These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

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

PubMed

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, (1)H NMR, (13)C 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 9.9×10(4) and 5.2×10(4) 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 (DPPH) 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. PMID:25238180

El-Sayed, Yusif S; Gaber, M

2015-02-25

2

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

3

Determination of the equilibrium formation constants of two U(VI)-peroxide complexes at alkaline pH.  

PubMed

The formation of uranyl-peroxide complexes was studied at alkaline media by using UV-Visible spectrophotometry and the STAR code. Two different complexes were found at a H(2)O(2)/U(VI) ratio lower than 2. A graphical method was used in order to obtain the formation constants of such complexes and the STAR program was used to refine the formation constants values because of its capacity to treat multiwavelength absorbance data and refining equilibrium constants. The values obtained for the two complexes identified were: UO(2)(2+) + H(2)O(2) + 4OH(-) UO(2)(O(2))(OH)(2)(2-) + 2H(2)O: log ?°(1,1,4) = 28.1 ± 0.1 (1). UO(2)(2+) + 2H(2)O(2) + 6OH(-) UO(2)(O(2))(2)(OH)(2)(4-) + 4H(2)O: log ?°(1,2,6) = 36.8 ± 0.2 (2). At hydrogen peroxide concentrations higher than 10(-5) mol dm(-3), and in the absence of carbonate, the UO(2)(O(2))(2)(OH)(2)(4-) complex is predominant in solution, indicating the significant peroxide affinity of peroxide ions for uranium and the strong complexes of uranium(VI) with peroxide. PMID:21743904

Meca, S; Martínez-Torrents, A; Martí, V; Giménez, J; Casas, I; de Pablo, J

2011-08-21

4

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

5

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

6

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

PubMed

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

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

2014-02-01

7

First reported correlation between the calculated gas-phase proton macroaffinities of some metal complexes with their measured formation constants in solution: Zn(II) complexes of a series of tripodal aliphatic tetraamines.  

PubMed

A theoretical study on the first protonation step of a series of metal complexes with the general formula {M(N[(CH2)nNH2][(CH2)mNH2][(CH2)pNH2])2+} (n = m = p = 2, tren; n = 3, m = p = 2, pee; n = m = 3, p = 2, ppe; n = m = p = 3, tpt; n = 2, m = 3, p = 4, epb; and n = m = 3, p = 4, ppb; and M = Zn2+) was reported using both the Hartree-Fock and DFT (B3LYP) levels of theory. For the first time, two kinds of our recently published definitions for gas-phase proton affinities of polybasic ligands, proton microaffinity and proton macroaffinity, were extended to their metal complexes. There is a good correlation between the calculated gas-phase proton macroaffinities and the corresponding formation constants in solution. PMID:18348546

Salehzadeh, Sadegh; Bayat, Mehdi; Ward, Michael D

2008-05-01

8

How the cosmological constant affects gravastar formation  

SciTech Connect

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

Chan, R. [Coordenação de Astronomia e Astrofísica, Observatório Nacional, Rua General José Cristino, 77, São Cristóvão, CEP 20921-400, Rio de Janeiro, RJ (Brazil); Silva, M.F.A. da [Departamento de Física Teórica, Instituto de Física, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier 524, Maracanã, CEP 20550-900, Rio de Janeiro - RJ (Brazil); Rocha, P., E-mail: chan@on.br, E-mail: mfasnic@gmail.com, E-mail: pedrosennarocha@gmail.com [Instituto de Física, Universidade Federal Fluminense, Av. Litorânea s/n, Boa Viagem, CEP 24210-340, Niterói, RJ (Brazil)

2009-12-01

9

Potentiometric determination of the formation constants for complexes of 3,2?,2?-triaminopropyldiethylamine with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II)  

Microsoft Academic Search

The tripodal tetraamine ligand N{(CH2)3NH2}{(CH2)2NH2}2 (pee), has been investigated as an asymmetrical tetraamine chelating agent for CoII, NiII, CuII, ZnII and CdII. The protonation constants for this ligand and the formation constants for its complexes have been determined potentiometrically in 0.1 M KCl at 25 °C. The successive protonation constants (log Kn) are: 10.22, 9.51, 8.78 and 1.60 (n =

Hassan Keypour; Masoud Dehdari; Sadegh Salehzadeh; Kevin P. Wainwright

2003-01-01

10

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

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

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

2014-12-10

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

Simulation of biomolecular diffusion and complex formation.  

PubMed Central

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

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

1986-01-01

15

Estimating Intrinsic Formation Constants of Mineral Surface Species Using a Genetic Algorithm  

Microsoft Academic Search

The application of a powerful evolutionary optimization technique for the estimation of intrinsic formation constants describing\\u000a geologically relevant adsorption reactions at mineral surfaces is introduced. We illustrate the optimization power of a simple\\u000a Genetic Algorithm (GA) for forward (aqueous chemical speciation calculations) and inverse (calibration of Surface Complexation\\u000a Models, SCMs) modeling problems of varying degrees of complexity, including problems where

Adrián Villegas-Jiménez; Alfonso Mucci

2010-01-01

16

Determination of formation constants at elevated temperatures by laser-induced photoacoustic spectroscopy  

SciTech Connect

A photoacoustic spectrometer has been developed for high-sensitivity optical absorption measurements of aqueous solutions at temperatures from ambient to 90 C. The light source is a Nd:YAG-pumped dye laser, and the photoacoustic signal is detected with a piezoelectric transducer coupled to a thermostatted quartz cell. The temperature dependence of the observed photoacoustic signal is compared to a theoretical model, and the application of the instrument to the determination of formation constants of metal-ligand complexes at elevated temperatures is discussed. Measurements of the temperature dependence of the formation constant for AmCO{sub 3}{sup +} are reported.

Wruck, D.A.; Kadkhodayan, B.; Russo, R.E. [Lawrence Livermore National Laboratory, CA (United States)] [and others

1994-12-31

17

Influence of soluble aluminosilicate complex formation on imogolite solubility determination  

NASA Astrophysics Data System (ADS)

In a earlier paper (Su and Harsh, 1994), we presented a free energy of formation for imogolite based on solubility studies and including a formation constant for a monomeric, soluble aluminosilicate complex (Browne and Driscoll, 1992). Farmer and Lumsdon (1994) have argued that the aluminosilicate formation constant is too high, calling into question solubility determinations utilizing this value. We have recalculated the log K value for imogolite dissolution using the new value for the aluminosilicate species. The result is a slight, but insignificant, increase in the log K for imogolite dissolution, supporting our earlier contention that the free energy of imogolite is larger than found in previous studies.

Su, Chunming; Harsh, James B.

1996-11-01

18

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

19

Pattern Formation in Complex Fluids  

NASA Astrophysics Data System (ADS)

Classical fluid instabilities -- such as the Saffman-Taylor instability in a Hele-Shaw cell -- are dramatically modified by using complex fluids. For example, polymeric liquids driven in a Hele-Shaw cell yield "dendritic" patterns with an apparent directional anisotropy. The dynamics of complex liquids can also lead to new instabilities and patterns, such as space-filling patterns formed by successive bucklings of growing "elastica" seen in the phase transition of a liquid crystalline material. Understanding such problems requires an interplay between physical modeling, mathematical analysis, and sophisticated nonlinear simulation. For the first problem, I will discuss a non-Newtonian version of Darcy's law for Hele-Shaw flow. This yields a free-boundary problem for the pattern formation, and requires the solution of a nonlinear elliptic equation in a time-dependent domain. This is pushing the development of adaptive grid methods that represent the geometry accurately and efficiently. Our simulations yield insight into how shear-thinning, as is evinced by polymeric liquids, can produce patterns reminiscent of experiment, with "dendritic fingers", side-branching, and reduced tip-splitting. In the second problem, a long filament in a smectic-A phase grows within an isotropic fluid. The splay deformation of the material gives this filament an elastic response. The macroscopic model describes the dynamics of a growing, elastic filament immersed in a Stokesian fluid. The model marries filament elasticity and tensile forces with a numerically tractable nonlocal slender-body theory. Analysis shows that growth of the filament, despite fluid drag, produces a buckling instability. When coupled to a nonlocal hydrodynamic self-interaction, our fully nonlinear simulations show that such instabilities iterate along the filament, and give "space-filling" patterns.

Shelley, Michael

2000-03-01

20

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

21

New insights into formation of trivalent actinides complexes with DTPA.  

PubMed

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

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

2012-12-01

22

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

23

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

PubMed

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

Salehzadeh, Sadegh; Shooshtari, Amir; Bayat, Mehdi

2009-04-21

24

Taurocholate and taurodeoxycholate: gel formation and protonation constants.  

PubMed

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

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

2007-01-01

25

Thermodynamics of Formation of Molecular Complexes of Aromatic Nitro Derivatives with Lincomycin and ?-Glycyrrhizic Acid  

Microsoft Academic Search

It was found that lincomycin and ß-glycyrrhizic acid form 1:2 molecular complexes with aromatic nitro derivatives. Quantum-chemical calculations of lincomycin and ß-glycyrrhizic acid were performed. These compounds form a cavity and, like podands, are capable of accommodating guest molecules. The formation constants and the thermodynamic characteristics of the complexes were calculated. A linear correlation was found between the formation constants

V. N. Gusakov; V. N. Maistrenko; P. P. Safiullin

2001-01-01

26

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

SciTech Connect

A new method has been developed for determining binding constants of complexes of cyclodextrins with surface-active compounds, including water-soluble ionic surfactants. The technique requires measuring the change in surface tension caused by addition of a cyclodextrin (CD) to aqueous solutions of the surfactant; the experimental results lead directly to inferred values of the thermodynamic activity of the surfactant. Surface tension results are reported for three different surfactants sodium dodecyl sulfate (SDS), cetylpyridinium chloride (CPC), and cetyltrimethylammonium bromide (CTAB) in the presence and in the absence of added [beta]-CD. Data for CPC have been obtained at surfactant concentrations below and above the critical micelle concentration. Correlations between surface tension and surfactant activity are expressed by the Szyszkowski equation, which subsumes the Langmuir adsorption model and the Gibbs equation. It is observed that the surface tension increases monotonically as [beta]-cyclodextrin is added to ionic surfactant solutions. At concentrations of CD well in excess of the surfactant concentration, the surface tension approaches that of pure water, indicating that neither the surfactant-CD complexes nor CD itself are surface active. Binding constants are inferred from a model that incorporates the parameters of the Szyszkowski equation and mass action constants relating to the formation of micelles from monomers of the surfactant and the counterion. Evidence is given that two molecules of CD can complex the C-16 hydrocarbon chain of the cetyl surfactants. 30 refs., 5 figs., 1 tab.

Dharmawardana, U.R.; Christian, S.D.; Tucker, E.E.; Taylor, R.W.; Scamehorn, J.F. (Univ. of Oklahoma, Norman, OK (United States))

1993-09-01

27

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

28

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

29

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

Microsoft Academic Search

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

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

2004-01-01

30

Star Formation in the Rosette Complex  

E-print Network

The Rosette Complex in the constellation of Monoceros is a magnificent laboratory for the study of star formation. The region presents an interesting scenario, in which an expanding HII region generated by the large OB association NGC 2244 is interacting with a giant molecular cloud. Inside the cloud a number of stellar clusters have formed recently. In this chapter we present a review of past and present research on the region, and discuss investigations relevant to the physics of the nebula and the molecular cloud. We also review recent work on the younger embedded clusters and individual nebulous objects located across this important star forming region.

Carlos G. Román-Zúñiga; Elizabeth A. Lada

2008-10-06

31

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.

32

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

33

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

PubMed

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

Negi, Jeetendra Singh; Singh, Shivpal

2013-02-15

34

Interactive formation control in complex environments.  

PubMed

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

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

2014-02-01

35

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

36

Thermodynamics of formation reaction and hydrometallurgical application of metal-ammonia complexes in aqueous solutions  

NASA Astrophysics Data System (ADS)

Critically selected activity coefficients of individual ions stepwise stability constants, and enthalpy and entropy changes during formation of metal-ammonia complexes in aqueous salt solutions are summarised and analysed. Special attention is paid to the specifics of ammonia complexation in solutions with high ammonia concentrations (>=1 mol dm-3), which are of interest in hydrometallurgy. Certain problems and prospects for use of metal-ammonia complexation in hydrometallurgy are discussed. The bibliography includes 154 references.

Mironov, V. E.; Pashkov, G. L.; Stupko, T. V.

1992-09-01

37

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

38

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

NASA Astrophysics Data System (ADS)

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

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

2003-05-01

39

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

40

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

SciTech Connect

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

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

1999-09-01

41

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

PubMed

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

Mikiciuk-Olasik, Elzbieta; Wojewoda, Emilia; Bilichowski, Ireneusz; Witczak, Ma?gorzata; Karwowski, Boles?aw; Wagrowska-Danilewicz, Ma?gorzata; Stasikowska, Olga

2010-01-01

42

On the Formation of "Hypercoordinated" Uranyl Complexes  

SciTech Connect

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

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

2011-09-05

43

Quadrics on complex Riemannian spaces of constant curvature, separation of variables, and the Gaudin magnet  

Microsoft Academic Search

Integrable systems that are connected with orthogonal separation of variables in complex Riemannian spaces of constant curvature are considered herein. An isomorphism with the hyperbolic Gaudin magnet, previously pointed out by one of the authors, extends to coordinates of this type. The complete classification of these separable coordinate systems is provided by means of the corresponding L matrices for the

E. G. Kalnins; V. B. Kuznetsov; Willard Miller; Jr

1994-01-01

44

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 ...

45

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

Microsoft Academic Search

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

David K. Ryan; James H. Weber

1982-01-01

46

Evaluation of stability constants of metal complexes with sulphonated azo-ligands.  

PubMed

An ion-exchange procedure is described for the determination of the stability constants for cadmium, copper, nickel and manganese complexes with three sulphonated azo ligands: calmagite, alizarin violet N and palatine chrome black. The results, log K values, show a good agreement with those obtained by a spectrophotometric technique. PMID:18966044

Abollino, O; Sarzanini, C; Mentasti, E; Liberatori, A

1994-07-01

47

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

SciTech Connect

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

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

1997-07-01

48

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

49

Dynamics of Lane Formation in Driven Binary Complex Plasmas  

SciTech Connect

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

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

2009-02-27

50

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

51

Formation of Phenylene Oligomers Using Platinum-Phosphine Complexes  

E-print Network

Formation of Phenylene Oligomers Using Platinum-Phosphine Complexes Nira Simhai, Carl N. Iverson, New York 14627 Received February 12, 2001 The reaction of biphenylene with a series of platinum bis by a variety of metal complexes.4 In addition, such a reaction is thermodynamically favored due

Jones, William D.

52

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

53

Complex I Function and Supercomplex Formation Are Preserved in Liver Mitochondria Despite Progressive Complex III Deficiency  

PubMed Central

Functional oxidative phosphorylation requires appropriately assembled mitochondrial respiratory complexes and their supercomplexes formed mainly of complexes I, III and IV. BCS1L is the chaperone needed to incorporate the catalytic subunit, Rieske iron-sulfur protein, into complex III at the final stage of its assembly. In cell culture studies, this subunit has been considered necessary for supercomplex formation and for maintaining the stability of complex I. Our aim was to assess the importance of fully assembled complex III for supercomplex formation in intact liver tissue. We used our transgenic mouse model with a homozygous c.232A>G mutation in Bcs1l leading to decreased expression of BCS1L and progressive decrease of Rieske iron-sulfur protein in complex III, resulting in hepatopathy. We studied supercomplex formation at different ages using blue native gel electrophoresis and complex activity using high-resolution respirometry. In isolated liver mitochondria of young and healthy homozygous mutant mice, we found similar supercomplexes as in wild type. In homozygotes aged 27–29 days with liver disorder, complex III was predominantly a pre-complex lacking Rieske iron-sulfur protein. However, the main supercomplex was clearly detected and contained complex III mainly in the pre-complex form. Oxygen consumption of complex IV was similar and that of complex I was twofold compared with controls. These complexes in free form were more abundant in homozygotes than in controls, and the mRNA of complex I subunits were upregulated. In conclusion, when complex III assembly is deficient, the pre-complex without Rieske iron-sulfur protein can participate with available fully assembled complex III in supercomplex formation, complex I function is preserved, and respiratory chain stability is maintained. PMID:24466228

Davoudi, Mina; Kotarsky, Heike; Hansson, Eva; Fellman, Vineta

2014-01-01

54

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

55

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

56

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

57

Cu(II) complex formation by ACES buffer.  

PubMed

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

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

2013-12-01

58

Quadrics on Complex Riemannian Spaces of Constant Curvature, Separation of Variables and the Gaudin Magnet  

E-print Network

We consider integrable systems that are connected with orthogonal separation of variables in complex Riemannian spaces of constant curvature. An isomorphism with the hyperbolic Gaudin magnet, previously pointed out by one of us, extends to coordinates of this type. The complete classification of these separable coordinate systems is provided by means of the corresponding $L$-matrices for the Gaudin magnet. The limiting procedures (or $\\epsilon $ calculus) which relate various degenerate orthogonal coordinate systems play a crucial result in the classification of all such systems.

E. G. Kalnins; V. B. Kuznetsov; Willard Miller, Jr

1993-08-23

59

Variation of lattice constant and cluster formation in GaAsBi  

SciTech Connect

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

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

2013-12-28

60

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

61

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

SciTech Connect

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

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

1985-06-01

62

Topology and Complexity of Formations Abubakr Muhammad1  

E-print Network

of Technology, Atlanta, GA 30332, USA. Abstract Biological multi-agent systems such as animal herds, insect no intelligence themselves, but interact using simple physical laws, and give rise to complex adaptive systems, animal herds, bacterial colonies, schools of fish, formations of flying birds, and so on. These group

Egerstedt, Magnus

63

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

64

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

65

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

Microsoft Academic Search

Studies of complexation equilibria of the antibiotic anions nalidixate and cinoxacinate with [Cu(phen)]2+ and [Cu(bipy)]2+ are reported. These studies indicate that the stability of this type of complex is strongly related to the metal environment. A correlation between the stability constants, determined here, with the sigma donation character of the ligand is proposed. This study shows that the stability constant

Guillermo Mendoza-Díaz; Raul Perez-Alonso; Rafael Moreno-Esparza

1996-01-01

66

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

67

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

68

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

NASA Astrophysics Data System (ADS)

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

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

1988-03-01

69

Dielectric Constant Enhancement of Epoxy Thermosets via Formation of Polyelectrolyte Nanophases.  

PubMed

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

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

2014-12-18

70

Polarographic determination of lead hydroxide formation constants at low ionic strength  

USGS Publications Warehouse

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

Lind, C.J.

1978-01-01

71

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

72

Mauritania Slide Complex: morphology, seismic characterisation and processes of formation  

Microsoft Academic Search

Recently acquired Parasound and high resolution multi-channel seismic reflection data have afforded a more detailed investigation\\u000a of the Mauritania Slide Complex. The slide is more complex than previously reported, and has affected an area in the order\\u000a of 34,000 km2 between ? 600 and > 3,500 m water depths. The ovate-shaped slide displays a long run-out distance > 300 km. Slide formation\\u000a was pre-conditioned mainly by

Andrew A. Antobreh; Sebastian Krastel

2007-01-01

73

Insulin-incorporated chitosan nanoparticles based on polyelectrolyte complex formation  

Microsoft Academic Search

Insulin-incorporated nanoparticles were prepared by polyelectrolyte complex formation using low-molecular weight water soluble\\u000a chitosan (LMWSC). Insulin-incorporated nanoparticles showed spherical shapes with a particle size of approximately 200 nm.\\u000a The average particle size, drug content and loading efficiency increased with increasing insulin feed. The zeta potential\\u000a decreased with increasing insulin feed, indicating that the electrostatic interaction increased with increasing insulin feed.

Joung-Pyo Nam; Changyong Choi; Mi-Kyeong Jang; Young-Il Jeong; Jae-Woon Nah; Sung-Hyun Kim

2010-01-01

74

Correlations between Community Structure and Link Formation in Complex Networks  

PubMed Central

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

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

2013-01-01

75

The Effect of Multiple Formats on Understanding Complex Visual Displays  

NSDL National Science Digital Library

Students in introductory science courses frequently have difficulty comprehending complex graphics such as contour maps. Computer-assisted instruction (CAI), because of its ability to convey the same information in different formats, may help students gain necessary graphic interpretation skills. This article describes a research project in which students practiced reading two temperature maps in either a standard black and white contour or a color-enhanced contour format. They were then divided into groups and tested using only standard contour maps. The tests examined comprehension of the distribution of sea surface temperature, oceanographic phosphate concentration, and brain activation. Results suggest that having students practice with differently formatted maps of the same information improves later comprehension of standard contour maps.

Holly Taylor

2004-03-01

76

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

77

An ultrasonic absorption study of the complex formation of zinc(II) thiocyanate in aqueous solution  

NASA Astrophysics Data System (ADS)

A new method of analysis for the ultrasonic absorption of systems involving multiple coupled equilibria is described. The method consists of calculating the relaxation frequencies and amplitudes under a postulated reaction mechanism using trial values of the rate constants and volume changes and of comparing the computed absorption ?/f2 (absorption coefficient over frequency squared) directly with the experimental one. Application of this method to the ultrasonic absorption study of aqueous zinc(II)-thiocyanate solutions reveals that the relaxation absorption is ascribed to the successive complex formation equilibria Zn(SCN)3-nn-1 +SCN-(kn?k-n)Zn(SCN)2-nn, n=1-4. The rate constants and volume changes of the above reactions are determined. The method proves to be especially effective when the absorption spectra are associated with multiple coupled equilibria and accordingly too broad to be separated to discrete relaxation processes by the usual method of analysis.

Tamura, Kiyoshi

1985-11-01

78

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

NASA Astrophysics Data System (ADS)

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

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

1998-08-01

79

Determination of Binding Constants by Flow Injection Gradient Technique  

E-print Network

for the determination of binding constants of substrates with cyclodextrins or micelles. The concentration gradient of inclusion complex formation between -cyclodextrin ( -CD) and phenolphthalein and of the incorporation

Reid, Scott A.

80

Titanium complex formation of organic ligands in titania gels.  

PubMed

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

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

2015-01-27

81

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

82

GABAergic complex basket formations in the human neocortex.  

PubMed

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

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

2010-12-15

83

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

84

In vitro study of magnetite-amyloid ? complex formation.  

PubMed

Biogenic magnetite (Fe(3)O(4)) has been identified in human brain tissue. However, abnormal concentration of magnetite nanoparticles in the brain has been observed in different neurodegenerative pathologies. In the case of Alzheimer's disease (AD), these magnetic nanoparticles have been identified attached to the characteristic brain plaques, which are mainly formed by fibrils of amyloid ? peptide (A?). However, few clues about the formation of the magnetite-A? complex have been reported. We have investigated the interaction between these important players in AD with superconducting quantum interference, scanning electron microscope, surface plasmon resonance, and magnetic force microscopy. The results support the notion that the magnetite-A? complex is created before the synthesis of the magnetic nanoparticles, bringing a highly stable interaction of this couple. . PMID:22115601

Mir, Mònica; Tahirbegi, Islam Bogachan; Valle-Delgado, Juan José; Fernàndez-Busquets, Xavier; Samitier, Josep

2012-08-01

85

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

86

Formation of categories for complex novel auditory stimuli  

NASA Astrophysics Data System (ADS)

Categorization of complex sounds with multiple, imperfectly valid cues is fundamental to phonetic perception. To study the general perceptual and cognitive processes that support complex sound categories, a novel stimulus set was created that allows tight control of category structure and input distributions. Stimuli were created from 300-ms noise bursts by applying bandstop filters at varying center frequencies and manipulating rise/fall time of stimulus onset and offset. Stimuli were assigned to one of two categories and presented to participants in a category identification and an AX discrimination task. Feedback was provided during identification trials, but not during discrimination tasks. Participants quickly learned to apply the category labels with high accuracy. Identification reaction times followed a pattern typical of speech stimuli with an apex in reaction time at category boundary. These results are consistent with formation of new auditory categories. Preliminary results indicate that discrimination performance is not tightly coupled with development of sharp identification functions and response-time peaks at category boundaries. Implications for mechanisms of speech categorization and category formation will be discussed. [Work supported by CNBC, NIH, and NSF.

Mirman, Daniel; Holt, Lori L.; McClelland, James L.

2002-05-01

87

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

88

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

89

Fluorimetric determination of sulphathiazole in honey by means the formation of CDs inclusion complexes.  

PubMed

The inclusion complex of sulphathiazole in ?-cyclodextrin has been investigated. A 1:2 stoichiometry of the complex was established and formation constants K2 (42.83 ± 3.27 M(-1)) and K1 (4.98 ± 0.36 M(-1)) were calculated by using the changes produced on the native fluorescence of the drug, when included on the hydrophobic cyclodextrin cavity. An enhancement in the fluorescence emission of sulphathiazole and protection of the drug against photochemical reactions has been attained upon inclusion. In solutions of ?-CD dual emission (458 nm) was noticed in STZ. Formation of the inclusion complex of STZ should result in dual emission, which is due to a twisted intramolecular charge transfer band (TICT). A fluorimetric method for the determination of sulphathiazole has been proposed and applied in honey without sample treatment. The optimized fluorimetric method showed detection and quantitation limits of 9.74 ng/g and 32.48 ng/g, respectively. Selectivity is high, showing no cross-reactivity to other chemically related antibiotics. The results obtained for blind honey samples (mean recovery 97%), were in good agreement with those obtained by liquid chromatography separation and mass spectrometry detection (LC-MS) (mean recovery 102%), showing that the proposed method might be used for the determination of sulphathiazole residues without expensive equipment. PMID:24528704

Lucas-Abellán, C; Guillén, I; Mercader-Ros, M T; Serrano-Martínez, A; Núñez-Delicado, E; Gabaldón, J A

2014-03-15

90

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

91

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

92

Micelle formation of coenzyme Q10 with dipotassium glycyrrhizate using inclusion complex of coenzyme Q10 with ?-cyclodextrin.  

PubMed

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

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

2014-10-01

93

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

94

Measurement of complexation properties of metal ions in natural conditions by ultrafiltration: measurement of equilibrium constants for complexation of zinc by synthetic and natural ligands  

SciTech Connect

A new ultrafiltration method is described to measure complexation properties (stability constants) of trace metal ions with natural aquatic ligands. The determination of stability constants is described theoretically and the best operational conditions are discussed theoretically and experimentally. Theory is tested with Zn, known synthetic ligands, and pedogenic fulvic acids of natural waters. The results obtained by this method compare well with the literature data. In particular, for natural mixture of complexing sites like fulvic acids, this method permits the determination of the detailed equilibrium function to be carried out instead of its average value, over a given range of metal to ligand ratio. The most important advantages of this method are the fact that there is no limitation with regard to the nature of metal ions and little for that of the ligands.

Buffle, J.; Staub, C.

1984-12-01

95

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

96

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

PubMed

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

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

2012-09-01

97

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

NASA Astrophysics Data System (ADS)

Spectrophotometric, FTIR and theoretical studies of the charge-transfer complexes between Isoniazid (pyridine-4-carboxylic acid hydrazide) and the acceptors (p-chloranil, chloranilic acid and tetracyanoethylene) in acetonitrile, their association constants, thermodynamic properties and other related properties were studied. Isoniazid (INH), a widely used anti tubercular agent was found to form beautifully colored charge-transfer complexes with p-chloranil, chloranilic acid and tetracyanoethylene in acetonitrile. The absorption maxima of the complexes were 484, 519 and 479 nm, respectively (isoniazid had no absorption, but the acceptors had absorption in these regions). The composition of the complexes were determined to be 1:1 from Job's method of continuous variations depending on the time period of experiments as the stability of some of the complexes (p-chloranil and tetracyanoethylene complexes) was time dependent. Solid complexes formed between isoniazid and the acceptors were isolated but p-chloranil was found to form two different complexes. FTIR spectra of the complexes and the acceptors were measured. FTIR spectra of the complexes showed considerable shift in absorption peaks, changes in intensities of the peaks and formation of the new band (probably due to hydrogen bonding) on complexation. The thermodynamic association constants and other thermodynamic parameters of the complexes were determined spectrophotometrically taking D and A in varying ratios (2:8-8:2) and also in equimolar ratios. The complex formation was found to be spontaneous and associated with negative changes of ?G0, ?H0 and ?S0. The energies h?CT of the charge-transfer complexes were compared with the theoretical values of h?CT of the complexes obtained from HOMO and LUMO of the donor and the acceptors. Density function theory utilizing different basis sets was used for calculation. h?CT (experimental) values of the transition energies of the complexes in acetonitrile differed from h?CT (theoretical) values in the gaseous state. IDV value of isoniazid was calculated. Charge-transfer complexes were assumed to be partial electrovalent compounds with organic dative ions D+ and A- (in the excited state) and attempts had been made to correlate the energy changes for the formation of the complexes with the energy changes for the formation of electrovalent compounds between M+ and X- ions.

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

98

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

99

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

100

Mechanistic information from volume profiles for water exchange and complex-formation reactions of aquated Ni(II). pH, buffer and medium effects.  

