Measurement of small scalar and dipolar couplings in purine and pyrimidinebases

A suite of spin-state-selective excitation ((SE)-E-3) NMR experiments for t he measurements of small one-bond (C-13-C-13, N-15-C-13) and two-bond (H-1- C-13, H-1-N-15) coupling constants in (1)3C,(1)5N labeled purine and pyrimi dine bases is presented. The incorporation of band-selective shaped pulses, elimination of the cross talk between alpha and beta sub-spectra, and accu racy and precision of the proposed approach are discussed. Merits of using (SE)-E-3 rather than alpha/beta -half-filter are demonstrated using results obtained on isotopically labeled DNA oligonucleotides.