HETERONUCLEAR DIPOLAR CROSS-CORRELATED CROSS-RELAXATION FOR THE INVESTIGATION OF SIDE-CHAIN MOTIONS

A new NMR technique is introduced and applied for the characterization of side-chain motion in biopolymers. It takes advantage of cross-correlated cross relaxation between 4S(z)I(1z)I(2z) and S-z spin orders in (CH2)-C-13 and (CH3)-C-13 subsystems. The basic process, called SIIS cross relaxation, relies on the motional cross correlation of two CH dipolar interactions. In a particular range of intramolecular motional correlation times, it allows the distinction of different models of restricted and unrestricted intramolecular motion based on the sign of the cross peaks in a 2D cross-relaxation spectrum. The technique is applied to the cyclic decapeptide antamanide and to the protein human ubiquitin. (C) 1994 Academic Press, Inc.