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1

Investigation of the Composition and Formation Constant of Molecular Complexes  

Microsoft Academic Search

It has been the purpose of the present paper to investigate and explore the conditions under which the linear relation between Delta \\/CD{}0 and Delta in the Hanna-Ashbaugh-Foster-Fyfe equation for the evaluation of equilibrium constants holds, (CD{}0 is initial concentration of a donor and Delta is the observed chemical shift relative to the chemical shift of the acceptor) to obtain

R. Sahai; G. L. Loper; S. H. Lin; H. Eyring

1974-01-01

2

Complexation of Group IIIA metals with asymmetric tridentate ligands: Synthesis, characterization, formation constants and cytotoxicity  

Microsoft Academic Search

A series of new aluminum(III), gallium(III) and indium(III) complexes with some tridentate Schiff base, viz., N-{pyridine-2-ylmethyl}-2-hydroxy-5-methoxy-benzylideneamine [HL1], N-{pyridine-2-ylmethyl}-2-hydroxy-benzylideneamine [HL2], N-{pyridine-2-ylmethyl}-2-hydroxy-5-nitro-benzylideneamine [HL3], N-{pyridine-2-ylmethyl}-2-hydroxy-5-bromo-benzylideneamine [HL4], N-{pyridine-2-ylethyl}-2-hydroxy-5-methoxy-benzylideneamine [HL5], N-{pyridine-2-ylethyl}-2-hydroxy-benzylideneamine [HL6], N-{pyridine-2-ylethyl}-2-hydroxy-5-nitro-benzylideneamine [HL7], N-{pyridine-2-ylethyl}-2-hydroxy-5-bromo-benzylideneamine [HL8], with the general formula [ML2][Y] (M=Al3+, Ga3+, In3+; Y=NO3?, ClO4?) were synthesised and characterized by elemental analysis, 1H NMR, FT-IR, UV–Vis spectrophotometry and mass spectrometry. The thermodynamic formation constants

Mozaffar Asadi; Maryam Mohammadikish; Khosro Mohammadi; Pegah Mousavi; Katayon Javidnia; Ramin Miri

2009-01-01

3

Equilibrium constants for the formation of Cu(I) halide complexes  

Microsoft Academic Search

The stoichiometric equilibrium constants, K\\u000a 3\\u000a *\\u000a , for the formation of CuX\\u000a 3\\u000a 2?\\u000a from CuX\\u000a 2\\u000a ?\\u000a +X? where X=Cl and Br, have been determined from spectral measurements. The measurements were made in NaCl and NaBr solutions\\u000a from I=0.5 to 6.0m at 5, 25 and 45°C. The measured constants were extrapolated to infinite dilution using the Pitzer equations.

Virender K. Sharma; Frank J. Millero

1990-01-01

4

Fundamental and overtone vibrational spectroscopy, enthalpy of hydrogen bond formation and equilibrium constant determination of the methanol-dimethylamine complex.  

PubMed

We have measured gas phase vibrational spectra of the bimolecular complex formed between methanol (MeOH) and dimethylamine (DMA) up to about 9800 cm(-1). In addition to the strong fundamental OH-stretching transition we have also detected the weak second overtone NH-stretching transition. The spectra of the complex are obtained by spectral subtraction of the monomer spectra from spectra recorded for the mixture. For comparison, we also measured the fundamental OH-stretching transition in the bimolecular complex between MeOH and trimethylamine (TMA). The enthalpies of hydrogen bond formation (?H) for the MeOH-DMA and MeOH-TMA complexes have been determined by measurements of the fundamental OH-stretching transition in the temperature range from 298 to 358 K. The enthalpy of formation is found to be -35.8 ± 3.9 and -38.2 ± 3.3 kJ mol(-1) for MeOH-DMA and MeOH-TMA, respectively, in the 298 to 358 K region. The equilibrium constant (Kp) for the formation of the MeOH-DMA complex has been determined from the measured and calculated transition intensities of the OH-stretching fundamental transition and the NH-stretching second overtone transition. The transition intensities were calculated using an anharmonic oscillator local mode model with dipole moment and potential energy curves calculated using explicitly correlated coupled cluster methods. The equilibrium constant for formation of the MeOH-DMA complex was determined to be 0.2 ± 0.1 atm(-1), corresponding to a ?G value of about 4.0 kJ mol(-1). PMID:23695525

Du, Lin; Mackeprang, Kasper; Kjaergaard, Henrik G

2013-05-21

5

Constantes de formation des complexes hydroxydés de l'aluminium en solution aqueuse de 20 a 70°C  

NASA Astrophysics Data System (ADS)

Les constantes de formation des complexes A1(OH) 2+ et Al(OH) 4 - ont été déterminées, par des réactions ne faisant intervenir que des ions en solution, dans la gamme de température 20-70°C. Le couple Al 3+ / A 1( OH ) 2+ a été étudié en mesurant le pH de solutions de concentrations variées de sels d'aluminium. Le couple Al 3+ / A 1( OH ) 4 - a été étudié en comparant les constantes de formation du complexe trioxalato-aluminium Al(C 2 O 4 ) 3 3- à partir de Al 3+ en milieu acide et de Al(OH) 4 - en milieu basique. La constante d'acidité * K 1 du couple Al 3+ / A 1( OH ) 2+ est égale à 10 -5.00 et H = 11.8 Kcal. La constante globale * 4 de Al 3+ / A 1( OH ) 4 - vaut 10 -22.2 et H = 42.45 kcal. Ces dernières valeurs ne sont pas en accord avec les valeurs actuellement admises pour G 0 f et H 0 f de Al 3+ et Al(OH) 4 - En conclusion, nous proposons une série cohérente de données thermodynamiques pour les espèces dissoutes et solides de l'aluminium et pour certains alumine-silicates. Abstract Stability constants of hydroxocomplexes of Al(III):Al(OH) 2+ and A1(OH) 4 - have been measured in the 20-70°C temperature range by reactions involving only dissolved species. The stability constant * K 1 of the first complex ion is studied by measuring pH of solutions of aluminium salts at several concentrations. * 4 of aluminate ion is deduced from equilibrium constants of the reaction between the trioxalato aluminium (III) complex ion and Al 3+ in acid medium, and between the same complex ion and A1(OH) 4 - in alkaline medium. The K values and the associated H are * K 1 = 10 -5.00 and H 1 = 11.8 Kcal; * 4 = 10 -22.20 and H 4 = 42.45 Kcal. These last results are not in agreement with the values of recent tables for G 0 f and H 0 f of Al 3+ and Al(OH) 4 - . We suggest a consistent set of data for dissolved and solid Al species and for some aluminosilicates.

Couturier, Yves; Michard, Gil; Sarazin, Gérard

1984-04-01

6

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

7

Determination of stoichiometric coefficients and apparent formation constants for ?-cyclodextrin complexes of trans-resveratrol using reversed-phase liquid chromatography  

Microsoft Academic Search

The complexation of trans-resveratrol with ?-cyclodextrin (?-CD) was investigated using reversed-phase liquid chromatography and mobile phases to which ?-CD was added. The decrease in the retention times with increasing concentrations of ?-CD (0–2.5mM) showed that trans-resveratrol forms a 1:1 complex with ?-CD, while the apparent formation constants (KF) were strongly dependent of the water–methanol proportion of the mobile phase employed.

José Manuel López-Nicolás; Estrella Núñez-Delicado; Antonio J. Pérez-López; Ángel Carbonell Barrachina; Paula Cuadra-Crespo

2006-01-01

8

Evaluation of apparent formation constants of pentacyclic triterpene acids complexes with derivatized ?- and ?-cyclodextrins by reversed phase liquid chromatography  

Microsoft Academic Search

A reversed phase HPLC method has been investigated in order to resolve three main pentacyclic triterpene acids (oleanolic-, betulinic- and ursolic acid) found in a lot of plants. Some of them (oleanolic and ursolic acids) are position isomers and their resolution is highly improved by the addition of derivatized cyclodextrins in mobile phase. The formation of 1:1 inclusion complexes was

B. Claude; Ph. Morin; M. Lafosse; P. Andre

2004-01-01

9

Spectrophotometric and electrochemical determination of the formation constants of the complexes Curcumin?Fe(III)?water and Curcumin?Fe(II)?water  

NASA Astrophysics Data System (ADS)

The formation of complexes among the Curcumin, Fe(III) and Fe(II) was studied in aqueous media within the 5-11 pH range by means of UV-Vis spectrophotometry and cyclic voltammetry. When the reaction between the Curcumin and the ions present in basic media took place, the resulting spectra of the systems Curcumin-Fe(III) and Curcumin-Fe(II) presented a similar behaviour. The cyclic voltammograms in basic media indicated that a chemical reaction has taken place between the Curcumin and Fe(III) before that of the formation of complexes. Data processing with SQUAD permitted to calculate the formation constants of the complexes Curcumin-Fe(III), corresponding to the species FeCur ( log ? 1 1 0 =22.25±0.03 ) and FeCur(OH) - ( log ? 1 1-1 =12.14±0.03 ), while for the complexes Curcumin-Fe(II) the corresponding formation constants of the species FeCur - ( log ? 1 1 0 =9.20±0.04 ), FeHCur ( log ? 1 1 1 =19.76±0.03 ), FeH 2Cur + ( log ? 1 1 2 =28.11±0.02 ).

Bernabé-Pineda, Marganta; Ram?´rez-Silva, Maria Teresa; Romero-Romo, Mario Alberto; González-Vergara, Enrique; Rojas-Hernández, Alberto

2004-04-01

10

Determination of stoichiometric coefficients and apparent formation constants for beta-cyclodextrin complexes of trans-resveratrol using reversed-phase liquid chromatography.  

PubMed

The complexation of trans-resveratrol with beta-cyclodextrin (beta-CD) was investigated using reversed-phase liquid chromatography and mobile phases to which beta-CD was added. The decrease in the retention times with increasing concentrations of beta-CD (0-2.5 mM) showed that trans-resveratrol forms a 1:1 complex with beta-CD, while the apparent formation constants (K(F)) were strongly dependent of the water-methanol proportion of the mobile phase employed. A slight decrease in K(F) was observed at 50-55% water in the mobile phase but a large increase from 55 to 70% water. The values of K(F) for the trans-resveratrol-beta-CD interaction decreased when the temperature was raised from 20 to 37 degrees C. In order to gain information about the mechanism aspect of the trans-resveratrol affinity for beta-CD, the thermodynamic parameters of the complexation were obtained. Complex formation of trans-resveratrol with beta-CD (DeltaG degrees =-17.01 kJ/mol) is largely driven by enthalpy (DeltaH degrees = -30.62 kJ/mol) and slightly entropy changes (DeltaS degrees = -45.68 J/mol K). PMID:17083948

López-Nicolás, José Manuel; Núñez-Delicado, Estrella; Pérez-López, Antonio J; Barrachina, Angel Carbonell; Cuadra-Crespo, Paula

2006-11-02

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

Rapid, simple and sensitive determination of the apparent formation constants of trans-resveratrol complexes with natural cyclodextrins in aqueous medium using HPLC  

Microsoft Academic Search

The study of the complexation of trans-resveratrol with natural cyclodextrins (CDs) in aqueous medium under different physico-chemical conditions of pH or temperature is essential if this antioxidant compound is to be used successfully in the food industry as ingredient of functional foods, due its poor stability, bioavailability and solubility. In this paper, a rapid, simple and sensitive determination of the

José Manuel López-Nicolás; Francisco García-Carmona

2008-01-01

14

Rate constants for the reactions of benzene-chlorine atom ?-complexes with alcohols in carbon tetrachloride  

Microsoft Academic Search

The reactivity and selectivity of benzene-chlorine atom ?-complexes for hydrogen atom abstraction from various alcohols were investigated. Benzene-chlorine atom ?-complexes were produced in liquid carbon tetrachloride using the technique of pulse radiolysis at room temperature. The effect of the concentration of benzene and absorbed doses on the formation and decay kinetics were examined and the equilibrium constant of the complex

T. Sumiyoshi

1997-01-01

15

Transport Method for Determining the Stability Constants of Complexes  

Microsoft Academic Search

A transport method was introduced to determine the stability constants of the 1: 1 complexes formed between cyclodextrins (a-, r3- and y-) as hosts and molecular iodine and triiodide anion as guests in an aqueous medium. The stability constants obtained when the guest is iodine are 3.7 x 10 3 , 2.4 X 10 2 and 1.4 x 10 2

CHIN LING LOH

2003-01-01

16

1-Hydroxybenzotriazole (HOBt) acidity, formation constant with different metals and thermodynamic parameters: Synthesis and characterization of some HOBt metal complexes – Crystal structures of two polymers: [Cu 2(H 2O) 5(OBt) 2(?-OBt) 2] · 2H 2O · EtOH ( 1A) and [Cu(?-OBt)(HOBt)(OBt)(EtOH)] ( 1B)  

Microsoft Academic Search

The dissociation constants of 1-hydroxybenzotriazole (HOBt) and the formation constants of its complexes with cobalt(II), copper(II), nickel(II), iron(III), zinc(II), lead(II), mercury(II), and cadmium(II) were evaluated at different temperatures (20–45°C) by potentiometric measurements in the presence of different percentages of ethanol–water and dioxane–water media. The thermodynamic parameters were calculated and discussed. HOBt complexes of copper, nickel, cobalt, and zinc were synthesized

Hassan H. Hammud; K. Travis Holman; Mamdouh S. Masoud; Ayman El-Faham; Hanan Beidas

2009-01-01

17

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

18

V(IV)O versus V(IV) complex formation by tridentate (O, N(arom), O) ligands: prediction of geometry, EPR 51V hyperfine coupling constants, and UV-Vis spectra.  

PubMed

Systems formed using the V(IV)O(2+) ion with tridentate ligands containing a (O, N(arom), O) donor set were described. Examined ligands were 3,5-bis(2-hydroxyphenyl)-1-phenyl-1H-1,2,4-triazole (H2hyph(Ph)), 4-[3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazol-1-yl]benzoic acid (H3hyph(C)), 4-[3,5-bis(2-hydroxyphenyl)-1H-1,2,4-triazol-1-yl]benzenesulfonic acid (H3hyph(S)), and 2,6-bis(2-hydroxyphenyl)pyridine (H2bhpp), with H3hyph(C) being an orally active iron chelator that is commercially available under the name Exjade (Novartis) for treatment of chronic iron overload arising from blood transfusions. The systems were studied using EPR, UV-Vis, and IR spectroscopies, pH potentiometry, and DFT methods. The ligands bind vanadium with the two terminal deprotonated phenol groups and the central aromatic nitrogen to give six-membered chelate rings. In aqueous solution the main species were the mono- and bis-chelated V(IV)O complexes, whereas in the solid state neutral non-oxido V(IV) compounds were formed. [V(hyph(Ph))2] and [V(bhpp)2] are hexacoordinated, with a geometry close to the octahedral and a meridional arrangement of the ligands. DFT calculations allow distinguishing V(IV)O and V(IV) species and predicting their structure, the (51)V hyperfine coupling constant tensor A, and the electronic absorption spectra. Finally, EPR spectra of several non-oxido V(IV) species were compared using relevant geometrical parameters to demonstrate that in the case of tridentate ligands the (51)V hyperfine coupling constant is related to the geometric isomerism (meridional or facial) rather than the twist angle ?, which measures the distortion of the hexacoordinated structure toward a trigonal prism. PMID:23581472

Pisano, Luisa; Várnagy, Katalin; Timári, Sarolta; Hegetschweiler, Kaspar; Micera, Giovanni; Garribba, Eugenio

2013-04-12

19

Pattern Formation and Complexity Emergence  

NASA Astrophysics Data System (ADS)

Success of nonlinear modelling of pattern formation and self-organization encourages speculations on informational and number theoretical foundations of complexity emergence. Pythagorean "unreasonable effectiveness of integers" in natural processes is perhaps extrapolatable even to universal emergence "out-of-nothing" (Leibniz, Wheeler). Because rational numbers (R = M/N) are everywhere dense on real axis, any digital string (hence any "book" from "Library of Babel" of J.L.Borges) is "recorded" infinitely many times in arbitrary many rationals. Furthermore, within any arbitrary small interval there are infinitely many Rs for which (either or both) integers (Ms and Ns) "carry" any given string of any given length. Because any iterational process (such as generation of fractal features of Mandelbrot Set) is arbitrary closely approximatable with rational numbers, the infinite pattern of integers expresses itself in generation of complexity of the world, as well as in emergence of the world itself. This "tunnelling" from Platonic World ("Platonia" of J.Barbour) to a real (physical) world is modern recast of Leibniz's motto ("for deriving all from nothing there suffices a single principle").

Berezin, Alexander A.

2001-03-01

20

New insights into formation of trivalent actinides complexes with DTPA.  

PubMed

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

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

2012-11-15

21

Determination of the compositions and instability constants of some oxalate complexes of Pu +3 by an ion exchange method  

Microsoft Academic Search

The complex formation of Pu+3 ions in oxalate solutions over the pH range 1.4–3.0 was studied by an ion exchange method. It was established that in this pH range the complex ions [Pu (C2O4)2]- and [Pu(HC2O4)4]- are formed and that their instability constants are KH=7.1·10-10 and KH?=1.1·10-11, respectively. The value of the instability constant of the complex ion [Pu(C2O4)2]} agrees

A. D. Gel'man; N. N. Matorina; A. I. Moskvin

1958-01-01

22

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

SciTech Connect

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

Giordano, T.H. (New Mexico State Univ., Las Cruces (United States)); Drummond, S.E. (Oak Ridge National Lab., TN (United States))

1991-09-01

23

Extraposition via Complex Domain Formation  

Microsoft Academic Search

We propose a novel approach to extraposition in German within an alternative conception of syntax in which syntactic structure and linear order are mediated not via encodings of hierarchical relations but instead via order domains. At the heart of our proposal is a new kind of domain formation which affords analyses of extraposition constructions that are linguistically more adequate than

Andreas Kathol; Carl Pollard

1995-01-01

24

Dielectric-Constant-Enhanced Hall Mobility in Complex Oxides  

SciTech Connect

The high dielectric constant of doped ferroelectric KTa{sub 1-x}Nb{sub x}O{sub 3} is shown to increase dielectric screening of electron scatterers, and thus to enhance the electronic mobility, overcoming one of the key limitations in the application of functional oxides. These observations are based on transport and optical measurements as well as band structure calculations.

Siemons, Wolter [ORNL; McGuire, Michael A [ORNL; Cooper, Valentino R [ORNL; Biegalski, Michael D [ORNL; Ivanov, Ilia N [ORNL; Jellison Jr, Gerald Earle [ORNL; Boatner, Lynn A [ORNL; Sales, Brian C [ORNL; Christen, Hans M [ORNL

2012-01-01

25

Spray formation with complex fluids  

NASA Astrophysics Data System (ADS)

Droplet formation through Faraday excitation has been tested in the low driving frequency limit. Kerosene was used to model liquid fuel with the addition of PIB in different proportions. All fluids were characterized in detail. The mechanisms of ejection were investigated to identify the relative influence of viscosity and surface tension. It was also possible to characterize the type of instability leading to the emission drop process.

Lustig, S.; Rosen, M.

2011-05-01

26

Size effect of nano-copper films on complex optical constant and permittivity in infrared region  

Microsoft Academic Search

Nano-copper films were prepared by DC magnetron sputtering. Their reflectivity and transmittivity to electromagnetic wave in infrared region were measured with Fourier Transformation Infrared Spectrometer (FTIR), by which their complex optical constant and permittivity were obtained. The results show that the complex optical constant and permittivity of nano-copper films depend upon the film thickness. This dependence is correlated with microstructure

H. Du; S. W. Lee; J. Gong; C. Sun; L. S. Wen

2004-01-01

27

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

NASA Astrophysics Data System (ADS)

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

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

1991-09-01

28

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

NASA Astrophysics Data System (ADS)

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

Smith, Gregory P.

2006-09-01

29

SOLUBILITY AND ION EXCHANGE METHODS FOR DETERMINING THE COMPLEX FORMATION OF PLUTONIUM AND AMERICIUM III IN AQUEOUS SOLUTIONS  

Microsoft Academic Search

The formation of Pu(IV) complexes in phosphoric acid solutions and the ; dissociation constants of Pu(IV) phosphate complexes were studied by solubility ; methods. The Me: addend ratio of various Pu(IV) phosphate complexes and ; complexes of other investigated systems tends to shift, with the increase of ; complex forming agent concentration, toward the side of complexes with larger ;

Moskin

1959-01-01

30

Binding of polyanions by biogenic amines. I. Formation and stability of protonated putrescine and cadaverine complexes with inorganic anions  

Microsoft Academic Search

The formation and stability of proton diamine-inorganic anion [Cl?, SO42?, HPO42?, P2O74? and Fe(CN)64?] complexes was studied potentiometrically [(H+)-glass electrode] at 25°C. Several general formula ALHr complexes are formed in these various systems. The stability of complexes formed between H2A2+ and different anions ranges from one to six (log formation constants). The formation constants are slightly dependent on the length

Alessandro De Robertis; Concetta De Stefano; Antonio Gianguzza; Silvio Sammartano

1998-01-01

31

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

SciTech Connect

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

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

1987-01-01

32

DETERMINATION OF THE COMPOSITION AND DISSOCIATION CONSTANT FOR OXALATE COMPLEXES OF Pu$sup +3$ COMPOUNDS BY ION EXCHANGE  

Microsoft Academic Search

The method of ionic exchange was used in the investigation of the Pu\\/sup ; 3+\\/ complex formation in oxalate solutions in the interval pH 1.4 to 3.0. It ; has been shown that the complex ions Pu(CâOâ)â⁻ and Pu(HC\\/; sub 2\\/Oâ)\\/⁻wi th the instability constants K⁠= 7. x 10⁻¹°; and Kâ = 1.1 x 10⁻¹¹ are forme d in

A. D. Gelman; N. N. Matorina; A. I. Moskvin

1958-01-01

33

Automatic measurement of complex dielectric constant and permeability at microwave frequencies  

Microsoft Academic Search

With the advent of the computer and automatic test equipment, new techniques for measuring complex dielectric constant (?) and permeability (µ) can be considered. Such a technique is described where a system is employed that automatically measures the complex reflection and transmission coefficients that result when a sample of material is inserted in waveguide or a TEM transmission line. Measurement

WILLIAM B. WEIR

1974-01-01

34

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

35

STABILITY CONSTANTS OF NP(V) COMPLEXES WITH FLOURIDE AND SULFATE AT VARIABLE TEMPERATURES  

SciTech Connect

A solvent extraction method was used to determine the stability constants of Np(V) complexes with fluoride and sulfate in 1.0 M NaClO{sub 4} from 25 C to 60 C. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of fluoride and sulfate were increased. Stability constants of the 1:1 Np(V)-fluoride complexes and the 1:1 Np(V)-sulfate and 1:2 Np(V)-sulfate complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [F{sup -}] and [SO{sub 4}{sup 2-}] on the distribution ratio. The enthalpy and entropy of complexation were calculated from the stability constants at different temperatures by using the Van't Hoff equation.

Y. Xia; J.I. Friese; D.A. Moore; L. Rao

2005-07-11

36

Mercury(ii) complex formation with N-acetylcysteine.  

PubMed

N-Acetylcysteine (H2NAC) is a potent antioxidant, a precursor for cysteine and glutathione, and a potential antidote against certain metal ions such as cadmium and mercury. Little is known about the structural aspects of complexes formed between Hg(ii) and N-acetylcysteine, despite many biological tests on its ability to bind to organic and inorganic mercury, and a few reports on formation constants for Hg(NAC)n (n = 1-3) complexes. We have combined several techniques, including Hg L3-edge EXAFS (extended X-ray absorption fine structure), (199)Hg NMR and Raman spectroscopy, to investigate the nature and structure of Hg(ii) N-acetylcysteine complexes formed in aqueous solution at pH 7.5 and 10.5. To allow measurements on the same samples, rather concentrated solutions containing CHg(ii) = 0.1 M and variable H2NAC/Hg(ii) mole ratios = 2.0-10.0 were used. At physiological pH, Hg(NAC)2(2-) and Hg(NAC)3(4-) complexes form, while in ligand excess and at alkaline pH (H2NAC/Hg(ii) > 4), a novel tetra-thiolate species Hg(NAC)4(6-) dominates. Comparison between the Hg(ii) complex formation with cysteine, penicillamine and N-acetylcysteine in alkaline aqueous solution has been made to elucidate the influence of the blocked amino group of N-acetylcysteine. PMID:23986393

Jalilehvand, Farideh; Parmar, Karnjit; Zielke, Stephen

2013-09-25

37

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

2013-09-23

38

Arsenazo III forms 2:1 complexes with Ca and 1:1 complexes with Mg under physiological conditions. Estimates of the apparent dissociation constants.  

PubMed Central

Experiments to determine the apparent dissociation constants of the Ca and Mg complexes of arsenazo III clearly indicated that the predominant Ca complex contains one Ca ion and two dye molecules, although previous reports have either claimed or assumed 1:1 complexing. The evidence is based on the effects of varying [dye] as well as [Ca] and [Mg], and clear evidence for the formation of 1:1 complexes with Ca was obtained only at submicromolar [dye], whereas Mg formed 1:1 complexes exclusively. The implications of these findings with regard to the use of arsenazo III as an indicator of intracellular free [Ca] are discussed, with particular reference to its selectivity for Ca and the interference effects of other ions.

Thomas, M V

1979-01-01

39

Rate constants for reactions of alkyl radicals with water and methanol complexes of triethylborane.  

PubMed

Reactions of secondary alkyl radicals with triethylborane and several of its complexes were studied. The H-atom transfer reactions from Et3B-OH2 and Et3B-OD2 were suppressed by addition of pyridine to the reaction mixture. Rate constants for reactions of secondary alkyl radicals with triethylborane and its complexes with water, deuterium oxide, methanol, and THF at ambient temperature were determined by radical clock methods. Cyclization of the 1-undecyl-5-hexenyl radical and ring opening of the 1-cyclobutyldodecyl radical were evaluated as clock reactions. The cyclobutylcarbinyl radical ring opening had the appropriate velocity for relatively precise determinations of the ratios of rate constants for H-atom transfer trapping and rearrangement, and these ratios combined with an estimated rate constant for the cyclobutylcarbinyl radical ring opening gave absolute values for the rate constants for the H-atom transfer reactions. For example, the triethylborane-water complex reacts with a secondary alkyl radical in benzene at 20 degrees C with a rate constant of 2 x 10(4) M(-1) s(-1). Variable temperature studies with the Et3B-CH3OH complex in toluene indicate that the hydrogen atom transfer reaction has unusually high entropic demand, which results in substantially more efficient hydrogen atom transfer trapping reactions in competition with radical ring opening and cyclization reactions at reduced temperatures. PMID:17579450

Jin, Jing; Newcomb, Martin

2007-06-19

40

Complex formation between uranyl and various thiosemicarbazide derivatives  

SciTech Connect

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

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

1987-01-01

41

Radiometric determination of stability constants of mercury species complexes with L-cysteine  

Microsoft Academic Search

Liquid-liquid distribution method has been applied for the determination of the composition and stability constants of mercury species with L-cysteine \\/H2L\\/. In the pH range 2–8, mercury \\/II\\/ forms a complex Hg\\/HL\\/2 with very high stability constant \\/lg 2 = 40.0\\/, whereas methylmercury and phenylmercury form complexes CH3HgHL \\/lg 1 = 15.56\\/ and C6H5HgHL \\/lg 1 = 16.5\\/. At pH13,

J. Starý; K. Kratzer

1988-01-01

42

Determination of the stability constants of uranyl complex with 8-hydroxyquinolinium sulfate  

Microsoft Academic Search

8-Hydroxyquinoline (8-HOQ) is known as an important chelating agent for several metal ions. This compound is practically insoluble in water. For this reason, in this study its water soluble sulfate salt has been used for complexing uranyl ions and the stability constants of the complex have been determined. The Irving-Rosotti method computing the Calvin-Bjerrum pH-titration data, was applied. Finally, the

P. Ünak; D. Özdemir; T. Ünak

1993-01-01

43

Characterization and Determination of the Stability Constant of Lanthanide Complexes with Carbonates. Final Report.  

National Technical Information Service (NTIS)

The stability constants of Europium (III) complexes with carbonate and bicarbonate ions are measured at 22 exp 0 C and at 0.5M ionic strength. Solvent extraction with 1.3-diphenyl 1.3-propanedione 5x10 exp -2 M in benzene is studied. The distribution betw...

B. Marcandalli G. Bidoglio

1983-01-01

44

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

45

Measurement of liquid complex dielectric constants using non-contact sensors  

Microsoft Academic Search

Our primary objective in this work is the accurate measurement of complex dielectric constant and conductivity of unknown liquids. In this paper we present design, fabrication, and testing results for an IDC (interdigitated capacitor) electrode sensor for use as a fluid monitoring component that can be integrated into a microfluidic system. Unlike prior work we show how to accurately extract

Jun Wan Kim; Praveen Pasupathy; Sheng Zhang; Dean P. Neikirk

2009-01-01

46

Surface tension method for determining binding constants for cyclodextrin inclusion complexes of ionic surfactants  

Microsoft Academic Search

A new method has been developed for determining binding constants of complexes of cyclodextrins with surface-active compounds, including water-soluble ionic surfactants. The technique requires measuring the change in surface tension caused by addition of a cyclodextrin (CD) to aqueous solutions of the surfactant; the experimental results lead directly to inferred values of the thermodynamic activity of the surfactant. Surface tension

Udeni R. Dharmawardana; Sherril D. Christian; Edwin E. Tucker; Richard W. Taylor; John F. Scamehorn

1993-01-01

47

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

48

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 ...

49

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

2012-12-03

50

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

51

Characterizing the dynamics of functionally relevant complexes of formate dehydrogenase  

PubMed Central

The potential for femtosecond to picosecond time-scale motions to influence the rate of the intrinsic chemical step in enzyme-catalyzed reactions is a source of significant controversy. Among the central challenges in resolving this controversy is the difficulty of experimentally characterizing thermally activated motions at this time scale in functionally relevant enzyme complexes. We report a series of measurements to address this problem using two-dimensional infrared spectroscopy to characterize the time scales of active-site motions in complexes of formate dehydrogenase with the transition-state-analog inhibitor azide (). We observe that the frequency–frequency time correlation functions (FFCF) for the ternary complexes with NAD+ and NADH decay completely with slow time constants of 3.2 ps and 4.6 ps, respectively. This result suggests that in the vicinity of the transition state, the active-site enzyme structure samples a narrow and relatively rigid conformational distribution indicating that the transition-state structure is well organized for the reaction. In contrast, for the binary complex, we observe a significant static contribution to the FFCF similar to what is seen in other enzymes, indicating the presence of the slow motions that occur on time scales longer than our measurement window.

Bandaria, Jigar N.; Dutta, Samrat; Nydegger, Michael W.; Rock, William; Kohen, Amnon; Cheatum, Christopher M.

2010-01-01

52

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

53

Method and apparatus for dielectric well logging of subsurface earth formations with a lumped constant antenna  

SciTech Connect

This patent describes a well logging tool for use in obtaining an indicator of the dielectric constant of subsurface earth formations traversed by a borehole, comprising: an antenna housing means defining an X axis extending longitudinally along the housing means for contacting the wall of the borehole; a first and a second transmitter antenna means carried by the housing means and spatially distributed along a line parallel to the X axis and adjacent respective ends of the housing means for transmitting electromagnetic energy of a preselected frequency into the formation; and a first and a second receiver antenna means carried by the housing means and spatially distributed adjacent each other along the line and intermediate of the first and second transmitter antenna means for receiving electromagnetic energy from the formation each antenna means comprising: an outer aperture defined by the housing; a feed-through terminal having an electrical contact extending in the outer aperture; a filler plug within the aperture; an antenna slot element disposed on the housing and defining with the outer aperture an electrically resonant cavity element defines an elongated lot extending in a direction perpendicular to the axis; an antenna insulator plug sealingly and slidably disposed within the slot; an elongate inductor carried on the filler plug adjacent the slot in the antenna slot element and in electrical contact with the housing at one end of the inductor; and a lumped constant resonating means interconnected between the terminal contact and the other end of the inductor forming an electrically resonating circuit.

Janes, T.A.

1987-07-07

54

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

55

Potentiometric measurement of stability constants of complexes between fulvic acid carboxylate and Fe 3+  

Microsoft Academic Search

The stability constants of complexes formed between iron (III) and fulvic acid extracted from organic manures and wastes such\\u000a as urban domestic sewage sludge, farmyard manure, poultry manure and sulfitation pressmud were investigated by the potentiometric\\u000a titration method in an ionic medium of 0.1 M KNO3 at 25±1 °C. A modification of the Katchalsky's model was employed for the estimation

S. B. Pandeya; A. K. Singh

2000-01-01

56

Numerical multimode calibration technique for extraction of complex propagation constants of substrate integrated waveguide  

Microsoft Academic Search

Integrated planar technique has always been considered as a reliable candidate for low-cost mass production of millimeter-wave circuits and systems. In this paper, a numerical multimode calibration procedure is proposed and developed with a commercial software package on the basis of a full-ware finite element method (FEM) for the accurate extraction of complex propagation constants of substrate integrated waveguide (SIW).

Feng Xu; Ke Wu

2004-01-01

57

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

SciTech Connect

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

Erten, H.N; Mohammed, A.K.; Choppin, G.R. [Florida State Univ., Tallahassee, FL (United States). Dept. of Chemistry

1993-12-31

58

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

59

Equilibrium star formation in a constant Q disc: model optimization and initial tests  

NASA Astrophysics Data System (ADS)

We develop a model for the distribution of the interstellar medium (ISM) and star formation in galaxies based on recent studies that indicate that galactic discs stabilize to a constant stability parameter, which we combine with prescriptions of how the phases of the ISM are determined and for the star formation law (SFL). The model predicts the gas surface mass density and star formation intensity of a galaxy given its rotation curve, stellar surface mass density and the gas velocity dispersion. This model is tested on radial profiles of neutral and molecular ISM surface mass density and star formation intensity of 12 galaxies selected from the H I Nearby Galaxy Survey sample. Our tests focus on intermediate radii (0.3 to 1 times the optical radius) because there are insufficient data to test the outer discs and the fits are less accurate in detail in the centre. Nevertheless, the model produces reasonable agreement with the ISM mass and star formation rate integrated over the central region in all but one case. To optimize the model, we evaluate four recipes for the stability parameter, three recipes for apportioning the ISM into molecular and neutral components, and eight versions of the SFL. We find no clear-cut best prescription for the two-fluid (gas and stars) stability parameter Q2f and therefore for simplicity, we use the Wang and Silk approximation (QWS). We found that an empirical scaling between the molecular-to-neutral ISM ratio (Rmol) and the stellar surface mass density proposed by Leroy et al. works marginally better than the other two prescriptions for this ratio in predicting the ISM profiles, and noticeably better in predicting the star formation intensity from the ISM profiles produced by our model with the SFLs we tested. Thus, in the context of our modelled ISM profiles, the linear molecular SFL and the two-component SFL work better than the other prescriptions we tested. We incorporate these relations into our `constant Q disc' model.

Zheng, Zheng; Meurer, Gerhardt R.; Heckman, Timothy M.; Thilker, David A.; Zwaan, Martin A.

2013-10-01

60

Stability Constants for Sulfate Complexation of Yttrium and the Rare Earth Elements  

NASA Astrophysics Data System (ADS)

In natural waters, yttrium and the rare earth elements (YREE) are mostly complexed with inorganic anions such as carbonate and chloride. YREE complexation with sulfate is minor (<5%) in seawater and generally negligible in fresh waters, yet it can be quite important in situations where oxidation of pyrite leads to high dissolved sulfate concentrations. The development of a consensus pattern of stability constants for YREE monosulfato-complexes has a quite convoluted history. It is based on a 1974 'compilation' that was derived from a much older, somewhat questionable, dataset, by adding interpolations and omitting a few elements. During subsequent transcriptions, some errors were introduced and the omitted data were interpolated rather than replaced with the original values. All this has resulted in a consensus pattern that is essentially flat, without any structure or fractionation between light and heavy REE. It is widely quoted and has been used to argue that sulfate complexation does not cause YREE fractionation. Conversely, flat YREE patterns in natural waters have been taken as evidence for substantial complexation of the YREE with sulfate. We have taken a new approach to measuring the stability constants of all YREE monosulfato-complexes with the greatest possible precision. Stability constants were determined by comparing the solubility of barium sulfate in YREE chloride solutions and in an ammonium chloride reference solution, all at the ionic strength of seawater. The reference solution and solutions of individual YREE chlorides were equilibrated with a small amount of high purity barium sulfate at t = 25°C for at least one week. The equilibrated solutions were then filtered and analyzed for concentrations of YREE and Ba (ICP-MS), chloride and sulfate (ion chromatography), and pH (glass electrode). A simple model was used to determine the stability constants from these measurements. Averaged results from four experiments, two with and two without added sulfate, have standard deviations of 0.03 log units or less. Within this precision, the pattern of stability constants is not flat, as has been assumed, but has a very distinct shape. The pattern is nearly flat from La to Gd, possibly with a slight maximum at Eu. From Gd to Lu it shows a gradual and almost linear decrease, with the stability constant of Lu being more than 0.2 log units below that of La. The stability constant of Y is close to that of Er. Our pattern is in broad agreement with several careful earlier studies that have been largely ignored in the recent literature. Comparison with the substantial body of existing work also indicates that our stability constants are well within the published range for individual YREE. This revised pattern may have significant consequences for the interpretation of YREE patterns in high-sulfate environments such as runoff from mine tailings and certain groundwaters.

