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1

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

2

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

NASA Astrophysics Data System (ADS)

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

Millero, Frank J.

1992-08-01

3

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

PubMed

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

Frycák, Petr; Schug, Kevin A

2008-03-01

4

Polymer supported ultrafiltration as a technique for selective heavy metal separation and complex formation constants prediction  

Microsoft Academic Search

This work is aimed at evaluating the affinity of partially ethoxylated polyethyleneimine (PEPEI) towards industrially valuable metal ions (Cu2+, Ni2+, Cd2+ and Zn2+). To face this aim, a characterization of polymer and macromolecular complexes by acid–base potentiometry was carried out. Next, lab-scale total recirculation mode ultrafiltration experiments were performed, checking that the affinity order was the same as that calculated

Javier Llanos; Rafael Camarillo; Ángel Pérez; Pablo Cañizares

2010-01-01

5

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

NASA Astrophysics Data System (ADS)

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

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

1996-07-01

6

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

SciTech Connect

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

Hamed, M.M.A.; Mahmoud, M.R. (Assiut Univ. (Egypt). Dept. of Chemistry); Saleh, M.B.; Ahmed, I.T. (El-Minia Univ. (Egypt). Dept. of Chemistry)

1994-07-01

7

Stability constants of aluminium fluoride complexes.  

PubMed

Pointwise titrations of aluminium nitrate solutions with sodium fluoride were made at ionic strengths of 0.5, 0.2, 0.1 and 0.05M and at temperatures of 25 degrees and 37 degrees . The total Al(3+) concentration was kept constant at 5 x 10(-4)M and the total F(-) concentration covered the range 5-20 x 10(-4)M with a minimum of 20 points per titration. It is shown that only mononuclear complexes were present with these solution compositions. Determinations of H(+) and F(-) in solution were made by the use of quinhydrone and lanthanum fluoride electrodes, respectively. Formation constants were calculated by three different procedures. Best results were obtained by a non-linear generalized least-squares method that (a) permits calculation of the formation constants with the simultaneous presence of all the complexes being taken into account, (b) does not require segregation of data according to the values of the formation function (n), and (c) yields standard errors that reflect the errors in all the experimental measurements. Values for the formation constants at infinite dilution were obtained by a linear least-squares adjustment of the values obtained for the four finite ionic strengths. The formation constants thus obtained for the reaction AlF(n-1) + F <==> AlF(n) (charges omitted) at 25 degrees have logarithmic values of 6.69 +/- 0.02, 5.35 +/- 0.03, 3.68 +/- 0.01 and 2.75 +/- 0.04 for n = 1, 2, 3 and 4, respectively. The corresponding values at 37 degrees are 6.68 +/- 0.10,5.34 +/- 0.02,3.94 +/- 0.04, and 3.29 +/- 0.05. PMID:18960958

Agarwal, R P; Moreno, E C

1971-09-01

8

Bacterial formate hydrogenlyase complex  

PubMed Central

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

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

2014-01-01

9

Bacterial formate hydrogenlyase complex.  

PubMed

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

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

2014-09-23

10

Formation of interpolymer complexes  

Microsoft Academic Search

Interpolymer complex formations of poly(methacrylic acid) (PMAA) or poly(acrylic acid) (PAA) with oligocations as well as poly(ethylene oxide) (PEO), and poly-(N-vinyl-2-pyrrolidone of various chain lengths were studied. For the case of complexation between PMAA and oligocations, the standard free energy change for the complexation ?G° was found to be linearly dependent on the number of interacting sites, n. The stability

Eishun Tsuchida; Yoshihito Osada; Hiroyuki Ohno

1980-01-01

11

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

ERIC Educational Resources Information Center

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

Larsen, Erik; Eriksen, J.

1975-01-01

12

Polarographic Study of Complex Formation Equilibria in Solutions  

NASA Astrophysics Data System (ADS)

Methods for the calculation of the coordination numbers and stability constants of complexes formed in solution from polarographic data are examined and methods for the determination of the parameters governing the formation of a single complex and stepwise complex formation as well as the formation of mixed and polynuclear complexes and complexonates are described. It is shown how kinetic and catalytic waves, the waves of the ligand, and the waves due to irreversible processes can be used for this purpose. Attention is drawn to the necessity to take into account the adsorption of the components of a system involving complex formation. The bibliography includes 64 references.

Mambetkaziev, E. A.; Zhdanov, Stepan I.

1980-04-01

13

Noniterative calculation of complex propagation constants in planar waveguides.  

PubMed

We adapt an efficient finite-difference procedure for determining complex propagation constants to the analysis of modes in planar waveguides. The method requires solving a single rather than multiple eigenvalue equations and does not require prior knowledge of either the nature of the solutions or the position of the modal eigenvalues in the complex plane. PMID:11688872

Ye, R Z; Yevick, D O

2001-11-01

14

Reverse hydrotropy by complex formation.  

PubMed

Self-aggregation of three di-N-alkylated diaza-18-crown-6 ethers (ACEs) was studied in non-polar solvents. The three ACEs differed by the length of the alkyl chain: n-decyl (ACE-10), n-hexadecyl (ACE-16) and n-tetracosane (ACE-24). From the previously reported interfacial tension isotherms, the formation of reverse micelles was expected above ACE concentrations of ?10(-3) M. However, the water content analysis in conjunction with Dynamic Light Scattering (DLS), Fluorescence Correlation Spectroscopy (FCS) and (1)H NMR Diffusion Ordered Spectroscopy (DOSY) do not provide any clear proof of the existence of aggregates. Only the Small Angle Neutron Scattering (SANS) of concentrated toluene ACE solutions reveals the existence of small reverse micelles (probably ACE dimers forming small cages hosting 1-2 water molecules). On the other hand, spectrophotometric and fluorescence dye dissolution studies using eosin Y, tropaeolin OO and methyl orange suggest that ACEs can dissolve these dyes without requiring the formation of aggregates. This discrepancy was interpreted assuming the dye-ACE complexation as the driving force for dye solubilisation, providing a possible mechanism of reverse hydrotropy ("lipotropy") in non-polar solvents. This example shows that special care should be taken when dye solubilisation is used to probe self-aggregation of an amphiphile in non-polar solvents. The amphiphile-dye complex formation might be responsible for false positive results and the aggregate formation should always be confirmed with other methods. PMID:25415596

Wojciechowski, Kamil; Gutberlet, Thomas; Raghuwanshi, Vikram Singh; Terry, Ann

2015-01-14

15

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

16

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

17

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

ERIC Educational Resources Information Center

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

Prasad, Rajendra; Prasad, Surendra

2009-01-01

18

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

SciTech Connect

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

Choppin, G.R.; Erten, H.N.; Xia, Y.X. [Florida State Univ., Tallahassee, FL (United States)

1995-09-01

19

Complex formation by phenols with tertiary amines in aprotic media  

Microsoft Academic Search

1.The equilibrium constants (Kg) and the enthalpies of formation of H-bonds in complex-formating reactions of phenols with tertiary amines in aprotic solvents fall with a rise in the polarity of the medium and in its capacity for specific solvation with the phenols.2.The introduction of the electron-accepting substituent chlorine into the para position of phenol leads to a considerable rise in

M. L. Keshtov; S. V. Vinogradova; V. A. Vasnev; V. V. Korshak

1980-01-01

20

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

2013-05-01

21

Stoichiometry and Formation Constant Determination by Linear Sweep Voltammetry.  

ERIC Educational Resources Information Center

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

Schultz, Franklin A.

1979-01-01

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

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

24

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

PubMed

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

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

2014-10-17

25

Laboratory measurement of the complex dielectric constant of soils  

NASA Technical Reports Server (NTRS)

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

Wiebe, M. L.

1971-01-01

26

Drop formation dynamics of constant low-viscosity, elastic fluids  

Microsoft Academic Search

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

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

2002-01-01

27

A polarographic study of the pyridine-copper-chloride complexes in methanol and determination of the stability constants.  

PubMed

Copper(I) chloride has been shown to form two complexes with pyridine in anhydrous methanol, CuCiPy and CuClPy(2). Formation constants have been determined and found to be log K(1) = 7.8 +/- 0.3 and log K(2) = 9.45 +/- 0.3. The role of the complexes in the catalytic oxidation of xylenol is discussed. PMID:18962177

Roubaty, J L; Revillon, A; Breant, M

1977-11-01

28

PYRIDIN2-YL-(I-PROPYLAMINO)METHANE PHOSPHONIC ACID PROTONATION AND METAL COMPLEX FORMATION - NMR-CONTROLLED TITRATION  

Microsoft Academic Search

Dissociation and stability constants for protolytic and complex formation equilibria of a polyfunctional ligand are determined. Deprotonation is monitored by NMR controlled titrations. Macroscopic and microscopic concepts are discussed. Nickel complexes are more stable than those of Ca and Mg.

A. Bier; S. Failla; P. Finocchiaro; G. Hägele; M. Latronico; E. Libertini; J. Ollig

1999-01-01

29

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

NASA Astrophysics Data System (ADS)

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

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

2011-04-01

30

Complex organic molecules and star formation  

NASA Astrophysics Data System (ADS)

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

Bacmann, A.; Faure, A.

2014-12-01

31

Formation and stability of nucleotide complexes: Raman titration investigation  

NASA Astrophysics Data System (ADS)

In order to monitor the formation of complexes between modified and wild type nucleotides, a concept based on spectroscopic titration combined with factor analysis data treatment has been developed. A set of samples containing two homopolynucleotides with complementary bases at various concentration ratios has been prepared. Other conditions, i.e. total nucleotide concentration, temperature, ionic strength, divalent ions percentage and pH, were conserved. The series of Raman and UV-absorption spectra obtained from these samples have been treated by factor analysis and the results then fitted to the equilibrium equations of 1 : 1 and 1 : 2 complexes. By this way, spectra of individual unpaired nucleotides, 1 : 1 and 1 : 2 complexes, and values of the stability constants can be determined at the same time. While the former characterise the structure of the individual species, the latter parameters implicate their percentage in each sample. The approach has been tested on a poly(rA)-poly(rU) model system.

Hanuš, J.; Št?pánek, J.; Turpin, P.-Y.; Bok, J.

1999-05-01

32

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

2013-10-01

33

Nonlinear Dynamics and Structure Formation in Complex Systems  

E-print Network

Nonlinear Dynamics and Structure Formation in Complex Systems F. Zonca - Complex behaviors AND STRUCTURE FORMATION IN COMPLEX SYSTEMS: CHALLENGES AND OPEN PROBLEM FOR MODERN PHYSICS September 21-22, 2009 ENEA, Frascati, Italy #12;Nonlinear Dynamics and Structure Formation in Complex Systems F. Zonca

Zonca, Fulvio

34

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

E-print Network

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

Reid, Scott A.

35

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

Microsoft Academic Search

This paper presents the results concerning the determination of the formation constants of the complexes between thymol blue, TB, and the metal ions Pb(II) or Cd(II). The experimental procedure was carried out in the presence of a nitrogen atmosphere at 25°C. The spectrophotometry data obtained were processed through the software SQUAD to calculate the complexation constants of the metal-indicator and

P. Balderashernandez; A. Rojashernandez; M. Galvan; M. Romero Romo; M. Palomarpardave; M. T. Ramírez-Silva

2007-01-01

36

Determination of stability constants of aminoglycoside antibiotics with their metal complexes  

NASA Astrophysics Data System (ADS)

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

Tiwow, Vanny M. A.

2014-03-01

37

Microchip-ESI-MS determination of dissociation constant of the lysozyme-NAG(3) complex.  

PubMed

An on-line microfluidic system for determination of dissociation constants of enzyme/substrate weak interactions by nanoESI-MS is introduced. The microchip was designed to permit the enzyme and the substrate to mix by molecular diffusion in a pressure-driven laminar flow. Introduction of reagent solutions into the chip was an optimized combination of a micropump and an autosampler to enable automation of the measurements. The system performance was tested for monitoring of non-covalent interactions of hen egg white lysozyme with N-acetyl glucosamine oligomers. Dissociation constant (K(D)) of the hen egg white lysozyme-N-acetyl glucosamine oligomer complex was determined by non-linear regression analysis, and the range of K(D) values (39+/-6 x 10(-6) and 19.6+/-8 x 10(-6) M for manual and automated infusions, respectively) confirms the previously reported values. Such miniaturization of a continuous-flow enzyme assay system to a microfluidic format can maximize the capabilities of mass spectrometric detection, reduce the sample size and analysis time required, as well as the associated costs for on-line enzymatic kinetic studies. PMID:20665926

Svobodová, Jaroslava; Mathur, Sonal; Muck, Alexander; Letzel, Thomas; Svatos, Ales

2010-08-01

38

Hormad1 Mutation Disrupts Synaptonemal Complex Formation, Recombination, and Chromosome  

E-print Network

Hormad1 Mutation Disrupts Synaptonemal Complex Formation, Recombination, and Chromosome Segregation and essential for reproduction. During the first meiotic division, homologous chromosomes pair, recombine the synaptonemal complex. The synaptonemal complex is a critical component for chromosome pairing, segregation

Nachman, Michael

39

Microprocessors are becoming increasingly complex and difficult to debug. Researchers are constantly looking  

E-print Network

1 ABSTRACT Microprocessors are becoming increasingly complex and difficult to debug. Researchers are constantly looking for new methods to increase the observability and control- lability of microprocessors to important internal signals without inter- rupting the microprocessor execution. The output

Al-Asaad, Hussain

40

Vortex formation in a complex plasma  

NASA Astrophysics Data System (ADS)

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

Ishihara, Osamu

41

Thermodynamics of Lead(II) Halide Complex Formation in Calcium Nitrate Tetrahydrate -Acetamide Melts  

NASA Astrophysics Data System (ADS)

The complex formation between lead(II) ions and chloride and bromide ions in melts of C a(N 03) 2 • 4 H2O • ?CH3CONH2 has been studied at different temperatures between 30 and 70 °C. The formation constants of the complexes PbX+ and PbX2 (X = Cl, Br) were determined from em f measurements by means of Ag/AgX electrodes. The dependence of the formation constants for PbCl+ on the solvent melt composition has been analysed. The thermodynamic parameters ?H011 and ?S011 for PbX+ complex formation have been estimated. The parameters are compared with the literature data for the same process in dilute aqueous solutions and in some hydrated and anhydrous salt melts.

Gadzuric, S. B.; Zsigrai, I. J.; Nikolic, R. M.

2001-12-01

42

Identification of the complex relative dielectric constant of porous polymers at different degrees of humidity  

NASA Astrophysics Data System (ADS)

In order to investigate the complex relative dielectric constant of different materials over a frequency range of 50 MHz to 3 GHz a setup has been built that allows rf-measurements in a climate chamber. Within this chamber the temperature and humidity can be changed and be measured by accurate sensors. The construction of the rf-part of the setup has been made with an outer cylindrical shell that allows climate interactions through its large orifices. Methods for calculating the complex relative dielectric constant from the measured scattering parameters are presented and the changes of the relative constants due to different humidity conditions are shown.

Haake, K.; Ter Haseborg, J. L.

2008-05-01

43

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

44

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

45

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

ERIC Educational Resources Information Center

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

Hurek, Jozef; Nackiewicz, Joanna

2013-01-01

46

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

NASA Astrophysics Data System (ADS)

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

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

1999-07-01

47

Measurements of Complex Piezoelectric d33 Constant in Ferroelectric Ceramics under High Electric Field Driving  

Microsoft Academic Search

A measurement system has been designed and constructed which is capable of automatic data collection for complex piezoelectric d33 constant (amplitude and phase), field-induced polarization and switching current under high electric field driving in ferroelectric materials. The system is based on the direct piezoelectric effect and d33 constant can be measured down to about 10 pC\\/N. Using this system, low

Yasuyoshi Saito

1995-01-01

48

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

SciTech Connect

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

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

2006-05-04

49

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

PubMed

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

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

2015-04-01

50

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

SciTech Connect

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

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

1990-04-20

51

The stability constants of the rare earth complexes with trimetaphosphoric acid.  

PubMed

The stability constants of the complexes formed between the rare earth metal ions and the anion of trimetaphosphoric acid have been determined at a temperature of 20 degrees C and an ionic strength of mu = 0.1 by the ion-exchange equilibrium method. The investigations indicate that stabilities of complexes increased from La to Lu. The highest and the lowest stability constant values (beta) were found to be 7.76 and 3.82 for Lu3+ and La3+ respectively. PMID:11507835

Sungur, S

2001-01-01

52

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 ...

53

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

NASA Astrophysics Data System (ADS)

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

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

1998-05-01

54

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

SciTech Connect

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

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

1986-07-16

55

Disulfide bond formation involves a quinhydrone-type chargetransfer complex  

E-print Network

Disulfide bond formation involves a quinhydrone-type charge­transfer complex James Regeimbal the spectral signal of a quinhydrone, a charge­transfer complex consisting of a hydroquinone and a quinone­benzoquinone pair that can be trapped on DsbB as a quinhydrone charge­transfer complex. Quinhydrones are known

Bardwell, James

56

Radial basis function networks in host–guest interactions: instant and accurate formation constant calculations  

Microsoft Academic Search

The application of the second most popular artificial neural networks (ANN), namely, the radial basis function (RBF) networks, have been developed for obtaining sufficient quantitative structure-formation relationships (QSFR) with improved accuracy. To this end, a data set of 17 barbiturates as guests complexing to ?- and ?-cyclodextrins (CDs) was examined using RBF and generalized regression neural networks (GRNN) as function

Yannis L Loukas

2000-01-01

57

Formation of Free Radicals from Molecular Complexes  

Microsoft Academic Search

The Review summarises results from various branches of chemistry having as a common theme the part played by donor-acceptor molecular complexes in the generation of free radicals. Attention is paid mainly to liquid-phase reactions. One section deals with polymerisations involving molecular complexes. A list of 200 references is included.

Gleb B. Sergeev; I. A. Leenson

1972-01-01

58

Formation of Free Radicals from Molecular Complexes  

Microsoft Academic Search

The Review summarises results from various branches of chemistry having as a common theme the part played by donor–acceptor molecular complexes in the generation of free radicals. Attention is paid mainly to liquid-phase reactions. One section deals with polymerisations involving molecular complexes. A list of 200 references is included.

Gleb B Sergeev; I A Leenson

1972-01-01

59

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. PMID:20161099

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

2009-01-01

60

Rovibrational energy and spectroscopic constant calculations of complexes pairing via dihydrogen bonds.  

PubMed

In the present investigation, we performed a thorough study of potential energy curves, rovibrational spectra, and spectroscopic constants for complexes pairing via dihydrogen bonds. In particular, we dealt with LiH[Symbol: see text][Symbol: see text][Symbol: see text]HX (X = F, CN, CCH, CCF, CCCl) complexes by employing accurate electronic energy calculations at the MP2/aug-cc-pVDZ level of theory. Following this, the Numerov method was applied to solve the nuclear Schrödinger equation, thus obtaining spectroscopic constants and rovibrational spectra. Good linear correlation between the magnitudes of the interaction energies for interaction of HX with LiH, and the most positive electrostatic potentials of hydrogen in HX, was established. PMID:25877527

Solimannejad, Mohammad; Jouypazadeh, Hamidreza; Farrokhpour, Hossein

2015-05-01

61

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

PubMed

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

Rowland, Brad A; Wyatt, Robert E

2007-10-28

62

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

SciTech Connect

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

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

2007-10-28

63

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

64

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

65

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

PubMed

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

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

2001-01-01

66

Formation of crystalline complexes between amylomaize dextrin and ceramide.  

PubMed

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

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

2014-01-30

67

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

PubMed

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

Morris, Robert H

2014-02-01

68

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

SciTech Connect

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

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

1988-05-01

69

Lead(II) Complex Formation with Glutathione  

PubMed Central

A structural investigation of complexes formed between the Pb2+ ion and glutathione (GSH, denoted AH3 in its triprotonated form) the most abundant non2protein thiol in biological systems, was carried out for a series of aqueous solutions at pH 8.5 and CPb2+ = 10 mM, and in the solid state. The Pb LIII-edge EXAFS oscillation for a solid compound with the empirical formula [Pb(AH2)]ClO4 was modeled with one Pb-S and two short Pb-O bond distances at 2.64 ± 0.04 Å and 2.28 ± 0.04 Å, respectively. In addition Pb···Pb interactions at 4.15 ± 0.05 Å indicate dimeric species in a network where the thiolate group forms an asymmetrical bridge between two Pb2+ ions. In aqueous solution at the mole ratio GSH / Pb(II) = 2.0 (CPb2+ = 10 mM, pH 8.5), lead(II) complexes with two thiolate ligands form, characterized by a ligand-to-metal charge transfer band (LMCT) S- ? Pb2+ at 317 nm in the UV-vis spectrum and mean Pb-S and Pb-(N/O) bond distances of 2.65 ± 0.04 Å and 2.51 ± 0.04 Å, respectively, from a Pb LIII-edge EXAFS spectrum. For solutions with higher mole ratios, GSH / Pb(II) ? 3.0, ESI-MS spectra identified a trisglutathionyl lead(II) complex, for which Pb LIII-edge EXAFS spectroscopy shows a mean Pb-S distance of 2.65 ± 0.04 Å in PbS3 coordination, 207Pb NMR spectroscopy displays a chemical shift of 2793 ppm, and in the UV-vis spectrum an S- ? Pb2+ LMCT band appears at 335 nm. The complex persists at high excess of glutathione, and also at ~25 K in frozen glycerol (33%) / water glasses for GSH / Pb(II) mole ratios from 4.0 to 10 (CPb2+ = 10 mM) measured by Pb LIII-edge EXAFS spectroscopy. PMID:22594853

Mah, Vicky

2012-01-01

70

Complex molecule formation around massive young stellar objects.  

PubMed

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

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

2014-01-01

71

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

PubMed

Thermodynamic parameters for protonation of 1,4-bis(3-aminopropyl)-piperazine (BAPP) and its metal complexation with some divalent metal ions were determined in aqueous solution at constant ionic strength (0.1?M NaNO(3)) using a potentiometric technique. The order of -?G(0) and -?H(0) was found to obey Co(2+) < Ni(2+) < Cu(2+) > Zn(2+), in accordance with the Irving-Williams order. The formation equilibria of zinc (II) complexes and the ternary complexes Zn(BAPP)L, where L?=?amino acid, amides, or DNA constituents), have been investigated. Ternary complexes are formed by a simultaneous mechanism. The concentration distribution of the complexes in solution was evaluated as a function of pH. Stoichiometry and stability constants for the complexes formed are reported and discussed. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameter ?log K. PMID:23226992

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

2012-01-01

72

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

PubMed Central

Thermodynamic parameters for protonation of 1,4-bis(3-aminopropyl)-piperazine (BAPP) and its metal complexation with some divalent metal ions were determined in aqueous solution at constant ionic strength (0.1?M NaNO3) using a potentiometric technique. The order of –?G0 and –?H0 was found to obey Co2+ < Ni2+ < Cu2+ > Zn2+, in accordance with the Irving-Williams order. The formation equilibria of zinc (II) complexes and the ternary complexes Zn(BAPP)L, where L?=?amino acid, amides, or DNA constituents), have been investigated. Ternary complexes are formed by a simultaneous mechanism. The concentration distribution of the complexes in solution was evaluated as a function of pH. Stoichiometry and stability constants for the complexes formed are reported and discussed. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameter ?log K. PMID:23226992

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

2012-01-01

73

Direct electronic probing of biological complexes formation  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

74

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

75

Variation of lattice constant and cluster formation in GaAsBi  

NASA Astrophysics Data System (ADS)

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

Puustinen, J.; Wu, M.; Luna, E.; Schramm, A.; Laukkanen, P.; Laitinen, M.; Sajavaara, T.; Guina, M.

2013-12-01

76

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

77

Nitrogenases of Klebsiella pneumoniae and Azotobacter chroococum. Complex formation between the component proteins.  

PubMed

1. Sedimentation velocity analyses of mixtures of highly purified component proteins of Azotobacter chroococcum are consistent with the formation of a tight 1 : 1 complex in the absence of Na2 S2 O4. 1 : 1 complex formation between complementary proteins from A. chroococcum and Klebsiella pneumoniae was also observed. The addition of 5 mM Na2 S2 O4 weakened the interaction between the A. chroococcum proteins and also the interaction between complementary proteins of A. chroococcum and K. pneumoniae. 2. Steady-state kinetic data for acetylene reduction at low protein concentrations have been used to calculate association constants at 30 degrees C for the 1 : 1 protein complexes of nitrogenase proteins from A. chroococcum, K. pneumoniae and mixtures of complementary proteins from both organisms. Values centered around 3 - 10(7) M-1 were obtained. 3. The temperature dependence of the association constant for the complex formed by the K. pneumoniae proteins exhibited a sharp break at 17 degrees C with deltaH = 0 and deltaH = 418 kJ - mol-1 above and below 17 degrees C, respectively. 4. The Arrhenius plot for acetylene reduction by the complex formed by the K. pneumoniae proteins was linear over the range 12-40 degrees C with deltaH = 80 kJ - mol-1. PMID:1101961

Thorneley, R N; Eady, R R; Yates, M G

1975-10-22

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

2013-01-15

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

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

PubMed

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

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

2012-08-01

81

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

SciTech Connect

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

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

2000-05-01

82

Complex lane formation in a system of dipolar microswimmers  

E-print Network

Using Brownian Dynamics (BD) simulations we investigate the non-equilibrium structure formation of a two-dimensional (2D) binary system of dipolar colloids propelling in opposite directions. Despite of a pronounced tendency for chain formation, the system displays a transition towards a laned state reminiscent of lane formation in systems with isotropic repulsive interactions. However, the anisotropic dipolar interactions induce novel features: First, the lanes have themselves a complex internal structure characterized by chains or clusters. Second, laning occurs only in a window of interaction strengths. We interprete our findings by a phase separation process and simple force balance arguments.

Florian Kogler; Sabine H. L. Klapp

2015-02-13

83

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

NASA Astrophysics Data System (ADS)

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

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

2007-01-01

84

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

PubMed

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

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

2007-01-01

85

Formation and characterization of polylactide and ?-cyclodextrin inclusion complex  

Microsoft Academic Search

Inclusion complex (ICs) of ?-cyclodextrin (?-CD) and polylactide (PLA) were prepared by a solution-ultrasonic technique. Results showed that the feeding ratios of ?-CD and PLA and the molecular weight of PLA had significant effects on the formation of the ICs, and the formed ICs could be dispersed in water when the molecular number weight (Mn) of PLA was lower than

D. M. Xie; K. S. Yang; W. X. Sun

2007-01-01

86

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, J.D., Jr.; Morey, G.B.

2008-01-01

87

Geology of the Biwabik Iron Formation and Duluth Complex.  

PubMed

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

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

2008-10-01

88

Metal ion coordination, conditional stability constants, and solution behavior of chelating surfactant metal complexes.  

PubMed

Coordination complexes of some divalent metal ions with the DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (4-C12-DTPA) have been examined in terms of chelation and solution behavior. The headgroup of 4-C12-DTPA contains eight donor atoms that can participate in the coordination of a metal ion. Conditional stability constants for five transition metal complexes with 4-C12-DTPA were determined by competition measurements between 4-C12-DTPA and DTPA, using electrospray ionization mass spectrometry (ESI-MS). Small differences in the relative strength between the coordination complexes of DTPA and 4-C12-DTPA indicated that the hydrocarbon tail only affected the chelating ability of the headgroup to a limited extent. The coordination of Cu(2+) ions was investigated in particular, using UV-visible spectroscopy. By constructing Job's plots, it was found that 4-C12-DTPA could coordinate up to two Cu(2+) ions. Surface tension measurements and NMR diffusometry showed that the coordination of metal ions affected the solution behavior of 4-C12-DTPA, but there were no specific trends between the studied divalent metal complexes. Generally, the effects of the metal ion coordination could be linked to the neutralization of the headgroup charge of 4-C12-DTPA, and the resulting reduced electrostatic repulsions between adjacent surfactants in micelles and monolayers. The pH vs concentration plots, on the other hand, showed a distinct difference between 4-C12-DTPA complexes of the alkaline earth metals and the transition metals. This was explained by the difference in coordination between the two groups of metal ions, as predicted by the hard and soft acid and base (HSAB) theory. PMID:24702119

Svanedal, Ida; Boija, Susanne; Almesåker, Ann; Persson, Gerd; Andersson, Fredrik; Hedenström, Erik; Bylund, Dan; Norgren, Magnus; Edlund, Håkan

2014-04-29

89

Complex unconstrained three-dimensional hand movement and constant equi-affine speed.  

PubMed

One long-established simplifying principle behind the large repertoire and high versatility of human hand movements is the two-thirds power law-an empirical law stating a relationship between local geometry and kinematics of human hand trajectories during planar curved movements. It was further generalized not only to various types of human movements, but also to motion perception and prediction, although it was unsuccessful in explaining unconstrained three-dimensional (3D) movements. Recently, movement obeying the power law was proved to be equivalent to moving with constant planar equi-affine speed. Generalizing such motion to 3D space-i.e., to movement at constant spatial equi-affine speed-predicts the emergence of a new power law, whose utility for describing spatial scribbling movements we have previously demonstrated. In this empirical investigation of the new power law, subjects repetitively traced six different 3D geometrical shapes with their hand. We show that the 3D power law explains the data consistently better than both the two-thirds power law and an additional power law that was previously suggested for spatial hand movements. We also found small yet systematic modifications of the power-law's exponents across the various shapes, which further scrutiny suggested to be correlated with global geometric factors of the traced shape. Nevertheless, averaging over all subjects and shapes, the power-law exponents are generally in accordance with constant spatial equi-affine speed. Taken together, our findings provide evidence for the potential role of non-Euclidean geometry in motion planning and control. Moreover, these results seem to imply a relationship between geometry and kinematics that is more complex than the simple local one stipulated by the two-thirds power law and similar models. PMID:19073811

Maoz, Uri; Berthoz, Alain; Flash, Tamar

2009-02-01

90

Simple scheme for universal linear-optics quantum computing with constant experimental complexity using fiber loops  

NASA Astrophysics Data System (ADS)

Recently, Motes, Gilchrist, Dowling, and Rohde [Phys. Rev. Lett. 113, 120501 (2014)., 10.1103/PhysRevLett.113.120501] presented a scheme for photonic boson sampling using a fiber-loop architecture. Here we show that the same architecture can be modified to implement full, universal linear-optics quantum computing, in various incarnations. The scheme employs two embedded fiber loops, a single push-button photon source, three dynamically controlled beamsplitters, and a single time-resolved photodetector. The architecture has only a single point of interference, and thus may be significantly easier to align than other schemes. The experimental complexity of the scheme is constant, irrespective of the size of the computation, limited only by fiber lengths and their respective loss rates.

Rohde, Peter P.

2015-01-01

91

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

PubMed

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

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

2011-05-01

92

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

93

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

94

Rosette: Understanding Star Formation in Molecular Cloud Complexes  

NASA Astrophysics Data System (ADS)

We propose Chandra imaging of three embedded clusters in the Rosette Molecular Cloud (RMC) complex. With complementary existing Spitzer and FLAMINGOS infrared surveys, the Chandra observation is critical for us to: (1) create a complete census of the young stars in the cloud; (2) study the spatial distribution of the young stars in different evolutionary stages within the RMC and the disk frequency in the embedded clusters; (3) construct X-ray Luminosity Function (XLF) and Initial Mass Function (IMF) for the clusters to examine XLF/IMF variations; (4) elucidate star formation history in this complex.

Wang, Junfeng

2010-09-01

95

Formation of complex and unstable chromosomal translocations in yeast.  

