Measurement of homonuclear proton couplings based on cross-peak nulling inCT-COSY

A method in which H-1-H-1 scalar and dipolar couplings are obtained from th e cross-peak nulling condition in a series of constant-time (CT) COSY spect ra, as a function of the duration of the CT period, is described. The metho d is best suited for measurement of H-1-H-1 couplings in the range 5-20 Hz. It is shown, however, that results can be sensitive to cross-correlated re laxation effects. Also, artifactual resonances, resulting from strong coupl ing, can be quite pronounced in CT-COSY spectra, even when \J(AB) /(delta ( A)- delta (B))\ < 0.1. The experiments are demonstrated for the DNA dodecam er d(CGCGAATTCGCG)(2), both in isotropic solution and in a liquid crystalli ne phase.