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1

Formation constants of mercury(II) with some buffer/masking agents and the formation of mixed-ligand complexes.  

PubMed

Values are given for the formation constants of complexes of mercury(II) with some buffer/masking agents. The mixed-ligand complex formation of mercury(II)-chelates with other complexing agents has also been studied. PMID:18961624

Van der Linden, W E; Beers, C

1975-01-01

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

Study of structural influence on the formation constants of lanthanide-polyamino polycarboxylate complexes  

SciTech Connect

This contribution describes the synthesis of three polyamino polycarboxylic acids (thiobis(ethylenenitrilo)tetraacetic acid, TEDTA; N,N-bis(2-aminoethyl)aniline-N',N',N'',N''-tetraacetic acid, BEATA; N,N-bis(2-aminoethyl)ethylamine-N',N',N'',N''-tetraacetic acid, DEATA) and reports the stability constant sequences of chelates formed by their anions with the lanthanide elements, as well as the consecutive anion protonation constants (at I = 0.10 and 25/sup 0/C). The data are compared to corresponding values for a number of analogous polyamino polycarboxylate species derived from tetravalent lanthanons. 32 references, 2 figures, 3 tables.

Tse, P.K.; Powell, J.E.

1985-08-28

4

Formation constants and composition of Ga3+ and In3+ complexes with iminodisuccinic acid in aqueous solutions according to potentiometric data  

NASA Astrophysics Data System (ADS)

The complexation of Ga3+ and In3+ with iminodisuccinic acid (H4L) at 25°C in 0.1, 0.4, 0.6, and 0.8 M KNO3 supporting solutions was studied by potentiometry and mathematical modeling. The thermodynamic constants of formation of neutral, protonated, and hydroxo complexes were calculated by extrapolating the concentration constants to the zero ionic strength using an equation with one individual parameter.

Tolkacheva, L. N.; Nikol'skii, V. M.

2013-09-01

5

Determination of the Stability Constants of a Number of Metal Fluoride Complexes and Their Rates of Formation.  

National Technical Information Service (NTIS)

The stability constants of the fluoride complexes of Al exp +3 , H sub 3 BO sub 3 , Cr exp +3 , Cr exp +6 , Fe exp +3 , Gd exp +3 , Nb exp +5 , UO sub 2+2 , and Zr exp +4 were determined in 0.96 and 2.88 M HNO sub 3 solutions in the temperature range 25 t...

R. R. Hammer

1979-01-01

6

205 T1NMR and UV-Visible spectroscopic determination of the formation constants of aqueous thallium(I) hydroxo-complexes  

Microsoft Academic Search

The hydrolysis of T1(I) has been studied at 25°C using205T1-NMR spectroscopy and UV-Vis spectrophotometry in aqueous solutions with ionic strengths maintained by NaC104 at 2, 4, 6, and 8M. The formation constant and the spectral characteristics for the hydroxo complex, T10H? have been determined.\\u000a At high hydroxide ion concentrations there is clear evidence from the UV-Vis data for the formation

P. Sipos; S. G. Capewell; P. M. May; G. T. Hefter; G. Laurenczy; F. Lukacs; R. Roulet

1997-01-01

7

Determination of the stability constants of a number of metal fluoride complexes and their rates of formation  

Microsoft Academic Search

The stability constants of the fluoride complexes of Al\\/sup +3\\/, HâBOâ, Cr\\/sup +3\\/, Cr\\/sup +6\\/, Fe\\/sup +3\\/, Gd\\/sup +3\\/, Nb\\/sup +5\\/, UOâ\\/sup +2\\/, and Zr\\/sup +4\\/ were determined in 0.96 and 2.88 M HNOâ solutions in the temperature range 25 to 60°C with a fluoride specific ion electrode. These data can be used to calculate the concentration of chemical species

1979-01-01

8

Short range solvation by fluorinated alcohols of proton transfer complex formation between pentachlorophenol and triethylamine: determination of solvation constants and stoichiometries  

NASA Astrophysics Data System (ADS)

Primary and secondary solvation binding constants and stoichiometries are reported for the protic solvation by pentadecafluorooctanol (PFO) and trifluoroethanol (TFE) of the non-bonding electrons on triethylamine (TEA) and on the oxygen of the proton-transfer complex formed by pentachlorophenol (PCP) and TEA. The solvation-sensitive apparent proton-transfer formation constant KPT is measured in varying low concentrations of the protic solvent S in benzene bulk solvent, and the solvation binding constants and stoichiometries are determined. A two-stage solvation model is supported, as observed in earlier studies of similar systems. The primary solvation stage involves a single solvent alcohol molecule, whereas the secondary stage involves several solvent molecules.

Lee, J. I.; Fagan, J.; Schullery, S. E.; Scott, R. M.

1996-07-01

9

Formation constants of copper(II) complexes with tripeptides containing Glu, Gly, and His: potentiometric measurements and modeling by generalized multiplicative analysis of variance.  

PubMed

We report a systematic study of the effects of types and positions of amino acid residues of tripeptides on the formation constants log?, acid dissociation constants pKa, and the copper coordination modes of the copper(II) complexes with 27 tripeptides formed from the amino acids glutamic acid, glycine, and histidine. log? values were calculated from pH titrations with l mmol L(-1):1 mmol L(-1) solutions of the metal and ligand and previously reported ligand pKa values. Generalized multiplicative analysis of variance (GEMANOVA) was used to model the log? values of the saturated, most protonated, monoprotonated, log?(CuL) - log?(HL), and pKa of the amide group. The resulting model of the saturated copper species has a two-term model describing an interaction between the central and the C-terminal residues plus a smaller, main effect of the N-terminal residue. The model supports the conclusion that two copper coordination modes exist depending on the absence or presence of His at the central position, giving species in which copper is coordinated via two or three fused chelate rings, respectively. The GEMANOVA model for pKamide, which is the same as that for the saturated complex, showed that Gly-Gly-His has the lowest pKamide values among the 27 tripeptides. Visible spectroscopy indicated the formation of metal-ligand dimers for tripeptides His-His-Gly and His-His-Glu, but not for His-His-His, and the formation of multiple ligand bis compexes CuL2 and Cu(HL)2 for tripeptides (Glu/Gly)-His-(Glu/Gly) and His-(Glu/Gly)-(Glu/Gly), respectively. PMID:24432726

Khoury, Rima Raffoul; Sutton, Gordon J; Ebrahimi, Diako; Hibbert, D Brynn

2014-02-01

10

Reaction rate constant of methane clathrate formation  

Microsoft Academic Search

Particle size distribution measurements were performed during the growth stage of methane hydrate formation in a semi-batch stirred tank crystallizer. Experiments were carried out at temperatures between 275.1 and 279.2K and pressures ranging from 3873 to 5593kPa. The reaction rate constant of methane hydrate formation was determined using the model of Bergeron and Servio (AIChE J 2008;54:2964). The experimental reaction

Sebastien Bergeron; Juan G. Beltrán; Phillip Servio

2010-01-01

11

Complex Formation between Dimethyl Methylphosphonate and Hexafluoroisopropanol.  

National Technical Information Service (NTIS)

A solvent/water partitioning method was used to measure the complex formation between dimethyl methylphosphonate (DMMP) and hexafluoroisopropanol (HFIP). The highest formation constant was obtained when n-hexane was used as the partitioning solvent. Other...

D. C. Leggett

1990-01-01

12

IR spectroscopy determination of the complexation constant for a cholesterol-diisopropyl sulfoxide complex  

NASA Astrophysics Data System (ADS)

We have studied the IR absorption spectra of cholesterol in the presence of diisopropyl sulfoxide in carbon tetrachloride. We show that complexation of cholesterol with diisopropyl sulfoxide occurs as a result of formation of a hydrogen bond between the hydrogen of the hydroxyl group of the cholesterol and the oxygen of the sulfoxide group of the diisopropyl sulfoxide. We have determined the complexation constant for the cholesterol—diisopropyl sulfoxide constant, K eq = 9.25 L/mol at 23°C.

Gabrielyan, L. S.; Melik-Ohanjanyan, L. G.; Markarian, S. A.

2013-03-01

13

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

14

Determination of the formation constants of ternary complexes of uranyl and carbonate with alkaline earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) using anion exchange method.  

PubMed

The formation constants of ternary complexes (MUO2(CO3)3(2-) and M2UO2(CO3)3(0)) of uranyl and carbonate with alkaline earth metals (M2+ denotes Mg2+, Ca2+, Sr2+, and Ba2+) were determined with an anion exchange method by varying the metal concentrations (0.1-5 mmol/L) at pH 8.1 and a constant ionic strength (0.1 mol/L NaNO3) under equilibrium with atmospheric CO2. The results indicate that the complexes of MUO2(CO3)3(2-) and M2UO2(CO3)3 are simultaneously formed for Ca2+ and Ba2+, while Mg2+ and Sr2+ form only the MUO2(CO3)3(2-) complex under our experimental conditions. The cumulative stability constants for the MUO2(CO3)3(2-) complex obtained at / = 0 are as follows: logbeta113 = 26.11 +/- 0.04, 27.18 +/- 0.06, 26.86 +/- 0.04, and 26.68 +/- 0.04 for Mg2+, Ca2+, Sr2+, and Ba2+, respectively. For M2UO2(CO3)3(0), the value of logbeta213 at / = 0 was measured to be 30.70 +/- 0.05 and 29.75 +/- 0.07 for Ca2+ and Ba2+, respectively. Based on the formation constants obtained in this study, speciation calculations indicate that at low Ca2+ concentration (e.g., <2.2 mmol/L), CaUO2(CO3)3(2-) is more important than Ca2UO2(CO3)3 and that the Ca2UO2(CO3)3 distribution increased with increasing Ca2+ concentration. Uranium sorption onto anion-exchange resins is inhibited by the formation of the neutral Ca2UO2(CO3)3(0) species. PMID:16913125

Dong, Wenming; Brooks, Scott C

2006-08-01

15

Model for porous alumina template formation: constant voltage anodization  

Microsoft Academic Search

In spite of the extensive experimental investigations reported in the literature on porous alumina templates, the theoretical mechanisms, and their dependence on process parameters such as potential difference, current density and electrolytes, are not well understood. A theoretical model developed and published for porous structure formation under constant current electrochemical anodization of aluminum is adopted for constant voltage anodization. The

P. Singaraju; R. Venkat; R. Kanakala; B. Das

2006-01-01

16

THE ANION EXCHANGE OF METAL COMPLEXES. XI. APPLICATION OF THE CONSTANT IONIC MEDIUM METHOD TO THE MERCURY HALIDE SYSTEM  

Microsoft Academic Search

The possibilities of the application of the constant ionic medium method ; to investigations of metal complex formation by anion exchange were studied. In ; the case of the mercury-- halide systems, it was necessary to use constants ; determined by another method, in order to determine stability constants for the ; resin phase, and using these, the constants for

I. Eliezer; Y. Marcus

1962-01-01

17

Ionophoretic technique for the determination of stability constants of metal-nitrilotriacetate-methionine mixed complexes  

Microsoft Academic Search

A method, involving the use of paper electrophoresis is described for the study of the equilibria in mixed ligand complex systems in solution. Plots of -log [methionine] against mobility were used to obtain information on the formation of mixed complexes and to calculate the stability constants. Metal (M)-methionine and M-nitrilotriacetate (NTA) binary equilibria were also studied since this is a

Brij Bhushan Tewari

1995-01-01

18

Stability constants of iron(II) sulfate complexes.  

PubMed

The complex formation equilibria between iron(II) and sulfate ions have been studied at 25 degrees C in 3 M NaClO4 ionic medium by measuring with a glass electrode the competition of Fe2+ and H+ ions for the sulfate ion. The concentrations of the metal and of the ligand were varied in the ranges 0.01 to 0.125 and 0.01 to 0.250 M, respectively. The analytical concentration of strong acid was chosen to be 0.01 or 0.03 M. The potentials of the glass electrode, corrected for the effect of replacement of medium ions with reagent species, have been interpreted with the equilibria [formula: see text] Stability constants valid in the infinite dilution reference state, logK zero = 1.98 +/- 0.16, log beta 1 zero = 2.1(5) +/- 0.2 and log beta 2 = 2.5 +/- 0.2, have been estimated by assuming the validity of the specific interaction theory. PMID:12125456

Ciavatta, Liberato; De Tommaso, Gaetano; Iuliano, Mauro

2002-01-01

19

Accurate values of stability constant of Ca 2+murexide complex  

Microsoft Academic Search

In published reports, the values of stability constants of 1:1 complex of Ca2+ and the dye ammonium purpurate (murexide) were not determined under controlled conditions and were not properly corrected for the binding of Ca2+ with ions of buffer used to maintain pH and that of the background electrolyte used to maintain ionic strength. We report the molar absorptivities (?)

Tapan Kumar Khan; Pinaki Gupta-Bhaya

1997-01-01

20

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

21

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

22

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

23

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

ERIC Educational Resources Information Center

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

Prasad, Rajendra; Prasad, Surendra

2009-01-01

24

Dissociation constants of some Schiff bases and stability constants of their copper, cobalt, nickel and zinc complexes  

Microsoft Academic Search

The stoichiometry and stability constant of metal complexes with 4-(3-methoxy-salicylideneamino)-5-hydroxynaphthalene-2,7-disulfonic\\u000a acid monosodium salt (H2L) and 4-(3-methoxysalicylideneamino)-5-hydroxy-6-(2,5-dichlorophenylazo)-2,7-naphthalene disulfonic acid monosodium salt\\u000a (H2L1) were studied by potentiometric titration. The stability constants of H2L and H2L1 Schiff bases have been investigated by potentiometric titration and u.v.–vis spectroscopy in aqueous media. The dissociation\\u000a constants of the ligand and the stability constants of the metal

Mehmet Tunçel; Hayati Sar?

2007-01-01

25

Laboratory measurement of the complex dielectric constant of soils  

NASA Technical Reports Server (NTRS)

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

Wiebe, M. L.

1971-01-01

26

Stability constants of thorium(IV) complexes with aryl- bis -(5-hydroxy-3-methyl-1-phenyl-4-pyrazolyl) methane ligands  

Microsoft Academic Search

Stability constants of complexes of aryl-bis-(5-hydroxy-3-methyl-1-phenyl-4-pyrazolyl) methane [ArBPyM] derivatives with thorium(IV) ions were determined by the potentiometric method at 30°C and an ionic strength of 0.1 mol·dm-3 (KNO3) in 75% (v\\/v) dioxane-water. The evaluation of the titration data indicated that four kinds of complexes ([ThL]2+, [ThLOH]+, [ThL2], and [ThL(OH)2]2-) were formed. The formation constants for all [ThL]2+ and [ThL2] complexes

S. L. Stefan

1994-01-01

27

Studies on molecular complexes of n-donors with iodine by the constant activity method  

Microsoft Academic Search

Iodine complexes of imidazoles in chloroform were studied by using the constant activity method. The equilibrium constants and the extinction coefficients of the complexes were determined and the results are compared with those obtained by using conventional spectral method. It was found that the equilibrium constants increase as the donor strength increases, while the extinction coefficients decrease. This behavior was

Refat A. Mahmoud; Ahmed A. El-Samahy; Mostafa M. Rabia

1984-01-01

28

A Computational Approach to Determining Stability Constants for Transition Metal Ion Complexes  

Microsoft Academic Search

The complexation of metal ions in natural waters plays a critical role in defining the metal's biogeochemistry, Numerous investigators have used various experimental techniques to measure complexation constants in the laboratory, but many constants are still poorly undefined or have yet to be investigated due to the difficulty of some of the experiments. A computational approach to obtaining these constants

Jason St. Clair

2000-01-01

29

The effects of intramolecular H-bond formation on the stability constant and water exchange rate of the Gd(III)-diethylenetriamine-N'-(3-amino-1,1-propylenephosphonic)-N, N,N'',N''-tetraacetate complex.  

PubMed

The binding interaction of metal chelates to biological macromolecules, though driven by properly devoted recognition synthons, may cause dramatic changes in some property associated with the coordination cage such as the thermodynamic stability or the exchange rate of the metal coordinated water. Such changes are due to electrostatic and H-bonding interactions involving atoms of the coordination cage and atoms of the biological molecule at the binding site. To mimic this type of H-bonding interactions, lanthanide(III) complexes with a DTPA-monophosphonate ligand bearing a propylamino moiety (H6NP-DTPA) were synthesized. Their thermodynamic stabilities and the exchange lifetime of the coordinated water molecule (for the Gd-complex) were compared with those of the analog complexes with DTPA and the parent DTPA-monophosphonate derivative (H6P-DTPA). It was found that the intramolecular H-bond between the epsilon-amino group and the phosphonate moiety in NP-DTPA complexes causes displacements of electric charges in their coordination cage that are markedly pH dependent. In turn, this affects the characteristic properties of the coordination cage. In particular it results in a marked elongation of the exchange lifetime of the coordinated water molecule. PMID:17451186

Baranyai, Zsolt; Gianolio, Eliana; Ramalingam, Kondareddiar; Swenson, Rolf; Ranganathan, Ramachandran; Brücher, E; Aime, Silvio

2007-01-01

30

Computational complexity via programming languages: constant factors do matter  

Microsoft Academic Search

.   The purpose of this work is to promote a programming-language approach to studying computability and complexity, with an\\u000a emphasis on time complexity. The essence of the approach is: a programming language, with semantics and complexity measure,\\u000a can serve as a computational model that has several advantages over the currently popular models and in particular the Turing\\u000a machine. An obvious

Amir M. Ben-amram; Neil D. Jones

2000-01-01

31

Prediction of Stability Constants for Cr(III) and Cr(II) Complexes  

Microsoft Academic Search

Regression analysis was used to derive equations for estimaing thermodynamic stability constants for complexes of Cr2+ (logß°1[Cr2+L] = 0.53logß°n[HnL]) and Cr3+ (logß°1[Cr3+L] = 0.88logß°n[HnL]) from the known protonation constants of HnL ligands and for determining stability constants of Cr2+ and Cr3+ complexes from the available stability constants of Cu2+ complexes (logß°1[Cr2+L] = 0.76logß°1[Cu2+L] and logß°1[Cr2+L] = 0.60logß°1[Cr3+L], respectively). Parameters of

E. G. Vinokurov

2003-01-01

32

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

33

Lesion Formation and Lesion Remineralization in Enamel under Constant Composition Conditions  

Microsoft Academic Search

A new apparatus for the de- and remineralization of enamel in vitro under constant composition conditions is described. A de- or remineralizing solution flows over the specimens at a controlled rate. During artificial lesion formation (using an acetate buffer containing methylhydroxydiphosphonate, MHDP), the composition of the solution is constant. The Ca and phosphate variation is less than 3%, pH variation

J. A. K. M. Buskes; J. Christoffersen; J. Arends

1985-01-01

34

Stability constants and thermodynamic parameters of complexes of lanthanide ions and ({+-})-norvaline  

Microsoft Academic Search

Amino acids are the structural units of proteins; hence the study of metal-amino acid complexes may lead to a better understanding of structure and binding sites in metalloproteins. The protonation constants of ({+-})-norvaline and the stability constants of complexes between lanthanide ions and ({+-})-norvaline at various ionic strengths (I{sub c}\\/mol\\/dm³ = 0.05, 0.10, and 0.15) at 300 K and at

V. D. Athawale; Vidyagauri Lele

1996-01-01

35

A novel microwave method for measuring the complex dielectric constant of polymer thin sheets  

Microsoft Academic Search

.   A new method of measuring the complex dielectric constant of a thin sheet of polymer samples at microwave frequency is presented.\\u000a In order to obtain the complex dielectric constant in terms of reflection coefficient, a higher order power series solution\\u000a has been introduced. Application of lower order power series solution to the greater thickness of the sample requires a

Thirumalizai Jambulingam Bhoopathy; Annamalai Anandavadivel

2002-01-01

36

Dissociation of Bimolecular ?IIb?3-Fibrinogen Complex under a Constant Tensile Force  

PubMed Central

The regulated ability of integrin ?IIb?3 to bind fibrinogen plays a crucial role in platelet aggregation, adhesion, and hemostasis. Employing an optical-trap-based electronic force clamp, we studied the thermodynamics and kinetics of ?IIb?3-fibrinogen bond formation and dissociation under constant unbinding forces, mimicking the forces of physiologic blood shear on a thrombus. The distribution of bond lifetimes was bimodal, indicating that the ?IIb?3-fibrinogen complex exists in two bound states with different mechanical stability. The ?IIb?3 antagonist, abciximab, inhibited binding without affecting the unbinding kinetics, whereas Mn2+ biased the ?IIb?3-fibrinogen complex to the strong bound state with reduced off-rate. The average bond lifetimes decreased exponentially with increasing pulling force from ?5 pN to 50 pN, suggesting that in this force range the ?IIb?3-fibrinogen interactions are classical slip bonds. We found no evidence for catch bonds, which is consistent with the known lack of shear-enhanced platelet adhesion on fibrinogen-coated surfaces. Taken together, these data provide important quantitative and qualitative characteristics of ?IIb?3-fibrinogen binding and unbinding that underlie the dynamics of platelet adhesion and aggregation in blood flow.

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

2011-01-01

37

Determination of stability constants of complexes of neutral analytes with charged cyclodextrins by affinity capillary electrophoresis.  

PubMed

A novel procedure for the determination of stability constants in systems with neutral analytes and charged complexation agents by affinity capillary electrophoresis was established. This procedure involves all necessary corrections to achieve precise and reliable data. Temperature, ionic strength, and viscosity corrections were applied. Based on the conductivity measurements, the average temperature of the background electrolyte in the capillary was kept at the constant value of 25°C by decreasing the temperature of the cooling medium. The viscosity correction was performed using the viscosity ratio determined by an external viscosimeter. The electrophoretical measurements were performed, at first, at constant ionic strength. In this case, the increase of ionic strength caused by increasing complexation agent concentration was compensated by changing of the running buffer concentration. Subsequently the dependence of the analyte effective mobility on the complexation agent concentration was measured without the ionic strength compensation (at variable ionic strength). The new procedure for determination of the stability constants even from such data was established. These stability constants are in a very good agreement with those obtained at the constant ionic strength. The established procedure was applied for determination of the thermodynamic stability constants of (R, R)-(+)- and (S, S)-(-)-hydrobenzoin and R- and S-(3-bromo-2-methylpropan-1-ol) complexing with 6-monodeoxy-6-mono(3-hydroxy)propylamino-?-cyclodextrin hydrochloride. PMID:22528423

Beneš, Martin; Zusková, Iva; Svobodová, Jana; Gaš, Bohuslav

2012-03-01

38

Microwave Spectrum, Structure, and Hyperfine Constants of Kr-AgCl: Formation of a Weak Kr-Ag Covalent Bond  

NASA Astrophysics Data System (ADS)

The pure rotational spectrum of the complex Kr-AgCl has been measured between 8-15 GHz using a cavity pulsed-jet Fourier transform microwave spectrometer. The complex was found to be linear and relatively rigid, with a Kr-Ag bond length of ˜2.641 Å. The Kr-Ag stretching frequency was estimated to be 117 cm -1. Ab initio calculations performed at the MP2 level of theory gave the geometry, vibration frequencies, Kr-Ag bond dissociation energy, and orbital populations. The Kr-Ag bond dissociation energy was estimated to be ˜28 kJ mol -1. The Kr-Ag force constant and dissociation energy are greater than those of Ar-Ag in Ar-AgCl. The chlorine nuclear quadrupole coupling constants show slight changes on complex formation. Ab initio orbital population analysis shows a small shift in ?-electron density from Kr to Ag on complex formation. The combined experimental and ab initio results are consistent with the presence of a weak Kr-Ag covalent bond.

Reynard, Linda M.; Evans, Corey J.; Gerry, Michael C. L.

2001-03-01

39

Quantum mechanical capture/phase space theory calculation of the rate constants for the complex-forming CH + H{sub 2} reaction.  

SciTech Connect

Six-dimensional wave packet calculations on an accurate potential energy surface are used to obtain the quantum mechanical capture (QM C) probabilities for CH + H{sub 2} corresponding to a variety of total angular momenta and internal reactant states. Rate constant calculations are made feasible by employing a Monte Carlo based sampling procedure. The QM C probabilities alone are also used to estimate the high pressure CH + H{sub 2} rate constants corresponding to stabilization or CH{sub 3} formation. The rate constants for CH + H{sub 2} {yields} CH{sub 2} + H reaction in the low pressure limit are obtained by combining the QM C probabilities with a phase space theory (PST) approximation for product formation from the complex. Our results are compared with the experimental results of Brownsword et al. (J. Chem. Phys. 1997, 106, 7662), as well as with purely classical PST calculations. The QM C probabilities are shown to be highly dependent on the initial rotational states of the reactants corresponding to orientational restrictions on complex formation. Consistent with this, our QM C high pressure rate constants for CH{sub 3} formation are lower than the purely classical PST rate constants. These QM C rate constants also are in reasonable accord with experiment. A similar but somewhat more subtle picture emerges regarding the QM C/PST rate constants for CH{sub 2} + H formation.

Saracibar, A.; Goldfield, E. M.; Gray, S. K.; Chemical Sciences and Engineering Division; Wayne State Univ.; Univ. del Pais Vasco

2008-11-01

40

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

2014-07-22

41

Antioxidant study of quercetin and their metal complex and determination of stability constant by spectrophotometry method.  

PubMed

Quercetin found chelate cadmium ions, scavenge free radicals produced by cadmium. Hence new complex, quercetin with cadmium was synthesised, and the synthesised complex structures were determined by UV-vis spectrophotometry, infrared spectroscopy, thermogravimetry and differential thermal analysis techniques (UV-vis, IR, TGA and DTA). The equilibrium stability constants of quercetin-cadmium complex were determined by Job's method. The determined stability constant value of quercetin-cadminum complex at pH 4.4 is 2.27×10(6) and at pH 7.4 is 7.80×10(6). It was found that the quercetin and cadmium ion form 1:1 complex in both pH 4.4 and pH 7.4. The structure of the compounds was elucidated on the basis of obtained results. Furthermore, the antioxidant activity of the free quercetin and quercetin-cadmium complexes were determined by DPPH and ABTS assays. PMID:24176370

Ravichandran, R; Rajendran, M; Devapiriam, D

2014-03-01

42

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

PubMed Central

Protein complexes are dynamic macromolecules that constantly dissociate into, and simultaneously are assembled from, free subunits. Dissociation rate constants, koff, provide structural and functional 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 stable isotope 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. 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. This study provided the theoretical foundation for future experiments that can validate and apply the MASE method.

Pan, Chongle

2011-01-01

43

A Simple Method for the Consecutive Determination of Protonation Constants through Evaluation of Formation Curves  

ERIC Educational Resources Information Center

A simple method is presented for the consecutive determination of protonation constants of polyprotic acids based on their formation curves. The procedure is based on generally known equations that describe dissociation equilibria. It has been demonstrated through simulation that the values obtained through the proposed method are sufficiently…

Hurek, Jozef; Nackiewicz, Joanna

2013-01-01

44

Solubility and Complex Formation Equilibria of Silver Chloride in Propylene Carbonate-Water Mixtures.  

National Technical Information Service (NTIS)

The solubility and complex formation equilibria of silver chloride in propylene carbonate-water mixtures (0.004 to 3.57 M H2O) were studied potentiometrically in a constant ionic medium of 0.1 M tetraethylammonium perchlorate, at 25C. The complexes are pr...

J. N. Butler D. R. Cogley W. Zurosky

1968-01-01

45

Complex formation between polyelectrolytes and ionic surfactants  

NASA Astrophysics Data System (ADS)

The interaction between polyelectrolyte and ionic surfactant is of great importance in different areas of chemistry and biology. In this Letter we present a theory of polyelectrolyte-ionic-surfactant solutions. The new theory successfully explains the cooperative transition observed experimentally, in which the condensed counterions are replaced by ionic surfactants. The transition is found to occur at surfactant densities much lower than those for a similar transition in non-ionic polymer-surfactant solutions. Possible application of DNA surfactant complex formation to polynucleotide delivery systems is also mentioned.

Kuhn, Paulo S.; Levin, Yan; Barbosa, Marcia C.

1998-12-01

46

A potentiometeric study of protonation and complex formation of xylenol orange with alkaline earth and aluminum ions  

Microsoft Academic Search

Xylenol orange (XO) is one of the complexometric indicators, that can bind to metal cations at both their amino and acidic groups. In this study the protonation constants and distribution diagrams of XO were studied pH-metrically, and the corresponding six protonation constants were calculated. The complex formation between XO (L) and alkaline earth ions (M) was investigated and the formation

M. B Gholivand; F Bamdad; J Ghasemi

1998-01-01

47

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

SciTech Connect

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

Aroua, M.K.; Benamor, A.; Haji-Sulaiman, M.Z. [Univ. of Malaya, Kuala Lumpur (Malaysia). Dept. of Chemical Engineering] [Univ. of Malaya, Kuala Lumpur (Malaysia). Dept. of Chemical Engineering

1999-09-01

48

Interactive formation control in complex environments.  

PubMed

The degrees of freedom of a crowd is much higher than that provided by a standard user input device. Typically, crowd-control systems require multiple passes to design crowd movements by specifying waypoints, and then defining character trajectories and crowd formation. Such multi-pass control would spoil the responsiveness and excitement of real-time control systems. In this paper, we propose a single-pass algorithm to control a crowd in complex environments. We observe that low-level details in crowd movement are related to interactions between characters and the environment, such as diverging/merging at cross points, or climbing over obstacles. Therefore, we simplify the problem by representing the crowd with a deformable mesh, and allow the user, via multitouch input, to specify high-level movements and formations that are important for context delivery. To help prevent congestion, our system dynamically reassigns characters in the formation by employing a mass transport solver to minimize their overall movement. The solver uses a cost function to evaluate the impact from the environment, including obstacles and areas affecting movement speed. Experimental results show realistic crowd movement created with minimal high-level user inputs. Our algorithm is particularly useful for real-time applications including strategy games and interactive animation creation. PMID:24356364

Henry, Joseph; Shum, Hubert P H; Komura, Taku

2014-02-01

49

Simultaneous Determination of Several Charge-transfer Complex Association Constants using Nuclear Magnetic Resonance  

Microsoft Academic Search

A METHOD for determining the association constants of organic charge-transfer complexes in solution using nuclear magnetic resonance has recently been described1,2. For a series of solutions containing an electron donor species (D) and an electron acceptor species (A) which interact by a very fast reversible process to form a 1 : 1 charge-transfer complex (DA), if one of the reactants,

R. Foster; C. A. Fyfe

1967-01-01

50

Redox method for the determination of stability constants of some trivalent metal complexes  

Microsoft Academic Search

Stability constants determination of very stable metal complexes using the redox method, based on the equilibrium of Fe3+Fe2+ followed by a couple of platinum\\/reference electrodes, was undertaken and tested to complexes of some trivalent metal ions with well known polyaminopolycarboxymethylated linear ligands (edta, nta, cdta, dtpa and ttha) and also to some new macrocyclic ligands. SUPERQUAD program was used for

Rita Delgado; M. do Carmo Figueira; Sandra Quintino

1997-01-01

51

Spectroscopic investigation on the inclusion complex formation between amisulpride and ?-cyclodextrin.  

PubMed

The purpose of this research was to investigate inclusion complex formation between poorly soluble drug amisulpride (AMI) and ?-cyclodextrin (?-CD). The solubility of AMI was enhanced by formation of inclusion complex of AMI with nano-hydrophobic cavity of ?-CD. The stoichiometry of inclusion complex was studied by continuous variation Job's plot method and found 1:1. The binding constant was found 1166.65 M(-1) by Benesi-Hildebrand plot. The molecular docking of AMI and ?-CD was done to investigate complexation. The inclusion complex formation was further confirmed by (1)H NMR and FT-IR, DSC and XRD analysis. The solubility of AMI was increased 3.74 times after inclusion complex formation with ?-CD. PMID:23399226

Negi, Jeetendra Singh; Singh, Shivpal

2013-02-15

52

Determining conditional stability constants for Pb complexation by carboxymethyl-?-cyclodextrin (CMCD)  

NASA Astrophysics Data System (ADS)

Carboxymethyl-?-cyclodextrin (CMCD) has been proposed for remediation of metal-contaminated sediments. This research presents stability constants for CMCD-lead complexes, and demonstrates a rigorous methodology for estimating stability constants for metal-complexing agents. The conditional stability constant for the lead-CMCD aqueous complex was determined to be 10 5.18 with the 95% confidence interval ranging from 10 5.14 to 10 5.22. The best fit for experimental data was made by assuming a reaction between divalent CMCD 2- and Pb 2+ and using the WATEQ activity coefficient formulation. The optimized value was derived from experimental data with the geochemical model PHREEQC coupled to UCODE_2005, a parameter optimization program. Like FITEQL, UCODE has a built-in option to optimize parameter values by minimizing the weighted sum of squared residuals (WSSR). However, our approach not only allows rapid, automatic optimization of the stability constant, but also allows determination of uncertainties in estimated parameter values and statistical analysis to assess the appropriateness of the conceptual model. The automation of the process allows testing of multiple conceptual models and the final values produced are internally consistent with the PHREEQC database. In this case five different conceptual models to describe the metal complexation and protonation reactions of CMCD were considered.

Skold, Magnus E.; Thyne, Geoffrey D.; Drexler, John W.; McCray, John E.

2007-08-01

53

Effect of temperature on the stability constants of chloro complexes of actinyl ions  

Microsoft Academic Search

Stability constants of chloride complexes of U(VI), Np(VI) and Pu(VI) have been determined by the method of extraction chromatography\\u000a at an ionic strength of 2.0 and [H+]=2.0M. Dilute HDEHP has been used as the stationary phase.

L. Bednarczyk; I. Fidelis

1983-01-01

54

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 ...

55

Fluorescence quenching titration for determination of complexing capacities and stability constants of fulvic acid  

Microsoft Academic Search

We describe a fluorescence tltration technique which can be used to determine complexing Capacities (C,) and 1:l con- ditlonai stability constants (K) of fluorescing ligands with paramagnetlc metal Ions at the micromolar level. An equa- tion, which we derive, allows calculation of the amount of ligand bound for fluorescence quenching curves. Further analysis of the data and fitting to a

David K. Ryan; James H. Weber

1982-01-01

56

Complex optimal sequences with constant magnitude for fast channel estimation initialization  

Microsoft Academic Search

Optimal sounding sequences which satisfy a certain autocorrelation property are useful for fast channel estimation techniques which are based on noniterative channel sounding methods. We study optimal sequences consisting of complex symbols with constant magnitude. An indirect sequence construction method is derived by considering the phase difference between sequence symbols. Our construction method includes periodic and nonperiodic optimal sequences, and

John C. L. Ng; Khaled Ben Letaief; Ross D. Murch

1998-01-01

57

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

SciTech Connect

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

Bennett, D.A. [California Univ., Berkeley, CA (USA). Dept. of Chemistry]|[Lawrence Berkeley Lab., CA (USA). Nuclear Science Div.

1990-04-20

58

Complex formation equilibria of palladium(II) complexes involving N, N?-dimethylethylenediamine, DNA constituents and cyclobutane dicarboxylic acid. The catalysis of glycine methyl ester hydrolysis through complex formation  

Microsoft Academic Search

Mixed-ligand complex formation equilibria of Pd(Me2en)–CBDCA–DNA constituent have been investigated (Me2en=N,N?-dimethylethylenediamine, CBDCA=cyclobutane dicarboxylic acid). The results show ring opening of CBDCA and monodentate complexation of the DNA constituent. Stoichiometries and stability constants of the complexes were determined at 25°C and at constant 0.1 M ionic strength. The kinetics of base hydrolysis of glycine methyl ester in presence of Pd(Me2en)2+ complex

Mahmoud M. A Mohamed; Mohamed M Shoukry

2002-01-01

59

Spectrophotometric study of molecular complex formation between o-chloranil and a series of methylated pyridines  

NASA Astrophysics Data System (ADS)

o-Chloranil has been shown to form 1:1 molecular complexes with pyridine and 2-, 3- and 4-picolines in CCl 4 medium. Isosbestic points have been found but charge-transfer bands could not be detected. The formation constants of the complexes exhibit a very good linear free energy relationship from which the Hammett ? parameter for the complexation reaction is found to be -3.67.

Ray, Asim Kumar; Bhattacharya, Sumanta; Banerjee, Manas; Mukherjee, Asok K.

2002-05-01

60

Star formation activities in Sharpless 311 complex  

NASA Astrophysics Data System (ADS)

The H II region NGC 2467, also known as Sharpless 311, is located at a distance of 4.1 kpc. This region is dominated by one O6 Vn star, HD 64315. There are also two stellar clusters in the area, Haffner 19 (H19) and Haffner 18ab (H18ab). Hubble Space Telescope (HST) Advanced Camera for Survey (ACS) data shows a large number of brightened ridges and cloud fragments in NGC 2467 (De Macro et al. 2006). Recently, Sinder et al. (2009) found several YSO candidates at the edge of the H II region, indicating a possible site of induced star formation. We present the results of optical and near-infrared (NIR) observations with the KISO and CTIO telescope, to search for very low mass young stellar objects in this region. We construct JHK color-color and J - H /J to identify very low luminosity young stellar objects and to estimate their masses. Based on these color-color and color-magnitude diagrams, we identified a population of embedded YSO candidates with infrared excesses (Class I and Class II), associated with the region. Based on these observations, we will present the nature of these YSO candidates and associated cluster properties. We will also try to interpret the possible star formation scenario in this complex.

Yadav, R. K.; Pandey, A. K.; Sharma, Saurabh

61

Stability Constants of Metal–Humic Acid Complexes and Its Role in Environmental Detoxification  

Microsoft Academic Search

Humic acid with hydroxyl-, phenoxyl-, and carboxyl-reactive groups can form coordination compounds with metals. The ion-exchange equilibrium method using Dowex AG 50W-X8, 20-25 mesh Na+ form was used to determine stability constants of complexes formed between humic acid (isolated from the soil) 50–250 ?g (?3×10?5–15×10?5 mol\\/liter) and metal salts solution 200 ?g at pH 3.5. The stability constant (log K)

Ashok K. Pandey; Shri Dhar Pandey; Virendra Misra

2000-01-01

62

Determination of the complex dielectric constant of an epithelial cell monolayer in the terahertz region  

NASA Astrophysics Data System (ADS)

We present a method to determine the complex dielectric constant of a cell monolayer using terahertz time-domain attenuated total reflection spectroscopy combined with a two-interface model. The imaginary part of the dielectric constant of the cell monolayer shows a lower absorption of slow relaxation mode than that of the liquid medium. This result allows us to estimate the intracellular water dynamics on a picosecond time scale, and the existence of weakly hydrated water molecules inside the cell monolayer was indicated. This method will provide a perspective to investigate the intracellular water dynamics in detail.

Shiraga, K.; Ogawa, Y.; Suzuki, T.; Kondo, N.; Irisawa, A.; Imamura, M.

2013-02-01

63

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).

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

2002-01-01

64

Measuring dissociation rate constants of protein complexes through subunit exchange: experimental design and theoretical modeling.  

PubMed

Protein complexes are dynamic macromolecules that constantly dissociate into, and simultaneously are assembled from, free subunits. Dissociation rate constants, k(off), provide structural and functional information on protein complexes. However, because all existing methods for measuring k(off) 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 k(off) using metabolic stable isotope 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. The subunit exchange process was modeled theoretically for a heterodimeric complex. The results showed that k(off) determines, and hence can be estimated from, the observed rate of subunit exchange. This study provided the theoretical foundation for future experiments that can validate and apply the MASE method. PMID:22194924

Pan, Chongle

2011-01-01

65

Pseudopolarographic determination of stability constants of labile zinc complexes in fresh water  

Microsoft Academic Search

The formation and distribution of labile zinc species in fresh water were investigated by using a pseudopolarographic approach. Pseudopolarograms were obtained by plotting the anodic stripping voltammetric peak current versus the deposition potential for a series of solutions containing 100 ?g\\/l Zn(II) and increasing amounts of ligand, at the pH of a typical river water sample. Stoichiometry and stability constants

M. Vega; R. Pardo; M. M. Herguedas; E. Barrado; Y. Castrillejo

1995-01-01

66

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

SciTech Connect

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

Aroua, M.K.; Amor, A.B.; Haji-Sulaiman, M.Z. [Univ. of Malaya, Kuala Lumpur (Malaysia). Dept. of Chemical Engineering] [Univ. of Malaya, Kuala Lumpur (Malaysia). Dept. of Chemical Engineering

1997-07-01

67

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

68

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

PubMed

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

Rowland, Brad A; Wyatt, Robert E

2007-10-28

69

Complex trajectories sans isochrones: Quantum barrier scattering with rectilinear constant velocity trajectories  

SciTech Connect

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

Rowland, Brad A.; Wyatt, Robert E. [Department of Chemistry and Biochemistry, Institute for Theoretical Chemistry, University of Texas at Austin, 1 University Station A5300, Austin, Texas 78712 (United States)

2007-10-28

70

Association constants and heats of formation of heteroassociates of anions of sulphophthaleine dyes  

NASA Astrophysics Data System (ADS)

The tendency of anions of sulphophthaleine dyes to heteroassociation was studied in aqueous solutions of phenol red, bromophenol blue, bromocresol green, bromocresol purple, and bromothymol blue. It was spectrophotometrically determined that single-(Han-) and double-charged anions (An2-) of sul-phophthaleines can form stable heteroassociates of 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 using semi-empirical methods, then correlated with experimentally determined values of equilibrium association constants.

