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81.
De Stefano C Milea D Porcino N Sammartano S 《Analytical and bioanalytical chemistry》2006,386(2):346-356
Interactions between myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate) (phytic acid) and cadmium(II) were studied by using potentiometry (at
25 °C with the ISE-H+ glass electrode) in different metal to ligand (Phy) ratios (1:1≤Cd2+:Phy≤4:1) in NaClaq at different ionic strengths (0.1≤I/mol L−1≤1). Nine CdiHjPhy(12−2i−j)− species are formed with i=1 and 2 and 4≤j≤7; and trinuclear Cd3H4Phy2−. Dependence of complex formation constants on ionic strength was modeled by using Specific ion Interaction Theory (SIT) equations.
Phytate and cadmium speciation are also dependent on the metal to ligand ratio. Stability of CdiHjPhy(12−2i−j)− species was modeled as a function of both the ligand protonation step (j) and the number of metal cations bound to phytate
(i), and relationships found were used for the prediction of species other than those experimentally determined (mainly di-
and tri-protonated complexes), allowing the possibility of modeling Phy and Cd(II) behavior in natural waters and biological
fluids. A critical evaluation of phytate sequestering ability toward cadmium(II) has been made under several experimental
conditions, and the determination of an empirical parameter has been proposed for an objective “quantification” of this ability.
A thorough analysis of literature data on phytate–cadmium(II) complexes has been performed.
Previous contributions to this series: [1–8] 相似文献
82.
Ongoing efforts to model P2Y receptors for extracellular nucleotides, i.e., endogenous ADP, ATP, UDP, UTP, and UDP-glucose, were summarized and correlated for the eight known subtypes. The rhodopsin-based homology modeling of the P2Y receptors is supported by a growing body of site-directed mutagenesis data, mainly for P2Y1 receptors. By comparing molecular models of the P2Y receptors, it was concluded that nucleotide binding could occur in the upper part of the helical bundle, with the ribose moiety accommodated between transmembrane domain (TM) 3 and TM7. The nucleobase was oriented towards TM1, TM2, and TM7, in the direction of the extracellular side of the receptor. The phosphate chain was oriented towards TM6, in the direction of the extracellular loops (ELs), and was coordinated by three critical cationic residues. In particular, in the P2Y1, P2Y2, P2Y4, and P2Y6 receptors the nucleotide ligands had very similar positions. ADP in the P2Y12 receptor was located deeper inside the receptor in comparison to other subtypes, and the uridine moiety of UDP-glucose in the P2Y14 receptor was located even deeper and shifted toward TM7. In general, these findings are in agreement with the proposed binding site of small molecules to other class A GPCRs. 相似文献
83.
Casalini S Battistuzzi G Borsari M Bortolotti CA Ranieri A Sola M 《The journal of physical chemistry. B》2008,112(5):1555-1563
The M80A variant of yeast iso-1-cytochrome c (cytc), which features a noncoordinating Ala residue in place of the axial heme iron Met ligand, was chemisorbed on a gold electrode coated with 4-mercaptopyridine or carboxyalkanethiol self-assembled monolayers (SAM) and investigated by cyclic voltammetry at varying conditions of temperature, pH, and O2 concentration. The E degrees ' value (standard reduction potential for the heme Fe(III)/Fe(II) couple) of M80A cytc on both SAMs is of approximately -200 mV (vs the standard hydrogen electrode, SHE) at pH 7, which is more than 400 mV lower than that of native cytochrome c in the same conditions. The thermodynamics of Fe(III) to Fe(II) reduction and the kinetics of heterogeneous electron transfer (ET) are dominated by the presence of a hydroxide ion as the sixth axial heme iron ligand above pH 6. On both SAMs, protonation of the bound hydroxide ion is mainly responsible for the changes in these parameters at low pH, since the distances of ET between the heme and the electrode are found to be independent of pH in the range of 5-11. The invariance of the electrochemical features up to pH 11 indicates that no changes in heme iron coordination occur at high pH, at variance with native cytc. Most notably, immobilized M80A cytc is found to act as an efficient biocatalyst for O2 reduction from pH 5 to 11.0. This finding makes M80A cytc a suitable candidate as a constituent of a biocatalytic interface for O2 biosensing and opens the way for the exploitation of engineered cytochrome c in the bio-based detection of chemicals of environmental and clinical interest. 相似文献
84.
Prediction methods of structural features in 1D represent a useful tool for the understanding of folding, classification, and function of proteins, and, in particular, for 3D structure prediction. Among the structural aspects characterizing a protein, solvent accessibility has received great attention in recent years. The available methods proposed for predicting accessibility have never considered the combination of the results deriving from different methods to construct a consensus prediction able to provide more reliable results. A consensus approach that increases prediction accuracy using three high-performance methods is described. The results of our method for three different protein data sets show that up to 3.0% improvement in prediction accuracy of solvent accessibility may be obtained by a consensus approach. The improvement also extends to the correlation coefficient. Application of our consensus approach to the accessibility prediction using only three prediction methods gives results better than single methods combined for consensus formation. Currently, the scarce availability of predictors with similar parameters defining solvent accessibility hinders the testing of other methods in our consensus procedure. 相似文献
85.
