aPrivolzhskii Kazan Federal University, 18 ul. Kremlevskaya, 420008 Kazan, Russian Federation. Fax: +7 (843) 292 7418. E mail: isnizamov@mail.ru bA. E. Arbuzov Institute of Organic and Physical Chemistry Kazan Scientific Center of the Russian Academy of Sciences, 8 ul. Akad. Arbuzova, 420088 Kazan, Russian Federation. Fax: +7 (843) 273 2253 cKazan State Medical University, 49 ul. Butlerova, 420012 Kazan, Russian Federation. Fax: +7 (843) 236 0393 dKazan Scientific Research Institute of Epidemiology and Microbiology, 67 ul. Bol shaya Krasnaya, 420015 Kazan, Russian Federation. Fax: +7 (843) 236 6741