of the imido complexes proceeds through unobserved iron–RN3 intermediates, which are indicated by QM/MM computations to be best described as iron(II) with an RN3 radical anion. The radical character on the organoazide bends its NNN linkage to enable easy N2 loss and imido complex formation. The product distribution between imidoiron(III) products and hexazene-bridged diiron(II) products is solvent-dependent, and the solvent dependence can be explained by coordination of certain solvents to the iron(I) precursor prior to interaction with the organoazide. PMID:20524625

Cowley, Ryan E.; DeYonker, Nathan J.; Eckert, Nathan A.; Cundari, Thomas R.; DeBeer, Serena; Bill, Eckhard; Ottenwaelder, Xavier; Flaschenriem, Christine; Holland, Patrick L.

2010-01-01

179

Complex Formation by Electrostatic Interaction between Carboxyl-Terminated Dendrimers and Oppositely Charged  

E-print Network

- enon in biological systems1 as well as in a number of technological processes;2 however, in the case because of the technological relevance of colloid-polymer interactions, we focus on complex formation charged particles depends predominantly on three variables: the ionic strength (I), the polymer linear

Dubin, Paul D.

180

The standard enthalpies of combustion and formation of crystalline cobalt tetrakis(4-metoxyphenyl)porphin complex  

NASA Astrophysics Data System (ADS)

The energy of combustion of cobalt tetrakis(4-metoxyphenyl)porphin was determined in an isothermic-shell liquid calorimeter with a stationary calorimetric bomb. The standard enthalpies of combustion and formation of the complex were calculated, -? c H o = 27334.06 ± 50.98 kJ/mol and ?f H o = 3062.90 ± 50.97 kJ/mol.

Tarasov, R. P.; Volkov, A. V.; Bazanov, M. I.; Semeikin, A. S.

2009-05-01

181

Transcription by RNA polymerase II: initiator-directed formation of transcription-competent complexes  

Microsoft Academic Search

Studies of transcription by RNA polymer- ase II have revealed two promoter elements, the TATA motif and the initiator (Inr), capable of directing specific transcription initiation. Although binding to the TATA motif by one of the components of the transcription machinery has been shown to be the initial recognition step in transcription complex formation, many promoters that lack a traditional

LISA WEIS; DANNY REINBERG

1992-01-01

182

The significance of ACTH for the process of formation of complex heparin compounds in the blood during immobilization stress  

NASA Technical Reports Server (NTRS)

Adrenocorticotropin (ACTH) was administered to rats at different times following adrenalectomy. Adrenocorticotropin caused a significant increase in the formation of heparin complexes even in the absence of stress factor. When ACTH secretion is blocked, immobilization stress is not accompanied by an increase in the process of complex formation. The effect of ACTH on the formation of heparin complexes was mediated through its stimulation of the adrenal cortex.

Kudryashov, B. A.; Shapiro, F. B.; Lomovskaya, F. B.; Lyapina, L. A.

1979-01-01

183

Geminin Inhibits a Late Step in the Formation of Human Pre-replicative Complexes*  

PubMed Central

The initial step in initiation of eukaryotic DNA replication involves the assembly of pre-replicative complexes (pre-RCs) at origins of replication during the G1 phase of the cell cycle. In metazoans initiation is inhibited by the regulatory factor Geminin. We have purified the human pre-RC proteins, studied their interactions in vitro with each other and with origin DNA, and analyzed the effects of HsGeminin on formation of DNA-protein complexes. The formation of an initial complex containing the human origin recognition complex (HsORC), HsCdt1, HsCdc6, and origin DNA is cooperative, involving all possible binary interactions among the components. Maximal association of HsMCM2–7, a component of the replicative helicase, requires HsORC, HsCdc6, HsCdt1, and ATP, and is driven by interactions of HsCdt1 and HsCdc6 with multiple HsMCM2–7 subunits. Formation of stable complexes, resistant to high salt, requires ATP hydrolysis. In the absence of HsMCM proteins, HsGeminin inhibits the association of HsCdt1 with DNA or with HsORC-HsCdc6-DNA complexes. However, HsGeminin does not inhibit recruitment of HsMCM2–7 to DNA to form complexes containing all of the pre-RC proteins. In fact, HsGeminin itself is a component of such complexes, and interacts directly with the HsMcm3 and HsMcm5 subunits of HsMCM2–7, as well as with HsCdt1. Although HsGeminin does not prevent the initial formation of DNA-protein complexes containing the pre-RC proteins, it strongly inhibits the formation of stable pre-RCs that are resistant to high salt. We suggest that bound HsGeminin prevents transition of the pre-RC to a state that is competent for initiation of DNA replication. PMID:25231993

Wu, Min; Lu, Wenyan; Santos, Ruth E.; Frattini, Mark G.; Kelly, Thomas J.

2014-01-01

184

Spring Constants  

NSDL National Science Digital Library

This inquiry activity should be completed before students have learned about spring constants. It should be pointed out to students that if a rubber band or spring is stretched too much, the spring constant is not constant. Graphs will vary based on the s

Horton, Michael

2009-05-30

185

Lethal synergism between organic and inorganic wood preservatives via formation of an unusual lipophilic ternary complex  

SciTech Connect

We have shown previously that exposing bacteria to wood preservatives pentachlorophenol (PCP) and copper-containing compounds together causes synergistic toxicity. However, it is not clear whether these findings also hold true in mammalian cells; and if so, what is the underlying molecular mechanism? Here we show that PCP and a model copper complex bis-(1,10-phenanthroline) cupric (Cu(OP){sub 2}), could also induce synergistic cytotoxicity in human liver cells. By the single crystal X-ray diffraction and atomic absorption spectroscopy assay, the synergism was found to be mainly due to the formation of a lipophilic ternary complex with unusual structural and composition characteristics and subsequent enhanced cellular copper uptake, which markedly promoted cellular reactive oxygen species (ROS) production, leading to apoptosis by decreasing mitochondrial membrane potential, increasing pro-apoptotic protein expression, releasing cytochrome c from mitochondria and activating caspase-3, and -9. Analogous results were observed with other polychlorinated phenols (PCPs) and Cu(OP){sub 2}. Synergistic cytotoxicity could be induced by PCP/Cu(OP){sub 2} via formation of an unusual lipophilic complex in HepG2 cells. The formation of ternary complexes with similar lipophilic character could be of relevance as a general mechanism of toxicity, which should be taken into consideration especially when evaluating the toxicity of environmental pollutants found at currently-considered non- or sub-toxic concentrations. -- Highlights: ? The combination of PCP/Cu(OP){sub 2} induces synergistic cytotoxicity in HepG2 cells. ? The synergism is mainly due to forming a lipophilic ternary complex between them. ? The formation of lipophilic ternary complex enhances cellular copper uptake. ? PCP/Cu(OP){sub 2} stimulates the cellular ROS production. ? The ROS promoted by PCP/Cu(OP){sub 2} induces mitochondria-dependent apoptosis.

Sheng, Zhi-Guo; Li, Yan; Fan, Rui-Mei; Chao, Xi-Juan [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085 (China)] [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085 (China); Zhu, Ben-Zhan, E-mail: bzhu@rcees.ac.cn [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085 (China) [State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085 (China); Linus Pauling Institute, Oregon State University, Corvallis, OR 97331 (United States)

2013-02-01

186

Constantes de stabilité de complexes organo-minéraux. Interactions des ions plombeux avec les composés organiques hydrosolubles des eaux gravitaires de podzol  

NASA Astrophysics Data System (ADS)

The complexation of lead(II) ions by water-soluble soil organic matter as ligand (recovered by percolating water through a A2 horizon of a podzolic soil) has been studied by potentiometric methods at 25°C in 0.1 M NaClO 4 medium. The total acidity of these solutions was resolved into strong, weak and very weak acidity. During the alkali titration, the dissociation of humic samples was characterized by an ? coefficient that may be determined according to a procedure derived from Irving-Rossotti's method. The so-called Henderson-Hasselbalch equation was used to obtain pK A values for each of the two weak acidities ( pKA = 4.80 (COOH) and pKA = 8.85 (OH)). For the determination of stability constants of metal-humate complexes (HA) in the acidic range, three methods have been investigated: - an approach using only pH measurements. - direct estimation of the free metal ion concentrations from ISE determinations. - application of Marinsky's method accounting for complications arising from the electric field at the surface of the polyelectrolyte which determines the effective concentration [A]. In these experiments typical values used for total lead(II) ion concentrations and total ligand concentrations are respectively in the range 4.10 -5 M to 4.10 -4 M and 0,33 to 0,57 meq·1 -1. All results agree with the existence of mono and bis-complexes PbA and PbA 2 with stability constants (protometric determinations): logK1 = 4.2 and logK2 = 3.7. The values obtained by direct estimation of free lead(II) concentration are slightly lower. An increase in stability constants was observed with increase in pH and also with decrease in total metal ion concentration (at constant pH). Ligand conformational properties are expected to be of great importance in the complexation phenomena.

Bizri, Y.; Cromer, M.; Scharff, J. P.; Guillet, B.; Rouiller, J.

1984-02-01

187

Numerical values of the fundamental constants and the anthropic principle  

NASA Astrophysics Data System (ADS)

It is noted that complex structures (especially living organisms) could not exist if the values of the fundamental constants were slightly different. This paper formulates the problem of searching for the set of parameters (islands of stability) describing the universe which admit the appearance of complex structural formations.

Novikov, I. D.; Polnarev, A. G.; Rozental, I. L.

188

Topoisomerase II? promotes activation of RNA polymerase I transcription by facilitating pre-initiation complex formation  

PubMed Central

Type II DNA topoisomerases catalyse DNA double-strand cleavage, passage and re-ligation to effect topological changes. There is considerable interest in elucidating topoisomerase II roles, particularly as these proteins are targets for anti-cancer drugs. Here we uncover a role for topoisomerase II? in RNA polymerase I-directed ribosomal RNA gene transcription, which drives cell growth and proliferation and is upregulated in cancer cells. Our data suggest that topoisomerase II? is a component of the initiation-competent RNA polymerase I? complex and interacts directly with RNA polymerase I-associated transcription factor RRN3, which targets the polymerase to promoter-bound SL1 in pre-initiation complex formation. In cells, activation of rDNA transcription is reduced by inhibition or depletion of topoisomerase II, and this is accompanied by reduced transient double-strand DNA cleavage in the rDNA-promoter region and reduced pre-initiation complex formation. We propose that topoisomerase II? functions in RNA polymerase I transcription to produce topological changes at the rDNA promoter that facilitate efficient de novo pre-initiation complex formation. PMID:23511463

Ray, Swagat; Panova, Tatiana; Miller, Gail; Volkov, Arsen; Porter, Andrew C. G.; Russell, Jackie; Panov, Konstantin I.; Zomerdijk, Joost C. B. M.

2013-01-01

189

Improved complexation of paraquat derivatives by the formation of crown ether-based cryptands.  

PubMed

Self-assembly allows the construction of advanced molecular or supramolecular systems from small building blocks. Host-guest recognition, for its self-selectivity, environmental responsiveness and convenient application to complex molecular devices, plays a significant role in self-assembled systems. During this process, the association constant between the host and guest is an important standard to identify the properties of the systems. In order to prepare mechanically interlocked structures and large supramolecular systems efficiently from small molecules based on a host-guest recognition motif, it is necessary to increase host-guest association constants. Crown ether-based cryptands have been designed and prepared to improve the binding of paraquat derivatives. This feature article aims to describe the design and syntheses of crown ether-based cryptand hosts for paraquat derivatives and the application of the cryptand/paraquat recognition motif in the fabrication of threaded structures, molecular switches and supramolecular polymers. PMID:20830438

Zhang, Mingming; Zhu, Kelong; Huang, Feihe

2010-11-21

190

Formation of host-guest complexes of ?-cyclodextrin and perfluorooctanoic acid.  

PubMed

Structural characterization and dynamic properties of solid-state inclusion complexes of ?-cyclodextrin (?-CD) with perfluorooctanoic acid (PFOA) were investigated by (19)F/(13)C solid-state and (19)F/(1)H solution NMR spectroscopy. The complexes in the solid state were prepared using dissolution and slow cool methods, where thermal analyses (DSC and TGA), PXRD, and FT-IR results provided complementary support that inclusion complexes were formed between ?-CD and PFOA with variable stoichiometry and inclusion geometry. (19)F DP (direct polarization) and (13)C CP (cross-polarization) with magic-angle spinning (MAS) solids NMR, along with (19)F/(1)H solution NMR were used to characterize the complexes in the solid and solution phases, respectively. The dynamics of the guest molecules in the inclusion complexes (ICs) were studied using variable temperature (VT) (19)F DP/MAS NMR experiments in the solid state. The guest molecules were observed to be in several different molecular environments, providing strong evidence of variable host-guest stoichiometry and inclusion geometry, in accordance with the preparation method of the complex and the conformational preference of PFOA. It was concluded from PXRD that ?-CD and PFOA form inclusion complexes with "channel-type" structures. Variable spin rate (VSR) (19)F DP/MAS NMR was used to assess the phase purity of the complexes, and it was revealed that slow cooling resulted in relatively pure phases. In the solution state, (1)H and (19)F NMR complexation-induced chemical shifts (CISs) of ?-CD and PFOA, respectively, provided strong support for the formation of 1:1 and 2:1 ?-CD/PFOA inclusion complexes. The dynamics of the guest molecule in the ?-CD/PFOA complexes in D(2)O solutions were probed using VT (19)F NMR and revealed some guest conformational and exchange dynamics as a function of temperature and the relative concentrations of the host and guest. PMID:21688796

Karoyo, Abdalla H; Borisov, Alex S; Wilson, Lee D; Hazendonk, Paul

2011-08-11

191

Formation of multiple focal spots using a high NA lens with a complex spiral phase mask  

NASA Astrophysics Data System (ADS)

The formation of a transversally polarized beam by transmitting a tightly focused double-ring-shaped azimuthally polarized beam through a complex spiral phase mask and high numerical aperture lens is presented based on vector diffraction theory. The generation of transversally polarized focal spot segment splitting and multiple focal spots is illustrated numerically. Moreover, we found that a properly designed complex spiral phase mask can move the focal spots along the optical axis in the z direction. Therefore, one can achieve a focal segment of two, three or multiple completely transversely polarized focal spots, which finds applications in optical trapping and in material processing technologies.

Lalithambigai, K.; Anbarasan, P. M.; Rajesh, K. B.

2014-07-01

192

On the Silver Effect and the Formation of Chloride-Bridged Digold Complexes  

PubMed Central

Abstraction of chloride anion from Au(I) complexes such as JohnPhosAuCl in noncoordinating solvents with 1 equiv of a silver salt, or even larger amounts, leads to the formation of chloride-bridged dinuclear gold(I) complexes, irrespective of the counteranion, which are substantially less reactive as catalysts. This incomplete removal of chloride ligand could lead to false negative results when using the in situ generation of the gold(I) active species by silver-promoted chloride abstraction. PMID:24195441

2013-01-01

193

The application of the constants of motion to nonlinear stationary waves in complex plasmas: a unified fluid dynamic viewpoint  

NASA Astrophysics Data System (ADS)

Perturbation reductive procedures, as used to analyse various weakly nonlinear plasma waves (solitons and periodic waves), normally lead to the dynamical system being described by KdV, Burgers' or a nonlinear Schrödinger-type equation, with properties that can be deduced from an array of mathematical techniques. Here we develop a fully nonlinear theory of one-dimensional stationary plasma waves, which elucidates the common nature of various diverse wave phenomena. This is accomplished by adopting an essentially fluid dynamic viewpoint. In this unified treatment the constants of the motion (for mass, momentum and energy) lead naturally to the construction of the wave structure equations. It is shown, for example, that electrostatic, Hall magnetohydrodynamic and ion cyclotron acoustic nonlinear waves all obey first-order differential equations of the same generic type for the longitudinal flow field of the wave. The equilibrium points, which define the soliton amplitude, are given by the compressive and/or rarefactive roots of a total plasma ‘energy’ or ‘momentum’ function characterizing the wave type. This energy function, which is an algebraic combination of the Bernoulli momentum and energy functions for the longitudinal flow field, is the fluid dynamic counterpart of the pseudo-potentials, which are characteristic of system structure equations formulated in other than fluid variables. Another general feature of the structure equation is the phenomenon of choked flow, which occurs when the flow speed becomes sonic. It is this trans-sonic property that limits the soliton amplitudes and defines the critical collective Mach numbers of the waves. These features are also obtained in multi-component plasmas where, for example, in a bi-ion plasma, momentum exchanges between protons and heavier ions are mediated by the Maxwell magnetic stresses. With a suitable generalization of the concept of a sonic point in a bi-ion system and the corresponding choked flow feature, the wave structures, although now more complicated, can also be understood within this overall fluid framework. Particularly useful tools in this context are the momentum hodograph (an algebraic relation between the bi-ion speeds and the electron speed, or magnetic field, which follows from the conservation of mass, momentum and charge-neutrality) and a generalized Bernoulli energy density for each species. Analysis shows that the bi-ion solitons are essentially compressive, but contain the remarkable feature of the presence of a proton rarefactive core. A new type of soliton, called an ‘oscilliton’ because embedded spatial oscillations are superimposed on the classical soliton, is also described and discussed. A necessary condition for the existence of this type of wave is that the linear phase velocity must exhibit an extremum where the phase speed matches the group speed. The remarkable properties of this wave are illustrated for the case of both whistler waves and bi-ion waves where, for the latter, the requisite condition is met near the cross-over frequencies. In the case of the whistler oscilliton, which propagates at speeds in excess of one half of the Alfvén speed (based on the electrons), an analytic solution has been constructed through a phase-portrait integral of the system in which the proton and electron dynamics must be placed on the same footing. The relevance of the different wave structures to diverse space environments is briefly discussed in relation to recently available high-time and spatial resolution data from satellite observations.

McKenzie, J. F.; Dubinin, E.; Sauer, K.; Doyle, T. B.

2004-08-01

194

Multinuclear complex formation between Ca(II) and gluconate ions in hyperalkaline solutions.  

PubMed

Alkaline solutions containing polyhydroxy carboxylates and Ca(II) are typical in cementitious radioactive waste repositories. Gluconate (Gluc(-)) is a structural and functional representative of these sugar carboxylates. In the current study, the structure and equilibria of complexes forming in such strongly alkaline solutions containing Ca(2+) and gluconate have been studied. It was found that Gluc(-) significantly increases the solubility of portlandite (Ca(OH)2(s)) under these conditions and Ca(2+) complexes of unexpectedly high stability are formed. The mononuclear (CaGluc(+) and [CaGlucOH](0)) complexes were found to be minor species, and predominant multinuclear complexes were identified. The formation of the neutral [Ca2Gluc(OH)3](0) (log ?213 = 8.03) and [Ca3Gluc2(OH)4](0) (log ?324 = 12.39) has been proven via H2/Pt-electrode potentiometric measurements and was confirmed via XAS, (1)H NMR, ESI-MS, conductometry, and freezing-point depression experiments. The binding sites of Gluc(-) were identified from multinuclear NMR measurements. Besides the carboxylate group, the O atoms on the second and third carbon atoms were proved to be the most probable sites for Ca(2+) binding. The suggested structure of the trinuclear complex was deduced from ab initio calculations. These observations are of relevance in the thermodynamic modeling of radioactive waste repositories, where the predominance of the binuclear Ca(2+) complex, which is a precursor of various high-stability ternary complexes with actinides, is demonstrated. PMID:24865662

Pallagi, Attila; Bajnóczi, Éva G; Canton, Sophie E; Bolin, Trudy; Peintler, Gábor; Kutus, Bence; Kele, Zoltán; Pálinkó, István; Sipos, Pál

2014-06-17

195

Change in Protein Flexibility Upon Complex Formation: Analysis of Ras-Raf Using Molecular Dynamics and a  

E-print Network

Change in Protein Flexibility Upon Complex Formation: Analysis of Ras-Raf Using Molecular Dynamics Changes in flexibility upon pro- tein­protein complex formation of H-Ras and the Ras-binding domain of C time of about one second, FIRST identifies flexible and rigid regions in a single, static three

196

Complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses  

NASA Astrophysics Data System (ADS)

The complex formation of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid (vanillic acid) was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses using the fluorescence properties of 4-hydroxy-3-methoxybenzoic acid. A 2:1 complex of neptunium(V) with 4-hydroxy-3-methoxybenzoic acid was found. The stability constant of this complex was determined to be log ?210 = 7.33 ± 0.10 at an ionic strength of 0.1 mol/l (NaClO 4) and at 21 °C. The determination of the stability constant required an investigation of the excited-state proton transfer of 4-hydroxy-3-methoxybenzoic acid over the whole pH range. It was realized that 4-hydroxy-3-methoxybenzoic acid undergoes excited-state reactions only at pH values below 5. At pH values above 5 stability constants can be determined without kinetic calculation of the proton transfer.

Vulpius, D.; Geipel, G.; Baraniak, L.; Bernhard, G.

2006-03-01

197

Formation of complexes between PAMAM-NH2 G4 dendrimer and L-?-tryptophan and L-?-tyrosine in water  

NASA Astrophysics Data System (ADS)

Interactions between electromagnetic radiation and the side substituents of aromatic amino acids are widely used in the biochemical studies on proteins and their interactions with ligand molecules. That is why the aim of our study was to characterize the formation of complexes between PAMAM-NH2 G4 dendrimer and L-?-tryptophan and L-?-tyrosine in water. The number of L-?-tryptophan and L-?-tyrosine molecules attached to the macromolecule of PAMAM-NH2 G4 dendrimer and the formation constants of the supramolecular complexes formed have been determined. The macromolecule of PAMAM-NH2 G4 can reversibly attach about 25 L-?-tryptophan molecules with equilibrium constant K equal to 130 ± 30 and 24 ± 6 L-?-tyrosine molecules. This characterization was deduced on the basis of the solubility measurements of the amino acids in aqueous dendrimer solutions, the 1H NMR and 2D-NOESY measurements of the dendrimer solutions with the amino acids, the equilibrium dialysis and the circular dichroism measurements of the dendrimer aqueous solutions with L-?-tryptophan. Our date confirmed the interactions of L-?-tryptophan and L-?-tyrosine with the dendrimer in aqueous solution and indicated a reversible character of the formed complexes.

Buczkowski, Adam; Urbaniak, Pawel; Belica, Sylwia; Sekowski, Szymon; Bryszewska, Maria; Palecz, Bartlomiej

2014-07-01

198

Formation of gels and complexes by pairwise interacting P. G. Higgs and R. C. Ball  

E-print Network

3285 Formation of gels and complexes by pairwise interacting polymers P. G. Higgs and R. C. Ball réseaux 2014 par exemple, des zones de jonction en double hélice dans les gels de biopolymère, ou à l maximum si le nombre de liaisons à l'équilibre est grand. Ceci suggère la possibilité d'existence de gels

Boyer, Edmond

199

Study of complex formation between aluminum bromide and benzene by 27Al NMR spectroscopy  

Microsoft Academic Search

The reaction of aluminum bromide with benzene in n-hexane was studied by 27Al NMR spectroscopy in the temperature range from –80 to +20 °C. The formation of C6H6·Al2Br6 (1 : 2) complexes is accompanied by broadening of the resonance line with d 178. No peak splitting following a decrease in the temperature was observed but the temperature dependence of the

V. B. Murachev; A. I. Nesmelov

2001-01-01

200

Formation and annihilation of H-point defect complexes in quenched Si doped with C  

Microsoft Academic Search

We investigated the formation and annihilation of H-point defect complexes formed in C-doped Si by heating at high temperatures followed by quenching in hydrogen gas. Specimens of C-doped Si were sealed in quartz capsules together with hydrogen (H) gas, at pressure 0.8-1.5 atm at high temperature, and were heated at high temperature for 1 h followed by quenching in water.

Naoki Fukata; Masashi Suezawa

2000-01-01

201

Dielectric well logging system with at least three transmitter coils and at least two receiver coils for determining resistivity and dielectric constant of a subsurface formation adjacent a fluid  

Microsoft Academic Search

A dielectric well logging apparatus is described for obtaining amplitude ratios and phase differences between electromagnetic wave energy signals which have passed different distances through a subsurface formation adjacent a well borehole, so that an analyst may determine resistivity and dielectric constants for the different distances of travel through the formation. The apparatus consists of: (a) sonde means for moving

P. T. Cox; R. A. Meador; R. G. Jr. Riedesel; K. D. Savage

1986-01-01

202

Almost enclosed buckyball joints: synthesis, complex formation, and computational simulations of pentypticene-extended tribenzotriquinacene.  

PubMed

We report the synthesis of a tribenzotriquinacene-based (TBTQ) receptor (3) for C60 fullerene, which is extended by pentiptycene moieties to provide an almost enclosed concave ball bearing. The system serves as a model for a self-assembling molecular rotor with a flexible and adapting stator. Unexpectedly, nuclear magnetic resonance spectroscopic investigations reveal a surprisingly low complex stability constant of K1 =213±37?M(-1) for [C60 ?3], seemingly inconsistent with the previously reported TBTQ systems. Molecular dynamics (MD) simulations have been conducted for three different [C60 ?TBTQ] complexes to resolve this. Because of the dominating dispersive interactions, the binding energies increase with the contact area between guest and host, however, only for rigid host structures. By means of free-energy calculations with an explicit solvent model it can be shown that the novel flexible TBTQ receptor 3 binds weakly because of hampering entropic contributions. PMID:25234364

Henne, Stefan; Bredenkötter, Björn; Alaghemandi, Mohammad; Bureekaew, Sareeya; Schmid, Rochus; Volkmer, Dirk

2014-12-01

203

Coat protein regulates formation of replication complexes during tobacco mosaic virus infection.  

PubMed

The genome of tobacco mosaic virus (TMV) encodes replicase protein(s), movement protein (MP), and capsid protein (CP). On infection, one or more viral proteins direct the assembly of virus replication complexes (VRCs), in association with host-derived membranes. The impact of CP-mediated resistance on the structures of the replication complexes was examined in nontransgenic and transgenic BY-2 cell lines that produce wild-type CP, mutant CP(T42W), and Ds-Red, which was targeted to endoplasmic reticulum by using immunofluorescence and 3D microscopy. We developed a model of VRCs that shows a clear association of MP with and surrounding the endoplasmic reticulum. Replicase is located within the MP bodies, as well as isolated sites throughout the cell. CP surrounds the VRCs. CP enhances the production of MP and increases the size of the VRC; however, the mutant CP(T42W) reduces the amount of MP and interferes with the formation of VRCs. We propose a regulatory role of the CP in the establishment of the VRC. We suggest that the lack of formation of VRCs restricts the efficiency of virus replication and the formation of virus movement complexes, resulting in restriction of cell-cell spread of infection. This results in higher levels of plant CP-mediated protection provided by CP(T42W). PMID:14745003

Asurmendi, S; Berg, R H; Koo, J C; Beachy, R N

2004-02-01

204

Formylglycinamide Ribonucleotide Amidotransferase from Thermotoga maritima: Structural Insights into Complex Formation  

SciTech Connect

In the fourth step of the purine biosynthetic pathway, formyl glycinamide ribonucleotide (FGAR) amidotransferase, also known as PurL, catalyzes the conversion of FGAR, ATP, and glutamine to formyl glycinamidine ribonucleotide (FGAM), ADP, P{sub i}, and glutamate. Two forms of PurL have been characterized, large and small. Large PurL, present in most Gram-negative bacteria and eukaryotes, consists of a single polypeptide chain and contains three major domains: the N-terminal domain, the FGAM synthetase domain, and the glutaminase domain, with a putative ammonia channel located between the active sites of the latter two. Small PurL, present in Gram-positive bacteria and archaea, is structurally homologous to the FGAM synthetase domain of large PurL, and forms a complex with two additional gene products, PurQ and PurS. The structure of the PurS dimer is homologous with the N-terminal domain of large PurL, while PurQ, whose structure has not been reported, contains the glutaminase activity. In Bacillus subtilis, the formation of the PurLQS complex is dependent on glutamine and ADP and has been demonstrated by size-exclusion chromatography. In this work, a structure of the PurLQS complex from Thermotoga maritima is described revealing a 2:1:1 stoichiometry of PurS:Q:L, respectively. The conformational changes observed in TmPurL upon complex formation elucidate the mechanism of metabolite-mediated recruitment of PurQ and PurS. The flexibility of the PurS dimer is proposed to play a role in the activation of the complex and the formation of the ammonia channel. A potential path for the ammonia channel is identified.

Morar, Mariya; Hoskins, Aaron A.; Stubbe, JoAnne; Ealick, Steven E. (MIT); (Cornell)

2008-10-02

205

Involvement of DPP-IV Catalytic Residues in Enzyme-Saxagliptin Complex Formation  

SciTech Connect

The inhibition of DPP-IV by saxagliptin has been proposed to occur through formation of a covalent but reversible complex. To evaluate further the mechanism of inhibition, we determined the X-ray crystal structure of the DPP-IV:saxagliptin complex. This structure reveals covalent attachment between S630 and the inhibitor nitrile carbon (C-O distance <1.3 Angstroms). To investigate whether this serine addition is assisted by the catalytic His-Asp dyad, we generated two mutants of DPP-IV, S630A and H740Q, and assayed them for ability to bind inhibitor. DPP-IVH740Q bound saxagliptin with an {approx}1000-fold reduction in affinity relative to DPP-IVWT, while DPP-IVS630A showed no evidence for binding inhibitor. An analog of saxagliptin lacking the nitrile group showed unchanged binding properties to the both mutant proteins, highlighting the essential role S630 and H740 play in covalent bond formation between S630 and saxagliptin. Further supporting mechanism-based inhibition by saxagliptin, NMR spectra of enzyme-saxagliptin complexes revealed the presence of three downfield resonances with low fractionation factors characteristic of short and strong hydrogen bonds (SSHB). Comparison of the NMR spectra of various wild-type and mutant DPP-IV:ligand complexes enabled assignment of a resonance at {approx}14 ppm to H740. Two additional DPP-IV mutants, Y547F and Y547Q, generated to probe potential stabilization of the enzyme-inhibitor complex by this residue, did not show any differences in inhibitor binding either by ITC or NMR. Together with the previously published enzymatic data, the structural and binding data presented here strongly support a histidine-assisted covalent bond formation between S630 hydroxyl oxygen and the nitrile group of saxagliptin.

Metzler,W.; Yanchunas, J.; Weigelt, C.; Kish, K.; Klei, H.; Xie, D.; Zhang, Y.; Corbett, M.; Tamura, J.; et al

2008-01-01

206

Fundamental Constants  

E-print Network

The notion of ``fundamental constant'' is heavily theory-laden. A natural, fairly precise formulation is possible in the context of the standard model (here defined to include gravity). Some fundamental constants have profound geometric meaning. The ordinary gravitational constant parameterizes the stiffness, or resistance to curvature, of space-time. The cosmological term parameterizes space-time's resistance to expansion -- which may be, and apparently is at present, a {\\it negative} resistance, i.e. a tendency toward expansion. The three gauge couplings of the strong, electromagnetic, and weak interactions parameterize resistance to curvature in internal spaces. The remaining fundamental couplings, of which there are a few dozen, supply an ungainly accommodation of inertia. The multiplicity and variety of fundamental constants are esthetic and conceptual shortcomings in our present understanding of foundational physics. I discuss some ideas for improving the situation. I then briefly discuss additional constants, primarily cosmological, that enter into our best established present-day world model. Those constants presently appear as macroscopic state parameters, i.e. as empirical ``material constants'' of the Universe. I mention a few ideas for how they might become fundamental constants in a future theory. In the course of this essay I've advertised several of my favorite speculations, including a few that might be tested soon.

Frank Wilczek

2007-08-31

207

Structure of solvated Fe(CO)5: complex formation during solvation in alcohols.  

PubMed

The equilibrium structure of iron pentacarbonyl, Fe(CO)5, solvated in various alcohols has been investigated by Fourier transform infrared (FTIR) measurements and density functional theory calculations. This system was studied because it is prototypical of a larger class of monometallic systems, which are electronically saturated but not sterically crowded. Upon solvation, the Fe(CO)5 is not just surrounded by a solvation shell. Instead, solute-solvent complexes are formed with the oxygen of the alcohol oriented toward an axial ligand of the Fe(CO)5 giving a formation energy on the order of -5 kJ/mol. This complexation is not a chemical reaction but rather a "preassembly" of the solute molecules with a single solvent molecule. For instance, at room temperature the interaction between Fe(CO)5 and ethanol results in 87% of all Fe(CO)5 molecules being complexated with a single ethanol molecule. This complexation was found in all the alcohol systems studied in this paper. The stability of these complexes was found to depend on the alcohol chain length and branching. The observed complexation mechanism is accompanied by an electron density shift from the complexed alcohol molecule toward Fe(CO)5 where it induces a dipole moment. The finding that Fe(CO)5 forms a complex with the hydroxyl group of a single solvent molecule might have significant implications for ligand substitution reactions. This implies that ligand substitution reactions do not have to proceed via a dissociative mechanism. Instead, the reaction might proceed through a concerted mechanism with the leaving CO simultaneously being replaced by the incoming alcohol that was complexed to Fe(CO)5 prior to the photoexcitation. PMID:18284220

Lessing, Joshua; Li, Xiaodi; Lee, Taewoo; Rose-Petruck, Christoph G

2008-03-20

208

Stability constants for mono- and dioxalato-complexes of Y and the REE, potentially important species in groundwaters and surface freshwaters  

NASA Astrophysics Data System (ADS)

We present the first measured set of stability constants for mono- and dioxalato-complexes of yttrium and all rare earths except Pm (Y+REE), Ox? n = [MOx n3-2n] [M 3+] -1 [Ox 2-] -n(where [ ] ? concentrations, M ? Y+REE, and Ox 2- ? C 2O 42-). Aqueous solutions of Y+REE were titrated with oxalic acid in the presence of a cation-exchange resin, and Y+REE concentrations in the solution phase were measured by ICP-MS. This method allows investigation of all Y+REE simultaneously under identical conditions and is thus very sensitive to subtle inter-element variations in log Ox? n. Experiments were performed at a single ionic strength ( I = 0.05 M), but at two values of pH. Patterns of log Ox? 1 and log Ox? 2, determined from our experiments, are similar in shape and reminiscent of those for carbonato-complexes. The average ratio of stepwise stability constants K 2/K 1 = Ox? 2/( Ox? 1) 2 is 0.05 ± 0.02 for Y+REE excluding La and Ce. Literature values of Ox? 1(Eu) for 0.03 mol/L ? I ? 1 mol/L were used to derive the relation log Ox? 1(Eu) = log Ox? 10(Eu) - 6.132? I/(1 + 1.47? I) + 0.902 I, where log Ox? 10(Eu) is the stability constant at infinite dilution. Applying this relation to all Y+REE, the following values of log Ox? 10 (at zero ionic strength) were found: 6.66 (Y), 5.87 (La), 5.97 (Ce), 6.25 (Pr), 6.31 (Nd), 6.43 (Sm), 6.52 (Eu), 6.53 (Gd), 6.63 (Tb), 6.74 (Dy), 6.77 (Ho), 6.83 (Er), 6.89 (Tm), 6.95 (Yb), 6.96 (Lu). These values, which are based on direct measurements for each individual Y+REE, agree quite well with published extrapolations that are mostly based on linear free-energy relationships. Total oxalate concentrations of 10 -5-10 -3 M have been reported for soil solutions. Free oxalate ions persist at much lower pH than free carbonate ions and a simple speciation model demonstrates that oxalato-complexes can dominate Y+REE speciation in mildly acidic groundwaters of low-to-moderate alkalinity.

Schijf, J.; Byrne, R. H.

2001-04-01

209

Anthrax Lethal Toxin Triggers the Formation of a Membrane-Associated Inflammasome Complex in Murine Macrophages?  

