New methylene specific experiments for the measurement of scalar spin-spin coupling constants between protons attached to 13C

New two- and three-dimensional NMR methods are proposed for the measurement of (3)J(H, H) coupling constants between two adjacent methylene moieties. The new experiment, which is based on a combination of the E.COSY principle and double/zero quantum heteronuclear spectroscopy, has been applied to diaceton-glucose and to the protein rhodniin. The coupling constants of CH-CH, groups have been compared with those obtained from a HCCH-E.COSY experiment to check the reliability of the results. An analysis of the coupling constants derived by comparison between experimental and simulated spectra is presented. Simulations were done with the program wtest considering fully correlated dipolar relaxation. Side-chain conformations in amino acids with adjacent methylene groups can be determined by the new experiment. (C) 1998 Academic Press.