Shapovalov, S. A.

2010-11-01

71

Spectroscopic study on the complex formation of chromogenic bridged calixarenes with aliphatic amines  

NASA Astrophysics Data System (ADS)

The complex formation between chromogenic capped calix 4 arene derivatives comprising indophenol indicator group(s), and aliphatic amines has been studied by UV/Vis spectroscopy. The equilibrium constants have been determined in ethanol, and—for one ligand—also in dimethylsulfoxide. The results have been interpreted in terms of various types of host-guest interactions and of steric effects.

Mohammed-Ziegler, I.; Poór, B.; Kubinyi, M.; Grofcsik, A.; Grün, A.; Bitter, I.

2003-05-01

72

Negative ion formation by Rydberg electron transfer: Isotope-dependent rate constants  

SciTech Connect

The formation of negative ions during collisions of rubidium atoms in selected ns and nd Rydberg states with carbon disulfide molecules has been studied for a range of effective principal quantum numbers (10 {le} n* {le} 25). For a narrow range of n* near n* = 17, rate constants for CS{sub 2}{sup {minus}} formation are found to depend upon the isotopic composition of the molecule, producing a negative ion isotope ratio (mass 78 to mass 76, amu) up to 10.5 times larger than the natural abundance ratio of CS{sub 2} isotopes in the reagent. The isotope ratio is found to depend strongly upon the initial quantum state of the Rydberg atom and perhaps upon the collision energy and CS{sub 2} temperature. 32 refs., 5 figs., 1 tab.

Carman, H.S. Jr.; Klots, C.E.; Compton, R.N.

1991-01-01

73

Analysis of association constant for ground state dye-electron acceptor complex of photoinitiator systems and the association constant effect on the kinetics of visible-light-induced polymerizations  

PubMed Central

We investigated the formation of ground state donor/acceptor complexes between xanthene dyes (rose Bengal (RB) and fluorescein (FL)) and a diphenyl iodonium salt (DPI) which is dissolved in 2-hydroxyethyl methacrylate (HEMA) monomer. To characterize the association constant of the complex, we have suggested a new analysis model based upon the Benesi-Hildebrand model. Because the assumption of the original Benesi-Hildebrand model is that the absorption bands are due only to the presence of the complex and that the absorption by the free component is negligible; the model cannot be applied to our systems, which is a dye-based initiator system. For each dye, the molar absorptivity of the ground state complex was evaluated as a function of wavelength and this analysis confirmed the validity of the modified Benesi-Hildebrand model. In addition, we observed the RB/DPI photoinitiator system failed to produce a perceptible polymerization rate but the FL/DPI photoinitiator system provided very high rates of polymerization. Based upon the association constant for these complexes, we concluded that the observed kinetic differences arise from the different association constant values of the ground state dye-acceptor complex, resulting in back electron transfer reaction.

Kim, Dongkwan; Scranton, Alec B.; Stansbury, Jeffrey W.

2009-01-01

74

FLUORESCENCE KINETICS OF COMPLEX FORMATION BETWEEN HUMAN SERUM ALBUMIN AND ZINC-PHTHALOCYANINE TETRASULFONIC ACID  

PubMed Central

Stopped-flow fluorescence was employed to measure the dissociation constant, activation energy, and frequency factor for zinc phthalocyanine tetrasulfonic acid binding to human serum albumin. A pseudo 1st order “Isolation Method” was used to measure temperature dependent rate constants at pH 7.00. Binding was followed by a relatively large emission signal that indicated the formation of a protein-ligand complex. The dissociation constant, activation energy and frequency factor were 3.3 (±0.3)×10?5 (M), 4.5 (±0.2)×104 J/mol, and 1.1 (±0.1)×108 min?1 respectively.

Fields, Althea; Thomas, Lana; Patel, Shreya; Biggins, Shanice

2012-01-01

75

Complex formation between copper. beta. -diketonates and polyoxypropylene glycols  

SciTech Connect

The complex formation between copper (II) dipivaloylmethanate Cu(dpm)/sub 2/ and copper (II) hexafluoroacetylacetonate Cu(hfacac)/sub 2/ and polyoxypropylene glycols (PPG) with molecular masses of 200 and 1050 was studied by spectrophotometry in the visible region and by ESR. The compositions of the complexes (1:1) and the thermodynamic parameters of complex formation were determined. In complexing power Cu(dpm)/sub 2/ is inferior to Cu(hfacac)/sub 2/. Complex formation between Cu(hfacac)/sub 2/ and PPG is accompanied by structural changes in the ..beta..-diketonate.

Nizel'skii, Y.N.; Ishchenko, S.S.

1987-06-01

76

Diffusion impregnation of alloys under conditions of complex formation  

SciTech Connect

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

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

1985-05-01

77

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

78

On the Complexity of Iterated Weak Dominance in Constant-Sum Games  

NASA Astrophysics Data System (ADS)

In game theory, a player’s action is said to be weakly dominated if there exists another action that, with respect to what the other players do, is never worse and sometimes strictly better. We investigate the computational complexity of the process of iteratively eliminating weakly dominated actions (IWD) in two-player constant-sum games, i.e., games in which the interests of both players are diametrically opposed. It turns out that deciding whether an action is eliminable via IWD is feasible in polynomial time whereas deciding whether a given subgame is reachable via IWD is NP-complete. The latter result is quite surprising as we are not aware of other natural computational problems that are intractable in constant-sum games. Furthermore, we slightly improve a result by Conitzer and Sandholm [6] by showing that typical problems associated with IWD in win-lose games with at most one winner are NP-complete.

Brandt, Felix; Brill, Markus; Fischer, Felix; Harrenstein, Paul

79

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

80

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

81

Complex formation reactions of palladium(II)-1,3-diaminopropane with various biologically relevant ligands. Kinetics of hydrolysis of glycine methyl ester through complex formation  

Microsoft Academic Search

The interaction of [Pd(DAP)(H2O)2]2+ (DAP = 1,3-diaminopropane) with some selected bio-relevant ligands, containing different functional groups, were investigated.\\u000a The ligands used are dicarboxylic acids, amino acids, peptides and DNA constituents. Stoichiometry and stability constants\\u000a of the complexes formed are reported at 25°C and 0.1 M ionic strength. The results show the formation of 1:1 complexes with\\u000a amino acids and dicarboxylic

Ahmed A. El-Sherif; Mohamed M. Shoukry; Ramadan M. El-Bahnasawy; Dalia M. Ahmed

2010-01-01

82

Determination of Stability Constants of Metal-methylcysteine and Metal-methylcysteine-cysteine Complexes by Paper Ionophoretic Technique  

Microsoft Academic Search

A method, involving the use of an advanced paper ionophoretic technique is described for the study of equilibria in mixed complex systems in solution. The method is based on the migra- tion of a spot of metal ion, with the complexants added in the background electrolyte. The con- centration of one of the complexants, methylcysteine, is kept constant while that

Brij B. Tewari

83

Formation of micelles with complex coacervate cores  

Microsoft Academic Search

Micelles are commonly regarded as colloidal structures spontaneously formed by amphiphilic molecules, that is, molecules consisting of two distinct parts of which one is soluble and the other is insoluble. This definition is too restrictive: other kinds of molecules can also form micelles. We report on the formation of micelles from a mixture of a (water-soluble) polyanion and a diblock

M. A. Cohen Stuart; N. A. M. Besseling; R. G. Fokkink

1998-01-01

84

Calibration of a Linear Free Energy Estimation Approach for Estimating Stability Constants for Metal-Bacterial Surface Complexes  

Microsoft Academic Search

In this study, we use the measured extent of metal adsorption onto bacterial cells to constrain a linear free energy relationship that allows estimation of unknown stability constants for metal-bacterial surface complexes based on the value of corresponding aqueous metal-acetate stability constants. A previous study (Fein et al., 2001) used metal adsorption experiments to constrain a similar relationship, but the

Brian R. Ginn; Jennifer E. S. Szymanowski; Jeremy B. Fein

2010-01-01

85

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

Microsoft Academic Search

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

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

2002-01-01

86

Stability constants of thiocyanato complexes of cobalt(II), nickel(II) and copper(II) in methanol  

Microsoft Academic Search

A spectrophotometric study of cobalt(II), nickel(II) and copper(II) thiocyanato complexes was carried out in methanol at 25°C and at a constant ionic strength of 1 M. Under the experimental conditions, two mononuclear complexes are identified with each of the three metal ions. Their stability constants are determined with a recent PC program SIRKO and the calculated values are: for cobalt,

Mustayeen Khan; Gilles Bouet; Roomina Tanveer; Riaz Ahmed

1999-01-01

87

Formation of complex films with water-soluble CTAB molecules  

NASA Astrophysics Data System (ADS)

This communication reports the formation of complex Langmuir monolayer at the air-water interface with the water-soluble N-cetyl N, N, N-trimethyl ammonium bromide (CTAB) molecules when interacted with the stearic acid (SA) molecules. The reaction kinetics of the formation of the CTAB-SA complex was monitored by observing the surface pressure versus time graph. Multilayered LB films of this complex doped with Congo red was successfully formed onto a quartz substrate. UV-Vis absorption and steady-state fluorescence spectroscopic characteristics of this doped LB films confirms the successful incorporation of Congo red molecules in to the CTAB-SA complex films.

Biswas, S.; Hussain, S. A.; Deb, S.; Nath, R. K.; Bhattacharjee, D.

2006-11-01

88

A QICAR approach for quantifying binding constants for metal-ligand complexes.  

PubMed

Relative metal-ligand complex stability is predicted by evaluating the relationships between physicochemical properties of metal ions and their experimental biotic and abiotic binding constants, K. Linear regression analysis showed that the softness index (?(p)) and the covalent index (?(2)(m) r) were especially useful in model construction for rainbow trout (Oncorhynchus mykiss), fathead minnows (Pimephales promelas) and crustaceansaquatic (Daphnia magna) based on RMSE and F-ratio criterion (F(observed)/F(critical) of ?4). The absolute value of the log of the first hydrolysis constant |logK(OH)| correlated best with logK values for barley (R(2)=0.74, p=0.02) and earthworm (R(2)=0.82, p=0.01). In contrast, the ionic index Z(2)/r explained most of the variability of logK values for the two clays kaolinite and montmorillonite, while |logK(OH)| was a better predictor of the generic NICA-Donnan parameters for HA and FA (0.67

Zhou, Dong-Mei; Li, Lian-Zhen; Peijnenburg, Willie J G M; Ownby, David R; Hendriks, A Jan; Wang, Peng; Li, Dan-Dan

2011-05-01

89

Complete physical map of the human immunoglobulin heavy chain constant region gene complex  

SciTech Connect

The authors have found by pulsed-field gel electrophoresis that the human immunoglobulin heavy chain constant region gene complex maps entirely to a 350-kilobase (kb) Mlu I fragment. The enzyme Eag I was used with pulsed-field gel electrophoresis alone and in double digests with Spe I to map the region. C{sub {gamma}}3 maps 60 kb to the 3{prime} side of C{sub {delta}}; C{gamma}2 maps 80 kb to the 3{prime} side of C{sub {alpha}}1. C{sub {psi}{gamma}} maps 35 kb to the 3{prime} side of C{sub {alpha}}1 and is in the same transcriptional orientation as the other genes. Although in the cloned DNA many CpG-containing restriction sites were identified, most of these were methylated in peripheral blood leukocytes. The sites that were not methylated were predominantly found in three clusters, or Hpa I tiny fragment islands. A region showing strong linkage disequilibrium between all C{sub {gamma}} genes spans at least 160 kb. The 70-kb C{sub {mu}}-C{sub {gamma}}3 region, however, shows no linkage disequilibrium, possibly indicating a recombination hot spot. The immunoglobulin heavy chain constant region has been almost entirely cloned and mapped, and thus most rearrangements occurring in this region should be detectable.

Hofker, M.H.; Walter, M.A.; Cox, D.W. (The Hospital For Sick Children, Toronto, Ontario (Canada))

1989-07-01

90

On the formation of iron(III) hydroxo acetate complexes.  

PubMed

The formation of hydroxo acetate complexes of iron (III) ion has been studied at 25 degrees C in 3 M (Na)ClO4 ionic medium by measuring with a glass electrode the hydrogen ion concentration in Fe(ClO4)3-HClO4-NaAc mixtures (Ac = acetate ion). The acetate/metal ratio ranged from 0 to 6, the metal concentration varied from 0.005 to 0.06 M, whereas [H+] was stepwise decreased from 0.1 M to initial precipitation of hydroxo-acetates. This occurred, depending on the acetate/metal ratio, in the -log[H+] range 1.85-2.7. The potentiometric data are consistent with the presence of Fe3(OH)3Ac3(3+), Fe2(OH)2(4+), Fe3(OH)4(5+), Fe3(OH)5(4+) and, as minor species, of Fe3(OH)2Ac6+, FeAc2+, FeAc2+, FeOH2+ and Fe(OH)2+. Previously published EMF measurements with redox and glass half-cells were recalculated to refine the stability constants of FeAc2+, FeAc2+ and Fe3(OH)2Ac6+. Formation constants *beta pqr for pFe(3+)+(q-r)H2O + rHAc reversible Fep(OH)(q-r)(Ac)r3p-q + qH+ (in parenthesis the infinite dilution value): log*beta 111 = -1.85 +/- 0.02 (-0.67 +/- 0.15), log*beta 122 = -3.43 +/- 0.02 (-1.45 +/- 0.15); log*beta 363 = -5.66 +/- 0.03 (-2.85 +/- 0.40), log*beta 386 = -8.016 +/- 0.006 (-4.06 +/- 0.15), log*beta 220 = -2.88 +/- 0.02 (-2.84 +/- 0.05), log*beta 340 = -6.14 +/- 0.18 (-6.9 +/- 0.4), log*beta 350 = -8.44 +/- 0.09 (-7.65 +/- 0.15). PMID:11507828

Ciavatta, L; De Tommaso, G; Iuliano, M

2001-01-01

91

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

92

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.  

PubMed

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. PMID:23099162

Naorem, Homendra; Devi, Seram Dushila

2013-01-15

93

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.

Mah, Vicky

2012-01-01

94

Lead(II) complex formation with glutathione.  

PubMed

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

Mah, Vicky; Jalilehvand, Farideh

2012-06-01

95

Formation of complex bacterial colonies via self-generated vortices  

Microsoft Academic Search

Depending on the environmental conditions bacterial colonies growing on agar surfaces can exhibit complex colony formation and various types of collective motion. Experimental results are presented concerning the hydrodynamics (vortices, migration of bacteria in clusters) and colony formation of a morphotype of Bacillus subtilis. Some of these features are not specific to this morphotype but also have been observed in

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

1996-01-01

96

Kinetics and Equilibria for Complex Formation between Palladium(II) and Chloroacetate  

Microsoft Academic Search

Kinetics and equilibria for the formation of a 1:1 complex between palladium(II) and chloroacetate were studied by spectrophotometric measurements in 1.00 mol$$\\\\cdot {\\\\rm dm}^{-3}$$ HClO4 at 298.2 K. The equilibrium constant, K, of the reaction\\u000a$$ {\\\\rm Pd}^{2 + } + {\\\\rm HL}^{K} {\\\\rm PdL}^+ +{\\\\rm H}^+ $$\\u000awas determined from multi-wavelength absorbance measurements of equilibrated solutions at variable temperatures

P?emysl Lubal; Lars I. Elding

2006-01-01

97

Formation of crystalline complexes between amylomaize dextrin and ceramide.  

PubMed

Complexes between amylomaize dextrin (average DP 311) and ceramide were prepared by using two different blending systems: an aqueous batch system containing ethanol and a two-phase system of isopropyl ether and water. The organic solvents and complex formation temperature (50-90°C) were important in determining the level of complex formation and its crystalline structure. Under X-ray diffraction analysis, the solvents as well as ceramide could form complexes with dextrin as weak V6I type crystals. However, the crystallinity of complexes was much higher in the presence of ceramide, which would enhance complex formation by forming ternary co-inclusion complexes of dextrin-solvent-ceramide. Compared to the two-phase system, the batch system yielded much higher crystallinity of complexes. With a minor use of ethanol (0.5 mL) in the batch system, aqueous blending of dextrin and ceramide at 50°C for 2 days followed by a storage at 25°C for 1 day produced well-defined V6I crystal particles as precipitates. The isolated particles had rectangular shapes with a size of 1 ?m or less, and contained about half of the ceramide initially added. The ceramide-dextrin complex exhibited enhanced water dispersibility, up to 45% based on the ceramide content in complex. PMID:24299790

Kim, Hee-Young; Lim, Jae Kag; Kim, Doun; Lim, Seung-Taik

2014-01-30

98

Complex formation of metal ions with xylenol orange  

SciTech Connect

The complex formation of metals with xylenol orange, purified by gel filtration on Molselekt G-10, was studied. The spectrophotometric characteristics of the complexes formed were refined. The chemistry of the reaction with xylenol orange was studied. A method was developed for the determination of aluminum in copper alloys.

Tikhonov, V.N.

1987-01-20

99

Polarographic study of composition and stability constants of Pb(II) N-(2-acetamido) imino diacetate complexes  

Microsoft Academic Search

The complexation of Pb(II) by N-(2-acetamido) imino diacetate (ADA) has been studied polarographically (dc and ac polarographic techniques). Ac polarographic studies have been particularly helpful in deciding the reversibility of the reduction of both simple and complexed metal ions and for confirmation of the overall stability constants. A weighted least squares numerical technique has been applied for the calculation of

H. A. Azab

1992-01-01

100

A new pH-metric methodology for the determination of thermodynamic inclusion constants of guest/cyclodextrin complexes.  

PubMed

A new methodology of pH-metric data treatment was developed to extract the stoichiometry and the thermodynamic association constants of guest-cyclodextrin inclusion complexes in dilute aqueous solution when the guest is a participant in an acid-base equilibrium. pH-metric titration curves in the presence of cyclodextrin (CD) were treated by a curve-fitting technique according to a nonlinear least-squares regression. Equations corresponding to the different kinds of acid-base pairs (AH/A-, BH+/B) and stoichiometries (1:1 and 1:2) were established. The methodology was validated by studying the 5-phenylbarbituric acid complexation with beta-CD and the 4-cyanobenzoic acid complexation with alpha-CD. Then it was applied to chlorpromazine. Both the acid form (constant K1 = 3260) and the base form (constant G1 = 13,100) gave complexes with beta-CD according to 1:1 stoichiometry. PMID:8537886

Boudeville, P; Burgot, J L

1995-09-01

101

Particle formation during oxidation catalysis with Cp* iridium complexes.  

PubMed

Real-time monitoring of light scattering and UV-vis profiles of four different Cp*Ir(III) precursors under various conditions give insight into nanoparticle formation during oxidation catalysis with NaIO(4) as primary oxidant. Complexes bearing chelate ligands such as 2,2'-bipyridine, 2-phenylpyridine, or 2-(2'-pyridyl)-2-propanolate were found to be highly resistant toward particle formation, and oxidation catalysis with these compounds is thus believed to be molecular in nature under our conditions. Even with the less stable hydroxo/aqua complex [Cp*(2)Ir(2)(?-OH)(3)]OH, nanoparticle formation strongly depended on the exact conditions and elapsed time. Test experiments on the isolated particles and comparison of UV-vis data with light scattering profiles revealed that the formation of a deep purple-blue color (~580 nm) is not indicative of particle formation during oxidation catalysis with molecular iridium precursors as suggested previously. PMID:22594951

Hintermair, Ulrich; Hashmi, Sara M; Elimelech, Menachem; Crabtree, Robert H

2012-06-13

102

The Runge-Lenz vector for quantum Kepler problem in the space of positive constant curvature and complex parabolic coordinates  

Microsoft Academic Search

By analogy with the Lobachevsky space H_{3}, generalized parabolic\\u000acoordinates (t_{1},t_{2},\\\\phi) are introduced in Riemannian space model of\\u000apositive constant curvature S_{3}. In this case parabolic coordinates turn out\\u000ato be complex valued and obey additional restrictions involving the complex\\u000aconjugation. In that complex coordinate system, the quantum-mechanical Coulomb\\u000aproblem is stu- died: separation of variables is carried out and

A. A. Bogush; V. S. Otchik; V. M. Red'kov

2006-01-01

103

Determination of protonation- and metal complex stability constants for a chelating monomer and its immobilized in polymer resin  

Microsoft Academic Search

An improved method is described for the calculation of complex stability constants for metal–ligand complexes considering ligands immobilized in resin phase. The applicability of it has been proved for N?-benzylethylene diamine N,N,N?-triacetic acid monomer (BEDTA) and for the ion exchange resin developed in the authors laboratory immobilizing this with styrene divinyl benzene. Calcium and magnesium metal ion complexes were investigated.

Ö. Szabadka; E. Varga; L. Nagy

2003-01-01

104

Different alternatives for stability constant determination of Zr and Hf 2-methyl lactate complexes by cation exchange  

Microsoft Academic Search

Three different alternatives are applied for the determination of the stability constants of zirconium and hafnium complexes\\u000a with 2-methyl lactic acid using cation exchange. Calculations based on the exchange equilibria of the highly charged metal\\u000a cations and the positively charged ligand complexes rather than that of the hydrolysed complex species are worked out according\\u000a to SCHUBERT and FRONAEUS, respectively. The

H. F. Aly; M. A. El-Haggan; A. A. Abdel-Rassoul

1976-01-01

105

Cu(II) complex formation by ACES buffer.  

PubMed

ACES (N-(2-Acetamido)-2-aminoethanesulfonic acid), a popular Good's buffer, binds Cu(II) ions with a moderate affinity. Although this interaction was the subject of previous studies, no consensus in the literature was found. We used potentiometry to establish binding constants, and controlled the potentiometric model selection and binding constant calculations by UV-vis spectroscopy. As a result, we obtained a consistent set of complex stoichiometries and binding constants in this system, which contains Cu(2+), CuL(+), CuL2, CuH-1L2(-1) and CuH(-)2L2(-2) complexes. The negative indexes at H atoms in these formulae denote the Cu(II) assisted deprotonation of the amide nitrogen present in the ACES molecule. The affinity of ACES for Cu(II) strongly depends on the concentration and ACES:Cu(II) ratio, reaching submicromolar apparent affinities at ratios higher than 100. These results will enable more accurate determinations of biologically relevant stability constants of Cu(II) complexes using ACES buffer. PMID:24077022

Zawisza, Izabela; Rózga, Ma?gorzata; Pozna?ski, Jaros?aw; Bal, Wojciech

2013-12-01

106

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

107

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

108

Theoretical estimate of the stability constants of metal complexes of aliphatic and heterocyclic amines in aqueous solutions  

Microsoft Academic Search

The stability constants of 1: 1 complexes of Mg2+, Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Mn2+, Ni2+, and Zn2+ with 29 N-donor ligands (ammonia, alkylamines, aniline, pyridine, imidazole, pyrazole, benzimidazole, isoquinoline, and their\\u000a alkyl-and halogen-substituted derivatives) in aqueous solutions at 298 K were calculated by integration of the ligand distribution\\u000a function. The stability constants are determined by the effective charge on

A. I. Mishustin

2008-01-01

109

Physicochemical aspects of polyethylene processing in an open mixer. Part 26: Formal kinetics of aldehyde and carboxylic acid formation at a constant rate  

Microsoft Academic Search

Formation of carboxylic acids at a constant rate can be easily explained. It seems to result from the formation and decomposition of ?,?-keto-hydroperoxides. Formal kinetics based on formation and decomposition of these structural units is in agreement with the experimental findings. The activation energy deduced from the calculations is negligible, in agreement with the experimental data showing the constant rate

F. Gugumus

2006-01-01

110

Mechanisms Underlying Methamphetamine-Induced Dopamine Transporter Complex Formation  

PubMed Central

Repeated, high-dose methamphetamine (METH) administrations cause persistent dopaminergic deficits in rodents, nonhuman primates, and humans. In rats, this treatment also causes the formation of high-molecular mass (greater than approximately 120 kDa) dopamine transporter (DAT)-associated complexes, the loss of DAT monomer immunoreactivity, and a decrease in DAT function, as assessed in striatal synaptosomes prepared 24 h after METH treatment. The present study extends these findings by demonstrating the regional selectivity of DAT complex formation and monomer loss because these changes in DAT immunoreactivity were not observed in the nucleus accumbens. Furthermore, DAT complex formation was not a consequence limited to METH treatment because it was also caused by intrastriatal administration of 6-hydroxydopamine. Pretreatment with the D2 receptor antagonist, eticlopride [S-(-)-3-chloro-5-ethyl-N-[(1-ethyl-2-pyrrolidinyl)methyl]-6-hydroxy-2-methoxybenzamide hydrochloride], but not the D1 receptor antagonist, SCH23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride], attenuated METH-induced DAT complex formation. Eticlopride pretreatment also attenuated METH-induced DAT monomer loss and decreases in DAT function; however, the attenuation was much less pronounced than the effect on DAT complex formation. Finally, results also revealed a negative correlation between METH-induced DAT complex formation and DAT activity. Taken together, these data further elucidate the underlying mechanisms and the functional consequences of repeated administrations of METH on the DAT protein. Furthermore, these data suggest a multifaceted role for D2 receptors in mediating METH-induced alterations of the DAT and its function.

Hadlock, Gregory C.; Baucum, Anthony J.; King, Jill L.; Horner, Kristen A.; Cook, Glen A.; Gibb, James W.; Wilkins, Diana G.; Hanson, Glen R.; Fleckenstein, Annette E.

2009-01-01

111

Mechanisms underlying methamphetamine-induced dopamine transporter complex formation.  

PubMed

Repeated, high-dose methamphetamine (METH) administrations cause persistent dopaminergic deficits in rodents, nonhuman primates, and humans. In rats, this treatment also causes the formation of high-molecular mass (greater than approximately 120 kDa) dopamine transporter (DAT)-associated complexes, the loss of DAT monomer immunoreactivity, and a decrease in DAT function, as assessed in striatal synaptosomes prepared 24 h after METH treatment. The present study extends these findings by demonstrating the regional selectivity of DAT complex formation and monomer loss because these changes in DAT immunoreactivity were not observed in the nucleus accumbens. Furthermore, DAT complex formation was not a consequence limited to METH treatment because it was also caused by intrastriatal administration of 6-hydroxydopamine. Pretreatment with the D2 receptor antagonist, eticlopride [S-(-)-3-chloro-5-ethyl-N-[(1-ethyl-2-pyrrolidinyl)methyl]-6-hydroxy-2-methoxybenzamide hydrochloride], but not the D1 receptor antagonist, SCH23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride], attenuated METH-induced DAT complex formation. Eticlopride pretreatment also attenuated METH-induced DAT monomer loss and decreases in DAT function; however, the attenuation was much less pronounced than the effect on DAT complex formation. Finally, results also revealed a negative correlation between METH-induced DAT complex formation and DAT activity. Taken together, these data further elucidate the underlying mechanisms and the functional consequences of repeated administrations of METH on the DAT protein. Furthermore, these data suggest a multifaceted role for D2 receptors in mediating METH-induced alterations of the DAT and its function. PMID:19141713

Hadlock, Gregory C; Baucum, Anthony J; King, Jill L; Horner, Kristen A; Cook, Glen A; Gibb, James W; Wilkins, Diana G; Hanson, Glen R; Fleckenstein, Annette E

2009-04-01

112

Rigorous Potentiometric Determination of Metal Complexes Stability Constants: An Undergraduate Laboratory Practice  

NASA Astrophysics Data System (ADS)

In the present work an undergraduate laboratory practice is described corresponding to both experimental and computational methods used in potentiometric equilibrium constants determinations. As an example of these determinations the system formed by Cu(II) and D-galacturonic acid was selected. Both the deprotonation constant for the ligand and the equilibrium constants for the metal chelates were determined by using the program BEST.

Escandar, Graciela M.; Federico Sala, Luis

1997-11-01

113

Complex Dielectric Constant of KH2PO4 at 9.2 Gc\\/sec  

Microsoft Academic Search

The temperature dependence of the dielectric constant and loss tangent in potassium dihydrogen phosphate along and normal to the optic axis has been measured by a cavity perturbation method at 9.2 Gc\\/sec. The dielectric constants agree with earlier low-frequency measurements. The parallel dielectric constant exhibits a modified Curie-Weiss behavior which may be described by (T-Tc)?c'=A'+BT, with Tc=119 °K, A'=2.27×103 °K,

I. P. Kaminow; G. O. Harding

1963-01-01

114

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

PubMed

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

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

2014-03-14

115

Synthesis, characterization and thermodynamics of complex formation of some new Schiff base ligands with some transition metal ions and the adduct formation of zinc Schiff base complexes with some organotin chlorides  

NASA Astrophysics Data System (ADS)

Four new complexes, [M(Salpyr)] where Salpyr = N,N'-bis(Salicylidene)-2,3- and 3,4-diiminopyridine and M = Co, Cu, Mn, Ni and Zn were synthesized and characterized by 1H NMR, IR spectroscopy, elemental analysis and UV-vis spectrophotometry. UV-vis spectrophotometric study of the adduct formation of the zinc(II) complexes, [Zn(2,3-Salpyr)] and [Zn(3,4-Salpyr)], as donor with R2SnCl2 (R = methyl, phenyl, n-butyl), PhSnCl3 and Bu3SnCl as acceptors has been investigated in methanol, as solvent. The formation constants and the thermodynamic free energies were measured using UV-vis spectrophotometry. Titration of the organotin chlorides with Zn(II) complexes at various temperatures (T = 283-313 K) leads to 1:1 adduct formation. The results show that the formation constants were decreased by increasing the temperature. The trend of the reaction of RnSnCl4-n as acceptors toward given zinc complexes was as follows: PhSnCl3 > Me2SnCl2 > Ph2SnCl2 > Bu2SnCl2 > Bu3SnCl By considering the formation constants and the ?G° of the complex formation for the Schiff base as donor and the M(II) as acceptor, the following conclusion was drawn: the formation constant for a given Schiff base changes according to the following trend: Ni > Cu > Co > Zn > Mn

Asadi, Mozaffar; Asadi, Zahra; Torabi, Susan; Lotfi, Najmeh

116

Synthesis, characterization and thermodynamics of complex formation of some new Schiff base ligands with some transition metal ions and the adduct formation of zinc Schiff base complexes with some organotin chlorides.  

PubMed

Four new complexes, [M(Salpyr)] where Salpyr=N,N'-bis(Salicylidene)-2,3- and 3,4-diiminopyridine and M=Co, Cu, Mn, Ni and Zn were synthesized and characterized by (1)H NMR, IR spectroscopy, elemental analysis and UV-vis spectrophotometry. UV-vis spectrophotometric study of the adduct formation of the zinc(II) complexes, [Zn(2,3-Salpyr)] and [Zn(3,4-Salpyr)], as donor with R(2)SnCl(2) (R=methyl, phenyl, n-butyl), PhSnCl(3) and Bu(3)SnCl as acceptors has been investigated in methanol, as solvent. The formation constants and the thermodynamic free energies were measured using UV-vis spectrophotometry. Titration of the organotin chlorides with Zn(II) complexes at various temperatures (T=283-313K) leads to 1:1 adduct formation. The results show that the formation constants were decreased by increasing the temperature. The trend of the reaction of R(n)SnCl(4-n) as acceptors toward given zinc complexes was as follows: PhSnCl3 > Me2SnCl2 > Ph2SnCl2 > Bu2SnCl2 > Bu3SnCl. By considering the formation constants and the ?G° of the complex formation for the Schiff base as donor and the M(II) as acceptor, the following conclusion was drawn: the formation constant for a given Schiff base changes according to the following trend: Ni > Cu > Co > Zn > Mn. PMID:22626922

Asadi, Mozaffar; Asadi, Zahra; Torabi, Susan; Lotfi, Najmeh

2012-08-01

117

Charge-transfer complex formation between p-chloranil and 1, n-dicarbazolylalkanes  

NASA Astrophysics Data System (ADS)

Dimer model compounds of polyvinylcarbazoles (1, n-di( N-carbazolyl)alkanes, when n = 1-5) were synthesized to model the effects of distance and orientation between carbazole groups in polymeric systems. Charge-transfer (CT) complexes of carbazole, N-ethylcarbazole and 1, n-di( N-carbazolyl)alkanes with p-chloranil ( p-CHL) have been investigated spectrophotometrically in dichloromethane. The colored products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptor. The formation constants of the CT complexes were determined by the Benesi-Hildebrand equation. The thermodynamic parameters were calculated by Van't Hoff equation. Stochiometries of the complexes formed between donors and acceptor were defined by the Job's method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands.

Arslan, Mustafa; Masnovi, John; Krafcik, Randolph

2007-04-01

118

Absorption spectrometric study of molecular complex formation between [60]fullerene and a series of methylated pyridines.  

PubMed

[60]fullerene has been shown to form 1:1 molecular complexes with pyridine and some methylated pyridines such as 2-picoline, 3-picoline, 4-picoline, 2,6-lutidine and 2,4,6-collidine in CCl4 medium by absorption spectrometric method. Well defined charge transfer (CT) bands have been observed for complexes of C60 with all the pyridines studied except 4-picoline. From an analysis of the trends in the CT absorption bands the ionisation potentials of the methylpyridines have been determined. The electron affinity of C60 has also been determined from the spectral data. The formation constants of the complexes exhibit a very good linear free energy relationship from which the Hammett p parameter for the complexation process is found to be -2.96. PMID:12396038

Bhattacharya, Sumanta; Banerjee, Manas; Mukherjee, Asok K

2002-10-01

119

Absorption spectrometric study of molecular complex formation between [60]fullerene and a series of methylated pyridines  

NASA Astrophysics Data System (ADS)

[60]fullerene has been shown to form 1:1 molecular complexes with pyridine and some methylated pyridines such as 2-picoline, 3-picoline, 4-picoline, 2,6-lutidine and 2,4,6-collidine in CCl 4 medium by absorption spectrometric method. Well defined charge transfer (CT) bands have been observed for complexes of C 60 with all the pyridines studied except 4-picoline. From an analysis of the trends in the CT absorption bands the ionisation potentials of the methylpyridines have been determined. The electron affinity of C 60 has also been determined from the spectral data. The formation constants of the complexes exhibit a very good linear free energy relationship from which the Hammett ? parameter for the complexation process is found to be -2.96.

Bhattacharya, Sumanta; Banerjee, Manas; Mukherjee, Asok K.

2002-10-01

120

Hierarchical star formation in M 51: star/cluster complexes  

NASA Astrophysics Data System (ADS)

We report on a study of young star cluster complexes in the spiral galaxy M 51. Recent studies have confirmed that star clusters do not form in isolation, but instead tend to form in larger groupings or complexes. We use HST broad and narrow band images (from both WFPC2 and ACS), along with BIMA-CO observations to study the properties and investigate the origin of these complexes. We find that the complexes are all young (<10 Myr), have sizes between ~85 and ~240 pc, and have masses between 3-30 × 104~ M?. Unlike that found for isolated young star clusters, we find a strong correlation between the complex mass and radius, namely M? R2.33 ± 0.19. This is similar to that found for giant molecular clouds (GMCs). By comparing the mass-radius relation of GMCs in M 51 to that of the complexes we can estimate the star formation efficiency within the complexes, although this value is heavily dependent on the assumed CO-to-H2 conversion factor. The complexes studied here have the same surface density distribution as individual young star clusters and GMCs. If star formation within the complexes is proportional to the gas density at that point, then the shared mass-radius relation of GMCs and complexes is a natural consequence of their shared density profiles. We briefly discuss possibilities for the lack of a mass-radius relation for young star clusters. We note that many of the complexes show evidence of merging of star clusters in their centres, suggesting that larger star clusters can be produced through the build up of smaller clusters.

Bastian, N.; Gieles, M.; Efremov, Yu. N.; Lamers, H. J. G. L. M.

2005-11-01

121

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

122

Molecular Dynamics Simulations of DNA-Polycation Complex Formation  

PubMed Central

Abstract Complexes formed from DNA and polycations are of interest because of their potential use in gene therapy; however, there remains a lack of understanding of the structure and formation of DNA-polycation complexes at atomic scale. In this work, molecular dynamics simulations of the DNA duplex d(CGCGAATTCGCG) in the presence of polycation chains are carried out to shed light on the specific atomic interaction that result in complex formation. The structures of complexes formed from DNA with polyethylenimine, which is considered one of the most promising DNA vector candidates, and a second polycation, poly-L-lysine, are compared. After an initial separation of ?50 Å, the DNA and polycation come together and form a stable complex within 10 ns. The DNA does not undergo any major structural changes on complexation and remains in the B-form. In the formed complex, the charged amine groups of the polycation mainly interact with DNA phosphate groups, with polycation intrusion into the major and minor grooves dependent on the identity and charge state of the polycation. The ability of the polycation to effectively neutralize the charge of the DNA phosphate groups and the resulting influence on the DNA helix interaction are discussed.

Ziebarth, Jesse; Wang, Yongmei

2009-01-01

123

Monte Carlo simulation on complex formation of proteins and polysaccharides.  

PubMed

In protein-polysaccharide complex systems, how nonspecific interactions such as electrostatic and van der Waals interactions affect complex formation has not been clearly understood. On the basis of a coarse-grained model with the specificity of a target system, we have applied Monte Carlo (MC) simulation to illustrate the process of complex coacervate formation from the association of proteins and polysaccharides. The coarse-grained model is based on serum albumin and a polycation system, and the MC simulation of pH impact on complex coacervation has been carried out. We found that complex coacervates could form three ways, but the conventional association through electrostatic attraction between the protein and polysaccharide still dominated the complex coacervation in such systems. We also observed that the depletion potential always participated in protein crowding and was weakened in the presence of strong electrostatic interactions. Furthermore, we observed that the sizes of polysaccharide chains nonmonotonically increased with the number of bound proteins. Our approach provides a new way to understand the details during protein-polysaccharide complex coacervation at multiple length scales, from interaction and conformation to aggregation. PMID:22280485

Li, Yunqi; Shi, Tongfei; An, Lijia; Huang, Qingrong

2012-03-15

124

Geology of the Biwabik Iron Formation and Duluth Complex.  

PubMed

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

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

2008-10-01

125

Effect of ternary complex formation on chromatographic selectivity using in situ complexation chromatography  

SciTech Connect

In situ complexation chromatography is a relatively novel form of reversed-phase chromatography. A method for controlling selectivity via ternary complex formation is discussed. This method is potentially useful, not only for controlling separations but also for enhancing detection of metal species. Limitations of the methods are discussed. 30 references, 5 figures, 4 tables.

O'Riordan, K.P.; Heneghan, G.; Wallace, G.G.

1985-06-01

126

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.

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

2008-01-01

127

Rapid-reaction Kinetic Characterization of the Pathway of Streptokinase-Plasmin Catalytic Complex Formation*  

PubMed Central

Binding of the fibrinolytic proteinase plasmin (Pm) to streptokinase (SK) in a tight stoichiometric complex transforms Pm into a potent proteolytic activator of plasminogen. SK binding to the catalytic domain of Pm, with a dissociation constant of 12 pm, is assisted by SK Lys414 binding to a Pm kringle, which accounts for a 11-20-fold affinity decrease when Pm lysine binding sites are blocked by 6-aminohexanoic acid (6-AHA) or benzamidine. The pathway of SK·Pm catalytic complex formation was characterized by stopped-flow kinetics of SK and the Lys414 deletion mutant (SK?K414) binding to Pm labeled at the active site with 5-fluorescein ([5F]FFR-Pm) and the reverse reactions by competitive displacement of [5F]FFR-Pm with active site-blocked Pm. The rate constants for the biexponential fluorescence quenching caused by SK and SK?K414 binding to [5F]FFR-Pm were saturable as a function of SK concentration, reporting encounter complex affinities of 62-110 nm in the absence of lysine analogs and 4900-6500 and 1430-2200 nm in the presence of 6-AHA and benzamidine, respectively. The encounter complex with SK?K414 was ?10-fold weaker in the absence of lysine analogs but indistinguishable from that of native SK in the presence of 6-AHA and benzamidine. The studies delineate for the first time the sequence of molecular events in the formation of the SK·Pm catalytic complex and its regulation by kringle ligands. Analysis of the forward and reverse reactions supports a binding mechanism in which SK Lys414 binding to a Pm kringle accompanies near-diffusion-limited encounter complex formation followed by two slower, tightening conformational changes.