PubMed

Genome instability, associated with chromosome breakage syndromes and most human cancers, is still poorly understood. In the yeast Saccharomyces cerevisiae, numerous genes with roles in the preservation of genome integrity have been identified. DNA-damage-checkpoint-deficient yeast cells that lack Sgs1, a RecQ-like DNA helicase related to the human Bloom's-syndrome-associated helicase BLM, show an increased rate of genome instability, and we have previously shown that they accumulate recurring chromosomal translocations between three similar genes, CAN1, LYP1 and ALP1. Here, the chromosomal location, copy number and sequence similarity of the translocation targets ALP1 and LYP1 were altered to gain insight into the formation of complex translocations. Among 844 clones with chromosomal rearrangements, 93 with various types of simple and complex translocations involving CAN1, LYP1 and ALP1 were identified. Breakpoint sequencing and mapping showed that the formation of complex translocation types is strictly dependent on the location of the initiating DNA break and revealed that complex translocations arise via a combination of interchromosomal translocation and template-switching, as well as from unstable dicentric intermediates. Template-switching occurred between sequences on the same chromosome, but was inhibited if the genes were transferred to different chromosomes. Unstable dicentric translocations continuously gave rise to clones with multiple translocations in various combinations, reminiscent of intratumor heterogeneity in human cancers. Base substitutions and evidence of DNA slippage near rearrangement breakpoints revealed that translocation formation can be accompanied by point mutations, and their presence in different translocation types within the same clone provides evidence that some of the different translocation types are derived from each other rather than being formed de novo. These findings provide insight into eukaryotic genome instability, especially the formation of translocations and the sources of intraclonal heterogeneity, both of which are often associated with human cancers. PMID:20711256

Schmidt, Kristina H; Viebranz, Emilie; Doerfler, Lillian; Lester, Christina; Rubenstein, Aaron

2010-01-01

96

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. PMID:21396112

2011-01-01

97

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

98

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

NASA Astrophysics Data System (ADS)

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

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

2002-01-01

99

A direct determination of the dissociation constant for the Cu(II) complex of amyloid beta 1-40 peptide.  

PubMed

Interactions of amyloid beta (Abeta) peptides with Cu(II) are believed to play a crucial role in the molecular mechanisms of neurotoxicity of Alzheimer's disease. There is, however, a serious disagreement regarding the strength of Cu(II) binding to these peptides. We used recombinant amyloid beta peptide 1-40 (Abeta40) to determine the stoichiometry and dissociation constants of Cu(II)-Abeta40 complexes using fluorescence spectroscopy. A single Cu(Abeta40) complex, characterized with the conditional dissociation constant K(d)(cond) = 57 +/- 5 nM was identified. This complex does not bind Hepes buffer molecules, as indicated by the total lack of relationship between K(d)(cond) values and Hepes concentration. The differences between this and other determinations of this constant and its relevance for the understanding of Cu(II) interaction with Abeta peptides are discussed. PMID:19911803

Rózga, Ma?gorzata; K?oniecki, Marcin; Dadlez, Micha?; Bal, Wojciech

2010-02-15

100

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

101

Mercury(II) penicillamine complex formation in alkaline aqueous solution.  

PubMed

The complex formation between mercury(II) and penicillamine (H(2)Pen = 3,3'-dimethyl cysteine) in alkaline aqueous solutions (pH approximately 2) has been investigated with extended X-ray absorption fine structure (EXAFS) and 199Hg NMR spectroscopy. By varying the penicillamine concentration (C(H(2)Pen) = 0.2-1.25 M) in approximately 0.1 M Hg(II) solutions, two coexisting major species [Hg(Pen)2](2-) and [Hg(Pen)3](4-) were characterized with mean Hg-S bond distances 2.34(2) and 2.44(2) A, respectively. The [Hg(Pen)2](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) A. The same type of coordination is also found for the corresponding [Hg(Cys)2](2-) complex in alkaline aqueous solution with the mean bond distances Hg-S 2.34(2) A and Hg-N 2.56(2) A. The relative amounts of the [Hg(Pen)2](2-) and [Hg(Pen)3](4-) complexes were estimated by fitting linear combinations of the EXAFS oscillations to the experimental spectra. Also their (199)Hg NMR chemical shifts were used to evaluate the complex formation, showing that the [Hg(Pen)3](4-) complex dominates already at moderate excess of the free ligand ([Pen(2-)] > approximately 0.1 M). PMID:17940647

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

2007-11-01

102

Ligand basicity and rigidity control formation of macrocyclic polyamino carboxylate complexes of gadolinium(III)  

SciTech Connect

The formation reaction rates of some macrocyclic polyamino carboxylate complexes of gadolinium, GdL (where L is DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, H[sub 3]L, HP-DO3A = 10-(hydroxyproyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, H[sub 3]L, and DO3MA = (1R,4R,7R)-[alpha],[alpha][prime],[alpha][double prime]-trimethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-triacetic acid, H[sub 3]L), have been measured at 25.0 [+-] 0.1 [degrees]C and at a constant ionic strength of 1.0 (NaCl) by an indicator method. The formation reactions are first order in the limiting reagent (ligand) and nearly independent of the excess reagent (gadolinium ion). A mechanism of the formation of the gadolinium complexes involves the formation of a precursor (intermediate) complex, Gd(*HL), in an equilibrium step followed by its deprotonation and reorganization to the final product in the rate-determining step. The stability constants (log K[sub Gd(*HL)]) of the intermediate have been determined from the kinetic data and the values are 8.9 (DO3A), 9.0(HP-DO3A), and 10.7 (DO3MA). The nature of the intermediate is proposed in which the metal is coordinated to oxygens and at least one nitrogen of the ligand. Deprotonation and reorganization of the intermediate are specific-base assisted. The second-order rate constants (k[sub OH], M[sup [minus]1]s[sup [minus]1]) for the reorganization of the intermediate, Gd(*HL) (L are given in the parentheses), are (2.1 [+-] 0.1) x 10[sup 7] (DO3A), (1.23 [+-] 0.04) x 10[sup 7] (HP-DO3A), and (7.2 [+-] 0.3) x 10[sup 4] (DO3MA), compared to the literature data (7.1 [+-] 1) x 10[sup 7] (NOTA) and (5.9 [+-] 0.2) x 10[sup 6] (DOTA). The specific-base assisted rate of reorganization of the intermediate, Gd(*HL), is correlated with the ligand strain energy and its first protonation constant.

Kumar, K.; Tweedle, M.F. (Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, NJ (United States))

1993-09-29

103

Selective Na(+)/K(+) effects on the formation of ?-cyclodextrin complexes with aromatic carboxylic acids: competition for the guest.  

PubMed

We investigated the effects of K(+) and Na(+) ions on the formation of ?-cyclodextrin complexes with ionized aromatic carboxylic acids. Using solution calorimetry and (1)H NMR, we performed the thermodynamic and structural investigation of ?-cyclodextrin complex formation with benzoic and nicotinic acids in different aqueous solutions containing K(+) and Na(+) ions as well as in pure water. The experiments show that the addition of sodium ions to solution leads to a decrease in the binding constants of the carboxylic acids with ?-cyclodextrin as compared to pure water and solutions containing potassium ions. From another side, the effect of potassium ions on the binding constants is insignificant as compared to pure water solution. We suggest that the selectivity of cation pairing with carboxylates is the origin of the difference between the effects of sodium and potassium ions on complex formation. The strong counterion pairing between the sodium cation and the carboxylate group shifts the equilibrium toward dissociation of the binding complexes. In turn, the weak counterion pairing between the potassium cation and the carboxylate group has no effect on the complex formation. We complemented the experiments with molecular modeling, which shows the molecular scale details of the formation of cation pairs with the carboxylate groups of the carboxylic acids. The fully atomistic molecular simulations show that sodium ions mainly form direct contact pairs with the carboxylate group. At the same time, potassium ions practically do not form direct contact pairs with the carboxylate groups and usually stay in the second solvation shell of carboxylate groups. That confirms our hypotheses that the selective formation of ion pairs is the main cause of the difference in the observed effects of sodium and potassium salts on the guest-host complex formation of ?-cyclodextrin with aromatic carboxylic acids. We propose a molecular mechanism explaining the effects of salts, based on competition between the cations and ?-cyclodextrin for binding with the ionized carboxylic acids. PMID:20843099

Terekhova, Irina V; Romanova, Anastasia O; Kumeev, Roman S; Fedorov, Maxim V

2010-10-01

104

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

PubMed

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

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

2014-11-26

105

FORMATION AND DISTRIBUTION OF NUCLEAR PORE COMPLEXES IN INTERPHASE  

PubMed Central

The possibility of nuclear pore formation in the interphase nucleus was investigated in control and phytohemagglutinin (PHA) stimulated lymphocytes by the freeze-etching technique. 48 hr after the addition of PHA, the newly formed blasts which had not as yet divided had at least twice the number of pores per nucleus as controls. This clearly demonstrates that in lymphocytes nuclear pore formation can take place during interphase. It has generally been assumed that the distribution of nuclear pore complexes in somatic animal cells is random. However, we have utilized freeze etched rat kidney cells and a computer program to evaluate pore distribution. We find a minimum pore center-to-center spacing of approximately 1300 A and multiples thereof with high frequency. This is strong evidence for a nonrandom distribution of nuclear pores. The nonrandomness may be related to an underlying chromosomal organization in interphase. Using three criteria for identifying prospective pore sites (membrane specialization, nonrandomness, and alteration of heterochromatin distribution), we have found forming pores in sectioned material from cultured human melanoma cells. While nuclear pore formation may take place in conjunction with reformation of the nuclear membrane, a mechanism also exists for their formation during interphase. PMID:5165267

Maul, Gerd G.; Price, Joseph W.; Lieberman, Michael W.

1971-01-01

106

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

107

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

108

Formation and working mechanism of the picornavirus VPg uridylylation complex.  

PubMed

The initiation of picornavirus replication is featured by the uridylylation of viral protein genome-linked (VPg). In this process, viral RNA-dependent RNA polymerase (RdRp) catalyzes two uridine monophosphate (UMP) molecules to the hydroxyl group of the third tyrosine residue of VPg. Subsequently, the uridylylated VPg (VPg-pUpU) functions as the protein primer to initiate the replication of the viral genome. Although a large body of functional and structural works has been performed to define individual snapshots for particular stages of the VPg uridylylation process, the formation, dynamics and mechanism of the whole VPg uridylylation complex still requires further elucidation. We would like to provide an overview of the current knowledge of the picornaviral VPg uridylylation complex in this paper. PMID:25240314

Sun, Yuna; Guo, Yu; Lou, Zhiyong

2014-12-01

109

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

110

Molecular determinants of orexin receptor-arrestinubiquitin complex formation  

PubMed Central

Background and Purpose:?The orexin system regulates a multitude of key physiological processes, particularly involving maintenance of metabolic homeostasis. Consequently, there is considerable potential for pharmaceutical development for the treatment of disorders from narcolepsy to metabolic syndrome. It acts through the hormonal activity of two endogenous peptides, orexin A binding to orexin receptors 1 and 2 (OX1 and OX2) with similar affinity, and orexin B binding to OX2 with higher affinity than OX1 receptors. We have previously revealed data differentiating orexin receptor subtypes with respect to their relative stability in forming orexin receptor-arrestin-ubiquitin complexes measured by BRET. Recycling and cellular signalling distinctions were also observed. Here, we have investigated, using BRET, the molecular determinants involved in providing OX2 receptors with greater ?-arrestin-ubiquitin complex stability. Experimental Approach:?The contribution of the C-terminal tail of the OX receptors was investigated by bulk substitution and site-specific mutagenesis using BRET and inositol phosphate assays. Key Results:?Replacement of the OX1 receptor C-terminus with that of the OX2 receptor did not result in the expected gain of function, indicating a role for intracellular domain configuration in addition to primary structure. Furthermore, two out of the three putative serine/threonine clusters in the C-terminus were found to be involved in OX2 receptor-?-arrestin-ubiquitin complex formation. Conclusions and Implications:?This study provides fundamental insights into the molecular elements that influence receptor-arrestin-ubiquitin complex formation. Understanding how and why the orexin receptors can be functionally differentiated brings us closer to exploiting these receptors as drug targets. Linked Articles:?This article is part of a themed section on Orexin Receptors. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-2 PMID:24206104

Jaeger, Werner C; Seeber, Ruth M; Eidne, Karin A; Pfleger, Kevin DG

2014-01-01

111

Depassivation of aged Fe 0 by divalent cations: correlation between contaminant degradation and surface complexation constants.  

PubMed

The dechlorination of trichloroethylene (TCE) by aged Fe(0) in the presence of a series of divalent cations was investigated with the result that while no significant degradation of TCE was observed in Milli-Q water or in solutions of Ba(2+), Sr(2+), or Ca(2+), very effective TCE removal was observed in solutions containing Mg(2+), Mn(2+), Co(2+), Fe(2+), Ni(2+), Zn(2+), Cu(2+), or Pb(2+). The rate constants of TCE removal in the presence of particular cations were positively correlated to the log K representing the affinity of the cations for hydrous ferric oxide (HFO) surface sites though the treatments with Co(2+) and Ni(2+) were found to provide particularly strong enhancement in TCE degradation rate. The extent of Fe(II) release to solution also increased with increase in log K, while the solution pH from both experimental measurement and thermodynamic calculation decreased with increasing log K. While the peak areas of Fe and O XPS spectra of the passivated ZVI in the presence of Ba(2+), Sr(2+), and Ca(2+) were very close to those in Milli-Q water, very significant increases in surface Fe and O (and OH) were observed in solutions of Mg(2+), Mn(2+), Co(2+), Fe(2+), Ni(2+), Zn(2+), Cu(2+) and Pb(2+), revealing that the surface oxide layer dissolution is consistent with the recovery of aged Fe(0) with respect to TCE degradation. The depassivation process is proposed to involve (i) surface complexation of cations on surface coatings of aged Fe(0), (ii) dissolution of the hydrated surface as a consequence of magnetite exposure, and (iii) transport of electrons from underlying Fe(0) via magnetite to TCE, resulting in TCE dechlorination and, for some cations (Co(2+), Ni(2+), Cu(2+), and Pb(2+)), reduction to their zero or +1 valence state (with potential for these reduced metals to enhance TCE degradation). PMID:25383907

Liu, Tongxu; Li, Xiaomin; Waite, T David

2014-12-16

112

Characterization of Hydrogen Complex Formation in III-V Semiconductors  

SciTech Connect

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

Williams, Michael D.

2006-09-28

113

Ion wake formation with dust charge fluctuation in complex plasma  

SciTech Connect

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

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

2013-11-15

114

Spectrophotometric quantification of the thermodynamic constants of the complexes formed by dopamine and Cu(II) in aqueous media.  

PubMed

The thermodynamic constants of the complex Cu(II)-dopamine in aqueous solution were evaluated from spectrophotometric data using the software SQUAD. It was found that there exist Cu(II):DA complexes with 1:1 and 1:2 stoichiometries and that their predominance depends on both the solution pH and the [Cu(II)]/[DA] ratio. Moreover, it is shown that the solubility of Cu(OH)2(s) increases drastically when these complexes are thermodynamically stable. PMID:25727295

Verastegui-Omaña, B; Palomar-Pardavé, M; Rojas-Hernández, A; Corona Avendaño, S; Romero-Romo, M; Ramírez-Silva, M T

2015-05-15

115

[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

116

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

SciTech Connect

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

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

2005-08-19

117

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

PubMed

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

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

2015-04-01

118

Incipient species formation in salamanders of the Ensatina?complex  

PubMed Central

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

Wake, David B.

1997-01-01

119

Quantitative serine protease assays based on formation of copper(II)-oligopeptide complexes.  

PubMed

A quantitative protease assay based on the formation of a copper-oligopeptide complex is developed. In this assay, when a tripeptide GGH fragment is cleaved from an oligopeptide chain by serine proteases, the tripeptide quickly forms a pink GGH/Cu(2+) complex whose concentration can be determined quantitatively by using UV-Vis spectroscopy. Therefore, activities of serine proteases can be determined from the formation rate of the GGH/Cu(2+) complex. This principle can be used to detect the presence of serine protease in a real-time manner, or measure proteolytic activities of serine protease cleaving different oligopeptide substrates. For example, by using this assay, we demonstrate that trypsin, a model serine protease, is able to cleave two oligopeptides GGGGKGGH () and GGGGRGGH (). However, the specificity constant (kcat/Km) for is higher than that of (6.4 × 10(3) mM(-1) min(-1)vs. 1.3 × 10(3) mM(-1) min(-1)). This result shows that trypsin is more specific toward arginine (R) than lysine (K) in the oligopeptide sequence. PMID:25386732

Ding, Xiaokang; Yang, Kun-Lin

2015-01-01

120

Viswanath's constant Mills' constant  

E-print Network

Viswanath's constant Mills' constant Conway's constant Constant Curiosity Norman Do Not all numbers Constant Curiosity #12;Viswanath's constant Mills' constant Conway's constant The Fibonacci sequence, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, . . . Norman Do Constant Curiosity #12;Viswanath

Do, Norman

121

Paramagnetic relaxation enhancements in acetate and its fluorine derivatives interacting with Gd3+: complex formation, structure, and transmetallation.  

PubMed

The relative spatial distribution and motion with respect to Gd(3+) of the (1)H and (19)F nuclei in the acetate ion and its fluorine derivatives are studied in D(2)O solutions through the paramagnetic relaxation rate enhancements (PREs) of these nuclei. We derive general theoretical expressions of the longitudinal PRE in terms of the analytical concentrations of metal and ligands, formation constants of the complexes, metal-nucleus distances, and coordination lifetimes of the ligands. The observed formation constants of the 1 metal: 1 ligand complexes markedly decrease with increasing number of fluorine atoms, the electronegativity of which reduces the negative partial charge of the coordinating COO(-) group. The coordination lifetimes are very short at the scale of the relaxation times of the protons of metal bound acetate, that is, shorter than about 10 ?s. The average distance of the acetate protons from Gd(3+) is in fair agreement with independent crystallographic determination. The release of free Gd(3+) from the very stable Gddtpa (dtpa=diethylene-triaminepentaacetate) complex caused by the competition of Zn(2+) for dtpa, is evidenced by an increase of the PREs with Zn(2+) concentration. The observed PRE increase is consistent with the known equilibrium constants governing the speciation involving Gd(3+), Zn(2+), and dtpa. The present case study illustrates a method which easily yields experimental tunable properties suitable to test the ongoing theories of lanthanide Ln(3+) complexation in solution. PMID:20979086

Bonnet, Célia S; Fries, Pascal H

2010-11-15

122

Thermodynamic study of complex formation between Ce3+ and cryptand 222 in some binary mixed nonaqueous solvents  

NASA Astrophysics Data System (ADS)

The stoichiometry, stability and the thermodynamic parameters of complex formation between cerium(III) cation and cryptand 222 (4,7,13,16,21,24-hexaoxa-1,10-diazabycyclo[8.8.8]-hexacosane) were studied by conductometric titration method in some binary solvent mixtures of dimethylformamide (DMF), 1,2-dichloroethane (DCE), ethyl acetate (EtOAc) and methyl acetate (MeOAc) with methanol (MeOH), at 288, 298, 308, and 318 K. A model based on 1: 1 stoichiometry has been used to analyze the conductivity data. The data have been fitted according to a non-linear least-squares analysis that provide the stability constant, K f, for the cation-ligand inclusion complex. The results revealed that the stability order of [Ce(cryptand 222)]3+ complex changes with the nature and composition of the solvent system. A non-linear relationship was observed between the stability constant (log K f) of [Ce(cryptand 222)]3+ complex versus the composition of the binary mixed solvent. Standard thermodynamic values were obtained from temperature dependence of the stability constant of the complex, show that the studied complexation process is mainly entropy governed and are influenced by the nature and composition of the binary mixed solvent solutions.

Rounaghi, G. H.; Dolatshahi, S.; Tarahomi, S.

2014-12-01

123

Cadmium(II) Complex Formation with Cysteine and Penicillamine  

PubMed Central

The complex formation between cadmium(II) and the ligands cysteine (H2Cys) or penicillamine (H2Pen = 3, 3?-dimethylcysteine) in aqueous solutions, containing CCd(II) ? 0.1 mol dm-3 and CH2L = 0.2 – 2 mol dm-3, was studied at pH = 7.5 and 11.0 by means of 113Cd-NMR and Cd K- and L3-edge X-ray absorption spectroscopy. For all cadmium(II)-cysteine mole ratios the mean Cd-S and Cd-(N/O) bond distances were found in the ranges 2.52 – 2.54 Å and 2.27 – 2.35 Å, respectively. The corresponding cadmium(II)-penicillamine complexes showed slightly shorter Cd-S bonds, 2.50 – 2.53 Å, but with the Cd-(N/O) bond distances in a similar wide range, 2.28 – 2.33 Å. For the mole ratio CH2L / CCd(II) = 2, the 113Cd chemical shifts, in the range 509 – 527 ppm at both pH values, indicated complexes with distorted tetrahedral CdS2N(N/O) coordination geometry. With a large excess of cysteine (mole ratios CH2Cys / CCd(II) ? 10) complexes with CdS4 coordination geometry dominate, consistent with the 113Cd NMR chemical shifts, ? ? 680 ppm at pH 7.5 and 636 - 658 ppm at pH 11.0, and their mean Cd-S distances of 2.53 ± 0.02 Å. At pH 7.5, the complexes are almost exclusively sulfur-coordinated as [Cd(S-cysteinate)4]n-, while at higher pH the deprotonation of the amine groups promotes chelate formation, and at pH 11.0 a minor amount of the [Cd(Cys)3]4- complex with CdS3N coordination is formed. For the corresponding penicillamine solutions with mole ratios CH2Pen / CCd(II) ? 10, the 113Cd-NMR chemical shifts, ? ? 600 ppm at pH 7.5 and 578 ppm at pH 11.0, together with the average bond distances Cd-S 2.53 ± 0.02 Å and Cd-O 2.30 – 2.33 Å, indicate that [Cd(penicillaminate)3]n- complexes with chelating CdS3(N/O) coordination dominate already at pH 7.5, and become mixed with CdS2N(N/O) complexes at pH 11.0. The present study reveals differences between cysteine and penicillamine as ligands to the cadmium(II) ion that can explain why cysteine-rich metallothionines are capable of capturing cadmium(II) ions, while penicillamine, clinically useful for treating the toxic effects of mercury(II) and lead(II) exposure, is not efficient against cadmium(II) poisoning. PMID:19469490

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

2009-01-01

124

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

125

Polyelectrolyte synthesis and in situ complex formation in ionic liquids.  

PubMed

For the first time, polyelectrolyte complex (PEC) capsules were prepared from a water insoluble polyanion, namely cellulose sulfates (CSs) with a degree of substitution (DS) below 0.2 in ionic liquids (IL). Capsules prepared via interaction with the polycation poly(dimethyldiallyammonium chloride) were free of residual IL and possessed an outer shell and a hollow inner core that made them ideal containers for enzyme mediated reactions. Due to the reestablished hydrogen bond system of the low substituted CS, the capsules showed increased stability, compared to the products obtained by application of the common aqueous preparation. Encapsulation of glucose oxidase demonstrated that the steps of CS preparation, PEC capsule formation, and encapsulation could be combined in a single pot, with the elimination of time and cost consuming isolation and purification steps. PMID:19754182

Gericke, Martin; Liebert, Tim; Heinze, Thomas

2009-09-23

126

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

127

IgA nephropathy: current views of immune complex formation.  

PubMed

Characteristic features of IgA nephropathy (IgAN) include IgA1-containing immune complexes (IC) in the circulation, urine, and renal mesangium. IC contain IgA1 deficient in hinge region-associated galactose (Gal) and antibodies specific for antigenic determinants present on the hinge region. The biological effects of IC are primarily related to their molecular size and composition: when added to a culture of human mesangial cells, large IC exhibit a proliferative effect while small complexes are inhibitory. These activities have been observed using IC obtained from sera of IgAN patients or generated in vitro. Specifically, various preparations of human IgA1 with modified glycan moieties formed IC in vitro when incubated with sera from IgAN patients or healthy individuals, cord blood serum, or tissue culture supernatants of EBV-immortalized peripheral blood B cells secreting IgG. Interestingly, IgG antibodies specific for the IgA1 Gal-deficient hinge region are commonly found in sera of hominoid as well as non-hominoid primates and many other vertebrate species, and suggest the evolutionary uniqueness of the human IgA1 hinge region. Because of the molecular defect in IgA1 glycosylation and its subsequent recognition by naturally-occurring antibodies, experimental approaches that diminish or prevent formation of large immunostimulatory IC should be further explored. PMID:17495438

Mestecky, Jiri; Suzuki, Hitoshi; Yanagihara, Takeshi; Moldoveanu, Zina; Tomana, Milan; Matousovic, Karel; Julian, Bruce A; Novak, Jan

2007-01-01

128

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

129

Simple and universal method to determine dissociation constants for enzyme/ligand complexes.  

PubMed

A simple and in principle universal method is proposed for measuring enzyme/ligand dissociation constants. The method is based on measuring enzyme activity remaining after heat treatment in the absence and in the presence of ligands. The method is especially suitable for enzymes interacting with nucleosides, nucleosides and oligonucleotides since for such enzymes convenient spectrophotometric assays are available. PMID:18776557

Bzowska, Agnieszka; Magnowska, Lucyna

2008-01-01

130

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

PubMed Central

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

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

2013-01-01

131

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

132

Formation and characterization of an insoluble polyelectrolyte complex: Chitosan-polyacrylic acid  

Microsoft Academic Search

Chitosan and polyacrylic acid mixtures were prepared in different mole ratios and at different pH values and ionic strengths (0.025–0.300). Complex formation was detected by turbidity measurement and quantified by weighing the freeze dried pellet recovered by centrifugation. No insoluble complex formation at pH=2 was detected. In the 3 to 6 pH range, the maximum complex formation occurred at different

Visith Chavasit; Carlos Kienzle-Sterzer; J. Antonio Torres

1988-01-01

133

Formation of discharge plasma on the surface of cathodes with different dielectric constants  

NASA Astrophysics Data System (ADS)

We present a detailed study of the spatial and temporal evolution of visible light emission from plasma formed on the surface of ferroelectrics [Pb(Zr,Ti)O3 and BaTiO3] and a printed-circuit board under the application of a high-voltage pulse. For all samples studied, plasma formation occurs within the first 5 ns from the start of the high-voltage pulse. It is shown that the plasma appears at the edges of the front strip electrodes. Further, the plasma spreads along the dielectric surface covering it partially. It is found that the uniformity of the plasma and the distance of its propagation along the surface depend on the properties of the dielectric, the polarity and amplitude of the high-voltage pulse, and the vacuum conditions. A qualitative model which explains the observed experimental data is suggested.

Krasik, Ya. E.; Dunaevsky, A.; Felsteiner, J.

1999-06-01

134

Integrin activation and focal complex formation in cardiac hypertrophy  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

135

Star Formation in the Northern Cloud Complex of NGC 2264  

E-print Network

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

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

2006-01-01

136

Star Formation in the Northern Cloud Complex of NGC 2264  

E-print Network

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

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

2006-03-09

137

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

138

Two-column ion-exchange method for the determination of copper-complexing capacity and conditional stability constants of copper complexes for ligands in natural waters.  

PubMed

Sample solutions titrated with Cu(2+) ions are passed sequentially through two ion-exchange columns in an automated flow system. The first column is packed with Chelex-100 resin and retains Cu(2+) ions that are free or derived from copper complexes that dissociate in the column. The second column is packed with AG MP-1 anion-exchange resin and retains negatively charged Cu(II) complexes. The retained copper species are then eluted from the columns and determined on-line with a flame atomic-absorption spectrophotometer. It is necessary to correct for a small fraction of free Cu(2+) ions that pass through the first column and are retained by the second column. The Cu(II)-complexing capacity of sample solutions is determined from plots of the concentration ratio of free Cu(2+) ions to Cu(II) complexes vs. the concentration of free Cu(2+) ions. Conditional stability constants of the copper complexes are also estimated from these plots. The complexing capacity of sample solutions is also determined rapidly by measuring the concentration of complexed Cu(II) after spiking the sample with an excess of Cu(2+) ions. The sample solutions tested were 4.0muM NTA, 4.0-mg/l. humic acid, and a river water. PMID:18964688

Liu, Y; Ingle, J D

1989-01-01

139

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

140

Ligand(s)-to-metal charge transfer as a factor controlling the equilibrium constants of late first-row transition metal complexes: revealing the Irving-Williams thermodynamical series.  

PubMed

A unified relationship between the experimental formation constants and the ligand(s)-to-metal charge transfer values of versatile ligand complexes of late transition series first-row bivalent metal ions is uncovered. The latter property not only explicates the Irving-Williams series but also rationalizes quantitatively Pearson's concept of hard and soft acids and bases by correlating the gas-phase to aqueous solution-phase chemistry in a broad sense. PMID:25414118

Varadwaj, Pradeep R; Varadwaj, Arpita; Jin, Bih-Yaw

2015-01-14

141

Determination of conditional stability constants for some divalent transition metal ion-EDTA complexes by electrospray ionization mass spectrometry.  

PubMed

Conditional stability constants of coordination complexes comprising divalent transition metals, Cu(2+), Ni(2+), Zn(2+), Co(2+), and ethylenediaminetetraacetic acid (EDTA) were determined utilizing electrospray ionization mass spectrometry. The deviation of signal response of a reference complex was monitored at addition of a second metal ion. The conditional stability constant for the competing metal was then determined through solution equilibria equations. The method showed to be applicable to a system where Co(2+) and Zn(2+) competed for EDTA at pH?5. When Cu(2+) and Ni(2+) competed for EDTA, the equilibrium changed over time. This change was shown to be affected in rate and size by the type of organic solvent added. In this work, 30% of either methanol or acetonitrile was used. It was found that if calibration curves are prepared for both metal complexes in solution and the measurements are repeated with sufficient time space, any change in equilibrium of sample solutions will be discovered. PMID:25044839

Boija, Susanne; Almesåker, Ann; Hedenström, Erik; Bylund, Dan; Edlund, Håkan; Norgren, Magnus

2014-07-01

142

Wind profile constants in a neutral atmospheric boundary layer over complex terrain  

Microsoft Academic Search

The roughness height z0 and the zero-plane displacement height d0 were determined for a region of complex terrain in the Pre-Alps of Switzerland. This region is characterized by hills of the order of 100 m above the valley elevations, and by distances between ridges of the order of 1 km; it lies about 20 to 30 km north from the

William P. Kustas; Wilfried Brutsaert

1986-01-01

143

Glutathione Complex Formation with Mercury(II) in Aqueous Solution at Physiological pH  

PubMed Central

The mercury(II) complexes formed in neutral aqueous solution with glutathione (GSH, here denoted AH3 in its tri-protonated form) were studied using Hg LIII-edge extended X-ray absorption fine structure (EXAFS) and 199Hg NMR spectroscopy, complemented with electrospray ionization mass spectrometric (ESI-MS) analyses. The [Hg(AH)2]2? complex, with the Hg-S bond distances 2.325 ± 0.01 Å in linear S-Hg-S coordination and the 199Hg NMR chemical shift ?984 ppm, dominates except at high excess of glutathione. In a series of solutions with CHg(II) ~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)3]4? complex. ESI-MS peaks appear at ?m/z values of 1208 and 1230 corresponding to the [Na4Hg(AH)2(A)]? and [Na5Hg(AH)(A)2]? 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 LIII-edge EXAFS and 199Hg NMR spectra show that at high excess of glutathione (~0.35 mol·dm?3) about ~ 70% of the total mercury(II) concentration is present as the [Hg(AH)3]4? complex, with the average Hg-S bond distance 2.42 ± 0.02 Å in trigonal HgS3 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)3]4? complex, and also for the [Hg(A)4]10? complex that is present at high pH. For Hg(II) in low concentration at physiological conditions (pH = 7.4, CGSH = 2.2 mM) the relative amounts in the HgS2 species [Hg(AH)2]2?, [Hg(AH)(A)]3? and the HgS3 complex [Hg(AH)3]4? was 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. PMID:21073204

Mah, Vicky; Jalilehvand, Farideh

2010-01-01

144

Glutathione complex formation with mercury(II) in aqueous solution at physiological pH.  

