Magnetic circular dichroism of heterocycles: thiophene

The existence of two transitions with opposite MCD in the 38000–45000 cm^?1 absorption of thiophene is demonstrated. The B-term for the lowest transition is negative, while it is positive for the higher one. Quantum mechanical calculations in the π-electron approximation resulted in energies, oscillator strengths and MCD terms in good agreement with the observed spectra.     

Simultaneous determination of ondansetron and tropisetron in human plasma using HPLC with UV detection

A rapid and sensitive HPLC method for the simultaneous quantitation of ondansetron and tropisetron, two serotonin (5-HT) receptor antagonists frequently used in treatment and prevention of nausea and emesis, is described. The procedure involves liquid-liquid extraction of human plasma with dichloromethane coupled with reversed-phase HPLC and UV detection. The lower limits of quantification (LOQ) were 0.62 ng/mL for ondansetron and 1.25 ng/mL or tropisetron. Intra- and inter-assay coefficients of variation ranged from 1.5 to 7.5% and 5.3 to 13.7%, respectively. The sensitivity and precision were sufficient for determination of plasma concentrations after therapeutic administration of both drugs and the method can be used for the estimation of pharmacokinetic parameters.     

Propene polymerization using homogeneous MAO-activated metallocene catalysts: Me2Si(Benz[e]Indenyl)2ZrCl2/MAO vs. Me2Si(2-Me-Benz[e]Indenyl)2ZrCl2/MAO

Propene was polymerized at 40°C and 2-bar propene in toluene using methylalumoxane (MAO) activated rac-Me₂Si(Benz[e]Indenyl)₂ZrCl₂ ( BI ) and rac-Me₂Si(2-Me-Benz[e]Indenyl)₂ZrCl₂ ( MBI ). Catalyst BI /MAO polymerizes propene with high activity to afford low molecular weight polypropylene, whereas MBI /MAO is less active and produces high molecular weight polypropylene. Variation of reaction conditions such as propene concentration, temperature, concentration of catalyst components, and addition of hydrogen reveals that the lower molecular weight polypropylene produced with BI /MAO results from chain transfer to propene monomer following a 2,1-insertion. A large fraction of both metallocene catalyst systems is deactivated upon 2,1-insertion. Such dormant sites can be reactivated by H₂-addition, which affords active metallocene hydrides. This effect of H₂-addition is reflected by a decreasing content of head-to-head enchainment and the formation of polypropylene with n-butyl end groups. Both catalysts show a strong dependence of activity on propene concentration that indicates a formal reaction order of 1.7 with respect to propene. MBI /MAO shows a much higher dependence of the activity on temperature than BI /MAO. At elevated temperatures, MBI /MAO polymerizes propene faster than BI /MAO. © 1995 John Wiley & Sons, Inc.     

Rapid determination of microorganisms using a flow-injection system

An automated method for the rapid determination of microorganisms using a flow-injection system is presented. Electrochemical measurement of a mediator reduced by microbial metabolism allowed the determination of fungi and bacteria in a few minutes. The lowest detection limit was 5 × 10⁶ colony-forming units (cfu) ml^?1 for Escherichia coli. Correlation between the flow-injection method and standard microbiological methods was excellent (r = 0.997, n = 4 for Beauveria bassiana; r = 0.997, n = 7 for E. coli). The flow-injection system was applied to the on-line control of an E. coli cultivation.     

Analysis of proteins from a glioma cell line by using micro-scale solution isoelectric focusing in combination with liquid chromatography/tandem mass spectrometry

In this study we have investigated whether micro-solution isoelectric focusing (microsol-IEF) can be used as a pre-fractionation step prior to liquid chromatography/tandem mass spectrometry (LC/MS/MS) and if extensive sample purification of the different fractions is required. We found that, in spite of the high concentrations of buffer and detergents, no clean up of the digested microsol-IEF fractions was necessary before analysis by LC/MS/MS. We also concluded that it is possible to identify at least twice as many proteins in a glioma cell lysate with the combination of microsol-IEF and LC/MS/MS than with LC/MS/MS alone. Furthermore, most of the proteins that were identified from one microsol-IEF fraction by using analytical narrow-range two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and peptide mass fingerprinting with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) were also identified by LC/MS/MS. Finally, we used the combination of microsol-IEF and LC/MS/MS to compare two sample preparation methods for glioma cells and found that several nuclear, mitochondria, and endoplasmic reticulum proteins were only present in the sample that had been subjected to lipid extraction by incubating the homogenized cells in chloroform/methanol/water.     

