Silver(I)-mediated hetero base pairs of 6-pyrazolylpurine and its deaza derivatives

A series of antiparallel-stranded and parallel-stranded DNA duplexes containing hetero base pairs of the artificial nucleobases 6-(1H-pyrazol-1-yl)-9H-purine (6PP), 1-deaza-6PP ((1D)6PP), 7-deaza-6PP ((7D)6PP), and 1,7-dideaza-6PP ((1,7D)6PP) were investigated with respect to their ability to form silver(I)-mediated base pairs. A close examination of the duplex melting temperatures in the absence and in the presence of silver(I) ions shows a strong sequence-dependence of the stability of the resulting silver(I)-mediated base pairs. The most stable silver(I)-mediated base pairs are formed when (1,7D)6PP is located in a purine-rich strand opposite either 6PP or (7D)6PP. This indicates that the silver(I) ions are coordinated via the Watson-Crick edge of the latter nucleobase, whereas they bind to the pyrazolyl moiety of the former. As a result, a [2+1] coordination environment is proposed for the silver(I) ions.

Automated summary

The study investigated the ability of DNA duplexes containing artificial nucleobases to form silver(I)-mediated base pairs. It was found that the stability of resulting silver(I)-mediated base pairs is strongly sequence-dependent. The most stable silver(I)-mediated base pairs are formed when specific artificial nucleobases are located opposite to certain natural nucleobases in the DNA duplex.