Schijf, J.; Byrne, R. H.

2002-12-01

61

Nonlinear problem of flow past a source with the formation of a stagnation region at different Bernoulli constants  

NASA Astrophysics Data System (ADS)

The paper examines unbounded fluid flow past a point source when the collision of two streams with different Bernoulli constants occurs with the formation of a bounded region of constant pressure. A nonlinear system of equations for the flow is derived, and a high-accuracy numerical solution is obtained. Calculation results are presented for different Bernoulli and cavitation numbers.

Zhuk, A. D.; Kuzmin, S. V.

1986-06-01

62

Binding constants and stoichiometries of glyceraldehyde 3-phosphate dehydrogenase-tubulin complexes.  

PubMed

The catalytic activity of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) decreased (almost linearly) as a function of increasing concentrations of tubulin; the total loss in activity was attained at a ratio of 1.2 to 1.8 tubulin dimer to GAPDH tetramer. Based on the inhibition data, a dissociation constant for the tubulin-GAPDH complex was calculated to be about 0.73 nM. The stoichiometry and the dissociation constants of the tubulin-GAPDH complex were found to be dependent upon the ionic strength of the assay media. Qualitatively similar results were obtained (i.e., inhibition and ionic strength effect) when the GAPDH-catalyzed reaction was measured in the presence of Sepharose-immobilized tubulin. The physical interaction between these two proteins, i.e., GAPDH and tubulin, was measured by the ability of one protein (immobilized on a Sepharose matrix) to copellet the other protein. By employing this copelleting technique, we measured the dissociation constant and stoichiometry of the immobilized tubulin-GAPDH complex to be about 6.4 nM and 0.91 tubulin dimer/GAPDH tetramer, respectively. The dissociation constant and stoichiometry thus obtained were found to be remarkably similar to those obtained by the tubulin-dependent GAPDH inhibition data. In contrast to these results, (soluble) tubulin had no effect on the catalytic activity of the immobilized GAPDH, albeit the soluble tubulin copelleted with the immobilized GAPDH. The dissociation constant and stoichiometry of immobilized GAPDH-tubulin complex were calculated to be 0.76 +/- 0.13 microM and 3.23 +/- 0.16 tubulin dimer/GAPDH tetramer, respectively. These data suggest that there are two classes of binding sites for tubulin on a tetrameric GAPDH; high-affinity and low-affinity sites. The enzyme is inhibited when tubulin binds at the high-affinity site while the catalytic function of the enzyme is unaffected when the tubulin binds at the low-affinity site. The latter site is suggested herein to be responsible for the cross-linking (bundling) of microtubules. PMID:8080270

Muronetz, V I; Wang, Z X; Keith, T J; Knull, H R; Srivastava, D K

1994-09-01

63

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

64

Proton transfer and complex formation of angiotensin I ions with gaseous molecules at various temperature  

NASA Astrophysics Data System (ADS)

Proton transfer reactions of angiotensin I ions for +2 charge state, [M + 2H]2+, to primary, secondary and aromatic amines were examined in the gas phase. Absolute reaction rate constants for proton transfer were determined from intensities of parent and product ions in the mass spectra. Temperature dependence of the reaction rate constants was measured. Remarkable change was observed for distribution of product ions and reaction rate constants. Proton transfer reaction was enhanced or reduced by complex formation of [M + 2H]2+ with gaseous molecules. The results relate to conformation changes of [M + 2H]2+ with change of temperature, which are induced by complex formation and or by thermal collision with He. Proton transfer reactions of angiotensin I ions for +3 charge state, [M + 3H]3+, were also studied. The reaction rates did not depend on temperature so definitely.

Nonose, Shinji; Yamashita, Kazuki; Sudo, Ayako; Kawashima, Minami

2013-09-01

65

Determining complex permittivity from propagation constant measurements with planar transmission lines  

NASA Astrophysics Data System (ADS)

A new two-standard calibration procedure is outlined for determining the complex permittivity of materials from the propagation constant measured with planar transmission lines. Once calibrated, a closed-form expression for the material permittivity is obtained. The effects of radiation and conductor losses are accounted for in the calibration. The multiline technique, combined with a recently proposed planar transmission-line configuration, is used to determine the line propagation constant. An uncertainty analysis is presented for the proposed calibration procedure that includes the uncertainties associated with the multiline technique. This allows line dimensions and calibration standards to be selected that minimize the total measurement uncertainty. The use of air and distilled water as calibration standards gives relatively small measurement uncertainty. Permittivity measurement results for five liquids, covering a wide permittivity range, agree very closely with expected values from 0.5-5 GHz.

Roelvink, J.; Trabelsi, S.; Nelson, S. O.

2013-10-01

66

Determination of the composition and instability constants of complex Pu +3 oxalate ions  

Microsoft Academic Search

The solubility of Pu2(C2O4)3 · 9H2O in aqueous solutions of K2C2O4 of various concentrations (0.01–2.4 moles \\/liter) has been determined at constant ionic strength of the solution at 20. It\\u000a was found that Pu+3 complexes are formed in these solutions. It was found from the results of Pu2(C2O4)3 · 9H2O solubility determinations that in the region of K2C2O4 concentrations studied

A. D. Gel'man; N. N. Matorina; A. I. Moskvin

1957-01-01

67

Synthesis, structure and dielectric constant property of two novel complexes based on protonated 1-aminoadamantane  

Microsoft Academic Search

The reaction of 1-aminoadamantane hydrochloride and divalent metal chloride in concentrated hydrochloric acid medium yields two unusual complexes containing protonated 1-aminoadamantane, (C10H18N)1+2[ZnCl4]2? (1), (C10H18N)1+2[MnCl4(H2O)2]2? (2a) and (C10H18N)1+2[MnCl4(D2O)2]2? (2b). Their crystal structures have been determined by X-ray crystallography. Both complexes contain molecular network of (C10H18N)+ cations and divalent metal chloride polyhedral anions (Mn and Zn site symmetry 2\\/m). Dielectric constants of

Min-Min Zhao; Jia-Zhen Ge; Zhi-Rong Qu

2010-01-01

68

On the Formation of "Hypercoordinated" Uranyl Complexes  

SciTech Connect

Recent gas phase experimental studies suggest the presence of hypercoordinated uranyl complexes. Coordination of acetone (Ace) to uranyl to form hypercoordinated species is examined using density functional theory (DFT) with a range of functionals and second order perturbation theory (MP2). Complexes with up to eight acetones were studied. It is shown that no more than six acetones can bind directly to uranium and that the observed uranyl complexes are not hypercoordinated.

Schoendorff, George E.; De Jong, Wibe A.; van Stipdonk, Michael J.; Gibson, John K.; Rios, Daniel; Gordon, Mark S.; Windus, Theresa L.

2011-09-05

69

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

2013-09-03

70

Microwave response due to light-induced changes in the complex dielectric constant of semiconductors  

NASA Astrophysics Data System (ADS)

Cavity perturbation theory was extended to account for light-induced changes in the complex dielectric constant, as a second perturbation, and the equations were used to interpret the microwave response in the advanced method of transient microwave photoconductivity (AMTMP). The equations obtained earlier from a simpler, first cavity perturbation theory, and those derived for simple geometries are shown to be special cases of this more general theory. For AMTMP, the harmonic-oscillator model can account for the changes in the real and imaginary parts of the dielectric constant made by free and trapped electrons, including plasma effects. The decay of the photoconductivity in semi-insulating (SI) GaAs is dominated by changes in the concentration of electrons, and changes in the mobility can be neglected. The difference between CdSe and SI GaAs in regard to changes in the real part of the dielectric constant is due to the substantially larger mobility in SI GaAs.

Grabtchak, Serguei; Cocivera, Michael

1998-08-01

71

The Complexity of Integrable Hamiltonian Systems on a Prescribed Three-Dimensional Constant-Energy Submanifold  

NASA Astrophysics Data System (ADS)

This paper is devoted to a description of \\mathcal{Q}-regions, i.e., domains in the molecular table of Fomenko that are filled with integrable systems with constant energy surfaces \\mathcal{Q} that occur most frequently in physics. Namely, the \\mathcal{Q}-regions for \\mathcal{Q}=S^3, \\mathbf{R}P^3, S^1\\otimes S^2, T^3, and \\char93 ^l S^1\\otimes S^2 are computed explicitly. The \\mathcal{Q}-regions for an arbitrary three-dimensional constant energy submanifold \\mathcal{Q} are determined up to a finite number of points. These results make it possible to predict the topological properties of integrable Hamiltonian systems as yet not discovered in physics. The concepts of the order of torsion of integrable Hamiltonian systems and of a minimal system are also introduced, and the connection between these concepts and the concepts of complexity of systems and complexity of three-manifolds due to Matveev is indicated.

T'en Zung, Nguen

1993-02-01

72

Studies of curcumin and curcuminoids. XXXVI. The stoichiometry and complexation constants of cyclodextrin complexes as determined by the phase-solubility method and UV–Vis titration  

Microsoft Academic Search

Cyclodextrin (CD) complex stoichiometry and complexation constant with two symmetric curcuminoids and two unsymmetric curcuminoid-like\\u000a compounds were investigated and compared by two independent methods, the phase-solubility method and ultraviolet-visible absorption\\u000a spectroscopy (UV–Vis) titration. Two different methods were applied in an effort to increase the apparent intrinsic solubility\\u000a of the compounds and make the investigation of stoichiometry and complexation constants possible.

Ravinder Singh; Hanne Hjorth Tønnesen; Stine Byskov Vogensen; Thorsteinn Loftsson; Már Másson

2010-01-01

73

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

PubMed

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 constants of the resulting complexes ML, MHL, M(2)L and M(2)HL were determined. The stabilities of both ML and M(2)L complexes were found to vary in the order Mg(2+)> Ca(2+)> Sr(2+)> Ba(2+). Studying the complex formation between Al(3+) ion (M) and XO (L), it was observed that four complexed species with stoichiometries ML, ML(2), MHL and MH(2)L could be formed in solution. It was also found that the Al L(2) complex can act as a chelating agent for further complexation with two cations other than Al(3+) ion (i.e. Ba, L, Al, L, Ba, Mg, L, Al, L, Mg, and Mg, L, Al, L, Ba). The formation constants of the resulting mixed complexes were determined and their distribution diagrams were investigated. PMID:18967209

Gholivand, M B; Bamdad, F; Ghasemi, J

1998-08-01

74

Formation of cis-enediyne complexes from rhenium alkynylcarbene complexes.  

PubMed

Dimerization of the alkynylcarbene complex Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(3) (8) occurs at 100 degrees C to give a 1.2:1 mixture of enediyne complexes [Cp(CO)(2)Re](2)[eta(2),eta(2)-TolC(triple bond)CC(CH(3))=C(CH(3))C(triple bond)CTol] (10-Eand 10-Z), showing no intrinsic bias toward trans-enediyne complexes. The cyclopropyl-substituted alkynylcarbene complex Cp(CO)(2)Re=C(Tol)C(triple bond)CC(3)H(5) (11) dimerizes at 120 degrees C to give a 5:1 ratio of enediyne complexes [Cp(CO)(2)Re](2)[eta(2),eta(2)-TolC(triple bond)C(C(3)H(5))C=C(C(3)H(5))C(triple bond)CTol] (12-E and 12-Z); no ring expansion product was observed. This suggests that if intermediate A formed by a [1,1.5] Re shift and having carbene character at the remote alkynyl carbon is involved, then interaction of the neighboring Re with the carbene center greatly diminishes the carbene character as compared with that of free cyclopropyl carbenes. The tethered bis-(alkynylcarbene) complex Cp(CO)(2)Re=C(Tol)C(triple bond)CCH(2)CH(2)CH(2)C(triple bond)CC(Tol)= Re(CO)(2)Cp (13) dimerizes rapidly at 12 degrees C to give the cyclic cis-enediyne complex [Cp(CO)(2)Re](2)[eta(2),eta(2)-TolC(triple bond)CC(CH(2)CH(2)CH(2))=CC(triple bond)CTol] (15). Attempted synthesis of the 1,8-disubstituted naphthalene derivative 1,8-[Cp(CO)(2)Re=C(Tol)C(triple bond)C](2)C(10)H(6) (16), in which the alkynylcarbene units are constrained to a parallel geometry, leads to dimerization to [Cp(CO)(2)Re](2)(eta(2),eta(2)-1,2-(tolylethynyl)acenaphthylene] (17). The very rapid dimerizations of both 13 and 16 provide compelling evidence against mechanisms involving cyclopropene intermediates. A mechanism is proposed which involves rate-determining addition of the carbene center of A to the remote alkynyl carbon of a second alkynylcarbene complex to generate vinyl carbene intermediate C, and rearrangement of C to the enediyne complex by a [1,1.5] Re shift. PMID:11890809

Casey, Charles P; Kraft, Stefan; Powell, Douglas R

2002-03-20

75

Rate Constants for the Quenching of Excited States of Metal Complexes in Fluid Solution  

SciTech Connect

The rate constants for the quenching of the excited states of metal ions and complexes in homogeneous fluid solution are reported in this compilation. Values of k/sub q/ for dynamic, collisional processes between excited species and quenchers have been critically evaluated, and are presented with the following information, among others, from the original publications, when available: description of the solution medium, temperature at which k/sub q/ was determined, experimental method, range of quencher concentration used, lifetime of the excited state in the absence of quencher, activation parameters, quenching mechanism. Data collection is complete through the end of 1986, and covers the coordination compounds of 26 metals, including the ions and complexes of the inner- and outer-transition metals, and porphyrin complexes of nontransition metals. Data for 261 excited states quenched by more than 400 inorganic quenchers and 600 organic quenchers have been extracted from almost 500 publications. The introduction to the work contains a discussion of the conceptual background to quenching, including a general treatment of the kinetics, an explanation of the tables, and a list of recent review articles. Uncommon kinetics mechanisms and equations, used to obtain the reported values of k/sub q/, are discussed in detail as part of the notes to the tables. Indexes of excited states, quenchers, and authors are appended.

Hoffman, M.Z.; Bolletta, F.; Moggi, L.; Hug, G.L.

1989-01-01

76

Structural determinants for the formation of sulfhemeprotein complexes  

PubMed Central

Several hemoglobins were explored by UV-Vis and resonance Raman spectroscopy to define sulfheme complex formation. Evaluation of these proteins upon the reaction with H2O2 or O2 in the presence of H2S suggest: (a) the formation of the sulfheme derivate requires a HisE7 residue in the heme distal site with an adequate orientation to form an active ternary complex; (b) that the ternary complex intermediate involves the HisE7, the peroxo or ferryl species, and the H2S molecule. This moiety precedes and triggers the sulfheme formation.

Roman-Morales, Elddie; Pietri, Ruth; Ramos-Santana, Brenda; Vinogradov, Serge N.; Lewis-Ballester, Ariel; Lopez-Garriga, Juan

2010-01-01

77

Steric Aspects of the Formation of Metal Chelate Complexes  

NASA Astrophysics Data System (ADS)

The geometrical and thermodynamic aspects of the formation of complexes between metal cations and organic ligands are examined theoretically from the standpoint of conformational analysis. Particular attention has been devoted to the problem of the selectivity of the complex formation, which is of practical importance. It is shown that the selectivity of complex formation is largely determined by the steric factor. The advantages and disadvantages of the available methods for the quantitative allowance for the steric factor as well as methods of calculation of the structure of coordination compounds are analysed. The bibliography includes 105 references.

Dashevskii, V. G.; Baranov, A. P.; Kabachnik, Martin I.

1983-02-01

78

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

2012-09-28

79

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

80

Dielectric relaxations and formation mechanism of giant dielectric constant step in CaCu3Ti4O12 ceramics  

Microsoft Academic Search

The dielectric relaxation behaviors of CaCu3Ti4O12 ceramics were evaluated together with the mixed-valence structure, and the formation mechanism of a giant dielectric constant step was discussed. The giant dielectric constant step was bounded by two dielectric relaxations in low and high temperature ranges. The low-temperature dielectric relaxation was intrinsic, and it was very similar to the electronic ferroelectricity, while the

Lei Ni; Xiang Ming Chen

2007-01-01

81

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

NASA Astrophysics Data System (ADS)

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

Sawada, Atsushi; Tarumi, Kazuaki; Naemura, Shohei

1999-03-01

82

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

NASA Astrophysics Data System (ADS)

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

Samsonov, Boris F.

2010-10-01

83

Predictive gold nanocluster formation controlled by metal-ligand complexes.  

PubMed

The formation of ligand-protected gold nanoclusters during size-selective syntheses is seemingly driven by the inherent properties of the protecting ligands, but a general description of the product formation has not been presented. This study uses diphosphine-protected Au clusters as a model system to examine i) control of metal-ligand complex distributions in methanol-chloroform solutions, ii) role of solution perturbations, e.g., oxidation, and iii) nanocluster formation through reduction of characterized complex distributions. By selectively reducing complexes and monitoring cluster formation with electrospray ionization mass spectrometry and UV-vis, data show the distribution of complexes can be controlled through ligand exchange, and the reduction of specific complexes produce characteristic ligated gold clusters based on ligand class. Specifically, 1,n-bis(diphenylphosphino)n-alkane ligands, L(n), where n = 1 through 6, are classified into two distinct sets. The classes represent ligands that either form mainly [AuL(n)(2)](+) (Class I, n = 1-3) or bridged [Au(2)L(n)(2)](2+) (Class II, n = 4-6) complexes after complete ligand exchange with AuClPPh(3). Selectively reducing gold-phosphine ligand complexes allows mapping of product formation, resulting collectively in a predictive tool for ligated gold cluster production by simply monitoring the initial complex distribution prior to reduction. PMID:22228703

Pettibone, John M; Hudgens, Jeffrey W

2012-01-09

84

Protonation and silver(I) complex-formation equilibria of some amino-alcohols  

Microsoft Academic Search

Formation constants of the silver(I) complexes with some amino-alcohols have been determined at 25°C in 0.5 M KNO3 by means of two independent potentiometric measurements employing glass and silver electrode. The ligands considered are: sec-butylamine, 2-amino-1-propanol, 2-amino-1-methoxy-propane, 2-amino-2-methyl-1-propanol, 2-amino-1-butanol, 2-amino-1-pentanol, 2-amino-1-hexanol, 2-amino-1,3-propanediol, 2-amino-1,3-hexandiol, 2-amino-2-methyl-1,3-propanediol and Tris(hydroxymethyl)-aminomethane. Protonation constants of the selected ligands have also been determined. Calculations were made using

Silvia Canepari; Vincenzo Carunchio; Paola Castellano; Antonella Messina

1997-01-01

85

Crk family adaptors–signalling complex formation and biological roles  

Microsoft Academic Search

Crk family adaptors are widely expressed and mediate the timely formation of signal transduction protein complexes upon a variety of extracellular stimuli, including various growth and differentiation factors. Selective formation of multi-protein complexes by the Crk and Crk-like (CRKL) proteins depends on specific motifs recognized by their SH2 and SH3 domains. In the case of the first SH3 domains [SH3(1)

Stephan M Feller

2001-01-01

86

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

PubMed

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

Walsh, Michael J; Ahner, Beth A

2013-07-16

87

Dynamics of Lane Formation in Driven Binary Complex Plasmas  

SciTech Connect

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

Suetterlin, K. R.; Ivlev, A. V.; Raeth, C.; Thomas, H. M.; Rubin-Zuzic, M.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85741 Garching (Germany); Wysocki, A.; Loewen, H. [Heinrich-Heine-Universitaet Duesseldorf, 40225 Duesseldorf (Germany); Goedheer, W. J. [FOM-Institute for Plasma Physics Rijnhuizen, 3430 BE Nieuwegein (Netherlands); Fortov, V. E.; Lipaev, A. M.; Molotkov, V. I.; Petrov, O. F. [Joint Institute for High Temperatures, 125412 Moscow (Russian Federation)

2009-02-27

88

Transition-Metal Complex Formation with Phenyl Isocyanate.  

National Technical Information Service (NTIS)

Complex formation between phenyl isocyanate and cobalt or manganese naphthenate in benzene was determined by the mole ratio method. Complexes of 3:1 for cobalt and 2:1 for manganese were found. The method of analysis in this study utilized the characteris...

L. Rand J. A. McLean

1968-01-01

89

Image formation in the eye: very specified complexity  

Microsoft Academic Search

The formation of an image, and its correct interpretation by sighted living creatures, is a unique example of specified complexity unlike anything else in nature. While many of the functional aspects of living organisms are extremely complex, only an image requires a unique mapping process by the eye-brain system to be useful to the organism. The transfer of light from

David E. Stoltzmann

2005-01-01

90

The thermodynamic characteristics of the formation of Al3+ ion complexes with iminodisuccinic acid in aqueous solutions  

NASA Astrophysics Data System (ADS)

Complex formation between Al3+ and iminodisuccinic acid (H4L) was studied at 25°C against the background of 0.1, 0.4, 0.6, and 0.8 N solutions of KNO3 by potentiometry and mathematical modeling. The extrapolation of concentration constants to zero ionic strength was used to calculate the thermodynamic constants of the formation of the AlL-, AlHL, and AlOHL2- complexes using an equation with one individual parameter (log?0 = 16.48 ± 0.08, 8.93 ± 0.14, and 22.88 ± 0.08, respectively).

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

2012-03-01

91

Positronium formation in solid transition metal losartanates complexes  

NASA Astrophysics Data System (ADS)

In this Letter, positron annihilation lifetime (PALS) measurements were performed in transition metal losartanates complexes, MT(Los)2, and in potassium losartanate, KLos, in order to built up insights about the positronium formation mechanism in molecular environment. A correlation was obtained between formation probability, I3, and the covalence of complexes, evaluated by molar electrical conductivity in dimethylformamide (DMF). Furthermore, some metallic ion properties, such as reduction potential and pauling electronegativity, were also correlated with I3. These results were analyzed in terms of the spur model and of the recently proposed mechanism, named cybotatic correlated system kinetic mechanism (CCSKM), which involves molecular excited states in positronium formation.

de Oliveira, F. C.; Denadai, A. M. L.; Fulgêncio, F.; da Silva, J. G.; Windmöller, D.; Marques-Netto, A.; Machado, J. C.; Magalhães, W. F.

2013-10-01

92

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

PubMed

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

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

2012-12-01

93

Measurements and analysis of dissociation rate constants of metal-fulvic acid complexes in aqueous solutions. Part II: measurement of decay rates by inductively-coupled plasma mass spectrometry and determination of rate constants for dissociation  

NASA Astrophysics Data System (ADS)

Rates of removal of metal ions from metal-fulvic acid complexes in aqueous solutions by Chelex-100 cation exchange resin have been measured using inductively-coupled plasma mass spectrometry (ICP-MS). When metal ions are complexed by the complexing agents, fulvic acid and ethylenediaminetetraacetic acid (each complexing agent is taken separately), the rate of uptake of metal ions by Chelex-100 has been related to the rate of dissociation of the metal complexes. The data were analyzed using the statistical methods described in Part 1. Complexes of lead with fulvic acid have a broad distribution of rate constants for dissociation, whereas complexes of aluminum with fulvic acid have a narrow distribution of dissociation rate constants. The rate constants for dissociation of both of these complexes decrease as the concentration of fulvic acid is increased at constant concentration of the metal. The results show that neither Zn nor Cd form strong complexes with fulvic acid.

Sekaly, Amina L. R.; Back, M. H.; Chakrabarti, C. L.; Grégoire, D. C.; Lu, Julia Y.; Schroeder, W. H.

1998-08-01

94

Formation of multinuclear metal-terpyridyl complexes covalently bound to carbon substrates.  

PubMed

Multinuclear complexes consisting of metal ions and a bis(terpyridyl) ligand were covalently bound to carbon substrates. The bonding of the complexes is initiated by the bonding of phenylterpyridine (PT) on the substrates using its in-situ-generated diazonium derivative, followed by stepwise coordination of the metal ions and the ligand on it. The bonding of the PT and the formation of the multinuclear complexes were confirmed by XPS, AFM, and CV measurements. The heterogeneous rate constant (k) at the Co complex-substrate interface was evaluated by chronoamperometry (CA). The estimated high k = (2.9-3.6) x 10(3) s(-1)) would be attributed to the C-C bond at the interface without interrupting the conjugation. These multinuclear complexes bound to the carbon substrates can facilitate electron transfer from redox species such as enzymes. PMID:19891463

Kubo, Wataru; Nagao, Masashi; Otsuka, Yoichi; Homma, Tsutomu; Miyata, Hirokatsu

2009-12-01

95

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, Agost Gyula; Peintler, Gábor; Forgo, Péter; Pálinkó, István; Sipos, Pál

2013-07-29

96

Simulation of Titan haze formation using a photochemical flow reactor. The optical constants of the polymer  

NASA Astrophysics Data System (ADS)

Solar UV is the principal energy source impinging the atmosphere of Titan while the energy from the electrons in Saturn's magnetosphere is less than 0.5% of the UV light. Titan haze analogs were prepared by the photolysis of a mixture of gases that simulate the composition of its atmosphere (nitrogen, methane, hydrogen, acetylene, ethylene, and cyanoacetylene). The real (n) and imaginary (k) parts of the complex refractive index of haze analogs formed from four different gas mixtures were calculated from the spectral properties of the solid polymer in UV-visible, near infrared and infrared wavelength spectral regions. The value of n was constant at 1.6±0.1 throughout the 0.2-2.5 ?m region. The variation of k with wavelength for the values derived for Titan has a lower error than the absolute values of k so the more significant comparisons are with the slopes of the k( ?) plots in the UV-VIS region. Three of the photochemical Titan haze analogs had slopes comparable to those derived for Titan from the Voyager data (Rages and Pollack, 1980, Icarus 41, 119-130; McKay and Toon, 1992, in: Proceedings of the Symposium on Titan, in: ESA SP, Vol. 338, pp. 185-190). The slopes of the k( ?) plots for haze analogs prepared by spark discharge (Khare et al., 1984, Icarus 60, 127-137) and plasma discharge (Ramirez et al., 2002, Icarus 156, 515-529) were also comparable to Titan's. These finding show that the k( ?) plots do not differentiate between different laboratory simulations of atmospheric chemistry on Titan in the UV-VIS near IR region (0.2-2.5 microns). There is a large difference between the k( ?) in the infrared between the haze analogs prepared photochemically and analogs prepared using a plasma discharges (Khare et al., 1984, Icarus 60, 127-137; Coll et al., 1999, Planet. Space Sci. 47, 1331-1340; Khare et al., 2002, Icarus 160, 172-182). The C/N ratio in the haze analog prepared by discharges is in the 2-11 range while that of the photochemical analogs is in the 18-24 range. The use of discharges and UV light for initiating the chemistry in Titan's atmosphere is discussed.

Tran, Buu N.; Joseph, Jeffrey C.; Ferris, James P.; Persans, Peter D.; Chera, John J.

2003-10-01

97

Grinding-induced equimolar complex formation between thiourea and ethenzamide.  

PubMed

We prepared and characterized a grinding-induced equimolar complex of thiourea with ethenzamide. When thiourea and ethenzamide were co-ground at a molar ratio of 3 : 1, new powder X-ray diffraction (PXRD) peaks were observed in addition to PXRD peaks of thiourea crystals. The optimum stoichiometry of the new structure was confirmed as 1 : 1 mol/mol. Effect of grinding time on the thiourea-ethenzamide equimolar complex formation was investigated by using PXRD, differential scanning calorimetry and Fourier transform infrared spectroscopy. The equimolar crystal structure was confirmed by X-ray diffraction measurements of the single crystal which was recrystallized from ethanol. It was found that the intermolecular hydrogen bond formations between thiourea and ethenzamide molecules contributed to the equimolar complex formation. The complex formation was not observed in the cases where benzamide, salicylamide or 3-ethoxybenzamide was co-ground with thiourea. 2-Alcoxyl benzamide structures should be required for the grinding-induced equimolar complex formation with thiourea. PMID:15133201

Moribe, Kunikazu; Tsuchiya, Masami; Tozuka, Yuichi; Yamaguchi, Kentaro; Oguchi, Toshio; Yamamoto, Keiji

2004-05-01

98

Effect of Hydrogen Bond Formation on the NMR Properties of Glycine-HCN Complexes.  

PubMed

The influence of the hydrogen bond formation on the nuclear magnetic resonance parameters has been investigated for the binary (1:1) and ternary (1:2) glycine-HCN complexes in the gas phase using high-level density functional theory with the B3LYP/6-31++G(2d,2p)//B3LYP/6-31++G(d,p) model of quantum chemistry. The calculated isotropic/anisotropic shielding parameters of the isolated glycine and HCN molecules are reported and compared with other theoretical results and experimental measurements. Six different conformations of hydrogen-bonded clusters have considered for both 1:1 and 1:2 glycine-HCN complexes. The isotropic and anisotropic chemical shifts for all the constituent atoms of the complexes have been calculated. The spin-spin coupling constants and the Fermi contact terms have also been analyzed in the context of hydrogen-bond formation. PMID:24020881

da Silva, Arnaldo Machado; Ghosh, Angsula; Chaudhuri, Puspitapallab

2013-09-25

99

Activation of immobilized plasminogen by tissue activator. Multimolecular complex formation  

SciTech Connect

Ternary complex formation of tissue plasminogen activator (TPA) and plasminogen (Plg) with thrombospondin (TSP) or histidine-rich glycoprotein (HRGP) has been demonstrated using an enzyme-linked immunosorbent assay, an affinity bead assay, and a rocket immunoelectrophoresis assay. The formation of these complexes was specific, concentration dependent, saturable, lysine binding site-dependent, and inhibitable by fluid phase plasminogen. Apparent Kd values were approximately 12-36 nM for the interaction of TPA with TSP-Plg complexes and 15-31 nM with HRGP-Plg complexes. At saturation the relative molar stoichiometry of Plg:TPA was 3:1 within the TSP-containing complexes and 1:1 within HRGP-containing complexes. The activation of Plg to plasmin by TPA on TSP- and HRGP-coated surfaces was studied using a synthetic fluorometric plasmin substrate (D-Val-Leu-Lys-7-amino-4-trifluoromethyl coumarin). Kinetic analysis demonstrated a marked increase in the affinity of TPA for plasminogen in the presence of surface-associated TSP or HRGP. Complex formation of locally released tissue plasminogen activator with Plg immobilized on TSP or HRGP surfaces may thus play an important role in effecting proteolytic events in nonfibrin-containing microenvironments.

Silverstein, R.L.; Nachman, R.L.; Leung, L.L.; Harpel, P.C.

1985-08-25

100

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

101

Enhancing electrorheological behaviors with formation of ?-cyclodextrin supramolecular complex  

Microsoft Academic Search

According to the point that the host structure and the properties can be easily modified by the formation of host–guest complex, the supramolecular complexes of ?-cyclodextrin cross-linking polymer\\/1-(2-pyridlazo)-2-naphthol (?-CDP-PAN) particles were synthesized. Then the electrorheological properties of the suspensions of ?-CDP-PAN particles in silicone oil have been investigated under DC electric fields. It was found that the yield stress of

Xiaopeng Zhao

2003-01-01

102

Isotope-dependent rate constants for CS sup minus sub 2 formation in Cs ( ns , nd )+CS sub 2 collisions  

SciTech Connect

Negative ion formation during collisions between Cs ({ital ns},{ital nd}) Rydberg atoms and CS{sub 2} molecules has been studied for intermediate values of the effective principal quantum number ({ital n}*=10--26). Rate constants for CS{sup {minus}}{sub 2} formation are found to be different for the two isotopes C{sup 32}S{sup 34}S and C{sup 32}S{sup 32}S for a narrow range of {ital n}* near {ital n}*=17, with the rate constant for {sup 12}C{sup 32}S{sup 34}S{sup {minus}} production being up to 4.5 times larger than that for {sup 12}C{sup 32}S{sup 32}S{sup {minus}}.

Carman, H.S. Jr.; Klots, C.E.; Compton, R.N. (Chemical Physics Section Health and Safety Research Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831-6125 (USA))

1990-05-01

103

Kinetics of formation of the host-guest complex of a viologen with cucurbit[7]uril.  

PubMed

Host-guest complexation between the dicationic viologen 1-tri(ethylene glycol)-1'-methyl-m-xylyl-4,4'-bipyridinium and cucurbit[7]uril (CB7) was studied at pH = 4.5 in water. The stability constants of the mono- and bis-CB7 adducts were determined at 25 °C by UV-vis spectroscopy. Stopped-flow kinetic experiments were performed to measure the formation and dissociation rate constants of the monoadduct: k(1) = (6.01 ± 0.03) × 10(6) M(-1)s(-1) and k(-1) = 52.7 ± 0.4 s(-1), respectively. Possible mechanisms of complexation are discussed in view of the kinetic results. PMID:22690827

Kalmár, József; Ellis, Shawna B; Ashby, Michael T; Halterman, Ronald L

2012-06-12

104

Preliminary estimate of the diffusion constant of polystyrene during film formation from the latex  

SciTech Connect

The radius of gyration of 3 x 10/sup 6/ gm/mol molecular weight polystyrene chains was found to be 167 A in 500 A latex particles, the constraining factor being about three. On film formation and subsequent annealing, the radius of gyration gradually increased, giving primary information about the mechanism of film formation.

Linne, M.A.; Klein, A.; Sperling, L.H.; Wignall, G.D.

1986-01-01

105

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

2012-05-14

106

Determination of the molecular complexation constant between alprostadil and alpha-cyclodextrin by conductometry  

Microsoft Academic Search

The binding constant between alprostadil (PGE1) and ?-cyclodextrin (?-CD) was determined at four temperatures using conductance measurements. Alpha-cyclodextrin is an excipient material in Caverject dual chamber syringe (DCS) that was added to enhance stability. The binding constant was used to calculate the amount of PGE1 free upon reconstitution and injection, since only the free drug is clinically active. The conductivity

Philip M. Sheehy; Tore Ramstad

2005-01-01

107

Reevaluation of the Formation Constants of The Hydrated Proton in Acetonitrile.  

National Technical Information Service (NTIS)

Values of the hydration constants K(f)(H(+)nw) of the proton in acetonitrile (AN) calculated previously from spectrophotometric measurements of the activity of the solvated proton, a(Hs+) in dilute perchloric acid solutions in the presence of water, using...

M. K. Chantooni I. M. Kolthoff

1969-01-01

108

Direct measurements of formation rate constants of allylic radical from hot olefins formed by internal conversion. I  

Microsoft Academic Search

The photofragmentation of 2,3,3-trimethyl-1-butene (TMB), 2,3-dimethyl-2-pentene (DMP), and tetramethylethylene (TME) has been studied in the gas phase by ArF (193 nm) laser flash photolysis. For the first time, the formation rate constants to the common product of trimethylallyl (TMA) radical have been measured directly under collision free conditions. The C–C bond (the C–H bond for TME) at the position ?

Nobuaki Nakashima; Noriaki Ikeda; Nobuo Shimo; Keitaro Yoshihara

1987-01-01

109

Estimation of composition, coordination model, and stability constant of some metal\\/phosphate complexes using spectral and potentiometric measurements  

Microsoft Academic Search

Complexation reactions in a binary metal\\/phosphate system were studied. Protolytic equilibria of phosphate in the presence\\u000a of cobalt, nickel, iron, copper, chromium and silver metal ions were investigated by potentiometric titrations in the pH range\\u000a of 2–11. Stability constants of the metal\\/phosphate complexes were determined by computer analysis of the potentiometric titration.\\u000a Potentiometric titrations suggest that the presence of metal

Khalid Abu-Shandi; Fadel Al-Wedian

2009-01-01

110

Transport method for determining the association constants of complexes formed between aromatic hydrocarbons and ? - and ? -cyclodextrin in water  

Microsoft Academic Search

The association constants of 1 : 1 complexes formed in water between six aromatic hydrocarbons (o-,m-, andp-xylene, naphthalene, anthracene, and pyrene) anda- andß-cyclodextrin were determined by the transport method. The values are in good agreement with those determined by other methods.

Bo-Long Poh; Yoke Mooi Chow

1992-01-01

111

Isolation of a uranyl amide by "ate" complex formation.  

PubMed

The uranyl amide [{Li(DME)}(2)Cl][Li(DME)][UO(2)(NC(5)H(10))(3)](2) has been synthesised and structurally characterised. Its stability is attributed to the saturation of the uranyl coordination sphere by "ate" complex formation. PMID:20631946

Seaman, Lani A; Schnaars, David D; Wu, Guang; Hayton, Trevor W

2010-03-25

112

[Kinetics of DNA-distaxin complex-formation].  

