The effect of chemical exchange on energy relaxation processes in nuclear magnetic resonance spectroscopy
Abstract
We have investigated the influence of chemical exchange on the line-shape in the n.m.r. longitudinal magnetization recovery curve and, for the first time, derived a general solution of the coupled expressions for the time evolution of the longitudinal magnetization of sites A and B for the same kind of nuclei for all conditions of each reaction rate of chemical exchange A ⇌ B in the presence of random molecular and atomic motion. The solution, covering the case where the product R*1,AτA of the spin–lattice relaxation rate, R*1,A(> R*1,B) and the lifetime, τA, for site A is larger than ca. 1, gives a non-single-exponential decay of the recovery curve in the energy relaxation process. In the extreme rapid exchange (i.e.R*1,AτA≪ 1) the time-dependent magnetization is determined by a slow relaxation rate, R1,B, at site B, and shows a single-exponential decay.