Mechanism of hydroxylamine mutagenesis: an infrared study of the association in non-polar solutions of 5-methyl-N4-hydroxycytosines.

An infrared spectroscopic study has been made of the structure and self-association of 1,5-dimethyl-N4-hydroxycytosine and 1,5-dimethyl-N4-methoxycytosine in several non-polar solvents as a function of concentration and temperature. Both compounds are predominantly in the imino form, and the overall results point to the existence of an intramolecular hydrogen bond between the ring N(3) hydrogen and the oxygen on the exocyclic N4, as previously found in the solid state. Furthermore, 1,5-dimethy-N4-hydroxycytosine forms linear associates in solution via hydrogen bonding, of the form N4-OH ... O=C2, with thermodynamic parameters delta H = -2.8 kcal/mol, delta S = -2.7 cal/deg . mol. As anticipated, the N4-methoxy derivatives does not form such associates. Neither of the compounds exhibits detectable association by hydrogen bonding with the potentially complementary 9-ethytl-adenine. Both compounds are also predominantly in the imino form in the gas phase.