NMR and dielectric studies of hydrated collagen and elastin: Evidence for a delocalized secondary relaxation

TL;DR

This study combines NMR and dielectric spectroscopy to investigate hydration water dynamics in connective tissue proteins, revealing a delocalized secondary relaxation process distinct from typical eta-relaxations, with implications for understanding glassy dynamics.

Contribution

It provides evidence for a delocalized, quasi-isotropic secondary relaxation in hydrated proteins, characterized by a Gaussian distribution of energy barriers, distinct from conventional eta-processes.

Findings

Water dynamics follow an Arrhenius law at sub-ambient temperatures.

Evidence for a Gaussian distribution of energy barriers in water reorientation.

Identification of a delocalized secondary relaxation process in hydrated proteins.

Abstract

Using a combination of dielectric spectroscopy and solid-state deuteron NMR, the hydration water dynamics of connective tissue proteins is studied at sub-ambient temperatures. In this range, the water dynamics follows an Arrhenius law. A scaling analysis of dielectric losses, 'two-phase' NMR spectra, and spin-lattice relaxation times consistently yield evidence for a Gaussian distribution of energy barriers. With the dielectric data as input, random-walk simulations of a large-angle, quasi-isotropic water reorientation provide an approximate description of stimulated-echo data on hydrated elastin. This secondary process takes place in an essentially rigid energy landscape, but in contrast to typical {\beta}-relaxations it is quasi-isotropic and delocalized. The delocalization is inferred from previous NMR diffusometry experiments. To emphasize the distinction from conventional {\beta}-processes, for aqueous systems such a matrix-decoupled relaxation was termed a {\nu}-process. It is emphasized that the phenomenology of this time-honored, 'new' process is shared by many non-aqueous binary glasses in which the constituent components exhibit a sufficient dynamical contrast.