Automatic polarographic elucidation of electrode mechanisms by means of a knowledge-based system : Part 1. Sampled d.c. polarography

A knowledge-based system has been developed for the automatic elucidation of electrochemical mechanisms. The system is based on sampled direct current (or Tast) polarography at a dropping mercury electrode as a technique for collecting experimental information and consists of a general expert system shell for the reasoning process, the specific set of rules and experimental modules. The set of rules allows the elucidation of eight relatively simple electrode reaction mechanisms fully atomatically. The computer system has been validated with chemical systems the electrochemical behaviour of which is well established. All parts of the program are written in FORTH language for Apple II microcomputers. This expert system has an open character and new rules can be added to extend the set of mechanisms that can be determined.     

The coulometric titration of acids and bases in dimethylsulfoxide media

The coulometric titration of 20–200 μeq of acids and bases in DMSO media is described. In the titration of bases, the electro-oxidation of hydrogen at a platinized platinum electrode is used as the source of protons. The conditions for 100 % current efficiency at this electrode are low current density to avoid passivity and regular treatment of the electrode with potassium dichromate—sulfuric acid to remove a poisoning sulfide layer. The accuracy of the titrations is better than ±1 %. Very weak acids like phenols (pK_a (DMSO) ≈16) can be titrated successfully. Tris(hydroxymethyl)aminomethane is the weakest base titrated.     

A knowledge-based system for the automatic chronopotentiometric elucidation of electrode reaction mechanisms

A knowledge-based system for the elucidation of electrode reaction mechanisms based on chronopotentiometric experiments is described. The system runs the diagnostic experiments and uses the results in the reasoning process. New mechanistic knowledge can be added directly to its knowledge base in the form of production rules. The system is fully modular and its domain- specific modules can easily be changed for application to other electrochemical techniques. Correct operation of the system is demonstrated with the familiar reduction mechanisms of cadmium (II), zinc (II), cystamine and cinnamaldehyde.     

Method of Determination of 9-(Alkylthio)Acridines in Urine by Capillary Liquid Chromatography

Reversed-phase capillary liquid chromatography was applied for quantification of thioderivatives of acridine. Ten 9-(alkylthio)acridines, three containing and seven lacking amino groups, were analyzed on Nucleosil C₁₈ with acetonitrile-water-triethylamine (90.0:9.0:1.0, v/v/v) mixture as the mobile phase. The presence of triethylamine in the eluent greatly improved the peak shape and markedly shortened the analysis time. Calibration curves of all the studied acridine derivatives were measured over a concentration range of 1.0·10^?6 – 1.0·10^?3 mol. L^?1 at two parallel detection wavelengths, 265 and 270 nm. Detection and quantification limits were evaluated for all the derivatives. The detection limits were in the region of μmol. L^?1 for most of the thioacridines. The calibration curves were used for quantification of the derivatives in human urine. No pretreatment of the real biological samples was necessary. The optimized CLC method enabled a good separation of the individual thioacridines from other compounds present in human urine samples and their quantification in a reasonable analysis time.     

Two calculation procedures for the determination of composition and mass thickness of thin samples by x-ray spectrometry

Two procedures are described for calculating the composition and mass thickness of thin samples from measured x-ray intensities. One procedure is suitable for use with a programmable hand calculator but gives correct results only for very thin samples. The other procedure utilizes the NRLXRF program and produces correct results for thin and thick films.     

The influence of morphology on the (hydrolytic degradation of as-polymerized and hot-drawn poly(L-lactide))

 The influence of morpho-logy on the hydrolytic degradation behavior of poly(L-lactide) has been studied. High molecular weight and highly crystalline as-polymerized poly(L-lactide) was obtained in high yields through melt polymerization. Poly(L-lactide) fiber with a draw ratio of 5.6 was obtained by hot-drawing solution-spun fiber. During the bulk degradation of as-polymerized poly(L-lactide), a rapid decrease of molecular weight and tensile properties was observed. This could be explained by the morphology of the material and the presence of thermal stresses and subsequent generation of micro-cracks. The lamellar crystallites in as-polymerized poly(L-lactide) appeared to be very stable towards hydrolysis. The resorption time of high molecular weight as-polymerized poly(L-lactide) in vivo was estimated at 40–50 yr by extrapolation of molecular weight data. Hot-drawn poly(L-lactide) fiber showed exceptional hydrolytic stability under a static load and substantially retained its mechanical properties over a period of more than 5 yr. The high perfection of the crystalline fiber and the elimination of micro-voids obtained by hot-drawing prevented penetration of water and induced surface erosion of the fiber. Received: 10 February 1998 Accepted: 15 May 1998     

Alkalische Erden

Ohne Zusammenfassung     

Mutagenicity and dark toxicity of the second-generation photosensitizer bacteriochlorin a

Bacteriochlorin a (BCA) is an effective second-generation photosensitizer both in vitro and in vivo. BCA has a high molecular absorption coefficient (32,000 M-1 cm-1) at 760 nm. At this wavelength tissue penetration of light is almost optimal and melanin absorption is relatively low. BCA is preferentially retained in a number of tumour model systems and is rapidly cleared from non-cancerous tissues, thus inducing no or minor skin photosensitivity. Mutagenicity of BCA has been tested using the Salmonella typhimurium strains TA97, TA98, TA100, TA102 and TA104. In all tester strains used, BCA induces, in the dark, a minute increase in the number of revertants. No linear correlation between the number of revertants and the BCA dose is observed. Incubation of isolated rat hepatocytes with BCA, in the dark, does not result in increased cell death as measured by leakage of cytosolic lactate dehydrogenase. A convenient bioassay to test possible genotoxicity in vivo is the established Somatic Mutation and Recombination Test (SMART) on Drosophila melanogaster. Bacteriochlorin was tested for induction of loss of heterozygosity in the white/white+ eye mosaic assay, which predominantly measures homologous mitotic recombination in somatic cells of Drosophila after treatment of larval stages. BCA did not induce loss of heterozygosity above the level of the incorporated controls, with or without illumination. Based on these results, obtained in prokaryotic and eukaryotic cells and in vivo, we are inclined to conclude that the dark toxicity and mutagenic properties of BCA, as measured by the applied bioassays, are negligible.