PubMed

The mercury(II) complexes formed in neutral aqueous solution with glutathione (GSH, here denoted AH(3) in its triprotonated form) were studied using Hg L(III)-edge extended X-ray absorption fine structure (EXAFS) and (199)Hg NMR spectroscopy, complemented with electrospray ionization mass spectrometric (ESI-MS) analyses. The [Hg(AH)(2)](2-) complex, with the Hg-S bond distances at 2.325 ± 0.01 Å in linear S-Hg-S coordination, and the (199)Hg NMR chemical shift at -984 ppm, dominates except at high excess of glutathione. In a series of solutions with C(Hg(II)) ?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)(3)](4-) complex. ESI-MS peaks appear at -m/z values of 1208 and 1230 corresponding to the [Na(4)Hg(AH)(2)(A)](-) and [Na(5)Hg(AH)(A)(2)](-) species, respectively. In another series of solutions at pH 7.0 with C(Hg(II)) ?50 mM and GSH/Hg(II) ratios from 2.0 to 10.0, the Hg L(III)-edge EXAFS and (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)(3)](4-) complex, with the average Hg-S bond distance 2.42 ± 0.02 Å in trigonal HgS(3) coordination. The proportions of HgS(n) 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)(3)](4-) complex and also for the [Hg(A)(4)](10-) complex that is present at high pH. For Hg(II) in low concentration at physiological conditions (pH 7.4, C(GSH) = 2.2 mM), the relative amounts of the HgS(2) species [Hg(AH)(2)](2-), [Hg(AH)(A)](3-), and the HgS(3) complex [Hg(AH)(3)](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. PMID:21073204

Mah, Vicky; Jalilehvand, Farideh

2010-11-15

145

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

SciTech Connect

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

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

2014-01-01

146

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

147

Hydrophobic and steric effects on the ion-pair formation of tris(1,10-phenanthroline)iron(II) and arenesulfonate ions. Kinetic determination of the formation constants of the ion pairs and a /sup 1/H NMR study of their structures  

SciTech Connect

Ion-pair formation constants (K) for Fe(phen)/sub 3//sup 2 +/ and six kinds of arenesulfonate ions were obtained from kinetic studies of the aquation of the complex ion in aqueous sodium arenesulfonate solutions: K = 5 +/- 1, 13 +/- 2, 28 +/- 5, 19 +/- 3, 8 +/- 2, and 5 +/- 1 mol/sup -1/ dm/sup 3/ for benzene-, 4-methylbenzene-, 4-ethylbenzene-, 2,4-dimethylbenzene-, 1-naphthalene-, and 2-naphthalenesulfonate, respectively. An arenesulfonate of greater hydrophobicity showed a larger formation constant, except that small formation constants were shown by bulky naphthalenesulfonates. The formation constant was smaller for an arenesulfonate than for an alkanesulfonate with the same number of carbon atoms. The /sup 1/H NMR signal of arenesulfonate in the ion pair was found to shift upfield. Comparison of the observed shifts with those calculated on the basis of the current loop model supported a model of the ion pair in which the arenesulfonate ion lies in the hydrophobic cavity between two phenanthroline ligands of the complex ion with the sulfonate group directed outside the cavity.

Tachiyashiki, S.; Yamatera, H.

1986-08-27

148

Controlled formation of synthetic metal - transition metal conjugated complex systems  

Microsoft Academic Search

The controlled complexation of the emeraldine base of poly(o-toluidine) with palladium(II) compounds was achieved in an organic solvent to afford structurally defined conjugated polymer complexes. Two coordination sites are used for complexation in the case of Pd(OAc)2 or PdCl2(MeCN)2, in contrast to only one coordination site available for the palladium(II) complex bearing the tridentate ligand. Two imine moieties are capable

Toshikazu Hirao; Satoshi Yamaguchi; Shinya Fukuhara

1999-01-01

149

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

150

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

151

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

152

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

Microsoft Academic Search

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

T. Takamatsu; T. Yoshida

1978-01-01

153

Potentiometric studies on the formation equilibria of binary and ternary complexes of cobalt(II) with adenosine-5?-mono-, -di-, and -triphosphate and some biologically important polybasic oxygen acids  

Microsoft Academic Search

Potentiometric equilibrium measurements have been made for the interaction of adenosine-5'-mono-,-di-, and -triphosphate, and Co(II) with biologically important secondary ligands (malic, maleic, succinic, tartaric, citric, and oxalic acid). The formation of various 1:1:1 mixed ligand complexes inferred from the potentiometric titration curves. Initial estimates of the formation constants of the resulting species and the acid dissociation constants ofAMP,ADP,ATP and the

H. A. Azab; A. M. El-Nady; A. Hassan; R. S. A. Azkal

1994-01-01

154

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

2012-12-21

155

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

Microsoft Academic Search

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

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

2005-01-01

156

Formation of metamorphic core complex in inherited wedges: A thermomechanical modelling study  

E-print Network

Formation of metamorphic core complex in inherited wedges: A thermomechanical modelling study B Férollerie, 45071 Orléans cedex 02, France Abstract Metamorphic Core Complexes (MCCs) form when a thickened in a nappe stack involving continental basement. 1. Introduction A metamorphic core complex (MCC) corresponds

Paris-Sud XI, Université de

157

Cyclodextrin-mediated enantioseparation of phenylalanine amide derivatives and amino alcohols by capillary electrophoresis-role of complexation constants and complex mobilities.  

PubMed

The separation of the enantiomers of phenylalanine amide and N-methyl derivatives as well as some amino alcohols was studied by CE in acidic BGEs using CDs as chiral selectors. The native CDs displayed only low chiral recognition ability at a concentration of 15 mg/mL in 20 mM sodium phosphate buffer, pH 2.5. In contrast, the analyte enantiomers were separated in the presence of randomly sulfated CDs under reversed polarity of the applied voltage. Sulfated ?-CD proved to be the most universal selector resulting in the enantioseparation of all analytes. Opposite enantiomer migration order depending on the size of the CD cavity was observed for phenylalanine amide and 2-amino-2-phenylethanol. The R-enantiomers migrated first in the presence of sulfated ?-CD and ?-CD while the S-enantiomers were detected first in the presence of sulfated ?-CD. The enantioseparations could be rationalized based on analyte complexation by the respective CDs except for 2-amino-2-phenylethanol and sulfated ?-CD where essentially equal complexation constants were derived for the enantiomers. In this case, the migration behavior could be attributed to the mobilities of the enantiomer-CD complexes adding another example to the CE-specific phenomenon of enantioseparations based primarily on complex mobilities. PMID:24890817

Aranyi, Anita; Péter, Antal; Ilisz, István; Fülöp, Ferenc; Scriba, Gerhard K E

2014-10-01

158

On the prediction of 51V hyperfine coupling constants in V(IV)O complexes through DFT methods.  

PubMed

Density functional theory (DFT) calculations of the (51)V hyperfine coupling constants for 22 representative V(IV)O complexes with different donor set, electric charge and geometry were performed with Gaussian 03 software. The prediction of A tensor was carried out with five functionals (B3LYP, B3P86, B3PW91, BHandHLYP and BHandH) and four basis sets (6-31g, 6-311g, 6-311+g and 6-311g(d,p)). An excellent agreement with the experimental A(z) value (A(z)(exptl)) was obtained using half-and-half hybrid functionals, such as BHandHLYP or BHandH. They, coupled with the 6-311g(d,p) basis set, yield deviations from |A(z)|(exptl) lower than 5% and, in most of the cases, lower than 3%. PMID:19259560

Micera, Giovanni; Garribba, Eugenio

2009-03-21

159

Complex formation reactions of lanthanum(III), cerium(III), thorium(IV), dioxouranyl(IV) complexes with tricine.  

PubMed

Equilibrium studies for the heavy metal ions La(III), Ce(III), Th(IV) and UO2(IV) (M) complexes of the zwitterionic buffer tricine (L) in aqueous solution are investigated. Stoichiometry and stability constants for the different complexes formed as well as hydrolysis products of the metal cations are determined at 25 degrees C and ionic strength 0.1 M NaNO3. The stability of the formed complexes are discussed in terms of the nature of the heavy metal cation. The solid complexes are synthesized and characterized by means of elemental analysis, FTIR, and TG analysis. The general molecular formulae of the obtained complexes is suggested to be [M(L)2](NO3)n-2(H2O)x, where n = the charge of the metal cation, x = no. of water molecules. PMID:17899888

Mohamed, Mahmoud M A

2007-08-01

160

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

161

Ferric-transferrin and ferric-transferrin-anion complexes: formation and characterization.  

E-print Network

FERRIC-TRANSFERRIN AND FFRRIC-TRANSFERRIN-ANION COMPLEXES'. FORMATION AND CHARACTERIZATION A Thesis by MICHAEL RAY SCHLABACH Submitted to the Graduate College of Texas A & M University in partial fulfillment of the requirements for the degree... of MASTER OF SCIENCE December 1974 Major Subject: Biochemistry FERRIC ? TRANSFERRIN AND FERRIC-TRANSFERRIN-ANION COMPLEXES: FORMATION AND CHARACTERIZATION A Thesis MICHAEL RAY SCHLABACH Approved as to style snd content by: (' Chai of Committee) (He...

Schlabach, Michael Ray

1974-01-01

162

Physicochemical Controls on the Formation of Polynuclear Metal Complexes at Clay Mineral Surfaces  

E-print Network

Physicochemical Controls on the Formation of Polynuclear Metal Complexes at Clay Mineral Surfaces R. G. Ford Metal sorption to clay minerals may lead to the formation of secondary precipitates structurally similar to the mineral takovite. Saturation with respect to this phase is promoted, in part

Sparks, Donald L.

163

Kinetics of formation and dissociation of lanthanide(III)-DOTA complexes  

Microsoft Academic Search

Formation rates of Ce(DOTA)â, Eu(DOTA)⁻, and Yb(DOTA)⁻ were studied spectrophotmetrically. (HâDOTA = 1,4,7,10-tetraazacyclododecane-N,Nâ²,Nâ³,Nâ³â²-tretraacetic acid.) Intermediates were detected and characterized by NMR, PH-metry, and spectrophotometry. Rate constants for rearrangements of intermediates and protonation of Gd(DOTA)⁻ are reported.

Eva Toth; E. Bruecher; Istvan Lazar; Imre Toth

1994-01-01

164

A spectrophotometric study of neodymium(III) complexation in sulfate solutions at elevated temperatures  

E-print Network

A spectrophotometric study of neodymium(III) complexation in sulfate solutions at elevated The formation constants of neodymium complexes in sulfate solutions have been determined spectrophotometrically

Long, Bernard

165

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

166

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

167

Micelle formation in a dilute solution of block copolymers with a polyelectrolyte block complexed with oppositely charged linear chains  

NASA Astrophysics Data System (ADS)

The theory of micelle formation in a dilute solution mixture of polyelectrolyte/neutral diblock copolymers and oppositely charged linear chains has been developed. The core of the micelles is formed by the hydrophobic monomer units of polyelectrolyte complexes between the oppositely charged polyions while the hydrophilic uncharged blocks of the block copolymers comprise the micellar corona. The process of the formation of polyelectrolyte complexes and micelles in the solution has been described as sets of association-dissociation reactions with certain chemical constants and the concentration distribution of micellar aggregates of a given composition has been calculated for various concentrations of linear chains and block copolymer macromolecules in the solution. It was shown that the micelles are formed by nearly fully neutralized block copolymers, so that the micellar charge is close to zero. The aggregation number of the micelles and their charge slightly depend on the concentration of the block copolymers as well as the linear chains in the solution. Micelles in the solution coexist with single block copolymer chain/linear polymer complexes of different composition.

Kramarenko, E. Yu.; Khokhlov, A. R.; Reineker, P.

2003-09-01

168

Module Based Complexity Formation: Periodic Patterning in Feathers and Hairs  

PubMed Central

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

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

2012-01-01

169

Biological pattern formation: from basic mechanisms to complex structures  

NASA Astrophysics Data System (ADS)

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

Koch, A. J.; Meinhardt, H.

1994-10-01

170

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

PubMed

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

Schurr, J Michael; Fujimoto, Bryant S

2013-12-01

171

Landscape complexity influences route-memory formation in navigating pigeons.  

PubMed

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

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

2014-01-01

172

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

PubMed Central

The regulation of enzyme activity through the transient formation of multiprotein assemblies plays an important role in the control of biosynthetic pathways. One of the first regulatory complexes to be discovered was cysteine synthase (CS), formed by the pyridoxal 5?-phosphate-dependent enzyme O-acetylserine sulfhydrylase (OASS) and serine acetyltransferase (SAT). These enzymes are at the branch point of the sulfur, carbon, and nitrogen assimilation pathways. Understanding the mechanism of complex formation helps to clarify the role played by CS in the regulation of sulfur assimilation in bacteria and plants. To this goal, stopped-flow fluorescence spectroscopy was used to characterize the interaction of SAT with OASS, at different temperatures and pH values, and in the presence of the physiological regulators cysteine and bisulfide. Results shed light on the mechanism of complex formation and regulation, so far poorly understood. Cysteine synthase assembly occurs via a two-step mechanism involving rapid formation of an encounter complex between the two enzymes, followed by a slow conformational change. The conformational change likely results from the closure of the active site of OASS upon binding of the SAT C-terminal peptide. Bisulfide, the second substrate and a feedback inhibitor of OASS, stabilizes the CS complex mainly by decreasing the back rate of the isomerization step. Cysteine, the product of the OASS reaction and a SAT inhibitor, slightly affects the kinetics of CS formation leading to destabilization of the complex. PMID:20164178

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

2010-01-01

173

The complex interplay between semantics and grammar in impression formation.  

PubMed

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

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

2014-09-01

174

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

175

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

176

Carbon–heteroatom bond formation catalysed by organometallic complexes  

PubMed Central

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

Hartwig, John F.

2010-01-01

177

Complex Formation History of Highly Evolved Basaltic Shergottite, Zagami  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

178

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

179

Oxidative peptide /and amide/ formation from Schiff base complexes  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

180

Interferogram formation in the presence of complex and large deformation  

USGS Publications Warehouse

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

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

2007-01-01

181

Modeling of the formation of complex molecules in protostellar objects  

NASA Astrophysics Data System (ADS)

The results of molecular composition modeling are presented for the well studied low-mass star-forming region TMC-1 and the massive star-forming region DR21(OH), which is poorly studied from a chemical point of view. The column densities of dozens of molecules, ranging from simple diatomic to complex organic molecules, are reproduced to within an order of magnitude using a one-dimensional model for the physical and chemical structure of these regions. The chemical ages of the regions are approximately 105 years in both cases. The main desorption mechanisms that are usually included in chemical models (photodesorption, thermal desorption, and cosmic-ray-induced desorption) do not provide sufficient gasphase abundances of molecules that are synthesized in surface reactions; however, this shortcoming can be removed by introducing small amount of reactive desorption into the model. It is possible to reproduce the properties of the TMC-1 chemical composition in a standard model, without requiring additional assumptions about an anomalous C/O ratio or the recent accretion of matter enriched with atomic carbon, as has been proposed by some researchers.

Kochina, O. V.; Wiebe, D. S.; Kalenskii, S. V.; Vasyunin, A. I.

2013-11-01

182

Factors leading to the formation of arc cloud complexes  

NASA Technical Reports Server (NTRS)

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

Welshinger, Mark John; Brundidge, Kenneth C.

1987-01-01

183

An illustration of the complexity of continent formation  

NASA Technical Reports Server (NTRS)

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

Burke, Kevin

1988-01-01

184

Theoretical study on the atmospheric reaction of SO2 with the HO2 and HO2·H2O complex formation HSO4 and H2SO3  

NASA Astrophysics Data System (ADS)

The influence of a single water molecule on the gas-phase reactivity of HO2 radical has been investigated by theoretical studying the reaction of SO2 with the HO2 radical and the HO2·H2O radical complex, respectively. The former leads to the formation of the HSO4 radical, while in the latter reaction the water slightly accelerates the SO2 + HO2 reaction to form HSO4·H2O radical complex and the HO2 acts as a positive catalyst for the formation H2SO3·HO2 complex in the SO2 + H2O reaction, respectively. The rate constants at 298 K are calculated using transition state theory.

Chen, Xiayu; Tao, Cen; Zhong, Li; Gao, Ya; Yao, Wei; Li, Shujin

2014-07-01

185

Intra-Golgi formation of IgM-glycosaminoglycan complexes promotes Ig deposition.  

PubMed

Immune complexes arise from interactions between secreted Ab and Ags in the surrounding milieu. However, it is not known whether intracellular Ag-Ab interactions also contribute to the formation of extracellular immune complexes. In this study, we report that certain murine B cell hybridomas accumulate intracellular IgM and release large, spherical IgM complexes. The complexes (termed "spherons") reach 2 ?m in diameter, detach from the cell surface, and settle out of solution. The spherons contain IgM multimers that incorporate the J chain and resist degradation by endoglycosidase H, arguing for IgM passage through the Golgi. Treatment of cells with inhibitors of proteoglycan synthesis, or incubation of spherons with chondroitinase ABC, degrades spherons, indicating that spheron formation and growth depend on interactions between IgM and glycosaminoglycans. This inference is supported by direct binding of IgM to heparin and hyaluronic acid. We conclude that, as a consequence of IgM binding to glycosaminoglycans, multivalent IgM-glycan complexes form in transit of IgM to the cell surface. Intra-Golgi formation of immune complexes could represent a new pathogenic mechanism for immune complex deposition disorders. PMID:21841132

Khan, Salar N; Cox, John V; Nishimoto, Satoru K; Chen, Ching; Fritzler, Marvin J; Hendershot, Linda M; Weigert, Martin; Radic, Marko

2011-09-15

186

Thermodynamics of the formation of copper(II) complexes with L-histidine in aqueous solution  

NASA Astrophysics Data System (ADS)

The heat effects from the reaction between L-histidine solutions and Cu(NO3)2 solutions at 298.15 K in the 0.2 to 1.0 (KNO3) range of ionic strength are measured by means of direct calorimetry. The experimental data is treated with allowance for the simultaneous proceeding of several processes. The heat effects of the formation of complexes Cu(His)+, Cu(His)2, CuHHis2+, CuH(His){2/+} and CuH2(His){2/2+} are calculated from calorimetric measurements. The standard enthalpies of formation for complexes of L-histidine with Cu2+ ions are obtained via extrapolation to zero ionic strength. The relationship between the thermodynamic characteristics of the formation of complexes of copper(II) with L-histidine and their structure is determined.

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

2015-02-01

187

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

188

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

2013-04-15

189

The conserved oligomeric Golgi complex is involved in double-membrane vesicle formation during autophagy  

PubMed Central

Macroautophagy is a catabolic pathway used for the turnover of long-lived proteins and organelles in eukaryotic cells. The morphological hallmark of this process is the formation of double-membrane autophagosomes that sequester cytoplasm. Autophagosome formation is the most complex part of macroautophagy, and it is a dynamic event that likely involves vesicle fusion to expand the initial sequestering membrane, the phagophore; however, essentially nothing is known about this process including the molecular components involved in vesicle tethering and fusion. In this study, we provide evidence that the subunits of the conserved oligomeric Golgi (COG) complex are required for double-membrane cytoplasm to vacuole targeting vesicle and autophagosome formation. COG subunits localized to the phagophore assembly site and interacted with Atg (autophagy related) proteins. In addition, mutations in the COG genes resulted in the mislocalization of Atg8 and Atg9, which are critical components involved in autophagosome formation. PMID:20065092

Yen, Wei-Lien; Shintani, Takahiro; Nair, Usha; Cao, Yang; Richardson, Brian C.; Li, Zhijian; Hughson, Frederick M.; Baba, Misuzu

2010-01-01

190

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. PMID:21363997

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

2011-01-01

191

Kinetics of formation and dissociation of lanthanide(III)-DOTA complexes  

SciTech Connect

Formation rates of Ce(DOTA){sub {minus}}, Eu(DOTA){sup {minus}}, and Yb(DOTA){sup {minus}} were studied spectrophotmetrically. (H{sub 4}DOTA = 1,4,7,10-tetraazacyclododecane-N,N{prime},N{double_prime},N{double_prime}{prime}-tretraacetic acid.) Intermediates were detected and characterized by NMR, PH-metry, and spectrophotometry. Rate constants for rearrangements of intermediates and protonation of Gd(DOTA){sup {minus}} are reported.

Toth, E.; Bruecher, E.; Lazar, I.; Toth, I. [Lajos Kossuth Univ., Debrecen (Hungary)

1994-08-31

192

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

193

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

PubMed Central

Induction of the human c-fos proto-oncogene by mitogens depends on the formation of a ternary complex by p62TCF with the serum response factor (SRF) and the serum response element (SRE). We demonstrate that Elk-1, a protein closely related to p62TCF in function, is a nuclear target of two members of the MAP kinase family, ERK1 and ERK2. Phosphorylation of Elk-1 increases the yield of ternary complex in vitro. At least five residues in the C-terminal domain of Elk-1 are phosphorylated upon growth factor stimulation of NIH3T3 cells. These residues are also phosphorylated by purified ERK1 in vitro, as determined by a combination of phosphopeptide sequencing and 2-D peptide mapping. Conversion of two of these phospho-acceptor sites to alanine impairs the formation of ternary complexes by the resulting Elk-1 proteins. Removal of these serine residues also drastically diminishes activation of the c-fos promoter in epidermal growth factor-treated cells. Analogous mutations at other sites impair activation to a lesser extent without affecting ternary complex formation in vitro. Our results indicate that phosphorylation regulates ternary complex formation by Elk-1, which is a prerequisite for the manifestation of its transactivation potential at the c-fos SRE. Images PMID:7889942

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

1995-01-01

194

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

2012-06-15

195

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

Microsoft Academic Search

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

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

2008-01-01

196

Cation-induced formation of a macro-glucan synthase complex  

SciTech Connect

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

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

1990-05-01

197

Spectroscopic studies on the formation of molecular complexes of sulfamethoxazole with novel 2,3,5-trichloro-6-alkoxy-1,4-benzoquinones  

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 alkoxy substituted 2,3,5-trichloro-1,4-benzoquinones and to characterize the reaction products. The interactions of these quinones with sulfamethoxazole (SULF) were found to proceed through the formation of donor-acceptor complex, containing radical anion and its conversion to the product. Fluorescence quenching studies indicated that the interaction between the donor and the acceptors are spontaneous. Correlation of association constants of the CT complexes with Taft's polar and steric constants indicated that polar factor plays a significant role in governing the reactivity. The results indicated that the electronic effects of the substituents play significant role in governing the reactivity of the quinones when compared to steric factor.

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

2013-02-01

198

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

NASA Astrophysics Data System (ADS)

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

Shoukry, Mohamed M.; Hassan, Safaa S.

2014-01-01

199

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

PubMed Central

A simple and sensitive spectrophotometric method was developed for the determination of acetazolamide (ACM) in pure form and pharmaceutical preparations. The proposed method is based on the complex formation of acetazolamide with Palladium (II) chloride in acetate buffer pH5.4 and measuring the absorbance at 308 nm. The absorbance- concentration plot was rectilinear over the concentration range of 5-70 ?g/ml with a minimum detection limit (LOD) of 0.98 ?g/ml, limit of quantification (LOQ) of 2.96 ?g/ml, and a molar absorptivity ?=2.7 × 103 L/mol.cm. The factors affecting the absorbance of the formed complex were carefully studied and optimized. The composition of the complex as well as its stability constant was also investigated. The proposed method was applied for the determination of acetazolamide in its tablets and the results obtained were favorably compared with those obtained using the official method. A proposal of the reaction pathway was postulated. PMID:23675188

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

2010-01-01

200

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

SciTech Connect

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

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

1990-12-01

201

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

PubMed

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

Slavin, L L; Bose, R N

1990-12-01

202

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

Microsoft Academic Search

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

L. L. Slavin; R. N. Bose

1990-01-01

203

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.

204

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

205

Dynamics of cadherin\\/catenin complex formation: novel protein interactions and pathways of complex assembly  

Microsoft Academic Search

Calcium-dependent cell-cell adhesion is mediated by the cadherin family of cell adhesion pro- teins. Transduction of cadherin adhesion into cellular reorganization is regulated by cytosolic proteins, termed ct-, ~-, and qc-catenin (plakoglobin), that bind to the cytoplasmic domain of cadherins and link them to the cytoskeleton. Previous studies of cadherin\\/cate- nin complex assembly and organization relied on the coimmunoprecipitation of

Lindsay Hinck; Inke S. Ntithke; Jackie Papkoff; W. James Nelson

1994-01-01

206

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

SciTech Connect

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

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

2013-02-15

207

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

PubMed

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. PMID:23650585

Zhang, Nan; Buck, Martin

2012-01-01

208

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. PMID:23650585

Zhang, Nan; Buck, Martin

2012-01-01

209

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

Microsoft Academic Search

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

C. M. G. van den Berg van Saparoea

1979-01-01

210

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

E-print Network

the dynamics of core complex formation in a three-layer model of the lithosphere. In this method a mathematical the Moho and topography flat across the detachments as observed in the Basin and Range (McKenzie et al model for an elastic-plastic upper crust. McKenzie et al. (2000) explored the nature of lower crustal

Boschetti, Fabio

211

Enthalpies of complex formation of boron and aluminum bromides with organic bases of high donor power  

SciTech Connect

By the calorimetric method enthalpies of complex formation were determined for boron and aluminum bromides with piperidine and hexamethylphosphoric triamide in benzene solutions and for boron bromide with pyridine in dichloroethane, and also enthalpies of solution were determined for BBr/sub 3/ and the adducts AlBr/sub 3/ x PPy and BBr/sub 2/ x Py in benzene and pyridine.

Grigor-ev, A.A.; Kondrat'ev, Y.V.; Suvorov, A.V.

1986-11-20

212

Photoinduced formation of stable Ag-nanoparticles from a ternary ligand-DNA-Ag(+) complex.  

PubMed

The combination of (i) the light-harvesting nature and excited-state redox reactivity of a cationic DNA intercalator, (ii) a conjugated Ag(+)-binding crown ether, and (iii) the stabilizing effect of DNA on AgNPs in one integral ternary complex enables the mild photoinduced formation of Ag nanoparticles. PMID:25690723

Berdnikova, Daria V; Ihmels, Heiko; Schönherr, Holger; Steuber, Marc; Wesner, Daniel

2015-03-11

213

In vivo dynamics of chromatin-associated complex formation in mammalian nucleotide excision repair  

Microsoft Academic Search

Chromatin is the substrate for many processes in the cell nucleus, including transcription, replication, and various DNA repair systems, all of which require the formation of multiprotein machineries on the chromatin fiber. We have analyzed the kinetics of in vivo assembly of the protein complex that is responsible for nucleotide excision repair (NER) in mammalian cells. Assembly is initiated by

M. J. Mone; T. Bernas; C. Dinant; F. A. Goedvree; E. M. M. Manders; M. Volker; A. B. Houtsmuller; J. H. J. Hoeijmakers; W. Vermeulen; Driel van R

2004-01-01

214

Monte Carlo simulations of complex formation between a mixed fluid vesicle and a charged colloid  

E-print Network

Monte Carlo simulations of complex formation between a mixed fluid vesicle and a charged colloid fluidlike vesicle to adhere to and encapsulate an oppositely charged spherical colloidal particle. The vesicle contains mobile charges that interact with the colloid and among themselves through a screened

Iglic, Ales

215

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

EPA Science Inventory

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

216

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

E-print Network

dissociation: (ij) (i, ) + (j, ) k- ij xij degradation/removal: (i, ) i x i synthesis: (i, ) i proteinGenerating functional analysis of complex formation and dissociation in large protein interaction, Sep 13-16, Kyoto ACC Coolen (KCL) Dynamics of protein interaction networks IWSMI-2009 1 / 31 #12

Coolen, ACC "Ton"

217

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

218

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

Microsoft Academic Search

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

LISA WEIS; DANNY REINBERG

1992-01-01

219

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

NASA Technical Reports Server (NTRS)

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 craters on Mars appears at diameters in the range of 3 to 8 km. Five features appear sequentially with increasing crater size, flat floors, central peaks and shallower depths, scalloped rims, and terraced walls. This order suggests that a shallow depth of excavation and a rebound mechanism have produced the central peaks, not centripetal collapse and deep sliding. Simple craters are relatively uniform in shape from planet to planet, but complex craters vary considerably. Both the average onset diameter for complex impact craters on Mars and the average depth of complex craters vary inversely with gravitational acceleration on four planets.

Pike, R. J.

1980-01-01

220

Radiation-mediated formation of complex damage to DNA: a chemical aspect overview  

PubMed Central

During the last three decades, a considerable amount of work has been undertaken to determine the nature, the mechanism of formation and the biological consequences of radiation-induced DNA lesions. Most of the information was obtained via the development of chemical approaches, including theoretical, analytical and organic synthesis methods. Since it is not possible to present all the results obtained in this review article, we will focus on recent data dealing with the formation of complex DNA lesions produced by a single oxidation event, as these lesions may play a significant role in cellular responses to ionizing radiation and also to other sources of oxidative stress. Through the description of specific results, the contribution of different chemical disciplines in the assessment of the structure, the identification of the mechanism of formation and the biological impacts in terms of repair and mutagenicity of these complex radiation-induced DNA lesions will be highlighted. PMID:24472775

Breton, J; Douki, T; Gasparutto, D; Grand, A; Rachidi, W; Sauvaigo, S

2014-01-01

221

Recrystallized Impact Glasses of the Onaping Formation and the Sudbury Igneous Complex, Sudbury Structure, Ontario, Canada  

NASA Technical Reports Server (NTRS)

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 nofite 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.

1996-01-01

222

Potentiometric calorimetric, and solution NMR studies of a tridentate ligand which has a marked preference for formation of bis(ligand) versus mono(ligand) lanthnide complexes and which exhibits high selectivity for heavier lanthanides  

SciTech Connect

A new water-soluble N{sub 4}O{sub 3} tripodal amine phenol ligand, tris(((2-hydroxy-5-sulfobenzyl)amino)ethyl)amine (H{sub 3}TRNS) has been synthesized, and its complexation properties with six lanthanide(III) ions (La, Nd, Gd, Ho, Yb, Lu) have been probed. In water, the ligand coordinates in a tridentate fashion through the three phenolato oxygen atoms to give mono- and bis(ligand) complexes. The bis complexes are proposed to be 7-coordinate containing one bound water as evinced by {sup 17}O NMR experiments on the Dy{sup 3+} complex, while the mono complexes are proposed to have a coordination number of eight or nine. The stepwise formation constants for the 1:1 and 2:1 (L:M) complexes have been measured. The formation constants show an increasing affinity and an unprecedented selectivity for the heavier lanthanides. Furthermore, the stepwise stability constant for the 2:1 complex is increasingly greater than that for the 1:1 complexes of Gd{sup 3+}, Ho{sup 3+}, and Yb{sup 3+}, while K{sub 1} and K{sub 2} for the 1:1 and 2:1 complexes of Nd{sup 3+} are approximately the same. Solution calorimetry shows that the selectivity for the heavier lanthanides is an enthalpic effect, while the anomalous behavior in formation constants (K{sub 2} > K{sub 1}) is predominantly entropic ({Delta}S{sub 2} > {Delta}S{sub 1}) and is rationalized in terms of solvation of the complexes. 61 refs., 7 figs., 2 tabs.

Caravan, P.; Liu, S.; Orvig, C. [Univ. of British Columbia, Vancouver (Canada); Hedlund, T.; Sjoeberg, S. [Umea Univ. (Sweden)

1995-11-15

223

Radiative association rate constant for the formation of CO: the importance of the first excited 1?+ state  

NASA Astrophysics Data System (ADS)

The thermal rate constant for production of carbon monoxide, in its electronic ground state, through radiative association of carbon (C) and oxygen (O) atoms is computed. A combination of quantum and classical dynamics methods are employed. In particular, we investigate the importance of the mechanism where C and O approach each other on the 21?+ potential energy curve. Accounting for this reaction turns out to add about 75 per cent to the rate constant at 10 000 K. We expect the results to be important for studies of the chemistry in interstellar gas, particularly in metal-rich ejecta of supernovae. Since a significant isotope effect has been predicted previously both stable carbon isotopes 12C and 13C are considered in the present study.