PubMed

Rate and activation parameters for the complex-formation reaction of Ni(2+) with 4-(2-pyridylazo)-N,N-dimethyl aniline (PADA) were studied as a function of pH in different buffers in both aqueous and sodium dodecyl sulfate (SDS) micelle solutions. In aqueous Tris buffer solution, the forward and backward rate constants increased with increasing pH, while the complex-formation constant decreased due to a larger increase in the backward rate constant. The activation entropy, DeltaS(#), and activation volume, DeltaV(#), changed with increasing pH from positive to negative values, suggesting an apparent changeover from a dissociative to a more associative mechanism. Complex-formation reactions with 2,2'-bipyridine in Tris buffer showed almost no increase in the forward and backward rate constants on increasing the pH, but the DeltaS(#) and DeltaV(#) values became more negative. N-ethylmorpholine buffer showed no pH effect on the rate constants and activation parameters. Water exchange reactions of aquated Ni(2+) were also studied as a function of pH under the same conditions. The reported rate and activation parameters for water exchange in Tris and N-ethylmorpholine buffers are consistent with those found for the complex-formation reactions of Ni(2+) with PADA. The observed pH and buffer effects for both the complex-formation and water exchange reactions of aquated Ni(2+) can be accounted for in terms of the formation of a Ni(2+)-Tris complex in Tris buffer and general base catalysis by the buffer components. In SDS micelle solution, the complex-formation reaction with PADA was much faster than in aqueous solution, but the increase in rate constant with increasing pH was less significant, while DeltaS(#) and DeltaV(#) became more positive, pointing to a more dissociative mechanism. For SDS micelle solutions there was no effect on the water exchange rate constant or activation volume. Mechanistic interpretations are offered for all observed pH, buffer and medium effects. PMID:19859604

Gazzaz, Hanaa Asaad; Ember, Erika; Zahl, Achim; van Eldik, Rudi

2009-11-21

101

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

PubMed

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

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

2012-01-01

102

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

NASA Astrophysics Data System (ADS)

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

Saha, Avijit; Mukherjee, Asok K.

2004-07-01

103

IR spectroscopic study of the complex formation between ammonia and water molecules in a KBr matrix  

NASA Astrophysics Data System (ADS)

The formation of complexes of ammonia and water molecules in a potassium bromide matrix is studied by means of IR spectroscopy. Ammonia and water complexes of variable composition are stabilized in a solid matrix using different approaches to saturating KBr powder with the initial components. Proton transfer can occur, leading to the formation of ammonium salts.

Vorotyntsev, I. V.; Grinvald, I. I.; Kagalaev, I. Yu.; Petukhov, A. N.; Sutyagina, E. A.; Vorotyntsev, A. V.; Derbisher, E. V.; Petukhova, N. A.; Vorotyntsev, V. M.

2014-04-01

104

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

105

Schrodinger-Newton equation with complex Newton constant and induced gravity  

E-print Network

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

Diósi, Lajos

2009-01-01

106

The microwave properties of the jovian clouds: A new model for the complex dielectric constant of aqueous ammonia  

NASA Astrophysics Data System (ADS)

A new model for the complex dielectric constant of aqueous ammonia (NH4OH) under conditions characteristic of the jovian clouds has been developed. The new model is based on laboratory measurements in the frequency range between 2 and 8.5 GHz for ammonia concentrations of 0-8.5% by volume and temperatures between 274 and 297 K. The new model is based on the Meissner and Wentz (Meissner, T., Wentz, F.J. [2004]. IEEE Trans. Geosci. Rem. Sens. 42, 1836-1849) model of the complex dielectric constant of pure water but contains corrections for dissolved ammonia. Assuming Raleigh scattering, these measurements are applied to a cloud attenuation model to calculate the range of opacity of the jovian aqueous ammonia clouds. These measurements will improve our understanding of the data collected by the Juno microwave radiometer (MWR) by better characterizing the absorption properties of the aqueous ammonia present in the jovian atmosphere. The new model has been validated for temperatures up to 313 K, and may be consistently used for the expected conditions for aqueous clouds in all of the outer planets. The model fits 60.26% of all laboratory measurements within 2-sigma uncertainty. Descriptions of the experimental setups, uncertainties associated with the laboratory measurements, the model fitting process, the new model, and its application to approximating jovian cloud opacity are provided.

Duong, Danny; Steffes, Paul G.; Noorizadeh, Sahand

2014-02-01

107

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

NASA Astrophysics Data System (ADS)

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

Zimmermann, Tomáš; Burda, Jaroslav V.

2009-10-01

108

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

109

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

NASA Astrophysics Data System (ADS)

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

Ben-Jacob, Eshel

1997-03-01

110

Theoretical Insights into the Formation, Structure, and Energetics of Some Cyclodextrin Complexes  

Microsoft Academic Search

To investigate the physicochemical aspects relevant for the formation of various cyclodextrin inclusion complexes and to search for corresponding general structure–complex-stability relationships, stability data of 1 : 1 complexes for 179, 310, and 51 guest molecules with unsubstituted a-, ß-, and ?-cyclodextrin were collected. Statistical analysis using structure-based parameters such as molecular size, hydrophobicity, rotatable bonds, electronic properties, and the

Nicholas Bodor; Peter Buchwald

2002-01-01

111

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

112

Charge-transfer inclusion complex formation of tropylium cation with pillar[6]arenes.  

PubMed

The complexation behavior of pillar[6]arene hosts towards a carbonium ion, tropylium tetrafluoroborate (T·BF4), and the formation of novel charge-transfer (CT) inclusion complexes are described. In contrast, smaller pillar[5]arenes and larger pillar[7]arenes cannot form such complexes due to the unsuitable cavity dimensions. PMID:23749258

Fan, Jiazeng; Deng, Hongmei; Li, Jian; Jia, Xueshun; Li, Chunju

2013-07-18

113

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

114

Constant p53 Pathway Inactivation in a Large Series of Soft Tissue Sarcomas with Complex Genetics  

PubMed Central

Alterations of the p53 pathway are among the most frequent aberrations observed in human cancers. We have performed an exhaustive analysis of TP53, p14, p15, and p16 status in a large series of 143 soft tissue sarcomas, rare tumors accounting for around 1% of all adult cancers, with complex genetics. For this purpose, we performed genomic studies, combining sequencing, copy number assessment, and expression analyses. TP53 mutations and deletions are more frequent in leiomyosarcomas than in undifferentiated pleomorphic sarcomas. Moreover, 50% of leiomyosarcomas present TP53 biallelic inactivation, whereas most undifferentiated pleomorphic sarcomas retain one wild-type TP53 allele (87.2%). The spectrum of mutations between these two groups of sarcomas is different, particularly with a higher rate of complex mutations in undifferentiated pleomorphic sarcomas. Most tumors without TP53 alteration exhibit a deletion of p14 and/or lack of mRNA expression, suggesting that p14 loss could be an alternative genotype for direct TP53 inactivation. Nevertheless, the fact that even in tumors altered for TP53, we could not detect p14 protein suggests that other p14 functions, independent of p53, could be implicated in sarcoma oncogenesis. In addition, both p15 and p16 are frequently codeleted or transcriptionally co-inhibited with p14, essentially in tumors with two wild-type TP53 alleles. Conversely, in TP53-altered tumors, p15 and p16 are well expressed, a feature not incompatible with an oncogenic process. PMID:20884963

Pérot, Gaëlle; Chibon, Frédéric; Montero, Audrey; Lagarde, Pauline; de Thé, Hugues; Terrier, Philippe; Guillou, Louis; Ranchère, Dominique; Coindre, Jean-Michel; Aurias, Alain

2010-01-01

115

Double layer formation at the interface of complex plasmas  

SciTech Connect

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

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

2008-08-15

116

>Cognitive complexity and impression formation in informal social interaction  

Microsoft Academic Search

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

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

1974-01-01

117

Dinuclear gold(I) dithiophosphonate complexes: formation, structure and reactivity  

Microsoft Academic Search

2,4-Diaryl- and 2,4-diferrocenyl-1,3-dithiaphosphetane disulfide dimers (1a–1c) react with a variety of alcohols, silanols and trialkylsilylalcohols to form dithiophosphonic acids in a facile manner. Their corresponding salts react with chlorogold(I) complexes to produce the first dinuclear gold(I) dithiophosphonate complexes of the type [AuS2PR(OR?)]2 (R=Ph, R?=Et (2); R=p-C6H4OMe, R?=SiPh3) (3)) in high yield (>70%). The dinuclear gold(I) complexes react with dppm (Ph2PCH2PPh2)

Werner E. van Zyl; Richard J. Staples

1998-01-01

118

Inhibition of hydroxyapatite formation in the presence of titanocene-aminoacid complexes: an experimental and computational study.  

PubMed

Organometallic compounds have been used in various fields of chemistry, medicine and materials science. Central metal, stereochemical configuration and functional groups of the substitutes give to the organometallic compounds very special and selective properties. These properties have been used successfully in selective-antitumor-targeting, as well as anti-arthritic drugs. In the present investigation we study the influence of two organometallic compounds on the inhibition of crystallization of hydroxyapatite. These compounds are complexes of Ti(IV) with the general formula [Cp2Ti(aa)2](2+)2Cl(-), where Cp = ? (5)-C5H5 cyclopentadienyl and aa the amino acid glycine or alanine. The experiments were conducted according to the constant composition technique in supersaturated solutions containing calcium and phosphate ions. The kinetic results indicate a surface diffusion controlled mechanism of the hydroxyapatite (HAP) crystals. The experiments prove that the presence of [Cp2Ti(Ala)2](2+)2Cl(-) and [Cp2Ti(Gly)2](2+)2Cl(-) complexes affects drastically the profile formation rate of the HAP crystals under biological conditions. The complex with the amino acid alanine provides a stronger inhibition of the formation rate comparing to the complex with glycine. The experimental observations are supported by computer calculations. PMID:25578695

Chrissanthopoulos, A; Klouras, N; Ntala, Ch; Sevastos, D; Dalas, E

2015-01-01

119

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

E-print Network

Recently, Motes, Gilchrist, Dowling & Rohde [Phys. Rev. Lett. 113, 120501 (2014)] 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 photo-detector. 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.

Peter P. Rohde

2014-10-02

120

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

PubMed

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

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

2013-11-01

121

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

NASA Astrophysics Data System (ADS)

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

El-Shall, M. S.

2010-04-01

122

On Lexicalized Valency and the Valency of (New) Complex Verbal Formations in Slovenian  

E-print Network

The paper considers the matter of so-called lexicalized valency within the framework of new complex verbal formations in Slovenian, and in consequence, the increasingly dominant accusative valency in the language, which can also indicate...

Žele, Andreja

2013-01-01

123

PVA-Iodine complexes: Formation, structure, and properties  

Microsoft Academic Search

The PVA-Iodine complexes formed in PVA films soaked in iodine-KI aqueous solutions without boric acid are studied from the structural point of view. First, iodine soaking at comparatively low iodine concentrations is studied where iodine sorption takes place mostly in the amorphous phase. There, our interest is concentrated on the following problems: What happens in PVA films during iodine soaking?

Keizo Miyasaka

124

Modelling formation of complex topography by the seagrass Posidonia oceanica  

Microsoft Academic Search

Posidonia oceanica is a slow growing seagrass species that extends via growing rhizomes that grow only centimetres both horizontally and vertically each year. Posidonia oceanica forms topographically complex biogenic reefs of dead rhizome and sediments that are up to 4m in height that are called “matte”. This study investigates the role of slow horizontal and vertical growth of rhizomes in

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

2005-01-01

125

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

126

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

PubMed Central

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

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

2013-01-01

127

Structural basis for cooperativity of CRM1 export complex formation  

PubMed Central

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

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

2013-01-01

128

Ligand exchange and complex formation kinetics studied by NMR exemplified on fac-[(CO) 3M(H 2O)] + (M = Mn, Tc, Re)  

Microsoft Academic Search

In this review ligand exchange and complex formation reactions on fac-[(CO)3M(H2O)3]+ (M=Mn, Tc, Re) and on fac-[(CO)2(NO)Re(H2O)3]2+ are presented. A variety of experimental NMR techniques are described and it is shown that sometimes combinations of techniques applied at variable temperature or variable pressure allowed to measure exchange rate constants and their activation parameters as well as thermodynamic parameters. Furthermore, the

Lothar Helm

2008-01-01

129

Advanced buckyball joints: synthesis, complex formation and computational simulations of centrohexaindane-extended tribenzotriquinacene receptors for C60 fullerene.  

PubMed

The synthesis of a structurally optimized tribenzotriquinacene receptor 9 is described, which is extended by centrohexaindane moieties to give rise to a half-round concave ball bearing, with optimum shape complementarity towards C(60) fullerene. Spectroscopic investigations reveal that this novel host forms a 1 : 1 host-guest complex with C(60) with a complex stability constant of K(1) = 14,550 ± 867 M(-1), which is considerably higher than those reported for structurally related tribenzotriquinacene hosts reported previously. Both the suppression for binding of a second receptor (i.e. formation of a 2 : 1 host-guest complex) as well as the increase of complex stability of the 1 : 1 complex can be rationalized in terms of multiple additive van der Waals and ?-? interactions between C(60) and the aromatic groups of the receptor, as revealed by DFT + D and force-field calculations. Combining results from spectroscopic and theoretical investigations leads to predictions in light of future receptor designs, which--apart from shape complementarity--will have to consider an optimized electronic match (i.e. partial charge transfer) between the receptor and the fullerene host. PMID:22476453

Henne, Stefan; Bredenkötter, Björn; Dehghan Baghi, Abbas A; Schmid, Rochus; Volkmer, Dirk

2012-05-21

130

Complex formation between hydroxypropylcellulose and hexadecyltrimethylamonium bromide as studied by light scattering and viscometry  

Microsoft Academic Search

Complex formation between a semiflexible nonionic polymer, hydroxypropylcellulose (HPC), and a cationic surfactant, hexadecyltrimethylamonium bromide (HTAB), is investigated by static and dynamic light scattering (DLS) and by viscometry. Upon addition of surfactant, at a fixed polymer concentration, the solution specific viscosity increases initially to a maximum value, and then decreases, in parallel with the hydrodynamic radius of the polymer–surfactant complex

P. Hormnirun; A. Sirivat; A. M. Jamieson

2000-01-01

131

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

PubMed Central

Background Nanoparticle-protein corona complex formation involves absorption of protein molecules onto nanoparticle surfaces in a physiological environment. Understanding the corona formation process is crucial in predicting nanoparticle behavior in biological systems, including applications of nanotoxicology and development of nano drug delivery platforms. Method This paper extends the modeling work in to derive a mathematical model describing the dynamics of nanoparticle corona complex formation from population balance equations. We apply nonlinear dynamics techniques to derive analytical results for the composition of nanoparticle-protein corona complex, and validate our results through numerical simulations. Results The model presented in this paper exhibits two phases of corona complex dynamics. In the first phase, proteins rapidly bind to the free surface of nanoparticles, leading to a metastable composition. During the second phase, continuous association and dissociation of protein molecules with nanoparticles slowly changes the composition of the corona complex. Given sufficient time, composition of the corona complex reaches an equilibrium state of stable composition. We find analytical approximate formulae for metastable and stable compositions of corona complex. Our formulae are very well-structured to clearly identify important parameters determining corona composition. Conclusion The dynamics of biocorona formation constitute vital aspect of interactions between nanoparticles and living organisms. Our results further understanding of these dynamics through quantitation of experimental conditions, modeling results for in vitro systems to better predict behavior for in vivo systems. One potential application would involve a single cell culture medium related to a complex protein medium, such as blood or tissue fluid. PMID:23741371

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

2013-01-01

132

Complex Formation between Chromatium vinosum Ferric Cytochrome c? and Bromophenol Blue  

Microsoft Academic Search

An unusual complex has been observed between the common electrophoresis tracer bromophenol blue (BPB) and the cytochrome c? from Chromatium vinosum during polyacrylamide gel electrophoresis. Complex formation results in a shift and increase in the intensity of the visible absorption band of BPB. Differential spectrophotometric titration of BPB with cytochrome c? indicates that one BPB binds to each of the

Anatoly L Mayburd; Yejun Tan; Richard J Kassner

2000-01-01

133

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

SciTech Connect

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

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

2012-08-23

134

Stable complex formation of thylakoidal processing peptidase and PGRL1.  

PubMed

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

Endow, Joshua K; Inoue, Kentaro

2013-07-11

135

Investigation of electron donor-acceptor complex formation between morpholine and 2,4,6-trimorpholino-1,3,5-triazin with iodine in two solvents with soft-modeling approaches  

NASA Astrophysics Data System (ADS)

Interaction between morpholine and a synthetic ligand (2,4,6-trimorpholino-1,3,5-triazin) with iodine was investigated spectrophotometrically in chloroform and dichloromethane solutions using soft-modeling approaches. Multivariate curve resolution-alternating least squares (MCR-ALS) and rank annihilation factor analysis (RAFA) methods were used for complete resolution of the measured spectrophotometric data. The concentration and spectral profiles of all species were calculated without any assumption of the chemical models and the complex formation constants in different solvents were determined. The influences of solvent properties on the formation constant of the resultant charge transfer complexes were discussed.

Madrakian, Tayyebeh; Mohammadnejad, Masoumeh; Hojati, Faezeh

2010-04-01

136

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

137

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

138

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

139

The heterogeneous nature of polyethylenimine-DNA complex formation affects transient gene expression.  

PubMed

Polyethylenimine has been used widely in transient gene expression with mammalian cells. To further understand its mediation of gene transfer, the transfection of HEK 293-F cells with dynamically prepared PEI/DNA complexes was studied with the help of fluorescent labeling. The efficiency of complex endocytosis/phagocytosis was found to correlate with the average sizes of complexes applied and complexes greater than 1 mum in diameter were likely excluded by the cells. Coupled with complex growth in size, the degree of association between PEI and DNA increased with the time of complex formation in the presence of competing ions. The blocking of transcription by complex formation necessitated complex dissociation in the nuclear environment for transcription to happen. Intracellularly, the fates of PEI complexed DNA therefore may be mostly determined by the degree of association. Results also suggested that the uptake of PEI/DNA complexes and subsequent protein expression were independent of the cell cycle stages of HEK 293-F cells. PMID:19649718

Han, Xiangzong; Fang, Qiangyi; Yao, Feng; Wang, Xiaoning; Wang, Jufang; Yang, Shengli; Shen, Bing Q

2009-08-01

140

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

141

The adenylate cyclase receptor complex and aqueous humor formation.  

PubMed

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

Caprioli, J; Sears, M

1984-01-01

142

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

143

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

144

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

PubMed Central

Background Plant MADS box proteins play important roles in a plethora of developmental processes. In order to regulate specific sets of target genes, MADS box proteins dimerize and are thought to assemble into multimeric complexes. In this study a large-scale yeast three-hybrid screen is utilized to provide insight into the higher-order complex formation capacity of the Arabidopsis MADS box family. SEPALLATA3 (SEP3) has been shown to mediate complex formation and, therefore, special attention is paid to this factor in this study. Results In total, 106 multimeric complexes were identified; in more than half of these at least one SEP protein was present. Besides the known complexes involved in determining floral organ identity, various complexes consisting of combinations of proteins known to play a role in floral organ identity specification, and flowering time determination were discovered. The capacity to form this latter type of complex suggests that homeotic factors play essential roles in down-regulation of the MADS box genes involved in floral timing in the flower via negative auto-regulatory loops. Furthermore, various novel complexes were identified that may be important for the direct regulation of the floral transition process. A subsequent detailed analysis of the APETALA3, PISTILLATA, and SEP3 proteins in living plant cells suggests the formation of a multimeric complex in vivo. Conclusions Overall, these results provide strong indications that higher-order complex formation is a general and essential molecular mechanism for plant MADS box protein functioning and attribute a pivotal role to the SEP3 'glue' protein in mediating multimerization. PMID:19243611

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

2009-01-01

145

[Mechanism of interaction between risperidone and tea catechin(1)complex formation of risperidone with epigallocatechin gallate].  

PubMed

The mechanism of complexation between risperidone (RISP) and (-)-epigallocatechin gallate (EGCg) was clarified by ¹H-NMR and molecular modeling studies. RISP and EGCg formed an insoluble complex with a 1 : 1 stoichiometry in aqueous solution. In the ¹H-NMR spectra of RISP in DMSO-d?, the chemical shifts of protons neighboring the N atom on the piperizine ring clearly moved downfield upon formation of the complex. In the molecular modeling study, the ¹H-chemical shifts for nine optimized structures of the complex were calculated to compare them with those of the experimental results. Only one conformer with the second minimum energy for the complex supported the downfield shifts of RISP protons. It was found from the structure of the complex that the two hydrogen bonds between hydroxyl groups of the galloyl ring in EGCg and N atoms in RISP, one of which was on the piperizine ring, were formed to stabilize the complex. PMID:21048420

Ikeda, Hirohito; Moriwaki, Hanae; Yukawa, Miho; Iwase, Yukiko; Aki, Hatsumi

2010-11-01

146

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

PubMed

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

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

2014-10-20

147

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

148

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

149

Dapper1 promotes autophagy by enhancing the Beclin1-Vps34-Atg14L complex formation  

PubMed Central

Autophagy is an intracellular degradation process to clear up aggregated proteins or aged and damaged organelles. The Beclin1-Vps34-Atg14L complex is essential for autophagosome formation. However, how the complex formation is regulated is unclear. Here, we show that Dapper1 (Dpr1) acts as a critical regulator of the Beclin1-Vps34-Atg14L complex to promote autophagy. Dpr1 ablation in the central nervous system results in motor coordination defect and accumulation of p62 and ubiquitinated proteins. Dpr1 increases autophagosome formation as indicated by elevated puncta formation of LC3, Atg14L and DFCP1 (Double FYVE-containing protein 1). Conversely, loss of Dpr1 impairs LC3 lipidation and causes p62/SQSTM1 accumulation. Dpr1 directly interacts with Beclin1 and Atg14L and enhances the Beclin1-Vps34 interaction and Vps34 activity. Together, our findings suggest that Dpr1 enhances the Atg14L-Beclin1-Vps34 complex formation to drive autophagy. PMID:24980960

Ma, Benyu; Cao, Weipeng; Li, Wenxia; Gao, Chan; Qi, Zhen; Zhao, Yan; Du, Jun; Xue, Hua; Peng, Junya; Wen, Jun; Chen, Hua; Ning, Yuanheng; Huang, Lei; Zhang, Hong; Gao, Xiang; Yu, Li; Chen, Ye-Guang

2014-01-01

150

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

SciTech Connect

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

Nomura, Masao; Kudo, Takashi; Adachi, Atsuhiko; Aida, Masao; Fujii, Yasuhiko [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, O-okayama Meguroku, Tokyo, 152-8550 (Japan)] [Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, O-okayama Meguroku, Tokyo, 152-8550 (Japan)

2013-11-13

151

The effect of complex-formation with polyanions on the redox properties of cytochrome c.  

PubMed Central

1. The stable complex formed between mammalian cytochrome c and phosvitin at low ionic strength was studied by partition in an aqueous two-phase system. Oxidized cytochrome c binds to phosvitin with a higher affinity than reduced cytochrome c. The difference was equivalent to a decrease of the redox potential by 22 mV on binding. 2. Complex-formation with phosvitin strongly inhibited the reaction of cytochrome c with reagents that react as negatively charged species, such as ascorbate, dithionite, ferricyanide and tetrachlorobenzoquinol. Reaction with uncharged reagents such as NNN'N'-tetramethylphenylenediamine and the reduced form of the N-methylphenazonium ion (present as the methylsulphate) was little affected by complex-formation, whereas oxidation of the reduced cytochrome by the positively charged tris-(phenanthroline)cobalt(III) ion was greatly stimulated. 3. A similar pattern of inhibition and stimulation of reaction rates was observed when phosvitin was replaced by other macromolecular polyanions such as dextran sulphate and heparin, indicating that the results were a general property of complex-formation with polyanions. A weaker but qualitatively similar effect was observed on addition of inositol hexaphosphate and ATP. 4. It is suggested that the effects of complex-formation with polyanions on the reactivity of cytochrome c with redox reagents are mainly the result of replacing the positive charge on the free cytochrome by a net negative charge. Any steric effects on polyanion binding are small in comparison with such electrostatic effects. PMID:6165356

Petersen, L C; Cox, R P

1980-01-01

152

Formation of P450•P450 Complexes and Their Effect on P450 Function  

PubMed Central

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

Reed, James R.; Backes, Wayne L.

2011-01-01

153

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

Microsoft Academic Search

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

R. A. Marcus

1970-01-01

154

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

155

Cytochrome P-450 complex formation by dirithromycin and other macrolides in rat and human livers.  

PubMed Central

Some macrolide antibiotics cause clinical drug interactions, resulting in altered metabolism of concomitantly administered drugs, via formation of an inactive cytochrome P-450 complex. In the present study, the formation of a cytochrome P-450 type I binding spectrum and a metabolic intermediate complex by troleandomycin and dirithromycin was assessed in liver microsomes obtained from untreated rats and phenobarbital- or dexamethasone-pretreated rats. Troleandomycin produced a type I binding spectrum and metabolic intermediate complex in microsomes from dexamethasone- and phenobarbital-pretreated rats. Dirithromycin did not produce a detectable type I binding spectrum but formed a small cytochrome P-450 metabolic intermediate complex (6% of that formed by troleandomycin) in microsomes from dexamethasone-pretreated rats only. The formation of a cytochrome P-450 type I binding spectrum and a metabolic intermediate complex by troleandomycin, erythromycin, dirithromycin, and erythromycylamine was also assessed in microsomes prepared from human livers. Troleandomycin and erythromycin formed a type I binding spectrum and a metabolic intermediate complex which were larger in microsomes from subjects on barbiturate therapy than in microsomes from subjects with no recent barbiturate exposure. Erythromycylamine did not form a detectable type I binding spectrum with any of the human microsomal samples, but a small metabolic intermediate complex was formed with microsomes from a subject on phenobarbital, phenytoin, and propranolol therapy. Dirithromycin did not form a detectable type I binding spectrum or a metabolic intermediate complex in any human liver sample. Preclinical quantitation of the human metabolic intermediate complex may be helpful in predicting the possibility of clinical drug interactions of new drug candidates. PMID:8452357

Lindstrom, T D; Hanssen, B R; Wrighton, S A

1993-01-01

156

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

157

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

PubMed

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

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

2006-03-01

158

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

159

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

160

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

161

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

162

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

163

Complex formation of Zn-, Ni-, and Pd-derivatives of purpurin-18 with serum albumin  

NASA Astrophysics Data System (ADS)

We analyzed the spectral characteristics of the complexes of Zn2+, Ni2+, and Pd2+ derivatives of purpurin-18 with human serum albumin (HSA) in aqueous buffer at pH 7.0. Pd2+ in the coordination sphere of purpurin-18 decreased the affinity to HSA compared to the respective complexes of zinc and nickel derivatives. Since the formation of complexes with HSA is an important parameter of photodynamic activity of tetrapyrrolic compounds, the differential affinity of metal derivatives of purpurin-18 to this protein should be considered for the optimization of photosensitizers.

Golovina, G. V.; Novikov, F. N.; Ol'shevskaya, V. A.; Kalinin, V. N.; Shtil, A. A.; Kuzmin, V. A.

2012-11-01

164

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

165

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

166

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

NASA Astrophysics Data System (ADS)

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.; Kim, Yousoo; Liu, Da-Jiang; Evans, J. W.; Thiel, P. A.

2013-02-01

167

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

PubMed Central

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

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

2010-01-01

168

The effect of an ?-globulin preparation and of polyribonuclease complexes on humoral antibody formation  

PubMed Central

The effects of bovine ?-globulin (BAG), bovine-ribonuclease serum albumin (BSA-RNase) and polyribonuclease (poly-RNase) complexes on the primary response of rodents to sheep erythrocytes have been investigated. These preparations frequently failed to cause marked suppression of humoral antibody formation. PMID:4173925

Pullar, Diane M.; James, K.; Naysmith, J. D.

1968-01-01

169

Carbon-Carbon Bond Formation Promoted by Organoruthenium Complexes. The First Unsubstituted  

E-print Network

Carbon-Carbon Bond Formation Promoted by Organoruthenium Complexes. The First Unsubstituted in toluene gives several products resulting from carbon-carbon bond coupling reactions; these include of [Cp*RuCl2]2 with propadiene also leads to a carbon- carbon bond coupling reaction, and the product

Girolami, Gregory S.

170

Vibrational deactivation in Kr/O$ collisions: Role of complex formation and potential anisotropy  

E-print Network

Vibrational deactivation in Kr/O$ collisions: Role of complex formation and potential anisotropy,CornellUniversity,Ithaca,New York14853 (Received 11 May 1992;accepted20 July 1992) We report a theoretical study of vibrational resonancebetweenhindered rota- tion and diatom vibration. I. INTRODUCTION An understanding of the dynamics of thermal ion

171

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

NASA Astrophysics Data System (ADS)

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

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

2009-05-01

172

Detection of complex formation between binuclear iron(III)–peroxide adduct and oligonucleotide by electrospray mass spectrometry  

Microsoft Academic Search

Electrospray mass spectrometry (ESI–Mass) gave clear evidence for complex formation between an iron(III) complex and a DNA chain, and also between a binuclear iron(III)–peroxide adduct and a DNA chain.

Teruyuki Kobayashi; Satoshi Nishino; Hideki Masuda; Hisahiko Einaga; Yuzo Nishida

2000-01-01

173

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

174

Enhanced CO2 hydrate formation kinetic under organo-mineral complex environment  

NASA Astrophysics Data System (ADS)

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

Kyung, D.; Lee, W.

2012-12-01

175

Geminin inhibits a late step in the formation of human pre-replicative complexes.  