Verhamme, Ingrid M.; Bock, Paul E.

2008-01-01

128

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

129

Photometric studies of the complex formation of Cu 2+ and Cr 3+ ions with Sudan Red B  

Microsoft Academic Search

Photometric method was used to study the complex formation of Sudan Red B with Cu2+ and Cr3+ ions. The absorption spectra were monitored and the conditions were optimized in terms of dye and metal concentration, pH and cationic and anionic effects. The log? (stability constants) of the metal–dye complex were calculated using Job's method and these were of the order

M. A. Rauf; Z. Akhter; S. Kanwal

2005-01-01

130

Determination of Stability Constants of Cadmium-Glycine Complexes by a Unified Treatment for Potentiometric and Polarographic Data  

NASA Astrophysics Data System (ADS)

The cadmium(II)-glycine system was studied by the two experimental techniques, ion sensitive electrode (ISE) and differential pulse polarography (DPP), and the experimental data obtained were used by a unified mathematical treatment to calculate the complex stability constants. The combination of the two techniques is of many advantages as ISE can be performed at low [LT]:[MT] ratios and significantly higher [MT], whereas DPP could be used well at large [LT]:[MT] ratios and much smaller [MT]. This makes it possible to study a metal-ligand system in a relatively broader range of experimental conditions that, in turn, provides more information about the metal-ligand system of interest. Applying the unified mathematical treatment to the cadmium-glycine system, two new complexes MHL and ML2(OH) as well as three complexes ML, ML2 and ML3, reported in literatures, could be modeled and all their stability constants have been refined.

Zhang, Jian-min; Shi, Qiu-zhi

2006-04-01

131

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

PubMed

Efficient method is proposed for computing thermal rate constant of recombination reaction that proceeds according to the energy transfer mechanism, when an energized molecule is formed from reactants first, and is stabilized later by collision with quencher. The mixed quantum-classical theory for the collisional energy transfer and the ro-vibrational energy flow [M. Ivanov and D. Babikov, J. Chem. Phys. 134, 144107 (2011)] is employed to treat the dynamics of molecule + quencher collision. Efficiency is achieved by sampling simultaneously (i) the thermal collision energy, (ii) the impact parameter, and (iii) the incident direction of quencher, as well as (iv) the rotational state of energized molecule. This approach is applied to calculate third-order rate constant of the recombination reaction that forms the (16)O(18)O(16)O isotopomer of ozone. Comparison of the predicted rate vs. experimental result is presented. PMID:22583284

Ivanov, Mikhail V; Babikov, Dmitri

2012-05-14

132

Application of electrophoresis technique for evaluating stability constant of ternary complexes  

Microsoft Academic Search

A method involving the use of paper electrophoresis is described for the study of equilibria in mixed ligand complex systems in solution. This method is based on the development of a spot by migration of a metal ion, with the complexants added in the background electrolyte (0.1 M perchloric acid). For the study of ternary complexes, the concentration of adenosine

Amita Yadav

1993-01-01

133

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

134

[sup 7]Li-NMR determination of stability constants as a function of temperature for lithium-crown ether complexes in a molten salt mixtures  

SciTech Connect

The stability constants of several crown ethers with lithium ion were determined by [sup 7]Li-NMR measurements. A room temperature, basic molten salt of the composition of 55/45 mol % 1-methyl-3-ethyl-imidazolium chloride to aluminum (III) chloride was used as solvent. On the basis of a 1:1 complex formation the following order was found for the stability constants of the investigated crown ethers: 18-crown-6 < 12-crown-4 < benzo-15-crown-5 < 15-crown-5. A temperature dependence study for 12-crown-4, benzo-15-crown-5, and 15-crown-5 was undertaken for the range 5-84[degree]C. Values of [Delta]H and [Delta]S were calculated. At 5.5[degree]C the splitting of the single, fast exchange peak into two separate signals was observed for benzo-15-crown-5, providing further evidence for the formation of the 1:1 complex. 34 refs., 4 figs., 5 tabs.

Gerhard, A. (Univ. of Utah, Salt Lake City, UT (United States) Univ. of Witten/Herdecke (Germany)); Cobranchi, D.P.; Garland, B.A.; Highley, A.M.; Huang, Y.H.; Konya, G.; Eyring, E.M. (Univ. of Utah, Salt Lake City, UT (United States)); Zahl, A.; Eldik, R. van (Univ. of Witten/Herdecke (Germany)); Petrucci, S. (Polytechnic Univ., Farmingdale, NY (United States))

1994-08-11

135

Massive Star Formation in the LMC HII Complex N44  

NASA Astrophysics Data System (ADS)

The star formation process can be characterized microscopically by the initial mass function (IMF) and macroscopically by the intensity of the activity as a function of space and time. To study the star formation process in a mild starburst environment, I have analyzed N44, one of the three top-ranking HII complexes in the Large Magellanic Cloud, using the most comprehensive inventory of resolved massive stars and young stellar objects (YSOs) derived from CTIO 4-m MOSAIC UBVI and ISPI JK images, supplemented by 0.9-m UBV images, and Spitzer Space Telescope IRAC and MIPS observations. The N44 complex can be divided into three regions that are coincident with three concentrations of giant molecular clouds but exhibiting different evolutionary states and intensities of star formation. The central concentration is associated with a prominent superbubble and bright HII regions along its periphery; the south concentration is associated with a group of bright HII regions; and the north concentration has only two faint little HII regions. I have defined and examined regions with contrasting star formation properties to determine their present-day mass functions (PDMFs). I find that comparisons of slopes of the IMF between star forming regions and the "field" is highly dependent on the definition of the regions. I have also used the Spitzer mid-IR observations to identify massive YSOs in order to study the current, on-going star formation. I have also used ground-based high-resolution UBVIJK observations to confirm their nature as YSOs and to model their spectral energy distributions for mass estimates. I find that the more massive YSOs are preferentially formed near sites previous active star formation has taken place. The stellar energy feedback may play some role in the formation of massive stars.

Chen, C. H. Rosie

2007-12-01

136

Formation and antimicrobial activity of complexes of beta-cyclodextrin and some antimycotic imidazole derivatives.  

PubMed

Complex formation between beta-cyclodextrin and six antimycotic imidazole derivatives has been studied. The solubility of all drugs was increased in the presence of beta-cyclodextrin. The smallest increase (approx. 5-fold) was observed for miconazol, and the largest increase (approx. 160-fold) was observed for bifonazol. Apparent 1:1-complex constants were measured and found to decrease in the order: bifonazol greater than ketoconazol greater than tioconazol greater than miconazol greater than itraconazol greater than clotrimazol. The complexes appeared to possess a low, if any, antimicrobial activity. Measurement of inhibition zone sizes, with four test organisms was used to study the release of the antimycotic drugs from topical preparations. The antimycotic drugs were more readily released from topical preparations containing beta-cyclodextrin than from the same vehicles without beta-cyclodextrin. The rationale of beta-cyclodextrin addition to antimycotic topical preparations is discussed. PMID:3393422

Van Doorne, H; Bosch, E H; Lerk, C F

1988-04-22

137

Contrasting Factors on the Kinetic Path to Protein Complex Formation Diminish the Effects of Crowding Agents  

PubMed Central

The crowded environment of cells poses a challenge for rapid protein-protein association. Yet, it has been established that the rates of association are similar in crowded and in dilute solutions. Here we probe the pathway leading to fast association between TEM1 ?-lactamase and its inhibitor protein BLIP in crowded solutions. We show that the affinity of the encounter complex, the rate of final complex formation, and the structure of the transition state are similar in crowded solutions and in buffer. The experimental results were reproduced by calculations based on the transient-complex theory for protein association. Both experiments and calculations suggest that while crowding agents decrease the diffusion constant of the associating proteins, they also induce an effective excluded-volume attraction between them. The combination of the two opposing effects thus results in nearly identical overall association rates in diluted and crowded solutions.

Phillip, Yael; Harel, Michal; Khait, Ruth; Qin, Sanbo; Zhou, Huan-Xiang; Schreiber, Gideon

2012-01-01

138

Contrasting factors on the kinetic path to protein complex formation diminish the effects of crowding agents.  

PubMed

The crowded environment of cells poses a challenge for rapid protein-protein association. Yet, it has been established that the rates of association are similar in crowded and in dilute solutions. Here we probe the pathway leading to fast association between TEM1 ?-lactamase and its inhibitor protein BLIP in crowded solutions. We show that the affinity of the encounter complex, the rate of final complex formation, and the structure of the transition state are similar in crowded solutions and in buffer. The experimental results were reproduced by calculations based on the transient-complex theory for protein association. Both experiments and calculations suggest that while crowding agents decrease the diffusion constant of the associating proteins, they also induce an effective excluded-volume attraction between them. The combination of the two opposing effects thus results in nearly identical overall association rates in diluted and crowded solutions. PMID:23009850

Phillip, Yael; Harel, Michal; Khait, Ruth; Qin, Sanbo; Zhou, Huan-Xiang; Schreiber, Gideon

2012-09-01

139

Multinuclear complex formation in aqueous solutions of Ca(II) and heptagluconate ions.  

PubMed

The equilibria and structure of complexes formed between the Ca(2+) ion and the heptagluconate (Hglu(-)) ion in both neutral and alkaline solutions have been studied. In alkaline solutions an uncharged, multinuclear complex is formed with the composition of Ca3Hglu2(OH)4 (or [Ca3Hglu2H(-4)](0)) with an unexpectedly high stability constant (lg ?(32-4) = 14.09). The formation of the trinuclear complex was deduced from potentiometry and confirmed by freezing-point depression measurements and conductometry as well. The binding sites of Hglu(-) were determined from NMR measurements. Besides the carboxylate group, the O atoms on the second and third carbon atoms proved to be the most probable sites for Ca(2+) binding. PMID:23629045

Pallagi, Attila; Csendes, Zita; Kutus, Bence; Czeglédi, Eszter; Peintler, Gábor; Forgo, Péter; Pálinkó, István; Sipos, Pál

2013-06-21

140

Molecular Matchmakers. [Formation of stable DNA-protein complexes  

SciTech Connect

Molecular matchmakers are a class of proteins that use the energy released from the hydrolysis of adenosine triphosphate to cause a conformational change in one or both components of a DNA binding protein pair to promote formation of a metastable DNA-protein complex. After matchmaking the matchmaker dissociates from the complex, permitting the matched protein to engage in other protein-protein interactions to bring about the effector function. Matchmaking is most commonly used under circumstances that require targeted, high-avidity DNA binding without relying solely on sequence specificity. Molecular matchmaking is an extensively used mechanism in repair, replication, and transcription and most likely in recombination and transposition reactions, too.

Sancar, A. (Univ. of North Carolina School of Medicine, Chapel Hill (United States)); Hearst, J.E. (Lawrence Berkely Lab., CA (United States))

1993-03-05

141

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

142

Ion-Selective Electrodes with Unusual Response Functions: Simultaneous Formation of Ionophore-Primary Ion Complexes with Different Stoichiometries  

PubMed Central

It is well known that the selectivity of an ion-selective electrode (ISE) depends on the stoichiometry of the complexes between its ionophore and the target and interfering ions. It is all the more surprising that the possibility for the simultaneous occurrence of multiple target ion complexes with different complex stoichiometries was mostly ignored in the past. Here we report on the simultaneous formation of 1:1 and 1:2 complexes of a fluorophilic crown ether in fluorous ISE membranes, and how this results in what look like super-Nernstian responses. These increased response slopes are not caused by mass transfer limitations and can be readily explained with a phase boundary model, a finding that is supported by experimentally determined complex formation constants and excellent fits of response curves. Not only Cs+ but also the smaller ions Li+, Na+, K+, and NH4+ form 1:1 and 1:2 complexes with the fluorophilic crown ether, with cumulative formation constants of up to 1015.0 and 1021.0 for of the 1:1 and 1:2 complexes, respectively. Super-Nernstian responses of the type observed with these electrodes are probably not particularly rare, but lacking in the past an adequate discussion in the literature remained ignored or misinterpreted. Preliminary calculations also predict sub-Nernstian responses and potential dips of a similar origin. The proper understanding of such phenomena will facilitate the development of new ISEs based on ionophores that form complexes of higher stoichiometries.

Miyake, Masafumi; Chen, Li D.; Pozzi, Gianluca; Buhlmann, Philippe

2011-01-01

143

An infrared spectroscopic study of complex formation between meta-cresol and propionitrile  

NASA Astrophysics Data System (ADS)

Fourier transform IR spectroscopy, together with factor analysis and band resolution techniques, has been used to study complex formation in binary mixtures of m-cresol and propionitrile in the concentration range 0.1-0.9 mole fraction of m-cresol. The profile of the C?N stretching band of propionitrile in the IR spectrum near 2250 cm -1 was studied to determine the nature of the association. Factor analysis indicated that there were only two linearly independent components in the band envelope. The appearance of a pseudo-isosbestic point in the normalized spectra supported this conclusion. For all concentrations, the C?N stretching band envelope was resolved into three bands: one assigned to free propionitrile, a second to an m-cresol-propionitrile complex and a third to an overtone or combination mode of the nitrile which does not involve C?N stretching. The results indicated the formation of a 1:1 complex. The equilibrium constant Kc for the formation of this complex was determined at various mole fractions of m-cresol. The calculated values of Kc exhibited a strong concentration dependence.

Quadri, S. M.; Shurvell, H. F.

1995-07-01

144

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

Microsoft Academic Search

The formation constants of a few lanthanide complexes with DOTA (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) and TETA (1,4,8,11-tetraazacyclotetradecane-N,N',N'',N'''-tetraacetic acid) have been measured by potentiometric and competition methods. The ligand DOTA forms the most stable lanthanide chelates known so far (log K\\/sub ML\\/ = 28.2-29.2) while the stability of the TETA compounds at 80 °C (log K\\/sub ML\\/ = 14.5-16.5) is comparable to the

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

1986-01-01

145

Rate constants for a mechanism including intermediates in the interconversion of ternary complexes by horse liver alcohol dehydrogenase  

SciTech Connect

Transient kinetic data for partial reactions of alcohol dehydrogenase and simulations of progress curves have led to estimates of rate constants for the following mechanism, at pH 8.0 and 25{degrees}C: E in equilibrium E-NAD+ in equilibrium *E-NAD+ in equilibrium E-NAD(+)-RCH2OH in equilibrium E-NAD+-RCH2O- in equilibrium *E-NADH-RCHO in equilibrium E-NADH-RCHO in equilibrium E-NADH in equilibrium E. Previous results show that the E-NAD+ complex isomerizes with a forward rate constant of 620 s-1. The enzyme-NAD(+)-alcohol complex has a pK value of 7.2 and loses a proton rapidly (greater than 1000 s-1). The transient oxidation of ethanol is 2-fold faster in D{sub 2}O, and proton inventory results suggest that the transition state has a charge of -0.3 on the substrate oxygen. Rate constants for hydride ion transfer in the forward or reverse reactions were similar for short-chain aliphatic substrates (400-600 s-1). A small deuterium isotope effect for transient oxidation of longer chain alcohols is apparently due to the isomerization of the E-NAD+ complex. The transient reduction of aliphatic aldehydes showed no primary deuterium isotope effect; thus, an isomerization of the E-NADH-aldehyde complex is postulated, as isomerization of the E-NADH complex was too fast to be detected. The estimated microscopic rate constants show that the observed transient reactions are controlled by multiple steps.

Sekhar, V.C.; Plapp, B.V. (Univ. of Iowa, Iowa City (USA))

1990-05-08

146

Processive Ubiquitin Chain Formation by the Anaphase-Promoting Complex  

PubMed Central

Progression through mitosis requires the sequential ubiquitination of cell cycle regulators by the anaphase-promoting complex, resulting in their proteasomal degradation. Although several mechanisms contribute to APC/C regulation during mitosis, the APC/C is able to discriminate between its many substrates by exploiting differences in the processivity of ubiquitin chain assembly. Here, we discuss how the APC/C achieves processive ubiquitin chain formation to trigger the sequential degradation of cell cycle regulators during mitosis.

Meyer, Hermann-Josef; Rape, Michael

2011-01-01

147

Complexation of arsenite with dissolved organic matter: Conditional distribution coefficients and apparent stability constants  

Microsoft Academic Search

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

Guangliang Liu; Yong Cai

2010-01-01

148

Complex dielectric constant spectra measurements by means of surface waves spectroscopy. principles, realizations, examples  

Microsoft Academic Search

The surface electromagnetic waves (SEW) applications for optical constants determination in broad ER spectral range is reviewed. The SEW configuration with the maximum field on the surfaces provides the high sensitivity for imaginary part determination. The real part can be interferometrically measured in the sample included into double beam interferometer with SEW excited by IR laser, free electron laser (FEL)

E. V. Alieva; L. A. Kuzik; A. A. Sigarev; V. A. Yakovlev; M. J. Van Der Wiel; G. N. Zhizhin

1996-01-01

149

Correlations between Community Structure and Link Formation in Complex Networks  

PubMed Central

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

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

2013-01-01

150

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

PubMed

Rate constants for the potentially important interstellar N((4)S) + CH(X(2)?r) reaction have been measured in a continuous supersonic flow reactor over the range 56 K ?T? 296 K using the relative rate technique employing both the N((4)S) + OH(X(2)?i) and N((4)S) + CN(X(2)?(+)) reactions as references. Excess concentrations of atomic nitrogen were produced by the microwave discharge method upstream of the Laval nozzle and CH and OH radicals were created by the in situ pulsed laser photolysis of suitable precursor molecules. In parallel, quantum dynamics calculations of the title reaction have been performed based on accurate global potential energy surfaces for the 1(3)A' and 1(3)A'' 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 in excellent agreement, predicting a positive temperature dependence of the rate constant, in contrast to earlier experimental work at low temperature. The effects of the new low temperature rate constants on interstellar N2 formation are tested using a dense cloud model, yielding N2 abundances 10-20% lower than previously predicted. PMID:23843017

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

2013-09-01

151

A novel equation for predicting stability constants of aqueous metal complexes and actinide binding to protein  

Microsoft Academic Search

Metal complexation with various inorganic or organic ligands in aqueous solutions directly controls the solubility, sorption, and toxicity of toxic metals including radionuclides in natural environments. The quantitative calculations of metal complexation thus have been routinely used in predicting the fate and impact of heavy metals in natural environments. The effectiveness of these calculations heavily depends on the completeness and

Huifang Xu; Yifeng Wang

2000-01-01

152

Determination of Stability Constants of Cadmium-Glycine Complexes by a Unified Treatment for Potentiometric and Polarographic Data  

Microsoft Academic Search

The cadmium(II)-glycine system was studied by the two experimental techniques, ion sensitive electrode (ISE) and differential pulse polarography (DPP), and the experimental data obtained were used by a unified mathematical treatment to calculate the complex stability constants. The combination of the two techniques is of many advantages as ISE can be performed at low [LT]:[MT] ratios and significantly higher [MT],

Jian-min Zhang; Qiu-zhi Shi

2006-01-01

153

Properties of high-dielectric constant complex materials based on transition and rare-earth metal oxides  

Microsoft Academic Search

It was found in elemental transition or rare earth metal (TM\\/RE) oxides that the electrical and material properties are much poor than those of the conventional gate dielectric materials such as silicon oxide or oxynitride. It was also found that the electrical and material properties of the high-dielectric constant (high-k) films can be improved or compromised by using complex structures

Hei Wong

2008-01-01

154

Potassium-39 nuclear magnetic resonance of potassium-ionophore complexes: Chemical shifts, relaxation times, and quadrupole coupling constants  

NASA Astrophysics Data System (ADS)

The complexation of K + by several ionophores was studied by 39K nuclear magnetic resonance. With the use of a high magnetic field (8.5 tesla) and a probe with sideways solenoid transmitter/receiver coil, very good signal-to-noise ratios could be obtained in a reasonable experiment time for concentrations as low as 20 m M and linewidths of the order of 250 Hz. Chemical shifts and spin-lattice relaxation times for 39K in the ionophore complexes are reported. The 39K chemical shifts show a large variation in different ligand environments. 13C spin-lattice relaxation times were measured for the potassium-ionophore complexes in order to derive correlation times. 39K quadrupole coupling constants in the different complexes could thus also be calculated. Despite the low sensitivity of 39K for the NMR experiment, the results indicate that 39K NMR studies of potassium-ligand interactions are feasible at millimolar concentrations.

Neurohr, Klaus J.; Drakenberg, Torbjorn; Forsén, Sture; Lilja, Hans

155

Spectroscopic and thermodynamic study of charge transfer complex formation between cloxacillin sodium and riboflavin in aqueous ethanol media of varying composition  

NASA Astrophysics Data System (ADS)

Cloxacillin sodium has been shown to form a charge transfer complex of 2:1 stoichiometry with riboflavin (Vitamin B 2) in aqueous ethanol medium. The enthalpy and entropy of formation of this complex have been determined by estimating the formation constant spectrophotometrically at five different temperatures in pure water medium. Pronounced effect of dielectric constant of the medium on the magnitude of K has been observed by determining K in aqueous ethanol mixtures of varying composition. This has been rationalized in terms of ionic dissociation of the cloxacillin sodium (D -Na +), hydrolysis of the anion D - and complexation of the free acid, DH with riboflavin.

Roy, Dalim Kumar; Saha, Avijit; Mukherjee, Asok K.

2006-03-01

156

STUDIES OF METAL COMPLEXES OF RADIOBIOLOGICAL INTEREST. I. THE ACIDITY CONSTANTS OF CROCONIC ACID  

Microsoft Academic Search

Potentiometric and spectrophotometric methods were used for the ; determination of the dissociation constants of croconic acid at 25 deg C. The ; potentiometric method gave only approximate values of pK⁠0.3-0.5 and p\\/K\\/; sub 2\\/ 1.4-1.6 (2 M (H, Na)Cl) and pK⁠approx equal 0.6 and pKâ ; approx equal 1.8 (0.1 M (H, Na) Cl). The ultraviolet spectra

Birger Carlqvist; David Dyrssen; Alfred Katz; K. Motzfeldt; Olof Theander

1962-01-01

157

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

158

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

SciTech Connect

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

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

1985-02-01

159

Kinetics, binding constant, and activation energy of the 48-kDa protein-rhodopsin complex by extra-metarhodopsin II  

SciTech Connect

We have found that the 48-kDa protein (or S-antigen 48k) of the rod photoreceptor enhances the light-induced formation of the photoproduct metarhodopsin II (MII) from prephosphorylated rhodopsin. The effect is analogous to the known enhancement of MII (extra-MII) that results from selective interaction of MII with G-protein. We have determined some parameters of the MII-48k interaction by measuring the extra-MII absorption change induced by the 48-kDa protein. The amplitude saturation yields a dissociation constant for the MII-48k complex on the order of 50 nM. At the technical limit of these measurements, 13.7 degrees C and 12 microM 48-kDa protein, we find a rate of 2.3 s-1 for formation of the 48k-MII complex. Extrapolation of these values to cellular conditions yields an occupation time of phosphorylated MII by 48k less than 200 ms. This is short compared to estimated rates of phosphorylation. The temperature dependence of the MII-48k formation rate is very high (Q10 for 5 degrees C/15 degrees C = 9-10). The related Arrhenius activation energy (165 kJ mol-1) is correspondingly high and indicates a considerable transient chemical change during the binding process.

Schleicher, A.; Kuehn, H.H.; Hofmann, K.P.

1989-02-21

160

Quantum-mechanical calculation of equilibrium geometry and force constants of complex polycyclic molecules  

SciTech Connect

Equilibrium molecular geometries have been calculated for cyclopropane, cyclobutane, cubane, and certain propellanes, using an algorithm for automatic construction of a system of independent optimization coordinates in the approximation of the semiempirical MINDO/3 method. In the vicinity of the energy minimum that was found, for all of these molecules, parameters of the potential function have been determined, assigned in a system of dependent natural coordinates. Calculations procedures are set forth, along with the principles used in selecting the significant potential constants with the presence of interrelationships among the internal geometric characteristics of the molecules.

Shatokhin, S.A.; Gribov, L.A.; Perelygin, I.S.

1986-09-01

161

Equilibrium constants of some protonated, nonprotonated and hydroxo complexes of uranium(VI) with xylenol orange  

Microsoft Academic Search

Summary The species, UO2H3L-, UO2H2L2-, UO2HL3-, UO2L4-, UO2(OH)L5- and UO2(OH)2L6- are found in the equilibria between uranyl ions and 3,3'-bis[N,N'-di(carboxymethyl)-aminomethyl]-o-cresolsulphonphthalein (H6L; xylenol orange; dcac) in aqueous solution. The equilibria have been studied by the potentiometric method at 25° and at an ionic strength of 0.1M (KNO3). New algebraic equations have been employed to evaluate the equilibrium constants.

Ram Nayan; Arun K. Dey

1976-01-01

162

A novel equation for predicting stability constants of aqueous metal complexes and actinide binding to protein  

NASA Astrophysics Data System (ADS)

Metal complexation with various inorganic or organic ligands in aqueous solutions directly controls the solubility, sorption, and toxicity of toxic metals including radionuclides in natural environments. The quantitative calculations of metal complexation thus have been routinely used in predicting the fate and impact of heavy metals in natural environments. The effectiveness of these calculations heavily depends on the completeness and quality of the thermodynamic databases on which the calculations are based. Unfortunately, the thermodynamic data for many metal complexes, especially those with radionuclides, are currently either unknown or poorly constrained. Therefore, there is a need for (1) developing a method to predict the unknown thermodynamic data based on a limited number of the existing measurements and (2) using this method to check the internal consistency of the thermodynamic databases that are used in the calculations. Such a method is discussed in this paper. .

Xu, Huifang; Wang, Yifeng

2000-07-01

163

Stability constants and molar absorption coefficients of mixed ligand complexes of tetravalent metals in systems containing 4-(2-pyridylazo)resorcinol  

Microsoft Academic Search

The compositions were determined, the stability constants were calculated, and the molar absorption constants of the mixed-ligand complexes were calculated for the Me(IV)-PAR-H\\/sub n\\/X systems Me = Ti, Zr, Hf, Th. It was shown that there is a linear relation between the logarithms of the stability constants of the mixed-ligand complexes (log ..beta..\\/sub ij\\/) and the pK..cap alpha.. value of

H. V. Kui; O. M. Petrukhin; Yu. A. Zolotov

1987-01-01

164

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

165

Focus Formation by a Murine Sarcoma-Leukemia Virus Complex  

PubMed Central

The transformation of cells in culture by a murine sarcoma-leukemia virus complex leads to the formation of identifiable foci. Titration patterns of focus counts vs. virus dilutions have been explained as being due to the interactions of three virions: leukemia, defective sarcoma, and competent hybrid. This interaction is analyzed quantitatively and equations are derived which permit determination of the composition of a sarcoma virus pseudotype as well as use of the technique for the assay of exogeneous leukemia virus. The analysis is based on the statistical distribution of virions in the culture cells and assumes that all virions have equal probability of infecting a cell and that transformation of any one cell will lead to focus formation. Limitations of the assumptions and expected measurement accuracy are discussed.

Hahn, G. M.; Decleve, A.; Lieberman, M.; Kaplan, H. S.

1970-01-01

166

Complex interactions between formative assessment, technology, and classroom practices  

NASA Astrophysics Data System (ADS)

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

2012-02-01

167

Model experiment for studying lane formation in binary complex plasmas  

NASA Astrophysics Data System (ADS)

We present the first experimental realisation on lane formation in binary complex plasmas under gravity conditions. The amount of penetrating particles can be controlled. The experiment can be operated with stable conditions continuously, which allows to study steady state. The driving force is independent of time and position and the background density is homogeneous and isotropic. This provides an ideal model system for comparison with numerical experiments and observations in colloidal suspensions. The experiment setup is based on PK-3 Plus laboratory operated on the International Space Station. Gravitation is compensated by thermophoretic force and penetrating particles are controlled via a toroidal vortex with poloidal flow. The evolution of lane formation along the penetration direction is illustrated by lane order parameter.

Du, C.-R.; Sütterlin, K. R.; Ivlev, A. V.; Thomas, H. M.; Morfill, G. E.

2012-08-01

168

Formation and characterization of thioglycolic acid-silver cluster complexes.  

PubMed

Gas phase reactivity observed in an ion trap was used to produce silver clusters protected with thioglycolic acid. Fragmentation pathways as well as optical properties were explored experimentally and theoretically. Sequential losses of SCH2 and CO2 in the ion trap lead to redox reactions with charge transfers between the metal part and the carboxylate and thiolate groups. This allows us to control the number of electrons in the metallic subunit and thus optical properties of the complexes. The presented formation process can be used as a prototype for tuning optical and chemical properties of ligated metal clusters by varying the number of confined electrons within the metallic subunit. PMID:23609144

Bellina, Bruno; Antoine, Rodolphe; Broyer, Michel; Gell, Lars; Sanader, Željka; Mitri?, Roland; Bona?i?-Koutecký, Vlasta; Dugourd, Philippe

2013-06-21

169

In vacuo formation of peptide-metal coordination complexes  

PubMed Central

Here we report on the reaction of rhenate anions (ReO3?) with multiply protonated peptide cations in a quadrupole linear ion trap mass spectrometer. These reactions effect the formation of an anion–cation complex that, upon collisional activation, dissociates along the peptide backbone rather than by displacement of the anion. Cleavage of the peptide backbone, with anion retention, leads us to conclude the anion–cationcomplexmust be tightly bound, most probably through coordination chemistry. We describe this chemistry and detail the possible application of such ion attachment reactions to the characterization of intact proteins.

McAlister, Graeme C.; Kiessel, Sharon E.B.; Coon, Joshua J.

2009-01-01

170

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

171

Characterization of Hydrogen Complex Formation in III-V Semiconductors  

SciTech Connect

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

Williams, Michael D.

2006-09-28

172

Simulation of Titan Haze Formation Using a Photochemical Flow Reactor. Optical Constants of the Simulated Haze  

NASA Astrophysics Data System (ADS)

A photochemical flow reactor has been used for the laboratory simulation of the formation of the volatiles and solids generated photochemically in Titan's stratosphere. These products were formed using mixing ratios of gases that approximated those on Titan (Clarke et al. 2000 Icarus in press). A detailed investigation of the real (n) and imaginary (k) parts of the refractive indices of the polymers formed in the 200 < lambda < 2,500 nm region are reported for comparison with laboratory data (Khare et al.1984, Icarus 60, 127) and observations from the Voyager spacecraft (McKay et al. 1989, Icarus 80, 23). The values of n and k were determined from a combination of transmittance and reflectance measurements in the UV and near IR. The method of calculation of Heavens (Heavans, 1965, Optical Properties of Thin Solid Films, Dover, 1965) was used to calculate n and k. n has a value of 1.5 - 1.6 throughout this wavelength region except for uncertainties in the 800-2,500 nm. The value of k increases throughout the wavelength region and has values consistent with Titan haze measurements (McKay et. al. 1989). The value of k increases from 0.02 to 0.1 in the 2,500- 12,500 nm region indicative of the absorption of functional groups including C-N, C=C and C-H. Some of the structural features of the polymer will be proposed from these and other spectral studies on this Titan haze analog. NASA funding from NAG5-9607 and the NY Center for Studies on the Origins of Life (NAG5-9607).

Tran, B. N.; Joseph, J. C.; Ferris, J. P.

2000-10-01

173

Translation initiation complex formation in the crenarchaeon Sulfolobus solfataricus  

PubMed Central

The function of initiation factors in and the sequence of events during translation initiation have been intensively studied in Bacteria and Eukaryotes, whereas in Archaea knowledge on these functions/processes is limited. By employing chemical probing, we show that translation initiation factor aIF1 of the model crenarchaeon Sulfolobus solfataricus binds to the same area on the ribosome as the bacterial and eukaryal orthologs. Fluorescence energy transfer assays (FRET) showed that aIF1, like its eukaryotic and bacterial orthologs, has a fidelity function in translation initiation complex formation, and that both aIF1 and aIF1A exert a synergistic effect in stimulating ribosomal association of the Met-tRNAiMet binding factor a/eIF2. However, as in Eukaryotes their effect on a/eIF2 binding appears to be indirect. Moreover, FRET was used to analyze for the first time the sequence of events toward translation initiation complex formation in an archaeal model system. These studies suggested that a/eIF2-GTP binds first to the ribosome and then recruits Met-tRNAiMet, which appears to comply with the operational mode of bacterial IF2, and deviates from the shuttle function of the eukaryotic counterpart eIF2. Thus, despite the resemblance of eIF2 and a/eIF2, recruitment of initiator tRNA to the ribosome is mechanistically different in Pro- and Eukaryotes.

Hasenohrl, David; Fabbretti, Attilio; Londei, Paola; Gualerzi, Claudio O.; Blasi, Udo

2009-01-01

174

A Study on the Effect of Stratified Mixture Formation on Combustion Characteristics in a Constant Volume Combustion Chamber  

NASA Astrophysics Data System (ADS)

It is well known that a lean burn engine caused by stratified mixture formation has many kinds of advantages to combustion characteristics, such as higher thermal efficiency and lower CO, NOx levels than conventional homogeneous mixture combustion. Although this combustion can achieve low fuel consumption, it produces much unburned hydrocarbon and soot because of inhomogeneity of the charge mixture in the combustion chamber. Therefore, it is necessary to investigate the effect of mixture formation on combustion characteristics in order to obtain the stable lean combustion. In this paper, fundamental studies for stratified combustion were carried out using a constant volume combustion chamber. The effect of mixture formation on the combustion characteristics in the chamber was examined experimentally. In addition, the effect of turbulence on stratified charge combustion process was observed by schlieren photography. From this study, as the swirl intensity increases, (Sv)max is rapidly enhanced and the period of combustion is shortened. We also find that the stratification degree can be quantified by using burning velocity and it was controlled by induced air pressure and turbulent intensity.

Lee, Kihyung; Lee, Changhee; Jeoung, Haeyoung

175

Thermodynamics of adduct formation of cobalt(II) tetraaza Schiff base complexes with organotin(IV)trichlorides  

NASA Astrophysics Data System (ADS)

UV-Vis. spectrophotometric study of the adduct formation of organotin(IV)trichlorides i.e. PhSnCl3 and MeSnCl3 as acceptors with Co(II) tetraaza complexes, such as [Co(ampen)] [N,N'-ethylenebis-(o-amino-?-phenylbenzylideneiminato)cobalt(II)], [Co(campen)] [N,N'-ethylenebis-(5-chloro-o-amino-?-phenylbenzylideneiminato)cobalt(II)], [Co(amaen)] [N,N'-ethylenebis-(o-amino-?-methylbenzylideneiminato)cobalt(II)], [Co(amppn)] [N,N'-propylene bis-(5-chloro-o-amino-?-phenylbenzylideneiminato)cobalt(II)] and [Co(camppn)] [N,N'-propylenebis-(5-chloro-o-amino-?-phenylbenzylideneiminato)cobalt(II)] as donors were studied spectrophotometrically under N2 atmosphere and in N,N'-dimethylformamide solvent. The formation constants and thermodynamic parameters were measured using spectrophotometric titration of adduct formation at various temperatures. The trend of the adduct formations of the cobalt(II) tetraaza complexes with a given organotintrichloride acceptor decreases as follow: [Co(amaen)] > [Co(amppn)] > [Co(ampen)] > [Co(camppn)] > [Co(campen)]. The trend of the formation constants for the studied organotintrichlorides with a given cobalt(II) tetraaza complexes is as follow: PhSnCl3 > MeSnCl3.

Asadi, Zahra; Asadi, Mozaffar; Setoodehkhah, Moslem

2013-08-01

176

Complex formation of yeast Rev1 with DNA polymerase eta.  

PubMed

In Saccharomyces cerevisiae, Rev1 functions in translesion DNA synthesis (TLS) together with polymerase zeta (Pol zeta), comprised of the Rev3 catalytic and Rev7 accessory subunits. Rev1 plays an indispensable structural role in promoting Pol zeta function, and deletion of the Rev1-C terminal region that is involved in physical interactions with Rev3 inactivates Pol zeta function in TLS. In humans, however, Rev1 has been shown to physically interact with the Y-family polymerases Pol eta, Pol iota, and Pol kappa, and the Rev1 C terminus mediates these interactions. Since all the available genetic and biochemical evidence in yeast support the requirement of Rev1 as a structural element for Pol zeta and not for Pol eta, these observations have raised the possibility that in its structural role, Rev1 has diverged between yeast and humans. Here we show that although in yeast a stable Rev1-Pol eta complex can be formed, this complex formation involves the polymerase-associated domain of Rev1 and not the Rev1 C terminus as in humans. We also found that the DNA synthesis activity of Rev1 is enhanced in this complex. We discuss the implications of these and other observations for the possible divergence of Rev1's structural role between yeast and humans. PMID:17875922

Acharya, Narottam; Haracska, Lajos; Prakash, Satya; Prakash, Louise

2007-12-01

177

Spectrophotometric, FTIR and theoretical studies of the charge-transfer complexes between isoniazid (pyridine-4-carboxylic acid hydrazide) and the acceptors (p-chloranil, chloranilic acid and tetracyanoethylene) in acetonitrile, their association constants, thermodynamic properties and other related properties.  

PubMed

Spectrophotometric, FTIR and theoretical studies of the charge-transfer complexes between Isoniazid (pyridine-4-carboxylic acid hydrazide) and the acceptors (p-chloranil, chloranilic acid and tetracyanoethylene) in acetonitrile, their association constants, thermodynamic properties and other related properties were studied. Isoniazid (INH), a widely used anti tubercular agent was found to form beautifully colored charge-transfer complexes with p-chloranil, chloranilic acid and tetracyanoethylene in acetonitrile. The absorption maxima of the complexes were 484, 519 and 479 nm, respectively (isoniazid had no absorption, but the acceptors had absorption in these regions). The composition of the complexes were determined to be 1:1 from Job's method of continuous variations depending on the time period of experiments as the stability of some of the complexes (p-chloranil and tetracyanoethylene complexes) was time dependent. Solid complexes formed between isoniazid and the acceptors were isolated but p-chloranil was found to form two different complexes. FTIR spectra of the complexes and the acceptors were measured. FTIR spectra of the complexes showed considerable shift in absorption peaks, changes in intensities of the peaks and formation of the new band (probably due to hydrogen bonding) on complexation. The thermodynamic association constants and other thermodynamic parameters of the complexes were determined spectrophotometrically taking D and A in varying ratios (2:8-8:2) and also in equimolar ratios. The complex formation was found to be spontaneous and associated with negative changes of ?G(0), ?H(0) and ?S(0). The energies h?(CT) of the charge-transfer complexes were compared with the theoretical values of h?(CT) of the complexes obtained from HOMO and LUMO of the donor and the acceptors. Density function theory utilizing different basis sets was used for calculation. h?(CT) (experimental) values of the transition energies of the complexes in acetonitrile differed from h?(CT) (theoretical) values in the gaseous state. I(D)(V) value of isoniazid was calculated. Charge-transfer complexes were assumed to be partial electrovalent compounds with organic dative ions D(+) and A(-) (in the excited state) and attempts had been made to correlate the energy changes for the formation of the complexes with the energy changes for the formation of electrovalent compounds between M(+) and X(-) ions. PMID:22580135

Bagchi Chattaraj, Seema; Sharma, Kakali; Chakrabortty, Ashutosh; Lahiri, Sujit Chandra

2012-09-01

178

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

PubMed

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

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

2014-07-16

179

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

SciTech Connect

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

Jiang, Xikai [ORNL] [ORNL; Huang, Jingsong [ORNL] [ORNL; Zhao, Hui [University of Nevada, Las Vegas] [University of Nevada, Las Vegas; Sumpter, Bobby G [ORNL] [ORNL; Qiao, Rui [Clemson University] [Clemson University

2014-01-01

180

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

181

Cadmium(II) Complex Formation with Cysteine and Penicillamine  

PubMed Central

The complex formation between cadmium(II) and the ligands cysteine (H2Cys) or penicillamine (H2Pen = 3, 3?-dimethylcysteine) in aqueous solutions, containing CCd(II) ? 0.1 mol dm-3 and CH2L = 0.2 – 2 mol dm-3, was studied at pH = 7.5 and 11.0 by means of 113Cd-NMR and Cd K- and L3-edge X-ray absorption spectroscopy. For all cadmium(II)-cysteine mole ratios the mean Cd-S and Cd-(N/O) bond distances were found in the ranges 2.52 – 2.54 Å and 2.27 – 2.35 Å, respectively. The corresponding cadmium(II)-penicillamine complexes showed slightly shorter Cd-S bonds, 2.50 – 2.53 Å, but with the Cd-(N/O) bond distances in a similar wide range, 2.28 – 2.33 Å. For the mole ratio CH2L / CCd(II) = 2, the 113Cd chemical shifts, in the range 509 – 527 ppm at both pH values, indicated complexes with distorted tetrahedral CdS2N(N/O) coordination geometry. With a large excess of cysteine (mole ratios CH2Cys / CCd(II) ? 10) complexes with CdS4 coordination geometry dominate, consistent with the 113Cd NMR chemical shifts, ? ? 680 ppm at pH 7.5 and 636 - 658 ppm at pH 11.0, and their mean Cd-S distances of 2.53 ± 0.02 Å. At pH 7.5, the complexes are almost exclusively sulfur-coordinated as [Cd(S-cysteinate)4]n-, while at higher pH the deprotonation of the amine groups promotes chelate formation, and at pH 11.0 a minor amount of the [Cd(Cys)3]4- complex with CdS3N coordination is formed. For the corresponding penicillamine solutions with mole ratios CH2Pen / CCd(II) ? 10, the 113Cd-NMR chemical shifts, ? ? 600 ppm at pH 7.5 and 578 ppm at pH 11.0, together with the average bond distances Cd-S 2.53 ± 0.02 Å and Cd-O 2.30 – 2.33 Å, indicate that [Cd(penicillaminate)3]n- complexes with chelating CdS3(N/O) coordination dominate already at pH 7.5, and become mixed with CdS2N(N/O) complexes at pH 11.0. The present study reveals differences between cysteine and penicillamine as ligands to the cadmium(II) ion that can explain why cysteine-rich metallothionines are capable of capturing cadmium(II) ions, while penicillamine, clinically useful for treating the toxic effects of mercury(II) and lead(II) exposure, is not efficient against cadmium(II) poisoning.

