摘要:

AbstractThe monomer‐dimer self‐association of 3‐ethyl‐2‐methyl‐pentanol in CCl4at four different temperatures has been studied using IR spectroscopy. The spectral band of the OH fundamental stretching for a free monomer and that for a hydrogen‐bonded dimer were resolved, and their respective integrated absorbances were calculated. The integrated absorbances of the monomer band for various concentrations at a given temperature were then employed based on Eq. 9 to obtain the molar absorptivity of the monomer band and the dimerization constant at that temperature. Similarly, those of the dimer band were employed based on Eq. 13 to determine the molar absorptivity of the dimer band and the dimerization constant at that temperature. Since the same dimerization constant can be determined independently either from the monomer band or from the dimer band, the discrepancy between the two determined values can serve as a criterion of the goodness of the determination. The standard enthalpy and entropy of the dimerization were also obtained from a van't Hoff plot for dimerization constants at different

ISSN:0009-4536    

DOI:10.1002/jccs.200400133

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY

摘要:

AbstractIn this study, two structural models (denoted as MproST and MproSH) of the main proteinase (Mpro) from the novel coronavirus associated with severe acute respiratory syndrome (SARS‐CoV) were constructed based on the crystallographic structures of Mprofrom transmissible gastroenteritis coronavirus (TGEV) (MproT) and human coronavirus HcoV‐229E (MproH), respectively. Various 200 ps molecular dynamics simulations were subsequently performed to investigate the dynamics behaviors of several structural features. Both MproST and MproSH exhibit similar folds as their respective template proteins. These structural models reveal three distinct functional domains as well as an intervening loop connecting domains II and III as found in both template proteins. In addition, domain III of these structures exhibits the least secondary structural conservation. A catalytic cleft containing the substrate binding subsites S1 and the S2 between domains I and II are also observed in these structural models. Although these structures share many common features, the most significant difference occurs at the S2 subsite, where the amino acid residues lining up this subsite are least conserved. It may be a critical challenge for designing anti‐SARS drugs by simply screening the known database of proteinase inhib

ISSN:0009-4536    

DOI:10.1002/jccs.200400134

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY

摘要:

AbstractA series of biologically active mononuclear complexes of Cu(II), Ni(II), Zn(II), and Fe(III) were prepared. The reactions of the Schiff base ligand 1‐phenyl‐2,3‐dimethyl‐4‐salicylalidene pyrazole‐5‐one, (HL), with the previous metals in the presence of LiOH as a deprotonating agent, yielded different types of complexes. The binary complexes react with the mixed ligands 2‐aminopyridine (2‐ampy), 8‐hydroxyquinoline (8‐OHqu) and Oxalic acid (Ox) to form the mixed ligand complexes. All the binary and mixed ligand complexes have octahedral configurations. The Schiff base ligand (HL) is coordinated to the central metal as monoanionic terdentate ONO ligand. Thermal studies explored the possibility of obtaining new complexes, which can not be prepared from solutions. Five coordinate Ni(II) and Zn(II) complexes were prepared pyrolytically. Also, the binuclear Fe(III) complex was prepared through the thermal transformation of its mononuclear complex to the binuclear one. All complexes and the corresponding thermal products were isolated and their structures were elucidated by elemental analyses, conductance, IR and electronic absorption spectra, magnetic moments,1H NMR and TG‐DSC measurements. The free ligand (HL) and its metal complexes showed higher antibacterial effects than that of some i

ISSN:0009-4536    

DOI:10.1002/jccs.200400135

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY

摘要:

AbstractThe method for measuring SmI2reduction rates is expanded to a wider range of organic compounds by using not only GC or GC/MS, but also HPLC as the detecting tool. The reduced substrates are not only confined to water insoluble compounds or low boiling compounds only. Water soluble cinnamic acid derivatives of high boiling points are chosen for this application.The absolute rate constants of SmI2reduction of cinnamic acid in the presence of hexamethylphosphoramide ort‐butanol is considered as a suitable proton source in this reaction. The rates are dependent on substrates and additives as:Rate ∞ [t‐BuOH][Cinnamic acid]and Rate ∞ [HMPA][Cinnamic acid]The reduction rates of α‐methylcinnamic acid, 2‐methylcinnamic acid, 4‐methylcinnamic acid, 2‐methoxycinnamic acid, 3‐methoxycinnamic acid, 4‐methoxycinnamic acid, 2‐hydroxycinnamic acid, 3‐hydroxycinnamic acid, 4‐hydroxycinnamic acid, 2‐chlorocinnamic acid, 3‐chlorocinnamic acid, 4‐chlorocinnamic acid were carefully measured

ISSN:0009-4536    

DOI:10.1002/jccs.200400136

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY

摘要:

