Biopolymers and cell. 1995; 11 (1): 36 - 39

ACIDiC-BASIC PROPERTIES OF MOLECULAR HYPOXANTHINE IN VACUUM

D. M. Govorun, I. V. Kondratyuk, N. V. Zheltovsky

By means of semiempirical quantum mechanical AMI method with full parameters optimization there were calculated the energies of protonation of exocyclic oxygen atom of «carbonyi group and of endocyclic proton free nitrogen atoms as well as energy of depro-Uonation NH- and CH-groups for two energetically prevalent hypoxanthine's (Hyp) tau-tomers N7H and N9H in vacuum. It was established, that endocyclic proton free nitrogen atom of imidazole ring is the most probable site of protonation; «amide» group H1N1C606 of Hyp has the better protonodonor and protonoacceptor properties than the «amide» groups H3N3C404, H3N3C202 of uracile and H1N1C606, H1N1C202 of xanthine. The most probable schemes for Hyp interaction through two cyclic H-bonds with neutral and deprotonated carboxylic group are proposed; they are in agree with experimental results (N. V. Zheltovsky et al., 1993).