PubMed

Kinetics of DNA--distaxines complexes formation was studied spectrophotometrically by means of the stop--flow method. It has been found that increase of number of bulky pyrrolcarboxamide group in the row of distaxines: -0, -1, -2, - slows down the binding reactions and increases the number of their stages. PMID:3814634

Sizova, I A; Poletaev, A I

113

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

114

Geology of the Biwabik Iron Formation and Duluth Complex  

USGS Publications Warehouse

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

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

2008-01-01

115

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

2007-10-01

116

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

117

Pattern formation of ion channels with state-dependent charges and diffusion constants in fluid membranes  

NASA Astrophysics Data System (ADS)

A model of mobile, charged ion channels in a fluid membrane is studied. The channels may switch between an open and a closed state according to a simple two-state kinetics with constant rates. The effective electrophoretic charge and the diffusion constant of the channels may be different in the closed and in the open state. The system is modeled by densities of channel species, obeying simple equations of electrodiffusion. The lateral transmembrane voltage profile is determined from a cable-type equation. Bifurcations from the homogeneous, stationary state appear as hard-mode, soft-mode, or hard-mode oscillatory transitions within physiologically reasonable ranges of model parameters. We study the dynamics beyond linear stability analysis and derive nonlinear evolution equations near the transitions to stationary patterns.

Kramer, Stephan C.; Kree, Reiner

2002-05-01

118

Calculation of the structure and nuclear magnetic shielding constants of some H-bonded carbon acid complexes  

Microsoft Academic Search

Electronic and spatial structure of some H-bonded complexes ((HCOOH)n (n=1–4), formic, acrylic acids and their complexes with water and dimethylsulfoxide) were studied by ab initio methods using MP2\\/RHF\\/\\/6-31G?, RHF\\/6-31G? basis sets, and also by using density functional theory (DFT) within the B3LYP approximation. The possibility of formation of chain and cyclic complexes of formic and acrylic acids with dimethylsulfoxide is

R. M Aminova; G. A Schamov; A. V Aganov

2000-01-01

119

Positronium formation studies in crystalline molecular complexes: Triphenylphosphine oxide – Acetanilide  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

120

[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

121

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

122

Applicability and limitations of affinity capillary electrophoresis and vacancy affinity capillary electrophoresis methods for determination of complexation constants.  

PubMed

ACE and vacancy affinity capillary electrophoresis (VACE) are the commonly used methods for determination of complexation constants by CE. The applicability and limitations of these methods were tested experimentally and by means of simulations using our simulation software Simul 5 Complex. It was shown that while the ACE method provides reliable and precise values of complexation parameters, those determined by VACE can be incorrect especially in the case of strong complexation. The effective mobilities of the system peaks in the VACE method, and consequently, the resulting complexation parameters were found to be a function of concentration of the analyte present in the BGE. Development of system peaks in VACE is discussed in the frame of the linear theory of electromigration. Dependence of mobility of system peaks on the composition of the BGE cannot be characterized by a simple analytical expression as in the case of ACE method. Thus, the VACE method fails and the resulting complexation constants might seriously differ from the reality. PMID:23254978

Dvo?ák, Martin; Svobodová, Jana; Beneš, Martin; Gaš, Bohuslav

2013-02-08

123

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

2013-04-30

124

Effect of anionic additive type on ion pair formation constants of basic pharmaceuticals  

Microsoft Academic Search

Due to their beneficial effect on selectivity, peak shape, and sample loading, the use of mobile phase anionic additives, such as formate (HCOO?), chloride (Cl?), and trifluoroacetate (CF3COO?), is increasing in both reversed-phase chromatography (RPLC) and liquid chromatography-mass spectrometry (LC\\/MS). Similarly, perchlorate is a common “ion pair” agent in reversed-phase separation of peptides. Although many studies have suggested that anions

Jun Dai; Shaun D. Mendonsa; Michael T. Bowser; Charles A. Lucy; Peter W. Carr

2005-01-01

125

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

126

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

2013-07-11

127

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

NASA Astrophysics Data System (ADS)

Rate constants for the potentially important interstellar N(4S) + CH(X2{\\Pi}r) reaction have been measured in a continuous supersonic flow reactor over the range 56 K < T < 296 K using the relative rate technique employing both the N(4S) + OH(X2{\\Pi}i) and N(4S) + CN(X2{\\Sigma}+) 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 13A' and 13A" states of HCN and HNC, brought about through a hierarchical construction scheme. Both adiabatic potential energy surfaces are barrierless, each one having two deep potential wells suggesting that this reaction is dominated by a complex-forming mechanism. The experimental and theoretical work are inexcellent agreement, 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.

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

128

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

129

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

130

Mechanism of formation of partially-crosslinked polyacrylamide complexes  

Microsoft Academic Search

A new type of partially-crosslinked polyacrylamide (PCPAM) which displays promising application in enhanced oil recovery (EOR) has been synthesized via aqueous solution polymerization under adiabatic conditions. Based on methods of real time infrared monitoring, two-dimensional infrared correlation spectroscopy and dynamic rheology measurement, an unusual complex formation mechanism of the PCPAM with the multi-functional initiator system is clearly disclosed. A process

Zhiqing Su; Zuming Jiang; Guangsu Huang; Li Li; Xiaoan Wang

2012-01-01

131

The catalytic role of uranyl in formation of polycatechol complexes  

PubMed Central

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

2011-01-01

132

Single-stranded nucleic acids promote SAMHD1 complex formation.  

PubMed

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

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

2013-01-31

133

Demixing-stimulated lane formation in binary complex plasma  

SciTech Connect

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

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

2011-11-29

134

In-situ measurement of the complex dielectric constant of sea ice from 1 to 10 GHz  

Microsoft Academic Search

Th authors have developed a new electromagnetic, hand-held, ultra wide-band probe for the in-situ measurement of the complex dielectric constant of sea ice in the frequency range of 1 to 10 GHz. The probe uses two antennas mounted on a cylinder. One of the antennas transmits a wide-band pulse that propagates through the ice and is received by the second

Elias Nassar; Robert Lee; Ken Jezek; Jonathan Young

1996-01-01

135

COMPLEX PROPAGATION CONSTANT OF POST-WALL WAVEGUIDE AND BEAM-SWITCHING SLOT ARRAY ANTENNAS FOR MODERN COMMUNICATIONS  

Microsoft Academic Search

This paper discusses the complex propagation constant of post-wall waveguide and millimeter-wave post-wall waveguide slot array antennas for modern communications. The guide wavelength of post-wall waveguide is expressed as a function of the post diameter and the post spacing by solving an eigen-value problem. We describe the beam-switching antenna by integrating a Butler matrix with slot array antennas in a

Jiro Hirokawa; Makoto Ando

136

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

137

Complex formation in the indolo[2,3-b]quinolines — methylene blue systems in aqueous solutions  

NASA Astrophysics Data System (ADS)

Changes in the absorption spectra of methylene blue (MB) aqueous solutions containing an indoloquinoline can be described by assuming complex formation between MB and the indolinoquinoline. At the low concentration range of the two reactants a simple 1:1 complex stoichiometry was postulated on the basis of the Benesi-Hildebrand, Scott and Scatchard linearization of spectroscopic data and augmented by the formation of an isosbestic point. The estimated association constants were correlated with the ab initio calculated electronic properties of indolo[2,3-b]quinolines.

Sadlej-Sosnowska, N.; Kaczmarek, ?.; Rotkiewicz, K.

2001-01-01

138

Recalculation, evaluation, and prediction of surface complexation constants for metal adsorption on iron and manganese oxides  

Microsoft Academic Search

The triple-layer model of the oxide\\/water interface can be used to calculate the partitioning of metals among solid and aqueous phases. The defensible use of the triple-layer model in groundwater\\/sediment systems requires an adequate and consistent set of intrinsic adsorption constants. In the present study, published values of p{sup *}K{sup int} for cation adsorption on iron and manganese oxides have

Robert W. Smith; E. A. Jenne

1991-01-01

139

C-C bond formation in diiron complexes.  

PubMed

The growing effort to design new sustainable synthetic methodologies, based on readily available and environmentally friendly transition metals, has boosted research on iron complexes. This review article focuses on C-C-bond-forming reactions occurring at bridging ligands in diiron complexes, aimed at evidencing distinctive aspects and advantages associated with the presence of two adjacent iron centres. A number of diiron-mediated C-C-bond-forming reactions reported in the literature, including nucleophilic and electrophilic additions and insertion and cycloaddition reactions, have been accumulated over the years, which, together with more recent developments, indicate that diiron complexes might provide promising alternatives to precious metals in the challenging field of metal-promoted C-C bond formation. PMID:22760971

Mazzoni, Rita; Salmi, Mauro; Zanotti, Valerio

2012-07-03

140

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

141

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

142

Mercury(II) Penicillamine Complex Formation in Alkaline Aqueous Solution  

SciTech Connect

The complex formation between mercury(II) and penicillamine (H{sub 2}Pen = 3,3'-dimethyl cysteine) in alkaline aqueous solutions (pH {approx}2) has been investigated with extended X-ray absorption fine structure (EXAFS) and {sup 199}Hg NMR spectroscopy. By varying the penicillamine concentration (C{sub H{sub 2}Pen} = 0.2--1.25 M) in {approx}0.1 M Hg(II) solutions, two coexisting major species [Hg(Pen){sub 2}]{sup 2-} and [Hg(Pen){sub 3}]{sub 4-} were characterized with mean Hg-S bond distances 2.34(2) and 2.44(2) {angstrom}, respectively. The [Hg(Pen){sub 2}]{sup 2-} complex with two deprotonated penicillamine ligands forms an almost linear S-Hg-S entity with two weak chelating Hg-N interactions at the mean Hg-N distance 2.52(2) {angstrom}. The same type of coordination is also found for the corresponding [Hg(Cys){sub 2}]{sup 2-} complex in alkaline aqueous solution with the mean bond distances Hg-S 2.34(2) {angstrom} and Hg-N 2.56(2) {angstrom}. The relative amounts of the [Hg(Pen){sub 2}]{sup 2-} and [Hg(Pen){sub 3}]{sup 4-} complexes were estimated by fitting linear combinations of the EXAFS oscillations to the experimental spectra. Also their {sup 199}Hg NMR chemical shifts were used to evaluate the complex formation, showing that the [Hg(Pen){sub 3}]{sup 4-} complex dominates already at moderate excess of the free ligand ([Pen{sup 2-}] > {approx} 0.1 M).

Leung, B.O.; Jalilehvand, F.; Mah, V.

2009-06-01

143

NMR diffusion spectroscopy as a measure of host-guest complex association constants and as a probe of complex size.  

PubMed

The complexes of cyclohexylacetic acid and cholic acid with beta-cyclodextrin were studied by NMR diffusion coefficient measurements. The diffusion coefficient of the 1:1 cyclohexylacetic acid/beta-cyclodextrin complex, K(a) = 1800 +/- 100 M(-1), is slightly slower (3.23 +/- 0.07 x 10(-6) cm(2) s(-1)) than that of beta-cyclodextrin (3.29 +/- 0.07 x 10(-6) cm(2) s(-1)). The diffusion coefficient of the 1:1 cholic acid/beta-cyclodextrin complex, K(a) = 5900 +/- 800 M(-1), is significantly slower (2.93 +/- 0.07 x 10(-6) cm(2) s(-1)) than that of beta-cyclodextrin. The results indicate that caution should be exercised when studying host-guest complexation by the so-called 'single point' technique. A novel data treatment is introduced which takes into account the diffusion behavior of all of the species when determining K(a). Experimentally determined diffusion coefficients of complexes are also a useful probe of the size of host-guest complexes. PMID:11597206

Cameron, K S; Fielding, L

2001-10-19

144

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

PubMed

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

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

2012-01-01

145

Equivalence of Mg2+ and Na+ ions in salt dependence of the equilibrium binding and dissociation rate constants of Escherichia coli RNA polymerase open complex.  

PubMed

Conflicting experimental data on the influence of Mg(2+) ions on the salt dependence of formation/dissociation of open transcription complex (RPo) of Escherichia coli RNA polymerase led us to carry systematic measurements of the dissociation rate constant (k(d)) and thermodynamic stability of complexes at lambdaP(R) and Pa promoters in a broad range of [NaCl] and [MgCl(2)] at 25, 31 and 37 degrees C, using fluorescence detected abortive transcription assay. Values of k(d) determined in MgCl(2) in the presence of heparin, as a commonly used anionic competitor, were shown to depend on heparin concentration whereas in NaCl this effect was not observed. Kinetics of dissociation was therefore determined in the course of salt-induced down-shift of the binding equilibrium. Salt derivatives of k(d)'s (n(d)) appeared to be similar in NaCl (approximately 8.5) and MgCl(2) (approximately 10) for both complexes. Isotherms of fractional occupancy of promoters by RNAP as a function of ln [salt] were shown to conform to a sigmoid Boltzman function parameterized to include binding constant of RPo and a net change (n(obs)) in the number of electrolyte ions associated with complex components upon its formation/dissociation. The fitted values of n(obs) appeared also similar in NaCl and in MgCl(2): approximately 18 for RPo/lambdaP(R) and approximately 20 for RPo/Pa, respectively. Overall unfavorable vant'Hoff enthalpy (DeltaH(obs)) of RPo proved to be much higher in MgCl(2) than in NaCl by ca. 20 kcal/mol for both complexes, rendering them profoundly less stable in the former salt. In both salts, DeltaH(obs) was higher by approximately 30 kcal/mol for RPo/Pa relative to RPo/lambdaP(R). Similarity of n(obs) and n(d) values for the two salts indicates thermodynamic equivalence of Mg(2+) and Na(+) in [salt]-controlled binding equilibrium of RPo. This finding remains in disagreement with earlier data and suggests that salt effects on open complex stability should be sought in global compensating changes in distribution of all ionic species around the interacting complex components. PMID:19345467

Lozi?ski, Tomasz; Bolewska, Krystyna; Wierzchowski, Kazimierz L

2009-03-14

146

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

147

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

ERIC Educational Resources Information Center

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

Marin, Dolores; Mendicuti, Francisco

1988-01-01

148

GABAergic complex basket formations in the human neocortex.  

PubMed

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

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

2010-12-15

149

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

150

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

151

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

152

Caldera formation in the Rum Central Igneous Complex, Scotland  

NASA Astrophysics Data System (ADS)

The Northern Marginal Zone of the Rum Central Igneous Complex in NW Scotland represents part of the early, felsic phase of the volcano. The marginal zone is a relic of the early caldera floor and the infilling of sedimentary and igneous rocks. Its formation has been explored through field examination of the ring fracture system of the Complex and its pyroclastic and epiclastic intracaldera facies. A sequence of magmatic tumescence and chamber growth caused initial doming, followed by the formation of a collapse structure without accompanying volcanism. This collapse structure, circular in plan, is akin in origin to a salt basin formed by crustal stretching above a rising diapir. We call this the proto-caldera. Collapse breccias, which represent the slumping and sliding of megablocks, blocks and boulders of the Torridonian sandstones which form the walls of the basin, were the original infilling. Logs of these deposits reveal considerable variation in thickness of the breccias (from 80-170 m) in the Complex, indicating an uneven floor to the proto-caldera, consistent with piecemeal collapse. Following accumulation of up to >70 m thickness of breccia, thin interbedded rhyodacitic crystal tuffs (10-30 cm) record the earliest eruptions of felsic magma in the caldera. Caldera formation was then interrupted by a period of quiescence, recorded by the presence of an epiclastic sandstone of locally several metres thickness, formed by washout of fines from the breccias. Subsequent resurgence created a fracture pattern characteristic of doming, along which rhyodacite magma rose in dykes and erupted up to perhaps 10 km3 of rhyodacitic intracaldera ignimbrites. This major eruption caused further incremental subsidence of the caldera floor into a now partly emptied magma chamber. Mafic inclusions in the ignimbrites point to the eruption being triggered by multiple injections of basic magma into a chamber occupied by felsic magma.

Troll, Valentin R.; Emeleus, C. Henry; Donaldson, Colin H.

2000-08-01

153

Redox reactions and complex formation of transplutonium elements in solutions  

SciTech Connect

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

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

1986-01-01

154

Theoretical calculations of stability constants and pKa values of metal complexes in solution: application to pyridoxamine-copper(ii) complexes and their biological implications in AGE inhibition.  

PubMed

Accurate prediction of thermodynamic constants of chemical reactions in solution is one of the current challenges in computational chemistry. We report a scheme for predicting stability constants (log??) and pKa values of metal complexes in solution by means of calculating free energies of ligand- and proton-exchange reactions using Density Functional Theory calculations in combination with a continuum solvent model. The accuracy of the predicted log?? and pKa values (mean absolute deviations of 1.4 and 0.2 units respectively) is equivalent to the experimental uncertainties. This theoretical methodology provides direct knowledge of log?? and pKa values of major and minor species, so it is of potential use in combination with experimental techniques to obtain a detailed description of the microscopic equilibria. In particular, the proposed methodology is shown to be especially useful for obtaining the real acidity constants of those chelates where the metal-ligand coordination changes as a result of ligand deprotonation. The stability and acidity constants of pyridoxamine-Cu(2+) chelates calculated with the proposed methodology show that pyridoxamine is an efficient scavenging agent of Cu(2+) under physiological pH conditions. This is of special interest as Cu(2+) overload is involved in the formation of advanced glycation end-products (AGEs) and their associated degenerative medical conditions. PMID:23999915

Casasnovas, Rodrigo; Ortega-Castro, Joaquín; Donoso, Josefa; Frau, Juan; Muñoz, Francisco

2013-09-03

155

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

156

The thermodynamic characteristics of complex formation of Cd 2+ with N,NBis(carboxymethyl)aspartic acid in aqueous solutions at 298.15 K  

Microsoft Academic Search

The equilibrium constants and heats of formation of complexes of N,N-bis(carboxymethyl)aspartic acid (H4Y) with Cd2+ ions at 298.15 K and ionic strengths of 0.2, 0.5, and 1.0 (KNO3) were determined by potentiometric titration and calorimetrically. The thermodynamic characteristics of formation of the\\u000a CdY2? complex at fixed and zero ionic strength values were calculated. The values obtained were interpreted.

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

2011-01-01

157

Rotational spectrum, nuclear quadrupole coupling constants, and structure of six isotopomers of the argon-chlorocyclobutane van der Waals complex  

NASA Astrophysics Data System (ADS)

The Fourier Transform Pulsed Jet Microwave spectra of the argon-chlorocyclobutane van der Waals complex have been assigned for six isotopomers. These include the 35Cl and 37Cl each with four 12Cs in the ring plus the four isotopomers of the 35Cl with one 13C at each position in the ring. The spectroscopic constants for the Ar-12C4H735Cl complex are A=2675.2641(6) MHz, B=977. 8306(3) MHz, C=764.9382(2) MHz; ?J=1.737(1), ?JK=7.176(6), ?K=15.28(2), ?J=0.4148(6), ?K=6.61(3) kHz; and ?aa=28.011(6) MHz, (?bb ?cc)=-80.378(6) MHz, ?ab=-22.8(1) MHz, ?ac=-5.4(7) MHz and ?bc=-26.47(9) MHz. The structure of the ground vibrational state of the complex has an equatorial chlorine as in the non-complexed ring and the argon coordinates are a=1.267 Å, b=2.824 Å and c=2.517 Å in the principal axis system of the monomer ring. The chlorine coordinate in this axis system is a=1.66, b=0.0 and c=0.08 Å. The argon is exo to the ring 2.4 Å above the C Cl bond but 2.8 Å to the side of the plane of symmetry of the chlorocyclobutane monomer. Argon is within the van der Waals radii of the nearest cross-ring methylene hydrogen and outside the van der Waals radii of chlorine. It is not directly above the ring as has been observed in other four-membered ring complexes. The off-diagonal quadrupole moment of the monomer, chlorocyclobutane, has been measured, ?ac=32.0(6) MHz. The quadrupole tensor for the chlorine in the complex was fit including all three off diagonal elements. The van der Waals bond does not significantly perturb the electronic gradients at the chlorine nucleus of the monomer, since each element of the quadrupole tensor measured for the complex, except one small off-diagonal constant, is within 3% of that projected onto the complex from chlorocyclobutane. The argon position is also consistent with the observation and intensities of a, b, and c-type rotational transitions from the projection of the monomer dipole moment onto the complex principal axis system.

Subramanian, Ranga; Szarko, Jodi M.; Pringle, Wallace C.; Novick, Stewart E.

2005-05-01

158

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

159

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

PubMed

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. PMID:23666357

Asadi, Zahra; Asadi, Mozaffar; Setoodehkhah, Moslem

2013-04-18

160

Vancomycin: ligand recognition, dimerization and super-complex formation.  

PubMed

The antibiotic vancomycin targets lipid II, blocking cell wall synthesis in Gram-positive bacteria. Despite extensive study, questions remain regarding how it recognizes its primary ligand and what is the most biologically relevant form of vancomycin. In this study, molecular dynamics simulation techniques have been used to examine the process of ligand binding and dimerization of vancomycin. Starting from one or more vancomycin monomers in solution, together with different peptide ligands derived from lipid II, the simulations predict the structures of the ligated monomeric and dimeric complexes to within 0.1 nm rmsd of the structures determined experimentally. The simulations reproduce the conformation transitions observed by NMR and suggest that proposed differences between the crystal structure and the solution structure are an artifact of the way the NMR data has been interpreted in terms of a structural model. The spontaneous formation of both back-to-back and face-to-face dimers was observed in the simulations. This has allowed a detailed analysis of the origin of the cooperatively between ligand binding and dimerization and suggests that the formation of face-to-face dimers could be functionally significant. The work also highlights the possible role of structural water in stabilizing the vancomycin ligand complex and its role in the manifestation of vancomycin resistance. PMID:23298227

Jia, ZhiGuang; O'Mara, Megan L; Zuegg, Johannes; Cooper, Matthew A; Mark, Alan E

2013-02-11

161

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  

NASA Astrophysics Data System (ADS)

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 ?G0, ?H0 and ?S0. 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. IDV 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.

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

162

The simultaneous multiple constraints of the IMF and SFR history in star formation complexes  

NASA Astrophysics Data System (ADS)

The multiple constraints method of the IMF and SFR history in star formation complexes (SFCs) attempts to match simultaneously the observed UBVR colours, Lyman continuum fluxes and chemical abundances by finding a best set of the IMF parameters (?, M_max), age t and SFR history. The method of using simultaneous multiple constraints of the IMF and SFR history in SFCs (SMC method) is based on the evolutionary synthesis models of stellar clusters, in which the SFR was either an instantaneous burst of age t (simultaneous star formation - SSF model) or a constant with duration t (constant star formation - CSF model) and, parameterized the IMF as a power law of index ? with upper and lower mass limits M_max, M_min. This procedure results in large uncertainties for individual star forming regions (?=0.35, ?M_max=30M_odot, ?_log(t)=0.20), but may be adequate for a study of the average properties of a large sample. The simultaneous multiple constraints of the IMF and SFR history in star formation complexes resolved the IMF-SFR ambiguity in 100 SFCs in 20 galaxies. Star formation episodes proceed either instantaneously or at continuous rate in individual regions. There are correlations between the parameters that define the star formation process (IMF, SFR), and the local properties of the parent galaxy (density, metallicity). The dependence of ages on linear sizes (S in parsec) of star forming regions derived from independent observations of star clusters in LMC (Efremov and Elmegreen: 1998, MNRAS 299, 588) is confirmed. SFR history depends on the star density of SFC. Low density regions demonstrate instantaneous starburst, while in high density SFCs one can see a continuous star formation process. A trend towards greater ages at high stellar densities in the case of constant SFR history indicates that the lifetimes of SFCs are longer than corresponding dynamical time scales of clouds, and that star formation seems to be no fast process on every scale The mechanisms that triggered the burst of star formation depend on the star density and metallicity of SFC. There is a trend toward flatter IMFs at low densities in both cases of SFR history. The density dependence of IMF indicates the role of interactions in protostellar clouds. Dust plays an important role in the transport and redistribution of the Lyc photons emitted by the OB stars; a fraction (1-f) of the Lyc photons escapes, not absorbed by gas in individual SFCs varies from 0 to 90% with a mean = (50+/-30)%. Different star formation episodes (SSF or CSF) show different correlations between the observed parameters (L, S, Z, f). Estimated empirical relations between IMF, ages and observed luminosities, sizes, and colour indices, allow to constrain integrated (cumulative) IMF in a parent galaxy between two extreme versions of star formation regimes SSF and CSF. It is shown that the integrated IMF in the parent galaxy depends not only on the distribution of IMF slopes in individual SFCs but also on the luminosity (size) distribution of SFCs.

Sakhibov, F. H.; Smirnov, M. A.

163

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

164

Complex Formation of Yeast Rev1 with DNA Polymerase ??  

PubMed Central

In Saccharomyces cerevisiae, Rev1 functions in translesion DNA synthesis (TLS) together with polymerase ? (Pol?), comprised of the Rev3 catalytic and Rev7 accessory subunits. Rev1 plays an indispensable structural role in promoting Pol? function, and deletion of the Rev1-C terminal region that is involved in physical interactions with Rev3 inactivates Pol? function in TLS. In humans, however, Rev1 has been shown to physically interact with the Y-family polymerases Pol?, Pol?, and Pol?, 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? and not for Pol?, 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? 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.

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

2007-01-01

165

The Synthesis and Complex Formation of 1,2-Ethane-dioic Acid-bis(phenylglyoxlidene hydrazide) and Investigation of some Analytical Properties  

Microsoft Academic Search

1,2-ethanedioic acid-bis(phenylglyoxylidene hydrazide), EDGH4, has been synthesized and various Cu(II), Ni(I1) and Co(I1) complexes of this compound have been isolated. Dissociation and formation constants of these complexes have been determined by spectrophotometric methods and spectrophotometric trace analyses of the Ni(I1) and Cu(I1) complexes have been performed. The structures of all isolated compounds were proposed on the basis of analyses, i.r.,

Abdülh?lik ?skender; Özer Bek?roglu

1981-01-01

166

Charge-scaled cavities in polarizable continuum model: Determination of acid dissociation constants for platinum-amino acid complexes  

NASA Astrophysics Data System (ADS)

The main aim of this study is the calculation of acid dissociation constants of the products of cisplatin reaction with the amino acids cysteine and methionine. In the first step, a suitable procedure for the calculation of solvation Gibbs free energies is found, based on the comparison of the calculated and experimental pKas of both amino acids and simple platinum complexes. The resulting approach combines the DFT/B3LYP density functional, 6-311++G(2df,2pd) basis set, the D-PCM formulation of the continuum solvation model, and modified UAHF cavities. Since the main area of applicability of the UAHF model is solvation of organic molecules, a minor modification of the UAHF algorithm was necessary to improve the accuracy when applying it to the transition metal complexes. Instead of the integer (or semi-integer) formal charges used in the original formulation, more realistic partial charges obtained from the electronic density using the NPA procedure are used to generate molecular cavity. All other parameters of the model remain unchanged. This simple modification of the UAHF model works markedly better than the original formulation. The root mean square error of calculated pKas over a set of molecules including zwitterions and divalent diaquaplatinum cation is equal to 0.74. In the second step, pKas of platinum amino-acid complexes with the total charge ranging from 0e to 2e were computed. It was found that the pKas of all ionizable groups of both amino acids are highly variable among the complexes studied. They range from -5 (in complexes containing protonated thiol or carboxyl groups directly bonded to platinum) to 14 (in monodentate complexes containing a positively charged amino group, which is stabilized by intramolecular hydrogen bonds).

Zimmermann, Tomáš; Burda, Jaroslav V.

2009-10-01

167

Control of H- and J-aggregate formation via host-guest complexation using cucurbituril hosts.  

PubMed

The binding interactions between two cyanine dyes, pseudoisocyanine (PIC) and pinacyanol (PIN), and the cucurbit[n]uril hosts, cucurbit[7]uril (CB7) and cucurbit[6]uril (CB6), were investigated by electronic absorption spectroscopy and DFT computational methods. The CB7 host forms more stable complexes with both dyes than CB6 and the computational studies suggest that the cavity of the smaller host CB6 is not threaded by the dyes. The equilibrium association constants (K) for complexation by CB7 were measured and found to be 2.05 x 10(4) and 3.84 x 10(5) M(-1) for PIC and PIN, respectively, in aqueous media at 23 degrees C. CB7 complexation was found to effectively disrupt the intermolecular forces responsible for the aggregation of both dyes. Thus, CB7 completely disrupts the J-aggregates formed by PIC and the H-aggregates (as well as lower concentrations of J-aggregates) formed by PIN. In both cases a competing guest, 1-aminoadamantane (AD), could be used to adjust the extent of aggregation of the cyanine dye. AD regulates aggregate formation because it forms an extremely stable complex with CB7 (K approximately = 10(12) M(-1)) and exerts a tight control on the CB7 concentration available to interact and bind with the dye. PMID:19007116

Gadde, Suresh; Batchelor, Elizabeth K; Weiss, Joshua P; Ling, Yonghua; Kaifer, Angel E

2008-12-17

168

Formation and reactivity of (octaethyltetraazaporphyrinato)rhodium complexes  

SciTech Connect

A series of (octaethyltetraazaporphyrinato)rhodium, (OETAP)Rh, complexes including (OETAP)Rh-I, (OETAP)Rh-CH[sub 3], and [(OETAP)Rh][sub 2] were prepared for comparison with the corresponding (octaethyltetraazaporphyrinato)rhodium, (OEP)Rh, derivatives. [(OETAP)Rh][sub 2] (1) reacts like [(OEP)Rh][sub 2] (2) with CH[sub 3]I, CH[sub 3]NC, (CH[sub 3]O)[sub 3]P, and CH[sub 2]=CH[sub 2] in forming (OETAP)Rh-CH[sub 3] and (OETAP)Rh-I, (OETAP)Rh(NC)(CH[sub 3]NC), (OETAP)Rh-P(O)(OCH[sub 3])[sub 2], and (OETAP)Rh-CH[sub 2]CH[sub 2]-Rh(OETAP), respectively, but reactions of 1 are invariably much slower than those of 2. [(OETAP)Rh][sub 2] fails to react with H[sub 2], CO, CH[sub 3]CHO, and CH[sub 3]C[sub 6]H[sub 5], which participate in prominent substrate reactions for 2. Reactivity and equilibrium studies indicate that a substantially larger Rh-Rh bond dissociation enthalpy for 1 compared with 2 is primarily responsible for the slower rates and reduced scope of substrate reactions for [(OETAP)Rh][sub 2]. Dissolution of 1 in pyridine results in formation of a persistent OETAP anion radical complex of Rh(III), (OETAP[sup [sm bullet][minus

Ni, Y.; Fitzgerald, J.P.; Carroll, P.; Wayland, B.B. (Univ. of Pennsylvania, Philadelphia, PA (United States) United States Naval Academy, Annapolis, MD (United States))

1994-04-27

169

Image formation in the eye: very specified complexity  

NASA Astrophysics Data System (ADS)

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

Stoltzmann, David E.

2005-08-01

170

Stability constants of uranium(VI) and thorium(IV) complexes formed with 8-hydroxyquinoline and its 5-sulfonic acid derivative  

Microsoft Academic Search

In this study, the stability constants of uranium(VI) and thorium(IV) complexes formed with 8-hydroxyquinoline (8-HOQ) and its 5-sulfonic acid (8-HOQ-5-SO3H) derivative have been determined using the Irving-Rossotti method, computing the Calvin-Bjerrum pH-titration data. As a result, it is determined that the thorium(IV) complexes are considerably more stable than the corresponding uranium(VI) complexes. On the other hand, the complexes formed between

P. Ünak; D. Özdemir; T. Ünak

1994-01-01

171

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

172

Deciphering complex soil/site formation in sands  

NASA Astrophysics Data System (ADS)

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

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

2008-10-01

173

Polyelectrolyte complexes of chitosan: formation, properties and applications  

NASA Astrophysics Data System (ADS)

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.

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

2008-09-01

174

The Effects of Sequence and Structure on Complex Concept Formation. Technical Report No. 4. Psychological and Educational Factors in Transfer of Training, Phase I.  

ERIC Educational Resources Information Center

|Several ways of structuring the early trials of a complex concept formation task were compared. Training trials were divided into two segments: (1) an asynchronous segment with one relevant and one irrelevant cue held constant while one relevant and one irrelevant cue varied and (2) a synchronous segment with all cues free to vary. The…

Davis, Daniel J.

175

Adhesion and formation of microbial biofilms in complex microfluidic devices  

SciTech Connect

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

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

2012-01-01

176

In vivo analysis of synaptonemal complex formation during yeast meiosis.  

PubMed Central

During meiotic prophase a synaptonemal complex (SC) forms between each pair of homologous chromosomes and is believed to be involved in regulating recombination. Studies on SCs usually destroy nuclear architecture, making it impossible to examine the relationship of these structures to the rest of the nucleus. In Saccharomyces cerevisiae the meiosis-specific Zip1 protein is found throughout the entire length of each SC. To analyze the formation and structure of SCs in living cells, a functional ZIP1::GFP fusion was constructed and introduced into yeast. The ZIP1::GFP fusion produced fluorescent SCs and rescued the spore lethality phenotype of zip1 mutants. Optical sectioning and fluorescence deconvolution light microscopy revealed that, at zygotene, SC assembly was initiated at foci that appeared uniformly distributed throughout the nuclear volume. At early pachytene, the full-length SCs were more likely to be localized to the nuclear periphery while at later stages the SCs appeared to redistribute throughout the nuclear volume. These results suggest that SCs undergo dramatic rearrangements during meiotic prophase and that pachytene can be divided into two morphologically distinct substages: pachytene A, when SCs are perinuclear, and pachytene B, when SCs are uniformly distributed throughout the nucleus. ZIP1::GFP also facilitated the enrichment of fluorescent SC and the identification of meiosis-specific proteins by MALDI-TOF mass spectroscopy.

White, Eric J; Cowan, Carrie; Cande, W Zacheus; Kaback, David B

2004-01-01

177

Ligand-induced formation of a transient tryptophan synthase complex with ??? subunit stoichiometry.  

PubMed

The prototypical tryptophan synthases form a stable heterotetrameric ???? complex in which the constituting TrpA and TrpB1 subunits activate each other in a bidirectional manner. The hyperthermophilic archaeon Sulfolobus solfataricus does not contain a TrpB1 protein but instead two members of the phylogenetically distinct family of TrpB2 proteins, which are encoded within (sTrpB2i) and outside (sTrpB2a) the tryptophan operon. It has previously been shown that sTrpB2a does not functionally or structurally interact with sTrpA, whereas sTrpB2i substantially activates sTrpA in a unidirectional manner. However, in the absence of catalysis, no physical complex between sTrpB2i and sTrpA could be detected. In order to elucidate the structural requirements for complex formation, we have analyzed the interaction between sTrpA (?-monomer) and sTrpB2i (??-dimer) by means of spectroscopy, analytical gel filtration, and analytical ultracentrifugation, as well as isothermal titration calorimetry. In the presence of the TrpA ligand glycerol 3-phosphate (GP) and the TrpB substrate l-serine, sTrpA and sTrpB2i formed a physical complex with a thermodynamic dissociation constant of about 1 ?M, indicating that the affinity between the ?- and ??-subunits is weaker by at least 1 order of magnitude than the affinity between the corresponding subunits of prototypical tryptophan synthases. The observed stoichiometry of the complex was 1 subunit of sTrpA per 2 subunits of sTrpB2i, which corresponds to a ??? quaternary structure and testifies to a strong negative cooperativity for the binding of the ?-monomers to the ??-dimer. The analysis of the interaction between sTrpB2i and sTrpA in the presence of several substrate, transition state, and product analogues suggests that the ??? complex remains stable during the whole catalytic cycle and disintegrates into ?- and ??-subunits upon the release of the reaction product tryptophan. The formation of a transient tryptophan synthase complex, together with the observed low affinity of sTrpB2i for l-serine, couples the rate of tryptophan biosynthesis in S. solfataricus to the cytosolic availability of l-serine. PMID:21090805

Ehrmann, Alexander; Richter, Klaus; Busch, Florian; Reimann, Julia; Albers, Sonja-Verena; Sterner, Reinhard

2010-12-06

178

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

179

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

180

Base specific complex formation of norfloxacin with DNA  

Microsoft Academic Search

We examined the base specificity of the norfloxacin–DNA interaction by measuring the binding constant of norfloxacin to various synthetic polynucleotides, using the Stern–Volmer and the Benesi–Hildebrand methods. The equilibrium constants were largest for poly[d(G–C)2] and poly(dG)·poly(dC), suggesting that norfloxacin binds preferentially to the G–C bases of calf thymus DNA. We also found that norfloxacin has a greater affinity for purine

Gwan-Su Son; Jeong-Ah Yeo; Jong-Moon Kim; Seog K. Kim; Hyung Rang Moon; Wonwoo Nam

1998-01-01

181

Constant energy surfaces of Hamiltonian systems, enumeration of three-dimensional manifolds in increasing order of complexity, and computation of volumes of closed hyperbolic manifolds  

Microsoft Academic Search

CONTENTS Introduction § 1. Hamiltonian systems and the class (H) § 2. The complexity of 3-manifolds § 3. The classification of manifolds of small complexity § 4. Computation of volumes of hyperbolic manifolds § 5. The list of 3-manifolds of complexity not greater than 6 References Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar

S. V. Matveev; A. T. Fomenko

1988-01-01

182

Complex formation during dissolution of metal oxides in molten alkali carbonates  

SciTech Connect

Dissolution of metal oxides in molten carbonates relates directly to the stability of materials for electrodes and construction of molten carbonate fuel cells. In the present work the solubilities of PbO, NiO, Fe{sub 2}O{sub 3}, and Bi{sub 2}O{sub 3} in molten Li/K carbonates have been measured at 650 C under carbon dioxide atmosphere. It is found that the solubilities of NiO and PbO decrease while those of Fe{sub 2}O{sub 3} and Bi{sub 2}O{sub 3} remain approximately constant as the lithium mole fraction increases from 0.43 to 0.62 in the melt. At a fixed composition of the melt, NiO and PbO display both acidic and basic dissolution as the partial pressure of carbon dioxide varies. By combination of solubility and electromotive force measurements, a model is constructed assuming the dissolution involves complex formation. The possible species for lead are proposed to be [Pb(CO{sub 3}){sub 2}]{sup {minus}2} and/or [Pb(CO{sub 3}){sub 3}]{sup {minus}4}. A similar complex chemistry for nickel oxide dissolution might be expected.

