NMR relaxation study of disorder in the mixed system BP x GPI(1–x) and the low temperature transition from classical to quantum rotation

Abstract

1H NMR spin-lattice relaxation time (T 1) studies have been carried out in the temperature range 100 K to 4 K, at two Larmor frequencies 11.4 and 23.3 MHz, in the mixed system of betaine phosphate and glycine phosphite (BPxGPI(1–x)), to study the effects of disorder on the proton group dynamics. Analysis of T 1 data indicates the presence of a number of inequivalent methyl groups and a gradual transition from classical reorientations to quantum tunneling rotations. At lower temperatures, microstructural disorder in the local environments of the methyl groups, result in a distribution in the activation energy (Ea ) and the torsional energy gap (E 01). For certain values of x, the magnetisation recovery shows biexponential behaviour at lower temperatures.