Hydration water dynamics in biopolymers from NMR relaxation in the rotating frame

Abstract

Assuming dipole–dipole interaction as the dominant relaxation mechanism of protons of water molecules adsorbed onto macromolecule (biopolymer) surfaces we have been able to model the dependences of relaxation rates on temperature and frequency. For adsorbed water molecules the correlation times are of the order of 10 −5 s, for which the dispersion region of spin–lattice relaxation rates in the rotating frame R 1 ρ = 1/ T 1 ρ appears over a range of easily accessible B 1 values. Measurements of T 1 ρ at constant temperature and different B 1 values then give the “dispersion profiles” for biopolymers. Fitting a theoretical relaxation model to these profiles allows for the estimation of correlation times. This way of obtaining the correlation time is easier and faster than approaches involving measurements of the temperature dependence of R 1 = 1/ T 1. The T 1 ρ dispersion approach, as a tool for molecular dynamics study, has been demonstrated for several hydrated biopolymer systems including crystalline cellulose, starch of different origins (potato, corn, oat, wheat), paper (modern, old) and lyophilized proteins (albumin, lysozyme).