Infrared spectra and the structure of 1-methyladenine in an argon matrix and solutions

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 1995-05, Vol.51 (5), p.843-853
• Main Authors: Pivovarov, V.B, Stepanian, S.G, Reva, I.D, Sheina, G.G, Blagoi, Yu.P
• Format: Article
• Language: English
• ISSN: 1386-1425
• DOI: 10.1016/0584-8539(94)00189-I

The spectral characteristics of the so-called “rare” imine form of methylated nucleotide purine base adenine is investigated. A study is made of 1-methyladenine (1-mAde) having generally the three tautomeric forms: amine, imino-N9H, and imino-N7H. IR spectra of 1-mAde isolated in Ar matrix at 12 K are obtained in the range 4000-400 cm −1. The normal-coordinate analysis is employed to interpret the experimental spectra. It is shown that isolated 1-mAde molecules can only exist as imine. The set of fundamental vibrational frequencies and force constants of the imine tautomer is found. The relative energies of the 1-mAde tautomers are calculated by the SCF MO LCAO method in the AM1 approximation with complete geometry optimization. This method predicts the stability of the tautomers in decreasing order: imine-N9H, imine-N7H, amine. An IR spectroscopic study of solutions of 1-mAde, and also adenine, 9-methyladenine, 1-methyladenosine, 2-aminopyrimidine, 2- and 4-oxopyrimidine in polar solvents in the range 1750-1500 cm − is carried out. The results show the presence of a considerable amount of the “rare” imine tautomer in water, as well in nonaqueous solutions.