PubMed Central

Multiple microbial components trigger the formation of an inflammasome complex that contains pathogen-specific nucleotide oligomerization and binding domain (NOD)-like receptors (NLRs), caspase-1, and in some cases the scaffolding protein ASC. The NLR protein Nalp1b has been linked to anthrax lethal toxin (LT)-mediated cytolysis of murine macrophages. Here we demonstrate that in unstimulated J774A.1 macrophages, caspase-1 and Nalp1b are membrane associated and part of ?200- and ?800-kDa complexes, respectively. LT treatment of these cells resulted in caspase-1 recruitment to the Nalp1b-containing complex, concurrent with processing of cytosolic caspase-1 substrates. We further demonstrated that Nalp1b and caspase-1 are able to interact with each other. Intriguingly, both caspase-1 and Nalp1b were membrane associated, while the caspase-1 substrate interleukin-18 was cytosolic. Caspase-1-associated inflammasome components included, besides Nalp1b, proinflammatory caspase-11 and the caspase-1 substrate ?-enolase. Asc was not part of the Nalp1b inflammasome in LT-treated macrophages. Taken together, our findings suggest that LT triggers the formation of a membrane-associated inflammasome complex in murine macrophages, resulting in cleavage of cytosolic caspase-1 substrates and cell death. PMID:19124602

Nour, Adel M.; Yeung, Yee-Guide; Santambrogio, Laura; Boyden, Eric D.; Stanley, E. Richard; Brojatsch, Jurgen

2009-01-01

210

A Requirement for the Saccharomyces cerevisiae Paf1 Complex in snoRNA 3?End Formation  

PubMed Central

Summary RNA synthesis and processing are coordinated by proteins that associate with RNA polymerase II (pol II) during transcription elongation. The yeast Paf1 complex interacts with RNA pol II and mediates histone modifications during elongation. To elucidate the functions of this complex, we isolated missense mutations in the gene encoding the Rtf1 subunit and used them to identify functionally interacting proteins. We identified NAB3 as a dosage suppressor of rtf1. Nab3, together with Nrd1, directs 3? end formation of nonpolyadenylated RNA pol II transcripts, such as snoRNAs. Deletion of Paf1, but not the Set1, Set2, or Dot1 histone methyltransferases, causes accumulation of snoRNA transcripts that are extended at their 3? ends. The Paf1 complex associates with and facilitates Nrd1 recruitment to the SNR47 gene, suggesting a direct involvement in 3? end formation. Our results reveal a posttranscriptional function for the Paf1 complex, which appears unrelated to its role in histone methylation. PMID:16246725

Sheldon, Kathryn E.; Mauger, David M.; Arndt, Karen M.

2007-01-01

211

Mammalian Sperm Head Formation Involves Different Polarization of Two Novel LINC Complexes  

PubMed Central

Background LINC complexes are nuclear envelope bridging protein structures formed by interaction of SUN and KASH proteins. They physically connect the nucleus with the peripheral cytoskeleton and are critically involved in a variety of dynamic processes, such as nuclear anchorage, movement and positioning and meiotic chromosome dynamics. Moreover, they are shown to be essential for maintaining nuclear shape. Findings Based on detailed expression analysis and biochemical approaches, we show here that during mouse sperm development, a terminal cell differentiation process characterized by profound morphogenic restructuring, two novel distinctive LINC complexes are established. They consist either of spermiogenesis-specific Sun3 and Nesprin1 or Sun1?, a novel non-nuclear Sun1 isoform, and Nesprin3. We could find that these two LINC complexes specifically polarize to opposite spermatid poles likely linking to sperm-specific cytoskeletal structures. Although, as shown in co-transfection/immunoprecipitation experiments, SUN proteins appear to arbitrarily interact with various KASH partners, our study demonstrates that they actually are able to confine their binding to form distinct LINC complexes. Conclusions Formation of the mammalian sperm head involves assembly and different polarization of two novel spermiogenesis-specific LINC complexes. Together, our findings suggest that theses LINC complexes connect the differentiating spermatid nucleus to surrounding cytoskeletal structures to enable its well-directed shaping and elongation, which in turn is a critical parameter for male fertility. PMID:20711465

Gob, Eva; Schmitt, Johannes; Benavente, Ricardo; Alsheimer, Manfred

2010-01-01

212

Actomyosin-dependent formation of the mechanosensitive talin-vinculin complex reinforces actin anchoring  

PubMed Central

The force generated by the actomyosin cytoskeleton controls focal adhesion dynamics during cell migration. This process is thought to involve the mechanical unfolding of talin to expose cryptic vinculin-binding sites. However, the ability of the actomyosin cytoskeleton to directly control the formation of a talin–vinculin complex and the resulting activity of the complex are not known. Here we develop a microscopy assay with pure proteins in which the self-assembly of actomyosin cables controls the association of vinculin to a talin-micropatterned surface in a reversible manner. Quantifications indicate that talin refolding is limited by vinculin dissociation and modulated by the actomyosin network stability. Finally, we show that the activation of vinculin by stretched talin induces a positive feedback that reinforces the actin–talin–vinculin association. This in vitro reconstitution reveals the mechanism by which a key molecular switch senses and controls the connection between adhesion complexes and the actomyosin cytoskeleton. PMID:24452080

Ciobanasu, Corina; Faivre, Bruno; Le Clainche, Christophe

2014-01-01

213

Formation and fate of a complete 31-protein RNA polymerase II transcription preinitiation complex.  

PubMed

Whereas individual RNA polymerase II (pol II)-general transcription factor (GTF) complexes are unstable, an assembly of pol II with six GTFs and promoter DNA could be isolated in abundant homogeneous form. The resulting complete pol II transcription preinitiation complex (PIC) contained equimolar amounts of all 31 protein components. An intermediate in assembly, consisting of four GTFs and promoter DNA, could be isolated and supplemented with the remaining components for formation of the PIC. Nuclease digestion and psoralen cross-linking mapped the PIC between positions -70 and -9, centered on the TATA box. Addition of ATP to the PIC resulted in quantitative conversion to an open complex, which retained all 31 proteins, contrary to expectation from previous studies. Addition of the remaining NTPs resulted in run-off transcription, with an efficiency that was promoter-dependent and was as great as 17.5% with the promoters tested. PMID:23303183

Murakami, Kenji; Calero, Guillermo; Brown, Christopher R; Liu, Xin; Davis, Ralph E; Boeger, Hinrich; Kornberg, Roger D

2013-03-01

214

Formation and Fate of a Complete 31-Protein RNA Polymerase II Transcription Preinitiation Complex*  

PubMed Central

Whereas individual RNA polymerase II (pol II)-general transcription factor (GTF) complexes are unstable, an assembly of pol II with six GTFs and promoter DNA could be isolated in abundant homogeneous form. The resulting complete pol II transcription preinitiation complex (PIC) contained equimolar amounts of all 31 protein components. An intermediate in assembly, consisting of four GTFs and promoter DNA, could be isolated and supplemented with the remaining components for formation of the PIC. Nuclease digestion and psoralen cross-linking mapped the PIC between positions ?70 and ?9, centered on the TATA box. Addition of ATP to the PIC resulted in quantitative conversion to an open complex, which retained all 31 proteins, contrary to expectation from previous studies. Addition of the remaining NTPs resulted in run-off transcription, with an efficiency that was promoter-dependent and was as great as 17.5% with the promoters tested. PMID:23303183

Murakami, Kenji; Calero, Guillermo; Brown, Christopher R.; Liu, Xin; Davis, Ralph E.; Boeger, Hinrich; Kornberg, Roger D.

2013-01-01

215

cAMP prevents TNF-induced apoptosis through inhibiting DISC complex formation in rat hepatocytes  

SciTech Connect

Highlights: Black-Right-Pointing-Pointer cAMP blocks cell death induced by TNF and actinomycin D in cultured hepatocytes. Black-Right-Pointing-Pointer cAMP blocks NF-{kappa}B activation induced by TNF and actinomycin D. Black-Right-Pointing-Pointer cAMP blocks DISC formation following TNF and actinomycin D exposure. Black-Right-Pointing-Pointer cAMP blocks TNF signaling at a proximal step. -- Abstract: Tumor necrosis factor {alpha} (TNF) is a pleiotropic proinflammatory cytokine that plays a role in immunity and the control of cell proliferation, cell differentiation, and apoptosis. The pleiotropic nature of TNF is due to the formation of different signaling complexes upon the binding of TNF to its receptor, TNF receptor type 1 (TNFR1). TNF induces apoptosis in various mammalian cells when the cells are co-treated with a transcription inhibitor like actinomycin D (ActD). When TNFR1 is activated, it recruits an adaptor protein, TNF receptor-associated protein with death domain (TRADD), through its cytoplasmic death effector domain (DED). TRADD, in turn, recruits other signaling proteins, including TNF receptor-associated protein 2 (TRAF2) and receptor-associated protein kinase (RIPK) 1, to form a complex. Subsequently, this complex combines with FADD and procaspase-8, converts into a death-inducing signaling complex (DISC) to induce apoptosis. Cyclic AMP (cAMP) is a second messenger that regulates various cellular processes such as cell proliferation, gene expression, and apoptosis. cAMP analogues are reported to act as anti-apoptotic agents in various cell types, including hepatocytes. We found that a cAMP analogue, dibutyryl cAMP (db-cAMP), inhibits TNF + ActD-induced apoptosis in rat hepatocytes. The protein kinase A (PKA) inhibitor KT-5720 reverses this inhibitory effect of cAMP on apoptosis. Cytoprotection by cAMP involves down-regulation of various apoptotic signal regulators like TRADD and FADD and inhibition of caspase-8 and caspase-3 cleavage. We also found that cAMP exerts its affect at the proximal level of TNF signaling by inhibiting the formation of the DISC complex upon the binding of TNF to TNFR1. In conclusion, our study shows that cAMP prevents TNF + ActD-induced apoptosis in rat hepatocytes by inhibiting DISC complex formation.

Bhattacharjee, Rajesh [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States)] [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States); Xiang, Wenpei [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States) [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States); Family Planning Research Institute, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, People's Republic of China (China); Wang, Yinna [Vascular Medicine Institute, University of Pittsburgh School of Medicine, 10051-5A BST 3, 3501 Fifth Avenue, Pittsburgh, PA 15261 (United States)] [Vascular Medicine Institute, University of Pittsburgh School of Medicine, 10051-5A BST 3, 3501 Fifth Avenue, Pittsburgh, PA 15261 (United States); Zhang, Xiaoying [Department of Medicine/Endocrinology Division, University of Pittsburgh Medical Center, 200 Lothrop St., Pittsburgh, PA 15213 (United States)] [Department of Medicine/Endocrinology Division, University of Pittsburgh Medical Center, 200 Lothrop St., Pittsburgh, PA 15213 (United States); Billiar, Timothy R., E-mail: billiartr@upmc.edu [Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213 (United States)

2012-06-22

216

Chelation of vanadium(IV) by a natural and edible biopolymer poly(gamma-glutamic acid) in aqueous solution: structure and binding constant of complex.  

PubMed

The naturally occurring edible biopolymer poly(gamma-glutamic acid) (gamma-PGA) is shown to be an efficient chelating agent of vanadium(IV). The structure of poly(gamma-glutamic acid)oxovanadium(IV) (VO-gamma-PGA) complex in solution has been analyzed by electron spin resonance and UV-visible absorption spectra. The equatorial coordination sphere of vanadium(IV) is proposed to be [2 x carboxylate (2O)-VO-(OH2)2]. The binding isotherm is determined for suspensions of gamma-PGA in vanadium(IV) oxide sulfate (VS) solutions of different concentrations, and the data have been adjusted to fit the modified Langmuir equation. The maximum amount of vanadium bound per gram of gamma-PGA is estimated to be 141 mmol . g(-1) with a binding constant of 22 L . g(-1) at pH 3. PMID:17941110

Karmaker, Subarna; Saha, Tapan K

2008-02-11

217

Aging, rejuvenation and thixotropy in complex fluids. Time-dependence of the viscosity at rest and under constant shear rate or shear stress  

E-print Network

Complex fluids exhibit time-dependent changes in viscosity that have been ascribed to both thixotropy and aging. However, there is no consensus for which phenomenon is the origin of which changes. A novel thixotropic model is defined that incorporates aging. Conditions under which viscosity changes are due to thixotropy and aging are unambiguously defined. Viscosity changes in a complex fluid during a period of rest after destructuring exhibit a bifurcation at a critical volume fraction PHIc2. For volume fractions less than PHIc2, the viscosity remains finite in the limit t => infinite. For volume fractions above critical the viscosity grows without limit, so aging occurs at rest. At constant shear rate there is no bifurcation, whereas under constant shear stress the model predicts a new bifurcation in the viscosity at a critical stress sB, identical to the yield stress sy observed under steady conditions. The divergence of the viscosity for stress s sB is best defined as aging. However, for s > sB, where the viscosity remains finite, it seems preferable to use the concepts of restructuring and destructuring, rather than aging and rejuvenation. Nevertheless, when a stress sA (sB) is applied during aging, slower aging is predicted and discussed as true rejuvenation. Plastic behaviour is predicted under steady conditions when s > sB. The Herschel-Bulkley model fits the flow curve for stresses close to sB, whereas the Bingham model gives a better fit for s >> sB. Finally, the model's predictions are shown to be consistent with experimental data from the literature for the transient behaviour of laponite gels.

Daniel Quemada

2008-08-25

218

Varying constants.  

PubMed

We review properties of theories for the variation of gravitation and fine structure 'constants'. We highlight some general features of the cosmological models that exist in these theories with reference to recent quasar data that are consistent with time variation in the fine structure constant since a redshift of 3.5. The behaviour of a simple class of varying-alpha cosmologies is outlined in the light of all the observational constraints. PMID:16147502

Barrow, John D

2005-09-15

219

Revised nomenclature and stratigraphic relationships of the Fredericksburg Complex and Quantico Formation of the Virginia Piedmont  

USGS Publications Warehouse

The Fredericksburg Complex, in part a migmatitic terrane in northeast Virginia, is subdivided on the basis of lithology, as well as aeromagnetic and aeroradiometric data, into two metamorphic suites. These suites are separated by the northeast-trending Spotsylvania lineament, a rectilinear geophysical feature that is probably the trace of an old fault zone. East of the lineament, the Po River Metamorphic Suite, of Proterozoic Z and (or) early Paleozoic age, consists dominantly of biotite gneiss, generally augen gneiss, and lesser amounts of hornblende gneiss and mica schist. West of the Spotsylvania lineament is the Ta River Metamorphic Suite, composed mostly of amphibolite and amphibole gneiss. However, to the southwest, along its strike belt, the Ta River contains abundant biotite gneiss and mica schist. Both the Ta River and Po River contain abundant foliated granitoid and pegmatoid bodies as concordant tabular masses and as crosscutting dikes; these rocks are considered part of the Ta River and Po River Metamorphic Suites. The amphibolitic Holly Corner Gneiss is interpreted to be a western allochthonous equivalent of the Ta River. Both the Ta River and Holly Corner are considered to be coeval, eastern, distal facies of the Lower Cambrian(?) Chopawamsic Formation. The Paleozoic Falls Run Granite Gneiss intrudes the Ta River Metamorphic Suite and the Holly Corner Gneiss; locally the Falls Run is interpreted to have been transported westward with the Holly Corner after intrusion. The Quantico Formation, in the core of the Quantico-Columbia synclinorium, rests with angular unconformity along its northwest and southeast limbs, respectively, on the Chopawamsic Formation and the Ta River Metamorphic Suite. The Quantico Formation is assigned the same Late Ordovician age and similar stratigraphic position as the Arvonia Slate of the Arvonia syncline. The youngest rocks of the area are the granitoid and pegmatoid bodies of the Falmouth Intrusive Suite. They consist of several generations of chiefly dikes and sills that are intrusive into the Fredericksburg Complex and into the Quantico Formation. Granitoid rocks also form small plutons. The Falmouth is isotopically dated as Carboniferous in age. Some of the metavolcanic rocks of the Evington Group and part of the amphibolite gneiss and amphibolite of the Hatcher Complex, named by W. B. Brown in 1969, are probably coeval with the Chopawamsic Formation and hence equivalents of the Ta River Metamorphic Suite and the Holly Corner Gneiss. The biotitic gneiss and granitoid rocks east of the Spotsylvania lineament in the Dillwyn area are considered to be coeval with the Po River Metamorphic Suite.

Pavlides, Louis

1980-01-01

220

Isolation and Characterization of FORMATE/NI(CYCLAM)^{2+} Complexes with Cryogenic Ion Vibrational Predissociation  

NASA Astrophysics Data System (ADS)

Transition metal-based organometallic catalysts are a promising means of converting CO_{2} to transportable fuels. Ni(cyclam)^{2+}(cyclam = 1,4,8,11-tetraazacyclotetradecane), a Ni^{II} complex ligated by four nitrogen centers, has shown promise as a catalyst selective for CO_{2} reduction in aqueous solutions. The cyclam ligand has four NH hydrogen bond donors that can adopt five conformations, each offering distinct binding motifs for coordination of CO_{2} close to the metal center. To probe the ligand conformation and the role of hydrogen bonding in adduct binding, we extract Ni(cyclam)^{2+} complexes with the formate anion and some of its analogs from solution using electrospray ionization, and characterize their structures using cryogenic ion vibrational predissociation spectroscopy. Using the signature vibrational features of the embedded carboxylate anion and the NH groups as reporters, we compare the binding motifs of oxalate, benzoate, and formate anions to the Ni(cyclam)^{2+} framework. Finally, we comment on possible routes to generate the singly charged Ni(cyclam)^{+} complex, a key intermediate that has been invoked in the catalytic CO_{2} reduction cycle, but has never been isolated through ion processing techniques.

Wolk, Arron B.; Fournier, Joseph A.; Wolke, Conrad T.; Johnson, Mark A.

2013-06-01

221

Complex conductivity response to microbial growth and biofilm formation on phenanthrene spiked medium  

NASA Astrophysics Data System (ADS)

Several laboratory studies have recently demonstrated the utility of geophysical methods for the investigation of microbial-induced changes over contaminated sites. However, it remains difficult to distinguish the effects due to the new physical properties imparted by microbial processes, to bacterial growth, or to the development of bacterial biofilm. We chose to study the influence of biofilm formation on geophysical response using complex conductivity measurements (0.1-1000 Hz) in phenanthrene-contaminated media. Biotic assays were conducted with two phenanthrene (PHE) degrading bacterial strains: Burkholderia sp (NAH1), which produced biofilm and Stenophomonas maltophilia (MATE10), which did not, and an abiotic control. Results showed that bacterial densities for NAH1 and MATE10 strains continuously increased at the same rate during the experiment. However, the complex conductivity signature showed noticeable differences between the two bacteria, with a phase shift of 50 mrad at 4 Hz for NAH1, which produced biofilm. Biofilm volume was quantified by Scanning Confocal Laser Microscopy (SCLM). Significant correlations were established between phase shift decrease and biofilm volume for NAH1 assays. Results suggest that complex conductivity measurements, specifically phase shift, can be a useful indicator of biofilm formation inside the overall signal of microbial activity on contaminated sites.

Albrecht, Remy; Gourry, Jean Christophe; Simonnot, Marie-Odile; Leyval, Corinne

2011-11-01

222

GTP binding controls complex formation by the human ROCO protein MASL1.  

PubMed

The human ROCO proteins are a family of multi-domain proteins sharing a conserved ROC-COR supra-domain. The family has four members: leucine-rich repeat kinase 1 (LRRK1), leucine-rich repeat kinase 2 (LRRK2), death-associated protein kinase 1 (DAPK1) and malignant fibrous histiocytoma amplified sequences with leucine-rich tandem repeats 1 (MASL1). Previous studies of LRRK1/2 and DAPK1 have shown that the ROC (Ras of complex proteins) domain can bind and hydrolyse GTP, but the cellular consequences of this activity are still unclear. Here, the first biochemical characterization of MASL1 and the impact of GTP binding on MASL1 complex formation are reported. The results demonstrate that MASL1, similar to other ROCO proteins, can bind guanosine nucleotides via its ROC domain. Furthermore, MASL1 exists in two distinct cellular complexes associated with heat shock protein 60, and the formation of a low molecular weight pool of MASL1 is modulated by GTP binding. Finally, loss of GTP enhances MASL1 toxicity in cells. Taken together, these data point to a central role for the ROC/GTPase domain of MASL1 in the regulation of its cellular function. PMID:24286120

Dihanich, Sybille; Civiero, Laura; Manzoni, Claudia; Mamais, Adamantios; Bandopadhyay, Rina; Greggio, Elisa; Lewis, Patrick A

2014-01-01

223

Free Radical Formation in Novel Carotenoid Metal Ion Complexes of Astaxanthin  

PubMed Central

The carotenoid astaxanthin forms novel metal ion complexes with Ca2+, Zn2+ and Fe2+. MS and NMR measurements indicate that the two oxygen atoms on the terminal cyclohexene ring of astaxanthin chelate the metal to form 1:1 complexes with Ca2+ and Zn2+ at low salt concentrations < 0.2 mM. The stability constants of these complexes increased by a factor of 85 upon changing the solvent from acetonitrile to ethanol for Ca2+ and by a factor of 7 for Zn2+ as a consequence of acetonitrile being a part of the complex. Optical studies showed that at high concentrations (> 0.2 mM) of salt 2:1 metal:astaxanthin complexes were formed in ethanol. In the presence of Ca2+ and Zn2+ salts the lifetime of the radical cation and dication formed electrochemically decreased relative to that of the carotenoid neutral radical. DFT calculations showed that the deprotonation of the radical cation at the carbon C3 position resulted in the lowest energy neutral radical while proton loss at the C5, C9 or C13 methyl groups was less favorable. Pulsed EPR measurements were carried out on UV-produced radicals of astaxanthin supported on silica-alumina, MCM-41 or Ti-MCM-41. The pulsed EPR measurements detected the radical cation and neutral radicals formed by proton loss at 77 K from the C3, C5, C9, and C13-methyl groups and a radical anion formed by deprotonation of the neutral radical at C3. There was more than an order of magnitude increase in the concentration of radicals on Ti-MCM-41 relative to MCM-41, and the radical cation concentration exceeded that of the neutral radicals. PMID:21114306

Polyakov, Nikolay E.; Focsan, A. Ligia; Bowman, Michael K.; Kispert, Lowell D.

2010-01-01

224

QSPR ensemble modelling of the 1:1 and 1:2 complexation of Co²?, Ni²?, and Cu²? with organic ligands: relationships between stability constants.  

PubMed

Quantitative structure-property relationship (QSPR) modeling of stability constants for the metal:ligand ratio 1:1 (logK) and 1:2 (log?2) complexes of 3 transition metal ions with diverse organic ligands in aqueous solution was performed using ensemble multiple linear regression analysis and substructural molecular fragment descriptors. The modeling was performed on the sets containing 396 and 132 (Co(2+)), 613 and 233 (Ni(2+)), 883 and 257 (Cu(2+)) logK and log? 2 values, respectively. The models have been validated in external fivefold cross-validations procedure as well as on the external test set containing new ligands recently reported in the literature. Predicted logK and log? 2 values were calculated as arithmetic means of several hundred individual models (consensus models) using their applicability domains in averaging. The root mean squared error of predictions varies from 0.94 to 1.2 (logK) and from 1.2 to 1.4 (log?2) which is close to observed experimental systematic errors. Linear correlations between experimental logK values for pair of metal ions were evaluated. For all metal ions and ligands forming both 1:1 and 1:2 complexes the following ratio is observed: log?2/logK = 1.8 ± 0.1, n = 492. PMID:24737030

Solov'ev, Vitaly; Varnek, Alexandre; Tsivadze, Aslan

2014-05-01

225

Magnetically Regulated Star Formation in 3D: The Case of Taurus Molecular Cloud Complex  

E-print Network

We carry out three-dimensional MHD simulations of star formation in turbulent, magnetized clouds, including ambipolar diffusion and feedback from protostellar outflows. The calculations focus on relatively diffuse clouds threaded by a strong magnetic field capable of resisting severe tangling by turbulent motions and retarding global gravitational contraction in the cross-field direction. They are motivated by observations of the Taurus molecular cloud complex (and, to a lesser extent, Pipe Nebula), which shows an ordered large-scale magnetic field, as well as elongated condensations that are generally perpendicular to the large-scale field. We find that stars form in earnest in such clouds when enough material has settled gravitationally along the field lines that the mass-to-flux ratios of the condensations approach the critical value. Only a small fraction (of order 1% or less) of the nearly magnetically-critical, condensed material is turned into stars per local free-fall time, however. The slow star formation takes place in condensations that are moderately supersonic; it is regulated primarily by magnetic fields, rather than turbulence. The quiescent condensations are surrounded by diffuse halos that are much more turbulent, as observed in the Taurus complex. Strong support for magnetic regulation of star formation in this complex comes from the extremely slow conversion of the already condensed, relatively quiescent C$^{18}$O gas into stars, at a rate two orders of magnitude below the maximum, free-fall value. We analyze the properties of dense cores, including their mass spectrum, which resembles the stellar initial mass function.

Fumitaka Nakamura; Zhi-Yun Li

2008-04-26

226

Peculiarities of latent inhibition formation in SHR rats in conditioned task of different complexity.  

PubMed

Inhibition of attention to irrelevant stimuli was studied in SHR rats using latent inhibition test. Latent inhibition was formed in two types of conditioned tasks with different levels of complexity and stress. Passive and active avoidance conditioning was preceded by preexposure to conditioned stimulus consisting of 20 and 100 non-reinforced presentations, respectively. Control Wistar rats demonstrated successful formation of latent inhibition in both tasks. SHR rats showed different degree of disruption of latent inhibition depending on the type of behavioral task. We assume that learning defect in these animals in respect to both novel and preexposed conditioned stimuli is associated with the lack of behavioral inhibition. PMID:22808479

Kostyunina, N V; Loskutova, L V

2012-05-01

227

Formation of complex two-dimensional dissipative solitons via spontaneous symmetry breaking  

NASA Astrophysics Data System (ADS)

We propose a complex Ginzburg-Landau equation (CGLE) with localized linear gain as a two-dimensional model for pattern formation proceeding via spontaneous breaking of the axial symmetry. Starting from steady-state solutions produced by an extended variational approximation, simulations of the CGLE generate a vast class of robust solitary structures. These are varieties of asymmetric rotating vortices carrying the topological charge (TC), and four- to ten-pointed revolving stars, whose angular momentum is decoupled from the TC. The four- and five-pointed stars feature a cyclic change of their structure in the course of the rotation.

Skarka, V.; Aleksi?, N. B.; Leki?, M.; Aleksi?, B. N.; Malomed, B. A.; Mihalache, D.; Leblond, H.

2014-08-01

228

E-ring conformation has a key role in cleavable complex formation: homocamptothecin versus camptothecins  

NASA Astrophysics Data System (ADS)

Homocamptothecin (hCPT) is a new camptothecin (CPT) derivative with a seven-membered ?-hydroxylactone E-ring. This modification provides higher lactone stability and did not impair its activity against topoisomerase I (top1), but rather appears to improve it compared to CPT. Such lactone modification was unexpected regarding the previous structure-activity relationship data inside the CPT series, and may have crucial mechanistic implications in the ternary cleavable complex formation. In this study, the detailed characterization of the E-ring homologation and lactone/carboxylate conversion, self-aggregation, influence of pH and polarity of the molecular environment have been performed for hCPT by frequency-domain fluorescence. The real-time spectrofluorometry confirmed the enhanced stability of hCPT. We have also investigated the E-ring status of hCPT within the top1 ternary complex with DNA, and with top1 or DNA binary complexes. Unlike CPT, no modification of the (?-hydroxy-) lactone-carboxylate conversion rates was observed, suggesting that E-ring opening is not required for cleavable complex stabilization in presence of hCPT. Comparison of the two structures by molecular modeling revealed similar conformation and steric volumes between the ?-hydroxylactone ring conformation of hCPT and the opened ring of CPT. The lack of hCPT E-ring opening was discussed in the light of these molecular modeling results.

Chauvier, D.; Chourpa, I.; Maizieres, M.; Riou, J.-F.; Dauchez, M.; Alix, A. J. P.; Manfait, M.

2003-06-01

229

Zeaxanthin Radical Cation Formation in Minor Light-Harvesting Complexes of Higher Plant Antenna  

SciTech Connect

Previous work on intact thylakoid membranes showed that transient formation of a zeaxanthin radical cation was correlated with regulation of photosynthetic light-harvesting via energy-dependent quenching. A molecular mechanism for such quenching was proposed to involve charge transfer within a chlorophyll-zeaxanthin heterodimer. Using near infrared (880-1100 nm) transient absorption spectroscopy, we demonstrate that carotenoid (mainly zeaxanthin) radical cation generation occurs solely in isolated minor light-harvesting complexes that bind zeaxanthin, consistent with the engagement of charge transfer quenching therein. We estimated that less than 0.5percent of the isolated minor complexes undergo charge transfer quenching in vitro, whereas the fraction of minor complexes estimated to be engaged in charge transfer quenching in isolated thylakoids was more than 80 times higher. We conclude that minor complexes which bind zeaxanthin are sites of charge transfer quenching in vivo and that they can assume Non-quenching and Quenching conformations, the equilibrium LHC(N)<--> LHC(Q) of which is modulated by the transthylakoid pH gradient, the PsbS protein, and protein-protein interactions.

Avenson, Thomas H.; Ahn, Tae Kyu; Zigmantas, Donatas; Niyogi, Krishna K.; Li, Zhirong; Ballottari, Matteo; Bassi, Roberto; Fleming, Graham R.

2008-01-31

230

Theoretical study of the formation of mercury (hg(2+)) complexes in solution using an explicit solvation shell in implicit solvent calculations.  

PubMed

The structures and harmonic vibrational frequencies of water clusters (H2O)n, n = 1-10, have been computed using the M06-L/, B3LYP/, and CAM-BLYP/cc-pVTZ levels of theories. On the basis of the literature and our results, we use three hexamer structures of the water molecules to calculate an estimated "experimental" average solvation free energy of [Hg(H2O)6](2+). Aqueous formation constants (log K) for Hg(2+) complexes, [Hg(L)m(H2O)n](2-mq), L = Cl(-), HO(-), HS(-), and S(2-), are calculated using a combination of experimental (solvation free energies of ligands and Hg(2+)) and calculated gas- and liquid-phase free energies. A combined approach has been used that involves attaching n explicit water molecules to the Hg(2+) complexes such that the first coordination sphere is complete, then surrounding the resulting (Hg(2+)-Lm)-(OH2)n cluster by a dielectric continuum, and using suitable thermodynamic cycles. This procedure significantly improves the agreement between the calculated log K values and experiment. Thus, for some neutral and anionic Hg(II) complexes, particularly Hg(II) metal ion surrounded with homo- or heteroatoms, augmenting implicit solvent calculations with sufficient explicit water molecules to complete the first coordination sphere is required-and adequate-to account for strong short-range hydrogen bonding interactions between the anion and the solvent. Calculated values for formation constants of Hg(2+) complexes with S(2-) and SH(-) are proposed. Experimental measurements of these log K values have been lacking or controversial. PMID:25076413

Afaneh, Akef T; Schreckenbach, Georg; Wang, Feiyue

2014-09-25

231

Synthesis and charge-transfer complex formations of 1,n-bis(3,6-diethylcarbazol-9-yl)alkanes with three ?-acceptors  

NASA Astrophysics Data System (ADS)

Dimeric 1,n-bis(3,6-diethylcarbazol-9-yl)alkanes (where n = 1-5) were synthesized and their structures were characterized via spectroscopic techniques. Structures of two of the dimers, 1,2-bis(3,6-diethylcarbazol-9-yl)ethane (2b) and 1,4-bis(3,6-diethylcarbazol-9-yl)butane (2d), were investigated by single crystal X-ray crystallographic techniques. The crystal structures of 2b and 2d were solved in the monoclinic space groups C2/c and P21/n, respectively. The methylene chain adopted an anti conformation in 2b and a gauche-anti-gauche conformation in 2d, enabling coplanar orientations of carbazole rings in both structures. The molecular packing in both structures was stabilized by intermolecular ?-? stacking. Charge transfer complexations of 2a-2e with the ?-acceptors p-chloranil, tetracyanoethylene, and tetracyanoquinodimethane in solution were investigated by determining their stoichiometries, molar absorptivities, equilibrium constants, enthalpies, and entropies. All the dimers formed weakly associated complexes with each of the acceptors having equilibrium constants between 1.32-8.94 M-1 in 1,2-dichloroethane. Complexations were driven by the slightly negative formation enthalpies between -2.00 and -4.24 kcal mol-1.

Asker, Erol; Filiz, Fahrettin

2013-05-01

232

Paleobiology of a Neoproterozoic tidal flat/lagoonal complex: the Draken Conglomerate Formation, Spitsbergen  

NASA Technical Reports Server (NTRS)

Carbonates and rare shales of the ca 700-800 Ma old Draken Conglomerate Formation, northeastern Spitsbergen, preserve a record of environmental variation within a Neoproterozoic tidal flat/lagoon complex. Forty-two microfossil taxa have been recognized in Draken rocks, and of these, 39 can be characterized in terms of their paleoenvironmental distributions along a gradient from the supratidal zone to permanently submerged lagoons. Supratidal to subtidal trends include: increasing microbenthic diversity, increasing abundance and diversity of included allochthonous (presumably planktonic) elements, decreasing sheath thickness of mat-building organisms (with significant taphonomic consequences), and an increasing sediment/fossil ratio in fossiliferous rocks. Five principal and several minor biofacies can be distinguished. The paleoecological resolution obtainable in the Draken Conglomerate Formation rivals that achieved for most Phanerozoic fossil deposits. It documents the complexity and diversity of Proterozoic coastal ecosystems and indicates that both environment and taphonomy need to be taken into explicit consideration in attempts to understand evolutionary trends in early fossil record. Three species, Coniunctiophycus majorinum, Myxococcoides distola, and M. chlorelloidea, are described as new; Siphonophycus robustum, Siphonophycus septatum, and Gorgonisphaeridium maximum are proposed as new combinations.

Knoll, A. H.; Swett, K.; Mark, J.

1991-01-01

233

Formation of stable sessile interstitial complexes in reactions between glissile dislocation loops in bcc Fe  

NASA Astrophysics Data System (ADS)

Clusters of self-interstitial atoms (loops) are commonly observed in the microstructure of irradiated metals. These clusters can be formed directly in high-energy displacement cascades or by growth as a result of interaction between individual self interstitials. The majority of these clusters have features of glissile dislocation loops and migrate by fast one-dimensional glide. In this paper, we present results of a systematic molecular dynamics (MD) study of reactions involving glissile interstitial loops. By the example of bcc iron we demonstrate that the reactions can produce a number of specific, stable microstructural features, with different properties compared to the reactants. Namely, the reactions between the most common glissile clusters of <1 1 1> crowdions can result in coarsening or formation of immobile self interstitial complexes. The coarsening leads to a decrease of the total dislocation line length and therefore is favourable. The structure and stability of the junction formed in the reactions has been studied using many-body potentials and density functional theory (DFT) techniques. No evidence of the formation of a <1 0 0> loop from two glissile <1 1 1> clusters was found among the studied reactions. The immobile self interstitial complexes that form as a result of these reaction have, however, high binding energies, of the order of tens of eV, implying that a relatively long life time should be assigned to the resulting configurations and therefore that such objects are expected to contribute to the evolution of the microstructure under irradiation.

Terentyev, Dmitry; Malerba, Lorenzo; Klaver, Peter; Olsson, Par

2008-12-01

234

Low Mass Star Formation in the Gum Nebula: The CG~30/31/38 complex  

E-print Network

We present photometric and spectroscopic results for the low mass pre-main sequence (PMS) stars with spectral types K - M in the cometary globule (CG) 30/31/38 complex. We obtained multi-object high resolution spectra for the targets selected as possible PMS stars from multi-wavelength photometry. We identified 11 PMS stars brighter than V = 16.5 with ages stars, CG clouds, and ionizing sources (O stars and supernova remnants) suggests a possible triggered origin of the star formation in this region. We confirm the youth of the photometrically selected PMS stars using the lithium abundances. The radial velocities of the low mass PMS stars are consistent with those of the cometary globules. Most of the PMS stars show weak Halpha emission with W(Halpha) stars shows a moderate near-IR excess, which suggests a short survival time (t star forming environment. In addition, we find five young late type stars and one Ae star which have no obvious relation to the CG 30/31/38 complex. We also discuss a possible scenario of star formation history in the CG 30/31/38 region.

