Biopolymers and cell. 2000; 16 (5): 384 - 402

Influence of methylation and interactions with amino acid carboxylic group on UV spectra of purine nucleotide bases and nucleosides in dimethylsulfoxide. 2. Guanine

A. V. Stepanyugin, I. M. Kotomiets, A. L. Potyahaylo, S. P. Samijlenko

p 29 L/Y absorption spectra of gua^ine derivatives m Gua, m2 ' Gua, m Gua, m% ' Gua, G, dG, m G, m G, m G as well as of its analogue isoGua have been studied in anhydrous DMSO. The changes in UV absorption of the Gua. derivatives in the presence of the amino acid derivatives with neutral carboxylic group — ac-Asp, ac-Glu, ac-Gly, ac-Asp-OMe and f-GlyONa and NaAc with deprotonated carboxylic groups have been investigated and interpreted. It has been shown that ml Gua and m Gua exist as the N9H tautomers in anhydrous DMSO. It has been established that most part of the Gua derivatives interact only with deprotonated carboxylic group, excluding m G, isoGua and m Gua which are capable to form the complexes with neutral carboxylic group as well. Energetic charac¬teristics of the Gua prototropic tautomers and their complexes with carboxylate ion were calculated by the semiempirical MNDO/H method at vacuum approximation.