CONTENTS &
ABSTRACTS
In English. Summaries in
Estonia
Proceedings
of the Estonian Academy of Sciences.
Chemistry
Volume
49 No. 2 June 2000
Bioethanol
as a fuel to reduce the greenhouse effect; 83–104
Jüri KANN and Heino RANG
Abstract. In the review with 208 references the greenhouse effect and the pollution problems from the exhaust gases of petrol (gasoline) engines are discussed. It is shown that ethanol is currently the only alternative renewable biofuel that has achieved noticeable market success, particularly in Brazil and to an extent as petrol blends in the USA. Investigations on gene engineering, process and apparatus developing, sources base enlargement, etc., carried out in many countries, especially in the USA, to produce bioethanol as a fuel economically are reported. It is shown that the production of bioethanol fuel is important for every country, because its main source will be agricultural, forestry, and municipal cellulosic wastes, which should be processed on the spot to avoid large transport costs.
Key words: ethanol, biofuel, biomass, greenhouse effect (GHE), air pollutants.
Kinetics
of tert-butylaminolysis of n-butyl trichloroacetate in heptane;
105–108
Agu-Tõnis TALVIK, Imbi TALVIK, and Ants TUULMETS
Abstract. Kinetics of tert-butylaminolysis of n-butyl trichloroacetate was investigated in heptane solutions by taking samples and analysing them for both ester and n-butyl alcohol content by gas–liquid chromatography. A bulky tert-butyl group in the amine causes a great decrease in the reaction rate and the aminolysis becomes reversible. The equilibrium constant is dependent on the composition of the reaction medium. The reaction is second-order in amine and the apparent activation energy is close to zero. These findings are compatible with the reaction mechanism adopted for less bulky amines. Thus, a shift of the rate-determining step of the reaction in case of tert-butylamine can be excluded.
Key words: aminolysis of esters, reaction mechanism, solvent effects.
L-buthionine-[S,R]-sulfoximine
may enhance the rate of haemato-porphyrin derivative photosensitized
inactivation of tumour cells without lowering the intracellular content of
glutathione; 109–120
Lyudmila CHEKULAYEVA, Igor SHEVCHUK, Raissa JÄÄLAID, and Vladimir CHEKULAYEV
Abstract. Haematoporphyrin derivative (HpD) is the most widely used photosensitizer (PS) for photodynamic therapy (PDT) of cancer. In the present study it was found that L-buthionine-[S,R]-sulfoximine (L-BSO), an inhibitor of glutathione (GSH) biosynthesis, added (jointly with HpD) to Ehrlich ascites carcinoma (EAC) cells for 5 min prior to photoirradiation (lmax = 630 nm, the range 590–830 nm) enhanced synergistically the rate of HpD-sensitized photoinactivation of the cells. Thus, L-BSO, at a concentration of 2.5 mM caused (as measured by trypan blue test and MTT assay) a substantial (approximately 20%) increase in the HpD-induced photocytotoxicity. However, this effect of potentiation was not observed when chlorin-e6 trimethyl ester was used as a PS. Studies on the mechanism revealed that the potentiating action of L-BSO on HpD–PDT was not induced by lowering the reduced GSH (a natural antioxidant) content in EAC cells. At the same time, L-BSO was found to weakly but significantly augment the uptake of HpD by the cells at all concentrations used (from 0.5 up to 2.5 mM). This finding explains the potentiating effect of L-BSO on the HpD-induced photokilling of EAC cells.
Key words: photodynamic therapy, haematoporphyrin derivative, tumour cells, buthionine sulfoximine.
Analysis
of commercial polyphosphates by thin-layer chromatography;
121–126
Meeme PYLDME and Juta PYLDME
Abstract. Analysis procedures of Na5P3O10 (STPh) and (NaPO3)n (SPPh) were investigated. The effect of solvent systems on separation quality and determination accuracy were studied. Suitable components of solvents were found: for the separation of polyphosphate anions – acetone, trichloroacetic acid, and water; for the separation of cyclophosphate anions – methyl-ethyl ketone, water, dimethylformamide, and isopropanol. Procedures were developed for determination of phosphate additives in STPh and SPPh. For all procedures limits and accuracy of determination were found. The limit of separation and determination for PO43– and (PO3–)3 was 0.04–0.06% P2O5 and for P2O74–, 0.08–0.10% P2O5. Typical accuracy of PO43– and (PO3–)3 determination at the content range of 0.10–0.30% P2O5 was up to ± 25%; at 2.0–8.0% P2O5, up to ± 4.0%. Determination accuracy of P2O74– at the content range of 0.80–1.0% P2O5 was up to ± 10%; at 4.6–8.2%, up to ± 2.5%.
Key words: polyphosphates, separation, determination.
Instructions
to authors; 127