Jinyoung Serena Kim; Frederick M. Walter; Scott J. Wolk

2005-02-15

235

Ammonium chloride complex formation during downstream microwave ammonia plasma treatment of parylene-C  

SciTech Connect

In this work, parylene-C is exposed to the effluent from a microwave ammonia plasma with a goal of producing primary amine groups on the parylene-C. These amine groups are desired as sites for the attachment of various biomolecules that will influence the biocompatibility of the parylene-C. Ammonia plasma treatment is an effective approach for creating amine species on polymers. In this work, attenuated total reflectance infrared spectroscopy studies showed that no primary amine groups resulted from this treatment of parylene-C. Instead, reactive nitrogen-bearing radicals from the plasma appear to have been complexed by chlorine in the polymer. The formation of these complexes scavenged nitrogen-bearing radicals from the plasma and prevented the formation of nitrogenous species, such as the desired primary amines, on the parylene-C. These results are consistent with results of ammonia plasma treatment of other chlorinated polymers and suggest that alternative approaches are required to create nitrogen-bearing species on parylene-C.

Pruden, K.G.; Beaudoin, S.P. [Department of Chemical and Materials Engineering, Arizona State University, Tempe, Arizona 85287-6006 (United States); Department of Chemical and Materials Engineering, Arizona State University, Tempe, Arizona 85287-6006 and School of Chemical Engineering, Purdue University, Forney Hall of Chemical Engineering, 480 Stadium Mall Drive, West Lafayette, Indiana 47907-2100 (United States)

2005-11-15

236

Vacancy formation on C60/Pt (111): unraveling the complex atomistic mechanism  

NASA Astrophysics Data System (ADS)

The interaction of fullerenes with transition metal surfaces leads to the development of an atomic network of ordered vacancies on the metal. However, the structure and formation mechanism of this intricate surface reconstruction is not yet understood at an atomic level. We combine scanning tunneling microscopy, high resolution and temperature programmed-x-ray photoelectrons spectroscopy, and density functional theory calculations to show that the vacancy formation in C60/Pt(111) is a complex process in which fullerenes undergo two significant structural rearrangements upon thermal annealing. At first, the molecules are physisorbed on the surface; next, they chemisorb inducing the formation of an adatom-vacancy pair on the side of the fullerene. Finally, this metastable state relaxes when the adatom migrates away and the vacancy moves under the molecule. The evolution from a weakly-bound fullerene to a chemisorbed state with a vacancy underneath could be triggered by residual H atoms on the surface which prevent a strong surface-adsorbate bonding right after deposition. Upon annealing at about 440 K, when all H has desorbed, the C60 interacts with the Pt surface atoms forming the vacancy-adatom pair. This metastable state induces a small charge transfer and precedes the final adsorption structure.

Pinardi, Anna L.; Biddau, Giulio; van De Ruit, Kees; Otero-Irurueta, Gonzalo; Gardonio, Sara; Lizzit, Silvano; Schennach, Robert; Flipse, Cees F. J.; López, María F.; Méndez, Javier; Pérez, Rubén; Martín-Gago, José A.

2014-09-01

237

Statistical considerations on the formation of circular photosynthetic light-harvesting complexes from Rhodopseudomonas palustris.  

PubMed

Depending on growth conditions, some species of purple photosynthetic bacteria contain peripheral light-harvesting (LH2) complexes that are heterogeneous owing to the presence of different protomers (containing different ??-apoproteins). Recent spectroscopic studies of Rhodopseudomonas palustris grown under low-light conditions suggest the presence of a C 3-symmetric LH2 nonamer comprised of two distinct protomers. The software program Cyclaplex, which enables generation and data-mining of virtual libraries of molecular rings formed upon combinatorial reactions, has been used to delineate the possible number and type of distinct nonamers as a function of numbers of distinct protomers. The yield of the C 3-symmetric nonamer from two protomers (A and B in varying ratios) has been studied under the following conditions: (1) statistical, (2) enriched (preclusion of the B-B sequence), and (3) seeded (pre-formation of an A-B-A block). The yield of C 3-symmetric nonamer is at most 0.98 % under statistical conditions versus 5.6 % under enriched conditions, and can be dominant under conditions of pre-seeding with an A-B-A block. In summary, the formation of any one specific nonamer even from only two protomers is unlikely on statistical grounds but must stem from enhanced free energy of formation or a directed assembly process by as-yet unknown factors. PMID:24510549

Taniguchi, Masahiko; Henry, Sarah; Cogdell, Richard J; Lindsey, Jonathan S

2014-07-01

238

Formation of neutral complexes of boric acid with 1,3-diols in organic solvents and in aqueous solution  

Microsoft Academic Search

From solubility measurements in organic media and extraction experiments, the values of the stability constants of neutral 1 : 1 complexes (HBL) formed between boric acid (HB) and 1,3-diols (L) have been obtained in aqueous solution (Kc(w)) and in organic solvents (Kc(s)). The values of the partition coefficients of the diols (PL) and the complexes (PHBL) between water and the

Nicolas Bachelier; Jean-François Verchere

1995-01-01

239

Measurement of two-dimensional binding constants between cell-bound major histocompatibility complex and immobilized antibodies with an acoustic biosensor.  

PubMed

Gaining insights into the dynamic processes of molecular interactions that mediate cell-substrate and cell-cell adhesion is of great significance in the understanding of numerous physiological processes driven by intercellular communication. Here, an acoustic-wave biosensor is used to study and characterize specific interactions between cell-bound membrane proteins and surface-immobilized ligands, using as a model system the binding of major histocompatibility complex class I HLA-A2 proteins to anti-HLA-A2 monoclonal antibodies. The energy of the acoustic signal, measured as amplitude change, was found to depend directly on the number of HLA-A2/antibody complexes formed on the device surface. Real-time acoustic data were used to monitor the surface binding of cell suspensions at a range of 6.0 x 10(4) to 6.0 x 10(5) cells mL(-1). Membrane interactions are governed by two-dimensional chemistry because of the molecules' confinement to the lipid bilayer. The two-dimensional kinetics and affinity constant of the HLA-A2/antibody interaction were calculated (k(a) = 1.15 x 10(-5) mum(2) s(-1) per molecule, k(d) = 2.07 x 10(-5) s(-1), and K(A) = 0.556 mum(2) per molecule, at 25 degrees C), based on a detailed acoustic data analysis. Results indicate that acoustic biosensors can emerge as a significant tool for probing and characterizing cell-membrane interactions in the immune system, and for fast and label-free screening of membrane molecules using whole cells. PMID:18708454

Saitakis, Michael; Dellaporta, Anastasia; Gizeli, Electra

2008-11-15

240

DFT 2H quadrupolar coupling constants of ruthenium complexes: a good probe of the coordination of hydrides in conjuction with experiments.  

PubMed

Transition metal (TM) hydrides are of great interest in chemistry because of their reactivity and their potential as catalysts for hydrogenation reactions. 2H solid-state NMR can be used in order to get information about the local environment of hydrogen atoms, and more particularly the coordination mode of hydrides in such complexes. In this work we will show that it is possible to establish at the level of density functional theory (DFT) a viable methodological strategy that allows the determination of 2H NMR parameters, namely the quadrupolar coupling constant (C(Q)) respectively the quadrupolar splitting (deltanuQ) and the asymmetry parameter (etaQ). The reliability of the method (B3PW91-DFT) and basis set effects have been first evaluated for simple organic compounds (benzene and fluorene). A good correlation between experimental and theoretical values is systematically obtained if the large basis set cc-pVTZ is used for the computations. 2H NMR properties of five mononuclear ruthenium complexes (namely Cp*RuD3(PPh3), Tp*RuD(THT)2, Tp*RuD(D2)(THT) and Tp*RuD(D2)2 and RuD2(D2)2(PCy3)2) which exhibit different ligands and hydrides involved in different coordination modes (terminal-H or eta2-H2), have been calculated and compared to previous experimental data. The results obtained are in excellent agreement with experiments. Although 2H NMR spectra are not always easy to analyze, assistance by quantum chemistry calculations allows unambiguous assignment of the signals of such spectra. As far as experiments can be achieved at very low temperatures in order to avoid dynamic effects, this hybrid theoretical/experimental tool may give useful insights in the context of the characterization of ruthenium surfaces or nanoparticles with solid-state NMR. PMID:19842483

del Rosal, Iker; Gutmann, Torsten; Maron, Laurent; Jolibois, Franck; Chaudret, Bruno; Walaszek, Bernadeta; Limbach, Hans-Heinrich; Poteau, Romuald; Buntkowsky, Gerd

2009-07-21

241

The Quantum Vacuum of Complex Media. A Unified Approach to the Dielectric Constant, the Spontaneous Emission and the Zero-Temperature Electromagnetic Pressure  

E-print Network

We study from a critical perspective several quantum-electrodynamic phenomena commonly related to vacuum electromagnetic (EM) fluctuations in complex media. We compute the resonance-shift, the spontaneous emission rate, the local density of states and the van-der-Waals-Casimir pressure in a dielectric medium using a microscopic diagrammatic approach. We find, in agreement with some recent works, that these effects cannot be attributed to variations on the energy of the EM vacuum but to variations of the dielectric self-energy. This energy is the result of the interaction of the bare polarizability of the dielectric constituents with the EM fluctuations of an actually polarized vacuum. We have found an exact expression for the spectrum of these fluctuations in a statistically homogeneous dielectric. Those fluctuations turn out to be different to the ones of normal radiative modes. It is the latter that carry the zero-point-energy (ZPE). Concerning spontaneous emission, we clarify the nature of the radiation and the origin of the so-called local field factors. Essential discrepancies are found with respect to previous works. We perform a detailed analysis of the phenomenon of radiative and non-radiative energy transfer. Analytical formulae are given for the decay rate of an interstitial impurity in a Maxwell-Garnett dielectric and for the decay rate of a substantial impurity sited in a large cavity. The construction of the effective dielectric constant is found to be a self-consistency problem. The van-der-Waals pressure in a complex medium is computed in terms of variations of the dielectric self-energy at zero-temperature. An additional radiative pressure appears associated to variations of the EM vacuum energy.

M. Donaire

2009-12-16

242

Sensitive and selective spectrophotometric assay of piroxicam in pure form, capsule and human blood serum samples via ion-pair complex formation  

NASA Astrophysics Data System (ADS)

A simple, accurate and highly sensitive spectrophotometric method has been developed for the rapid determination of piroxicam (PX) in pure and pharmaceutical formulations. The proposed method involves formation of stable yellow colored ion-pair complexes of the amino derivative (basic nitrogen) of PX with three sulphonphthalein acid dyes namely; bromocresol green (BCG), bromothymol blue (BTB), bromophenol blue (BPB) in acidic medium. The colored species exhibited absorption maxima at 438, 429 and 432 nm with molar absorptivity values of 9.400 × 103, 1.218 × 103 and 1.02 × 104 L mol-1 cm-1 for PX-BCG, PX-BTB and PX-BPB complexes, respectively. The effect of optimum conditions via acidity, reagent concentration, time and solvent were studied. The reactions were extremely rapid at room temperature and the absorbance values remained constant for 48 h. Beer’s law was obeyed with a good correlation coefficient in the concentration ranges 1-100 ?g mL-1 for BCG, BTB complexes and 1-95 ?g mL-1 for BPB complex. The composition ratio of the ion-pair complexes were found to be 1:1 in all cases as established by Job’s method. No interference was observed from common additives and excipients which may be present in the pharmaceutical preparations. The proposed method was successfully applied for the determination of PX in capsule and human blood serum samples with good accuracy and precision.

Alizadeh, Nina; Keyhanian, Fereshteh

2014-09-01

243

Enantiomeric and mesomeric mandelate complexes of molybdenum -- on their stereospecific formations and absolute configurations.  

PubMed

The stereospecific formation and absolute configuration of R-homocitrate coordinated FeMo-co in nitrogenase was mimicked through the structural analyses of a collection of enantiomeric and mesomeric mandelato molybdenum complexes, i.e., (NH(4))(2)[Mo(Delta)O(2)(R-mand)(2)]x3H(2)O (1a), (NH(4))(2)[Mo(Lambda)O(2)(S-mand)(2)]x3H(2)O (1b), (NH(4))(4)[Mo(Delta)O(2)(RS-mand)(2)][Mo(Lambda)O(2)(RS-mand)(2)]x8H(2)O (2), (NH(4))(2)[W(Delta)O(2)(R-mand)(2)]x2H(2)O (3a), (NH(4))(2)[W(Lambda)O(2)(S-mand)(2)]x2H(2)O (3b) (H(2)mand=mandelic acid, C(8)H(8)O(3)), which have been characterized by elemental analyses, optical rotation, circular dichroism, IR, NMR spectroscopes and X-ray single crystal studies. The R and S chiral mandelic acids induce the formations of the enantiomeric pair of chiral complexes, which are supported by the characterizations of optical rotation and circular dichroism. The configuration of the resulted metal center could be assigned as Delta or Lambda. While the RS racemic reagent yields only mesomeric compound. The Delta(R,R)-complexes 1a and 3a are enantiomers of Lambda(S,S)-1b and 3b, respectively. Of the five complexes, Mo and W atoms are all hexa-coordinated by two cis-oxo groups and two bidentate mandelate ligands through the deprotonated alpha-alkoxyl and alpha-carboxyl groups, forming a stable five-membered chelated rings. The average Mo(VI)-O bond distances with alpha-alkoxyl and alpha-carboxyl are 1.944 and 2.210 A, respectively. Further comparison indicates that bonds of alpha-alkoxyl groups in the hydroxycarboxylato molybdenum complexes are much sensitive to the change in the oxidation state of molybdenum, which support the possible Mo activation model in FeMo-co through the protonation and cleavage of alpha-alkoxyl group in homocitrate ligand. PMID:15522406

Zhou, Zhao-Hui; Zhao, Hong; Tsai, Khi-Rui

2004-11-01

244

Incorporation of polyoxotungstate complexes in silica spheres and in situ formation of tungsten trioxide nanoparticles.  

PubMed

In this paper, we demonstrated a new convenient route for in situ fabrication of well separated small sized WO(3) nanoparticles in silica spheres, through a predeposition of surfactant encapsulated polyoxotungates as tungsten source, and followed by a calcination process. In a typical procedure, selected polyoxotungates with different charges were enwrapped with dioctadecyldimethylammonium cations through electrostatic interaction. Elemental analysis, thermogravimetric analysis, and spectral characterization confirmed the formation of prepared complexes with the anticipated chemical structure. The complexes were then phase-transferred into aqueous solution that predissolved surfactant cetyltrimethylammonium bromide, and finally incorporated into silica spheres through a joint sol-gel reaction with tetraethyl orthosilicate in a well dispersed state under the protection of organic layer for polyoxotungates from the alkaline reaction condition. Transmission electron microscopic images illustrated the well dispersed WO(3) nanoparticles in the size range of ca. 2.2 nm in the silica spheres after the calcination at 465 °C. The sizes of both the silica spheres and WO(3) nanoparticles could be adjusted independently through changing the doping content to a large extent. Meanwhile, the doped polyoxotungate complexes acted as the template for the mesoporous structure in silica spheres after the calcination. Along with the increase of doping content and surfactant, the mesopore size changed little (2.0-2.9 nm), but the specific surface areas increased quite a lot. Importantly, the WO(3)-nanoparticle-doped silica spheres displayed an interesting photovoltaic property, which is favorable for the funtionalization of these nanomaterials. PMID:20715875

Zhao, Yuanyuan; Fan, Haimei; Li, Wen; Bi, Lihua; Wang, Dejun; Wu, Lixin

2010-09-21

245

Spectrophotometric determination of tizanidine and orphenadrine via ion pair complex formation using eosin Y  

PubMed Central

A simple, sensitive and rapid spectrophotometric method was developed and validated for the determination of two skeletal muscle relaxants namely, tizanidine hydrochloride (I) and orphenadrine citrate (II) in pharmaceutical formulations. The proposed method is based on the formation of a binary complex between the studied drugs and eosin Y in aqueous buffered medium (pH 3.5). Under the optimum conditions, the binary complex showed absorption maxima at 545 nm for tizanidine and 542 nm for orphenadrine. The calibration plots were rectilinear over concentration range of 0.5-8 ?g/mL and 1-12 ?g/mL with limits of detection of 0.1 ?g/mL and 0.3 ?g/mL for tizanidine and orphenadrine respectively. The different experimental parameters affecting the development and stability of the complex were studied and optimized. The method was successfully applied for determination of the studied drugs in their dosage forms; and to the content uniformity test of tizanidine in tablets. PMID:21982341

2011-01-01

246

Intermediates in Reactions of Copper(I) Complexes with N-Oxides: From Formation of Stable Adducts to Oxo Transfer  

PubMed Central

Reactions of Cu(I) complexes of bidentate N-donor supporting ligands with pyridine- and trimethylamine-N-oxides or PhIO were explored. Key results include the identification of novel Cu(I)-N-oxide adducts, aryl substituent hydroxylation, and bis(?-oxo)dicopper complex formation via a route involving oxo transfer. PMID:19425587

Hong, Sungjun; Gupta, Aalo K.; Tolman, William B.

2009-01-01

247

Improving immunogenicity of HIV-1 envelope gp120 by glycan removal and immune complex formation  

PubMed Central

HIV-1 envelope (Env) gp120 is an important target for neutralizing antibody (Ab) responses against the virus; however, developing gp120 vaccines that elicit potent and broad neutralizing Abs has proven to be a formidable challenge. Previously, removal of an N-linked glycan at residue 448 by an N to Q mutation (N448Q) has been found to enhance the in vitro antigenicity of neutralizing epitopes in the V3 loop. In this study the mutated gp120 was first compared with wild type gp120 for immunogenicity in mice using a DNA prime and protein boost immunization regimen. The N448Q mutant did not elicit higher titers of anti-gp120 serum Abs and failed to generate anti-V3 Abs. The sera also had no virus-neutralizing activity, even though the mutant induced higher levels of lymphoproliferation and cytokine production. Subsequently, the N448Q mutant was used to construct an immune complex vaccine with the anti-CD4 binding site monoclonal antibody (mAb) 654. The N448Q/654 complex stimulated comparably high levels of serum Abs to gp120 and V3 as the wild type complex. However, Abs against the C1 and C2 regions in the gp120 core were more elevated. Importantly, the mutant complex also elicited higher titers of neutralizing Abs activity than the wild type counterpart. Similar results were achieved with a complex made with gp120 bearing an N448E mutation, confirming the importance of the N448-linked glycan in modulating gp120 immunogenicity. Neutralizing activity was directed to V3 and other undefined neutralizing epitopes. Improved immunogenicity of the immune complexes correlated with alterations in exposure of V3 and other Ab epitopes and their stability against proteases. These data demonstrate the advantage of combining site-specific N-glycan removal and immune complex formation as a novel vaccine strategy to improve immunogenicity of targeted Ab epitopes on critical regions of HIV-1 gp120. PMID:21945958

Kumar, Rajnish; Tuen, Michael; Li, Hualin; Tse, Doris B.; Hioe, Catarina E.

2012-01-01

248

Multicomponent complex formation between vinpocetine, cyclodextrins, tartaric acid and water-soluble polymers monitored by NMR and solubility studies  

Microsoft Academic Search

This work deals with multicomponent complex formation of vinpocetine (VP) with ?-cyclodextrin (?CD), sulfobutyl ether ?-cyclodextrin (SBE?CD) and tartaric acid (TA), in the presence or absence of water-soluble polymers, in aqueous solution. Complexation was monitored by phase-solubility and proton nuclear magnetic resonance (1H NMR) studies. TA demonstrated a synergistic effect on VP solubility, and in the complexation efficiency of ?CD

Laura Ribeiro; Rui A. Carvalho; Domingos C. Ferreira; Francisco J. B. Veiga

2005-01-01

249

Galvanic Cells and the Determination of Equilibrium Constants  

ERIC Educational Resources Information Center

Readily assembled mini-galvanic cells can be employed to compare their observed voltages with those predicted from the Nernst equation and to determine solubility products for silver halides and overall formation constants for metal-ammonia complexes. Results obtained by students in both an honors-level first-year course in general chemistry and…

Brosmer, Jonathan L.; Peters, Dennis G.

2012-01-01

250

Changes in solvent accessibility of wild-type and deamidated ?B2-crystallin following complex formation with ?A-crystallin  

PubMed Central

Aberrant protein interactions can lead to aggregation and insolubilization, such as occurs during cataract formation. Deamidation, a prevalent age-related modification in the lens of the eye, decreases stability of the major lens proteins, crystallins. The mechanism of deamidation altering interactions between ?A-crystallin and ?B2-crystallin was investigated by detecting changes in solvent accessibility upon complex formation during heating. Solvent accessibility was determined by measuring hydrogen/deuterium exchange levels of backbone amides by high-resolution mass spectrometry. Deuterium levels in wild type ?B2-crystallin increased 50-60% in both domains following complex formation with ?A-crystallin. This increased solvent accessibility indicated a general loosening along the backbone amides. Peptides with the greatest deuterium increases were located at the buried monomer-monomer interface, suggesting that the ?B2 dimer was disrupted. The only region where the deuterium levels decreased was in ?B2 peptide 123-139, containing an outside loop, and may be a potential site of interaction with ?A. Mimicking deamidation at the ?B2 dimer interface prevented complex formation with ?A. When temperatures were lowered, an ?A/?B2 Q70E/Q162E complex formed with similar solvent accessibilities as ?A/WT ?B2. Deamidation did not disrupt specific ?A/?B2 interactions but favored aggregation before complex formation with ?A. We conclude that deamidation contributes to cataract formation through destabilization of crystallins before they can be rescued by ?-crystallin. PMID:22982024

Lampi, Kirsten J.; Fox, Cade B.; David, Larry L.

2012-01-01

251

The formation of glycine and other complex organic molecules in exploding ice mantles.  

PubMed

Complex Organic Molecules (COMs), such as propylene (CH3CHCH2) and the isomers of C2H4O2 are detected in cold molecular clouds (such as TMC-1) with high fractional abundances (Marcelino et al., Astrophys. J., 2007, 665, L127). The formation mechanism for these species is the subject of intense speculation, as is the possibility of the formation of simple amino acids such as glycine (NH2CH2COOH). At typical dark cloud densities, normal interstellar gas-phase chemistries are inefficient, whilst surface chemistry is at best ill defined and does not easily reproduce the abundance ratios observed in the gas phase. Whatever mechanism(s) is/are operating, it/they must be both efficient at converting a significant fraction of the available carbon budget into COMs, and capable of efficiently returning the COMs to the gas phase. In our previous studies we proposed a complementary, alternative mechanism, in which medium- and large-sized molecules are formed by three-body gas kinetic reactions in the warm high density gas phase. This environment exists, for a very short period of time, after the total sublimation of grain ice mantles in transient co-desorption events. In order to drive the process, rapid and efficient mantle sublimation is required and we have proposed that ice mantle 'explosions' can be driven by the catastrophic recombination of trapped hydrogen atoms, and other radicals, in the ice. Repeated cycles of freeze-out and explosion can thus lead to a cumulative molecular enrichment of the interstellar medium. Using existing studies we based our chemical network on simple radical addition, subject to enthalpy and valency restrictions. In this work we have extended the chemistry to include the formation pathways of glycine and other large molecular species that are detected in molecular clouds. We find that the mechanism is capable of explaining the observed molecular abundances and complexity in these sources. We find that the proposed mechanism is easily capable of explaining the large abundances of all three isomers of C2H4O2 that are observationally inferred for star-forming regions. However, the model currently does not provide an obvious explanation for the predominance of methyl formate, suggesting that some refinement to our (very simplistic) chemistry is necessary. The model also predicts the production of glycine at a (lower) abundance level, that is consistent with its marginal detection in astrophysical sources. PMID:25302390

Rawlings, J M C; Williams, D A; Viti, S; Cecchi-Pestellini, C; Duley, W W

2014-01-01

252

Coronavirus Replicase-Reporter Fusions Provide Quantitative Analysis of Replication and Replication Complex Formation  

PubMed Central

ABSTRACT The replication of coronaviruses occurs in association with multiple virus-induced membrane structures that evolve during the course of infection; however, the dynamics of this process remain poorly understood. Previous studies of coronavirus replication complex organization and protein interactions have utilized protein overexpression studies and immunofluorescence of fixed cells. Additionally, live-imaging studies of coronavirus replicase proteins have used fluorescent reporter molecules fused to replicase proteins, but expressed from nonnative locations, mostly late-transcribed subgenomic mRNAs, in the presence or absence of the native protein. Thus, the timing and targeting of native replicase proteins expressed in real time from native locations in the genome remain unknown. In this study, we tested whether reporter molecules could be expressed from the replicase polyprotein of murine hepatitis virus as fusions with nonstructural protein 2 or 3 and whether such reporters could define the targeting and activity of replicase proteins during infection. We demonstrate that the fusion of green fluorescent protein and firefly luciferase with either nonstructural protein 2 or 3 is tolerated and that these reporter-replicase fusions can be used to quantitate replication complex formation and virus replication. The results show that the replicase gene has flexibility to accommodate a foreign gene addition and can be used directly to study replicase complex formation and evolution during infection as well as to provide highly sensitive and specific markers for protein translation and genome replication. IMPORTANCE Coronaviruses are a family of enveloped, positive-sense RNA viruses that are important agents of disease, including severe acute respiratory syndrome coronavirus and Middle East respiratory syndrome coronavirus. Replication is associated with multiple virus-induced membrane structures that evolve during infection; however, the dynamics of this process remain poorly understood. In this study, we tested whether reporter molecules expressed from native locations within the replicase polyprotein of murine hepatitis virus as fusions with nonstructural proteins could define the expression and targeting of replicase proteins during infection in live cells. We demonstrate that the replicase gene tolerates the introduction of green fluorescent protein or firefly luciferase as fusions with replicase proteins. These viruses allow early quantitation of virus replication as well as real-time measurement of replication complexes. PMID:24623413

Freeman, Megan Culler; Graham, Rachel L.; Lu, Xiaotao; Peek, Christopher T.

2014-01-01

253

Thermodynamics of the complex formation of copper(II) with L-phenylalanine in aqueous ethanol solutions  

NASA Astrophysics Data System (ADS)

Constants of the acid dissociation and complexation of L-phenylalanine (HPhe) with copper(II) ions are determined by potentiometry in aqueous ethanol solutions containing 0 to 0.7 molar fraction of alcohol. Changes in the Gibbs energy for the transfer from water to a binary solvent of L-phenylalanine, Phe- anion, and [CuPhe]+ complex are calculated. It is found that the weakening of solvation of the ligand donor groups in solvents with high ethanol contents is accompanied by an increase in the stability of [CuPhe]+ complex.

Burov, D. M.; Ledenkov, S. F.; Vandyshev, V. N.

2013-05-01

254

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles  

PubMed Central

Summary Deprotonation of indazolium salts at low temperatures gives N-heterocyclic carbenes of indazoles (indazol-3-ylidenes) which can be trapped as rhodium complexes (X-ray analysis). In the absence of Rh, the indazol-3-ylidenes spontaneously dimerize under ring cleavage of one of the N,N-bonds and ring closure to an indazole–indole spiro compound which possesses an exocyclic imine group. The E/Z isomers of the imines can be separated by column chromatography when methanol is used as eluent. We present results of a single crystal X-ray analysis of one of the E-isomers, which equilibrate in solution as well as in the solid state. Heating of the indazole–indole spiro compounds results in the formation of quinazolines by a ring-cleavage/ring-closure sequence (X-ray analysis). Results of DFT calculations are presented. PMID:24778738

Guan, Zong; Namyslo, Jan C; Drafz, Martin H H; Nieger, Martin

2014-01-01

255

Formation of Large Polysulfide Complexes during the Lithium-Sulfur Battery Discharge  

SciTech Connect

Sulfur cathodes have much larger capacities than transition-metal-oxide cathodes used in commercial lithium-ion batteries but suffer from unsatisfactory capacity retention and long-term cyclability. Capacity degradation originates from soluble lithium polysulfides gradually diffusing into the electrolyte. Understanding of the formation and dynamics of soluble polysulfides during the discharging process at the atomic level remains elusive, which limits further development of lithium-sulfur (Li-S) batteries. Here we report first-principles molecular dynamics simulations and density functional calculations, through which the discharging products of Li-S batteries are studied. We find that, in addition to simple Li2Sn (1 n 8) clusters generated from single cyclooctasulfur (S8) rings, large Li-S clusters form by collectively coupling several different rings to minimize the total energy. At high lithium concentration, a Li-S network forms at the sulfur surfaces. The results can explain the formation of the soluble Li-S complex, such as Li2S8, Li2S6, and Li2S4, and the insoluble Li2S2 and Li2S structures. In addition, we show that the presence of oxygen impurities in graphene, particularly oxygen atoms bonded to vacancies and edges, may stabilize the lithium polysulfides that may otherwise diffuse into the electrolyte.

Wang, Bin [Vanderbilt University, Nashville; Alhassan, Saeed M. [The Petroleum Institute; Pantelides, Sokrates T [ORNL

2014-01-01

256

Carbonates in CM chondrites: Complex formational histories and comparison to carbonates in CI chondrites  

NASA Astrophysics Data System (ADS)

CM chondrites are primitive solar-system materials that have undergone high degrees of aqueous alteration, resulting in the formation of secondary minerals including carbonates. Two different carbonate minerals (calcite/aragonite and dolomite) together constitute 1.4-2.8 vol% of CM chondrites. In contrast, CI chondrites contain four different carbonate minerals: calcite/aragonite, dolomite, breunnerite, and siderite. CI chondrites have abundant dolomite, a mineral that seems to be absent in the most aqueously altered CM chondrites. In this study, carbonates in seven CM chondrites (Y-791198, LaPaz Icefield 04796, Cold Bokkeveld, Nogoya, Queen Alexandra Range 93005, Allan Hills 83100, and Meteorite Hills 01070) were studied petrographically and by electron microprobe. The results indicate that carbonate formation in CM chondrites differs from that in CI chondrites and is more complex than previously recognized. Our studies of CM chondrites indicate that (1) carbonates formed on the parent asteroid in an aqueous environment that gradually changed in composition, (2) at some stage, Ca and Mg activities in the environment were high enough to form metastable dolomite, and (3) dolomites disappeared in the most aqueously altered CM chondrites.

de Leuw, Simone; Rubin, Alan E.; Wasson, John T.

2010-04-01

257

Formation of Large Polysulfide Complexes during the Lithium-Sulfur Battery Discharge  

NASA Astrophysics Data System (ADS)

Sulfur cathodes have much larger capacities than transition-metal-oxide cathodes used in commercial lithium-ion batteries but suffer from unsatisfactory capacity retention and long-term cyclability. Capacity degradation originates from soluble lithium polysulfides gradually diffusing into the electrolyte. Understanding of the formation and dynamics of soluble polysulfides during the discharging process at the atomic level remains elusive, which limits further development of lithium-sulfur (Li-S) batteries. Here we report first-principles molecular dynamics simulations and density functional calculations, through which the discharging products of Li-S batteries are studied. We find that, in addition to simple Li2Sn (1?n ?8) clusters generated from single cyclooctasulfur (S8) rings, large Li-S clusters form by collectively coupling several different rings to minimize the total energy. At high lithium concentration, a Li-S network forms at the sulfur surfaces. The results can explain the formation of the soluble Li-S complex, such as Li2S8, Li2S6, and Li2S4, and the insoluble Li2S2 and Li2S structures. In addition, we show that the presence of oxygen impurities in graphene, particularly oxygen atoms bonded to vacancies and edges, may stabilize the lithium polysulfides that may otherwise diffuse into the electrolyte.

Wang, Bin; Alhassan, Saeed M.; Pantelides, Sokrates T.

2014-09-01

258

Generalized additive models reveal the intrinsic complexity of wood formation dynamics  

PubMed Central

The intra-annual dynamics of wood formation, which involves the passage of newly produced cells through three successive differentiation phases (division, enlargement, and wall thickening) to reach the final functional mature state, has traditionally been described in conifers as three delayed bell-shaped curves followed by an S-shaped curve. Here the classical view represented by the ‘Gompertz function (GF) approach’ was challenged using two novel approaches based on parametric generalized linear models (GLMs) and ‘data-driven’ generalized additive models (GAMs). These three approaches (GFs, GLMs, and GAMs) were used to describe seasonal changes in cell numbers in each of the xylem differentiation phases and to calculate the timing of cell development in three conifer species [Picea abies (L.), Pinus sylvestris L., and Abies alba Mill.]. GAMs outperformed GFs and GLMs in describing intra-annual wood formation dynamics, showing two left-skewed bell-shaped curves for division and enlargement, and a right-skewed bimodal curve for thickening. Cell residence times progressively decreased through the season for enlargement, whilst increasing late but rapidly for thickening. These patterns match changes in cell anatomical features within a tree ring, which allows the separation of earlywood and latewood into two distinct cell populations. A novel statistical approach is presented which renews our understanding of xylogenesis, a dynamic biological process in which the rate of cell production interplays with cell residence times in each developmental phase to create complex seasonal patterns. PMID:23530132

Cuny, Henri E.

2013-01-01

259

Complex Organic Molecules during Low-mass Star Formation: Pilot Survey Results  

NASA Astrophysics Data System (ADS)

Complex organic molecules (COMs) are known to be abundant toward some low-mass young stellar objects (YSOs), but how these detections relate to typical COM abundance are not yet understood. We aim to constrain the frequency distribution of COMs during low-mass star formation, beginning with this pilot survey of COM lines toward six embedded YSOs using the IRAM 30 m Telescope. The sample was selected from the Spitzer c2d ice sample and covers a range of ice abundances. We detect multiple COMs, including CH3CN, toward two of the YSOs, and tentatively toward a third. Abundances with respect to CH3OH vary between 0.7% and 10%. This sample is combined with previous COM observations and upper limits to obtain a frequency distributions of CH3CN, HCOOCH3, CH3OCH3, and CH3CHO. We find that for all molecules more than 50% of the sample have detections or upper limits of 1%-10% with respect to CH3OH. Moderate abundances of COMs thus appear common during the early stages of low-mass star formation. A larger sample is required, however, to quantify the COM distributions, as well as to constrain the origins of observed variations across the sample. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Öberg, Karin I.; Lauck, Trish; Graninger, Dawn

2014-06-01

260

Generalized additive models reveal the intrinsic complexity of wood formation dynamics.  

PubMed

The intra-annual dynamics of wood formation, which involves the passage of newly produced cells through three successive differentiation phases (division, enlargement, and wall thickening) to reach the final functional mature state, has traditionally been described in conifers as three delayed bell-shaped curves followed by an S-shaped curve. Here the classical view represented by the 'Gompertz function (GF) approach' was challenged using two novel approaches based on parametric generalized linear models (GLMs) and 'data-driven' generalized additive models (GAMs). These three approaches (GFs, GLMs, and GAMs) were used to describe seasonal changes in cell numbers in each of the xylem differentiation phases and to calculate the timing of cell development in three conifer species [Picea abies (L.), Pinus sylvestris L., and Abies alba Mill.]. GAMs outperformed GFs and GLMs in describing intra-annual wood formation dynamics, showing two left-skewed bell-shaped curves for division and enlargement, and a right-skewed bimodal curve for thickening. Cell residence times progressively decreased through the season for enlargement, whilst increasing late but rapidly for thickening. These patterns match changes in cell anatomical features within a tree ring, which allows the separation of earlywood and latewood into two distinct cell populations. A novel statistical approach is presented which renews our understanding of xylogenesis, a dynamic biological process in which the rate of cell production interplays with cell residence times in each developmental phase to create complex seasonal patterns. PMID:23530132

Cuny, Henri E; Rathgeber, Cyrille B K; Kiessé, Tristan Senga; Hartmann, Felix P; Barbeito, Ignacio; Fournier, Meriem

2013-04-01

261

Mammalian target of rapamycin complex 1 activation in podocytes promotes cellular crescent formation.  