PubMed

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

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

2014-10-31

176

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

PubMed Central

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

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

2014-01-01

177

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

178

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

PubMed Central

The light-induced assembly of light-harvesting complex (LHC) II has been followed during the biogenesis of the plastid. Seedlings grown in intermittent light (IML) accumulate only small amounts of chlorophyll b. The minor LHC II apoproteins are present; however, the apoprotein levels of the major LHC II complex, LHC IIb, are severely depressed after exposure to IML. The levels of all LHC II apoproteins increase rapidly upon exposure to continuous illumination. The 25-kD, type 3 LHC IIb subunit appears to be more abundant during the early hours of greening in relation to its level in mature thylakoids. The LHC IIb apoproteins are initially associated with pigments to form monomeric pigment-protein complexes. The abundance of monomeric LHC IIb complexes gradually decreases during exposure to continuous light and a concomitant increase occurs in the amount of the trimeric and higher-order oligomeric forms. Pulse-chase experiments verify that labeled LHC IIb monomeric complexes are intermediates in the formation of trimeric and higher-order oligomeric LHC IIb-pigmented complexes. Therefore, the assembly of LHC II occurs via the initial pigmentation of the apoproteins to form monomeric complexes and proceeds in a sequential manner. PMID:12232371

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

1994-01-01

179

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

SciTech Connect

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

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

2008-07-16

180

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

PubMed

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

181

Drosophila Orc6 Facilitates GTPase Activity and Filament Formation of the Septin Complex  

PubMed Central

The origin recognition complex or ORC is a six-subunit protein important for DNA replication and other cell functions. Orc6, the smallest subunit of ORC, is essential for both replication and cytokinesis in Drosophila, and interacts with the septin protein Pnut, which is part of the Drosophila septin complex. In this study, we describe the analysis of the interaction of Orc6 with Pnut and whole Drosophila septin complex. Septin complex was purified from Drosophila embryos and also reconstituted from recombinant proteins. The interaction of Orc6 with the septin complex is dependent on the coiled-coil domain of Pnut. Furthermore, the binding of Orc6 to Pnut increases the intrinsic GTPase activity of the Drosophila septin complex, whereas in the absence of GTP it enhances septin complex filament formation. These results suggest an active role for Orc6 in septin complex function. Orc6 might be a part of a control mechanism directing the cytokinesis machinery during the final steps of mitosis. PMID:18987337

Huijbregts, Richard P.H.; Svitin, Anton; Stinnett, Monica W.; Renfrow, Matthew B.

2009-01-01

182

The role of focal adhesion complexes in fibroblast mechanotransduction during scar formation.  

PubMed

Historically, great efforts have been made to elucidate the biochemical pathways that direct the complex process of wound healing; however only recently has there been recognition of the importance that mechanical signals play in the process of tissue repair and scar formation. The body's physiologic response to injury involves a dynamic interplay between mechanical forces and biochemical cues which directs a cascade of signals leading ultimately to the formation of fibrotic scar. Fibroblasts are a highly mechanosensitive cell type and are also largely responsible for the generation of the fibrotic matrix during scar formation and are thus a critical player in the process of mechanotransduction during tissue repair. Mechanotransduction is initiated at the interface between the cell membrane and the extracellular matrix where mechanical signals are first translated into a biochemical response. Focal adhesions are dynamic multi-protein complexes through which the extracellular matrix links to the intracellular cytoskeleton. These focal adhesion complexes play an integral role in the propagation of this initial mechanical cue into an extensive network of biochemical signals leading to widespread downstream effects including the influx of inflammatory cells, stimulation of angiogenesis, keratinocyte migration, fibroblast proliferation and collagen synthesis. Increasing evidence has demonstrated the importance of the biomechanical milieu in healing wounds and suggests that an integrated approach to the discovery of targets to decrease scar formation may prove more clinically efficacious than previous purely biochemical strategies. PMID:23623400

Rustad, Kristine C; Wong, Victor W; Gurtner, Geoffrey C

2013-10-01

183

Regulated clearance of histone deacetylase 3 protects independent formation of nuclear receptor corepressor complexes.  

PubMed

An important step in transcriptional regulation by corepressors N-CoR and SMRT is the formation of a stable and active histone deacetylase 3 (HDAC3)-containing complex. Although N-CoR and SMRT are thought to bind HDAC3 competitively, multiple studies have shown that they do not interfere with the function of each other. How this functional independence is sustained under the competitive interaction is unclear. Here, we show that the coupling of corepressor expression with HDAC3 degradation allows cells to maintain a stable level of uncomplexed HDAC3, thereby preventing mutual interference in the assembly of N-CoR and SMRT complexes. The free uncomplexed HDAC3 is highly unstable. Unexpectedly, the rate of HDAC3 degradation is inversely correlated with the expression level of corepressors. Our results indicate that reducing one corepressor accelerates HDAC3 clearance, thus preventing an increase in complex formation between HDAC3 and the other corepressor. In addition, this study also indicates that the formation of a stable and active HDAC3-corepressor complex is a stepwise process in which the C terminus of HDAC3 plays a critical role at late steps of the assembly process. PMID:22337871

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

2012-04-01

184

Live imaging system for visualizing nuclear pore complex (NPC) formation during interphase in mammalian cells.  

PubMed

Nuclear pore complexes (NPCs) are 'supramolecular complexes' on the nuclear envelope assembled from multiple copies of approximately 30 different proteins called nucleoporins (Nups) that provide aqueous channels for nucleocytoplasmic transport during interphase. Although the structural aspects of NPCs have been characterized in detail, NPC formation and its regulation, especially during interphase, are poorly understood. In this study, using the temperature-sensitive RCC1 mutant tsBN2, a baby hamster kidney 21 cell line, we found that a lack of RCC1 activity inhibited NPC formation during interphase, suggesting that RanGTP is required for NPC formation during interphase in mammalian cells. Utilizing the reversible RCC1 activity in tsBN2 cells, we established a live-cell system that allows for the inhibition or initiation of NPC formation by changes in temperature. Our system enables the examination of NPC formation during interphase in living cells. As a lack of RCC1 decreased some Nups containing unstructured phenylalanine-glycine repeats in the NPC structure, we propose that RCC1 is also involved in maintaining NPC integrity during interphase in mammalian cells. PMID:20465562

Iino, Haruki; Maeshima, Kazuhiro; Nakatomi, Reiko; Kose, Shingo; Hashikawa, Tsutomu; Tachibana, Taro; Imamoto, Naoko

2010-06-01

185

Theoretical model of the frequency and temperature dependence of the complex dielectric constant of ferroelectric liquid crystals near the smectic-C*-smectic-A phase transition  

Microsoft Academic Search

Using the generalized Landau model [Phys. Rev. A 36, 1484 (1987)], the temperature and frequency dependence of the complex dielectric constant of the ferroelectric smectic-C* (Sm-C*) phase and the corresponding smectic-A (Sm-A) phase is calculated. It is demonstrated how the dielectric response of the Sm-C* phase generally consists of four modes-two high-frequency polarization modes and two modes of lower frequency

T. Carlsson; B. Zeks; C. Filipic; A. Levstik

1990-01-01

186

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

187

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

188

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

PubMed

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

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

2014-06-17

189

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

PubMed

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

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

2013-10-01

190

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

PubMed

A simple, precise, reproducible and accurate spectrofluorimetric method for estimation of Salbutamol sulphate (SAL) in bulk drug and various dosage forms has been developed. This method is based on formation of inclusion complex of SAL in ?-cyclodextrin (BCD) which gives fluorescence at excitation wavelength of 279.6 nm and emission wavelength of 609.8 nm in water. Formation of inclusion complex of drug with BCD enhances fluorescence intensity of drug leads to increased sensitivity. The developed method was validated according to ICH guidelines with respect to accuracy, precision, linearity, limit of detection, limit of quantification. Linearity was observed in the range of 4-20 ?g/ml with correlation coefficient of 0.9982. The simplicity of the method permitted rapid analysis suitable for routine control. The developed method was successfully applied for the estimation of SAL in different marketed dosage forms like tablets, syrup and aerosol. PMID:23781416

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

2010-10-01

191

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

PubMed

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

192

Formation, structure and wettability of fluorescent nanolayers of oligoperoxide europium complexes adsorbed to glass surface  

Microsoft Academic Search

Formation kinetics and the nanolayer structure are determined for fluorescent complexes, which are composed of oligoperoxide and europium (OP–Eu), and are adsorbed to glass from water–ammonia solutions. The effective surface fraction x modified by OP–Eu is evaluated (with the Cassie equation) from receding contact angles. Its temporal behavior is repeated by the average adlayer thickness d, determined from ellipsometry, indicating

Yu. Stetsyshyn; A. Kostruba; J. Jaczewska; A. Zaichenko; N. Mitina; A. Budkowski; P. Kuzyk; ?. Voloshinovskii

2010-01-01

193

Formation of titanium(IV) transferrin by reaction of human serum apotransferrin with titanium complexes  

Microsoft Academic Search

The reaction of human serum apotransferrin with titanium(IV) citrate under physiological conditions results in the formation of a specific bis-titanium(IV) transferrin adduct (Ti2Tf hereafter) with two titanium(IV) ions loaded at the iron binding sites. The same specific Ti2Tf complex is formed by reacting apotransferrin with titanium(III) chloride and exposing the sample to air. The derivative thus obtained was characterized by

Luigi Messori; Pierluigi Orioli; Vivien Banholzer; Istvan Pais; Paolo Zatta

1999-01-01

194

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

195

Display format and highlight validity effects on search performance using complex visual displays  

NASA Technical Reports Server (NTRS)

Display format and highlight validity were shown to affect visual display search performance; however, these studies were conducted on small, artificial displays of alphanumeric stimuli. A study manipulating these variables was conducted using realistic, complex Space Shuttle information displays. A 2x2x3 within-subjects analysis of variance found that search times were faster for items in reformatted displays than for current displays. The significant format by highlight validity interaction showed that there was little difference in response time to both current and reformatted displays when the highlight validity was applied; however, under the non or invalid highlight conditions, search times were faster with reformatted displays. Benefits of highlighting and reformatting displays to enhance search and the necessity to consider highlight validity and format characteristics in tandem for predicting search performance are discussed.

Donner, Kimberly A.; Mckay, Tim; O'Brien, Kevin M.; Rudisill, Marianne

1991-01-01

196

Spectrophotometric and spectrofluorimetric determination of certain diuretics through ternary complex formation with eosin and lead (II).  

PubMed

Simple and sensitive spectrophotometric and spectrofluorimetric methods have been developed for the determination of hydrochlorothiazide (I), indapamide (II) and xipamide(III) based on ternary complex formation with eosin and lead (II) in the presence of methylcellulose as surfactant. The methods do not involve solvent extraction. For spectrophotometric method, the ternary complex showed an absorption maximum at 543 nm. The factors affecting the formation of ternary complex were studied and optimized. The method obeys Beer's law over concentration range of 8-40 microg mL(-1). A fluorescence quenching method for the determination of the cited drugs by forming this ternary complex was also investigated for the purpose of enhancing the sensitivity of the determination. The analytical performance of both methods was fully validated, and the results were satisfactory. The methods have been successfully applied for the determination of the studied drugs in their pharmaceutical tablets and the results obtained ware in good agreement with those obtained by the reference method. Common excipients used as additives in tablets do not interfere with the proposed methods. PMID:19823922

Omar, Mahmoud A

2010-01-01

197

Selective formation and unusual reactivity of tetraarsabicyclo[1.1.0]butane complexes.  

PubMed

The selective formation of the dinuclear butterfly complexes [{Cp'''Fe(CO)2}2(?,?(1:1)-E4)] (E = P (1?a), As (1?b)) and [{Cp*Cr(CO)3}2(?,?(1:1)-E4)] (E = P (2?a), As (2?b)) as new representatives of this rare class of compounds was found by reaction of E4 with the corresponding dimeric carbonyl complexes. Complexes 1?b and 2?b are the first As4 butterfly compounds with a bridging coordination mode. Moreover, first studies regarding the reactivity of 1?b and 2?b are presented, revealing the formation of the unprecedented As8 cuneane complexes [{Cp'''Fe(CO)2}2{Cp'''Fe(CO)}2(?4,?(1:1:2:2)-As8)] (3?b) and [{Cp*Cr(CO)3}4(?4,?(1:1:1:1)-As8)] (4). The compounds are fully characterized by NMR and IR spectroscopy as well as by X-ray structure analysis. In addition, DFT calculations give insight into the transformation pathway from the E4 butterfly to the corresponding cuneane structural motif. PMID:25123699

Schwarzmaier, Christoph; Timoshkin, Alexey Y; Balázs, Gábor; Scheer, Manfred

2014-08-18

198

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

199

Antimony(V) complex formation with adenine nucleosides in aqueous solution.  

PubMed

Despite the clinical use of pentavalent antimonial drugs for over half a century, their mode of action against leishmaniasis remains poorly understood. In this paper, we investigated the ability of Sb(V) to form in aqueous solution complexes with adenine nucleosides and deoxynucleosides, using circular dichroism (CD) and (1)H and (13)C NMR spectroscopies. We report that the ribonucleosides, adenosine (A) and adenosine monophosphate (AMP), form in water complexes with Sb(V), as evidenced by the changes induced in their CD spectra. On the other hand, 2'-deoxyadenosine (dA) did not show such a change. CD titration of the ribonucleosides with Sb(V) suggests the formation of 1:2 Sb(V)-nucleoside complexes. NMR analysis indicates that Sb(V) binds to the sugar moiety at the 2' position. Furthermore, the incubation of the antimonial drug, meglumine antimonate, with adenosine at 37 degrees C led to the transfer of Sb(V) from its original ligand to the nucleoside molecule, at acidic pH (pH 5), but not at neutral pH (7.2). Our data therefore suggests that the formation of such complexes may take place in vivo within the acidic cell compartments, including the phagolysosome of macrophage in which Leishmania resides. PMID:12020809

Demicheli, Cynthia; Frézard, Frédéric; Lecouvey, Marc; Garnier-Suillerot, Arlette

2002-04-15

200

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

201

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

PubMed

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

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

2014-12-01

202

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

PubMed Central

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

Cesme, Mustafa; Tarinc, Derya; Golcu, Aysegul

2011-01-01

203

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

PubMed Central

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

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

2014-01-01

204

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

205

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...

206

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

207

Formation of DNA adducts using nickel(II) complexes of redox-active ligands: a comparison of salen and peptide complexes  

Microsoft Academic Search

A series of water-soluble Ni(salen) complexes have been synthesized and studied under oxidative conditions with DNA. Experiments involving gel electrophoretic analysis, substituent effect studies, and mass spectral characterization point to the formation of covalent adducts of the salen ligand with guanine nucleobases. The mechanism of this novel reactivity of transition metal complexes with nucleic acids is discussed in comparison with

James G. Muller; Lou Anne Kayser; Sari J. Paikoff; Victor Duarte; Ning Tang; Ronelito J. Perez; Steven E. Rokita; Cynthia J. Burrows

1999-01-01

208

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

PubMed

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

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

2011-04-01

209

Human mitochondrial holocytochrome c synthase's heme binding, maturation determinants, and complex formation with cytochrome c.  

PubMed

Proper functioning of the mitochondrion requires the orchestrated assembly of respiratory complexes with their cofactors. Cytochrome c, an essential electron carrier in mitochondria and a critical component of the apoptotic pathway, contains a heme cofactor covalently attached to the protein at a conserved CXXCH motif. Although it has been known for more than two decades that heme attachment requires the mitochondrial protein holocytochrome c synthase (HCCS), the mechanism remained unknown. We purified membrane-bound human HCCS with endogenous heme and in complex with its cognate human apocytochrome c. Spectroscopic analyses of HCCS alone and complexes of HCCS with site-directed variants of cytochrome c revealed the fundamental steps of heme attachment and maturation. A conserved histidine in HCCS (His154) provided the key ligand to the heme iron. Formation of the HCCS:heme complex served as the platform for interaction with apocytochrome c. Heme was the central molecule mediating contact between HCCS and apocytochrome c. A conserved histidine in apocytochrome c (His19 of CXXCH) supplied the second axial ligand to heme in the trapped HCCS:heme:cytochrome c complex. We also examined the substrate specificity of human HCCS and converted a bacterial cytochrome c into a robust substrate for the HCCS. The results allow us to describe the molecular mechanisms underlying the HCCS reaction. PMID:23150584

San Francisco, Brian; Bretsnyder, Eric C; Kranz, Robert G

2013-02-26

210

Formation of Membrane-bound Ring Complexes by Prohibitins in Mitochondria  

PubMed Central

Prohibitins comprise a remarkably conserved protein family in eukaryotic cells with proposed functions in cell cycle progression, senescence, apoptosis, and the regulation of mitochondrial activities. Two prohibitin homologues, Phb1 and Phb2, assemble into a high molecular weight complex of ?1.2 MDa in the mitochondrial inner membrane, but a nuclear localization of Phb1 and Phb2 also has been reported. Here, we have analyzed the biogenesis and structure of the prohibitin complex in Saccharomyces cerevisiae. Both Phb1 and Phb2 subunits are targeted to mitochondria by unconventional noncleavable targeting sequences at their amino terminal end. Membrane insertion involves binding of newly imported Phb1 to Tim8/13 complexes in the intermembrane space and is mediated by the TIM23-translocase. Assembly occurs via intermediate-sized complexes of ?120 kDa containing both Phb1 and Phb2. Conserved carboxy-terminal coiled-coil regions in both subunits mediate the formation of large assemblies in the inner membrane. Single particle electron microscopy of purified prohibitin complexes identifies diverse ring-shaped structures with outer dimensions of ?270 × 200 Å. Implications of these findings for proposed cellular activities of prohibitins are discussed. PMID:15525670

Tatsuta, Takashi; Model, Kirstin; Langer, Thomas

2005-01-01

211

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

USGS Publications Warehouse

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

Pavlides, Louis

1980-01-01

212

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

213

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

214

Structure and properties of hydrogen bonded complexes of pyridine-N-oxide and its derivatives  

E-print Network

and the enthalpy of IHB complex formation was established in Refs. [7,8]. We note that only complexes with the 1 of pyridine-N-oxide derivatives, the logarithm of the complex formation equilibrium constant correlates with the charge on the oxygen atom of the N­O group. A method to calculate the first and second complex formation

215

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

SciTech Connect

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

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

1990-03-07

216

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

217

Hydroxyl radical formation from the auto-reduction of a ferric citrate complex.  

PubMed

When a ferric citrate complex is prepared from citric acid and ferric chloride, and the pH value left unchanged, a reduction of the iron moiety takes place. Within several hours a substantial yield of ferrous ions can be detected in the solution. When placed in a phosphate buffer pH 7.0 with a suitable detector molecule, oxidative damage to the detector molecule can be observed. Thus, deoxyribose is degraded with the release of thiobarbituric acid-reactive material and benzoate is hydroxylated to form fluorescent dihydroxy products. Damage can be prevented by scavengers of the hydroxyl radical such as mannitol, formate the thiourea, by catalase and by the protein caeruloplasmin, suggesting that Fenton chemistry occurs leading to the formation of hydroxyl radicals. PMID:1665838

Gutteridge, J M

1991-01-01

218

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

219

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 1.0M 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

220

Spectrophotometric determination of flunarizine dihydrochloride through the formation of charge-transfer complex with iodine.  

PubMed

A spectrophotometric method is described for the assay of flunarizine dihydrochloride. The method is based on the molecular interaction between the drug and iodine, to form a charge-transfer complex in which the drug acts as n-donor and iodine as sigma-acceptor. The iodine was found to form charge-transfer complex in a 1:1 stoichiometry with absorption bands at 295 and 355 nm. The concentrations were linear over 8-13 micrograms ml-1 at both 295 and 355 nm, respectively. A complete, detailed investigation of the formed complex was made with respect to its composition, associated constant and free energy change. The method has been applied successfully to the analysis of commercially available flunarizine dihydrochloride capsules without interference from the capsules excipient. To validate the proposed method, its accuracy and precision, the results were statistically compared with a newly developed reversed-phase HPLC procedure using Student-t and F-ratio tests. PMID:7718634

el Walily, A F; el Gindy, A; Wahbi, A A

1995-01-01

221

A new method for recycling asymmetric catalysts via formation of charge transfer complexes.  

PubMed

[reaction: see text]. A new concept for recycling asymmetric bis(oxazoline)-type catalysts is reported. The formation of charge-transfer complexes between the chiral ligand and trinitrofluorenone and their subsequent precipitation and reuse by addition of new substrate solutions is described. The efficiency of this procedure is demonstrated in a Diels-Alder reaction to reach the expected endo product as major isomer (up to 97% de and 94% ee): the catalyst was used up to 12 times without loss of either activity or selectivity. PMID:16435879

Chollet, Guillaume; Rodriguez, Fernand; Schulz, Emmanuelle

2006-02-01

222

C–C bond formation through olefin–thiocarbyne coupling in diiron complexes  

Microsoft Academic Search

The bridging diiron thiocarbyne complex [Fe2{?-CS(Me)}(?-CO)(CO)2(Cp)2][SO3CF3] (1) reacts with activated olefins (methyl acrylate, acrylonitrile, styrene, diethyl maleate), in the presence of Me3NO and NaH, to give the corresponding ?-allylidene complexes [Fe2{?-?1:?3-C?(SMe)C?(R?)C?(H)(R?)} (?-CO)(CO)(Cp)2] (R?=CO2Me, R?=H, 3a; R? = CN, R?=H, 3b; R?=C6H5, R?=H, 3c; R?=R?=CO2Et, 3d). The coupling reaction of olefin with thiocarbyne is regio- and stereospecific, leading to the formation

Luigi Busetto; Fabio Marchetti; Mauro Salmi; Stefano Zacchini; Valerio Zanotti

2007-01-01

223

Mechanisms of copy number variation and hybrid gene formation in the KIR immune gene complex  

PubMed Central

The fine-scale structure of the majority of copy number variation (CNV) regions remains unknown. The killer immunoglobulin receptor (KIR) gene complex exhibits significant CNV. The evolutionary plasticity of the KIRs and their broad biomedical relevance makes it important to understand how these immune receptors evolve. In this paper, we describe haplotype re-arrangement creating novel loci at the KIR complex. We completely sequenced, after fosmid cloning, two rare contracted haplotypes. Evidence of frequent hybrid KIR genes in samples from many populations suggested that re-arrangements may be frequent and selectively advantageous. We propose mechanisms for formation of novel hybrid KIR genes, facilitated by protrusive non-B DNA structures at transposon recombination sites. The heightened propensity to generate novel hybrid KIR receptors may provide a proactive evolutionary measure, to militate against pathogen evasion or subversion. We propose that CNV in KIR is an evolutionary strategy, which KIR typing for disease association must take into account. PMID:19959527

Traherne, James A.; Martin, Maureen; Ward, Rosemary; Ohashi, Maki; Pellett, Fawnda; Gladman, Dafna; Middleton, Derek; Carrington, Mary; Trowsdale, John

2010-01-01

224

Time-resolved fluorescence spectroscopic investigation of cationic polymer/DNA complex formation  

NASA Astrophysics Data System (ADS)

Since DNA is not internalized efficiently by cells, the success of gene therapy depends on the availability of carriers to efficiently deliver genetic material into target cells. Gene delivery vectors can be broadly categorized into viral and non-viral ones. Non-viral gene delivery systems are represented by cationic lipids and polymers rely on the basics of supramolecular chemistry termed "self-assembling": at physiological pH, they are cations and spontaneously form lipoplexes (for lipids) and polyplexes (for polymers) complexing nucleic acids. In this scenario, cationic polymers are commonly used as non-viral vehicles. Their effectiveness is strongly related to key parameters including DNA binding ability and stability in different environments. Time-resolved fluorescence spectroscopy of SYBR Green I (DNA dye) was carried out to characterize cationic polymer/DNA complex (polyplex) formation dispersed in aqueous solution. Both fluorescence amplitude and lifetime proved to be very sensitive to the polymer/DNA ratio (N/P ratio, +/-).

D'Andrea, Cosimo; Bassi, Andrea; Taroni, Paola; Pezzoli, Daniele; Volonterio, Alessandro; Candiani, Gabriele

2011-07-01

225

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

226

Spectrophotometric determination of ciprofloxacin, enrofloxacin and pefloxacin through charge transfer complex formation.  

PubMed

A spectrophotometric method was described for the determination of the antibacterial quinolone derivatives, ciprofloxacin, enrofloxacin and pefloxacin through charge transfer complex formation with three different acceptors. Chloranilic acid (CL) was utilized for their determination, forming charge transfer complex with lambdamax 520 nm. The proposed method was applied for determination of Ciprocin tablets, Enroxil oral solution, Peflacin ampoules and Peflacin tablets, with mean percentage accuracies, 99.58+/-1.25,99.94+/-0.96,100.91+/-1.59 and 99.86+/-1.003. Also, tetracyanoethylene (TCNE) was utilized in the determination of the concerned compounds forming charge transfer complexes with maximum absorbances at lambdamax 335 nm for ciprofloxacin and at lambdamax 290 nm for both enrofloxacin and pefloxacin. The procedure was applied for determination of Ciprocin tablets, Enroxil 10% oral solution, Peflacine tablets and Peflacine ampoules with mean percentage accuracies 99.40+/-1.27,99.95+/-0.90,98.98+/-1.565 and 99.88+/-0.998, respectively. Also, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) was utilized for determination of pefloxacin forming charge transfer complex with maximum absorbance at lambdamax 460 nm. The procedure was applied for determination of peflacine tablets and peflacine ampoules with mean percentage accuracies 100.40+/-0.76 and 99.91+/-0.623, respectively. Statistical analysis of the obtained results showed no significant difference between the proposed method and other official and reported methods as evident from the t-test and variance ratio. PMID:11682219

Mostafa, Samia; El-Sadek, Mohamed; Alla, Esmail Awad

2002-01-01

227

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

228

Asymmetrical Macromolecular Complex Formation of Lysophosphatidic Acid Receptor 2 (LPA2) Mediates Gradient Sensing in Fibroblasts.  

PubMed

Chemotactic migration of fibroblasts toward growth factors relies on their capacity to sense minute extracellular gradients and respond to spatially confined receptor-mediated signals. Currently, mechanisms underlying the gradient sensing of fibroblasts remain poorly understood. Using single-particle tracking methodology, we determined that a lysophosphatidic acid (LPA) gradient induces a spatiotemporally restricted decrease in the mobility of LPA receptor 2 (LPA2) on chemotactic fibroblasts. The onset of decreased LPA2 mobility correlates to the spatial recruitment and coupling to LPA2-interacting proteins that anchor the complex to the cytoskeleton. These localized PDZ motif-mediated macromolecular complexes of LPA2 trigger a Ca(2+) puff gradient that governs gradient sensing and directional migration in response to LPA. Disruption of the PDZ motif-mediated assembly of the macromolecular complex of LPA2 disorganizes the gradient of Ca(2+) puffs, disrupts gradient sensing, and reduces the directional migration of fibroblasts toward LPA. Our findings illustrate that the asymmetric macromolecular complex formation of chemoattractant receptors mediates gradient sensing and provides a new mechanistic basis for models to describe gradient sensing of fibroblasts. PMID:25542932

Ren, Aixia; Moon, Changsuk; Zhang, Weiqiang; Sinha, Chandrima; Yarlagadda, Sunitha; Arora, Kavisha; Wang, Xusheng; Yue, Junming; Parthasarathi, Kaushik; Heil-Chapdelaine, Rick; Tigyi, Gabor; Naren, Anjaparavanda P

2014-12-26

229

Ice Complex formation in arctic East Siberia during the MIS3 Interstadial  

NASA Astrophysics Data System (ADS)

A continuous 15 m long sequence of Ice Complex permafrost (Yedoma) exposed in a thermo-cirque at the southern coast of Bol'shoy Lyakhovsky Island (New Siberian Archipelago, Dmitry Laptev Strait) was studied to reconstruct past landscape and environmental dynamics. The sequence accumulated during the Marine Isotope Stage 3 (MIS3) Interstadial between >49 and 29 ka BP in an ice-wedge polygon. The frozen deposits were cryolithologically described and sampled on a vertical bluff between two ice wedges. According to sedimentological and geochronological data, the section is subdivided into three units which correlate with environmental conditions of the early, middle, and late MIS3 period. Palynological data support this stratification. The stable isotope signature of texture ice in the polygon structure reflects fractionation due to local freeze-thaw processes, while the signature of an approximately 5 m wide and more than 17 m high ice wedge fits very well into the regional stable-water isotope record. Regional climate dynamics during the MIS3 Interstadial and local landscape conditions of the polygonal patterned ground controlled the Ice Complex formation. The sequence presented here completes previously published MIS3 permafrost records in Northeast Siberia. Late Quaternary stadial-interstadial climate variability in arctic West Beringia is preserved at millennial resolution in the Ice Complex. A MIS3 climate optimum was revealed between 48 and 38 ka BP from the Ice Complex on Bol'shoy Lyakhovsky Island.

Wetterich, Sebastian; Tumskoy, Vladimir; Rudaya, Natalia; Andreev, Andrei A.; Opel, Thomas; Meyer, Hanno; Schirrmeister, Lutz; Hüls, Matthias

2014-01-01

230

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

231

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

232

Effect of Solvent Dielectric Constant and Acidity on the OH Vibration Frequency in Hydrogen-Bonded Complexes of Fluorinated Ethanols.  

PubMed

Infrared spectroscopy measurements were used to characterize the OH stretching vibrations in a series of similarly structured fluoroethanols, RCH2OH (R = CH3, CH2F, CHF2, CF3), a series which exhibits a systematic increase in the molecule acidity with increasing number of F atoms. This study, which expands our earlier efforts, was carried out in non-hydrogen-bonding solvents comprising molecules with and without a permanent dipole moment, with the former solvents being classified as polar solvents and the latter designated as nonpolar. The hydrogen bond interaction in donor-acceptor complexes formed in solution between the fluorinated ethanol H-donors and the H-acceptor base DMSO was investigated in relation to the solvent dielectric and to the differences ?PA of the gas phase proton affinities (PAs) of the conjugate base of the fluorinated alcohols and DMSO. We have observed that ?OH decreases as the acidity of the alcohol increases (?PA decreases) and that ?OH varies inversely with ?, exhibiting different slopes for nonpolar and polar solvents. These 1/? slopes tend to vary linearly with ?PA, increasing with increasing acidity. These experimental findings, including the ?PA trends, are described with our recently published two-state Valence Bond-based theory for acid-base H-bonded complexes. Lastly, the correlation of the alcohol's conjugate base PAs with Taft ?* values of the fluorinated ethyl groups CHnF3-nCH2- provides a connection of the inductive effects for these groups with the acidity parameter ?PA associated with the H-bonded complexes. PMID:25420059

Pines, Dina; Keinan, Sharon; Kiefer, Philip M; Hynes, James T; Pines, Ehud

2014-12-01

233

The Interaction of Arp2/3 Complex with Actin: Nucleation, High Affinity Pointed End Capping, and Formation of Branching Networks of Filaments  

NASA Astrophysics Data System (ADS)

The Arp2/3 complex is a stable assembly of seven protein subunits including two actin-related proteins (Arp2 and Arp3) and five novel proteins. Previous work showed that this complex binds to the sides of actin filaments and is concentrated at the leading edges of motile cells. Here, we show that Arp2/3 complex purified from Acanthamoeba caps the pointed ends of actin filaments with high affinity. Arp2/3 complex inhibits both monomer addition and dissociation at the pointed ends of actin filaments with apparent nanomolar affinity and increases the critical concentration for polymerization at the pointed end from 0.6 to 1.0 ? M. The high affinity of Arp2/3 complex for pointed ends and its abundance in amoebae suggest that in vivo all actin filament pointed ends are capped by Arp2/3 complex. Arp2/3 complex also nucleates formation of actin filaments that elongate only from their barbed ends. From kinetic analysis, the nucleation mechanism appears to involve stabilization of polymerization intermediates (probably actin dimers). In electron micrographs of quick-frozen, deep-etched samples, we see Arp2/3 bound to sides and pointed ends of actin filaments and examples of Arp2/3 complex attaching pointed ends of filaments to sides of other filaments. In these cases, the angle of attachment is a remarkably constant 70 ± 7 degrees. From these in vitro biochemical properties, we propose a model for how Arp2/3 complex controls the assembly of a branching network of actin filaments at the leading edge of motile cells.

