CONTENTS & ABSTRACTS
In English. Summaries in Estonian
Proceedings of the Estonian Academy of Sciences.
Volume 50 No. 4 December 2001
Fifty years of publications on chemistry in the Proceedings of the Estonian Academy of Sciences; 203–204(full article in PDF format)
Xylidine-polluted groundwater purification. Adsorption experiments and breakthrough calculations; 205–216(full article in PDF format)
Janek REINIK, Andres VIIROJA, and Juha KALLAS
Abstract. 2,4-Xylidine is a carcinogenic component originating from missile fuel, and it often dominates in polluted groundwater in the areas of abandoned Soviet missile bases in Eastern Europe. One of the possible processes for its removal is adsorption onto granulated activated carbon. However, the corresponding equilibrium relationships as well as information on the process kinetics are not available. In this work Langmuir’s and Freundlich’s isotherm parameters were obtained from batch adsorption equilibrium tests. Initial concentration of 2,4-xylidine was varied in the range of 200–300 mg/L in the experiments. The solid phase diffusion coefficient was obtained from the batch kinetic runs. The breakthrough curves were measured during dynamic experiments in two packed bed columns with diameters of 16 and 26 mm. The obtained experimental curves were compared to those calculated by the Thomas and Rice methods. In some cases a satisfactory fit was achieved, but in several cases more advanced modelling methods should be used for better prediction of the xylidine-contaminated groundwater breakthrough profiles in a packed bed reactor.
Key words: 2,4-xylidine, adsorption isotherm, kinetics, dynamics, packed bed adsorber design, breakthrough curves.
Determination of peppermint and orange aroma compounds in food and beverages; 217–225(full article in PDF format)
Anne ORAV and Jüri KANN
Abstract. Qualitative and quantitative variation of volatile aroma compounds in different foods and beverages containing peppermint and orange aroma was studied using the simultaneous distillation and extraction micromethod for isolating the aroma fraction and capillary gas chromatography for analysing the extracts. In peppermint aroma 41 constituents and in orange aroma 22 compounds were identified. The yields of aroma fractions from different materials varied from 0.2 up to 24 mg/g (peppermint) and from 0.03 up to 2 mg/g (orange).
Key words: Mentha piperita, Citrus sinensis, aroma compounds, tea, juice, chewing-gum, sweets, SDE, capillary GC.
Behaviour of 1-butoxy-9-tetradecyne in superbasic MEDA/EDA media; 226–228(full article in PDF format)
Anton KOTLJAROV, Artur JÕGI, Sirje MÄEORG, and Uno MÄEORG
Abstract. The first example of the isomerization of a non-propargylic alkoxyalkyne, 1-butoxy-9-tetradecyne, in superbasic media MEDA/EDA (M = Li, Na) is presented. The extent of the competitive elimination reaction and the influence of the type of metal in superbase on the composition of product were determined.
Key words: alkoxyalkyne, triple bond, isomerization, superbase, MEDA.
Changes in membrane fluidity during the micelle formation determine the efficiency of the solubilization of muscarinic receptors; 229–240(full article in PDF format)
Sergei KOPANCHUK and Ago RINKEN
Abstract. The influence of various concentrations of 15 detergents at different temperatures on the fluidity of membranes was analysed by fluorescence anisotropy of inserted 1,6-diphenyl-1,3,5-hexatriene in rat cortical and Sf9 cell membranes. Comparison of the obtained data with the abilities of the detergents to solubilize muscarinic receptor subtypes indicated that not only the fluidity of the micelles formed but also the micelle formation process, the lipid/protein ratio, and presence of sterols have significant influence on the efficiency of the solubilization of mAChR. Digitonin seems to exploit efficiently all these factors by its biphasic modulatory effect on membrane fluidity during the receptor solubilization.
Key words: membrane fluidity, solubilization, detergents, muscarinic receptors, rat cerebral cortex, digitonin, cholesterol.
Phosphorus–carbon diad tautomerism in phosphonium compounds. Theoretical study; 241–253(full article in PDF format)
Peeter BURK, Uldo MÖLDER, and Kaido TÄMM
Abstract. Phosphorus–carbon diad tautomerism was studied in phosphonium compounds with such strong electron acceptor substituents as cyano-, nitro-, fluorosulphonyl-, and trifluoromethylsulphonyl groups using semiempirical, ab initio, and DFT methods. It was shown that in the gas phase all studied monosubstituted species are in the phosphoryl form and no enol forms should be detectable. In contrast, for doubly substituted compounds enol forms should be well detectable and in some cases even predominant. Comparison of different calculation methods indicated that ab initio (HF/6-31 + G*) and DFT (B3LYP/6-311 + G**) calculations give close results. Both applied semiempirical methods (PM3 and MNDO/d) seem to overestimate strongly the stability of the enol form. It was also found that the MNDO/d method gives unrealistic results for compounds containing both hypervalent phosphorus and sulphur.
Key words: enolization, phosphoryl group, calculation, PM3, MNDO/d, DFT.
Contents of volume 50; 254–256