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

2009-01-01

182

Complex dielectric constant of a nematic liquid crystal containing two types of ions: limit of validity of the superposition principle.  

PubMed

We investigate the influence of two groups of ions on the complex dielectric constant of a nematic liquid crystal limited by perfectly blocking electrodes. The analysis is performed by solving the equations of continuity for the two groups of cations and anions, and the equation of Poisson relating the actual electric field to the net density of charge. We consider a typical experiment of impedance spectroscopy, and evaluate the equivalent resistance and reactance of the cell, in the series representation, versus the frequency of the applied voltage to the cell. We show that the presence of two groups of ions gives rise to two plateaux in the spectrum of the resistance, similar to those related to the ambipolar and free diffusion in the case where there is only one type of ions, but for which the cations and anions have different diffusion coefficients. The correspondence between the usual ambipolar and free diffusion coefficients and those related to the presence of two groups of ions is discussed. The spectra of the real and imaginary parts of the complex dielectric constant are obtained, and their dependence on the bulk densities of the two types of ions is investigated. The nonvalidity of the superposition principle is discussed. PMID:19827753

Alexe-Ionescu, A L; Barbero, G; Lelidis, I

2009-11-01

183

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

184

Formation of bubbles, blobs, and surface cusps in complex plasmas.  

PubMed

Investigations of the dynamical evolution of a complex plasma, in which a vertical temperature gradient compensates gravity, were carried out. At low power the formation of microparticle bubbles, blobs, and spraying cusps was observed. This activity can be turned on and off by changing control parameters, such as the rf power and the gas pressure. Several observational effects indicate the presence of surface tension, even at small "nanoscales" of a few 100's of particles. By tracing the individual microparticle motion the detailed (atomistic) dynamics can be studied as well as the pressure dependence of the forces. A possible mechanism that could drive the observed phenomena is analogous to the Rayleigh-Taylor instability. PMID:19659088

Schwabe, M; Rubin-Zuzic, M; Zhdanov, S; Ivlev, A V; Thomas, H M; Morfill, G E

2009-06-26

185

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

186

Visualization of Gas-to-Liquid (GTL) Fuel Liquid Length and Soot Formation in the Constant Volume Combustion Chamber  

NASA Astrophysics Data System (ADS)

In this research, GTL spray combustion was visualized in an optically accessible quiescent constant-volume combustion chamber. The results were compared with the spray combustion of diesel fuel. Fast-speed photography with direct laser sheet illumination was used to determine the fuel liquid-phase length, and shadowgraph photography was used to determine the distribution of the sooting area in the fuel jet. The results showed that the fuel liquid-phase length of GTL fuel jets stabilized at about 20-22mm from the injector orifice and mainly depended on the ambient gas temperature and fuel volatility. GTL had a slightly shorter liquid length than that of the diesel fuel. This tendency was also maintained when multiple injection strategy was applied. The penetration of the tip of the liquid-phase fuel during pilot injection was a little shorter than the penetration during main injection. The liquid lengths during single and main injections were identical. In the case of soot formation, the results showed that soot formation was mainly affected by air-fuel mixing, and had very weak dependence on fuel volatility.

Azimov, Ulugbek; Kim, Ki-Seong

187

An effective method for refining predicted protein complexes based on protein activity and the mechanism of protein complex formation  

PubMed Central

Background Identifying protein complexes from protein-protein interaction network is fundamental for understanding the mechanism of cellular component and protein function. At present, many methods to identify protein complexes are mainly based on the topological characteristics or the functional similarity features, neglecting the fact that proteins must be in their active forms to interact with others and the formation of protein complex is following a just-in-time mechanism. Results This paper firstly presents a protein complex formation model based on the just-in-time mechanism. By investigating known protein complexes combined with gene expression data, we find that most protein complexes can be formed in continuous time points, and the average overlapping rate of the known complexes during the formation is large. A method is proposed to refine the protein complexes predicted by clustering algorithms based on the protein complex formation model and the properties of known protein complexes. After refinement, the number of known complexes that are matched by predicted complexes, Sensitivity, Specificity, and f-measure are significantly improved, when compared with those of the original predicted complexes. Conclusion The refining method can discard the spurious proteins by protein activity and generate new complexes by just-in-time assemble mechanism, which can enhance the ability to predict complex.

2013-01-01

188

Dual specificity and the formation of stable autoimmune complexes.  

PubMed

Since dual specificity at the antibody active-site level involves new principles relative to monospecific antigen-antibody interactions and may be a general property of autoantibodies, it was important to further characterize such antibodies. Four lupus derived autoantibodies were studied to understand parameters and mechanisms involved in the participation of dual-specific antibody molecules in the formation of highly stable immune complexes. Because the dual-specific binding properties of selected lupus-related murine autoantibodies had been previously described using a solid-phase polystyrene-based ELISA, a conformational sensitive membrane based assay (CSI) was used on a comparative basis to further characterize NZB/NZW F1 murine monoclonal anti-DNA autoantibodies BV 04-01 (anti-ssDNA), BV 16-19 (anti-ssDNA), BV 17-45 (anti-dsDNA), and BV 16-13 (anti-dsDNA). All four monoclonal autoantibodies exhibited anti-IgG binding in the solid-phase ELISA. However in the CSI assay, only anti-dsDNA monoclonal autoantibodies BV 17-45 and BV 16-13 demonstrated anti-IgG binding, while anti-ssDNA autoantibodies BV 04-01 and BV 16-19 did not. Upon subjection to time-dependent thermal denaturation, with and without thiol reduction at 100 degrees C in the CSI, the self-binding activities of BV 17-45 and BV 16-13 were abrogated demonstrating that the recognized IgG autoepitope(s) possessed conformational or discontinuous three-dimensional properties. The immunological implications of dual specificity are discussed on a structure-function basis and its correlation with formation of pathogenic immune complexes. PMID:9587872

Workman, C J; Pfund, W P; Voss, E W

1997-01-01

189

Ordered complexes of cytochrome c fragments. Kinetics of formation of the reduced (ferrous) forms.  

PubMed

The kinetics of formation of noncovalently bound ferrous complexes derived from fragments of horse heart cytochrome c have been investigated. When the reactions are initiated by combining ferrous heme fragments with an appropriate apofragment, in the presence of 50 mM imidazole, second order rate processes are observed with rate constants essentially the same as those reported with ferric heme fragments (Parr, G. R., and Taniuchi, H. (1979) J. Biol. Chem. 254, 4836-4842). An additional, probably consecutive, kinetic process is also demonstrated. If imidazole is not present in the reaction buffer, the kinetic profiles are dramatically altered. While this is partially due to aggregation (dimerization) of the ferrous heme fragments, it can nevertheless be demonstrated that the complementation reactions with apofragments are much faster than those observed with the corresponding ferric heme fragments (in the absence of imidazole). These results reflect the effect of the oxidation state of the heme iron on the folding mechanism and, thus, the manifold nature of protein folding pathways. The rate of reduction of productive ferric complexes by sodium ascorbate was investigated and biphasic reactions were found in all cases. The data indicate an equilibrium between two forms of the ferric complexes. The results of an experiment in which the complementation of ferric (1-25)H and (23-104) was carried out in the presence of sodium ascorbate indicate that the intermediate complex (Parr, G. R., and Taniuchi, H. (1980) J. Biol. Chem. 255, 8914-8918) is not reducible by ascorbate. Thus, the increase in oxidation-reduction potential occurring on formation of the productive complex from the unbound heme fragment occurs at a late stage of the overall reaction, possibly coinciding with ligation of methionine 80 to the heme iron. PMID:6256341

Parr, G R; Taniuchi, H

1981-01-10

190

A critical review on the stability constants of the fluoride complexes of actinides in aqueous solution and their correlation with fundamental properties of the ions  

Microsoft Academic Search

Literature data on the stability constants of the fluoride complexes of the actinides in different oxidation states have been\\u000a compiled. In order to have a reasonable inter-comparison, the stability constant (?1) values obtained in diverse ionic strength media are converted to so called thermodynamic stability constants, ?\\u000a 1\\u000a 0\\u000a using the DAVIES equation (a modification of Debye-Huckel equation). A correlation

N. K. Chaudhuri; R. M. Sawant; D. D. Sood

1999-01-01

191

Modelling formation of complex topography by the seagrass Posidonia oceanica  

NASA Astrophysics Data System (ADS)

Posidonia oceanica is a slow growing seagrass species that extends via growing rhizomes that grow only centimetres both horizontally and vertically each year. Posidonia oceanica forms topographically complex biogenic reefs of dead rhizome and sediments that are up to 4 m in height that are called "matte". This study investigates the role of slow horizontal and vertical growth of rhizomes in the formation of topographic complexity in P. oceanica matte using agent-based modelling. The simulated infilling of landscapes by P. oceanica was run over 600 iterations (years) for 10 random starts of 150 agents each. Initial infilling rates were very slow and P. oceanica had limited cover after a century of growth. Growth accelerated after 100 years but plateaued after 400 years such that after 600 years only two-thirds of the landscape was occupied by P. oceanica. The pattern of spread of agents was initially random in direction but after larger patches were formed spread was radial from these patches. The seagrass landscape was initially highly fragmented with many small separate patches made up of a few agents each, with a Landscape Division index close to 1. Between 300 and 600 years Landscape Division declined sharply to 0.42, indicating patches had coalesced into larger more continuous meadows forming a less fragmented landscape. Perimeter to area ratio of seagrass patches declined exponentially from >1 to approximately 0.2 over 600 years of simulation. The matte developed from growth of patches and its greatest height occurred in more continuously occupied cells of the grid. The topography of the reef that occupied two-thirds of the landscape after six centuries of growth could be described as a pattern of channels between reef plateaus elevated 1-2 m above channels. These results demonstrate that development in P. oceanica meadows of three-dimensional structure, in the formation of biogenic reefs, can be explained by, and is an emergent property of, slow horizontal and vertical rhizome growth rates combined with the time it takes for the accumulation of rhizomes in any region of the landscape. As such, the model provides a parsimonious explanation for the development of complex matte topography.

Kendrick, Gary A.; Marbà, Núria; Duarte, Carlos M.

2005-12-01

192

Adsorption of cadmium on alumina and silica: analysis of the values of stability constants of surface complexes calculated for different parameters of triple layer model  

Microsoft Academic Search

The calculated values of stability constants of surface complexes formed by heavy metal ions depend on the assumed model of the electric double layer and its parameters. Using various parameters of the triple-layer model (TLM) (which fit the titration data almost equally well), one obtains stability constants in a range as wide as two orders of magnitude. On the other

Marek Kosmulski

1996-01-01

193

Equilibrium dialysis-ligand exchange: adaptation of the method for determination of conditional stability constants of radionuclide-fulvic acid complexes  

Microsoft Academic Search

The equilibrium dialysis-ligand exchange technique (EDLE) has been adapted to measure conditional stability constants for the complexation of metal ions with fulvic acid. Since fulvic acid permeates across the membrane during the experiment, the quantities involved have to be determined analytically and taken into account when calculating the conditional stability constants. It is shown here that the larger diffusion rates

M. A. Glaus; W. Hummel; L. R. Van Loon

1995-01-01

194

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

195

Isotachophoretic determination of stability constants of Ho and Y complexes with diethylenetriaminepentaacetic acid and 1,4,7,10-tetraazadodecane-N,N?,N?,N?-tetraacetic acid  

Microsoft Academic Search

The method of capillary isotachophoresis with conductivity detection was applied for the determination of the physico-chemical characteristics (conditional stability constants log ??) of holmium and yttrium complexes with DTPA (diethylenetriaminepentaacetic acid) and DOTA (1,4,7,10-tetraazadodecane-N,N?,N?,N?-tetraacetic acid). The log ?? determination is based on the linear relation between the stability constants of lanthanide–DTPA (lanthanide–DOTA) complexes and the reduction of the zone of

Michaela Koudelková; Hana Vinšová; V?ra Jedináková-K???žová

2003-01-01

196

Silver(I) Complex formation with Cysteine, Penicillamine and Glutathione  

PubMed Central

The complex formation between silver(I) and cysteine (H2Cys), penicillamine (H2Pen) or glutathione (H3Glu) in alkaline aqueous solution was examined using extended X-ray absorption fine structure (EXAFS) and 109Ag NMR spectroscopic techniques. The complexes formed in 0.1 mol·dm?3 Ag(I) solutions with cysteine and penicillamine were investigated for ligand/Ag(I) (L/Ag) mole ratios increasing from 2.0 to 10.0. For the series of cysteine solutions (pH 10 - 11) a mean Ag-S bond distance 2.45 ± 0.02 Å consistently emerged, while for penicillamine (pH 9) the average Ag-S bond distance gradually increased from 2.40 to 2.44 ± 0.02 Å. EXAFS and 109Ag NMR spectra of a concentrated Ag(I)-cysteine solution (CAg(I) = 0.8 mol·dm?3, L/Ag = 2.2) showed the mean Ag-S bond distance 2.47 ± 0.02 Å and ?(109Ag) = 1103 ppm, consistent with prevailing, partially oligomeric AgS3 coordinated species, while for penicillamine (CAg(I) = 0.5 mol·dm?3, L/Ag = 2.0) the mean Ag-S bond distance 2.40 ± 0.02 Å and ?(109Ag) = 922 ppm indicate that mononuclear AgS2 coordinated complexes dominate. For Ag(I)-glutathione solutions (CAg(I) = 0.01 mol·dm?3, pH ~ 11), mononuclear AgS2 coordinated species with the mean Ag-S bond distance 2.36 ± 0.02 Å dominate for L/Ag mole ratios from 2.0 to 10.0. The crystal structure of the silver(I)-cysteine compound (NH4)Ag2(HCys)(Cys)·H2O (1) precipitating at pH ~ 10 was solved and showed a layer structure with both AgS3 and AgS3N coordination to the cysteinate ligands. A redetermination of the crystal structure of Ag(HPen)·H2O (2) confirmed the proposed digonal AgS2 coordination environment to bridging thiolate sulfur atoms in polymeric intertwining chains forming a double helix. A survey of Ag-S bond distances for crystalline Ag(I) complexes with S-donor ligands in different AgS2, AgS2(O/N) and AgS3 coordination environments was used, together with a survey of 109Ag NMR chemical shifts, to assist assignments of the Ag(I) coordination in solution.

Leung, Bonnie O.; Jalilehvand, Farideh; Mah, Vicky; Parvez, Masood; Wu, Qiao

2013-01-01

197

Polyelectrolyte complexes of chitosan: formation, properties and applications  

Microsoft Academic Search

The results of studies of polyelectrolyte complexes of chitosan are summarised and described systematically. Chitosan complexes with biopolyelectrolytes, with modified natural polyelectrolytes and with synthetic polyanions are considered. Medical and biotechnological applications of chitosan complexes are discussed.

M. A. Krayukhina; N. A. Samoilova; I. A. Yamskov

2008-01-01

198

Solvent effect on the complex formation of a crown ether derivative with sodium and potassium ions. Thermodynamic background of selectivity  

NASA Astrophysics Data System (ADS)

The complexation properties of dimethyl-pyridino-18-crown-6 ether (M2P18C6) with Na+ and K+ in different primary alcohols including methanol (MeOH), ethanol (EtOH) and n-propanol (n-PrOH) were investigated by UV-vis spectroscopy. Stability constants and thermodynamic parameters have been determined applying the van't Hoff theory. In the cases of both Na+ and K+ the stability constants increase with decreasing permittivity of the solvent used. M2P18C6 always exhibits better affinity to K+ in each alcoholic solution compared to Na+. Thermodynamic studies suggest that in both cases there is a correlation between the permittivity of the solvent and the enthalpy and entropy change of complex formation.

Li, Yin; Huszthy, Péter; Móczár, Ildikó; Szemenyei, Balázs; Kunsági-Máté, Sándor

2013-01-01

199

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

200

Charge transfer complex formation between p-chloranil and 1, n-di(9-anthryl)alkanes  

NASA Astrophysics Data System (ADS)

Dimer model compounds of polyvinylanthracenes (1, n-di(9-anthryl)alkanes, when n = 1-5) were synthesized to model the effects of distance and orientation between anthracene groups in polymeric systems. Charge transfer (CT) complexes of anthracene, 9-methylanthracene and 1, n-di(9-anthryl)alkanes with p-chloranil ( p-CHL) have been investigated spectrophotometrically in dichloromethane. The colored products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptor. The formation constants of the CT complexes were determined by the Benesi-Hildebrand equation. The thermodynamic parameters were calculated by Van't Hoff equation. Stochiometries of the complexes formed between donors and acceptor were defined by the Job's method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands.

Arslan, Mustafa; Masnovi, John

2006-06-01

201

Microcalorimetric studies on the complex formation between cellobiohydrolase I (CBH I) from Trichoderma reesei and the (R)- and (S)-enantiomers of the ?-receptor blocking agent alprenolol  

Microsoft Academic Search

The thermodynamic quantities for the complex formation between the enantiomers of the ?-blocking drug alprenolol and cellobiohydrolase I (CBH I), that earlier has been used as a chiral selector for aminoalcohols, revealed positive ?H0 — values in all cases implying an entropy driven process. Association constants (Ka) for cellulase and the (R)- and (S)-enantiomers of alprenolol were determined by isothermal

Mikael Hedeland; Hongbin Henriksson; Per Bäckman; Roland Isaksson; Göran Pettersson

2000-01-01

202

On the complex formation equilibria between iron (III) and sulfate ions.  

PubMed

The equilibria have been investigated at 25 degrees C in 3 M NaClO4 using potentiometry, glass and redox Fe3+/Fe2+ half-cells, and UV optical absorptiometry. The concentration of the reagents was chosen in the intervals: 10(-4) < or = [Fe(III)] < or = 5.10(-3) M, 0.01 < or = [SO4(2-)]tot < or = 0.65 M. The value of [H+] was kept at 0.1 M or more to reduce the hydrolysis of the Fe3+ ion to less than 1%. Auxiliary constants, corresponding to the formation of Fe(II)-sulfate complexes and to the association of H+ with SO4(2-) ions, were taken from previous determinations. The experimental data could be explained with the equilibria [formula: see text] Equilibrium constants at infinite dilution, log beta 101 degrees = 3.82 +/- 0.17, log beta 102 degrees = 5.75 +/- 0.17 and log beta 111 degrees = 3.68 +/- 0.35, have been evaluated by applying the specific interaction theory. PMID:12185748

Ciavatta, Liberato; De Tommaso, Gaetano; Iuliano, Mauro

2002-01-01

203

Silver(I) complex formation with cysteine, penicillamine, and glutathione.  

PubMed

The complex formation between silver(I) and cysteine (H2Cys), penicillamine (H2Pen), and glutathione (H3Glu) in alkaline aqueous solution was examined using extended X-ray absorption fine structure (EXAFS) and (109)Ag NMR spectroscopic techniques. The complexes formed in 0.1 mol dm(-3) Ag(I) solutions with cysteine and penicillamine were investigated for ligand/Ag(I) (L/Ag) mole ratios increasing from 2.0 to 10.0. For the series of cysteine solutions (pH 10-11) a mean Ag-S bond distance of 2.45 ± 0.02 Å consistently emerged, while for penicillamine (pH 9) the average Ag-S bond distance gradually increased from 2.40 to 2.44 ± 0.02 Å. EXAFS and (109)Ag NMR spectra of a concentrated Ag(I)-cysteine solution (C(Ag(I)) = 0.8 mol dm(-3), L/Ag = 2.2) showed a mean Ag-S bond distance of 2.47 ± 0.02 Å and ?((109)Ag) 1103 ppm, consistent with prevailing, partially oligomeric AgS3 coordinated species, while for penicillamine (C(Ag(I)) = 0.5 mol dm(-3), L/Ag = 2.0) the mean Ag-S bond distance of 2.40 ± 0.02 Å and ?((109)Ag) 922 ppm indicate that mononuclear AgS2 coordinated complexes dominate. For Ag(I)-glutathione solutions (C(Ag(I)) = 0.01 mol dm(-3), pH ?11), mononuclear AgS2 coordinated species with a mean Ag-S bond distance of 2.36 ± 0.02 Å dominate for L/Ag mole ratios from 2.0 to 10.0. The crystal structure of the silver(I)-cysteine compound (NH4)Ag2(HCys)(Cys)·H2O (1) precipitating at pH ?10 was solved and showed a layer structure with both AgS3 and AgS3N coordination to the cysteinate ligands. A redetermination of the crystal structure of Ag(HPen)·H2O (2) confirmed the proposed digonal AgS2 coordination environment to bridging thiolate sulfur atoms in polymeric intertwining chains forming a double helix. A survey of Ag-S bond distances for crystalline Ag(I) complexes with S-donor ligands in different AgS2, AgS2(O/N), and AgS3 coordination environments was used, together with a survey of (109)Ag NMR chemical shifts, to assist assignments of the Ag(I) coordination in solution. PMID:23556419

Leung, Bonnie O; Jalilehvand, Farideh; Mah, Vicky; Parvez, Masood; Wu, Qiao

2013-04-15

204

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

205

Density functional theory study on aqueous aluminum-fluoride complexes: exploration of the intrinsic relationship between water-exchange rate constants and structural parameters for monomer aluminum complexes.  

PubMed

Density functional theory (DFT) calculation is carried out to investigate the structures, (19)F and (27)Al NMR chemical shifts of aqueous Al-F complexes and their water-exchange reactions. The following investigations are performed in this paper: (1) the microscopic properties of typical aqueous Al-F complexes are obtained at the level of B3LYP/6-311+G**. Al-OH(2) bond lengths increase with F(-) replacing inner-sphere H(2)O progressively, indicating labilizing effect of F(-) ligand. The Al-OH(2) distance trans to fluoride is longer than other Al-OH(2) distance, accounting for trans effect of F(-) ligand. (19)F and (27)Al NMR chemical shifts are calculated using GIAO method at the HF/6-311+G** level relative to F(H(2)O)(6)(-) and Al(H(2)O)(6)(3+) references, respectively. The results are consistent with available experimental values; (2) the dissociative (D) activated mechanism is observed by modeling water-exchange reaction for [Al(H(2)O)(6-i)F(i)]((3-i)+) (i = 1-4). The activation energy barriers are found to decrease with increasing F(-) substitution, which is in line with experimental rate constants (k(ex)). The log k(ex) of AlF(3)(H(2)O)(3)(0) and AlF(4)(H(2)O)(2)(-) are predicted by three ways. The results indicate that the correlation between log k(ex) and Al-O bond length as well as the given transmission coefficient allows experimental rate constants to be predicted, whereas the correlation between log k(ex) and activation free energy is poor; (3) the environmental significance of this work is elucidated by the extension toward three fields, that is, polyaluminum system, monomer Al-organic system and other metal ions system with high charge-to-radius ratio. PMID:21133367

Jin, Xiaoyan; Qian, Zhaosheng; Lu, Bangmei; Yang, Wenjing; Bi, Shuping

2011-01-01

206

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

207

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

SciTech Connect

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

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

1993-12-31

208

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

209

A thermodynamic study of complexation of 18-crown-6 with Zn 2+ , Tl + , Hg 2+ and cations in acetonitrile-dimethylformamide binary media and study the effect of anion on the stability constant of (18C6Na + ) complex in methanol solutions  

Microsoft Academic Search

The equilibrium constants and thermodynamic parameters for complex formation of 18-crown-6(18C6) with Zn2+, Tl+, Hg2+ and \\u000a $$ {\\\\text{UO}}^{{{\\\\text{2 + }}}}_{{\\\\text{2}}} $$ cations have been determined by conductivity measurements in acetonitrile(AN)-dimethylformamide(DMF) binary solutions. 18-crown-6\\u000a forms 1:1 complexes [M:L] with Zn2+, Hg2+ and $$ {\\\\text{UO}}^{{{\\\\text{2 + }}}}_{{\\\\text{2}}} $$ cations, but in the case of Tl+ cation, a 1:2 [M:L2] complex is formed

G. H. Rounaghi; M. H. Arbab Zavvar; K. Badiee; F. Boosaidi; M. S. Kazemi

2007-01-01

210

Estimation of stability constants for metal–ligand complexes containing neutral nitrogen donor atoms with applications to natural organic matter  

NASA Astrophysics Data System (ADS)

Linear free energy relationships (LFERs) were developed for estimating 1:1 metal–ligand stability constants (log KML) for small organic molecules containing neutral nitrogen donor atoms. A data set of 44 monodentate and 112 bidentate ligands for six metal ions: Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ was employed to parameterize the LFER equations. Monodentate and bidentate log KML values were adequately described using Irving–Rossotti LFERs previously developed for ligands containing negatively-charged oxygen functional groups. Modifications to the LFER equations were necessary to account for steric hindrances to metal complexation by primary, secondary, and tertiary amines. The resulting LFER equations can be used to estimate log KML values for monodentate and bidentate ligands with neutral nitrogen donor groups where such values do not currently exist in the literature. Comparison of these results to our previous work with negatively-charged oxygen donor atoms reveals that neutral nitrogen functional groups are weaker than their oxygen counterparts for metal ions classified as "hard" on the basis of Hard–Soft Acid–Base (HSAB) theory. For "soft" metals, the opposite is true. These LFERs can be used to incorporate nitrogen functional groups in models for metal ion binding to natural organic matter (NOM).

Atalay, Yasemin B.; Di Toro, Dominic M.; Carbonaro, Richard F.

2013-12-01

211

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

PubMed

The reaction of Re(NC6H4R)Cl3(PPh3)2 (R = H, 4-Cl, 4-OMe) with 1,2-bis(diphenylphosphino)ethane (dppe) is investigated in refluxing ethanol. The reaction produces two major products, Re(NC6H4R)Cl(dppe)(2)2+ (R = H, 1-H; R = Cl, 1-Cl; R = OMe, 1-OMe) and the rhenium(III) species Re(NHC6H4R)Cl(dppe)2+ (R = H, 2-H; R = Cl, 2-Cl). Complexes 1-H (orthorhombic, Pcab, a = 22.3075(10) A, b = 23.1271(10) A, c = 23.3584(10) A, Z = 8), 1-Cl (triclinic, P1, a = 11.9403(6) A, b = 14.6673(8) A, c = 17.2664(9) A, alpha = 92.019(1) degrees, beta = 97.379(1) degrees, gamma = 90.134(1) degrees, Z = 2), and 1-OMe (triclinic, P1, a = 11.340(3) A, b = 13.134(4) A, c = 13.3796(25) A, alpha = 102.370(20) degrees, beta = 107.688(17) degrees, gamma = 114.408(20) degrees, Z = 1) are crystallographically characterized and show an average Re-N bond length (1.71 A) typical of imidorhenium(V) complexes. There is a small systematic decrease in the Re-N bond length on going from Cl to H to OMe. Complex 2-Cl (monoclinic, Cc, a = 24.2381(11) A, b = 13.4504(6) A, c = 17.466(8) A, beta = 97.06900(0) degrees, Z = 4) is also crystallographically characterized and shows a Re-N bond length (1.98 A) suggestive of amidorhenium(III). The rhenium(III) complexes exhibit unusual proton NMR spectra where all of the resonances are found at expected locations except those for the amido protons, which are at 37.8 ppm for 2-Cl and 37.3 ppm for 1-H. The phosphorus resonances are also unremarkable, but the 13C spectrum of 2-Cl shows a significantly shifted resonance at 177.3 ppm, which is assigned to the ipso carbon of the phenylamido ligand. The extraordinary shifts of the amido hydrogen and ipso carbon are attributed to second-order magnetism that is strongly focused along the axially compressed amido axis. The reducing equivalents for the formation of the Re(III) product are provided by oxidation of the ethanol solvent, which produces acetal and acetaldehyde in amounts as much as 30 equiv based on the quantity of rhenium starting material. Equal amounts of hydrogen gas are produced, suggesting that the catalyzed reaction is the dehydrogenation of ethanol to produce acetaldehyde and hydrogen gas. Metal hydrides are detected in the reaction solution, suggesting a mechanism involving beta-elimination of ethanol at the metal center. Formation of the amidorhenium(III) product possibly arises from migration of a metal hydride in the imidorhenium(V) complex. PMID:11151507

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

2000-12-25

212

Investigation of the solid-state conductivity and the potentiometric stability constant relationships of new amino acid-Schiff bases and their complexes  

Microsoft Academic Search

CuII, NiII and CoII complexes of new tridentate amino acid-Schiff bases derived from furfural and DL-alanine, DL-valine and DL-phenylalanine were prepared and characterized by analytical, spectroscopic, (i.r., u.v.–vis., 1H-n.m.r and 13C-n.m.r) techniques, molar conductivity, magnetic and thermal measurements. Protonation constants of the Schiff bases and stability constants of the complexes have been determined potentiometrically in water. Solid-state conductivities of the

Nur?en Sarì; Perihan Gürkan

2003-01-01

213

Hierarchical star formation in M 51: star\\/cluster complexes  

Microsoft Academic Search

We report on a study of young star cluster complexes in the spiral galaxy M 51. Recent studies have confirmed that star clusters do not form in isolation, but instead tend to form in larger groupings or complexes. We use HST broad and narrow band images (from both WFPC2 and ACS), along with BIMA-CO observations to study the properties and

N. Bastian; M. Gieles; Yu. N. Efremov

2005-01-01

214

A calorimetric comparison of trypsin and its anhydro modification in complex formation with Kunitz soybean inhibitor.  

PubMed

The heat of complex formation between native trypsin or its anhydro modification (Ako, H., Foster, R. J., and Ryan, C. J. (1972) Biochem. Biophys. Res Commun. 47, 1402--1407) with native or cleaved Kunitz soybean inhibitor (Finkenstadt, W. R., and Laskowski, M., Jr. (1965) J. Biol. Chem. 240, 962--963) has been observed from pH 3.5 to 7.5. Steep dependence of reaction heat upon pH between pH 3.5 and 4.25 is observed with native inhibitor in reaction with both trypsin and anhydrotrypsin. The character of this heat-pH relationship is consistent with a cooperative process involving three to four ionizable groups. Above pH 4.25, trypsin and anhydrotrypsin in reaction with native inhibitor have quite different pH dependencies. Native trypsin shows an apparent pK near pH 5, whereas anhydrotrypsin + inhibitor reaction heat remains nearly constant from pH 4.5 to 6, and shows an apparent pK near pH 7.0. Above pH 4, the reaction heat-pH relations for native or cleaved inhibitor in reaction with trypsin are only slightly different (Barnhill, M. T., Jr., and Trowbridge, C. G. (1975) J. Biol. Chem. 250, 5501--5507). On the other hand, substitution of cleaved for native inhibitor in reaction with anhydrotrypsin causes a greatly reduced reaction heat, with no clearly developed pH dependence from pH 5.5 to 7.5. The reaction heat-pH relationships are analyzed thermodynamically in terms of the temperature coefficient of a pH-dependent equilibrium constant. It is clear that conversion of the active site serine side chain of trypsin to dehydroalanine changes the pH dependence of its reaction heat with soybean inhibitor, and that the complex formed is sensitive to the state of the scissile inhibitor bond. These differences provide a comparison of a protein-protein association with and without covalent bond formation between reactants. PMID:7191852

Yung, B Y; Trowbridge, C G

1980-10-25

215

Dynamics of Research Team Formation in Complex Networks  

Microsoft Academic Search

Most organizations encourage the formation of teams to accomplish complicated tasks, and vice verse, effective teams could\\u000a bring lots benefits and profits for organizations. Network structure plays an important role in forming teams. In this paper,\\u000a we specifically study the dynamics of team formation in large research communities in which knowledge of individuals plays\\u000a an important role on team performance

Caihong Sun; Yuzi Wan; Yu Chen

2009-01-01

216

Formation of a Dynamic Kinetochore Microtubule Interface through Assembly of the Dam1 Ring Complex  

Microsoft Academic Search

How kinetochore proteins form a dynamic interface with microtubules is largely unknown. In budding yeast, the 10-protein Dam1 complex is an Aurora kinase target that plays essential roles maintaining the integrity of the mitotic spindle and regulating interactions with the kinetochore. Here, we investigated the biochemical properties of purified Dam1 complex. The complex oligomerized into rings around microtubules. Ring formation

Stefan Westermann; Agustin Avila-Sakar; Hong-Wei Wang; Hanspeter Niederstrasser; Jonathan Wong; David G. Drubin; Eva Nogales; Georjana Barnes

2005-01-01

217

Investigation of S-nitrosothiol formation in complex I and model compounds by FTIR spectroscopy  

Microsoft Academic Search

In addition to its role as a regulator of vascular tone, synaptic signalling and cellular defence, nitric oxide (NO) has been shown to inhibit complex I and cytochrome c oxidase of the respiratory electron transfer chain. It has been suggested that the mechanism by which NO inhibits complex I involves the formation of S-nitrosothiols on the complex which are deleterious

Doug Marshall

218

A spectrophotometric and thermodynamic study of the sitting-atop complex formation from reaction between free base meso-tetraarylporphyrins and zirconyl nitrate in chloroform solution  

NASA Astrophysics Data System (ADS)

The sitting-atop complexation of meso-tetraarylporphyrins and its para-substituted derivatives (H 2t(4-X)pp, X:H, Br, Cl, CH(CH 3) 2, OCH 3, CH 3), as electron donors, with zirconyl, as an electron acceptor, have been investigated spectrophotometrically in chloroform. The mole ratio studies based on physicochemical techniques were employed clearly and revealed the formation of 1:1 sitting-atop complexes which was confirmed by UV-vis, 1H NMR and IR spectroscopic data. The value of the formation constant was estimated for each complex using a nonlinear optimization of the complex absorbance vs. mole ratio data by package KINFIT. The results showed that the stability of these complexes decreases with the temperature enhancement. Thermodynamic parameters, ? G°, ? H° and ? S°, of the SAT complexes have been determined from the temperature dependence of formation constants by Van't Hoff equation. Also, the influence of the substituents of the aryl rings in H 2t(4-X)pp on the stability of the SAT complexes is discussed.

Dehghani, Hossein; Mansournia, Mohammad Reza

2009-10-01

219

The Optical Biosensor Studies on the Role of Hydrophobic Tails of NADPH-Cytochrome P450 Reductase and Cytochromes P450 2B4 and b5 upon Productive Complex Formation within a Monomeric Reconstituted System  

Microsoft Academic Search

The optical biosensor study of interaction between microsomal proteins—NADPH-cytochrome P450 reductase, cytochrome P450 2B4, and cytochrome b5—was carried out in the monomeric reconstituted system in the absence of phospholipids. The formation of individual complexes was kinetically characterized and their association and dissociation rate constants were determined. The association rate constants for the complexes formed were found to be close to

Yuri D. Ivanov; Irina P. Kanaeva; Vadim Yu. Kuznetsov; Michael Lehnerer; Johannes Schulze; Peter Hlavica; Alexander I. Archakov

1999-01-01

220

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

SciTech Connect

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

Filippova, E. V., E-mail: kostya@eimb.relarn.ru; Polyakov, K. M. [Russian Academy of Sciences, Engelhardt Institute of Molecular Biology (Russian Federation); Tikhonova, T. V.; Stekhanova, T. N.; Boiko, K. M.; Sadykhov, I. G. [Russian Academy of Sciences, Bach Institute of Biochemistry (Russian Federation); Tishkov, V. I. [Moscow State University (Russian Federation); Popov, V. O. [Russian Academy of Sciences, Bach Institute of Biochemistry (Russian Federation); Labru, N. [Agricultural University (Greece)

2006-07-15

221

Parametric Signal Fitting by Gaussian Peak Adjustment: implementation of 2D transversal constraints and its application for the determination of pKa and complexation constants by differential pulse voltammetry.  

PubMed

A new method, GPA2D, is presented as a significant improvement of the previously described Gaussian Peak Adjustment (GPA) which includes, for the first time, transversal constraints to increase the consistency of the resolution along the different signals of a voltammetric dataset. The constraints deal with the evolution of peak potentials versus pH and with the implementation of chemical equilibrium constants. Moreover, pkavolt, a new tool for the pKa determination, is proposed as an example of the great versatility of the PSF-GPA (Parametric Signal Fitting by Gaussian Peak Adjustment) methodology. GPA2D and pkavolt have been successfully tested on the systems Cd(ii):phytochelatin, Cu(ii):6-benzylaminopurine, Cd(ii):1,10-phenanthroline, Zn(ii):oxalate and captopril drug by determining formation constants (metal complex systems) or pKa values (captopril). PMID:23431558

Cavanillas, Santiago; Serrano, Núria; Díaz-Cruz, José Manuel; Ariño, Cristina; Esteban, Miquel

2013-04-01

222

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

223

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

Microsoft Academic Search

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 0.1mol\\/l (NaClO4) and at 21°C. The

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

2006-01-01

224

Hard- and soft-modeling approaches for resolution of complex formation of Co2+ and Ni2+ with glycine.  

PubMed

Principal component analysis (PCA) was used to obtain information about the number of components in the complex formation equilibria of Co(2+) and Ni(2+) with glycine (Gly). In order to obtain a clearer insight into these complex formation systems, multivariate curve resolution-alternating least squares (MCR-ALS) was used. Using MCR-ALS as a soft-modeling method, well-defined concentration and spectral profiles were obtained under unimodality, non-negativity, and closure constraints. Based on the obtained results, an equilibrium model was proposed and subsequently, a hard-modeling method was used to resolve the complex formation equilibria completely. Due to the presence of multiple equilibria, the resolution of such systems is very difficult. The Co-Gly system was best described by a model consisting of M(GlyH), M(Gly), M(Gly)(2), M(Gly)(2)H, and M(Gly)(3) (M = Co(2+)) with the overall stability constants determined to be 7.10 ± 0.011, 5.14 ± 0.006, 9.28 ± 0.009, 13.75 ± 0.016, and 11.10 ± 0.010, respectively. On the other hand, the system of Ni-Gly was best fitted by a model containing M(GlyH), M(Gly), M(Gly)(2), M(Gly)(3), and M(Gly)(2)(OH) (M = Ni(2+)) with overall stability constants of 10.95 ± 0.04, 6.41 ± 0.03, 11.31 ± 0.03, 15.39 ± 0.06, and 14.32 ± 0.02, respectively. PMID:22449325

Shariati-Rad, Masoud; Hasani, Masoumeh; Shamsipur, Mojtaba

2012-04-01

225

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

226

Formation of - Complexes between Phenanthrene and Model Acceptor Humic Subunits  

Microsoft Academic Search

aromatic hydrocarbons (PAHs), an important class of pollutants that can act as strong donors. Although - Interactions may play a role in association of aromatic com- desolvation of apolar organic compounds or their parts pounds with natural organic substances. Complexation in aqueous solvents was studied between the donor, phenanthrene (PHEN), (i.e., the \\

Hotze Wijnja; Joseph J. Pignatello; Kalumbu Malekani

227

Interferogram formation in the presence of complex and large deformation  

Microsoft Academic Search

Sierra Negra volcano in Isabela island, Galápagos, erupted from October 22 to October 30 in 2005. During the 8 days of eruption, the center of Sierra Negra's caldera subsided about 5.4 meters. Three hours prior to the onset of the eruption, an earthquake (Mw 5.4) occurred, near the caldera. Because of the large and complex phase gradient due to the

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

2007-01-01

228

Search Graph Formation for Minimizing the Complexity of Planning  

Microsoft Academic Search

A large number of path planning problems are solved by the use of graph based search algorithms. There are a variety of techniques available to optimize the search within these graphs as well as thorough studies of the complexity involved in searching through them. However, little eort has been dedicated to construct- ing the graphs so that the results of

Alberto Lacaze; Stephen Balakirsky

229

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

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

230

Controlling Elastic Instabilities: From Complex Pattern Formation to Functionality  

NASA Astrophysics Data System (ADS)

Exploiting elastic instability in thin films has proven a robust method for creating complex patterns and structures across a wide range of lengthscales. Even the simplest of systems, an elastic membrane with a lattice of pores, under stress, generates a plethora of complex patterns featuring long-range orientational order. Harnessing the underlying elastic instability allows for the rational design of materials with highly desirable properties: from a film with a switchable photonic bandgap to a material with a negative Poisson ratio. Within the framework of linear elasticity, we model the system as a lattice of interacting deformation elements, or ``dislocation dipoles,'' which captures the configuration and orientational order present in any conceivable deformation of the system. In addition, when we promote this system to a curved surface, a novel set of features, patterns and broken symmetries appears.