Dyche Mullins, R.; Heuser, John A.; Pollard, Thomas D.

1998-05-01

234

Determination of conditional stability constants of cadmium-humic acid complexes in freshwater by use of a competitive ligand equilibration-solvent extraction technique  

SciTech Connect

A technique for determining organic complexation of cadmium in freshwater using competitive ligand equilibration coupled with solvent extraction was evaluated. The method involves a competitive equilibration of the sample with potassium iodide and pyridine followed by extraction of the mixed cadmium-iodide-pyridine complex into a benzene phase. The final distribution of the metal is measured by gamma ray spectrometry. The method's suitability was verified by performing extractions on the model ligand 8-hydroxyquinoline-5-sulfonic acid (sulfoxine), which forms well-characterized complexes with cadmium. The speciation results so obtained were in excellent agreement with results calculated with a chemical speciation model. The method was applied to study complexation of cadmium with two commercially available humic acids in reconstituted freshwater at relatively high cadmium concentrations to mimic polluted freshwaters. The obtained titration data were fitted to a one-site Langmuir adsorption model, yielding values of 10{sup 6.59} and 10{sup 6.52} for the respective conditional stability constants, and 0.57 and 0.90 {micro}M for the respective ligand concentrations.

Van Ginneken, L.; Blust, R.

2000-02-01

235

Annual Logging Symposium, June 19-23, 2010 Formation Evaluation in the Bakken Complex Using Laboratory Core Data  

E-print Network

SPWLA 51st Annual Logging Symposium, June 19-23, 2010 Formation Evaluation in the Bakken Complex reservoirs, such as the Bakken Shale and its adjoining formations, the Three Forks dolomite, Sanish mudstone (below), and Lodgepole limestone (above). The primary oil targets within the Upper Devonian Bakken

236

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

E-print Network

We present photometric and spectroscopic results for the low mass pre-main sequence (PMS) stars with spectral types K - M in the cometary globule (CG) 30/31/38 complex. We obtained multi-object high resolution spectra for the targets selected as possible PMS stars from multi-wavelength photometry. We identified 11 PMS stars brighter than V = 16.5 with ages < 5 Myr at a distance of approximately 200 pc. The spatial distribution of the PMS stars, CG clouds, and ionizing sources (O stars and supernova remnants) suggests a possible triggered origin of the star formation in this region. We confirm the youth of the photometrically selected PMS stars using the lithium abundances. The radial velocities of the low mass PMS stars are consistent with those of the cometary globules. Most of the PMS stars show weak Halpha emission with W(Halpha) < 10 A. Only 1 out of the 11 PMS stars shows a moderate near-IR excess, which suggests a short survival time (t < 5 Myr) of circumstellar disks in this star forming environment. In addition, we find five young late type stars and one Ae star which have no obvious relation to the CG 30/31/38 complex. We also discuss a possible scenario of star formation history in the CG 30/31/38 region.

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

2005-02-15

237

The effects of upstream DNA on open complex formation by Escherichia coli RNA polymerase  

PubMed Central

Binding of activators to upstream DNA sequences regulates transcription initiation by affecting the stability of the initial RNA polymerase (RNAP)–promoter complex and/or the rate of subsequent conformational changes required to form the open complex (RPO). Here we observe that the presence of nonspecific upstream DNA profoundly affects an early step in formation of the transcription bubble. Kinetic studies with the ?PR promoter and Escherichia coli RNAP reveal that the presence of DNA upstream of base pair -47 greatly increases the rate of forming RPO, without significantly affecting its rate of dissociation. We find that this increase is largely due to an acceleration of the rate-limiting step (isomerization) in RPO formation, a step that occurs after polymerase binds. Footprinting experiments reveal striking structural differences downstream of the transcription start site (+1) in the first kinetically significant intermediate when upstream DNA is present. On the template strand, the DNase I downstream boundary of this early intermediate is +20 when upstream DNA is present but is shortened by approximately two helical turns when upstream DNA beyond -47 is removed. KMnO4 footprinting reveals an identical initiation bubble (-11 to +2), but unusual reactivity of template strand upstream cytosines (-12, -14, and -15) on the truncated promoter. Based on this work, we propose that early wrapping interactions between upstream DNA and the polymerase exterior strongly affect the events that control entry and subsequent unwinding of the DNA start site in the jaws of polymerase. PMID:15626761

Davis, Caroline A.; Capp, Michael W.; Record, M. Thomas; Saecker, Ruth M.

2005-01-01

238

Prostaglandin E2 modifies SMAD2 and promotes SMAD2-SMAD4 complex formation.  

PubMed

We report that PGE2 promotes Smad2-Smad4 complex formation and this phenomenon could be blocked by DIDS, an anion transporter inhibitor. Our data suggest that PGE2 had no effects on Smad2 phosphorylation, suggesting that PGE2-mediated Smad2-Smad4 complex formation is independent of TGF-? signaling and that PGE2 induced Smad2 modification which is different from TGF-?-mediated phosphorylation. We demonstrate that in primary human glomerular mesangial cells PGE2 caused modification of Smad2 as detected by Smad2N antibody, raised against a peptide near the N-terminus of Smad2. We hypothesize that Smad2 protein is post-translationaly modified by PGE2. Direct evidence of Smad2 modification by PGE2 was achieved by avidin pulldown assay which showed that endogenous Smad2 and recombinant Smad2 protein were attached by biotin-labeled PGE2. Taken together, our results provided evidence that post-translational modification of Smad2 could be a mechanism for the action of PGE2 in the pathogenesis of human pathologies. PMID:24613014

Yang, Chen; Chen, Chen; Sorokin, Andrey

2014-05-01

239

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

240

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

241

Ternary complex formation between AmtB, GlnZ and the nitrogenase regulatory enzyme DraG reveals a  

E-print Network

Ternary complex formation between AmtB, GlnZ and the nitrogenase regulatory enzyme DraG revealsZ and the nitrogenase re- gulatory enzyme DraG, which was stimulated by ADP. The stoichiometry of this complex was 1:1 (DraG monomer : GlnZ trimer). We have previously reported that in vivo high levels of extracellular

Merrick, Mike

242

Critical evaluation of thermodynamics of complex formation of metal ions in aqueous solutions I. A description of evaluation methods  

Microsoft Academic Search

An important step for the reliable evaluation of the thermodynamics of aqueous complex species is the appropriate choice of a model for interpolation and extrapolation of experimental values of log K and ?rH of complex formation reactions in different ionic media. Several models proposed for the representation of activity coefficients in aqueous solutions are briefly discussed. It has been shown

Mingsheng Wang; Yu Zhang; Mamoun Muhammed

1997-01-01

243

Promotion of metastasis by a specific complex of coagulation factors may be independent of fibrin formation.  

PubMed Central

Coumarins inhibit metastasis in a number of animal models, but the mechanism of this effect remains unclear. We have investigated the relationship between the coagulation system and metastasis using a new model system, involving i.v. injection of Mtln3 rat mammary carcinoma cells into Fischer 344 rats, and subsequent estimation of pulmonary seeding. Injection of factors II, VII, IX and X elevated the median number of surface pulmonary seedlings per animal to 182, and injection of factors II, IX and X to 181, compared with a median for control animals of 12 (P less than 0.001). Injection of factor VII alone, or of bovine serum albumin did not significantly affect pulmonary seeding. In a second experiment, arvin defibrination reduced the mean plasma fibrinogen concentration to 76.8 mg dl-1 from a control value of 228 mg dl-1. This degree of defibrination had no significant effects on pulmonary seeding, nor on the enhancing effects of factor complex injection (median numbers of seedlings per animal; control 15, arvin 21, arvin plus factors II, VII, IX and X 170, factors II, VII, IX and X only, 157). Factor complex injections did not detectably shorten thrombotest clotting times. In vitro testing suggested that Mtln3 cells contain little or no conventional factor X activating cancer procoagulant. The complex of coagulation factors II, IX and X appears to contain a component which greatly enhances metastasis in this model. This may explain the previously reported antimetastatic effect of coumarin anticoagulants, which suppress factors II, VII, IX and X. The enhancing effect of the factor complex does not appear to be altered by significant reductions in fibrin forming capacity, and defibrination itself has no effect on metastasis. These findings suggest the possibility that the effect of this factor complex on metastasis may be mediated via mechanisms other than the formation of a fibrin clot. PMID:3166906

McCulloch, P.; George, W. D.

1988-01-01

244

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

245

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

246

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

PubMed

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

Dash, Uma; Misra, Pramila K

2011-05-15

247

Hydride-Meisenheimer Complex Formation and Protonation as Key Reactions of 2,4,6Trinitrophenol Biodegradation by Rhodococcus erythropolis  

Microsoft Academic Search

Biodegradation of 2,4,6-trinitrophenol (picric acid) by Rhodococcus erythropolis HLPM-1 proceeds via initial hydrogenation of the aromatic ring system. Here we present evidence for the formation of a hydride-Meisen- heimer complex (anionic s-complex) of picric acid and its protonated form under physiological conditions. These complexes are key intermediates of denitration and productive microbial degradation of picric acid. For comparative spectroscopic identification

PAUL-GERHARD RIEGER; VOLKER SINNWELL; ANDREA PREUß; WITTKO FRANCKE; HANS-JOACHIM KNACKMUSS

1999-01-01

248

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

PubMed Central

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

2011-01-01

249

Formation mechanism of monodisperse CdS particles from concentrated solutions of Cd-EDTA complexes  

SciTech Connect

The formation mechanism of monodisperse spherical CdS particles in a condensed homogeneous solution of Cd-EDTA complexes in the presence of thioacetamide (TAA), ammonium acetate, ammonia, and gelatin was studied. The monodisperse particles were formed through a consecutive process with an almost instantaneous nucleation and succeeding gradual growth without renucleation. The Cd-EDTA and TAA worked only as reservoirs of Cd{sup 2+} and S{sup 2{minus}} ions, but the rate-determining step of particle growth was found to be the dissociation process of the Cd-EDTA complexes and not of the TAA. Ammonia played a decisive role as a complexing agent at high concentrations of Cd(NH{sub 3}){sub n}{sup 2+}, which could promptly release free Cd{sup 2+} ions, in promoting nucleation as well as growth even under a low supersaturation, and thus achieved excellent monodispersity by lowering the supersaturation below the critical level during their growth. The important role of CH{sub 3}COONH{sub 4}-NH{sub 3} as a powerful pH buffer for maintaining the activity of both NH{sub 3} and TAA was also proved. Moreover, size control of the final product was achieved in a range from 0.038 to 0.51 {micro}m.

Sugimoto, Tadao; Dirige, G.E.; Muramatsu, Atsushi [Tohoku Univ., Sendai (Japan). Inst. for Advanced Materials Processing] [Tohoku Univ., Sendai (Japan). Inst. for Advanced Materials Processing

1996-09-25

250

Substrate-Na{sup +} complex formation: Coupling mechanism for {gamma}-aminobutyrate symporters  

SciTech Connect

Crystal structures of transmembrane transport proteins belonging to the important families of neurotransmitter-sodium symporters reveal how they transport neurotransmitters across membranes. Substrate-induced structural conformations of gated neurotransmitter-sodium symporters have been in the focus of research, however, a key question concerning the mechanism of Na{sup +} ion coupling remained unanswered. Homology models of human glial transporter subtypes of the major inhibitory neurotransmitter {gamma}-aminobutyric acid were built. In accordance with selectivity data for subtype 2 vs. 3, docking and molecular dynamics calculations suggest similar orthosteric substrate (inhibitor) conformations and binding crevices but distinguishable allosteric Zn{sup 2+} ion binding motifs. Considering the occluded conformational states of glial human {gamma}-aminobutyric acid transporter subtypes, we found major semi-extended and minor ring-like conformations of zwitterionic {gamma}-aminobutyric acid in complex with Na{sup +} ion. The existence of the minor ring-like conformation of {gamma}-aminobutyric acid in complex with Na{sup +} ion may be attributed to the strengthening of the intramolecular H-bond by the electrostatic effect of Na{sup +} ion. Coupling substrate uptake into cells with the thermodynamically favorable Na{sup +} ion movement through substrate-Na{sup +} ion complex formation may be a mechanistic principle featuring transmembrane neurotransmitter-sodium symporter proteins.

Pallo, Anna; Simon, Agnes [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary)] [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary); Bencsura, Akos [Department of Theoretical Chemistry, Institute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest (Hungary)] [Department of Theoretical Chemistry, Institute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest (Hungary); Heja, Laszlo [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary)] [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary); Kardos, Julianna, E-mail: jkardos@chemres.hu [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary)] [Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences (Hungary)

2009-07-24

251

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

PubMed

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

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

2012-11-01

252

Role for Nhp6, Gcn5, and the Swi\\/Snf Complex in Stimulating Formation of the TATA-Binding Protein-TFIIA-DNA Complex  

Microsoft Academic Search

The TATA-binding protein (TBP), TFIIA, and TFIIB interact with promoter DNA to form a complex required for transcriptional initiation, and many transcriptional regulators function by either stimulating or inhibiting formation of this complex. We have recently identified TBP mutants that are viable in wild-type cells but lethal in the absence of the Nhp6 architectural transcription factor. Here we show that

Debabrata Biswas; Anthony N. Imbalzano; Peter Eriksson; Yaxin Yu; David J. Stillman

2004-01-01

253

Spring Constants  

NSDL National Science Digital Library

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

Horton, Michael

2009-05-30

254

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

255

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

256

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

257

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

PubMed Central

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

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

2014-01-01

258

[Analysis of the fragment D-fibrin monomer complex formation by salting-out fractionation].  

PubMed

The fragment D-fibrin monomer complex formation was studied by ammonium sulfate fractionation of the reaction mixtures initially consisting of 0.15-4.00 mg/ml of fragment D and 1.00 mg/ml of fibrin monomer, It was shown that in these mixtures the equilibrium was reached in not more than 15 sec. Fragment D binding to fibrin dependent on the fragment concentration. The Scatchard analysis of this dependence revealed a maximum of fragment D binding to one fibrin molecule of 2.95 +/- 0.28 with a Ka value of (9.04 +/- 1.08) x 10(-5) M-1 (n = 6), thus indicating a strong fragment--fibrin affinity. PMID:7115809

Pozdniakova, T M; Rybachuk, V N; Vovk, E v

1982-06-01

259

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

PubMed

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

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

2013-01-14

260

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

PubMed

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

Karmaker, Subarna; Saha, Tapan K

2008-02-11

261

Validation of a Parcel-Based Reduced-Complexity Model for River Delta Formation (Invited)  

NASA Astrophysics Data System (ADS)

Reduced-Complexity Models (RCMs) take an intuitive yet quantitative approach to represent processes with the goal of getting maximum return in emergent system-scale behavior with minimum investment in computational complexity. This approach is in contrast to reductionist models that aim at rigorously solving the governing equations of fluid flow and sediment transport. RCMs have had encouraging successes in modeling a variety of geomorphic systems, such as braided rivers, alluvial fans, and river deltas. Despite the fact that these models are not intended to resolve detailed flow structures, questions remain on how to interpret and validate the output of RCMs beyond qualitative behavior-based descriptions. Here we present a validation of the newly developed RCM for river delta formation with channel dynamics (Liang, 2013). The model uses a parcel-based 'weighted-random-walk' method that resolves the formation of river deltas at the scale of channel dynamics (e.g., avulsions and bifurcations). The main focus of this validation work is the flow routing model component. A set of synthetic test cases were designed to compare hydrodynamic results from the RCM and Delft3D, including flow in a straight channel, around a bump, and flow partitioning at a single bifurcation. Output results, such as water surface slope and flow field, are also compared to field observations collected at Wax Lake Delta. Additionally, we investigate channel avulsion cycles and flow path selection in an alluvial fan with differential styles of subsidence and compare model results to laboratory experiments, as a preliminary effort in pairing up numerical and experimental models to understand channel organization at process scale. Strengths and weaknesses of the RCM are discussed and potential candidates for model application identified.

Liang, M.; Geleynse, N.; Passalacqua, P.; Edmonds, D. A.; Kim, W.; Voller, V. R.; Paola, C.

2013-12-01

262

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

263

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

264

Plants can utilize iron form Fe?N,N'?di?(2?hydroxybenzoyl)?ethylenediamine?N,N'?diacetic acid, a ferric chelate with 10greater formation constant than Fe?EDDHA  

Microsoft Academic Search

HBED [N,N'?di?(2?hydroxybenzoyl)?ethylenediamine?N,N'?diacetic acid] was synthesized in 1967, but it only recently became available in the quantities needed for plant nutrition research. This chelator is a close relative of EDDHA, but has a Fe?chelate formation or stability constant (at ionic strength, ?+ 0.1) of 39.68 compared to 33.91 for EDDHA. Even the Fe selectivity (i.e. Fe\\/Ca stability constant ratios) is greater

Rufus L. Chaney

1988-01-01

265

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

266

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

267

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

268

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

PubMed

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

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

2014-11-01

269

Critical evaluation of thermodynamics of complex formation of metal ions in aqueous solutions II. Hydrolysis and hydroxo-complexes of Cu 2+ at 298.15 K  

Microsoft Academic Search

The standard thermodynamic properties of the Cu2+ hydrolysis reactions and the Cu2+ hydroxo-complexes formation were evaluated on the basis of published experimental studies and the Specific Interaction Theory (SIT) for activity coefficients modelling. A set of thermodynamic data and interaction coefficients were obtained.

Natalia V. Plyasunova; Mingsheng Wang; Yu Zhang; Mamoun Muhammed

1997-01-01

270

Control of Cyclic Photoinitiated Electron Transfer between Cytochrome c Peroxidase (W191F) and Cytochrome c by Formation of Dynamic Binary and Ternary Complexes.  

PubMed

Extensive studies of the physiological protein-protein electron-transfer (ET) complex between yeast cytochrome c peroxidase (CcP) and cytochrome c (Cc) have left unresolved questions about how formation and dissociation of binary and ternary complexes influence ET. We probe this issue through a study of the photocycle of ET between Zn-protoporphyrin IX-substituted CcP(W191F) (ZnPCcP) and Cc. Photoexcitation of ZnPCcP in complex with Fe(3+)Cc initiates the photocycle: charge-separation ET, [(3)ZnPCcP, Fe(3+)Cc] ? [ZnP(+)CcP, Fe(2+)Cc], followed by charge recombination, [ZnP(+)CcP, Fe(2+)Cc] ? [ZnPCcP, Fe(3+)Cc]. The W191F mutation eliminates fast hole hopping through W191, enhancing accumulation of the charge-separated intermediate and extending the time scale for binding and dissociation of the charge-separated complex. Both triplet quenching and the charge-separated intermediate were monitored during titrations of ZnPCcP with Fe(3+)Cc, Fe(2+)Cc, and redox-inert CuCc. The results require a photocycle that includes dissociation and/or recombination of the charge-separated binary complex and a charge-separated ternary complex, [ZnP(+)CcP, Fe(2+)Cc, Fe(3+)Cc]. The expanded kinetic scheme formalizes earlier proposals of "substrate-assisted product dissociation" within the photocycle. The measurements yield the thermodynamic affinity constants for binding the first and second Cc: KI = 10(-7) M(-1), and KII = 10(-4) M(-1). However, two-site analysis of the thermodynamics of formation of the ternary complex reveals that Cc binds at the weaker-binding site with much greater affinity than previously recognized and places upper bounds on the contributions of repulsion between the two Cc's of the ternary complex. In conjunction with recent nuclear magnetic resonance studies, the analysis further suggests a dynamic view of the ternary complex, wherein neither Cc necessarily faithfully adopts the crystal-structure configuration because of Cc-Cc repulsion. PMID:25629200

Page, Taylor R; Hoffman, Brian M

2015-02-10

271

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

SciTech Connect

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

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

2010-09-01

272

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

273

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

274

In Silico Inhibition Studies of Jun-Fos-DNA Complex Formation by Curcumin Derivatives  

PubMed Central

Activator protein-1 (AP1) is a transcription factor that consists of the Jun and Fos family proteins. It regulates gene expression in response to a variety of stimuli and controls cellular processes including proliferation, transformation, inflammation, and innate immune responses. AP1 binds specifically to 12-O-tetradecanoylphorbol-13-acetate (TPA) responsive element 5?-TGAG/CTCA-3? (AP1 site). It has been found constitutively active in breast, ovarian, cervical, and lung cancers. Numerous studies have shown that inhibition of AP1 could be a promising strategy for cancer therapeutic applications. The present in silico study provides insights into the inhibition of Jun-Fos-DNA complex formation by curcumin derivatives. These derivatives interact with the amino acid residues like Arg155 and Arg158 which play a key role in binding of Jun-Fos complex to DNA (AP1 site). Ala151, Ala275, Leu283, and Ile286 were the residues present at binding site which could contribute to hydrophobic contacts with inhibitor molecules. Curcumin sulphate was predicted to be the most potent inhibitor amongst all the natural curcumin derivatives docked. PMID:25374685

Kumar, Anil; Bora, Utpal

2012-01-01

275

Constraining the process of Eoarchean TTG formation in the Itsaq Gneiss Complex, southern West Greenland  

NASA Astrophysics Data System (ADS)

We present new major and trace element, high-precision high-field-strength-element, hafnium and neodymium isotope data for well preserved Eoarchean TTGs within the Itsaq Gneiss Complex (IGC) of southern West Greenland. These data are combined with thermodynamic model predictions of partial melting and fractional crystallization to gain new insights into continental crust formation in the Archean. Our results show that the observed compositional range of Eoarchean TTGs can be explained by a combination two processes: (1) 5-25% partial melting of amphibolite within thickened mafic crust and (2) subsequent fractional crystallization processes. The Eoarchean TTG suite of SW Greenland probably formed through mixing of melt batches that originally formed at different source depths between 10 and 14 kbar and ponded as plutons at mid-crustal levels. The trace element compositions of some TTGs point to subsequent fractional crystallization processes involving plagioclase, clinopyroxene, amphibole and garnet. Our model is consistent with recent studies proposing that the Eoarchean Itsaq Gneiss Complex TTGs from the IGC formed by re-working of mafic protocrust that stabilized as accreted juvenile crustal terranes in the Eoarchean. The model is also in good agreement with field observations from the area.

Hoffmann, J. Elis; Nagel, Thorsten J.; Münker, Carsten; Næraa, Tomas; Rosing, Minik T.

2014-02-01

276

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

277

Spectrophotometric determination of nizatidine and ranitidine through charge transfer complex formation.  

PubMed

Two Spectrophotometric procedures are presented for the determination of two commonly used H2-receptor antagonists, nizatidine (I) and ranitidine hydrochloride (II). The methods are based mainly on charge transfer complexation reaction of these drugs with either p-chloranilic acid (rho-CA) or 2, 3 dichloro-5, 6-dicyanoquinone (DDQ). The produced colored products are quantified spectrophotometrically at 515 and 467 nm in chloranilic acid and DDQ methods, respectively. The molar ratios for the reaction products and the optimum assay conditions were studied. The methods determine the cited drugs in concentration ranges of 20-200 and 20-160 microg/mL for nizatidine and ranges of 20-240 and 20-140 microg/mL for ranitidine with chloranilic acid and DDQ methods, respectively. A more detailed investigation of the complexes formed was made with respect to their composition, association constant, molar absorptivity and free energy change. The proposed procedures were successfully utilized in the determination of the drugs in pharmaceutical preparations. The standard addition method was applied by adding nizatidine and ranitidine to the previously analyzed tablets or capsules. The recovery of each drug was calculated by comparing the concentration obtained from the spiked mixtures with those of the pure drug. The results of analysis of commercial tablets and the recovery study (standard addition method) of the cited drugs suggested that there is no interference from any excipients, which are present in tablets or capsules. Statistical comparison of the results was performed with regard to accuracy and precision using student's t-test and F-ratio at 95% confidence level. There is no significant difference between the reported and proposed methods with regard to accuracy and precision. PMID:15356997

Walash, M; Sharaf-El Din, M; Metwalli, M E-S; RedaShabana, M

2004-07-01

278

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

SciTech Connect

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

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

2010-06-10

279

Formation of a Eu(III) borate solid species from a weak Eu(III) borate complex in aqueous solution.  

PubMed

In the presence of polyborates (detected by (11)B-NMR) the formation of a weak Eu(III) borate complex (lg ?11 ~ 2, estimated) was observed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation of this solid in solution was investigated by TRLFS as a function of the total boron concentration: the lower the total boron concentration, the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD and solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid. PMID:24849080

Schott, Juliane; Kretzschmar, Jerome; Acker, Margret; Eidner, Sascha; Kumke, Michael U; Drobot, Björn; Barkleit, Astrid; Taut, Steffen; Brendler, Vinzenz; Stumpf, Thorsten

2014-08-14

280

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

NASA Astrophysics Data System (ADS)

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

Komeda, Tadahiro; Katoh, Keiichi; Yamashita, Masahiro

2014-05-01

281

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

282

Formative assessment in an online learning environment to support flexible on-the-job learning in complex professional domains  

Microsoft Academic Search

This article describes a blueprint for an online learning environment that is based on prominent instructional design and\\u000a assessment theories for supporting learning in complex domains. The core of this environment consists of formative assessment\\u000a tasks (i.e., assessment for learning) that center on professional situations. For each professional situation, three levels of situational complexity\\u000a are defined, and within each of

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

2010-01-01

283

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

284

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

NASA Astrophysics Data System (ADS)

Metamorphic Core Complexes (MCCs) form when a thickened domain with a low-strength lower crust is submitted to extension. These structures are characteristic of post-orogenic extension, and field observations suggest that several MCCs rework a crustal nappe-stack emplaced before extension begins. These MCCs therefore develop within heterogeneous crusts that contain pre-existing dipping heterogeneities, such as thrust faults and dipping nappes in a crustal wedge. Although very common, this first order structural inheritance has never been considered in studies modelling MCCs. Our contribution therefore investigates the effect of an inherited crustal wedge structure on the dynamics and kinematics of formation of the MCCs, using fully coupled thermomechanical modelling. The wealth of petrological, structural and time informations available in the Cycladic MCCs (Aegean domain) allows setting up more realistic initial conditions for the experiments than usual flat-lying setups. It also allows the results of the numerical computation to be directly validated with final geometries, P-T paths and exhumation rates. The experiments using dipping heterogeneities are characterised by a much more complex evolution and final structure than their flat-lying layered equivalents. Dipping heterogeneities drive lateral strength contrasts and help to re-localise the deformation on successive detachments. The dip of the inherited wedge structures imposes kinematic constraints on the flow, which provides a model that explains the regional scale asymmetry of the Cycladic MCCs. The P-T paths, the exhumation rates and the final crustal structure that come out of an initial shallow-dipping wedge model provide a much more realistic comparison with their natural counter-parts than common flat-lying models. Other parameters, like crustal-scale density inversion, thermal structure and creep law parameters are of second order when compared to the initial wedge structure. Being little dependent on these second order parameters, the proposed model for the formation of MCCs within inherited crustal wedges is likely to be applied to other areas where the MCCs formed in a nappe stack involving continental basement.

Huet, B.; Le Pourhiet, L.; Labrousse, L.; Burov, E. B.; Jolivet, L.

2011-09-01

285

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

PubMed

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

2014-02-01

286

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

PubMed

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

Valente, Artur J M; Söderman, Olle

2014-03-01

287

EPR demonstration of iron-nitrosyl complex formation by cytotoxic activated macrophages  

SciTech Connect

Activated macrophage cytotoxicity is characterized by loss of intracellular iron and inhibition of certain enzymes that have catalytically active nonheme-iron coordinated to sulfur. This phenomenon involves the oxidation of one of the terminal guanidino nitrogen atoms of L-arginine, which results in the production of citrulline and inorganic nitrogen oxides (NO2-, NO3-, and NO). We report here the results of an electron paramagnetic resonance spectroscopic study performed on cytotoxic activated macrophage (CAM) effector cells, which develop the same pattern of metabolic inhibition as their targets. Examination of activated macrophages from mice infected with Mycobacterium bovis (strain bacillus Calmette-Guerin) that were cultured in medium with lipopolysaccharide and L-arginine showed the presence of an axial signal at g = 2.039, which is similar to previously described iron-nitrosyl complexes formed from the destruction of iron-sulfur centers by nitric oxide (NO). Inhibition of the L-arginine-dependent pathway by addition of NG-monomethyl-L-arginine (methyl group on a terminal guanidino nitrogen) inhibits the production of nitrite, nitrate, citrulline, and the g = 2.039 signal. Comparison of the hyperfine structure of the signal from cells treated with L-arginine with terminal guanidino nitrogen atoms of natural abundance N14 atoms or labeled with N15 atoms showed that the nitrosyl group in this paramagnetic species arises from one of these two atoms. These results show that loss of iron-containing enzyme function in CAM is a result of the formation of iron-nitrosyl complexes induced by the synthesis of nitric oxide from the oxidation of a terminal guanidino nitrogen atom of L-arginine.