PubMed

Podocytes play a key role in the formation of cellular crescents in experimental and human diseases. However, the underlying mechanisms for podocytes in promoting crescent formation need further investigation. Here, we demonstrated that mammalian target of rapamycin complex 1 (mTORC1) signaling was remarkably activated and hypoxia-inducible factor (HIF) 1? expression was largely induced in cellular crescents from patients with crescentic glomerular diseases. Specific deletion of Tsc1 in podocytes led to mTORC1 activation in podocytes and kidney dysfunction in mice. Interestingly, 33 of 36 knockouts developed cellular or mixed cellular and fibrous crescents at 7 wk of age (14.19 ± 3.86% of total glomeruli in knockouts vs. 0% in control littermates, n = 12-36, P = 0.04). All of the seven knockouts developed crescents at 12 wk of age (30.92 ± 11.961% of total glomeruli in knockouts vs. 0% in control littermates, n = 4-7, P = 0.002). Most notably, bridging cells between the glomerular tuft and the parietal basement membrane as well as the cellular crescents were immunostaining positive for WT1, p-S6, HIF1?, and Cxcr4. Furthermore, continuously administrating rapamycin starting at 7 wk of age for 5 wk abolished crescents as well as the induction of p-S6, HIF1?, and Cxcr4 in the glomeruli from the knockouts. Together, it is concluded that mTORC1 activation in podocytes promotes cellular crescent formation, and targeting this signaling may shed new light on the treatment of patients with crescentic glomerular diseases. PMID:24990893

Mao, Junhua; Zeng, Zhifeng; Xu, Zhuo; Li, Jiangzhong; Jiang, Lei; Fang, Yi; Xu, Xianlin; Hu, Zhangxue; He, Weichun; Yang, Junwei; Dai, Chunsun

2014-11-01

262

MOZ increases p53 acetylation and premature senescence through its complex formation with PML  

PubMed Central

Monocytic leukemia zinc finger (MOZ)/KAT6A is a MOZ, Ybf2/Sas3, Sas2, Tip60 (MYST)-type histone acetyltransferase that functions as a coactivator for acute myeloid leukemia 1 protein (AML1)- and Ets family transcription factor PU.1-dependent transcription. We previously reported that MOZ directly interacts with p53 and is essential for p53-dependent selective regulation of p21 expression. We show here that MOZ is an acetyltransferase of p53 at K120 and K382 and colocalizes with p53 in promyelocytic leukemia (PML) nuclear bodies following cellular stress. The MOZ–PML–p53 interaction enhances MOZ-mediated acetylation of p53, and this ternary complex enhances p53-dependent p21 expression. Moreover, we identified an Akt/protein kinase B recognition sequence in the PML-binding domain of MOZ protein. Akt-mediated phosphorylation of MOZ at T369 has a negative effect on complex formation between PML and MOZ. As a result of PML-mediated suppression of Akt, the increased PML–MOZ interaction enhances p21 expression and induces p53-dependent premature senescence upon forced PML expression. Our research demonstrates that MOZ controls p53 acetylation and transcriptional activity via association with PML. PMID:23431171

Rokudai, Susumu; Laptenko, Oleg; Arnal, Suzzette M.; Taya, Yoichi; Kitabayashi, Issay; Prives, Carol

2013-01-01

263

MOZ increases p53 acetylation and premature senescence through its complex formation with PML.  

PubMed

Monocytic leukemia zinc finger (MOZ)/KAT6A is a MOZ, Ybf2/Sas3, Sas2, Tip60 (MYST)-type histone acetyltransferase that functions as a coactivator for acute myeloid leukemia 1 protein (AML1)- and Ets family transcription factor PU.1-dependent transcription. We previously reported that MOZ directly interacts with p53 and is essential for p53-dependent selective regulation of p21 expression. We show here that MOZ is an acetyltransferase of p53 at K120 and K382 and colocalizes with p53 in promyelocytic leukemia (PML) nuclear bodies following cellular stress. The MOZ-PML-p53 interaction enhances MOZ-mediated acetylation of p53, and this ternary complex enhances p53-dependent p21 expression. Moreover, we identified an Akt/protein kinase B recognition sequence in the PML-binding domain of MOZ protein. Akt-mediated phosphorylation of MOZ at T369 has a negative effect on complex formation between PML and MOZ. As a result of PML-mediated suppression of Akt, the increased PML-MOZ interaction enhances p21 expression and induces p53-dependent premature senescence upon forced PML expression. Our research demonstrates that MOZ controls p53 acetylation and transcriptional activity via association with PML. PMID:23431171

Rokudai, Susumu; Laptenko, Oleg; Arnal, Suzzette M; Taya, Yoichi; Kitabayashi, Issay; Prives, Carol

2013-03-01

264

Dimerization of Human XPA and Formation of XPA2-RPA Protein Complex  

PubMed Central

XPA plays an important role in the DNA damage recognition during human nucleotide excision repair. Here we report that the XPA is a homodimer either in the free state or as a complex with human RPA in solution under normal conditions. The human XPA protein purified from baculovirus-infected sf21 insect cells has a molecular mass of 36 317 Da, as determined by mass spectroscopy. However, the apparent molecular mass of XPA determined by the native gel filtration chromatography was about 71 kDa, suggesting that XPA is a dimer. This observation was supported by a native PFO-PAGE and fluorescence spectroscopy analysis. XPA formed a dimer (XPA2) in a broad range of XPA and NaCl concentrations, and the dimerization was not due to the disulfide bond formation. Furthermore, a titration analysis of the binding of XPA to the human RPA indicated that it was the XPA2 that formed the complex with RPA. Finally, the difference between the mass spectrometric and the calculated masses of XPA implies that the protein contains posttranslational modifications. Taken together, our data suggest that the dimerization of XPA may play an important role in the DNA damage recognition of nucleotide excision repair. PMID:12390028

Yang, Zheng-guan; Mao, Leslie Y.; Zou, Yue; Liu, Yang; Zhang, Jian-Ting

2006-01-01

265

Radiation increases the cellular uptake of exosomes through CD29/CD81 complex formation.  

PubMed

Exosomes mediate intercellular communication, and mesenchymal stem cells (MSC) or their secreted exosomes affect a number of pathophysiologic states. Clinical applications of MSC and exosomes are increasingly anticipated. Radiation therapy is the main therapeutic tool for a number of various conditions. The cellular uptake mechanisms of exosomes and the effects of radiation on exosome-cell interactions are crucial, but they are not well understood. Here we examined the basic mechanisms and effects of radiation on exosome uptake processes in MSC. Radiation increased the cellular uptake of exosomes. Radiation markedly enhanced the initial cellular attachment to exosomes and induced the colocalization of integrin CD29 and tetraspanin CD81 on the cell surface without affecting their expression levels. Exosomes dominantly bound to the CD29/CD81 complex. Knockdown of CD29 completely inhibited the radiation-induced uptake, and additional or single knockdown of CD81 inhibited basal uptake as well as the increase in radiation-induced uptake. We also examined possible exosome uptake processes affected by radiation. Radiation-induced changes did not involve dynamin2, reactive oxygen species, or their evoked p38 mitogen-activated protein kinase-dependent endocytic or pinocytic pathways. Radiation increased the cellular uptake of exosomes through CD29/CD81 complex formation. These findings provide essential basic insights for potential therapeutic applications of exosomes or MSC in combination with radiation. PMID:24667602

Hazawa, Masaharu; Tomiyama, Kenichi; Saotome-Nakamura, Ai; Obara, Chizuka; Yasuda, Takeshi; Gotoh, Takaya; Tanaka, Izumi; Yakumaru, Haruko; Ishihara, Hiroshi; Tajima, Katsushi

2014-04-18

266

Reactivity of thiosemicarbazides with redox active metal ions: controlled formation of coordination complexes versus heterocyclic compounds.  

PubMed

The reactions of 1,1-dimethyl-4-phenylthiosemicarbazide (LH) with Cu(II) and Sn(IV) have been investigated. If THF or methanol is used as solvent with Cu(II), oxidative cyclisation and coupling are observed, yielding a 1,2,4-thiadiazole or a 1,3,4-thiadiazolium salt. SnI(4) is also able to induce oxidative coupling of two thiosemicarbazide ligands, yielding 1,2,4-thiadiazolium or 1,2,4-triazolium salts, with I(3)(-) as the counterion, depending on the reaction conditions. By contrast, reaction of LH with SnI(4) in acetone yields a 1,3-thiazolium salt, with I(-) as counterion. Reaction with Cu(II) salts or SnI(4) in basic media leads to the formation of metal complexes containing two deprotonated thiosemicarbazide ligands. In the reaction of CuCl(2) in water in the presence of acid a complex containing two neutral ligands is obtained. Reactions with SnCl(4) are not able to induce ligand cyclisation, although a coordination compound with two neutral ligands was isolated from methanol. PMID:19180593

López-Torres, Elena; Dilworth, Jonathan R

2009-01-01

267

Spectrophotometric determination of some fluoroquinolone antibacterials by binary complex formation with xanthene dyes.  

PubMed

Two simple, rapid and sensitive spectrophotometric methods for the determination of levofloxacin, norfloxacin and ciprofloxacin have been performed in pure form, pharmaceutical tablets and spiked human urine. Both methods are based on the formation of a binary complex between the drugs and one of the two xanthene dyes, eosin Y or merbromin in aqueous buffered medium. Under the optimum conditions, the binary complexes showed absorption maxima at 547 nm for eosin Y and 545 nm for merbromin. Using eosin Y, the calibration graph was linear over the range 2-8 microg ml(-1) for the three drugs with mean percentage recoveries 99.935 +/- 0.648, 99.973 +/- 0.678 and 100.011 +/- 0.606 for levofloxacin, norfloxacin and ciprofloxacin, respectively. While in case of merbromin, the concentration range was 2-15 microg ml(-1) with mean percentage recoveries 99.960 +/- 0.491, 100.017 +/- 0.510 and 99.980 +/- 0.506 for the three drugs, respectively. The proposed methods were successfully applied to determine these drugs in their tablet formulations and spiked human urine and the results compared favorably to that of reference methods. The suggested methods have the advantage of being applicable for the determination of the three drugs without prior extraction. They are recommended for quality control and routine analysis where time, cost effectiveness and high specificity of analytical techniques are of great importance. PMID:15474058

El-Brashy, Amina Mohamed; El-Sayed Metwally, Mohamed; El-Sepai, Fawzi Abdallah

2004-10-01

268

Labeled EF-Tus for Rapid Kinetic Studies of Pretranslocation Complex Formation.  

PubMed

The universally conserved translation elongation factor EF-Tu delivers aminoacyl(aa)-tRNA in the form of an aa-tRNA·EF-Tu·GTP ternary complex (TC) to the ribosome where it binds to the cognate mRNA codon within the ribosomal A-site, leading to formation of a pretranslocation (PRE) complex. Here we describe preparation of QSY9 and Cy5 derivatives of the variant E348C-EF-Tu that are functional in translation elongation. Together with fluorophore derivatives of aa-tRNA and of ribosomal protein L11, located within the GTPase associated center (GAC), these labeled EF-Tus allow development of two new FRET assays that permit the dynamics of distance changes between EF-Tu and both L11 (Tu-L11 assay) and aa-tRNA (Tu-tRNA assay) to be determined during the decoding process. We use these assays to examine: (i) the relative rates of EF-Tu movement away from the GAC and from aa-tRNA during decoding, (ii) the effects of the misreading-inducing antibiotics streptomycin and paromomycin on tRNA selection at the A-site, and (iii) how strengthening the binding of aa-tRNA to EF-Tu affects the rate of EF-Tu movement away from L11 on the ribosome. These FRET assays have the potential to be adapted for high throughput screening of ribosomal antibiotics. PMID:25126896

Liu, Wei; Kavaliauskas, Darius; Schrader, Jared M; Poruri, Kiran; Birkedal, Victoria; Goldman, Emanuel; Jakubowski, Hieronim; Mandecki, Wlodek; Uhlenbeck, Olke C; Knudsen, Charlotte R; Goldman, Yale E; Cooperman, Barry S

2014-10-17

269

Dynamics of DNA-protein complex formation in rat liver during induction by phenobarbital and triphenyldioxane.  

PubMed

CYP2B gene expression in liver of rats treated with phenobarbital and triphenyldioxane at early stage of induction (40 min-18 h) was studied using electrophoretic mobility shift assay (EMSA) and RT-PCR. During first 6 h after induction, differences in the dynamics of formation of DNA-protein complexes were shown for each inducer. Later (18 h after induction), the intensity pattern of these complexes became the same for both phenobarbital and triphenyldioxane treated animals. This suggests the existence of specific signaling for each inducer only in early stages of CYP2B activation. Increase in nuclear protein (possible transcription factor) binding to Barbie-box regulatory sequence of CYP2B genes was accompanied by their increased expression. Thus, we have demonstrated for the first time that early stages of induction (40 min and 3 h after administration of phenobarbital and triphenyldioxane, respectively) are accompanied by activation of nuclear proteins that can bind to Barbie-box element of CYP2B. Although various chemical inducers cause distinct activation of such binding, this process involves activation of gene transcription. PMID:15527410

Pustylnyak, V O; Zacharova, L Yu; Gulyaeva, L F; Lyakhovich, V V; Slynko, N M

2004-10-01

270

A SPITZER VIEW OF STAR FORMATION IN THE CYGNUS X NORTH COMPLEX  

SciTech Connect

We present new images and photometry of the massive star-forming complex Cygnus X obtained with the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer for Spitzer (MIPS) on board the Spitzer Space Telescope. A combination of IRAC, MIPS, UKIRT Deep Infrared Sky Survey, and Two Micron All Sky Survey data are used to identify and classify young stellar objects (YSOs). Of the 8231 sources detected exhibiting infrared excess in Cygnus X North, 670 are classified as class I and 7249 are classified as class II. Using spectra from the FAST Spectrograph at the Fred L. Whipple Observatory and Hectospec on the MMT, we spectrally typed 536 sources in the Cygnus X complex to identify the massive stars. We find that YSOs tend to be grouped in the neighborhoods of massive B stars (spectral types B0 to B9). We present a minimal spanning tree analysis of clusters in two regions in Cygnus X North. The fraction of infrared excess sources that belong to clusters with {>=}10 members is found to be 50%-70%. Most class II objects lie in dense clusters within blown out H II regions, while class I sources tend to reside in more filamentary structures along the bright-rimmed clouds, indicating possible triggered star formation.

Beerer, I. M. [Department of Astronomy, University of California, Berkeley, CA (United States); Koenig, X. P.; Hora, J. L.; Keto, E.; Smith, H. A.; Fazio, G. G. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA (United States); Gutermuth, R. A. [Smith College, Northampton, MA (United States); Bontemps, S.; Schneider, N. [Observatoire de Bordeaux, BP 89, 33270 Floirac (France); Megeath, S. T. [Department of Physics and Astronomy, University of Toledo, Toledo, OH (United States); Motte, F. [AIM/SAp, CEA-Saclay, 91191 Gif Sur Yvette Cedex (France); Carey, S. [Spitzer Science Center, Pasadena, CA (United States); Simon, R. [I. Physik. Institut, Universitaet zu Koeln, 50937 Koeln (Germany); Allen, L. E. [NOAO, 950 North Cherry Avenue, Tucson, AZ (United States); Kraemer, K. E.; Price, S. [Air Force Research Laboratory, Hanscom AFB, MA (United States); Mizuno, D. [Institute for Scientific Research, Boston College, Boston, MA (United States); Adams, J. D. [Cornell University, Department of Radiophysics Space Research, Ithaca, NY (United States); Hernandez, J. [Centro de Investigaciones de AstronomIa, Apdo. Postal 264, Merida 5101-A (Venezuela, Bolivarian Republic of); Lucas, P. W. [Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield (United Kingdom)

2010-09-01

271

Complement C1q formation of immune complexes with milk caseins and wheat glutens in schizophrenia  

PubMed Central

Immune system factors including complement pathway activation are increasingly linked to the etiology and pathophysiology of schizophrenia. Complement protein, C1q, binds to and helps to clear immune complexes composed of immunoglobulins coupled to antigens. The antigenic stimuli for C1q activation in schizophrenia are not known. Food sensitivities characterized by elevated IgG antibodies to bovine milk caseins and wheat glutens have been reported in individuals with schizophrenia. Here, we examined the extent to which these food products might comprise the antigen component of complement C1q immune complexes in individuals with recent onset schizophrenia (n=38), non-recent onset schizophrenia (n=61) and non-psychiatric controls (n=63). C1q seropositivity was significantly associated with both schizophrenia groups (recent onset, odds ratio (OR)=8.02, p?0.008; non-recent onset, OR=3.15, p?0.03) compared to controls (logistic regression models corrected for age, sex, race and smoking status). Casein- and/or gluten-IgG binding to C1q was significantly elevated in the non-recent onset group compared to controls (OR=4.36, p?0.01). Significant amounts of C1q-casein/gluten-related immune complexes and C1q correlations with a marker for gastrointestinal inflammation in non-recent onset schizophrenia suggests a heightened rate of food antigens in the systemic circulation, perhaps via a disease-associated altered intestinal permeability. In individuals who are in the early stages of disease onset, C1q activation may reflect the formation of immune complexes with non-casein- or non-gluten-related antigens, the presence of C1q autoantibodies, and/or a dissociated state of immune complex components. In conclusion, complement activation may be a useful biomarker to diagnose schizophrenia early during the course of the disease. Future prospective studies should evaluate the impacts of casein- and gluten-free diets on C1q activation in schizophrenia. PMID:22801085

Severance, Emily G.; Gressitt, Kristin; Halling, Meredith; Stallings, Cassie R.; Origoni, Andrea E.; Vaughan, Crystal; Khushalani, Sunil; Alaedini, Armin; Dupont, Didier; Dickerson, Faith B.; Yolken, Robert H.

2012-01-01

272

Synthesis of mono(dinitrogen) complexes of molybdenum. Formation of ammonia and hydrazine  

SciTech Connect

The synthesis and reactivity of a series of mono-N/sub 2/ complexes of molybdenum are reported. Reduction of MoCl/sub 3/(triphos), where triphos = PhP(CH/sub 2/CH/sub 2/PPh/sub 2/)/sub 2/, with sodium amalgam in the presence of 2L or L/sub 2/ and with a regulated amount of N/sub 2/ led to the formation of Mo(N/sub 2/)(triphos)(L/sub 2/) (1-5): 1, L = PMe/sub 2/Ph; 2, L/sub 2/ = Me/sub 2/PCH/sub 2/PMe/sub 2/, dmpm; 3, L/sub 2/ = 1,2-(Me/sub 2/As)/sub 2/C/sub 6/H/sub 4/, diars; 4, L/sub 2/ = Ph/sub 2/PCH/sub 2/PPh/sub 2/, dppm; 5, L/sub 2/ = Ph/sub 2/PCH/sub 2/CH/sub 2/PPh/sub 2/, dppe. Complexes 3 and 5 were each a mixture of two isomeric mono-N/sub 2/ complexes. Complexes 1-5 reacted with excess HX (X = Br, Cl) to afford varying yields of ammonia, hydrazine, and N/sub 2/ (and some H/sub 2/). Loss of N/sub 2/ occurred readily from 1 when it was evacuate in the solid state to give 7. Five-coordinate 7 reacted with H/sub 2/, CO, and C/sub 2/H/sub 4/ in the solid state to form MoH/sub 2/(triphos)(PMe/sub 2/Ph)/sub 2/ (8), Mo(CO)(triphos)(PMe/sub 2/Ph)/sub 2/ (9), and Mo(C/sub 2/H/sub 4/)(triphos)(PMe/sub 2/Ph)/sub 2/ (10), respectively. Reaction of solids 7, 8, and 10 with N/sub 2/ regenerated 1. Structural assignments of the new complexes are based upon /sup 31/P and /sup 1/H NMR spectral data. Triphos is shown to adopt both fac and mer configurations. 33 references, 1 table.

George, T.A.; Tisdale, R.C.

1988-08-24

273

The earliest phases of high-mass star formation: the NGC 6334-NGC 6357 complex  

NASA Astrophysics Data System (ADS)

Context. Our knowledge of high-mass star formation has been mainly based on follow-up studies of bright sources found by IRAS, and has thus been incomplete for its earliest phases, which are inconspicuous at infrared wavelengths. With a new generation of powerful bolometer arrays, unbiased large-scale surveys of nearby high-mass star-forming complexes now search for the high-mass analog of low-mass cores and class 0 protostars. Aims: Following the pioneering study of Cygnus X, we investigate the star-forming region NGC 6334-NGC 6357 (~1.7 kpc). Methods: We study the complex NGC 6334-NGC 6357 in an homogeneous way following the previous work of Motte and collaborators. We used the same method to extract the densest cores which are the most likely sites for high-mass star formation. We analyzed the SIMBA/SEST 1.2 mm data presented in Munoz and coworkers, which covers all high-column density areas (A v ? 15 mag) of the NGC 6334-NGC 6357 complex and extracted dense cores following the method used for Cygnus X. We constrain the properties of the most massive dense cores (M > 100 M_?) using new molecular line observations (as SiO, N2H+,H13CO+, HCO+ (1-0) and CH3CN) with Mopra and a complete cross-correlation with infrared databases (MSX, GLIMPSE, MIPSGAL) and literature. Results: We extracted 163 massive dense cores of which 16 are more massive than 200 M_?. These high-mass dense cores have a typical FWHM size of 0.37 pc, an average mass of M ~ 600 M_?, and a volume-averaged density of ~ 1.5 × 105 cm-3. Among these massive dense cores, 6 are good candidates for hosting high-mass infrared-quiet protostars, 9 cores are classified as high-luminosity infrared protostars, and we find only one high-mass starless clump (~0.3 pc, ~ 4 × 104 cm-3) that is gravitationally bound. Conclusions: Since our sample is derived from a single molecular complex and covers every embedded phase of high-mass star formation, it provides a statistical estimate of the lifetime of massive stars. In contrast to what is found for low-mass class 0 and class I phases, the infrared-quiet protostellar phase of high-mass stars may last as long as their more well known high-luminosity infrared phase. As in Cygnus X, the statistical lifetime of high-mass protostars is shorter than found for nearby, low-mass star-forming regions which implies that high-mass pre-stellar and protostellar cores are in a dynamic state, as expected in a molecular cloud where turbulent and/or dynamical processes dominate. Based on observations made with Mopra telescope. The Mopra telescope is part of the Australia Telescope which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.Table 1 and Appendix are only available in electronic form at http://www.aanda.orgProfiles as FITS files are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A55

Russeil, D.; Zavagno, A.; Motte, F.; Schneider, N.; Bontemps, S.; Walsh, A. J.

2010-06-01

274

SPITZER ANALYSIS OF H II REGION COMPLEXES IN THE MAGELLANIC CLOUDS: DETERMINING A SUITABLE MONOCHROMATIC OBSCURED STAR FORMATION INDICATOR  

SciTech Connect

H II regions are the birth places of stars, and as such they provide the best measure of current star formation rates (SFRs) in galaxies. The close proximity of the Magellanic Clouds allows us to probe the nature of these star forming regions at small spatial scales. To study the H II regions, we compute the bolometric infrared flux, or total infrared (TIR), by integrating the flux from 8 to 500 {mu}m. The TIR provides a measure of the obscured star formation because the UV photons from hot young stars are absorbed by dust and re-emitted across the mid-to-far-infrared (IR) spectrum. We aim to determine the monochromatic IR band that most accurately traces the TIR and produces an accurate obscured SFR over large spatial scales. We present the spatial analysis, via aperture/annulus photometry, of 16 Large Magellanic Cloud (LMC) and 16 Small Magellanic Cloud (SMC) H II region complexes using the Spitzer Space Telescope's IRAC (3.6, 4.5, 8 {mu}m) and MIPS (24, 70, 160 {mu}m) bands. Ultraviolet rocket data (1500 and 1900 A) and SHASSA H{alpha} data are also included. All data are convolved to the MIPS 160 {mu}m resolution (40 arcsec full width at half-maximum), and apertures have a minimum radius of 35''. The IRAC, MIPS, UV, and H{alpha} spatial analysis are compared with the spatial analysis of the TIR. We find that nearly all of the LMC and SMC H II region spectral energy distributions (SEDs) peak around 70 {mu}m at all radii, from {approx}10 to {approx}400 pc from the central ionizing sources. As a result, we find the following: the sizes of H II regions as probed by 70 {mu}m are approximately equal to the sizes as probed by TIR ({approx}70 pc in radius); the radial profile of the 70 {mu}m flux, normalized by TIR, is constant at all radii (70 {mu}m {approx} 0.45TIR); the 1{sigma} standard deviation of the 70 {mu}m fluxes, normalized by TIR, is a lower fraction of the mean (0.05-0.12 out to {approx}220 pc) than the normalized 8, 24, and 160 {mu}m normalized fluxes (0.12-0.52); and these results are the same for the LMC and the SMC. From these results, we argue that 70 {mu}m is the most suitable IR band to use as a monochromatic obscured star formation indicator because it most accurately reproduces the TIR of H II regions in the LMC and SMC and over large spatial scales. We also explore the general trends of the 8, 24, 70, and 160 {mu}m bands in the LMC and SMC H II region SEDs, radial surface brightness profiles, sizes, and normalized (by TIR) radial flux profiles. We derive an obscured SFR equation that is modified from the literature to use 70 {mu}m luminosity, SFR(M {sub sun} yr{sup -1}) = 9.7(0.7) x 10{sup -44} L {sub 70}(ergs s{sup -1}), which is applicable from 10 to 300 pc distance from the center of an H II region. We include an analysis of the spatial variations around H II regions between the obscured star formation indicators given by the IR and the unobscured star formation indicators given by UV and H{alpha}. We compute obscured and unobscured SFRs using equations from the literature and examine the spatial variations of the SFRs around H II regions.

Lawton, B.; Gordon, K. D.; Meixner, M.; Sewilo, M.; Shiao, B. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Babler, B.; Bracker, S.; Meade, M. [Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706 (United States); Block, M.; Engelbracht, C. W.; Misselt, K. [Steward Observatory, University of Arizona, 933 North Cherry Ave., Tucson, AZ 85721 (United States); Bolatto, A. D. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Carlson, L. R. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD (United States); Hora, J. L.; Robitaille, T. [Harvard-Smithsonian, CfA, 60 Garden St., MS 65, Cambridge, MA 02138-1516 (United States); Indebetouw, R. [Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903-0818 (United States); Madden, S. C. [Service d'Astrophysique, CEA/Saclay, l'Orme des Merisiers, 91191 Gif-sur-Yvette (France); Oey, M. S. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042 (United States); Oliveira, J. M. [School of Physical and Geographical Sciences, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom); Vijh, U. P., E-mail: lawton@stsci.ed, E-mail: kgordon@stsci.ed [Ritter Astrophysical Research Center, University of Toledo, Toledo, OH 43606 (United States)

2010-06-10

275

Double-decker phthalocyanine complex: Scanning tunneling microscopy study of film formation and spin properties  

NASA Astrophysics Data System (ADS)

We review recent studies of double-decker and triple-decker phthalocyanine (Pc) molecules adsorbed on surfaces in terms of the bonding configuration, electronic structure and spin state. The Pc molecule has been studied extensively in surface science. A Pc molecule can contain various metal atoms at the center, and the class of the molecule is called as metal phthalocyanine (MPc). If the center metal has a large radius, like as lanthanoid metals, it becomes difficult to incorporate the metal atom inside of the Pc ring. Pc ligands are placed so as to sandwich the metal atom, where the metal atom is placed out of the Pc plane. The molecule in this configuration is called as a multilayer-decker Pc molecule. After the finding that the double-decker Pc lanthanoid complex shows single-molecule magnet (SMM) behavior, it has attracted a large attention. This is partly due to a rising interest for the ‘molecular spintronics’, in which the freedoms of spin and charge of an electron are applied to the quantum process of information. SMMs represent a class of compounds in which a single molecule behaves as a magnet. The reported blocking temperature, below which a single SMM molecule works as an quantum magnet, has been increasing with the development in the molecular design and synthesis techniques of multiple-decker Pc complex. However, even the bulk properties of these molecules are promising for the use of electronic materials, the films of multi-decker Pc molecules is less studied than those for the MPc molecules. An intriguing structural property is expected for the multi-decker Pc molecules since the Pc planes are linked by metal atoms. This gives an additional degree of freedom to the rotational angle between the two Pc ligands, and they can make a wheel-like symmetric rotation. Due to a simple and well-defined structure of a multi-decker Pc complex, the molecule can be a model molecule for molecular machine studies. The multi-decker Pc molecules can provide interesting spin configuration. The center metal atom, including a lanthanoid metal of Tb, tends to be 3+ cation, while the Pc ligand to be 2- anion. This realizes two-spin system, in which spins from 4f electrons and ? radical coexist. Though the spins of 4f orbitals of those molecules have been studied, the importance of the ? radicals has been highlighted recently from the measurement of electronic conductance properties of these molecules. In this article, recent researches on multi-decker Pc molecules are reviewed. The manuscript is organized with groups of chapters as follows: (1) Film formation, (2) Spin of TbPc2 film and Kondo resonance observation, (3) Rotation of double-decker Pc complex and chemical modification for spin control, (4) Device formation using double-decker Pc complex.

Komeda, Tadahiro; Katoh, Keiichi; Yamashita, Masahiro

2014-05-01

276

Mercury(II) Complex Formation With Glutathione in Alkaline Aqueous Solution  

SciTech Connect

The structure and speciation of the complexes formed between mercury(II) ions and glutathione (GSH = L-glutamyl-L-cysteinyl-glycine) have been studied for a series of alkaline aqueous solutions (C{sub Hg{sup 2+}} {approx} 18 mmol dm{sup -3} and C{sub GSH} = 40-200 mmol dm{sup -3} at pH {approx} 10.5) by means of extended X-ray absorption fine structure (EXAFS) and {sup 199}Hg NMR spectroscopy at ambient temperature. The dominant complexes are [Hg(GS){sub 2}]{sup 4-} and [Hg(GS){sub 3}]{sup 7-}, with mean Hg-S bond distances of 2.32(1) and 2.42(2) {angstrom} observed in digonal and trigonal Hg-S coordination, respectively. The proportions of the Hg{sup 2+}-glutathione complexes were evaluated by fitting linear combinations of model EXAFS oscillations representing each species to the experimental EXAFS spectra. The [Hg(GS){sub 4}]{sup 10-} complex, with four sulfur atoms coordinated at a mean Hg-S bond distance of 2.52(2) {angstrom}, is present in minor amounts (<30%) in solutions containing a large excess of glutathione (C{sub GSH} {ge} 160 mmol dm{sup -3}). Comparable alkaline mercury(II) cysteine (H{sub 2}Cys) solutions were also investigated and a reduced tendency to form higher complexes was observed, because the deprotonated amino group of Cys{sup 2-} allows the stable [Hg(S,N-Cys){sub 2}]{sup 2-} chelate to form. The effect of temperature on the distribution of the Hg{sup 2+}-glutathione complexes was studied by comparing the EXAFS spectra at ambient temperature and at 25 K of a series of glycerol/water (33/67, v/v) frozen glasses with and C{sub Hg{sup 2+}} {approx} 7 mmol dm{sup -3} and C{sub GSH} = 16-81 mmol dm{sup -3}. Complexes with high Hg-S coordination numbers, [Hg(GS){sub 3}]{sup 7-} and [Hg(GS){sub 4}]{sup 10-}, became strongly favored when just a moderate excess of glutathione (C{sub GSH} {ge} 28 mmol dm{sup -3}) was used in the glassy samples, as expected for a stepwise exothermic bond formation. Addition of glycerol had no effect on the Hg(II)-glutathione speciation, as shown by the similarity of the EXAFS spectra obtained at room temperature for two parallel series of Hg(II)-glutathione solutions with C{sub Hg{sup 2+}} {approx} 7 mmol dm{sup -3}, with and without 33% glycerol. Also, the {sup 199}Hg NMR chemical shifts of a series of {approx} 18 mmol dm{sup -3} mercury(II) glutathione solutions with 33% glycerol were not significantly different from those of the corresponding series in aqueous solution.

Mah, V.; Jalilehvand, F.

2009-05-19

277

Temperature and dose dependence of defect complex formation with ion implanted Mn\\/Fe in ZnO  

Microsoft Academic Search

57Fe Mössbauer spectroscopy following ion implantation of radioactive 57Mn+ ( T1\\/2=85.4s) has been applied to study the formation of Fe\\/Mn implantation-induced defects in ZnO at temperatures between 319 and 390K. The formation of ferric iron–vacancy complexes is found to depend strongly on the implanted dose and to be faster and more efficient at higher temperatures. The results at these temperatures

T. E. Mølholt; R. Mantovan; H. P. Gunnlaugsson; K. Bharuth-Ram; M. Fanciulli; H. P. Gíslason; K. Johnston; Y. Kobayashi; G. Langouche; H. Masenda; D. Naidoo; S. Ólafsson; R. Sielemann; G. Weyer

2009-01-01

278

The formation of host-guest complexes between surfactants and cyclodextrins.  

PubMed

Cyclodextrins are able to act as host molecules in supramolecular chemistry with applications ranging from pharmaceutics to detergency. Among guest molecules surfactants play an important role with both fundamental and practical applications. The formation of cyclodextrin/surfactant host-guest compounds leads to an increase in the critical micelle concentration and in the solubility of surfactants. The possibility of changing the balance between several intermolecular forces, and thus allowing the study of, e.g., dehydration and steric hindrance effects upon association, makes surfactants ideal guest molecules for fundamental studies. Therefore, these systems allow for obtaining a deep insight into the host-guest association mechanism. In this paper, we review the influence on the thermodynamic properties of CD-surfactant association by highlighting the effect of different surfactant architectures (single tail, double-tailed, gemini and bolaform), with special emphasis on cationic surfactants. This is complemented with an assessment of the most common analytical techniques used to follow the association process. The applied methods for computation of the association stoichiometry and stability constants are also reviewed and discussed; this is an important point since there are significant discrepancies and scattered data for similar systems in the literature. In general, the surfactant-cyclodextrin association is treated without reference to the kinetics of the process. However, there are several examples where the kinetics of the process can be investigated, in particular those where volumes of the CD cavity and surfactant (either the tail or in special cases the head group) are similar in magnitude. This will also be critically reviewed. PMID:24011696

Valente, Artur J M; Söderman, Olle

2014-03-01

279

Assessment of the CCSD and CCSD(T) Coupled-Cluster Methods in Calculating Heats of Formation for Zn Complexes  

PubMed Central

Heats of formation were calculated using coupled-cluster methods for a series of zinc complexes. The calculated values were evaluated against previously conducted computational studies using density functional methods as well as experimental values. Heats of formation for nine neutral ZnXn complexes [X = -Zn, -H, -O, -F2, -S, -Cl, -Cl2, -CH3, (-CH3)2] were determined at the CCSD and CCSD(T) levels using the 6–31G** and TZVP basis sets, as well as the LANL2DZ-6–31G** (LACVP**) and LANL2DZ-TZVP hybrid basis sets. The CCSD(T)/6–31G** level of theory was found to predict the heat of formation for the non-alkyl Zn complexes most accurately. The alkyl Zn species were problematic in that none of the methods that were tested accurately predicted the heat of formation for these complexes. For the seven non-alkyl species, the CCSD(T)/6–31G** level of theory was shown to predict the most accurate heat of formation values. In instances where experimental geometric parameters were available, these were most accurately predicted by the CCSD/6–31G** level of theory; going to CCSD(T) did not improve agreement with the experimental values. PMID:19691272

Weaver, Michael N.; Yang, Yue

2010-01-01

280

Molecular constants for the I1Pig and J1Deltag states of the 3d complex in H2, HD, and D2  

Microsoft Academic Search

The experimental rovibronic energies of the 3dpi I1Pig- and 3ddelta J1Deltag- states of H2 and D2 (v = 0-4 and N = 1-11) have been fitted by rovibronic constants, including L-uncoupling through constants BvPiDelta and DvPiDelta. Comparison of the constants obtained for H2 and D2 yields information on the Born-Oppenheimer and adiabatic electronic energies TeBO and TeAD, and on the

P. Quadrelli; K. Dressler

1981-01-01

281

Investigation of plague lipopolysaccharide complex formation with artificial phospholipid vesicles by elastic laser radiation scattering  

NASA Astrophysics Data System (ADS)

This paper describes the investigation of incorporation processes of the plague lipopolysaccharide (LPS) into artificial phospholipid vesicles (PLV) on the basis of elastic laser radiation scattering. For this purpose, the angular light scattering dependencies of PLV suspensions, containing various LPS concentrations (0 - 5 mg/ml), were measured using the polarization nephelometer. The design of the polarization nephelometer and the measurement technique are described in detail. Measuring results are compared with electron microscopy data. The most pronounced variation as a result of LPS incorporation into PLV appeared to be the light scattering integral intensity (LSII) at angles exceeding 100. It is shown that the LPS adding into the PLV suspension causes the LSII to increase by a factor 2 - 6 for a LPS concentration range from 0.5 to 5 mg/ml as compared with `empty' PLV. Proceeding from the electron microscopy data it was found that the LSII increase, in general case, is conditioned by variation of the PLV membrane refraction index and formation of PLV aggregates. It was shown that the LSII measurement for the PLV suspension containing LPS can be used as a qualitative express analysis for the LPS incorporation into PLV as well as procedure for determination of the aggregate formation stage from PLV. The LPS of the plague, which as determinants being common for various gram-negative bacteria, is of great interest from the viewpoint of creating preparations for prophylactic measures against the endotoxin infections. However, the LPS toxicity due to the lipid A presence is a disadvantage of this weak antigen. Incorporation of the LPS int bilayer phospholipid membranes leads to its lower toxicity and higher immunization ability. The immunization ability and toxicity of the LPS complexes with bilayer membranes depend essentially on the LPS quantity sorbed in the membrane, as well as on the shapes and sizes of aggregates formed by the LPS and membranes in water environment.

