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,Aτ_A of the spin–lattice relaxation rate, R^*_1,A(> R^*_1,B) and the lifetime, τ_A, 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,Aτ_A≪ 1) the time-dependent magnetization is determined by a slow relaxation rate, R_1,B, at site B, and shows a single-exponential decay.