On the tautomeric states of guanine and cytosine

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Abstract

Recently Chan and coworkers reported that the H8 proton of guanine and H5 proton of cytosine have unusually broad resonances in the PMR spectrum under certain conditions of temperatures and pD, and interpreted their results as indicating that the minor tautomers of guanine and cytosine were present to the extent of 15 ± 3%. We find, however, that the previously reported phenomena are not reproducible with purified samples of 2′ GMP and 5′ CMP, but with addition of paramagnetic impurities the pD and temperature dependence of GH8 and CH5 proton linewidth broadening previously reported can be reproduced. This study, therefore, raises serious questions about the existence of 15% minor tautomers in cytosine and guanine at room temperature in neutral aqueous solution.

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