Lancaster, J.R. Jr.; Hibbs, J.B. Jr. (Utah State Univ., Logan (USA))

1990-02-01

288

Interaction of IF2 with the ribosomal GTPase-associated center during 70S initiation complex formation.  

PubMed

Addition of an Escherichia coli 50S subunit (50S(Cy5)) containing a Cy5-labeled L11 N-terminal domain (L11-NTD) within the GTPase-associated center (GAC) to an E. coli 30S initiation complex (30SIC(Cy3)) containing Cy3-labeled initiation factor 2 complexed with GTP leads to rapid development of a FRET signal during formation of the 70S initiation complex (70SIC). Initiation factor 2 (IF2) and elongation factor G (EF-G) induce similar changes in ribosome structure. Here we show that such similarities are maintained on a dynamic level as well. Thus, movement of IF2 toward L11-NTD after initial 70S ribosome formation follows GTP hydrolysis and precedes P(i) release, paralleling movement of EF-G following its binding to the ribosome [Seo, H., et al. (2006) Biochemistry 45, 2504-2514], and in both cases, the rate of such movement is slowed if GTP hydrolysis is prevented. The 30SIC(Cy3):50S(Cy5) FRET signal also provides a sensitive probe of the ability of initiation factor 3 to discriminate between a canonical and a noncanonical initiation codon during 70SIC formation. We employ Bacillus stearothermophilus IF2 as a substitute for E. coli IF2 to take advantage of the higher stability of the complexes it forms with E. coli ribosomes. While Bst-IF2 is fully functional in formation of E. coli 70SIC, relative reactivities toward dipeptide formation of 70SICs formed with the two IF2s suggest that the Bst-IF2.GDP complex is more difficult to displace from the GAC than the E. coli IF2.GDP complex. PMID:19366171

Qin, Haiou; Grigoriadou, Christina; Cooperman, Barry S

2009-06-01

289

STAR FORMATION AND YOUNG POPULATION OF THE H II COMPLEX Sh2-294  

SciTech Connect

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 {mu}m observed with the Spitzer Space Telescope Infrared Array Camera (IRAC), coupled with H{sub 2} (2.12 {mu}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 H{sub 2} 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{sub Sun }) YSOs; however, we also detected a massive YSO ({approx}9 M{sub Sun }) of Class I nature, embedded in a cloud of visual extinction of {approx}24 mag. Present analysis suggests that the Class I sources are indeed a younger population of the region relative to Class II sources (age {approx} 4.5 Multiplication-Sign 10{sup 6} 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 {approx}4 Multiplication-Sign 10{sup 6} yr B0 main-sequence star.

Samal, M. R.; Pandey, A. K.; Chauhan, N.; Jose, J. [Aryabhatta Research Institute of Observational Sciences, Nainital 263129 (India); Ojha, D. K. [Tata Institute of Fundamental Research, Mumbai 400005 (India); Pandey, B., E-mail: manash.samal@oamp.fr [Physics Department, D.S.B. Campus, Kumaun University, Nainital 263129 (India)

2012-08-10

290

Superoxide-dependent formation of hydroxyl radicals from ferric-complexes and hydrogen peroxide: an evaluation of fourteen iron chelators.  

PubMed

When a variety of ferric chelates are reacted with hydrogen peroxide in phosphate buffer deoxyribose is damaged and this damage is protected against by formate, thiourea and mannitol. Damage done by ferric complexes of citrate, EDTA, NTA, EGTA and HEDA is substantially inhibited by superoxide dismutase (SOD) whereas complexes of PLA, ADP and CDTA are moderately inhibited by SOD. The effects of SOD argue against hydrogen peroxide acting as a reductant in Fenton chemistry driven by ferric complexes and hydrogen peroxide. EDTA has proved to be a useful model for Fenton chemistry that is inhibited by SOD although, it is not unique in this respect. PMID:2161386

Gutteridge, J M

1990-01-01

291

Are Fundamental Constants Really Constant?  

ERIC Educational Resources Information Center

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

Swetman, T. P.

1972-01-01

292

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

E-print Network

We present photometric and spectroscopic results for the low mass pre-main sequence (PMS) stars with spectral types K - M in the cometary globule (CG) 30/31/38 complex. We obtained multi-object high resolution spectra for the targets selected as possible PMS stars from multi-wavelength photometry. We identified 11 PMS stars brighter than V = 16.5 with ages < 5 Myr at a distance of approximately 200 pc. The spatial distribution of the PMS stars, CG clouds, and ionizing sources (O stars and supernova remnants) suggests a possible triggered origin of the star formation in this region. We confirm the youth of the photometrically selected PMS stars using the lithium abundances. The radial velocities of the low mass PMS stars are consistent with those of the cometary globules. Most of the PMS stars show weak Halpha emission with W(Halpha) < 10 A. Only 1 out of the 11 PMS stars shows a moderate near-IR excess, which suggests a short survival time (t < 5 Myr) of circumstellar disks in this star forming envir...

Kim, J S; Wolk, S J; Kim, Jinyoung Serena; Walter, Frederick M.

2005-01-01

293

Formation and identification of unresolved complex mixtures in lacustrine biodegraded oil from Nanxiang Basin, China.  

PubMed

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

294

Complex solitary wave dynamics, pattern formation and chaos in the gain-loss nonlinear Schrödinger equation  

NASA Astrophysics Data System (ADS)

A numerical exploration of a gain-loss nonlinear Schrödinger equation was carried out utilizing over 180?000 core hours to conduct more than 10?000 unique simulations in an effort to characterize the model's six dimensional parameter space. The study treated the problem in full generality, spanning a minimum of eight orders of magnitude for each of three linear and nonlinear gain terms and five orders of magnitude for higher order nonlinearities. The gain-loss nonlinear Schrödinger equation is of interest as a model for spin wave envelopes in magnetic thin film active feedback rings and analogous driven damped nonlinear physical systems. Bright soliton trains were spontaneously driven out of equilibrium and behaviors stable for tens of thousands of round trip times were numerically identified. Nine distinct complex dynamical behaviors with lifetimes on the order of ms were isolated as part of six identified solution classes. Numerically located dynamical behaviors include: (i) low dimensional chaotic modulations of bright soliton trains; (ii) spatially symmetric/asymmetric interactions of solitary wave peaks; (iii) dynamical pattern formation and recurrence; (iv) steady state solutions; and (v) intermittency. Simulations exhibiting chaotically modulating bright soliton trains were found to qualitatively match previous experimental observations. Ten new dynamical behaviors, eight demonstrating long lifetimes, are predicted to be observable in future experiments.

Anderson, Justin Q.; Ryan, Rachel A.; Wu, Mingzhong; Carr, Lincoln D.

2014-02-01

295

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

296

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

297

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

PubMed Central

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

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

2001-01-01

298

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

299

Simulation of chain length recognition observed in formation of inclusion complex  

NASA Astrophysics Data System (ADS)

We carried out Brownian dynamics simulations to investigate the mechanism of chain length recognition observed in the formation of inclusion complexes (ICs) between cyclodextrins (CDs) and polymer chains. In our simulations, we used rings and chains as models to represent CDs and polymer chains, respectively. We used two types of chains with different lengths to determine which chain was preferred by the rings to form ICs. At low concentration of rings, we observed that almost all the rings formed ICs with the long chains. Chain length recognition could be reproduced in our simulation, and it occurred because of the difference in the inclusion time between the long chains and the short chains in the ICs. On the other hand, at high concentration of rings, the number of rings forming ICs with the long chains increased, and pseudo-polyrotaxanes (PPRXs) were formed. ICs were also formed with the short chains, because the inclusion time for each ring contained in the PPRXs reduced with an increase in the number of rings therein, and then, the dissociated rings formed ICs with the short chains. As a result, chain length recognition was not observed. From these results, we conclude that the difference in the inclusion time between the rings and the chains controls chain length recognition.

Urakami, Naohito; Imada, Junko; Yamamoto, Takashi

2011-01-01

300

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

301

The long-range electrostatic interactions control tRNA–aminoacyl-tRNA synthetase complex formation  

PubMed Central

In most cases aminoacyl-tRNA synthetases (aaRSs) are negatively charged, as are the tRNA substrates. It is apparent that there are driving forces that provide a long-range attraction between like charge aaRS and tRNA, and ensure formation of "close encounters." Based on numerical solutions to the nonlinear Poisson-Boltzmann equation, we evaluated the electrostatic potential generated by different aaRSs. The 3D-isopotential surfaces calculated for different aaRSs at 0.01 kT/e contour level reveal the presence of large positive patches—one patch for each tRNA molecule. This is true for classes I and II monomers, dimers, and heterotetramers. The potential maps keep their characteristic features over a wide range of contour levels. The results suggest that nonspecific electrostatic interactions are the driving forces of primary stickiness of aaRSs–tRNA complexes. The long-range attraction in aaRS–tRNA systems is explained by capture of negatively charged tRNA into "blue space area" of the positive potential generated by aaRSs. Localization of tRNA in this area is a prerequisite for overcoming the barrier of Brownian motion. PMID:12761395

Tworowski, Dmitry; Safro, Mark

2003-01-01

302

The long-range electrostatic interactions control tRNA-aminoacyl-tRNA synthetase complex formation.  

PubMed

In most cases aminoacyl-tRNA synthetases (aaRSs) are negatively charged, as are the tRNA substrates. It is apparent that there are driving forces that provide a long-range attraction between like charge aaRS and tRNA, and ensure formation of "close encounters." Based on numerical solutions to the nonlinear Poisson-Boltzmann equation, we evaluated the electrostatic potential generated by different aaRSs. The 3D-isopotential surfaces calculated for different aaRSs at 0.01 kT/e contour level reveal the presence of large positive patches-one patch for each tRNA molecule. This is true for classes I and II monomers, dimers, and heterotetramers. The potential maps keep their characteristic features over a wide range of contour levels. The results suggest that nonspecific electrostatic interactions are the driving forces of primary stickiness of aaRSs-tRNA complexes. The long-range attraction in aaRS-tRNA systems is explained by capture of negatively charged tRNA into "blue space area" of the positive potential generated by aaRSs. Localization of tRNA in this area is a prerequisite for overcoming the barrier of Brownian motion. PMID:12761395

Tworowski, Dmitry; Safro, Mark

2003-06-01

303

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

NASA Astrophysics Data System (ADS)

We develop a reduced-complexity model (RCM) delta formation model, in contrast to reductionist models based on high-resolution computational fluid dynamics. The basic framework of this model (referred in this paper as "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 flow field, water surface topography and bed topography that evolves in time. Results show that DeltaRCM is able to: (1) resolve a wide range of channel dynamics, including elongation, bifurcation, avulsion and migration; (2) in response to the changes in input parameters, produce different types of deltas such as alluvial fan deltas at experimental scale. We also identify three key areas of particular model sensitivity, even at the RCM level: (1) avulsion dynamics is sensitive to dynamic free-surface topography; (2) channel network structure is sensitive to instability at channel mouths which creates bars; and (3) out-of-channel sedimentation is sensitive to water surface slope along channel margins. We also demonstrate a simple stratigraphy tracking component which can display the structure of the deposit in terms of distribution of coarse and fine materials along with the age of the deposit. DeltaRCM is a useful tool for understanding the dynamics of river deltas within a relatively simple cellular representation of water and sediment transport.

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

2014-07-01

304

GEOC Martial Taillefert Wednesday, April 10, 2013 187 Mechanisms of ferrihydriteorganic matter complex formation via adsorption and coprecipitation  

E-print Network

complex formation via adsorption and coprecipitation Chunmei Chen1, cmchen@udel.edu, Jay J Dynes2, Jian Wang2, Tom Regier2, Donald L Sparks1. (1) Plant and Soil sciences, University of Delaware, Newark structure (NEXAFS) spectroscopy at the C edge and Fourier transform infrared (FTIR) spectroscopy, we

Sparks, Donald L.

305

Control of AmtB-GlnK Complex Formation by Intracellular Levels of ATP, ADP, and 2-Oxoglutarate*S  

E-print Network

Control of AmtB-GlnK Complex Formation by Intracellular Levels of ATP, ADP, and 2-Oxoglutarate of the most widespread families of signal transduction proteins in nature, being ubiquitous throughout bacteria, archaea, and plants. They play a major role in coordi- nating nitrogen metabolism by interacting

Merrick, Mike

306

Complex formation, rearrangement, and reaction in PhOH Vibrational mode effects, recoil velocities, and ab initio studies  

E-print Network

Complex formation, rearrangement, and reaction in PhOH¿ ¿ND3: Vibrational mode effects, recoil that a combina- tion of measuring the effects of reactant vibrational excita- tion and collision energy, together,2 Vibrational effects tend to probe events early along the reaction coordinate, provid- ing insight

Anderson, Scott L.

307

Role of homogeneous formate complexes in the water gas shift reaction catalyzed by the group 6 metal carbonyls  

Microsoft Academic Search

The mechanism of the homogeneous water gas shift reaction catalyzed by the group 6 metal carbonyls involves the intermediacy of a formate complex. Catalytic pressure reactions as well as stoichiometric photolysis and pyrolysis experiments provide support for this mechanism. 10 references, 1 table.

William A. R. Slegeir; Richard S. Sapienza; Richard Rayford; Lillian Lam

1982-01-01

308

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

309

The challenge of formative evaluation in complex policy environments: the case of community strategies in England: A Working Paper1  

Microsoft Academic Search

Formative evaluation presents a number of challenges for the evaluator, in particular managing expectations between the evaluator and the evaluand, the ability to innovate and present clear-cut, workable and timely policy solutions as well as good communication between all parties. These challenges are particularly acute when undertaking evaluations within complex policy environments that are experiencing rapid change and where there

Alison Darlow; Sukvinder Jassi; Martin Purcell

310

Preparative separation of structurally related and racemic hydroxyl-containing compounds through the formation of crystalline molecular complexes  

NASA Astrophysics Data System (ADS)

The published data concerning the development of the methods for preparative separation of structurally related and racemic hydroxyl-containing organic compounds through the formation of crystalline molecular complexes are generalised. Special attention is focused on the resolution of racemic alcohols and phenols into enantiomers.

Kurilov, D. V.; Vinogradov, M. G.

2008-07-01

311

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

312

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

313

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

PubMed

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

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

2012-04-01

314

WAVE and Arp2/3 jointly inhibit filopodium formation by entering into a complex with mDia2.  

PubMed

Lamellipodia/ruffles and filopodia are protruding organelles containing short and highly branched or long and unbranched actin filaments, respectively. The microscopic morphology, dynamic development and protein signature of both lamellipodia/ruffles and filopodia have been investigated; however, little is known about the mechanisms by which cells coordinate the formation of these actin-based extensions. Here, we show that WAVE holds mDia2 and the Arp2/3 complex in a multimolecular complex. WAVE- and Arp2/3-dependent ruffling induced by EGF does not require mDia2. Conversely, the emission of mDia2-dependent filopodia correlates with its disengagement from WAVE. Consistently, the ability of EGF, Cdc42 and serum to induce mDia2-dependent formation of filopodia is increased in the absence of either the WAVE/Abi1/Nap1/PIR121 (WANP) or the Arp2/3 complex. Reintroduction of WAVE2 into WANP-complex knockdown cells markedly reduces filopodia formation independently of actin polymerization. Thus, WAVE and the Arp2/3 complex jointly orchestrate different types of actin-based plasma membrane protrusions by promoting ruffling and inhibiting mDia2-induced filopodia. PMID:18516090

Beli, Petra; Mascheroni, Debora; Xu, Dalu; Innocenti, Metello

2008-07-01

315

Mixed ligand complex formation of Fe III with boric acid and typical N-donor multidentate ligands  

Microsoft Academic Search

Equilibrium study of the mixed ligand complex formation of FeIII with boric acid in the absence and in the presence of 2,2?-bipyridine, 1,10-phenanthroline, diethylenetriamine and triethylenetetramine\\u000a (L) in different molar ratios provides evidence of formation of Fe(OH)2+, Fe(OH)\\u000a 2\\u000a +\\u000a , Fe(L)3+, Fe(H2BO4),Fe(OH)(H2BO4), Fe(OH)2(H2BO4)2-, Fe(L)(H2BO4) and Fe2(L)2(BO4)+ complexes. Fe(L)\\u000a 2\\u000a 3+\\u000a , Fe(L)2(H2BO4) and Fe2(L)4(BO4)+ complexes are also indicated with

G. N. Mukherjee; Ansuman Das

2002-01-01

316

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

PubMed

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

317

Structural backgrounds for the formation of a catalytically competent complex with NADP(H) during hydride transfer in ferredoxin-NADP(+) reductases.  

PubMed

The role of the highly conserved C266 and L268 of pea ferredoxin-NADP(+) reductase (FNR) in formation of the catalytically competent complex of the enzyme with NADP(H) was investigated. Previous studies suggest that the volume of these side-chains, situated facing the side of the C-terminal Y308 catalytic residue not stacking the flavin isoalloxazine ring, may be directly involved in the fine-tuning of the catalytic efficiency of the enzyme. Wild-type pea FNR as well as single and double mutants of C266 and L268 residues were analysed by fast transient-kinetic techniques and their midpoint reduction potentials were determined. For the C266A, C266M and C266A/L268A mutants a significant reduction in the overall hydride transfer (HT) rates was observed along with the absence of charge-transfer complex formation. The HT rate constants for NADPH oxidation were lower than those for NADP(+) reduction, reaching a 30-fold decrease in the double mutant. In agreement, these variants exhibited more negative midpoint potentials with respect to the wild-type enzyme. The three-dimensional structures of C266M and L268V variants were solved. The C266M mutant shows a displacement of E306 away from the relevant residue S90 to accommodate the bulky methionine introduced. The overall findings indicate that in FNR the volume of the residue at position 266 is essential to attain the catalytic architecture between the nicotinamide and isoalloxazine rings at the active site and, therefore, for an efficient HT process. In addition, flexibility of the 268-270 loop appears to be critical for FNR to achieve catalytically competent complexes with NADP(H). PMID:22542899

Sánchez-Azqueta, Ana; Musumeci, Matías A; Martínez-Júlvez, Marta; Ceccarelli, Eduardo A; Medina, Milagros

2012-07-01

318

Origin of 13C complexation shifts in the adduct formation of 2-butyl phenyl ethers with a dirhodium tetracarboxylate complex.  

PubMed

Complexation of the oxygen atom in 2-butyl phenyl ethers to a rhodium atom of the dirhodium tetracarboxylate Rh(II) 2[(R)-(+)-MTPA]4(Rh*, MTPA-H = methoxytrifluoromethylphenylacetic acid identical with Mosher's acid) deshields an sp3-hybridized 13C nucleus directly bonded to the ether oxygen; apparently, the inductive effect of the oxygen is enhanced when it is complexed to the rhodium atom. On the other hand, deshielding complexation shifts of aromatic ipso-carbons (alpha-positioned) are minute but ortho- and para-carbon signals are influenced by the resonance effect of oxygen. This effect can be modulated by further substituents at the benzene ring. In turn, this modulation of the resonance correlates linearly ith the magnitude of the inductive effect exerted on the aliphatic alpha-carbon atoms. Diastereomeric dispersion effects at 13C signals can be observed for most compounds, indicating that enantiodifferentiation is possible in this class of ethers. PMID:18098227

Díaz Gómez, Edison; Duddeck, Helmut

2008-01-01

319

Crystal structure and solution species of Ce(III) and Ce(IV) formates: from mononuclear to hexanuclear complexes.  

PubMed

Cerium(III) and cerium(IV) both form formate complexes. However, their species in aqueous solution and the solid-state structures are surprisingly different. The species in aqueous solutions were investigated with Ce K-edge EXAFS spectroscopy. Ce(III) formate shows only mononuclear complexes, which is in agreement with the predicted mononuclear species of Ce(HCOO)(2+) and Ce(HCOO)2(+). In contrast, Ce(IV) formate forms in aqueous solution a stable hexanuclear complex of [Ce6(?3-O)4(?3-OH)4(HCOO)x(NO3)y](12-x-y). The structural differences reflect the different influence of hydrolysis, which is weak for Ce(III) and strong for Ce(IV). Hydrolysis of Ce(IV) ions causes initial polymerization while complexation through HCOO(-) results in 12 chelate rings stabilizing the hexanuclear Ce(IV) complex. Crystals were grown from the above-mentioned solutions. Two crystal structures of Ce(IV) formate were determined. Both form a hexanuclear complex with a [Ce6(?3-O)4(?3-OH)4](12+) core in aqueous HNO3/HCOOH solution. The pH titration with NaOH resulted in a structure with the composition [Ce6(?3-O)4(?3-OH)4(HCOO)10(NO3)2(H2O)3]·(H2O)9.5, while the pH adjustment with NH3 resulted in [Ce6(?3-O)4(?3-OH)4(HCOO)10(NO3)4]·(NO3)3(NH4)5(H2O)5. Furthermore, the crystal structure of Ce(III) formate, Ce(HCOO)3, was determined. The coordination polyhedron is a tricapped trigonal prism which is formed exclusively by nine HCOO(-) ligands. The hexanuclear Ce(IV) formate species from aqueous solution is widely preserved in the crystal structure, whereas the mononuclear solution species of Ce(III) formate undergoes a polymerization during the crystallization process. PMID:24090406

Hennig, Christoph; Ikeda-Ohno, Atsushi; Kraus, Werner; Weiss, Stephan; Pattison, Philip; Emerich, Hermann; Abdala, Paula M; Scheinost, Andreas C

2013-10-21

320

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

PubMed Central

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

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

2014-01-01

321

Inclusion complex formation of ionic liquids with 4-sulfonatocalixarenes studied by competitive binding of berberine alkaloid fluorescent probe  

NASA Astrophysics Data System (ADS)

A clinically important natural isoquinoline alkaloid, berberine, was used as a fluorescent probe to study the encapsulation of 1-alkyl-3-methylimidazolium (C nMIm +) type ionic liquids in 4-sulfonato-substituted calix[4]arene (SCX4) and calix[6]arene (SCX6) at pH 2. Addition of ionic liquids to the aqueous solution of berberine-SCXn inclusion complexes brought about considerable fluorescence intensity diminution due to the extrusion of berberine from the macrocycle into the aqueous phase by the competitive inclusion of C nMIm + cation. The lengthening of the aliphatic side chain of the imidazolium moiety diminished the equilibrium constant of complexation with SCX4, but enhanced the stability of SCX6 complexes. Larger binding strength was found for SCX4.

Miskolczy, Zsombor; Biczók, László

2009-07-01

322

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

323

Dynamic microtubules catalyze formation of navigator-TRIO complexes to regulate neurite extension.  

PubMed

Neurite extension is regulated by multiple signaling cascades that ultimately converge on the actin and microtubule networks [1]. Rho GTPases, molecular switches that oscillate between an inactive, GDP-bound state and an active, GTP-bound state, play a pivotal role in controlling actin cytoskeleton dynamics in the growth cone, whereas the dynamic behavior and interactions of microtubules are largely regulated by proteins called plus-end-tracking proteins (+TIPs), which associate with the ends of growing microtubules. Here, we show that the +TIP Navigator 1 (NAV1) is important for neurite outgrowth and interacts and colocalizes with TRIO, a Rho guanine nucleotide exchange factor that enables neurite outgrowth by activating the Rho GTPases Rac1 and RhoG. We find that binding of NAV1 enhances the affinity of TRIO for Rac1 and RhoG, and that NAV1 regulates TRIO-mediated Rac1 activation and neurite outgrowth. TRIO is also a +TIP, as it interacts with the core +TIP EB1 and tracks microtubule plus ends via EB1 and NAV1. Strikingly, the EB1-mediated recruitment of TRIO to microtubule ends is required for proper neurite outgrowth, and stabilization of the microtubule network by paclitaxel affects both the TRIO-NAV1 interaction and the accumulation of these proteins in neurite extensions. We propose that EB1-labeled ends of dynamic microtubules facilitate the formation and localization of functional NAV1-TRIO complexes, which in turn regulate neurite outgrowth by selectively activating Rac1. Our data reveal a novel link between dynamic microtubules, actin cytoskeleton remodeling, and neurite extension. PMID:25065758

van Haren, Jeffrey; Boudeau, Jérôme; Schmidt, Susanne; Basu, Sreya; Liu, Zhe; Lammers, Dave; Demmers, Jeroen; Benhari, Jabran; Grosveld, Frank; Debant, Anne; Galjart, Niels

2014-08-01

324

Histone deacetylase inhibitors synergize p300 autoacetylation that regulates its transactivation activity and complex formation.  

PubMed

p300/cyclic AMP-responsive element binding protein-binding protein (CBP) are general coactivators for multiple transcription factors involved in various cellular processes. Several highly conserved domains of p300/CBP serve as interacting sites for transcription factors and regulatory proteins. Particularly, the intrinsic histone acetyltransferase (HAT) activity and transactivation domains (TAD) play essential roles for their coactivating function. Autoacetylation of p300/CBP is commonly observed in cell-free HAT assays and has been implicated in the regulation of their HAT activity. Here, we show that six lysine-rich regions in several highly conserved functional domains of p300 are targeted by p300HAT for acetylation in cell-free systems. We show that p300 is susceptible to acetylation in cultured tumor cells and that its acetylation status is affected by histone deacetylase inhibitor trichostatin A. We further show that either treatment with deacetylase inhibitors or coexpression of Gal4-p300HAT, which alone has no transactivation activity, stimulates the activity of the COOH-terminal TAD of p300 (p300C-TAD). We have defined the minimal p300C-TAD and show that it is sufficient to respond to deacetylase inhibitors and is a substrate for p300HAT. Finally, we show that acetylated p300 possesses enhanced ability to interact with p53. Taken together, our data suggest that acetylation regulates p300C-TAD and that acetylation of p300/CBP may contribute to the dynamic regulation of their complex formation with various interacting partners. PMID:17332356

Stiehl, Daniel P; Fath, Donna M; Liang, Dongming; Jiang, Yubao; Sang, Nianli

2007-03-01

325

Protection of Metal Artifacts with the Formation of Metal–Oxalates Complexes by Beauveria bassiana  

PubMed Central

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

2012-01-01

326

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

327

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

328

Loading antifungal drugs onto silica particles grafted with cyclodextrins by means of inclusion complex formation at the solid surface.  

PubMed

Immobilization of antifungal drugs to solid particles has been addressed in order to limit the skin penetration to the skin surface during topical administration. Antifungal drug griseofulvin has been immobilized at the surface of silica particles by formation of its inclusion complex with ?-cyclodextrins grafted to silica. A simple and fast process for loading griseofulvin into the hydrophobic cavity of cyclodextrins at the surface of the solid particles in aqueous suspension has been designed. It allowed the formation of the griseofulvin:cyclodextrin inclusion complex of 1:1 stoichiometry to completion. Grafting ?-cyclodextrins to silica surface has been performed in a two-step procedure. The coupling agent 3-amino-propylmethyldiethoxysilane was reacted onto fumed silica particles as a first step. The second step was the reaction of grafted primary amino groups with tosylated ?-cyclodextrin that led to ?-cyclodextrin grafted silica. Loading griseofulvin onto grafted silica particles have been investigated by IR spectroscopy and by tracking possible crystals of griseofulvin in aqueous suspension by optical and scanning electron microscopy and X-ray diffraction. Successful formation of the inclusion complex at the surface of grafted silica suggested a strong adsorption of griseofulvin by means of heterogeneous nucleation of crystals, followed by inclusion complexation taking place between the partners being in close proximity at the surface of silica particles. The high adsorption capacity of CD-grafted silica for griseofulvin compared to bare silica and amino-grafted silica supports this interpretation. PMID:23018113

Hbaieb, Souhaira; Kalfat, Rafik; Chevalier, Yves

2012-12-15

329

Brazilin selectively disrupts proximal IL-1 receptor signaling complex formation by targeting an IKK-upstream signaling components.  

PubMed

The ligation of interleukin-1 receptor (IL-1R) or tumor necrosis factor receptor 1 (TNFR1) induces the recruitment of adaptor proteins and their concomitant ubiquitination to the proximal receptor signaling complex, respectively. Such are upstream signaling events of IKK that play essential roles in NF-?B activation. Thus, the discovery of a substance that would modulate the recruitment of key proximal signaling elements at the upstream level of IKK has been impending in this field of study. Here, we propose that brazilin, an active compound of Caesalpinia sappan L. (Leguminosae), is a potent NF-?B inhibitor that selectively disrupts the formation of the upstream IL-1R signaling complex. Analysis of upstream signaling events revealed that brazilin markedly abolished the IL-1?-induced polyubiquitination of IRAK1 and its interaction with IKK-? counterpart. Notably, pretreatment of brazilin drastically interfered the recruitment of the receptor-proximal signaling components including IRAK1/4 and TRAF6 onto MyD88 in IL-1R-triggerd NF-?B activation. Interestingly, brazilin did not affect the TNF-induced RIP1 ubiquitination and the recruitment of RIP1 and TRAF2 to TNFR1, suggesting that brazilin is effective in selectively suppressing the proximal signaling complex formation of IL-1R, but not that of TNFR1. Moreover, our findings suggest that such a disruption of IL-1R-proximal complex formation by brazilin is not mediated by affecting the heterodimerization of IL-1R and IL-1RAcP. Taken together, the results suggest that the anti-IKK activity of brazilin is induced by targeting IKK upstream signaling components and subsequently disrupting proximal IL-1 receptor signaling complex formation. PMID:24735611

Jeon, Juhee; Lee, Ji Hoon; Park, Kyeong Ah; Byun, Hee Sun; Lee, Hyunji; Lee, Yoonjung; Zhang, Tiejun; Kang, Kidong; Seok, Jeong Ho; Kwon, Hyun-Jung; Han, Man-Deuk; Kang, Seong Wook; Hong, Jang Hee; Hur, Gang Min

2014-06-15

330

Adsorption of oppositely charged polyelectrolyte/surfactant complexes at the air/water interface: formation of interfacial gels.  

