Structure and tautomeric properties of cytosine derivatives generated by ahydroxyl radical in aerobic conditions

The tautomeric properties of four hydroxyl radical cytosine derivatives wer e characterised by an ab initio quantum chemistry method. 5,6-dihydroxycyto sine (I), 5,6-dihydroxyuracil (2), isodialuric acid (3) and uracil glycol ( 4) were characterised based on 6-311G** full gradient geometry optimisation and single point MP2(6-311G**) energy calculation. Solvent effects were es timated on the basis of the SCI-PCM(6-311G**) model. The most stable tautom er of 5,6-dihydrocytosine (I) is in keto-amino form. The most probable stru cture of the remaining studied derivatives corresponds to a diketo tautomer . No significant impact of environment polarity on the tautomer succession was observed for all studied derivatives. The most probable isomers in vacu um remained the most preferred in water and other solvents. Due to the stab ility of major tautomeric forms, the coding ability of 5,6-dihydroxycytosin e (I) may be described as (+ - -) (acceptor-donor-donor). The formal coding abilities of the other studied derivatives correspond to a (- + -) scheme (donor-acceptor-donor). (C) 1999 Elsevier Science BV. All rights reserved.