Li Qingfeng; Borup, F.; Petrushina, I.; Bjerrum, N.J. [Technical Univ. of Denmark, Lyngby (Denmark). Dept. of Chemistry

1999-07-01

183

Mathematical Constants  

NSDL National Science Digital Library

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

184

The thermodynamic characteristics of complex formation between Cd2+ and iminodisuccinic acid in aqueous solution  

NASA Astrophysics Data System (ADS)

The enthalpies of complex formation between iminodisuccinic acid (H4L) and the Cd2+ ion were determined calorimetrically at 298.15 K and ionic strengths 0.5, 1.0, and 1.5 (KNO3). The thermodynamic characteristics of formation of CdL2- and CdHL- complexes at fixed and zero ionic strength values were calculated.

Lytkin, A. I.; Chernyavskaya, N. V.; Litvinenko, V. E.; Nikol'Skii, V. M.

2010-06-01

185

Nidogen mediates the formation of ternary complexes of basement membrane components  

Microsoft Academic Search

Nidogen mediates the formation of ternary complexes of basement membrane components. Using a recombinant nidogen we have probed the calcium binding potential of various nidogen domains, examined the binding of nidogen to various basement membrane proteins and assessed the ability of nidogen to mediate the formation of ternary complexes between laminin and heparan sulfate proteoglycan and collagen IV and laminin.

Monique Aumailley; Cristina Battaglia; Ulrike Mayer; Dieter Reinhardt; Roswitha Nischt; Rupert Timpl; Jay W Fox

1993-01-01

186

Positronium formation studies in solid molecular complexes: Triphenylphosphine oxide-triphenylmethanol  

NASA Astrophysics Data System (ADS)

Positronium formation in triphenylphosphine oxide (TPPO), triphenylmethanol (TPM), and systems [TPPO(1-X)?TPMX] has been studied. The low probability of positronium formation in complex [TPPO0.5?TPM0.5] was attributed to strong hydrogen bond and sixfold phenyl embrace interactions. These strong interactions in complex reduce the possibility of the n- and ?-electrons to interact with positrons on the spur and consequently, the probability of positronium formation is lower. The ?3 parameter and free volume (correlated to ?3) were also sensitive to the formation of hydrogen bonds and sixfold phenyl embrace interactions within the complex. For physical mixture the positron annihilation parameters remained unchanged throughout the composition range.

Oliveira, F. C.; Denadai, A. M. L.; Fulgêncio, F. H.; Magalhães, W. F.; Alcântara, A. F. C.; Windmöller, D.; Machado, J. C.

2012-06-01

187

[Formation of a new type of dinitrosyl iron complexes bound to cysteine modified with methylglyoxal].  

PubMed

It has been shown that interaction of cysteine dinitrosyl iron complexes with methylglyoxal leads to the formation of a new type of dinitrosyl iron complexes., EPR spectrum of these complexes essentially differs from spectra of dinitrosyl iron complexes containing unmodified thiol. The products of the cysteine reaction with methylglyoxal are hemithioacetals, Schiff bases and thiazolidines, which most likely serve as ligands for the new type of dinitrosyl iron complexes. It has been shown that the new type of dinitrosyl iron complexes as cysteine dinitrosyl iron complexes, which are physiological donors of nitric oxide, exert a vasodilator effect. It has also been found that the oxidative destruction of the new type of dinitrosyl iron complexes occurs at normal oxygen partial pressure, but these dinitrosyl iron complexes remain rather stable under hypoxia modeling. An assumption that the destruction of the new type of dinitrosyl iron complexes is caused by the formation of a bound peroxynitrite-containing intermediate is made. PMID:23755548

Shumaev, K B; Gubkina, S A; Vanin, A F; Burbaev, D Sh; Mokh, V P; Topunov, A F; Ruuge, E K

188

Axial ligand effect on the rate constant of aromatic hydroxylation by iron(IV)-oxo complexes mimicking cytochrome P450 enzymes.  

PubMed

The cytochromes P450 are important iron-heme based monoxygenases that catalyze a range of different oxygen atom transfer reactions in nature. One of the key bioprocesses catalyzed by these enzymes is the aromatic hydroxylation of unactivated arenes. To gain insight into axial ligand effects and, in particular, how it affects aromatic hydroxylation processes by P450 model complexes, we studied the effects of the axial ligand on spectroscopic parameters (trans-influence) as well as on aromatic hydroxylation kinetics (trans-effect) using a range of [Fe(IV)(O)(Por(+•))X] oxidants with X = SH(-), Cl(-), F(-), OH(-), acetonitrile, GlyGlyCys(-), CH(3)COO(-), and CF(3)COO(-). These systems give red-shifted Fe-O vibrations that are dependent on the strength of the axial ligand. Despite structural changes, however, the electron affinities of these oxidants are very close in energy, but sharp differences in pK(a) values are found. The aromatic hydroxylation of the para-position of ethylbenzene was tested with these oxidants, and they all show two-state-reactivity patterns although the initial low-spin C-O bond formation barrier is rate determining. We show, for the first time, that the rate determining barrier for aromatic hydroxylation is proportional to the strength of the O-H bond in the corresponding iron(IV)-hydroxo complex, i.e., BDE(OH), hence this thermochemical property of the oxidant drives the reaction and represents the axial ligand effect. We have rationalized our observed barrier heights for these axially ligated systems using thermochemical cycles and a valence bond curve crossing diagram to explain the origins of the rate constants. PMID:22132821

Kumar, Devesh; Sastry, G Narahari; de Visser, Sam P

2011-12-13

189

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

Microsoft Academic Search

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

Douglas Gibbs; James Varani; Isaac Ginsburg

1989-01-01

190

From snowflake formation to growth of bacterial colonies II: Cooperative formation of complex colonial patterns  

NASA Astrophysics Data System (ADS)

In nature, bacterial colonies must often cope with hostile environmental conditions. To do so they have developed sophisticated cooperative behaviour and intricate communication capabilities, such as direct cell- cell physical interactions via extra-membrane polymers, collective production of extracellular 'wetting' fluid for movement on hard surfaces, longrange chemical signalling such as quorum sensing and chemotactic (bias of movement according to gradient of chemical agent) signalling, collective activation and deactivation of genes and even exchange of genetic material. Utilizing these capabilities, the bacterial colonies develop complex spatio-temporal patterns in response to adverse growth conditions. We present a wealth of beautiful patterns formed during colonial development of various bacterial strains and for different environmental conditions. Invoking ideas from pattern formation in non-living systems and using generic modelling we are able to reveal novel bacterial strategies which account for the salient features of the evolved patterns. Using the models, we demonstrate how bacterial communication leads to colonial self-organization that can only be achieved via cooperative behaviour of the cells. It can be viewed as the action of a singular feedback between the microscopic level (the individual cells) and the macroscopic level (the colony) in the determination of the emerging patterns.

Ben-Jacob, Eshel

1997-03-01

191

Inhibitory mechanism of pancreatic amyloid fibril formation: formation of the complex between tea catechins and the fragment of residues 22-27.  

PubMed

Islet amyloid polypeptide (IAPP) is a major component of pancreatic amyloid deposits associated with type 2 diabetes. Polyphenols contained in plant foods have been found to inhibit amyloid fibril formation of proteins and/or peptides. However, the inhibition mechanism is not clear for a variety of systems. Here the inhibition mechanism of green tea polyphenols, catechins, on amyloid fibril formation of the IAPP fragment (IAPP22-27), which is of sufficient length for formation of ?-sheet-containing amyloid fibrils, was investigated by means of kinetic analysis. A quartz crystal microbalance (QCM) determined that the association constants of gallate-type catechins [epicatechin 3-gallate (ECg) and epigallocatechin 3-gallate] for binding to IAPP22-27 immobilized on the gold plate in QCM were 1 order of magnitude larger than those of the free IAPP22-27 peptide, and also those of epicatechin and epigallocatechin. Kinetic analysis using a two-step autocatalytic reaction mechanism revealed that ECg significantly reduced the rate constants of the first nucleation step of amyloid fibril formation, while the rate of autocatalytic growth was less retarded. (1)H nuclear magnetic resonance studies clarified that a IAPP22-27/ECg complex clearly forms as viewed from the (1)H chemical shift changes and line broadening. Our study suggests that tea catechins specifically inhibit the early stages of amyloid fibril formation to form amyloid nuclei by interacting with the unstructured peptide and that this inhibition mechanism is of great therapeutic value because stabilization of the native state could delay the pathogenesis of amyloid diseases and also the toxicity of the small oligomer (protofibril) is reported to be greater than that of the mature fibril. PMID:23205879

Kamihira-Ishijima, Miya; Nakazawa, Hiromi; Kira, Atsushi; Naito, Akira; Nakayama, Tsutomu

2012-12-12

192

Surfactant-Induced Trans-Interface Transportation and Complex Formation of Giant Polyoxomolybdate-Based Clusters  

Microsoft Academic Search

The interaction and complex formation between cationic surfactants dimethyldioctadecylammonium Bromide (DODA-Br) and a polyoxomolybdate (POM)-based giant cluster {Mo72Fe30}, in its both single cluster (in aqueous solution, these clusters exist as anions) format and supramolecular format in aqueous solution, are studies by using laser light scattering (LLS) techniques. DODA\\/{Mo72Fe30} complexes containing basically single {Mo72Fe30} clusters are observed when the {Mo72Fe30} aqueous

Tianbo Liu

2003-01-01

193

Double layer formation at the interface of complex plasmas  

SciTech Connect

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

Yaroshenko, V. V.; Thoma, M. H.; Thomas, H. M.; Morfill, G. E. [Max Planck Institute for Extraterrestrial Physics, 85741 Garching (Germany)

2008-08-15

194

Influence of complexing agents on texture formation of electrodeposited copper  

Microsoft Academic Search

Ethylenediaminetetraacetic acid (EDTA) and sodium citrate were used as complexing agents for copper coated on Ni–P substrate via the electrodeposited copper procedure. X-ray diffraction (XRD) has been used to examine the effect of complexing agents on the texture of copper films. The experimental results showed that copper films deposited without any additives have two different texture types, (111) and (110)

Bo Hong; Chuan-hai Jiang; Xin-jian Wang

2007-01-01

195

>Cognitive complexity and impression formation in informal social interaction  

Microsoft Academic Search

While awaiting the arrival of the experimenter, pairs of subjects participated in ten minutes of spontaneous casual interaction. The impression which each formed of the other was assessed. Analyses of these impressions compared subjects differing in initial level of cognitive complexity. High complexity subjects, in comparison with noncomplex subjects, formed more differentiated, more abstract, more highly organized, and less evaluatively

Jesse G. Delia; Ruth Anne Clark; David E. Switzer

1974-01-01

196

Determination of stability constants between complexing agents and At(I) and At(III) species present at ultra-trace concentrations  

Microsoft Academic Search

A competition method is proposed to determine the complexation constants between At(I) and At(III) species and complexing agents. The method, tested with an inorganic ligand, thiocyanate ion (SCN?), and an organic macromolecule, thiacalix[4]arenetetrasulfonate (LH4) is based on solid\\/liquid separation or liquid\\/liquid extraction. For the solid\\/liquid separation, the cationic exchanger Dowex 50X8 was used. The interaction of At(I) and At(III) with

J. Champion; C. Alliot; S. Huclier; D. Deniaud; Z. Asfari; G. Montavon

2009-01-01

197

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

ERIC Educational Resources Information Center

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

Ibanez, Jorge G.; And Others

1988-01-01

198

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

ERIC Educational Resources Information Center

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

Ibanez, Jorge G.; And Others

1988-01-01

199

End-to-end distance distributions and intrachain diffusion constants in unfolded polypeptide chains indicate intramolecular hydrogen bond formation  

Microsoft Academic Search

Characterization of the unfolded state is essential for the understanding of the protein folding reaction. We performed time-resolved FRET measurements to gain information on the dimensions and the internal dynamics of unfolded polypeptide chains. Using an approach based on global analysis of data obtained from two different donor-acceptor pairs allowed for the determination of distance distribution functions and diffusion constants

Andreas Möglich; Karin Joder; Thomas Kiefhaber

2006-01-01

200

Determination of stability constants of copper(II) complex of glycine in water + alcohol mixed solvents with ion selective electrode technique.  

PubMed

The first stability constants (log beta(1)) of the copper(II) complex of glycine in water and in 13 water + alcohol (isopropanol, tert-butanol, 1,2-propylene glycol and glycerol) solvents have been determined at 25 degrees C and an ionic strength of 0.10, from pH and pCu measurements of cells containing copper(II) ion selective electrode. It has been shown that as the proportion of the alcohol increases, the stability constants become increasing positive in all of the mixed solvents examined. An almost linear relation between log beta(1) and the mole fraction of alcohol was found for the complex in aqueous solutions of isopropanol, tert-butanol and glycerol. The response of the copper(II) ion selective electrode in water and in water + alcohol mixed solvents was also investigated. The advantages of using an ion selective electrode to determine the stability constants in mixed solvents are discussed. PMID:18966232

Fan, J

1995-03-01

201

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

Microsoft Academic Search

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

R. A. Marcus

1970-01-01

202

Caratterizzazione e Determinazione di Costanti di Stabilita di Carbonato-Complessi di Lantanidi (Characteristics and Definition of Stability Constants of Lanthanide Carbonate Complexes).  

National Technical Information Service (NTIS)

The stoichiometric stability constants of complexes consisting of trivalent europium ion with carbonates and bicarbonates were measured at 22C, with an ionic concentration of 0.5 M, using NaClO4 as the supporting electrolyte. In this study, the method use...

G. Bidoglio B. Marcandalli

1983-01-01

203

Study of Complex Formation and Precipitation Conditions of Beryllium Hydroxide.  

National Technical Information Service (NTIS)

The percentage of beryllium present under the form of different complex ions is established. Three analytical concentrations taken with pH are observed. Data study results of equilibrium conditions of the different ions in solution are presented. (Atomind...

J. F. Oliveira M. M. A. El-Naggar

1984-01-01

204

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

205

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

2013-02-21

206

Antibody formation in the mouse induced by hapten-carrier complexes.  

PubMed Central

The influence of hapten, carrier and their ratio in a complex on T-cell helper stimulation and antibody formation against the dinitrophenyl (DNP) hapten was studied. Complexes of DNP with bovine serum albumin (BSA), bovine gamma-globulin (BGG), isologous mouse immunoglobulin (MIG) and polyvinylpyrrolidone (PVP) as carriers were used. Optimal antibody formation against DNP was obtained with complexes with an intermediate hapten:carrier ratio (DNP 16-minusBSA, DNP 43-minusBGG and DNP 48-MINUSMIG). DNP-PVP complexes were not active either in the primary or in the secondary response. The anti-BSA titre was independent of the number of DNP groups on the complex used for immunization. Inhibition of DNP-plaque formation by spleen cells of immunized mice shows an increase of the inhibitory capacity of the complex with the increase of the hapten-carrier ratio. DNP 16-minusPVP was the only PVP complex which was inhibitory. These results suggest that helper cells involved in the antibody formation against BSA and DNP are reactive with different parts of the complex. Priming of mice with carrier or complex after cyclophosphamide (Cy) treatment followed by a secondary injection with complex 10 days later gave strong indications that there is a greater involvement in stimulation of helper T cells by determinants of the complex (new antigenic determinants (NAD) or NAP-DNP groups) or DNP, than by true BSA determinants. This holds for both the IgM and IgG responses.

Snippe, H; Graven, W G; Willems, P J

1975-01-01

207

Hydrolysis of (CH{sub 3})Hg{sup +} in different ionic media: Salt effects and complex formation  

SciTech Connect

The hydrolysis of monomethylmercury(II) was studied potentiometrically, in NaNO{sub 3}, Na{sub 2}SO{sub 4}, and NaCl aqueous solution, in a wide range of ionic strengths (NaNO{sub 3}, 0 {le} I {le} 1; NaCl, 0 {le} 1 {le} 3 mol/dm{sup 3}) and at t = 25 C. For the reaction (CH{sub 3})Hg{sup +} = (CH{sub 3})Hg(OH){degree} + H{sup +}, the authors found log K{sub 1} = {minus}4.528 (I = 0 mol/dm{sup 3}). The species [(CH{sub 3})Hg]{sub 2}(OH){sup +} was also found, with log {beta}{sub 2} = {minus}2.15. Monomethylmercury(II) forms quite strong complexes with Cl{sup {minus}} (log K = 5.45, I = 0 mol/dm{sup 3}) and SO{sub 4}{sup 2{minus}} (log K = 2.64, I = 0 mol/dm{sup 3}). The dependence on ionic strength of formation constants was considered by using a Debye-Hueckel type equation. Hydrolysis and complex formation constants (at different ionic strengths) obtained were used to calculate the interaction parameters of Pitzer equations.

Robertis, A. de; Foti, C.; Patane, G.; Sammartano, S. [Univ. di Messina, Agata (Italy)

1998-11-01

208

The H{sup +}/Zn{sup 2+} exchange stoichiometry of surface complex formation on synthetic amorphous aluminosilicate  

SciTech Connect

Surface complex formation between synthetic amorphous aluminosilicate and Zn{sup 2+} ion in 0.1 N NaNO{sub 3} was studied at 25 {+-} 0.1 C by potentiometry. The concentration of Zn{sup 2+} in the suspension was varied, while the concentration of the aluminosilicate was kept constant at 1 g air-dried aluminosilicate in 11. The pH value of the suspension was kept constant at 6.50 by 0.01 N NaOH with an automatic titration system to neutralize H{sup +} released from the solid phase. The amount of Zn(II) retained on the solid phase was calculated from the difference between the total Zn{sup 2+} concentration in the suspension and the equilibrated concentration of Zn{sup 2+} in the liquid phase. The molar ratio of Zn(II) retained on the solid surface to H{sup +} released from the solid phase is 1:2, suggesting ion exchange of two surface H{sup +} and one aqueous Zn{sup 2+} ion with conservation of charge balance. The surface complex formation between synthetic amorphous aluminosilicate and Zn{sup 2+} ion in aqueous solution can be described as 2 [Al, Si-OH] + Zn{sup 2+} (aq) = [(Al, Si-O){sub 2}Zn] + 2H{sup +}(aq), where [] represents the chemical species on the solid surface.

Miyazaki, Akane; Tsurumi, Makoto [Tokyo Inst. of Tech., Yokohama (Japan)

1995-06-15

209

Real-time observation of multiple-protein complex formation with single-molecule FRET.  

PubMed

Current single-molecule techniques do not permit the real-time observation of multiple proteins interacting closely with each other. We here report an approach enabling us to determine the single-molecule fluorescence resonance energy transfer (FRET) kinetics of multiple protein-protein interactions occurring far below the diffraction limit. We observe a strongly cooperative formation of multimeric soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes, which suggests that formation of the first SNARE complex triggers a cascade of SNARE complex formation. PMID:23808880

Bae, Woori; Choi, Mal-Gi; Hyeon, Changbong; Shin, Yeon-Kyun; Yoon, Tae-Young

2013-07-09

210

Dynamics of microtubule aster formation by motor complexes  

Microsoft Academic Search

The polymerisation of filaments and their moving by motor proteins contribute to the organisation of the cytoskeleton of higher cells. What a mixture of such elements is capable of doing, is not yet understood. Using computer simulations, we study here in a simple system the kinetics of aster formation by motors and growing microtubules. We find that the system can

François Nédélec; Thomas Surrey

2001-01-01

211

[Characteristics of complex formation between monomeric and dimeric bisbenzimidazoles and AT-containing polynucleotide].  

PubMed

Double-stranded DNA is a one of the most important intracellular anticancer agent targets. Disturbance of DNA functions as well as DNA structure lead to disorder of such processes as transcription and/or translation thus inducing tumor cells death. Complex formation between novel dimeric bisbenzimidazole DB(7) and poly(dA-dT) duplex in comparison with known monomeric bisbenzimidazole MB(Ac) was investigated in this study. DB(7)-poly(dA-dT) binding constant was determined by fluorescence spectroscopy using Scatchard plot and it values 1.18 x 10(8) M(-1) that is two orders of magnitude larger than MB(Ac) one (2.06 x 10(6) M(-1)). Thus, from findings mentioned above it could be concluded that the presence of two bisbenzimidazole moieties in the ligand structure significantly increases its affinity to the polynucleotide which motivates the synthesis of new potential anticancer drugs based on dimeric bisbenzimidazoles. PMID:23350239

Lisitsina, E S; Durandin, N A; Ivanov, A A; Strel'tsov, S A; Susova, O Iu; Shtil', A A; Zhuze, A L; Kuz'min, V A

212

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

PubMed

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

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

2013-08-22

213

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

214

Formation of hydrogen-vacancy complexes in alpha iron  

NASA Astrophysics Data System (ADS)

An extended variant of Smirnov statistic theory [12] is presented that describes the equilibrium concentrations of vacancy-hydrogen atom complexes as a function of temperature. Calculations based on the first-principle values of interaction energy show that, at low temperatures, the majority of vacancies are bound with several hydrogen atoms, and the concentration of vacancies sharply increases.

Mirzaev, D. A.; Mirzoev, A. A.; Okishev, K. Yu.; Shaburov, A. D.; Ruzanova, G. E.; Ursaeva, A. V.

2012-10-01

215

Ribonucleoprotein complex formation by the human hepatitis B virus polymerase.  

PubMed

Human hepatitis B virus (HBV) polymerase (pol or RT), when expressed in Xenopus oocytes upon injection of synthetic minimal pol RNA (RT RNA), assembles into a higher molecular weight complex with the characteristics of a ribonuclear protein (RNP) complex. In vitro RNA competition binding data suggest that RT RNA is preferentially packaged into this complex even though it lacks the authentic viral encapsidation signal, epsilon, and viral capsid protein sequences. Consistent with this finding, the in vitro polymerase reaction performed in pol-expressing oocyte extracts generates primarily HBV-specific DNAs even when the pol template is challenged with a coinjected non-HBV competitor RNA. These results suggest that interaction between pol and its cognate RNA can be mediated by sequences other than the known packaging elements. We speculate that HBV RNP complexes containing at least polymerase and viral RNA may play a role in viral nucleocapsid assembly and may help to segregate HBV reverse transcription from the cellular milieu in vivo. PMID:8724861

Seifer, M; Standring, D N

1995-01-01

216

Complex formation of elements of the third group of the periodic system with chromazurol s  

SciTech Connect

An attempt is made to establish the composition and spectrophotometric characteristics of colored complexes of elements of the third group of the periodic system, produced with chromazurol S purified according to the procedure described. For a comparison of data on complexes of various elements with this reagent the authors used published results of an investigation of the complex formation of aluminium and those results they themselves obtained. The complex formation of aluminum, gallium, indium, scandium, yttrium, lanthanum, and cerium (III) were studied with the chromazurol S. The mechanism of the reaction of aluminum, gallium, scandium, and yttrium with chromazurol S was examined.

Tikhonov, V.N.

1985-03-01

217

Effect of Heavy Doping on Complex Formation and Diffusivity of Sb in Si.  

National Technical Information Service (NTIS)

The complex formation and diffusivity during rapid thermal annealing of low concentrations of ion-implanted Sb in silicon have been studied as functions of donor concentration by combination of Rutherford backscattering spectroscopy, Hall effect/resistivi...

A. N. Larsen P. Tidemand-Petersson P. E. Andersen G. Weyer

1988-01-01

218

[Characteristics of marketing complex formation in rendering of sanatorium resort services].  

PubMed

Basic positions in sanatorium resort marketing and its evolution with description of its main components are considered. Marketing research management in sanatorium resort institutions, marketing theory, analysis of services market, characteristics of marketing complex formation are presented. PMID:17004381

Kemalov, R F

219

Structural basis for cooperativity of CRM1 export complex formation  

PubMed Central

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

Monecke, Thomas; Haselbach, David; Voss, Bela; Russek, Andreas; Neumann, Piotr; Thomson, Emma; Hurt, Ed; Zachariae, Ulrich; Stark, Holger; Grubmuller, Helmut; Dickmanns, Achim; Ficner, Ralf

2013-01-01

220

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

221

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

SciTech Connect

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

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

1986-03-01

222

[Kinetics of the formation of AT-specific DNA-distamin complex].  

PubMed

Kinetics of DNA--distamin complex formation was studied by means of the stop-flow method. It has been found that the binding reaction is much faster than in the case with distamycin A and has only two stages. The differences in kinetic properties of the complexes of distamin and distamycin A with DNA has been interpreted as resulting from the formation of different bonds by protonated positively charged N-containing groups of ligands with negatively charged DNA phosphates. PMID:3778954

Sizova, I A; Poletaev, A I

223

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

Microsoft Academic Search

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

Oleg V. Mikhailov

1995-01-01

224

Enthalpies of formation of hexahalide complexes of uranium(III)  

Microsoft Academic Search

The enthalpies of solution of uranium-containing elpasolites in a solution of 4 M HCl + 0.005 M NaâSiFâ + 10⁻⁶ M HâPtClâ were measured with a calorimeter with an isothermal casing. The standard enthalpies of formation at 298.15°K from binary halides (and from the elements and gaseous bromine) were calculated in kJ\\/mole: -23.0 +\\/- 2.2 (-2184.4 +\\/- 4.0) for KâNaUClâ;

N. A. Aurov; D. E. Chirkst

2009-01-01

225

Formation of Complex Structures in Dusty Plasmas under Temperature Gradients  

SciTech Connect

Thermophoretic effects on dust structures under temperature gradients in glow and radio-frequency discharge plasmas are studied experimentally. The geometry of dust structures consisting of micrometer-sized polydisperse grains depends on heat release in the plasma. Thermophoretic forces associated with heat release can control the formation of dust structures of different geometries. A theoretical model is proposed to describe dust separation with respect to grain size caused by the effects of radial electrostatic and thermophoretic forces. The glow discharge currents under critical conditions for grain separation predicted by the model agree with those observed experimentally.

Vasilyak, L.M.; Vetchinin, S.P.; Polyakov, D.N.; Fortov, V.E. [Institute for High Energy Densities, Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 (Russian Federation)

2005-05-01

226

Biofilm Formation and Acyl Homoserine Lactone Production in the Burkholderia cepacia Complex  

Microsoft Academic Search

Acyl homoserine lactone (acyl-HSL)-mediated gene regulation has been shown to influence biofilm formation in one Burkholderia cepacia cystic fibrosis isolate, but it is not known whether this relationship is a consistent feature of the several genomic species that make up the B. cepacia complex (BCC). We screened strains belonging to genomovars I to V of the BCC for biofilm formation

Barbara-Ann D. Conway; Vicnays Venu; David P. Speert

2002-01-01

227

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

228

Stable complex formation of thylakoidal processing peptidase and PGRL1.  

PubMed

The thylakoid-transfer signal is required for energy-dependent translocation of preproteins into the thylakoid lumen and is removed by the thylakoidal processing peptidase (TPP). PGRL1 is an essential component of antimycin A-sensitive photosynthetic cyclic electron flow in chloroplasts. Here we report that one of the TPP isoforms, Plsp1, forms a stable complex with PGRL1. Genetic data demonstrate that PGRL1 is not essential for Plsp1 activity in vivo, leading to a possibility that PGRL1 may act as a regulator of TPP. PMID:23727204

Endow, Joshua K; Inoue, Kentaro

2013-05-31

229

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

PubMed

Protection against infectious diseases is mediated by the immune system (1,2). T lymphocytes are the master coordinators of the immune system, regulating the activation and responses of multiple immune cells (3,4). T-cell activation is dependent on the recognition of specific antigens displayed by antigen presenting cells (APCs). The T-cell antigen receptor (TCR) is specific to each T-cell clone and determines antigen specificity (5). The binding of the TCR to the antigen induces the phosphorylation of components of the TCR complex. In order to promote T-cell activation, this signal must be transduced from the membrane to the cytoplasm and the nucleus, initiating various crucial responses such as recruitment of signaling proteins to the TCR;APC site (the immune synapse), their molecular activation, cytoskeletal rearrangement, elevation of intracellular calcium concentration, and changes in gene expression (6,7). The correct initiation and termination of activating signals is crucial for appropriate T-cell responses. The activity of signaling proteins is dependent on the formation and termination of protein-protein interactions, post translational modifications such as protein phosphorylation, formation of protein complexes, protein ubiquitylation and the recruitment of proteins to various cellular sites (8). Understanding the inner workings of the T-cell activation process is crucial for both immunological research and clinical applications. Various assays have been developed in order to investigate protein-protein interactions; however, biochemical assays, such as the widely used co-immunoprecipitation method, do not allow protein location to be discerned, thus precluding the observation of valuable insights into the dynamics of cellular mechanisms. Additionally, these bulk assays usually combine proteins from many different cells that might be at different stages of the investigated cellular process. This can have a detrimental effect on temporal resolution. The use of real-time imaging of live cells allows both the spatial tracking of proteins and the ability to temporally distinguish between signaling events, thus shedding light on the dynamics of the process (9,10). We present a method of real-time imaging of signaling-complex formation during T-cell activation. Primary T-cells or T-cell lines, such as Jurkat, are transfected with plasmids encoding for proteins of interest fused to monomeric fluorescent proteins, preventing non-physiological oligomerization (11). Live T cells are dropped over a coverslip pre-coated with T-cell activating antibody (8,9), which binds to the CD3/TCR complex, inducing T-cell activation while overcoming the need for specific activating antigens. Activated cells are constantly imaged with the use of confocal microscopy. Imaging data are analyzed to yield quantitative results, such as the colocalization coefficient of the signaling proteins. PMID:23851483

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

2013-06-23

230

Formation of aqueous MgUO2(CO3)3(2-) complex and uranium anion exchange mechanism onto an exchange resin.  

PubMed

The formation of and stability constants for aqueous Mg-UO2-CO3 complexes were determined using an anion exchange method. Magnesium concentration was varied (up to 20 mmol/L) at constant ionic strength (I = 0.101, 0.202, 0.304, 0.406, and 0.509 mol/kg NaNO3), pH 8.1, total [U(VI)] = 10.4 micromol/L under equilibrium with atmospheric CO2. The results indicate that only the MgUO2(CO3)3(2-) complex is formed. The cumulative formation constant extrapolated to zero ionic strength is similar regardless of the activity correction convention used: logbeta113(0) = 25.8 +/- 0.5 using the Davies equation and = 25.02 +/- 0.08 using specific ion interaction theory (SIT). Uranium sorption onto the exchange resin decreased in the presence of Mg putatively due to the formation of MgUO2(CO3)3(2-) that had a lower affinity for the resin than UO2(CO3)3(4-). Uranium sorption results are consistent with an equivalent anion exchange reaction between NO3- and UO2(CO3)3(4-) species to retain charge neutrality regardless of Mg concentration. No Mg was associated with the anion exchange resin indicating that the MgUO2(CO3)3(2-) complex did not sorb. PMID:18409624

Dong, Wenming; Brooks, Scott C

2008-03-15

231

Complexity, segregation, and pattern formation in rotating-drum flows  

NASA Astrophysics Data System (ADS)

Rotating-drum flows span a variety of research areas, ranging from physics of granular matter through hydrodynamics of suspensions to pure liquid coating flows. Recent years have seen an intensified scientific activity associated with this unique geometrical configuration, which has contributed to our understanding of related subjects such as avalanches in granules and segregation in suspensions. The existing literature related to rotating-drum flows is reviewed, highlighting similarities and differences between the various flow realizations. Scaling laws expressing the importance of different mechanisms underlying the observed phenomena have been focused on. An emphasis is placed on pattern formation phenomena. Rotating-drum flows exhibit stationary patterns as well as traveling and oscillating patterns; they exhibit reversible transitions as well as hysteresis. Apart from the predominant cylindrical configuration, this review covers recent work done with tumblers having other geometries, such as the sphere and the Hele-Shaw cell.

Seiden, G.; Thomas, P. J.

2011-10-01

232

Reversible carbon-carbon bond formation between carbonyl compounds and a ruthenium pincer complex.  

PubMed

This communication describes the reversible reaction of a ruthenium pincer complex with a variety of carbonyl compounds. Both NMR spectroscopic and X-ray crystallographic characterization of isomeric carbonyl adducts are reported, and the equilibrium constants for carbonyl binding have been determined. PMID:23832007

Huff, Chelsea A; Kampf, Jeff W; Sanford, Melanie S

2013-08-18

233

Neuronal inputs to hippocampal formation in Alzheimer's disease and in parkinsonism-dementia complex on Guam  

Microsoft Academic Search

This study concerns the expression of synaptophysin in the hippocampal formation of normal controls, of patients with Alzheimer's disease (AD) and of patients with parkinsonism-dementia complex on Guam (P-D complex). A monoclonal antibody was used to visualize synaptophysin, an integral component of presynaptic vesicle membranes. In the normal controls, a strong synaptophysin immunoreactivity was seen in the stratum pyramidale, stratum

S. Goto; A. Hirano

1990-01-01

234

Formation of complex impact craters - Evidence from Mars and other planets  

Microsoft Academic Search

An analysis of the depth vs diameter data of Arthur (1980), is given along with geomorphic data for 73 Martian craters. The implications for the formation of complex impact craters on solid planets is discussed. The analysis integrates detailed morphological observations on planetary craters with geologic data from terrestrial meteorite and explosion craters. The simple to complex transition for impact

R. J. Pike

1980-01-01

235

The nature and extent of synaptonemal complex formation in haploid barley  

Microsoft Academic Search

Normal synaptonemal complexes have been found in haploid barley meiotic prophase at stages equivalent to pachytene in diploids. Reconstructions of serially sectioned nuclei have shown that up to 60% of the haploid chromosomes may pair in either intra- or interchromosomal associations. The extent and nature of the synaptonemal complex formation suggest that the chromosome pairing is non-homologous. From the virtual

C. B. Gillies

1974-01-01

236

An electron microscopic study of synaptonemal complex formation at zygotene in rye  

Microsoft Academic Search

A spreading technique was used to allow ultrastructural analysis of seventeen zygotene nuclei of rye (Secale cereale). Twenty pachytene nuclei were also examined. Lateral element lengths of the haploid complements decreased from 742 µm at the beginning of zygotene to 451 µm at the end of zygotene. Variation in pachytene synaptonemal complex lengths was also noted. Zygotene synaptonemal complex formation

C. B. Gillies

1985-01-01

237

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

238

Study of magnetic field effect on Py-DMA exciplex luminescence in THF-DMF binary solvents: Evidence of multiple exciplex formation at higher bulk dielectric constant  

NASA Astrophysics Data System (ADS)

Magnetic field effects (MFE) on pyrene-DMA (N,N-dimethylaniline) exciplex system in THF-DMF binary solvents of varying bulk dielectric constant ( ?) has been studied. The MFE has been wavelength resolved over the emission band of the exciplex. The data indicates formation of two types of exciplexes at higher bulk value of ?. At lower value of ? ( ? < 9) essentially there is a single type of exciplex which is supported by the wavelength resolved MFE and life-time ( ?) measurements. However, at higher value of ? ( ? > 15) when the solvent reorganization energy is more prominent; the wavelength resolved MFE and life-time studies show evidence of two types of exciplexes.

Roy, Partha; Jana, Amit Kumar; Das, Doyel; Nath, Deb Narayan

2009-06-01

239

20S cyclosome complex formation and proteolytic activity inhibited by the cAMP\\/PKA pathway  

Microsoft Academic Search

THE 20S cyclosome complex (also known as the anaphase-promoting complex) has ubiquitin ligase activity and is required for mitotic cyclin destruction1-3 and sister chromatid separation4,5. The formation and activation of the 20S cyclosome complex is regulated by an unknown mechanism. Here we show that Cut4 (ref. 6) is an essential component of the cyclosome in fission yeast. Cut4 shares sequence

Yukiko M. Yamashita; Yukinobu Nakaseko; Itaru Samejima; Kazuki Kumada; Hiroshi Yamada; David Michaelson; Mitsuhiro Yanagida

1996-01-01

240

Distinct domains of syntaxin are required for synaptic vesicle fusion complex formation and dissociation  

Microsoft Academic Search

Membrane fusion resulting in neurotransmitter secretion forms the basis of neural communication. Three multimeric complexes of the protein syntaxin are important in this process: syntaxin and n-sect; syntaxin, VAMP, and SNAP-25; and syntaxin, VAMP, SNAP-25, ?SNAP, and NSF (20S complex). In this report, we demonstrate that unique, yet overlapping, domains of syntaxin are required to form these complexes. The formation

Yun Kee; Richard C Lin; Shu-Chan Hsu; Richard H Scheller

1995-01-01

241

Method for inhibiting the formation of SET1 family core complexes  

US Patent & Trademark Office Database

Disclosed in this specification is a method for inhibiting the formation of SET1 family core complexes. A guanidinium-containing molecule is used to competitively inhibit the binding of the N-SET region of a SET1 protein to WDR5, thus inhibiting the formation of the SET1 family core complex. The guanidinium-containing molecule may be, for example, an arginine-containing peptide. When bound to WDR5, the guanidinium moiety is bound between the F-133 and F-263 residues of the WDR5 when a crystal structure of the bound complex is obtained.

