[Tautomerism of purine and pyrimidyne bases].

In this paper, I am presenting the background and a short outline of the research on the neutral and ionic tautomeric forms of pyrimidines, purines and their derivatives, carried out in the late 1960s under the guidance of professor David Shugar, in the Biophysics Department of Warsaw University.

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 .

Structure and tautomerism of the neutral and monoanionic forms of 2-thiouracil, 2,4-dithiouracil, their nucleosides, and some related derivatives.

Ultraviolet and infrared spectrophotometric techniques have been utilized to demonstrate that the monoanionic form of 2-thiouracil in aqueous medium consists of an equilibrium mixture of two tautomeric monoanions, one due to dissociation of the N1 proton, the other to dissociation of the N3 proton, in the approximate ratio 1:1. In contrast to 2,4-diketopyrimidines, and 4-thiouracil, where monoanion formation involves charge delocalization, the two tautomeric monoanions of 2-thiouracil appear to have the charge localized on the O4 position. The neutral forms of 2,4-dithiouracil and 2,4-dithiouridine are in the dithione form in both aqueous and non-aqueous media.