Gusev, V. V.; Guseva, N. P.; Tatarintsev, S. N.

1995-01-01

282

Swarming and complex pattern formation in Paenibacillus vortex studied by imaging and tracking cells  

PubMed Central

Background Swarming motility allows microorganisms to move rapidly over surfaces. The Gram-positive bacterium Paenibacillus vortex exhibits advanced cooperative motility on agar plates resulting in intricate colonial patterns with geometries that are highly sensitive to the environment. The cellular mechanisms that underpin the complex multicellular organization of such a simple organism are not well understood. Results Swarming by P. vortex was studied by real-time light microscopy, by in situ scanning electron microscopy and by tracking the spread of antibiotic-resistant cells within antibiotic-sensitive colonies. When swarming, P. vortex was found to be peritrichously flagellated. Swarming by the curved cells of P. vortex occurred on an extremely wide range of media and agar concentrations (0.3 to 2.2% w/v). At high agar concentrations (> 1% w/v) rotating colonies formed that could be detached from the main mass of cells by withdrawal of cells into the latter. On lower percentage agars, cells moved in an extended network composed of interconnected "snakes" with short-term collision avoidance and sensitivity to extracts from swarming cells. P. vortex formed single Petri dish-wide "supercolonies" with a colony-wide exchange of motile cells. Swarming cells were coupled by rapidly forming, reversible and non-rigid connections to form a loose raft, apparently connected via flagella. Inhibitors of swarming (p-Nitrophenylglycerol and Congo Red) were identified. Mitomycin C was used to trigger filamentation without inhibiting growth or swarming; this facilitated dissection of the detail of swarming. Mitomycin C treatment resulted in malcoordinated swarming and abortive side branch formation and a strong tendency by a subpopulation of the cells to form minimal rotating aggregates of only a few cells. Conclusion P. vortex creates complex macroscopic colonies within which there is considerable reflux and movement and interaction of cells. Cell shape, flagellation, the aversion of cell masses to fuse and temporary connections between proximate cells to form rafts were all features of the swarming and rotation of cell aggregates. Vigorous vortex formation was social, i.e. required > 1 cell. This is the first detailed examination of the swarming behaviour of this bacterium at the cellular level. PMID:18298829

Ingham, Colin J; Jacob, Eshel Ben

2008-01-01

283

MutY DNA glycosylase: base release and intermediate complex formation.  

PubMed

MutY protein, a DNA glycosylase found in Escherichia coli, recognizes dA:dG, dA:8-oxodG, and dA:dC mismatches in duplex DNA, excising the adenine moiety. We have investigated the mechanism of action of MutY, addressing several points of disagreement raised by previous studies of this enzyme. MutY forms a covalent intermediate with its DNA substrate but does not catalyze strand cleavage. The covalent intermediate has a half-life of approximately 2.6 h, 2 orders of magnitude greater than the half-life of Schiff bases formed when E. coli formamidopyrimidine-DNA glycosylase (Fpg) and endonuclease III react with their respective substrates. The covalent complex between MutY and its DNA substrate involves Lys-142; however, the position of this residue in the presumptive active site differs from that of catalytic residues involved in Schiff base formation associated with endonuclease III and related DNA glycosylases/AP lyases. MutY converts DNA duplexes containing the dA:8-oxodG mispair to a product containing an abasic site; heat-induced cleavage of this product may account for the several reports in the literature that ascribe AP lyase activity to MutY. The MutY-DNA intermediate complex is highly stable and hinders access by Fpg to DNA, thereby avoiding a double-strand break. Cross-linking of MutY to DNA may play an important role in the regulation of base excision repair. PMID:9730810

Zharkov, D O; Grollman, A P

1998-09-01

284

Solvent-induced deuterium isotope effects on 19F chemical shifts of some substituted fluorobenzenes. Formation of inclusion complexes  

NASA Astrophysics Data System (ADS)

Deuterium solvent-induced isotope effects on 19F NMR chemical shifts of a number of fluorophenols, fluorobenzenes, and fluorubenzoic acid derivatives have been determined along with their 19F chemical shifts in water. Solvent-induced isotope effects of fluorine compounds complexed with ?- and ?-cyclodextrin and deoxycholate have also been investigated. Binding constants and bound chemical shifts of the inclusion complexes with ?-cyclodextrins are determined. These model studies demonstrate that the SIIS decrease with increased inclusion and that the degree of exposure may be determined using SIIS.

Hansen, Poul E.; Dettman, Heather D.; Sykes, Brian D.

285

Analysis of the Enhanced Stability of R(+)-Alpha Lipoic Acid by the Complex Formation with Cyclodextrins  

PubMed Central

R(+)-alpha lipoic acid (RALA) is one of the cofactors for mitochondrial enzymes and, therefore, plays a central role in energy metabolism. RALA is unstable when exposed to low pH or heat, and therefore, it is difficult to use enantiopure RALA as a pharma- and nutra-ceutical. In this study, we have aimed to stabilize RALA through complex formation with cyclodextrins (CDs). ?-CD, ?-CD and ?-CD were used for the formation of these RALA-CD complexes. We confirmed the complex formation using differential scanning calorimetry and showed by using HPLC analysis that complexed RALA is more stable than free RALA when subjected to humidity and high temperature or acidic pH conditions. Scanning electron microscopy studies showed that the particle size and shape differed depending on the cyclodextrin used for complexation. Further, the complexes of CD and RALA showed a different particle size distribution pattern compared with that of CD itself or that of the physical mixture of RALA and CD. PMID:23434662

Ikuta, Naoko; Sugiyama, Hironori; Shimosegawa, Hiroshi; Nakane, Rie; Ishida, Yoshiyuki; Uekaji, Yukiko; Nakata, Daisuke; Pallauf, Kathrin; Rimbach, Gerald; Terao, Keiji; Matsugo, Seiichi

2013-01-01

286

Analysis of the enhanced stability of r(+)-alpha lipoic Acid by the complex formation with cyclodextrins.  

PubMed

R(+)-alpha lipoic acid (RALA) is one of the cofactors for mitochondrial enzymes and, therefore, plays a central role in energy metabolism. RALA is unstable when exposed to low pH or heat, and therefore, it is difficult to use enantiopure RALA as a pharma- and nutra-ceutical. In this study, we have aimed to stabilize RALA through complex formation with cyclodextrins (CDs). ?-CD, ?-CD and ?-CD were used for the formation of these RALA-CD complexes. We confirmed the complex formation using differential scanning calorimetry and showed by using HPLC analysis that complexed RALA is more stable than free RALA when subjected to humidity and high temperature or acidic pH conditions. Scanning electron microscopy studies showed that the particle size and shape differed depending on the cyclodextrin used for complexation. Further, the complexes of CD and RALA showed a different particle size distribution pattern compared with that of CD itself or that of the physical mixture of RALA and CD. PMID:23434662

Ikuta, Naoko; Sugiyama, Hironori; Shimosegawa, Hiroshi; Nakane, Rie; Ishida, Yoshiyuki; Uekaji, Yukiko; Nakata, Daisuke; Pallauf, Kathrin; Rimbach, Gerald; Terao, Keiji; Matsugo, Seiichi

2013-01-01

287

Inducer effect on the complex formation between rat liver nuclear proteins and cytochrome P450 2B gene regulatory elements.  

PubMed

DNA gel retardation assay has been applied to the investigation of complexes between rat liver nuclear proteins and Barbie box positive regulatory element of cytochrome P450 2B (CYP2B) genes. The intensities of B1 and B2 bands detected in the absence of an inducer increased after 30 min protein incubation with phenobarbital (PB) or triphenyldioxane (TPD), but not with 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOPOB). In addition, a new complex (B3 band) was for the first time detected under induction by PB, TPD, and TCPOPOB. Increase in the incubation time up to 2 h facilitated the formation of other new complexes (B4 and B5 bands), which were detected only in the presence of TPD. The use of [3H]TPD in hybridization experiments revealed that this inducer, capable of binding to Barbie box DNA, is also present in B4 and B5 complexes. It is probable that the investigated compounds activate the same proteins at the initial induction steps, which correlates with the formation of B1, B2, and B3 complexes. The further induction step might be inducer-specific, as indicated by the formation of B4 and B5 complexes in the presence of TPD only. Thus, the present data suggest the possibility of specific gene activation signaling pathways that are dependent on a particular inducer. PMID:12387719

Duzhak, T G; Schwartz, E I; Gulyaeva, L F; Lyakhovich, V V

2002-09-01

288

A peroxynitrite complex of copper: formation from a copper-nitrosyl complex, transformation to nitrite and exogenous phenol oxidative coupling or nitration  

PubMed Central

Reaction of nitrogen monoxide with a copper(I) complex possessing a tridentate alkylamine ligand gives a Cu(I)–(·NO) adduct, which when exposed to dioxygen generates a peroxynitrite (O=NOO?)–Cu(II) species. This undergoes thermal transformation to produce a copper(II) nitrito (NO2?) complex and 0.5 mol equiv O2. In the presence of a substituted phenol, the peroxynitrite complex effects oxidative coupling, whereas addition of chloride ion to dissociate the peroxynitrite moiety instead leads to phenol ortho nitration. Discussions include the structures (including electronic description) of the copper–nitrosyl and copper–peroxynitrite complexes and the formation of the latter, based on density functional theory calculations and accompanying spectroscopic data. PMID:19662443

Park, Ga Young; Deepalatha, Subramanian; Puiu, Simona C.; Lee, Dong-Heon; Mondal, Biplab; Sarjeant, Amy A. Narducci; del Rio, Diego; Pau, Monita Y. M.; Solomon, Edward I.; Karlin, Kenneth D.

2010-01-01

289

Oxy radical formation during redox cycling of the bleomycin-iron (III) complex by NADPH-cytochrome P-450 reductase.  

PubMed

Bleomycin was aerobically incubated with FeCl3, NADPH, isolated rat-liver microsomal cytochrome P-450 reductase and methional. The conversion of methional to ethene, which indicates oxy radicals, was determined. Ethene formation depended on oxygen, NADPH, FeCl3 and the enzyme. About equimolar concentrations of bleomycin and FeCl3 resulted in optimal ethene formation. Dimethyl sulfoxide, mannitol, glycerol, glutathione and glutathione disulfide inhibited ethene formation. These results indicate that oxy radicals are formed after reduction of the bleomycin-Fe-complex by NADPH-cytochrome P-450 reductase. PMID:2412562

Mahmutoglu, I; Kappus, H

1985-09-01

290

Monitoring the formation of dynamic G-protein-coupled receptor-protein complexes in living cells.  

PubMed

GPCRs (G-protein-coupled receptors) play an extremely important role in transducing extracellular signals across the cell membrane with high specificity and sensitivity. They are central to many of the body's endocrine and neurotransmitter pathways, and are consequently a major drug target. It is now clear that GPCRs interact with a range of proteins, including other GPCRs. Identifying and elucidating the function of such interactions will significantly enhance our understanding of cellular function, with the promise of new and improved pharmaceuticals. Biophysical techniques involving resonance energy transfer, namely FRET (fluorescence resonance energy transfer) and BRET (bioluminescence resonance energy transfer), now enable us to monitor the formation of dynamic GPCR-protein complexes in living cells, in real time. Their use has firmly established the concept of GPCR oligomerization, as well as demonstrating GPCR interactions with GPCR kinases, beta-arrestins, adenylate cyclase and a subunit of an inwardly rectifying K+ channel. The present review examines recent technological advances and experimental applications of FRET and BRET, discussing particularly how they have been adapted to extract an ever-increasing amount of information about the nature, specificity, stoichiometry, kinetics and agonist-dependency of GPCR-protein interactions. PMID:15504107

Pfleger, Kevin D G; Eidne, Karin A

2005-02-01

291

Floatation-spectrophotometric Determination of Thorium, Using Complex Formation with Eriochrome Cyanine R  

PubMed Central

A novel and sensitive floatation-spectrophotometric method is presented for determination of trace amounts of thorium in water samples. The method is based on the ion-associated formation between thorium, Eriochrome cyanine R and Brij-35 at pH = 4 media. The complex was floated in the interface of the aqueous phase and n-hexane by vigorous shaking. After removing the aqueous phase the floated particles were dissolved in methanol and the absorbance was measured at 607 nm. The influence of different important parameters such as Eriochrome cyanine R and surfactants concentration, pH, volume of n-hexane, standing time and interfering ions were evaluated. Under optimized conditions the calibration graph was linear in the range of 6–230 ng mL?1 of thorium with a correlation coefficient of 0.9985. The limit of detections (LOD), based on signal to noise ratio (S/N) of 3 was 1.7 ng mL?1. The relative standard deviations for determination of 150 and 30 ng ml?1 of thorium were 3.26 and 4.41%, respectively (n = 10). The method showed a good linearity, recoveries, as well as some advantages such as sensitivity, simplicity, affordability and a high feasibility. The method was successfully applied to determine thorium in different water and urine samples. PMID:21340019

Shiri, Sabah; Delpisheh, Ali; Haeri, Ali; Poornajaf, Abdolhossein; Khezeli, Tahereh; Badkiu, Nadie

2011-01-01

292

Reovirus ?NS Protein Is Required for Nucleation of Viral Assembly Complexes and Formation of Viral Inclusions  

PubMed Central

Progeny virions of mammalian reoviruses are assembled in the cytoplasm of infected cells at discrete sites termed viral inclusions. Studies of temperature-sensitive (ts) mutant viruses indicate that nonstructural protein ?NS and core protein ?2 are required for synthesis of double-stranded (ds) RNA, a process that occurs at sites of viral assembly. We used confocal immunofluorescence microscopy and ts mutant reoviruses to define the roles of ?NS and ?2 in viral inclusion formation. In cells infected with wild-type (wt) reovirus, ?NS and ?2 colocalize to large, perinuclear structures that correspond to viral inclusions. In cells infected at a nonpermissive temperature with ?NS-mutant virus tsE320, ?NS is distributed diffusely in the cytoplasm and ?2 is contained in small, punctate foci that do not resemble viral inclusions. In cells infected at a nonpermissive temperature with ?2-mutant virus tsH11.2, ?2 is distributed diffusely in the cytoplasm and the nucleus. However, ?NS localizes to discrete structures in the cytoplasm that contain other viral proteins and are morphologically indistinguishable from viral inclusions seen in cells infected with wt reovirus. Examination of cells infected with wt reovirus over a time course demonstrates that ?NS precedes ?2 in localization to viral inclusions. These findings suggest that viral RNA-protein complexes containing ?NS nucleate sites of viral replication to which other viral proteins, including ?2, are recruited to commence dsRNA synthesis. PMID:11152519

Becker, Michelle M.; Goral, Mehmet I.; Hazelton, Paul R.; Baer, Geoffrey S.; Rodgers, Steven E.; Brown, Earl G.; Coombs, Kevin M.; Dermody, Terence S.

2001-01-01

293

Cluster formation by allelomimesis in real-world complex adaptive systems  

NASA Astrophysics Data System (ADS)

Animal and human clusters are complex adaptive systems and many organize in cluster sizes s that obey the frequency distribution D(s)?s-? . The exponent ? describes the relative abundance of the cluster sizes in a given system. Data analyses reveal that real-world clusters exhibit a broad spectrum of ? values, 0.7 (tuna fish schools) ???4.61 (T4 bacteriophage gene family sizes). Allelomimesis is proposed as an underlying mechanism for adaptation that explains the observed broad ? spectrum. Allelomimesis is the tendency of an individual to imitate the actions of others and two cluster systems have different ? values when their component agents display unequal degrees of allelomimetic tendencies. Cluster formation by allelomimesis is shown to be of three general types: namely, blind copying, information-use copying, and noncopying. Allelomimetic adaptation also reveals that the most stable cluster size is formed by three strongly allelomimetic individuals. Our finding is consistent with available field data taken from killer whales and marmots.

Juanico, Dranreb Earl; Monterola, Christopher; Saloma, Caesar

2005-04-01

294

Complex Structure Formation in a Ternary Mixture Driven Through the Patterned Microchannel  

NASA Astrophysics Data System (ADS)

Through the computer simulations, we probe the behavior of a A/B/C ternary mixture in which two immiscible components, A and B, undergo the interfacial chemical reaction and produce third component, C. The reverse chemical reaction, namely consumption of the A and B species from the C components, is also possible. This mixture is driven by the imposed pressure gradient (Poiseuille flow) through the three dimensional microchannel. The microchannel is decorated with chemically distinct patches that display preferential wetting interactions for the A or B components. Namely, A(B)-like patches are placed in the way of B(A)-rich fluid stream. At the beginning of the simulation two streams of fluid, A and B, are flowing parallel each other. As system evolves to it's steady state, the C component is formed in the A/B interfacial area. Simultaneously, A(B) reach fluid diffuses to A(B) -like patches, so that two stream flow distorts and additional interfacial regions, where chemical reaction may occur, are created. Interplay between the advection of all three components by imposed flow and all the diffusion processes in the presence of spatially non-uniform interactions with the substrate, lead to the formation of complex structures, periodic in space and time.

Kuksenok, Olga; Balazs, Anna

2003-03-01

295

SEPT12-Microtubule Complexes Are Required for Sperm Head and Tail Formation  

PubMed Central

The septin gene belongs to a highly conserved family of polymerizing GTP-binding cytoskeletal proteins. SEPTs perform cytoskeletal remodeling, cell polarity, mitosis, and vesicle trafficking by interacting with various cytoskeletons. Our previous studies have indicated that SEPTIN12+/+/+/? chimeras with a SEPTIN12 mutant allele were infertile. Spermatozoa from the vas deferens of chimeric mice indicated an abnormal sperm morphology, decreased sperm count, and immotile sperm. Mutations and genetic variants of SEPTIN12 in infertility cases also caused oligozoospermia and teratozoospermia. We suggest that a loss of SEPT12 affects the biological function of microtublin functions and causes spermiogenesis defects. In the cell model, SEPT12 interacts with ?- and ?-tubulins by co-immunoprecipitation (co-IP). To determine the precise localization and interactions between SEPT12 and ?- and ?-tubulins in vivo, we created SEPTIN12-transgene mice. We demonstrate how SEPT12 interacts and co-localizes with ?- and ?-tubulins during spermiogenesis in these mice. By using shRNA, the loss of SEPT12 transcripts disrupts ?- and ?-tubulin organization. In addition, losing or decreasing SEPT12 disturbs the morphogenesis of sperm heads and the elongation of sperm tails, the steps of which are coordinated and constructed by ?- and ?-tubulins, in SEPTIN12+/+/+/? chimeras. In this study, we discovered that the SEPTIN12-microtubule complexes are critical for sperm formation during spermiogenesis. PMID:24213608

Kuo, Pao-Lin; Chiang, Han-Sun; Wang, Ya-Yun; Kuo, Yung-Che; Chen, Mei-Feng; Yu, I-Shing; Teng, Yen-Ni; Lin, Shu-Wha; Lin, Ying-Hung

2013-01-01

296

Spectrofluorimetric Determination of Famotidine in Pharmaceutical Preparations and Biological Fluids through Ternary Complex Formation with Some Lanthanide Ions: Application to Stability Studies  

PubMed Central

A simple, sensitive and specific method was developed for the determination of famotidine (FMT) in pharmaceutical preparations and biological fluids. The proposed method is based on ternary complex formation of famotidine (FMT) with EDTA and terbium chloride TbCl3 in acetate buffer of pH 4. Alternatively, the complex is formed via the reaction with hexamine and either lanthanum chloride LaCl3, or cerous chloride CeCl3 in borate buffer of pH6.2 and 7.2 respectively. In all cases, the relative fluorescence intensity of the formed complexes was measured at 580 nm after excitation at 290 nm. The fluorescence intensity - concentration plots were rectilinear over the concentration range of 10-100, 5-70, and 5-60 ng/ml, with minimum quantification limits (LOQ) of 2.4, 2.2, and 5.2 ng/ml, and minimum limits of detection (LOD) of 0.79, 0.74, and 1.7 ng/ml upon using TbCl3, LaCl3, and CeCl3 respectively. The proposed method was applied successfully for the analysis of famotidine in dosage forms and in human plasma. The kinetics of both alkaline and oxidative induced degradation of the drug was studied using the proposed method. The apparent first order rate constant and half life time were calculated. A proposal of the reaction pathways is presented. PMID:23675130

Walash, M. I.; El-Brashy, A.; El-Enany, N.; Wahba, M. E. K.

2009-01-01

297

Heterocomplex formation by Arp4 and ?-actin is involved in the integrity of the Brg1 chromatin remodeling complex.  

PubMed

Although nuclear actin and Arps (actin-related proteins) are often identified as components of multi-protein chromatin-modifying enzyme complexes, such as chromatin remodeling and histone acetyltransferase (HAT) complexes, their molecular functions still remain largely elusive. Here, we investigated the role of human Arp4 (BAF53, also known as actin-like protein 6A) in Brg1-containing chromatin remodeling complexes. Depletion of Arp4 by RNA interference impaired the integrity of these complexes and accelerated the degradation of Brg1, indicating a crucial role in their maintenance, at least in certain human cell lines. We further found that Arp4 can form a heterocomplex with ?-actin. Based on structural similarities between conventional actin and Arp4, and the assumption that actin-Arp4 binding might mimic actin-actin binding, we introduced a series of mutations in Arp4 that might be expected to impair its interaction with ?-actin. Some of them indeed caused reduced binding to ?-actin. Interestingly, such mutant Arp4 proteins also showed reduced incorporation into Brg1 complexes, and their interaction with Myc-associated complexes as well as Tip60 HAT complexes were also impaired. Based on these findings, we propose that ?-actin-Arp4 complex formation might be a crucial feature in some chromatin-modifying enzyme complexes, such as the Brg1 complex. PMID:22573825

Nishimoto, Naoki; Watanabe, Masanori; Watanabe, Shinya; Sugimoto, Nozomi; Yugawa, Takashi; Ikura, Tsuyoshi; Koiwai, Osamu; Kiyono, Tohru; Fujita, Masatoshi

2012-08-15

298

Neutral metal cluster formation and oxidation reactions in the photolysis of iron carbonyl van der Waals complexes  

SciTech Connect

Iron pentacarbonyl van der Waals complexes and mixed complexes containing iron pentacarbonyl and oxygen, carbon dioxide, or water are produced in pulsed supersonic expansions and probed with ultraviolet multiphoton ionization time-of-flight mass spectroscopy. Photochemical rearrangement and oxidation reactions occur within these complexes prior to photoionization, resulting in the formation of neutral iron clusters, iron cluster carbonyls, and iron cluster monoxides. Two laser time-delayed experiments, as well as excimer laser wavelength and power dependences, are used to probe the mechanism of this fascinating photoinduced chemistry, which occurs in cluster species containing 1-25 iron atoms.

Wheeler, R.G.; Duncan, M.A.

1986-08-14

299

Study of the Ternary Complex Formation Between Vanadium(III), Dipicolinic Acid and Small Blood Serum Bioligands  

Microsoft Academic Search

Ternary complex formation reactions were studied between vanadium(III), dipicolinic acid and small molecular weight blood\\u000a serum components: lactic, oxalic, citric and ortophosphoric acids. The electromotive force measurement permitted us to determine\\u000a the chemical speciation of the complexes formed. In the vanadium(III)–dipicolinic acid–lactic acid system the complexes detected\\u000a were: V(dipic)(lac), V(dipic)(lac)(OH)? and V(dipic)(lac). In the vanadium(III)–dipicolinic acid–oxalic acid system the observed

Freya Da Costa; Giuseppe Lubes; Mildred Rodríguez; Vito Lubes

2011-01-01

300

Structure Formation of Ultrathin PEO Films at Solid Interfaces--Complex Pattern Formation by Dewetting and Crystallization  

PubMed Central

The direct contact of ultrathin polymer films with a solid substrate may result in thin film rupture caused by dewetting. With crystallisable polymers such as polyethyleneoxide (PEO), molecular self-assembly into partial ordered lamella structures is studied as an additional source of pattern formation. Morphological features in ultrathin PEO films (thickness < 10 nm) result from an interplay between dewetting patterns and diffusion limited growth pattern of ordered lamella growing within the dewetting areas. Besides structure formation of hydrophilic PEO molecules, n-alkylterminated (hydrophobic) PEO oligomers are investigated with respect to self-organization in ultrathin films. Morphological features characteristic for pure PEO are not changed by the presence of the n-alkylgroups. PMID:23385233

Braun, Hans-Georg; Meyer, Evelyn

2013-01-01

301

Monitoring the formation of carbide crystal phases during the thermal decomposition of 3d transition metal dicarboxylate complexes.  

PubMed

Single molecule precursors can help to simplify the synthesis of complex alloys by minimizing the amount of necessary starting reagents. However, single molecule precursors are time consuming to prepare with very few being commercially available. In this study, a simple precipitation method is used to prepare Fe, Co, and Ni fumarate and succinate complexes. These complexes were then thermally decomposed in an inert atmosphere to test their efficiency as single molecule precursors for the formation of metal carbide phases. Elevated temperature X-ray diffraction was used to identify the crystal phases produced upon decomposition of the metal dicarboxylate complexes. Thermogravimetric analysis coupled with an infrared detector was used to identify the developed gaseous decomposition products. All complexes tested showed a reduction from the starting M(2+) oxidation state to the M(0) oxidation state, upon decomposition. Also, each complex tested showed CO2 and H2O as gaseous decomposition products. Nickel succinate, iron succinate, and iron fumarate complexes were found to form carbide phases upon decomposition. This proves that transition metal dicarboxylate salts can be employed as efficient single molecule precursors for the formation of metal carbide crystal phases. PMID:24905401

Huba, Zachary J; Carpenter, Everett E

2014-08-28

302

Ablation of MMP9 gene ameliorates paracellular permeability and fibrinogen-amyloid beta complex formation during hyperhomocysteinemia.  

PubMed

Increased blood level of homocysteine (Hcy), called hyperhomocysteinemia (HHcy) accompanies many cognitive disorders including Alzheimer's disease. We hypothesized that HHcy-enhanced cerebrovascular permeability occurs via activation of matrix metalloproteinase-9 (MMP9) and leads to an increased formation of fibrinogen-?-amyloid (Fg-A?) complex. Cerebrovascular permeability changes were assessed in C57BL/6J (wild type, WT), cystathionine-?-synthase heterozygote (Cbs+/-, a genetic model of HHcy), MMP9 gene knockout (Mmp9-/-), and Cbs and Mmp9 double knockout (Cbs+/-/Mmp9-/-) mice using a dual-tracer probing method. Expression of vascular endothelial cadherin (VE-cadherin) and Fg-A? complex formation was assessed in mouse brain cryosections by immunohistochemistry. Short-term memory of mice was assessed with a novel object recognition test. The cerebrovascular permeability in Cbs+/- mice was increased via mainly the paracellular transport pathway. VE-cadherin expression was the lowest and Fg-A? complex formation was the highest along with the diminished short-term memory in Cbs+/- mice. These effects of HHcy were ameliorated in Cbs+/-/Mmp9-/- mice. Thus, HHcy causes activation of MMP9 increasing cerebrovascular permeability by downregulation of VE-cadherin resulting in an enhanced formation of Fg-A? complex that can be associated with loss of memory. These data may lead to the identification of new targets for therapeutic intervention that can modulate HHcy-induced cerebrovascular permeability and resultant pathologies. PMID:24865997

Muradashvili, Nino; Tyagi, Reeta; Metreveli, Naira; Tyagi, Suresh C; Lominadze, David

2014-09-01

303

Spontaneous formation of giant unilamellar vesicles from microdroplets of a polyion complex by focused infrared laser irradiation  

Microsoft Academic Search

Spontaneous formation of a giant polymer vesicle from a single micrometer-sized droplet of polyion complex (PIC) of diblock copolymers and its derivative by thermal perturbation, which is achieved by irradiation with a focused infrared laser is presented. The thermal perturbation induces a microphase separation inside of the PIC droplet and the generated water rich phase in the PIC droplet becomes

Hidehiro Oana; Akihiro Kishimura; Yuichi Yamasaki; Masao Washizu; Kazunori Kataoka

2009-01-01

304

Formative Assessment in an Online Learning Environment to Support Flexible On-the-Job Learning in Complex Professional Domains  

ERIC Educational Resources Information Center

This article describes a blueprint for an online learning environment that is based on prominent instructional design and assessment theories for supporting learning in complex domains. The core of this environment consists of formative assessment tasks (i.e., assessment "for" learning) that center on professional situations. For each professional…

van Gog, Tamara; Sluijsmans, Dominique M. A.; Joosten-ten Brinke, Desiree; Prins, Frans J.

2010-01-01

305

Escherichia coli SeqA protein affects DNA topology and inhibits open complex formation at oriC.  

PubMed

Chromosome replication in Escherichia coli is initiated by the DnaA protein. Binding of DnaA to the origin, oriC, followed by formation of an open complex are the first steps in the initiation process. Based on in vivo studies the SeqA protein has been suggested to function negatively in the initiation of replication, possibly by inhibiting open complex formation. In vitro studies have shown that SeqA inhibits oriC-dependent replication. Here we show by KMnO(4) probing that SeqA inhibits open complex formation. The inhibition was not caused by prevention of DnaA binding to the oriC plasmids, indicating that SeqA prevented strand separation in oriC either directly, by interacting with the AT-rich region, or indirectly, by changing the topology of the oriC plasmids. SeqA was found to restrain the negative supercoils of the oriC plasmid. In comparison with the effect of HU on plasmid topology, SeqA seemed to act more cooperatively. It is likely that the inhibition of open complex formation is caused by the effect of SeqA on the topology of the plasmids. SeqA also restrained the negative supercoils of unmethylated oriC plasmids, which do not bind SeqA specifically, suggesting that the effect on topology is not dependent on binding of SeqA to a specific sequence in oriC. PMID:10469666

Torheim, N K; Skarstad, K

1999-09-01

306

Escherichia coli SeqA protein affects DNA topology and inhibits open complex formation at oriC.  

PubMed Central

Chromosome replication in Escherichia coli is initiated by the DnaA protein. Binding of DnaA to the origin, oriC, followed by formation of an open complex are the first steps in the initiation process. Based on in vivo studies the SeqA protein has been suggested to function negatively in the initiation of replication, possibly by inhibiting open complex formation. In vitro studies have shown that SeqA inhibits oriC-dependent replication. Here we show by KMnO(4) probing that SeqA inhibits open complex formation. The inhibition was not caused by prevention of DnaA binding to the oriC plasmids, indicating that SeqA prevented strand separation in oriC either directly, by interacting with the AT-rich region, or indirectly, by changing the topology of the oriC plasmids. SeqA was found to restrain the negative supercoils of the oriC plasmid. In comparison with the effect of HU on plasmid topology, SeqA seemed to act more cooperatively. It is likely that the inhibition of open complex formation is caused by the effect of SeqA on the topology of the plasmids. SeqA also restrained the negative supercoils of unmethylated oriC plasmids, which do not bind SeqA specifically, suggesting that the effect on topology is not dependent on binding of SeqA to a specific sequence in oriC. PMID:10469666

Torheim, N K; Skarstad, K

1999-01-01

307

Using Model Substrates To Study the Dependence of Focal Adhesion Formation on the Affinity of Integrin-Ligand Complexes  

E-print Network

Using Model Substrates To Study the Dependence of Focal Adhesion Formation on the Affinity into focal adhesion complexes. This paper examines the effect of one mechanistic variable, ligand affinity RGD is a higher affinity ligand than linear RGD. 3T3 Swiss fibroblasts attached to substrates

Mrksich, Milan

308

Competitive displacement of drugs from cyclodextrin inclusion complex by polypseudorotaxane formation with poloxamer: implications in drug solubilization and delivery.  

PubMed

The competitive interactions between the poly-[propylene oxide] (POO)-poly-[ethylene oxide] (PEO) block copolymer poloxamer 407 (Pluronic F127) and two drugs, triamcinolone acetonide and ciclopirox olamine, by the formation of inclusion complexes with two cyclodextrin hydrophilic derivatives, hydroxypropyl-?-cyclodextrin (HP?CD; molar substitution (MS) 0.65) and partially methylated-?-cyclodextrin (M?CD; MS 0.57), were studied by means of one-dimensional (1)H NMR, 2D ROESY experiments, solubility studies and drug release studies. 1D and 2D NMR and solubility studies indicate that both triamcinolone acetonide and ciclopirox olamine form stable inclusion complexes with the cyclodextrin derivatives. In the case of ciclopirox olamine the complex was more stable at pH 1. Effective complexation of poloxamer with the two cyclodextrins (CDs) was also evidenced by NMR analysis, and competitive displacement of the drugs from the CD cavity by the polymer was observed. Drug solubility in CD solutions was not modified by the addition of polymers, indicating that a decrease in solubility due to the competitive displacement is probably compensated by the solubilizing effect of polymer micellization. Finally, polypseudorotaxanes formation has a significant influence on the release of the drugs studied. Changes in the release rate depend on the stability of drug-CD inclusion complex and on cyclodextrin concentration in the bulk solution; so polypseudorotaxane formation can be employed to modulate drug controlled release from thermosensitive hydrogels. PMID:22182528

Nogueiras-Nieto, Luis; Sobarzo-Sánchez, Eduardo; Gómez-Amoza, José Luis; Otero-Espinar, Francisco J

2012-04-01

309

Processes of (Xe2D)*-excimer complex formation in ternary solid Kr-Xe-D2 solutions  

NASA Astrophysics Data System (ADS)

The article presents study results of VUV and UV cathodoluminescence spectra, of solid ternary Kr-Xe-D2 solutions, and Xe-D2, Kr-D2, Xe-Kr solid binary cryoalloys. The object of study is the dependence of the spectral band intensity distribution, on the concentration of impurities, and the dosage dependence of luminescence. All emission bands were identified. It is demonstrated that the formation of emitting states is caused by a transfer of energy through the system of its own electron excitation matrices. An emission from (Xe2D)* complexes is observed, if Xe is present in ternary solid solutions. It is shown that the process of forming (Xe2D)*-complexes has multiple steps, and includes the formation of an intermediate [XeD2]* non-stable state at the first stage, the nonradiative decay of which leads to the dissociation of the admixture molecular deuterium. It is suggested that the formation of [XeD2]* complexes occurs due to the high proton affinity of Xe, and its negative affinity to the electron in the D2 molecule, as a result of which, the intermediate complex acquires the features of a charge-transfer complex.

