TAUTOMERISM OF NEUTRAL AND PROTONATED 6-THIOGUANINE IN THE GAS-PHASE AND IN AQUEOUS-SOLUTION - AN AB-INITIO STUDY

The tautomerism of g-thioguanine in its neutral and protonated forms was studied in the gas phase using high-level ab initio methods. The effect of the aqueous environment on the reactive properties and on the tautomer population of neutral and protonated 6-thioguanine was examined using an optimized ab initio SCRF method. The results predict that the N9(H) thiol is the most stable tautomer for the neutral form in the gas phase, while the N1,7(H) thione is preferred in aqueous solution. For the protonated molecule the N1,7,9(H) thione and two thiol forms exhibit a close stability in the gas phase, but only the thione form N1,7,9(H) is expected to be found in aqueous solution.