PubMed

The adsorption and complexation of polystyrene sulfonate (a highly charged anionic polyelectrolyte) and dodecyltrimethylammonium bromide (a cationic surfactant) at the air-water interface can lead to interfacial gels that strongly influence foam-film drainage and stability. The formation and characteristics of these gels have been studied by combining surface tension, ellipsometry, and foam-film drainage experiments. Simultaneously, the solution electromotive force is measured and used to track the polymer-surfactant interactions in the bulk solution. We find that surface gelation occurs above the critical aggregation concentration in solution but before bulk precipitation of the polymer-surfactant complexes. Furthermore, we reveal that strong readsorption of polymer-surfactant complexes occurs during the resolubilization of the precipitated complexes at high surfactant concentrations (i.e., >critical micelle concentration). Seemingly overlooked in the past, this readsorption significantly influences the surface rheological properties and foam-film drainage of these systems. PMID:15745000

Monteux, C; Williams, C E; Meunier, J; Anthony, O; Bergeron, V

2004-01-01

331

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

PubMed Central

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

2014-01-01

332

Electrostatic Interactions and Complex Formation of N-carboxyethylchitosan with Pectin  

NASA Astrophysics Data System (ADS)

Attractive, electrostatic interactions between oppositely charged polyelectrolytes have been used to prepare a novel complex between a polyampholyte - N-carboxyethylchitosan (CECh) and a natural polyanion - pectin. The complex CECh/pectin is formed in the pH range 2.4-6.0. The optimum stoichiometry of the complexes at different pH has been determined. All the complexes are non-stoichiometric and positively charged.

Marudova-Zsivanovits, M. G.; Yancheva, E. L.; Zsivanovits, G. I.; Rashkov, I. B.

2007-04-01

333

The Large Magellanic Cloud's Largest Molecular Cloud Complex: Spitzer Analysis of Embedded Star Formation  

NASA Astrophysics Data System (ADS)

We present a mid-infrared analysis of star-formation activity in the Large Magellanic Cloud's molecular ridge (south of 30 Doradus). The Magellanic Clouds are a rare laboratory in which extragalactic star-formation diagnostics can be tested at high spatial resolution. The southern part of the molecular ridge is particularly interesting as a potential extreme in the range of molecular cloud conditions, because of the apparent paucity (in optical tracers) of star formation compared to its gas mass. Our Spitzer observations are sensitive to protostars gsim3 M sun, and we estimate a total star-formation luminosity of 5 × 106 L sun in 2 × 106 M sun of molecular material. Detailed modeling of individual infrared-detected star-formation regions yields a total mass of star formation in the region consistent with that predicted by the gas surface density via the Schmitt-Kennicutt relation. The star-formation activity is distributed in rather low-luminosity regions, so the total star-formation rate determined by our infrared analysis is higher than would be predicted simply by the total H? and 24 ?m luminosities. Detailed analysis in very nearby galaxies, like the Magellanic Clouds, allows us to test and better understand the scaling relations used in unresolved and distant star-formation regions. Finally, we analyze the star-formation regions in the context of their individual molecular clouds and find that clouds with a higher ratio of CO mass to virial mass are more vigorously forming stars.

Indebetouw, R.; Whitney, B. A.; Kawamura, A.; Onishi, T.; Meixner, M.; Meade, M. R.; Babler, B. L.; Hora, J. L.; Gordon, K.; Engelbracht, C.; Block, M.; Misselt, K.

2008-10-01

334

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

PubMed Central

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

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

2013-01-01

335

Study of the dynamic complex formation of pentanoic acid with ?-cyclodextrin by using an ultrasonic relaxation method  

NASA Astrophysics Data System (ADS)

This study examined the effects of pentanoic acid as a guest molecule on the inclusion complex formation with ?-cyclodextrin ( ?-CD). Ultrasonic absorption measurements were carried out for ?-CD solutions with pentanoic acid over the frequency range from 0.2 to 45 MHz. A single relaxational absorption resulting from the perturbation of chemical equilibrium was observed for the inclusion of pentanoic acid into the ?-CD cavity. The undissociated form of pentanoic acid produced a more stable complex with ?-CD than its dissociated form. An ultrasonic relaxation associated with a protontransfer reaction was also observed when no additive was present in the solution.

Bae, Jong-Rim

2013-07-01

336

TPR domain of NrfG mediates complex formation between heme lyase and formate-dependent nitrite reductase in Escherichia coli O157:H7.  

PubMed

Escherichia coli synthesize C-type cytochromes only during anaerobic growth in media supplemented with nitrate and nitrite. The reduction of nitrate to ammonium in the periplasm of Escherichia coli involves two separate periplasmic enzymes, nitrate reductase and nitrite reductase. The nitrite reductase involved, NrfA, contains cytochrome C and is synthesized coordinately with a membrane-associated cytochrome C, NrfB, during growth in the presence of nitrite or in limiting nitrate concentrations. The genes NrfE, NrfF, and NrfG are required for the formate-dependent nitrite reduction pathway, which involves at least two C-type cytochrome proteins, NrfA and NrfB. The NrfE, NrfF, and NrfG genes (heme lyase complex) are involved in the maturation of a special C-type cytochrome, apocytochrome C (apoNrfA), to cytochrome C (NrfA) by transferring a heme to the unusual heme binding motif of the Cys-Trp-Ser-Cys-Lys sequence in apoNrfA protein. Thus, in order to further investigate the roles of NrfG in the formation of heme lyase complex (NrfEFG) and in the interaction between heme lyase complex and formate-dependent nitrite reductase (NrfA), we determined the crystal structure of NrfG at 2.05 A. The structure of NrfG showed that the contact between heme lyase complex (NrfEFG) and NrfA is accomplished via a TPR domain in NrfG which serves as a binding site for the C-terminal motif of NrfA. The portion of NrfA that binds to TPR domain of NrfG has a unique secondary motif, a helix followed by about a six-residue C-terminal loop (the so called "hook conformation"). This study allows us to better understand the mechanism of special C-type cytochrome assembly during the maturation of formate-dependent nitrite reductase, and also adds a new TPR binding conformation to the list of TPR-mediated protein-protein interactions. PMID:17803240

Han, Dohyun; Kim, Kyunggon; Oh, Jongkil; Park, Jungeun; Kim, Youngsoo

2008-02-15

337

Superoxide dismutase and Fenton chemistry. Reaction of ferric-EDTA complex and ferric-bipyridyl complex with hydrogen peroxide without the apparent formation of iron(II).  

PubMed

A ferric-EDTA complex, prepared directly from FeCl3 or from an oxidized ferrous salt, reacts with H2O2 to form hydroxyl radicals (.OH), which degrade deoxyribose and benzoate with the release of thiobarbituric acid-reactive material, hydroxylate benzoate to form fluorescent dihydroxy products and react with 5,5-dimethylpyrrolidine N-oxide (DMPO) to form a DMPO-OH adduct. Degradation of deoxyribose and benzoate and the hydroxylation of benzoate are substantially inhibited by superoxide dismutase and .OH-radical scavengers such as formate, thiourea and mannitol. Inhibition by the enzyme superoxide dismutase implies that the reduction of the ferric-EDTA complex for participation in the Fenton reaction is superoxide-(O2.-)-dependent, and not H2O2-dependent as frequently implied. When ferric-bipyridyl complex at a molar ratio of 1:4 is substituted for ferric-EDTA complex (molar ratio 1:1) and the same experiments are conducted, oxidant damage is low and deoxyribose and benzoate degradation were poorly if at all inhibited by superoxide dismutase and .OH-radical scavengers. Benzoate hydroxylation, although weak, was, however, more effectively inhibited by superoxide dismutase and .OH-radical scavengers, implicating some role for .OH. The iron-bipyridyl complex had available iron-binding capacity and therefore would not allow iron to remain bound to buffer or detector molecules. Most .OH radicals produced by the iron-bipyridyl complex and H2O2 are likely to damage the bipyridyl molecules first, with few reacting in free solution with the detector molecules. Deoxyribose and benzoate degradation appeared to be mediated by an oxidant species not typical of .OH, and species such as the ferryl ion-bipyridyl complex may have contributed to the damage observed. PMID:2165392

Gutteridge, J M; Maidt, L; Poyer, L

1990-07-01

338

Metal-assisted oxazolidine/oxazine ring formation in dinuclear zinc(II) complexes: synthesis, structural aspects, and bioactivity.  

PubMed

Three novel dinuclear Zn(II) complexes of phenol-based compartmental macrocyclic ligands have been synthesized and characterized by routine physicochemical techniques as well as by X-ray single-crystal structure analysis. The dinuclear macrocyclic complexes 1, 2, and 3 were obtained through a 1:2 condensation reaction of 2,6-diformyl-4-methylphenol and N-(hydroxyalkyl) ethylenediamine (L(1), L(2), and L(3), respectively) in the presence of zinc(II) acetate, followed by the addition of thiocyanate anion [L(1) = N-(2-hydroxyethyl)ethylenediamine, L(2) = N-(3-hydroxypropyl)ethylenediamine, and L(3) = N-(2-hydroxypropyl)ethylenediamine]. The synthesized 18-membered macrocycles are noted to be structurally unique, and their formation proceeds with the generation of two oxazolidine side rings in complexes 1 and 3 and two oxazine side rings in 2, along with the creation of four new chiral centers in each case. Complexes 1 and 2 are characterized by a butterfly-like arrangement with the SCN ligands situated on the same side with respect to the Zn(2)O(2) moiety, whereas the centrosymmetric complex 3 exhibits a stepped arrangement with parallel methyl-phenoxy fragments (spaced at ca. 1.5 A) and trans located SCN ligands with respect to the Zn(2)O(2) core. The formation of these unusual macrocycles is considered to be zinc-mediated. Preliminary studies with the complexes show that all of them exhibit an inhibitory effect, on the cell proliferation of human stomach cancer cell line AGS, though with different degrees, where complex 3 shows the highest efficiency. PMID:19708676

Banerjee, Arpita; Ganguly, Subhalakshmi; Chattopadhyay, Tanmay; Banu, Kazi Sabnam; Patra, Amarendra; Bhattacharya, Santanu; Zangrando, Ennio; Das, Debasis

2009-09-21

339

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

Microsoft Academic Search

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

Da-Guang Yu

2007-01-01

340

Complex Formation by the Human Rad51B and Rad51C DNA Repair Proteins and Their Activities in Vitro*  

E-print Network

Complex Formation by the Human Rad51B and Rad51C DNA Repair Proteins and Their Activities in Vitro. In addition to Rad51 pro- tein, five paralogs have been identified: Rad51B/ Rad51L1, Rad51C/Rad51L2, Rad51D-(His)6, and Rad51C proteins were individually expressed employ- ing the baculovirus system, and each

Kowalczykowski, Stephen C.

341

Crossover\\/Noncrossover Differentiation, Synaptonemal Complex Formation, and Regulatory Surveillance at the Leptotene\\/Zygotene Transition of Meiosis  

Microsoft Academic Search

Yeast mutants lacking meiotic proteins Zip1, Zip2, Zip3, Mer3, and\\/or Msh5 (ZMMs) were analyzed for recombination, synaptonemal complex (SC), and meiotic progression. At 33°C, recombination-initiating double-strand breaks (DSBs) and noncrossover products (NCRs) form normally while formation of single-end invasion strand exchange intermediates (SEIs), double Holliday junctions, crossover products (CRs), and SC are coordinately defective. Thus, during wild-type meiosis, recombinational interactions

G. Valentin Börner; Nancy Kleckner; Neil Hunter

2004-01-01

342

Evidence for partial quenching of orbital angular momentum upon complex formation in the infrared spectrum of OH-acetylene.  

PubMed

The entrance channel leading to the addition reaction between the hydroxyl radical and acetylene has been examined by spectroscopic characterization of the asymmetric CH stretching band of the pi-hydrogen bonded OH-acetylene reactant complex. The infrared action spectrum observed at 3278.6 cm(-1) (origin) consists of seven peaks of various intensities and widths, and is very different from those previously reported for closed-shell HF/HCl-acetylene complexes. The unusual spectrum arises from a partial quenching of the OH orbital angular momentum in the complex, which in turn is caused by a significant splitting of the OH monomer orbital degeneracy into (2)A(') and (2)A(") electronic states. The magnitude of the (2)A(')-(2)A(") splitting as well as the A rotational constant for the OH-acetylene complex are determined from the analysis of this b-type infrared band. The most populated OH product rotational state, j(OH)=9/2, is consistent with intramolecular vibrational energy transfer to the nu2 C triple bonded C stretching mode of the departing acetylene fragment. The lifting of the OH orbital degeneracy and partial quenching of its electronic orbital angular momentum indicate that the electronic changes accompanying the evolution of reactants into products have begun to occur in the reactant complex. PMID:15367011

Marshall, Mark D; Davey, James B; Greenslade, Margaret E; Lester, Marsha I

2004-09-22

343

Evidence for partial quenching of orbital angular momentum upon complex formation in the infrared spectrum of OH-acetylene  

NASA Astrophysics Data System (ADS)

The entrance channel leading to the addition reaction between the hydroxyl radical and acetylene has been examined by spectroscopic characterization of the asymmetric CH stretching band of the ?-hydrogen bonded OH-acetylene reactant complex. The infrared action spectrum observed at 3278.6 cm-1 (origin) consists of seven peaks of various intensities and widths, and is very different from those previously reported for closed-shell HF/HCl-acetylene complexes. The unusual spectrum arises from a partial quenching of the OH orbital angular momentum in the complex, which in turn is caused by a significant splitting of the OH monomer orbital degeneracy into 2A' and 2A? electronic states. The magnitude of the 2A'-2A? splitting as well as the A rotational constant for the OH-acetylene complex are determined from the analysis of this b-type infrared band. The most populated OH product rotational state, jOH=9/2, is consistent with intramolecular vibrational energy transfer to the ?2 C?C stretching mode of the departing acetylene fragment. The lifting of the OH orbital degeneracy and partial quenching of its electronic orbital angular momentum indicate that the electronic changes accompanying the evolution of reactants into products have begun to occur in the reactant complex.

Marshall, Mark D.; Davey, James B.; Greenslade, Margaret E.; Lester, Marsha I.

2004-09-01

344

Formation of Complex Organics by Gas Phase and Intracluster Ion-Molecule Reactions Involving Acetylene and Hydrogen Cyanide  

NASA Astrophysics Data System (ADS)

Many complex organics including polycyclic aromatic hydrocarbons are present in flames and combustion processes as well as in interstellar clouds and solar nebulae. Here, we present evidence for the formation of complex covalent organics by gas phase and intracluster reactions of the benzene, phenylium, pyridine, pyrimidine, phenylacetylene and benzonitrile cations with acetylene and hydrogen cyanide molecules. These reactions are studied using mass-selected ion mobility, chemical reactivity, collisional dissociation, and ab initio calculations. Measurements of collision cross sections in helium provide structural information on the adducts and allow probing structural changes at different temperatures (isomerization). We observed multiple additions of five acetylene molecules on the pyridine cation at room temperature. This is a remarkable result considering that only two acetylene molecules were added to the phenyl cation and no addition was observed on the benzene cation at room temperature. The experimental results are in full agreement with the ab initio calculations which predict that the first and second acetylenes add to the pyridine ion in barrierless, highly exothermic reactions. Similar reactions have been observed for the pyrimidine radical cation although the extent of the addition reactions is limited to only two acetylene molecules at room temperature. The results provide the first evidence for the incorporation of nitrogen in the formation cyclic hydrocarbons via the gas phase reactions of pyridine and pyrimidine ions with acetylene molecules. In addition, the formation of covalent adducts in the ionized acetylene/HCN system will be reported for the first time. Sequential reactions leading to the formation of pyridine and pyrimidine radical cations and higher adducts are observed over a wide range of temperature and pressure. The formation of these covalent adducts may represent a general class of addition reactions that can form complex heterocyclic species in ionizing environments.

El-Shall, S.; Hamed, A.; Soliman, A. R.; Momoh, P. O.

2011-05-01

345

Complexities of Identity Formation: A Narrative Inquiry of an EFL Teacher  

ERIC Educational Resources Information Center

This article explores teachers' identity formation through a narrative inquiry of the professional identity of an EFL teacher, Minfang, in the People's Republic of China. Drawing on Wenger's (1998) social theory of identity formation as a dual process of identification and negotiation of meanings, it examines the lived experience of Minfang as an…

Tsui, Amy B. M.

2007-01-01

346

Complexity, Critical Mass and Industry Formation: A Comparison of Selected Industries  

Microsoft Academic Search

This paper uses a typology of industries to summarize and contrast the challenges involved with industry formation and to examine why specific industries were formed in some countries before other ones. The formation of most new industries depends on the introduction of products that provide a superior “value proposition” to some set of users where their introduction requires new R&D-related

Jeffrey L. Funk

2010-01-01

347

Complex Formation of Myrosinase Isoenzymes in Oilseed Rape Seeds Are Dependent on the Presence of Myrosinase-Binding Proteins1  

PubMed Central

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

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

2002-01-01

348

Imine-functionalised protic NHC complexes of Ir: direct formation by C-H activation.  

PubMed

N-Arylimine-functionalised protic NHC (pNHC) Ir(i) and Ir(iii) complexes are obtained directly from neutral or cationic Ir(i) imidazole complexes using excess [Ir(cod)(?-Cl)]2 or TlPF6, respectively. N-Arylimine-functionalised imidazolium salts lead to imidazole or pNHC complexes by competing N-H or C-H bond activation depending on the type of imidazolium counterion. PMID:25586232

He, Fan; Braunstein, Pierre; Wesolek, Marcel; Danopoulos, Andreas A

2015-02-01

349

[Mechanism of the formation of complexes between monomer fibrin and the inhibitor of its polymerization - fragment D].  

PubMed

It was found that fragment D derived from fibrinogen may be coupled with the fibrin monomer to produce complexes of unstable and stable types. The native fibrin monomer forms unstable complexes; the stable ones arise when the labile peripheral domains of the fibrin molecules are reversibly modified and their specific intermolecular affinity for the thrombin-activated central domains is lowered or eliminated. Fragment D, the free peripheral domain possessing polymerization centers, is strongly bound to the modified monomer occupying the polymerization sites of its central domain. The modification was induced by using acid pH (around 3.7) or by urea or NaBr taken at concentrations which caused no denaturation. In neutral media the acid-modified monomer passes to its normal state which is accompanied by simultaneous decrease of fragment D binding and restoration of codgulability. Fragment D presumably competes with the peripheral domain for the central one. Peripheral domains of the intact monomer are predominant competitors; fragment D only reduces the rate of polymerization due to temporary complex formation. However, modification results in a formation of stable complexes and thus decreases the accumulation of polymeric fibrin. PMID:6830911

Belitser, V A; Pozdniakova, T M; Vovk, E V; Rybachuk, V N

1983-01-01

350

Uncoupling of XB/U-cadherin-catenin complex formation from its function in cell-cell adhesion.  

PubMed

Xenopus XB/U-cadherin forms functional complexes with mouse alpha- and beta-catenins and p120(cas) when expressed in murine L-TK- fibroblasts. These cells were stably transfected with cDNAs encoding different cytoplasmic XB/U-cadherin mutants, each partially deleted in the different parts of the 38 most carboxyl-terminal amino acids. The binding of p120(cas) was not affected by carboxyl-terminal deletions, confirming its binding to a region more amino-terminal and distinct from the catenins. alpha- and beta-catenins associate with truncated XB/U-cadherins if either 19 amino acid half of the cadherin 38 amino acid tail is present, indicating that the site of catenin interaction is upstream of the deletions. However, for adhesive function of XB/U-cadherin constructs, the most carboxyl-terminal 19 amino acids are essential; if these amino acids are deleted, cadherin-catenin complexes unable to mediate cell-cell adhesion are formed. Nonadhesive complexes are solubilized by mild detergent, whereas functional complexes are stable. Provided that detergent stability of cadherin-catenin complexes is taken as a measure of their cytoskeletal association, our results give first evidence that cytoskeletal stabilization occurs independent of cadherin-catenin complex formation and requires the 19-amino acid cadherin carboxyl terminus. PMID:9115244

Finnemann, S; Mitrik, I; Hess, M; Otto, G; Wedlich, D

1997-05-01

351

Reaction of aromatic diazonium salts with carrier-free radioiodine and astatine, evidence for complex formation  

Microsoft Academic Search

Systematic studies of the astatodiazoniation reaction and a comparison with iododediazoniation under comparable conditions are reported. The yields for all astatohalobenzenes and -toluenes were nearly constant and unaffected by the nature of the diazonium compound, its isomeric form, and the number of isomers used at the same time. Only astatofluorobenzenes were obtained at higher yields. An electron-transfer mechanism is proposed

G. J. Meyer; K. Roessler; G. Stoecklin

1979-01-01

352

Distortion of ethyne on formation of a ? complex with silver chloride: C2H2⋯Ag-Cl characterised by rotational spectroscopy and ab initio calculations  

NASA Astrophysics Data System (ADS)

C2H2⋯Ag-Cl was formed from ethyne and AgCl in the gas phase and its rotational spectrum observed by both the chirped-pulse and Fabry-Perot cavity versions of Fourier-transform microwave spectroscopy. Reaction of laser-ablated silver metal with CCl4 gave AgCl which then reacted with ethyne to give the complex. Ground-state rotational spectra of the six isotopologues 12C2H2⋯107Ag35Cl, 12C2H2⋯109Ag35Cl, 12C2H2⋯107Ag37Cl, 12C2H2⋯109Ag37Cl, 13C2H2⋯107Ag35Cl, and 13C2H2⋯109Ag35Cl were analysed to yield rotational constants A0, B0, and C0, centrifugal distortion constants ?J, ?JK, and ?J, and Cl nuclear quadrupole coupling constants ?aa(Cl) and ?bb(Cl) -?cc(Cl). A less complete analysis was possible for 12C2D2⋯107Ag35Cl and 12C2D2⋯109Ag35Cl. Observed principal moments of inertia were interpreted in terms of a planar, T-shaped geometry of C2v symmetry in which the AgCl molecule lies along a C2 axis of ethyne and the Ag atom forms a bond to the midpoint (*) of the ethyne ? bond. r0 and r_m^{(1)} geometries and an almost complete rs-geometry were established. The ethyne molecule distorts on complex formation by lengthening of the C?C bond and movement of the two H atoms away from the C?C internuclear line and the Ag atom. The r_m^{(1)} bond lengths and angles are as follows: r(*⋯Ag) = 2.1800(3) Å, r(C-C) = 1.2220(20) Å, r(Ag-Cl) = 2.2658(3) Å and the angle H-C?* has the value 187.79(1)°. Ab initio calculations at the coupled-cluster singles and doubles level of theory with a perturbative treatment of triples (F12*)/cc-pVTZ yield a re geometry in excellent agreement with the experimental r_m^{(1)} version, including the ethyne angular distortion.

Stephens, Susanna L.; Mizukami, Wataru; Tew, David P.; Walker, Nicholas R.; Legon, Anthony C.

2012-11-01

353

Structural and Functional Analysis of Nup120 Suggests Ring Formation of the Nup84 Complex  

SciTech Connect

The Nup84 complex constitutes a key building block in the nuclear pore complex (NPC). Here we present the crystal structure of one of its 7 components, Nup120, which reveals a ? propeller and an ?-helical domain representing a novel fold. We discovered a previously unidentified interaction of Nup120 with Nup133 and confirmed the physiological relevance in vivo. As mapping of the individual components in the Nup84 complex places Nup120 and Nup133 at opposite ends of the heptamer, our findings indicate a head-to-tail arrangement of elongated Nup84 complexes into a ring structure, consistent with a fence-like coat for the nuclear pore membrane. The attachment site for Nup133 lies at the very end of an extended unstructured region, which allows for flexibility in the diameter of the Nup84 complex ring. These results illuminate important roles of terminal unstructured segments in nucleoporins for the architecture, function, and assembly of the NPC.

Seo, H.; Ma, Y; Debler, E; Wacker, D; Kutik, S; Blobel, G; Hoelz, A

2009-01-01

354

The effect of pH values on the phase formation and properties of BaFe 12O 19 prepared by citrate–EDTA complexing method  

Microsoft Academic Search

Barium hexaferrites (BaFe12O19) have been prepared by citrate–EDTA complexing method using citrate and EDTA as complexing chelating agents with various pH values. Complexation stability constant analysis, XRD patterns and SEM investigations all display that the chelation between metallic ions and ligand may reach an excellent degree in the condition of pH 6. The precursor with more uniformly distributed Fe3+ and

Lixi Wang; Qitu Zhang

2008-01-01

355

Constant dimensions  

NSDL National Science Digital Library

This complete lesson plan requires students to measure the length and width of a rectangle using both standard and non-standard units of measure, such as pennies, beads, etc. As students graph the ordered pairs, they discover that the ratio of length to width of a rectangle is constant, in spite of the units. This leads to the definition of a linear function and to the rule that relates the dimensions of this rectangle. An activity sheet and questions for class discussion are included.

Kristen Chandler

2000-01-01

356

Oxo-group-14-element bond formation in binuclear uranium(V) Pacman complexes.  

PubMed

Simple and versatile routes to the functionalization of uranyl-derived U(V)-oxo groups are presented. The oxo-lithiated, binuclear uranium(V)-oxo complexes [{(py)3LiOUO}2(L)] and [{(py)3LiOUO}(OUOSiMe3)(L)] were prepared by the direct combination of the uranyl(VI) silylamide "ate" complex [Li(py)2][(OUO)(N")3] (N" = N(SiMe3)2) with the polypyrrolic macrocycle H4L or the mononuclear uranyl (VI) Pacman complex [UO2(py)(H2L)], respectively. These oxo-metalated complexes display distinct U-O single and multiple bonding patterns and an axial/equatorial arrangement of oxo ligands. Their ready availability allows the direct functionalization of the uranyl oxo group leading to the binuclear uranium(V) oxo-stannylated complexes [{(R3Sn)OUO}2(L)] (R = nBu, Ph), which represent rare examples of mixed uranium/tin complexes. Also, uranium-oxo-group exchange occurred in reactions with [TiCl(OiPr)3] to form U-O-C bonds [{(py)3LiOUO}(OUOiPr)(L)] and [(iPrOUO)2(L)]. Overall, these represent the first family of uranium(V) complexes that are oxo-functionalised by Group 14 elements. PMID:23794441

Jones, Guy M; Arnold, Polly L; Love, Jason B

2013-07-29

357

Shatter Complex Formation in the Twin Craters Lava Flow, Zuni-Bandera Field, New Mexico  

NASA Astrophysics Data System (ADS)

Lava channels, tubes and sheets are transport structures that deliver flowing lava to a flow front. The type of structure can vary within a flow field and evolve throughout an eruption. The 18.0 × 1.0 ka Twin Craters lava flow in the Zuni-Bandera lava field provides a unique opportunity to study morphological changes of a lava flow partly attributable to interaction with a topographic obstacle. Facies mapping and airborne image analysis were performed on an area of the Twin Craters flow that includes a network of channels, lava tubes, shatter features, and disrupted pahoehoe flows surrounding a 45 m tall limestone bluff. The bluff is 1000 m long (oriented perpendicular to flow.) The general flow characteristics upstream from the bluff include smooth, lobate pahoehoe flows and a >2.5 km long lava tube (see Samuels et al., this meeting.) Emplacement characteristics change abruptly where the flow encountered the bluff, to include many localized areas of disrupted pahoehoe and several pahoehoe-floored depressions. Each depression is fully or partly surrounded by a raised rim of blocky material up to 4 m higher than the surrounding terrain. The rim is composed of 0.05 - 4 m diameter blocks, some of which form a breccia that is welded by lava, and some of which exhibit original flow textures. The rim-depression features are interpreted as shatter rings based on morphological similarity to those described by Orr (2011.Bul Volcanol.73.335-346) in Hawai';i. Orr suggests that shatter rings develop when fluctuations in the lava supply rate over-pressurize the tube, causing the tube roof to repeatedly uplift and subside. A rim of shattered blocks and breccias remains surrounding the sunken tube roof after the final lava withdraws from the system. One of these depressions in the Twin Craters flow is 240 m wide and includes six mounds of shattered material equal in height to the surrounding undisturbed terrain. Several mounds have depressed centers floored with rubbly pahoehoe. Prominent ';a';a channels travel around the bluff, leaving a 'wake' of uncovered ground on the downstream side. We interpret this shatter area to have been a branching tube network within an active sheet. The limestone bluff acted as an obstacle that caused a backup of lava within the tubes, driving episodes of shattering. The mounds likely represent earlier solidified sections between active, possibly braided, tube branches, which remained as mounds within the shatter area after the adjacent crust subsided. When lava broke out from the pressurized sheet-like lobe, it formed the ';a';a channels. This section of the flow field is interpreted using inferences from shatter ring formation, but is perhaps better termed a shatter sheet or shatter complex. This study has implications for understanding lava flow dynamics at constriction points, as well as the evolution and morphology of shatter rings.

von Meerscheidt, H. C.; Bleacher, J. E.; Brand, B. D.; deWet, A.; Samuels, R.; Hamilton, C.; Garry, W. B.; Bandfield, J. L.

2013-12-01

358

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

359

[UV-spectroscopic study of complex formation between nonactin and picrates of monovalent cations].  