Belov, A. G.; Bludov, M. A.

2014-09-01

310

Electrocatalytic Oxidation of Formate by [Ni(PR2NR`2)2(CH3CN)]2+ Complexes  

SciTech Connect

New [Ni(PR2NR`2)2(CH3CN)]2+ complexes with R = Ph, R` = 4-MeOPh; R = Cy, R` = Ph and a mixed ligand [Ni(PR2NR`2)(PR``2NR`2)]2+ with R = Cy, R` = Ph, R`` = Ph have been synthesized and characterized by single crystal X-ray crystallography. These complexes are shown to be electrocatalysts for the oxidation of formate in solution to produce CO2, protons, and electrons with rates which are first order in catalyst and in formate at formate concentrations below approximately 0.05 M. For the catalysts studied, maximum observed turnover frequencies vary from <1.1 s-1 to 12.5 s-1 at room temperature, which are the highest rates yet reported for formate oxidation by homogeneous catalysts. A mechanistic scheme is proposed which involves an initial nickel complex bound ?1-OC(O)H followed by a rate limiting hydride transfer step. An acetate complex demonstrating the ?1-OC(O)CH3 binding mode to nickel has also been synthesized and characterized by single crystal X-ray crystallography. The pendant amines have been demonstrated to be essential for this electrocatalytic activity as no activity toward formate was found for the similar [Ni(depe)2][BF4]2 (depe = diethylphosphinoethane) complex. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Galan, Brandon R.; Schoffel, Julia; Linehan, John C.; Seu, Candace; Appel, Aaron M.; Roberts, John A.; Helm, Monte L.; Kilgore, Uriah J.; Yang, Jenny Y.; DuBois, Daniel L.; Kubiak, Cliff

2011-09-07

311

Stability constant estimator user`s guide  

SciTech Connect

The purpose of the Stability Constant Estimator (SCE) program is to estimate aqueous stability constants for 1:1 complexes of metal ions with ligands by using trends in existing stability constant data. Such estimates are useful to fill gaps in existing thermodynamic databases and to corroborate the accuracy of reported stability constant values.

Hay, B.P.; Castleton, K.J.; Rustad, J.R.

1996-12-01

312

In vivo analysis of formation and endocytosis of the Wnt/?-Catenin signaling complex in zebrafish embryos  

PubMed Central

ABSTRACT After activation by Wnt/?-Catenin ligands, a multi-protein complex assembles at the clustering membrane-bound receptors and intracellular signal transducers into the so-called Lrp6-signalosome. However, the mechanism of signalosome formation and dissolution is yet not clear. Our imaging studies of live zebrafish embryos show that the signalosome is a highly dynamic structure. It is continuously assembled by Dvl2-mediated recruitment of the transducer complex to the activated receptors and partially disassembled by endocytosis. We find that, after internalization, the ligand-receptor complex and the transducer complex take separate routes. The Wnt–Fz–Lrp6 complex follows a Rab-positive endocytic path. However, when still bound to the transducer complex, Dvl2 forms intracellular aggregates. We show that this endocytic process is not only essential for ligand-receptor internalization but also for signaling. The ?2-subunit of the endocytic Clathrin adaptor Ap2 interacts with Dvl2 to maintain its stability during endocytosis. Blockage of Ap2?2 function leads to Dvl2 degradation, inhibiton of signalosome formation at the plasma membrane and, consequently, reduction of signaling. We conclude that Ap2?2-mediated endocytosis is important to maintain Wnt/?-catenin signaling in vertebrates. PMID:25074807

Hagemann, Anja I. H.; Kurz, Jennifer; Kauffeld, Silke; Chen, Qing; Reeves, Patrick M.; Weber, Sabrina; Schindler, Simone; Davidson, Gary; Kirchhausen, Tomas; Scholpp, Steffen

2014-01-01

313

In vivo analysis of formation and endocytosis of the Wnt/?-catenin signaling complex in zebrafish embryos.  

PubMed

After activation by Wnt/?-Catenin ligands, a multi-protein complex assembles at the clustering membrane-bound receptors and intracellular signal transducers into the so-called Lrp6-signalosome. However, the mechanism of signalosome formation and dissolution is yet not clear. Our imaging studies of live zebrafish embryos show that the signalosome is a highly dynamic structure. It is continuously assembled by Dvl2-mediated recruitment of the transducer complex to the activated receptors and partially disassembled by endocytosis. We find that, after internalization, the ligand-receptor complex and the transducer complex take separate routes. The Wnt-Fz-Lrp6 complex follows a Rab-positive endocytic path. However, when still bound to the transducer complex, Dvl2 forms intracellular aggregates. We show that this endocytic process is not only essential for ligand-receptor internalization but also for signaling. The ?2-subunit of the endocytic Clathrin adaptor Ap2 interacts with Dvl2 to maintain its stability during endocytosis. Blockage of Ap2?2 function leads to Dvl2 degradation, inhibiton of signalosome formation at the plasma membrane and, consequently, reduction of signaling. We conclude that Ap2?2-mediated endocytosis is important to maintain Wnt/?-catenin signaling in vertebrates. PMID:25074807

Hagemann, Anja I H; Kurz, Jennifer; Kauffeld, Silke; Chen, Qing; Reeves, Patrick M; Weber, Sabrina; Schindler, Simone; Davidson, Gary; Kirchhausen, Tomas; Scholpp, Steffen

2014-09-15

314

CONTINUOUS MULTILIGAND DISTRIBUTION MODEL USED TO PREDICT THE STABILITY CONSTANT OF CU(II) METAL COMPLEXATION WITH HUMIC MATERIAL FROM FLUORESCENCE QUENCHING DATA  

EPA Science Inventory

We report the use of a pH-dependent continuous multiligand distribution model to determine the stability constant between Cu(II) and dissolved humic material. luorescence quenching of the humic material by Cu(II) is used to produce spectral titration curves. he values form the ti...

315

Activation of the cisplatin and transplatin complexes in solution with constant pH and concentration of chloride anions; quantum chemical study.  

PubMed

The thermodynamics of cisplatin and transplatin hydration is studied within the model of constant pH solution. Several implicit solvation models were chosen for the determination of pK(a) and pK constants of the hydration reactions. The polarizable dielectric model (DPCM), integral equation formalism polarizable model (IEFPCM), and polarizable conductor model (CPCM) were combined with the 'united atom model for Hartree-Fock' (UAHF) method for cavity construction and the B3LYP/6-31++G(2dp,2pd) level of calculations for the determination of electronic energies. The results were compared with the COSMO-RS and SM8 model developed by Truhlar (with M06 and MPWX functionals and the charge model CM4). The RMS difference between experimental and calculated pK(a) values of cis/transplatin, water, HCl, and NH (4) (+) was used to evaluate accuracy of calculations. The DPCM model was confirmed to perform the best. The predicted pK(a) constants were used in Legendre transformation for the estimation of the ?G' energies in the constant-pH model. The dependence of the pK constant on pH is plotted and compared with experimental value at pH=7.4. The influence of various chloride concentrations on the molar fractions of dissolved forms of cisplatin is examined for the DPCM model. The increased ratio of cisplatin active aqua-forms is clearly visible for 4 mM chloride solution in comparison with 104 mM Cl(-) concentration. PMID:21523556

Zimmermann, Tomáš; Leszczynski, Jerzy; Burda, Jaroslav V

2011-09-01

316

Formation of Complement Membrane Attack Complex in Mammalian Cerebral Cortex Evokes Seizures and Neurodegeneration  

Microsoft Academic Search

The complement system consists of30 proteins that interact in a carefully regulated manner to destroy invading bacteria and prevent the deposition of immune complexes in normal tissue. This complex system can be activated by diverse mechanisms proceeding through distinct pathways, yet all converge on a final common pathway in which five proteins assemble into a multimolecular complex, the membrane attack

Zhi-Qi Xiong; Weihua Qian; Katsuaki Suzuki; James O. McNamara

2003-01-01

317

Review: Formation of Peptide Radical Ions Through Dissociative Electron Transfer in Ternary Metal-Ligand-Peptide Complexes  

SciTech Connect

The formation and fragmentation of odd-electron ions of peptides and proteins is of interest to applications in biological mass spectrometry. Gas-phase redox chemistry occurring during collision-induced dissociation of ternary metal-ligand-peptide complexes enables the formation of a variety of peptide radicals including the canonical radical cations, M{sup +{sm_bullet}}, radical dications, [M{sup +}H]{sup 2+{sm_bullet}}, radical anions, [M-2H]{sup -{sm_bullet}}. In addition, odd-electron peptide ions with well-defined initial location of the radical site are produced through side chain losses from the radical ions. Subsequent fragmentation of these species provides information on the role of charge and the location of the radical site on the competition between radical-induced and proton-driven fragmentation of odd-electron peptide ions. This account summarizes current understanding of the factors that control the efficiency of the intramolecular electron transfer (ET) in ternary metal-ligand-peptide complexes resulting in formation of odd-electron peptide ions. Specifically, we discuss the effect of the metal center, the ligand and the peptide structure on the competition between the ET, proton transfer (PT), and loss of neutral peptide and neutral peptide fragments from the complex. Fundamental studies of the structures, stabilities, and the energetics and dynamics of fragmentation of such complexes are also important for detailed molecular-level understanding of photosynthesis and respiration in biological systems.

Chu, Ivan K.; Laskin, Julia

2011-12-31

318

AIP augments CARMA1-BCL10-MALT1 complex formation to facilitate NF-?B signaling upon T cell activation  

PubMed Central

Background The CARMA1-BCL10-MALT1 (CBM) complex bridges T cell receptor (TCR) signaling to the canonical I?B kinase (IKK)/NF-?B pathway. The CBM complex constitutes a signaling cluster of more than 1 Mio Dalton. Little is known about factors that facilitate the rapid assembly and maintenance of this dynamic higher order complex. Findings Here, we report the novel interaction of the aryl hydrocarbon receptor (AHR) interacting protein (AIP) and the molecular scaffold protein CARMA1. In T cells, transient binding of CARMA1 and AIP enhanced formation of the CBM complex. Thereby, AIP promoted optimal IKK/NF-?B signaling and IL-2 production in response to TCR/CD28 co-stimulation. Conclusions Our data demonstrate that AIP acts as a positive regulator of NF-?B signaling upon T cell activation. PMID:25245034

2014-01-01

319

Three-color single molecule imaging shows WASP detachment from Arp2/3 complex triggers actin filament branch formation  

PubMed Central

During cell locomotion and endocytosis, membrane-tethered WASP proteins stimulate actin filament nucleation by the Arp2/3 complex. This process generates highly branched arrays of filaments that grow toward the membrane to which they are tethered, a conflict that seemingly would restrict filament growth. Using three-color single-molecule imaging in vitro we revealed how the dynamic associations of Arp2/3 complex with mother filament and WASP are temporally coordinated with initiation of daughter filament growth. We found that WASP proteins dissociated from filament-bound Arp2/3 complex prior to new filament growth. Further, mutations that accelerated release of WASP from filament-bound Arp2/3 complex proportionally accelerated branch formation. These data suggest that while WASP promotes formation of pre-nucleation complexes, filament growth cannot occur until it is triggered by WASP release. This provides a mechanism by which membrane-bound WASP proteins can stimulate network growth without restraining it. DOI: http://dx.doi.org/10.7554/eLife.01008.001 PMID:24015360

Smith, Benjamin A; Padrick, Shae B; Doolittle, Lynda K; Daugherty-Clarke, Karen; Correa, Ivan R; Xu, Ming-Qun; Goode, Bruce L; Rosen, Michael K; Gelles, Jeff

2013-01-01

320

Synthesis, mechanism of formation, and catalytic activity of Xantphos nickel ?-complexes.  

PubMed

A general synthetic route to the first Xantphos nickel alkyne and alkene complexes has been discovered. Various Ni ?-complexes were prepared and characterized. NMR experiments indicate benzonitrile undergoes ligand exchange with a Xantphos ligand of (Xant)2Ni, a compound that was previously believed to be unreactive. The Ni ?-complexes were also shown to be catalytically competent in cross coupling and cycloaddition reactions. (Xant)2Ni is also catalytically active for these reactions when activated by a nitrile or coordinating solvent. PMID:25356514

Staudaher, Nicholas D; Stolley, Ryan M; Louie, Janis

2014-12-21

321

Down-regulation of MUC1 in cancer cells inhibits cell migration by promoting E-cadherin/catenin complex formation  

SciTech Connect

MUC1, a tumor associated glycoprotein, is over-expressed in most cancers and can promote proliferation and metastasis. The objective of this research was to study the role of MUC1 in cancer metastasis and its potential mechanism. Pancreatic (PANC1) and breast (MCF-7) cancer cells with stable 'knockdown' of MUC1 expression were created using RNA interference. {beta}-Catenin and E-cadherin protein expression were upregulated in PANC1 and MCF-7 cells with decreased MUC1 expression. Downregulation of MUC1 expression also induced {beta}-catenin relocation from the nucleus to the cytoplasm, increased E-cadherin/{beta}-catenin complex formation and E-cadherin membrane localization in PANC1 cells. PANC1 cells with 'knockdown' MUC1 expression had decreased in vitro cell invasion. This study suggested that MUC1 may affect cancer cell migration by increasing E-cadherin/{beta}-catenin complex formation and restoring E-cadherin membrane localization.

Yuan Zhenglong; Wong, Sandy; Borrelli, Alexander [Department of Surgery, Rhode Island Hospital, Brown University, 2 Dudley Street, Suite 470, Providence, RI 02905 (United States); Chung, Maureen A. [Department of Surgery, Rhode Island Hospital, Brown University, 2 Dudley Street, Suite 470, Providence, RI 02905 (United States)], E-mail: mchung@usasurg.org

2007-10-26

322

Quantitative structure-polarization relationships (QSPR) study of BTEX tracers for the formation of antibody-BTEX-EDF complex.  

PubMed

The multiple linear regression (MLR) analysis and back propagation neural networks (NN) were performed to examine the quantitative structure-polarization relationships (QSPR) for the formation of antibody-BTEX-EDF complex. Five descriptors out of 18 ones were selected for both MLR and NN, respectively, and the selected descriptors in MLR were the same as those in NN. These descriptors were the number of atoms, which can form hydrogen bonds (HA), connolly surface area (Area), the highest occupied molecular orbital energy (HOMO), partial charge of C3 carbon atom (C3), and HOMO pi coefficient of C2 carbon atom (P2). The fact that the descriptors in MLR are identical to those in NN suggests that these descriptors have good linear relationships and play a significant role in the formation of antibody-tracer complex. PMID:15177453

Moon, Taesung; Chi, Myung Whan; Choi, Myung Ja; Yoon, Chang No

2004-07-01

323

Copper deposition onto silicon by galvanic displacement: Effect of Cu complex formation in NH 4F solutions  

Microsoft Academic Search

Copper was deposited onto rotating Si substrates by galvanic displacement in 6.0M NH4F to determine the effects of Cu complex formation on deposition rates. Deposition rates decreased with increasing rotation speed, indicating that Cu(I) intermediates, stabilized by NH3, diffuse away from the Cu surface before they reduce to Cu(0). UV–visible spectra of contacting solutions and direct measurements of mass changes

Calvin P. daRosa; Enrique Iglesia; Roya Maboudian

2009-01-01

324

Formation of colloidal silver nanoparticles stabilized by Na +–poly(?-glutamic acid)–silver nitrate complex via chemical reduction process  

Microsoft Academic Search

Macromolecular and polyanionic Na+–poly(?-glutamic acid) (PGA) silver nitrate complex acted as both a metal ion provider and a particle protector to fabricate nanosized silver colloids under chemical reduction by dextrose. The formation and size of particles have been characterized from transmission electron microscopy (TEM), dynamic light scattering analysis and UV–vis spectrophotometer. The results showed that the average particle size was

Da-Guang Yu

2007-01-01

325

Annexin A2 Is Involved in the Formation of Hepatitis C Virus Replication Complex on the Lipid Raft  

PubMed Central

The hepatitis C virus (HCV) RNA replicates in hepatic cells by forming a replication complex on the lipid raft (detergent-resistant membrane [DRM]). Replication complex formation requires various viral nonstructural (NS) proteins as well as host cellular proteins. In our previous study (C. K. Lai, K. S. Jeng, K. Machida, and M. M. Lai, J. Virol. 82:8838–8848, 2008), we found that a cellular protein, annexin A2 (Anxa2), interacts with NS3/NS4A. Since NS3/NS4A is a membranous protein and Anxa2 is known as a lipid raft-associated scaffold protein, we postulate that Anxa2 helps in the formation of the HCV replication complex on the lipid raft. Further studies showed that Anxa2 was localized at the HCV-induced membranous web and interacted with NS4B, NS5A, and NS5B and colocalized with them in the perinuclear region. The silencing of Anxa2 decreased the formation of membranous web-like structures and viral RNA replication. Subcellular fractionation and bimolecular fluorescence complementation analysis revealed that Anxa2 was partially associated with HCV at the lipid raft enriched with phosphatidylinositol-4-phosphate (PI4P) and caveolin-2. Further, the overexpression of Anxa2 in HCV-nonsusceptible HEK293 cells caused the enrichment of HCV NS proteins in the DRM fraction and increased the colony-forming ability of the HCV replicon. Since Anxa2 is known to induce the formation of the lipid raft microdomain, we propose that Anxa2 recruits HCV NS proteins and enriches them on the lipid raft to form the HCV replication complex. PMID:22301157

Saxena, Vikas; Lai, Chao-Kuen; Chao, Ti-Chun; Jeng, King-Song

2012-01-01

326

Reactions of guanine with methyl chloride and methyl bromide: O6-methylation versus charge transfer complex formation  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) at the B3LYP/6-31+G* and B3LYP/AUG-cc-pVDZ levels was employed to study O6-methylation of guanine due to its reactions with methyl chloride and methyl bromide and to obtain explanation as to why the methyl halides cause genotoxicity and possess mutagenic and carcinogenic properties. Geometries of the various isolated species involved in the reactions, reactant complexes (RCs), and product complexes (PCs) were optimized in gas phase. Transition states connecting the reactant complexes with the product complexes were also optimized in gas phase at the same levels of theory. The reactant complexes, product complexes, and transition states were solvated in aqueous media using the polarizable continuum model (PCM) of the self-consistent reaction field theory. Zero-point energy (ZPE) correction to total energy and the corresponding thermal energy correction to enthalpy were made in each case. The reactant complexes of the keto form of guanine with methyl chloride and methyl bromide in water are appreciably more stable than the corresponding complexes involving the enol form of guanine. The nature of binding in the product complexes was found to be of the charge transfer type (O6mG+ · X-, X dbond Cl, Br). Binding of HCl, HBr, and H2O molecules to the PCs obtained with the keto form of guanine did not alter the positions of the halide anions in the PCs, and the charge transfer character of the PCs was also not modified due to this binding. Further, the complexes obtained due to the binding of HCl, HBr, and H2O molecules to the PCs had greater stability than the isolated PCs. The reaction barriers involved in the formation of PCs were found to be quite high (?50 kcal/mol). Mechanisms of genotoxicity, mutagenesis and carcinogenesis caused by the methyl halides appear to involve charge transfer-type complex formation. Thus the mechanisms of these processes involving the methyl halides appear to be quite different from those that involve the other strongly carcinogenic methylating agents.

Shukla, P. K.; Mishra, P. C.; Suhai, S.

327

The formation stability, hydrolytic behavior, mass spectrometry, DFT study, and luminescence properties of trivalent lanthanide complexes of H2ODO2A.  

PubMed

The trivalent lanthanide complex formation constants (log K(f)) of the macrocyclic ligand H(2)ODO2A (4,10-dicarboxymethyl-1-oxa-4,7,10-triazacyclododecane) have been determined by pH titration techniques to be in the range 10.84-12.62 which increase with increasing lanthanide atomic number, and are smaller than those of the corresponding H(2)DO2A (1,7-dicarboxylmethyl-1,4,7,10-tetraazacyclododecane) complexes. The equilibrium formation of the dinuclear hydrolysis species, e.g. Ln(2)(ODO2A)(2)(?-OH)(+) and Ln(2)(ODO2A)(2)(?-OH)(2), dominates over the mononuclear species, e.g. LnODO2A(OH) and LnODO2A(OH)(2)(-). Mass spectrometry confirmed the presence of [Eu(ODO2A)](+), [Eu(ODO2A)(OH)+H](+), [Eu(2)(ODO2A)(2)(OH(2))(2)+H](+), [Eu(ODO2A)(OH)(2)](-) and [Eu(2)(ODO2A)(2)(OH(2))(3)](-) species at pH > 7. Density function theory (DFT) calculated structures of the EuODO2A(H(2)O)(3)(+) and EuDO2A(H(2)O)(3)(+) complexes indicate that three inner-sphere coordinated water molecules are arranged in a meridional configuration, i.e. the 3 water molecules are on the same plane perpendicular to that of the basal N(3)O or N(4) atoms. However, luminescence lifetime studies reveal that the EuODO2A(+) and TbODO2A(+) complexes have 4.1 and 2.9 inner-sphere coordinated water molecules, respectively, indicating that other equilibrium species are also present for the EuODO2A(+) complex. The respective emission spectral intensities and lifetimes at 615 nm (?(ex) = 395 nm) and 544 nm (?(ex) = 369 nm) of the EuODO2A(+) and TbODO2A(+) complexes increase with increasing pH, consistent with the formation of ?-OH-bridged dinuclear species at higher pH. Additional DFT calculations show that each Y(iii) ion is 8-coordinated in the three possible cis-[Y(2)(ODO2A)(2)(?-OH)(H(2)O)(2)](+), trans-[Y(2)(ODO2A)(2)(?-OH)(H(2)O)(2)](+) and [Y(2)(ODO2A)(2)(?-OH)(2)] dinuclear complex structures. The first and the second include 6-coordination by the ligand ODO2A(2-), one by the bridged ?-OH ion and one by a water molecule. The third includes 6-coordination by the ligand ODO2A(2-) and two by the bridged ?-OH ions. The two inner-sphere coordinated water molecules in the cis- and trans-[Y(2)(ODO2A)(2)(?-OH)(H(2)O)(2)](+) dinuclear complexes are in a staggered conformation with torsional angles of 82.21° and 148.54°, respectively. PMID:23073230

Chang, C Allen; Wang, I-Fan; Lee, Hwa-Yu; Meng, Ching-Ning; Liu, Kuan-Yu; Chen, Ya-Fen; Yang, Tsai-Hua; Wang, Yun-Ming; Tsay, Yeou-Guang

2012-12-28

328

Photosynthesis. Electronic structure of the oxygen-evolving complex in photosystem II prior to O-O bond formation.  

PubMed

The photosynthetic protein complex photosystem II oxidizes water to molecular oxygen at an embedded tetramanganese-calcium cluster. Resolving the geometric and electronic structure of this cluster in its highest metastable catalytic state (designated S3) is a prerequisite for understanding the mechanism of O-O bond formation. Here, multifrequency, multidimensional magnetic resonance spectroscopy reveals that all four manganese ions of the catalyst are structurally and electronically similar immediately before the final oxygen evolution step; they all exhibit a 4+ formal oxidation state and octahedral local geometry. Only one structural model derived from quantum chemical modeling is consistent with all magnetic resonance data; its formation requires the binding of an additional water molecule. O-O bond formation would then proceed by the coupling of two proximal manganese-bound oxygens in the transition state of the cofactor. PMID:25124437

Cox, Nicholas; Retegan, Marius; Neese, Frank; Pantazis, Dimitrios A; Boussac, Alain; Lubitz, Wolfgang

2014-08-15

329

Complex formation of myrosinase isoenzymes in oilseed rape seeds are dependent on the presence of myrosinase-binding proteins.  

PubMed

The enzyme myrosinase (EC 3.2.3.1) degrades the secondary compounds glucosinolates upon wounding and serves as a defense to generalist pests in Capparales. Certain myrosinases are present in complexes together with other proteins such as myrosinase-binding proteins (MBP) in extracts of oilseed rape (Brassica napus) seeds. Immunhistochemical analysis of wild-type seeds showed that MBPs were present in most cells but not in the myrosin cells, indicating that the complex formation observed in extracts is initiated upon tissue disruption. To study the role of MBP in complex formation and defense, oilseed rape antisense plants lacking the seed MBPs were produced. Western blotting and immunohistochemical staining confirmed depletion of MBP in the transgenic seeds. The exclusive expression of myrosinase in idioblasts (myrosin cells) of the seed was not affected by the down-regulation of MBP. Using size-exclusion chromatography, we have shown that myrosinases with subunit molecular masses of 62 to 70 kD were present as free dimers from the antisense seed extract, whereas in the wild type, they formed complexes. In accordance with this, MBPs are necessary for myrosinase complex formation of the 62- to 70-kD myrosinases. The product formed from sinalbin hydrolysis by myrosinase was the same whether MBP was present or not. The performance of a common beetle generalist (Tenebrio molitor) fed with seeds, herbivory by flea beetles (Phyllotreta undulata) on cotyledons, or growth rate of the Brassica fungal pathogens Alternaria brassicae or Lepthosphaeria maculans in the presence of seed extracts were not affected by the down-regulation of MBP, leaving the physiological function of this protein family open. PMID:12177471

Eriksson, Susanna; Andréasson, Erik; Ekbom, Barbara; Granér, Georg; Pontoppidan, Bo; Taipalensuu, Jan; Zhang, Jiaming; Rask, Lars; Meijer, Johan

2002-08-01

330

Evidence of complex formation between FADD and c-FLIP death effector domains for the death inducing signaling complex  

PubMed Central

Adaptor protein FADD forms the death inducing signaling complex (DISC) by recruiting the initiating caspases-8 and -10 through homotypic death effector domain (DED) interactions. Cellular FLICE-inhibitory protein (c-FLIP) is an inhibitor of death ligand-induced apoptosis downstream of death receptors, and FADD competes with procaspase-8/10 for recruitment for DISC. However, the mechanism of action of FADD and c-FLIP proteins remain poorly understood at the molecular level. In this study, we provide evidence indicating that the death effector domain (DED) of FADD interacts directly with the death effector domain of human c-FLIP. In addition, we use homology modeling to develop a molecular docking model of FADD and c-FLIP proteins. We also find that four structure-based mutants (E80A, L84A, K169A and Y171A) of c-FLIP DEDs disturb the interaction with FADD DED, and that these mutations lower the stability of the c-FLIP DED. [BMB Reports 2014; 47(9): 488-493] PMID:24355299

Hwang, Eun Young; Jeong, Mi Suk; Park, So Young; Jang, Se Bok

2014-01-01

331

Evidence of complex formation between FADD and c-FLIP death effector domains for the death inducing signaling complex.  

PubMed

Adaptor protein FADD forms the death inducing signaling complex (DISC) by recruiting the initiating caspases-8 and -10 through homotypic death effector domain (DED) interactions. Cellular FLICE-inhibitory protein (c-FLIP) is an inhibitor of death ligand-induced apoptosis downstream of death receptors, and FADD competes with procaspase-8/10 for recruitment for DISC. However, the mechanism of action of FADD and c-FLIP proteins remain poorly understood at the molecular level. In this study, we provide evidence indicating that the death effector domain (DED) of FADD interacts directly with the death effector domain of human c-FLIP. In addition, we use homology modeling to develop a molecular docking model of FADD and c-FLIP proteins. We also find that four structure-based mutants (E80A, L84A, K169A and Y171A) of c-FLIP DEDs disturb the interaction with FADD DED, and that these mutations lower the stability of the c-FLIP DED. [BMB Reports 2014; 47(9): 488-493]. PMID:24355299

Hwang, Eun Young; Jeong, Mi Suk; Park, So Young; Jang, Se Bok

2014-09-01

332

Solute-Solvent Complex Kinetics and Thermodynamics Probed by 2D-IR Vibrational Echo Chemical Exchange Spectroscopy  

E-print Network

temperature. The correlation between the complex enthalpies of formation and dissociation rate constants can/mol. It was found that the inverse of the solute-solvent complex dissociation rate constant is linearly related, 2008 The formation and dissociation kinetics of a series of triethylsilanol/solvent weakly hydrogen

Fayer, Michael D.

333

Probing 3'-ssDNA Loop Formation in E. coli RecBCD/RecBC-DNA Com-plexes using Non-natural DNA: A Model for "Chi" Recognition Complexes  

E-print Network

Ã?Ã? Ã? Ã?Ã?Ã? Ã? Ã?Ã? Probing 3'-ssDNA Loop Formation in E. coli RecBCD/RecBC-DNA Com- plexes using Non-naturalBCD/RecBC-DNA Complexes using Non-natural DNA: A Model for "Chi" Recognition Complexes, Journal of Molecular Biology (2006 Probing 3'-ssDNA Loop Formation in E. coli RecBCD/RecBC- DNA Complexes using Non-natural DNA: A Model

Ju, Tao

334

Formation of Complex Extrachromosomal T-DNA Structures in Agrobacterium tumefaciens-Infected Plants1[C][W][OA  

PubMed Central

Agrobacterium tumefaciens is a unique plant pathogenic bacterium renowned for its ability to transform plants. The integration of transferred DNA (T-DNA) and the formation of complex insertions in the genome of transgenic plants during A. tumefaciens-mediated transformation are still poorly understood. Here, we show that complex extrachromosomal T-DNA structures form in A. tumefaciens-infected plants immediately after infection. Furthermore, these extrachromosomal complex DNA molecules can circularize in planta. We recovered circular T-DNA molecules (T-circles) using a novel plasmid-rescue method. Sequencing analysis of the T-circles revealed patterns similar to the insertion patterns commonly found in transgenic plants. The patterns include illegitimate DNA end joining, T-DNA truncations, T-DNA repeats, binary vector sequences, and other unknown “filler” sequences. Our data suggest that prior to T-DNA integration, a transferred single-stranded T-DNA is converted into a double-stranded form. We propose that termini of linear double-stranded T-DNAs are recognized and repaired by the plant’s DNA double-strand break-repair machinery. This can lead to circularization, integration, or the formation of extrachromosomal complex T-DNA structures that subsequently may integrate. PMID:22797657

Singer, Kamy; Shiboleth, Yoel M.; Li, Jianming; Tzfira, Tzvi

2012-01-01

335

Formation of complex features using electron-beam direct-write decomposition of palladium acetate  

Microsoft Academic Search

A focused electron beam has been used to selectively decompose thin films of palladium acetate, (Pd-Ac), resulting in the formation of < 50 nm wide conductive Pd-rich features. The formation of features from various film thicknesses of Pd-Ac has been investigated using a wide range of electron energies. Monte Carlo simulations of electron energy loss distributions in Pd-Ac films were

T. J. Stark; T. M. Mayer; D. P. Griffis; P. E. Russell

2008-01-01

336

Granitoids and extensional shear zones in the Aegean Sea (Greece), interactions during Metamorphic Core Complexes formation  

NASA Astrophysics Data System (ADS)

Over the past thirty years, intense research has been devoted to interrelations of plutons emplacement and shear zones localization and development in various tectonic settings, from strike-slip, extensional to compressional. Within deforming continental regions, especially regions where Metamorphic Core Complexes (MCC) developed, emplacement of plutons interacts with processes of shear localization in the crust, and shear zones nucleation and their subsequent propagation are often coeval with the crystallization of magmas in plutonic bodies. Despite existing interest, the question of how and why plutons interact with extensional shear zones is still poorly understood. It is thus essential to recognize localizing events during emplacement and cooling of magmatic bodies, measure their kinematic and temporal indicators and evaluate their ability to localize deformation at the local and regional-scale. The Cyclades (Aegean Sea, Greece) form a well-suited area to study this relationship as the development of crustal-scale structures, metamorphism and emplacement of magmatic bodies are shown to be synchronous. The Cycladic granitoids (17-8Ma) intruded the middle/upper crust during thinning of the Aegean domain. They were all emplaced in close interaction with Miocene high-temperature metamorphic domes and associated crustal-scale detachments. Integrating existing data and our new observations performed on Serifos, Mykonos, Naxos and Ikaria Islands, we describe (1) the geometrical relationships between the granitoids, the host rocks and the crustal-scale detachments (2) kinematic indicators inside and outside the granitoids (3) distribution, localization and evolution of deformation within each pluton during emplacement and cooling. Intrusion, cooling and internal deformation of all granitoids were coeval and kinematically compatible with the development of detachments. One can indeed recognize a continuum of deformation from late-magmatic to brittle conditions within magmatic bodies during their emplacement and cooling, consistent with shearing recorded within host rocks. Plutons have an influence on the activity of detachments: in several examples the intrusion of a plutonic body makes the detachment migrate upward in the crust, progressively inactivating the deep branches of detachments (Mykonos, Tinos and Serifos). On the other hand the distribution and evolution of deformation in plutons show that their emplacements were largely tectonically controlled by active detachments and that the deformation tends to localize through time at the contact between granitoids and host rocks during their cooling. While the system of detachments exerts a control on the shape and final location of intrusions, the Serifos pluton recorded within a short time span strain localization resulting in shear zone nucleation and growth during its cooling. This study emphasizes once more the importance of regional tectonics and particularly that of detachments system in the control of granitic plutons emplacement, and introduces some additional constraints on the relationship between MCC formation, detachments and pluton emplacement in the Aegean Sea.

Rabillard, Aurélien; Jolivet, Laurent; Arbaret, Laurent; Laurent, Valentin; Bessiere, Eloïse; Menant, Armel

2014-05-01

337

Hair dye-incorporated poly-?-glutamic acid/glycol chitosan nanoparticles based on ion-complex formation  

PubMed Central

Background p-Phenylenediamine (PDA) or its related chemicals are used more extensively than oxidative hair dyes. However, permanent hair dyes such as PDA are known to have potent contact allergy reactions in humans, and severe allergic reactions are problematic. Methods PDA-incorporated nanoparticles were prepared based on ion-complex formation between the cationic groups of PDA and the anionic groups of poly(?-glutamic acid) (PGA). To reinforce PDA/PGA ion complexes, glycol chitosan (GC) was added. PDA-incorporated nanoparticles were characterized using field-emission scanning electron microscopy, Fourier- transform infrared (FT-IR) spectroscopy, dynamic light scattering, and powder X-ray diffractometry (XRD). Results Nanoparticles were formed by ion-complex formation between the amine groups of PDA and the carboxyl groups of PGA. PDA-incorporated nanoparticles are small in size (<100 nm), and morphological observations showed spherical shapes. FT-IR spectra results showed that the carboxylic acid peak of PGA decreased with increasing PDA content, indicating that the ion complexes were formed between the carboxyl groups of PGA and the amine groups of PDA. Furthermore, the intrinsic peak of the carboxyl groups of PGA was also decreased by the addition of GC. Intrinsic crystalline peaks of PDA were observed by XRD. This crystalline peak of PDA was completely nonexistent when nanoparticles were formed by ion complex between PDA, PGA, and GC, indicating that PDA was complexed with PGA and no free drug existed in the formulation. During the drug-release experiment, an initial burst release of PDA was observed, and then PDA was continuously released over 1 week. Cytotoxicity testing against HaCaT human skin keratinocyte cells showed PDA-incorporated nanoparticles had lower toxicity than PDA itself. Furthermore, PDA-incorporated nanoparticles showed reduced apoptosis and necrosis reaction at HaCaT cells. Conclusion The authors suggest that these microparticles are ideal candidates for a vehicle for decreasing side effects of hair dye. PMID:22131834

Lee, Hye-Young; Jeong, Young-IL; Choi, Ki-Choon

2011-01-01

338

Terminal Axonal Arborization and Synaptic Bouton Formation Critically Rely on Abp1 and the Arp2/3 Complex  

PubMed Central

Neuronal network formation depends on properly timed and localized generation of presynaptic as well as postsynaptic structures. Although of utmost importance for understanding development and plasticity of the nervous system and neurodegenerative diseases, the molecular mechanisms that ensure the fine-control needed for coordinated establishment of pre- and postsynapses are still largely unknown. We show that the F-actin-binding protein Abp1 is prominently expressed in the Drosophila nervous system and reveal that Abp1 is an important regulator in shaping glutamatergic neuromuscular junctions (NMJs) of flies. STED microscopy shows that Abp1 accumulations can be found in close proximity of synaptic vesicles and at the cell cortex in nerve terminals. Abp1 knock-out larvae have locomotion defects and underdeveloped NMJs that are characterized by a reduced number of both type Ib synaptic boutons and branches of motornerve terminals. Abp1 is able to indirectly trigger Arp2/3 complex-mediated actin nucleation and interacts with both WASP and Scar. Consistently, Arp2 and Arp3 loss-of-function also resulted in impairments of bouton formation and arborization at NMJs, i.e. fully phenocopied abp1 knock-out. Interestingly, neuron- and muscle-specific rescue experiments revealed that synaptic bouton formation critically depends on presynaptic Abp1, whereas the NMJ branching defects can be compensated for by restoring Abp1 functions at either side. In line with this presynaptic importance of Abp1, also presynaptic Arp2 and Arp3 are crucial for the formation of type Ib synaptic boutons. Interestingly, presynaptic Abp1 functions in NMJ formation were fully dependent on the Arp2/3 complex, as revealed by suppression of Abp1-induced synaptic bouton formation and branching of axon terminals upon presynaptic Arp2 RNAi. These data reveal that Abp1 and Arp2/3 complex-mediated actin cytoskeletal dynamics drive both synaptic bouton formation and NMJ branching. Our data furthermore shed light on an intense bidirectional functional crosstalk between pre- and postsynapses during the development of synaptic contacts. PMID:24841972

Koch, Nicole; Kobler, Oliver; Thomas, Ulrich; Qualmann, Britta; Kessels, Michael M.