AbstractThe complexation reactions between Mg2+, Ca2+, Sr2+and Ba2+cations with macrocyclic ligand, dibenzo‐24‐crown‐8 (DB24C8) were studied in acetonitrile‐dimethylformamide (AN‐DMF) binary mixtures at different temperatures using the conductometry method. In all cases, DB24C8 forms 1:1 complexes with these cations. The values of stability constants of complexes which were obtained from conductometric data, show that the stability of complexes is affected by the nature and composition of the solvent. In many cases, the stability constants of complexes in these solvent systems increase with increasing the concentration of acetonitrile which has a lower donor number than dimethylformamide. However, in the case of complex formation between Mg2+and Sr2+cations with DB24C8, an anomalous behaviour was observed for the stability constants (LogKf) with increasing the mole fraction of acetonitrile in AN‐DMF binary mixtures at all temperatures. A non‐linear behaviour was observed for variation of LogKfof the metal ion complexes vs the composition of the mixed solvents. This behaviour may be related to heteroselective solvation of cations and also solvent‐solvent interactions in these binary systems. The obtained results show that the order of selectivity of DB24C8 ligand for the metal cations in different concentrations of acetonitrile in AN‐DMF binary systems is: Ba2+>Sr2+>Ca2+>Mg2+, but a reversal in selectivity is observed in a certain composition of the mixed solvents. The values of thermodynamic parameters (ΔH°cand ΔS°c) for formation of complexes were obtained from temperature dependence of stability constants of complexes using the van't Hoff plots. The results show that in most cases, the complexation reactions are enthalpy destabilized but entropy stabilized, and the values of these thermodynamic parameters are influenced by the nature and composition

ISSN:0009-4536    

DOI:10.1002/jccs.200400137

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY

摘要:

AbstractSynthesis and characterization of some novel di and tri‐benzyl tin(IV) complexes of some Schiff bases are reported. The1H‐NMR,13C‐NMR,119Sn‐NMR, IR, Elemental Analysis and119Sn Mössauber studies are made for structural determination. Spectroscopic data reveals that the ligand molecule is bound to the tin atom through oxygen. On the basis of spectroscopic data tetrahedral geometry is proposed for the synthesized compounds. The synthesized compounds have been tested against various microorganisms. The results obtained show that the synthesized compounds have promising activity against all the tested micro

ISSN:0009-4536    

DOI:10.1002/jccs.200400138

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY

摘要:

AbstractThe combination of ultrasonic vibratory beam and gas chromatography‐mass spectrometry techniques was used to produce monomers of new organo‐multi‐silicon coating materials. The reactants of these materials were exposed to high passive conditions through all the experimental phase. By the aid of a capillary column, RTX‐5MS, and an EI detector of the Finnigan‐Mat GC, a sample was analyzed on the basis of the rules of the predominant M‐1(s) ions of the main chromatographic pattern. Fragmentation analysis of the high resolution mass spectrometry patterns led to detection of three new compound structures, designated A, B, and C isomers. These isomers were identified by the differences between their retention times. The mechanistic root for each of the three isomers is fully discussed herein by a process of stepped number of cleavages p

ISSN:0009-4536    

DOI:10.1002/jccs.200400139

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY

摘要:

AbstractWe describe a method for controlled preparation of nanostructural ZrO2‐coated SiO2particles by layer‐by‐layer assembly technique. ZrO2colloids were synthesized by the sol‐gel method. The samples were characterized by FIIR, DTA‐TG, SEM, EDS, XPS and XRD techniques. The experimental results show that ZrO2nanopowders on the surface of SiO2particles are well distributed and compact; the amount of ZrO2is increased with adding coating layers; the structure of this coating is tetrago

ISSN:0009-4536    

DOI:10.1002/jccs.200400140

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY

摘要:

AbstractA new simple and sensitive spectrophotometric method for the determination of nicotine is described. The method is based on the bromination of nicotine to form dibromonicotine which reacts with potassium iodide to liberate iodine. The iodine liberated then selectively oxidizes leuco crystal violet, and the crystal violet dye formed shows maximum absorbance at 592 nm. Beer's law is obeyed over the concentration range 0.2 μg–2.2 μg of nicotine in a final solution volume of 25 mL (0.008–0.088 ppm). The molar absorptivity of the colour system is 1.40 × 1061 mol−1cm−1. The method is free from the interference of other major toxicants. The various analytical parameters were optimized, and the method was applied for the determination of nicotine in cigarette smoke, food, and biologic

ISSN:0009-4536    

DOI:10.1002/jccs.200400141

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY

摘要:

AbstractThe solid‐phase microextraction (SPME) technique using a 100 μm film poly(dimethylsiloxane) (PDMS) has been examined with the aim to determine butachlor in aqueous samples. The feasibility of SPME gas chromatography‐electron capture detection (GC‐ECD) analysis has been evaluated. From this study the equilibrium distribution constant between PDMS coating and water for butachlor obtained was 1.9 × 103with a 5.3% RSD. Extraction time of 40 min, desorption time of 3 min and desorption temperature of 250 °C were selected. The effect of salt addition was examined. The inhibitions of methanol and humic acid to the extraction of butachlor were observed. A standard addition method for calibration was recommended to reduce the deviation from matrix interference. Linear ranges from 0.1 to 12 μg/L and limits of detection of 0.007 μg/L for deionized water, 0.010 μg/L for ground water, and 0.016 μg/L for irrigated water were obtained. The proposed method was applied to determine butachlor in irrigated water. The degradation of butachlor in aqueous solution under the irradiation of 253.7 nm light has been measured by the developed SPME‐GC‐ECD procedure. The half‐life of the aqueous butachlor fou

ISSN:0009-4536    

DOI:10.1002/jccs.200400142

出版商:WILEY‐VCH Verlag    

年代:2004

数据来源: WILEY