Gustafsson, Magnus; Nyman, Gunnar

2015-04-01

224

Characterizing Extragalactic Star Formation with GALEX Legacy Photometric Analysis of UV-Bright Stellar Complexes  

NASA Astrophysics Data System (ADS)

At the close of nearly a decade of observing, GALEX has accumulated an unprecedented archive of ultraviolet (UV) images revealing both the scope and intricacy of star formation (SF) in many thousands of galaxies inhabiting the local universe. If the observed hierarchical SF morphology can be quantified systematically, and physically interpreted with multi-wavelength ancillary data and modeling, then the low redshift GALEX legacy will approach completion. However, the GALEX GR6 pipeline database contains a highly incomplete census of young stellar complexes even for very well-studied galaxies. We propose to apply a dedicated photometry algorithm that has been optimized for measuring the properties of irregularly shaped sources in crowded galaxy images containing spatially variant, diffuse intra-clump emission. Structures will be selected in the UV, but we will compile UV-visible-MIR SEDs for each detection utilizing Pan-STARRS1+SDSS and WISE data. These SEDs will then be fit using population-synthesis models to derive estimated stellar mass, age, and extinction. Processing will be completed for the entire diameter-limited GALEX Large Galaxy Atlas (GLGA) sample of 20,000+ galaxies, at a variety of standardized spatial resolutions. Although the precise categorization of the cataloged substructures will depend on galaxy distance, the outcome of our analysis will be a catalog similar to the stellar association surveys of past decades for very nearby galaxies based on resolved stars (e.g. van den Bergh 1964, Hodge 1986, Efremov et al. 1987), except that our investigation will probe a galaxy sample of dramatically larger size using the integrated UV light from such groupings of young stars. Our algorithm is multi-scale in nature and will thus preserve the hierarchical properties of the stellar distribution, by linking sub-clumps to their larger-scale parent feature(s). The resulting database will be a fundamental resource for follow-up multi-wavelength studies probing SF-driven galaxy evolution using both existing NASA databases and operating instruments, in addition to upcoming space telescopes. While a legacy of our project will be the hierarchical photometric database (disseminated via MAST and NED) which supports extragalactic community science, our own goals from the proposed comprehensive measurements address some vital issues: (i) Currently there is controversy regarding the power-law slope of the empirical star formation law (SFL). Is there constant star formation efficiency above the HI-to-H_2 transition gas surface density (implying ~unity slope, see papers by Bigiel et al. and Leroy et al.), or is the SFL relation a stronger function of gas density with a super-linear form (as observed by Kennicutt et al. 2007)? Liu et al. (2011) have shown that the answer may depend critically on whether or not diffuse emission underlying star-forming substructures is removed. Our analysis will allow firm resolution of this issue, as we will also apply our photometry algorithm to Spitzer imaging for a subset of our sample galaxies, thus providing background-subtracted L(UV) and L(IR) measurements for substructures which can then be compared to existing and forthcoming (ALMA) CO imaging. (ii) We will also verify/calibrate our SED-fit based determination of age, extinction, and mass for UV-bright structures via direct comparison to the ground-truth stemming from resolved stellar populations (e.g. in ANGST galaxies) and also high-resolution HST UV-optical star cluster surveys (further out in the Local Volume). (iii) Finally, we will measure the diffuse UV fraction in a few hundred of the nearest galaxies (accounting for variation tied only to spatial resolution), trying to ascertain the characteristic fraction in galaxies of different Hubble type and dust-to-gas ratio. Systematic local variations in diffuse fraction and color will also be quantified as a function of environment.

Thilker, David

225

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

SciTech Connect

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

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

2013-02-01

226

Ensuring complete absence of Ce(IV) and measurement of the stability constant of the fluoride complex of Ce(III).  

PubMed

Literature survey revealed a wide variation in the measured stability constant values of the aqueous fluoride complexes of trivalent cerium. This could be due to inadequate care for full conversion and maintenance of the oxidation state of cerium to trivalent state. In the present work quinhydrone has been used to ensure complete absence of Ce(IV) and the stability constant of CeF(2+) in 1 M NaClO(4) has been measured potentiometrically using a fluoride ion selective electrode. Log beta(1) obtained in this work was 2.936+/-0.024 and fitted well with the general trend of stability constants of the lanthanide (rare earths) fluorides in aqueous solution. PMID:18968159

Sawant, R M; Chaudhuri, N K; Ramakumar, K L

2001-01-01

227

Determination of stability constants of the inclusion complexes of beta-blockers in heptakis (2,3-dimethyl-6-sulfato)-beta-cyclodextrin.  

PubMed

The beta-blockers possess at least one chiral center and the S(-)-enantiomer shows higher affinity for binding to the beta-adrenergic receptors than antipode. The stability constants of acebutolol, celiprolol, propranolol and terbutaline in the inclusion complexes with single-isomer heptakis (2,3-dimethyl-6-sulfato)-beta-cyclodextrin (HDMS-beta-CD) were determined by capillary electrophoresis. The approximation and linear double reciprocal methods were adapted with comparable results. Among the beta-blockers studied, propranolol had the lowest stability constant but the highest enantioselectivity, indicating that the magnitudes of the stability constants carried little information about enantioseparation. The magnitudes of enantioselectivities between the enantiomer pair were in the order of propranolol > celiprolol > terbutaline > acebutolol. PMID:15646805

Phuong, Nuyen Thi; Lee, Kyung Ah; Kim, Kyung Ho; Choi, Jung Kap; Kim, Jong Moon; Kang, Jong Seong

2004-12-01

228

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

229

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

PubMed Central

The tight electrostatic binding of the chemokine platelet factor 4 (PF4) to polyanions induces heparin-induced thrombocytopenia, a prothrombotic adverse drug reaction caused by immunoglobulin G directed against PF4/polyanion complexes. This study demonstrates that nucleic acids, including aptamers, also bind to PF4 and enhance PF4 binding to platelets. Systematic assessment of RNA and DNA constructs, as well as 4 aptamers of different lengths and secondary structures, revealed that increasing length and double-stranded segments of nucleic acids augment complex formation with PF4, while single nucleotides or single-stranded polyA or polyC constructs do not. Aptamers were shown by circular dichroism spectroscopy to induce structural changes in PF4 that resemble those induced by heparin. Moreover, heparin-induced anti-human–PF4/heparin antibodies cross-reacted with human PF4/nucleic acid and PF4/aptamer complexes, as shown by an enzyme immunoassay and a functional platelet activation assay. Finally, administration of PF4/44mer–DNA protein C aptamer complexes in mice induced anti–PF4/aptamer antibodies, which cross-reacted with murine PF4/heparin complexes. These data indicate that the formation of anti-PF4/heparin antibodies in postoperative patients may be augmented by PF4/nucleic acid complexes. Moreover, administration of therapeutic aptamers has the potential to induce anti-PF4/polyanion antibodies and a prothrombotic diathesis. PMID:23673861

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

2013-01-01

230

Functional insight into the role of Orc6 in septin complex filament formation in Drosophila  

PubMed Central

Septins belong to a family of polymerizing GTP-binding proteins that are important for cytokinesis and other processes that involve spatial organization of the cell cortex. We reconstituted a recombinant Drosophila septin complex and compared activities of the wild-type and several mutant septin complex variants both in vitro and in vivo. We show that Drosophila septin complex functions depend on the intact GTP-binding and/or hydrolysis domains of Pnut, Sep1, and Sep2. The presence of the functional C-terminal domain of septins is required for the integrity of the complex. Drosophila Orc6 protein, the smallest subunit of the origin recognition complex (ORC), directly binds to septin complex and facilitates septin filament formation. Orc6 forms dimers through the interactions of its N-terminal, TFIIB-like domains. This ability of the protein suggests a direct bridging role for Orc6 in stimulating septin polymerization in Drosophila. Studies reported here provide a functional dissection of a Drosophila septin complex and highlight the basic conserved and divergent features among metazoan septin complexes. PMID:25355953

Akhmetova, Katarina; Balasov, Maxim; Huijbregts, Richard P. H.; Chesnokov, Igor

2015-01-01

231

Direct determination of self-exchange electron-transfer rate constants of nickel(III,II) complexes by sup 62 Ni EPR line broadening  

SciTech Connect

A novel method, based on the influence of {sup 61}Ni on the room-temperature electron paramagnetic resonance spectra of Ni(III) complexes, is used for the measurement of electron-transfer self-exchange rate constants of nickel(III,II) complexes. An electron-transfer self-exchange rate constant (k{sub 11} = 450 {plus minus} 50 M{sup {minus}1} s{sup {minus}1} at 24{degree}C) is measured for the Ni{sup III}(H{sub {minus}2}Aib{sub 3})(H{sub 2}O){sub 2} and Ni{sup II}(H{sub {minus}2}Aib{sub 3}){sup {minus}} couple, where Aib{sub 3} is the tripeptide of {alpha}-aminoisobutyric acid and H{sub {minus}2} designates two deprotonated-N(peptide) groups. This k{sub 11} value reflects an inner-sphere enhancement attributed to bridging by an axial water molecule. The exchange rate decreases when pyridine replaces one of the axial water molecules of the nickel(III) complexes. The electron-transfer rate constant between Ni{sup III}(H{sub {minus}2}Aib{sub 3})(py)(H{sub 2}O) and Ni{sup II}(H{sub {minus}2}Aib{sub 3}){sup {minus}} is 103 {plus minus} 8 M{sup {minus}1} s{sup {minus}1} at 23{degree}C. 36 refs., 4 figs., 3 tabs.

Wang, Jean-Fu; Kumar, K.; Margerum, D.W. (Purdue Univ., West Lafayette, IN (USA))

1989-09-06

232

Complex formation, thermal behavior and stability competition between Cu(II) ion and Cu0 nanoparticles with some new azo dyes. Antioxidant and in vitro cytotoxic activity  

NASA Astrophysics Data System (ADS)

Four triazole and thiadiazole-based azo chromophores namely [(E)-4-((1H-1,2,4-triazol-3-yl)diazenyl)benzene-1,3-diol.(HL1), (E)-4-((5-(methylthio)-1H-1,2,4-triazol-3-yl)diazenyl)benzene-1,3-diol.(HL2), (E)-4-((1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol.(HL3) and (E)-4-((5-mercapto-1,3,4-thiadiazol-2-yl)diazenyl)benzene-1,3-diol.(HL4)] 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 Cu0 surface through anchoring sbnd 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.

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

2013-04-01

233

Formation of Ternary Complexes with MgATP: Effects on the Detection of Mg2+ in Biological Samples by Bidentate Fluorescent Sensors  

PubMed Central

Fluorescent indicators based on ?-keto-acid bidentate coordination motifs display superior metal selectivity profiles compared to current o-aminophenol-N,N,O-triacetic acid (APTRA) based chelators for the study of biological magnesium. These low denticity chelators, however, may allow for the formation of ternary complexes with Mg2+ and common ligands present in the cellular milieu. In this work, absorption, fluorescence, and NMR spectroscopy were employed to study the interaction of turn-on and ratiometric fluorescent indicators based on 4-oxo-4H-quinolizine-3-carboxylic acid with Mg2+ and ATP, the most abundant chelator of biological magnesium, thus revealing the formation of ternary complexes under conditions relevant to fluorescence imaging. The formation of ternary species elicits comparable or greater optical changes than those attributed to the formation of binary complexes alone. Dissociation of the fluorescent indicators from both ternary and binary species have apparent equilibrium constants in the low millimolar range at pH 7 and 25 °C. These results suggest that these bidentate sensors are incapable of distinguishing between free Mg2+ and MgATP based on ratio or intensity-based steady-state fluorescence measurements, thus posing challenges in the interpretation of results from fluorescence imaging of magnesium in nucleotide-rich biological samples. PMID:24593871

2015-01-01

234

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

PubMed

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

Zhang, Mingming; Zhu, Kelong; Huang, Feihe

2010-11-21

235

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

236

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

237

General theory of acceptor-oxygen-vacancy complex single donor in high-dielectric-constant metallic oxide insulators  

NASA Astrophysics Data System (ADS)

Previously, we showed experimentally that Si /O-vacancy complex single donors and C /O-vacancy complex single donors in tantalum oxide films have smaller ionization energies than the first ionization energy of O-vacancy double donors [W. S. Lau, L. L. Leong, T. Han, and N. P. Sandler, Appl. Phys. Lett. 83, 2835 (2003)]. In this letter, a theory based on a larger electron orbit for acceptor O-vacancy complex single donors compared to the O-vacancy double donors is proposed to explain the physics behind our previously reported experimental observation and why Si or C may cause an increase in leakage current in tantalum oxide films.

Lau, W. S.; Han, Taejoon

2005-04-01

238

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

SciTech Connect

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

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

1995-01-01

239

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

PubMed Central

It is vital to design effective nitrogen fixation systems that operate under mild conditions, and to this end we recently reported an example of the catalytic formation of ammonia using a dinitrogen-bridged dimolybdenum complex bearing a pincer ligand, where up to twenty three equivalents of ammonia were produced based on the catalyst. Here we study the origin of the catalytic behaviour of the dinitrogen-bridged dimolybdenum complex bearing the pincer ligand with density functional theory calculations, based on stoichiometric and catalytic formation of ammonia from molecular dinitrogen under ambient conditions. Comparison of di- and mono-molybdenum systems shows that the dinitrogen-bridged dimolybdenum core structure plays a critical role in the protonation of the coordinated molecular dinitrogen in the catalytic cycle. PMID:24769530

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

2014-01-01

240

Ab-Initio Based Computation of Rate Constants of Spin Forbidden Transitions in (Bio)inorganic Complexes and Metalloproteins  

Microsoft Academic Search

Some (bio)chemical reactions are non-adiabatic processes whereby the total spin angular momentum, before and after the reaction, is not conserved. These are named spin- forbidden reactions. The application of spin density functional theory (SDFT) to the prediction of rate constants is a challenging task of fundamental and practical importance. We apply non-adiabatic transition state theory in conjunction with SDFT to

Abdullah Ozkanlar; Jorge H. Rodriguez

2009-01-01

241

Good neighbors are hard to find: computational complexity of network formation  

Microsoft Academic Search

We investigate the computational complexity of several decision problems in a simple strategic game of network formation.\\u000a We find that deciding if a player has a strategy that guarantees him a certain payoff against a given strategy profile of\\u000a the other players is an NP-complete problem. Deciding if there exists a strategy profile that guarantees a certain aggregate payoff is

Richard Baron; Jacques Durieu; Hans Haller; Rahul Savani; Philippe Solal

2008-01-01

242

Excitation energy transfer and carotenoid radical cation formation in light harvesting complexes — A theoretical perspective  

Microsoft Academic Search

Light harvesting complexes have been identified in all chlorophyll-based photosynthetic organisms. Their major function is the absorption of light and its transport to the reaction centers, however, they are also involved in excess energy quenching, the so-called non-photochemical quenching (NPQ). In particular, electron transfer and the resulting formation of carotenoid radical cations have recently been discovered to play an important

Michael Wormit; Philipp H. P. Harbach; Jan M. Mewes; Sergiu Amarie; Josef Wachtveitl; Andreas Dreuw

2009-01-01

243

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...

244

Formation of 1:1 and 2:1 host-guest inclusion complexes of ?-cyclodextrin with cycloalkanols: A 1H and 13C NMR spectroscopic study  

NASA Astrophysics Data System (ADS)

Binding constants (Ka's) for the formation of inclusion complexes of ?-cyclodextrin (?-CD) with cycloalkanols (c-CnOH; n = 4-8) were determined by means of 1H and 13C NMR titration, under two different conditions: (i) only 1:1 host-guest inclusion complexes are formed when the guest is in excess; (ii) the formation of 2:1 inclusion complexes occurs only after that of 1:1 inclusion complexes, when the host is in excess. The results of this work showed that ?-CD can include c-C4OH or c-C5OH only when the molar ratio is 1:1; larger ring-sized cycloalkanols such as c-C6OH, c-C7OH or c-C8OH can be included only when the molar ratio is 2:1. These findings, together with those obtained for the four derivatives of ?-CD, per-6-O-methyl-?-CD, per-2-O-methyl-?-CD, per-3-O-methyl-?-CD, and per-2,6-di-O-methyl-?-CD, suggested that ?-CD forms 2:1 inclusion complexes with c-C6OH, c-C7OH or c-C8OH in a tail-to-tail manner, in which the secondary hydroxy sides of the two CD molecules face each other. Two-dimensional ROESY measurements confirmed our results.

Akita, Tomoki; Yoshikiyo, Keisuke; Yamamoto, Tatsuyuki

2014-09-01

245

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

PubMed

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

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

1985-12-01

246

Complete stereocontrol in the synthesis of macrocyclic lanthanide complexes: direct formation of enantiopure systems for circularly polarised luminescence applications.  

PubMed

Mono-C-substitution of the 1,4,7-triazacyclononane ring induces formation of single enantiomers of Eu(III) complexes with nonadentate N6O3 ligands. The absolute configuration of each complex is determined by the stereogenicity of the C-substituent, revealed by comparison of the sign and sequence of CPL transitions for a series of complexes. PMID:24036681

Evans, Nicholas H; Carr, Rachel; Delbianco, Martina; Pal, Robert; Yufit, Dmitry S; Parker, David

2013-11-28

247

Disulfide bond formation involves a quinhydrone-type charge-transfer complex.  

PubMed

The chemistry of disulfide exchange in biological systems is well studied. However, the detailed mechanism of how oxidizing equivalents are derived to form disulfide bonds in proteins is not clear. In prokaryotic organisms, it is known that DsbB delivers oxidizing equivalents through DsbA to secreted proteins. DsbB becomes reoxidized by reducing quinones that are part of the membrane-bound electron-transfer chains. It is this quinone reductase activity that links disulfide bond formation to the electron transport system. We show here that purified DsbB contains the spectral signal of a quinhydrone, a charge-transfer complex consisting of a hydroquinone and a quinone in a stacked configuration. We conclude that disulfide bond formation involves a stacked hydroquinone-benzoquinone pair that can be trapped on DsbB as a quinhydrone charge-transfer complex. Quinhydrones are known to be redox-active and are commonly used as redox standards, but, to our knowledge, have never before been directly observed in biological systems. We also show kinetically that this quinhydrone-type charge-transfer complex undergoes redox reactions consistent with its being an intermediate in the reaction mechanism of DsbB. We propose a simple model for the action of DsbB where a quinhydrone-like complex plays a crucial role as a reaction intermediate. PMID:14612576

Regeimbal, James; Gleiter, Stefan; Trumpower, Bernard L; Yu, Chang-An; Diwakar, Mithun; Ballou, David P; Bardwell, James C A

2003-11-25

248

Disulfide bond formation involves a quinhydrone-type charge–transfer complex  

PubMed Central

The chemistry of disulfide exchange in biological systems is well studied. However, the detailed mechanism of how oxidizing equivalents are derived to form disulfide bonds in proteins is not clear. In prokaryotic organisms, it is known that DsbB delivers oxidizing equivalents through DsbA to secreted proteins. DsbB becomes reoxidized by reducing quinones that are part of the membrane-bound electron-transfer chains. It is this quinone reductase activity that links disulfide bond formation to the electron transport system. We show here that purified DsbB contains the spectral signal of a quinhydrone, a charge–transfer complex consisting of a hydroquinone and a quinone in a stacked configuration. We conclude that disulfide bond formation involves a stacked hydroquinone–benzoquinone pair that can be trapped on DsbB as a quinhydrone charge–transfer complex. Quinhydrones are known to be redox-active and are commonly used as redox standards, but, to our knowledge, have never before been directly observed in biological systems. We also show kinetically that this quinhydrone-type charge–transfer complex undergoes redox reactions consistent with its being an intermediate in the reaction mechanism of DsbB. We propose a simple model for the action of DsbB where a quinhydrone-like complex plays a crucial role as a reaction intermediate. PMID:14612576

Regeimbal, James; Gleiter, Stefan; Trumpower, Bernard L.; Yu, Chang-An; Diwakar, Mithun; Ballou, David P.; Bardwell, James C. A.

2003-01-01

249

The SWI/SNF chromatin remodeling complex regulates germinal center formation by repressing Blimp-1 expression.  

PubMed

Germinal center (GC) reaction is crucial in adaptive immune responses. The formation of GC is coordinated by the expression of specific genes including Blimp-1 and Bcl-6. Although gene expression is critically influenced by the status of chromatin structure, little is known about the role of chromatin remodeling factors for regulation of GC formation. Here, we show that the SWI/SNF chromatin remodeling complex is required for GC reactions. Mice lacking Srg3/mBaf155, a core component of the SWI/SNF complex, showed impaired differentiation of GC B and follicular helper T cells in response to T cell-dependent antigen challenge. The SWI/SNF complex regulates chromatin structure at the Blimp-1 locus and represses its expression by interacting cooperatively with Bcl-6 and corepressors. The defect in GC reactions in mice lacking Srg3 was due to the derepression of Blimp-1 as supported by genetic studies with Blimp-1-ablated mice. Hence, our study identifies the SWI/SNF complex as a key mediator in GC reactions by modulating Bcl-6-dependent Blimp-1 repression. PMID:25646472

Choi, Jinwook; Jeon, Shin; Choi, Seungjin; Park, Kyungsoo; Seong, Rho Hyun

2015-02-17

250

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

251

Toward understanding the role of the neuron-specific BAF chromatin remodeling complex in memory formation  

PubMed Central

The long-term storage of memory requires the finely tuned coordination of intracellular signaling with the transcriptional, translational and epigenetic regulations of gene expression. Among the epigenetic mechanisms, however, we know relatively little about the involvement of chromatin remodeling-dependent control of gene expression in cognitive brain functions, compared with our knowledge of other such mechanisms (for example, histone modifications and DNA methylation). A few recent studies have implicated the Brm/Brg-associated factor (BAF) chromatin-remodeling complex, a mammalian homolog of the yeast Swi/Snf complex, in neuronal structural/functional plasticity and memory formation. The BAF complex was previously known to have a critical role in neurodevelopment, but these recent findings indicate that it also contributes to both cognitive functions in the adult brain and human mental disorders characterized by intellectual disability. In this review, we provide a brief overview of the BAF complexes, introduce recent research findings that link their functions to memory formation, and speculate on the yet-unknown molecular mechanisms that may be relevant to these processes.

Choi, Kwang-Yeon; Yoo, Miran; Han, Jin-Hee

2015-01-01

252

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

253

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

254

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

PubMed

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

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

2011-10-10

255

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

SciTech Connect

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

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

2012-06-22

256

On-line dynamic titration: determination of dissociation constants for noncovalent complexes using Gaussian concentration profiles by electrospray ionization mass spectrometry.  

PubMed

A new method for determination of dissociation constants (Kd) using on-line titration by electrospray ionization mass spectrometry is presented. Unlike in common titration experiments, where a set of discrete solutions with a fixed concentration of host and increasing concentration of guest is measured, here a continuous Gaussian concentration profile of guest, formed by band-broadening dispersion during passage through a long tubing, is utilized. An equation allowing access to dissociation constant values from experimental data fit to a 1:1 binding model was derived and incorporated into an in-house-written computer program for automated data processing. The new method is demonstrated for noncovalent complexes of cinchona alkaloid carbamate chiral selectors with N-dinitrobenzoylleucine enantiomers and a series of cyclodextrins with sulfonated azo dyes. PMID:17542559

Frycák, Petr; Schug, Kevin A

2007-07-15

257

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

NASA Astrophysics Data System (ADS)

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

Hill, M.; Guest, B.

2011-12-01

258

Biofilm formation and acyl homoserine lactone production in the Burkholderia cepacia complex.  

PubMed

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. PMID:12270826

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

2002-10-01

259

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. PMID:12270826

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

2002-01-01

260

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

Microsoft Academic Search

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

Mark P. Hampton

261

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

PubMed

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

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

2013-05-01

262

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

2010-03-01

263

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. 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

2010-01-01

264

Studies on the weak interactions and CT complex formations between chloranilic acid, 2,3-dichloro-5,6-dicyano-p-benzoquinone, tetracyanoethylene and papaverine in acetonitrile and their thermodynamic properties, theoretically, spectrophotometrically aided by FTIR.  

PubMed

Spectrophotometric, FTIR and theoretical studies of the charge-transfer complexes between mild narcotic drug papaverine and the acceptors chloranilic acid (Cl-A), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetracyanoethylene (TCNE) in acetonitrile, their association constants, thermodynamic (?G(0), ?H(0) and ?S(0)) and other related properties had been described. Papaverine was found to form colored charge-transfer complexes with Cl-A, DDQ and TCNE in acetonitrile. The absorption maxima of the complexes were 518.5, 584.0 and 464.0nm for Cl-A complex, DDQ complex, and TCNE complex respectively. The compositions of the papaverine complexes were determined to be 1:1 from Job's method of continuous variation. Solid complexes formed between papaverine and the acceptors were isolated. Comparison of the FTIR spectra of the solid complexes between papaverine and the acceptors and their constituents showed considerable shift in absorption peaks, changes in intensities of the peaks and formation of the new bands on complexation. However, no attempt has been made to purify the complexes and study the detailed spectra both theoretically and experimentally. 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. The reasons for the differences in h?CT values were explained. Density function theory was used for calculation. h?CT (experimental) values of the transition energies of the complexes in acetonitrile differed from h?CT (theoretical) values. ID(V) value of papaverine was calculated. Charge-transfer complexes were assumed to be partial electrovalent compounds with organic dative ions D(+) and A(-) (in the excited state) and attempts had been made to correlate the energy changes for the formation of the complexes with the energy changes for the formation of electrovalent compounds between M(+) and X(-) ions. PMID:25813169

Datta, Asim Sagar; Chattaraj, Seema Bagchi; Chakrabortty, Ashutosh; Lahiri, Sujit Chandra

2015-07-01

265

Complex formation of human papillomavirus E7 proteins with the retinoblastoma tumor suppressor gene product.  

PubMed

The E7 proteins encoded by the human papillomaviruses (HPVs) associated with anogenital lesions share significant amino acid sequence homology. The E7 proteins of these different HPVs were assessed for their ability to form complexes with the retinoblastoma tumor suppressor gene product (p105-RB). Similar to the E7 protein of HPV-16, the E7 proteins of HPV-18, HBV-6b and HPV-11 were found to associate with p105-RB in vitro. The E7 proteins of HPV types associated with a high risk of malignant progression (HPV-16 and HPV-18) formed complexes with p105-RB with equal affinities. The E7 proteins encoded by HPV types 6b and 11, which are associated with clinical lesions with a lower risk for progression, bound to p105-RB with lower affinities. The E7 protein of the bovine papillomavirus type 1 (BPV-1), which does not share structural similarity in the amino terminal region with the HPV E7 proteins, was unable to form a detectable complex with p105-RB. The amino acid sequences of the HPV-16 E7 protein involved in complex formation with p105-RB in vitro have been mapped. Only a portion of the sequences that are conserved between the HPV E7 proteins and AdE1A were necessary for association with p105-RB. Furthermore, the HPV-16 E7-p105-RB complex was detected in an HPV-16-transformed human keratinocyte cell line. PMID:2556261

Münger, K; Werness, B A; Dyson, N; Phelps, W C; Harlow, E; Howley, P M

1989-12-20

266

In vivo dynamics of chromatin-associated complex formation in mammalian nucleotide excision repair.  

PubMed

Chromatin is the substrate for many processes in the cell nucleus, including transcription, replication, and various DNA repair systems, all of which require the formation of multiprotein machineries on the chromatin fiber. We have analyzed the kinetics of in vivo assembly of the protein complex that is responsible for nucleotide excision repair (NER) in mammalian cells. Assembly is initiated by UV irradiation of a small area of the cell nucleus, after which the accumulation of GFP-tagged NER proteins in the DNA-damaged area is measured, reflecting the establishment of the dual-incision complex. The dynamic behavior of two NER proteins, ERCC1-XPF and TFIIH, was studied in detail. Results show that the repair complex is assembled with a rate of approximately 30 complexes per second and is not diffusion limited. Furthermore, we provide in vivo evidence that not only binding of TFIIH, but also its helicase activity, is required for the recruitment of ERCC1-XPF. These studies give quantitative insight into the de novo assembly of a chromatin-associated protein complex in living cells. PMID:15520397

Moné, Martijn J; Bernas, Tytus; Dinant, Christoffel; Goedvree, Feliks A; Manders, Erik M M; Volker, Marcel; Houtsmuller, Adriaan B; Hoeijmakers, Jan H J; Vermeulen, Wim; van Driel, Roel

2004-11-01

267

Synaptonemal complex formation and meiotic checkpoint signaling are linked to the lateral element protein Red1  

PubMed Central

Meiosis generates four haploid daughters from a diploid parental cell. Central steps of meiosis are the pairing and recombination of homologous chromosomes followed by their segregation in two rounds of cell division. Meiotic recombination is monitored by a specialized DNA damage checkpoint pathway and is guided by a unique chromosomal structure called synaptonemal complex (SC), but how these events are coordinated is unclear. Here, we identify the SC protein Red1 as a crucial regulator of early meiosis. Red1 interacts with two subunits of the 9-1-1 checkpoint complex via two distinct 9-1-1 subunit-specific motifs. Association of 9-1-1 with Red1 is essential not only for meiotic checkpoint activation but for SC formation. Moreover, Red1 becomes SUMO-modified, which fosters interaction of Red1 with the central SC element Zip1, thereby securing timely SC formation. Thus, Red1, in addition to its structural role in the SC, is a crucial coordinator of meiosis by coupling checkpoint signaling to SC formation. PMID:20534433

Eichinger, Christian S.; Jentsch, Stefan

2010-01-01

268

Varicella-Zoster Virus Infection Triggers Formation of an Interleukin-1? (IL-1?)-processing Inflammasome Complex*  

PubMed Central

Innate cellular immunity is the immediate host response against pathogens, and activation of innate immunity also modulates the induction of adaptive immunity. The nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are a family of intracellular receptors that recognize conserved patterns associated with intracellular pathogens, but information about their role in the host defense against DNA viruses is limited. Here we report that varicella-zoster virus (VZV), an alphaherpesvirus that is the causative agent of varicella and herpes zoster, induces formation of the NLRP3 inflammasome and the associated processing of the proinflammatory cytokine IL-1? by activated caspase-1 in infected cells. NLRP3 inflammasome formation was induced in VZV-infected human THP-1 cells, which are a transformed monocyte cell line, primary lung fibroblasts, and melanoma cells. Absent in melanoma gene-2 (AIM2) is an interferon-inducible protein that can form an alternative inflammasome complex with caspase-1 in virus-infected cells. Experiments in VZV-infected melanoma cells showed that NLRP3 protein recruits the adaptor protein ASC and caspase-1 to form an NLRP3 inflammasome complex independent of AIM2 protein and in the absence of free radical reactive oxygen species release. NLRP3 was also expressed extensively in infected skin xenografts in the severe combined immunodeficiency mouse model of VZV pathogenesis in vivo. We conclude that NLRP3 inflammasome formation is an innate cellular response to infection with this common pathogenic human herpesvirus. PMID:21385879

Nour, Adel M.; Reichelt, Mike; Ku, Chia-Chi; Ho, Min-Yin; Heineman, Thomas C.; Arvin, Ann M.

2011-01-01

269

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. PMID:21124995

Perrimon, Norbert

2010-01-01

270

Rheb activation disrupts spine synapse formation through accumulation of syntenin in tuberous sclerosis complex.  

PubMed

Rheb is a small GTP-binding protein and its GTPase activity is activated by the complex of Tsc1 and Tsc2 whose mutations cause tuberous sclerosis complex (TSC). We previously reported that cultured TSC neurons showed impaired spine synapse morphogenesis in an mTORC1-independent manner. Here we show that the PDZ protein syntenin preferentially binds to the GDP-bound form of Rheb. The levels of syntenin are significantly higher in TSC neurons than in wild-type neurons because the Rheb-GDP-syntenin complex is prone to proteasomal degradation. Accumulated syntenin in TSC neurons disrupts spine synapse formation through inhibition of the association between syndecan-2 and calcium/calmodulin-dependent serine protein kinase. Instead, syntenin enhances excitatory shaft synapse formation on dendrites by interacting with ephrinB3. Downregulation of syntenin in TSC neurons restores both spine and shaft synapse densities. These findings suggest that Rheb-syntenin signalling may be a novel therapeutic target for abnormalities in spine and shaft synapses in TSC neurons. PMID:25880340

Sugiura, Hiroko; Yasuda, Shin; Katsurabayashi, Shutaro; Kawano, Hiroyuki; Endo, Kentaro; Takasaki, Kotaro; Iwasaki, Katsunori; Ichikawa, Masumi; Kobayashi, Toshiyuki; Hino, Okio; Yamagata, Kanato

2015-01-01

271

Complexation-flocculation combined with microwave-assisted headspace solid-phase microextraction in determining the binding constants of hydrophobic organic pollutants to dissolved humic substances.  

