Investigation of Protein Hydration by Proton Spin Relaxation Time Measurements

Abstract

Summary Spin-lattice relaxation times T1 in aqueous solutions of dialysed egg white were measured for concentrations between 4.5 and 9.3 wt. % in the magnetic field range corresponding to proton Larmor frequencies from 0.01 to 160 MHz. A strong dependence of T1 on the magnetic field begins at approx. 0.5 MHz. It can be described by a log-Gauss distribution of rotational correlation times in the solvation layer with the maximum at 1.52·10−9 sec. The greater part of the distribution lies below the correlation time for the reorientation of the ovalbumin molecule itself. This means that the adsorbed water molecules have some freedom of motion with respect to the protein molecule. The width of the distribution is somewhat dependent on the concentration. This paper also contains the results of neutron activation, spectrochemical analysis and EPR measurements, which show that the amount of paramagnetic ions present in samples of protein solutions cannot be responsible for the decrease of T1 with respect to pure water.