2012-03-13

242

Microbanded manganese formations; protoliths in the Franciscan Complex, California  

USGS Publications Warehouse

The Buckeye manganese deposit, 93 km southeast of San Francisco in the California Coast Ranges, preserves a geologic history that provides clues to the origin of numerous lenses of manganese carbonate, oxides, and silicates that occur with interbedded radiolarian chert and metashale of the Franciscan Complex. Compositionally and mineralogically laminated Mn-rich protoliths were deformed and dismembered, in a manner that mimics in smaller scale the deformation of the host complex, and then were incipiently metamorphosed at blueschistfacies conditions. Eight phases occur as almost monomineralic protoliths and mixtures: rhodochrosite, caryopilite, chlorite, gageite, taneyamalite, braunite, hausmannite, and laminated chert (quartz). Braunite, gageite, and some chlorite and caryopilite layers were deposited as gel-like materials; rhodochrosite, most caryopilite, and at least some hausmannite layers as lutites; and the chert as turbidites of radiolarian sand. Some gel-like materials are now preserved as transparent, sensibly isotropic relics of materials that fractured or shattered when deformed, creating curved surfaces. In contrast, the micrites flowed between the fragments of gel-like materials. The orebody and most of its constituent minerals have unusually Mn-rich compositions that are described by the system MnO-SiO2-O2-CO2-H2O. High values of Mn/Fe and U/Th, and low concentrations of Co, Cu, and Ni, distinguish the Buckeye deposit from many high-temperature hydrothermal deposits and hydrogenous or diagenetic manganese and ferromanganese nodules and pavements. This chemical signature suggests that ore deposition was related to fluids from the sediment column and seawater. Tungsten is associated exclusively with gageite, in concentrations as high as 80 parts per million. The source of the manganese is unknown; because basalts do not occur near the deposit, it was probably manganese leached from the sediment column by reducing solutions. Low concentrations of calcium (CaO approximately 0.6 weight percent) suggest that the host sediments formed beneath the carbonate-compensation depth. The most probable cause of the microbanding is changing proportions of chemical fluxes supplied to the sediment-seawater interface. The principal fluxes were biogenic silica from the water column, carbon dioxide from organic matter in the sediment column, O2 and other seawater constituents, and Mn +2-bearing fluid. The presence of Al2O3 and TiO2 (supplied by a detrital flux) in the metashale but not the ore lens suggests rapid ore deposition. Material supply-rate changes were probably due to a complex combination of episodic variations in the hydrothermal flux and periodic flows of radiolarian sand (silica and CO2 fluxes) that may be related to climate variations. The processes that form recent marine hydrothermal mounds may be the same as processes that formed the Buckeye deposit. Features common to both include the presence of Mn-oxyhydroxide crusts (corresponding to the Buckeye orebody), a large Mn/Fe ratio, low abundances of most minor elements, and small size. The most important differences are the absence of rhodochrosite and manganese silicates, interlayered with oxide, and the absence of adjacent chert in the contemporary deposits. These differences may be due to an absence of the debris of siliceous pelagic organisms, which accumulated in the Buckeye paleoenvironment. Periodic turbidity flows of chert-forming radiolarian sand could provide the changes in the fluxes of silica and organic matter necessary to form manganese carbonate and silicates. Turbidity flows of graywacke indicate proximity to an environment with high relief. A possible paleodepositional environment is an oceanic spreading center approaching a continental margin at which subduction occurred.

Huebner, J. Stephen; Flohr, Marta J.

1990-01-01

243

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

2008-12-04

244

Norfloxacin Zn(II)-based complexes: acid base ionization constant determination, DNA and albumin binding properties and the biological effect against Trypanosoma cruzi.  

PubMed

Zn(II) complexes with norfloxacin (NOR) in the absence or in the presence of 1,10-phenanthroline (phen) were obtained and characterized. In both complexes, the ligand NOR was coordinated through a keto and a carboxyl oxygen. Tetrahedral and octahedral geometries were proposed for [ZnCl2(NOR)]·H2O (1) and [ZnCl2(NOR)(phen)]·2H2O (2), respectively. Since the biological activity of the chemicals depends on the pH value, pH titrations of the Zn(II) complexes were performed. UV spectroscopic studies of the interaction of the complexes with calf-thymus DNA (CT DNA) have suggested that they can bind to CT DNA with moderate affinity in an intercalative mode. The interactions between the Zn(II) complexes and bovine serum albumin (BSA) were investigated by steady-state and time-resolved fluorescence spectroscopy at pH 7.4. The experimental data showed static quenching of BSA fluorescence, indicating that both complexes bind to BSA. A modified Stern-Volmer plot for the quenching by complex 2 demonstrated preferential binding near one of the two tryptophan residues of BSA. The binding constants obtained (K b ) showed that BSA had a two orders of magnitude higher affinity for complex 2 than for 1. The results also showed that the affinity of both complexes for BSA was much higher than for DNA. This preferential interaction with protein sites could be important to their biological mechanisms of action. The analysis in vitro of the Zn(II) complexes and corresponding ligand were assayed against Trypanosoma cruzi, the causative agent of Chagas disease and the data showed that complex 2 was the most active against bloodstream trypomastigotes. PMID:23897315

Gouvea, Ligiane R; Martins, Darliane A; da Gama Jean Batista, Denise; de Nazaré C Soeiro, Maria; Louro, Sonia R W; Barbeira, Paulo J S; Teixeira, Letícia R

2013-07-30

245

Regulation of complement membrane attack complex formation in myocardial infarction.  

PubMed Central

Recent studies have suggested that the complement (C) system is involved in the development of tissue injury of myocardial infarction. As it is not known why the strictly controlled C system starts to react against autologous heart tissue, we have analyzed the expression of various membrane regulators of C (CR1, DAF, MCP, CD59, C8 binding protein) and the pattern of deposition of C components and plasma C regulators (C4b binding protein and vitronectin) in normal (n = 7) and infarcted (n = 13) human myocardium. In the infarcted myocardium deposits of the C membrane attack complex (MAC) were observed by immunofluorescence microscopy, and lesions resembling the transmembrane channels of MAC were detected by transmission electron microscopy. CD59 and C8 binding protein were strongly expressed by muscle cells of normal myocardial tissue. Little or no CR1, MCP, and DAF was observed on these cells. The assembly of MAC was accompanied by the deposition of vitronectin (S-protein) and C4b binding protein in the infarcted areas of myocardium. In accordance with our earlier results the expression of CD59 but not of C8 binding protein was clearly diminished in the lesions. The results show that C8 binding protein, vitronectin, and C4b binding protein do not prevent complement attack against the infarcted myocardium but rather become codeposited with the MAC. Ischemia-induced transformation of nonviable cells into complement activators, acquired loss of resistance to the MAC by shedding of CD59, and recruitment of multifunctional serum proteins by MAC could thus constitute a general process aimed at the clearance of injured tissue. Images Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Vakeva, A.; Laurila, P.; Meri, S.

1993-01-01

246

Hierarchical network between the components of the multi-tRNA synthetase complex: implications for complex formation.  

PubMed

The macromolecular tRNA synthetase complex consists of nine different enzymes and three non-enzymatic factors. This complex was recently shown to be a novel signalosome, since many of its components are involved in signaling pathways in addition to their catalytic roles in protein synthesis. The structural organization and dynamic relationships of the components of the complex are not well understood. Here we performed a systematic depletion analysis to determine the effects of structural intimacy and the turnover of the components. The results showed that the stability of some components depended on their neighbors. Lysyl-tRNA synthetase was most independent of other components for its stability whereas it was most required for the stability of other components. Arginyl- and methionyl-tRNA synthetases had the opposite characteristics. Thus, the systematic depletion of the components revealed the functional reason for the complex formation and the assembly pattern of these multi-functional enzymes and their associated factors. PMID:17062567

Han, Jung Min; Lee, Min Ji; Park, Sang Gyu; Lee, Sun Hee; Razin, Ehud; Choi, Eung-Chil; Kim, Sunghoon

2006-10-24

247

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

248

Spring Constants  

NSDL National Science Digital Library

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

Horton, Michael

2009-05-30

249

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

250

Effect of fatty acid chain length and saturation on formation of the acylenzyme complex by the isolated aortic enzyme fraction.  

PubMed

Formation of acylenzyme complexes between the protein fraction isolated from pig thoracic aortas and palmitic, stearic, oleic, linoleic, linolenic and arachidic acid, was studied. The reaction brings about transformations of the periodically variable sinusoidal function of the enzyme absorbancy (energy level) depending on the kind of substrate utilized. Different changes in the enzyme energy level in the elementary process are induced by the saturated and polyunsaturated fatty acids and by oleic acid as demonstrated by the intermediate course of the function for oleylenzyme. The reaction rate constants were calculated and their negative curvilinear dependence upon molecular weight of the substrates has been shown. The differences in the acyl-enzyme reaction course and preferences are discussed with respect to the arterial metabolism and different accumulation of lipids. PMID:2641424

Swidzi?ska, K; Patelski, J; Szwajca, T

251

Substituent effect on the electron acceptor property of 1,4-benzoquinone towards the formation of molecular complex with sulfamethoxazole.  

PubMed

UV-Vis, (1)H NMR, FT-IR, LC-MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of sulfamethoxazole with varying number of methoxy/chloro substituted 1,4-benzoquinones (MQ1-4) and to characterize the reaction products. The interactions of MQ1-4 with sulfamethoxazole (SULF) were found to proceed through the formation of a donor-acceptor complex, containing radical anion and its conversion to the product. Fluorescence quenching studies showed that the interaction between the donor and the acceptors are spontaneous. The results indicated that the progressive replacement of chlorine atom (-I effect) by methoxy group (+M effect) in the quinone decreased the electron acceptor property of the quinone. The results of the correlation of experimentally measured binding constants with electrochemical data and ab initio DFT calculations supported these observations. PMID:23416920

Ganesh, K; Satheshkumar, A; Balraj, C; Elango, K P

2013-01-23

252

Substituent effect on the electron acceptor property of 1,4-benzoquinone towards the formation of molecular complex with sulfamethoxazole  

NASA Astrophysics Data System (ADS)

UV-Vis, 1H NMR, FT-IR, LC-MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of sulfamethoxazole with varying number of methoxy/chloro substituted 1,4-benzoquinones (MQ1-4) and to characterize the reaction products. The interactions of MQ1-4 with sulfamethoxazole (SULF) were found to proceed through the formation of a donor-acceptor complex, containing radical anion and its conversion to the product. Fluorescence quenching studies showed that the interaction between the donor and the acceptors are spontaneous. The results indicated that the progressive replacement of chlorine atom (-I effect) by methoxy group (+M effect) in the quinone decreased the electron acceptor property of the quinone. The results of the correlation of experimentally measured binding constants with electrochemical data and ab initio DFT calculations supported these observations.

Ganesh, K.; Satheshkumar, A.; Balraj, C.; Elango, K. P.

2013-04-01

253

Donor complex formation due to a high-dose Ge implant into Si  

SciTech Connect

To investigate boron deactivation and/or donor complex formation due to a high-dose Ge and C implantation and the subsequent solid phase epitaxy, SiGe and SiGeC layers were fabricated and characterized. Cross-sectional transmission electron microscopy indicated that the SiGe layer with a peak Ge concentration of 5 at. % was strained; whereas, for higher concentrations, stacking faults were observed from the surface to the projected range of the Ge as a result of strain relaxation. Photoluminescence (PL) results were found to be consistent with dopant deactivation due to Ge implantation and the subsequent solid phase epitaxial growth of the amorphous layer. Furthermore, for unstrained SiGe layers (Ge peak concentration [ge]7 at. %), the PL results support our previously proposed donor complex formation. These findings were confirmed by spreading resistance profiling. A model for donor complex formation is proposed.

Gupta, A.; Rahman, M.M.; Qiao, J.; Yang, C.Y. (Microelectronics Laboratory, Santa Clara University, Santa Clara, California 95053 (United States)); Im, S.; Cheung, N.W. (Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720 (United States)); Yu, P.K.L. (Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California 92093 (United States))

1994-04-15

254

Spectroscopic investigation on the mechanism of formation of molecular complexes of albendazole and trimethoprim with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.  

PubMed

UV-vis, (1)H NMR, FT-IR, mass and fluorescence spectral techniques were employed to investigate the mechanism of interaction of albendazole and trimethoprim with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and to characterize the reaction products. The interaction of DDQ with trimethoprim (TMP) and albenadazole (ALB) were found to proceed through the formation of donor-acceptor complex, containing DDQ radical anion and its conversion to the product. Fluorescence quenching studies indicated that the interaction between the donors and the acceptor are spontaneous and the interaction of TMP-DDQ (binding constant=2.9×10(5)) is found to be stronger than that the ALB-DDQ (binding constant=3×10(3)) system. Also, the binding constant increased with an increase in polarity of the medium indicating the involvement of radical anion as intermediate. PMID:22402578

Ganesh, K; Balraj, C; Satheshkumar, A; Elango, K P

2012-02-16

255

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

256

Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel)  

Microsoft Academic Search

Wilson, M.A., Wolfe, K.R., and Avni, Y. 2005. Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel). Isr. J. Earth Sci. 54: 171-178. The Zohar Formation (Callovian, Middle Jurassic) is exposed as a sequence of limestones, dolomites, siltstones, and shales near the center of Makhtesh Qatan in the Negev Desert of southern Israel. Two dolomite units

Mark A. Wilson; Kevin R. Wolfe; Yoav Avni

2005-01-01

257

Kinetics of complex formation between palladium(II) acetate and bis(diphenylphosphino)ferrocene  

Microsoft Academic Search

The kinetics of complex formation between palladium(II) acetate, and 1,1’-bis(diphenylphosphino)ferrocene, dppf, in two different deuterated solvents CDCl3 and DMSO-d6 were investigated using 31P NMR spectroscopy. The mole ratio and the 31P-chemical shifts in DMSO-d6 solution revealed the formation of an intermediate, which is gradually converted into the more stable [Pd(dppf)OAc)2] species with a dppf acting as a chelate ligand. In

Mahbubeh Pourshahbaz; Mohsen Irandoust; Ezzat Rafiee; Mohammad Joshaghani

2009-01-01

258

Complex Formation and Functional Versatility of Mre11 of Budding Yeast in Recombination  

Microsoft Academic Search

Meiotic recombination of S. cerevisiae contains two temporally coupled processes, formation and processing of double-strand breaks (DSBs). Mre11 forms a complex with Rad50 and Xrs2, acting as the binding core, and participates in DSB processing. Although these proteins are also involved in DSB formation, Mre11 is not necessarily holding them. The C-terminal region of Mre11 is required only for DSB

Takehiko Usui; Tsutomu Ohta; Hiroyuki Oshiumi; Jun-ichi Tomizawa; Hideyuki Ogawa; Tomoko Ogawa

1998-01-01

259

Formation of ATP by the adenosine triphosphatase complex from spinach chloroplasts reconstituted together with bacteriorhodopsin.  

PubMed

The energy-linked ATPase complex has been isolated from spinach chloroplasts. This protein complex contained all the subunits of the chloroplast coupling factor (CF1) as well as several hydrophobic compoenents. When the activated complex was reconstituted with added soybean phospholipids, it catalyzed the exchange of radioactive inorganic phosphate with ATP. Sonication of the complex into proteoliposomes together with bacteriorhodopsin yield vesicles that catalyzed light-dependent ATP formation. Both the 32Pi-ATP exchange reactions and ATP formation were sensitive to uncouplers such as 3-tert-butyl-5,2'-dichloro-4'-nitrosalicylanilide, bis-(hexafluoroacetonyl)acetone and carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazone, that act to dissipate a proton gradient. The energy transfer inhibitors dicyclohexylcarbodiimide, triphenyltin chloride and 2-beta-D-glucopyranosyl-4,6'-dihydroxydihydrochalcone were also effective inhibitors of both reactions. PMID:141938

Winget, G D; Kanner, N; Racker, E

1977-06-01

260

The coactivator p15 (PC4) initiates transcriptional activation during TFIIA-TFIID-promoter complex formation.  

PubMed Central

We have analyzed the mechanisms underlying stimulation of transcription by the activator GAL4-AH and the recombinant coactivator p15 (PC4). We show that p15 binds to both double-stranded and single-stranded DNA. Analyses of deletion mutants correlates binding to double-stranded DNA with the ability to mediate activator-dependent transcription. Consistent with this finding, phosphorylation of p15 by casein kinase II inhibits binding to double-stranded DNA and the activity of p15. The functional characterization suggests interactions of p15 with both DNA and components of the TFIID complex. GAL4-AH functions in concert with p15 during formation of TFIIA-TFIID-promoter (DA) complexes, as concluded from order-of-addition experiments. At limiting TFIID concentrations, the number of DA complexes is enhanced. The activator also stimulates transcription moderately after DA complex formation, independently of the concentrations of general transcription factors. Images

Kaiser, K; Stelzer, G; Meisterernst, M

1995-01-01

261

Surface-complex formation between Zn ions and amorphous aluminosilicate in aquatic systems  

SciTech Connect

Surface-complex formation on oxides, especially clay minerals, significantly contributes to determining the composition of river, ground, and soil water. To understand the fate of heavy metals in natural aquatic systems it is important to accumulate information about the surface-complex formation of heavy metals at low concentrations of the solid. Surface-complex formation between synthesized amorphous aluminosilicate and Zn ions has been studied by potentiometry. A batch adsorption experiment was performed at 25 {+-} 0.1 C while the pH value of the suspension was kept at 6.50 and the solid concentration was kept at 0.1 g/liter. The amount of Zn adsorbed on the aluminosilicate and the amount of H{sup +} released from the solid were determined. The observed molar ratio of released H{sup +} to adsorbed Zn was 2 when the total concentration of Zn in the system was relatively high (1.5--13 mmol/liter). This was consistent with the charge balance. However, when the total concentration of Zn in the system was relatively low (0--1.5 mmol/liter), the molar ratio of Zn to H{sup +} was found not to be 2, but near 1. This observation suggests the possibility of surface complex formation between amorphous aluminosilicate and a monovalent Zn complex ion, such as Zn(NO{sub 3}){sup +} and Zn(OH){sup +}.

Miyazaki, Akane; Matsuo, Motoyuki [Univ. of Tokyo (Japan); Tsurumi, Makoto [Hirosaki Univ., Aomori (Japan). Dept. of Earth Science

1996-02-10

262

Intense phosphorescence triggered by alcohols upon formation of a cyclodextrin ternary complex  

Microsoft Academic Search

Intense phosphorescence is observed when alcohols (ROH) are introduced to aqueous solutions containing 1 -bromonaphthalene (1 -BrNp) and a glucosyl-modified cyclodextrin (G@-CD). Steady- state and time-resolved luminescence measurements and equilibrium constant data are consistent with phosphorescence arising from l-BrNp as part of a l-BrNpG@-CD*ROH ternary complex. The association of the l-BrNp to Gj3-CD is increased in the presence of the

Adrian Ponce; Peter A. Wong; Daniel G. Nocera

1993-01-01

263

Effects of water and alcohol on the formation of inclusion complexes of d-limonene and cyclodextrins  

Microsoft Academic Search

Systematic studies have been carried out on the role of water and alcohol in the formation of inclusion complexes between d-limonene and ?-, ?- and ?-cyclodextrin (CD) by a micro-aqueous method. The inclusion complex was barely formed at zero water content for all CDs. Above the specific water content for each CD, formation of the inclusion complex correlated well with

Takeshi Furuta; Hidefumi Yoshii; Atsuyuki Miyamoto; Akira Yasunishi; Hiroshi Hirano

1993-01-01

264

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

Microsoft Academic Search

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.

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

2009-01-01

265

+The effect of amylose–lipid complex formation on enzyme susceptibility of sago starch  

Microsoft Academic Search

Native sago starch was incubated at 60°C with lysophosphatidylcholine, monomyristin, monopalmitin, and monostearin. Differential scanning calorimetry peaks centred at 100–120°C indicated formation of amylose–lipid complexes. Among the four lipids, lysophosphatidylcholine showed the highest complexing ability, while that of the monoglycerides decreased with the increasing chain length. Part of the amylose leached during the incubation, and the amount of leached material

R. Cui; C. G. Oates

1999-01-01

266

Relaxation Study of Complex Formation between Monovalent Cations and Cyclic Polyethers  

PubMed Central

Equilibrium quotients for the 1:1 complexes of dibenzo-30-crown-10 with Na+, K+, Rb+, Cs+, NH4+, and T1+ in methanol solution have been determined spectrophotometrically. The observed selectivity pattern is discussed in terms of the hydration energy of the cations and the cation-ligand binding energy. The rate of complex formation is diffusion-controlled. Relaxation amplitude data are consistent with a mechanism that involves conformational change of the crown compound. Images

Chock, P. B.

1972-01-01

267

The role of synthetic and bone extracted Ca-phospholipid-PO 4 complexes in hydroxyapatite formation  

Microsoft Academic Search

Summary The calcium-phospholipid-phosphate (Ca-PL-PO4) complex isolated from young bone has been shown to initiate hydroxyapatite formation from a metastable calcium phosphate solution. The action of the complex was compared to that of the acidic phospholipids: phosphatidyl serine, phosphatidyl inositol and phosphatidic acid. These phospholipids first remove calcium, and a small amount of phosphate from the metastable solution forming a material

Adele L. Boskey; Aaron S. Posner

1977-01-01

268

Inclusion complex formation of ionic liquids and other cationic organic compounds with cucurbit[7]uril studied by 4',6-diamidino-2-phenylindole fluorescent probe.  

PubMed

The encapsulation of 4',6-diamidino-2-phenylindole (DAPI) in the cucurbit[7]uril (CB7) cavity was studied by absorption, fluorescence, and NMR spectroscopic methods in aqueous solution. The profound change in the fluorescence characteristics was attributed to the formation of a very stable 1:1 inclusion complex. Three independent methods provided (1.1+/-0.1)x10(7) M(-1) value for the binding constant. DAPI proved to be an excellent fluorescent probe for the investigation of the competitive binding of ionic liquids, surfactants, and biologically important compounds to CB7. The equilibrium constant of 1-alkyl-3-methylimidazolium inclusion was found to go through a maximum as the aliphatic chain length was increased, reaching the highest value for the hexyl derivative. The variation of the anion had a small effect. Among cationic surfactants containing a dodecyl tail, the stability of CB7 complex diminished with the growing hydrophobicity of the head group. PMID:19159198

Miskolczy, Zsombor; Biczók, László; Megyesi, Mónika; Jablonkai, István

2009-02-12

269

In situ formation of heterobimetallic salen complexes containing titanium and/or vanadium ions.  

PubMed

A combination of high-resolution electrospray mass spectrometry and (1)H NMR spectroscopy has been used to prove that when a mixture of [(salen)TiO]2 complexes containing two different salen ligands (salen and salen') is formed, an equilibrium is established between the homodimers and the heterodimer [(salen)TiO2Ti(salen')]. Depending upon the structure and stereochemistry of the two salen ligands, the equilibrium may favor either the homodimers or the heterodimer. Extension of this process to mixtures of titanium(salen) complexes [(salen)TiO]2 and vanadium (V)(salen') complexes [(salen')VO] (+)Cl (-) allowed the in situ formation of the heterobimetallic complex [(salen)TiO2V(salen')] (+)X (-) to be confirmed for all combinations of salen ligands studied except when the salen ligand attached to titanium contained highly electron-withdrawing nitro-groups. The rate of equilibration between heterobimetallic complexes is faster than that between two titanium complexes as determined by line broadening in the (1)H NMR spectra. These structural results explain the strong rate-inhibiting effect of vanadium (V)(salen) complexes in asymmetric cyanohydrin synthesis catalyzed by [(salen)TiO]2 complexes. It has also been demonstrated for the first time that the titanium and vanadium complexes can undergo exchange of salen ligands and that this is catalyzed by protic solvents. However, the ligand exchange is relatively slow (occurring on a time scale of days at room temperature) and so does not complicate studies aimed at using heterobimetallic titanium and vanadium salen complexes as asymmetric catalysts. Attempts to obtain a crystal structure of a heterobimetallic salen complex led instead to the isolation of a trinuclear titanium(salen) complex, the formation of which is also consistent with the catalytic results obtained previously. PMID:18396859

Belokon, Yuri N; Harrington, Ross W; North, Michael; Young, Carl

2008-04-09

270

Formation of Stable Cationic Lipid/DNA Complexes for Gene Transfer  

NASA Astrophysics Data System (ADS)

Stable cationic lipid/DNA complexes were formed by solubilizing cationic liposomes with 1% octylglucoside and complexing a DNA plasmid with the lipid in the presence of detergent. Removal of the detergent by dialysis yielded a lipid/DNA suspension that was able to transfect tissue culture cells up to 90 days after formation with no loss in activity. Similar levels of gene transfer were obtained by mixing the cationic lipid in a liposome form with DNA just prior to cell addition. However, expression was completely lost 24 hr after mixing. The transfection efficiency of the stable complex in 15% fetal calf serum was 30% of that obtained in the absence of serum, whereas the transient complex was completely inactivated with 2% fetal calf serum. A 90-day stability study comparing various storage conditions showed that the stable complex could be stored frozen or as a suspension at 4 degrees C with no loss in transfection efficiency. Centrifugation of the stable complex produced a pellet that contained approximately 90% of the DNA and 10% of the lipid. Transfection of cells with the resuspended pellet and the supernatant showed that the majority of the transfection activity was in the pellet and all the toxicity was in the supernatant. Formation of a stable cationic lipid/DNA complex has produced a transfection vehicle that can be stored indefinitely, can be concentrated with no loss in transfection efficiency, and the toxicity levels can be greatly reduced when the active complex is isolated from the uncomplexed lipid.

Hofland, Hans E. J.; Shephard, Lee; Sullivan, Sean M.

1996-07-01

271

TAR RNA decoys inhibit tat-activated HIV-1 transcription after preinitiation complex formation.  

PubMed Central

The ability of the HIV-1 Tat protein to trans -activate HIV-1 transcription in vitro is specifically inhibited by a circular TAR RNA decoy. This inhibition is not overcome by adding an excess of Tat to the reaction but is partially overcome by adding Tat in combination with nuclear extract, suggesting that TAR RNA might function by interacting with a complex containing Tat and cellular factor(s). A cell-free transcription system involving immobilized DNA templates was used to further define the factor(s) that interact with TAR RNA. Preinitiation complexes formed in the presence or absence of Tat were purified on immobilized templates containing the HIV-1 promoter. After washing, nucleotides and radiolabelled UTP were added and transcription was measured. The presence of Tat during preinitiation complex formation resulted in an increase in the level of full-length HIV-1 transcripts. This Tat-activated increase in HIV-1 transcription was not inhibited by circular TAR decoys added during preinitiation complex formation but was inhibited by circular TAR decoys subsequently added during the transcription reaction. These results suggest that TAR decoys inhibit Tat-activated HIV-1 transcription after preinitiation complex formation, perhaps by interacting with components of transcription complexes.

Bohjanen, P R; Liu, Y; Garcia-Blanco, M A

1997-01-01

272

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

273

Reconstitution of core light-harvesting complexes of photosynthetic bacteria using chemically synthesized polypeptides. 1. Minimal requirements for subunit formation.  

PubMed

Described are the chemical synthesis, isolation and characterization of each of three polypeptides whose amino acid sequences reproduce portions of the amino acid sequence of the beta-polypeptides of the core light-harvesting complex (LH1) of Rhodobacter sphaeroides or Rhodospirillum rubrum. The native beta-polypeptides of LH1 of these organisms contain 48 and 54 amino acids, respectively. The smallest synthetic polypeptide had an amino acid sequence identical to that of the last 16 amino acids of the beta-polypeptide of Rb. sphaeroides (sph beta 16) but failed to form either a subunit- or LH1-type complex under reconstitution conditions. Also, this polypeptide, lengthened on the N terminus by adding the sequence Lys-Ile-Ser-Lys to enhance solubility, failed to form a subunit- or LH1-type complex. In contrast, polypeptides containing either the 31 amino acids at the C terminus of the beta-polypeptide of Rb. sphaeroides (sph beta 31) or the equivalent 31 amino acids of the beta-polypeptide of Rs. rubrum (rr beta 31) were fully competent in forming a subunit-type complex and exhibited association constants for complex formation comparable to or exceeding those of the native beta-polypeptides. The absorption and CD spectra of these subunit-type complexes were nearly identical to those of subunit complexes formed with native beta-polypeptides. It may be concluded that all structural features required to make the subunit complex are present in the well-defined, chemically synthesized polypeptides. Neither polypeptide appeared to interact with the native alpha-polypeptides to form a LH1-type complex. However, sph beta 31 formed a LH1-type complex absorbing at 849 nm without an alpha-polypeptide. Although chemical syntheses of polypeptides of this size are common, the purification of membrane-spanning segments is much more challenging because the polypeptides lack solubility in water. The chemical syntheses reported here represent the first such syntheses of membrane-spanning polypeptides which display native activity upon reconstitution. PMID:9521662

Meadows, K A; Parkes-Loach, P S; Kehoe, J W; Loach, P A

1998-03-10

274

The free radical chemistry of tert-butyl formate: rate constants for hydroxyl radical, hydrated electron and hydrogen atom reaction in aqueous solution  

NASA Astrophysics Data System (ADS)

Transients generated in situ by advanced oxidation technologies (AOTs) to destroy organic contaminants in ground and drinking water often give large concentrations of chemical by-products. These by-products may have adverse health effects, and can also interfere with the desired chemical removal by competing for the generated transients, thus lowering the overall efficiency of the remediation process. To allow for a quantitative evaluation of the influence of tert-butyl formate (TBF), a major by-product formed in the AOT destruction of methyl tert-butyl ether, rate constants for TBF reaction with the hydroxyl radical, the hydrated electron and the hydrogen atom in aqueous solution were measured in this study. Absolute values of (5.23+/-0.07)×108, (5.48+/-0.09)×108 and (3.58+/-0.07)×106M-1s-1, were determined at 22°C, respectively.

Hardison, D. Ransom; Cooper, William J.; Mezyk, Stephen P.; Bartels, David M.

2002-11-01

275

Adhesive but not lateral E-cadherin complexes require calcium and catenins for their formation.  

PubMed

We examined intercadherin interactions in epithelial A-431 cells producing endogenous E-cadherin and recombinant forms of E-cadherin tagged either by myc or by flag epitopes. Three distinct E-cadherin complexes were found. The first is a conventional E-cadherin-catenin complex consisting of one E-cadherin molecule linked either to beta-catenin/alpha-catenin or to plakoglobin/alpha-catenin dimers. The second is a lateral E-cadherin complex incorporating two E-cadherin- catenin conventional complexes combined in parallel fashion via dimerization of the NH2-terminal extracellular domain of E-cadherin. The third complex is likely to contain two E-cadherin-catenin conventional complexes derived from two opposing cells and arranged in an antiparallel fashion. Formation of the antiparallel but not lateral complex strictly depends on extracellular calcium and E-cadherin binding to catenins. Double amino acid substitution Trp156Ala/Val157Gly within the extracellular NH2-terminal E-cadherin domain completely abolished both lateral and antiparallel inter-E-cadherin association. These data support an idea that the antiparallel complex has the adhesion function. Furthermore, they allow us to suggest that antiparallel complexes derive from lateral dimers and this complex process requires catenins and calcium ions. PMID:9700170

Chitaev, N A; Troyanovsky, S M

1998-08-10

276

Formation of MgF3?-dependent complexes between an AAA+ ATPase and ?54  

PubMed Central

The widely distributed bacterial ?54-dependent transcription regulates pathogenicity and numerous adaptive responses in diverse bacteria. Formation of the ?54-dependent open promoter complex is a multi-step process driven by AAA+ ATPases. Non-hydrolysable nucleotide analogues are particularly suitable for studying such complexity by capturing various intermediate states along the energy coupling pathway. Here we report a novel ATP analogue, ADP–MgF3?, which traps an AAA+ ATPase with its target ?54. The MgF3?-dependent complex is highly homogeneous and functional assays suggest it may represent an early transcription intermediate state valuable for structural studies.

Zhang, Nan; Buck, Martin

2012-01-01

277

Ionophore A23187: the effect of H+ concentration on complex formation with divalent and monovalent cations and the demonstration of K+ transport in mitochondria mediated by A23187.  

PubMed

The two-phase extraction technique has been used to study the equilibrium between A23187, metal cations, and H+. Under these conditions the ionophore forms charge neutral isostoichiometric complexes with divalent cations in which both carboxylate groups of the 2:1 A23187:M2+ complexes are deprotonated. In ethanol, however, the methyl ester of A23187 also binds divalent cations indicating that protonated complexes between A23187 and cations should also exist. With monovalent cations, A23187 forms two charge-neutral complexes of stoichiometries and relative stabilities: A2HM greater than AM. Examination of energy utilization K+ and H+ movements, and light scattering capacity of mitochondria in the presence of divalent cation chelators, A23187, and valinomycin demonstrates that A23187 can act as a nigericin type K+ ionophore under appropriate conditions. Formation constants for the A2HM complexes with monovalent cations indicate that with appropriate conditions transport of Li+ and Na+ mediated by A23187 would also be expected. The binding constant data and associated free energies of complex formation are compared as a function of ionic radius and of cation charge. The data indicate that lack of conformational mobility in A23187 is responsible for the high cation size selectivity of this compound. To explain the transport selectivity of A23187 for divalent cations, it is proposed that this ionophore forms a family of five complexes, isostoichiometric between cations of different valence but of which only charge-neutral species are permeant to membranes. The charge of a given complex is in turn determined by that of the cation. The concept is consistent with the divalent cation transport specificity of A23187, explains the observed monovalent cation transport, and is useful in rationalizing the differences in charge selectivity between A23187 and X-537A. PMID:3212

Pfeiffer, D R; Lardy, H A

1976-03-01

278

Motion Constants  

Microsoft Academic Search

A Bose condensate of electrons may exist in nickel hydrogen and palladium hydrogen systems. The motion constants associated with the gravitational and nuclear forces motion tend toward the electromagnetic in these systems. The change in the motion constants produces unexpected gravitomagnetic and nuclear affects.

Frank Znidarsic

2000-01-01

279

Factors determining the formation of complexes between alpha-cyclodextrin and alkylated substances in aqueous solutions: a calorimetric study at 25 degrees C.  

PubMed

The formation of complexes of alpha-cyclodextrin with cycloalkanediols, monoalkylamines and 1-alkanols has been studied calorimetrically at 25 degrees C in water, in phosphoric acid, pH 1.3, and in phosphate buffer, pH 5.5, respectively. When a complex is formed, calorimetry enables the calculation of both the enthalpy and the association constant, from which the free energy and the entropy of the process can be obtained. A model is proposed to explain the unusual trend of the association parameters for substances having alkyl chains longer than six-seven carbon atoms. The main role played by the different functional groups, and the forces involved in the association process, are discussed in the light of the signs and values of the thermodynamic parameters obtained. The effect of the variation of the aqueous medium on the hydration of the interacting substances and the consequent changes in the association parameters have been investigated. To this end, the thermodynamic parameters for the formation of the complexes between the cyclodextrin and 1-pentanol were determined at increasing concentrations of phosphate buffer. There is an increase in the association constant due to a positive entropy contribution originating from the relaxation of water molecules from the hydrophobic hydration cosphere of the alkanol to an increasingly disordered bulk. Deaquation of the interacting substances is the main factor determining the stability of the inclusion complex. PMID:10839121

Castronuovo, G; Elia, V; Iannone, A; Niccoli, M; Velleca, F

2000-05-01

280

Tying synaptonemal complex initiation to the formation and programmed repair of DNA double-strand breaks  

Microsoft Academic Search

During meiosis, homologous chromosomes recombine and become closely apposed along their lengths within the synaptonemal complex (SC). In part because Spo11 is required both to make the double-strand breaks (DSBs) that initiate recombination and to promote normal SC formation in many organisms, it is clear that these two processes are intimately coupled. The molecular nature of this linkage is not

Kiersten A. Henderson; Scott Keeney

2004-01-01

281

The simultaneous multiple constraints of the IMF and SFR history in star formation complexes  

Microsoft Academic Search

The multiple constraints method of the IMF and SFR history in star formation complexes (SFCs) attempts to match simultaneously the observed UBVR colours, Lyman continuum fluxes and chemical abundances by finding a best set of the IMF parameters (alpha, M_max), age t and SFR history. The method of using simultaneous multiple constraints of the IMF and SFR history in SFCs

F. H. Sakhibov; M. A. Smirnov

2001-01-01

282

Formation of unusual ruthenium(III) carbonyl complex through ONS tricoordination of salicylaldehyde- N-phenylthiosemicarbazone  

Microsoft Academic Search

An unusual coordination mode of salicylaldehyde-N-phenylthiosemicarbazone (H2-Sal-Ptsc) ligand was observed in unusual ruthenium(III) carbonyl complex for the first time when it was reacted with [RuHCl(CO)(PPh3)3]. The EPR and electrochemical analysis conformed the formation of Ru(III) species.