PubMed

A macrotetrolide preparation including nonactin (about 75 per cent), monactin (about 23 pr cent) and traces of dinactin and trinactin was analyzed with the method of UV spectroscopy. It was shown to form hydrophobic complexes in organic solvents with picrates of univalent cations of ammonium, potassium and sodium. The complex strength depended not only on the cation nature, but also on the solvent and pH of the picrate aqueous solutions. The comparison of methylene chloride used for tetrananactin with chloroform demonstrated that nonactin formed stable complexes in chloroform at neutral pH of the aqueous phase, a solution of picric acid and ammonium chloride. PMID:7654094

Sverdlova, A N; Solov'eva, I V; Nefelova, M V

1995-04-01

360

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

E-print Network

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

Akana, Jennifer Anne

2007-01-01

361

Ikaros DNA-Binding Proteins Direct Formation of Chromatin Remodeling Complexes in Lymphocytes  

Microsoft Academic Search

The Ikaros gene family encodes zinc finger DNA-binding proteins essential for lineage determination and control of proliferation in the lymphoid system. Here, we report that, in the nucleus of a T cell, a major fraction of Ikaros and Aiolos proteins associate with the DNA-dependent ATPase Mi-2 and histone deacetylases, in a 2 MD complex. This Ikaros–NURD complex is active in

John Kim; Saïd Sif; Beverly Jones; Audrey Jackson; Joseph Koipally; Elizabeth Heller; Susan Winandy; Alain Viel; Alan Sawyer; Toru Ikeda; Robert Kingston; Katia Georgopoulos

1999-01-01

362

Studies of complex formation between the bromophenol blue and some important aminoquinoline antimalarials  

Microsoft Academic Search

A simple and rapid colorimetric method for the assay of amodiaquine hydrochloride, chloroquine phosphate and primaquine phosphate\\u000a is described. The method is based on the interaction of the drug base with bromophenol blue to give a stable ion-pair complex.\\u000a The spectra of the complex shows a maxima at 415–420 nm with high apparent molar absorptivities. Beer's law was obeyed in

Saadia Mohamed El-Ashry; Fatma Ahmed Aly; Amina Mohamed El-Brashy

1994-01-01

363

Formation of bioinorganic complexes by the corrosive adsorption of (s)-proline on ni/au(111).  

PubMed

Nickel nanoparticles modified by the adsorption of chiral amino acids are known to be effective enantioselective heterogeneous catalysts. The leaching of nickel by amino acids has a number of potential effects including the induction of chirality in the nickel atoms left behind in the nanoparticle and the creation of catalytically active nickel complexes. The adsorption of (S)-proline onto Au(111) precovered by two-dimensional nickel nanoclusters was investigated by scanning tunneling microscopy, X-ray photoelectron spectroscopy, and high-resolution electron energy loss spectroscopy. Adsorption of (S)-proline at 300 K resulted in the corrosion of the nickel clusters, the oxidation of the leached nickel, and the on-surface formation of bioinorganic complexes, which are concluded to contain three prolinate species in an octahedral arrangement around the central Ni ion. Two distinguishable forms of nickel prolinate complexes were identified. One form self-assembles into 1-D chains, and the other form gives rise to porous 2-D islands. Octahedral complexes of the type M(AB)3 are intrinsically chiral, resulting in two pairs of enantiomers. The mirror symmetry of each pair of enantiomers is broken when, as in this study, the bidentate ligand itself possesses a chiral center. DFT calculations are used to examine the relative energies of each Ni(prolinate)3 complex as isolated gas phase species and isolated adsorbed species. PMID:25495197

Seljamäe-Green, Riho T; Simpson, Grant J; Grillo, Federico; Greenwood, John; Francis, Stephen M; Schaub, Renald; Gano, Jerome E; Früchtl, Herbert A; Lacovig, Paolo; Baddeley, Christopher J

2015-01-13

364

Photocatalytic CO2 reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes.  

PubMed

Previously undescribed supramolecules constructed with various ratios of two kinds of Ru(II) complexes-a photosensitizer and a catalyst-were synthesized. These complexes can photocatalyze the reduction of CO(2) to formic acid with high selectivity and durability using a wide range of wavelengths of visible light and NADH model compounds as electron donors in a mixed solution of dimethylformamide-triethanolamine. Using a higher ratio of the photosensitizer unit to the catalyst unit led to a higher yield of formic acid. In particular, of the reported photocatalysts, a trinuclear complex with two photosensitizer units and one catalyst unit photocatalyzed CO(2) reduction (?(HCOOH) = 0.061, TON(HCOOH) = 671) with the fastest reaction rate (TOF(HCOOH) = 11.6 min(-1)). On the other hand, photocatalyses of a mixed system containing two kinds of model mononuclear Ru(II) complexes, and supramolecules with a higher ratio of the catalyst unit were much less efficient, and black oligomers and polymers were produced from the Ru complexes during photocatalytic reactions, which reduced the yield of formic acid. The photocatalytic formation of formic acid using the supramolecules described herein proceeds via two sequential processes: the photochemical reduction of the photosensitizer unit by NADH model compounds and intramolecular electron transfer to the catalyst unit. PMID:22908243

Tamaki, Yusuke; Morimoto, Tatsuki; Koike, Kazuhide; Ishitani, Osamu

2012-09-25

365

Direct observation of R-loop formation by single RNA-guided Cas9 and Cascade effector complexes  

PubMed Central

Clustered, regularly interspaced, short palindromic repeats (CRISPR)/CRISPR-associated (Cas) systems protect bacteria and archaea from infection by viruses and plasmids. Central to this defense is a ribonucleoprotein complex that produces RNA-guided cleavage of foreign nucleic acids. In DNA-targeting CRISPR-Cas systems, the RNA component of the complex encodes target recognition by forming a site-specific hybrid (R-loop) with its complement (protospacer) on an invading DNA while displacing the noncomplementary strand. Subsequently, the R-loop structure triggers DNA degradation. Although these reactions have been reconstituted, the exact mechanism of R-loop formation has not been fully resolved. Here, we use single-molecule DNA supercoiling to directly observe and quantify the dynamics of torque-dependent R-loop formation and dissociation for both Cascade- and Cas9-based CRISPR-Cas systems. We find that the protospacer adjacent motif (PAM) affects primarily the R-loop association rates, whereas protospacer elements distal to the PAM affect primarily R-loop stability. Furthermore, Cascade has higher torque stability than Cas9 by using a conformational locking step. Our data provide direct evidence for directional R-loop formation, starting from PAM recognition and expanding toward the distal protospacer end. Moreover, we introduce DNA supercoiling as a quantitative tool to explore the sequence requirements and promiscuities of orthogonal CRISPR-Cas systems in rapidly emerging gene-targeting applications. PMID:24912165

Szczelkun, Mark D.; Tikhomirova, Maria S.; Sinkunas, Tomas; Gasiunas, Giedrius; Karvelis, Tautvydas; Pschera, Patrizia; Siksnys, Virginijus; Seidel, Ralf

2014-01-01

366

Evaluation of bone formation guided by DNA/protamine complex with FGF-2 in an adult rat calvarial defect model.  

PubMed

DNA/protamine complex paste (D/P) and D/P complex paste with Fibroblast Growth Factor-2 (FGF-2) (D/P-FGF) were prepared to investigate their new bone formation abilities using an ?40-week-old rat calvarial defect model. It was found that D/P could release FGF-2 proportionally in an in vitro experiment with an enzyme-linked immunosorbent assay. It was also found that aging adversely affected self-bone healing of rats by comparison with the results in a previous study using 10-week-old rats. Microcomputed tomography and histopathological examinations showed that new bone formation abilities of D/P and D/P-FGF were superior to that of the control (sham operation). Control, D/P and D/P-FGF showed newly formed bone areas of 6.7, 58.3, and 67.0%, respectively, 3 months after the operation. Moreover, it was found that FGF-2 could support the osteoanagenesis ability of D/P. It was considered that FGF-2 could play an important role in new bone formation at early stages because it induced the genes such as collagen I, CBFA, OSX, and OPN, which are initiated first in the process of osteogenesis. Therefore, D/P-FGF will be a useful injectable biomaterial with biodegradable properties for the repair of bone defects in the elderly. PMID:24664968

Shinozaki, Yosuke; Toda, Masako; Ohno, Jun; Kawaguchi, Minoru; Kido, Hirofumi; Fukushima, Tadao

2014-11-01

367

Light-scattering study of polyelectrolyte complex formation between anionic and cationic nanogels in an aqueous salt-free system.  

PubMed

We studied complex formation in an aqueous salt-free system (pH approximately 3 and at 25 degrees C) between nanogel particles having opposite charges. Anionic gel (AG) and cationic gel (CG) particles consist of lightly cross-linked N-isopropylacrylamide (NIPA) copolymers with 2-acrylamido-2-methylpropane sulfonic acid and with 1-vinylimidazole, respectively. The number of charges per particle was -4490 for AG and +20 300 for CG, as estimated from their molar masses (3.33 MD for AG and 11.7 MD for CG) by static light scattering (SLS) and their charge densities (1.35 mmol/g for AG and 1.74 mmol/g for CG) by potentiometric titration. The complexes were formed through the addition of AG to CG and vice versa using a turbidimetric titration technique. At the endpoint of the titration, the aggregate formed was a complex based upon stoichiometric charge neutralization: CG(n)()(+) + xAG(m)()(-) --> CG(n)()(+) (AG(m)()(-))(x)() where x = (n)()/(m)(). At different stages of the titration before the endpoint, the resulting complexes were examined in detail using dynamic light scattering, SLS, and electrophoretic light scattering (ELS). The main results are summarized as follows: (i) When AG with a hydrodynamic radius (R(h)) of 119 nm is added to CG (R(h) approximately 156 nm), the (R(h)) of the complex size decreases from 156 to 80 nm. (ii) In contrast to this (R(h)) change, the molar mass increases from 11.7 MD to 24 MD with increasing amounts of added AG. (iii) Upon addition of CG to AG, the complex formed has the same size ((R(h)) approximately 80 nm) and the same molar mass (55 +/- 2.5 MD) until 55 +/- 5% of AG has been consumed in the complexation. To understand these results, we used the following two models: the random model (RM), in which the added AG particles uniformly bind to all of the CG particles in the system via a strong electrostatic attraction, and the all-or-none model (AONM), in which part of the AG particles in the system preferably bind to the added CG particles to neutralize their electric charges but the other AG particles are uncomplexed and remain in the system. The complex formations upon addition of AG to CG and CG to AG were elucidated in terms of RM and AONM, respectively. PMID:16893235

Miyake, Masafumi; Ogawa, Kazuyoshi; Kokufuta, Etsuo

2006-08-15

368

Formation and Thermodynamics of Mg-Al-Ti-O Complex Inclusions in Mg-Al-Ti-Deoxidized Steel  

NASA Astrophysics Data System (ADS)

The formation of Mg-Al-Ti-O complex inclusions in steel was investigated by laboratory experiments and thermodynamic calculation. The composition evolutions of Mg-Al-Ti-O inclusions in steel with different contents of [Al], [Mg], and [Ti] were discussed. Mg-Al-Ti-O complex inclusion with high TiOx content was liquid at 1873 K (1600 °C), indicating MgAl2O4 spinel inclusions can be modified to low melting temperature ones by combining TiOx component. The stability diagram of Al-Mg-Ti-O system inclusions in the molten steel at 1873 K (1600 °C) was calculated, considering many kinds of oxide inclusions such as MgO, Al2O3, TiOx, MgTi2O4, MgAl2O4, Al2TiO5, and liquid inclusion. The thermodynamic calculations are in good agreement with experimental results, which can predict the formation of Al-Mg-Ti-O complex inclusions in molten steel with a large concentration range of [Al], [Mg], and [Ti].

Ren, Ying; Zhang, Lifeng; Yang, Wen; Duan, Haojian

2014-12-01

369

Association of phycoerythrin and phycocyanin: in vitro formation of a functional energy transferring phycobilisome complex of Porphyridium sordidum  

SciTech Connect

Functional in vitro association and dissociation of a phycobiliprotein complex, isolated from phycobilisomes of the red alga Porphyridium sordidum, were studied. The complex contained large bangiophyceaen phycoerythrin and cyanophytan phycocyanin in an equimolar ratio and had absorption maxima at 625, 567, and 550 nm and a shoulder at 495 nm. Emission at 655 nm (with excitation at 545 nm) from phycocyanin indicated functional coupling. The complex was stable over a wide buffer concentration range, and, notably, it was maximally stable in low phosphate, <0.01 M, unlike the phycobilisomes, which dissociate at this concentration. Its molecular weight was estimated to be ca. 510 000, and by electron microscopy it was seen to consist of two units of similar size. The complex in 0.1 M phosphate was separated on a sucrose gradient into a homogeneous phycoerythrin band and a spectrally heterogeneous phycocyanin band. In vitro association of phycoerythrin and phycocyanin resulted in a complex with the same absorbance, emission, sedimentation, and molar pigment ratio as those of the native complex. The spectrally heterogeneous phycocyanin fractions from the dissociation gradient varied in the degree of association with phycoerythrin. Phycocyanin fractions absorbing from 622 to 633 nm exhibited high associability (>70%), whereas those with maxima at 617-620 nm had low associability (<30%). The presence of a 30 000 molecular weight polypeptide accompanied high associability, where it was ca. 2-fold more prominent. It is suggested that this polypeptide is involved in complex formation and could serve either in the stabilization of the conformational state of cyanophytan phycocyanin or as a direct linker between phycobiliproteins.

Lipschultz, C.A.; Gantt, E.

1981-01-01

370

Oxidative double dehalogenation of tetrachlorocatechol by a bio-inspired CuII complex: formation of chloranilic acid.  

PubMed

Copper(II) complexes of the potentially tripodal N,N,O ligand 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its conjugate acid HL1 have been synthesised and structurally and spectroscopically characterised. The reaction of equimolar amounts of ligand and CuII resulted in the complexes [Cu(L1)]n(X)n (X=OTf-, PF6(-); n=1,2), for which a new bridging coordination mode of L1 is inferred. Although these complexes showed moderate catecholase activity in the oxidation of 3,5-di-tert-butylcatechol, surprising reactivity with the pseudo-substrate tetrachlorocatechol was observed. A chloranilato-bridged dinuclear CuII complex was isolated from the reaction of [Cu(L1)]n(PF6)n with tetrachlorocatechol. This stoichiometric oxidative double dehalogenation of tetrachlorocatechol to chloranilic acid by a biomimetic copper(II) complex is unprecedented. The crystal structure of the product, [Cu2(ca)Cl2(HL1)2], shows a bridging bis-bidentate chloranilato (ca) ligand and ligand L1 coordinated as its conjugate acid (HL1) in a tridentate fashion. Magnetic susceptibility studies revealed weak antiferromagnetic coupling (J= -35 cm(-1)) between the two copper centres in the dinuclear complex. Dissolution of the green complex [Cu2(ca)Cl2(HL1)2] resulted in the formation of new pink-purple mononuclear compound [Cu(ca)(HL1)(H2O)], the crystal structure of which was determined. It showed a terminal bidentate chloranilato ligand and N,N-bidentate coordination of ligand HL1, which illustrates the flexible coordination chemistry of ligand L1. PMID:18449873

Bruijnincx, Pieter C A; Viciano-Chumillas, Marta; Lutz, Martin; Spek, Anthony L; Reedijk, Jan; van Koten, Gerard; Klein Gebbink, Robertus J M

2008-01-01

371

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

NSDL National Science Digital Library

Show Caption Hide This diagram shows the relationship of Gibbs Free Energy to composition. In this diagram there are two minima represented for free energy which is achieved by unmixing of two distinct phases each with definite composition. The dashed line, which is tangential to the two minima in the free energy curves, gives the composition of the coexisting minerals at a specific temperature. From: Klein, C., and Dutrow, B., Manual of Mineral Science, 23rd ed., J. Wiley and Sons. Used with permission. The phenomenon of solid solution is common in many rock-forming minerals. At high temperatures, thermal vibrations permit accomodation of ions with size differences on the order of 15-30%. However, as physical conditions change, ions no longer fit into similar sites which creates internal (lattice) strain energy. Consequently, the mineral composition must adjust to relieve this strain energy and minimize the Gibbs Free Energy of the system. One possible response of the system is for elements in a crystal to move from one chemical site to another via intracrystalline diffusion. This results in segregated domains that are enriched in one element or another--this is a process called exsolution. A good example of this process can be seen in the alkali feldspar mineral group. At high temperature the mineral anorthoclase (K,Na)AlSi3O8 shows complete solid solution, i.e. there is a random distribution of K and Na in the alkali sites of the crystal. Upon cooling, Na and K segregate into more ordered domains creating areas that are rich in albite NaAl Si3O8 and microcline KAlSi3O8(see Figure 1). The purpose of this exercise is to provide a number of activities to demonstrate how exsolution works and to demonstrate complex-system behavior in this relatively common natural phenomenon. Part I: Images of naturally occurring perthite. The following images show minerals that have undergone exsolution at different scales. The image on the top left shows exsolution as viewed with a Transmission Electron Microscope (TEM; field of view is 10 microns). The image on the top right is a photomicrograph of exsolution in microcline as seen in thin section (cross-polarized light, field of view is 2 mm). The picture on the bottom left is a hand sample of perthitic microcline as seen in hand sample (field of view is 10 cm). The picture on the bottom right is a picture of plagioclase feldspar showing the "schiller" effect. This is caused by sub-microscopic unmixing of two distinct plagioclase phases in the compositional range of labradorite (An50 - An70) which results in the beautiful play of colors seen in this photo; (field of view of 20 centimeters). This series of pictures is a good example of scale invariance of this physical phenomenon. Examine perthite textures from hand samples and thin sections from your own mineralogy collection. We can easily envision unmixing of two immiscible fluids--for example oil and vinegar salad dressing. The same thing happens when we unmix (i.e. exsolve) solid phases--the process just takes a bit longer as atoms have to migrate in the crystal lattice by intracrystalline diffusion! How can such a common feature as perthite be understood in terms of complex-system behavior? Exsolution observed on a sub-microscopic scale in this TEM picture; this microstructure shows unmixing of labradorite in very fine essentially parallel lamellae. From Champness, P.E., and G.W Lorimer, 1976. Exsolution in silicates. Chapter 4.1 in Electron Microscopy in Mineralogy. H.R. Wenk, ed. Springer-Verlag, New York. Field of view is 10 microns. Perthite observed in thin section. Field of view is 2 mm. Perthite observed in hand sample. Field of View is 10 cm. Unmixing of parallel lamellae, as observed in a hand specimen of labradorite from Madagascar. These lamellae act as diffraction grating for white light, producing spectral colors known as labradorescence or the "schiller effect"; the field of view is 20 cm. Photo by B. Dutrow; used by permission.] Part II: Exsolution Puzzle Exercise. This exercise is done in groups of 2-3 students. Coins are initially randomly distributed on a chessboard, and are then subsequently moved to create domains of increasing order (regions that are dominated by either pennies or nickels). This is a kinesthetic learning exercise that creates a physical model that simulates how the exsolution process works. (Inspired by Greg Marfleet, Carleton College) Randomly distribute 20 pennies and 20 nickels on the attached 7x7 chessboard (Microsoft Word 33kB Dec1 10). The random distribution of pennies and nickels is analogous to the random distribution of Na and K in the high temperature alkali feldspar, anorthosite. (See Figure 1) The goal is to have a given coin completely surrounded by similar neighbors (i.e. 8 nearest neighbors of the same type of coin located on adjacent edges and the diagonal squares. Each student will sequentially move a coin into an adjacent open position (horizontal, vertical and diagonal moves are allowed) to achieve this desired configuration. Perfect ordering of nickels and pennies into discrete domains is analogous to perfectly ordered crystals of albite and microcline. [NOTE: in this exercise we are modeling the diffusivity of only the alkali elements, Na and K. The ordering of Si and Al in the tetrahedral sites of a feldspar crystal is a related, but entirely different process]. Systems tend to minimize Gibbs Free Energy (see Figure 2) on their way towards a state of equilibrium. In this example, the surface area surrounding domains of the segregated compositions (nickels/Na and pennies/potassium) is proportional to the excess Gibbs Free Energy of those domains. As clusters of similar coins evolve (segregate) and get bigger, the bounding surface areas are minimized and the energetics of the system are decreased. INSTRUCTIONS For the initial random state, determine the area surrounding each type of element; do this by assuming the unit length along each edge is 1 and add all the surfaces surrounding Na/nickel and K/potassium coins or aggregates of coins. Count any edges that are not adjacent to another similar coin (i.e. count all nickel-penny interfaces, and any edge where a nickel or penny is adjacent to an open space. Do not count the external edges on the outer border of the chessboard). Make 10 moves of the coins (always moving into an adjacent open space either right, left, up, down, or on a diagonal) and again determine the bounding surface areas. Record these surface area values for pennies and nickels. Repeat after 20, 30, 40, 50, and 100 moves. After each set of moves, report your surface area measurements for both pennies and nickels to your instructor; record these values on a spread sheet for later plotting and analysis. This part of the exercise should take about 45 minutes to complete the sets of movements and measurement of the surface areas. Here is an example experiment showing the progressive ordering of pennies (potassium) and nickels (sodium). Show pictures of the 2-D distribution of pennies and nickels after 10,20, 30, 40, 50 and 100 successive moves Hide Original random distribution of coins. Distribution of coins after 10 moves. Distribution of coins after 20 moves. Distribution of coins after 30 moves. Distribution of coins after 40 moves. Distribution of coins after 50 moves. Distribution of coins after 100 moves; perfect order. Plot your results. Assume that each move requires 1 unit of time. Plot your data on a X-Y plot with surface area on the Y axis and time on the X-axis. What is the distribution of your data? (Try plotting data for pennies, nickels, their sum, and their averages). Create a "best fit" curve through the data as plotted on this X-Y diagram (easily done with functions programmed into Excel). . What type of mathematical function is represented by a curve that has a steep slope to begin (left side of the plot), and becomes asymptotic to the X-axis away from the origin? Did you notice that the first set of coin moves produced the largest change in surface area, and that subsequent sets of moves produced smaller and smaller changes to the surface area? Have you seen other plots with similar profiles from your other studies in Earth Science? Show Answer: Hide radioactive decay; longitudinal profile of rivers.... It appears that many processes in Earth Science may follow the same mathematical laws. Now plot your data on a log-log plot with surface area on the ordinate (Y-axis) and time on the abscissa (X-axis). Create a "best fit" curve through these data (easily done with functions programmed into Excel). What is the shape of this curve? Does this relationship demonstrate a) an exponential function? b) a power law? Here is an example dataset (Excel 74kB Dec1 10) for 12 experiments completed by the spring 2010 Mineralogy class at Montana State University. Raw data and corresponding graphs are presented in the attached spreadsheet file. Compare your results with those shown in this example exercise. Intracrystalline Diffusion and Fick's Law The rate of transport of mass (and energy) through a fixed medium can be described mathematically by Fick's Law of Diffusion. Show details about Fick's Law of Diffusion Hide. The fundamental expression of Fick's First Law of Diffusion can be written as: J = -D(c/x) Jis the flux of a material along a compositional gradient (e.g. mol / length2time1 ), the amount of material (e.g. atoms or moles) that will flow through a small area during a fixed time interval. Dis the diffusion coefficient (length2 time -1); c is the concentration (amount of material per volume, mol/m3), and x is the length (m) Fick's Law shows that the flux of an ion diffusing through a stationary medium (like the crystalline lattice in our example) is proportional to the concentration gradient (c/x). As diffusion proceeds, the concentration is always changing, and thus, the flux is always changing. Can you see why this process exhibits non-linear behavior and must be represented as a power law? Note that The diffusivity, D, scales with temperature: D ~ (kT/h) exp(-Q*/RT) where k is Boltzmann's constant, h is Planck's constant, and Q* is an activation energy. This means that the rate of diffusion decreases with temperature. Consequently, exsolution will ultimately grind to a halt as temperature decreases. This is why we can observe perthite development in alkali feldspars in a wide variety of igneous and metamorphic rocks...the perthite texture gives us information about the cooling history of the mineral up to a point, but then exsolution will slow to a stop and the perthite will continue to exist in a metastable state at the surface of the earth. Different types of diffusion pathways include: intragranular (volume) diffusion, grain boundary diffusion, diffusion in a bulk fluid, and diffusion related to crystal defects. In our example of perthite exsolution, intragranular (volume) diffusion is the operative process. This process is most effective at high temperatures. Note that generally material tends to move in a direction from high to low concentrations, and thus, compositional gradients tend to be minimized by diffusion. However, in the case of exsolution and perthite development during cooling of a high-temperature, homogeneous alkali feldspar (anorthite), just the opposite effect happens--segregated domains of albite and microcline become more stable at lower temperatures. Why is this the case? The answer lies in the overall energetics of the system. It turns out that lattice strain that is induced upon cooling of anorthite results in large excess energy in the system. To minimize this excess energy, a single homogeneous grain of anorthite (stable at high temperature), will undergo "spinodal" decomposition upon cooling. This results in two energy minima, one for each phase, as illustrated in Figure 2. Upon further cooling, these energy minima continue to separate, thus resulting in two stable phases whose compositions increasingly approach the end member compositions of albite and microcline. A more complete description of this process can be found in Chapters 5 and 7 of Putnis A. and McConnell J.D.C. Principles of Mineral Behaviour 258pp. Blackwell Scientific Publications. Oxford. 1980. Part III: Computer Simulation Model output from the NetLogo "segregation"program; 2000 objects achieved 70% similarity.The computer program NetLogo can be used to model complex system behavior. This computer program was developed by Uri Wilensky (1999) at the Center for Connected Learning and Computer-Based Modeling, Northwestern University. Evanston, IL. For this exercise, we will use the pre-programmed function for Segregation Experiment with this program by changing the input parameters to try to reproduce a) the pattern you developed in the puzzle model above, and b) perthite patterns observed in the natural microcline crystals. Part IV: Visualization of the Development of Exsolution The binary solvus phase diagram for the alkali feldspar system at low pressure. Figure provided by Dexter Perkins, used with permission.The binary "solvus" phase diagram (showing the relation of temperature to composition) is typically used to show the phase relations for alkali feldspars. A single homogeneous alkali feldspar occurs at high temperatures (Figure 1a), but as the system cools eventually the phase boundary (solvus) is intersected and the exsolution (unmixing) process begins. "Underneath" the solvus a single feldspar is no longer thermodynamically stable, and the system begins to separate into two phases that become increasingly Na-rich or K-rich upon further cooling. This visualization demonstrates the cooling history of an alkali feldspar, including use of the "lever rule" to calculate phase composition (mineral) and relative proportions. Examine the accompanying illustrations and track the "state" of the system as temperature changes. Binary Solvus for the Alkali Feldspar System. The accompanying illustrations on the right show the "state of the system" in terms of the relative proportions of the phases present for each assigned temperature. Relate these products and processes to natural occurrences of perthite, and think about the changes that have to take place on the atomic scale to produce the mesoscopic features that are visible in hand samples. Part V: Thought Questions Driving forces: in equilibrium thermodynamics, the system always drives towards the lowest Gibbs Free Energy. At equilibrium, chemical potential is zero. This typically means there are no compositional gradients. Why does this system drive towards segregated domains that are rich in Na and K? Consider entropy "in the system". What do we mean by "the system"? Refer to Ilya Prigogine's (winner of the 1977 Nobel Prize for Chemistry) classic work on this subject: Order out of Chaos, Man's New Dialogue with Nature (1984, Bantam Books, 394 pp.)

Mogk, David; Dutrow, Barb

372

Roles of mono-ubiquitinated Smad4 in the formation of Smad transcriptional complexes  

SciTech Connect

TGF-{beta} activates receptor-regulated Smad (R-Smad) through phosphorylation by type I receptors. Activated R-Smad binds to Smad4 and the complex translocates into the nucleus and stimulates the transcription of target genes through association with co-activators including p300. It is not clear, however, how activated Smad complexes are removed from target genes. In this study, we show that TGF-{beta} enhances the mono-ubiquitination of Smad4. Smad4 mono-ubiquitination was promoted by p300 and suppressed by the c-Ski co-repressor. Smad4 mono-ubiquitination disrupted the interaction with Smad2 in the presence of constitutively active TGF-{beta} type I receptor. Furthermore, mono-ubiquitinated Smad4 was not found in DNA-binding Smad complexes. A Smad4-Ubiquitin fusion protein, which mimics mono-ubiquitinated Smad4, enhanced localization to the cytoplasm. These results suggest that mono-ubiquitination of Smad4 occurs in the transcriptional activator complex and facilitates the turnover of Smad complexes at target genes.

Wang Bei [Department of Experimental Pathology, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki 305-8575 (Japan); Suzuki, Hiroyuki [Department of Experimental Pathology, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki 305-8575 (Japan)], E-mail: h-suzuki@md.tsukuba.ac.jp; Kato, Mitsuyasu [Department of Experimental Pathology, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Ibaraki 305-8575 (Japan)

2008-11-14

373

Regulation of focal adhesion formation by a vinculin-Arp2/3 hybrid complex.  

