Biopolym. Cell. 1994; 10(6):61-64.
http://dx.doi.org/10.7124/bc.0003C4
Acidic-basic properties of molecular xanthine and its complex formation ability
1Govorun D. M., 1Kondratyuk I. V., 1Zheltovsky N. V.
  1. Institute of Molecular Biology and Genetics, NAS of Ukraine
    150, Akademika Zabolotnoho Str., Kyiv, Ukraine, 03680

Abstract

By means of semiempirical quantum mechanical AMI method with full parameters optimization there were calculated the energies of: protonation of exocyclic oxigen atoms of carbonyl groups and of endocyclic nitrogen atoms as well as energy of deprotonation NH- and CH-groups for two energetically prevalent xanthine's (Xan) tautomers N7H and N9H, for the main diketoform of uracile (Ura) and for imidazole (Im). It was established, that endocyclic proton free nitrogen atom of Im ring of Xan is the most probable site of protonation; pyrimidine ring of Xan N9H is the better protonodonor and protonoacceptor than Ura. It was suggested "that in vacuum Xan N9H forms cyclic H-pairing (for example, with nucleotide bases) through pyrimidine fragment as well as Ura. The most probable schemes for Xan 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).
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