PubMed

The binding constants, KDOC, of selected polycyclic aromatic hydrocarbons (PAHs)-phenanthrene, anthracene, fluoranthene, and pyrene-to dissolved humic substances (DHS) were determined by complexation-flocculation combined with microwave-assisted headspace solid-phase microextraction (CF-MA-HS-SPME). The results obtained are comparable with KDOC data reported in the literature. No disruption of the PAH to DHS binding equilibrium was observed during the complexation-flocculation process. The present study, which is the first to determine KDOC by CF-MA-HS-SPME, provides an alternative approach to determine the KDOC of PAHs. CF-MA-HS-SPME provides some advantages over other methods, such as no limitation of fluorescent compounds, greater determination speed, and the capability of measuring various compounds simultaneously. PMID:25568896

Hsieh, Ping-Chieh; Lee, Chon-Lin; Jen, Jen-Fon; Chang, Kuei-Chen

2015-02-21

272

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

Microsoft Academic Search

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

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

1986-01-01

273

Free Radical Formation in Novel Carotenoid Metal Ion Complexes of Astaxanthin  

PubMed Central

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

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

2010-01-01

274

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

275

Heat-induced formation of myosin oligomer-soluble filament complex in high-salt solution.  

PubMed

Heat-induced aggregation of myosin into an elastic gel plays an important role in the water-holding capacity and texture of meat products. Here, we investigated thermal aggregation of porcine myosin in high-salt solution over a wide temperature range by dynamic light scattering experiments. The myosin samples were readily dissolved in 1.0 M NaCl at 25 °C followed by dilution into various salt concentrations. The diluted solutions consistently contained both myosin monomers and soluble filaments. The filament size decreased with increasing salt concentration and temperature. High temperatures above Tm led to at least partial dissociation of soluble filaments and thermal unfolding, resulting in the formation of soluble oligomers and binding to the persistently present soluble filaments. Such a complex formation between the oligomers and filaments has never been observed. Our results provide new insight into the heat-induced myosin gelation in high-salt solution. PMID:25445683

Shimada, Masato; Takai, Eisuke; Ejima, Daisuke; Arakawa, Tsutomu; Shiraki, Kentaro

2015-02-01

276

High-Throughput Metagenomic Technologies for Complex Microbial Community Analysis: Open and Closed Formats  

PubMed Central

ABSTRACT?  Understanding the structure, functions, activities and dynamics of microbial communities in natural environments is one of the grand challenges of 21st century science. To address this challenge, over the past decade, numerous technologies have been developed for interrogating microbial communities, of which some are amenable to exploratory work (e.g., high-throughput sequencing and phenotypic screening) and others depend on reference genes or genomes (e.g., phylogenetic and functional gene arrays). Here, we provide a critical review and synthesis of the most commonly applied “open-format” and “closed-format” detection technologies. We discuss their characteristics, advantages, and disadvantages within the context of environmental applications and focus on analysis of complex microbial systems, such as those in soils, in which diversity is high and reference genomes are few. In addition, we discuss crucial issues and considerations associated with applying complementary high-throughput molecular technologies to address important ecological questions. PMID:25626903

He, Zhili; Yang, Yunfeng; Deng, Ye; Tringe, Susannah G.; Alvarez-Cohen, Lisa

2015-01-01

277

High-throughput metagenomic technologies for complex microbial community analysis: open and closed formats.  

PubMed

Understanding the structure, functions, activities and dynamics of microbial communities in natural environments is one of the grand challenges of 21st century science. To address this challenge, over the past decade, numerous technologies have been developed for interrogating microbial communities, of which some are amenable to exploratory work (e.g., high-throughput sequencing and phenotypic screening) and others depend on reference genes or genomes (e.g., phylogenetic and functional gene arrays). Here, we provide a critical review and synthesis of the most commonly applied "open-format" and "closed-format" detection technologies. We discuss their characteristics, advantages, and disadvantages within the context of environmental applications and focus on analysis of complex microbial systems, such as those in soils, in which diversity is high and reference genomes are few. In addition, we discuss crucial issues and considerations associated with applying complementary high-throughput molecular technologies to address important ecological questions. PMID:25626903

Zhou, Jizhong; He, Zhili; Yang, Yunfeng; Deng, Ye; Tringe, Susannah G; Alvarez-Cohen, Lisa

2015-01-01

278

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

PubMed Central

The Burkholderia cepacia complex (Bcc) consists of 17 closely related species that are problematic opportunistic bacterial pathogens for cystic fibrosis patients and immunocompromised individuals. These bacteria are capable of utilizing two different chemical languages: N-acyl homoserine lactones (AHLs) and cis-2-unsaturated fatty acids. Here we summarize the current knowledge of the underlying molecular architectures of these communication systems, showing how they are interlinked and discussing how they regulate overlapping as well as specific sets of genes. A particular focus is laid on the role of these signaling systems in the formation of biofilms, which are believed to be highly important for chronic infections. We review genes that have been implicated in the sessile lifestyle of this group of bacteria. The new emerging role of the intracellular second messenger cyclic dimeric guanosine monophosphate (c-di-GMP) as a downstream regulator of the fatty acid signaling cascade and as a key factor in biofilm formation is also discussed. PMID:23799665

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

2013-01-01

279

Interaction of ortho-Phospho-l-serine with Hydroxyapatite: Formation of a Surface Complex  

PubMed

ortho-Phospho-l-serine (H2Psi, where Psi represents the serinephosphato ion), a constituent of salivary proteins, seems to play an important role in the mineralization of teeth. To understand the basic mechanism of this interaction, the uptake of o-phospho-l-serine from relatively concentrated aqueous solutions (up to 100 mmol/L) onto synthetic hydroxyapatite was studied. Previous studies have shown that in the dilute concentration range (<12.5 mmol/L) the uptake followed a regular Langmuirian adsorption plot. At higher concentrations the uptake curve increased steeply, but no formation of a separate phase in the reacted apatite was discernible, either by optical or by scanning electron microscopy. The dissolution of apatite released phosphate and calcium ions into the solution in amounts linearly related to the uptake of serine with P/Psi = 1 and Ca/Psi = 2. The charge and mass balance of the reaction can be reconciled with the formation of the surface complex (shown within brackets):Ca10(OH)2(PO4)6 + 6H2Psi --> [Ca6(HPsi)2(HPO4)2(PO4)2] + 4Ca2+ + 2HPsi1- + 2Psi2- + 2H2PO1-4 + 2H2O.The formation of two other surface complexes is possible; however, the complex shown above probably disrupts the apatite lattice the least. Traces of CaPsi·H2O precipitate out from the filtrates of highly concentrated solutions after 6 days. Copyright 1997 Academic Press. Copyright 1997Academic Press PMID:9367603

Misra

1997-10-01

280

Anatomy of the S255-S257 complex - triggered high-mass star formation  

NASA Astrophysics Data System (ADS)

We present a multi-wavelength (NIR to radio) and multi-scale (1 AU to 10 pc) study of the S255-S257 complex of young high-mass (proto)stars. The complex consists of two evolved HII regions and a molecular gas filament in which new generations of high mass stars form. Three distinct regions are identified within this dusty filament: a young NIR/optical source clusters, a (sub) millimetre continuum and molecular clump in global collapse and a reservoir of cold gas. Interestingly, a binary high-mass protostellar system is detected through methanol maser and mid-IR emission at the interface between the NIR clusters and the cold gas clump. The collapsing clump is locating north to the NIR clusters and hosts a young high-mass star associated with an outflow that is observed in mid-IR, methanol maser and radio emission. We interpret this anatomy as the possible result of triggered star formation, starting with the formation of two HII regions, followed by the compression of a molecular gas filament in which a first generation of high-mass stars form (the NIR cluster), which then triggers the formation of high mass protostars in its near environment (the massive binary). The global collapse of the northern clump might be due to both the HII region expansion that squash the filament and the NIR cluster expansion. In conclusion, we witness the formation of four generations of clusters of high-mass stars in S255-S257.

Minier, V.; Peretto, N.; Longmore, S. N.; Burton, M. G.; Cesaroni, R.; Goddi, C.; Pestalozzi, M. R.; André, Ph.

281

Formation of Copper Impurity-Defect Complexes and Their Impact on Electrical Properties of Silicon  

NASA Astrophysics Data System (ADS)

Nature and types of structural defects in the p-type silicon doped with copper are determined by the methods of infrared microscopy and measuring of the specific resistivity, concentration, and lifetime (?) of charge carriers. It is found that the value of ? is increased and stabilized due to the formation of a trap level associated with the "copper-oxygen" complex [Cu-O] in silicon. It is shown that the copper atoms migrate from a saturated dislocation to the volume of lightly doped silicon during slow cooling after high-temperature diffusion, which is associated with the decomposition of the Si-Cu solid solution.

K?rimov, M.; Machkamov, Sh.; ?ursunov, N. ?.; Bakiev, S. ?.; ??chmudov, Sh. ?.; Sattiev, ?. R.; Akramov, F. S.

2014-05-01

282

Photo-induced living radical polymerization of acrylates utilizing a discrete copper(ii)-formate complex.  

PubMed

A photo-polymerization protocol, utilizing a pre-formed and well-characterized Cu(ii) formate complex, [Cu(Me6-Tren)(O2CH)](ClO4), mediated by UV light is described. In the absence of additional reducing agents and/or photosensitizers, ppm concentrations of the oxidatively stable [Cu(Me6-Tren)(O2CH)](ClO4), furnish near-quantitative conversions within 2 h, yielding poly(acrylates) with low dispersities (?1.10) and exceptional end-group fidelity, capable of undergoing in situ chain extension and block copolymerization. PMID:25621847

Anastasaki, Athina; Nikolaou, Vasiliki; Brandford-Adams, Francesca; Nurumbetov, Gabit; Zhang, Qiang; Clarkson, Guy J; Fox, David J; Wilson, Paul; Kempe, Kristian; Haddleton, David M

2015-03-17

283

Formation of charge-transfer-complex in organic:metal oxides systems  

NASA Astrophysics Data System (ADS)

It is found that composite systems consisting of 4,4'-bis(carbazol-9-yl)biphenyl (CBP) and molybdenum trioxide (MoO3) form an IR absorption band around 847 nm. It is also found that the vibrational modes of the CBP, as measured by Fourier Transform Infrared Spectroscopy, are quenched upon the formation of charge-transfer-complex (CTC) between CBP and MoO3. By examining several sets of organic:metal oxides systems, we discovered that the IR absorption band of the CTCs follow two distinct mechanisms depending on the nature and location of the HOMOs in the organic molecules.

Wu, S. P.; Kang, Y.; Liu, T. L.; Jin, Z. H.; Jiang, N.; Lu, Z. H.

2013-04-01

284

Formation and dynamics of "waterproof" photoluminescent complexes of rare earth ions in crowded environment.  

PubMed

Understanding behavior of rare-earth ions (REI) in crowded environments is crucial for several nano- and bio-technological applications. Evolution of REI photoluminescence (PL) in small compartments inside a silica hydrogel, mimic to a soft matter bio-environment, has been studied and explained within a solvation model. The model uncovered the origin of high PL efficiency to be the formation of REI complexes, surrounded by bile salt (DOC) molecules. Comparative study of these REI-DOC complexes in bulk water solution and those enclosed inside the hydrogel revealed a strong correlation between an up to 5×-longer lifetime of REIs and appearance of the DOC ordered phase, further confirmed by dynamics of REI solvation shells, REI diffusion experiments and morphological characterization of microstructure of the hydrogel. PMID:25379879

Ignatova, Tetyana; Blades, Michael; Duque, Juan G; Doorn, Stephen K; Biaggio, Ivan; Rotkin, Slava V

2014-12-28

285

Formation and tunable disassembly of polyelectrolyte-Cu2+ layer-by-layer complex film.  

PubMed

Layer-by-layer assembly of films containing metal ions was investigated. A complex between various metal ions and branched polyethyleneimine is formed in solution and then assembled into multilayer films with poly(acrylic acid). The metal-ligand complex formation results in brightly colored materials that deposit as thick layers. Cu(2+)-containing films were chosen as a model for studying the disassembly of these films in response to various stimuli, including pH, salt, and surfactants. The range of pH instability corresponds to the pH range over which pores are formed in the film. We demonstrate controllable disassembly of these materials, which could be used for antifungal or antibacterial applications. PMID:24059689

Huang, Xiayun; Schubert, Amanda B; Chrisman, James D; Zacharia, Nicole S

2013-10-22

286

Formation of Gels and Films from Hexamine and Hexamidecobalt(II) Carbonylcobalt Complexes  

Microsoft Academic Search

When kept in dilute acetonitrile solutions, complexes [CoB6][Co(CO)4]2 [B = C5H5N, Me2NC(O)H] form gels CoBx(MeCN)y](OH)2·2[CoCO3·2CoO·2H2O] (x = 2, 3, y = 4, 3), while the polyfunctional complex [Co{(EtO)3SiCH2CH2CH2NH2)}][Co(CO)4]2 gives a mixed carbonate-siloxane gel. The gel formation is accompanied by complete decomposition of [Co(CO)4]- anions under the action of air oxygen and moisture, to give CoCO3·2CoO·2H2O. Mechanistically, the gel and film

V. V. Semenov; N. F. Cherepennikova; M. A. Lopatin; S. Ya. Khorshev; Zh. Yu. Fominykh; A. I. Kirillov; V. N. Sedel'nikova; G. A. Domrachev

2002-01-01

287

Theoretical study of the formation of mercury (Hg2+) complexes in solution using an explicit solvation shell in implicit solvent calculations.  

PubMed

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

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

2014-09-25

288

Structure of Soybean Serine Acetyltransferase and Formation of the Cysteine Regulatory Complex as a Molecular Chaperone*  

PubMed Central

Serine acetyltransferase (SAT) catalyzes the limiting reaction in plant and microbial biosynthesis of cysteine. In addition to its enzymatic function, SAT forms a macromolecular complex with O-acetylserine sulfhydrylase. Formation of the cysteine regulatory complex (CRC) is a critical biochemical control feature in plant sulfur metabolism. Here we present the 1.75–3.0 ? resolution x-ray crystal structures of soybean (Glycine max) SAT (GmSAT) in apoenzyme, serine-bound, and CoA-bound forms. The GmSAT-serine and GmSAT-CoA structures provide new details on substrate interactions in the active site. The crystal structures and analysis of site-directed mutants suggest that His169 and Asp154 form a catalytic dyad for general base catalysis and that His189 may stabilize the oxyanion reaction intermediate. Glu177 helps to position Arg203 and His204 and the ?1c-?2c loop for serine binding. A similar role for ionic interactions formed by Lys230 is required for CoA binding. The GmSAT structures also identify Arg253 as important for the enhanced catalytic efficiency of SAT in the CRC and suggest that movement of the residue may stabilize CoA binding in the macromolecular complex. Differences in the effect of cold on GmSAT activity in the isolated enzyme versus the enzyme in the CRC were also observed. A role for CRC formation as a molecular chaperone to maintain SAT activity in response to an environmental stress is proposed for this multienzyme complex in plants. PMID:24225955

Yi, Hankuil; Dey, Sanghamitra; Kumaran, Sangaralingam; Lee, Soon Goo; Krishnan, Hari B.; Jez, Joseph M.

2013-01-01

289

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

290

The dependence of the electrophoretic mobility of small organic ions on ionic strength and complex formation.  

PubMed

The ionic strength dependence of the electrophoretic mobility of small organic anions with valencies up to -3 is investigated in this study. Provided the anions are not too aspherical, it is argued that shape and charge distribution have little influence on mobility. To a good approximation, the electrophoretic mobility of a small particle should be equal to that of a model sphere with the same hydrodynamic radius and same net charge. For small ions, the relaxation effect (distortion of the ion atmosphere from equilibrium due to external electric and flow fields) is significant even for monovalent ions. Alternative procedures of accounting for the relaxation effect are examined. In order to account for the ionic strength dependence of a specific set of nonaromatic and aromatic anions in aqueous solution, it is necessary to include complex formation between the anion with species in the BGE. A number of possible complexes are considered. When the BGE is Tris-acetate, the most important of these involves the complex formed between anion and Tris, the principle cation in the BGE. When the BGE is sodium borate, an anion-anion (borate) complex appears to be important, at least when the organic anion is monovalent. An algorithm is developed to analyze the ionic strength dependence of the electrophoretic mobility. This algorithm is applied to two sets of organic anions from two independent research groups. PMID:20191555

Allison, Stuart A; Pei, Hongxia; Baek, Saerom; Brown, Jocelyn; Lee, Min Y; Nguyen, Vu; Twahir, Umar T; Wu, Hengfu

2010-03-01

291

Dinitrosyl iron complexes with cysteine. Kinetics studies of the formation and reactions of DNICs in aqueous solution.  

PubMed

Kinetics studies provide mechanistic insight regarding the formation of dinitrosyl iron complexes (DNICs) now viewed as playing important roles in the mammalian chemical biology of the ubiquitous bioregulator nitric oxide (NO). Reactions in deaerated aqueous solutions containing FeSO4, cysteine (CysSH), and NO demonstrate that both the rates and the outcomes are markedly pH dependent. The dinuclear DNIC Fe2(?-CysS)2(NO)4, a Roussin's red salt ester (Cys-RSE), is formed at pH 5.0 as well as at lower concentrations of cysteine in neutral pH solutions. The mononuclear DNIC Fe(NO)2(CysS)2(-) (Cys-DNIC) is produced from the same three components at pH 10.0 and at higher cysteine concentrations at neutral pH. The kinetics studies suggest that both Cys-RSE and Cys-DNIC are formed via a common intermediate Fe(NO)(CysS)2(-). Cys-DNIC and Cys-RSE interconvert, and the rates of this process depend on the cysteine concentration and on the pH. Flash photolysis of the Cys-RSE formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 5.0 solution led to reversible NO dissociation and a rapid, second-order back reaction with a rate constant kNO = 6.9 × 10(7) M(-1) s(-1). In contrast, photolysis of the mononuclear-DNIC species Cys-DNIC formed from Fe(II)/NO/cysteine mixtures in anaerobic pH 10.0 solution did not labilize NO but instead apparently led to release of the CysS(•) radical. These studies illustrate the complicated reaction dynamics interconnecting the DNIC species and offer a mechanistic model for the key steps leading to these non-heme iron nitrosyl complexes. PMID:25479566

Pereira, José Clayston Melo; Iretskii, Alexei V; Han, Rui-Min; Ford, Peter C

2015-01-14

292

Luminescence color tuning of Pt(II) complexes and a kinetic study of trimer formation in the photoexcited state.  

PubMed

We investigated the luminescence properties and color tuning of [Pt(dpb)Cl] (dpbH=1,3-di(2-pyridyl)benzene) and its analogues. An almost blue emission was obtained for the complex [Pt(Fmdpb)CN] (FmdpbH=4-fluoro-1,3-di(4-methyl-2-pyridyl)benzene), modified by the introduction of ?F and ?CH3 groups to the dpb ligand and the substitution of ?Cl by ?CN. As the concentration of the solution was increased, the color of the emission varied from blue to white to orange. The color change resulted from a monomer-excimer equilibrium in the excited state. A broad emission spectrum around 620?nm was clearly detected along with a structured monomer emission around 500?nm. Upon further increases in concentration, another broad peak appeared in the longer wavelength region of the spectrum. We assigned the near-infrared band to the emission from an excited trimer generated by the reaction of the excimer with the ground-state monomer. The emission lifetimes of the monomer, dimer, and trimer were evaluated as ?M =12.8??s, ?D =2.13??s, and ?T =0.68??s, respectively, which were sufficiently long to allow association with another Pt(II) complex and dissociation into a lower order aggregate. Based on equilibrium constants determined from a kinetic study, the formation of the excimer and the excited trimer were concluded to be exothermic processes, with ?G*D =-24.5?kJ?mol(-1) and ?G*T =-20.4?kJ?mol(-1) respectively, at 300?K. PMID:25327871

Kayano, T; Takayasu, S; Sato, K; Shinozaki, K

2014-12-01

293

Complex formation of quercetin with lanthanum enhances binding to plant viral satellite double stranded RNA.  

PubMed

Due to the broad spectrum of biological activities of flavonoids, their target molecules in the cell are intensively studied. We examined the interactions of the flavonoid quercetin (Q) and its lanthanum complex (QLa(3+)) with very recently isolated plant viral satellite (sat) dsRNA. Comparison of the cumulative binding affinity and the estimated intercalative binding constant pointed towards an additional binding mode of quercetin to exclusively viral dsRNA, which is not recorded for synthetic dsRNAs. The QLa(3+) showed significantly higher affinity toward viral dsRNA than Q and La(3+) alone, most likely as the consequence of quercetin intercalation accompanied by additional electrostatic interaction of La(3+) with the negatively charged viral RNA backbone. PMID:19766320

Rusak, Gordana; Piantanida, Ivo; Bretschneider, Sabine; Ludwig-Müller, Jutta

2009-12-01

294

31P nuclear magnetic resonance spectra and dissociation constants of lac repressor headpiece.duplex operator complexes: the importance of phosphate backbone flexibility in protein.DNA recognition.  

PubMed

An alkaline phosphatase assay was used to determine the dissociation constants (KD) of the lac repressor N-terminal 56 amino acid fragment of the wild type and of a Y7I mutant complexed to 22 base pair (bp) wild-type and mutant symmetrical operator sequences. KD's in 0.35 M monovalent salt ranged from 5.4 X 10(-8) M for the wild-type repressor.wild-type operator complex to approximately > 1 X 10(-6) M for the wild-type repressor.nonspecific DNA complex. Mutant operators O2 (G5 --> A5 and G16 --> T16) and O4 (G5 --> C5 and C16 --> G16) bind nearly as tightly as the wild-type headpiece, while mutant O3 (A8 --> T8 and T13 --> A13) binds over 5-fold poorer. Operators O1, O2, and O4 bind ca. 10-fold poorer to the Y7I mutant headpiece. Operator O3 binds 2-fold poorer to the mutant headpiece. The temperature and salt dependence on the dissociation constants of wild-type headpiece binding to 22-bp operator support the conclusion that the headpiece contains the major DNA recognition portion of the protein and that electrostatics plays as important a role in the binding of operator to headpiece as it does in the whole repressor. The 31P NMR spectra of shortened 14-bp wild-type and mutant symmetrical operators bound to the N-terminal 56-residue headpiece of the Y7I mutant repressor were compared to the spectra of the same operator bound to the wild-type repressor headpiece. These results are consistent with a recent proposal [Karslake, C., Botuyan, M. V., & Gorenstein, D. G. (1992) Biochemistry 31, 1849-1858] that specific, tight-binding operator.protein complexes retain the inherent phosphate ester conformational flexibility of the operator itself, whereas the phosphate esters are conformationally restricted in the weak-binding operator-protein complexes. This retention of backbone torsional freedom in tight complexes is entropically favorable and provides a mechanism for protein discrimination of different operator binding sites. PMID:8334119

Botuyan, M V; Keire, D A; Kroen, C; Gorenstein, D G

1993-07-13

295

Complex Dynamics of Osteoclast Formation and Death in Long-Term Cultures  

PubMed Central

Background Osteoclasts, cells responsible for bone resorption, contribute to the development of degenerative, metabolic and neoplastic bone diseases, which are often characterized by persistent changes in bone microenvironment. We aimed to investigate the dynamics of osteoclast formation and death in cultures that considerably exceeded the length of standard protocol and to design a mathematical model describing osteoclastogenesis. Methodology/Principal Findings RAW 264.7 monocytic cells fuse to form multinucleated osteoclasts upon treatment with pro-resorptive cytokine RANKL. We have found that in long-term experiments (15–26 days), the dynamics of changes in osteoclast numbers was remarkably complex and qualitatively variable in different experiments. Whereas 19 of 46 experiments exhibited single peak of osteoclast formation, in 27 experiments we observed development of successive waves of osteoclast formation and death. Periodic changes in osteoclast numbers were confirmed in long-term cultures of mouse bone marrow cells treated with M-CSF and RANKL. Because the dynamics of changes in osteoclast numbers was found to be largely independent of monocytes, a two-species model of ordinary differential equations describing the changes in osteoclasts and monocytes was ineffective in recapitulating the oscillations in osteoclast numbers. Following experimental observation that medium collected from mature osteoclasts inhibited osteoclastogenesis in fresh cultures, we introduced a third variable, factor f, to describe osteoclast-derived inhibitor. This model allowed us to simulate the oscillatory changes in osteoclasts, which were coupled to oscillatory changes in the factor f, whereas monocytes changed exponentially. Importantly, to achieve the experimentally observed oscillations with increasing amplitude, we also had to assume that osteoclast presence stimulates osteoclast formation. Conclusions/Significance This study identifies the critical role for osteoclast autocrine regulation in controlling long-term dynamic of osteoclast formation and death and describes the complementary roles for negative and positive feedback mediators in determining the sharp dynamics of activation and inactivation of osteoclasts. PMID:18461134

Akchurin, Timur; Aissiou, Tayeb; Kemeny, Naomi; Prosk, Erin; Nigam, Nilima; Komarova, Svetlana V.

2008-01-01

296

Chilling out: a cool aqueous environment promotes the formation of gas-surface complexes.  

PubMed

SO(2), an important atmospheric pollutant, has been implicated in environmental phenomena such as acid rain, climate change, and cloud formation. In addition, SO(2) is fundamentally interesting because it forms spectroscopically identifiable complexes with water at aqueous surfaces. Vibrational sum frequency spectroscopy (VSFS) is used here to further investigate the mechanism by which SO(2) adsorbs to water at tropospherically relevant temperatures (0-23 °C). The spectral results lead to two important conclusions. SO(2) surface affinity is enhanced at colder temperatures, with nearly all of the topmost water molecules showing evidence of binding to SO(2) at 0 °C as compared to a much lower fraction at room temperature. This surface adsorption results in significant changes in water orientation at the surface, but is reversible at the temperatures examined here. Second, the SO(2) complex formation at aqueous surfaces is independent of aqueous solution acidity. One challenge in previous uptake studies was the ability to distinguish between the effects of surface adsorption as compared to bulk accommodation. The surface and vibrational specificity of these studies make this distinction possible, allowing a selective study of how the aqueous properties temperature and pH influence SO(2) surface affinity. PMID:21520889

Ota, Stephanie T; Richmond, Geraldine L

2011-05-18

297

Probing formation of cargo/importin-? transport complexes in plant cells using a pathogen effector  

PubMed Central

Importin-?s are essential adapter proteins that recruit cytoplasmic proteins destined for active nuclear import to the nuclear transport machinery. Cargo proteins interact with the importin-? armadillo repeat domain via nuclear localization sequences (NLSs), short amino acids motifs enriched in Lys and Arg residues. Plant genomes typically encode several importin-? paralogs that can have both specific and partially redundant functions. Although some cargos are preferentially imported by a distinct importin-? it remains unknown how this specificity is generated and to what extent cargos compete for binding to nuclear transport receptors. Here we report that the effector protein HaRxL106 from the oomycete pathogen Hyaloperonospora arabidopsidis co-opts the host cell's nuclear import machinery. We use HaRxL106 as a probe to determine redundant and specific functions of importin-? paralogs from Arabidopsis thaliana. A crystal structure of the importin-?3/MOS6 armadillo repeat domain suggests that five of the six Arabidopsis importin-?s expressed in rosette leaves have an almost identical NLS-binding site. Comparison of the importin-? binding affinities of HaRxL106 and other cargos in vitro and in plant cells suggests that relatively small affinity differences in vitro affect the rate of transport complex formation in vivo. Our results suggest that cargo affinity for importin-?, sequence variation at the importin-? NLS-binding sites and tissue-specific expression levels of importin-?s determine formation of cargo/importin-? transport complexes in plant cells. PMID:25284001

Wirthmueller, Lennart; Roth, Charlotte; Fabro, Georgina; Caillaud, Marie-Cécile; Rallapalli, Ghanasyam; Asai, Shuta; Sklenar, Jan; Jones, Alexandra M E; Wiermer, Marcel; Jones, Jonathan D G; Banfield, Mark J

2015-01-01

298

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

299

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

PubMed

A simple, accurate and highly sensitive spectrophotometric method has been developed for the rapid determination of piroxicam (PX) in pure and pharmaceutical formulations. The proposed method involves formation of stable yellow colored ion-pair complexes of the amino derivative (basic nitrogen) of PX with three sulphonphthalein acid dyes namely; bromocresol green (BCG), bromothymol blue (BTB), bromophenol blue (BPB) in acidic medium. The colored species exhibited absorption maxima at 438, 429 and 432 nm with molar absorptivity values of 9.400×10(3), 1.218×10(3) and 1.02×10(4) L mol(-1) cm(-1) for PX-BCG, PX-BTB and PX-BPB complexes, respectively. The effect of optimum conditions via acidity, reagent concentration, time and solvent were studied. The reactions were extremely rapid at room temperature and the absorbance values remained constant for 48h. Beer's law was obeyed with a good correlation coefficient in the concentration ranges 1-100 ?g mL(-1) for BCG, BTB complexes and 1-95 ?g mL(-1) for BPB complex. The composition ratio of the ion-pair complexes were found to be 1:1 in all cases as established by Job's method. No interference was observed from common additives and excipients which may be present in the pharmaceutical preparations. The proposed method was successfully applied for the determination of PX in capsule and human blood serum samples with good accuracy and precision. PMID:24792197

Alizadeh, Nina; Keyhanian, Fereshteh

2014-09-15

300

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

1996-06-19

301

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

NASA Astrophysics Data System (ADS)

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

Alizadeh, Nina; Keyhanian, Fereshteh

2014-09-01

302

Spectrophotometric and atomic absorption spectrometric determination of ramipril and perindopril through ternary complex formation with eosin and Cu(II)  

Microsoft Academic Search

Two sensitive, spectrophotometric and atomic absorption spectrometric procedures are developed for the determination of ramipril and perindopril. Both methods are based on the formation of a ternary complex, extractable with chloroform, between copper(II), eosin and the two cited drugs. Spectrophotometrically under the optimum condition, the ternary complexes showed an absorption maximum at 535 nm, with apparent molar absorptivities of 6.55

Hisham E. Abdellatef; Magda M. Ayad; Elham A. Taha

1999-01-01

303

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

304

Formation of complex organic molecules in cold objects: the role of gas-phase reactions  

NASA Astrophysics Data System (ADS)

While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas-phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm ( ? 30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain-surface and gas-phase chemistry. We propose here a new model to form DME and MF with gas-phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthesized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairly well the observations towards L1544. It also explains, in a natural way, the observed correlation between DME and MF. We conclude that gas-phase reactions are major actors in the formation of MF, DME and methoxy in cold gas. This challenges the exclusive role of grain-surface chemistry and favours a combined grain-gas chemistry.

Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney

2015-04-01

305

PRELP Protein Inhibits the Formation of the Complement Membrane Attack Complex*  

PubMed Central

PRELP is a 58-kDa proteoglycan found in a variety of extracellular matrices, including cartilage and at several basement membranes. In rheumatoid arthritis (RA), the cartilage tissue is destroyed and fragmented molecules, including PRELP, are released into the synovial fluid where they may interact with components of the complement system. In a previous study, PRELP was found to interact with the complement inhibitor C4b-binding protein, which was suggested to locally down-regulate complement activation in joints during RA. Here we show that PRELP directly inhibits all pathways of complement by binding C9 and thereby prevents the formation of the membrane attack complex (MAC). PRELP does not interfere with the interaction between C9 and already formed C5b-8, but inhibits C9 polymerization thereby preventing formation of the lytic pore. The alternative pathway is moreover inhibited already at the level of C3-convertase formation due to an interaction between PRELP and C3. This suggests that PRELP may down-regulate complement attack at basement membranes and on damaged cartilage and therefore limit pathological complement activation in inflammatory disease such as RA. The net outcome of PRELP-mediated complement inhibition will highly depend on the local concentration of other complement modulating molecules as well as on the local concentration of available complement proteins. PMID:22267731

Happonen, Kaisa E.; Fürst, Camilla Melin; Saxne, Tore; Heinegård, Dick; Blom, Anna M.