EARLY CELL KINETIC EFECTS OF A SINGLE DOSE OF NARROW-BANDED ULTRAVIOLET B IRRADIATION ON THE RAT CORNEAL EPITHELUM

Abstract— The right eyes of 40 rats were exposed to a signal erythemogenic dose fo ultraviolet B irradiation (UVB) at 297nm. The irradiation was directed perpenddicualr to the center of the cornea. The left eyes served as controls. The animals were randomly assigned into 10 groups. The labelling index (LI) after pluse labeling the tritiated thymidine and the mitotic rate (MR) after Colcemid administration were registered in the corneal epithelium at predetermined intervals up to 96 h after the irradiation. A mathematical method was used to corealted corresponding corneal areas from the different animals. In the central the LI was considerably reduced up to 36h after the irradiation. The LI increased toward the peripheral cornea and reached normal values at the limbal area. The MR was also reduced up to 36h. However, this reduction was over the entire epithelium. The block in cell proliferation was followed by increased proliferation.     

Metal- and ligand-directed one-pot syntheses,crystal structures,and properties of novel oxo-centered tetra- and hexametallic clusters

Starting from closely related metal-ligand combinations, completely different oligomeric metal clusters are synthesized. Whereas, picoline-tetrazolylamide HL(1) (1) and zinc or nickel acetate afforded [2x2] grids [M(4)(L(1))(8)] (2), slightly different N-(2-methylthiazole-5-yl)-thiazole-2-carboxamide HL(2) (5 a) and nickel acetate yielded the monometallic complex [Ni(L(2))(2)(OH(2))(2)] (6). In contrast, reaction of 5 a with zinc acetate produced the tetrametallic zinc cluster [Zn(4)O(L(2))(4)(OAc)(2)] (7). Even more surprising, when 3-methyl-substituted HL(3) (5 b) instead of 2-methyl-substituted HL(2) (5 a) was allowed to react under identical conditions with zinc acetate, the cluster [Zn(4)O(L(3))(4)Cl(2)] (8) crystallized from dichloromethane. Clusters 7 and 8 are isostructural. As for 7, in 8 two of the edges of the tetrahedron of zinc ions are doubly bridged, two are singly bridged, and the other two are nonbridged. On the other hand, when iron(II) acetate under aerobic conditions was allowed to react with 5 a, the unprecedented complex [[Fe(3)O(L(2))(2)(OAc)(4)](2)O] (9) was isolated. Cluster 9 is composed of two trimetallic, triangular mu(3)-O(2-)-centered [Fe(3)O(L(2))(2)(OAc)(4)](+) modules, linked by an almost linear mu(2)-O(2-) bridge. The M?ssbauer spectrum together with cyclic voltammetric and square-wave voltammetric measurements of 9 are reported, and 6-9 were characterized unequivocally by single-crystal X-ray structure analyses.     

Aurophilicity-coordination interplay in the design of cyano-bridged nickel(II)-Gold(I) bimetallic assemblies: structural and computational studies of the gold(I)-gold(I) interactions

Two polymorphic cyano-bridged Au(I)-Ni(II) bimetallic complexes of formulas [Ni(en)2Au(CN)2][Au(CN)2] (1) and [Ni(en)2[Au(CN)2]2] (2) have been prepared from the 1:2 reaction between [Au(CN)2]- and either [Ni(en)2Cl2]Cl or [Ni(en)3]Cl2.2H2O, respectively. The structure of 1 consists of polymeric cationic chains of alternating [Au(CN)2]- and [Ni(en)2]2+ units running along the a axis and [Au(CN)2]- anions lying between the chains. The noncoordinated dicyanoaurate anions are aligned perpendicular to the ac plane and involved in aurophilic interactions with the bridging dicyanoaurate groups, ultimately leading to a 2D bimetallic grid. The structure of 2 consists of trinuclear molecules made of two [Au(CN)2]- anions linked to [Ni(en)2]2+ unit in trans configuration. Trinuclear units are joined by aurophilic interactions to form 1D zigzag chains. The magnetic properties of these compounds are strongly dominated by the local anisotropy of the octahedral Ni(II) ions, thus indicating that the magnetic exchange interaction mediated by dicyanoaurate bridging groups, if it exists, is very weak. To get insight into the electronic properties of the inter- and intramolecular interactions of the [Au(CN)2]- building blocks, the structures of different aggregates of dicyanogold units were optimized and then analyzed by making use of atoms-in-molecules (AIM) theory. Moreover, bond indices were calculated by methods based upon nonlinear population analysis.