Measurement of vicinal couplings from cross peaks in COSY spectra

Abstract

Vicinal proton-proton couplings can provide useful structural information on both small and large molecules. For large molecules, couplings are in principle accessible from cross-peak multiplets in two-dimensional phase-sensitive COSY spectra. Direct measurement, however, often provides unrealistically large values because of cancellation of antiphase components. A method which allows accurate calculation of scalar couplings from measurement of separations of extrema in dispersive and absorptive plots of rows through cross peaks is presented. The method is applied to both simulated and real data on a small protein and is shown to be effective in analyzing spectra with moderate to high signal-to-noise ratios.