Benfatto M Della Longa S Hatada K Hayakawa K Gawelda W Bressler C Chergui M 《The journal of physical chemistry. B》2006,110(29):14035-14039
A full multiple theoretical model (MXAN) is applied to fit picosecond difference X-ray absorption spectra at the ruthenium L(3) edge upon photoexcitation of aqueous [RuII(bpy)3]2+. We show that fitting difference spectra allows an increase in sensitivity, such that slight structural changes can be retrieved, which are not detected in fitting full spectra. The Ru-N bond distances of the excited complex in the (3)MLCT state are in good agreement with recently published values. The implementation of the present approach to L-edge spectra and its high sensitivity opens opportunities for its extension to a large class of experiments where difference X-ray absorption spectra are recorded. 相似文献
86.
Adriano Boni Tiziana Funaioli Guido Pampaloni Stefano Zacchini 《Journal of organometallic chemistry》2011,696(22):3551-3556
The dimetallacyclopentenone complexes [Fe2Cp2(CO)(μ−CO){μ−η1:η3−CαHCβ(R)C(O)}] (R = CH2OH, 1a; R = CMe2OH, 1b; R = Ph, 1c) were prepared by photolytic reaction of [Fe2Cp2(CO)4] with alkyne according to the literature procedure. The X-ray and the electrochemical characterization of 1c are presented. The μ-allenyl compound [Fe2Cp2(CO)2(μ−CO){μ−η1:η2α,β−CαHCβCMe2][BF4] ([2][BF4]), obtained by reaction of 1b with HBF4, underwent monoelectron reduction to give a radical species which was detected by EPR at room temperature. The EPR signal has been assigned to [Fe2Cp2(CO)2(μ−CO){μ−η1:η2α,β-CαHCβCMe2}], [2]•. The molecular structures of [2]+ and [2]• were optimized by DFT calculations. The unpaired electron in [2]• is localized mainly at the metal centers and, coherently, [2]• does not undergo carbon-carbon dimerization, by contrast with what previously observed for the μ-vinyl radical complex [Fe2Cp2(CO)2(μ−CO){μ−η1:η2-CHCH(Ph)}]•, [3]•. Electron spin density distributions similar to the one of [2]• were found for the μ-allenyl radical complexes [Fe2Cp2(CO)2(μ-CO){μ-η1:η2α,β-CαHCβC(R1)(R2)}]• (R1 = R2 = H, [4]•; R1 = H, R2 = Ph, [5]•; R1 = R2 = Ph, [6]•). 相似文献
87.
Francesco Trotta Giancarlo Cravotto Stefano Rossignoli 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):293-296
Oxidative couplings of 2-naphthol, 6-bromo-2-naphthol and2-naphthylamine were achieved at room temperature in the presence of H2O2, horseradish peroxidase and a suitable cyclodextrin.2-Thionaphthol behaved differently, yielding the corresponding disulfide. Yields of binaphthyl derivatives were generally excellent, and a fairly good enantiomeric excess was observed. Under similar reaction conditions methyl 2-(6-methoxy-2-naphthyl) propanoate, when treated with esterase in the presence of cyclodextrin, yielded naproxen (a well-known anti-inflammatory drug) with a good enantiomeric excess. No reaction product was detected in the absence of cyclodextrin. Cyclodextrins do not act as simple transfer agents. 相似文献
88.
Mohammad Hayatifar Claudia Forte Guido Pampaloni Yury V. Kissin Anna Maria Raspolli Galletti Stefano Zacchini 《Journal of polymer science. Part A, Polymer chemistry》2013,51(19):4095-4102
This report describes propylene polymerization reactions with titanium complexes bearing carbamato ligands, Ti(O2CNMe2)Cl2 ( I ) and Ti(O2CR2)4 [R2 = NMe2 ( II ), NEt2 ( III ) and ( IV )]. Combinations of these complexes and MAO form catalysts for the synthesis of atactic polypropylene, as confirmed by FT‐IR, DSC and 13C NMR analysis. Effects of main reaction parameters on the catalyst activity were studied including the type of complex, solvent, temperature, and the [Al]/[Ti] molar ratio. The highest activity was observed when chlorobenzene was used as a solvent and AlMe3‐depleted MAO was employed as a cocatalyst. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4095–4102 相似文献
89.
Barbero M Cadamuro S Cauda F Dughera S Gervasio G Venturello P 《The Journal of organic chemistry》2012,77(9):4278-4287
An initial study has been accomplished into the synthetic feasibility of the preparation of diarylcarbenium salt via the direct coupling of aryl (or heteroaryl) aldehydes and arenes (or heteroaryl analogues) in the presence of a strong organic Br?nsted acid. A number of stabilized aryl or heteroaryl(3-indolyl)carbenium ions, never previously prepared in the solid state, have been isolated in excellent yields as highly stable o-benzenedisulfonimide salts and have been fully characterized. Their purity has been proven by spectroscopic methods and chemical reduction with NaBH(4). An X-ray crystal structure analysis has been performed on one of the products: an azafulvenium species was shown to be the exclusive structure in the solid state. 相似文献
90.
Manca F Giordano S Palla PL Zucca R Cleri F Colombo L 《The Journal of chemical physics》2012,136(15):154906
Stretching experiments on single molecules of arbitrary length opened the way for studying the statistical mechanics of small systems. In many cases in which the thermodynamic limit is not satisfied, different macroscopic boundary conditions, corresponding to different statistical mechanics ensembles, yield different force-displacement curves. We formulate analytical expressions and develop Monte Carlo simulations to quantitatively evaluate the difference between the Helmholtz and the Gibbs ensembles for a wide range of polymer models of biological relevance. We consider generalizations of the freely jointed chain and of the worm-like chain models with extensible bonds. In all cases we show that the convergence to the thermodynamic limit upon increasing contour length is described by a suitable power law and a specific scaling exponent, characteristic of each model. 相似文献