Isomers and aza-analogues of indoxyl containing nitrogen at a ring-fusion position: Coupling reactions with electrophiles and attempted oxidations

Derivatives of four series of compounds derived from isomers of indoxyl with the nitrogen at the bridgehead and two further series of aza-analogues are prepared and their absorption properties studied.     

New trends in teaching Analytical Chemistry: How to present COBAC (Computer Based Analytical Chemistry)

Summary Teaching of Computer Based Analytical Chemistry (COBAC) is considered with emphasis on a regular course in the education of chemists. A proposal for conducting a COBAC course is made and discussed from the point of view of introducing basic principles in lectures and of putting the presented methods into practice in parallel tutorial computer sessions.     

A fully reversible fiber optic lactate biosensor based on the intrinsic fluorescence of lactate monooxygenase

Summary The intrinsic fluorescence intensity of the enzyme lactate monooxygenase is used as the analytical parameter in a new type of lactate biosensor. It is found that the fluorescence quantum yield of the coenzyme changes during its interaction with lactate at the point of saturation. The changes in intensity are fully reversible in the presence of molecular oxygen and can be monitored via fiber optic light guides. Enzyme solutions were entrapped at the fiber end using a semipermeable membrane which retains the enzyme. The change in fluorescence occurs within a rather small range of lactate concentration (0.5–1 mmol/l) with an lactate-invariable signal at higher levels. Response times of 7.5 to 25 min (to reach the full steady state) and regeneration times between 1 and 8 min are observed. Measurements are performed in flowing air-saturated solutions containing 0.1 mol/l pH 7.0 citrate buffer. The effect of pH has also been investigated. In order to achieve a more expanded analytical range (e.g., 1.4–10 mmol/l) and shorter response times, kinetic measurements are performed in a fashion similar to flow-injection analysis.

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Vollreversibler faseroptischer Lactatbiosensor aufgrund der Eigenfluorescenz der Lactatmonooxygenase

     

Fast Response Oxygen Micro-Optodes Based on Novel Soluble Ormosil Glasses

 A new type of phenyl substituted ormosils as a matrix for oxygen-sensitive micro-optodes is described. The new ormosils combine features of classical polymers such as solubility in organic solvents and those of sol–gel glasses such as mechanical stability and a porous structure. They make possible a simple and fast fabrication of microsensors with reproducible properties. The influence of the conditions during the polymerisation process (precursor composition and thermal treatment) on the sensing properties has been studied in detail. Oxygen-sensitive films with ruthenium(II)–tris-(4,7-diphenyl-1,10-phenanthroline) and platinum(II)–octaethylporphyrin as indicators were characterised with respect to their mechanical and photophysical properties. Photostability, oxygen sensitivity, response behaviour and signal intensities of the sensing films and the micro-optodes were examined. Micro-optodes based on the new sensing materials are fast responding, photostable and can be produced with a sufficient batch to batch reproducibility. Compared to previously described oxygen micro-optodes, where polystyrene was used as immobilisation matrix, the new sensors can be autoclaved and show favourable properties such as a faster response and a higher sensitivity. They possess many potential applications in medical and biological research. Received June 12, 1998. Revision December 10, 1998.     

Lubrication approximation with prescribed nonzero contact anggle

We prove long existence for a weak solutions ss(t,x)≥0 of the lubrication approximation ?_t+?_x(s?s)=0 in{s>0> with prescribed contact anglo of, say,(?_xs)²=1 on ?{s>0}