Broad-line NMR study of H2O and D2O in collagen fibers.

Abstract

The deuterium NMR spectra of D2O absorbed in parallel collagen fibers have been recorded for samples containing four different percentages of D2O. In all cases, the spectra consisted of a pair of lines, the separation of which is given by K(3 cos2θ − 1), where K is small compared to the rigid-lattice value and decreases with increasing moisture content of the fibers, and θ is the angle between the fiber axis and the magnetic field. The splitting is ascribed to quadrupole perturbation of the Zeeman levels of deuterium caused by slightly anisotropic but rapid reorientation of D2O molecules in the fiber lattice. Contrary to the interpretation by others, we have concluded from a comparison of the spectra of D2O and H2O in collagen: (1) that the center line in the H2O spectra is not due to water, and (2) that line broadening in the H2O spectra, both at high temperatures and in the presence of added salts, is due to proton exchange between the water molecules. Molecular motion causes both H2O and D2O splittings to be reduced to approximately the same fraction of their respective rigid-lattice splittings.