Rathinasabapathi Prabhakaran; Rui Huang; Ramasamy Karvembu; Chinnasamy Jayabalakrishnan; Karuppannan Natarajan

2007-01-01

283

The Integral Membrane Nucleoporin pom121 Functionally Links Nuclear Pore Complex Assembly and Nuclear Envelope Formation  

Microsoft Academic Search

The metazoan nuclear envelope (NE) breaks down and reforms at each mitosis. Nuclear pore complexes (NPCs), which allow nucleocytoplasmic transport during interphase, assemble into the reforming NE at the end of mitosis. Using in vitro NE assembly assays, we show that one of the two transmembrane nucleoporins, pom121, is essential for NE formation, whereas the second, gp210, is dispensable. Depletion

Wolfram Antonin; Cerstin Franz; Uta Haselmann; Claude Antony; Iain W. Mattaj

2005-01-01

284

Method of fracturing a subterranean formation using delayed crosslinker compositions containing organic titanium complexes  

Microsoft Academic Search

A method is described of fracturing a subterranean formation penetrated by a well, comprising: (a) producing a gel solution by adding to an aqueous solution of an organic crosslinkable polymer; (i) a sufficient amount of a crosslinker composition to result in delayed crosslinking of the polymer. The crosslinker composition has an organic titanium complex to crosslink the polymer, an organic

1987-01-01

285

Method of fracturing a subterranean formation using delayed crosslinker compositions containing organic titanium complexes  

Microsoft Academic Search

A method of fracturing a subterranean formation penetrated by a well is described comprising: (a) producing a gel solution by adding to an aqueous solution of an organic crosslinkable polymer: (i) a sufficient amount of a crosslinker composition to result in delayed crosslinking of the polymer, the crosslinker composition having an organic titanium complex to crosslink the polymer, an organic

1988-01-01

286

Interaction of cationized antigen with rat glomerular basement membrane: In situ immune complex formation  

Microsoft Academic Search

Interaction of cationized antigen with rat glomerular basement membrane: In situ immune complex formation. The influence of charge and size on antigen binding to the rat glomerular basement membrane (GBM) was investigated. Chemically cationized ovalbumin, human serum albumin (HSA), human immunoglobulin G (Hu IgG), horse spleen ferritin and human immunoglobulin M (Hu IgM) were injected into rats intravenously. By immunofluorescence

Arnold Vogt; Rolf Rohrbach; Fujio Shimizu; Haruo Takamiya; Stephen Batsford

1982-01-01

287

Reduction of persimmon astringency by complex formation between pectin and tannins  

Microsoft Academic Search

The effects of interactions between soluble pectin and soluble tannins on the astringency of persimmon fruit were studied. The astringency of both fresh juice and a solution of tannins purified from persimmon fruit was significantly reduced by the addition of soluble pectin. The change was probably due to complex formation between the pectin and soluble tannins. In intact fruit, a

Satoshi Taira; Miki Ono; Naoko Matsumoto

1997-01-01

288

Nuclear pore complex assembly studied with a biochemical assay for annulate lamellae formation  

Microsoft Academic Search

Formation of the nuclear pore is an intricate process involving membrane fusion and the ordered as- sembly of up to 1,000 pore proteins. As such, the study of pore assembly is not a simple one. Interestingly, an- nulate lamellae, a cytoplasmic organelle consisting of stacks of flattened membrane cisternae perforated by numerous pore complexes, have been found to form spontaneously

Eva Meier; Brian R. Miller; Douglass J. Forbes

1995-01-01

289

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

290

Polyanion-polycation complex formation as a function of the position of the functional groups  

Microsoft Academic Search

A method consisting of the combination of turbidimetry and conductometry was investigated to detect polyanion-polycation complex formation. We used ‘strong acid’ polyelectrolytes varying in charge density and ‘strong basic’ polyelectrolytes varying in the length of the spacer groups and in the accessibility of the quaternary ammonium function. Our systematic investigations have shown a predominantly 1:1 stoichiometry at the turbidimetric as

Peter Zarras; Otto Vogl

1996-01-01

291

Spectroscopic and conductometric studies of molecular complex formation between 2,4,6-trinitrophenol and diaza-18-crown-6, tetraaza-14-crown-4 and cryptand C222 in 1,2-dichloroethane solution  

NASA Astrophysics Data System (ADS)

The formation of molecular complexes between 2,4,6-trinitrophenol (TNP) and aza-substituted macrocycles diaza-18-crown-6 (DA18C6), tetraaza-14-crown-4 (TA14C4) and cryptand C222 in 1,2-dichloroethane solution was investigated spectrophotometrically and conductometrically. The mole ratio and continuous variations studies based on both physicochemical techniques employed clearly revealed the formation of both 1:1 and 2:1 (TNP:macrocycle) adducts in solution. Formation of the resulting complexes was also confirmed by 1H NMR and IR spectroscopic studies. Formation constants of the resulting complexes were evaluated from computer fitting of the corresponding mole ratio data. Stability of the resulting complexes was found to vary in the order C222 ? TA14C4 > DA18C6.

Hasani, Masoumeh; Irandoust, Mohsen; Shamsipur, Mojtaba

2006-02-01

292

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

293

Simulation of the effects of complex- formation equilibria in electrophoresis: II. experimental verification.  

PubMed

The complete mathematical model of electromigration in systems with complexation agents introduced in the Part I of this article (V. Hruška et al., Eletrophoresis, 2012, 33, this issue), which was implemented into our simulation program Simul 5, was verified experimentally. Three different chiral selector (CS) systems differing in the type of the CS, the magnitude of the complexation constants as well as in the experimental conditions were selected for verification. The experiments and simulations were performed at various concentrations of the CSs in order to discuss the influence of the concentration of the CS on the separation. The simulated and experimental electropherograms show very good agreement in the position, shape and amplitude of the analyte peaks. The new Simul 5 Complex offers a deep insight into electrophoretical separations that take place in systems containing complexing agents, for example into enantiomer separations. Using Simul 5 Complex we were able to predict and explain the significant electromigration dispersion of analyte peaks. It was clarified that the electromigration dispersion in these systems results directly from complexation. The new Simul 5 Complex was also shown to be a useful and powerful tool for the prediction of the results of enantioseparations. PMID:22528415

Svobodová, Jana; Beneš, Martin; Hruška, Vlastimil; Ušelová, Kate?ina; Gaš, Bohuslav

2012-03-01

294

Mechanism of Acyl-Enzyme Complex Formation from the Henry-Michaelis Complex of Class C ?-Lactamases with ?-Lactam Antibiotics.  

PubMed

Bacteria that cause most of the hospital-acquired infections make use of class C ?-lactamase (CBL) among other enzymes to resist a wide spectrum of modern antibiotics and pose a major public health concern. Other than the general features, details of the defensive mechanism by CBL, leading to the hydrolysis of drug molecules, remain a matter of debate, in particular the identification of the general base and role of the active site residues and substrate. In an attempt to unravel the detailed molecular mechanism, we carried out extensive hybrid quantum mechanical/molecular mechanical Car-Parrinello molecular dynamics simulation of the reaction with the aid of the metadynamics technique. On this basis, we report here the mechanism of the formation of the acyl-enzyme complex from the Henry-Michaelis complex formed by ?-lactam antibiotics and CBL. We considered two ?-lactam antibiotics, namely, cephalothin and aztreonam, belonging to two different subfamilies. A general mechanism for the formation of a ?-lactam antibiotic-CBL acyl-enzyme complex is elicited, and the individual roles of the active site residues and substrate are probed. The general base in the acylation step has been identified as Lys67, while Tyr150 aids the protonation of the ?-lactam nitrogen through either the substrate carboxylate group or a water molecule. PMID:24010547

Tripathi, Ravi; Nair, Nisanth N

2013-09-23

295

Recrystallized impact glasses of the Onaping Formation and the Sudbury Igneous Complex, Sudbury Structure, Ontario, Canada  

NASA Astrophysics Data System (ADS)

The origin of the Sudbury Structure and of the associated heterolithic breccias of the Onaping Formation and the Sudbury Igneous Complex have been controversial. While an impact origin of the structure has gained wide acceptance over the last 15 years, the origin of the recrystallized Onaping Formation glasses and of the igneous complex is still being debated. Recently the interpretation of the breccias of the Onaping Formation as suevitic fall-back impact breccias has been challenged. The igneous complex is interpreted either as a differentiated impact melt sheet or as a combination of an upper impact melt represented by the granophyre, and a lower, impact-triggered magmatic body consisting of the norite-sublayer formations. The Onaping Formation contains glasses as fluidal and nonfluidal fragments of various shapes and sizes. They are recrystallized, and our research indicates that they are petrographically heterogeneous and span a wide range of chemical compositions. These characteristics are not known from glasses of volcanic deposits. This suggests an origin by shock vitrification, an interpretation consistent with their association with numerous and varied country rock clasts that exhibit microscopic shock metamorphic features. The recrystallized glass fragments represent individual solid-state and liquid-state vitrified rocks or relatively small melt pods. The basal member lies beneath the Gray and Black members of the Onaping Formation and, where not metamorphic, has an igneous matrix. Igneous-textured melt bodies occur in the upper two members and above the Basal Member. A comparison of the chemical compositions of recrystallized glasses and of the matrices of the Basal Member and the melt bodies with the components and the bulk composition of the igneous complex is inconclusive as to the origin of the igneous complex. Basal Member matrix and Melt Bodies, on average, are chemically similar to the granophyre of the Sudbury Igneous Complex, suggesting that they are genetically related. Our chemical results allow interpretation of the entire igneous complex as a differentiated impact melt. However, they are also consistent with the granophyre alone being the impact melt and the norite and quartz gabbro beneath it representing an impact-triggered magmatic body. This interpretation is preferred, as it is consistent with a number of field observations. A re-evaluation and extension of structural field studies and of geochemical data, as well as a systematic study of the contact relationships of the various igneous phases of the igneous complex, are needed to establish a Sudbury impact model consistent with all data and observations.

Dressler, B. O.; Weiser, T.; Brockmeyer, P.

1996-06-01

296

Crucial role of lysosomal iron in the formation of dinitrosyl iron complexes in vivo.  

PubMed

Dinitrosyl non-heme-iron complexes (DNIC) are found in many nitric oxide producing tissues. A prerequisite of DNIC formation is the presence of nitric oxide, iron and thiol/imidazole groups. The aim of this study was to investigate the role of the cellular labile iron pool in the formation of DNIC in erythroid K562 cells. The cells were treated with a nitric oxide donor in the presence of a permeable (salicylaldehyde isonicotinoyl hydrazone) or a nonpermeable (desferrioxamine mesylate) iron chelator and DNIC formation was recorded using electron paramagnetic resonance. Both chelators inhibited DNIC formation up to 50% after 6 h of treatment. To further investigate the role of lysosomal iron in DNIC formation, we prevented lysosomal proteolysis by pretreatment of whole cells with NH4Cl. Pretreatment with NH4Cl inhibited the formation of DNIC in a time-dependent manner that points to the importance of the degradation of iron metalloproteins in DNIC formation in vivo. Fractionation of the cell content after treatment with the nitric oxide donor revealed that DNIC is formed predominantly in the endosomal/lysosomal fraction. Taken together, these data indicate that lysosomal iron plays a crucial role in DNIC formation in vivo. Degradation of iron-containing metalloproteins seems to be important for this process. PMID:17136409

Lewandowska, Hanna; Meczy?ska, Sylwia; Sochanowicz, Barbara; Sad?o, Jaros?aw; Kruszewski, Marcin

2006-11-29

297

Formation and study of single metal ion-phospholipid complexes in biphasic electrospray ionization mass spectrometry.  

PubMed

Single metal ion-phospholipid complexes are observed in biphasic electrospray ionization mass spectrometry (BESI-MS) using a dual-channel microsprayer. Such a microsprayer makes it possible to put into contact two immiscible liquids within the Taylor cone. Thus, L-?-dipalmitoyl phosphatidylcholine (DPPC) dissolved in 1,2-dichloroethane (DCE) reacts with aqueous metal cations (M = Na(+), K(+), Ca(2+), Cu(2+), La(3+)) yielding the formation of [M-DPPC(n)](z+) complexes. The number of phospholipid molecules ranges from 1 to 4 for monovalent ions, to 8 for divalent and to more than 10 for trivalent ions respectively. The large number of ligands observed involves the formation of solvent free single ion-phospholipid complexes. PMID:21072386

Prudent, Michel; Méndez, Manuel A; Jana, Daniel F; Corminboeuf, Clémence; Girault, Hubert H

2010-05-20

298

HCF-1 self-association via an interdigitated Fn3 structure facilitates transcriptional regulatory complex formation  

PubMed Central

Host-cell factor 1 (HCF-1) is an unusual transcriptional regulator that undergoes a process of proteolytic maturation to generate N- (HCF-1N) and C- (HCF-1C) terminal subunits noncovalently associated via self-association sequence elements. Here, we present the crystal structure of the self-association sequence 1 (SAS1) including the adjacent C-terminal HCF-1 nuclear localization signal (NLS). SAS1 elements from each of the HCF-1N and HCF-1C subunits form an interdigitated fibronectin type 3 (Fn3) tandem repeat structure. We show that the C-terminal NLS recruited by the interdigitated SAS1 structure is required for effective formation of a transcriptional regulatory complex: the herpes simplex virus VP16-induced complex. Thus, HCF-1N–HCF-1C association via an integrated Fn3 structure permits an NLS to facilitate formation of a transcriptional regulatory complex.

Park, Jihye; Lammers, Fabienne; Herr, Winship; Song, Ji-Joon

2012-01-01

299

Effect of citrate on the local Fe coordination in ferrihydrite, arsenate binding, and ternary arsenate complex formation  

NASA Astrophysics Data System (ADS)

In oxic environments contaminated with arsenate (As(V)), small polyhydroxycarboxylates such as citrate may impact the structure of precipitating ferrihydrite (Fh) and thus the surface speciation of As(V). In this study, '2-line' Fh was precipitated from ferric nitrate solutions that were neutralized to pH 6.5 in the presence of increasing citrate concentrations and in the absence or presence of As(V). The initial citrate/Fe and As/Fe ratios were 0-50 mol% and 5 mol%, respectively. The reaction products, enriched with up to 0.32 mol citrate per mole Fe, were characterized by X-ray diffraction, transmission electron microscopy, and Fe and As K-edge X-ray absorption spectroscopy. Citrate decreased the particle size of Fh by impairing the polymerization of Fe(O,OH) 6 octahedra via edge and corner linkages. In the presence of citrate and As(V), coordination numbers of Fe decreased by up to 28% relative to pure Fh. Citrate significantly reduced the static disorder of Fe-O bonds, implying a decreased octahedral distortion in Fh. Mean bond distances in Fh were not affected by citrate and remained constant within error at 1.98 Å for Fe-O, 3.03 Å for Fe-Fe1, and 3.45 Å for Fe-Fe2. Likewise, citrate had no effect on the As-Fe (3.31 Å) bond distance in As(V) coprecipitated with Fh. The As K-edge EXAFS data comply with the formation of (i) only monodentate binuclear ( 2C) As(V) surface complexes and (ii) combinations of 2C, monodentate mononuclear ( 1V), and outersphere As(V) surface complexes. Our results suggest that increasing citrate concentrations led to a decreasing 1V/ 2C ratio and/or that citrate increasingly impaired the formation of outersphere As(V) complexes. Moreover, citrate stabilized colloidal suspensions of Fh (pH 4.3-6.6, I ˜0.45 M) and reduced Fh formation at the expense of soluble Fe(III)-citrate complexes. At initial citrate/Fe ratios ?25 mol%, between 8% and 41% of total Fe was bound in Fe(III)-citrate complexes after Fh formation. Polynuclear Fe(III)-citrate species were found to bind As(V) via surface complexes indistinguishable by EXAFS from those of As(V) adsorbed to or coprecipitated with Fh. Our study implies that low molecular weight polyhydroxycarboxylates may enhance the mobility of As(V) in aqueous systems of high ionic strength (e.g., neutralizing acid mine drainage) by colloidal stabilization of suspended Fh particles and the formation of ternary As(V) complexes.

Mikutta, Christian; Frommer, Jakob; Voegelin, Andreas; Kaegi, Ralf; Kretzschmar, Ruben

2010-10-01

300

The mechanism of complex formation between Fli-1 and SRF transcription factors  

PubMed Central

The mechanisms of multicomponent transcription factor complex assembly are currently poorly defined. A paradigm for this type of complex is the ETS-domain transcription factor Elk-1 and the MADS-box transcription factor SRF which form a ternary complex with the c-fos serum response element (SRE). In this study we have analysed how a different ETS-domain transcription factor Fli-1 interacts with SRF to form ternary complexes with this element. Two regions of Fli-1 that are required for ternary complex formation have been identified. These SRF binding motifs are located on either side of the ETS DNA-binding domain. Hydrophobic amino acids within these motifs have been identified that play important roles in binding to SRF and ternary complex formation. By using Fli-1 derivatives with mutations in the N-terminal SRF binding motif, the significance of Fli-1–SRF interactions in recruitment of Fli-1 to the c-fos SRE in vivo has been demonstrated. Collectively our data provide a model of how Fli-1 interacts with SRF that differs significantly from the mechanism used by a different ETS-domain protein, Elk-1.

Dalgleish, Pamela; Sharrocks, Andrew D.

2000-01-01

301

Functional cooperation between FACT and MCM is coordinated with cell cycle and differential complex formation  

PubMed Central

Background Functional cooperation between FACT and the MCM helicase complex constitutes an integral step during DNA replication initiation. However, mode of regulation that underlies the proper functional interaction of FACT and MCM is poorly understood. Methods & Results Here we present evidence indicating that such interaction is coordinated with cell cycle progression and differential complex formation. We first demonstrate the existence of two distinct FACT-MCM subassemblies, FACT-MCM2/4/6/7 and FACT-MCM2/3/4/5. Both complexes possess DNA unwinding activity and are subject to cell cycle-dependent enzymatic regulation. Interestingly, analysis of functional attributes further suggests that they act at distinct, and possibly sequential, steps during origin establishment and replication initiation. Moreover, we show that the phosphorylation profile of the FACT-associated MCM4 undergoes a cell cycle-dependent change, which is directly correlated with the catalytic activity of the FACT-MCM helicase complexes. Finally, at the quaternary structure level, physical interaction between FACT and MCM complexes is generally dependent on persistent cell cycle and further stabilized upon S phase entry. Cessation of mitotic cycle destabilizes the complex formation and likely leads to compromised coordination and activities. Conclusions Together, our results correlate FACT-MCM functionally and temporally with S phase and DNA replication. They further demonstrate that enzymatic activities intrinsically important for DNA replication are tightly controlled at various levels, thereby ensuring proper progression of, as well as exit from, the cell cycle and ultimately euploid gene balance.

2010-01-01

302

Assembly of the Light-Harvesting Complexes (LHCs) of Photosystem II (Monomeric LHC IIb Complexes Are Intermediates in the Formation of Oligomeric LHC IIb Complexes).  

PubMed Central

The light-induced assembly of light-harvesting complex (LHC) II has been followed during the biogenesis of the plastid. Seedlings grown in intermittent light (IML) accumulate only small amounts of chlorophyll b. The minor LHC II apoproteins are present; however, the apoprotein levels of the major LHC II complex, LHC IIb, are severely depressed after exposure to IML. The levels of all LHC II apoproteins increase rapidly upon exposure to continuous illumination. The 25-kD, type 3 LHC IIb subunit appears to be more abundant during the early hours of greening in relation to its level in mature thylakoids. The LHC IIb apoproteins are initially associated with pigments to form monomeric pigment-protein complexes. The abundance of monomeric LHC IIb complexes gradually decreases during exposure to continuous light and a concomitant increase occurs in the amount of the trimeric and higher-order oligomeric forms. Pulse-chase experiments verify that labeled LHC IIb monomeric complexes are intermediates in the formation of trimeric and higher-order oligomeric LHC IIb-pigmented complexes. Therefore, the assembly of LHC II occurs via the initial pigmentation of the apoproteins to form monomeric complexes and proceeds in a sequential manner.

Dreyfuss, B. W.; Thornber, J. P.

1994-01-01

303

Base-sequence dependence of noncovalent complex formation and reactivity of benzo(a)pyrene diol epoxide with polynucleotides  

SciTech Connect

The base-sequence selectivity of the noncovalent binding of (/plus minus/)-trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BPDE) to a series of synthetic polynucleotides in aqueous solutions (5 mM sodium cacodylate buffer, 20 mM NaCl, pH 7.0, 22/degrees/C) was investigated. The magnitude of a red-shifted absorbance at 353 nm, attributed to intercalative complex formation, was utilized to determine values of the association constant K/sub ic/. Intercalation in the alternating pyridine-purine polymers poly(dA-dT)/times/(dA-dT), poly(dG-dC)/times/(dG-dC), and poly(dA-dC)/times/(dG-dT) is distinctly favored over intercalation in their nonalternating counterparts poly(dA)/times/(dT), poly(dG)/times/(dC), and poly(dA-dG)/times/(dT-dC). Methylation at the 5-position of cytosine gives rise to a significant enhancement of intercalative binding, and K/sub ic/is 22,000 M/sup -1/ in poly(dG-m/sup 5/dG)/times/(dG-m/sup 5/dC). In a number of these polynucleotides, values of K/sub ic/ for pyrene qualitatively follow those exhibited by BPDE, suggesting that the pyrenyl residue in BPDE is a primary factor in determining the extent of intercalation. A model in which catalysis is mediated by physical complex formation accounts well for the experimentally observed enhancement in reaction rates of BPDE in the alternating polynucleotides; however, in the nonalternating polymers a different or more complex catalysis mechanism may be operative. Finally, complex formation and catalysis at different binding sites are related to the level of covalent binding, one of the critical factors in the expression of the mutagenic and tumorigenic potentials of BPDE and related compounds in cells.

Geacintov, N.E.; Shahbaz, M.; Ibanez, V.; Moussaoui, K.; Harvey, R.G.

1988-11-01

304

Tectonic evolution of the Priest River complex, northern Idaho and Washington: A reappraisal of the Newport fault with new insights on metamorphic core complex formation  

Microsoft Academic Search

New geologic mapping, 40Ar\\/39Ar thermochronometry, and geobarometry in the Middle Eocene Priest River metamorphic core complex provide the basis for unraveling the role of en echelon fault systems in core complex formation and for determining the scale of crustal fragments that form during continental extension. Four faults occur in the Priest River complex. The east verging Purcell Trench fault zone

P. Ted Doughty; Raymond A. Price

1999-01-01

305

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

PubMed

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

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

2013-01-01

306

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

307

Regulated Clearance of Histone Deacetylase 3 Protects Independent Formation of Nuclear Receptor Corepressor Complexes*  

PubMed Central

An important step in transcriptional regulation by corepressors N-CoR and SMRT is the formation of a stable and active histone deacetylase 3 (HDAC3)-containing complex. Although N-CoR and SMRT are thought to bind HDAC3 competitively, multiple studies have shown that they do not interfere with the function of each other. How this functional independence is sustained under the competitive interaction is unclear. Here, we show that the coupling of corepressor expression with HDAC3 degradation allows cells to maintain a stable level of uncomplexed HDAC3, thereby preventing mutual interference in the assembly of N-CoR and SMRT complexes. The free uncomplexed HDAC3 is highly unstable. Unexpectedly, the rate of HDAC3 degradation is inversely correlated with the expression level of corepressors. Our results indicate that reducing one corepressor accelerates HDAC3 clearance, thus preventing an increase in complex formation between HDAC3 and the other corepressor. In addition, this study also indicates that the formation of a stable and active HDAC3-corepressor complex is a stepwise process in which the C terminus of HDAC3 plays a critical role at late steps of the assembly process.

Guo, Chun; Gow, Chien-Hung; Li, Yali; Gardner, Amanda; Khan, Sohaib; Zhang, Jinsong

2012-01-01

308

Inclusion complex formation of sanguinarine alkaloid with cucurbit[7]uril: inhibition of nucleophilic attack and photooxidation.  

PubMed

The inclusion of sanguinarine, a biologically active natural benzophenanthridine alkaloid, in cucurbit[7]uril (CB7) was studied by NMR and ground-state absorption spectroscopy, as well as steady-state and time-resolved fluorescence measurements in aqueous solution. The iminium form of sanguinarine (SA(+)) produces very stable 1 : 1 inclusion complex with CB7 (K = 1.0 × 10(6) M(-1)), whereas the equilibrium constant for the binding of the second CB7 is about 3 orders of magnitude smaller. Marked fluorescence quantum yield and fluorescence lifetime enhancements are found upon encapsulation of SA(+) due to the deceleration of the radiationless deactivation from the single-excited state, but the fluorescent properties of 1 : 1 and 1 : 2 complexes barely differ. The equilibrium between the iminium and alkanolamine forms is shifted 3.69 pK unit upon addition of CB7 as a consequence of the preferential encapsulation of the iminium form and the protection of the 6 position of sanguinarine against the nucleophilic attack by hydroxide anion. On the basis of thermodynamic cycle, about 225 M(-1) is estimated for the equilibrium constant of the complexation between the alkanolamine form of sanguinarine (SAOH) and CB7. The confinement in the CB7 macrocycle can be used to impede the nucleophilic addition of OH(-) to SA(+) and to hinder the photooxidation of SAOH. PMID:21152661

Miskolczy, Zsombor; Megyesi, Mónika; Tárkányi, Gábor; Mizsei, Réka; Biczók, László

2010-12-14

309

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

2013-01-31

310

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

NASA Astrophysics Data System (ADS)

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

Schijf, J.; Byrne, R. H.

2001-04-01

311

Complex formation in the systems uranium halide--alkali metal halide. Enthalpy of formation of RbâUBrâ and CsâUBrâ  

Microsoft Academic Search

Standard enthalpies of formation of RbâUBrâ and CsâUBr\\/; sub 6\\/ at 25 deg C were determined. The determination was made by measuring the ; enthalpy of solution of the compounds studied in 0.5% FeClâ solution in 2% ; HCl. The enthalpy of formation of the hexabromouranate (IV) ion and the energy ; of the U-Br bond remain constant with a

V. M. Vdovenko; I. G. Suglobova; D. E. Chirkst

1973-01-01

312

Formation of the complex oxide NaNdTiO 4  

Microsoft Academic Search

The processes of phase formation in the Na2CO3-TiO2 and Na2CO3-TiO2-Nd2O3 systems are investigated in the temperature range 600–900°C. The high-temperature solid-phase reactions underlying the process\\u000a of formation of complex oxide NaNdTiO4 are studied. It is established that the synthesis of the NaNdTiO4 compound occurs through the reaction of the intermediate product Na8Ti5O14 with neodymium oxide in the temperature range 720–780°C.

I. A. Zvereva; O. I. Silyukov; A. V. Markelov; A. B. Missyul’; M. V. Chislov; I. A. Rodionov; D.-Sh. Li

2008-01-01

313

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

PubMed Central

Tumor necrosis factor ? (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; Xiang, Wenpei; Wang, Yinna; Zhang, Xiaoying; Billiar, Timothy R.

2013-01-01

314

Effect of ligand basicity on the formation and dissociation equilibria and kinetics of Gd{sup 3+} complexes of macrocyclic polyamino carboxylates  

SciTech Connect

Formation and dissociation equilibria and reaction kinetics for Gd(III) complexes of GdL(L is HE-DO3A = 10-(2-hydroxyethyl)-1,4,7,10-tetraazacyclodecance-1,4,7-triacetic acid, HP-DO3A = 10-(2-hydroxyisopropyl)1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, AND HIP-DO3A = 10-(2-hydroxyisopropyl)-1,4,7,10-tetraazacyclododecnae-1,4,7-triacetic acid). Stability constants were measured and reaction kinetics were studied. Relationships of ligand basicity to reaction rate and stability was discussed.

Kumar, K.; Tweedle, M.F. [Bristol-Myers Squibb Pharmaceutical Research Inst., Princeton, NJ (United States); Tianzhu Jin; Xiangym Wang; Desreux, J.F. [Univ. of Liege (Belgium)

1994-08-17

315

Numerical Modeling of Hydraulic Fractures Interaction in Complex Naturally Fractured Formations  

NASA Astrophysics Data System (ADS)

A recently developed unconventional fracture model (UFM) is able to simulate complex fracture network propagation in a formation with pre-existing natural fractures. A method for computing the stress shadow from fracture branches in a complex hydraulic fracture network (HFN) based on an enhanced 2D displacement discontinuity method with correction for finite fracture height is implemented in UFM and is presented in detail including approach validation and examples. The influence of stress shadow effect from the HFN generated at previous treatment stage on the HFN propagation and shape at new stage is also discussed.

Kresse, Olga; Weng, Xiaowei; Gu, Hongren; Wu, Ruiting

2013-05-01

316

Threshold formation of an intermolecular charge transfer complex of a semiconducting polymer  

NASA Astrophysics Data System (ADS)

It has been found that the formation of an intermolecular charge transfer complex in the ground electronic state between the model conjugated polymer (poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and the low-molecular-weight organic acceptor (2,4,7-trinitrofluorenone, TNF) occurs stepwise with an increase in the acceptor concentration in the blend as is observed in the optical absorption spectra of solutions. The threshold dependence of the absorption of the charge transfer complex is attributed to the stepwise change in the concentration of the charge transfer complexes, which is not explained by the standard model describing the optical characteristics of intermolecular charge transfer complexes. A kinematic model has been proposed to explain the threshold increase in the concentration of charge transfer complexes: at low acceptor concentrations, the charge transfer complex is formed primarily on the surface of a polymer coil, whereas as the acceptor fraction in the solution increases, TNF molecules penetrate inside the polymer coils, forming the charge transfer complex with the units of the polymer inside the coil.

Parashchuk, O. D.; Sosorev, A. Yu.; Bruevich, V. V.; Paraschuk, D. Yu.

2010-04-01

317

Cell growth control by stable Rbg2/Gir2 complex formation under amino acid starvation.  

PubMed

The molecular fine-tuning mechanisms underlying adaptive responses to environmental stresses in eukaryotes remain largely unknown. Here, we report on a novel stress-induced cell growth control mechanism involving a highly conserved complex containing Rbg2 and Gir2 subunits, which are the budding yeast orthologs of human Drg2 and Dfrp2, respectively. We found that the complex is responsible for efficient cell growth under amino acid starvation. Using native PAGE analyses, we observed that, individually, Rbg2 and Gir2 were labile proteins. However, they formed a complex that stabilized each other, and this stability became significantly enhanced after amino acid starvation. We observed that the stabilization of the complex was strictly dependent on GDP or GTP binding to Rbg2. A point mutation (S77N) that inactivated nucleotide binding impaired formation of the complex and disrupted the stress-induced cell growth. Interestingly, the complex bound the translational activator Gcn1 in a dose-dependent manner according to the stress level, suggesting a dynamic association with the cellular translational machinery. We propose that the Rbg2/Gir2 complex is a modulator that maintains cellular homoeostasis, thus promoting the survival of eukaryotic organisms in stressful environments. PMID:23899355

Ishikawa, Kosuke; Ito, Koichi; Inoue, Jun-Ichiro; Semba, Kentaro

2013-07-31

318

Effects of Electric Double Layer and Space Charge Polarization by Plural Kinds of Ions on Complex Dielectric Constant of Liquid Crystal Materials  

NASA Astrophysics Data System (ADS)

The complex dielectric constant of a liquid crystal material, 4-cyano-4?-alkyl-biphenyl (5CB), was measured in low-frequency regions below 1000 Hz. The anomalous increasing behavior was analyzed using an equivalent circuit which takes two kinds of contributions into account: one is from the electric double layer and the other is from the space charge polarization. It was found by numerical calculations that these two effects exhibit different dependences of dielectric dispersion on the thickness of a specimen, and both effects were successfully distinguished in the experimental results. In the analysis of the space charge polarization, the experimental results were best fitted by the calculated results with five kinds of ions in terms of the diffusion coefficient. These measurements can be applied to a precise determination of the attributes of plural kinds of ions, such as the diffusion coefficient and the number density.

Sawada, Atsushi; Tarumi, Kazuaki; Naemura, Shohei

1999-03-01

319

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

320

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

PubMed

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. PMID:22711701

Llano, Elena; Herrán, Yurema; García-Tuñón, Ignacio; Gutiérrez-Caballero, Cristina; de Álava, Enrique; Barbero, José Luis; Schimenti, John; de Rooij, Dirk G; Sánchez-Martín, Manuel; Pendás, Alberto M

2012-06-18

321

Spectrofluorimetric estimation of salbutamol sulphate in different dosage forms by formation of inclusion complex with ?-cyclodextrin  

PubMed Central

A simple, precise, reproducible and accurate spectrofluorimetric method for estimation of Salbutamol sulphate (SAL) in bulk drug and various dosage forms has been developed. This method is based on formation of inclusion complex of SAL in ?-cyclodextrin (BCD) which gives fluorescence at excitation wavelength of 279.6 nm and emission wavelength of 609.8 nm in water. Formation of inclusion complex of drug with BCD enhances fluorescence intensity of drug leads to increased sensitivity. The developed method was validated according to ICH guidelines with respect to accuracy, precision, linearity, limit of detection, limit of quantification. Linearity was observed in the range of 4-20 ?g/ml with correlation coefficient of 0.9982. The simplicity of the method permitted rapid analysis suitable for routine control. The developed method was successfully applied for the estimation of SAL in different marketed dosage forms like tablets, syrup and aerosol.

Pandya, Harshit Narmadashankar; Berawala, Hiren Harshadlal; Khatri, Deepak Mohanlal; Mehta, Priti Jignesh

2010-01-01

322

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

Microsoft Academic Search

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

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

2002-01-01

323

Anionization of an antigen promotes glomerular binding and immune complex formation  

Microsoft Academic Search

Anionization of an antigen promotes glomerular binding and immune complex formation. Bovine serum albumin (BSA, pI 4.9) was maleylated to yield highly anionic MBSA (pI 3.0). Maleylation of BSA lead to an expansion of molecular size of native BSA from an effective molecular radius (EMR) of 37 Å to 57 Å for MBSA as assessed by gel filtration chromatography. MBSA,

Jeffrey L Barnes; Mary J Reznicek; Robert A Radnik; Manjeri A Venkatachalam

1988-01-01

324

Geometrical Changes and Their Energies in the Formation of Donor–Acceptor Complexes  

Microsoft Academic Search

We have mapped the energy demands of the geometrical changes in donor–acceptor complexes BH3·NH3 and AlCl3·NH3 and in the course of their formation from their monomers. We have varied the individual geometrical parameters systematically and performed ab initio quantum chemical calculations for these structures. We investigated the energy requirements to change bond lengths and bond angles in both the monomers

Viktória Horváth; István Hargittai

2004-01-01

325

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

Microsoft Academic Search

Multiple microbial components trigger the formation of an inflammasome complex that contains pathogen- specific nucleotide oligomerization and binding domain (NOD)-like receptors (NLRs), caspase-1, and in some cases the scaffolding protein ASC. The NLR protein Nalp1b has been linked to anthrax lethal toxin (LT)- mediated cytolysis of murine macrophages. Here we demonstrate that in unstimulated J774A.1 macrophages, caspase-1 and Nalp1b are

Adel M. Nour; Laura Santambrogio; Eric D. Boyden; E. Richard Stanley; Jurgen Brojatsch

2009-01-01

326

Cytochrome P-450 Complex Formation in Rat Liver by the Antibiotic Tiamulin  

Microsoft Academic Search

Tiamulin is a semisynthetic diterpene antibiotic frequently used in farm animals. The drug has been shown to produce clinically important—often lethal—interactions with other compounds. It has been suggested that this is caused by a selective inhibition of oxidative drug metabolism via the formation of a cytochrome P-450 metabolic intermediate complex. In the present study, rats were treated orally for 6

RENGER F. WITKAMP; SANDRA M. NIJMEIJER

327

Understanding Star Formation in the Rosette Molecular Complex: A Chandra View of the Embedded Young Clusters  

NASA Astrophysics Data System (ADS)

The Rosette Molecular Cloud (RMC) complex represents an ideal laboratory for understanding star formation processes, and we have carried out a Chandra imaging survey of the embedded clusters to characterize the young stellar populations. We present new X-ray results on the embedded young star cluster RMC PL6 and in particular the massive young stellar object AFGL 961, which is previously resolved in the near-infrared (the Rosette Eye, Li et al. 2008).

