Ab initio calculations of electrostatic potentials and deformation densities for a series of choline ester model systems

Ab initio LCAO-MO-SCF calculations using a double zeta basis set have been performed for the methyl esters of acetic acid, carbamic acid, methylcarbonic acid, and trifluoracetic acid, in order to model the corresponding choline esters. The systems have been compared by means of population analyses, electron density differences, electrostatic potentials and potential differences. The significance of the electrostatic potential in connection with crystal structure and packing has been studied. The differences in the proton affinity of the compounds have been correlated to differences in the potentials.     

Synthesis of aryl- and heteroaryl-substituted 3-benzyloxyisothiazoles via Suzuki and Negishi cross-coupling reactions

Introduction of aryl and heteroaryl substituents into the 5-position of 3-benzyloxyisothiazole (1) using palladium-catalyzed Suzuki and Negishi cross-coupling reactions was investigated. Attempts to generate synthetically viable nucleophilic species from 1 for Suzuki- or Negishi-type cross-couplings were unsuccessful. However, using 3-benzyloxy-5-iodoisothiazole 2 as an intermediate, a range of aromatic and heteroaromatic substituents were successfully introduced under Suzuki or Negishi cross-coupling conditions in good to excellent yields.     

XANTHENE DYES AS SENSITIZERS FOR THE PHOTOREDUCTION OF WATER

Abstract— Some photochemical and photophysical properties of a group of xanthene dyes have been studied in relation to their roles as sensitizers for the photoreduction of water. New spectroscopic and kinetic measurements have been carried out with these dyes. The triplet states of the dyes undergo energy-transfer and electron-transfer, but with rate constants differing by two orders of magnitude in favour of the former pathway. The very efficient transfer of triplet energy from a group of dyes to an acceptor molecule led to the design of a greatly improved system for the photochemical production of hydrogen.     

Determination of trace elements in biological materials by neutron activation and extraction with TOPO

Solvent extraction with TOPO from 6M hydrochloric acid is proposed as a method for the elimination of interfering activities in neutron activation analysis of biological material for trace elements. By this procedure²⁴Na,⁴²K,³²P,⁸²Br, and⁴⁷Ca are efficiently removed, and a number of trace element activities can be measured by Ge(Li) spectrometry. Chemical yields are determined by re-activation. Data for Cu, Zn, Mo, and Cd in two biological standards are presented.     

Determination of methyldibromoglutaronitrile in cosmetic products by high-performance liquid chromatography with electrochemical detection. Method validation

An increased frequency of contact allergy to methyldibromoglutaronitrile (MDBGN), a commonly used preservative in cosmetics and other consumer products, has been reported in recent years. A high-performance liquid chromatography (HPLC) method for the determination of MDBGN in cosmetic products has been validated in the present study. The identification is performed by reductive electrochemical detection of the bromine present in the molecule. The method is suitable for compliance testing of cosmetic products as well as for the research to support clinical and epidemiological studies.     

Evolution of a hotspot in a thin BSCCO structured film

Two voltage jumps were found in the current–voltage characteristic of a thin superconducting film of Bi₂Sr₂CaCu₂O_x at temperature 58 K. The fluorescent thermal imaging technique revealed a localized heat dissipation (hotspot) nucleated at the current causing the second jump, and the hotspots’ temperature is close to the critical temperature of the superconducting film.     

The propagation of magnetostatic surface waves in ferrite/superconductor structures

An electrodynamic model that describes the dispersion of magnetostatic surface waves in ferrite/superconductor structures is suggested. On its basis, a new approach to determining the microwave sheet resistance R _S of superconducting films in a magnetic field is elaborated. The values calculated (R _S =0.20–0.96 mΩ) agree with results obtained by the Tauber method. For YIG/YBCO structures, the controllable phase shift is about 1.5π when the depth of magnetostatic wave penetration into the YBCO film varies from 2.0 to 0.8 μm.     

New evidence of earthquake precursory phenomena in the 17 January 1995 Kobe earthquake, Japan

Significant advances, both in the theoretical understanding of rupture processes in heterogeneous media and in the methodology for characterizing critical behavior, allows us to reanalyze the evidence for criticality and especially log-periodicity in the previously reported chemical anomalies that preceded the Kobe earthquake. The ion (Cl^-, K⁺, Mg⁺⁺, NO₃ ^- and SO₄ ^-) concentrations of ground-water issued from deep wells located near the epicenter of the 1995 Kobe earthquake are taken as proxies for the cumulative damage preceding the earthquake. Using both a parametric and non-parametric analysis, the five data sets are compared extensively to synthetic time series. The null-hypothesis that the patterns documented on these times series result from noise decorating a simple power law is rejected with a very high confidence level. Received 21 January 2000     

Review of secondary metabolites and mycotoxins from the <Emphasis Type="Italic">Aspergillus niger</Emphasis> group

Filamentous fungi in the Aspergillus section Nigri (the black aspergilli) represent some of the most widespread food and feed contaminants known but they are also some of the most important workhorses used by the biotechnological industry. The Nigri section consists of six commonly found species (excluding A. aculeatus and its close relatives) from which currently 145 different secondary metabolites have been isolated and/or detected. From a human and animal safety point of view, the mycotoxins ochratoxin A (from A. carbonarius and less frequently A. niger) and fumonisin B₂ (from A. niger) are currently the most problematic compounds. Especially in foods and feeds such as coffee, nuts, dried fruits, and grape-based products where fumonisin-producing fusaria are not a problem, fumonisins pose a risk. Moreover, compounds such as malformins, naptho-γ-pyrones, and bicoumarins (kotanins) call for monitoring in food, feed, and biotechnology products as well as for a better toxicological evaluation, since they are often produced in large amounts by the black aspergilli. For chemical differentiation/identification of the less toxic species the diketopiperazine asperazine can be used as a positive marker since it is consistently produced by A. tubingensis (177 of 177 strains tested) and A. acidus (47 of 47 strains tested) but never by A. niger (140 strains tested). Naptho-γ-pyrones are the compounds produced in the highest quantities and are produced by all six common species in the group (A. niger 134 of 140; A. tubingensis 169 of 177; A. acidus 44 of 47; A. carbonarius 40 of 40, A. brasiliensis 18 of 18; and A. ibericus three of three).