2012-01-01

306

Complex formation between ovalbumin and strong polyanion PSSNa: study of structure and properties.  

PubMed

The mixture system of long-chain polyelectrolyte complexed with a globular protein was investigated based on dynamic light scattering and turbidimetric measurements. We have discussed at different pH values the influence of high salt concentration and mass ratio (protein:PSSNa) on the behavior of the mixture. In dilute concentration regime, the PSSNa chain contracts at pHc by patch binding. We found two critical values of mass ratio: The first corresponds to the maximum shrinking of PSSNa. The second indicates the system that became more stable where the number of proteins attached to the PSSNa chain was constant. The screen of electrostatic interaction shows a high contribution of hydrophobic interaction at large salt concentration to form the coacervates. By building phase diagram, the continuity of pH?1 in over whole range of salt concentrations and the widening of pH window (pH?1-pH?2) were observed. At certain salt concentrations, we can obtain the coexistence of two types of complex particles formed by electrostatic and hydrophobic interactions. PMID:25063122

Trabelsi, Saber; Aschi, Adel; Othman, Tahar; Gharbi, Abdelhafidh

2014-09-01

307

A new approach to determination of hydration equilibria constants for the case of [Er(EDTA)(H2O)(n)](-) complexes.  

PubMed

Two anionic complexes [Er(EDTA)(H2O)2](-) and [Er(EDTA)(H2O)3](-) were obtained in the form of the following compounds: [C(NH2)3]2[Er(EDTA)(H2O)2]ClO4·6H2O () and Na[Er(EDTA)(H2O)3]·5H2O (), respectively. The UV-vis-NIR absorption spectra of both monocrystals were measured at room temperature and at 4.2 K. The influence of the coordination number changes on intensities of the f-f transitions and the crystal field splitting of (2S+1)LJ multiplets are discussed. The weighted sum of molar absorption coefficients of f-f transitions in the spectra of and was used to reproduce the absorption bands of the Er(3+)-EDTA complex in aqueous solution. This approach allowed us to estimate that the complex in solution exists in 95% as the 8-coordinate [Er(EDTA)(H2O)2](-) species and in 5% as the 9-coordinate [Er(EDTA)(H2O)3](-) ones as well as to calculate the conditional hydration equilibrium constant (Kaqua) of the reaction: [Er(EDTA)(H2O)3](-) ? [Er(EDTA)(H2O)2](-) + H2O which is rather difficult to determine by using other methods. The Kaqua value was found to be 19 ± 1. PMID:25373563

Janicki, Rafa?; Mondry, Anna

2014-12-28

308

Complex Formation Between Ca(II), Mg(II), Al(III) Ions and Salicylglycine  

PubMed Central

For modelling the interactions of proteins/peptides with hard metal ions the complex formation of salicylglycine (SalGly) with Ca(II), Mg(ll) and AI(III) ions was studied in aqueous solution using pHpotentiometric and UV-vis spectroscopic techniques. Al(lll) ion was found to form more stable complexes with SalGiy than Ca(ll) or Mg(ll) ions. While AI(III) ion forms various 1:1 complexes of different protonation states in the pH range 2-7, Ca(ll), Mg(ll) ions seem to interact with SalGly only in the basic pH range and form mixed hydroxo species MLH-1 at pH ~ 8. According to the UV-vis spectroscopic measurements in the species MLH-1 the carboxylate-O- atom and the phenolate-O- coordinate to the metal ions. SaIGiy is able to keep Al(lll) in solution through inner and outer sphere coordination to metastable amorphous AI(OH)3 particles. Deprotonation of the peptide amide Nil does not occur in these systems. PMID:18365063

Kilyén, Melinda; Labádi, lmre; Tombácz, Etelka; Kiss, Tamás

2003-01-01

309

BAG3 regulates formation of the SNARE complex and insulin secretion.  

PubMed

Insulin release in response to glucose stimulation requires exocytosis of insulin-containing granules. Glucose stimulation of beta cells leads to focal adhesion kinase (FAK) phosphorylation, which acts on the Rho family proteins (Rho, Rac and Cdc42) that direct F-actin remodeling. This process requires docking and fusion of secretory vesicles to the release sites at the plasma membrane and is a complex mechanism that is mediated by SNAREs. This transiently disrupts the F-actin barrier and allows the redistribution of the insulin-containing granules to more peripheral regions of the ? cell, hence facilitating insulin secretion. In this manuscript, we show for the first time that BAG3 plays an important role in this process. We show that BAG3 downregulation results in increased insulin secretion in response to glucose stimulation and in disruption of the F-actin network. Moreover, we show that BAG3 binds to SNAP-25 and syntaxin-1, two components of the t-SNARE complex preventing the interaction between SNAP-25 and syntaxin-1. Upon glucose stimulation BAG3 is phosphorylated by FAK and dissociates from SNAP-25 allowing the formation of the SNARE complex, destabilization of the F-actin network and insulin release. PMID:25766323

Iorio, V; Festa, M; Rosati, A; Hahne, M; Tiberti, C; Capunzo, M; De Laurenzi, V; Turco, M C

2015-01-01

310

BAG3 regulates formation of the SNARE complex and insulin secretion  

PubMed Central

Insulin release in response to glucose stimulation requires exocytosis of insulin-containing granules. Glucose stimulation of beta cells leads to focal adhesion kinase (FAK) phosphorylation, which acts on the Rho family proteins (Rho, Rac and Cdc42) that direct F-actin remodeling. This process requires docking and fusion of secretory vesicles to the release sites at the plasma membrane and is a complex mechanism that is mediated by SNAREs. This transiently disrupts the F-actin barrier and allows the redistribution of the insulin-containing granules to more peripheral regions of the ? cell, hence facilitating insulin secretion. In this manuscript, we show for the first time that BAG3 plays an important role in this process. We show that BAG3 downregulation results in increased insulin secretion in response to glucose stimulation and in disruption of the F-actin network. Moreover, we show that BAG3 binds to SNAP-25 and syntaxin-1, two components of the t-SNARE complex preventing the interaction between SNAP-25 and syntaxin-1. Upon glucose stimulation BAG3 is phosphorylated by FAK and dissociates from SNAP-25 allowing the formation of the SNARE complex, destabilization of the F-actin network and insulin release. PMID:25766323

Iorio, V; Festa, M; Rosati, A; Hahne, M; Tiberti, C; Capunzo, M; De Laurenzi, V; Turco, M C

2015-01-01

311

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

E-print Network

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

Daniel Quemada

2008-08-25

312

Transient kinetics of redox reactions of flavodoxin: effects of chemical modification of the flavin mononucleotide prosthetic group on the dynamics of intermediate complex formation and electron transfer.  

PubMed

The effects of structural modifications of the flavin mononucleotide (FMN) prosthetic group of Clostridium pasteurianum flavodoxin on the kinetics of electron transfer to the oxidized form (from 5-deazariboflavin semiquinone produced by laser flash photolysis) and from the semiquinone form (to horse heart cytochrome c by using stopped-flow spectrophotometry) have been investigated. The analogues used were 7,8-dichloro-FMN, 8-chloro-FMN, 7-chloro-FMN, and 5,6,7,8-tetrahydro-FMN. The ionic strength dependence of cytochrome c reduction was not affected by chlorine substitution, although the specific rate constants for complex formation and decay were appreciably smaller. On the other hand, all of the chlorine analogues had the same rate constant for deazariboflavin semiquinone oxidation. The rate constants for tetrahydro-FMN flavodoxin semiquinone reduction of cytochrome c were considerably smaller than those for the native protein. The implications of these results for the electron-transfer mechanism of flavodoxin are discussed. PMID:6307350

Simondsen, R P; Tollin, G

1983-06-01

313

Differences in determinants required for complex formation and transactivation in related VP16 proteins.  

PubMed

VP16-H is an essential structural protein of herpes simplex virus type 1 (HSV-1) and is also a potent activator of virus immediate-early (IE) gene expression. Current models of functional determinants within VP16-H indicate that it consists of two domains, an N-terminal domain involved in recruiting VP16-H to a multicomponent DNA binding complex with two host proteins, Oct-1 and host cell factor (HCF), and an acidic C-terminal domain exclusively involved in transactivation. VP16-E, from equine herpesvirus 1 (EHV-1), exhibits strong conservation with the N-terminal domain of VP16-H but, with the exception of a short segment at the extreme C terminus, lacks almost the entire acidic C-terminal domain. Studies of key activation determinants within the C terminus of VP16-H would predict that VP16-E may activate poorly, if at all. However, VP16-E is a potent activator of both EHV-1 and HSV-1 IE gene transcription. We show that VP16-E does not follow the simple two-domain model of VP16-H. Thus, despite the conservation in the N-terminal domains, this region in VP16-E is not sufficient for assembly into the DNA binding complex with Oct-1 and HCF. The short conserved determinant close to the C terminus is completely dispensable in VP16-H but is absolutely required in VP16-E. In activation studies, the potency of intact VP16-E was not recapitulated in chimeric proteins in which it was fused with a GAL4 DNA binding domain. Furthermore, a chimeric protein consisting of the C-terminal region of VP16-E fused to the N-terminal domain of VP16-H, while able to promote complex formation, nevertheless exhibited very weak activation. These results indicate that the mode of recruitment of the activation domain, i.e., through complex formation with Oct-1 and HCF, may be crucial for activation and that key determinants required for activation in VP16-E, and possibly VP16-H, may involve interactions between regions of the C terminus and the N terminus rather than discrete domains with independent functions. PMID:11024140

Grapes, M; O'Hare, P

2000-11-01

314

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

PubMed Central

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

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

2014-01-01

315

The development of folds and cleavages in slate belts by underplating in accretionary complexes: A comparison of the Kodiak Formation, Alaska and the Calaveras Complex, California  

NASA Astrophysics Data System (ADS)

The development of folds and cleavages in slate and graywacke belts is commonly attributed to arc-continent or continent-continent collisions. However, the Kodiak Formation of southern Alaska and the Calaveras Complex of the western Sierra Nevada, California, are two slate and graywacke belts in which folds and slaty cleavages developed during simple underthrusting and underplating within accretionary wedges. The Maastrichtian Kodiak Formation is composed dominantly of coherent turbidites but includes lesser pebbly mudstone, minor conglomerate, and rare chert. The Kodiak Formation is part of a large accretionary complex that youngs in age seaward, but bedding tops generally show landward younging. A progression of structures has been determined by crosscutting relationships and includes (1) syndeformational depositional features; (2) broken formation; (3) slaty cleavage, folds, and thrust faults; (4) crenulations and crenulation cleavage; (5) late brittle thrust faults; and (6) right-lateral strike-slip faults. Broken formation, slaty cleavage, thrust faults, and folds developed during underthrusting and underplating within an accretionary wedge. Crenulations and brittle thrust faults are related to subsequent intrawedge shortening. Based on peak metamorphism in the uppermost zeolite to prehnite-pumpellyite facies, underplating occurred at a minimum depth of 10 km. The Calaveras Complex is composed of argillite, chert, graywacke, pebbly mudstone, limestone, and volcanic rocks. Its age of deposition has a maximum range from Permian to Early Jurassic. Overall, the unit appears to young westward, but local facing indicators show eastward younging of individual blocks. The sequence of structures developed in the Calaveras Complex is (1) syn-depositional olistostromes; (2) broken formation; (3) slaty cleavage, folds, and thrust faults; and (4) younger Jura-Triassic folds and crenulation cleavages. Broken formation and slaty cleavage developed during underthrusting and underplating in an accretionary wedge, in an analogous fashion to the Kodiak Formation. Greenschist facies metemorphism during underplating suggests that the Calaveras Complex was accreted at deeper levels, or in a wedge with a higher geothermal gradient, than the Kodiak Formation. Some other probable examples of slate/graywacke belts that became folded and well-foliated during underplating include part of the Dunnage Zone (Newfoundland), the Southern Uplands complex (Scotland), the Torlesse terrane (New Zealand), part of the Hamburg klippe (Pennsylvania), and the Taconic allochthons (New York). Peak metamorphism in these belts indicates that they were accreted in accretionary wedges with geothermal gradients higher than usually assumed for such tectonic settings; such wedges may have been fairly common features at convergent margins.

Paterson, Scott R.; Sample, James C.

1988-08-01

316

Formation of mRNA 3' termini: stability and dissociation of a complex involving the AAUAAA sequence.  

PubMed Central

Formation of the 3' termini of mRNAs in animal cells involves endonucleolytic cleavage of a pre-mRNA, followed by polyadenylation of the newly formed end. Here we demonstrate that, during cleavage in vitro, the highly conserved AAUAAA sequence of the pre-mRNA forms a complex with a factor present in a crude nuclear extract. This complex is required for cleavage and polyadenylation. It normally is transient, but is very stable on cleaved RNA to which a single terminal cordycepin residue has been added. The complex can form either during the cleavage reaction, or on a synthetic RNA that ends at the polyadenylation site. Mutations which prevent cleavage also prevent complex formation. The complex dissociates during or after polyadenylation, enabling the released activities to catalyze a second round of cleavage. Images Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6. Fig. 7. Fig. 8. PMID:2438129

Zarkower, D; Wickens, M

1987-01-01

317

The complex formation of 2,2,2-trichloroethanol and 2,2,2-tribromoethanol with some sulfur-oxygen electron donors  

NASA Astrophysics Data System (ADS)

The formation of 1:1 hydrogen-bonded complexes of 2,2,2,-trichloroethanol and 2,2,2-tribomoethanol with sulfoxides, sulfinamides, sulfones and sulfonamides has been studied by i.r. spectroscopy in carbon tetrachloride solution at 288.15, 298.15, 308.15 and 318.15 K. The equilibrium constants have been measured from the change in intensity of the free OH-stretching band of alcohols. The results show that the equilibrium constants ( K) and OH-stretching wavenumber shifts (? overline?OH) are in every case greater for the 2,2,2-trichloroethanol complexes than for the corresponding 2,2,2-tribromoethanol ones. Furthermore the proton acceptor strengths of sulfoxides and sulfinamides seem to be of the same order of magnitude, as also the much lower strengths of sulfones and sulfonamides, in agreement with earlier suggestion that inductive effects predominate over resonance effects in determining the polarity of sulfur-oxygen bonds in sulfinamides and sulfonamides.

Ruostesuo, P.; Karjalainen, J.

318

Use of charge-transfer complex formation for the spectrophotometric determination of nortriptyline.  

PubMed

Three simple and selective methods are proposed for the determination of nortriptyline hydrochloride in bulk form and in tablets. The first two methods are based on the formation of charge-transfer complexes between the drug base as a n-donor and quinhydrone or p-chloranil as pi-acceptor. The products exhibit absorption maxima at 497 and 560 nm in acetonitrile for quinhydrone and p-chloranil, respectively. The third method is based on the interaction of N-alkylvinylamine formed from the condensation of the free secondary amine group and acetaldehyde with p-chloranil to give a vinylamino substituted quinone. The coloured product exhibits an absorption maximum at 650 nm in dioxane. All variables were studied to optimize reaction conditions. Beer's law was obeyed and the relative standard deviations were found to be less than 1.5%. The methods have been applied to the analysis of nortriptyline hydrochloride in the bulk drug and in tablets. PMID:11204939

Attia, F M

2000-01-01

319

Thermally induced oxidative decarboxylation of copper complexes of amino acids and formation of strecker aldehyde.  

PubMed

In the Maillard reaction, independent degradations of amino acids play an important role in the generation of amino-acid-specific products, such as Strecker aldehydes or their Schiff bases. Such oxidative decarboxylation reactions are expected to be enhanced in the presence of metals. Preliminary studies performed through heating of alanine and various metal salts (Cu, Fe, Zn, and Ca) under pyrolytic conditions indicated that copper(II) and iron(III) because of their high oxidation potentials were the only metals able to induce oxidative decarboxylation of amino acids and formation of Strecker aldehyde or its derivatives as detected by gas chromatography/mass spectrometry. Furthermore, studies performed with synthetic alanine and glycine copper complexes indicated that they constituted the critical intermediates undergoing free-radical oxidative degradation, followed by the loss of carbon dioxide and the generation of Strecker aldehydes, which were detected either as stable Schiff base adducts or incorporated in moieties, such as pyrazine or pyridine derivatives. PMID:25078730

Nashalian, Ossanna; Yaylayan, Varoujan A

2014-08-20

320

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

PubMed Central

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. Mg2+ 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

2012-01-01

321

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

2012-10-01

322

Acceleration of enzymatic reaction of trypsin through the formation of water-soluble complexes with poly(ethylene glycol)-block-poly(alpha,beta-aspartic acid).  

PubMed

The amidase activity of bovine pancreas trypsin in water-soluble complexes with poly(ethylene glycol)-block-poly(alpha,beta-aspartic acid) (PEG-PAA) was evaluated by a colorimetric assay using L-lysine p-nitroanilide as a substrate. The enzymatic reaction of trypsin was accelerated through the complexation with PEG-PAA. By determining the kinetic parameters of the enzymatic reaction of trypsin, it was confirmed that the catalytic rate constant of the complexed trypsin was 15 times higher than that of the native trypsin. From the evaluation of pH dependence of initial reaction rate, it was indicated that this acceleration was induced by a stabilization of the imidazolium ion of the His residue in the catalytic site, the Asp-His-Ser triad, of trypsin due to the Asp units of PEG-PAA. The hydrogen bonded Asp-His pairs are critical constituents in several key enzymatic reactions including serine protease and apurinic endonucleases, and it was expected that the acceleration of the catalytic reaction might occur for other enzymes by the formation of water-soluble complexes with PEG-PAA. PMID:15762622

Kawamura, Akifumi; Yoshioka, Yuriko; Harada, Atsushi; Kono, Kenji

2005-01-01

323

Hydration of the sulfuric acid-methylamine complex and implications for aerosol formation.  

PubMed

The binary H2SO4-H2O nucleation is one of the most important pathways by which aerosols form in the atmosphere, and the presence of ternary species like amines increases aerosol formation rates. In this study, we focus on the hydration of a ternary system of sulfuric acid (H2SO4), methylamine (NH2CH3), and up to six waters to evaluate its implications for aerosol formation. By combining molecular dynamics (MD) sampling with high-level ab initio calculations, we determine the thermodynamics of forming H2SO4(NH2CH3)(H2O)n, where n = 0-6. Because it is a strong acid-base system, H2SO4-NH2CH3 quickly forms a tightly bound HSO4(-)-NH3CH3(+) complex that condenses water more readily than H2SO4 alone. The electronic binding energy of H2SO4-NH2CH3 is -21.8 kcal mol(-1) compared with -16.8 kcal mol(-1) for H2SO4-NH3 and -12.8 kcal mol(-1) for H2SO4-H2O. Adding one to two water molecules to the H2SO4-NH2CH3 complex is more favorable than adding to H2SO4 alone, yet there is no systematic difference for n ? 3. However, the average number of water molecules around H2SO4-NH2CH3 is consistently higher than that of H2SO4, and it is fairly independent of temperature and relative humidity. PMID:24730699

Bustos, Danielle J; Temelso, Berhane; Shields, George C

2014-09-01

324

Altered tyrosine metabolism and melanization complex formation underlie the developmental regulation of melanization in Manduca sexta.  

PubMed

The study of hemolymph melanization in Lepidoptera has contributed greatly to our understanding of its role in insect immunity. Manduca sexta in particular has been an excellent model for identifying the myriad components of the phenoloxidase (PO) cascade and their activation through exposure to pathogen-associated molecular patterns (PAMPs). However, in a process that is not well characterized or understood, some insect species rapidly melanize upon wounding in the absence of added PAMPs. We sought to better understand this process by measuring wound-induced melanization in four insect species. Of these, only plasma from late 5th instar M. sexta was unable to melanize, even though each contained millimolar levels of the putative melanization substrate tyrosine (Tyr). Analysis of Tyr metabolism using substrate-free plasmas (SFPs) from late 5th instar larvae of each species showed that only M. sexta SFP failed to melanize with added Tyr. In contrast, early instar M. sexta larvae exhibited wound-induced melanization and Tyr metabolism, and SFPs prepared from these larvae melanized in the presence of Tyr. Early instar melanization in M. sexta was associated with the formation of a high mass protein complex that could be observed enzymatically in native gels or by PO-specific immunoblotting. Topical treatment of M. sexta larvae with the juvenile hormone (JH) analog methoprene delayed pupation and increased melanizing ability late in the instar, thus linking development with immunity. Our results demonstrate that melanization rates are highly variable in Lepidoptera, and that developmental stage can be an important factor for melanization within a species. More specifically, we show that the physiological substrate for melanization in M. sexta is Tyr, and that melanization is associated with the formation of a PO-containing protein complex. PMID:25596090

Clark, Kevin D

2015-03-01

325

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

PubMed

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

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

2013-04-01

326

Generalized additive models reveal the intrinsic complexity of wood formation dynamics  

PubMed Central

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

Cuny, Henri E.

2013-01-01

327

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

SciTech Connect

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

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

2014-01-01

328

N-palmitoyl-sulfatide participates in lateral domain formation in complex lipid bilayers.  

PubMed

Sulfatides (galactosylceramidesulfates) are negatively charged glycosphingolipids that are important constituents of brain myelin membranes. These membranes are also highly enriched in galactosylceramide and cholesterol. It has been implicated that sulfatides, together with other sphingolipids, take part in lateral domain formation in biological membranes. This study was conducted to characterize the lateral phase behavior of N-palmitoyl-sulfatide in mixed bilayer membranes. Going from simple lipid mixtures with sulfatide as the only sphingolipid in a fluid matrix of POPC, to more complex membranes including other sphingolipids, we have examined 1) ordered domain formation with sulfatide, 2) sterol enrichment in such domains and 3) stabilization of the domains against temperature by the addition of calcium. Using two distinct phase selective fluorescent probes, trans-parinaric acid and cholestatrienol, together with a quencher in the fluid phase, we were able to distinguish between ordered domains in general and ordered domains enriched in sterol. We found that N-palmitoyl-sulfatide formed ordered domains when present as the only sphingolipid in a fluid phospholipid bilayer, but these domains did not contain sterol and their stability was unaffected by calcium. However, at low, physiologically relevant concentrations, sulfatide partitioned favorably into domains enriched in other sphingolipids and cholesterol. These domains were stabilized against temperature in the presence of divalent cations. We conclude that sulfatides are likely to affect the lateral organization of biomembranes. PMID:18206111

Björkqvist, Y J E; Nybond, S; Nyholm, T K M; Slotte, J P; Ramstedt, B

2008-04-01

329

Unraveling the complexities of circadian and sleep interactions with memory formation through invertebrate research  

PubMed Central

Across phylogeny, the endogenous biological clock has been recognized as providing adaptive advantages to organisms through coordination of physiological and behavioral processes. Recent research has emphasized the role of circadian modulation of memory in generating peaks and troughs in cognitive performance. The circadian clock along with homeostatic processes also regulates sleep, which itself impacts the formation and consolidation of memory. Thus, the circadian clock, sleep and memory form a triad with ongoing dynamic interactions. With technological advances and the development of a global 24/7 society, understanding the mechanisms underlying these connections becomes pivotal for development of therapeutic treatments for memory disorders and to address issues in cognitive performance arising from non-traditional work schedules. Invertebrate models, such as Drosophila melanogaster and the mollusks Aplysia and Lymnaea, have proven invaluable tools for identification of highly conserved molecular processes in memory. Recent research from invertebrate systems has outlined the influence of sleep and the circadian clock upon synaptic plasticity. In this review, we discuss the effects of the circadian clock and sleep on memory formation in invertebrates drawing attention to the potential of in vivo and in vitro approaches that harness the power of simple invertebrate systems to correlate individual cellular processes with complex behaviors. In conclusion, this review highlights how studies in invertebrates with relatively simple nervous systems can provide mechanistic insights into corresponding behaviors in higher organisms and can be used to outline possible therapeutic options to guide further targeted inquiry. PMID:25136297

Michel, Maximilian; Lyons, Lisa C.

2014-01-01

330

From PII Signaling to Metabolite Sensing: A Novel 2-Oxoglutarate Sensor That Details PII - NAGK Complex Formation  

PubMed Central

The widespread PII signal transduction proteins are known for integrating signals of nitrogen and energy supply and regulating cellular behavior by interacting with a multitude of target proteins. The PII protein of the cyanobacterium Synechococcus elongatus forms complexes with the controlling enzyme of arginine synthesis, N-acetyl-L-glutamate kinase (NAGK) in a 2-oxoglutarate- and ATP/ADP-dependent manner. Fusing NAGK and PII proteins to either CFP or YFP yielded a FRET sensor that specifically responded to 2-oxoglutarate. The impact of the fluorescent tags on PII and NAGK was evaluated by enzyme assays, surface plasmon resonance spectroscopy and isothermal calorimetric experiments. The developed FRET sensor provides real-time data on PII - NAGK interaction and its modulation by the effector molecules ATP, ADP and 2-oxoglutarate in vitro. Additionally to its utility to monitor 2-oxoglutarate levels, the FRET assay provided novel insights into PII - NAGK complex formation: (i) It revealed the formation of an encounter-complex between PII and NAGK, which holds the proteins in proximity even in the presence of inhibitors of complex formation; (ii) It revealed that the PII T-loop residue Ser49 is neither essential for complex formation with NAGK nor for activation of the enzyme but necessary to form a stable complex and efficiently relieve NAGK from arginine inhibition; (iii) It showed that arginine stabilizes the NAGK hexamer and stimulates PII - NAGK interaction. PMID:24349456

Lüddecke, Jan; Forchhammer, Karl

2013-01-01

331

Star Formation and Young Population of the H II Complex Sh2-294  

NASA Astrophysics Data System (ADS)

The Sh2-294 H II region ionized by a single B0V star features several infrared excess sources, a photodissociation region, and also a group of reddened stars at its border. The star formation scenario in this region seems to be quite complex. In this paper, we present follow-up results of Sh2-294 H II region at 3.6, 4.5, 5.8, and 8.0 ?m observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H2 (2.12 ?m) observation, to characterize the young population of the region and to understand its star formation history. We identified 36 young stellar object (YSO, Class I, Class II, and Class I/II) candidates using IRAC color-color diagrams. It is found that Class I sources are preferentially located at the outskirts of the H II region and associated with enhanced H2 emission; none of them are located near the central cluster. Combining the optical to mid-infrared (MIR) photometry of the YSO candidates and using the spectral energy distribution fitting models, we constrained stellar parameters and the evolutionary status of 33 YSO candidates. Most of them are interpreted by the model as low-mass (<4 M ?) YSOs; however, we also detected a massive YSO (~9 M ?) of Class I nature, embedded in a cloud of visual extinction of ~24 mag. Present analysis suggests that the Class I sources are indeed a younger population of the region relative to Class II sources (age ~ 4.5 × 106 yr). We suggest that the majority of the Class I sources, including the massive YSOs, are second-generation stars of the region whose formation is possibly induced by the expansion of the H II region powered by a ~4 × 106 yr B0 main-sequence star.

Samal, M. R.; Pandey, A. K.; Ojha, D. K.; Chauhan, N.; Jose, J.; Pandey, B.

2012-08-01

332

Localization and dynamics of amylose-lipophilic molecules inclusion complex formation in starch granules.  

PubMed

Inclusion complex formation between lipophilic dye molecules and amylose polymers in starch granules is investigated using laser spectroscopy and microscopy. By combining confocal laser scanning microscopy (CLSM) with spatial resolved photoluminescence (PL) spectroscopy, we are able to discriminate the presence of amylose in the peripheral region of regular and waxy granules from potato and corn starch, associating a clear optical fingerprint with the interaction between starch granules and lipophilic dye molecules. We show in particular that in the case of regular starch the polar head of the lipophilic dye molecules remains outside the amylose helix experiencing a water-based environment. The measurements performed on samples that have been extensively washed provide a strong proof of the specific interaction between lipid dye molecules and amylose chains in regular starch. These measurements also confirm the tendency of longer amylopectin chains, located in the hilum of waxy starch granules, to form inclusion complexes with ligands. Through real-time recording of CLSM micrographs, within a time frame of tens of seconds, we measured the dynamics of occurrence of the inclusion process between lipids and amylose located at the periphery of starch granules. PMID:25715960

Manca, Marianna; Woortman, Albert J J; Mura, Andrea; Loos, Katja; Loi, Maria Antonietta

2015-03-11

333

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

PubMed

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

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

2013-03-01

334

Electrocatalytic Oxidation of Formate with Nickel Diphosphane Dipeptide Complexes: Effect of Ligands Modified with Amino Acids  

SciTech Connect

A series of nickel bis-diphosphine complexes with dipeptides appended to the ligands were investigated for the catalytic oxidation of formate. Typical rates of ~7 s-1 were found, similar to the parent complex (~8 s-1), with amino acid size and positioning contributing very little to rate or operating potential. Hydroxyl functionalities did result in lower rates, which were recovered by protecting the hydroxyl group. The results suggest that the overall dielectric introduced by the dipeptides does not play an important role in catalysis, but free hydroxyl groups do influence activity suggesting contributions from intra- or intermolecular interactions. These observations are important in developing a fundamental understanding of the affect that an enzyme-like outer coordination sphere can have upon molecular catalysts. This work was funded by the US DOE Basic Energy Sciences, Chemical Sciences, Geoscience and Biosciences Division (BRG, AJ, AMA, WJS), the US DOE Basic Energy Sciences, Physical Bioscience program (MLR). Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

Galan, Brandon R.; Reback, Matthew L.; Jain, Avijita; Appel, Aaron M.; Shaw, Wendy J.

2013-10-28

335

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

PubMed

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

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

2004-10-01

336

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

2013-10-01

337

A calorimetric study of the hydrolysis and peroxide complex formation of the uranyl(VI) ion.  

PubMed

The enthalpies of reaction for the formation of uranyl(vi) hydroxide {[(UO2)2(OH)2](2+), [(UO2)3(OH)4](2+), [(UO2)3(OH)5](+), [(UO2)3(OH)6](aq), [(UO2)3(OH)7](-), [(UO2)3(OH)8](2-), [(UO2)(OH)3](-), [(UO2)(OH)4](2-)} and peroxide complexes {[UO2(O2)(OH)](-) and [(UO2)2(O2)2(OH)](-)} have been determined from calorimetric titrations at 25 °C in a 0.100 M tetramethyl ammonium nitrate ionic medium. The hydroxide data have been used to test the consistency of the extensive thermodynamic database published by the Nuclear Energy Agency (I. Grenthe, J. Fuger, R. J. M. Konings, R. J. Lemire, A. B. Mueller, C. Nguyen-Trung and H. Wanner, Chemical Thermodynamics of Uranium, North-Holland, Amsterdam, 1992 and R. Guillaumont, T. Fanghänel, J. Fuger, I. Grenthe, V. Neck, D. J. Palmer and M. R. Rand, Update on the Chemical Thermodynamics of Uranium, Neptunium, Plutonium, Americium and Technetium, Elsevier, Amsterdam, 2003). A brief discussion is given about a possible structural relationship between the trinuclear complexes [(UO2)3(OH)n](6-n), n = 4-8. PMID:24301256

Zanonato, Pier Luigi; Di Bernardo, Plinio; Grenthe, Ingmar

2014-02-14

338

A reduced-complexity model for river delta formation - Part 1: Modeling deltas with channel dynamics  

NASA Astrophysics Data System (ADS)

In this work we develop a reduced-complexity model (RCM) for river delta formation (referred to as DeltaRCM in the following). It is a rule-based cellular morphodynamic model, in contrast to reductionist models based on detailed computational fluid dynamics. The basic framework of this model (DeltaRCM) consists of stochastic parcel-based cellular routing schemes for water and sediment and a set of phenomenological rules for sediment deposition and erosion. The outputs of the model include a depth-averaged flow field, water surface elevation and bed topography that evolve in time. Results show that DeltaRCM is able (1) to resolve a wide range of channel dynamics - including elongation, bifurcation, avulsion and migration - and (2) to produce a variety of deltas such as alluvial fan deltas and deltas with multiple orders of bifurcations. We also demonstrate a simple stratigraphy recording component which tracks the distribution of coarse and fine materials and the age of the deposits. Essential processes that must be included in reduced-complexity delta models include a depth-averaged flow field that guides sediment transport a nontrivial water surface profile that accounts for backwater effects at least in the main channels, both bedload and suspended sediment transport, and topographic steering of sediment transport.

