Biopolymers and cell. 2003; 19 (4): 378 - 381

Cytosine self-association in anhydrous DMSO through two equivalent H-bonds N1H...O-C2 lowers the barrier of amino group turn: H NMR spectroscopy data

S. P. Samijlenko, I. V. Kondratyuk, A. L. Potyahaylo, D. M. Hovorun

By H NMR spectroscopy it was established in anhydrous DMSO-d6 that under increase of cytosine concentration from 5 up to 35 mM the doublet signal of its amino group becomes gradually transformed into the singlet one. This observation is interpreted as a result of lowering the barrier of amino group turn due to central symmetrical self-association of the base through two equivalent intermolecular H-bonds N1H...O"C2, which is likely to weaken px-conjugation of the lone electron pair of amino nitrogen atom with the ring ji-electron system. Cytosine NI-methylsubstitution was shown to impact amino group in the similar way as self-association.