Matsumoto, Elisabetta; Kamien, Randall

2010-03-01

231

Hydrophobic core formation in protein complex of cathepsin.  

PubMed

The "fuzzy oil drop" model assumes that the idealized hydrophobic core in a protein body can be described by a 3D Gauss function. The structure of the 1ICF protein (cathepsin), which participates in the proteolysis process and has cysteine-type peptidase activity, has been analyzed on the basis of the "fuzzy oil drop" model. The authors have determined the contribution of individual exon fragments to the creation of a common hydrophobic core and assessed the involvement of each chain in this process, depending on the number of complexed chains. Quantitative assessment of exons, chains, dimers, and the whole complex suggest that each of these units plays a different role in shaping the protein's hydrophobic core. PMID:23826628

Piwowar, Monika; Banach, Mateusz; Konieczny, Leszek; Roterman, Irena

2014-07-01

232

Reactions of chloride complexes of ruthenium (IV) with formic acid and sodium formate in aqueous solutions  

SciTech Connect

Study of the reactions of (NH/sub 4/)/sub 2/RuCl/sub 6/ with formic acid and sodium formate showed that, depending on the conditions, chlorocarbonyl, chloroformatocarbonyl, or chloroformato complexes of ruthenium(III) are formed.

Simanova, S.A.; Krylova, G.S.; Maslov, E.I.

1982-04-20

233

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

234

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

235

Formation of ruthenium thiolates via complexes of molecular hydrogen  

SciTech Connect

RuH[sub 2](DMPE)[sub 2][DMPE = 1,2-bis(dimethylphosphino)ethane] was synthesized by reduction of trans-RuCl[sub 2](DMPE)[sub 2] with sodium/2-propanol. Protonation of RuH[sub 2](DMPE)[sub 2] with weak organic acids such as methanol, ethanol, and thiols affords the molecular hydrogen complex trans-[RuH([eta][sup 2]-H[sub 2])(DMPE)[sub 2

Field, L.D.; Hambley, T.W.; Yau, B.C.K. (Univ. of Sydney, Sydney (Australia))

1994-04-27

236

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

237

Structural Basis of Clostridium perfringens Toxin Complex Formation  

SciTech Connect

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

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

2008-01-01

238

Tube formation by complex cellular processes in Ciona intestinalis notochord  

PubMed Central

In the course of embryogenesis multicellular structures and organs are assembled from constituent cells. One structural component common to many organs is the tube, which consists most simply of a luminal space surrounded by a single layer of epithelial cells. The notochord of ascidian Ciona forms a tube consisting of only 40 cells, and serves as a hydrostatic “skeleton” essential for swimming. While the early processes of convergent extension in ascidian notochord development have been extensively studied, the later phases of development, which include lumen formation, have not been well characterized. Here we used molecular markers and confocal imaging to describe tubulogenesis in the developing Ciona notochord. We found that during tubulogenesis each notochord cell established de novo apical domains, and underwent a mesenchymal-epithelial transition to become an unusual epithelial cell with two opposing apical domains. Concomitantly, extracellular luminal matrix was produced and deposited between notochord cells. Subsequently, each notochord cell simultaneously executed two types of crawling movements bi-directionally along the anterior/posterior axis on the inner surface of notochordal sheath. Lamellipodia-like protrusions resulted in cell lengthening along the anterior/posterior axis, while the retraction of trailing edges of the same cell led to the merging of the two apical domains. As a result, the notochord cells acquired endothelial-like shape and formed the wall of the central lumen. Inhibition of actin polymerization prevented the cell movement and tube formation. Ciona notochord tube formation utilized an assortment of common and fundamental cellular processes including cell shape change, apical membrane biogenesis, cell/cell adhesion remodeling, dynamic cell crawling, and lumen matrix secretion.

Dong, Bo; Horie, Takeo; Denker, Elsa; Kusakabe, Takehiro; Tsuda, Motoyuki; Smith, William C.; Jiang, Di

2009-01-01

239

Thermodynamics of Cationic Lipid-DNA Complex Formation as Studied by Isothermal Titration Calorimetry  

Microsoft Academic Search

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 1kcal absorbed per mole of lipid or DNA charge. This enthalpy change was attributed to DNA-DNA mutual

Edwin Pozharski; Robert C. MacDonald

2002-01-01

240

Modeling of solid–liquid equilibria for systems with solid-complex phase formation  

Microsoft Academic Search

The Perturbed-Chain SAFT (PC-SAFT) equation of state (EOS) is applied to model the solid–liquid equilibria (SLE) of binary and ternary systems showing a solid-complex phase formation. Modeling results for mixtures composed of associating components, e.g. water, alcohols, phenol, bisphenol A (BPA), as well as acetamide are presented. The solid-complex phase formation is modeled as a chemical reaction between species in

Feelly Tumakaka; Igor V. Prikhodko; Gabriele Sadowski

2007-01-01

241

Intermolecular dynamics and exciplex formation of the 1-cyanonaphthalene\\/triethylamine van der Waals complex  

Microsoft Academic Search

The exciplex formation dynamics of the 1-cyanonaphthalene\\/triethylamine van der Waals complex upon excitation has been examined under collision free conditions. Mode-specificity has been found in the excitation of a combination band between intra- and intermolecular vibrational modes in the S1 state of the vdW complex to promote the exciplex formation reaction. The specificity is lost at higher excess energies since

Hiroyuki Saigusa; Michiya Itoh; Masaaki Baba; Ichiro Hanazaki

1987-01-01

242

Complexation of Copper in Natural Waters. Determination of Complexing Capacities and Conditional Stability Constants in Natural Waters by MnO?, and the Implications for Phytoplankton Toxicity  

Microsoft Academic Search

After a recapitulation of complexation theory, a theory is developed for the determination of copper complexation for mono- and bidentate complexes and for 2:1 complexes (CuL?) by ion exchange. This theory can be applied in principle to other ion exchange methods that make use of weak ion exchange media with an adsorption behavior of metal ions similar to Langmuir adsorption.

C. M. G. van den Berg van Saparoea

1979-01-01

243

Chemical complexity and star-formation in merging galaxies  

NASA Astrophysics Data System (ADS)

When galaxies merge the resulting conditions are some of the most extreme found anywhere in nature. Large gas flows, shocks and active black holes all can affect the ISM. Nearby merging galaxies with strong starbursts are the only places where we can conduct detailed study of star formation in conditions that mimic those under which the majority of stars in the universe formed. Here we study molecular gas tracers in 8 galaxies selected from the VIRUS-P Investigation of the eXtreme ENvironments of Starbursts (VIXENS) survey. Each galaxy has also been observed using the integral field unit spectrograph VIRUS-P, allowing us to investigate the relation between the chemical state of the gas, star formation and total gas content. Full details can be found in Heiderman et al. (2011). Here we report on new results obtained from IRAM-30m/NRO-45m 3mm line surveys towards 14 positions in these 8 merging galaxies. We detect ? 25 different molecular transitions towards these objects, many which have never been observed in these galaxies before. Our measurements show that the mean fraction of dense gas increases in later-stage mergers (Fig. 1, left), as does the average optical depth of the gas. Molecular diagnostic diagrams (Fig. 1, right) show that molecular regions we probe are, in general, UV photon dominated. Triggered AGN activity, and/or cosmic ray ionisation (from SNe II in the starburst) are not yet energetically important in determining the state of the gas.

Davis, T. A.; Heiderman, A.; Iono, D.; VIXENS Team

2013-03-01

244

Biological pattern formation: from basic mechanisms to complex structures  

NASA Astrophysics Data System (ADS)

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

Koch, A. J.; Meinhardt, H.

1994-10-01

245

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.

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

2012-01-01

246

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

247

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

248

Landscape complexity influences route-memory formation in navigating pigeons.  

PubMed

Observations of the flight paths of pigeons navigating from familiar locations have shown that these birds are able to learn and subsequently follow habitual routes home. It has been suggested that navigation along these routes is based on the recognition of memorized visual landmarks. Previous research has identified the effect of landmarks on flight path structure, and thus the locations of potentially salient sites. Pigeons have also been observed to be particularly attracted to strong linear features in the landscape, such as roads and rivers. However, a more general understanding of the specific characteristics of the landscape that facilitate route learning has remained out of reach. In this study, we identify landscape complexity as a key predictor of the fidelity to the habitual route, and thus conclude that pigeons form route memories most strongly in regions where the landscape complexity is neither too great nor too low. Our results imply that pigeons process their visual environment on a characteristic spatial scale while navigating and can explain the different degrees of success in reproducing route learning in different geographical locations. PMID:24451267

Mann, Richard P; Armstrong, Chris; Meade, Jessica; Freeman, Robin; Biro, Dora; Guilford, Tim

2014-01-01

249

Complex formation at indium donors in p-CdTe  

NASA Astrophysics Data System (ADS)

After diffusion of silver into p-CdTe at room temperature, two electric field gradients (EFG) are observed at {111In}/{111Cd} probe atoms at T = 77 K: ?Q1 = 61 MHz, ?1 = 0.15 and ?Q2 = 30 MHz, ?2 = 0.46. The assignment of EFG 1 to In-A centers leads to the conclusion that the 0/- level of the Cd-vacancy is located deeper in the band gap than the shallow doping and that the two EFGs are caused by the neutral and singly negative Cd-vacancy. The reason for In-A center formation and subsequent dissociation (aging) after Ag diffusion is explained.

Reislöhner, U.; Achtziger, N.; Rüb, M.; Witthuhn, W.

1996-02-01

250

The complex interplay between semantics and grammar in impression formation.  

PubMed

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

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

2014-09-01

251

Formation of Soluble Complexes of Metals with Humic Acid and Its Environmental Significance  

Microsoft Academic Search

In order to investigate the role of functional groups present in humic acid(s) (HA) during complex formation, water soluble complexes between HA isolated from soil and metals (Pb, Ca, As, Ni, Cr, Co, Cu, Cd, Fe, Mn, Mg and Zn) were prepared and subjected to infrared (IR) spectroscopy. the IR data revealed the involvement of the - OH group of

Ashok Kumar Pandey; Shri Dhar Pandey; Virendra Misra; P. N. Viswanathan

1999-01-01

252

Dynamics of Nanoparticle-Protein Corona Complex Formation: Analytical Results from Population Balance Equations  

PubMed Central

Background Nanoparticle-protein corona complex formation involves absorption of protein molecules onto nanoparticle surfaces in a physiological environment. Understanding the corona formation process is crucial in predicting nanoparticle behavior in biological systems, including applications of nanotoxicology and development of nano drug delivery platforms. Method This paper extends the modeling work in to derive a mathematical model describing the dynamics of nanoparticle corona complex formation from population balance equations. We apply nonlinear dynamics techniques to derive analytical results for the composition of nanoparticle-protein corona complex, and validate our results through numerical simulations. Results The model presented in this paper exhibits two phases of corona complex dynamics. In the first phase, proteins rapidly bind to the free surface of nanoparticles, leading to a metastable composition. During the second phase, continuous association and dissociation of protein molecules with nanoparticles slowly changes the composition of the corona complex. Given sufficient time, composition of the corona complex reaches an equilibrium state of stable composition. We find analytical approximate formulae for metastable and stable compositions of corona complex. Our formulae are very well-structured to clearly identify important parameters determining corona composition. Conclusion The dynamics of biocorona formation constitute vital aspect of interactions between nanoparticles and living organisms. Our results further understanding of these dynamics through quantitation of experimental conditions, modeling results for in vitro systems to better predict behavior for in vivo systems. One potential application would involve a single cell culture medium related to a complex protein medium, such as blood or tissue fluid.

Darabi Sahneh, Faryad; Scoglio, Caterina; Riviere, Jim

2013-01-01

253

Complex formation in the ternary system Mg(II)CO 2 -H 2 O  

Microsoft Academic Search

The carbonato and hydrogencarbonato complexes of Mg 2+ were investigated at 25 and 50° in solutions of the constant ClO 4 - molality (3 M) consisting preponderantly of NaClO 4 . The experimental data could be explained assuming the following equilibria: Mg 2+ + CO 2 B + H 2 O ag MgHCO + 3 + H + , log

Walter Riesen; Heinz Gamsjäger; Paul W. Schindler

1977-01-01

254

Organic versus inorganic trace metal complexes in sulfidic marine waters--some speculative calculations based on available stability constants  

Microsoft Academic Search

A theoretical model has been developed in order to test the hypothesis that simple organic acids are the chief agents of trace metal solubility in H 2 S-rich marine waters. The model utilizes stability constant given by and (1964, 1971) and assumes that the free cation activity of each metal is controlled by simple solubility products. Typical values of pH,

Leonard Robert Gardner

1974-01-01

255

A rapid and convenient method for the formation of (diene)Fe(CO) 3 complexes  

Microsoft Academic Search

The formation of (diene)Fe(CO)3 complexes has been achieved in the absence of solvent by the action of mild heat on a mixture of the diene and a preformed mixture of Fe2(CO)9 and silica gel. The yield of complex obtained compares well with literature examples especially for polar substrates. The first complexation of Danishefsky’s diene, 1-methoxy-3-trimethylsilyloxybuta-1,3-diene, to Fe(CO)3 has been achieved

Gordon F. Docherty; Graham R. Knox; Peter L. Pauson

1998-01-01

256

In situ formation of solid-supported lipid/DNA complexes  

NASA Astrophysics Data System (ADS)

Solid-supported lipid/DNA complexes were prepared by using highly aligned 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) multibilayers as a template. The complex formation was promoted in situ and followed in time. The resulting DOTAP/DNA complex shows a good degree of orientation along the normal to the support as revealed by combined time-resolved energy dispersive X-ray diffraction (EDXD) and surface synchrotron small angle X-ray scattering (SAXS) measurements.

Caracciolo, Giulio; Amenitsch, Heinz; Sadun, Claudia; Caminiti, Ruggero

2005-04-01

257

The application of luminescence-kinetic methods in the study of the formation of lanthanide ion complexes in solution  

Microsoft Academic Search

The mechanisms of nonradiative transitions in lanthanide ions in solutions are discussed. The results of the use of this phenomenon in the study of the structures and stability constants of complexes of lanthanide ions in solutions are described. The possible uses of the nonradiative energy transfer between lanthanide ions in the determination of the stability constants of their complexes and

Valerii L Ermolaev; E B Sveshnikova

1994-01-01

258

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

259

A Two-step Process Controls the Formation of the Bienzyme Cysteine Synthase Complex*  

PubMed Central

The regulation of enzyme activity through the transient formation of multiprotein assemblies plays an important role in the control of biosynthetic pathways. One of the first regulatory complexes to be discovered was cysteine synthase (CS), formed by the pyridoxal 5?-phosphate-dependent enzyme O-acetylserine sulfhydrylase (OASS) and serine acetyltransferase (SAT). These enzymes are at the branch point of the sulfur, carbon, and nitrogen assimilation pathways. Understanding the mechanism of complex formation helps to clarify the role played by CS in the regulation of sulfur assimilation in bacteria and plants. To this goal, stopped-flow fluorescence spectroscopy was used to characterize the interaction of SAT with OASS, at different temperatures and pH values, and in the presence of the physiological regulators cysteine and bisulfide. Results shed light on the mechanism of complex formation and regulation, so far poorly understood. Cysteine synthase assembly occurs via a two-step mechanism involving rapid formation of an encounter complex between the two enzymes, followed by a slow conformational change. The conformational change likely results from the closure of the active site of OASS upon binding of the SAT C-terminal peptide. Bisulfide, the second substrate and a feedback inhibitor of OASS, stabilizes the CS complex mainly by decreasing the back rate of the isomerization step. Cysteine, the product of the OASS reaction and a SAT inhibitor, slightly affects the kinetics of CS formation leading to destabilization of the complex.

Salsi, Enea; Campanini, Barbara; Bettati, Stefano; Raboni, Samanta; Roderick, Steven L.; Cook, Paul F.; Mozzarelli, Andrea

2010-01-01

260

Metal complexes stability constant determination by hyphenation of capillary electrophoresis with inductively coupled plasma mass spectrometry: The case of 1:1 metal-to-ligand stoichiometry  

Microsoft Academic Search

Nuclear energy development has raised new issues like radionuclides biogeochemistry. The modelling of their biochemical properties involves the accurate determination of thermodynamical data, like stability constants. This can be achieved by using hyphenated capillary electrophoresis (CE)–ICPMS and the method was applied successfully on 1:1 lanthanum–oxalate and uranyl–oxalate complexes. Several significant steps are discussed: choice of analytical conditions, electrophoretic mobility calculation,

Jeremy Petit; Valérie Geertsen; Catherine Beaucaire; Moncef Stambouli

2009-01-01

261

Stoichiometry and conditional stability constants of Cu(II) or Zn(II) clioquinol complexes; implications for Alzheimer's and Huntington's disease therapy  

Microsoft Academic Search

Successful trials with 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol, CQ) for Alzheimer's disease treatment prompted renewed interest in assessing whether its therapeutic action is related to the coordination of neurotoxic trace metals, such as Cu(II) and Zn(II). We now report conditional stability constants (KC?) for CQ Cu(II) and Zn(II) complexes measured in a biological buffer containing Ca(II) and Mg(II) ions. UV–vis spectroscopy and polarography

Evandro Ferrada; Verónica Arancibia; Bárbara Loeb; Ester Norambuena; Claudio Olea-Azar; J. Pablo Huidobro-Toro

2007-01-01

262

Unsaturated selenacrown ethers: synthesis, structure, and formation of silver complexes.  

PubMed

The unsaturated selenacrown ethers, (Z,Z,Z,Z,Z)-1,4,7,10,13-pentaselenacyclopentadeca-2,5,8,11,14-pentaene (15-US-5) (2), (Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16-hexaselenacyclooctadeca-2,5,8,11,14,17-hexaene (18-US-6) (3), (Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19-heptaselenacycloheneicosa-2,5,8,11,14,17,20-heptaene (21-US-7) (4), (Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22-octaselenacyclotetracosa-2,5,8,11,14,17,20,23-octaene (24-US-8) (5), and (Z,Z,Z,Z,Z,Z,Z,Z,Z)-1,4,7,10,13,16,19,22,25-nonaselenacycloheptacosa-2,5,8,11,14,17,20,23,26-nonaene (27-US-9) (6), were obtained together with 1,4-diselenin (1) by reacting sodium selenide with cis-dichloroethene in the presence of a phase-transfer catalyst. The crystal structures of 2-5 were determined by X-ray crystallographic analysis. The UV spectra of the selenacrown ethers showed absorption maximums in the range of 251-262 nm, which were assigned to n-->pi transitions. The cyclic voltammograms indicated that the large unsaturated selenacrown ethers were oxidized more easily than the small ones. The thermal reactions of the unsaturated selenacrown ethers afforded 1,4-diselenin (1) along with polymeric materials, whereas 1 was thermally stable even at 100 degrees C. The reactions of 1 or unsaturated selenacrown ethers 2-5 with silver ion yielded various novel silver complexes, Ag(C(4)H(4)Se(2))(CF(3)COO) (7), Ag(C(4)H(4)Se(2))(2)(CF(3)COO) (8), Ag(15-US-5)(CF(3)COO) (9), Ag(5)(18-US-6)(3)(CF(3)COO)(5) (10), Ag(7)(21-US-7)(CF(3)COO)(5) (11), Ag(24-US-8)(2)(CF(3)COO) (12), Ag(2)(24-US-8)(CF(3)COO)(2) (13), Ag(3)(24-US-8)(2)(CF(3)COO)(3) (14), Ag(15-US-5)NO(3) (15), and Ag(21-US-7)BF(4) (16). The stoichiometry for the complexation with silver trifluoroacetate in solution was examined by (1)H NMR measurement. The titration plots of 2 and 5 under the dilution conditions showed a distinct inflection point at the 1/1 metal/macrocycle ratio, whereas the plots of 1 and 3 showed gradual change. PMID:15960503

Shimizu, Toshio; Kawaguchi, Mari; Tsuchiya, Takahiro; Hirabayashi, Kazunori; Kamigata, Nobumasa

2005-06-24

263

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

264

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

265

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

PubMed Central

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.

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

2014-01-01

266

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

267

Oxidative peptide /and amide/ formation from Schiff base complexes  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

268

An illustration of the complexity of continent formation  

NASA Technical Reports Server (NTRS)

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

Burke, Kevin

1988-01-01

269

Rate constants for hydrogen atom transfer reactions from bis(cyclopentadienyl)titanium(III) chloride-complexed water and methanol to an alkyl radical.  

PubMed

Rate constants for hydrogen atom transfer reactions of the water, deuterium oxide, and methanol complexes of bis(cyclopentadienyl)titanium(III) chloride with the secondary alkyl radical 1-cyclobutyldodecyl (2) were determined using indirect kinetic methods. The rate constant for reaction of Cp2Ti(III)Cl-H2O in THF at ambient temperature was 1.0 x 10(5) M(-1) s(-1), and the kinetic isotope effect was kH/kD = 4.4. In benzene containing 0.95 M methanol, the rate constant for reaction of the Cp2Ti(III)Cl-MeOH at ambient temperature was 7.5 x 10(4) M(-1) s(-1). An Arrhenius function for reaction of the Cp2Ti(III)Cl-H2O complex in THF was log k = 9.1 - 5.5/2.3 RT (kcal/mol). The entropic term for reaction of Cp2Ti(III)Cl-H2O was normal, whereas the entropic term previously found for reaction of the Et3B-H2O complex with radical 2 was unusually small (Jin, J.; Newcomb, M. J. Org. Chem. 2007, 72, 5098). PMID:18800812

Jin, Jing; Newcomb, Martin

2008-10-17

270

Ionic Exchange in p-Sulfonatocalix[4]arene-Mediated Formation of Metal-Ligand Complexes.  

PubMed

The effect of alkali and transition metal cations in the formation of host-guest complexes with the water-soluble p-sulfonatocalix[4]arene (SC4) was studied using 2-chloropyridine and Na(+) and Cu(2+) as model guest and model cations, respectively. The results obtained from isothermal titration calorimetry and NMR experiments provide evidence for the formation of 1:1:1 ternary complexes for both cations with Cu(2+) showing positive cooperativity and Na(+) negative cooperativity. The formation of ternary complexes comprising transition metal cations has been scarcely explored but present high potential for devising catalytic systems/models or for enhancing the stability and selectivity of SC4 complexes. Because transition metal cations are usually present in solution together with other SC4 countercations (e.g., Na(+)), a general binding model that considers the dynamic formation of all possible complexes (including ionic exchange between ternary complexes) is presented. This model allows the optimization of the conditions required to selectively form target complexes. PMID:24725072

Francisco, Vitor; Basílio, Nuno; García-Río, Luis

2014-05-01

271

Formation of anionic carbonylrhodium complexes from Wilkinson's complex under conditions of hydroformylation of formaldehyde  

Microsoft Academic Search

The compositions and the dynamics of transformations of carbonylrhodium complexes formed from Wilkinson's complex, RhCl(PPh3)3, dissolved in mesitylene—N,N-dimethylacetamide (DMAA) mixtures in which the DMAA concentration varied from 0 to 100 %, in an atmosphere of synthesis gas\\u000a$$p_{{\\\\text{CO + H}}_{\\\\text{2}} } $$\\u000a = 6 MPa,T=373 K) were investigatedin situ by IR spectroscopy. The anion complexes, [Rh(CO)2(PPh3)x(DMAA)y]- (x=1, 2;y=1, 0) and

N. N. Ezhova; G. A. Korneeva; V. I. Kurkin; M. P. Filatova; E. V. Slivinsky

1995-01-01

272

Comparison of the self-exchange and interfacial charge-transfer rate constants for methyl- versus tert-butyl-substituted Os(III) polypyridyl complexes.  

PubMed

Differences in the self-exchange and interfacial electron-transfer rate constants have been evaluated for a relatively unhindered Os(III/II) redox system, osmium(III/II) tris(4,4'-di-methyl-2,2'-bipyridyl), [Os(Me2bpy)3]3+/2+, relative to those of a relatively hindered system, osmium(III/II) tris(4,4'-di-tert-butyl-2,2'-bipyridyl), [Os(t-Bu2bpy)3]3+/2+. In contrast to the predicted increase in rate constant by a factor of 2-3 due to the difference in reorganization energy of the two complexes, introduction of the tert-butyl functionality decreased the self-exchange rate constant, as measured by NMR line-broadening techniques, by a factor of approximately 50 as compared to that of the analogous methyl-substituted osmium complex. Steady-state current density versus potential measurements, in conjunction with differential capacitance versus potential measurements, were used to compare the interfacial electron-transfer rate constants at n-type ZnO electrodes of [Os(t-Bu2bpy)3]3+/2+ and [Os(Me2bpy)3]3+/2+. The interfacial electron-transfer rate constant for the reduction of [Os(t-Bu2bpy)3]3+ was 100 times smaller than that for [Os(Me2bpy)3]3+. The results indicate that the tert-butyl group can act as a spacer on an outer-sphere redox couple and significantly decrease the electronic coupling of the electron-transfer reaction in both self-exchange and interfacial electron-transfer processes. PMID:17166001

Hamann, Thomas W; Brunschwig, Bruce S; Lewis, Nathan S

2006-12-21

273

SEPALLATA3: the 'glue' for MADS box transcription factor complex formation  

PubMed Central

Background Plant MADS box proteins play important roles in a plethora of developmental processes. In order to regulate specific sets of target genes, MADS box proteins dimerize and are thought to assemble into multimeric complexes. In this study a large-scale yeast three-hybrid screen is utilized to provide insight into the higher-order complex formation capacity of the Arabidopsis MADS box family. SEPALLATA3 (SEP3) has been shown to mediate complex formation and, therefore, special attention is paid to this factor in this study. Results In total, 106 multimeric complexes were identified; in more than half of these at least one SEP protein was present. Besides the known complexes involved in determining floral organ identity, various complexes consisting of combinations of proteins known to play a role in floral organ identity specification, and flowering time determination were discovered. The capacity to form this latter type of complex suggests that homeotic factors play essential roles in down-regulation of the MADS box genes involved in floral timing in the flower via negative auto-regulatory loops. Furthermore, various novel complexes were identified that may be important for the direct regulation of the floral transition process. A subsequent detailed analysis of the APETALA3, PISTILLATA, and SEP3 proteins in living plant cells suggests the formation of a multimeric complex in vivo. Conclusions Overall, these results provide strong indications that higher-order complex formation is a general and essential molecular mechanism for plant MADS box protein functioning and attribute a pivotal role to the SEP3 'glue' protein in mediating multimerization.

Immink, Richard GH; Tonaco, Isabella AN; de Folter, Stefan; Shchennikova, Anna; van Dijk, Aalt DJ; Busscher-Lange, Jacqueline; Borst, Jan W; Angenent, Gerco C

2009-01-01

274

Normal and recombinant human growth hormone administered by constant infusion feminize catechol estrogen formation by rat liver microsomes.  

PubMed

Human GH or recombinant DNA-derived human GH administered to normal mature male rats by constant infusion decreased hepatic 2-hydroxylation of estradiol to female levels, as measured by 3H2O release and isolation of the catechol estrogen product. PRL had no effect under the same conditions. The maximum response to GH was attained at an infusion rate of 0.02 IU/h . kg after 5-7 days, and a significant change was observed within 1-2 days. The effect of GH was primarily on hydroxylation of C-2 of the estrogen, as demonstrated by comparative studies with estradiol labeled with 3H at C-4 or C-6,7, and appeared to be mediated by the cytochrome P-450 system of the liver microsomes. Ascorbic acid at 1 mM did not affect 2-hydroxylation significantly while protecting the catechol estrogen produced from further oxidation. The results indicate that GH has the potential to regulate estrogen metabolism in the liver and provide evidence for another component in the hypothalamic-pituitary-liver axis. PMID:2998732

Jellinck, P H; Quail, J A; Crowley, C A

1985-12-01

275

{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

276

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

PubMed

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

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

2007-10-01

277

Complex formation and kinetics of phosphodiester cleavage in the hydrogen peroxide–lanthanide(III) system  

Microsoft Academic Search

Potentiometric and spectrophotometric titrations of hydrogen peroxide in the presence of La(III), Nd(III), Pr(III) and Eu(III) cations reveal formation of several types of di-, tri- and tetranuclear species. Complexes M2(O2)2(OH)2 or the respective tetranuclear complexes M4(O2)4(OH)4 as well as their monoprotonated forms are observed for all cations studied. In addition, a complex M2(O2)3 is observed with M=La and a complex

Yamilet Mej??a-Radillo; Anatoly K. Yatsimirsky

2003-01-01

278

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

PubMed

Bond dissociation and formation in diatomic molecules are analyzed in terms of the reaction force F(R) and the reaction force constant kappa(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 kappa(R) comes a two-stage description of dissociation/formation. In dissociation, the first stage involves stretching of the bond, which is opposed by an increasingly negative retarding force F(R). This reaches a minimum and then begins to weaken in the second stage, which is the transition from stretched molecule to free atoms. Bond formation begins with the reverse transition, driven by a positive F(R) which reaches a maximum for the stretched molecule and then becomes a decreasing restoring force. In the stages in which the system is a stretched molecule, kappa(R) is positive with its maximum at the equilibrium bond length; it is zero at the minimum or maximum of F(R), and negative throughout the transition stages, going through a minimum. kappa(R) <0 has been found to characterize the transition portion of a reaction. This description of dissociation/formation is reinforced by computed B3LYP and Hartree-Fock force constants at different atom separations for the singlet molecules. Hartree-Fock wave function stability assessments suggest that, for the single-bonded singlet molecules, the onset of electron unpairing in dissociation comes in the neighborhood of the F(R) minimum. PMID:19052782

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

2009-06-01

279

In vitro complex formation and biodistribution of mouse antitumor monoclonal antibody in cancer patients  

SciTech Connect

The serum clearance and biodistribution of a murine monoclonal antibody were compared to the in vitro complex formation of the antibody with patients' sera. Iodine-125-labeled 9.2.27, an anti-melanoma antibody, was incubated with sera from ten melanoma patients who had received 9.2.27 in an earlier study. Complexes were observed in all patients using size exclusion high performance liquid chromatography and complex formation was partially blocked by nonspecific murine antibody, suggesting the presence of human anti-murine antibody in serum. All patients subsequently underwent imaging studies with ({sup 131}I) 9.2.27 given intravenously. The serum levels of the antibody obtained after the second administration were inversely correlated with the level of in vitro complex formation. Patients whose serum formed high levels of complex showed a rapid serum clearance, high hepatic uptake, and accelerated whole body clearance and urinary excretion of {sup 131}I. This suggests that in patients who receive repetitive administration of murine antibody the serum clearance rate and biodistribution of intravenously injected antibody are altered by antibody complex formation in the serum.

Sakahara, H.; Reynolds, J.C.; Carrasquillo, J.A.; Lora, M.E.; Maloney, P.J.; Lotze, M.T.; Larson, S.M.; Neumann, R.D. (National Cancer Institute, Bethesda, MD (USA))

1989-08-01

280

Stability constants of some metal cation complexes of tetraphenyl p - tert -butylcalix[4]arene tetraketone in nitrobenzene saturated with water  

Microsoft Academic Search

\\u000a Abstract  From extraction experiments and ?-activity measurements, the exchange extraction constants corresponding to the general equilibrium\\u000a $$ {\\\\text{M}}^{2 + } \\\\left( {\\\\text{aq}} \\\\right) + {\\\\mathbf{1}} \\\\cdot {\\\\text{Sr}}^{2 + } \\\\left( {\\\\text{nb}} \\\\right) \\\\rightleftarrows {\\\\mathbf{1}} \\\\cdot {\\\\text{M}}^{2 + } \\\\left( {\\\\text{nb}} \\\\right) + {\\\\text{Sr}}^{2 + } \\\\left( {\\\\text{aq}} \\\\right) $$ taking place in the two-phase water–nitrobenzene system (M2+ = Ca2+, Ba2+, Cu2+, Zn2+, Cd2+,

Emanuel Makrlík; J. Budka; P. Va?ura; P. Selucký

2009-01-01

281

Paramagnetic complexes of manganese(II), iron(III), and gadolinium(III) as contrast agents for magnetic resonance imaging. The influence of stability constants on the biodistribution of radioactive aminopolycarboxylate complexes  

SciTech Connect

Paramagnetic complexes of manganese(II), iron(III), and gadolinium(III) with many ligands appear to undergo ligand substitution in vivo, producing biodistribution data similar to the hydrated metal ions. To identify ligands likely to be valuable in the preparation of paramagnetic contrast agents, a series of aminopolycarboxylate complexes with stability constants increasing in the order iminodiacetic acid (IDA) less than nitrilotriacetic acid (NTA) less than EDTA less than CDTA less than or equal to DTPA was prepared with /sup 54/Mn(II), /sup 59/Fe(III), and /sup 153/Gd(III) at both tracer and carrier levels. Biodistribution studies in mice suggested that complexes remained unchanged in vivo if their stability constants (K1) were approximately greater than 10(16) for Mn(II) and Gd(III) and greater than 10(22) for Fe(III) complexes at tracer levels. Metal complexes with added carrier appeared to be effectively more stable in vivo, possibly due to dissociation and saturation of metal-binding sites. To avoid the accumulation of metal ions in tissues, new paramagnetic contrast agents containing these metal ions will require stability constants equal to or greater than those identified here.

Fornasiero, D.; Bellen, J.C.; Baker, R.J.; Chatterton, B.E.

1987-04-01

282

Studying of kinetics of rear earth ion (REI) nanoscale complex formation by resonant energy transfer  

NASA Astrophysics Data System (ADS)

We observed formation of nanoscale complexes between multivalent REIs (Tb and Eu) and negatively charged DNA wrapped SWNTs, ionized in the water solution. Foerster Resonance Energy Transfer (FRET) was found to be an ideal method to confirm the complex formation. Because of its high sensitivity and non-destructive characterization approach FRET can be used to trace the kinetics of the complex formation. Strong dependence of SWNT photoluminescence (PL) on the REI concentration was detected and interpreted as a competition between the REI absorption on the SWNTs and subsequent FRET enhanced PL and the SWNT agglomeration followed by PL quenching. We measured the distance between REI and SWNT which appears to be much shorter than the one from their relative concentration in solution. We speculate that Manning condensation of the REIs on the SWNT/DNA surface happens thereby significantly reducing their spacing and making FRET possible.

Ignatova, Tetyana; Pristinski, Denis; Rotkin, Slava V.

2011-03-01

283

Hydrogen bond energies of 2-aminopyridine dimer and 2-aminopyridine-2-pyridone complex formation  

NASA Astrophysics Data System (ADS)

The formation energies of 2-aminopyridine dimer and 2-aminopyridine-2-pyridone complex were measured in C 6D 6 solution by 1H-NMR spectroscopy and values of 25.1 and 44.6 kJ/mol were obtained. The former value is about twice the magnitude of hydrogen bond energies which are generally observed for the N---H?N system, and latter value is about half the sum of the formation energies of the 2-aminopyridine and 2-pyridone dimers. The formation energies of 2-aminopyridine dimer and 2-aminopyridine-2-pyridone complex were calculated by the CNDO/2 method, and their formation energies (-? H) were estimated to be 28.5 and 42.8 kJ/mol, respectively.

Inuzuka, Kozo; Fujimoto, Akira

284

Control of cell fate by the formation of an architecturally complex bacterial community.  

PubMed

Bacteria form architecturally complex communities known as biofilms in which cells are held together by an extracellular matrix. Biofilms harbor multiple cell types, and it has been proposed that within biofilms individual cells follow different developmental pathways, resulting in heterogeneous populations. Here we demonstrate cellular differentiation within biofilms of the spore-forming bacterium Bacillus subtilis, and present evidence that formation of the biofilm governs differentiation. We show that motile, matrix-producing, and sporulating cells localize to distinct regions within the biofilm, and that the localization and percentage of each cell type is dynamic throughout development of the community. Importantly, mutants that do not produce extracellular matrix form unstructured biofilms that are deficient in sporulation. We propose that sporulation is a culminating feature of biofilm formation, and that spore formation is coupled to the formation of an architecturally complex community of cells. PMID:18381896

Vlamakis, Hera; Aguilar, Claudio; Losick, Richard; Kolter, Roberto

2008-04-01

285

Metabolic Intermediate Complex Formation of Human Cytochrome P450 3A4 by Lapatinib  

PubMed Central

Lapatinib, an oral breast cancer drug, has recently been reported to be a mechanism-based inactivator of cytochrome P450 (P450) 3A4 and also an idiosyncratic hepatotoxicant. It was suggested that formation of a reactive quinoneimine metabolite was involved in mechanism-based inactivation (MBI) and/or hepatotoxicity. We investigated the mechanism of MBI of P450 3A4 by lapatinib. Liquid chromatography-mass spectrometry analysis of P450 3A4 after incubation with lapatinib did not show any peak corresponding to irreversible modifications. The enzymatic activity inactivated by lapatinib was completely restored by the addition of potassium ferricyanide. These results indicate that the mechanism of MBI by lapatinib is quasi-irreversible and mediated via metabolic intermediate complex (MI complex) formation. This finding was verified by the increase in a signature Soret absorbance at approximately 455 nm. Two amine oxidation products of the metabolism of lapatinib by P450 3A4 were characterized: N-hydroxy lapatinib (M3) and the oxime form of N-dealkylated lapatinib (M2), suggesting that a nitroso or another related intermediate generated from M3 is involved in MI complex formation. In contrast, P450 3A5 was much less susceptible to MBI by lapatinib via MI complex formation than P450 3A4. In addition, P450 3A5 had a significantly lower ability than 3A4 to generate M3, consistent with N-hydroxylation as the initial step in the pathway to MI complex formation. In conclusion, our results demonstrate that the primary mechanism for MBI of P450 3A4 by lapatinib is not irreversible modification by the quinoneimine metabolite, but quasi-irreversible MI complex formation mediated via oxidation of the secondary amine group of lapatinib.

Takakusa, Hideo; Wahlin, Michelle D.; Zhao, Chunsheng; Hanson, Kelsey L.; New, Lee Sun; Chan, Eric Chun Yong

2011-01-01

286

Henry's law constants of 2,2,2-trifluoroethyl formate, ethyl trifluoroacetate, and non-fluorinated analogous esters  

NASA Astrophysics Data System (ADS)

Henry's law constants of two fluorinated esters [CF 3CH 2OC(O)H and C 2H 5OC(O)CF 3] and four related non-fluorinated esters [CH 3OC(O)H, C 2H 5OC(O)H, n-C 3H 7OC(O)H and C 2H 5OC(O)CH 3] were determined at 278-298 K by a column-stripping method. From the van't Hoff equation of H=Hexp[-{?H}/{R}({1}/{T}-{1}/{298})], the H298 (M atm -1) and ? Hsol (kJ mol -1) values obtained were 0.55±0.04, -39±3 (CF 3CH 2OC(O)H); 0.09±0.01, -41±5 (C 2H 5OC(O)CF 3); 4.2±0.2, -33±2 (CH 3OC(O)H); 3.4±0.2, -38±2 (C 2H 5OC(O)H); 2.6±0.1, -42±1 ( n-C 3H 7OC(O)H); and 6.0±0.5, -49±3 (C 2H 5OC(O)CH 3), respectively. Errors reported are at 95% confidence levels and represent precision only. Hydrolysis was observed only for C 2H 5OC(O)CF 3. Replacement of CH 3 by CF 3 decreases H298 values by 6, 11, and 67 times, respectively, for CF 3CH 2OC(O)H, CF 3CH 2OC(O)CH 3, and C 2H 5OC(O)CF 3, while the differences in the ? Hsol values were small with these substitutions. Sodium chloride salting-out effects are examined for all of the esters. C 2H 5OC(O)CF 3 has the largest salting coefficient (0.74). The estimated lifetime of CF 3CH 2OC(O)H suggests that dissolution into seawater serves as a tropospheric sink for this compound. On the basis of the solubility and reactivity of the esters studied herein, clouds and the ocean are discussed as possible sinks for the dissolution of tropospheric CF 3CF 2OC(O)H, which is an atmospheric oxidation product of a substitute for hydrofluorocarbons as CF 3CF 2OCH 3.

