LONGITUDINAL NUCLEAR-RELAXATION OF AN ABX SPIN SYSTEM APPLICATION TO A C-13-C-13-H-1 FRAGMENT WITH AND WITHOUT PROTON IRRADIATION

The longitudinal relaxation and the nuclear Overhauser enhancement, relative to the A and B transitions of an ABX spin system, are studied theoretically. A complete treatment based on density matrix equations is given, with and without irradiation of X transitions. Assuming a doubly enriched fragment of the type (diagram presented) numerical simulations have been performed with the aim to study the effects of cross-correlation spectral densities and motional anistropy. For the example considered, the initial slopes of carbonyl lines recovery curves yield a wealth of information. This interesting behavior arises from mixing effects produced by the observing pulse. The other data (recovery curves and NOE factors) can be, to a good approximation, interpreted in terms of generalized Solomon equations. These latter conclusions are however valid regarding the geometry of the considered fragment and, in the general case, cross-correlation terms must be taken into account. © 1979 American Institute of Physics.