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81.
The use of phase sensitive alternating current polarography (ACP) for the evaluation of complex formation constants of systems where electrodic adsorption is present has been proposed. The applicability of the technique implies the previous selection of the phase angle where contribution of capacitive current is minimized. This is made using Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) in the analysis of ACP measurements at different phase angles. The method is checked by the study of the complexation of Cd by polymethacrylic (PMA) and polygalacturonic (PGA) acids, and the optimal phase angles have been ca. −10° for Cd-PMA and ca. −15° for Cd-PGA systems. The goodness of phase sensitive ACP has been demonstrated comparing the determined complex formation constants with those obtained by reverse pulse polarography, a technique that minimizes the electrode adsorption effects on the measured currents. 相似文献
82.
Bertosa B Kojić-Prodić B Wade RC Ramek M Piperaki S Tsantili-Kakoulidou A Tomić S 《Journal of chemical information and computer sciences》2003,43(5):1532-1541
The activity of a biological compound is dependent both on specific binding to a target receptor and its ADME (Absorption, Distribution, Metabolism, Excretion) properties. A challenge to predict biological activity is to consider both contributions simultaneously in deriving quantitative models. We present a novel approach to derive QSAR models combining similarity analysis of molecular interaction fields (MIFs) with prediction of logP and/or logD. This new classification method is applied to a set of about 100 compounds related to the auxin plant hormone. The classification based on similarity of their interaction fields is more successful for the indole than the phenoxy compounds. The classification of the phenoxy compounds is however improved by taking into account the influence of the logP and/or the logD values on biological activity. With the new combined method, the majority (8 out of 10) of the previously misclassified derivatives of phenoxy acetic acid are classified in accord with their bioassays. The recently determined crystal structure of the auxin-binding protein 1 (ABP1) enabled validation of our approach. The results of docking a few auxin related compounds with different biological activity to ABP1 correlate well with the classification based on similarity of MIFs only. Biological activity is, however, better predicted by a combined similarity of MIFs + logP/logD approach. 相似文献
83.
Highly reliable and accurate analytical methods are needed for the determination of magnetic resonance imaging (MRI) contrast agents in complex matrices of clinical interest. We demonstrate the reliability of capillary zone electrophoresis (CZE) coupled with electrospray ionization-mass spectrometry (ESI-MS) for the analysis of MultiHance (gadobenate dimeglumine), a gadolinium-based MRI agent. A sheath liquid interface connected the CE system with an electrospray mass spectrometer equipped with an ion-trap analyzer. CZE with ultraviolet (CZE-UV) and with mass detection (CZE-MS) were compared by analyzing gadobenate dimeglumine and the free ligand diluted in water and in biological fluids (i.e., human serum and urine). The optimization of some relevant CZE-MS parameters was accomplished, like CE buffer composition, sheath liquid composition and flow, and type and length of the separation capillary. CZE-UV was highly influenced by the biological sample components, which hindered a reliable quantification of both gadobenate and free ligand in serum and urine. In CZE-MS, on the other hand, the electrophoretic runs turned out to be independent of the clinical matrices, due to the informative potential and to the selectivity of MS detection. 相似文献
84.
Johansson A Håkansson M Jagner S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(18):5311-5318
Stereochemically labile copper and zinc complexes with the N,N'-dimethylethylenediamine ligand (dmeda) have been shown to be promising precursors for the total spontaneous resolution of chiral covalent networks. (N,N')-[Cu(NO3)2(dmeda)]infinity crystallises as a conglomerate and yields either enantiopure (R,R)-1 or enantiopure (S,S)-1. A mixed-valence copper(I/II) complex, [{Cu(II)Br2(dmeda)}3(Cu(I)Br)2]infinity (2), which crystallises as a pair of interpenetrating chiral (10,3)-a nets, is formed from CuBr, CuBr2 and dmeda. One net contains ligands with solely (R,R) configuration and exhibits helices with (P) configuration while the other has solely (S,S)-dmeda ligands and gives rise to a net in which the helices have (M) configuration. The whole crystalline arrangement is racemic, because the interpenetrating chiral nets are of opposite handedness. With zinc chloride (R,S)-[ZnCl(dmeda)2]2[ZnCl4] (3) is obtained, which is a network structure, although not chiral. Total spontaneous resolution of stereochemically labile metal complexes formed from achiral or racemic building blocks is suggested as a viable route for the preparation of covalent chiral networks. Once the absolute structure of the compound has been determined by X-ray crystallography, a quantitative determination of the enantiomeric excess of the bulk product can be undertaken by means of solid-state CD spectroscopy. 相似文献
85.