Kutsuna, Shuzo; Chen, Liang; Abe, Takashi; Mizukado, Junji; Uchimaru, Tadafumi; Tokuhashi, Kazuaki; Sekiya, Akira

287

Complex formation between azacrown derivatives of dibenzylidenecyclopentanone and alkali-earth metal ions  

Microsoft Academic Search

The complex formation of 2,5-bis[4-(1,7,10,13-tetraoxa-4-azacyclopentadec-4-yl)benzylidene]cyclopentanone and several model compounds, prospective metal-sensitive fluorescent probes, with Mg2+, Ca2+, and Ba2+ ions in acetonitrile was studied. The azacrown derivatives of dibenzylidenecyclopentanone have two complex formation centers, azacrown cycle and carbonyl group. The sequence of binding to these sites is different for different ions. The efficient ejection of the Ca2+ and Ba2+ ions from

A. O. Doroshenko; A. V. Grigorovich; E. A. Posokhov; V. G. Pivovarenko; A. P. Demchenko; A. D. Sheiko

2001-01-01

288

Mass-dependent and -independent fractionation of isotopes in Ni and Pb chelate complex formation reactions  

NASA Astrophysics Data System (ADS)

Mass independent fractionation (MIF) has been a very interesting topic in the field of inorganic isotope chemistry, in particular, geo- and cosmo- chemistry. In the present work, we studied the isotope fractionation of Ni(II) and Pb(II) ions in complex formation with chelating reagent EDTA. To obtain clear results on the mass dependence of the isotope fractionation, we have conducted long-distance ion exchange chromatography of Ni(II) and Pb(II), using chelate complex reagent EDTA. The results apparently show that the isotope fractionation in Ni complex formation system is governed by the mass dependent rule. On the other hand the isotope fractionation in the Pb complex system is governed by the mass independent rule or the nuclear volume effect.

Nomura, Masao; Kudo, Takashi; Adachi, Atsuhiko; Aida, Masao; Fujii, Yasuhiko

2013-11-01

289

ERK phosphorylation potentiates Elk-1-mediated ternary complex formation and transactivation.  

PubMed Central

Induction of the human c-fos proto-oncogene by mitogens depends on the formation of a ternary complex by p62TCF with the serum response factor (SRF) and the serum response element (SRE). We demonstrate that Elk-1, a protein closely related to p62TCF in function, is a nuclear target of two members of the MAP kinase family, ERK1 and ERK2. Phosphorylation of Elk-1 increases the yield of ternary complex in vitro. At least five residues in the C-terminal domain of Elk-1 are phosphorylated upon growth factor stimulation of NIH3T3 cells. These residues are also phosphorylated by purified ERK1 in vitro, as determined by a combination of phosphopeptide sequencing and 2-D peptide mapping. Conversion of two of these phospho-acceptor sites to alanine impairs the formation of ternary complexes by the resulting Elk-1 proteins. Removal of these serine residues also drastically diminishes activation of the c-fos promoter in epidermal growth factor-treated cells. Analogous mutations at other sites impair activation to a lesser extent without affecting ternary complex formation in vitro. Our results indicate that phosphorylation regulates ternary complex formation by Elk-1, which is a prerequisite for the manifestation of its transactivation potential at the c-fos SRE. Images

Gille, H; Kortenjann, M; Thomae, O; Moomaw, C; Slaughter, C; Cobb, M H; Shaw, P E

1995-01-01

290

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

291

Subvolcanic bodies of the Bodrak Complex in the Southwestern Crimea: Structure, composition, and formation conditions  

Microsoft Academic Search

The structure and composition of three subvolcanic bodies of the Bodrak Complex are considered in detail. The data on their\\u000a petrography and results of microprobe and chemical analyses are presented. We arrived at a conclusion about the comagmatic\\u000a relations of two bodies and established different depths of their formation. The chemical composition of olivine in rocks\\u000a of the Bodrak Complex

A. I. Sysolin; N. V. Pravikova

2008-01-01

292

Study on formation of starch–lipid complexes during extrusion-cooking of almond flour  

Microsoft Academic Search

A blend containing almond and wheat flours (about 1:2.5, dry basis) was extruded through a co-rotating twin-screw extruder with a screw diameter of 25mm. The effects of barrel temperature (61.72–118.28°C) and feed moisture (21.17–26.83%) on starch–lipid complex formation (X-ray diffraction, melting enthalpy, and complexing index) as well as on fat loss (which occurs during extrusion processing), break strength, deformability and

Teresa De Pilli; Kirsi Jouppila; Jarno Ikonen; Jarno Kansikas; Antonio Derossi; Carla Severini

2008-01-01

293

Mechanisms of Lipoplex Formation: Dependence of the Biological Properties ofTransfection Complexes on Formulation Procedures  

Microsoft Academic Search

Phospholipid-DNA complexes were made of the cationic triester derivative of phosphatidylcholine, EDOPC (1,2-dioleoyl-sn-glycero-3-ethylphosphocholine), by varying conditions of complex formation, in particular, the rate and direction of mixing, as well as by changing the mode of dispersing the lipid (extrusion or vortexing). The biological effects of variations in the formulation procedure were assessed by measuring transfection activity and cell association in

V. A. Rakhmanova; E. V. Pozharski; R. C. MacDonald

2004-01-01

294

Complex formation of p-nitrocalix[6]arene with rare earth metal ions.  

PubMed

p-Nitrocalix[6]arene (CALX-N6, L) formed a 1:1 metal complex, ML, with light rare earth metal ions (M3+), such as La3+, Pr3+ and Nd3+ except Ce3+, but formed a 1:2 (M(3+):L) complex, ML2 (the charge of the complex is omitted) with heavy rare earth metal ions, such as Sm(3+)-Lu3+ including Y3+. The conditional stability constants of these 1:1 and 1:2 complexes, KML and KML2, were measured by a ligand displacement method using absorption spectrophotometry in 4% (v/v) acetone aqueous solution at pH 9.65 +/- 0.15 and 25 degrees C. PMID:16733323

Kajiwara, Makiko; Koga, Masayoshi; Nishida, Masashi; Yoshida, Isao

2006-03-01

295

Separate and independent control of interfacial band alignments and dielectric constants in transition metal rare earth complex oxides  

Microsoft Academic Search

Spectroscopic studies of transition metal (Tm) and rare earth (Re) oxides, combined with ab initio theory, identify the band edge electronic structure of alternative high-k dielectrics. The lowest conduction band states are derived from anti-bonding transition metal d*-states with a ? symmetry and show strong final state effects. Applied to the complex Tm\\/Re mixed oxides of the general form ReTmO3,

G. Lucovsky; Y. Zhang; J. L. Whitten; D. G. Schlom; J. L. Freeouf

2004-01-01

296

Cation-induced formation of a macro-glucan synthase complex  

SciTech Connect

Incubation of Chaps or digitonin-solubilized membrane proteins from cotton fiber with Ca{sup 2+} in combination with Mg{sup 2+}, leads to formation of a complex which can be sedimented within 15 min at 15,000 g. The complex is enriched >10-fold in callose synthase activity and possesses a characteristic pattern of enriched polypeptides when analyzed by SDS-PAGE. Although cation dependent, formation of the complex is not dependent upon the presence of the callose synthase substrate, UDP-glc, indicating that complex formation is not due to entrapment of the enzyme by association with glucan product. The enriched polypeptides include: >200, 50, and 46 kD, all of which have been shown by direct photo-labeling to interact with {sup 92}P-UDP-glc in a Ca{sup 2+} or beta-glucoside dependent reaction are considered likely subunits of callose synthase; a 60-62 kD doublet which is recognized by our MAb 2-1 which can form an immune complex with callose synthase; 74 and 34 kD polypeptides which also interact with UDP-glc, but do not associate with callose synthase in the presence of EDTA. A similar phenomenon is also observed with solubilized membrane proteins from mung beans. Possible functions of each of the enriched polypeptides, the catalytic properties, and ultra-structure of this macro-glucan synthase complex are currently under investigation.

Delmer, D.; Solomon, M.; Andrawis, A.; Amor, Y. (Hebrew Univ., Jerusalem (Israel))

1990-05-01

297

Simulation of the effects of complex- formation equilibria in electrophoresis: I. mathematical model.  

PubMed

Simul 5 Complex is a one-dimensional dynamic simulation software designed for electrophoresis, and it is based on a numerical solution of the governing equations, which include electromigration, diffusion and acid-base equilibria. A new mathematical model has been derived and implemented that extends the simulation capabilities of the program by complexation equilibria. The simulation can be set up with any number of constituents (analytes), which are complexed by one complex-forming agent (ligand). The complexation stoichiometry is 1:1, which is typical for systems containing cyclodextrins as the ligand. Both the analytes and the ligand can have multiple dissociation states. Simul 5 Complex with the complexation mode runs under Windows and can be freely downloaded from our web page http://natur.cuni.cz/gas. The article has two separate parts. Here, the mathematical model is derived and tested by simulating the published results obtained by several methods used for the determination of complexation equilibrium constants: affinity capillary electrophoresis, vacancy affinity capillary electrophoresis, Hummel-Dreyer method, vacancy peak method, frontal analysis, and frontal analysis continuous capillary electrophoresis. In the second part of the paper, the agreement of the simulated and the experimental data is shown and discussed. PMID:22528414

Hruška, Vlastimil; Beneš, Martin; Svobodová, Jana; Zusková, Iva; Gaš, Bohuslav

2012-03-01

298

Validated Stability indicating Spectrophotometric Method for the Determination of Acetazolamide in Dosage Forms through Complex Formation with Palladium (II)  

PubMed Central

A simple and sensitive spectrophotometric method was developed for the determination of acetazolamide (ACM) in pure form and pharmaceutical preparations. The proposed method is based on the complex formation of acetazolamide with Palladium (II) chloride in acetate buffer pH5.4 and measuring the absorbance at 308 nm. The absorbance- concentration plot was rectilinear over the concentration range of 5-70 ?g/ml with a minimum detection limit (LOD) of 0.98 ?g/ml, limit of quantification (LOQ) of 2.96 ?g/ml, and a molar absorptivity ?=2.7 × 103 L/mol.cm. The factors affecting the absorbance of the formed complex were carefully studied and optimized. The composition of the complex as well as its stability constant was also investigated. The proposed method was applied for the determination of acetazolamide in its tablets and the results obtained were favorably compared with those obtained using the official method. A proposal of the reaction pathway was postulated.

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

2010-01-01

299

Complex formation between neptunium(V) and N,N'-bis(salicylidene)ethylenediamine in aqueous alcohol solutions  

SciTech Connect

Complex formation between neptunium(V) and N,N'-bis(salicylidene)ethylenediamine has been studied spectrophotometrically in aqueous alcohol solutions in the pH range 6-10 and at t = 25 +/- 1/sup 0/C and ..mu.. = 0.05. Only one complex has been shown to be formed with this ligand system under the experimental conditions examined; it is a mononuclear complex of composition NpO/sub 2/X/sup -/. The concentration stability constant and molar extinction coefficient for NpO/sub 2/X/sup -/ have been determined and lambda/sub max/ = 1002 nm, and are equal to (3.2 +/- 0.27) x 10/sup 7/ (log ..beta.. = 7.5 +/- 0.035) and 500 +/- 3 liter/mole cm, respectively. Based on the results obtained herein, it is proposed that the compound formed between Np(V) and N,N'-bis(salicylidene)ethylenediamine can be used for the spectrophotometric determination of neptunium(V) in aqueous alcohol solutions.

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

1987-01-01

300

Complex formation equilibria of binary and ternary complexes involving 3,3-bis(1-methylimidazol-2yl)propionic acid and bio-relevant ligands as 1-aminocyclopropane carboxylic acid with reference to plant hormone.  

PubMed

The formation equilibria for the binary complexes of Cu(II) with 1-aminocyclopropane carboxylic acid (ACC) and 3,3-bis(1-methylimidazol-2-yl)propionic acid (BIMP) were investigated. ACC and BIMP form the complexes 110, 120 and 11-1. The ternary complexes of Cu(II) with BIMP and biorelevant ligands as some selected amino acids, peptides and DNA constituents are formed in a stepwise mechanism. The stability constants of the complexes formed were determined and their distribution diagrams were evaluated. The kinetics of hydrolysis of glycine methyl ester in presence of [Cu(BIMP)](+) was investigated by pH-stat technique and the mechanism was discussed. PMID:24051283

Shoukry, Mohamed M; Hassan, Safaa S

2014-01-24

301

Complex formation equilibria of binary and ternary complexes involving 3,3-bis(1-methylimidazol-2yl)propionic acid and bio-relevant ligands as 1-aminocyclopropane carboxylic acid with reference to plant hormone  

NASA Astrophysics Data System (ADS)

The formation equilibria for the binary complexes of Cu(II) with 1-aminocyclopropane carboxylic acid (ACC) and 3,3-bis(1-methylimidazol-2-yl)propionic acid (BIMP) were investigated. ACC and BIMP form the complexes 1 1 0, 1 2 0 and 1 1 -1. The ternary complexes of Cu(II) with BIMP and biorelevant ligands as some selected amino acids, peptides and DNA constituents are formed in a stepwise mechanism. The stability constants of the complexes formed were determined and their distribution diagrams were evaluated. The kinetics of hydrolysis of glycine methyl ester in presence of [Cu(BIMP)]+ was investigated by pH-stat technique and the mechanism was discussed.

Shoukry, Mohamed M.; Hassan, Safaa S.

2014-01-01

302

Stability constants of complexes of Zn 2+ , Cd 2+ , and Hg 2+ with organic ligands: QSPR consensus modeling and design of new metal binders  

Microsoft Academic Search

QSPR modeling of the stability constant log K of the complexes of Zn2+, Cd2+ and Hg2+ with various 556 (Zn2+), 347 (Cd2+) and 76 (Hg2+) organic ligands in water for the M2+ + L = (M2+)L equilibrium at 298 K and an ionic strength 0.1 M was performed. Two machine-learning methods were used: Multiple Linear\\u000a Regression Analysis (MLR) and Partial Robust M-regression Algorithm (PRM). The PRM

Vitaly Solov’ev; Igor Sukhno; Vladimir Buzko; Aleksey Polushin; Gilles Marcou; Aslan Tsivadze; Alexandre Varnek

303

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

304

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.

305

Identification of functional targets of the Zta transcriptional activator by formation of stable preinitiation complex intermediates.  

PubMed

Transcriptional activator proteins stimulate the formation of a preinitiation complex that may be distinct from a basal-level transcription complex in its composition and stability. Components of the general transcription factors that form activator-dependent stable intermediates were determined by the use of Sarkosyl and oligonucleotide challenge experiments. High-level transcriptional activation by the Epstein-Barr virus-encoded Zta protein required an activity in the TFIID fraction that is distinct from the TATA-binding protein (TBP) and the TBP-associated factors. This additional activity copurifies with and is likely to be identical to the previously defined coactivator, USA (M. Meisterernst, A. L. Roy, H. M. Lieu, and R. G. Roeder, Cell 66:981-994, 1991). The formation of a stable preinitiation complex intermediate resistant to Sarkosyl required the preincubation of the promoter DNA with Zta, holo-TFIID (TBP and TBP-associated factors), TFIIB, TFIIA, and the coactivator USA. The formation of a Zta response element-resistant preinitiation complex required the preincubation of promoter DNA with Zta, holo-TFIID, TFIIB, and TFIIA. Agarose gel electrophoretic mobility shift showed that a preformed Zta-holo-TFIID-TFIIA complex was resistant to Sarkosyl and to Zta response element oligonucleotide challenge. DNase I footprinting suggests that only Zta, holo-TFIID, and TFIIA make significant contacts with the promoter DNA. These results provide functional and physical evidence that the Zta transcriptional activator influences at least two distinct steps in preinitiation complex assembly, the formation of the stable holo-TFIID-TFIIA-promoter complex and the subsequent binding of TFIIB and a USA-like coactivator. PMID:7969171

Lieberman, P

1994-12-01

306

Stability and Solubility Constants for Silver Halides in Propionitrile-Sulfur Dioxide Mixtures.  

National Technical Information Service (NTIS)

Studies on the complex solubilities of AgCl, AgBr, and AgI are reported in propionitrile (PN) and in PN-SO2 mixtures. Values of the complex ion formation constant and the stability constant were found to decrease rapidly upon addition of SO2 to PN while t...

B. K. Stevenson M. Salomon

1973-01-01

307

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.

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

308

STUDY USING A THREE-DIMENSIONAL SMOG FORMATION MODEL UNDER CONDITIONS OF COMPLEX FLOW  

EPA Science Inventory

To clarify the photochemical smog formation mechanisms under conditions of complex flow, the SAI Urban Airshed Model was evaluated using a 1981 field observed data base. In the Tokyo Metropolitan Area higher O3 concentrations are usually observed near the shore in the morning. As...

309

Formation of an Equilibrium Complex of Lactate Dehydrogenase with Chlorin e 6  

Microsoft Academic Search

Using spectrophotometric, spectral-luminescent, and polarization methods, we have detected the formation of strong equilibrium complexes of a key glycolytic enzyme — lactate dehydrogenase — with a promising photodynamic sensitizer — chlorin e6. It has been established that enzymes serve as the most sensitive targets destroying tumor cells subjected to photodynamic therapy.

V. Yu. Plavskii; V. A. Mostovnikov; G. R. Mostovnikova; A. I. Tret'yakova; A. V. Mikulich

2003-01-01

310

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

311

Filopodia Formation in the Absence of Functional WAVE- and Arp2/3-Complexes  

PubMed Central

Cell migration is initiated by plasma membrane protrusions, in the form of lamellipodia and filopodia. The latter rod-like projections may exert sensory functions and are found in organisms as distant in evolution as mammals and amoeba such as Dictyostelium discoideum. In mammals, lamellipodia protrusion downstream of the small GTPase Rac1 requires a multimeric protein assembly, the WAVE-complex, which activates Arp2/3-mediated actin filament nucleation and actin network assembly. A current model of filopodia formation postulates that these structures arise from a dendritic network of lamellipodial actin filaments by selective elongation and bundling. Here, we have analyzed filopodia formation in mammalian cells abrogated in expression of essential components of the lamellipodial actin polymerization machinery. Cells depleted of the WAVE-complex component Nck-associated protein 1 (Nap1), and, in consequence, of lamellipodia, exhibited normal filopodia protrusion. Likewise, the Arp2/3-complex, which is essential for lamellipodia protrusion, is dispensable for filopodia formation. Moreover, genetic disruption of nap1 or the WAVE-orthologue suppressor of cAMP receptor (scar) in Dictyostelium was also ineffective in preventing filopodia protrusion. These data suggest that the molecular mechanism of filopodia formation is conserved throughout evolution from Dictyostelium to mammals and show that lamellipodia and filopodia formation are functionally separable.

Steffen, Anika; Faix, Jan; Resch, Guenter P.; Linkner, Joern; Wehland, Juergen; Small, J. Victor

2006-01-01

312

Catalytic role of Mn(IV) oxide in the formation of humic-enzyme complexes in the soil ecosystem  

Microsoft Academic Search

We investigated the effects of short-range ordered Mn(IV), Fe(III), and Al oxides, which are common in soils, on the formation of phenolic-enzyme complexes. Mn(IV) oxide (birnessite) markedly promoted the formation of phenolic-lysozyme complexes with different molecular weights (17–68 kD) in the hydroquinone (diphenol)-lysozyme (enzyme) system. However, promotive effects of Fe(III) and Al oxides on the formation of the complexes were

Haruo Shindo; Toru Oshita; Naotoshi Matsudomi; Keiji Usui; Tee Boon Goh

1996-01-01

313

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

314

Structure and kinetics of formation of catechol complexes of ferric soybean lipoxygenase-1  

SciTech Connect

Ferric soybean lipoxygenase forms stable complexes with 4-substituted catechols. The structure of the complex between the enzyme and 3,4-dihydroxybenzonitrile has been studied by resonance Raman, electron paramagnetic resonance, visible, and X-ray spectroscopies. It is a bidentate iron-catecholate complex with at least one water ligand. The kinetics of formation of complexes between lipoxygenase and 3,4-dihydroxybenzonitrile and 3,4-dihydroxyacetophenone have been studied by stopped-flow spectroscopy. The data are consistent with two kinetically distinct, reversible steps. The pH dependence of the first step suggests that the substrate for the reaction is the catechol monoanion. When these results are combined, plausible mechanisms for the complexation reaction are suggested. 51 refs., 12 figs., 2 tabs.

Nelson, M.J.; Brennan, B.A.; Chase, D.B. [E.I. du Pont de Nemours & Co., Wilmington, DE (United States)]|[Haverford College, PA (United States)] [and others

1995-11-21

315

Formation and Reactivity of a Persistent Radical in a Dinuclear Molybdenum Complex  

SciTech Connect

The reactivity of the S-H bond in Cp*Mo(? S)2(? SMe)(? SH)MoCp* has been explored by hydrogen atom abstraction to form the radical Cp*Mo(? S)3(? SMe)MoCp*, as well as hydrogen addition to the radical to reform the S-H complex. The rate expression for abstraction of hydrogen atom by benzyl radical has been determined, giving log(kabs/M 1 s 1) = (2.41 ? 0.37)/(2.303RT) + (7.88 ? 0.25) with kabs = 1.3 x 106 M 1 s 1 at 25?C. The radical termination product of the Mo2S4 core was found to be the benzyl cross-termination product, Cp*Mo(? S)2(? SMe)(? SBz)MoCp*. Structures are presented for this complex as well as the cationic Cp*Mo(? S2)(? S)(? SMe)MoCp*(OTf), a precursor of the radical and the alkylated derivatives. The radical undergoes reversible dimerization to form the tetranuclear complex (Cp*Mo(? S)2(? SMe)MoCp*)2(? S2), as shown by the solid state structure. In solution, the radical and the dimer are in equilibrium, and the equilibrium constant for dimerization has been estimated from magnetic susceptibility and EPR data. The rate of dissociation of the dimer has been determined to be 640 s-1 at 25?C, based on variable temperature 1H NMR data. The rate constant for dimerization of the radical has been estimated to be ?1x107 M-1 s-1, based on the dimer dissociation rate constant and the lower limit of the equilibrium constant for dimerization.

Appel, Aaron M.; Lee, Suh-Jane; Franz, James A.; DuBois, Daniel L.; Rakowski DuBois, Mary; Birnbaum, Jerome C.; Twamley, Brendan

2008-07-16

316

Terabit bandwidth-adaptive transmission using low-complexity format-transparent digital signal processing.  

PubMed

In this paper, we propose a low-complexity format-transparent digital signal processing (DSP) scheme for next generation flexible and energy-efficient transceiver. It employs QPSK symbols as the training and pilot symbols for the initialization and tracking stage of the receiver-side DSP, respectively, for various modulation formats. The performance is numerically and experimentally evaluated in a dual polarization (DP) 11 Gbaud 64QAM system. Employing the proposed DSP scheme, we conduct a system-level study of Tb/s bandwidth-adaptive superchannel transmissions with flexible modulation formats including QPSK, 8QAM and 16QAM. The spectrum bandwidth allocation is realized in the digital domain instead of turning on/off sub-channels, which improves the performance of higher order QAM. Various transmission distances ranging from 240 km to 6240 km are demonstrated with a colorless detection for hardware complexity reduction. PMID:24663520

Zhuge, Qunbi; Morsy-Osman, Mohamed; Chagnon, Mathieu; Xu, Xian; Qiu, Meng; Plant, David V

2014-02-10

317

Standard thermodynamic functions of complex formation between Cu2+ and glycine in aqueous solution  

NASA Astrophysics Data System (ADS)

Heat effects of the interaction of copper(II) solutions with aminoacetic acid (glycine) are measured by the direct calorimetry at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 against a background of potassium nitrate. Standard enthalpy values for reactions of the formation of aminoacetic acid copper complexes in aqueous solutions are obtained using an equation with a single individual parameter by extrapolating it to zero ionic strength. The standard thermodynamic characteristics of complex formation in the Cu2+-glycine system are calculated. It is shown that glycine-like coordination is most likely in Cu(II) complexes with L-asparagine, L-glutamine, and L-valine.

Gorboletova, G. G.; Metlin, A. A.

2013-05-01

318

Enhanced CO2 hydrate formation kinetic under organo-mineral complex environment  

NASA Astrophysics Data System (ADS)

CO2 hydrate formation under marine sediments can be one of the feasible options to mitigate atmospheric concentration of CO2, main source of global warming. For the better application of CO2 sequestration via hydrate form under ocean, it is indispensable to understand the effects of marine environmental factors on hydrate formation kinetic and equilibrium. In this study, we investigated the effect of organo-mineral complex (i.e., Na-montmorillonite (Na-MMT) and glycine complex) on hydrate formation kinetic both experimentally and computationally. Organo-mineral complex suspension showed much more favorable hydrate formation kinetic (2-6 min) than pure water control (48-80 min). TEM image showed that glycine are well distributed and strongly adsorbed on Na-MMT surface and FT/IR results (i.e., increased frequency of N-H stretch) also proved that amine part of glycine can make strong hydrogen bonding with silicon atoms of Na-MMT. Molecular dynamics (MD) simulation was performed to fully understand the CO2 hydrate nucleation on the organo-mineral complex and its result showed that high concentration of CO2 molecules are located near Na-MMT surface and glycine attached on Na-MMT can attract water molecules to form intermediate hydrate structure. This one plays a key role in complete hydrate formation as nucleation seeds and can significantly enhance the hydrate formation kinetic. This fundamental knowledge could provide idea to select proper CO2 storage site under marine sediments and be applied to in-situ swapping technology to recover CH4 from deep sea gas hydrate deposits and sequester the CO2 to CH4 hydrate layer.

Kyung, D.; Lee, W.

2012-12-01

319

Shock-tube measurement of the rate constant for excited OH (A/sup 2/. sigma. /sup +/) formation in the hydrogen-oxygen reaction  

SciTech Connect

H/sub 2/-O/sub 2/ mixtures highly diluted with Ar were heated to temperatures in the range 1200 to 3200/sup 0/K behind reflected shock waves. The intensity and temporal variation of emission from the OH* A/sup 2/..sigma../sup +/-X/sup 2/II transition were studied in order to determine the reaction and rate constant for OH* formation. The OH* was found to be formed mainly by the reaction H + O + M = OH* + M under the experimental conditions below 2000/sup 0/K; thermal emission made significant contributions at higher temperatures. The rate constant was found to be k/sub 1/ = 1.2 x 10/sup 13/exp(-6940 cal/RT) cm/sup 6/mol/sup -2/s/sup -1/. This expression accounts for the OH* intensity and its temporal variation, including the ignition delay times t/sub m/ and t/sub m/ and t/sub 5/, for the experimental conditions used.

Hidaka, Y. (Ehime Univ., Matsuyama, Japan); Takahashi, S.; Kawano, H.; Suga, M.; Gardiner, W.C. Jr.

1982-04-15

320

Notable effects of metal salts on UV-vis absorption spectra of ?-, ?-, ?-, and ?-tocopheroxyl radicals in acetonitrile solution. The complex formation between tocopheroxyls and metal cations.  

PubMed

The measurements of the UV-vis absorption spectra of ?-, ?-, ?-, and ?-tocopheroxyl (?-, ?-, ?-, and ?-Toc(•)) radicals were performed by reacting aroxyl (ArO(•)) radical with ?-, ?-, ?-, and ?-tocopherol (?-, ?-, ?-, and ?-TocH), respectively, in acetonitrile solution including three kinds of alkali and alkaline earth metal salts (LiClO(4), NaClO(4), and Mg(ClO(4))(2)) (MX or MX(2)), using stopped-flow spectrophotometry. The maximum wavelengths (?(max)) of the absorption spectra of the ?-, ?-, ?-, and ?-Toc(•) located at 425-428 nm without metal salts increased with increasing concentrations of metal salts (0-0.500 M) in acetonitrile and approached some constant values, suggesting (Toc(•)···M(+) (or M(2+))) complex formations. Similarly, the values of the apparent molar extinction coefficient (?(max)) increased drastically with increasing concentrations of metal salts in acetonitrile and approached some constant values. The result suggests that the formations of Toc(•) dimers were suppressed by the metal ion complex formations of Toc(•) radicals. The stability constants (K) were determined for Li(+), Na(+), and Mg(2+) complexes of ?-, ?-, ?-, and ?-Toc(•). The K values increased in the order of NaClO(4) < LiClO(4) < Mg(ClO(4))(2), being independent of the kinds of Toc(•) radicals. Furthermore, the K values increased in the order of ?- < ?- < ?- < ?-Toc(•) radicals for each metal salt. The alkali and alkaline earth metal salts having a smaller ionic radius of the cation and a larger charge of the cation gave a larger shift of the ?(max) value, a larger ?(max) value, and a larger K value. The result of the DFT molecular orbital calculations indicated that the ?-, ?-, ?-, and ?-Toc(•) radicals were stabilized by the (1:1) complex formation with metal cations (Li(+), Na(+), and Mg(2+)). Stabilization energy (E(S)) due to the complex formation increased in the order of Na(+) < Li(+) < Mg(2+) complexes, being independent of the kinds of Toc(•) radicals. The calculated result also indicated that the metal cations coordinate to the O atom at the sixth position of ?-, ?-, ?-, and ?-Toc(•) radicals. PMID:22775471

Mukai, Kazuo; Kohno, Yutaro; Ouchi, Aya; Nagaoka, Shin-ichi

2012-08-01

321

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

322

Spectrophotometric determination of penicillamine and carbocisteine based on formation of metal complexes.  

PubMed

A simple spectrophotometric method was developed for the determination of penicillamine and carbocisteine. The method depends on complexation of penicillamine with Ni, Co and Pb ions in acetate buffer pH of 6.3, 6.5 and 5.3, respectively, and carbocisteine with Cu and Ni ions in borate buffer pH of 6.7; 1-70 microg/ml of these drugs could be determined by measuring the absorbance of each complex at its specific lambdamax. The results obtained are in good agreement with those obtained using the official methods. The proposed method was successfully applied for the determination of these compounds in their dosage forms. Also, the molar ratio and stability constant of the metal complexes were calculated and a proposal of the reaction pathway was postulated. PMID:15178313

Walash, M I; El-Brashy, A M; Metwally, M E-S; Abdelal, A A

2004-06-01

323

Hydrogen-bonding and protonation effects on the formation of charge transfer complex between para-benzoquinone and 2,6-dimethoxy phenol  

NASA Astrophysics Data System (ADS)

Formation of CT complex of series of quinines of increasing basicity (chloranil to duroquinone) were checked systematically in methylenechloride with different aromatic donors in presence of hydroxylic additives of increasing hydrogen-bonding power (tetra-butyl-alcohol to hexafluoro-2-propanol) or acidity. The effect of the basic additives of increasing basicity (pyridine to 4- N, N-dimethylaminopyridine) was also observed. The formation constant ( KCT) of CT complex between para-benzoquinone and 2,6-dimthoxyphenol was enhanced approximately 50 times by TFA and approximately two times by HFIPA due to protonation and strong hydrogen-bonding interaction of BQ with TFA and HPIPA, respectively. Similarly, KCT increased approximately six times by DMAPy due to hydrogen-bonding with DMOPh.

Bangal, Prakriti Ranjan

2005-01-01

324

DNA supercoiling facilitates formation of the transcription initiation complex on the fibroin gene promoter.  

PubMed

Transcription of the Bombyx mori fibroin gene in a posterior silk gland extract can be separated into three functional steps on the basis of sensitivity to Sarkosyl: 1) formation of an initiation complex, which is blocked by 0.025% Sarkosyl; 2) conversion of the initiation complex to an elongation complex, a step sensitive to 0.05% Sarkosyl; 3) the subsequent elongation of RNA chain which occurs in the presence of 0.05% Sarkosyl. Whereas the last two steps are rapid and unaffected by template topology, the first step is slow and affected by DNA conformation. In the posterior silk gland extract, closed circular DNA forms a superhelical state and supports more rapid assembly of the initiation complex than linear DNA does. Both DNA supercoiling and rapid assembly of the initiation complex require ATP and are abolished by the addition of a topoisomerase II inhibitor VP16. These results suggest that DNA supercoiling enhances the fibroin gene transcription by facilitating formation of the initiation complex. PMID:2459121

Tabuchi, H; Hirose, S

1988-10-25

325

Complex formation with nucleic acids and aptamers alters the antigenic properties of platelet factor 4  

PubMed Central

The tight electrostatic binding of the chemokine platelet factor 4 (PF4) to polyanions induces heparin-induced thrombocytopenia, a prothrombotic adverse drug reaction caused by immunoglobulin G directed against PF4/polyanion complexes. This study demonstrates that nucleic acids, including aptamers, also bind to PF4 and enhance PF4 binding to platelets. Systematic assessment of RNA and DNA constructs, as well as 4 aptamers of different lengths and secondary structures, revealed that increasing length and double-stranded segments of nucleic acids augment complex formation with PF4, while single nucleotides or single-stranded polyA or polyC constructs do not. Aptamers were shown by circular dichroism spectroscopy to induce structural changes in PF4 that resemble those induced by heparin. Moreover, heparin-induced anti-human–PF4/heparin antibodies cross-reacted with human PF4/nucleic acid and PF4/aptamer complexes, as shown by an enzyme immunoassay and a functional platelet activation assay. Finally, administration of PF4/44mer–DNA protein C aptamer complexes in mice induced anti–PF4/aptamer antibodies, which cross-reacted with murine PF4/heparin complexes. These data indicate that the formation of anti-PF4/heparin antibodies in postoperative patients may be augmented by PF4/nucleic acid complexes. Moreover, administration of therapeutic aptamers has the potential to induce anti-PF4/polyanion antibodies and a prothrombotic diathesis.

Jaax, Miriam E.; Krauel, Krystin; Marschall, Thomas; Brandt, Sven; Gansler, Julia; Furll, Birgitt; Appel, Bettina; Fischer, Silvia; Block, Stephan; Helm, Christiane A.; Muller, Sabine; Preissner, Klaus T.

2013-01-01

326

Complex formation, chemical exchange, species structure, and stereoselective effects in the copper(II)-L/DL-histidine systems.  

PubMed

The formation of copper(II) complexes with L- and DL-histidine (HisH) has been studied by means of pH-potentiometry and spectrophotometry over a wide range of pH (2-14), ligand-to-metal ratio (1?:?1-15?:?1), and temperature (15-55 °C) in aqueous solutions with 1.0 mol dm(-3) KNO(3) as background. Formation constants and spectral characteristics of 13 complex types were found. Fine stereoselective effects have been detected with preferential coordination of two ligands with identical configuration in Cu(His)(HisH)(+) and opposite configuration in Cu(His)(2). The stereoselective effect for Cu(His)(HisH)(+) is explained by hydrogen bond formation between the carboxyl and imidazolyl groups of neighboring ligands at cis-arrangement of amino groups (3N(eq)-form). The opposite sign of stereoselective effect for Cu(His)(2) is derived from favourable axial coordination of the imidazole group in meso-form with cis-structure (3N(eq)N(ax)-form). A significant tetrahedral distortion was revealed for the first time in the prevalent cis-isomer of the Cu(L-His)(2) 4N(eq)-form. These findings were confirmed by EPR data and DFT computations at the B3LYP/TZVP level. The prevalence of cis-isomers for these complexes has been assigned to the rather strong trans effect of the amino groups. The structures of other detected complexes are briefly discussed on the basis of spectroscopic data. Chemical exchange reactions in the copper(II)-L/DL-hishidine systems have been investigated by the NMR relaxation of water protons. A unique proton exchange reaction with short-term proton dissociation from the coordinated imidazolyl group catalyzed by hydroxide ion was characterised for the first time. The discovered enantioselective effects in the ligand exchange reactions between Cu(His)(2) and HisH or His(-) species were attributed to the associative substitution mechanism. PMID:22120906

Shtyrlin, Valery G; Zyavkina, Yulia I; Gilyazetdinov, Edward M; Bukharov, Mikhail S; Krutikov, Alexander A; Garipov, Ruslan R; Mukhtarov, Anvar S; Zakharov, Alexey V

2012-01-28

327

Protein complex directs hemoglobin-to-hemozoin formation in Plasmodium falciparum  

PubMed Central

Malaria parasites use hemoglobin (Hb) as a major nutrient source in the intraerythrocytic stage, during which heme is converted to hemozoin (Hz). The formation of Hz is essential for parasite survival, but to date, the underlying mechanisms of Hb degradation and Hz formation are poorly understood. We report the presence of a ?200-kDa protein complex in the food vacuole that is required for Hb degradation and Hz formation. This complex contains several parasite proteins, including falcipain 2/2?, plasmepsin II, plasmepsin IV, histo aspartic protease, and heme detoxification protein. The association of these proteins is evident from coimmunoprecipitation followed by mass spectrometry, coelution from a gel filtration column, cosedimentation on a glycerol gradient, and in vitro protein interaction analyses. To functionally characterize this complex, we developed an in vitro assay using two of the proteins present in the complex. Our results show that falcipain 2 and heme detoxification protein associate with each other to efficiently convert Hb to Hz. We also used this in vitro assay to elucidate the modes of action of chloroquine and artemisinin. Our results reveal that both chloroquine and artemisinin act during the heme polymerization step, and chloroquine also acts at the Hb degradation step. These results may have important implications in the development of previously undefined antimalarials.

Chugh, Monika; Sundararaman, Vidhya; Kumar, Saravanan; Reddy, Vanga S.; Siddiqui, Waseem A.; Stuart, Kenneth D.; Malhotra, Pawan

2013-01-01

328

Formation of a ligand-assisted complex of two RNA hairpin loops.  

PubMed

The hairpin structure is one of the most common secondary structures in RNA and holds a central position in the stream of RNA folding from a non-structured RNA to structurally complex and functional ribonucleoproteins. Since the RNA secondary structure is strongly correlated to the function and can be modulated by the binding of small molecules, we have investigated the modulation of RNA folding by a ligand-assisted formation of loop-loop complexes of two RNA hairpin loops. With a ligand (NCT6), designed based on the ligand binding to the G-G mismatches in double-stranded DNA, we successfully demonstrated the formation of both inter- and intra-molecular NCT6-assisted complex of two RNA hairpin loops. NCT6 selectively bound to the two hairpin loops containing (CGG)3 in the loop region. Native polyacrylamide gel electrophoresis analysis of two doubly-labeled RNA hairpin loops clearly showed the formation of intermolecular NCT6-assisted loop-loop complex. Förster resonance energy-transfer studies of RNA constructs containing two hairpin loops, in which each hairpin was labeled with Alexa488 and Cy3 fluorophores, showed the conformational change of the RNA constructs upon binding of NCT6. These experimental data showed that NCT6 simultaneously bound to two hairpin RNAs at the loop region, and can induce the conformational change of the RNA molecule. These data strongly support that NCT6 functions as molecular glue for two hairpin RNAs. PMID:24644006

Hong, Changfeng; Otabe, Takahiro; Matsumoto, Saki; Dohno, Chikara; Murata, Asako; Hagihara, Masaki; Nakatani, Kazuhiko

2014-04-25

329

A QUANTITATIVE KINETIC SCHEME FOR 70S TRANSLATION INITIATION COMPLEX FORMATION  

PubMed Central

SUMMARY Association of the 30S initiation complex (30SIC) and the 50S ribosomal subunit, leading to formation of the 70S initiation complex (70SIC), is a critical step of the translation initiation pathway. The 70SIC contains initiator tRNA, fMet-tRNAfMet, bound in the P (peptidyl)-site in response to the AUG start codon. We have formulated a quantitative kinetic scheme for the formation of an active 70SIC from 30SIC and 50S subunits on the basis of parallel rapid kinetics measurements of GTP hydrolysis, Pi release, light scattering, and changes in fluorescence intensities of fluorophore-labeled IF2 and fMet-tRNAfMet. According to this scheme, an initially formed labile 70S complex, which promotes rapid IF2-dependent GTP hydrolysis, either dissociates reversibly into 30S and 50S subunits or is converted to a more stable form, leading to 70SIC formation. The latter process takes place with intervening conformational changes of ribosome-bound IF2 and fMet-tRNAfMet, which are monitored by spectral changes of fluorescent derivatives of IF2 and fMet-tRNAfMet. The availability of such a scheme provides a useful framework for precisely elucidating the mechanisms by which substituting the nonhydrolyzable analogue GDPCP for GTP or adding thiostrepton inhibit formation of a productive 70SIC. GDPCP does not affect stable 70S formation, but perturbs fMet-tRNAfMet positioning in the P-site. In contrast, thiostrepton severely retards stable 70S formation, but allows normal binding of fMet-tRNAfMet(prf20) to the P-site.

