DIRECT MEASUREMENT OF ANGLES BETWEEN BOND VECTORS IN HIGH-RESOLUTION NMR

Angles between two interatomic vectors are measured for structure eluc idation in solution nuclear magnetic resonance (NMR). The angles can b e determined directly by using the effects of dipole-dipole cross-corr elated relaxation of double-quantum and zero-quantum coherences. The m easured rates can be directly related to the angular geometry without need for calibration of a Karplus-type curve, as is the case for scala r coupling measurements, and depend only on the rotational correlation time of the molecule as an empirical parameter. This makes the determ ination of torsional angles independent from the measurement of coupli ng constants. The two interatomic vectors can in principle be arbitrar ily far apart. The method was demonstrated on the measurement of the p eptide backbone angle psi in the protein rhodniin, which is difficult to determine in solution by NMR spectroscopy.