2014-01-01

339

Catalytic C-N and C-F bond formation by organometallic group 11 complexes  

E-print Network

This thesis presents a study of the reaction between an (NHC)gold(I) fluoride complex (NHC = N-heterocyclic carbene) and alkynes (Chapter 1). Gold(I) and fluoride add trans across the triple bond of 3-hexyne and ...

Akana, Jennifer Anne

2007-01-01

340

Increase in dissociation rate constants of cardiotonic steroid-brain (Na+ + K+)-ATPase complexes by reduction of the unsaturated lactone.  

PubMed

Several cardiotonic steroids have been modified by reduction of the unsaturated lactone and their interactions with the sodium- and potassium-activated ATPase ((Na+ + K+)-ATPase) have been investigated. Reduction of the unsaturated lactone results in a decrease in binding affinity due primarily to an increase in the dissociation rate constant concomitant with a decrease in the activation free energy of dissociation. This decrease in activation free energy is about 2 to 4 kcal, which is approximately equal to the energy of one hydrogen bond. It is suggested that the increase in dissociation rate due to reduction of the unsaturated lactone may make possible the use of these compounds as affinity ligands for purification of the (Na+ + K+)-ATPase or an ouabain-binding fragment. PMID:127794

Clark, A F; Swanson, P D; Stahl, W L

1975-12-25

341

Formation of divalent ion mediated anionic disc bicelle-DNA complexes.  

PubMed

Disc-shaped bicelles are formed by mixing long-chain lipids with short-chain lipids at suitable molar ratios and they have a relatively uniform size, typically around a few tens of nanometers in diameter. Different from the typically formulated cationic or anionic liposome–DNA complexes, which are used as nonviral vectors for improving the transfection efficiency of gene therapy, a novel way of packing the DNA can be developed by using the much smaller disc-like bicelles. We demonstrate that anionic lipid bicelle-ion–DNA (AB–DNA) complexes can be formed with the help of divalent ions. Multi-stacked AB–DNA complexes can be formed with diameters of around 50–100 nm and lengths of around 50–150 nm as revealed by TEM. Using the anionic lipid–DNA complexes has the advantage of lower cytotoxicity than using cationic lipids. The interaction of DNA with anionic bicelles was investigated by SAXS. It was found that the anionic bicelle could not form stable complexes with DNA at low calcium ion concentrations, such as 1 mM. The AB–DNA complexes can be formed in the investigated range of 10 mM to 100 mM calcium ion concentrations. However, for an equal anionic lipid charge and DNA charge system, an ion-membrane phase (multilamellar vesicles) would gradually appear as the calcium ion concentration is increased above a critical concentration. It indicates that DNA could be packed closer at above the critical divalent ion concentration. If more DNA is added to such a two-phase coexistence system (originally with the total anionic lipid charge equal to that of DNA), the ion-membrane phase could be transformed into the AB–DNA complexes. As a result, more DNA can be packed in the form of AB–DNA complexes at above the critical calcium ion concentration. PMID:24795965

Yang, Po-Wei; Lin, Tsang-Lang; Hu, Yuan; Jeng, U-Ser

2014-04-01

342

Coordinate expression of the murine Hox-5 complex homoeobox-containing genes during limb pattern formation  

Microsoft Academic Search

The homoeobox-containing genes of the Hox-5 complex are expressed in different but overlapping domains in limbs during murine development. The more 5' the position of these genes in the complex, the later and more distal is their expression. Antero-posterior differences are also observed. A model is proposed that accounts for the establishment of these expression domains in relation to the

Pascal Dollé; Juan-Carlos Izpisúa-Belmonte; Hildegard Falkenstein; Armand Renucci; Denis Duboule

1989-01-01

343

Modeling Exsolution (and Perthite Formation) as an Example of Complex-System Behavior  

NSDL National Science Digital Library

Show Caption Hide This diagram shows the relationship of Gibbs Free Energy to composition. In this diagram there are two minima represented for free energy which is achieved by unmixing of two distinct phases each with definite composition. The dashed line, which is tangential to the two minima in the free energy curves, gives the composition of the coexisting minerals at a specific temperature. From: Klein, C., and Dutrow, B., Manual of Mineral Science, 23rd ed., J. Wiley and Sons. Used with permission. The phenomenon of solid solution is common in many rock-forming minerals. At high temperatures, thermal vibrations permit accomodation of ions with size differences on the order of 15-30%. However, as physical conditions change, ions no longer fit into similar sites which creates internal (lattice) strain energy. Consequently, the mineral composition must adjust to relieve this strain energy and minimize the Gibbs Free Energy of the system. One possible response of the system is for elements in a crystal to move from one chemical site to another via intracrystalline diffusion. This results in segregated domains that are enriched in one element or another--this is a process called exsolution. A good example of this process can be seen in the alkali feldspar mineral group. At high temperature the mineral anorthoclase (K,Na)AlSi3O8 shows complete solid solution, i.e. there is a random distribution of K and Na in the alkali sites of the crystal. Upon cooling, Na and K segregate into more ordered domains creating areas that are rich in albite NaAl Si3O8 and microcline KAlSi3O8(see Figure 1). The purpose of this exercise is to provide a number of activities to demonstrate how exsolution works and to demonstrate complex-system behavior in this relatively common natural phenomenon. Part I: Images of naturally occurring perthite. The following images show minerals that have undergone exsolution at different scales. The image on the top left shows exsolution as viewed with a Transmission Electron Microscope (TEM; field of view is 10 microns). The image on the top right is a photomicrograph of exsolution in microcline as seen in thin section (cross-polarized light, field of view is 2 mm). The picture on the bottom left is a hand sample of perthitic microcline as seen in hand sample (field of view is 10 cm). The picture on the bottom right is a picture of plagioclase feldspar showing the "schiller" effect. This is caused by sub-microscopic unmixing of two distinct plagioclase phases in the compositional range of labradorite (An50 - An70) which results in the beautiful play of colors seen in this photo; (field of view of 20 centimeters). This series of pictures is a good example of scale invariance of this physical phenomenon. Examine perthite textures from hand samples and thin sections from your own mineralogy collection. We can easily envision unmixing of two immiscible fluids--for example oil and vinegar salad dressing. The same thing happens when we unmix (i.e. exsolve) solid phases--the process just takes a bit longer as atoms have to migrate in the crystal lattice by intracrystalline diffusion! How can such a common feature as perthite be understood in terms of complex-system behavior? Exsolution observed on a sub-microscopic scale in this TEM picture; this microstructure shows unmixing of labradorite in very fine essentially parallel lamellae. From Champness, P.E., and G.W Lorimer, 1976. Exsolution in silicates. Chapter 4.1 in Electron Microscopy in Mineralogy. H.R. Wenk, ed. Springer-Verlag, New York. Field of view is 10 microns. Perthite observed in thin section. Field of view is 2 mm. Perthite observed in hand sample. Field of View is 10 cm. Unmixing of parallel lamellae, as observed in a hand specimen of labradorite from Madagascar. These lamellae act as diffraction grating for white light, producing spectral colors known as labradorescence or the "schiller effect"; the field of view is 20 cm. Photo by B. Dutrow; used by permission.] Part II: Exsolution Puzzle Exercise. This exercise is done in groups of 2-3 students. Coins are initially randomly distributed on a chessboard, and are then subsequently moved to create domains of increasing order (regions that are dominated by either pennies or nickels). This is a kinesthetic learning exercise that creates a physical model that simulates how the exsolution process works. (Inspired by Greg Marfleet, Carleton College) Randomly distribute 20 pennies and 20 nickels on the attached 7x7 chessboard (Microsoft Word 33kB Dec1 10). The random distribution of pennies and nickels is analogous to the random distribution of Na and K in the high temperature alkali feldspar, anorthosite. (See Figure 1) The goal is to have a given coin completely surrounded by similar neighbors (i.e. 8 nearest neighbors of the same type of coin located on adjacent edges and the diagonal squares. Each student will sequentially move a coin into an adjacent open position (horizontal, vertical and diagonal moves are allowed) to achieve this desired configuration. Perfect ordering of nickels and pennies into discrete domains is analogous to perfectly ordered crystals of albite and microcline. [NOTE: in this exercise we are modeling the diffusivity of only the alkali elements, Na and K. The ordering of Si and Al in the tetrahedral sites of a feldspar crystal is a related, but entirely different process]. Systems tend to minimize Gibbs Free Energy (see Figure 2) on their way towards a state of equilibrium. In this example, the surface area surrounding domains of the segregated compositions (nickels/Na and pennies/potassium) is proportional to the excess Gibbs Free Energy of those domains. As clusters of similar coins evolve (segregate) and get bigger, the bounding surface areas are minimized and the energetics of the system are decreased. INSTRUCTIONS For the initial random state, determine the area surrounding each type of element; do this by assuming the unit length along each edge is 1 and add all the surfaces surrounding Na/nickel and K/potassium coins or aggregates of coins. Count any edges that are not adjacent to another similar coin (i.e. count all nickel-penny interfaces, and any edge where a nickel or penny is adjacent to an open space. Do not count the external edges on the outer border of the chessboard). Make 10 moves of the coins (always moving into an adjacent open space either right, left, up, down, or on a diagonal) and again determine the bounding surface areas. Record these surface area values for pennies and nickels. Repeat after 20, 30, 40, 50, and 100 moves. After each set of moves, report your surface area measurements for both pennies and nickels to your instructor; record these values on a spread sheet for later plotting and analysis. This part of the exercise should take about 45 minutes to complete the sets of movements and measurement of the surface areas. Here is an example experiment showing the progressive ordering of pennies (potassium) and nickels (sodium). Show pictures of the 2-D distribution of pennies and nickels after 10,20, 30, 40, 50 and 100 successive moves Hide Original random distribution of coins. Distribution of coins after 10 moves. Distribution of coins after 20 moves. Distribution of coins after 30 moves. Distribution of coins after 40 moves. Distribution of coins after 50 moves. Distribution of coins after 100 moves; perfect order. Plot your results. Assume that each move requires 1 unit of time. Plot your data on a X-Y plot with surface area on the Y axis and time on the X-axis. What is the distribution of your data? (Try plotting data for pennies, nickels, their sum, and their averages). Create a "best fit" curve through the data as plotted on this X-Y diagram (easily done with functions programmed into Excel). . What type of mathematical function is represented by a curve that has a steep slope to begin (left side of the plot), and becomes asymptotic to the X-axis away from the origin? Did you notice that the first set of coin moves produced the largest change in surface area, and that subsequent sets of moves produced smaller and smaller changes to the surface area? Have you seen other plots with similar profiles from your other studies in Earth Science? Show Answer: Hide radioactive decay; longitudinal profile of rivers.... It appears that many processes in Earth Science may follow the same mathematical laws. Now plot your data on a log-log plot with surface area on the ordinate (Y-axis) and time on the abscissa (X-axis). Create a "best fit" curve through these data (easily done with functions programmed into Excel). What is the shape of this curve? Does this relationship demonstrate a) an exponential function? b) a power law? Here is an example dataset (Excel 74kB Dec1 10) for 12 experiments completed by the spring 2010 Mineralogy class at Montana State University. Raw data and corresponding graphs are presented in the attached spreadsheet file. Compare your results with those shown in this example exercise. Intracrystalline Diffusion and Fick's Law The rate of transport of mass (and energy) through a fixed medium can be described mathematically by Fick's Law of Diffusion. Show details about Fick's Law of Diffusion Hide. The fundamental expression of Fick's First Law of Diffusion can be written as: J = -D(c/x) Jis the flux of a material along a compositional gradient (e.g. mol / length2time1 ), the amount of material (e.g. atoms or moles) that will flow through a small area during a fixed time interval. Dis the diffusion coefficient (length2 time -1); c is the concentration (amount of material per volume, mol/m3), and x is the length (m) Fick's Law shows that the flux of an ion diffusing through a stationary medium (like the crystalline lattice in our example) is proportional to the concentration gradient (c/x). As diffusion proceeds, the concentration is always changing, and thus, the flux is always changing. Can you see why this process exhibits non-linear behavior and must be represented as a power law? Note that The diffusivity, D, scales with temperature: D ~ (kT/h) exp(-Q*/RT) where k is Boltzmann's constant, h is Planck's constant, and Q* is an activation energy. This means that the rate of diffusion decreases with temperature. Consequently, exsolution will ultimately grind to a halt as temperature decreases. This is why we can observe perthite development in alkali feldspars in a wide variety of igneous and metamorphic rocks...the perthite texture gives us information about the cooling history of the mineral up to a point, but then exsolution will slow to a stop and the perthite will continue to exist in a metastable state at the surface of the earth. Different types of diffusion pathways include: intragranular (volume) diffusion, grain boundary diffusion, diffusion in a bulk fluid, and diffusion related to crystal defects. In our example of perthite exsolution, intragranular (volume) diffusion is the operative process. This process is most effective at high temperatures. Note that generally material tends to move in a direction from high to low concentrations, and thus, compositional gradients tend to be minimized by diffusion. However, in the case of exsolution and perthite development during cooling of a high-temperature, homogeneous alkali feldspar (anorthite), just the opposite effect happens--segregated domains of albite and microcline become more stable at lower temperatures. Why is this the case? The answer lies in the overall energetics of the system. It turns out that lattice strain that is induced upon cooling of anorthite results in large excess energy in the system. To minimize this excess energy, a single homogeneous grain of anorthite (stable at high temperature), will undergo "spinodal" decomposition upon cooling. This results in two energy minima, one for each phase, as illustrated in Figure 2. Upon further cooling, these energy minima continue to separate, thus resulting in two stable phases whose compositions increasingly approach the end member compositions of albite and microcline. A more complete description of this process can be found in Chapters 5 and 7 of Putnis A. and McConnell J.D.C. Principles of Mineral Behaviour 258pp. Blackwell Scientific Publications. Oxford. 1980. Part III: Computer Simulation Model output from the NetLogo "segregation"program; 2000 objects achieved 70% similarity.The computer program NetLogo can be used to model complex system behavior. This computer program was developed by Uri Wilensky (1999) at the Center for Connected Learning and Computer-Based Modeling, Northwestern University. Evanston, IL. For this exercise, we will use the pre-programmed function for Segregation Experiment with this program by changing the input parameters to try to reproduce a) the pattern you developed in the puzzle model above, and b) perthite patterns observed in the natural microcline crystals. Part IV: Visualization of the Development of Exsolution The binary solvus phase diagram for the alkali feldspar system at low pressure. Figure provided by Dexter Perkins, used with permission.The binary "solvus" phase diagram (showing the relation of temperature to composition) is typically used to show the phase relations for alkali feldspars. A single homogeneous alkali feldspar occurs at high temperatures (Figure 1a), but as the system cools eventually the phase boundary (solvus) is intersected and the exsolution (unmixing) process begins. "Underneath" the solvus a single feldspar is no longer thermodynamically stable, and the system begins to separate into two phases that become increasingly Na-rich or K-rich upon further cooling. This visualization demonstrates the cooling history of an alkali feldspar, including use of the "lever rule" to calculate phase composition (mineral) and relative proportions. Examine the accompanying illustrations and track the "state" of the system as temperature changes. Binary Solvus for the Alkali Feldspar System. The accompanying illustrations on the right show the "state of the system" in terms of the relative proportions of the phases present for each assigned temperature. Relate these products and processes to natural occurrences of perthite, and think about the changes that have to take place on the atomic scale to produce the mesoscopic features that are visible in hand samples. Part V: Thought Questions Driving forces: in equilibrium thermodynamics, the system always drives towards the lowest Gibbs Free Energy. At equilibrium, chemical potential is zero. This typically means there are no compositional gradients. Why does this system drive towards segregated domains that are rich in Na and K? Consider entropy "in the system". What do we mean by "the system"? Refer to Ilya Prigogine's (winner of the 1977 Nobel Prize for Chemistry) classic work on this subject: Order out of Chaos, Man's New Dialogue with Nature (1984, Bantam Books, 394 pp.)

Mogk, David; Dutrow, Barb

344

Evaluation of CO2 migration and formation storage capacity in the Dalders formations, Baltic Sea - Preliminary analysis by means of models of increasing complexity  

NASA Astrophysics Data System (ADS)

We present preliminary data analysis and modeling of CO2 injection into selected parts of the Dalders Monocline and Dalders Structure, formations situated under the Baltic Sea and of potential interest for CO2 geological storage. The approach taken is to use models of increasing complexity successively, thereby increasing the confidence and reliability of the predictions. The objective is to get order-of-magnitude estimates of the behavior of the formations during potential industrial scale CO2 injection and subsequent storage periods. The focus has been in regions with best cap-rock characteristics, according to the present knowledge. Data has been compiled from various sources available, such as boreholes within the region. As the first approximation we use analytical solutions, in order to get an initial estimate the CO2 injection rates that can be used without causing unacceptable pressure increases. These preliminary values are then used as basis for more detailed numerical analyses with TOUGH2/TOUGH2-MP (e.g. Zhang et al, 2008) simulator and vertical equilibrium based (e.g. Gasda et al, 2009) models. With the numerical models the variations in material properties, formation thickness etc., as well as more processes such as CO2 dissolution can also be taken into account. The presentation discusses results from these preliminary analyses in terms of estimated storage capacity, CO2 and pressure plume extent caused by various injection scenarios, as well as CO2 travel time after the end of the injection. The effect of factors such as number of injection wells and the positioning of these, the effect of formation properties and the boundary conditions are discussed as are the benefits and disadvantages of the various modeling approaches used. References: Gasda S.E. et al, 2009. Computational Geosciences 13, 469-481. Zhang et al, 2008. Report LBNL-315E, Lawrence Berkeley National Laboratory.

Niemi, Auli; Yang, Zhibing; Tian, Liang; Jung, Byeongju; Fagerlund, Fritjof; Joodaki, Saba; Pasquali, Riccardo; O'Neill, Nick; Vernon, Richard

2014-05-01

345

Roles of Mg2+ in the mechanism of formation and dissociation of open complexes between Escherichia coli RNA polymerase and the lambda PR promoter: kinetic evidence for a second open complex requiring Mg2+.  

PubMed

Comparative studies of the effects of Mg2+ vs Na+ and of acetate (OAc-) vs Cl- on the kinetics of formation and dissociation of E. coli RNA polymerase (E sigma 70)-lambda PR promoter open complexes have been used to probe the mechanism of this interaction. Composite second-order association rate constants ka and first-order dissociation rate constants kd, and their power dependences on salt concentration SKa (SKa identical to d log ka/d log [salt]) and Skd (Skd identical to d log kd/d log [salt]), were determined in MgCl2 and NaOAc to compare with the results of Roe and Record (1985) in NaCl. Replacement of NaCl by MgCl2 reduces the magnitude of Ska 2-fold (Ska = -11.9 +/- 1.1 in NaCl; Ska = -5.2 +/- 0.3 in MgCl2) and (by extrapolation) drastically reduces the magnitude of ka at any specified salt concentration (e.g., approximately 10(6)-fold at 0.2 M). Replacement of NaCl by NaOAc does not significantly affect Ska (Ska = -12.0 +/- 0.7 in NaOAc) and (by extrapolation) increased ka by approximately 80-fold at any fixed [Na+]. In the absence of Mg2+, replacement of NaCl by NaOAc is found to increase the half-life of the open complex by approximately 560-fold at fixed [Na+] without affecting Skd [Skd = 7.6 +/- 0.1 in NaOAc; in NaCl, Skd = 7.7 +/- 0.2 (Roe & Record, 1985)]. Replacement of NaCl by MgCl2 drastically reduces both Skd and the half-life of the open complex at any salt concentration below approximately 0.2 M. Strikingly, Skd = 0.4 +/- 0.1 in MgCl2, indicating that the net uptake of Mg2+ ions in the kinetically significant steps in dissociation of the open complex is much smaller than that expected by analogy with the uptake of approximately 8 Na+ ions in the corresponding steps in NaCl. In NaCl/MgCl2 mixtures, at a constant [NaCl] in the range 0.1-0.2 M, initial addition of MgCl2 (0.5 mM less than or equal to [MgCl2] less than or equal to 1 mM) increases the half-life of the open complex; further addition of MgCl2 causes the half-life to decrease, though the effect of [MgCl2] on kd is always less than that predicted by a simple competitive model. The observed effects of MgCl2 on Skd and kd differ profoundly from those expected from the behavior of kd and Skd in NaCl and NaOAc and indicate that the role of Mg2+ in dissociation is not merely that of a nonspecific divalent competitor with RNAP for interactions with DNA phosphates and of a DNA helix-stabilizer, both of which should cause kd to increase monotonically with increasing [Mg2+].(ABSTRACT TRUNCATED AT 400 WORDS) PMID:1387321

Suh, W C; Leirmo, S; Record, M T

1992-09-01

346

Diffusion NMR study of complex formation in membrane-associated peptides  

E-print Network

Pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) is used to obtain the true hydrodynamic size of complexes of peptides with sodium dodecyl sulfate SDS micelles. The peptide used in this study is a 19-residue antimicrobial peptide, GAD-2. Two smaller dipeptides, alanine-glycine (Ala-Gly) and tyrosine-leucine (Tyr-Leu), are used for comparison. We use PFG-NMR to simultaneously measure diffusion coefficients of both peptide and surfactant. These two inputs, as a function of SDS concentration, are then fit to a simple two species model that neglects hydrodynamic interactions between complexes. From this we obtain the fraction of free SDS, and the hydrodynamic size of complexes in a GAD-2--SDS system as a function of SDS concentration. These results are compared to those for smaller dipeptides and for peptide-free solutions. At low SDS concentrations ([SDS] $\\leq$ 25 mM), the results self-consistently point to a GAD-2--SDS complex of fixed hydrodynamic size R =(5.5 $\\pm$ 0.3) nm. At intermediate SDS concentrations (25 mM $peptide ratio within a complex, most likely implying an increase in the number of peptides in a complex. For peptide-free solutions, the self-diffusion coefficients of SDS with and without buffer are significantly different at low SDS concentrations but merge above [SDS]=60 mM. We find that in order to obtain unambiguous information about the hydrodynamic size of a peptide-surfactant complex from diffusion measurements, experiments must be carried out at or below [SDS] = 25 mM.

Suliman Barhoum; Valerie Booth; Anand Yethiraj

2012-10-24

347

Photocatalytic CO2 reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes  

PubMed Central

Previously undescribed supramolecules constructed with various ratios of two kinds of Ru(II) complexes—a photosensitizer and a catalyst—were synthesized. These complexes can photocatalyze the reduction of CO2 to formic acid with high selectivity and durability using a wide range of wavelengths of visible light and NADH model compounds as electron donors in a mixed solution of dimethylformamide–triethanolamine. Using a higher ratio of the photosensitizer unit to the catalyst unit led to a higher yield of formic acid. In particular, of the reported photocatalysts, a trinuclear complex with two photosensitizer units and one catalyst unit photocatalyzed CO2 reduction (?HCOOH = 0.061, TONHCOOH = 671) with the fastest reaction rate (TOFHCOOH = 11.6 min-1). On the other hand, photocatalyses of a mixed system containing two kinds of model mononuclear Ru(II) complexes, and supramolecules with a higher ratio of the catalyst unit were much less efficient, and black oligomers and polymers were produced from the Ru complexes during photocatalytic reactions, which reduced the yield of formic acid. The photocatalytic formation of formic acid using the supramolecules described herein proceeds via two sequential processes: the photochemical reduction of the photosensitizer unit by NADH model compounds and intramolecular electron transfer to the catalyst unit. PMID:22908243

Tamaki, Yusuke; Morimoto, Tatsuki; Koike, Kazuhide; Ishitani, Osamu

2012-01-01

348

Autophosphorylation is crucial for CDK-activating kinase (Ee;CDKF;1) activity and complex formation in leafy spurge.  

PubMed

Ee;CDKF;1 protein is a leafy spurge (Euphorbia esula) CDK-activating kinase that is involved in a phosphorylation cascade linked to early stages of cell cycle progression. Yeast two-hybrid screening performed using Ee;CDKF;1 as a bait indicated that one of the interacting proteins was Ee;CDKF;1. Protein-protein interaction of Ee;CDKF;1 was further confirmed by yeast two-hybrid interaction and in vitro pull-down assays. Gel exclusion chromatography and/or native PAGE showed that GST-CDKF;1, MBP-CDKF;1, GST-CDKF;1 devoid of GST, and endogenous Ee;CDKF;1 were capable of forming homo protein complexes which are in dimer, trimer, and/or higher molecular-mass complex in its native state. In addition, Ee;CDKF;1 complexes were autophosphorylated and able to phosphorylate CDK. Moreover, mutant forms of Ee;CDKF;1 (106G/A, 166K/A), which lost autophosphorylation capability completely, were unable to form homo protein complexes in their native state. The result thus demonstrated that autophosphorylation of Ee;CDKF;1 is crucial for both kinase activity and complex formation. PMID:21421369

Jia, Ying; Anderson, James V; Chao, Wun S

2011-02-01

349

?-Synuclein assembles into higher-order multimers upon membrane binding to promote SNARE complex formation.  

PubMed

Physiologically, ?-synuclein chaperones soluble NSF attachment protein receptor (SNARE) complex assembly and may also perform other functions; pathologically, in contrast, ?-synuclein misfolds into neurotoxic aggregates that mediate neurodegeneration and propagate between neurons. In neurons, ?-synuclein exists in an equilibrium between cytosolic and membrane-bound states. Cytosolic ?-synuclein appears to be natively unfolded, whereas membrane-bound ?-synuclein adopts an ?-helical conformation. Although the majority of studies showed that cytosolic ?-synuclein is monomeric, it is unknown whether membrane-bound ?-synuclein is also monomeric, and whether chaperoning of SNARE complex assembly by ?-synuclein involves its cytosolic or membrane-bound state. Here, we show using chemical cross-linking and fluorescence resonance energy transfer (FRET) that ?-synuclein multimerizes into large homomeric complexes upon membrane binding. The FRET experiments indicated that the multimers of membrane-bound ?-synuclein exhibit defined intermolecular contacts, suggesting an ordered array. Moreover, we demonstrate that ?-synuclein promotes SNARE complex assembly at the presynaptic plasma membrane in its multimeric membrane-bound state, but not in its monomeric cytosolic state. Our data delineate a folding pathway for ?-synuclein that ranges from a monomeric, natively unfolded form in cytosol to a physiologically functional, multimeric form upon membrane binding, and show that only the latter but not the former acts as a SNARE complex chaperone at the presynaptic terminal, and may protect against neurodegeneration. PMID:25246573

Burré, Jacqueline; Sharma, Manu; Südhof, Thomas C

2014-10-01

350

Grating formation in bi-layered DNA-complex devices: application to thin-film tunable dye lasers  

NASA Astrophysics Data System (ADS)

Interaction of some organic dyes with DNA induces fluorescence enhancement through intercalation or groove binding, stimulating the development of compact tunable thin-film dye lasers. We have demonstrated amplified spontaneous emission (ASE), laser emission and its tuning via distributed feedback (DFB) with a dynamic grating formed in DNA-surfactant complexes doped with cyanine or hemicyanine dyes. The formation of semi-persistent (or quasi-dynamic) grating is more preferable in order to realize stable and easily tunable laser sources, so we fabricated bi-layered devices composed of a DNA-CTMA layer doped with pyridine 1 (Py1) and an PMMA layer including an azo dye, Disperse Red 1 (DR1). Under simultaneous excitation of the azo layer with interfering two beams for grating formation and the emission layer with another beam as pumping, we observed laser emission from the device. The oscillation wavelength was controlled by varying the incident beam angles allowing the fast tuning suitable to applications. Furthermore, monolithic DNA device having two functions of lasing and grating formation would be more promising. DNA-CTMA complex had been considered to be a poor matrix for grating inscription, but we found that doping of an azo-carbazole compound made it possible to inscribe gratings with relatively high diffraction efficiency and with fast response which could be applicable to monolithic tunable laser system.

Kawabe, Yutaka; Chida, Toshifumi; Matsuoka, Toshinori; Fukuzawa, Kodai; Tada, Kazuhiro

2013-10-01

351

Using Formative Assessment to Support Complex Learning in Conditions of Social Adversity  

ERIC Educational Resources Information Center

This article reports on research into formative assessment within a task design that produces multiple opportunities for teacher and pupil dialogue. It draws upon in-depth case studies conducted in schools in socially deprived areas of Scotland, using policy and documentary analysis, video-observation, and an iterative series of interviews with…

Crossouard, Barbara

2011-01-01

352

TOM-independent complex formation of Bax and Bak in mammalian mitochondria during TNFalpha-induced apoptosis.  

PubMed

The Bcl-2 family proteins Bax and Bak are activated in response to many apoptotic stimuli. As a consequence of activation, Bax and Bak oligomerize and permeabilize the outer mitochondrial membrane to permit the release of apoptosis-inducing factors. It still remains unclear whether these proteins require components of the mitochondrial protein import machinery for their function at the mitochondria. Here, we addressed this question by using inducible RNA interference for the study of protein import in mammalian mitochondria. After induction of apoptosis, we could not detect any impact of the absence of Tom22, Tom70, Tom40, Sam50 or metaxins on the translocation of Bax and formation of Bax and Bak complexes in mitochondria. In in vitro import studies, loss of these import and assembly proteins had no or only slight effect on the formation of complexes by radiolabeled Bax and Bak. We conclude that the import and assembly machineries of mammalian mitochondria have no impact on the translocation and complex assembly of Bax and Bak upon apoptosis induction. PMID:19165229

Ross, K; Rudel, T; Kozjak-Pavlovic, V

2009-05-01

353

Inhibition of interferon-inducible gene expression by adenovirus E1A proteins: Block in transcriptional complex formation  

SciTech Connect

Infection with wild-type adenovirus 5, but not with a mutant lacking the E1A gene, prevented the induction by interferon (IFN) {alpha} of chloramphenicol acetyltransferase (CAT) activity in HeLaM cell lines that had been permanently transfected with chimeric CAT reporter genes driven by the transcriptional regulatory regions of the IFN-inducible CAT activity was observed in cells that were cotransfected with the same reporter genes and plasmids expressing either the E1A 289- or 243-amino acid protein. These proteins also prevented the induction of CAT activity by IFN-{gamma} from a cotransfected HLA-DR{alpha}-CAT gene. Experiments with E1A mutants mapped the inhibitory activity to amino acid residues 38-65 of these proteins. In a HeLa cell line permanently expressing the E1A 289-amino acid protein, the replication of vesicular stomatitis virus and encephalomyocarditis virus was not inhibited by IFN-{alpha}, suggesting a global blockade of IFN responses. The observed transcriptional inhibition could be attributed to the lack of formation of the crucial IFN-stimulated gene factor 3 (ISGF3) transcriptional complex. As shown by mobility shift assays, this complex was not formed in the nuclear extracts of IFN-treated adenovirus-infected cells or IFN-treated E1A-producing cells. These nuclear extracts were deficient in both ISGF3{alpha} and ISGF3{gamma} subunits. However, they did not block the formation of ISGF3 complex from exogenously added components.

Kalvakolanu, D.V.R.; Bandyopadhyay, S.K.; Harter, M.L.; Sen, G.C. (Cleveland Clinic Foundation, OH (United States))

1991-09-01

354

Formation and Thermodynamics of Mg-Al-Ti-O Complex Inclusions in Mg-Al-Ti-Deoxidized Steel  

NASA Astrophysics Data System (ADS)

The formation of Mg-Al-Ti-O complex inclusions in steel was investigated by laboratory experiments and thermodynamic calculation. The composition evolutions of Mg-Al-Ti-O inclusions in steel with different contents of [Al], [Mg], and [Ti] were discussed. Mg-Al-Ti-O complex inclusion with high TiO x content was liquid at 1873 K (1600 °C), indicating MgAl2O4 spinel inclusions can be modified to low melting temperature ones by combining TiO x component. The stability diagram of Al-Mg-Ti-O system inclusions in the molten steel at 1873 K (1600 °C) was calculated, considering many kinds of oxide inclusions such as MgO, Al2O3, TiO x , MgTi2O4, MgAl2O4, Al2TiO5, and liquid inclusion. The thermodynamic calculations are in good agreement with experimental results, which can predict the formation of Al-Mg-Ti-O complex inclusions in molten steel with a large concentration range of [Al], [Mg], and [Ti].

Ren, Ying; Zhang, Lifeng; Yang, Wen; Duan, Haojian

2014-08-01

355

The influence of host-guest inclusion complex formation on the biotransformation of cortisone acetate Delta(1)-dehydrogenation.  

PubMed

An intensive and systematic investigation had been carried out on the Delta(1)-dehydrogenation of cortisone acetate (CA) to prednisone acetate (PA) by Arthrobacter simplex TCCC 11037 in the presence of native and modified beta-cyclodextrins (beta-CDs). The biotransformation was improved through the formation of the host-guest inclusion complex between CA and CDs in aqueous solution. The inclusion complexes of CDs with CA were investigated by means of phase solubility, 2D NMR spectroscopy and differential scanning calorimetry (DSC). The structural difference of CDs resulted in the stoichiometric differences between the complexes, the RM-beta-CD-CA, SBE-beta-CD-CA, HP-beta-CD-CA complexes were 1:1 whereas beta-CD-CA gave both 1:1 and 2:1 complexes, of which the 2:1 complex decreased the soluble CA concentration and inhibited the dissociation of beta-CD-CA in aqueous solution. The increase in solubility of CA was in the order of RM-beta-CD>SBE-beta-CD>HP-beta-CD>beta-CD. RM-beta-CD-CA, SBE-beta-CD-CA and HP-beta-CD-CA exhibited the higher biotransformation rate in comparison with native beta-CD. And the solubilization of CDs for CA in aqueous medium plays a key role in the biotransformation process. The article focuses on the various factors influencing the substrate water solubility, complex stability and biotransformation of CA through the addition of CDs in order to solve many problems associated with the process of drug delivery and biotransformation of different novel steroids. PMID:19744560

Ma, Yin-Hu; Wang, Min; Fan, Zhi; Shen, Yan-Bing; Zhang, Li-Ting

2009-11-01

356

Structure-property relationships based on Hammett constants in cyclometalated iridium(III) complexes: their application to the design of a fluorine-free FIrPic-like emitter.  