Wang, Junfeng

2012-05-01

328

A Function for the AP3 Coat Complex in Synaptic Vesicle Formation from Endosomes  

Microsoft Academic Search

Synaptic vesicles can be coated in vitro in a reaction that is ARF-, ATP-, and temperature-dependent and requires synaptic vesicle membrane proteins. The coat is largely made up of the heterotetrameric complex, adaptor protein 3, recently implicated in Golgi-to-vacuole traffic in yeast. Depletion of AP3 from brain cytosol inhibits small vesicle formation from PC12 endosomes in vitro. Budding from washed

Victor Faúndez; Jim-Tong Horng; Regis B Kelly

1998-01-01

329

Energetics of complex formation of the dna hairpin structure d(GCGAAGC) with aromatic ligands  

Microsoft Academic Search

The energy contributions of various physical interactions to the total Gibbs energy of complex formation of the biologically\\u000a important DNA hairpin d(GCGAAGC) with aromatic antitumor antibiotics daunomycin and novantrone and mutagens ethidium bromide\\u000a and proflavin have been calculated. It has been shown that the relatively small value of the total energy of binding of the\\u000a ligands to the hairpin is

V. V. Kostyukov

2011-01-01

330

CT complexes in radiation polymerisation processes including grafting, curing and hydrogel formation  

NASA Astrophysics Data System (ADS)

Parameters influencing the grafting of a typical charge transfer (CT) complex, maleic anhydride /triethylene glycol divinyl ether, to representative substrates, cellulose and polypropylene, initiated by UV and ionising radiation have been investigated. The variables studied include effect of solvent, role of donor involving the type of ether and the nature of the acceptor including the use of common monomers like methyl methacrylate. A novel application of this CT grafting work is reported involving hydrogel formation with subsequent controlled release of incorporated reagent.

Garnett, John L.; Ng, Loo-Teck; Nguyen, Duc; Swami, Salesh; Zilic, Elvis F.

2002-03-01

331

Electron Bihole Complex Formation in Neutralization of Ne{sup +} on LiF(001)  

SciTech Connect

Neutralization of low keV Ne{sup +} ions at a LiF(001) surface is studied in a grazing incidence geometry. The combination of energy loss and electron spectroscopy in coincidence reveals two neutralization channels of comparable importance. Besides the Auger process, the Ne{sup +} neutralization can proceed via peculiar target excitation, corresponding to the formation of an electron bihole complex termed trion.

Khemliche, H.; Villette, J.; Borisov, A. G.; Momeni, A.; Roncin, P.

2001-06-18

332

How important is polyelectrolyte complex formation in biomimetic mineralisation? Manipulation via alcohol addition.  

PubMed

Understanding the formation of biominerals like nacre can lead to the fabrication of more advanced biomimetic materials. Several factors are known to influence the final form of both native nacre and biomimetic synthetic variants. Two important components in calcium carbonate biominerals such as nacre are the organic scaffold and the acidic proteins. Interactions between these two components may also influence final composite characteristics. In this investigation chitosan hydrogels were prepared from acidic aqueous solution using four alcohols as cosolvents. The addition of alcohol enables direct modification of the network of the chitosan hydrogel (and thereby the nanometre and micrometre length-scale structure of the hydrogel). Both alcohol-modified chitosan and subsequently reacetylated chitin scaffolds were then mineralised with a combined soaking mineralisation method in the presence of poly(acrylic acid), the latter of which mimics the role of the acidic proteins in the native system. The effects of these structural variations of the hydrogel, induced by the presence of alcohol during fabrication, on (1) the formation of a polyelectrolyte complex between the chitosan or chitin and the poly(acrylic acid) and (2) the subsequent polymorph and morphology of calcium carbonate crystals mineralised within the hydrogel scaffold were investigated. Increasing the amount of the alcohols 1,2-propanediol or 1,3-propanediol led to increased disruption of the hydrogen bonding of the hydrogel scaffold and significant changes to, or reduced formation of, the polyelectrolyte complex formed between the scaffold carbohydrate and the poly(acrylic acid). The disruption of the polyelectrolyte complex in turn led to a loss of control over which polymorph of calcium carbonate is nucleated. These results show that the physical form of the polymer scaffold in these organic/inorganic composites, and the formation of the polyelectrolyte complex play a crucial role in determining the final composite structure and the calcium carbonate polymorphs and morphologies. PMID:23595573

Munro, Natasha H; McGrath, Kathryn M

2013-04-17

333

Role of precipitating and nonprecipitating antibodies in glomerular immune complex formation  

Microsoft Academic Search

Role of precipitating and nonprecipitating antibodies in glomerular immune complex formation. The present study compared directly the ability of precipitating and nonprecipitating antibodies to form and sustain glomerular immune deposits. The antigen phenylated gelatin (DNP-GL) was injected i.v. into rats. DNP-GL is cleared from the circulation rapidly and becomes localized in glomeruli. Two hours later, rats received either precipitating or

Fernando G Cosio; Alan P Bakaletz; John D Mahan

1990-01-01

334

Formation of BaSO4 Fibres with Morphological Complexity in Aqueous Polymer Solutions  

Microsoft Academic Search

BaSO4 fibres with morpho- logical complexity were formed in aque- ous solution with polyacrylate and par- tially monophosphonated poly(ethyle- neoxide)-block-poly(methacrylic acid) additives by a simple precipitation reac- tion. For polyacrylate, formation of the fibrous deposits was strongly dependent on the level of supersaturation (S) and Ba2á:polymer molar ratio (R). At Sà 60 to 80, and Rà 3 to 14, highly

Limin Qi; Helmut Clfen; Markus Antonietti; Mei Li; Jeremy D. Hopwood; Alexandra J. Ashley; Stephen Mann

2001-01-01

335

A density functional study on the formation of charge transfer complexes between alkaloids and iodine monochloride  

Microsoft Academic Search

The formation of charge-transfer (CT) complexes between N-methyl-6,7-methylenedioxy-tetrahydro-4-isoquinolone (MMDTIQ, the model molecule of alkaloids) and iodine monochloride has been studied with the density functional B3LYP method. The competition for ICl between n-donor(s) and ?-donor in the same molecule has been compared for the first time. The results indicate that the electron-donating ability of various donor sites decreases in the following

Ling-Tian Tang; Yu Wei; Yi Wang; Shao-Wen Hu; Xin-Qi Liu; Tai-Wei Chu; Xiang-Yun Wang

2004-01-01

336

Recombination-enhanced formation of the metastable boron-oxygen complex in crystalline silicon  

NASA Astrophysics Data System (ADS)

The formation process of the boron- and oxygen-related defect complex in crystalline silicon, responsible for the performance degradation of solar cells made on boron-doped Czochralski silicon (Cz-Si), is investigated on Cz-Si solar cells as a function of the applied voltage in the dark at temperatures ranging from 298 to 373 K. We show that the defect formation is not only a consequence of illumination or the application of a forward bias voltage but also occurs under equilibrium conditions at elevated temperatures in the dark. It can be partly suppressed by applying a reverse voltage. Our findings provide clear experimental evidence that a recombination-enhanced mechanism correlated with the total recombination rate is the driving force of the formation of the metastable defect.

Bothe, Karsten; Hezel, Rudolf; Schmidt, Jan

2003-08-01

337

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

338

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

SciTech Connect

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

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

2008-10-02

339

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

340

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

341

Structure formation in metal complex/polymer hybrid nanomaterials prepared by miniemulsion.  

PubMed

Polymer/complex hybrid nanostructures were prepared using a variety of hydrophobic metal ?-diketonato complexes. The mechanism of structure formation was investigated by electron paramagnetic resonance (EPR) spectroscopy and small-angle X-ray scattering (SAXS) in the liquid phase. Structure formation is attributed to an interaction between free coordination sites of metal ?-diketonato complexes and coordinating anionic surfactants. Lamellar structures are already present in the miniemulsion. By subsequent polymerization the lamellae can be embedded in a great variety of different polymeric matrices. The morphology of the lamellar structures, as elucidated by transmission electron microscopy (TEM), can be controlled by the choice of anionic surfactant. Using sodium alkylsulfates and sodium dodecylphosphate, "nano-onions" are formed, while sodium carboxylates lead to "kebab-like" structures. The composition of the hybrid nanostructures can be described as bilayer lamellae, embedded in a polymeric matrix. The metal complexes are separated by surfactant molecules which are arranged tail-to-tail; by increasing the carbon chain length of the surfactant the layer distance of the structured nanomaterial can be adjusted between 2 and 5 nm. PMID:21977909

Hauser, Christoph P; Jagielski, Nicole; Heller, Jeannine; Hinderberger, Dariush; Spiess, Hans W; Lieberwirth, Ingo; Weiss, Clemens K; Landfester, Katharina

2011-10-06

342

Lowstand transgressive upper Cretaceous (Coniacian) gravelly deltaic complexes of the Cardium formation, West Central Alberta, Canada  

SciTech Connect

A detailed facies and sequence stratigraphic analysis is used to demonstrate the reservoir compartmentalization of gravelly deltaic complexes deposited on a ramp margin in the Western Canadian Sedimentary Basin. Gravelly deltas of the Carrot Creek Member of the Cardium Formation in the Cyn Pem Field area of West Central Alberta occur along well defined backslapping shoreline trends that represent high frequency lowstand to transgressive systems tracts that followed the second order sea level fall ([approximately]90 Ma) of the Turonian. The Cyn Pem Cardium D pool is used to illustrate the detailed sedimentologly and stratigraphy of a gravelly deltaic complex. The pool consists of two distinct coarse-grained delta lobes oriented along a northwest-trending shoreline. Up to 21 meters of gravelly stream mouth bar and distributary channel facles were deposited unconformably on distal marine highstand deposits of the Raven River Member (Turonian) of the Cardium Formation. Production data and facies analysis indicates excellent communication along high permeability (>l Darcy) Gilbert-type deltaic foresets oriented parallel to strike and moderate to poor communication in a depositional dip direction. Poorly sorted gravelly distributary channels dissect the deltaic ioresets. A complex history of high frequency lowstand and transgressive erosion resulted in substantial paleotopographic relief that both bounds and compartmentalizes these gravelly deltaic complexes.

Thomas, D.V. (Imperial Oil Resources Limited., Calgary, Alberta (Canada))

1996-01-01

343

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

344

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

345

Germ cell differentiation and synaptonemal complex formation are disrupted in CPEB knockout mice.  

PubMed

CPEB is a sequence-specific RNA binding protein that regulates translation during vertebrate oocyte maturation. Adult female CPEB knockout mice contained vestigial ovaries that were devoid of oocytes; ovaries from mid-gestation embryos contained oocytes that were arrested at the pachytene stage. Male CPEB null mice also contained germ cells arrested at pachytene. The germ cells from the knockout mice harbored fragmented chromatin, suggesting a possible defect in homologous chromosome adhesion or synapsis. Two CPE-containing synaptonemal complex protein mRNAs, which interact with CPEB in vitro and in vivo, contained shortened poly(A) tails and mostly failed to sediment with polysomes in the null mice. Synaptonemal complexes were not detected in these animals. CPEB therefore controls germ cell differentiation by regulating the formation of the synaptonemal complex. PMID:11702780

Tay, J; Richter, J D

2001-08-01

346

Mechanistic studies on the formation and reactivity of dioxygen adducts of diiron complexes supported by sterically hindered carboxylates.  

PubMed

Dioxygen activation by enzymes such as methane monooxygenase, ribonucleotide reductase, and fatty acid desaturases occurs at a nonheme diiron active site supported by two histidines and four carboxylates, typically involving a (peroxo)diiron(III,III) intermediate in an early step of the catalytic cycle. Biomimetic tetracarboxylatodiiron(II,II) complexes with the familiar "paddlewheel" topology comprising sterically bulky o-dixylylbenzoate ligands with pyridine, 1-methylimidazole, or THF at apical sites readily react with O(2) to afford thermally labile peroxo intermediates that can be trapped and characterized spectroscopically at low temperatures (193 K). Cryogenic stopped-flow kinetic analysis of O(2) adduct formation carried out for the three complexes reveals that dioxygen binds to the diiron(II,II) center with concentration dependences and activation parameters indicative of a direct associative pathway. The pyridine and 1-methylimidazole intermediates decay by self-decomposition. However, the THF intermediate decays much faster by oxygen transfer to added PPh(3), the kinetics of which has been studied with double mixing experiments in a cryogenic stopped-flow apparatus. The results show that the decay of the THF intermediate is kinetically controlled by the dissociation of a THF ligand, a conclusion supported by the observation of saturation kinetic behavior with respect to PPh(3), inhibition by added THF, and invariant saturation rate constants for the oxidation of various phosphines. It is proposed that the proximity of the reducing substrate to the peroxide ligand on the diiron coordination sphere facilitates the oxygen-atom transfer. This unique investigation of the reaction of an O(2) adduct of a biomimetic tetracarboxylatodiiron(II,II) complex provides a synthetic precedent for understanding the electrophilic reactivity of like adducts in the active sties of nonheme diiron enzymes. PMID:15018538

Kryatov, Sergey V; Chavez, Ferman A; Reynolds, Anne M; Rybak-Akimova, Elena V; Que, Lawrence; Tolman, William B

2004-03-22

347

Effects of formate binding on the quinone-iron electron acceptor complex of photosystem II.  

PubMed

EPR was used to study the influence of formate on the electron acceptor side of photosystem II (PSII) from Thermosynechococcus elongatus. Two new EPR signals were found and characterized. The first is assigned to the semiquinone form of Q(B) interacting magnetically with a high spin, non-heme-iron (Fe²(+), S=2) when the native bicarbonate/carbonate ligand is replaced by formate. This assignment is based on several experimental observations, the most important of which were: (i) its presence in the dark in a significant fraction of centers, and (ii) the period-of-two variations in the concentration expected for Q(B)(•-) when PSII underwent a series of single-electron turnovers. This signal is similar but not identical to the well-know formate-modified EPR signal observed for the Q(A)(•-)Fe²(+) complex (W.F.J. Vermaas and A.W. Rutherford, FEBS Lett. 175 (1984) 243-248). The formate-modified signals from Q(A)(•-)Fe²(+) and Q(B)(•-)Fe²(+) are also similar to native semiquinone-iron signals (Q(A)(•-)Fe²(+)/Q(B)(•-)Fe²(+)) seen in purple bacterial reaction centers where a glutamate provides the carboxylate ligand to the iron. The second new signal was formed when Q(A)(•-) was generated in formate-inhibited PSII when the secondary acceptor was reduced by two electrons. While the signal is reminiscent of the formate-modified semiquinone-iron signals, it is broader and its main turning point has a major sub-peak at higher field. This new signal is attributed to the Q(A)(•-)Fe²(+) with formate bound but which is perturbed when Q(B) is fully reduced, most likely as Q(B)H? (or possibly Q(B)H(•-) or Q(B)(²•-)). Flash experiments on formate-inhibited PSII monitoring these new EPR signals indicate that the outcome of charge separation on the first two flashes is not greatly modified by formate. However on the third flash and subsequent flashes, the modified Q(A)(•-)Fe²(+)Q(B)H? signal is trapped in the EPR experiment and there is a marked decrease in the quantum yield of formation of stable charge pairs. The main effect of formate then appears to be on Q(B)H? exchange and this agrees with earlier studies using different methods. PMID:21036139

Sedoud, Arezki; Kastner, Lisa; Cox, Nicholas; El-Alaoui, Sabah; Kirilovsky, Diana; Rutherford, A William

2010-10-29

348

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

349

Biofilm Formation and Acyl Homoserine Lactone Production in the Burkholderia cepacia Complex  

PubMed Central

Acyl homoserine lactone (acyl-HSL)-mediated gene regulation has been shown to influence biofilm formation in one Burkholderia cepacia cystic fibrosis isolate, but it is not known whether this relationship is a consistent feature of the several genomic species that make up the B. cepacia complex (BCC). We screened strains belonging to genomovars I to V of the BCC for biofilm formation on an abiotic surface and for acyl-HSL synthesis. We determined that organisms from each of these genomovars were capable of biofilm formation. Similarly, acyl-HSL was synthesized by organisms from each of genomovars I to V, with most isolates producing octanoyl-HSL in greatest abundance. When biofilms were grown in Luria broth, acyl-HSL synthesis and biofilm formation appeared to be associated, but these phenotypes were independent when the biofilms were grown in basal salts containing citrate. Genomovar V strains synthesized the greatest quantities of acyl-HSL, and genomovar II and III-A strains elaborated the most abundant biofilms. Quorum sensing may play a role in BCC pathogenesis, but it may not regulate biofilm formation under all growth conditions.

Conway, Barbara-Ann D.; Venu, Vicnays; Speert, David P.

2002-01-01

350

Toward a Reduced Complexity Channel Resolving Model for Sedimentary Delta Formation  

NASA Astrophysics Data System (ADS)

Predicting styles of delta growth in restoration areas is a challenge as we try to restore impacted coastlines. Cellular and rule-based reduced complexity models offer a worthwhile means of uncovering key dynamics in delta morphodynamics without the need to fully solve the governing transport equations. In terms of modeling sedimentary delta building processes a critical ingredients is accounting for the formation and bifurcation of channels; phenomena that can be related to the formation of levees and mouth-bars. To that end, we have developed a reduced complexity model that uses a simplified shallow-water solver to study channel formation, mouth bar deposition, and delta development under different forcings. Under the assumption that the flow has a very low Froude Number (Fr2<<1), the inertia term is dropped out and only the gravitational term and friction term remain in the momentum equation. The coupled mass conservation equation becomes a non-linear diffusive equation, which is linearized by a Kirchhoff transformation. Directional diffusivity is added to this system to compensate the loss of inertia and promote spreading of the turbulent jet. We test the reduced model against flow over Gaussian-shaped bumps of various heights. Comparison of results from this model with results from a full scale commercial code (Delft3D) show a satisfactory agreement on the critical mouth bar height needed to divert flow around the bar. Based on the same diffusive equation, we develop a low-Froude water-routing method for reduced complexity morphodynamics models. The preliminary results show that the method is capable of producing reasonable channel forms and mouth bar formation, and provides a good starting point for development of a channel resolving delta building model.

Liang, M.; Voller, V. R.; Edmonds, D. A.; Paola, C.

2010-12-01

351

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

2012-12-03

352

Regulation of synaptic vesicle recycling by complex formation between intersectin 1 and the clathrin adaptor complex AP2  

PubMed Central

Clathrin-mediated synaptic vesicle (SV) recycling involves the spatiotemporally controlled assembly of clathrin coat components at phosphatidylinositiol (4, 5)-bisphosphate [PI(4,5)P2]-enriched membrane sites within the periactive zone. Such spatiotemporal control is needed to coordinate SV cargo sorting with clathrin/AP2 recruitment and to restrain membrane fission and synaptojanin-mediated uncoating until membrane deformation and clathrin coat assembly are completed. The molecular events underlying these control mechanisms are unknown. Here we show that the endocytic SH3 domain-containing accessory protein intersectin 1 scaffolds the endocytic process by directly associating with the clathrin adaptor AP2. Acute perturbation of the intersectin 1-AP2 interaction in lamprey synapses in situ inhibits the onset of SV recycling. Structurally, complex formation can be attributed to the direct association of hydrophobic peptides within the intersectin 1 SH3A-B linker region with the “side sites” of the AP2 ?- and ?-appendage domains. AP2 appendage association of the SH3A-B linker region inhibits binding of the inositol phosphatase synaptojanin 1 to intersectin 1. These data identify the intersectin-AP2 complex as an important regulator of clathrin-mediated SV recycling in synapses.

Pechstein, Arndt; Bacetic, Jelena; Vahedi-Faridi, Ardeschir; Gromova, Kira; Sundborger, Anna; Tomlin, Nikolay; Krainer, Georg; Vorontsova, Olga; Schafer, Johannes G.; Owe, Simen G.; Cousin, Michael A.; Saenger, Wolfram; Shupliakov, Oleg; Haucke, Volker

2010-01-01

353

Regulation of synaptic vesicle recycling by complex formation between intersectin 1 and the clathrin adaptor complex AP2.  

PubMed

Clathrin-mediated synaptic vesicle (SV) recycling involves the spatiotemporally controlled assembly of clathrin coat components at phosphatidylinositiol (4, 5)-bisphosphate [PI(4,5)P(2)]-enriched membrane sites within the periactive zone. Such spatiotemporal control is needed to coordinate SV cargo sorting with clathrin/AP2 recruitment and to restrain membrane fission and synaptojanin-mediated uncoating until membrane deformation and clathrin coat assembly are completed. The molecular events underlying these control mechanisms are unknown. Here we show that the endocytic SH3 domain-containing accessory protein intersectin 1 scaffolds the endocytic process by directly associating with the clathrin adaptor AP2. Acute perturbation of the intersectin 1-AP2 interaction in lamprey synapses in situ inhibits the onset of SV recycling. Structurally, complex formation can be attributed to the direct association of hydrophobic peptides within the intersectin 1 SH3A-B linker region with the "side sites" of the AP2 alpha- and beta-appendage domains. AP2 appendage association of the SH3A-B linker region inhibits binding of the inositol phosphatase synaptojanin 1 to intersectin 1. These data identify the intersectin-AP2 complex as an important regulator of clathrin-mediated SV recycling in synapses. PMID:20160082

Pechstein, Arndt; Bacetic, Jelena; Vahedi-Faridi, Ardeschir; Gromova, Kira; Sundborger, Anna; Tomlin, Nikolay; Krainer, Georg; Vorontsova, Olga; Schäfer, Johannes G; Owe, Simen G; Cousin, Michael A; Saenger, Wolfram; Shupliakov, Oleg; Haucke, Volker

2010-02-16

354

Structure and magnetic properties of an unprecedented syn-anti ?-nitrito-1?O:2?O' bridged Mn(III)-salen complex and its isoelectronic and isostructural formate analogue.  

PubMed

The preparation, crystal structures and magnetic properties of two new isoelectronic and isomorphous formate- and nitrite-bridged 1D chains of Mn(III)-salen complexes, [Mn(salen)(HCOO)](n) (1) and [Mn(salen)(NO(2))](n) (2), where salen is the dianion of N,N'-bis(salicylidene)-1,2-diaminoethane, are presented. The structures show that the salen ligand coordinates to the four equatorial sites of the metal ion and the formate or nitrite ions coordinate to the axial positions to bridge the Mn(III)-salen units through a syn-anti?-1?O:2?O' coordination mode. Such a bridging mode is unprecedented in Mn(III) for formate and in any transition metal ion for nitrite. Variable-temperature magnetic susceptibility measurements of complexes 1 and 2 indicate the presence of ferromagnetic exchange interactions with J values of 0.0607 cm(-1) (for 1) and 0.0883 cm(-1) (for 2). The ac measurements indicate negligible frequency dependence for 1 whereas compound 2 exhibits a decrease of ?(ac)' and a concomitant increase of ?(ac)'' on elevating frequency around 2 K. This finding is an indication of slow magnetization reversal characteristic of single-chain magnets or spin-glasses. The ?-nitrito-1?O:2?O' bridge seems to be a potentially superior magnetic coupler to the formate bridge for the construction of single-molecule/-chain magnets as its coupling constant is greater and the ?(ac)' and ?(ac)'' show frequency dependence. PMID:21344112

Kar, Paramita; Biswas, Rituparna; Drew, Michael G B; Ida, Yumi; Ishida, Takayuki; Ghosh, Ashutosh

2011-02-23

355

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

356

Experimental studies of complex crater formation under cluster implantation of solids  

NASA Astrophysics Data System (ADS)

The results of a systematic study of surface defect formation after energetic Arn+ (n = 12, 22, 32, 54) and Xen+ (n = 4, 16) cluster ion implantation into silicon and sapphire are presented. Implantation energies vary from 3 to 18 keV/ion. Two cases of comparative studies are carried out: the same cluster species are implanted into two different substrates, i.e. Arn+ cluster ions into silicon and sapphire and two different cluster species Arn+ and Xen+ are implanted into the same kind of substrate (silicon). Atomic force, scanning electron and transmission electron microscopies (AFM, SEM and TEM) are used to study the implanted samples. The analysis reveals the formation of two types of surface erosion defects: simple and complex (with centrally positioned hillock) craters. It is found that the ratio of simple to complex crater formation as well as the hillock dimensions depend strongly on the cluster species, size and impact energy as well as on the type of substrate material. Qualitative models describing the two comparative cases of cluster implantation, the case of different cluster species and the case of different substrate materials, are proposed.

Prasalovich, S.; Popok, V.; Persson, P.; Campbell, E. E. B.

2005-10-01

357

Complex Formation and Interactions between Transcription Factors Essential for Human Prolactin Receptor Gene Transcription ?  

PubMed Central

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.

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

2011-01-01

358

Sarcomere Formation Occurs by the Assembly of Multiple Latent Protein Complexes  

PubMed Central

The stereotyped striation of myofibrils is a conserved feature of muscle organization that is critical to its function. Although most components that constitute the basic myofibrils are well-characterized biochemically and are conserved across the animal kingdom, the mechanisms leading to the precise assembly of sarcomeres, the basic units of myofibrils, are poorly understood. To gain insights into this process, we investigated the functional relationships of sarcomeric protein complexes. Specifically, we systematically analyzed, using either RNAi in primary muscle cells or available genetic mutations, the organization of myofibrils in Drosophila muscles that lack one or more sarcomeric proteins. Our study reveals that the thin and thick filaments are mutually dependent on each other for striation. Further, the tension sensor complex comprised of zipper/Zasp/?-actinin is involved in stabilizing the sarcomere but not in its initial formation. Finally, integrins appear essential for the interdigitation of thin and thick filaments that occurs prior to striation. Thus, sarcomere formation occurs by the coordinated assembly of multiple latent protein complexes, as opposed to sequential assembly.

Perrimon, Norbert

2010-01-01

359

Vps45p stabilizes the syntaxin homologue Tlg2p and positively regulates SNARE complex formation  

PubMed Central

Sec1p-like/Munc-18 (SM) proteins bind to t-SNAREs and inhibit ternary complex formation. Paradoxically, the absence of SM proteins does not result in constitutive membrane fusion. Here, we show that in yeast cells lacking the SM protein Vps45p, the t-SNARE Tlg2p is down-regulated, to undetectable levels, by rapid proteasomal degradation. In the absence of Vps45p, Tlg2p can be stabilized through abolition of proteasome activity. Surprisingly, the stabilized Tlg2p was targeted to the correct intracellular location. However, the stabilized Tlg2p is non-functional and unable to bind its cognate SNARE binding partners, Tlg1p and Vti1p, in the absence of Vps45p. A truncation mutant lacking the first 230 residues of Tlg2p no longer bound Vps45p but was able to form complexes with Tlg1p and Vti1p in the absence of the SM protein. These data provide us with two valuable insights into the function of SM proteins. First, SM proteins act as chaperone-like molecules for their cognate t-SNAREs. Secondly, SM proteins play an essential role in the activation process allowing their cognate t-SNARE to participate in ternary complex formation.

Bryant, Nia J.; James, David E.

2001-01-01

360

A new model of grain-boundary segregation with the formation of atomic complexes in a grain boundary  

NASA Astrophysics Data System (ADS)

The process of grain-boundary segregation (GBS) has been considered under an assumption that the formation of associates (atomic complexes with a composition that corresponds to the nearest chemical composition in the phase diagram) is possible in a grain boundary (GB). The grain boundary is considered as a two-component mixture of A and B atoms, which can exist both in free and bound states (bound in a complex). The formation of complexes with an arbitrary composition and complexes of an AB type have been considered. It has been shown that, even in the absence of segregation ( b = 1), the interactions of atoms in a GB that induce the formation of complexes leads to an enrichment of GBs in impurity atoms. It has been demonstrated that under certain conditions, a GBS isotherm can exhibit saturation corresponding to the chemical composition of the complex.

Bokshtein, B. S.; Esin, V. A.; Rodin, A. O.

2010-04-01

361

Complex formation reactions of uranyl(VI) with neutral N-donors in dimethyl sulfoxide. Influence of small amounts of water  

SciTech Connect

Quantitative information about the existence and thermodynamic stability of uranyl(VI) ion complexes based solely upon nitrogen coordination has been obtained in the solvent dimethyl sulfoxide. Calorimetric, potentiometric, and FT-IR investigations, under controlled anhydrous conditions, show that the uranyl(VI) ion can form both mono and bis chelates with the ethylenediamine ligand and only a mono chelate of rather low stability with propylenediamine. With the monodentate ligand n-butylamine only a very weak metal-ligand interaction has been detected. The stability constants and the enthalpy and entropy changes have been calculated for the identified coordinated species. All data refer to 25.0{degree}C and a tetraethylammonium perchlorate medium of ionic strength 0.1 M. All the complexes are enthalpy stabilized whereas the entropy contributions oppose the complex formation. Calorimetric and FT-IR measurements carried out to investigate the effects of small amounts of water present show that a very low water concentration, comparable to that of the coordinating metal ion, can give rise to hydrolysis reactions that may compete with complex formation. This is due to the combined action of different factors that are discussed. 39 refs., 6 figs., 1 tab.

Cassol, A.; Di Bernardo, P.; Zanonato, P. (Universita di Padova (Italy)); Portanova, R.; Tolazzi, M. (Universita di Udine (Italy) CNR, Padova (Italy))

1990-03-07

362

X-ray diffraction study of concentrated chromium (III) chloride solutions. I. Complex formation analysis in equilibrium conditions  

NASA Astrophysics Data System (ADS)

Concentrated chromium (III) chloride solutions, both acidic and neutral, have been examined by x-ray diffraction in equilibrium conditions; i.e., a long period of time after their preparation. Complex formation between Cr3+ and Cl- ions have been quantitatively analyzed through direct comparison of experimental and calculated structure functions. The average number of chloride ions bonded to chromium in each solution has been determined. The values obtained are consistent with the indications given by the distribution curves and in good agreement with those expected on the grounds of equilibrium constants. The average aggregation numbers were determined by assuming the presence, in neutral solutions, of the charged species Cr(H2O)3+6, Cr(H2O)5Cl2+, and Cr(H2O)4Cl+2. In addition experimental evidence of the neutral species Cr(H2O)3Cl3 in the acidic solution has been obtained. Octahedral water coordination for chloride ions has been confirmed. Well defined second coordination shell around Cr3+ ions is strongly supported by the structural parameters obtained for water molecules belonging to two subsequent hydration shells of the cations.

Magini, Mauro

1980-09-01

363

Hyperfine Coupling Constants on Inner-Sphere Water Molecules of a Triazacyclononane-based Mn(II) Complex and Related Systems Relevant as MRI Contrast Agents.  

PubMed

We report the synthesis of the ligand H2MeNO2A (1,4-bis(carboxymethyl)-7-methyl-1,4,7-triazacyclononane) and a detailed experimental and computational study of the hyperfine coupling constants (HFCCs) on the inner-sphere water molecules of [Mn(MeNO2A)] and related Mn(2+) complexes relevant as potential contrast agents in magnetic resonance imaging (MRI). Nuclear magnetic relaxation dispersion (NMRD) profiles, (17)O NMR chemical shifts, and transverse relaxation rates of aqueous solutions of [Mn(MeNO2A)] were recorded to determine the parameters governing the relaxivity in this complex and the (17)O and (1)H HFCCs. DFT calculations (TPSSh model) performed in aqueous solution (PCM model) on the [Mn(MeNO2A)(H2O)]·xH2O and [Mn(EDTA)(H2O)](2-)·xH2O (x = 0-4) systems were used to determine theoretically the (17)O and (1)H HFCCs responsible for the (17)O NMR chemical shifts and the scalar contributions to (17)O and (1)H NMR relaxation rates. The use of a mixed cluster/continuum approach with the explicit inclusion of a few second-sphere water molecules is critical for an accurate calculation of HFCCs of coordinated water molecules. The impact of complex dynamics on the calculated HFCCs was evaluated with the use of molecular dynamics simulations within the atom-centered density matrix propagation (ADMP) approach. The (17)O and (1)H HFCCs calculated for these complexes and related systems show an excellent agreement with the experimental data. Both the (1)H and (17)O HFCCs (Aiso values) are dominated by the spin delocalization mechanism. The Aiso values are significantly affected by the distance between the oxygen atom of the coordinated water molecule and the Mn(2+) ion, as well as by the orientation of the water molecule plane with respect to the Mn-O vector. PMID:24070368

Patinec, Véronique; Rolla, Gabriele A; Botta, Mauro; Tripier, Raphaël; Esteban-Gómez, David; Platas-Iglesias, Carlos

2013-09-26

364

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

365

Two quorum sensing systems control biofilm formation and virulence in members of the Burkholderia cepacia complex.  

PubMed

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. PMID:23799665

Suppiger, Angela; Schmid, Nadine; Aguilar, Claudio; Pessi, Gabriella; Eberl, Leo

2013-07-01

366

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

367

Galvanic Cells and the Determination of Equilibrium Constants  

ERIC Educational Resources Information Center

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

Brosmer, Jonathan L.; Peters, Dennis G.

2012-01-01

368

Pancreatic beta-cell granule peptides form heteromolecular complexes which inhibit islet amyloid polypeptide fibril formation.  

PubMed Central

Islet amyloid polypeptide (IAPP), or 'amylin', is co-stored with insulin in secretory granules of pancreatic islet beta-cells. In Type 2 diabetes, IAPP converts into a beta-sheet conformation and oligomerizes to form amyloid fibrils and islet deposits. Granule components, including insulin, inhibit spontaneous IAPP fibril formation in vitro. To determine the mechanism of this inhibition, molecular interactions of insulin with human IAPP (hIAPP), rat IAPP (rIAPP) and other peptides were examined using surface plasmon resonance (BIAcore), CD and transmission electron microscopy (EM). hIAPP and rIAPP complexed with insulin, and this reaction was concentration-dependent. rIAPP and insulin, but not pro-insulin, bound to hIAPP. Insulin with a truncated B-chain, to prevent dimerization, also bound hIAPP. In the presence of insulin, hIAPP did not spontaneously develop beta-sheet secondary structure or form fibrils. Insulin interacted with pre-formed IAPP fibrils in a regular repeating pattern, as demonstrated by immunoEM, suggesting that the binding sites for insulin remain exposed in hIAPP fibrils. Since rIAPP and hIAPP form complexes with insulin (and each other), this could explain the lack of amyloid fibrils in transgenic mice expressing hIAPP. It is likely that IAPP fibrillogenesis is inhibited in secretory granules (where the hIAPP concentration is in the millimolar range) by heteromolecular complex formation with insulin. Alterations in the proportions of insulin and IAPP in granules could disrupt the stability of the peptide. The increase in the proportion of unprocessed pro-insulin produced in Type 2 diabetes could be a major factor in destabilization of hIAPP and induction of fibril formation.

Jaikaran, Emma T A S; Nilsson, Melanie R; Clark, Anne

2004-01-01

369

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

370

Cosmological constants  

Microsoft Academic Search

Gathering the seminal papers of such greats as Einstein, Hubble, Sakharov, Weinberg, and Friedmann, this book is a unique and indispensable sourcebook. The articles describe the theoretical and observational foundations of the expanding universe, the discovery of cosmic background radiation, the formation of helium and deuterium during the first minutes of the universe, the observed asymmetry between matter and antimatter,

J. Bernstein; G. Feinberg

1986-01-01

371

[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

372

Formation and Tunable Disassembly of Polyelectrolyte-Cu(2+) 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

2013-10-09

373

A structural role for ATP in the formation and stability of the human origin recognition complex.  

PubMed

The locally restricted recruitment of the multisubunit origin recognition complex (ORC) to eukaryotic chromosomes defines the position of origins of DNA replication. In budding yeast and metazoans the DNA binding activity of ORC is stimulated by ATP and requires an AAA+-type nucleotide binding domain in the largest subunit. Little else is known about the mechanisms behind the ATP requirement for ORC in its initiator function and, specifically, the relevance of nucleotide binding domains present on other subunits. Here we show that ATP is required for specific subunit interactions in the human ORC, with the Orc4 subunit playing a critical role in this dynamic process. ATP is essential for the maintenance of ORC integrity and facilitates complex formation. Thus, besides its previously identified role in DNA binding, ATP serves also as a structural cofactor for human ORC. PMID:16549788

Ranjan, Anand; Gossen, Manfred

2006-03-20

374

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

375

Formation of iron(II)-nitrosoalkane complexes: a new activity of microperoxidase 8.  

PubMed

Microperoxidase 8 (MP8) is a heme octapeptide, obtained by enzymatic hydrolysis of heart cytochrome c, in which a histidine is axially coordinated to the heme iron, and acts as its fifth ligand. It exhibits two kinds of activities: a peroxidase-like activity and a cytochrome P450-like activity. We here show that MP8 is not only able to oxidize various aliphatic and aromatic hydroxylamines with the formation of MP8-Fe(II)-nitrosoalkane or -arene complexes absorbing around 414 nm, but also that these complexes can be obtained by reduction of nitroalkanes. This is the first example of fully characterized iron(II)-metabolite complexes of MP8. Such complexes constitute good models for those obtained upon oxidation of amphetamine or macrolids by cytochromes P450. In addition, this is a new catalytic activity of MP8, which validates the use of this mini-enzyme as a convenient model for hemoproteins of interest in toxicology and pharmacology such as cytochromes P450 and peroxidases. PMID:11071875

Ricoux, R; Boucher, J L; Mansuy, D; Mahy, J P

2000-11-11

376

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

377

The role of miRNAs in complex formation and control  

PubMed Central

Summary: microRibonucleic acid (miRNAs) are small regulatory molecules that act by mRNA degradation or via translational repression. Although many miRNAs are ubiquitously expressed, a small subset have differential expression patterns that may give rise to tissue-specific complexes. Motivation: This work studies gene targeting patterns amongst miRNAs with differential expression profiles, and links this to control and regulation of protein complexes. Results: We find that, when a pair of miRNAs are not expressed in the same tissues, there is a higher tendency for them to target the direct partners of the same hub proteins. At the same time, they also avoid targeting the same set of hub-spokes. Moreover, the complexes corresponding to these hub-spokes tend to be specific and nonoverlapping. This suggests that the effect of miRNAs on the formation of complexes is specific. Contact: wongls@comp.nus.edu.sg Supplementary information: Supplementary data are available at Bioinformatics online.

