CONTENTS & ABSTRACTS
InEnglish. Summaries in Estonian
Proceedings of the Estonian Academy of Sciences.
Chemistry
Volume 52 No. 3September 2003
Hydroxystilbenesin the roots of Rheum rhaponticum; 99–107
Aavo Aaviksaar, Mati Haga, KristinaKuzina, Tõnu Püssa, Ain Raal, and George Tsoupras
Abstract. Stilbenederivatives 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 ofresveratrol in the roots of R. rhaponticumincreased sharply in October, while the concentrations of other stilbenesmaintained the values close to the concentrations at the beginning of thevegetation period in April–May. The roots of R. rhaponticum could be an effective raw material for producingnatural resveratrol and other pharmacologically active stilbenoids.
Key words: resveratrol, piceatannol, hydroxystilbenes, Rheum rhaponticum, Polygonum cuspidatum.
Electrochemical(redox) behaviour of microporous polyethylene-based conducting polypyrrolecomposites; 108–119
Jekaterina Reut, Elena Rosova, Galina K. Elyashevich,Katrin Idla, and Andres Öpik
Abstract. The redox behaviour of an electrically conductive compositeobtained by gas-phase oxidative polymerization of pyrrole on the microporouspolyethylene (PE) film [ PE–PPy(Cl)] was investigated by cyclic voltammetry. Itwas found that the composite is electrochemically active in aqueous NaClsolution. The possibility of modification of this composite by electrochemicaldeposition of an additional polypyrrole layer was demonstrated. The redoxbehaviour of the obtained new polymeric electrically conductive compositestructure (PE–PPy(Cl)/PPy(X)el), where X– is doping anion(Cl–, NO3–, p-toluensulphonate,naphthalene sulphonate, dodecyl benzene sulphonate), was investigated. Dopinganions and the thickness of the electrochemically deposited PPy layer werefound to influence the cation and/or anion exchange during the redox processesin the new composite structure. The stability of the redox processes in thecomposite structure was tested in aqueous NaCl solution with continuous cyclingup to 100 times. It was shown that the composite structure that contains smallinorganic anions such as Cl– or NO3– iselectrochemically more stable than that with large organic anions (naphthalenesulphonate).
Key words: polypyrrole, polyethylene, composite, cyclic voltammetry.
Nitrogenremoval from wastewater by heterotrophic denitrification with nitrite used asan electron acceptor; 120–129
Taimar Ala, Helen Sulg, Kaja Orupõld, and Toomas Tenno
Abstract. The objective of the research was to determine the bestconditions for heterotrophic denitrification by using nitrite as an electronacceptor. The results of the experiments indicate that heterotrophicdenitrification where nitrite is used as the electron acceptor is practicableand feasible. However, the concentration of nitrite in the anoxic zone of thewastewater treatment plant has to be monitored constantly, as the accumulationof nitrite could cause a decrease in the denitrification activity. The processof full denitrification could be inhibited, if the concentration of NO2–-Nrose over 10–35 mg/L, depending on the operating conditions of the system.
Key words: denitrification, nitrite, activatedsludge.
Advancesin petrol additives research; 130–142
Heino Rang and Jüri Kann
Abstract. A reviewabout the use of petrol additives and the latest results in respective researchand development is presented. Today it is not possible to guarantee the stablework of an engine and cleaner air by reducing the concentration of toxiccompounds in exhaust gases without petrol additives. These additives controldeposits, give an antiknock effect, enhance the combustion process, stabilizepetrol, prevent corrosion, etc. Today it is known that the most importantadditives are the deposit control additives. Ethanol with a small amount ofwater and other additives enhance the combustion process. The improvedcombustion decreases fuel consumption and reduces air pollution.
Key words: petrol blends,additives, detergents, combustion improvers, antiknock agents, ethanol, water.
Instructionsto authors; 143–145
