In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.



Volume 52 No. 3 September 2003


Hydroxystilbenes in the roots of Rheum rhaponticum; 99–107

Aavo Aaviksaar, Mati Haga, Kristina Kuzina, Tõnu Püssa, Ain Raal, and George Tsoupras

Abstract. Stilbene derivatives trans-3,4¢,5-trihydroxystilbene (resveratrol) and its 3-O-β-D-glucopyranoside (piceid), trans-3,5-dihydroxy-4¢-methoxystilbene (deoxyrhapontigenin) and its 3-O-β-D-glucopyranoside (deoxyrhapontin), trans-3,3¢,5-trihydroxy-4¢-methoxystilbene (rhaponti­genin) and its 3-O-β-D-glucopyranoside (rhapontin) as well as two 3,3¢,4¢,5-tetrahydroxystilbene (piceatannol) glucosides were identified in the roots of common rhubarb Rheum rhaponticum cultivated in Estonia. The concentration of resveratrol in the roots of R. rhaponticum increased sharply in October, while the concentrations of other stilbenes maintained the values close to the concentrations at the beginning of the vegetation period in April–May. The roots of R. rhaponticum could be an effective raw material for producing natural resveratrol and other pharmacologically active stilbenoids.

Key words: resveratrol, piceatannol, hydroxystilbenes, Rheum rhaponticum, Polygonum cuspidatum.

Electrochemical (redox) behaviour of microporous polyethylene-based conducting polypyrrole composites; 108–119

Jekaterina Reut, Elena Rosova, Galina K. Elyashevich, Katrin Idla, and Andres Öpik

Abstract. The redox behaviour of an electrically conductive composite obtained by gas-phase oxidative polymerization of pyrrole on the microporous polyethylene (PE) film [PE–PPy(Cl)] was investigated by cyclic voltammetry. It was found that the composite is electrochemically active in aqueous NaCl solution. The possibility of modification of this composite by electrochemical deposition of an additional polypyrrole layer was demonstrated. The redox behaviour of the obtained new polymeric electrically conductive composite structure (PE–PPy(Cl)/PPy(X)el), where X is doping anion (Cl, NO3, p-toluensulphonate, naphthalene sulphonate, dodecyl benzene sulphonate), was investigated. Doping anions and the thickness of the electrochemically deposited PPy layer were found to influence the cation and/or anion exchange during the redox processes in the new composite structure. The stability of the redox processes in the composite structure was tested in aqueous NaCl solution with continuous cycling up to 100 times. It was shown that the composite structure that contains small inorganic anions such as Cl or NO3 is electrochemically more stable than that with large organic anions (naphthalene sulphonate).

Key words: polypyrrole, polyethylene, composite, cyclic voltammetry.

Nitrogen removal from wastewater by heterotrophic denitrification with nitrite used as an electron acceptor; 120–129

Taimar Ala, Helen Sulg, Kaja Orupõld, and Toomas Tenno

Abstract. The objective of the research was to determine the best conditions for heterotrophic denitrification by using nitrite as an electron acceptor. The results of the experiments indicate that heterotrophic denitrification where nitrite is used as the electron acceptor is practicable and feasible. However, the concentration of nitrite in the anoxic zone of the wastewater treatment plant has to be monitored constantly, as the accumulation of nitrite could cause a decrease in the denitrification activity. The process of full denitrification could be inhibited, if the concentration of NO2-N rose over 10–35 mg/L, depending on the operating conditions of the system.

Key words: denitrification, nitrite, activated sludge.

Advances in petrol additives research; 130–142

Heino Rang and Jüri Kann

Abstract. A review about the use of petrol additives and the latest results in respective research and development is presented. Today it is not possible to guarantee the stable work of an engine and cleaner air by reducing the concentration of toxic compounds in exhaust gases without petrol additives. These additives control deposits, give an antiknock effect, enhance the combustion process, stabilize petrol, prevent corrosion, etc. Today it is known that the most important additives are the deposit control additives. Ethanol with a small amount of water and other additives enhance the combustion process. The improved combustion decreases fuel consumption and reduces air pollution.

Key words: petrol blends, additives, detergents, combustion improvers, antiknock agents, ethanol, water.

Instructions to authors; 143–145