Grigoriadou, Christina; Marzi, Stefano; Kirillov, Stanislas; Gualerzi, Claudio O.; Cooperman, Barry S.

2007-01-01

330

A quantitative kinetic scheme for 70 S translation initiation complex formation.  

PubMed

Association of the 30 S initiation complex (30SIC) and the 50 S ribosomal subunit, leading to formation of the 70 S initiation complex (70SIC), is a critical step of the translation initiation pathway. The 70SIC contains initiator tRNA, fMet-tRNA(fMet), bound in the P (peptidyl)-site in response to the AUG start codon. We have formulated a quantitative kinetic scheme for the formation of an active 70SIC from 30SIC and 50 S subunits on the basis of parallel rapid kinetics measurements of GTP hydrolysis, Pi release, light-scattering, and changes in fluorescence intensities of fluorophore-labeled IF2 and fMet-tRNA(f)(Met). According to this scheme, an initially formed labile 70 S complex, which promotes rapid IF2-dependent GTP hydrolysis, either dissociates reversibly into 30 S and 50 S subunits or is converted to a more stable form, leading to 70SIC formation. The latter process takes place with intervening conformational changes of ribosome-bound IF2 and fMet-tRNA(fMet), which are monitored by spectral changes of fluorescent derivatives of IF2 and fMet-tRNA(fMet). The availability of such a scheme provides a useful framework for precisely elucidating the mechanisms by which substituting the non-hydrolyzable analog GDPCP for GTP or adding thiostrepton inhibit formation of a productive 70SIC. GDPCP does not affect stable 70 S formation, but perturbs fMet-tRNA(fMet) positioning in the P-site. In contrast, thiostrepton severely retards stable 70 S formation, but allows normal binding of fMet-tRNA(fMet)(prf20) to the P-site. PMID:17868692

Grigoriadou, Christina; Marzi, Stefano; Kirillov, Stanislas; Gualerzi, Claudio O; Cooperman, Barry S

2007-10-26

331

Cyclin-dependent kinase promotes formation of the synaptonemal complex in yeast meiosis.  

PubMed

Cyclin-dependent protein kinases (CDKs) are required for various cell cycle events both in mitosis and in meiosis. During the meiotic prophase of Saccharomyces cerevisiae, only one CDK, Cdc28, which forms a complex with B-type cyclins, Clb5 or Clb6, promotes not only the onset of premeiotic DNA replication but also the formation of meiotic double-strand breaks (DSBs). In this study, we showed that Cdc28 exhibits punctate staining on chromosomes during meiotic prophase I. Chromosomal localization of Cdc28, dependent on Clb5 and/or Clb6, is frequently observed in zygotene and pachytene, when formation of the synaptonemal complex (SC) occurs. Interestingly, the CDK localization is independent of DSB formation, but rather dependent on meiosis-specific chromosome components such as Red1, Hop1 and a cohesin subunit Rec8. Compromised CDK activity in meiotic prophase leads to defective SC formation without affecting DSB formation. These results suggest that CDK-dependent phosphorylation regulates meiotic chromosome morphogenesis. PMID:20825495

Zhu, Zhihui; Mori, Saori; Oshiumi, Hiroyuki; Matsuzaki, Kenichiro; Shinohara, Miki; Shinohara, Akira

2010-10-01

332

Complex formation, thermal behavior and stability competition between Cu(II) ion and Cu(0) nanoparticles with some new azo dyes. Antioxidant and in vitro cytotoxic activity.  

PubMed

Four triazole and thiadiazole-based azo chromophores namely [(E)-4-((1H-1,2,4-triazol-3-yl)diazenyl)benzene-1,3-diol.(HL(1)), (E)-4-((5-(methylthio)-1H-1,2,4-triazol-3-yl)diazenyl)benzene-1,3-diol.(HL(2)), (E)-4-((1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol.(HL(3)) and (E)-4-((5-mercapto-1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol.(HL(4))] were synthesized and characterized by elemental analyses, IR, UV-Vis as well as mass spectroscopy. Cu(II) complexes of the investigated azo dyes have been synthesized and characterized by elemental analyses, IR, electronic and ESR spectra, magnetic susceptibility and thermogravimetric analyses. The bond lengths and bond angles have been calculated to confirm the geometry of the ligands and their Cu(II) complexes. The mode of interaction of the azodyes to copper nanoparticles was described as coordination mode of charged dye molecules on the colloidal Cu(0) surface through anchoring OH(-) group. The apparent association constants of the colloidal copper nanoparticles azodye complexes in solution were evaluated using the spectral method and compared with the formation constant of the Cu(II) azo complexes. The antitumor and antioxidant activities of the synthesized azo dyes and their Cu(II) azo complexes have been evaluated. PMID:23434564

Gaber, M; El-Sayed, Y S; El-Baradie, K Y; Fahmy, R M

2013-04-15

333

Coordination chemistry of microbial iron transport compounds. IX. Stability constants for catechol models of enterobactin  

Microsoft Academic Search

The stability constants of ferric complexes with several substituted catechol (1,2-dihydroxybenzene) ligands in aqueous solutions of low ionic strength have been determined at 27°C in the pH range 2 to 11. Enterobactin, the principal siderophore of enteric bacteria, is a tricatechol and, from the formation constants reported here, is estimated to have a formation constant with ferric ion which is

Alex Avdeef; Stephen R. Sofen; Thomas L. Bregante; Kenneth N. Raymond

1978-01-01

334

Are Fundamental Constants Really Constant?  

ERIC Educational Resources Information Center

Dirac's classical conclusions, that the values of e2, M and m are constants and the quantity of G decreases with time. Evoked considerable interest among researchers and traces historical development by which further experimental evidence points out that both e and G are constant values. (PS)

Swetman, T. P.

1972-01-01

335

Formation of the Open Complex by Bacterial RNA Polymerase--A Quantitative Model  

PubMed Central

Over the last two decades, a large amount of data on initiation of transcription by bacterial RNA polymerase (RNAP) has been obtained. However, a question of how the open complex is formed still remains open, and several qualitative hypotheses for opening of DNA by RNAP have been proposed. To provide a theoretical framework needed to analyze the assembled experimental data, we here develop the first quantitative model of the open complex formation by bacterial RNAP. We first show that a simple hypothesis (which might follow from recent bioinformatic and experimental results), by which promoter DNA is melted in one step through thermal fluctuations, is inconsistent with experimental data. We next consider a more complex two-step view of the open complex formation. According to this hypothesis, the transcription bubble is formed in the ?10 region, and consequently extends to the transcription start site. We derive how the open complex formation rate depends on DNA duplex melting energy and on interaction energies of RNAP with promoter DNA in the closed and open complex. This relationship provides an explicit connection between transcription initiation rate and physical properties of the promoter sequence and promoter-RNAP interactions. We compare our model with both biochemical measurements and genomics data and report a very good agreement with the experiments, with no free parameters used in model testing. This agreement therefore strongly supports both the quantitative model that we propose and the qualitative hypothesis on which the model is based. From a practical point, our results allow efficient estimation of promoter kinetic parameters, as well as engineering of promoter sequences with the desired kinetic properties.

Djordjevic, Marko; Bundschuh, Ralf

2008-01-01

336

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

337

Dissecting the role of the Atg12-Atg5-Atg16 complex during autophagosome formation  

PubMed Central

The activity of the conserved Atg12–Atg5-Atg16 complex is essential for autophagosome formation. However, little is known about its mechanism of action during this process. In our study we employed in vitro systems consisting of purified proteins and giant unilamellar vesicles (GUVs) or small liposomes to investigate membrane binding by the Atg12–Atg5-Atg16 complex and its interplay with the Atg8 conjugation system. We showed that Atg5 directly binds membranes and that this membrane binding is negatively regulated by Atg12 conjugation but activated by Atg16. Membrane binding by the Atg12–Atg5-Atg16 complex is required for efficient promotion of Atg8 lipidation. Additionally, we found that the Atg12–Atg5-Atg16 complex tethered vesicles in an Atg8-independent manner. In yeast, membrane binding by Atg5 is not required for its recruitment to the phagophore assembly site (PAS) but is essential for efficient promotion of autophagy and the cytoplasm-to-vacuole targeting (Cvt) pathway at a stage preceding Atg8 lipidation and autophagosome closure. Our findings provide new insights into the role of the Atg12–Atg5-Atg16 complex during autophagosome formation.

Walczak, Marta; Martens, Sascha

2013-01-01

338

Dissecting the role of the Atg12-Atg5-Atg16 complex during autophagosome formation.  

PubMed

The activity of the conserved Atg12-Atg5-Atg16 complex is essential for autophagosome formation. However, little is known about its mechanism of action during this process. In our study we employed in vitro systems consisting of purified proteins and giant unilamellar vesicles (GUVs) or small liposomes to investigate membrane binding by the Atg12-Atg5-Atg16 complex and its interplay with the Atg8 conjugation system. We showed that Atg5 directly binds membranes and that this membrane binding is negatively regulated by Atg12 conjugation but activated by Atg16. Membrane binding by the Atg12-Atg5-Atg16 complex is required for efficient promotion of Atg8 lipidation. Additionally, we found that the Atg12-Atg5-Atg16 complex tethered vesicles in an Atg8-independent manner. In yeast, membrane binding by Atg5 is not required for its recruitment to the phagophore assembly site (PAS) but is essential for efficient promotion of autophagy and the cytoplasm-to-vacuole targeting (Cvt) pathway at a stage preceding Atg8 lipidation and autophagosome closure. Our findings provide new insights into the role of the Atg12-Atg5-Atg16 complex during autophagosome formation. PMID:23321721

Walczak, Marta; Martens, Sascha

2013-03-01

339

Protein complexing in a methanogen suggests electron bifurcation and electron delivery from formate to heterodisulfide reductase.  

PubMed

In methanogenic Archaea, the final step of methanogenesis generates methane and a heterodisulfide of coenzyme M and coenzyme B (CoM-S-S-CoB). Reduction of this heterodisulfide by heterodisulfide reductase to regenerate HS-CoM and HS-CoB is an exergonic process. Thauer et al. [Thauer, et al. 2008 Nat Rev Microbiol 6:579-591] recently suggested that in hydrogenotrophic methanogens the energy of heterodisulfide reduction powers the most endergonic reaction in the pathway, catalyzed by the formylmethanofuran dehydrogenase, via flavin-based electron bifurcation. Here we present evidence that these two steps in methanogenesis are physically linked. We identify a protein complex from the hydrogenotrophic methanogen, Methanococcus maripaludis, that contains heterodisulfide reductase, formylmethanofuran dehydrogenase, F(420)-nonreducing hydrogenase, and formate dehydrogenase. In addition to establishing a physical basis for the electron-bifurcation model of energy conservation, the composition of the complex also suggests that either H(2) or formate (two alternative electron donors for methanogenesis) can donate electrons to the heterodisulfide-H(2) via F(420)-nonreducing hydrogenase or formate via formate dehydrogenase. Electron flow from formate to the heterodisulfide rather than the use of H(2) as an intermediate represents a previously unknown path of electron flow in methanogenesis. We further tested whether this path occurs by constructing a mutant lacking F(420)-nonreducing hydrogenase. The mutant displayed growth equal to wild-type with formate but markedly slower growth with hydrogen. The results support the model of electron bifurcation and suggest that formate, like H(2), is closely integrated into the methanogenic pathway. PMID:20534465

Costa, Kyle C; Wong, Phoebe M; Wang, Tiansong; Lie, Thomas J; Dodsworth, Jeremy A; Swanson, Ingrid; Burn, June A; Hackett, Murray; Leigh, John A

2010-06-15

340

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

341

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.

2013-01-01

342

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

343

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

PubMed

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 (1)H 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. PMID:24704481

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

2014-07-15

344

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, Eva G; Canton, Sophie E; Bolin, Trudy; Peintler, Gábor; Kutus, Bence; Kele, Zoltán; Pálinkó, István; Sipos, Pál

2014-06-17

345

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

346

Meiotic cohesin complexes are essential for the formation of the axial element in mice  

PubMed Central

Cohesin is a conserved multisubunit protein complex that participates in chromosome segregation, DNA damage repair, chromatin regulation, and synaptonemal complex (SC) formation. Yeast, but not mice, depleted of the cohesin subunit Rec8 are defective in the formation of the axial elements (AEs) of the SC, suggesting that, in mammals, this function is not conserved. In this paper, we show that spermatocytes from mice lacking the two meiosis-specific cohesin subunits RAD21L and REC8 were unable to initiate RAD51- but not DMC1-mediated double-strand break repair, were not able to assemble their AEs, and arrested as early as the leptotene stage of prophase I, demonstrating that cohesin plays an essential role in AE assembly that is conserved from yeast to mammals.

Herran, Yurema; Garcia-Tunon, Ignacio; Gutierrez-Caballero, Cristina; de Alava, Enrique; Barbero, Jose Luis; Schimenti, John; de Rooij, Dirk G.; Sanchez-Martin, Manuel

2012-01-01

347

Microbial growth and biofilm formation in geologic media is detected with complex conductivity measurements  

NASA Astrophysics Data System (ADS)

Complex conductivity measurements (0.1-1000 Hz) were obtained from biostimulated sand-packed columns to investigate the effect of microbial growth and biofilm formation on the electrical properties of porous media. Microbial growth was verified by direct microbial counts, pH measurements, and environmental scanning electron microscope imaging. Peaks in imaginary (interfacial) conductivity in the biostimulated columns were coincident with peaks in the microbial cell concentrations extracted from sands. However, the real conductivity component showed no discernible relationship to microbial cell concentration. We suggest that the observed dynamic changes in the imaginary conductivity (??) arise from the growth and attachment of microbial cells and biofilms to sand surfaces. We conclude that complex conductivity techniques, specifically imaginary conductivity measurements are a proxy indicator for microbial growth and biofilm formation in porous media. Our results have implications for microbial enhanced oil recovery, CO2 sequestration, bioremediation, and astrobiology studies.

Davis, Caroline A.; Atekwana, Estella; Atekwana, Eliot; Slater, Lee D.; Rossbach, Silvia; Mormile, Melanie R.

2006-09-01

348

Unique behaviour of dinitrogen-bridged dimolybdenum complexes bearing pincer ligand towards catalytic formation of ammonia  

PubMed Central

It is vital to design effective nitrogen fixation systems that operate under mild conditions, and to this end we recently reported an example of the catalytic formation of ammonia using a dinitrogen-bridged dimolybdenum complex bearing a pincer ligand, where up to twenty three equivalents of ammonia were produced based on the catalyst. Here we study the origin of the catalytic behaviour of the dinitrogen-bridged dimolybdenum complex bearing the pincer ligand with density functional theory calculations, based on stoichiometric and catalytic formation of ammonia from molecular dinitrogen under ambient conditions. Comparison of di- and mono-molybdenum systems shows that the dinitrogen-bridged dimolybdenum core structure plays a critical role in the protonation of the coordinated molecular dinitrogen in the catalytic cycle.

Tanaka, Hiromasa; Arashiba, Kazuya; Kuriyama, Shogo; Sasada, Akira; Nakajima, Kazunari; Yoshizawa, Kazunari; Nishibayashi, Yoshiaki

2014-01-01

349

Formation of geometrically complex lipid nanotube-vesicle networks of higher-order topologies  

PubMed Central

We present a microelectrofusion method for construction of fluid-state lipid bilayer networks of high geometrical complexity up to fully connected networks with genus = 3 topology. Within networks, self-organizing branching nanotube architectures could be produced where intersections spontaneously arrange themselves into three-way junctions with an angle of 120° between each nanotube. Formation of branching nanotube networks appears to follow a minimum-bending energy algorithm that solves for pathway minimization. It is also demonstrated that materials can be injected into specific containers within a network by nanotube-mediated transport of satellite vesicles having defined contents. Using a combination of microelectrofusion, spontaneous nanotube pattern formation, and satellite-vesicle injection, complex networks of containers and nanotubes can be produced for a range of applications in, for example, nanofluidics and artificial cell design. In addition, this electrofusion method allows integration of biological cells into lipid nanotube-vesicle networks.

Karlsson, Mattias; Sott, Kristin; Davidson, Maximillian; Cans, Ann-Sofie; Linderholm, Pontus; Chiu, Daniel; Orwar, Owe

2002-01-01

350

Formation of palladium(II) hydroxychloride complexes and precipitates in sodium chloride solutions and seawater  

NASA Astrophysics Data System (ADS)

Spectrophotometric measurements of Pd(II) in 0.5 M NaCl indicate that the PdCl 3OH 2- formation constant at 25°C is ClK?1 = [PdCl 3OH 2-][H +][Cl -][PdCl 42-] -1 = 10 -8.98. This constant is more than two orders of magnitude smaller than previous results derived through solubility analysis. Kinetic experiments indicate that equilibration between PdCl 42- and PdCl 3OH 2- is complete in less than one second. The discrepancy between depictions of Pd(II) speciation obtained by using spectrophotometric and solubility analysis is apparently caused by the formation of mixed hydroxychloride solid phases (PdCl aOH 2-a), rather than pure Pd(OH) 2(s), when Pd(OH) 2(s) is equilibrated in concentrated chloride solutions at high pH. In Pd(II) solubility analysis, and solubility analyses of other strongly hydrolyzed metals in seawater, the composition of the solid phase must be carefully examined for appropriate deconvolution of data.

Byrne, Robert H.; Yao, Wensheng

2000-12-01

351

Identification of a Ribonucleoprotein Intermediate of Tomato Mosaic Virus RNA Replication Complex Formation  

Microsoft Academic Search

The replication of eukaryotic positive-strand RNA virus genomes occurs in the membrane-bound RNA replication complexes. Previously, we found that the extract of evacuolated tobacco BY-2 protoplasts (BYL) is capable of supporting the translation and subsequent replication of the genomic RNAs of plant positive-strand RNA viruses, including Tomato mosaic virus (ToMV). Here, to dissect the process that precedes the formation of

Keisuke Komoda; Natsuki Mawatari; Yuka Hagiwara-Komoda; Satoshi Naito; Masayuki Ishikawa

2007-01-01

352

Microbial growth and biofilm formation in geologic media is detected with complex conductivity measurements  

Microsoft Academic Search

Complex conductivity measurements (0.1–1000 Hz) were obtained from biostimulated sand-packed columns to investigate the effect of microbial growth and biofilm formation on the electrical properties of porous media. Microbial growth was verified by direct microbial counts, pH measurements, and environmental scanning electron microscope imaging. Peaks in imaginary (interfacial) conductivity in the biostimulated columns were coincident with peaks in the microbial

Caroline A. Davis; Estella Atekwana; Eliot Atekwana; Lee D. Slater; Silvia Rossbach; Melanie R. Mormile

2006-01-01

353

Electrochemically Controllable Reversible Formation of Cucurbit[8]uril-Stabilized Charge-Transfer Complex on Surface  

Microsoft Academic Search

The reversible formation of cucurbit[8]uril (CB[8])-stabilized charge-transfer (CT) complex on gold, which can be regulated by electrochemical stimuli, is reported. A viologen-based thread molecule with a thiol terminus was designed to synthesise a stable CB[8]-threaded [2]pseudorotaxane (5 ). A mixed self-assembled monolayer (SAM) of 5 and 3-mercaptopropionic acid (3-MPA) on gold was prepared and characterised by reflectance FT-IR spectroscopy. The

Jin-Koo Kang; Ilha Hwang; Young Ho Ko; Woo Sung Jeon; Hee-Joon Kim; Kimoon Kim

2008-01-01

354

Effective staining of tumor cells by coumarin-6 depends on the stoichiometry of cyclodextrin complex formation  

Microsoft Academic Search

In a comprehensive picture of inclusion complex formation of the highly fluorescent dye coumarin-6 (C6) and betacyclodextrin\\u000a (beta-CD), which was obtained using various fluorescence spectroscopic methods, it was demonstrated that up to three beta-CD\\u000a rings can thread on the rod like dye molecule. Interaction of coumarins and modified coumarins with cellular organelles or\\u000a proteins has been reported in several publications.

Michael Edetsberger; Martin Knapp; Erwin Gaubitzer; Christoph Miksch; Kathuna Elizbarowna Gvichiya; Gottfried Köhler

355

Clathrate-formation mediated adsorption of methane on Cu-complex crystals.  

PubMed

We measured adsorption and desorption isotherms of methane on [Cu(4, 4'-bipyridine)2(BF4)2] (LPC) at 258, 273, and 303 K. Adsorption proceeds almost vertically at a definite pressure, which is named gate pressure. The lower the measurement temperature, the smaller the gate pressure. The temperature dependence of the gate pressure is expressed by the Clapeyron-Clausius equation, giving a thermodynamic evidence on the clathrate formation between the Cu complex and methane. PMID:16852737

Noguchi, Hiroshi; Kondoh, Atsushi; Hattori, Yoshiyuki; Kanoh, Hirofumi; Kajiro, Hiroshi; Kaneko, Katsumi

2005-07-28

356

Spectrophotometric Determination of Metoprolol Tartrate in Pharmaceutical Dosage Forms on Complex Formation with Cu(II)  

PubMed Central

A new, simple, sensitive and accurate spectrophotometric method has been developed for the assay of metoprolol tartrate (MPT), which is based on the complexation of drug with copper(II) [Cu(II)] at pH 6.0, using Britton-Robinson buffer solution, to produce a blue adduct. The latter has a maximum absorbance at 675 nm and obeys Beer's law within the concentration range 8.5-70 ?g/mL. Regression analysis of the calibration data showed a good correlation coefficient (r = 0.998) with a limit of detection of 5.56 ?g/mL. The proposed procedure has been successfully applied to the determination of this drug in its tablets. In addition, the spectral data and stability constant for the binuclear copper(II) complex of MPT (Cu2MPT2Cl2) have been reported.

Cesme, Mustafa; Tarinc, Derya; Golcu, Aysegul

2011-01-01

357

Luminescent complexes of the zinc triad with N-substituted 8-amino-quinoline ligands: Synthesis and comparative study on the stability constants and related photophysical properties  

Microsoft Academic Search

The potentially fluorescent terdentate ligand bis-quinolin-8-yl-amine (BQAH) yields the bis-chelate complexes [M(BQAH)2](ClO4)2 (M=Zn, Cd, Hg) and the mono-chelate [M(BQAH)Cl2] (M=Zn, Cd). The aminic proton of the coordinated BQAH displays a remarkable acidity. Thus, in polar solvents (CH3CN and methanol) the formation of the deprotonated derivatives [M(BQA)2] and [M(BQA)Cl] is observed whose absorption and fluorescent spectra are identical with those of

Luciano Canovese; Fabiano Visentin; Gavino Chessa; Carlo Levi; Peter Nikolov

2009-01-01

358

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

359

Rapid formation of cell-particle complexes via dielectrophoretic manipulation for the detection of surface antigens.  

PubMed

A rapid and simple method for the fabrication of the island patterns with particles and cells was applied to detect the presence of specific antigens on the cell surface. An upper interdigitated microband array (IDA) electrode was mounted on a lower substrate with the same design to fabricate a microfluidic-channel device for dielectrophoretic manipulation. The electrode grid structure was fabricated by rotating the upper template IDA by 90° relative to the lower IDA. A suspension of anti-CD33 modified particles and HL-60 cells was introduced into the channel. An AC electrical signal (typically 20V peak-to-peak, 100kHz) was then applied to the bands of the upper and lower IDAs, resulting in the formation of island patterns at the intersections with low electric fields. Immunoreactions between the antibodies immobilized on the accumulated particles and the CD33 present on the surface of the cells led to the formation of complexes comprising corresponding antigen-antibody pairs. Non-specific pairs accumulated at the intersection, which did not form complexes, were then dispersed after removal of the applied field. The time required for the detection of the formation/dispersion of the complexes is as short as 6min in the present procedure. Furthermore, this novel cell binding assay does not require pretreatment such as target labeling or washing of the unbound cells. PMID:24892783

Horii, Takuma; Yamamoto, Masashi; Yasukawa, Tomoyuki; Mizutani, Fumio

2014-11-15

360

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

361

Nephrin Regulates Lamellipodia Formation by Assembling a Protein Complex That Includes Ship2, Filamin and Lamellipodin  

PubMed Central

Actin dynamics has emerged at the forefront of podocyte biology. Slit diaphragm junctional adhesion protein Nephrin is necessary for development of the podocyte morphology and transduces phosphorylation-dependent signals that regulate cytoskeletal dynamics. The present study extends our understanding of Nephrin function by showing in cultured podocytes that Nephrin activation induced actin dynamics is necessary for lamellipodia formation. Upon activation Nephrin recruits and regulates a protein complex that includes Ship2 (SH2 domain containing 5? inositol phosphatase), Filamin and Lamellipodin, proteins important in regulation of actin and focal adhesion dynamics, as well as lamellipodia formation. Using the previously described CD16-Nephrin clustering system, Nephrin ligation or activation resulted in phosphorylation of the actin crosslinking protein Filamin in a p21 activated kinase dependent manner. Nephrin activation in cell culture results in formation of lamellipodia, a process that requires specialized actin dynamics at the leading edge of the cell along with focal adhesion turnover. In the CD16-Nephrin clustering model, Nephrin ligation resulted in abnormal morphology of actin tails in human podocytes when Ship2, Filamin or Lamellipodin were individually knocked down. We also observed decreased lamellipodia formation and cell migration in these knock down cells. These data provide evidence that Nephrin not only initiates actin polymerization but also assembles a protein complex that is necessary to regulate the architecture of the generated actin filament network and focal adhesion dynamics.

Venkatareddy, Madhusudan; Cook, Leslie; Abuarquob, Kamal; Verma, Rakesh; Garg, Puneet

2011-01-01

362

Formation and conformation of baicalin-berberine and wogonoside-berberine complexes.  

PubMed

It is well-known that baicalin-berberine complex (1) precipitates in the water decoction of numerous Chinese Medicinal formulae containing Radix Scutellariae and Rhizoma Coptidis or Cortex Phellodendri. In the current study, ionic interaction between the carboxylate ion of baicalin and the quaternary ammonium ion of berberine was revealed to be responsible for the formation of 1 and wogonoside-berberine (2) by using FAB-MS and NMR titration experiments. In addition, nuclear Overhauser effect spectroscopy (NOESY) correlations observed in 1 and 2 suggested quite different conformation of the two complexes, which was further supported by the fact that the [?](D) of the canadine obtained by reduction of 1 is of an opposite sign to that obtained from 2. Partition coefficients (n-octanol/water) determination demonstrated 12-20 times larger partition coefficient of each complex (1, 2) than that of each single compound (baicalin, wogonoside, and berberine), indicating the significant role of the formation of the complex in the bioavailability enhancement of these pharmacologically active constituents. PMID:22689420

Wang, Jing-Rong; Tanaka, Takashi; Zhang, Hong; Kouno, Isao; Jiang, Zhi-Hong

2012-01-01

363

Modifications of the acyl-d-alanyl-d-alanine terminus affecting complex-formation with vancomycin  

PubMed Central

Vancomycin forms complexes with peptides terminating in d-alanyl-d-alanine that are analogous to the biosynthetic precursors of bacterial mucopeptides. The specificity of complex-formation has been studied by means of many synthetic peptides, prepared by both solid-phase and conventional methods. The following conclusions can be drawn: (a) three amide linkages are required to form a stable complex; (b) the terminal carboxyl group must be free; (c) the carboxyl terminal and subterminal residues must be either glycine or of the d-configuration; (d) the size of the side chain in these residues greatly influences the affinity for vancomycin, a methyl group being the optimum in each case; (e) the nature of the side chain in the third and fourth residues has a smaller effect on complex-formation, but an l-configuration was somewhat better than a d-configuration in the third position. In addition to acyl-d-alanyl-d-alanine, other peptides that occur in bacterial cell walls will combine with vancomycin, although less strongly, e.g. acyl-d-alanyl-d-?-amino acid (where the terminal d-residue may form the cross-link in mucopeptide structure) and acyl-l-alanyl-d-glutamylglycine (a sequence found in the mucopeptide of Micrococcus lysodeikticus and related organisms). These results throw some light on the specificity of the uptake of vancomycin by living bacteria.

Nieto, M.; Perkins, H. R.

1971-01-01

364

Monitoring complex formation in the blood-coagulation cascade using aptamer-coated SAW sensors.  

PubMed

Specific binding of the anticoagulants heparin and antithrombin III to the blood clotting cascade factor human thrombin was recorded as a function of time with a Love-wave biosensor array consisting of five sensor elements. Two of the sensor elements were used as references. Three sensor elements were coated with RNA or DNA aptamers for specific binding of human thrombin. The affinity between the aptamers and thrombin, measured using the biosensor, was within the same range as the value of K(D) measured by filter binding experiments. Consecutive binding of the thrombin inhibitors heparin, antithrombin III or the heparin-antithrombin III complex to the immobilized thrombin molecules, and binding of a ternary complex of heparin, anithrombin III, and thrombin to aptamers was evaluated. The experiments showed attenuation of binding to thrombin due to heparin-antithrombin III complex formation. Binding of heparin activated the formation of the inhibitory complex of antithrombin III with thrombin about 2.7-fold. Binding of the DNA aptamer to exosite II appeared to inhibit heparin binding to exosite I. PMID:15741074

Gronewold, T M A; Glass, S; Quandt, E; Famulok, M

2005-04-15

365

Thermodynamics of formation for the 18-crown-6-triglycine molecular complex in water-dimethylsulfoxide solvents  

NASA Astrophysics Data System (ADS)

The effect of a water-dimethylsulfoxide (DMSO) solvent on the formation of a molecular complex of 18-crown-6 (18C6) with triglycine (diglycylglycine, 3Gly) is studied via calorimetric titration. It is found that switching from water to an H2O-DMSO mixture with DMSO mole fraction of 0.30 is accompanied by a monotonic increase in the stability of [3Gly18C6] complex, from log K ? = 1.10 to log K ? = 2.44, and an increase in the exothermicity of the reaction of its formation, from -5.9 to -16.9 kJ/mol. It is shown that the [3Gly18C6] complex exhibits enthalpy stabilization with negative values of enthalpy and entropy over the investigated range of H2O-DMSO solvents. Analysis of the reagents' solvation characteristics reveals that the increase in the reaction's exothermicity of transfer is due to differences in the solvation of [3Gly18C6] and 18C6 with a small solvation contribution from 3Gly. It is concluded that the change in the Gibbs energy of the reaction 3Glysolv + 18C6solv ? [3Gly18C6]solv is due to differences in the change in the solvation state of the complex and the peptide (?tr G ?([3Gly18C6])-?tr G ?(3Gly)).

Usacheva, T. R.; Lan, Pham Thi; Sharnin, V. A.

2014-06-01

366

On the complex formation equilibria between dioxouranium(VI) and sulfate ions.  

PubMed

The complexation equilibria between UO2(2+) and SO4(2-) ions have been studied at 25 degrees C in the ionic medium 3 M NaClO4 by potentiometry, by spectrophotometry and by solubility measurements of UO2(IO3)2. The potentiometric investigation was carried out with the Hg-Hg2SO4(s)-SO4(2-) half-cell and glass electrode in the sulfate concentration range 0.005 to 0.07 M. The optical absorbances in the UV-visible region and the solubility data cover the ligand concentration range 0.005 to 0.3 M. The data could be explained by assuming the complexes and equilibrium constants [Table: see text]. The constants in the infinite dilution reference state, log beta1o = 3.08 +/- 0.15 and log beta2o = 4.28 +/- 0.15, estimated by assuming the validity of the specific interaction theory, are practically coincident with literature data. PMID:12737489

Ciavatta, Liberato; De Tommaso, Gaetano; Iuliano, Mauro

2003-03-01

367

Beta-lactoglobulin/folic acid complexes: formation, characterization, and biological implication.  

PubMed

Beta-lactoglobulin (beta-LG), the major whey protein in bovine milk, binds to a wide range of compounds. Folic acid (FA) is a synthetic form of the B group vitamin known as folates, which are essential cofactors for a variety of physiological processes. The interaction of beta-LG with FA was studied using fluorescence spectroscopy to determine the FA binding constant and mode and the influence of the protein on FA photodegradation. At < or = 20 microM FA, which may be the critical self-association concentration, the binding constant and number are 2.0 (+/-0.6) x 10(6) M(-1) and 1.30 (+/-0.03) when excited at 280 nm and 4.3 (+/-2.2) x 10(5) M(-1) and 1.17 (+/-0.04) at 295 nm, as determined by protein intrinsic fluorescence. FA binds to the surface of beta-LG, possibly in the groove between the alpha-helix and the beta-barrel. Fluorescence analysis of the pterin portion of FA shows that complexation with beta-LG improves FA photostability. It is suggested that beta-LG complexes could be used as an effective carrier of FA in functional foods. PMID:20411963

Liang, Li; Subirade, Muriel

2010-05-20

368

Mössbauer study of peroxynitrito complex formation with FeIII-chelates  

NASA Astrophysics Data System (ADS)

The reaction of the ?-oxo-diiron(III)-L complex (L = EDTA, ethylene diamine tetraacetate, HEDTA, hydroxyethyl ethylene diamine triacetate, and CyDTA, cyclohexane diamine tetraacetate) with peroxynitrite in alkaline solution was studied by Mössbauer spectroscopy using rapid-freezing technique. These complexes yield an (L)FeIII( ? 2-O2)^{3-} complex ion when they react with hydrogen peroxide and the formation of the peroxide adduct results in a deep purple coloration of the solution. The same color appears when the reaction occurs with peroxinitrite. Although spectrophotometry indicated some difference between the molar extinction coefficients of the peroxo and the peroxinitrito adducts, the Mössbauer parameters proved to be the same within experimental error. It is concluded that the peroxynitrite ion decomposes when reacting with FeIII(L) and the peroxo adduct forms.

Homonnay, Zoltan; Buszlai, Peter; Nádor, Judit; Sharma, Virender K.; Kuzmann, Erno; Vértes, Attila

2012-03-01

369

Amylose's recognition of chirality in polylactides on formation of inclusion complexes in vine-twining polymerization.  

PubMed

Amylose selectively includes poly(L-lactide) (PLLA) among the poly(lactide)s (PLAs) to produce an inclusion complex when the phosphorylase-catalyzed polymerization of ?-D-glucose 1-phosphate is performed in the presence of PLLA, poly(D-lactide) (PDLA), or poly(DL-lactide) (PDLLA) (vine-twining polymerization). This result indicates that amylose recognizes the chirality in PLAs on the formation of an inclusion complex in vine-twining polymerization. Modeling calculations support the amylose's chiral recognition in favor of PLLA and the atomistic details of the inclusion complex which involved the preferred orientation of the constituent molecular chains with respect to their fiber axis is proposed. PMID:21830300

Kaneko, Yoshiro; Ueno, Koji; Yui, Toshifumi; Nakahara, Keisuke; Kadokawa, Jun-ichi

2011-10-10

370

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

NASA Astrophysics Data System (ADS)

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.

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

2014-01-01

371

Mechanistic insights into the formation of N2O by a nickel nitrosyl complex.  

PubMed

Reaction of [Ni(NO)(bipy)(Me2phen)][PF6] with 1 equiv of nitric oxide (NO) in CH2Cl2 results in the formation of N2O and [{(Me2phen)Ni(NO)}2(?-?(1)-N:?(1)-O)-NO2)][PF6] (3), along with the known complex, [Ni(bipy)3][PF6]2 (4). The isolation of complex 3, which contains a nitrite ligand, demonstrates that the reaction of [Ni(NO)(bipy)(Me2phen)][PF6] with exogenous NO results in NO disproportionation and not NO reduction. Complex 3 could also be accessed by reaction of [Ni(NO)(Me2phen)][PF6] (5) with (Me2phen)Ni(NO)(NO2) (7) in good yield. Complexes 3, 5, and 7 were fully characterized, including analysis by X-ray crystallography in the case of 3 and 7. Furthermore, addition of 0.5 equiv of bipy to [Ni(NO)(bipy)][PF6] results in formation of the hyponitrite complex, [{(bipy)Ni(?(2)-O2N2)}?(1):?(1)-N,N-{Ni(NO)(bipy)}2][PF6]2 (9), in modest yield. Importantly, the hyponitrite ligand in 9 is thought to form via coupling of two NO(-) ligands and not by coupling of a nucleophilic nitrosyl ligand (NO(-)) with an electrophilic nitrosyl ligand (NO(+)). X-ray crystallography reveals that complex 9 features a new binding mode of the cis-hyponitrite ligand. PMID:24597563

Wright, Ashley M; Zaman, Homaira T; Wu, Guang; Hayton, Trevor W

2014-03-17

372

Transitional Facies and Sequence Stratigraphic Complexity of Shallow-Marine Star Point Formation to Coastal-Plain Blackhawk Formation Along Depositional-Strike, Wasatch Plateau, Utah  

Microsoft Academic Search

Facies and stratigraphic architecture right at the transition from marine to non-marine environments is poorly documented. In the Cretaceous outcrops of Utah, Star Point and Blackhawk Formations are well studied. The nature of spatio-temporal transition of these two Formations, in the deposition-strike orientation, remains undocumented. This study characterizes facies and stratigraphic complexity at the transition of the two Formations that

Ranson Andrew M

2012-01-01

373

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

374

Structural Complexities Influencing Biostratigraphic Interpretations of the Permian Nansen Formation type-section, Ellesmere Island, Canada  

NASA Astrophysics Data System (ADS)

The Carboniferous to Permian aged Nansen Formation is a cyclic carbonate shelf deposit and potential hydrocarbon reservoir. This formation is the thickest, most widespread carbonate sequence in the Sverdrup Basin. Deformed during the Eurekan Orogeny, the Nansen Fm. is topographically prominent and responsible for the rugged topography on Axel Heiburg and Ellesmere Island. The type-section for the Nansen Fm. is located on the north side of Hare Fiord, along Girty Creek. At this location there is an estimated stratigraphic thickness of 2 km. Due to easier access most of the stratigraphic work has been completed on nearby glacially exposed sections that traverse parallel to Girty Creek along glacial margins. Extensive biostratigraphy was completed on a glacier section to the west, however, in a glacier section to the east of Girty Creek, structural complexities appear to be repeating sections of the formation. Here, the Nansen formation is bounded by two regional reverse faults. This has produced duplex structures, with clearly exposed stacked horses, footwall synclines, and truncations. By projecting the structures observed along the eastern glacier section to the western glacier section that was used for biostratigraphic studies, it is clear that these structures would affect biostratigraphic interpretations. It was previously noted by biostratigraphers that thrust faults appear to be repeating sections of the Nansen formation. However by correlating all observed faults with the biostratigraphy, we can determine the extent to which the faulting has affected the interpretations, and whether all faults or stratigraphic repetitions are accounted for.

Hill, M.; Guest, B.

2011-12-01

375

Experimental investigation on lane formation in complex plasmas under microgravity conditions  

NASA Astrophysics Data System (ADS)

A series of experiments dedicated to probing the phenomenon of lane formation in binary complex plasmas over a broad range of parameters has been performed with the PK-3 Plus laboratory on board the International Space Station (ISS) under microgravity conditions. In the experiments, bunches of small particles were driven through a background of big particles. We show that the dynamics of lane formation varies considerably with the density of the background and the size ratio between small and big particles. For consecutive injections of small particles a memory effect of the previous penetration was discovered for the first time. This memory effect was investigated quantitatively with respect to the structure formation and the penetration speed. We show that the memory effect in lane formation is linear. In addition, we studied the crossover from lane formation to phase separation driven by the nonadditive interactions between small and big particles. We found that during this transition the small penetrating particles effectively cage the background particles.

Du, C.-R.; Sütterlin, K. R.; Jiang, K.; Räth, C.; Ivlev, A. V.; Khrapak, S.; Schwabe, M.; Thomas, H. M.; Fortov, V. E.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F.; Malentschenko, Y.; Yurtschichin, F.; Lonchakov, Y.; Morfill, G. E.

