HYDROGEN-BOND ASSOCIATION OF N(4)-HYDROXYCYTOSINE WITH PURINES

Recent spectroscopic work has shown that in aqueous solution pyrimidines and purines form vertical stacks with no evidence of in-plane hydrogen-bonding between pairs of bases1,2. The conformations of polynucleotides in aqueous solution are probably largely determined by the interactions responsible for the vertical stacking of mono-meric species3. In non-aqueous solution, vertical stacking is much less important1,4, and studies of mixtures of the nucleic acid bases indicate specific hydrogen-bonding between those pairs of bases that are complementary in DNA4-10. In solvents which are not hydrogen-bond donors, regardless of polarity, the association constant for the guanine-cytosine pair is several times greater than that for the adenine-thymine (uracil) pair, but in both cases the mixed complex is preferred to a mixture of self-dimers; mixtures of non-complementary bases show no association, although mixed hydrogen-bonded pairs can in principle be drawn. © 1969 Nature Publishing Group.