The highly mutagenic nucleoside dP (6-(2-deoxy-beta-D-erythro-pentofuranosyl)-3,4-dihydro-6H,8H-pyrimido[4,5-c][1,2]oxazin-2-one) is a bicyclic analogue of N4-methoxy-2'-deoxycytidine. It exists as a mixture of its imino and amino tautomers in solution with a ratio of about 10:1 based on its tautomeric constant. The bicyclic nature of the heterocycle P restrains the amino substituent in an anti...

We have firstly shown that the T·T(w) and C·C(w) DNA mismatches with wobble (w) geometry stay in slow tautomeric equilibrium with short T·T*(WC) and C·C*(WC) Watson-Crick (WC) mispairs. These non-dissociative tautomeric rearrangements are controlled by the plane-symmetric, highly stable, highly polar and zwitterionic transition states. The obtained results allow us to understand in what way the...

In the title compound, C14H14N2O5S, the mol-ecule exists in the enamine (C=C-NH) tautomeric form. The hydrazone fragment derived from the 3-acetyl-4-hy-droxy-6-methyl-2H-pyran-2-one moiety is approximately planar, with a maximum deviation of 0.1291 (11) Å for the N atom bound to the S atom of the benzensulfono-hydrazide group. The latter adopts a gauche conformation relative to the hydrazone N-...

The crystal structures of the silver complexes [Ag2(5HtpO)2][NO3]2 1, [Ag2(5HtpO)2][ClO4]2 2H2O 2 and {[Ag(7HtpO)]ClO4}n 3, where the ligands are the triazolopyrimidine derivatives 4,5-dihydro-5-oxo[1,2,4]triazolo[1,5-a]pyrimidine (5HtpO) and 4,7-dihydro-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine (7HtpO), are described. 1 and 2 are binuclear compounds, with two ligands bridging two silver atoms thro...

Quantum-chemical calculations were performed for all possible isomers of neutral aniline and its redox forms, and intramolecular proton-transfer (prototropy) accompanied by π-electron delocalization was analyzed. One-electron oxidation (PhNH(2) - e → [PhNH(2)](+•)) has no important effect on tautomeric preferences. The enamine tautomer is preferred for oxidized aniline similarly as for the neut...

Tautomerism in organic chemistry has been extensively studied in condensed phase by spectrometric methods, mainly by IR and NMR techniques. Mass spectrometry studies start 40 years ago but just recently it has been recognized the importance of the mass spectral data for the study of tautomerism in the gas phase. Mass spectrometry can provide valuable information in regard to tautomeric equilibr...

Ab initio and DFT methods have been used to study the seven tautomeric forms of 5-methylcytosine molecule.The related tautomer in gas phase have been studied at HF/6-31G, HF/6-31G* and B3LYP/6-31G* levels oftheory. The structures,enthalpies,entropies,Gibbs free energies,relative tautomerization energies of tautomersand tautomeric equilibrium constants were compared and analyzed along with full ...