Neue hochselektive spektralphotometrische Cyanidbestimmung durch Zerstörung des Platin-3,4-Diaminobenzoesäure-Komplexes

An accurate sensitive and simple method for the determination of cyanide was developed from the fact that cyanide interferes strongly in the determination of platinum with 3,4-diaminobenzoic acid. The influence of a great number of cations and anions was tested. Due to the high selectivity the method is especially suited for the analysis of more complex samples such as waste waters. The sensitivity of <0.02 μg CN^?/ml compares favourably with the known methods. About 30–40 samples can be analysed per day.     

Spektralphotometrische Bestimmung von schwerem Wasser in H2O/D2O-Gemischen im nahen Infrarot

Three different methods are described for the determination of D₂O in H₂O/D₂O mixtures by means of IR absorption. Wave-lengths, concentration ranges and accuracies are as follows: 2500 nm: 99–100 Mol-% D₂O, ±0.001%; 1670 nm: 0–20 Mol-% D₂O, ±0.02%; 1368 nm: 0–100% D₂O, ±0.1%. The methods are simple and rapid and have been successfully used for several years.     

Einflu? variabler18O-Gehalte auf die refraktometrische und spektralphotometrische D-Gehaltsbestimmung in Wasser

Zusammenfassung Mit Hilfe von hochangereichertem H₂ ¹⁸O und D₂ ¹⁸O wird der Einfluß des¹⁸O-Gehaltes auf einige Methoden der optischen D/H-Analyse von Wasser untersucht. Bei der refraktometrischen D-Gehaltsbestimmung entsprechen dem instrumentellen Fehler von ±0,1% D Variationen von 6 Atom-%¹⁸O in H₂O und 20%¹⁸O in D₂O.Der Einfluß auf einige spektralphotometrische D-Bestimmungsmethoden im nahen Infrarot wird anhand von Differenzspektren von D₂ ¹⁸O gegen D₂ ¹⁶O und von H₂ ¹⁸O gegen H₂ ¹⁶O ermittelt. Es werden auch geeignete Wellenlängen für minimale Störung der D-Analyse durch den¹⁸O-Gehalt angegeben und Möglichkeiten für die spektralphotometrische¹⁸O-Analyse in H₂O und D₂O diskutiert.

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Influence of varying¹⁸O contents on the refractometric and spectrophotometric D-determination in water

The influence of varying¹⁸O-contents on the D-analysis of water by some optical methods is investigated by means of highly enriched H₂ ¹⁸O and D₂ ¹⁸O. The instrumental error of ±0.1% D in the refractometric D-analysis of water was found to correspond to differences of 6 atom%¹⁸O in H₂O and 20%¹⁸O in D₂O.The sensitivity of several spectrophotometric methods of D-analysis to differences in¹⁸O content is determined on the basis of differential spectra between D₂ ¹⁸O and D₂ ¹⁶O and H₂ ¹⁸O and H₂ ¹⁶O, respectively. Wavelengths for minimum interference of¹⁸O-content with D-analysis are given and possibilities of spectrophotometric¹⁸O-analysis are discussed.

     

Reactive Monte Carlo and grand-canonical Monte Carlo simulations of the propene metathesis reaction system

The influence of silicalite-1 pores on the reaction equilibria and the selectivity of the propene metathesis reaction system in the temperature range between 300 and 600 K and the pressure range from 0.5 to 7 bars has been investigated with molecular simulations. The reactive Monte Carlo (RxMC) technique was applied for bulk-phase simulations in the isobaric-isothermal ensemble and for two phase systems in the Gibbs ensemble. Additionally, Monte Carlo simulations in the grand-canonical ensemble (GCMC) have been carried out with and without using the RxMC technique. The various simulation procedures were combined with the configurational-bias Monte Carlo approach. It was found that the GCMC simulations are superior to the Gibbs ensemble simulations for reactions where the bulk-phase equilibrium can be calculated in advance and does not have to be simulated simultaneously with the molecules inside the pore. The confined environment can increase the conversion significantly. A large change in selectivity between the bulk phase and the pore phase is observed. Pressure and temperature have strong influences on both conversion and selectivity. At low pressure and temperature both conversion and selectivity have the highest values. The effect of confinement decreases as the temperature increases.     

Pattern recognition strategies for molecular surfaces. II. Surface complementarity

Fuzzy logic based algorithms for the quantitative treatment of complementarity of molecular surfaces are presented. Therein, the overlapping surface patches defined in article I1 of this series are used. The identification of complementary surface patches can be considered as a first step for the solution of molecular docking problems. Standard technologies can then be used for further optimization of the resulting complex structures. The algorithms are applied to 33 biomolecular complexes. After the optimization with a downhill simplex method, for all these complexes one structure was found, which is in very good agreement with the experimental results.     

Über die Bildung tertiärer Amine bei der Reduktion von Nitrilen und von Karbonylverbindungen in basischer Lösung

Ohne Zusammenfassung     

Titanium Dioxide/Electrolyte Solution Interface: Electron Transfer Phenomena

Electron transfer between a titanium dioxide/electrolyte solution interface has been studied. As found by other researchers of similar interfaces (TiO(2)- and ZnO-electrolyte solution), a slow consumption of OH(-) ions takes place in this type of interface. A theoretical model has been developed for calculating the change in the Fermi energy of both electrolyte solution and semiconductor, showing that ion consumption from the solution is favoured by the decrease of the difference between their Fermi energies. A kinetic constant (upsilon) is found to characterise the consumption process, its value increasing with electrolyte and semiconductor mass concentrations. Furthermore, this process may be used to estimate the point of zero charge of a titanium dioxide colloidal dispersion. Copyright 2000 Academic Press.