Liang, M.; Voller, V. R.; Paola, C.

2015-01-01

339

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

PubMed Central

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

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

2012-01-01

340

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

341

Evidence for formation of metamorphic core complexes without pre-thickened crust in North China Craton  

NASA Astrophysics Data System (ADS)

Initially thickened orogenic crust is often regarded as a crucial precondition for formation of metamorphic core complexes (MCCs). However, numerous doubts are raised on applicability of this scenario to the formation of MCCs within normal crust during Mesozoic to early Cenozoic in North China Craton (NCC). In eastern NCC, no high pressure metamorphism has been reported before and during formation of the MCCs, and no trace of any suture zone following the trend of the extension zone has been described. In the meantime, widespread syn-tectonic plutons and still unclear mechanisms of cratonic destruction make the tectonic setting of NCC quite enigmatic. Recently, different multi-disciplinary researches have largely contributed to build a database on structural and lithological constrains, together with rheological and paleo-thermal state that provide an opportunity to extend the survey region. We therefore implement 2-D numerical thermo-mechanical modelling approach to investigate the possibility, as well as first-order controlling parameters for formation of MCC in normal crust. In the experiments, we set the initial Moho depth to a normal value of 35km and consider low lithospheric extension rates (< 1cm/y) corresponding to the observed highly limited lithospheric stretching in Late Mesozoic. Considering Moho temperatures derived from the surface heat flux recorded by vitrinite reflectance, we test three different thermal profiles and explore the influence of rheological structure on lower crust and lithospheric mantle deformation. The experiments demonstrate the possibility of MCC development under "hot" conditions of normal crust in case of slow extension rates. Due to the low Péclet numbers characterizing this specific situation, the predicted PT paths are quite different from those inferred for other known MCCs, just confirming the particularity of the NCC case. We show that the synthetic model data are in good correlation with the geological field observations, cooling history based on thermochronology data and with Moho geometry derived from gravity data. This model provides insights on the mechanisms and process of large scale continental extension and cratonic destruction.

Wang, Kun; Burov, Evgueni; Gumiaux, Charles; Chen, Yan; Zhao, Liang; Lu, Gang

2014-05-01

342

Formation of whey protein\\/ ?-casein complexes in heated milk: Preferential reaction of whey protein with ?-casein in the casein micelles  

Microsoft Academic Search

Studies of the formation of soluble ?-casein\\/whey protein (WP) complexes in heated (90°C10min?1) milk and related mixtures of proteins have been made. The use of milk samples containing different genetic variants, and having different compositions, allowed the effects of changing the natural protein balance on the formation of particles to be investigated. In addition, studies were made of the effects

Laurence Donato; Fanny Guyomarc’h; Sylvie Amiot; Douglas G. Dalgleish

2007-01-01

343

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

SciTech Connect

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

Mah, V.; Jalilehvand, F.

2009-05-19

344

A rapid and sensitive assay method for measuring amine oxidase based on hydrogen peroxide–titanium complex formation  

Microsoft Academic Search

Hydrogenperoxide (H2O2) is an end product of diamine and polyamine oxidation by their respective oxidase enzymes. A new sensitive assay method is based on a H2O2–titanium (Ti) complex formation as an indicator of H2O2 production due to polyamine oxidation. The orange–yellow coloured H2O2–Ti complex was measured at 410 nm in a Shimadzu spectrophotometer. The assay conditions for maximum diamine oxidase

Sudipa Nag; Kalpana Saha; Monojit A Choudhuri

2000-01-01

345

Structure, electronic properties, and formation mechanisms of hydrogen-nitrogen complexes in GaPyN1-y alloys  

Microsoft Academic Search

The structure, formation energies, chemical bonding, and electronic properties of N-H complexes in the GaP0.97N0.03 alloy have been investigated by density functional theory and local density approximation theoretical methods. The achieved results closely parallel those previously found in the case of the GaAs0.97N0.03 alloy. In particular, they show that a same H*2-like complex can neutralize the N effects on the

A. Amore Bonapasta; F. Filippone; P. Giannozzi

2004-01-01

346

Determination of astemizole, terfenadine and flunarizine hydrochloride by ternary complex formation with eosin and lead(II)  

Microsoft Academic Search

A simple and sensitive spectrophotometric method has been established for the determination of astemizole(I), terfenadine(II) and flunarizine hydrochloride(III) based on ternary complex formation with eosin and lead(II). The method does not involve solvent extraction. The colour of the produced complex is measured at 547.5 nm for (I) and (III), while (II) is measured at 540.7 nm. Appropriate conditions were established

Khadiga Kelani; Lories I. Bebawy; Laila Abdel-Fattah

1999-01-01

347

Spectrophotometric Determination of Sparfloxacin in Pharmaceutical Preparations by Ternary Complex Formation with Pd(II) and Eosin  

Microsoft Academic Search

A simple, sensitive, and direct spectrophotometric method has been developed for the assay of sparfloxacin in bulk and pharmaceutical preparations. The proposed method is based on the formation of ternary complex between an investigated drug, palladium(II) ion and eosin in the presence of methylcellulose as surfactant and acetate buffer of pH 4.2. Spectrophotometrically, under the optimum conditions, the ternary complex

2007-01-01

348

Nonstoichiometric polyelectrolyte complex of carboxymethylcellulose andN-methylated poly(2-vinylpyridine): Formation of a gel-like structure  

Microsoft Academic Search

The formation of polyelectrolyte complexes between carboxymethylcellu- lose and N-methylated poly(2-vinylpyridine), at a nonstoichiometric mixing ratio, was studied. Various methods, such as viscometry, turbidimetry, electrophoresis, and opti- cal spectroscopy, were used to investigate the complexes with respect to their compo- sition, structure, and stability in aqueous systems of different ionic strengths. A gel-like structure was proposed for the nonstoichiometric polyelectrolyte

B. Vishalakshi; Soumyadeb Ghosh

2003-01-01

349

Determination of clemastine hydrogen fumarate, desloratadine, losartan potassium and moxepril HCl through binary complex formation with eosin  

Microsoft Academic Search

A simple and sensitive spectrophotometric method has been established for the determination of clemastine hydrogen fumarate (I), desloratadine (II), losartan potassium(III) and moxepril HCl(IV) based on binary complex formation with eosin. The method does not involve solvent extraction through the use of a non-ionic surfactant (methylcellulose). The color of the produced complex was measured at 552, 549nm for (I), (II)

Soad S. Abd El-Hay; Magda Y. El-Mammli; Abdalla A. Shalaby

350

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

PubMed Central

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

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

2013-01-01

351

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

PubMed

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

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

2013-01-01

352

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

PubMed Central

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

Ingham, Colin J; Jacob, Eshel Ben

2008-01-01

353

Adherence to Bürgi–Dunitz stereochemical principles requires significant structural rearrangements in Schiff-base formation: insights from transaldolase complexes  

PubMed Central

The Bürgi–Dunitz angle (?BD) describes the trajectory of approach of a nucleophile to an electrophile. The adoption of a stereoelectronically favorable ?BD can necessitate significant reactive-group repositioning over the course of bond formation. In the context of enzyme catalysis, interactions with the protein constrain substrate rotation, which could necessitate structural transformations during bond formation. To probe this theoretical framework vis-à-vis biocatalysis, Schiff-base formation was analysed in Francisella tularensis trans­aldolase (TAL). Crystal structures of wild-type and Lys?Met mutant TAL in covalent and noncovalent complexes with fructose 6-­phosphate and sedoheptulose 7-phosphate clarify the mechanism of catalysis and reveal that substrate keto moieties undergo significant conformational changes during Schiff-base formation. Structural changes compelled by the trajectory considerations discussed here bear relevance to bond formation in a variety of constrained enzymic/engineered systems and can inform the design of covalent therapeutics. PMID:24531488

Light, Samuel H.; Minasov, George; Duban, Mark-Eugene; Anderson, Wayne F.

2014-01-01

354

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

PubMed Central

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

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

2010-01-01

355

Reactions of a Chromium(III)-Superoxo Complex and Nitric Oxide That Lead to the Formation of Chromium(IV)-Oxo and Chromium(III)-Nitrito Complexes  

PubMed Central

The reaction of an end-on Cr(III)-superoxo complex bearing a 14-membered tetraazamacrocyclic TMC ligand, [CrIII(14-TMC)(O2)(Cl)]+, with nitric oxide (NO) resulted in the generation of a stable Cr(IV)-oxo species, [CrIV(14-TMC)(O)(Cl)]+, via the formation of a Cr(III)-peroxynitrite intermediate and homolytic O-O bond cleavage of the peroxynitrite ligand. Evidence for the latter comes from EPR spectroscopy, computational chemistry, and the observation of phenol nitration chemistry. The Cr(IV)-oxo complex does not react with nitrogen dioxide (NO2), but reacts with NO to afford a Cr(III)-nitrito complex, [CrIII(14-TMC)(NO2)(Cl)]+. The Cr(IV)-oxo and Cr(III)-nitrito complexes were also characterized spectroscopically and/or structurally. PMID:24066924

Yokoyama, Atsutoshi; Cho, Kyung-Bin

2013-01-01

356

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

PubMed

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

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

2009-06-01

357

Enantioseparation of mandelic acid derivatives by high performance liquid chromatography with substituted ?-cyclodextrin as chiral mobile phase additive and evaluation of inclusion complex formation.  

PubMed

The enantioseparation of ten mandelic acid derivatives was performed by reverse phase high performance liquid chromatography with hydroxypropyl-?-cyclodextrin (HP-?-CD) or sulfobutyl ether-?-cyclodextrin (SBE-?-CD) as chiral mobile phase additives, in which inclusion complex formations between cyclodextrins and enantiomers were evaluated. The effects of various factors such as the composition of mobile phase, concentration of cyclodextrins and column temperature on retention and enantioselectivity were studied. The peak resolutions and retention time of the enantiomers were strongly affected by the pH, the organic modifier and the type of ?-cyclodextrin in the mobile phase, while the concentration of buffer solution and temperature had a relatively low effect on resolutions. Enantioseparations were successfully achieved on a Shimpack CLC-ODS column (150×4.6mm i.d., 5?m). The mobile phase was a mixture of acetonitrile and 0.10molL(-1) of phosphate buffer at pH 2.68 containing 20mmolL(-1) of HP-?-CD or SBE-?-CD. Semi-preparative enantioseparation of about 10mg of ?-cyclohexylmandelic acid and ?-cyclopentylmandelic acid were established individually. Cyclodextrin-enantiomer complex stoichiometries as well as binding constants were investigated. Results showed that stoichiometries for all the inclusion complex of cyclodextrin-enantiomers were 1:1. PMID:24893270

Tong, Shengqiang; Zhang, Hu; Shen, Mangmang; Ito, Yoichiro; Yan, Jizhong

2014-07-01

358

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

PubMed Central

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

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

2009-01-01

359

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

PubMed

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

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

2012-08-15

360

Pair formation and promiscuity of cytokeratins: formation in vitro of heterotypic complexes and intermediate-sized filaments by homologous and heterologous recombinations of purified polypeptides  

PubMed Central

Cytokeratins are expressed in different types of epithelial cells in certain combinations of polypeptides of the acidic (type I) and basic (type II) subfamilies, showing "expression pairs." We have examined in vitro the ability of purified and denatured cytokeratin polypeptides of human, bovine, and rat origin to form the characteristic heterotypic subunit complexes, as determined by various electrophoretic techniques and chemical cross-linking, and, subsequently, intermediate-sized filaments (IFs), as shown by electron microscopy. We have found that all of the diverse type I cytokeratin polypeptides examined can form complexes and IFs when allowed to react with equimolar amounts of any of the type II polypeptides. Examples of successful subunit complex and IF formation in vitro include combinations of polypeptides that have never been found to occur in the same cell type in vivo, such as between epidermal cytokeratins and those from simple epithelia, and also heterologous combinations between cytokeratins from different species. The reconstituted complexes and IFs show stability properties, as determined by gradual "melting" and reassociation, that are similar to those of comparable native combinations or characteristic for the specific new pair combination. The results show that cytokeratin complex and IF formation in vitro requires the pairing of one representative of each the type I and type II subfamilies into the heterotypic tetramer but that there is no structural incompatibility between any of the members of the two subfamilies. These findings suggest that the co-expression of specific pair combinations observed in vivo has other reasons than general structural requirements for IF formation and probably rather reflects the selection of certain regulatory programs of expression during cell differentiation. Moreover, the fact that certain cytokeratin polypeptide pairs that readily form complexes in vitro and coexist in the same cells in vivo nevertheless show preferential, if not exclusive, partner relationships in the living cell points to the importance of differences of stabilities among cytokeratin complexes and/or the existence of extracytokeratinous factors involved in the specific formation of certain cytokeratin pairs. PMID:2414304

1985-01-01

361

Complexation and thermodynamics of Cm(III) at high temperatures: the formation of [Cm(SO4)(n)](3-2n) (n = 1, 2, 3) complexes at T = 25 to 200 °C.  

PubMed

The formation of [Cm(SO(4))(n)](3-2n) complexes (n = 1, 2, 3) in an aquatic solution is studied by time resolved laser fluorescence spectroscopy as a function of the ligand concentration, the ionic strength (NaClO(4)) and the temperature (25 to 200 °C). The experiments are performed in a custom-built high temperature cell for spectroscopic measurements at high pressures and temperatures. The single component spectra of the individual species are identified by slope analysis at every studied temperature and their molar fractions are determined by peak deconvolution of the emission spectra. The results show a strong shift of the chemical equilibrium towards the complexed species at increased temperatures. With the determined speciation, the conditional stepwise stability constants are calculated and extrapolated to zero ionic strength, using the specific ion interaction theory (SIT). The log K(0)(n)(T) values increase by several orders of magnitude in the studied temperature range. The fitting of the temperature dependency of the first and second stability constant (log K(0)(1) and log K(0)(2)) requires an extended van't Hoff equation, taking into account a constant heat capacity of the reaction (?(r)C(0)(p,m) = const.). Contrarily, the temperature dependency of the log K(0)(3) is very well described by the linear van't Hoff equation, assuming ?(r)C(0)(p,m) = 0. Thus, the thermodynamic standard state data (?(r)H(0)(m), ?(r)S(0)(m), ?(r)C(0)(p,m)) of the stepwise complexation of Cm(III) with SO(4)(2-) are determined. Additionally, the ion interaction coefficients of the stepwise complexation reactions (??(n)) are determined as a function of the temperature. The fluorescence lifetimes of Cm(III) are recorded at different sulphate concentrations as a function of the temperature. The results give a strong indication that at T > 100 °C the first excited state of Cm(III) ((6)D'(7/2)) is effectively quenched by a temperature dependent enhancement of the energy transfer from the metal ion to OH vibrations of first shell water molecules. PMID:23085717

Skerencak, Andrej; Panak, Petra J; Fanghänel, Thomas

2013-01-14

362

Immune complex formation in human diabetic retina enhances toxicity of oxidized LDL towards retinal capillary pericytes.  

PubMed

Recently it has been shown that levels of circulating oxidized LDL immune complexes (ox-LDL-ICs) predict the development of diabetic retinopathy (DR). This study aimed to investigate whether ox-LDL-ICs are actually present in the diabetic retina, and to define their effects on human retinal pericytes versus ox-LDL. In retinal sections from people with type 2 diabetes, costaining for ox-LDL and IgG was present, proportionate to DR severity, and detectable even in the absence of clinical DR. In contrast, no such staining was observed in retinas from nondiabetic subjects. In vitro, human retinal pericytes were treated with native LDL, ox-LDL, and ox-LDL-IC (0-200 mg protein/l), and measures of viability, receptor expression, apoptosis, endoplasmic reticulum (ER) and oxidative stresses, and cytokine secretion were evaluated. Ox-LDL-IC exhibited greater cytotoxicity than ox-LDL toward retinal pericytes. Acting through the scavenger (CD36) and IgG (CD64) receptors, low concentrations of ox-LDL-IC triggered apoptosis mediated by oxidative and ER stresses, and enhanced inflammatory cytokine secretion. The data suggest that IC formation in the diabetic retina enhances the injurious effects of ox-LDL. These findings offer new insights into pathogenic mechanisms of DR, and may lead to new preventive measures and treatments. PMID:24616481

Fu, Dongxu; Yu, Jeremy Y; Wu, Mingyuan; Du, Mei; Chen, Ying; Abdelsamie, Souzan A; Li, Yanchun; Chen, Junping; Boulton, Michael E; Ma, Jian-Xing; Lopes-Virella, Maria F; Virella, Gabriel; Lyons, Timothy J

2014-05-01

363

SMYD2-dependent HSP90 methylation promotes cancer cell proliferation by regulating the chaperone complex formation.  

PubMed

Heat shock protein 90 (HSP90) is a highly conserved molecular chaperone that facilitates the maturation of a wide range of proteins, and it has been recognized as a crucial facilitator of oncogene addiction and cancer cell survival. Although HSP90 function is regulated by a variety of post-translational modifications, the physiological significance of methylation has not fully been elucidated. Here we demonstrate that HSP90AB1 is methylated by the histone methyltransferase SMYD2 and that it plays a critical role in human carcinogenesis. HSP90AB1 and SMYD2 can interact through the C-terminal region of HSP90AB1 and the SET domain of SMYD2. Both in vitro and in vivo methyltransferase assays revealed that SMYD2 could methylate HSP90AB1 and mass spectrometry analysis indicated lysines 531 and 574 of HSP90AB1 to be methylated. These methylation sites were shown to be important for the dimerization and chaperone complex formation of HSP90AB1. Furthermore, methylated HSP90AB1 accelerated the proliferation of cancer cells. Our study reveals a novel mechanism for human carcinogenesis via methylation of HSP90AB1 by SMYD2, and additional functional studies may assist in developing novel strategies for cancer therapy. PMID:24880080

Hamamoto, Ryuji; Toyokawa, Gouji; Nakakido, Makoto; Ueda, Koji; Nakamura, Yusuke

2014-08-28

364

Decamethylytterbocene Complexes of Bipyridines and Diazabutadienes: Multiconfigurational Ground States and Open-Shell Singlet Formation  

SciTech Connect

Partial ytterbium f-orbital occupancy (i.e., intermediate valence) and open-shell singlet formation are established for a variety of bipyridine and diazabutadiene adducts with decamethylytterbocene, (C5Me5)2Yb, abbreviated as Cp*2Yb. Data used to support this claim include ytterbium valence measurements using Yb LIII-edge X-ray absorption near-edge structure spectroscopy, magnetic susceptibility, and complete active space self-consistent field (CASSCF) multiconfigurational calculations, as well as structural measurements compared to density functional theory calculations. The CASSCF calculations indicate that the intermediate valence is the result of a multiconfigurational ground-state wave function that has both an open-shell singlet f13(?*)1, where pi* is the lowest unoccupied molecular orbital of the bipyridine or dpiazabutadiene ligands, and a closed-shell singlet f14 component. A number of other competing theories for the unusual magnetism in these materials are ruled out by the lack of temperature dependence of the measured intermediate valence. These results have implications for understanding chemical bonding not only in organolanthanide complexes but also for f-element chemistry in general, as well as understanding magnetic interactions in nanoparticles and devices.

Booth, Corwin H.; Walter, Marc D.; Kazhdan, Daniel; Hu, Yung-Jin; Lukens, Wayne W.; Bauer, Eric D.; Maron, Laurent; Eisenstein, Odile; Andersen, Richard A.

2009-04-22

365

Decamethylytterbocene complexes of bipyridines and diazabutadines: multiconfigurational ground states and open-shell singlet formation  

SciTech Connect

Partial ytterbium f-orbital occupancy (i.e. intermediate valence) and open-shell singlet Draft 12/formation are established for a variety of bipyridine and diazabutadiene adducts to decamethylytterbocene, (C{sub 5}Me{sub 5}){sub 2}Yb or Cp*{sub 2}Yb. Data used to support this claim includes ytterbium valence measurements using Yb Lm-edge x-ray absorption near-edge structure (XANES) spectroscopy, magnetic susceptibility and Complete Active Space Self-Consistent Field (CASSCF) multi configurational calculations, as well as structural measurements compared to density-functional theory (DFT) calculations. The CASSCF calculations indicate that the intermediate valence is the result of a multiconfigurational ground state wave function that has both an open-shell singlet f{sup 13} and a closed-shell singlet f{sup 14} component. A number of other competing theories for the unusual magnetism in these materials are ruled out by the presence of intermediate valence and its lack of any significant temperature dependence. These results have implications for understanding chemical bonding not only in organolanthanide complexes, but also for organometallic chemistry in general, as well as understanding magnetic interactions in nanopartic1es and devices.

Bauer, Eric D [Los Alamos National Laboratory; Booth, C H [LBNL; Walter, M D [LBNL; Kazhdan, D [LBNL; Hu, Y - J [LBNL; Lukens, Wayne [LBNL; Maron, Laurent [INSA TOULOUSE; Eisentein, Odile [UNIV MONTPELLIER 2; Anderson, Richard [LBNL

2009-01-01

366

[Pattern formation in microcosm: the role of self-assembly in complex biological envelopes development].  

PubMed

The data on the development of pollen/spore walls (of sporoderm) were reconsidered in the light of our hypothesis regarding a considerable role of self-assembling processes in the formation of this complex pattern. The premises that (1) glycocalyx (cell surface coating) is a self-assembling colloidal solution, and that (2) exine, formed on a glycocalyx framework, appears as a result of the self-assembly of the biopolymer (sporopollenin microemulsion), were independently suggested by the authors of this paper (Gabarayeva, 1990, 1993; Hemsley et al., 1992). Afterwards a joint hypothesis has been worked out which interpreted the processes of sporoderm development through regularities of colloidal chemistry. It was shown that all of the successive developmental stages, seen in transmission electron microscope (TEM) in the course of pollen wall development, correspond to successive micelle mesophases of a colloidal solution of surface-active substances which self-assemble when their concentration increases. Such an interpretation implies that all of the microstructures, observed in mature pollen walls (granules; rods-columellae; hexagonally packed layers of rods; bilayers, separated with a gap) are somewhat like "stiff history" of their appearance as a micellar sequence, immortalized by chemically resistant sporopollenin. Since self-assembling processes have nonlinear, spasmodic character, and microstructures of pollen wall, mentioned above, are arranged, as a rule, in successive layers, it has been suggested that these layers of heterogeneous microstructures occur as a result of the abrupt phase transitions typical for self-assembling micellar systems. PMID:20865932

Gabaraeva, N I; Hemsley, A R

2010-01-01

367

Formation and Identification of Unresolved Complex Mixtures in Lacustrine Biodegraded Oil from Nanxiang Basin, China  

PubMed Central

A comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC/TOFMS) method has been developed for the formation and identification of unresolved complex mixtures (UCMs) in lacustrine biodegraded oils that with the same source rock, similar maturity, and increasing degradation rank from Nanxiang Basin, China. Normal alkanes, light hydrocarbons, isoprenoids, steranes, and terpanes are degraded gradually from oil B330 to oil G574. The compounds in biodegraded oil (oil G574) have fewer types, the polarity difference of compounds in different types is minor, and the relative content of individual compounds is similar. All the features make the compounds in biodegraded oil coelute in GC analysis and form the raised “baseline hump” named UCMs. By injecting standard materials and analyzing mass spectrums of target compounds, it is shown that cyclic alkanes with one to five rings are the major components of UCMs. Furthermore, UCMs were divided into six classes. Classes I and II, composed of alkyl-cyclohexanes, alkyl-naphthanes, and their isomers, are originated from the enrichment of hydrocarbons resistant to degradation in normal oils. Classes III ~ VI, composed of sesquiterpenoids, tricyclic terpanes, low molecular steranes, diasteranes, norhopanes, and their isomers, are probably from some newly formed compounds during the microbial transformation of oil. PMID:25177711

Guo, Pengfei; He, Sheng; Zhu, Shukui; Chai, Derong; Yin, Shiyan; Dai, Wei; Zhang, Wanfeng

2014-01-01

368

Late neoproterozoic igneous complexes of the western Baikal-Muya Belt: Formation stages  

NASA Astrophysics Data System (ADS)

The paper presents new geological, geochemical, and isotopic data on igneous rocks from a thoroughly studied area in the western Baikal-Muya Belt, which is a representative segment of the Neoproterozoic framework of the Siberian Craton. Three rock associations are distinguished in the studied area: granulite-enderbite-charnockite and ultramafic-mafic complexes followed by the latest tonalite-plagiogranitegranite series corresponding to adakite in geochemical characteristics. Tonalites and granites intrude the metamorphic and gabbroic rocks of the Tonky Mys Point, as well as Slyudyanka and Kurlinka intrusions. The tonalites yielded a U-Pb zircon age of 595 ± 5 Ma. The geochronological and geological information indicate that no later than a few tens of Ma after granulite formation they were transferred to the upper lithosphere level. The Sm-Nd isotopic data show that juvenile material occurs in rocks of granitoid series (?Nd(t) = 3.2-7.1). Ophiolites, island-arc series, eclogites, and molasse sequences have been reviewed as indicators of Neoproterozoic geodynamic settings that existed in the Baikal-Muya Belt. The implications of spatially associated granulites and ultramafic-mafic intrusions, as well as granitoids with adakitic geochemical characteristics for paleogeodynamic reconstructions of the western Baikal-Muya Belt, are discussed together with other structural elements of the Central Asian Belt adjoining the Siberian Platform in the south.

Fedotova, A. A.; Razumovskiy, A. A.; Khain, E. V.; Anosova, M. O.; Orlova, A. V.

2014-07-01

369

RNA polymerase III subunit architecture and implications for open promoter complex formation  

PubMed Central

Transcription initiation by eukaryotic RNA polymerase (Pol) III relies on the TFIIE-related subcomplex C82/34/31. Here we combine cross-linking and hydroxyl radical probing to position the C82/34/31 subcomplex around the Pol III active center cleft. The extended winged helix (WH) domains 1 and 4 of C82 localize to the polymerase domains clamp head and clamp core, respectively, and the two WH domains of C34 span the polymerase cleft from the coiled-coil region of the clamp to the protrusion. The WH domains of C82 and C34 apparently cooperate with other mobile regions flanking the cleft during promoter DNA binding, opening, and loading. Together with published data, our results complete the subunit architecture of Pol III and indicate that all TFIIE-related components of eukaryotic and archaeal transcription systems adopt an evolutionarily conserved location in the upper part of the cleft that supports their functions in open promoter complex formation and stabilization. PMID:23132938

Wu, Chih-Chien; Herzog, Franz; Jennebach, Stefan; Lin, Yu-Chun; Pai, Chih-Yu; Aebersold, Ruedi; Cramer, Patrick; Chen, Hung-Ta

2012-01-01

370

On the formation and survival of complex prebiotic molecules in interstellar grain aggregates  

NASA Astrophysics Data System (ADS)

The aggregation of interstellar grains as a result of ballistic collisions produces loosely packed structures with much of their internal volume composed by vacuum (cavities). The molecular material present on the surfaces of the cavities gives rise to a series of reactions induced by cosmic rays, UV radiation, thermal shocks, etc., in high reducing conditions. Thus, a terrestrial type chemistry is given the possibility to evolve inside these cavities. The resulting products are different and of a wider range than those from gas-phase or surface chemistry in molecular clouds. Under conditions similar to those in the aggregate cavities, laboratory experiments have produced amino acids, sugars and other organic compounds from simple precursors. In dense star-forming regions, the molecular species inside aggregates are efficiently shielded against the local UV field. The same molecules were incorporated in the material which formed the Earth, as well as other planets, during the process of its formation and afterwards fell on the surface via comets, meteorites, interstellar dust, etc. This was the source material that can produce, under favorable circumstances, the biopolymers needed for life. The astronomical observations of organic molecules in star-forming regions and the results of analyses of meteorites and cometary dust seem to support the present hypothesis that complex prebiotic molecules form inside dust aggregates and therein survive the journey to planetary systems. The Miller experiment is revisited through innumerable repetitions inside dust grain aggregates.

Cecchi-Pestellini, Cesare; Scappini, Flavio; Saija, Rosalba; Iatì, Maria Antonia; Giusto, Arianna; Aiello, Santi; Borghese, Ferdinando; Denti, Paolo

2004-10-01

371

Complexation and Sequestration of BMP-2 from an ECM Mimetic Hyaluronan Gel for Improved Bone Formation  

PubMed Central

Bone morphogenetic protein-2 (BMP-2) is considered a promising adjuvant for the treatment of skeletal non-union and spinal fusion. However, BMP-2 delivery in a conventional collagen scaffold necessitates a high dose to achieve an efficacious outcome. To lower its effective dose, we precomplexed BMP-2 with the glycosaminoglycans (GAGs) dermatan sulfate (DS) or heparin (HP), prior to loading it into a hyaluronic acid (HA) hydrogel. In vitro release studies showed that BMP-2 precomplexed with DS or HP had a prolonged delivery compared to without GAG. BMP-2-DS complexes achieved a slightly faster release in the first 24 h than HP; however, both delivered BMP-2 for an equal duration. Analysis of the kinetic interaction between BMP-2 and DS or HP showed that HP had approximately 10 times higher affinity for BMP-2 than DS, yet it equally stabilized the protein, as determined by alkaline phosphatase activity. Ectopic bone formation assays at subcutaneous sites in rats demonstrated that HA hydrogel-delivered BMP-2 precomplexed with GAG induced twice the volume of bone compared with BMP-2 delivered uncomplexed to GAG. PMID:24167632

Kisiel, Marta; Klar, Agnieszka S.; Ventura, Manuela; Buijs, Jos; Mafina, Marc-Krystelle; Cool, Simon M.; Hilborn, Jöns

2013-01-01

372

SEPT12-microtubule complexes are required for sperm head and tail formation.  

PubMed

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

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

2013-01-01

373

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

PubMed Central

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

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

2013-01-01

374

Endocytic Rab proteins are required for hepatitis C virus replication complex formation  

PubMed Central

During infection, hepatitis C virus (HCV) NS4B protein remodels host membranes to form HCV replication complexes (RC) which appear as foci under fluorescence microscopy (FM). To understand the role of Rab proteins in forming NS4B foci, cells expressing the HCV replicon were examined biochemically and via FM. First, we show that an isolated NS4B-bound subcellular fraction is competent for HCV RNA synthesis. Further, this fraction is differentially enriched in Rab1, 2, 5, 6 & 7. However, when examined via FM, NS4B foci appear to be selectively associated with Rab5 & Rab7 proteins. Additionally, dominant negative (DN) Rab6 expression impairs Rab5 recruitment into NS4B foci. Further, silencing of Rab5 or Rab7 resulted in a significant decrease in HCV genome replication. Finally, expression of DN Rab5 or Rab7 led to a reticular NS4B subcellular distribution, suggesting that endocytic proteins Rab5 and Rab7, but not Rab11, may facilitate NS4B foci formation. PMID:20005553

Manna, David; Aligo, Jason; Xu, Chenjia; Park, Wei Sun; Koc, Hasan; Do Heo, Won; Konan, Kouacou V.

2009-01-01

375

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

PubMed Central

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

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

2011-01-01

376

A complex Quaternary ignimbrite-forming phonolitic eruption: the Poris Member of the Diego Hernández Formation (Tenerife, Canary Islands)  

Microsoft Academic Search

The Poris Member (0.28 Ma) of the Diego Hernández Formation (Tenerife, Canary Islands) is a widespread succession of plinian fall, surge and non-welded ignimbrite deposits. It was erupted from the northeastern sector of the multicyclic Las Cañadas Caldera, the summit caldera complex of the Las Cañadas Edifice. We present new stratigraphic data which allow the evolution of the eruption to

C. J Edgar; J. A Wolff; H. J Nichols; R. A. F Cas; J. Marti

2002-01-01

377

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

ERIC Educational Resources Information Center

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

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

2010-01-01

378

Substitution effects on the formation of T-shaped palladium carbene and thioketone complexes from Li/Cl carbenoids.  

