CONTENTS & ABSTRACTS
In English. Summaries in Estonian
Proceedings of theEstonian Academy of Sciences.
Chemistry
Volume 51 No. 1March 2002
Solvatochromismof fullerene C60 in solvent mixtures: application of thepreferential solvation model; 3–18
Urmas Pille, Koit Herodes, Ivo Leito, Peeter Burk, ViljarPihl, and Ilmar Koppel
Abstract. Absorption spectra of fullerene C60 were recordedbetween 300 and 700 nm in seven different binary solvent mixtures(toluene–acetic acid, toluene–methanol, toluene–acetonitrile, toluene–dimethylsulphoxide, toluene–dimethylformamide, pyridine–methanol, and pyridine–water).The appearance of the UV-vis spectra of fullerene C60 was found tobe influenced by the composition of the mixture. The influence of thecomposition of the mixture on the position of four absorption bands and was studied. Thesolvent-induced shifts of the absorption maxima were generally in the range ofseveral nanometers, the longest being 10.3 nm in the mixture of tolueneand dimethylformamide. The data were analysed in terms of the preferentialsolvation model. Fullerene was found to be strongly preferentially solvated bytoluene and pyridine compared to the more polar components of the mixtures. Theselective solvation model was found to be applicable to the description ofsolvatochromism of C60 in binary solvent mixtures, at leastformally. Particularly interesting solvent effects – marked changes in the shapeof the spectrum – were found in the mixtures toluene–dimethylformamide andpyridine–water.
Key words: binary mixtures, UV-vis spectroscopy, solvent-induced shifts,absorption maxima.
Isobaricvapour–liquid equilibria of the ternary system hexan-2-one + o-xylene + nonane; 19–28
Enn Siimer, Helle Kirss, Mati Kuus, and LudmillaKudryavtseva
Abstract. Boilingtemperatures (T) vs liquid-phase mole fractions (x) were measured for the systemhexan-2-one + o-xylene + nonaneand for two constituent binaries containing hexan-2-one at pressures 26.66,53.33, 79.99, and 101.32 kPa. Hexan-2-one formed minimum boiling azeotropewith nonane while the binary system hexan-2-one + o-xylene was nonazeotropic. The modifiedWilson model was used to correlate the binary T–x data and to predict vapour–liquid equilibria in the ternarysystem. The excess Gibbs energy calculated by the modified Wilson model andexperimental HE data at318.15 K of the ternary system are treated simultaneously.
Key words: phase equilibria modified Wilson equation.
Acomputerized flow injection analysis manifold for interference determination inflame atomic absorption spectrometry; 29–37
Riina Lahne, Anu Viitak, Helvi Hödrejärv, Maili Treumann, MargusFriedenthal, and Mihkel Kaljurand
Abstract. A computerized flow injection analysis (FIA) manifold was setup and its performance is described for automatic determination of theinfluence of interferences in flame atomic absorption (FAA) spectrometry. Themanifold operates on the principle of multiple injection of the sample solutionof the metal to be determined with the interference to the FAA-spectrometer.The sample is simultaneously diluted with a pure solution of the analyte, whichallows covering a wide range of interference concentrations. As an example,calcium determination with phosphate as the interference and lanthanum as theinterference suppressor is demonstrated. The method was applied to studycalcium concentration in milk.
Key words: atomic absorption spectrometer, flowinjection, interference phosphate, calcium, milk.
Non-steady-stateprocesses in amperometric biosensors: modelling studies; 38–48
Siiri Velling, Kaido Tammeveski, Alexey Mashirin, andToomas Tenno
Abstract. Thenon-steady-state processes of a biosensor based on a diffusion-limited oxygensensor were investigated. The effect of various processes occurring in thebiosensor on its overall response was studied. A mathematical model oftransient processes of the biosensor was elaborated. The maximum rate ofcurrent change was taken as a measure of sensor response to substrateconcentration. The validity of the model was tested by using a biosensor withimmobilized microorganisms.
Key words: microbialbiosensor, agarose-gel film mathematical modelling, non-steady-state process,dynamic method.
Kineticstudies on the mechanism of haematoporphyrin derivative photobleaching; 49–70
LyudmilaChekulayeva, Igor Shevchuk, Vladimir Chekulayev, and Raissa Jäälaid
Abstract. Haematoporphyrinderivative (HPD), a sensitizer used in photodynamic therapy (PDT) of tumours,is progressively destroyed (photobleached) during illumination. However, themechanism of the sensitizer photobleaching remains unclear, although itsdegradation presents both potential problems and potential advantages. This papersurveys the effects of reaction conditions, photooxidizable biomolecules,electron acceptors, and other agents on the quantum yield (QY) and kinetics ofthe photodestruction of HPD in solution. The initial QY of HPD photobleachingin pH 7.4 phosphate buffer in air was measured as 3.6 ´ 10–5. The yield decreased significantly in organicsolvents with a low dielectric constant and in the presence of varioussurfactants. Ionic strength, pH, and temperature had relatively slight effectson the photobleaching yield of HPD. For example, raising the temperature from10 to 43 °C caused only a moderate (about 2-fold) increase in the QY of HPDphotobleaching. It was found that oxygen is needed for the photobleaching ofHPD. However, the QY of HPD photodestruction increased only slightly (by 55%)in D2O. Sodium azide, an efficient physical quencher of singletoxygen (1O2), had only a slight effect on thephotobleaching yield, even at 50 mM. Our data suggest that besides 1O2,free radical reactions are involved in the photodegradation of HPD in aqueoussolution. In fact, the QY of HPD photobleaching decreased in the presence ofhydroxyl radical scavengers, such as mannitol, sodium benzoate, ethanol, anddeferoxamine. In addition, the photodestruction of HPD could be associated withthe formation of very reactive cation radicals of the sensitizer. Somephotooxidizable substrates and model electron acceptors increased markedly thephotobleaching efficiency of HPD. At certain concentrations, the QY of HPDphotobleaching was enhanced by the presence of histidine, reduced glutathione,dithiothreitol, and lecithin. Electron acceptors, such as metronidazole andflavin mononucleotide, also increased the photobleaching yield. In contrast,NADH and cysteine, which are electron donors, inhibited the rate of HPDphotodestruction. High concentrations (> 1 mM)of biological antioxidants, such as ascorbic acid and α-tocopherol, alsoincreased the photostability of HPD in solution. These results suggest that themechanism(s) of the photobleaching of HPD in cells and tissues during PDT maybe complex.
Key words: haematoporphyrinderivative, photobleaching, photodynamic therapy, tumour.
Instructions to authors; 71–73
Copyright Transfer Agreement; 74