PubMed

Focal adhesions (FAs) are large multi-protein complexes that act as transmembrane links between the extracellular matrix and the actin cytoskeleton. Recently, FAs were extensively characterized, yet the molecular mechanisms underlying their mechanical and signalling functions remain unresolved. To address this question, we isolated protein complexes containing different FA components, from chicken smooth muscle, and characterized their properties. Here we identified 'hybrid complexes' consisting of the actin-nucleating subunits of Arp2/3 and either vinculin or vinculin and ?-actinin. We further show that suppression of p41-ARC, a central component of native Arp2/3, which is absent from the hybrid complexes, increases the levels of the Arp2/3-nucleating core in FA sites and stimulates FA growth and dynamics. In contrast, overexpression of p41-ARC adversely affects FAs. These results support the view that Arp2/3 can form modular 'hybrid complexes' containing an actin-nucleating 'functional core', and 'anchoring domains' (vinculin/p41-ARC) that regulate its subcellular localization. PMID:24781749

Chorev, Dror S; Moscovitz, Oren; Geiger, Benjamin; Sharon, Michal

2014-01-01

374

A Novel Chitosan-?PGA Polyelectrolyte Complex Hydrogel Promotes Early New Bone Formation in the Alveolar Socket Following Tooth Extraction  

PubMed Central

A novel chitosan-?PGA polyelectrolyte complex hydrogel (C-PGA) has been developed and proven to be an effective dressing for wound healing. The purpose of this study was to evaluate if C-PGA could promote new bone formation in the alveolar socket following tooth extraction. An animal model was proposed using radiography and histomorphology simultaneously to analyze the symmetrical sections of Wistar rats. The upper incisors of Wistar rats were extracted and the extraction sockets were randomly treated with gelatin sponge, neat chitosan, C-PGA, or received no treatment. The extraction sockets of selected rats from each group were evaluated at 1, 2, 4, or 6 wk post-extraction. The results of radiography and histopathology indicated that the extraction sockets treated with C-PGA exhibited lamellar bone formation (6.5%) as early as 2 wk after the extraction was performed. Moreover, the degree of new bone formation was significantly higher (P < 0.05) in the extraction sockets treated with C-PGA at 6 wk post-extraction than that in the other study groups. In this study, we demonstrated that the proposed animal model involving symmetrical sections and simultaneous radiography and histomorphology evaluation is feasible. We also conclude that the novel C-PGA has great potential for new bone formation in the alveolar socket following tooth extraction. PMID:24658174

Chang, Hao-Hueng; Wang, Yin-Lin; Chiang, Yu-Chih; Chen, Yen-Liang; Chuang, Yu-Horng; Tsai, Shang-Jye; Heish, Kuo-Huang; Lin, Feng-Huei; Lin, Chun-Pin

2014-01-01

375

The influence of the ratio between the selenium: Polyvinylpyrrolidone complex components on the formation and morphological characteristics of nanostructures  

NASA Astrophysics Data System (ADS)

Optical and spectral methods were used to study nanostructures formed in the reduction of ionic selenium in the selenite-ascorbate redox system in aqueous solutions of polyvinylpyrrolidone, a physiologically active polymer. The weight ratio between the selenium: polymer complex components (?) was varied over a wide range (? = 0.01-0.2). The adsorption of a substantial number of macromolecules (up to 1000 at ? = 0.1-0.2) on selenium nanoparticles was observed experimentally. This resulted in the formation of supramolecular spherical nanostructures with a high polymeric shell density. The Gibbs energies of macromolecule-Se0 nanoparticle interactions were calculated for polymeric nanostructures in the region of the formation of stable dispersions. The flow birefringence, dynamic light scattering, and spectrophotometry methods were used to determine the region of saturation of the adsorption capacity of selenium nanoparticles in selenium-containing nanocomposites (? = 0.1-0.2).

Valueva, S. V.; Borovikova, L. N.; Kipper, A. I.

2008-06-01

376

Redistribution of material and formation of polygenic mélanges in the External Ligurian accretionary complex (Northern Apennines, Italy)  

NASA Astrophysics Data System (ADS)

Tectonic, sedimentary and diapiric processes may strongly control the dynamics of the shallower part of subduction-accretionary complexes, and formation of polygenic mélanges at different scales. In modern accretionary complexes, drill cores and seismic images provide in-situ samples and measurements about large-scale features, and crucial informations on the structural processes that control their dynamics. However, minor-scale geological features and processes that are responsible for their formation are still difficult to decipher based on these techniques alone. On-land, exhumed accretionary complexes, on the other hand, can provide essential informations at all scales about (i) 3D features and structural architecture of mélanges, (ii) the role and interplay of different processes of mélange formation, and (iii) the redistribution of material in shallower parts of accretionary complexes (Festa et al., 2010). Detailed structural-stratigraphic observations in the exhumed Ligurian accretionary complex in the westernmost Northern Apennines show that a larger part of it (i.e., the Argille varicolori Formation) represents a composite chaotic unit consisting of diverse scale mélange types formed by tectonic, sedimentary and diapiric processes and their mutual superposition. Here, the spatial and temporal relationships between these mélange types resulted from two main episodes of deformation: (i) late Cretaceous-middle Eocene accretion, producing tectonic deformation of sediments at the wedge-front and formation of tectonically disrupted bodies through layer-parallel extension and contraction. Episodes of dynamic instability of the wedge-front alternating with steady-state accretion caused the removal of material locally and the subsequent emplacement of gravity-driven chaotic bodies within the tectonically disrupted bodies; (ii) late Oligocene-middle Miocene out-of-sequence thrusting, overprinting the previously formed chaotic bodies and producing a new and polygenic type of tectonically disrupted bodies through shearing close to the main thrusts. This deformation event also led to the emplacement of large (regional-scale) olistostromes at the wedge-front. The rapid burial due to the emplacement of these olistostromes and/or the tectonic shaking of unconsolidated sediments might have triggered the focused mobilization of overpressured fluids forming diapiric mélanges. We conclude that superposition of tectonic, sedimentary and diapiric processes resulted in the occurrence at different scales of different types of mélanges and polygenic mélanges in the Ligurian accretionary complex. Our recognition of these polygenic mélanges in the rock record is highly important for better understanding the dynamics, crustal architecture, and structural evolution of other ancient subduction-accretionary complexes around the world. Festa A., Pini G.A., Dilek Y. and Codegone G. (2010) - Mélanges and mélange-forming processes: a historical overview and new concepts. International Geology Review, v. 52, n. 10-12, p. 1040-1105.

Codegone, G.; Festa, A.; Dilek, Y.; Pini, G.

2011-12-01

377

Lysozyme conjugate immune complex formation and the effects on substrate hydrolysis.  

PubMed

The defined estrone glucuronide-lysozyme conjugate E3, that is acylated solely at K33, was used as a probe for the steric requirements of the active site cleft of chicken type lysozymes. When the immune complex was formed with an anti-estrone glucuronide antiserum, the rate of lysis of the E3 conjugate with the large bacterial substrate Micrococcus lysodeikticus was inhibited by over 90%. However, when the small hexamer of N-acetyl glucosamine was used as the substrate, the rate of hydrolysis by the immune complex was accelerated by 350% compared with the control rate. Thus, inhibition by the anti-estrone glucuronide cannot be caused simply by steric occlusion of the active site. Other factor(s) in the immune complex activate the hydrolysis reaction, most likely by favouring the conformations that lead to the transition state. PMID:12727231

Smales, C Mark; Blackwell, Leonard F

2003-05-16

378

Detailed chemical characterization of unresolved complex mixtures in atmospheric organics: Insights into emission sources, atmospheric processing, and secondary organic aerosol formation  

NASA Astrophysics Data System (ADS)

Recent studies suggest that semivolatile organic compounds (SVOCs) are important precursors to secondary organic aerosol (SOA) in urban atmospheres. However, knowledge of the chemical composition of SVOCs is limited by current analytical techniques, which are typically unable to resolve a large number of constitutional isomers. Using a combination of gas chromatography and soft photoionization mass spectrometry, we characterize the unresolved complex mixture (UCM) of semivolatile aliphatic hydrocarbons observed in Pasadena, California (~16 km NE of downtown Los Angeles), and Bakersfield, California, during the California Research at the Nexus of Air Quality and Climate Change 2010. To the authors' knowledge, this work represents the most detailed characterization of the UCM in atmospheric samples to date. Knowledge of molecular structures, including carbon number, alkyl branching, and number of rings, provides important constraints on the rate of atmospheric processing, as the relative amounts of branched and linear alkanes are shown to be a function of integrated exposure to hydroxyl radicals. Emissions of semivolatile branched alkanes from fossil fuel-related sources are up to an order of magnitude higher than those of linear alkanes, and the gas-phase OH rate constants of branched alkanes are ~30% higher than their linear isomers. Based on a box model considering gas/particle partitioning, emissions, and reaction rates, semivolatile branched alkanes are expected to play a more important role than linear alkanes in the photooxidation of the UCM and subsequent transformations into SOA. Detailed speciation of semivolatile compounds therefore provides essential understanding of SOA sources and formation processes in urban areas.

Chan, Arthur W. H.; Isaacman, Gabriel; Wilson, Kevin R.; Worton, David R.; Ruehl, Christopher R.; Nah, Theodora; Gentner, Drew R.; Dallmann, Timothy R.; Kirchstetter, Thomas W.; Harley, Robert A.; Gilman, Jessica B.; Kuster, William C.; Gouw, Joost A.; Offenberg, John H.; Kleindienst, Tadeusz E.; Lin, Ying H.; Rubitschun, Caitlin L.; Surratt, Jason D.; Hayes, Patrick L.; Jimenez, Jose L.; Goldstein, Allen H.

2013-06-01

379

2-Methoxystypandrone represses RANKL-mediated osteoclastogenesis by down-regulating formation of TRAF6–TAK1 signalling complexes  

PubMed Central

BACKGROUND AND PURPOSE 2-Methoxystypandrone (2-MS) is a naphthoquinone isolated from Polygonum cuspidatum, a Chinese herb used to treat bone diseases. Here we have determined whether 2-MS antagonised osteoclast development and bone resorption. EXPERIMENTAL APPROACH RAW264.7 cells were treated with receptor activator of nuclear factor ?B (NF-?B) ligand (RANKL) to induce differentiation into osteoclasts. RT-PCR and Western blot were used to analyse osteoclast-associated gene expression and signalling pathways. KEY RESULTS The number of multinuclear osteoclasts, actin rings and resorption pit formation were markedly inhibited by 2-MS, targeting osteoclast differentiation at an early stage and without significant cytotoxicity. The anti-resorption effect of 2-MS was accompanied by decreasing dendritic cell-specific transmembrane protein and matrix metalloproteinase-9 (MMP-9) mRNA expression. RANKL-increased MMP-9 gelatinolytic activity was also attenuated by concurrent, but not by subsequent addition of 2-MS. 2-MS markedly inhibited not only the RANKL-triggered nuclear translocations of NF-?B, c-Fos and nuclear factor of activated T cells c1 (NFATc1), but also the subsequent NFATc1 induction. Degradation of I?B and phosphorylation of mitogen-activated protein kinases were also suppressed. RANKL facilitated the formation of singaling complexes of tumour necrosis factor receptor-associated factor 6 and transforming growth factor ?-activated kinase 1 (TRAF6–TAK1), important for osteoclastogenesis and formation of such signalling complexes was prevented by 2-MS. CONCLUSIONS AND IMPLICATIONS The anti-osteoclastogenic effects of 2-MS could reflect the block of RANKL-induced association of TRAF6–TAK1 complexes with consequent decrease of I?B-mediated NF-?B and mitogen-activated protein kinases-mediated c-Fos activation pathways and suppression of NFATc1 and other gene expression, essential for bone resorption. PMID:20735418

Chiou, WF; Liao, JF; Huang, CY; Chen, CC

2010-01-01

380

Considerable fluorescence enhancement upon supramolecular complex formation between berberine and p-sulfonated calixarenes  

NASA Astrophysics Data System (ADS)

Remarkably strong binding of berberine to 4-sulfonatocalix[8]arene was found in aqueous solution, which led to fluorescence quantum yield increase of a factor about 40 at pH 2. The hypsochromic shift of the fluorescence maximum implied that berberine sensed less polar microenvironment when confined to SCX8. The stability of the supramolecular complex significantly diminished when sulfocalixarenes of smaller ring size served as host compounds but the pH affected the association strength to a much lesser extent. All berberine complexes proved to be barely fluorescent at pH 12.2 because of excited state quenching by the hosts via electron transfer.

Megyesi, Mónika; Biczók, László

2006-06-01

381

Fluorimetric determination of some sulfur containing compounds through complex formation with terbium (Tb+3) and uranium (U+3).  

PubMed

Two simple, sensitive and specific fluorimetric methods have been developed for the determination of some sulphur containing compounds namely, Acetylcysteine (Ac), Carbocisteine (Cc) and Thioctic acid (Th) using terbium Tb+3 and uranium U+3 ions as fluorescent probes. The proposed methods involve the formation of a ternary complex with Tb+3 in presence of Tris-buffer method (I) and a binary complex with aqueous uranyl acetate solution method (II). The fluorescence quenching of Tb+3 at 510, 488 and 540 nm (lambda(ex) 250, 241 and 268 nm) and of uranyl acetate at 512 nm (lambda(ex) 240 nm) due to the complex formation was quantitatively measured for Ac, Cc and Th, respectively. The reaction conditions and the fluorescence spectral properties of the complexes have been investigated. Under the described conditions, the proposed methods were applicable over the concentration range (0.2-2.5 microg ml(-1)), (1-4 microg ml(-1)) and (0.5-3.5 microg ml(-1)) with mean percentage recoveries 99.74+/-0.36, 99.70+/-0.52 and 99.43+/-0.23 for method (I) and (0.5-6 microg ml(-1)), (0.5-5 microg ml(-1)), and (1-6 microg ml(-1)) with mean percentage recoveries 99.38+/-0.20, 99.82+/-0.28 and 99.93+/-0.32 for method (II), for the three cited drugs, respectively. The proposed methods were successfully applied for the determination of the studied compounds in bulk powders and in pharmaceutical formulations, as well as in presence of their related substances. The results obtained were found to be in agree statistically with those obtained by official and reported ones. The two methods were validated according to USP guidelines and also assessed by applying the standard addition technique. PMID:17440799

Taha, Elham Anwer; Hassan, Nagiba Yehya; Aal, Fahima Abdel; Fattah, Laila El-Sayed Abdel

2007-05-01

382

Bond Formation and Coupling between Germyl and Bridging Germylene Ligands in Dinuclear Palladium(I) Complexes.  

PubMed

The dinuclear palladium(I) complexes [L(Ar2 HGe)Pd(?-GeAr2 )2 Pd(GeHAr2 )L] (Ar=Ph, p-Tol; L=PMe3 , tBuNC) contain terminal germyl and bridging germylene ligands with the experimentally observed Ge???Ge bond lengths of 2.8263(4)?Å (L=PMe3 ) and 2.928(1)?Å (L=tBuNC), which are close to the longest Ge?Ge bond reported to date [2.714(1)?Å]. Significant Ge???Ge interactions between the germylene and germyl ligands (PMe3 complexes > tBuNC complexes) are supported by DFT calculations, Wiberg bond indices (WBI), and natural bond orbital (NBO) analyses. Exchanging tBuNC for PMe3 ligands increases the Ge???Ge interaction, and simultaneously activates two Pd?Ge bonds. Adding the chelating diphosphine 1,2-bis(diethylphosphino)ethane (depe) to the PMe3 complexes results in the intramolecular coupling of germyl and germylene ligands followed by extrusion of a digermane. PMID:25641406

Tanabe, Makoto; Omine, Shumpei; Ishikawa, Naoko; Osakada, Kohtaro; Hayashi, Yoshihiro; Kawauchi, Susumu

2015-02-23

383

Formation of Neoproterozoic metamorphic complex during oblique convergence (Eastern Desert, Egypt)  

Microsoft Academic Search

Major portions of the Pan-African Orogen in the Eastern Desert of Egypt were formed by island-arc accretion in the Neoproterozoic. These areas are characterized by their lack of major crustal thickening. Metamorphic core complexes occur parallel to the strike of the Eastern Desert Orogen. These domes exhibit polyphase metamorphism and deformation in contrast to the structurally overlying nappes which include

H. Fritz; E. Wallbrecher; A. A. Khudeir; F. Abu el Ela; D. R. Dallmeyer

1996-01-01

384

Formation of Neoproterozoic metamorphic core complexes during oblique convergence (Eastern Desert, Egypt)  

Microsoft Academic Search

Major portions of the Pan-African Orogen in the Eastern Desert of Egypt were formed by island-arc accretion in the Neoproterozoic. These areas are characterized by their lack of major crustal thickening. Metamorphic core complexes occur parallel to the strike of the Eastern Desert Orogen. These domes exhibit polyphase metamorphism and deformation in contrast to the structurally overlying nappes which include

H. FRITZ; E. WALLBRECHER; A. A. KHUDEIR; F. ABU EL ELA; D. R. DALLMEYER

1996-01-01

385

Molecular Orbital Studies of Titanium Nitride Chemical Vapor Deposition: Gas Phase Complex Formation,  

E-print Network

Molecular Orbital Studies of Titanium Nitride Chemical Vapor Deposition: Gas Phase Complex Received June 6, 2000 The chemical vapor deposition (CVD) of titanium nitride can be carried out with TiCl4 Titanium nitride thin films have a variety of proper- ties, such as extreme hardness, high chemical

Schlegel, H. Bernhard

386

[Fluorescence spectroscopy determination of lomefloxacin by charge transfer complex formation with chloranilic acid].  

PubMed

Charge-transfer complex was formed between LMX as the donor and Chloranilic Acid (CL) as the acceptor has been studied by fluorimetry. It was shown that the n-pi complex can be formed at ambient temperature, which can emit, which strong fluorescence. Different variables and parameters affecting the reactions were studied and optimized. Based on this, a simple and reliable fluorescence spectroscopy method for the determination of Lomefloxacin (LMX) has been developed. Interference from some co-formulated drugs was also studied. No interference was observed due to additives commonly present in the pharmaceutical preparations. The proposed methods could be applied successfully to the investigated pure compounds and pharmaceutical dosage forms with good accuracy and precision. The linear range is 0.04-0.8 mg x L(-1), the detection limit is 0.04 mg x L(-1), the recoveries of LMX are 97.4%-99.3%, and RSD is 1.3%-2.6%. Finally, the charge-transfer reaction mechanism was discussed. The composition of the change-transfer complex was found to be 1:1 by Bent-French and curved intersection methods. This ratio may be due to the presence of the fluorine atom acting as an electron drawing group in the molecule of lomefloxacin. The benzene ring has lower electron density, but nitrogen atom in 4' of piperazingl has higher electron density and is less sterically hindered. So n-pi charge transfer complexes were formed. PMID:15828343

Du, Li-ming; Zhou, Jing; Yuan, Jian-mei

2004-12-01

387

Formation and isolation of nanocrystal complexes between dextrins and n-butanol  

Microsoft Academic Search

Starch dextrins of different molecular sizes (DPn 311, 142 and 39) were prepared by hydrolyzing a high amylose maize starch in acidic alcohol solutions. The dextrins were dissolved in an aqueous dimethyl sulfoxide solution (90% DMSO), and then the solution was allowed to migrate down into n-butanol separated by a membrane filter. The complex was gradually formed between the dextrin

Jong-Yea Kim; Jae-Wook Yoon; Seung-Taik Lim

2009-01-01

388

Separation of drug stereoisomers by the formation of. beta. -cyclodextrin inclusion complexes  

Microsoft Academic Search

For many drugs, only racemic mixtures are available for clinical use. Because different stereoisomers of drugs often cause different physiological responses, the use of pure isomers could elicit more exact therapeutic effects. Differential complexation of a variety of drug stereoisomers by immobilized ..beta..-cyclodextrin was investigated. Chiral recognition and racemic resolution were observed with a number of compounds from such clinically

D. W. Armstrong; T. J. Ward; R. D. Armstrong; T. E. Beesley

1986-01-01

389

Formation of water-soluble metal cyanide complexes from solid minerals by Pseudomonas plecoglossicida.  

PubMed

A few Pseudomonas species are able to form hydrocyanic acid (HCN), particularly when grown under glycine-rich conditions. In the presence of metals, cyanide can form water-soluble metal complexes of high chemical stability. We studied the possibility to mobilize metals as cyanide complexes from solid minerals using HCN-forming microorganisms. Pseudomonas plecoglossicida was cultivated in the presence of copper- and nickel-containing solid minerals. On powdered elemental nickel, fast HCN generation within the first 12 h of incubation was observed and water-soluble tetracyanaonickelate was formed. Cuprite, tenorite, chrysocolla, malachite, bornite, turquoise, millerite, pentlandite as well as shredded electronic scrap was also subjected to a biological treatment. Maximum concentrations of cyanide-complexed copper corresponded to a solubilization of 42% and 27% when P. plecoglossicida was grown in the presence of cuprite or tenorite, respectively. Crystal system, metal oxidation state and mineral hydrophobicity might have a significant influence on metal mobilization. However, it was not possible to allocate metal mobilization to a single mineral property. Cyanide-complexed gold was detected during growth on manually cut circuit boards. Maximum dicyanoaurate concentration corresponded to a 68.5% dissolution of the total gold added. These findings represent a novel type of microbial mobilization of nickel and copper from solid minerals based on the ability of certain microbes to form HCN. PMID:16684101

Faramarzi, Mohammad A; Brandl, Helmut

2006-06-01

390

Variant PRC1 complex-dependent H2A ubiquitylation drives PRC2 recruitment and polycomb domain formation.  

PubMed

Chromatin modifying activities inherent to polycomb repressive complexes PRC1 and PRC2 play an essential role in gene regulation, cellular differentiation, and development. However, the mechanisms by which these complexes recognize their target sites and function together to form repressive chromatin domains remain poorly understood. Recruitment of PRC1 to target sites has been proposed to occur through a hierarchical process, dependent on prior nucleation of PRC2 and placement of H3K27me3. Here, using a de novo targeting assay in mouse embryonic stem cells we unexpectedly discover that PRC1-dependent H2AK119ub1 leads to recruitment of PRC2 and H3K27me3 to effectively initiate a polycomb domain. This activity is restricted to variant PRC1 complexes, and genetic ablation experiments reveal that targeting of the variant PCGF1/PRC1 complex by KDM2B to CpG islands is required for normal polycomb domain formation and mouse development. These observations provide a surprising PRC1-dependent logic for PRC2 occupancy at target sites in vivo. PMID:24856970

Blackledge, Neil P; Farcas, Anca M; Kondo, Takashi; King, Hamish W; McGouran, Joanna F; Hanssen, Lars L P; Ito, Shinsuke; Cooper, Sarah; Kondo, Kaori; Koseki, Yoko; Ishikura, Tomoyuki; Long, Hannah K; Sheahan, Thomas W; Brockdorff, Neil; Kessler, Benedikt M; Koseki, Haruhiko; Klose, Robert J

2014-06-01

391

Variant PRC1 Complex-Dependent H2A Ubiquitylation Drives PRC2 Recruitment and Polycomb Domain Formation  

PubMed Central

Summary Chromatin modifying activities inherent to polycomb repressive complexes PRC1 and PRC2 play an essential role in gene regulation, cellular differentiation, and development. However, the mechanisms by which these complexes recognize their target sites and function together to form repressive chromatin domains remain poorly understood. Recruitment of PRC1 to target sites has been proposed to occur through a hierarchical process, dependent on prior nucleation of PRC2 and placement of H3K27me3. Here, using a de novo targeting assay in mouse embryonic stem cells we unexpectedly discover that PRC1-dependent H2AK119ub1 leads to recruitment of PRC2 and H3K27me3 to effectively initiate a polycomb domain. This activity is restricted to variant PRC1 complexes, and genetic ablation experiments reveal that targeting of the variant PCGF1/PRC1 complex by KDM2B to CpG islands is required for normal polycomb domain formation and mouse development. These observations provide a surprising PRC1-dependent logic for PRC2 occupancy at target sites in vivo. PMID:24856970

Blackledge, Neil P.; Farcas, Anca M.; Kondo, Takashi; King, Hamish W.; McGouran, Joanna F.; Hanssen, Lars L.P.; Ito, Shinsuke; Cooper, Sarah; Kondo, Kaori; Koseki, Yoko; Ishikura, Tomoyuki; Long, Hannah K.; Sheahan, Thomas W.; Brockdorff, Neil; Kessler, Benedikt M.; Koseki, Haruhiko; Klose, Robert J.

2014-01-01

392

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

EPA Science Inventory

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

393

Complexation of peptide with Cu2+ responsible to inducing and enhancing the formation of ?-helix conformation  

Microsoft Academic Search

Role of some metal ions on the conformations of peptides was examined by using a series of short alanine-based peptides with single Trp-His (W-H) interaction in different environments. Circular dichroism (CD), Trp (W) fluorescence emission, and Fourier transform infrared (FTIR) spectroscopy revealed that there is a conformational role of Cu2+ in inducing and enhancing the formation of a-helix conformation. The

Jin Zou; Naoki Sugimoto

2000-01-01

394

Formation of a cobalt(III)-phenoxyl radical complex by acetic acid promoted aerobic oxidation of a Co(II)salen complex.  

PubMed

The activation of N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino Co(II), [Co(II)(1)], by the addition of acetic acid under aerobic conditions has been investigated by a range of spectroscopic techniques including continuous-wave EPR, HYSCORE, pulsed ENDOR, and resonance Raman. These measurements have revealed for the first time the formation of a coordinated cobalt(III)-bound phenoxyl radical labeled [Co(III)(1(*))(OAc)(n)](OAc)(m) (n = m = 1 or n = 2, m = 0). This cobalt(III)-bound phenoxyl radical is characterized by the following spin Hamiltonian parameters: g(x) = 2.0060, g(y) = 2.0031, g(z) = 1.9943, A(x) = 17 MHz, A(y) = 55 MHz, and A(z) = 14 MHz. Although the radical contains coordinated acetate(s), the experiments unambiguously proved that the phenoxyl radical is situated on ligand (1) as opposed to a phenoxyl radical ligated to cobalt in the axial position. Density functional theory computations on different models corroborate the stability of such a phenoxyl radical species and suggest the ligation of one or two acetate molecules to the complex. A mechanism is proposed, which accounts for the formation of this unusual and extremely robust phenoxyl radical, never previously observed for [Co(1)]. PMID:20121216

Vinck, Evi; Murphy, Damien M; Fallis, Ian A; Strevens, Robert R; Van Doorslaer, Sabine

2010-03-01

395

On Magnetic Activity Band Overlap, Interaction, and the Formation of Complex Solar Active Regions  

NASA Astrophysics Data System (ADS)

Recent work has revealed a phenomenological picture of the how the ~11 yr sunspot cycle of the Sun arises. The production and destruction of sunspots is a consequence of the latitudinal-temporal overlap and interaction of the toroidal magnetic flux systems that belong to the 22 yr magnetic activity cycle and are rooted deep in the Sun's convective interior. We present a conceptually simple extension of this work, presenting a hypothesis on how complex active regions can form as a direct consequence of the intra- and extra-hemispheric interaction taking place in the solar interior. Furthermore, during specific portions of the sunspot cycle, we anticipate that those complex active regions may be particularly susceptible to profoundly catastrophic breakdown, producing flares and coronal mass ejections of the most severe magnitude.

McIntosh, Scott W.; Leamon, Robert J.

2014-11-01

396

The effect of Ph gene alleles on synaptonemal complex formation in Triticum aestivum × T. kotschyi hybrids  

Microsoft Academic Search

Chromosome pairing at zygotene-pachytene was studied in Triticum aestivum × T. kotschyi hybrids (2n=5x=35, genomic constitution ABDCUSv) by electron microscopy of synaptonemal complexes in spread microsporocyte nuclei. Hybrids carrying either the Ph allele or the ph allele, which differ markedly in metaphase I pairing, are both capable of greater than 90% pachytene pairing, although pairing in the Ph hybrids appeared

C. B. Gillies

1987-01-01

397

New insights into the formation of active nonsense-mediated decay complexes  

Microsoft Academic Search

In the nonsense-mediated mRNA decay (NMD) pathway, an exon-junction protein complex (EJC) and hUpf proteins mediate rapid downregulation of aberrant mRNAs that terminate translation upstream of the last splice junction. Two EJC subunits, Y14 and RNPS1, have been proposed to act as a link between splicing and NMD by recruiting hUpf3 and the other hUpf proteins. New studies now present

Guramrit Singh; Jens Lykke-Andersen

2003-01-01

398

Unique P Spectral Response to the Formation of a Specific Restriction Enzyme–DNA Complex  

Microsoft Academic Search

Protein-induced distortion is a dramatic but not universally observed feature of sequence-specific DNA interactions. This is illustrated by the crystal structures of restriction enzyme–DNA complexes: While some of these structures exhibit DNA distortion, others do not. Among the latter is PvuII endonuclease, a small enzyme that is also amenable to NMR spectroscopic studies. Here P NMR spectroscopy is applied to

Cynthia M. Dupureur

2006-01-01

399

Computational assessment of non-heteroatom-stabilized carbene complexes reactivity: formation of oxazine derivatives.  

PubMed

A complete DFT-level mechanism elucidation of the two-step reaction of non-heteroatom-stabilized carbenes with imines, followed by addition of alkynes to yield oxazine derivatives, is presented. These compounds show different reactivity than the equivalent Fischer carbene complexes. A rationale of the experimental outcome is presented together with some suggestion for increasing the scope of the reaction, with special attention to the solvent effects in the regioselectivity. PMID:25389797

Funes-Ardoiz, Ignacio; Sampedro, Diego

2014-12-01

400

Formation of ion-conducting channels by the membrane attack complex proteins of complement.  

PubMed Central

The effects of sequential additions of purified human complement proteins C5b-6, C7, C8, and C9 to assemble the C5b-9 membrane attack complex (MAC) of complement on electrical properties of planar lipid bilayers have been analyzed. The high resistance state of such membranes was impaired after assembly of large numbers of C5b-8 complexes as indicated by the appearance of rapidly fluctuating membrane currents. The C5b-8 induced conductance was voltage dependent and rectifying at higher voltages. Addition of C9 to membranes with very few C5b-8 complexes caused appearance of few discrete single channels of low conductance (5-25 pS) but after some time very large (greater than 0.5 nS) jumps in conductance could be monitored. This high macroscopic conductance state was dominated by 125-pS channels having a lifetime of approximately 1 s. The high conductance state was not stable and declined again after a period of 1-3 h. Incorporation of MAC extracted from complement-lysed erythrocytes into liposomes and subsequent transformation of such complexes into planar bilayers via an intermediate monolayer state resulted in channels with characteristics similar to the ones produced by sequential assembly of C5b-9. Comparison of the high-conductance C5b-9 channel characteristics (lifetime, ion preference, ionic-strength dependence) with those produced by poly(C9) (the circular or tubular aggregation product of C9) as published by Young, J.D.-E., Z.A. Cohn, and E.R. Podack. (1986. Science [Wash. DC]. 233:184-190.) indicates that the two are significantly different. PMID:1720679

Shiver, J W; Dankert, J R; Esser, A F

1991-01-01