PubMed

The preparation of palladium thioketone and T-shaped carbene complexes by treatment of thiophosphoryl substituted Li/Cl carbenoids with a Pd(0) precursor is reported. Depending on the steric demand, the anion-stabilizing ability of the silyl moiety (by negative hyperconjugation effects) and the remaining negative charge at the carbenic carbon atom, isolation of a three-coordinate, T-shaped palladium carbene complex is possible. In contrast, insufficient charge stabilization results in the transfer of the sulfur of the thiophosphoryl moiety and thus in the formation of a thioketone complex. While the thioketones are stable compounds the carbene complexes are revealed to be highly reactive and decompose under elimination of Pd metal. Computational studies revealed that both complexes are formed by a substitution mechanism. While the ketone turned out to be the thermodynamically favored product, the carbene is kinetically favored and thus preferentially formed at low reaction temperatures. PMID:24664573

Molitor, Sebastian; Feichtner, Kai-Stephan; Kupper, Claudia; Gessner, Viktoria H

2014-08-18

379

Hemolymph Melanization in the Silkmoth Bombyx mori Involves Formation of a High Molecular Mass Complex That Metabolizes Tyrosine*  

PubMed Central

The phenoloxidase (PO) cascade regulates the melanization of blood (hemolymph) in insects and other arthropods. Most studies indicate that microbial elicitors activate the PO cascade, which results in processing of the zymogen PPO to PO. PO is then thought to oxidize tyrosine and o-diphenols to quinones, which leads to melanin. However, different lines of investigation raise questions as to whether these views are fully correct. Here we report that hemolymph from the silkmoth, Bombyx mori, rapidly melanizes after collection from a wound site. Prior studies indicated that in vitro activated PPO hydroxylates Tyr inefficiently. Measurement of in vivo substrate titers, however, suggested that Tyr was the only PO substrate initially present in B. mori plasma and that it is rapidly metabolized by PO. Fractionation of plasma by gel filtration chromatography followed by bioassays indicated that melanization activity was primarily associated with a high mass complex (?670 kDa) that contained PO. The prophenoloxidase-activating protease inhibitor Egf1.0 blocked formation of this complex and Tyr metabolism, but the addition of phenylthiourea to plasma before fractionation enhanced complex formation and Tyr metabolism. Mass spectrometry analysis indicated that the complex contained PO plus other proteins. Taken together, our results indicate that wounding alone activates the PO cascade in B. mori. They also suggest that complex formation is required for efficient use of Tyr as a substrate. PMID:23553628

Clark, Kevin D.; Strand, Michael R.

2013-01-01

380

RIPK3 regulates p62-LC3 complex formation via the caspase-8-dependent cleavage of p62.  

PubMed

RIPK3 is a key molecule for necroptosis, initially characterized by necrotic cell death morphology and the activation of autophagy. Cell death and autophagic signaling are believed to tightly regulate each other. However, the associated recruitment of signaling proteins remains poorly understood. p62/sequestosome-1 is a selective autophagy substrate and a selective receptor for ubiquitinated proteins. In this study, we illustrated that both mouse and human RIPK3 mediate p62 cleavage and that RIPK3 interacts with p62, resulting in complex formation. In addition, RIPK3-dependent p62 cleavage is restricted by the inhibition of caspases, especially caspase-8. Moreover, overexpression of A20, a ubiquitin-editing enzyme and an inhibitor of caspase-8 activity, inhibits RIPK3-dependent p62 cleavage. To further investigate the potential role of RIPK3 in selective autophagy, we analyzed p62-LC3 complex formation, revealing that RIPK3 prevents the localization of LC3 and ubiquitinated proteins to the p62 complex. In addition, RIPK3-dependent p62-LC3 complex disruption is regulated by caspase inhibition. Taken together, these results demonstrated that RIPK3 interacts with p62 and regulates p62-LC3 complex formation. These findings suggested that RIPK3 serves as a negative regulator of selective autophagy and provides new insights into the mechanism by which RIPK3 regulates autophagic signaling. PMID:25450619

Matsuzawa, Yu; Oshima, Shigeru; Nibe, Yoichi; Kobayashi, Masanori; Maeyashiki, Chiaki; Nemoto, Yasuhiro; Nagaishi, Takashi; Okamoto, Ryuichi; Tsuchiya, Kiichiro; Nakamura, Tetsuya; Watanabe, Mamoru

2015-01-01

381

RNA polymerase II phosphorylation: uncoupling from GAL4-VP16 directed open complex formation and transcription in a reconstituted system.  

PubMed Central

An activated transcription system was constructed using substantially purified liver factors, Hela TFIID and GAL4-VP16. The system was used to study the relationship between RNA polymerase II large subunit phosphorylation and other ATP-dependent processes occurring during activated transcription. When C-terminal domain (CTD) kinase activity was inhibited, activator dependent open promoter complex formation proceeded normally. These open complexes could function to produce RNA in the absence of CTD phosphorylation, although the level of RNA produced was changed somewhat. The results demonstrate that RNA polymerase II CTD phosphorylation is not generally required for the formation of activator-dependent, functional open promoter complexes. Taken together with prior results the experiments suggest that a requirement for CTD phosphorylation may be situation-dependent and thus serve a regulatory function. Images PMID:7800486

Jiang, Y; Gralla, J D

1994-01-01

382

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

PubMed Central

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

Braun, Hans-Georg; Meyer, Evelyn

2013-01-01

383

P62 regulates resveratrol-mediated Fas/Cav-1 complex formation and transition from autophagy to apoptosis.  

PubMed

Resveratrol is a potential polyphenol drug used in cancer treatment. We examined the relationship between autophagy and apoptosis in RSV-treated non-small lung adenocarcinoma A549 cells. Resveratrol treatment increased autophagy and autophagy-mediated degradation of P62. Immunocytochemistry revealed P62 co-localized with Fas/Cav-1 complexes, known to induce apoptosis. However, siRNA-mediated P62 downregulation enhanced formation of Fas/Cav-1 complexes, suggesting that P62 inhibited Fas/Cav-1 complex formation. Fas/Cav-1 complexes triggered caspase-8 activation and cleavage of Beclin-1, releasing a C-terminal Beclin-1 peptide that translocated to the mitochondria and initiate apoptosis. Inhibition of autophagy by siRNA-mediated repression of Beclin-1 also blocked RSV-induced apoptosis, showing a dependence of apoptosis on autophagy. P62 knockdown by siRNA accelerated the activation of caspase-8 and initiate apoptosis, while Cav-1 knockdown inhibited apoptosis, but increased autophagy. Inhibition of autophagy by 3-MA prevented both P62 degradation and induction of apoptosis, whereas inhibition of apoptosis by z-IETD-FMK or z-DEVD-FMK enhanced both P62 induction and autophagic cell death. In conclusion, P62 links resveratrol-induced autophagy to apoptosis. P62 blocks apoptosis by inhibiting Fas/Cav-1 complex formation, but RSV-induced autophagic degradation of P62 enables formation of Fas/Cav-1 complexes which then activate caspase-8-mediated Beclin-1 cleavage, resulting in translocation of the Beclin-1 C-terminal fragment to the mitochondria to initiate apoptosis. PMID:25596736

Zhang, Jun; Ma, Ke; Qi, Tingting; Wei, Xiaoning; Zhang, Qing; Li, Guanwu; Chiu, Jen-Fu

2015-01-20

384

P62 Regulates resveratrol-mediated Fas/Cav-1 complex formation and transition from autophagy to apoptosis  

PubMed Central

Resveratrol is a potential polyphenol drug used in cancer treatment. We examined the relationship between autophagy and apoptosis in RSV-treated non-small lung adenocarcinoma A549 cells. Resveratrol treatment increased autophagy and autophagy-mediated degradation of P62. Immunocytochemistry revealed P62 co-localized with Fas/Cav-1 complexes, known to induce apoptosis. However, siRNA-mediated P62 downregulation enhanced formation of Fas/Cav-1 complexes, suggesting that P62 inhibited Fas/Cav-1 complex formation. Fas/Cav-1 complexes triggered caspase-8 activation and cleavage of Beclin-1, releasing a C-terminal Beclin-1 peptide that translocated to the mitochondria and initiate apoptosis. Inhibition of autophagy by siRNA-mediated repression of Beclin-1 also blocked RSV-induced apoptosis, showing a dependence of apoptosis on autophagy. P62 knockdown by siRNA accelerated the activation of caspase-8 and initiate apoptosis, while Cav-1 knockdown inhibited apoptosis, but increased autophagy. Inhibition of autophagy by 3-MA prevented both P62 degradation and induction of apoptosis, whereas inhibition of apoptosis by z-IETD-FMK or z-DEVD-FMK enhanced both P62 induction and autophagic cell death. In conclusion, P62 links resveratrol-induced autophagy to apoptosis. P62 blocks apoptosis by inhibiting Fas/Cav-1 complex formation, but RSV-induced autophagic degradation of P62 enables formation of Fas/Cav-1 complexes which then activate caspase-8-mediated Beclin-1 cleavage, resulting in translocation of the Beclin-1 C-terminal fragment to the mitochondria to initiate apoptosis. PMID:25596736

Zhang, Jun; Ma, Ke; Qi, Tingting; Wei, Xiaoning; Zhang, Qing; Li, Guanwu; Chiu, Jen-Fu

2015-01-01

385

Influence of the lipid environment on valinomycin structure and cation complex formation  

NASA Astrophysics Data System (ADS)

Carrier-type molecular ionophores, such as the cyclic dodecadepsipeptide valinomycin, often must undergo structural changes during the binding and transport of a cation across the lipid membrane. Observing the structural fluctuations that occur during this process experimentally has proven extremely difficult due to the complexities of spectroscopic analysis of protein structure/dynamics in native lipid bilayer environments. Currently, our understanding of how valinomycin selectively transports ions across membranes is derived from atomic structures solved of the cyclic macromolecule solvated in various organic solvents and complimentary in silico dynamics experiments. We have shown recently that deep-UV excited resonance Raman spectroscopy (DUVRR) has a unique ability to characterize secondary structure content and simultaneously provide information about the relative solvation of the probed peptide backbone C.M. Halsey, J. Xiong, O. Oshokoya, J.A. Johnson, S. Shinde, J.T. Beatty, G. Ghirlanda, R.D. JiJi, J.W. Cooley, Simultaneous observation of peptide backbone lipid solvation and a-helical structure by deep-UV resonance Raman spectroscopy, ChemBioChem 12 (2011) 2125-2128, [16]. Interpretation of DUVRR spectra of valinomycin in swelled lipid and unilamellar lipid bilayer environments indicate that the uncomplexed valinomycin molecule dynamically samples both the open and closed conformations as described for the structures derived from polar and non-polar organic solvents, respectively. Upon introduction of potassium, the structure of valinomycin in swelled lipid environments resembles more closely that of the open conformation. The shift in structure upon complexation is accompanied by a significant decrease in the valinomycin DUVRR spectral amide I intensity, indicating that the open conformation is more water solubilized and is seemingly "trapped" or predominantly located close to the lipid-water interface. The trapping of the valinomycin in the act of complex of potassium at the bilayer-solvent interface and its analysis by DUVRR represents the first spectroscopic description of this state. Conversely, an opposite trend is observed in the amide I intensity upon potassium complexation in unilamellar (or extruded) vesicles, implying the predominant conformation upon potassium binding in native bilayers is one where the peptide backbone of valinomycin is desolvated as would be expected if the molecule were more readily able to traverse a bilayer interior. Interpretation of the DUVRR spectral features is also consistent with the loss or formation of hydrogen bonds observed in the open and closed structures, respectively. Valinomycin must then sample several conformations in the absence of appropriate ions depending upon its locale in the lipid bilayer until potassium causes a greater degree of closure of the open conformer and an increased residency within the more non-polar interior. The potassium induced decreased solubility enables diffusion across the membrane where potassium release can occur by equilibration at the opposite lipid water interface.

Halsey, Christopher M.; Benham, Derek A.; JiJi, Renee D.; Cooley, Jason W.

2012-10-01

386

Core Formation in Planetesimals: Textural Analyses From 3D Synchrotron Imaging and Complex Systems Modeling  

NASA Astrophysics Data System (ADS)

Recent scenarios of core formation in planetesimals using calculations from planetary dynamists and from extinct radionuclides (e.g. 26Al, 60Fe), call for segregation of a metal liquid (core) from both solid silicate and a partially molten silicate - a silicate mush - matrix. These segregation scenarios require segregation of metallic metal along fracture networks or by the growth of molten core material into blebs large enough to overcome the strength of the mush matrix. Such segregation scenarios usually involve high strain rates so that separation can occur, which is in agreement with the accretion model of planetary growth. Experimental work has suggested deformation and shear can help develop fracture networks and coalesce metallic blebs. Here, we have developed an innovative approach that currently combines 2D textures in experimental deformation experiments on a partially molten natural meteorite with complex network analyses. 3D textural data from experimental samples, deformed at high strain rates, with or without silicate melts present, have been obtained by synchrotron-based high resolution hard x-ray microtomography imaging. A series of two-dimensional images is collected as the sample is rotated, and tomographic reconstruction yields the full 3D representation of the sample. Virtual slices through the 3D object in any arbitrary direction can be visualized, or the full data set can be visualized by volume rendering. More importantly, automated image filtering and segmentation allows the extraction of boundaries between the various phases. The volumes, shapes, and distributions of each phase, and the connectivity between them, can then be quantitatively analysed, and these results can be compared to models. We are currently using these new visual data sets to augment our 2D data. These results will be included in our current complex system analytical approach. This integrated method can elucidate and quantify the growth of metallic blebs in regions where a silicate mush matrix is present and help predict separation, in addition to addressing rates and timescales predicted by earlier modelling on silicate-free samples.

Rushmer, T. A.; Tordesillas, A.; Walker, D. M.; Parkinson, D. Y.; Clark, S. M.

2012-12-01

387

Protection of Metal Artifacts with the Formation of Metal-Oxalates Complexes by Beauveria bassiana.  

PubMed

Several fungi present high tolerance to toxic metals and some are able to transform metals into metal-oxalate complexes. In this study, the ability of Beauveria bassiana to produce copper oxalates was evaluated. Growth performance was tested on various copper-containing media. B. bassiana proved highly resistant to copper, tolerating concentrations of up to 20?g?L(-1), and precipitating copper oxalates on all media tested. Chromatographic analyses showed that this species produced oxalic acid as sole metal chelator. The production of metal-oxalates can be used in the restoration and conservation of archeological and modern metal artifacts. The production of copper oxalates was confirmed directly using metallic pieces (both archeological and modern). The conversion of corrosion products into copper oxalates was demonstrated as well. In order to assess whether the capability of B. bassiana to produce metal-oxalates could be applied to other metals, iron and silver were tested as well. Iron appears to be directly sequestered in the wall of the fungal hyphae forming oxalates. However, the formation of a homogeneous layer on the object is not yet optimal. On silver, a co-precipitation of copper and silver oxalates occurred. As this greenish patina would not be acceptable on silver objects, silver reduction was explored as a tarnishing remediation. First experiments showed the transformation of silver nitrate into nanoparticles of elemental silver by an unknown extracellular mechanism. The production of copper oxalates is immediately applicable for the conservation of copper-based artifacts. For iron and silver this is not yet the case. However, the vast ability of B. bassiana to transform toxic metals using different immobilization mechanisms seems to offer considerable possibilities for industrial applications, such as the bioremediation of contaminated soils or the green synthesis of chemicals. PMID:22291684

Joseph, Edith; Cario, Sylvie; Simon, Anaële; Wörle, Marie; Mazzeo, Rocco; Junier, Pilar; Job, Daniel

2011-01-01

388

Cisplatin-incorporated hyaluronic acid nanoparticles based on ion-complex formation.  

PubMed

The aim of this study is to prepare cisplatin-incorporated nanoparticles based on ion complex formation between hyaluronic acid (HA) and cisplatin for antitumor drug delivery. To prepare nanoparticles using HA, bulk HA was degraded by hyaluronidases (HAses). Cisplatin-incorporated HA nanoparticles were prepared by mixing cisplatin with an aqueous solution of HA and then the nanoparticle solution was dialyzed to remove trace elements. Since glioma tumor cell lines are able to secrete HAse, extracts from U343MG and U87MG cell lines were used to test the release of cisplatin from the nanoparticles. The morphological observation of the cisplatin-incorporated nanoparticles showed that they had spherical shapes with a particle size around 100-200 nm. The loading efficiency of cisplatin in the nanoparticles was about 67-81% (w/w) and cisplatin was continuously released from the nanoparticles for 4 days. Especially, the release rate of cisplatin from the nanoparticles increased when HAse was added to the release medium. In the results of the HA zymography, the U343MG cell line secreted HAse, while the U87MG cell line did not. When the extracts from U343MG were added to the release medium, the release rate of cisplatin was slightly increased, while the extracts from U87MG did not significantly affect the release rate of cisplatin. In conclusion, cisplatin-incorporated nanoparticles have sufficiently small particle sizes to use as a drug targeting system. The release of cisplatin from the nanoparticles was responsive to the secretion of HAse. These nanoparticles are suitable vehicles for an antitumor drug targeting system. PMID:17674407

Jeong, Young-Il; Kim, Seong-Taek; Jin, Shu-Guang; Ryu, Hyang-Hwa; Jin, Yong-Hao; Jung, Tae-Young; Kim, In-Young; Jung, Shin

2008-03-01

389

Complex formation between heme oxygenase and phytochrome during biosynthesis in Pseudomonas syringae pv. tomato.  

PubMed

The plant pathogen Pseudomonas syringae pv. tomato carries two genes encoding bacterial phytochromes. Sequence motifs identify both proteins (PstBphP1 and PstBphP2, respectively) as biliverdin IX? (BV)-binding phytochromes. PstbphP1 is arranged in an operon with a heme oxygenase (PstBphO)-encoding gene (PstbphO), whereas PstbphP2 is flanked downstream by a gene encoding a CheY-type response regulator. Expression of the heme oxygenase PstBphO yielded a green protein (?(max) = 650 nm), indicative for bound BV. Heterologous expression of PstbphP1 and PstbphP2 and in vitro assembly with BV IX? yielded the apoproteins for both phytochromes, but only in the case of PstBphP1 a light-inducible chromoprotein. Attempts to express the endogenous heme oxygenase BphO and either of the two phytochromes from two plasmids yielded only holo-PstBphP1. Relatively small amounts of soluble holo-PstBphP2 were just obtained upon co-expression with BphO from P. aeruginosa. Expression of the operon containing PstbphO:PstbphP1 led to an improved yield and better photoreactivity for PstBphP1, whereas an identical construct, exchanging PstbphP1 for PstbphP2 (PstbphO:PstbphP2), again yielded only minute amounts of chromophore-loaded BphP2-holoprotein. The improved yield for PstBphP1 from the PstbphO:PstbphP1 operon expression is apparently caused by complex formation between both proteins during biosynthesis as affinity chromatography of either protein using two different tags always co-purified the reaction partner. These results support the importance of protein-protein interactions during tetrapyrrole metabolism and phytochrome assembly. PMID:22415794

Shah, Rashmi; Schwach, Julia; Frankenberg-Dinkel, Nicole; Gärtner, Wolfgang

2012-06-01

390

Petrological and geochemical constraints on granitoid formation: The Waldoboro Pluton Complex, Maine  

SciTech Connect

The Waldoboro Pluton Complex (WPC) comprises seven units ranging from qtz-diorite to aplite. The country rocks are biotite-rich metagraywackes with minor shales mostly belonging to the Proterozoic Z-Ordovician Bucksport Formation. Field evidence strongly suggests that the WPC formed in-situ: contacts with the country rock are cryptic, transitional and concordant; restitic minerals in the granitoids are identical to those in the country rocks; prolific metasedimentary enclaves in the WPC are locally derived. Major and trace element data for country rock and the most voluminous units of the WPC define consistent linear trends suggesting limited melt segregation and retention of a high proportion of restite. Mixing models and partial melting models require 54--76% melting for generation of the gneissic granites and two-mica granites. Garnet-biotite geothermometry and garnet-Al[sub 2]SiO[sub 5]-SiO[sub 2]-plagioclase geobarometry indicate that the WPC formed at T = 740--780 C and P = 0.4--0.7 GPa. Published experimental data show that < 50% melting is likely under these conditions if melting is controlled by dehydration reactions. Bucksport lithologies contain < 20% biotite, suggesting that the maximum amount of melt that could have formed by dehydration melting is < 20%, even if all biotite was consumed during melting. It seems probable that a free fluid phase was required to generate the WPC. Migmatization is apparent in all lithologies (including amphibolites) in the vicinity of the WPC, consistent with fluid-present melting. Fluid may have ingressed along the St. George thrust, but the source of the fluid is unknown.

Barton, M. (Ohio State Univ., Columbus, OH (United States). Dept. of Geological Science); Sidle, W.S. (Oak Ridge National Lab., TN (United States))

1992-01-01

391

Complex formation of vanadium(IV) with 1,3,5-triamino-1,3,5-trideoxy-cis-inositol and related ligands.  

PubMed

The complex formation of vanadium(IV) with 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) and 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (tdci) was studied in aqueous solution and in the solid state. The formation constants of [V(IV)O(taci)](2+), [V(IV)O(tdci)](2+), and [V(IV)(tdci)(2)](4+) and of the deprotonation product [V(IV)(tdci)(2)H(-)(1)](3+) were determined (25 degrees C, 0.1 M KNO(3)). Cyclic voltammetry measurements established a reversible one-electron transfer for the [V(IV)(tdci)(2)H(-)(m)]((4)(-)(m))/[V(III)(tdci)(2)H(-)(n)]((3)(-)(n)) couple (0 complexes. An additional quasi-reversible electron transfer at strongly positive potentials (1.2-0.5 V) was assigned to the [V(V)(taci)(2)H(-)(m)]((5)(-)(m))/[V(IV)(taci)(2)H(-)(n)]((4)(-)(n)) couple. The structures of [V(IV)(taci)(2)](SO(4))(2).12H(2)O (1), [V(IV)(tdci)(2)][V(4)(V)O(12)].14.5H(2)O (2), and [V(IV)(tdci)(2)H(-)(1)]Cl(3).15H(2)O (3) were determined by single-crystal X-ray analysis. The cations of 1-3 exhibit a structure of approximate D(3)(d) symmetry. The vanadium centers have an almost regular octahedral geometry. The coordinated oxygen donors are deprotonated, and their protons are transferred to the amino groups which act as internal bases. For both ligands, EPR measurements support the formation of non-oxo V(IV) complexes, with a d(z)2 ground state, in aqueous solution above pH 7. The spectral features are indicative of hexacoordinated complexes with a geometry distorted toward a trigonal prism. Finally, a mechanism is proposed for the decomposition of [V(IV)L(2)H(-)(x)]((4)(-)(x)) (L = taci and tdci) in strongly alkaline media (pH approximately 13). PMID:15132617

Morgenstern, Bernd; Steinhauser, Stefan; Hegetschweiler, Kaspar; Garribba, Eugenio; Micera, Giovanni; Sanna, Daniele; Nagy, László

2004-05-17

392

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

SciTech Connect

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

Chu, Ivan K.; Laskin, Julia

2011-12-31

393

The role of the cell adhesion molecule uvomorulin in the formation and maintenance of the epithelial junctional complex  

PubMed Central

The role of the epithelial adhesion molecule uvomorulin in the formation of the epithelial junctional complex in the Madin-Darby canine kidney (MDCK) cell line was investigated. Experiments were carried out to determine whether specific inhibition of uvomorulin function would interfere selectively with the formation, stability, or function of the apical zonula adherens (ZA) and zonula occludens (ZO), or whether it would interfere with all forms of intercellular contact including the desmosomes. The effects of blocking antibodies and Fab fragments to uvomorulin on the formation of the junctional complex was examined with a Ca2+ switch assay for de novo junction assembly. The formation of the ZO, the ZA, and the desmosomes was assayed by fluorescence staining with an antibody to the tight junction-specific protein ZO-1, with rhodamine-phalloidin for ZA-associated actin filaments, and with an anti-desmoplakin antibody, respectively. Under different conditions and times of antibody treatment the extent of inhibition of the formation of each of the junctional elements was very similar. The ability of the cells to eventually overcome the inhibitory effect of the antibodies and form junctions correlated with the reappearance of uvomorulin at the regions of cell-cell contact. Therefore uvomorulin seems to mediate an early adhesion event between epithelial cells that is a prerequisite for the assembly of all elements of the junctional complex. In contrast, the transepithelial electrical resistance of confluent, well-established monolayers of MDCK cells grown on filters was not greatly affected by treatment with the various antibodies or Fab fragments. A small transient decrease in resistance observed with the polyclonal alpha-uvomorulin IgG may be due to a more subtle modulation of the junctional complex. PMID:3049625

1988-01-01

394

FORMATION OF ARROWHEAD COMPLEXES WITH HEAVY MEROMYOSIN IN A VARIETY OF CELL TYPES  

Microsoft Academic Search

Heavy meromyosin (HMM) forms characteristic arrowhead complexes with actin filaments in situ .These complexes are readily visualized in sectioned muscle . FollowingHMM treat- ment similar complexes appear in sectioned fibroblasts, chondrogenic cells, nerve cells, and several types of epithelial cells . Thin filaments freshly isolated from chondrogenic cells also bind HMM and form arrowhead structures in negatively stained preparations .

HARUNORI ISHIKAWA; RICHARD BISCHOFF; HOWARD HOLTZER

395

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

SciTech Connect

A dielectric well logging apparatus is described for obtaining amplitude ratios and phase differences between electromagnetic wave energy signals which have passed different distances through a subsurface formation adjacent a well borehole, so that an analyst may determine resistivity and dielectric constants for the different distances of travel through the formation. The apparatus consists of: (a) sonde means for moving through the well borehole; (b) at least three transmitter coils for emitting radio frequency energy into the formation at different depths in the borehole, the coils being spaced from each other in the sonde means for disposition at different depths in the borehole; (c) control means for controlling the activation of the transmitter coils; (d) receiver coils for receiving energy from the transmitter coils after passage through the formation and borehole, the receiver coils being spaced from each other and from the transmitter coils in the sonde for disposition at different depths in the borehole; (e) the receiver coils forming in groups of two different transmitter-receiver pairs, differently spaced from the other receiver pairs, with each of the transmitter coils; (f) receiver circuit means for forming signals representing the electromagnetic wave energy received in the receiver coils; and (g) processing circuit means for forming output signals representative of the phase difference and amplitude ratio for each of the different transmitter-receiver pairs so that the analyst may determine the resistivity and dielectric constants for the different distances of travel to determine if fluid invasion is present in the formation.

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

1986-09-02

396

JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 4, Tome 33, Avril 1972, page C2-103 MEASUREMENTS OF COMPLEX PIEZOELECTRIC CONSTANTS  

E-print Network

to the dielectric constant E , , . The relaxation is caused by jumping point defects and can phenomenologically displacement [I], [2]. The defects effect a slight dielectric relaxation also in the b-direction, whilst E and in the free dielectric constant 2 1 . It is concluded from a thermodynamical analysis that the clamped

Paris-Sud XI, Université de

397

Role of biologically active inorganic anions Cl- and Br- in inclusion complex formation of ?-cyclodextrin with some aromatic carboxylic acids  

NASA Astrophysics Data System (ADS)

1H NMR spectroscopy was used to evaluate the effects of biologically active anions Cl- and Br- in inclusion complex formation of ?-cyclodextrin with some aromatic carboxylic acids. It was demonstrated that presence of Br- anions induces the decrease in ?-cyclodextrin binding affinity to carboxylic acids, while Cl- has no a noticeable effect. The observed difference was discussed in terms of selective interactions of ?-cyclodextrin with Br- and Cl-. Only Br- anions are able to penetrate into ?-cyclodextrin cavity and compete with carboxylic acid molecule for the macrocyclic cavity. This competition shifts the ?-cyclodextrin/acid equilibrium in the direction of complex dissociation.

Terekhova, Irina; Chibunova, Ekaterina; Kumeev, Roman; Alper, Gennady

2013-02-01

398

Complexes of polyglutamic acid and long-chain alkanoylcholines: nanoparticle formation and drug release.  

PubMed

Ionic complexes of microbial poly(?-glutamic acid) and alkanoylcholines are fully bio-based comb-like systems able to self-organize in an ordered amphiphilic structure made of hydrophobic and hydrophilic alternating layers. Incubation of complex films under physiological conditions for one month promoted dissociation of the complex and hydrolysis of the choline ester without almost degradation of polyglutamic acid. Complex decomposition rates were depending on alkanoyl chain length and on complex stoichiometry as well. Nanoparticles with 50-100 nm diameter were successfully prepared from the stearoylcholine complex with a surfactant to polymer ratio of 0.75 and loaded with theophylline, carbamazepine or doxorubicin drugs. The releasing of the drugs from nanoparticles took place upon incubation at very different rates depending on the drug. Theophylline and carbamazepine were discharged in hours whereas doxorubicin was very slowly delivered along months. The observed differences were related to the different interaction mechanism operating between the drug and the complex. PMID:24582932

Tolentino, Ainhoa; Alla, Abdelilah; Martínez de Ilarduya, Antxon; Muñoz-Guerra, Sebastián

2014-05-01

399

HPV16E6-dependent c-fos expression contributes to AP-1 complex formation in SiHa cells.  

PubMed

To date, the major role of HPV16E6 in cancer has been considered to be its ability to inhibit the p53 tumor-suppressor protein, thereby thwarting p53-mediated cytotoxic responses to cellular stress signals. Here, we show that HPV16E6-dependent c-fos oncogenic protein expression contributes to AP-1 complex formation under oxidative stress in SiHa cells (HPV16-positive squamous cell carcinoma of the cervix). In addition, we examined the role of HPV16E6 in TGF-?-induced c-fos expression and found that the c-fos protein expression induced by TGF-? is HPV16E6 dependent. Thus, our results provide the first evidence that HPV16E6 contributes to AP-1 complex formation after both ligand-dependent and independent EGFR activation, suggesting a new therapeutic approach to the treatment of HPV-associated tumors. PMID:21822357

Liang, Feixin; Kina, Shinichiro; Takemoto, Hiroyuki; Matayoshi, Akira; Phonaphonh, Thongsavanh; Sunagawa, Nao; Arakaki, Keiichi; Arasaki, Akira; Kuang, Hai; Sunakawa, Hajime

2011-01-01

400

Characterization for Binding Complex Formation with Site-Directly Immobilized Antibodies Enhancing Detection Capability of Cardiac Troponin I  

PubMed Central

The enhanced analytical performances of immunoassays that employed site-directly immobilized antibodies as the capture binders have been functionally characterized in terms of antigen-antibody complex formation on solid surfaces. Three antibody species specific to cardiac troponin I, immunoglobulin G (IgG), Fab, and F(ab?)2 were site-directly biotinylated within the hinge region and then immobilized via a streptavidin-biotin linkage. The new binders were more efficient capture antibodies in the immunoassays compared to randomly bound IgG, particularly, in the low antibody density range. The observed improvements could have resulted from controlled molecular orientation and also from flexibility, offering conditions suitable for binding complex formations. PMID:19809518

Cho, Il-Hoon; Seo, Sung-Min; Jeon, Jin-Woo; Paek, Se-Hwan

2009-01-01

401

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

SciTech Connect

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

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

2007-10-26

402

The formation of carbon surface oxygen complexes by oxygen and ozone. The effect of transition metal oxides  

Microsoft Academic Search

Various surface oxygen complexes (SOCs) have been identified by DRIFT spectroscopy on the surface of carbon black (Printex-U) after partial non-catalytic conversion in 10% O2 in Ar and ozone. An in situ DRIFT analysis of the oxidation of fullerene C60 showed the formation of similar functionalities and validated the use of C60 as a carbon black model compound for DRIFT

G. Mul; J. P. A. Neeft; F. Kapteijn; J. A. Moulijn

1998-01-01