Goh, Wilson Wen Bin; Oikawa, Hirotaka; Sng, Judy Chia Ghee; Sergot, Marek; Wong, Limsoon

2012-01-01

378

Optical excitations and coupling constants in FeO42- and CrO44- complexes in oxides: Density functional study  

NASA Astrophysics Data System (ADS)

The experimental crystal field (CF) and charge transfer (CT) spectra due to Fe6+-doped K2XO4 (X=S, Se, Cr) and Cr4+ in oxides have been investigated by density functional (DF) calculations on FeO42- and CrO44- complexes at different values of the metal-ligand distance, R. To this aim the coupling constants, A? and A?, with the A1 and the Jahn-Teller E modes have also been calculated. The present results explain reasonably the transition energies and coupling constants observed for Fe6+ and Cr4+ in oxides and account for the following experimental features: (i) The different nature of the first CF and CT excitations observed on passing from Fe6+ to Cr4+ in oxides. (ii) Why for Fe6+ in oxides the dominant coupling is with the E mode for the CF states while with the A1 mode for CT states. (iii) Why on going from Cr4+ to Fe6+ in oxides the coupling constant A? of CT states decreases while the opposite is found for CF ones. The role played by the covalency on these questions is explained on simple grounds, stressing that it drastically decreases the A? value for CT states. This fact together with the value ??=820 cm-1 accounts for the low value of the Huang-Rhys factor S?=2.5 in the assigned 1t1?-->4t2? CT excitation of K2SeO4:Fe6+. As a salient feature the R dependence of 10Dq (which determines A? for the 3T2 CF state) is found to be greatly sensitive to the small admixture (~0.5%) of 2s(O) orbitals in the antibonding 2e level. The electronic relaxation decreases the energy of the first CT transition of FeO42- by 19 000 cm-1, the charge distribution being however the same as that of the ground state. The important role played by the trigonal distortion for reducing the Jahn-Teller effect in the first excited state of Cr4+ in oxides is analyzed through a phenomenological model. Though no further neighbors of the host lattice are included, the calculated equilibrium distances for FeO42- and CrO44- are only 3% and 8% higher than experimental values found for Cr4+ to Fe6+ in oxides. Moreover the calculated value of the ?? frequency at the right equilibrium distance essentially coincides with experimental findings indicating that force constants between oxygen and further neighbors likely play a minor role. In comparison with recent ab initio plus configuration interaction results on FeO42- the DF scheme offers a simpler description of ground and CT states.

Wissing, K.; Barriuso, M. T.; Aramburu, J. A.; Moreno, M.

1999-12-01

379

The thermodynamic characteristics of complex formation in the zinc(II) ion-threonine system in aqueous solution  

NASA Astrophysics Data System (ADS)

The heat effects of complex formation between D,L-threonine and zinc(II) ions at 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 were determined calorimetrically against the background of potassium nitrate. The thermochemical results were processed taking step equilibria into account. Along with complex formation, side protolytic processes were considered. The standard heat effects of complex formation in the system studied were determined by extrapolation to zero ionic strength with the use of an equation with one individual parameter. The heats of solution of D,L-threonine in water and aqueous alkali were used to calculate the standard enthalpies of formation of the complexes.

Kochergina, L. A.; Ratkova, E. L.; Gorboletova, G. G.

2007-04-01

380

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

381

The thermodynamic characteristics of complex formation between Cd2+ and ethylenediamine-N,N'-disuccinic acid in aqueous solution  

NASA Astrophysics Data System (ADS)

The enthalpies of complex formation between ethylenediamine-N,N'-disuccinic acid (H4A) and Cd2+ ions were determined calorimetrically at 298.15 K and ionic strengths of 0.5, 1.0, and 1.5 (KNO3). The thermodynamic characteristics of formation of the CdA2- and CdHA- complexes at fixed and zero ionic strengths were calculated. The values obtained were interpreted.

Lytkin, A. I.; Chernyavskaya, N. V.; Nikol'Skii, V. M.; Gridchin, S. N.; Litvinenko, V. E.

2009-06-01

382

Formation process of Cd and Zn chalcogenide-doped glasses via gels containing thiourea or selenourea complexes  

Microsoft Academic Search

The formation process of glasses doped with cadmium and zinc sulfide or selenide microcrystallites has been studied, along with the characterization of the glasses obtained. Sulfide microcrystallite-doped SiO2 glasses were prepared by the heat-treatment at around 400 degree(s)C of gels in which thiourea complexes were confined. The formation of thiourea complexes of Cd(NO3)2 and Zn(NO3)2 in the starting solutions to

Noboru Tohge; Tsutomu Minami

1992-01-01

383

The Oct-1 homoeodomain directs formation of a multiprotein-DNA complex with the HSV transactivator VP16  

Microsoft Academic Search

The herpes simplex virus transactivator VP16 par-ticipates in the formation of a multiprotein-DNA complex with the ubiquitous octamer-motif-binding factor Oct-1. Complex formation is dependent on specific amino acids in the Oct-1 homoeodomain which are in positions analogous to positive control mutations in helix 2 of the lambda phage repressor helix-turn-helix motif, indicating that this structure is an ancient target for

Seth Stern; Masafumi Tanaka; Winship Herr

1989-01-01

384

A POTENTIOMETRIC AND CALORIMETRIC STUDY OF THE THERMODYNAMICS OF FORMATION OF SOME OF THE COMPLEXES OF THE d METAL IONS SILVER(I), MERCURY(II), AND CADMIUM(II) WITH THIODIGLYCOL, THIOUREA, AND THE SULPHITE ION  

Microsoft Academic Search

The standard free energy, enthalpy, and entropy changes of complex formation of the d metal ions Ag(I), Hg(H), and Cd(II) with the S-donor-atom ligands thiodiglycol, thiourea, and sulphite were investigated at 298.15 ± 0.05 K. The free-energy changes ?Gi° were calculated from stability constants ?i, which were determined by silver- and mercury-electrode potentiometry, if suitable literature data were not available.

Fabrizio Marsicano; Robert D. Hancock

1976-01-01

385

The lambda spanin components Rz and Rz1 undergo tertiary and quaternary rearrangements upon complex formation  

PubMed Central

Phage holins and endolysins have long been known to play key roles in lysis of the host cell, disrupting the cytoplasmic membrane and peptidoglycan (PG) layer, respectively. For phages of Gram-negative hosts, a third class of proteins, the spanins, are involved in disrupting the outer membrane (OM). Rz and Rz1, the components of the lambda spanin, are, respectively, a class II inner membrane protein and an OM lipoprotein, are thought to span the entire periplasm by virtue of C-terminal interactions of their soluble domains. Here, the periplasmic domains of Rz and Rz1 have been purified and shown to form dimeric and monomeric species, respectively, in solution. Circular dichroism analysis indicates that Rz has significant alpha-helical character, but much less than predicted, whereas Rz1, which is 25% proline, is unstructured. Mixture of the two proteins leads to complex formation and an increase in secondary structure, especially alpha-helical content. Moreover, transmission electron-microscopy reveals that Rz–Rz1 complexes form large rod-shaped structures which, although heterogeneous, exhibit periodicities that may reflect coiled-coil bundling as well as a long dimension that matches the width of the periplasm. A model is proposed suggesting that the formation of such bundles depends on the removal of the PG and underlies the Rz–Rz1 dependent disruption of the OM.

Berry, Joel; Savva, Christos; Holzenburg, Andreas; Young, Ry

2010-01-01

386

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

SciTech Connect

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

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

2005-11-15

387

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

Microsoft Academic Search

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

Nicolas Bachelier; Jean-François Verchere

1995-01-01

388

Kinetics and thermodynamics of complex formation with iron of a new series of dicatecholspermidine siderophore-like ligands.  

PubMed

This article deals with the kinetics and thermodynamics of complex formation between Fe(3+) and a series of four synthetic chelators of the 1,2-dicatecholspermidine family (LA5, LA3, LE5 and LE3). LA5 and LA3 bear a carboxylic moiety linked to the central nitrogen by either a C(5) or a C(3) chain, whereas LE5 and LE3 bear an ethyl ester moiety. The following data concern LE5, LE3, LA5 and LA3, respectively. Each species undergoes four acid-base dissociations of the hydroxyls of the catechols with, for the two hydroxyls in position 1; average pK(2a)=7.30, 7.25, 7.45, 7.34 and, for the two hydroxyl in position 2; average pK(3a)=12.35, 12.65, 12.10, 12.60. The LA5 and LA3 species also undergo proton-dissociations of their carboxylic moieties; pK(1a)=5.20 and 5.10. The four species form one-to-one iron complexes with, for the 1-hydroxyl; an average pK(22a)=2.65, 2.25, 2.95, 2.80, for the 2-hydroxyl; pK(33a)=5.20, 5.40, 6.10, 5.40 and, for the carboxylic moieties; pK(11a)=3.90 and 4.45. In the vicinity of pH 5, Fe(3+) is rapidly exchanged between FeNta and the four ligands. This occurs with direct rate constants: k(1)=(1.3+/-0.1)x10(4), (1.4+/-0.2)x10(4), (3.3+/-0.2)x10(4), (1.4+/-0.1)x10(4)M(-1)s(-1), and reverse rate constants: k(-1)=(7+/-0.5)x10(4), (9+/-1)x10(4), (1.15+/-0.15)x10(5), (7+/-0.5)x10(4)M(-1)s(-1). The kinetic data, the pK(a) values of the free ligands, those of the iron complexes and the beta value of FeNta allow us to determine the affinity constants of the four ligands for iron: logbeta(1)=33, 34, 33, 34, and pFe=23.3, 24.6, 22.2, 24.3. This implies that these ligands of the dicatecholspermidine family may act as siderophores. They may also be used as drug carriers which can utilize the bacterial iron-acquisition paths. PMID:18037492

Sindi, Kais; El Hage Chahine, Jean-Michel

2007-10-24

389

Electrostatic and hydrophobic interactions during complex formation and electron transfer in the ferredoxin/ferredoxin: NADP{sup +} reductase system from Anabaena  

SciTech Connect

Transient kinetics and protein-protein binding measurements over a wide range of ionic strength (I) have been used to characterize the interactions occurring during complex formation and electron transfer (et) between recombinant ferredoxin (Fd) and both native and recombinant ferredoxin: NADP{sup +} reductase (FNR) from the cyanobacterium Anabaena. Between I = 12 mM and I = 100 mM, the dissociation constant (K{sub d}) for the complex formed between oxidized Fd and oxidized native FNR increases from 4.5 to 8.1 {mu}M, whereas K{sub d} for the Fd complex with recombinant FNR increases from 0.3 to 3.3 {mu}M. For both pairs of proteins, the ionic strength dependence of k{sub obs} for the et reaction is biphasic. Electrostatic analysis of the kinetic data above I = 100 mM allows a prediction of the ionic strength dependence of the K{sub d} values, if electrostatic interactions are the only determinant of complex stability. The predicted dependence is dramatically larger than the observed one, indicating that hydrophobic interactions make an important contribution to complex stability. The differences in binding between native and recombinant FNR are ascribed to proteolytic cleavage at the N-terminus, which occurs during preparation of the native enzyme and which removes two positively charged residues, thereby decreasing the electrostatic interactions with Fd. 39 refs., 4 figs., 1 tab.

Hurley, J.K.; Tollin, G. [Univ. of Arizona, Tucson, AZ (United States); Fillat, M.F.; Gomez-Moreno, C. [Universidad de Zaragoza (Spain)

1996-06-19

390

Conspicuous histomorphological anomalies in the hippocampal formation of rats exposed prenatally to a complex sequenced magnetic field within the nanoTesla range.  

PubMed

The brains of adult rats, exposed prenatally to one of four intensities (between 10 nanoTesla and 1.2 microTesla) of either a frequency-modulated magnetic field or a complex sequenced field designed to affect brain development, were examined histologically. Although from each intensity some rats that had been exposed to the complex sequenced magnetic field showed minor anomalies, those exposed to intensities between 30 nT and 180 nT exhibited conspicuous anomalous organizations of cells within the hippocampal formation. In other studies, rats that had been exposed during their entire prenatal development to the complex sequenced field displayed significantly more activity in the open field and poorer spatial memory during maze learning. Photomicrographs are shown of one conspicuous morphological anomaly within the right hippocampus of an adult rat exposed prenatally to the complex sequenced magnetic field with intensities between .3 mG and .5 mG (30 nT to 50 nT). The results suggest that complex magnetic fields, whose temporal structures approach the time constants of normal biochemical processes, can permanently alter the development of the brain. PMID:15002875

St-Pierre, Linda S; Persinger, Michael A

2003-12-01

391

Mechanistic complexity of subvisible particle formation: links to protein aggregation are highly specific.  

PubMed

There is little knowledge available on the mechanistic features of the protein aggregation pathway, which lead to subvisible particles (SVPs) (0.1-100 µm in size). Additionally, the relationship between soluble aggregates (SAs) (those that are less than 0.1 µm in size) and SVP formation is largely unknown. To better understand these relationships and the mechanism of SVP formation, we conducted agitation experiments on three different classes of proteins; two antibodies [an immunoglobulin G (IgG) 1 and an IgG4] and a glycoprotein. A quantification of SVPs, using the Brightwell Microfluidics Instrument, and levels of SAs by size-exclusion chromatography were determined as a function of agitation time. Not surprisingly, the propensity to aggregate and particulate was different for each protein. However, integrated mass analysis in these studies showed that the relationship between SA and SVP formation is also protein and formulation dependent, and can vary greatly between molecules. Morphological and statistical analysis of SVPs in agitated and nonagitated samples revealed that changes in both the shape and the size distribution of the SVPs population are also protein dependent and highly defined. Collectively, these results suggest/illustrate the complexity of elucidating an aggregation mechanism that encompasses both SAs and SVPs. PMID:22911674

Simler, B Robert; Hui, Guodong; Dahl, Jennifer E; Perez-Ramirez, Bernardo

2012-08-21

392

New evidence for the complexity of river terrace formation in Northern Bavaria  

NASA Astrophysics Data System (ADS)

Fluvial terraces are widespread geomorphic features and their formation occurred dominantly during the Quaternary. Besides tectonic reasons, the formation of Quaternary fluvial terraces is related to paleoclimatic changes and their corresponding changes in fluvial discharge and sediment load. However, within the Pleistocene, the exact timing and the paleoenvironmental conditions for terrace formation are still under debate and traditional concepts are questioned. To shed light on the question of Pleistocene environmental conditions for terrace formation, we investigate their timing by establishing a terrace chronostratigraphy based on numerical dating. The study is located in a dry valley north of the city of Bayreuth, Bavaria, Germany. Here, within a former interconnection between the Red Main/Steinach drainage system in the south and the White Main River in the north, five Pleistocene terrace levels are distinguished. The terraces are interpreted as the result of a very complex landscape evolution, which is characterized by at least twofold river deflection. Because of this river deflection, fluvial and periglacial slope sediments are still widely preserved and can now be used as sediment archives for reconstructing the timing of fluvial and therefore paleoenvironmental change. In a first step, we focused the investigations on dating the youngest Pleistocene terrace (T2). Following the traditional explanations, this terrace level is interpreted as a Weichselian (Würmian) formation, developed during the last glacial maximum. First optically stimulated luminescence (OSL) dating results, however, indicate a significantly older age for the aggradation of the gravel and, thus, point to a much earlier deflection of the primary Steinach River. The correctness of the OSL ages is supported by radiocarbon AMS dating. These results indicate a significant Weichselian (Würmian) fluvial geomorphodynamic during the Lower or Middle Pleniglacial rather than during the Upper Pleniglacial. Furthermore they show that the response of fluvial systems to environmental changes is complex and in addition strongly depends on local conditions. Our findings raise new questions concerning climatic conditions during the Middle and Lower Pleniglacial and their impacts on geomorphological processes relating to the forming of fluvial terraces.

Kolb, Thomas; Fuchs, Markus; Zöller, Ludwig

2013-04-01

393

Organization of amphiphiles: XII. Evidence in favor of formation of hydrophobic complexes in aqueous solution.  

PubMed

The effects of nonionic surfactants OP-10 and OP-30 (polyoxyethylated octyl phenols with 10 and 30 oxyethylene groups, respectively) in surfactant mixtures with ionic surfactants hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) have been investigated by a conductometric method in conjunction with fluorescence, surface tension, zeta potential, and DLS measurements. The interactions are found to be antagonistic in nature for each of the systems; i.e., micellization of CTAB as well as SDS is hindered on addition of the nonionic surfactants. The antagonism is found to be more prominent in the presence of OP-10 compared to that of OP-30. Two types of mechanistic paths, path A operating below the critical micellar concentration and path B operating beyond the critical micellar concentration of nonionic surfactants, have been suggested. In path A, the retardation in micellization has been attributed to a decrease in monomeric concentration of the ionic surfactants from solution as a result of the formation of a hydrophobic complex between nonionic and ionic surfactants. In path B, the decrease in monomer concentration is due to the solubilization of the ionic surfactant in micelles of the nonionic surfactants in a 1:1 stoichiometric ratio. A theoretical treatment to the interaction in each ionic-nonionic pair yields a positive value of the interaction parameter supporting the concept of antagonism. The formation of the hydrophobic complex is supported by fluorescence and surface tension measurements. A schematic representation of the stabilization of these hydrophobic complexes has been suggested. The association of ionic surfactants by nonionic micelles is suggested by zeta potential and DLS studies. PMID:21396651

Dash, Uma; Misra, Pramila K

2011-02-01

394

The influence of host–guest inclusion complex formation on the biotransformation of cortisone acetate ? 1-dehydrogenation  

Microsoft Academic Search

An intensive and systematic investigation had been carried out on the ?1-dehydrogenation of cortisone acetate (CA) to prednisone acetate (PA) by Arthrobacter simplex TCCC 11037 in the presence of native and modified ?-cyclodextrins (?-CDs). The biotransformation was improved through the formation of the host–guest inclusion complex between CA and CDs in aqueous solution. The inclusion complexes of CDs with CA

Yin-Hu Ma; Min Wang; Zhi Fan; Yan-Bing Shen; Li-Ting Zhang

2009-01-01

395

PHYSICOCHEMICAL STUDY OF THE COMPLEX FORMATION OF BERYLLIUM IONS WITH ORGANIC LIGANDS. PART IV. WITH MALONIC ACID AND ITS DERIVATIVES  

Microsoft Academic Search

Beryllium sulfate was found to form 1: 1 complexes with malonic acid, ; sodium malonate, and diethyl malonate. The complex formation was studied by the ; electrical conductance data, potentiometric data, and spectrophotometric data in ; the ultraviolet region with the help of Job's continuous variation method. The ; values of the dissociation contants thus obtained are 9.55 x 10⁻⁴

A. K. Bhattacharya; G. S. Rao

1962-01-01

396

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

PubMed Central

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

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

2009-01-01

397

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

PubMed

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

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

2010-09-21

398

Rapamycin inhibits trypanosome cell growth by preventing TOR complex 2 formation  

PubMed Central

Target of rapamycin (TOR) kinases control cell growth through two functionally distinct multiprotein complexes. TOR complex 1 (TORC1) controls temporal cell growth and is sensitive to rapamycin, whereas TOR complex 2 (TORC2) is rapamycin resistant and regulates spatial cell growth. Here, we identified two TOR orthologues, TbTOR1 and TbTOR2, in the protozoan parasite Trypanosoma brucei, as well as orthologues of the well-known TORC1 and TORC2 partners, KOG1/raptor and AVO3/rictor. TbTOR proteins differ in their functions, subcellular localization, and rapamycin sensitivity. TbTOR1 controls cell growth by regulating cell cycle, nucleolus structure, and protein synthesis, whereas TbTOR2 coordinates cell polarization and cytokinesis. Rapamycin treatment of bloodstream trypanosomes resulted in a pronounced reduction of cell proliferation, with an EC50 of 152 nM. Unique for a eukaryote, we observed that rapamycin acted exclusively by preventing TORC2 formation, with no effect on TORC1. Our findings on TOR signaling in this protozoan, which is located in a distal position in the eukaryotic cell lineage, highlight the clinical possibilities of rapamycin derivates and provide valuable insights into understanding rapamycin-mediated inhibition of TORC2.

Barquilla, Antonio; Crespo, Jose L.; Navarro, Miguel

2008-01-01

399

Autophagosome formation-The role of ULK1 and Beclin1-PI3KC3 complexes in setting the stage.  

PubMed

Autophagy is a conserved and highly regulated degradative membrane trafficking pathway, maintaining energy homeostasis and protein synthesis during nutrient stress. Our understanding of how the autophagy machinery is regulated has expanded greatly over recent years. The ULK and Beclin1-PI3KC3 complexes are key signaling complexes required for autophagosome formation. The nutrient and energy sensors mTORC1 and AMPK signal directly to the ULK complex and affect its activity. Formation and activation of distinct Beclin1-PI3KC3 complexes produces PI3P, a signaling lipid required for the recruitment of autophagy effectors. In this review we discuss how the mammalian ULK1 and Beclin1 complexes are controlled by post-translational modifications and protein-protein interactions and we highlight data linking these complexes together. PMID:23727157

Wirth, Martina; Joachim, Justin; Tooze, Sharon A

2013-05-29

400

STAR FORMATION ACTIVITY IN THE GALACTIC H II COMPLEX S255-S257  

SciTech Connect

We present results on the star formation activity of an optically obscured region containing an embedded cluster (S255-IR) and molecular gas between two evolved H II regions, S255 and S257. We have studied the complex using optical and near-infrared (NIR) imaging, optical spectroscopy, and radio continuum mapping at 15 GHz, along with Spitzer-IRAC results. We found that the main exciting sources of the evolved H II regions S255 and S257 and the compact H II regions associated with S255-IR are of O9.5-B3 V nature, consistent with previous observations. Our NIR observations reveal 109 likely young stellar object (YSO) candidates in an area of {approx}4.'9 x 4.'9 centered on S255-IR, which include 69 new YSO candidates. To see the global star formation, we constructed the V - I/V diagram for 51 optically identified IRAC YSOs in an area of {approx}13' x 13' centered on S255-IR. We suggest that these YSOs have an approximate age between 0.1 and 4 Myr, indicating a non-coeval star formation. Using spectral energy distribution models, we constrained physical properties and evolutionary status of 31 and 16 YSO candidates outside and inside the gas ridge, respectively. The models suggest that the sources associated with the gas ridge are younger (mean age {approx}1.2 Myr) than the sources outside the gas ridge (mean age {approx}2.5 Myr). The positions of the young sources inside the gas ridge at the interface of the H II regions S255 and S257 favor a site of induced star formation.

Ojha, D. K.; Ghosh, S. K. [Tata Institute of Fundamental Research, Mumbai (Bombay) 400 005 (India); Samal, M. R.; Pandey, A. K.; Sharma, Saurabh [Aryabhatta Research Institute of Observational Sciences, Nainital 263 129 (India); Bhatt, B. C. [Indian Institute of Astrophysics, Koramangala, Bangalore 560 034 (India); Tamura, M. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Mohan, V. [Inter-University Centre for Astronomy and Astrophysics, Pune 411 007 (India); Zinchenko, I., E-mail: ojha@tifr.res.in [Institute of Applied Physics of the Russian Academy of Sciences, Ulyanova 46, 603950 Nizhny Novgorod (Russian Federation)

2011-09-10

401

NMR of paramagnetic complexes of radicals with organic ligands  

Microsoft Academic Search

Complex formation between stable amine oxide radicals and organic molecules generates paramagnetic shifts in the NMR spectra of the ligand nuclei and corresponding line broadening in these spectra. Analysis of the paramagnetic shifts yielded the magnitudes and signs of the isotopic hyperfine interaction constants for the protons in the radical complexes with hydroxyl-containing ligands. The equilibrium constants for the complex

N. A. Sysoeva; A. L. Buchachenko

1972-01-01

402

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

Microsoft Academic Search

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

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

2005-01-01

403

Variable inhibitory effects on the formation of dinitrosyl iron complexes by deferoxamine and salicylaldehyde isonicotinoyl hydrazone in K562 cells.  

PubMed

A prerequisite of dinitrosyl iron complexes (DNIC) formation is the presence of nitric oxide (NO), iron (Fe) and thiol/imidazole groups. The aim of this study was to investigate the influence of Fe chelators on the formation of DNIC in erythroid K562 cells. The cells were treated with lipophilic salicylaldehyde isonicotinoyl hydrazone (SIH) (0.1 mM) and hydrophilic deferoxamine mesylate (DFO) (1 mM), a membrane permeable and non permeable Fe chelator, respectively. Dinitrosyl Fe complexes were generated by addition of 0.07 mM diethylamine NO. The DNIC formation was recorded using electron paramagnetic resonance (EPR). Both chelators inhibited DNIC formation up to 50% after 6 hours of treatment. Taken together, our data suggest that an intracellular low molecular weight labile Fe pool (LIP) and protein-bound Fe participate in DNIC formation in K562 cells to a similar extent. PMID:18274993

Meczynska, Sylwia; Lewandowska, Hanna; Sochanowicz, Barbara; Sadlo, Jaroslaw; Kruszewski, Marcin

2008-01-01

404

Formation of impeller-like helical DNA-silica complexes by polyamines induced chiral packing.  

PubMed

The helicity of DNA and its long-range chiral packing are widespread phenomena; however, the packing mechanism remains poorly understood both in vivo and in vitro. Here, we report the extraordinary DNA chiral self-assembly by silica mineralization, together with circular dichroism measurements and electron microscopy studies on the structure and morphology of the products. Mg(2+) ion and diethylenetriamine were found to induce right- and left-handed chiral DNA packing with two-dimensional-square p4mm mesostructures, respectively, to give corresponding enantiomeric impeller-like helical DNA-silica complexes. Moreover, formation of macroscopic impeller-like helical architectures depends on the types of polyamines and co-structure-directing agents and pH values of reaction solution. It has been suggested that interaction strength between negatively charged DNA phosphate strands and positively charged counterions may be the key factor for the induction of DNA packing handedness. PMID:24098845

Liu, Ben; Han, Lu; Che, Shunai

2012-02-22

405

Nuclear pore complex assembly studied with a biochemical assay for annulate lamellae formation  

PubMed Central

Formation of the nuclear pore is an intricate process involving membrane fusion and the ordered assembly of up to 1,000 pore proteins. As such, the study of pore assembly is not a simple one. Interestingly, annulate lamellae, a cytoplasmic organelle consisting of stacks of flattened membrane cisternae perforated by numerous pore complexes, have been found to form spontaneously in a reconstitution system derived from Xenopus egg extracts, as determined by electron microscopy (Dabauvalle et al., 1991). In this work, a biochemical assay for annulate lamellae (AL) formation was developed and used to study the mechanism of AL assembly in general and the assembly of individual nucleoporins into pore complexes in particular. Upon incubation of Xenopus egg cytosol and membrane vesicles, the nucleoporins nup58, nup60, nup97, nup153, and nup200 initially present in a disassembled form in the cytosol became associated with membranes and were pelletable. The association was time and temperature dependent and could be measured by immunoblotting. Thin-section electron microscopy as well as negative staining confirmed that annulate lamellae were forming coincident with the incorporation of pore proteins into membranes. Homogenization and subsequent flotation of the membrane fraction allowed us to separate a population of dense membranes, containing the integral membrane pore protein gp210 and all other nucleoporins tested, from the bulk of cellular membranes. Electron microscopy indicated that annulate lamellae were enriched in this dense, pore protein-containing fraction. GTP gamma S prevented incorporation of the soluble pore proteins into membranes. To address whether AL form in the absence of N-acetylglucosaminylated pore proteins, AL assembly was carried out in WGA-sepharose-depleted cytosol. Under these conditions, annulate lamellae formed but were altered in appearance. When the membrane fraction containing this altered AL was homogenized and subjected to flotation, the pore protein- containing membranes still sedimented in a distinct peak but were less dense than control annulate lamellae.

1995-01-01

406

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

PubMed

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

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

2013-03-25

407

Effects of salt concentration on formation and dissociation of beta-lactoglobulin/pectin complexes.  

PubMed

The formation and dissociation of beta-lactoglobulin/pectin complexes at various sodium chloride concentrations (CNaCl) have been studied by turbidimetric titration. An increase of CNaCl up to 0.1 M shifts the critical pHphi1, which designates the formation of beta-lactoglobulin/pectin coacervates, to higher pH values, whereas further increase of CNaCl from 0.1 to 0.8 M decreases pHphi1 values. These salt effects can be explained in terms of a salt-enhanced effect at lower salt concentrations or a salt-reduced effect at higher salt concentrations, respectively. On the other hand, the value of pHphi2, which corresponds to the dissociation of beta-lactoglobulin/pectin coacervates, tends to have smaller pH values when CNaCl increases from 0.1 to 0.3 M. No observable pHphi2 values are found at CNaCl higher than 0.3 M. The disappearance of pHphi2 is mainly attributed to the strong self-aggregation capability of beta-lactoglobulin at higher CNaCl. The aggregation of beta-lactoglobulin at high CNaCl is reversible, as suggested by the atomic force microscopy results. PMID:17979233

Wang, Xiaoyong; Wang, Yu-Wen; Ruengruglikit, Chada; Huang, Qingrong

2007-11-03

408

Reaction time dependent formation of Pd(II) and Pt(II) complexes of bis(methyl)thiasalen podand.  

PubMed

Thiasalen podand 9 having S2N2 donor set has been synthesized by the condensation of 2-methylthiobenzaldehyde with ethylenediamine. The reaction of the thiasalen podand ligand with Pd(II) afforded two complexes depending on the reaction time. Shorter reaction time (5 min) afforded thioether complex 10; whereas with increase in reaction time (4 h) thioether-thiolate complex 11 was obtained via cleavage of one of the two S-C(Me) bonds of bis(methyl)thiasalen podand upon complexation. The reaction of 9 with Pt(II) afforded only thiolate-thioether complex 12 independent of the reaction time. The cleavage of both the S-C(Me) bonds of bis(methyl)thiasalen to afford bisthiolate complexes has never been observed. The structures of thiasalen podands and all three complexes have been determined by single crystal X-ray diffraction analysis. All three complexes possess a square planar geometry around the metal centres. Weak van der Waals interactions through C-H···F interactions are present in all three complexes leading to the formation of supramolecular synthons and the supramolecular structures are stabilized by aromatic ?···? interactions, which leads to the formation of 3D pseudo-double helical network packing. Under similar conditions bis(methyl)salen did not form any complexes with Pd(II) and Pt(II). PMID:23073301

Dutta, Pradip Kr; Panda, Snigdha; Krishna, G Rama; Reddy, C Malla; Zade, Sanjio S

2012-10-17

409

Functionalized organotin-chalcogenide complexes that exhibit defect heterocubane scaffolds: formation, synthesis, and characterization.  

PubMed

The synthesis of new functionalized organotin-chalcogenide complexes was achieved by systematic optimization of the reaction conditions. The structures of compounds [(R(1,?2) Sn)3 S4 Cl] (1, 2), [((R(2) Sn)2 SnS4 )2 (?-S)2 ] (3), [(R(1,?2) Sn)3 Se4 ][SnCl3 ] (4, 5), and [Li(thf)n ][(R(3) Sn)(HR(3) Sn)2 Se4 Cl] (6), in which R(1) =CMe2 CH2 C(O)Me, R(2) =CMe2 CH2 C(NNH2 )Me, and R(3) =CH2 CH2 COO, are based on defect heterocubane scaffolds, as shown by X-ray diffraction, (119) Sn?NMR spectroscopy, and ESI mass spectrometry analyses. Compounds 4, 5, and 6 constitute the first examples of defect heterocubane-type metal-chalcogenide complexes that are comprised of selenide ligands. Comprehensive DFT calculations prompted us to search for the formal intermediates [(R(1) SnCl2 )2 (?-S)] (7) and [(R(1) SnCl)2 (?-S)2 ] (8), which were isolated and helped to understand the stepwise formation of compounds 1-6. PMID:23963989

Eußner, Jens P; Barth, Beatrix E K; Leusmann, Eliza; You, Zhiliang; Rinn, Niklas; Dehnen, Stefanie

2013-08-21

410

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

PubMed Central

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

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

2013-01-01

411

Requirements of fission yeast septins for complex formation, localization, and function.  

PubMed

Septins are GTP binding proteins important for cytokinesis in many eukaryotes. The Schizosaccaromyces pombe genome sequence predicts orthologues of four of five Saccharomyces cerevisiae septins involved in cytokinesis and these are named Spns1-4p. That spns1-4 are not essential genes permitted the application of a combined genetic and proteomics approach to determine their functional relationships. Our findings indicate that Spns1-4p are present throughout interphase as a diffusely localized approximately 8.5S complex containing two copies of each septin linked together as a chain in the order Spn3p-Spn4p-Spn1p-Spn2p. Septin recruitment to the medial region of the cell is genetically separable from ring formation, and whereas it is normally restricted to mitosis, it can be promoted without activation of the mitotic cell cycle machinery. Coalescence into ring structures requires Spn1p and Spn4p associate with at least one other septin subunit and the expression of Mid2p that is normally restricted to mitosis. This study establishes the functional requirements for septin complex organization in vivo. PMID:15385632

An, Hanbing; Morrell, Jennifer L; Jennings, Jennifer L; Link, Andrew J; Gould, Kathleen L

2004-09-22

412

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

PubMed

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

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

2004-10-01

413

Tetrathiafulvalene-oligo(para-phenyleneethynylene) conjugates: formation of multiple mixed-valence complexes upon electrochemical oxidation.  

PubMed

Short monodisperse oligo- (para-phenyleneethynylene) (pOPE) units bearing laterally attached tetrathio-substituted tetrathiofulvalene (TTF) units have been synthesised from functionalised aromatic building blocks by using the Sonogashira cross-coupling methodology. The unusual redox properties of these TTF-pOPE conjugates were observed by employing electrochemical methods, such as cyclic voltammetry and exhaustive electrolysis. We found that formally one half of the TTF units in the pOPE monomer 1, dimer 2, and trimer 3 (with 2, 4, and 6 TTF units, respectively) are electrochemically silent during the first-step oxidation at 0.49?V. We propose the formation of persistent mixed-valence complexes from the TTF and TTF(+·) units present in an equal ratio. Such mixed-valence dyads (single or multiple in the partially oxidised 1-3) exhibit an unusual stability towards oxidation until the potential of the second oxidation at 0.84?V is achieved. This finding suggests that below this potential the oxidation of the respective mix-valence complexes is extremely slow. PMID:23495131

Lipnická, Šárka; B?lohradský, Martin; Kolivoška, Viliam; Pospíšil, Lubomír; Hromadová, Magdaléna; Pohl, Radek; Chocholoušová, Jana Vacek; Vacek, Jaroslav; Fiedler, Jan; Stará, Irena G; Starý, Ivo

2013-03-13

414

Formation of protein complexes in crowded environments--from in vitro to in vivo.  

PubMed

Traditionally, biochemical studies are performed in dilute homogenous solutions, which are very different from the dense mixture of molecules found in cells. Thus, the physiological relevance of these studies is in question. This recognition motivated scientists to formulate the effect of crowded solutions in general, and excluded volume in particular, on biochemical processes. Using polymers or proteins as crowders, it was shown that while crowding tends to significantly enhance the formation of complexes containing many subunits, dimerizations are only mildly affected. Computer simulations, together with experimental evidence, indicate soft interactions and diffusion as critical factors that operate in a concerted manner with excluded volume to modulate protein binding. Yet, these approaches do not truly mimic the cellular environment. In vivo studies may overcome this shortfall. The few studies conducted thus far suggest that in cells, binding and folding occur at rates close to those determined in dilute solutions. Obtaining quantitative biochemical information on reactions inside living cells is currently a main challenge of the field, as the complexity of the intracellular milieu was what motivated crowding research to begin with. PMID:23337873

Phillip, Yael; Schreiber, Gideon

2013-01-18

415

Structural basis of protein complex formation and reconfiguration by polyglutamine disease protein Ataxin-1 and Capicua  

PubMed Central

Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease caused by polyglutamine expansion in Ataxin-1 (ATXN1). ATXN1 binds to the transcriptional repressor Capicua (CIC), and the interaction plays a critical role in SCA1 pathogenesis whereby reducing CIC levels rescues SCA1-like phenotypes in a mouse model. The ATXN1/HBP1 (AXH) domain of ATXN1 mediates its homodimerization as well as the interaction with CIC. Here, we present the crystal structure of ATXN1's AXH domain bound to CIC and show that the binding pocket of the AXH domain to CIC overlaps with the homodimerization pocket of the AXH domain. Thus, the binding to CIC disrupts the homodimerization of ATXN1. Furthermore, the binding of CIC reconfigures the complex to allow another form of dimerization mediated by CIC, showing the intricacy of protein complex formation and reconfiguration by ATXN1 and CIC. Identifying the surfaces mediating the interactions between CIC and ATXN1 reveals a critical role for CIC in the reconfiguration of the AXH dimers and might provide insight into ways to target the ATXN1/CIC interactions to modulate SCA1 pathogenesis.

Kim, Eunji; Lu, Hsiang-Chih; Zoghbi, Huda Y.; Song, Ji-Joon

2013-01-01

416