2012-07-01

376

The reaction of platinum(II) complexes with DNA. Kinetics of intrastrand crosslink formation in vitro.  

PubMed Central

The kinetics of the formation of bifunctional DNA platinum(II) adducts (DNA-crosslinks) have been investigated by endonuclease digestion and subsequent HPLC analysis of the soluble nucleotides and nucleotide platinum(II) adducts. The results indicate two waves of crosslinking [rate constants (0.2-0.3) min-1 and (0.015-0.025) min-1] that correlate with changes in ultra violet absorbance and ethidium bromide dependent fluorescence intensity, previously interpreted in terms of two consecutive, local conformational rearrangements of platinum-DNA (Schaller, W., Reisner, H., and Holler, E. (1987) Biochemistry 26, 943-950). The formation of crosslinks at sequences d(GpG) and d(GpNpG) follows identical kinetics. A minimal reaction mechanism is proposed for the binding of cis-diamminedichloroplatinum(II) to DNA under in vitro conditions. The approximately 3-fold higher rate for meso-[1,2-bis(2,6-dichloro-4- hydroxyphenyl)ethylenediamine]diaquaplatinum(II) in comparison to the rate for cis-diamminediaquaplatinum(II) indicates that crosslink formation is affected by the nature of the non-leaving platinum ligand(s).

Bernges, F; Holler, E

1991-01-01

377

Complex formation equilibria of Cu(II) and Zn(II) with triethylenetetramine and its mono- and di-acetyl metabolites.  

PubMed

Triethylenetetramine (TETA) dihydrochloride, or trientine, is a therapeutic molecule that has long been used as a copper-chelating agent for the second-line treatment of patients with Wilson's disease. More recently, it has also been employed as an experimental therapeutic molecule in diabetes where it improves cardiac structure in patients with diabetic cardiomyopathy and left-ventricular hypertrophy. TETA is metabolized by acetylation, which leads to the formation of two main metabolites in humans and other mammals, monoacetyl-TETA (MAT) and diacetyl-TETA (DAT). These metabolites have been identified in the plasma and urine of healthy and diabetic subjects treated with TETA, and could themselves play a role in TETA-mediated copper chelation and restoration of physiological copper regulation in diabetes. In this regard, a potentiometric and spectrophotometric study of Cu(II)-complex formation equilibria of TETA, MAT and DAT is presented here, to provide a comprehensive evaluation of the stoichiometries of the complexes formed and of their relative stability constants. A potentiometric study has also been conducted on the corresponding Zn(II) complexes, to evaluate any possible interference with TETA-mediated Cu(II) binding by this second physiological transition-metal ion, which is present in similar concentrations in human plasma and which also binds to TETA. An ESI-MS study of these systems has both confirmed the complex formation mechanisms established from the potentiometric and spectrophotometric results, and in addition provided direct information on the stoichiometry of the complexes formed in solution. These data when taken together show that the 1 : 1 complexes formed with Cu(II) and Zn(II) have different degrees of protonation. The stability of the Cu(II) and Zn(II) complexes with the three ligands, evaluated by the parameters pCu and pZn, decreases with the introduction of the acetyl groups. Nevertheless the stability of Cu(II) complexes with MAT is sufficiently high to enable its participation in copper scavenging from the patient. A speciation study of the behavior of TETA and MAT with Cu(II) in the presence of Zn(II) at peri-physiological plasma concentrations is also presented. While Zn(II) did not hinder copper binding, the possibility is raised that prolonged TETA treatment could possibly alter the homeostatic regulation of this essential metal ion. The lack of reliable literature stability constants concerning the Cu(II) and Zn(II) interaction with the major transport proteins in plasma is also briefly considered. PMID:23202417

Nurchi, Valeria M; Crisponi, Guido; Crespo-Alonso, Miriam; Lachowicz, Joanna I; Szewczuk, Zbigniew; Cooper, Garth J S

2013-05-01

378

Reinvestigation of the formation of a mononuclear Fe(III) hydroperoxido complex using high pressure kinetics.  

PubMed

Previous stopped flow kinetic experiments suggested an interchange associative mechanism for the ligand substitution reaction, [Fe(bztpen)(OMe)](2+) + H(2)O(2)--> {[Fe(bztpen)(OMe)(HOOH)](2+)}(++)--> [Fe(bztpen)(OOH)](2+) + MeOH (bztpen = N-benzyl-N, N',N'tris(2-methylpyridyl)-ethylenediamine). Thus a seven-coordinate transition state containing both the leaving methoxide and the incoming hydrogen peroxide ligands was proposed. On the basis of high pressure kinetic data we can now conclude that this is not the case since the rate of the reaction is independent of pressure for the formation of the purple low spin transient hydroperoxido complex, [Fe(bztpen)(OOH)](2+). [Fe(bztpen)(OOH)](2+) has so far proved to be too short-lived for solid state isolation. As part of our ongoing pursuit of this elusive species we have structurally characterised the nitrosyl and acetate iron(II) complexes, [Fe(bztpen)(NO)](OTf)(2) and [Fe(bztpen)(OAc)](BPh(4)), as well as the air stable Co(II) complexes [Co(bztpen)Cl)]BF(4), [Co(metpen)Cl]SbF(6) and [Co(bztpen)(OAc)]BPh(4). We did not realise our aim of accessing stable Co(III) hydroperoxido or peroxido complexes by reaction of the cobalt complexes with H(2)O(2). PMID:20648392

Nebe, Thomas; Beitat, Alexander; Würtele, Christian; Dücker-Benfer, Carlos; van Eldik, Rudi; McKenzie, Christine J; Schindler, Siegfried

2010-09-01

379

Structural and Thermodynamic Characterization of Cadherin·?-Catenin·?-Catenin Complex Formation.  

PubMed

The classical cadherin·?-catenin·?-catenin complex mediates homophilic cell-cell adhesion and mechanically couples the actin cytoskeletons of adjacent cells. Although ?-catenin binds to ?-catenin and to F-actin, ?-catenin significantly weakens the affinity of ?-catenin for F-actin. Moreover, ?-catenin self-associates into homodimers that block ?-catenin binding. We investigated quantitatively and structurally ?E- and ?N-catenin dimer formation, their interaction with ?-catenin and the cadherin·?-catenin complex, and the effect of the ?-catenin actin-binding domain on ?-catenin association. The two ?-catenin variants differ in their self-association properties: at physiological temperatures, ?E-catenin homodimerizes 10× more weakly than does ?N-catenin but is kinetically trapped in its oligomeric state. Both ?E- and ?N-catenin bind to ?-catenin with a Kd of 20 nm, and this affinity is increased by an order of magnitude when cadherin is bound to ?-catenin. We describe the crystal structure of a complex representing the full ?-catenin·?N-catenin interface. A three-dimensional model of the cadherin·?-catenin·?-catenin complex based on these new structural data suggests mechanisms for the enhanced stability of the ternary complex. The C-terminal actin-binding domain of ?-catenin has no influence on the interactions with ?-catenin, arguing against models in which ?-catenin weakens actin binding by stabilizing inhibitory intramolecular interactions between the actin-binding domain and the rest of ?-catenin. PMID:24692547

Pokutta, Sabine; Choi, Hee-Jung; Ahlsen, Goran; Hansen, Scott D; Weis, William I

2014-05-01

380

Inhibition of human amylin fibril formation by insulin-mimetic vanadium complexes.  

PubMed

The toxicity of amyloid-forming proteins can be linked to many degenerative and systemic diseases. Human islet amyloid polypeptide (hIAPP, amylin) has been associated with type II diabetes. Methods for efficient inhibition of amyloid fibril formation are highly clinically important. This study demonstrated the significant inhibitory effects of six vanadium complexes on hIAPP aggregation. Vanadium complexes, such as bis(maltolato)-oxovanadium (BMOV), have been used as insulin-mimetic agents for the treatment of diabetes for many years. Different biophysical methods were applied to investigate the interaction between V complexes and hIAPP. The results indicated that the selected compounds affected the peptide aggregation by different action modes and protected the cells from the cytotoxicity induced by hIAPP. Both the high binding affinity and the ligand spatial effect on inhibiting hIAPP aggregation are significant. Although some of these compounds undergo biotransformation under the conditions of the experiments, and the active species are not identified, it is understood that the effect results from a particular compound and its conversion products. Importantly, our work provided information on the effects of the selected V complexes on hIAPP and demonstrated multiple levels of effects of V complexes against amyloid-related diseases. PMID:24714786

He, Lei; Wang, Xuesong; Zhao, Cong; Zhu, Dengsen; Du, Weihong

2014-04-23

381

Young stellar population and ongoing star formation in the H II complex Sh2-252  

NASA Astrophysics Data System (ADS)

In this paper, an extensive survey of the star-forming complex Sh2-252 has been undertaken with an aim to explore its hidden young stellar population as well as to understand the structure and star formation history for the first time. This complex is composed of five prominent embedded clusters associated with the subregions A, C, E, NGC 2175s and Teu 136. We used Two Micron All Sky Survey-near-infrared and Spitzer-Infrared Array Camera, Multiband Imaging Photometer for Spitzer photometry to identify and classify the young stellar objects (YSOs) by their infrared (IR) excess emission. Using the IR colour-colour criteria, we identified 577 YSOs, of which, 163 are Class I, 400 are Class II and 14 are transition disc YSOs, suggesting a moderately rich number of YSOs in this complex. Spatial distribution of the candidate YSOs shows that they are mostly clustered around the subregions in the western half of the complex, suggesting enhanced star formation activity towards its west. Using the spectral energy distribution and optical colour-magnitude diagram-based age analyses, we derived probable evolutionary status of the subregions of Sh2-252. Our analysis shows that the region A is the youngest (˜0.5 Myr), the regions B, C and E are of similar evolutionary stage (˜1-2 Myr) and the clusters NGC 2175s and Teu 136 are slightly evolved (˜2-3 Myr). Morphology of the region in the 1.1 mm map shows a semicircular shaped molecular shell composed of several clumps and YSOs bordering the western ionization front of Sh2-252. Our analyses suggest that next generation star formation is currently under way along this border and that possibly fragmentation of the matter collected during the expansion of the H II region as one of the major processes is responsible for such stars. We observed the densest concentration of YSOs (mostly Class I, ˜0.5 Myr) at the western outskirts of the complex, within a molecular clump associated with water and methanol masers and we suggest that it is indeed a site of cluster formation at a very early evolutionary stage, sandwiched between the two relatively evolved CH II regions A and B.

Jose, Jessy; Pandey, A. K.; Samal, M. R.; Ojha, D. K.; Ogura, K.; Kim, J. S.; Kobayashi, N.; Goyal, A.; Chauhan, N.; Eswaraiah, C.

2013-07-01

382

Complex formation and interactions between transcription factors essential for human prolactin receptor gene transcription.  

PubMed

The protein association of estrogen receptor ? ER? with DNA-bound SP1 and C/EBP? is essential for the 17?-estradiol (E2)-induced activation of human prolactin receptor (hPRLR) gene transcription. Protein-protein interaction and complex formation at the hPIII promoter of hPRLR was investigated. The basic region and leucine zipper (bZIP) of C/EBP?, zinc finger (ZF) motifs of SP1, and the DNA binding domain of ER? were identified as regions responsible for the interactions between transfactors. The E2-induced interaction was confirmed by bioluminescence resonance energy transfer (BRET) assays of live cells. The combination of BRET/bimolecular luminescence complementation assay revealed that ER? exists as a constitutive homodimer, and E2 induced a change(s) in ER? homodimer conformation favorable for its association with C/EBP? and SP1. Chromatin immunoprecipitation and small interfering RNA knockdown of members of the complex in breast cancer cells demonstrated the endogenous recruitment of components of the complex onto the hPIII promoter of the hPRLR gene. SP1 is the preferred transfactor for the recruitment of ER? to the complex that facilitates the C/EBP? association. The E2/ER?-induced hPRLR transcription was demonstrated in ER?-negative breast cancer cells. This study indicates that the enhanced complex formation of ER? dimer with SP1 and C/EBP? by E2 has an essential role in the transcriptional activation of the hPRLR gene. PMID:21670145

Kang, Jung-Hoon; Tsai-Morris, Chon-Hwa; Dufau, Maria L

2011-08-01

383

Stepwise formation of iridium(III) complexes with monocyclometalating and dicyclometalating phosphorus chelates.  

PubMed

With the motivation of assembling cyclometalated complexes without nitrogen-containing heterocycle, we report here the design and systematic synthesis of a class of Ir(III) metal complexes functionalized with facially coordinated phosphite (or phosphonite) dicyclometalate tripod, together with a variety of phosphine, chelating diphosphine, or even monocyclometalate phosphite ancillaries. Thus, treatment of [IrCl(3)(tht)(3)] with stoichiometric amount of triphenylphosphite (or diphenyl phenylphosphonite), two equiv of PPh(3), and in presence of NaOAc as cyclometalation promoter, gives formation of respective tripodal dicyclometalating complexes [Ir(tpit)(PPh(3))(2)Cl] (2a), [Ir(dppit)(PPh(3))(2)Cl] (2b), and [Ir(dppit)(PMe(2)Ph)(2)Cl] (2c) in high yields, where tpitH(2) = triphenylphosphite and dppitH(2) = diphenyl phenylphosphonite. The reaction sequence that afforded these complexes is established. Of particular interest is isolation of an intermediate [Ir(tpitH)(PPh(3))(2)Cl(2)] (1a) with monocyclometalated phosphite, together with the formation of [Ir(tpit)(tpitH)(PPh(3))] (3a) with all tripodal, bidentate, and monodentate phosphorus donors coexisting on the coordination sphere, upon treatment of 2a with a second equiv of triphenylphosphite. Spectroscopic studies were performed to explore the photophysical properties. For all titled Ir(III) complexes, virtually no emission can be observed in either solution at room temperature or 77 K CH(2)Cl(2) matrix. Time-dependent DFT calculation indicates that the lowest energy triplet manifold involves substantial amount of metal centered (3)MC dd contribution. Due to its repulsive potential energy surface (PES) that touches the PES of ground state, the (3)MC dd state executes predominant nonradiative deactivation process. PMID:22272818

Lin, Cheng-Huei; Lin, Chih-Yuan; Hung, Jui-Yi; Chang, Yao-Yuan; Chi, Yun; Chung, Min-Wen; Chang, Yuh-Chia; Liu, Chun; Pan, Hsiao-An; Lee, Gene-Hsiang; Chou, Pi-Tai

2012-02-01

384

Inhibition of breast cancer metastasis by dual liposomes to disturb complex formation.  

PubMed

The interaction between tumour cells and blood components, mainly platelets, plays an important role in metastasis. In this study, the anti-metastatic effect of vesicles containing the cytotoxic drug perifosine (OPP) and the haemostatic inhibitor dipyridamole (DIP) was tested. These dual liposomes (DIP/OPP-L) encapsulating up to 400microg DIP/ml and 6mM OPP were prepared by extrusion technique. In vitro, DIP/OPP-L significantly inhibited the aggregation of platelets and reduced their adhesion to immobilized MT3 cells by up to 60% and 24.7%, respectively. Complex formation between platelets and tumour cells in vitro was completely prevented by DIP/OPP-vesicles. These combinatory liposomes also inhibited the metastatic capacity of circulating tumour cells by reducing the complex formation with platelets. Formation of lung and extrapulmonary metastases after intravenous administration of MT3 breast cancer cells was significantly reduced when mice were treated with a single intravenous dose of DIP/OPP-L containing 100nmol lipid 6h before tumour cell inoculation. PMID:19100823

Wenzel, Jane; Zeisig, Reiner; Fichtner, Iduna

2009-03-31

385

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

386

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

387

Hrs regulates early endosome fusion by inhibiting formation of an endosomal SNARE complex  

PubMed Central

Movement through the endocytic pathway occurs principally via a series of membrane fusion and fission reactions that allow sorting of molecules to be recycled from those to be degraded. Endosome fusion is dependent on SNARE proteins, although the nature of the proteins involved and their regulation has not been fully elucidated. We found that the endosome-associated hepatocyte responsive serum phosphoprotein (Hrs) inhibited the homotypic fusion of early endosomes. A region of Hrs predicted to form a coiled coil required for binding the Q-SNARE, SNAP-25, mimicked the inhibition of endosome fusion produced by full-length Hrs, and was sufficient for endosome binding. SNAP-25, syntaxin 13, and VAMP2 were bound from rat brain membranes to the Hrs coiled-coil domain. Syntaxin 13 inhibited early endosomal fusion and botulinum toxin/E inhibition of early endosomal fusion was reversed by addition of SNAP-25(150–206), confirming a role for syntaxin 13, and establishing a role for SNAP-25 in endosomal fusion. Hrs inhibited formation of the syntaxin 13–SNAP-25–VAMP2 complex by displacing VAMP2 from the complex. These data suggest that SNAP-25 is a receptor for Hrs on early endosomal membranes and that the binding of Hrs to SNAP-25 on endosomal membranes inhibits formation of a SNARE complex required for homotypic endosome fusion.

Sun, Wei; Yan, Qing; Vida, Thomas A.; Bean, Andrew J.

2003-01-01

388

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

389

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.

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

2010-01-01

390

Charge-transfer complex formation in gelation: the role of solvent molecules with different electron-donating capacities.  

PubMed

A naphthalenediimide (NDI)-based synthetic peptide molecule forms gels in a particular solvent mixture (chloroform/aromatic hydrocarbon, 4:1) through charge-transfer (CT) complex formation; this is evident from the corresponding absorbance and fluorescence spectra at room temperature. Various aromatic hydrocarbon based solvents, including benzene, toluene, xylene (ortho, meta and para) and mesitylene, have been used for the formation of the CT complex. The role of different solvent molecules with varying electron-donation capacities in the formation of CT complexes has been established through spectroscopic and computational studies. PMID:24677404

Basak, Shibaji; Bhattacharya, Sumantra; Datta, Ayan; Banerjee, Arindam

2014-05-01

391

Complex-formation reactions of dicholoro(S-methyl-L-cysteine)palladium(II) with bio-relevant ligands. Labilization induced by S-donor chelates.  

PubMed

The complex-formation equilibria of [Pd(SMC)(H2O)2]+, where SMC = S-methyl-l-cysteinate, with bio-relevant ligands such as amino acids, peptides, dicarboxylic acids and DNA constituents were studied and their formation constants were determined. The binding mode of the ligands containing various functional groups was studied and the speciation diagrams were evaluated. The kinetics of base hydrolysis of amino acid esters bound to [Pd(SMC)(H2O)2]+ was studied in aqueous solution at 25 degrees C and 0.1 M ionic strength. The effect of solvent polarity and temperature on the hydrolysis of coordinated glycine methyl ester was investigated. The activation parameters are evaluated and discussed. PMID:18239833

Shehata, Mohamed R; Shoukry, Mohamed M; Nasr, Fatma M H; van Eldik, Rudi

2008-02-14

392

Rate of carotenoid triplet formation in solubilized light-harvesting complex II (LHCII) from spinach.  

PubMed Central

In the present study the rate of triplet transfer from chlorophyll to carotenoids in solubilized LHCII was investigated by flash spectroscopy using laser pulses of approximately 2 ns for both pump and probe. Special attention has been paid to calibration of the experimental setup and to avoid saturation effects. Carotenoid triplets were identified by the pronounced positive peak at approximately 507 nm in the triplet-singlet difference spectra. DeltaOD (507 nm) exhibits a monoexponential relaxation kinetics with characteristic lifetimes of 2-9 micros (depending on the oxygen content) that was found to be independent of the pump pulse intensity. The rise of DeltaOD (507 nm) was resolved via a pump probe technique where an optical delay of up to 20 ns was used. A thorough analysis of these experimental data leads to the conclusion that the kinetics of carotenoid triplet formation in solubilized LHCII is almost entirely limited by the lifetime of the excited singlet state of chlorophyll but neither by the pulse width nor by the rate constant of triplet-triplet transfer. Within the experimental error the rate constant of triplet-triplet transfer from chlorophyll to carotenoids was estimated to be kTT > (0.5 ns)-1. This value exceeds all data reported so far by at least one order of magnitude. The implications of this finding are briefly discussed.

Schodel, R; Irrgang, K D; Voigt, J; Renger, G

1998-01-01

393

Conductance studies on complex formation between c-methylcalix[4]resorcinarene and titanium (III) in acetonitrile-H?O binary solutions.  

PubMed

Calixresorcinarenes have proved to be unique molecules for molecular recognition via hydrogen bonding, hydrophobic and ionic interactions with suitable substrates such as cations. The study of the interactions involved in the complexation of different cations with calixresorcinarenes in solvent mixtures is important for a better understanding of the mechanism of biological transport, molecular recognition, and other analytical applications. This article summarizes different aspects of the complexes of the Ti(3+) metal cation with c-methylcalix[4]resorcinarene (CMCR) as studied by conductometry in acetonitrile (AN)-water (H?O) binary mixtures at different temperatures. Conductance data show that the metal cation/ligand (ML) stoichiometry of the complexes in solution is 1:1 in all cases. Non-linear behaviour was observed for the variation of logKf of the complexes vs. the composition of the binary solvent mixtures. Selectivity of CMCR for the Ti(3+) cation is sensitive to solvent composition; in some cases and at certain compositions of the mixed solvent systems, the selectivity order is changed. Values of thermodynamic parameters (?H(c)(0), ?S(c)(0)) for formation of the CMCR-Ti(3+) complexes in AN-H?O binary systems were obtained from the temperature dependence of stability constants, and the results show that the thermodynamics of complexation reactions are affected by the nature and composition of the mixed solvents. PMID:24084013

Rezayi, Majid; Alias, Yatimah; Abdi, Mahnaz M; Saeedfar, Kasra; Saadati, Naghmeh

2013-01-01

394

A new mechanism for the control of phenoloxidase activity: inhibition and complex formation with quinone isomerase.  

PubMed

Insect phenoloxidases participate in three physiologically important processes, viz., cuticular hardening (sclerotization), defense reactions (immune reaction), and wound healing. Arrest or even delay of any of these processes compromises the survival of insects. Since the products of phenoloxidase action, viz., quinones, are cytotoxic, uncontrolled phenoloxidase action is deleterious to the insects. Therefore, the activity of this important enzyme has to be finely controlled. A novel inhibition of insect phenoloxidases, which serves as a new regulatory mechanism for control of its activity, is described. The activity of phenoloxidases isolated from both Sarcophaga bullata and Manduca sexta is drastically inhibited by quinone isomerase (isolated from Calliphora), an enzyme that utilizes the phenoloxidase-generated 4-alkylquinones. In turn, phenoloxidase reciprocated the inhibition of isomerase. By forming a complex and controlling each other's activity, these two enzymes seem to regulate the levels of endogenously quinones. In support of this contention, an endogenous complex consisting of phenoloxidase, quinone isomerase, and quinone methide isomerase was characterized from the insect, Calliphora. This sclerotinogenic complex was isolated and purified by borate extraction of the larval cuticle, ammonium sulfate precipitation, and Sepharose 6B column chromatography. The complex exhibited a molecular mass of about 620-680 kDa, as judged by size-exclusion chromatography on Sepharose 6B and HPLC and did not even enter 3% polyacrylamide gel during electrophoresis. The phenoloxidase activity of the complex exhibited a wide substrate specificity. Incubation of the complex with N-acetyldopamine rapidly generated N-acetylnorepinephrine, dehydro-N-acetyldopamine, and its dimers. In addition, transient accumulation of N-acetyldopamine quinone was also observed. These results confirm the presence of phenoloxidase, quinone isomerase, and quinone methide isomerase in the complex. Attempts to dissociate the complex with even trace amounts of SDS ended in the total loss of quinone isomerase activity. The complex does not seems to be made up of stoichiometric amounts of individual enzymes as the ratio of phenoloxidase to quinone isomerase varied from preparation to preparation. It is proposed that the complex formation between sequential enzymes of sclerotinogenic pathway is advantageous for the organism to effectively channel various reactive intermediates during cuticular hardening. PMID:10898942

Sugumaran, M; Nellaiappan, K; Valivittan, K

2000-07-15

395

The Protein Kingdom Extended: Ordered and Intrinsically Disordered Proteins, Their Folding, Supramolecular Complex Formation, and Aggregation  

PubMed Central

The native state of a protein is usually associated with a compact globular conformation possessing a rigid and highly ordered structure. At the turn of the last century certain studies arose which concluded that many proteins cannot, in principle, form a rigid globular structure in an aqueous environment, but they are still able to fulfill their specific functions — i.e., they are native. The existence of the disordered regions allows these proteins to interact with their numerous binding partners. Such interactions are often accompanied by the formation of complexes that possess a more ordered structure than the original components. The functional diversity of these proteins, combined with the variability of signals related to the various intra-and intercellular processes handled by these proteins and their capability to produce multi-variant and multi-directional responses allow them to form a unique regulatory net in a cell. The abundance of disordered proteins inside the cell is precisely controlled at the synthesis and clearance levels as well as via interaction with specific binding partners and posttranslational modifications. Another recently recognized biologically active state of proteins is the functional amyloid. The formation of such functional amyloids is tightly controlled and therefore differs from the uncontrolled formation of pathogenic amyloids which are associated with the pathogenesis of several conformational diseases, the development of which is likely to be determined by the failures of the cellular regulatory systems rather than by the formation of the proteinaceous deposits and/or by the protofibril toxicity.

Turoverov, Konstantin K.; Kuznetsova, Irina M.; Uversky, Vladimir N.

2010-01-01

396

Two quorum sensing systems control biofilm formation and virulence in members of the Burkholderia cepacia complex  

PubMed Central

The Burkholderia cepacia complex (Bcc) consists of 17 closely related species that are problematic opportunistic bacterial pathogens for cystic fibrosis patients and immunocompromised individuals. These bacteria are capable of utilizing two different chemical languages: N-acyl homoserine lactones (AHLs) and cis-2-unsaturated fatty acids. Here we summarize the current knowledge of the underlying molecular architectures of these communication systems, showing how they are interlinked and discussing how they regulate overlapping as well as specific sets of genes. A particular focus is laid on the role of these signaling systems in the formation of biofilms, which are believed to be highly important for chronic infections. We review genes that have been implicated in the sessile lifestyle of this group of bacteria. The new emerging role of the intracellular second messenger cyclic dimeric guanosine monophosphate (c-di-GMP) as a downstream regulator of the fatty acid signaling cascade and as a key factor in biofilm formation is also discussed.

Suppiger, Angela; Schmid, Nadine; Aguilar, Claudio; Pessi, Gabriella; Eberl, Leo

2013-01-01

397

IR dust bubbles: gas, dust and star formation in the S21-S24 complex  

NASA Astrophysics Data System (ADS)

Churchwell et al. (2006) identified many IR dust bubbles in the GLIMPSE images at 8 ?m. Among these bubbles, S21, S22, S23, and S24 conform a poorly studied complex plenty of small scale bubbles, with IRDCs and signposts of recent star formation, located at about 4.5 kpc. Based on 12CO(2-1), 13CO(2-1), and 13CO(3-2) line observations obtained with the APEX telescope (angular resolution of 20"-30"), LABOCA continuum observations at 870 ?m (angular resolution of 18.5") also from APEX, Spitzer-IRAC and -MIPS images in the near and mid IR (3.6 to 24 ?m, and Herschel-PACS and -SPIRE images in the far infrared (70-500 ?m), we performed an analysis of the characteristics of the gas and dust in this high density complex. This study allowed molecular shells linked to these bubbles to be revealed, and to estimate new distances, excitation conditions, masses, and ambient densities. Cold dust counterparts were revealed by Herschel and LABOCA images, showing the material available for new generations of stars. In addition to the presence of EGOs and methanol masers, a search for young stellar objets in the complex using the available data at several wavelengths in the infrared revealed many active areas of star formation coincident with the densest regions. We compare our results with those for other IR dust bubbles and investigate the possibility that the expansion of the bubbles has triggered the star formation activity.

Cappa, E. C.; Romero, A. G.; Vasquez, J.; Firpo, V.; Dorunea, N.; Rubio, M.; Kobilnicky, C.

2013-06-01

398

Formation of Copper Impurity-Defect Complexes and Their Impact on Electrical Properties of Silicon  

NASA Astrophysics Data System (ADS)

Nature and types of structural defects in the p-type silicon doped with copper are determined by the methods of infrared microscopy and measuring of the specific resistivity, concentration, and lifetime (?) of charge carriers. It is found that the value of ? is increased and stabilized due to the formation of a trap level associated with the "copper-oxygen" complex [Cu-O] in silicon. It is shown that the copper atoms migrate from a saturated dislocation to the volume of lightly doped silicon during slow cooling after high-temperature diffusion, which is associated with the decomposition of the Si-Cu solid solution.

K?rimov, M.; Machkamov, Sh.; ?ursunov, N. ?.; Bakiev, S. ?.; ??chmudov, Sh. ?.; Sattiev, ?. R.; Akramov, F. S.

2014-05-01

399

[Thermodynamic analysis of complex formation of ethidium bromide with DNA in water solutions].  

PubMed

A thermodynamic analysis of two types of binding of ethidium bromide with DNA: intercalation and binding to the outer surface of a biopolymer has been performed by spectrophotometry. It has been shown that the dominant contribution to the energy of external binding of the ligand to DNA is made by hydrophobic interactions, which lead to less negative values of enthalpy and entropy and more severe negative changes in the heat capacity of complex formation as compared with the intercalation type of binding. PMID:21542352

Baranovski?, S F; Chernyshev, D N; Buchel'nikov, A S; Evstigneev, M P

2011-01-01

400

OFF-OFF-ON switching of fluorescence and electron transfer depending on stepwise complex formation of a host ligand with guest metal ions.  

PubMed

Stepwise complex formation is observed between 2,3,5,6-tetrakis(2-pyridyl)pyrazine (TPPZ) and a series of metal ions (M(n+) = Sc3+, Y3+, Ho3+, Eu3+, Lu3+, Nd3+, Zn2+, Mg2+, Ca2+, Ba2+, Sr2+, Li+), where TPPZ forms a 2:1 complex [(TPPZ)2-M(n+)] and a 1:1 complex [TPPZ-M(n+)] with Mn+ at low and high concentrations of metal ions, respectively. The fluorescence intensity of TPPZ begins to increase at high concentrations of metal ions, when the 2:1 (TPPZ)2-M(n+) complex is converted to the fluorescent 1:1 TPPZ-M(n+) complex. This is regarded as an "OFF-OFF-ON" fluorescence sensor for metal ions depending on the stepwise complex formation between TPPZ and metal ions. The fluorescence quantum yields of the TPPZ-M(n+) complex vary depending on the metal valence state, in which the fluorescence quantum yields of the divalent metal complexes (TPPZ-M2+) are much larger than those of the trivalent metal complexes (TPPZ-M3+). On the other hand, the binding constants of (TPPZ)2-M(n+) (K1) and TPPZ-M(n+) (K2) vary depending on the Lewis acidity of metal ions (i.e., both K1 and K2 values increase with increasing Lewis acidity of metal ions). Sc3+, which acts as the strongest Lewis acid, forms the (TPPZ)2-Sc3+ and TPPZ-Sc3+ complexes stoichiometrically with TPPZ. In such a case, "OFF-OFF-ON" switching of electron transfer from cobalt(II) tetraphenylporphyrin (CoTPP) to O2 is observed in the presence of Sc3+ and TPPZ depending on the ratio of Sc3+ to TPPZ. Electron transfer from CoTPP to O2 occurs at Sc3+ concentrations above the 1:2 ratio ([Sc3+]/[TPPZ]0 > 0.5), when the (TPPZ)2-Sc3+ complex is converted to the TPPZ-Sc3+ complex and TPPZ-(Sc3+)2, which act as promoters of electron transfer (ON) by the strong binding of O2*- with Sc3+. In sharp contrast, no electron transfer occurs without metal ion (OFF) or in the presence at Sc3+ concentrations below the 1:2 ratio (OFF), when the (TPPZ)2-Sc3+ complex has no binding site available for O2*-. PMID:18092776

Yuasa, Junpei; Fukuzumi, Shunichi

2008-01-16

401

Modified bimolecular fluorescence complementation assay to study the inhibition of transcription complex formation by JAZ proteins.  

PubMed

The jasmonate (JA) ZIM-domain (JAZ) proteins of Arabidopsis thaliana repress JA signaling and negatively regulate the JA responses. Recently, JAZ proteins have been found to inhibit the transcriptional function of several transcription factors, among which the basic helix-loop-helix (bHLH) (GLABRA3 [GL3], ENHANCER OF GLABRA3 [EGL3], and TRANSPARENT TESTA8 [TT8]) and R2R3-MYB (GL1 and MYB75) that can interact with each other to form bHLH-MYB complexes and further control gene expression. The bimolecular fluorescence complementation (BiFC) assay is a widely used technique to study protein-protein interactions in living cells. Here we describe a modified BiFC experimental procedure to study the inhibition of the formation of the bHLH (GL3)-MYB (GL1) complex by JAZ proteins. PMID:23615997

Qi, Tiancong; Song, Susheng; Xie, Daoxin

2013-01-01

402

A study of Ca(2+)-heparin complex-formation by polarimetry.  

PubMed Central

Possible inflexions in isothermal binding plots derived from equilibrium-dialysis measurements and in equivalent plots obtained by polarimetric measurements accord with the possibility that discrete Ca(2+)-heparin-water complexes/phases may exist, the nature and proportions of which depend on the conditions under which the interaction occurs. Analysis of the plots obtained by polarimetric study of chemically modified heparins suggests, for individual substituents groups, an order of importance of carboxylate greater than N-sulphonate greater than N-acetyl greater than O-sulphate for the Ca(2+)-heparin interaction occurring at [Ca2+]/[heparin disaccharide] ratios of less than 0.5. At higher ratios, transitions occur that eventually lead to the formation of a complex in which the stoichiometry of association is 1 Ca2+ ion/heparin disaccharide unit.

Grant, D; Long, W F; Moffat, C F; Williamson, F B

1992-01-01

403

Formation and tunable disassembly of polyelectrolyte-Cu2+ layer-by-layer complex film.  

PubMed

Layer-by-layer assembly of films containing metal ions was investigated. A complex between various metal ions and branched polyethyleneimine is formed in solution and then assembled into multilayer films with poly(acrylic acid). The metal-ligand complex formation results in brightly colored materials that deposit as thick layers. Cu(2+)-containing films were chosen as a model for studying the disassembly of these films in response to various stimuli, including pH, salt, and surfactants. The range of pH instability corresponds to the pH range over which pores are formed in the film. We demonstrate controllable disassembly of these materials, which could be used for antifungal or antibacterial applications. PMID:24059689

Huang, Xiayun; Schubert, Amanda B; Chrisman, James D; Zacharia, Nicole S

2013-10-22

404

Time-resolved fluorescence spectroscopic investigation of cationic polymer/DNA complex formation  

NASA Astrophysics Data System (ADS)

Since DNA is not internalized efficiently by cells, the success of gene therapy depends on the availability of carriers to efficiently deliver genetic material into target cells. Gene delivery vectors can be broadly categorized into viral and non-viral ones. Non-viral gene delivery systems are represented by cationic lipids and polymers rely on the basics of supramolecular chemistry termed "self-assembling": at physiological pH, they are cations and spontaneously form lipoplexes (for lipids) and polyplexes (for polymers) complexing nucleic acids. In this scenario, cationic polymers are commonly used as non-viral vehicles. Their effectiveness is strongly related to key parameters including DNA binding ability and stability in different environments. Time-resolved fluorescence spectroscopy of SYBR Green I (DNA dye) was carried out to characterize cationic polymer/DNA complex (polyplex) formation dispersed in aqueous solution. Both fluorescence amplitude and lifetime proved to be very sensitive to the polymer/DNA ratio (N/P ratio, +/-).

D'Andrea, Cosimo; Bassi, Andrea; Taroni, Paola; Pezzoli, Daniele; Volonterio, Alessandro; Candiani, Gabriele

2011-06-01

405

A kinetic study of the formation of beta-cyclodextrin complexes with monomolecular films of fatty acids and glycerides spread at the air/water interface.  

PubMed

The kinetics of formation of inclusion complexes between beta-cyclodextrin and monolayers of one-, two- and three-chained lipid molecules, namely, oleic acid (OA), monoolein (MO), diolein (DO) and triolein (TO), was investigated at various pH using three independent dynamic methods. The formation and solubilization of soluble inclusion beta-CD/OA and beta-CD/MO complexes was detected by measuring the decrease of the surface area and surface pressure of the OA and MO monolayers in the presence of beta-CD within a wide range of concentrations. A third approach, describing the dilatational properties of the monolayers, influenced by the formation and solubilization of the complexes, was developed. Using the three above-mentioned independent methods, the rate constants of formation (k1) and dissociation (k2) of beta-CD/OA and beta-CD/MO, were determined. We observed that solubilization flux i s for OA monolayer increases with pH and at pH 11 reached a value, which is closed to the diffusion flux iD and the process thus becomes diffusion controlled. For MO monolayer no significant effects of pH was observed above pH 6. The surface pressure (Deltapi)--area per molecule (A) and surface potential (DeltaV)--area per molecule (A) isotherms and rheological properties of DO and TO monolayers were measured in the presence or absence of beta-CD. DO and TO form water-insoluble complexes with beta-CD, as visualized by AFM images. PMID:15784322

Alahverdjieva, Veneta; Ivanova, Margarita; Verger, Robert; Panaiotov, Ivan

2005-04-25

406

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

407

Cas1-Cas2 complex formation mediates spacer acquisition during CRISPR-Cas adaptive immunity.  

PubMed

The initial stage of CRISPR-Cas immunity involves the integration of foreign DNA spacer segments into the host genomic CRISPR locus. The nucleases Cas1 and Cas2 are the only proteins conserved among all CRISPR-Cas systems, yet the molecular functions of these proteins during immunity are unknown. Here we show that Cas1 and Cas2 from Escherichia coli form a stable complex that is essential for spacer acquisition and determine the 2.3-Å-resolution crystal structure of the Cas1-Cas2 complex. Mutations that perturb Cas1-Cas2 complex formation disrupt CRISPR DNA recognition and spacer acquisition in vivo. Active site mutants of Cas2, unlike those of Cas1, can still acquire new spacers, thus indicating a nonenzymatic role of Cas2 during immunity. These results reveal the universal roles of Cas1 and Cas2 and suggest a mechanism by which Cas1-Cas2 complexes specify sites of CRISPR spacer integration. PMID:24793649

Nuñez, James K; Kranzusch, Philip J; Noeske, Jonas; Wright, Addison V; Davies, Christopher W; Doudna, Jennifer A

2014-06-01

408

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

409

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

410

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

411

Measurement of Two-Dimensional Binding Constants between Cell-Bound Major Histocompatibility Complex and Immobilized Antibodies with an Acoustic Biosensor  

PubMed Central

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 × 104 to 6.0 × 105 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 (ka = 1.15 × 10?5 ?m2 s?1 per molecule, kd = 2.07 × 10?5 s?1, and KA = 0.556 ?m2 per molecule, at 25°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.

Saitakis, Michael; Dellaporta, Anastasia; Gizeli, Electra

2008-01-01

412

Supramolecular dimerisation of middle-chain Phe pentapeptides via CB[8] host-guest homoternary complex formation.  

PubMed

Pentapeptides containing a Phe residue in the middle of the sequence exhibit ternary complex formation in the presence of cucurbit[8]uril, thus opening new perspectives on supramolecular peptide dimerisation studies. PMID:23963082

Sonzini, Silvia; Ryan, Seán T J; Scherman, Oren A

2013-10-01

413

COPPER(II), NICKEL AND URANYL COMPLEXES OF SOME AMINO ACIDS  

Microsoft Academic Search

The formation constants of copper(II) and nickel complexes of ; hydroxyproline, asparagine and N,Ndimethylglycine have been obtained. The pK\\/; sub 2\\/ of asparagine and the formation constants of its complexes are independeut ; of the optical configanration. The nickel complexes of serine methyl ester and ; glycine methyl ester are equally stable, indicating that the serine ester ; coordinates to

N. C. Li; B. E. Doody; J. M. White

1958-01-01

414

Spatiotemporal Patterns and Nonclassical Kinetics of Competing Elementary Reactions:  Chromium Complex Formation with Xylenol Orange in a Capillary  

Microsoft Academic Search

kinetically different species that react competitively with xylenol orange. The parameters that determine whether pattern formation is observable at the front are the ratios of (1) the microscopic reaction constants of the competing reactions and (2) the concentrations of the competing species. Under the parameter values studied, which allowed clear spatiotemporal separation of the two competing reactions, we find that

Andrew Yen; Anna L. Lin; Yong-Eun Lee Koo; Baruch Vilensky; Haim Taitelbaum; Raoul Kopelman

1997-01-01

415