Biopolym. Cell. 2003; 19(4):378-381.
http://dx.doi.org/10.7124/bc.00066B
Molecular Biophysics
Cytosine self-association in anhydrous DMSO through two equivalent H-bonds N1H...O=C2 lowers the barrier of amino group turn: 1H NMR spectroscopy data
1Samijlenko S. P., 1Kondratyuk I. V., 1Potyahaylo A. L., 1Hovorun D. M.
  1. Institute of Molecular Biology and Genetics, NAS of Ukraine
    150, Akademika Zabolotnoho Str., Kyiv, Ukraine, 03680

Abstract

By 1H 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 pπ-conjugation of the lone electron pair of amino nitrogen atom with the ring π-electron system. Cytosine N1-methylsubstitution was shown to impact amino group in the similar way as self-association.
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