PubMed

While phosphorescent cyclometalated iridium(iii) complexes have been widely studied, only correlations between oxidation potential EOX and Hammett constant ?, and between the redox gap (?EREDOX = EOX-ERED) and emission or absorption wavelength (?abs, ?em) have been reported. We present now a quantitative model based on Hammett parameters that rationalizes the effect of the substituents on the properties of cyclometalated iridium(iii) complexes. This simple model allows predicting the apparent redox potentials as well as the electrochemical gap of homoleptic complexes based on phenylpyridine ligands with good accuracy. In particular, the model accounts for the unequal effect of the substituents on both the HOMO and the LUMO energy levels. Consequently, the model is used to anticipate the emission maxima of the corresponding complexes with improved reliability. We demonstrate in a series of phenylpyridine emitters that electron-donating groups can effectively replace electron-withdrawing substituents on the orthometallated phenyl to induce a blue shift of the emission. This result is in contrast with the common approach that uses fluorine to blue shift the emission maximum. Finally, as a proof of concept, we used electron-donating substituents to design a new fluorine-free complex, referred to as EB343, matching the various properties, namely oxidation and reduction potentials, electrochemical gap and emission profile, of the standard sky-blue emitter FIrPic. PMID:24345847

Frey, Julien; Curchod, Basile F E; Scopelliti, Rosario; Tavernelli, Ivano; Rothlisberger, Ursula; Nazeeruddin, Mohammad K; Baranoff, Etienne

2014-04-21

357

Unprecedented formation of a doubly bridged ?-peroxo-?-pyrazolyldicarboxylato-dicobalt(III) complex  

Microsoft Academic Search

The reaction of an aqueous solution containing Co(ClO4)2, di(2-pyridymethyl)amine (DPA) and 3,5-pyrazole dicarboxylate anion (Hpzdc2?) afforded the unprecedented diamagnetic dicobalt(III)-peroxo complex [Co2(DPA)2(?-pzdc)(?-?1:?1-O2)]ClO4·3H2O (1) where the pyrazole group was fully deprotonated. The complex was structurally characterized by IR and UV–vis spectroscopy. X-ray crystal structure of 1 reveals the existence of the doubly bridged nature of cis-?-?1:?1-peroxo (end-on) and the dicarboxylato pyrazole.

Febee R. Louka; Lam T. Nguyen; Jörg H. Albering; Franz A. Mautner; Salah S. Massoud

358

Discovery of a Strongly-Interrelated Gene Network in Corals under Constant Darkness by Correlation Analysis after Wavelet Transform on Complex Network Model  

PubMed Central

Coral reefs occupy a relatively small portion of sea area, yet serve as a crucial source of biodiversity by establishing harmonious ecosystems with marine plants and animals. Previous researches mainly focused on screening several key genes induced by stress. Here we proposed a novel method—correlation analysis after wavelet transform of complex network model, to explore the effect of light on gene expression in the coral Acropora millepora based on microarray data. In this method, wavelet transform and the conception of complex network were adopted, and 50 key genes with large differences were finally captured, including both annotated genes and novel genes without accurate annotation. These results shed light on our understanding of coral's response toward light changes and the genome-wide interaction among genes under the control of biorhythm, and hence help us to better protect the coral reef ecosystems. Further studies are needed to explore how functional connections are related to structural connections, and how connectivity arises from the interactions within and between different systems. The method introduced in this study for analyzing microarray data will allow researchers to explore genome-wide interaction network with their own dataset and understand the relevant biological processes. PMID:24651851

Zhou, Xilong; Liu, Xuefeng; Zhang, Zhaobao; Wang, Xumin; Liu, Tao; Liu, Guiming

2014-01-01

359

Formation of water-soluble metal cyanide complexes from solid minerals by Pseudomonas plecoglossicida.  

PubMed

A few Pseudomonas species are able to form hydrocyanic acid (HCN), particularly when grown under glycine-rich conditions. In the presence of metals, cyanide can form water-soluble metal complexes of high chemical stability. We studied the possibility to mobilize metals as cyanide complexes from solid minerals using HCN-forming microorganisms. Pseudomonas plecoglossicida was cultivated in the presence of copper- and nickel-containing solid minerals. On powdered elemental nickel, fast HCN generation within the first 12 h of incubation was observed and water-soluble tetracyanaonickelate was formed. Cuprite, tenorite, chrysocolla, malachite, bornite, turquoise, millerite, pentlandite as well as shredded electronic scrap was also subjected to a biological treatment. Maximum concentrations of cyanide-complexed copper corresponded to a solubilization of 42% and 27% when P. plecoglossicida was grown in the presence of cuprite or tenorite, respectively. Crystal system, metal oxidation state and mineral hydrophobicity might have a significant influence on metal mobilization. However, it was not possible to allocate metal mobilization to a single mineral property. Cyanide-complexed gold was detected during growth on manually cut circuit boards. Maximum dicyanoaurate concentration corresponded to a 68.5% dissolution of the total gold added. These findings represent a novel type of microbial mobilization of nickel and copper from solid minerals based on the ability of certain microbes to form HCN. PMID:16684101

Faramarzi, Mohammad A; Brandl, Helmut

2006-06-01

360

Diffusion NMR study of complex formation in membrane-associated peptides  

E-print Network

Pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) is used to obtain the true hydrodynamic size of complexes of peptides with sodium dodecyl sulfate SDS micelles. The peptide used in this study is a 19-residue antimicrobial peptide, GAD-2. Two smaller dipeptides, alanine-glycine (Ala-Gly) and tyrosine-leucine (Tyr-Leu), are used for comparison. We use PFG-NMR to simultaneously measure diffusion coefficients of both peptide and surfactant. These two inputs, as a function of SDS concentration, are then fit to a simple two species model that neglects hydrodynamic interactions between complexes. From this we obtain the fraction of free SDS, and the hydrodynamic size of complexes in a GAD-2--SDS system as a function of SDS concentration. These results are compared to those for smaller dipeptides and for peptide-free solutions. At low SDS concentrations ([SDS] $\\leq$ 25 mM), the results self-consistently point to a GAD-2--SDS complex of fixed hydrodynamic size R =(5.5 $\\pm$ 0.3) nm. At intermediate SDS conc...

Barhoum, Suliman; Yethiraj, Anand

2012-01-01

361

Complex caddisfly-dominated bioherms from the Eocene Green River Formation  

Microsoft Academic Search

Complex, caddisfly-dominated (Insecta: Trichoptera) carbonate mounds up to 9 m tall and 40 m in diameter formed in the nearshore environment of Eocene Lake Gosiute. The mounds outcrop for 70 km in reef-like geometries along the northern margin of Lake Gosiute in Wyoming. The relationships among the caddisfly larvae, the benthic microbial mat and physicochemical nearshore processes of Eocene Lake

V. Leroy Leggitt; Robert A. Cushman Jr

2001-01-01

362

Complexation versus thiadiazole formation for reactions of thiosemicarbazides with copper(II).  

PubMed

The reactions of N,N-substituted thiosemicarbazides with copper salts have been investigated and either copper(II) thiosemicarbazide complexes, 1,3,4-thiadiazolium salts or 1,3,5-thiadiazoles are obtained depending on the Cu(II) salt and solvent used. PMID:17353950

López-Torres, Elena; Cowley, Andrew R; Dilworth, Jonathan R

2007-03-28

363

Swarming and complex pattern formation in Paenibacillus vortex studied by imaging and tracking cells  

Microsoft Academic Search

BACKGROUND: Swarming motility allows microorganisms to move rapidly over surfaces. The Gram-positive bacterium Paenibacillus vortex exhibits advanced cooperative motility on agar plates resulting in intricate colonial patterns with geometries that are highly sensitive to the environment. The cellular mechanisms that underpin the complex multicellular organization of such a simple organism are not well understood. RESULTS: Swarming by P. vortex was

Colin J Ingham; Eshel Ben Jacob

2008-01-01

364

Separation of drug stereoisomers by the formation of. beta. -cyclodextrin inclusion complexes  

Microsoft Academic Search

For many drugs, only racemic mixtures are available for clinical use. Because different stereoisomers of drugs often cause different physiological responses, the use of pure isomers could elicit more exact therapeutic effects. Differential complexation of a variety of drug stereoisomers by immobilized ..beta..-cyclodextrin was investigated. Chiral recognition and racemic resolution were observed with a number of compounds from such clinically

D. W. Armstrong; T. J. Ward; R. D. Armstrong; T. E. Beesley

1986-01-01

365

Separation of Drug Stereoisomers by the Formation of beta Cyclodextrin Inclusion Complexes  

Microsoft Academic Search

For many drugs, only racemic mixtures are available for clinical use. Because different stereoisomers of drugs often cause different physiological responses, the use of pure isomers could elicit more exact therapeutic effects. Differential complexation of a variety of drug stereoisomers by immobilized beta -cyclodextrin was investigated. Chiral recognition and racemic resolution were observed with a number of compounds from such

Daniel W. Armstrong; Timothy J. Ward; R. Douglas Armstrong; Thomas E. Beesley

1986-01-01

366

Influence of temperature on ion-exchange equilibrium accompanied by complex formation in resins  

Microsoft Academic Search

The paper deals with finding the correlation between the influence of temperature on the ionic selectivity of ion-exchange resins studied experimentally and their chemical structures. The effects of temperature on selectivity of resins are compared with the data for the soluble complexing reagents. The physicochemical basis of the influence of temperature on ion-exchange selectivity is considered.

V. A. Ivanov; V. I. Gorshkov; V. D. Timofeevskaja; N. V. Drozdova

1998-01-01

367

Redistribution of material and formation of polygenic mélanges in the External Ligurian accretionary complex (Northern Apennines, Italy)  

NASA Astrophysics Data System (ADS)

Tectonic, sedimentary and diapiric processes may strongly control the dynamics of the shallower part of subduction-accretionary complexes, and formation of polygenic mélanges at different scales. In modern accretionary complexes, drill cores and seismic images provide in-situ samples and measurements about large-scale features, and crucial informations on the structural processes that control their dynamics. However, minor-scale geological features and processes that are responsible for their formation are still difficult to decipher based on these techniques alone. On-land, exhumed accretionary complexes, on the other hand, can provide essential informations at all scales about (i) 3D features and structural architecture of mélanges, (ii) the role and interplay of different processes of mélange formation, and (iii) the redistribution of material in shallower parts of accretionary complexes (Festa et al., 2010). Detailed structural-stratigraphic observations in the exhumed Ligurian accretionary complex in the westernmost Northern Apennines show that a larger part of it (i.e., the Argille varicolori Formation) represents a composite chaotic unit consisting of diverse scale mélange types formed by tectonic, sedimentary and diapiric processes and their mutual superposition. Here, the spatial and temporal relationships between these mélange types resulted from two main episodes of deformation: (i) late Cretaceous-middle Eocene accretion, producing tectonic deformation of sediments at the wedge-front and formation of tectonically disrupted bodies through layer-parallel extension and contraction. Episodes of dynamic instability of the wedge-front alternating with steady-state accretion caused the removal of material locally and the subsequent emplacement of gravity-driven chaotic bodies within the tectonically disrupted bodies; (ii) late Oligocene-middle Miocene out-of-sequence thrusting, overprinting the previously formed chaotic bodies and producing a new and polygenic type of tectonically disrupted bodies through shearing close to the main thrusts. This deformation event also led to the emplacement of large (regional-scale) olistostromes at the wedge-front. The rapid burial due to the emplacement of these olistostromes and/or the tectonic shaking of unconsolidated sediments might have triggered the focused mobilization of overpressured fluids forming diapiric mélanges. We conclude that superposition of tectonic, sedimentary and diapiric processes resulted in the occurrence at different scales of different types of mélanges and polygenic mélanges in the Ligurian accretionary complex. Our recognition of these polygenic mélanges in the rock record is highly important for better understanding the dynamics, crustal architecture, and structural evolution of other ancient subduction-accretionary complexes around the world. Festa A., Pini G.A., Dilek Y. and Codegone G. (2010) - Mélanges and mélange-forming processes: a historical overview and new concepts. International Geology Review, v. 52, n. 10-12, p. 1040-1105.

Codegone, G.; Festa, A.; Dilek, Y.; Pini, G.

2011-12-01

368

Detailed chemical characterization of unresolved complex mixtures in atmospheric organics: Insights into emission sources, atmospheric processing, and secondary organic aerosol formation  

NASA Astrophysics Data System (ADS)

Recent studies suggest that semivolatile organic compounds (SVOCs) are important precursors to secondary organic aerosol (SOA) in urban atmospheres. However, knowledge of the chemical composition of SVOCs is limited by current analytical techniques, which are typically unable to resolve a large number of constitutional isomers. Using a combination of gas chromatography and soft photoionization mass spectrometry, we characterize the unresolved complex mixture (UCM) of semivolatile aliphatic hydrocarbons observed in Pasadena, California (~16 km NE of downtown Los Angeles), and Bakersfield, California, during the California Research at the Nexus of Air Quality and Climate Change 2010. To the authors' knowledge, this work represents the most detailed characterization of the UCM in atmospheric samples to date. Knowledge of molecular structures, including carbon number, alkyl branching, and number of rings, provides important constraints on the rate of atmospheric processing, as the relative amounts of branched and linear alkanes are shown to be a function of integrated exposure to hydroxyl radicals. Emissions of semivolatile branched alkanes from fossil fuel-related sources are up to an order of magnitude higher than those of linear alkanes, and the gas-phase OH rate constants of branched alkanes are ~30% higher than their linear isomers. Based on a box model considering gas/particle partitioning, emissions, and reaction rates, semivolatile branched alkanes are expected to play a more important role than linear alkanes in the photooxidation of the UCM and subsequent transformations into SOA. Detailed speciation of semivolatile compounds therefore provides essential understanding of SOA sources and formation processes in urban areas.

Chan, Arthur W. H.; Isaacman, Gabriel; Wilson, Kevin R.; Worton, David R.; Ruehl, Christopher R.; Nah, Theodora; Gentner, Drew R.; Dallmann, Timothy R.; Kirchstetter, Thomas W.; Harley, Robert A.; Gilman, Jessica B.; Kuster, William C.; Gouw, Joost A.; Offenberg, John H.; Kleindienst, Tadeusz E.; Lin, Ying H.; Rubitschun, Caitlin L.; Surratt, Jason D.; Hayes, Patrick L.; Jimenez, Jose L.; Goldstein, Allen H.

2013-06-01

369

Increased complexity of radiation-induced chromosome aberrations consistent with a mechanism of sequential formation.  

PubMed

Complex chromosome aberrations (any exchange involving three or more breaks in two or more chromosomes) are effectively induced in peripheral blood lymphocytes (PBL) after exposure to low doses (mostly single particles) of densely ionising high-linear energy transfer (LET) alpha-particle radiation. The complexity, when observed by multiplex fluorescence in situ hybridisation (m-FISH), shows that commonly four but up to eight different chromosomes can be involved in each rearrangement. Given the territorial organisation of chromosomes in interphase and that only a very small fraction of the nucleus is irradiated by each alpha-particle traversal, the aim of this study is to address how aberrations of such complexity can be formed. To do this, we applied theoretical "cycle" analyses using m-FISH paint detail of PBL in their first cell division after exposure to high-LET alpha-particles. In brief, "cycle" analysis deconstructs the aberration "observed" by m-FISH to make predictions as to how it could have been formed in interphase. We propose from this that individual high-LET alpha-particle-induced complex aberrations may be formed by the misrepair of damaged chromatin in single physical "sites" within the nucleus, where each "site" is consistent with an "area" corresponding to the interface of two to three different chromosome territories. Limited migration of damaged chromatin is "allowed" within this "area". Complex aberrations of increased size, reflecting the path of alpha-particle nuclear intersection, are formed through the sequential linking of these individual sites by the involvement of common chromosomes. PMID:16276088

Anderson, R M; Papworth, D G; Stevens, D L; Sumption, N D; Goodhead, D T

2006-01-01

370

Initial formation of an indigenous crop complex in eastern North America at 3800 B.P  

PubMed Central

Although geneticists and archaeologists continue to make progress world-wide in documenting the time and place of the initial domestication of a growing number of plants and animals, far less is known regarding the critically important context of coalescence of various species into distinctive sets or complexes of domesticates in each of the world's 10 or more independent centers of agricultural origin. In this article, the initial emergence of a crop complex is described for one of the best-documented of these independent centers, eastern North America (ENA). Before 4000 B.P. there is no indication of a crop complex in ENA, only isolated evidence for single indigenous domesticate species. By 3800 B.P., however, at least 5 domesticated seed-bearing plants formed a coherent complex in the river valley corridors of ENA. Accelerator mass spectrometer radiocarbon dates and reanalysis of archaeobotanical assemblages from a short occupation of the Riverton Site in Illinois documents the contemporary cultivation at 3800 B.P. of domesticated bottle gourd (Lagenaria siceraria), marshelder (Iva annua var. macrocarpa), sunflower (Helianthus annuus var. macrocarpus), and 2 cultivated varieties of chenopod (Chenopodium berlandieri), as well as the possible cultivation of Cucurbita pepo squash and little barley (Hordeum pusillum). Rather than marking either an abrupt developmental break or a necessary response to population-packing or compressed resource catchments, the coalescence of an initial crop complex in ENA appears to reflect an integrated expansion and enhancement of preexisting hunting and gathering economies that took place within a context of stable long-term adaptation to resource-rich river valley settings. PMID:19366669

Smith, Bruce D.; Yarnell, Richard A.

2009-01-01

371

Initial formation of an indigenous crop complex in eastern North America at 3800 B.P.  

PubMed

Although geneticists and archaeologists continue to make progress world-wide in documenting the time and place of the initial domestication of a growing number of plants and animals, far less is known regarding the critically important context of coalescence of various species into distinctive sets or complexes of domesticates in each of the world's 10 or more independent centers of agricultural origin. In this article, the initial emergence of a crop complex is described for one of the best-documented of these independent centers, eastern North America (ENA). Before 4000 B.P. there is no indication of a crop complex in ENA, only isolated evidence for single indigenous domesticate species. By 3800 B.P., however, at least 5 domesticated seed-bearing plants formed a coherent complex in the river valley corridors of ENA. Accelerator mass spectrometer radiocarbon dates and reanalysis of archaeobotanical assemblages from a short occupation of the Riverton Site in Illinois documents the contemporary cultivation at 3800 B.P. of domesticated bottle gourd (Lagenaria siceraria), marshelder (Iva annua var. macrocarpa), sunflower (Helianthus annuus var. macrocarpus), and 2 cultivated varieties of chenopod (Chenopodium berlandieri), as well as the possible cultivation of Cucurbita pepo squash and little barley (Hordeum pusillum). Rather than marking either an abrupt developmental break or a necessary response to population-packing or compressed resource catchments, the coalescence of an initial crop complex in ENA appears to reflect an integrated expansion and enhancement of preexisting hunting and gathering economies that took place within a context of stable long-term adaptation to resource-rich river valley settings. PMID:19366669

Smith, Bruce D; Yarnell, Richard A

2009-04-21

372

Complex formation and background impurity of Oxygen in the PbTe:Eu doped crystals grown from melt by the Bridgman method  

NASA Astrophysics Data System (ADS)

The magnetic field dependence of magnetization M(B) at the temperature 1.72 K in magnetic fields up to 5 T and the temperature dependence of magnetic susceptibility ( MS) ?(T) in the temperature range 1.7-400 K of six PbTe:Eu samples with the concentration of Eu impurity of the order of 1×10 19-1×10 20 cm -3, prepared from the doped crystals grown from the melt by the Bridgman method, have been investigated. It is shown that the dependence of M(B) and ?(T) can be quantitatively explained by the contribution of the single centers of Eu ions, their pairs, and the matrix of the doped crystals using the same set of parameters for each sample. This is true provided we use in our analysis the values of the exchange integrals between Eu ions in EuO normalized with the lattice constant of PbTe, i.e., J1/k B=0.056 K for the ferromagnetic interaction of the NN (nearest neighbor) pairs and J2/k B=-0.13 K for the antiferromagnetic interaction of the NNN (next nearest neighbor) pairs, as well as different values of the MS of crystal ?matrix. It is revealed that the probability of the formation of complexes based on the magnetic impurity pairs is higher in the incipient section of a doped ingot, and it decreases towards the ingot end where the single centers of Eu ions become the only centers of the impurity. We conclude that the pairs of Eu 2+ ions, which are formed during the growth of the PbTe:Eu ingots from melt by the Bridgman method, are the constituents of the complexes of the magnetic impurities with the background Oxygen impurities in the crystal matrix of the doped lead telluride. It is shown that the formation of the complexes leads to an increase of the MS of crystal matrix ?matrix and can even cause the change of its sign from minus to plus, i.e., it can convert the crystal matrix from the diamagnetic to paramagnetic state. The possible causes of this effect are analyzed.

Zayachuk, D. M.; Mikityuk, V. I.; Shlemkevych, V. V.; Kaczorowski, D.

2012-01-01

373

Order formation processes of complex systems including different parity order parameters  

NASA Astrophysics Data System (ADS)

In the present study, we focus on the parity of the order parameters and clarify the order formation process in a system including two order parameters. Each order parameter shows different parity under a gauge transformation, namely even and odd order parameters. For example, in a spin-glass model, the even order parameter corresponds to the spin-glass order parameter while the odd one corresponds to the magnetization. We introduce phenomenologically a set of Langevin equations to express the ordering process under a white Gaussian noise. Using two kinds of Fokker-Planck equations, we analyze the order formation process and the entropy production. Furthermore, we show the noise dependence of the onset time.

Hashizume, Yoichiro; Suzuki, Masuo; Okamura, Soichiro

2014-06-01

374

The G305 star-forming complex: embedded massive star formation discovered by Herschel Hi-GAL  

NASA Astrophysics Data System (ADS)

We present a Herschel far-infrared study towards the rich massive star-forming complex G305, utilizing PACS 70, 160 ?m and SPIRE 250, 350, and 500 ?m observations from the Hi-GAL survey of the Galactic plane. The focus of this study is to identify the embedded massive star-forming population within G305, by combining far-infrared data with radio continuum, H2O maser, methanol maser, MIPS and Red MSX Source survey data available from previous studies. By applying a frequentist technique we are able to identify a sample of the most likely associations within our multiwavelength data set, which can then be identified from the derived properties obtained from fitted spectral energy distributions (SEDs). By SED modelling using both a simple modified blackbody and fitting to a comprehensive grid of model SEDs, some 16 candidate associations are identified as embedded massive star-forming regions. We derive a two-selection colour criterion from this sample of log (F70/F500) ? 1 and log (F160/F350) ? 1.6 to identify an additional 31 embedded massive star candidates with no associated star formation tracers. Using this result we can build a picture of the present-day star formation of the complex, and by extrapolating an initial mass function, suggest a current population of ?2 × 104 young stellar objects (YSOs) present, corresponding to a star formation rate (SFR) of 0.01-0.02 M? yr-1. Comparing this resolved SFR, to extragalactic SFR tracers (based on the Kennicutt-Schmidt relation), we find that the star formation activity is underestimated by a factor of ?2 in comparison to the SFR derived from the YSO population. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Faimali, A.; Thompson, M. A.; Hindson, L.; Urquhart, J. S.; Pestalozzi, M.; Carey, S.; Shenoy, S.; Veneziani, M.; Molinari, S.; Clark, J. S.

2012-10-01

375

Assembly of the functional membrane attack complex of human complement: formation of disulfide-linked C9 dimers.  

PubMed

The 158,000 Mr protein, previously designated C5c, present in fully assembled complement (C) membrane attack complexes (MC5b-9) has been identified as a disulfide-bonded dimer of C9. This conclusion was based on the observations that: (i) a portion of the 125I-radiolabeled precursor C9 incorporated into MC5b-9 complexes comigrated with the 158,000 Mr protein band in NaDodSO4/polyacrylamide slab gels; (ii) monospecific antisera produced against native C9 and the 158,000 Mr protein immunologically crossreacted with monomeric native C9 by double immunodiffusion and with monomeric C9 and the 158,000 Mr protein on immunoreplication procedures; and (iii) two-dimensional NaDodSO4/polyacrylamide slab gel electrophoresis, in which the second dimension was conducted under reducing conditions, revealed that the 158,000 Mr protein contained two identical 71,000 Mr subunits which comigrated with monomeric C9. Molar ratio estimates indicated that 1 mol of C5b, C9 dimer, C6, C7, and C8 and 3-4 mol of C9 monomer were present per MC5b-9 complex. Each fully assembled membrane-bound MC5b-9 complex would therefore have a calculated Mr of 982,000. The presence of C9 dimers in the hemolytically active 29S dimeric form of the MC5b-9 complex and the absence of C9 dimers in the hemolytically inactive 23S monomeric form of the fluid phase SC5b-9 complex strongly suggest an important role for C9 dimer formation in MC5b-9 complex structure and function. The most probable function of C9 dimers would be the formation of intercomplex disulfide crosslinks which would provide a mechanism to stabilize the assembly of MC5b-9 into aggregates of increasing size on the target membrane surface which would thus be responsible for the observed pore size heterogeneity of functional C lesions. PMID:6796960

Ware, C F; Kolb, W P

1981-10-01

376

A complex microbiota from snowball Earth times: Microfossils from the Neoproterozoic Kingston Peak Formation, Death Valley, USA  

PubMed Central

A thin carbonate unit associated with a Sturtian-age (?750–700 million years ago) glaciogenic diamictite of the Neoproterozoic Kingston Peak Formation, eastern California, contains microfossil evidence of a once-thriving prokaryotic and eukaryotic microbial community (preserved in chert and carbonate). Stratiform stromatolites, oncoids, and rare columnar stromatolites also occur. The microbial fossils, which include putative autotrophic and heterotrophic eukaryotes, are similar to those found in chert in the underlying preglacial units. They indicate that microbial life adapted to shallow-water carbonate environments did not suffer the significant extinction postulated for this phase of low-latitude glaciation and that trophic complexity survived through snowball Earth times. PMID:12682298

Corsetti, Frank A.; Awramik, Stanley M.; Pierce, David

2003-01-01

377

The Formation of Cluster Cooling Cores within a Complex Supercluster Environment  

NASA Astrophysics Data System (ADS)

We present preliminary results from the simulation of cluster formation that include the effects of radiative cooling by the gas for a ? CDM cosmological model. In adiabatic simulations of structure formation, a network of filaments is observed which conveys material into the clusters. This phenomena of highly non-spherical accretion is also observed when radiative cooling is present. In addition, the accreted substructures often possess dense cores that may donate pre-cooled gas to the primary cooling core or disrupt the signature of the dominant cooling core. The simulations indicate a cluster history that differs greatly from the view of an isolated, spherically symmetric cooling flow and paints a new picture for the formation of cooling cores in rich clusters as the result of accretion of cool groups from supercluster filaments. We will examine the implications of the interaction of the central cooling core with its environment for the interpretation of recent X-Ray observations. An adaptive mesh Eulerian code was used in the simulations. The highest level of refinement employed corresponds to 15 h-1 kpc within a computational volume of 2563 h-3 Mpc3. The computations presented were performed on the SGI Origin 2000 cluster at NCSA.

Motl, P. M.; Burns, J. O.; Loken, C.; Norman, M. L.

2001-11-01

378

Use of spectroscopic technique to develop a reagent for Mo(VI) utilizing micellar effects on complex formation  

NASA Astrophysics Data System (ADS)

Ultraviolet and visible spectral properties of aqueous solutions of molybdenum(VI) (Mo), gallic acid (GA), Lalanine (Ala), and L-Phenylalanine (Phe), and of their binary and ternary solutions were investigated in the absence and presence of anionic, cationic, and nonionic surfactant micelles. Evaluation of the spectra in a comparative way revealed that both Ala and Phe form ternary complexes with Mo and GA. The formation of a quaternary complex between Mo, GA, Phe, and cetyltrimethylammonium bromide at pH 4.5 provided a reagent system with a strikingly high sensitivity (1.2•106 l/(mol•cm)) for use in the spectrophotometric determination of Mo. A mechanism of micellar effects was discussed in terms of the substrate molecular charge and hydrophobicity, and rationalized on the basis of the spectral data obtained above and below the isoelectric pH of the amino acids.

Ta?cio?lu, Sülin; Kaki, E.; Ta?cio?lu, Senay

2012-09-01

379

Physalin H from Solanum nigrum as an Hh signaling inhibitor blocks GLI1-DNA-complex formation.  

PubMed

Hedgehog (Hh) signaling plays an important role in embryonic development, cell maintenance and cell proliferation. Moreover, Hh signaling contributes to the growth of cancer cells. Physalins are highly oxidized natural products with a complex structure. Physalins (1-7) were isolated from Solanum nigrum (Solanaceae) collected in Bangladesh by using our cell-based assay. The isolated physalins included the previously reported Hh inhibitors 5 and 6. Compounds 1 and 4 showed strong inhibition of GLI1 transcriptional activity, and exhibited cytotoxicity against cancer cell lines with an aberrant activation of Hh signaling. Compound 1 inhibited the production of the Hh-related proteins patched (PTCH) and BCL2. Analysis of the structures of different physalins showed that the left part of the physalins was important for Hh inhibitory activity. Interestingly, physalin H (1) disrupted GLI1 binding to its DNA binding domain, while the weak inhibitor physalin G (2) did not show inhibition of GLI1-DNA complex formation. PMID:24454566

Arai, Midori A; Uchida, Kyoko; Sadhu, Samir K; Ahmed, Firoj; Ishibashi, Masami

2014-01-13

380

Physalin H from Solanum nigrum as an Hh signaling inhibitor blocks GLI1-DNA-complex formation  

PubMed Central

Summary Hedgehog (Hh) signaling plays an important role in embryonic development, cell maintenance and cell proliferation. Moreover, Hh signaling contributes to the growth of cancer cells. Physalins are highly oxidized natural products with a complex structure. Physalins (1–7) were isolated from Solanum nigrum (Solanaceae) collected in Bangladesh by using our cell-based assay. The isolated physalins included the previously reported Hh inhibitors 5 and 6. Compounds 1 and 4 showed strong inhibition of GLI1 transcriptional activity, and exhibited cytotoxicity against cancer cell lines with an aberrant activation of Hh signaling. Compound 1 inhibited the production of the Hh-related proteins patched (PTCH) and BCL2. Analysis of the structures of different physalins showed that the left part of the physalins was important for Hh inhibitory activity. Interestingly, physalin H (1) disrupted GLI1 binding to its DNA binding domain, while the weak inhibitor physalin G (2) did not show inhibition of GLI1-DNA complex formation. PMID:24454566

Uchida, Kyoko; Sadhu, Samir K; Ahmed, Firoj

2014-01-01

381

[Investigation of protonation and complex formation processes of some new polyamino carboxylic acids].  

PubMed

The medicinal chemistry often needs chemical compound with special properties. The preparation of compounds with special properties generally needs 10-20 steps of preparation and the final product is available in small amount. The characterisation of this kinds of compounds needs special methods and procedures for investigation. This kind of method has been developed and used for characterisation of some new polyaminopolycarboxylic acid derivatives. Protolytic equilibrium of 2,2',2",2'"-[terpyridine-6,6"diyl)bis(methylenenitrilo)]tetrakisacetic acid and 3,5-bis[6'-bis (N,N-bis(carboxymethyl)aminomethyl]-2'-pyridyl)-1H,2, 4-triazole was investigated by pH-metric and spectrophotometric methods. The pK values of the aromatic nitrogen atoms were estimated. Complexation of Eu(III)ion with both ligands are studied by spectrophotometric method. Composition(ML2) and stability of complexes were determined. PMID:11379022

Hargitai, J; Labádi, I; Harri, L

2000-01-01

382

Absolute potential of the Fermi level of single-walled carbon nanotubes via hydrogenase complex formation.  

NASA Astrophysics Data System (ADS)

The absolute potential of the Fermi level of nanotubes as a function of nanotube type is not presently understood, and is important for many nanotube applications and sorting strategies. Here, we study complexes of recombinant [FeFe] hydrogenases and single-walled carbon nanotubes. We find evidence that novel charge-transfer complexes are formed and are stable, which enables further study and application of this system. The hydrogenase functions as a hydrogen electrode sensitizing the nanotubes to the redox half-reaction for hydrogen. Thus the potential can be altered by changing the molecular hydrogen concentration, and this tunability is utilized to bleach various semiconducting nanotube transitions. By observing which are bleached and which remain emissive, we determine the alignment of the potential of the Fermi level of semiconducting single-walled carbon nanotubes. The experimentally determined Fermi level alignment is confirmed theoretically by the first-principles DFT-PBE method.

McDonald, Timothy; Svedruzic, Drazenka; Kim, Yong-Hyun; Blackburn, Jeffrey; Zhang, Shengbai; King, Paul; Heben, Michael

2007-03-01

383

Facies control on reservoir properties within a barrier island complex, Sparta Formation, Pointe Coupee Parish, Louisiana  

SciTech Connect

Analysis of conventional core, well logs, and petrophysical data has yielded an interpretation of the Sparta B sandstone in south-central Louisiana as a prograding barrier island complex. Four sedimentary facies possess reservoir potential: lower shoreface, upper shoreface, storm washover, and tidal-inlet channel sandstone facies. Distinct porosity and permeability values are associated with each reservoir facies. Predictable porosity and permeability trends associated with the Sparta B sandstone barrier island complex allows for identification of distinct fluid flow units within the sequence. In addition, individual sedimentary facies possess characteristic well log signatures; therefore, the geometry, thickness variability, and lateral continuity of each fluid flow unit can be determined and heterogeneities within the reservoir interval can be resolved.

Lemoine, R.C.; Moslow, T.F.; Ferrell, R.E.

1988-02-01

384

On Magnetic Activity Band Overlap, Interaction, and the Formation of Complex Solar Active Regions  

E-print Network

Recent work has revealed an phenomenological picture of the how the $\\sim$11-year sunspot cycle of Sun arises. The production and destruction of sunspots is a consequence of the latitudinal-temporal overlap and interaction of the toroidal magnetic flux systems that belong to the 22-year magnetic activity cycle and are rooted deep in the Sun's convective interior. We present a conceptually simple extension of this work, presenting a hypothesis on how complex active regions can form as a direct consequence of the intra- and extra-hemispheric interaction taking place in the solar interior. Furthermore, during specific portions of the sunspot cycle we anticipate that those complex active regions may be particular susceptible to profoundly catastrophic breakdown---producing flares and coronal mass ejections of most severe magnitude.

McIntosh, Scott W

2014-01-01

385

Formation and characterization of stable fluorescent complexes between neutral conjugated polymers and cyclodextrins.  

PubMed

Solubilisation and stabilization of conjugated polymers, CPs, in aqueous media remains a challenge for many researches trying to extend the biological and environmental applications of this kind of polymers. A number of different alternatives have been considered to address this problem, which are mostly based on the enhancement of the macromolecule polarity, by appending hydrophilic side chains on the polymer backbone. In this work we have investigated a new strategy in which water solubilization is reached by external addition of classical cyclodextrins (?-, ?- and ?-CDs) to a solution of non-polar CPs. This strategy allows working with such polymers eliminating the need to synthesize new water-soluble species. The polymer selected for the study was poly-[9,9-bis(6'-bromohexyl-2,7-fluoren-dyil)-co-alt-(benzene-1,4-diy)], PFPBr(2), a polyfluorene previously synthesized in our laboratory. Results show that PFPBr(2) forms fluorescent complexes in aqueous media with ?-CD and ?-CD, and much less efficiently with ?-CD, probably due to the small size of its cavity. The new PFPBr(2)/CD complexes are stable in time and in a large range of pH, however, at high concentration and temperature, they tend to aggregate and precipitate. In order to increase stabilization and minimize polymer aggregation, complexes were encapsulated inside the pores of silica glasses fabricated using the sol-gel process, obtaining transparent and fluorescent hybrid matrices which were stable in time and temperature. In addition, immobilization of the complexes allows an easy manipulation of the material, thus offering promising applications in the development of biological and chemical sensors. PMID:22993121

Martínez-Tomé, Maria José; Esquembre, Rocío; Mallavia, Ricardo; Mateo, C Reyes

2013-01-01

386

Optical study of complex formation in Ag-doped CdTe  

Microsoft Academic Search

The thermal instability of substitutional Ag doping on Cd sites in CdTe is studied with optical spectroscopy. For Ag doping levels above 1016 cm-3 the AgCd concentration decreases gradually during sev