Photochemistry of N6-methoxyadenosine and of N4-hydroxycytidine and its methyl derivatives I: spectroscopic and quantum chemical investigation of ionic and tautomeric forms: syn-anti isomerization

Abstract

The individual absorption spectra of various ionic and tautomeric species and the corresponding equilibrium constants for N 6-methoxyadenosine and for N 4-hydroxycytidine and its methyl derivatives were determined by computer analysis of the integrated spectra of these compounds measured at different pH values. The individual spectra of the ionic, tautomeric and isomeric species were decomposed into bands corresponding to the separate electronic transitions. Quantum chemical calculations of the electronic structure and spectra of all the ionic, tautomeric and isomeric species of the compounds studied were carried out using the complete neglect of differential overlap (CNDO/S) and Pariser—Parr—Pople approximations. The calculated results are in good agreement with the experimental spectral and photochemical data. The photoinitiated and dark syn—anti isomerization reactions of N (3)-methyl- N 4-hydroxycytidine and N (3)-methyl- N 4-methoxycytidine were investigated theoretically and experimentally.