Pulse sequences for detection of NH2 center dot center dot center dot N hydrogen bonds in sheared G center dot A mismatches via remote, non-exchangeable protons

The non-detectability of NH . . .N hydrogen bonds in nucleic acids due to e xchange broadened imino/amino protons has recently been addressed via the u se of non-exchangeable protons for detecting internucleotide (2h)J(NN) coup lings. in these applications, the appropriate non-exchangeable proton is se parated by two bonds from the NH . . .N bond. in this paper, we extend the scope of this approach to protons which are separated by four bonds from th e NH . . .N moiety. specifically, we consider the case of the commonly occu rring sheared G . A mismatch alignment, in which we use the adenine H2 prot on to report on the (A)N6H6(1,2). . . N3(G) hydrogen bond, in the presence of undetectable, exchange broadened N6H6(1,2) protons. two sequences, the ' straight- through' (H6)N6N3H2 and 'out-and-back' H2N6N3 experiments, are pr esented for observing these correlations in H2O and D2O solution, respectiv ely. the sequences are demonstrated on two uniformly N-15,C-13 labelled dna samples: d(G(1)G(2)G(3)T(4)T(5)C(6)A(7)G(8)G(9))(2), containing a G3.(C6-A 7) triad involving a sheared G3.A7 mismatch, and d(G(1)G(2)G(3)C(4)A(5)G(6) G(7)T(8))(4), containing an A5.(G3.G6.G3.G6).A5 hexad involving a sheared G 3.A5 mismatch.