Kim IB Dunkhorst A Bunz UH 《Langmuir : the ACS journal of surfaces and colloids》2005,21(17):7985-7989
Two carboxylate-substituted, fluorescent (Phi = 0.08), water-soluble poly(p-phenyleneethynylene)s (PPE) and a water-soluble model compound were exposed to a series of proteins and bovine serum. While the anionic PPEs do not have any specific binding sites, they form stable complexes with histone, lysozyme, myoglobin, and hemoglobin. The complex formation was evidenced by fluorescence quenching. Bovine serum albumin does not quench the fluorescence of the PPEs but enhances it, probably due to its surfactant character. These results imply that the use of charged conjugated polymers as biosensors, while an attractive proposition, has to take into account strong nonspecific interactions between conjugated polymers and the host of proteins that is found in cells and complex biological fluids. 相似文献
86.
Norbert Klempier Anna De Raadt Herfried Griengl Gottfried Heinisch 《Journal of heterocyclic chemistry》1992,29(1):93-95
Chemoselective hydrolysis of heterocyclic nitriles can be achieved by an easy to use immobilized biocatalyst prepared from Rhodococcus sp. Pyrimidine-2-carbonitrile ( 2a ) and 3-chloropyridazine-4-carbonitrile ( 4a ) were converted into the corresponding amides while from 2-ethoxycarbonyl-4-pyridinecarbonitrile ( 1a ), 6-methylpyridazine-3-carbonitrile ( 3a ), 3-chloropyridazine-4-carbonitrile ( 4a ), 3-ethoxycarbonyl-4,5-dihydroisoxazole-5-carbonitrile ( 8a ), indole-3-carbonitrile ( 9a ) and indole-3-ylacetonitrile ( 10a ) the acids were formed. 相似文献
87.
Anna Painelli Francesca Terenziani Zoltán G. Soos 《Theoretical chemistry accounts》2007,117(5-6):915-931
We discuss electron-transfer processes that govern the physics of several materials or systems of interest for advanced applications.
The discussion touches upon several topics, ranging from solvatochromism to solvent-induced symmetry breaking, from excitonic
to cooperative effects in molecular crystals, from phase transitions to vibrational contributions to the dielectric constant
in organic materials, from spectroscopy to molecular transport. In all these diverse systems electron transfer (ET) plays
a major role and is discussed with reference to simple models for delocalized charges. 相似文献
88.
Sek S Tolak A Misicka A Palys B Bilewicz R 《The journal of physical chemistry. B》2005,109(39):18433-18438
Polyalanine derivatives containing cysteamine linker R-(Ala)14NH-(CH2)2-SH, where R is ferrocenecarbonyl or hydrogen, were synthesized and then used to form self-assembled monolayers on gold. The tilt angles and the packing density of the molecules within monolayer assemblies were determined by FTIR spectroscopy and scanning tunneling microscopy, respectively. Electrochemical properties of monolayer-modified electrodes were studied using cyclic voltammetry and impedance spectroscopy. Measurements of electron-transfer rates using electrochemical techniques and scanning tunneling spectroscopy revealed asymmetry dependent on the applied voltage. It is suggested that the observed electron-transfer behavior is connected with the electric field generated by the molecular dipole of the polyalanine helix. 相似文献
89.
The ferric ion binding characteristics of a novel chelating probe for detecting reactive oxygen and nitrogen species are reported. The probe comprises a polyaminocarboxylic acid chelator (EDTA) conjugated with aromatic amino acids. The probe (i) complexes redox-active and non-redox active metal ions and (ii) differentiates between different reactive oxygen/nitrogen species based upon the reaction products with same. The ferric ion binding characteristics were measured using species distribution and electronic absorption spectroscopic investigations. Over the physiological pH range a favoured one to one complex exists. 相似文献
90.
Eneyskaya EV Ivanen DR Shabalin KA Kulminskaya AA Backinowsky LV Brumer Iii H Neustroev KN 《Organic & biomolecular chemistry》2005,3(1):146-151
Transglycosylation catalyzed by a beta-D-xylosidase from Aspergillus sp. was used to synthesize a set of 4-methylumbelliferyl (MU) beta-1-->4-D-xylooligosides having the common structure [beta-D-Xyl-(1-->4)]2-5-beta-D-Xyl-MU. MU xylobioside synthesized chemically by the condensation of protected MU beta-D-xylopyranoside with ethyl 2,3,4-tri-O-acetyl-1-thio-beta-D-xylopyranoside was used as a substrate for transglycosylation with the beta-D-xylosidase from Aspergillus sp. to produce higher MU xylooligosides. The structures of oligosaccharides obtained were established by 1H and 13C NMR spectroscopy and electrospray tandem mass spectrometry. MU beta-D-xylooligosides synthesized were tested as fluorogenic substrates for the GH-10 family beta-D-xylanase from Aspergillus orizae and the GH-11 family beta-D-xylanase I from Trichoderma reesei. Both xylanases released the aglycone from MU xylobioside and the corresponding trioside. With substrates having d.p. 4 and 5, the enzymes manifested endolytic activities, splitting off MU, MUX, and MUX2 primarily. 相似文献