| Abstract: |
Trans-hydrogen bond coupling constants across 15Nd - H⋯15Na hydrogen bonds [2hJ(N,N)] have been immensely beneficial in providing direct evidence for these hydrogen bonds in nucleic acids and their complexes. A very commonly occurring hydrogen bonding topology is the Ha - Ca - Na⋯Hd - Nd alignment, which is usually identified via 1Hd-15Na correlated spectra (HNN-COSY, soft HNN-COSY) or 1Ha-15Nd correlated spectra [H(C)NN(H)]. In these experiments, the donor/acceptor nitrogens need to be assigned independently, which is often compromised by degeneracy problems among the 15N nuclei. Recently, we have designed NMR techniques for alleviating these problems by providing direct 1Ha-1Hd correlations across Ha - Ca - Na⋯Hd - Nd hydrogen bonds in G·G·G·G tetrads and sheared G·A mismatches. Here, we present further demonstrations of these H(NN)H sequences as useful tools for identifying Ha - Ca - Na⋯Hd - Nd alignments in G·G and A·A mismatches, and reverse A-T Watson-Crick base pairs, on two uniformly 13C/15N-labeled dimeric DNA molecules, d(GGAGGAT) and d(G2A2G2T3G3AT). Copyright © 2001 John Wiley & Sons, Ltd. |
