2H NMR studies of glycerol dynamics in protein matrices

Abstract

We use (2)H NMR spectroscopy to investigate the rotational motion of glycerol molecules in matrices provided by the connective tissue proteins elastin and collagen. Analyzing spin-lattice relaxation, line-shape properties, and stimulated-echo decays, we determine the rates and geometries of the motion as a function of temperature and composition. It is found that embedding glycerol in an elastin matrix leads to a mild slowdown of glycerol reorientation at low temperatures and glycerol concentrations, while the effect vanishes at ambient temperatures or high solvent content. Furthermore, it is observed that the nonexponential character of the rotational correlation functions is much more prominent in the elastin matrix than in the bulk liquid. Results from spin-lattice relaxation and line shape measurements indicate that, in the mixed systems, the strong nonexponentiality is in large part due to the existence of distributions of correlation times, which are broader on the long-time flank and, hence, more symmetric than in the neat system. Stimulated-echo analysis of slow glycerol dynamics reveals that, when elastin is added, the mechanism for the reorientation crosses over from small-angle jump dynamics to large-angle jump dynamics and the geometry of the motion changes from isotropic to anisotropic. The results are discussed against the background of present and previous findings for glycerol and water dynamics in various protein matrices and compared with observations for other dynamically highly asymmetric mixtures so as to ascertain in which way the viscous freezing of a fast component in the matrix of a slow component differs from the glassy slowdown in neat supercooled liquids.

2H NMR Studies on the Dynamics of Pure and Mixed Hydrogen-Bonded Liquids in Confinement

“…These results are consistent with findings in previous studies on glycerol in protein matrices, which reported essentially unaffected time scale, but significantly increased dynamical heterogeneity with respect to the bulk behavior, in particular, enhanced slow contributions [27,52].…”

“…While the CC spectral densities corresponds to a symmetric distribution G(log τ), the HN and, in particular, the CD forms conform to asymmetric ones. Details of our 2 H SLR analyses using HN, CC, and CD spectral densities can be found in previous works [3,26,27].…”

Component dynamics in polyvinylpyrrolidone concentrated aqueous solutions

“…27, 28, and 90-92) and by 2 H NMR spectroscopy on different protein water systems. [63][64][65] The value of the activation energy E a ≈ 0.5 eV seems to be rather universal for these systems.…”

“…The observation of both features is characteristic of the existence of a broad distribution of correlation times. A fraction of the water molecules have relaxation times much faster than the inverse of the quadrupolar frequency (τ relaxation times much slower than 1 δ , leading to an averaged and a non-averaged motion 37,[63][64][65] in the μs time scale. We assumed that the results between 225 K and 180 K can be described as the sum of a Lorentzian and a Pake spectrum,…”

Effects of solvent concentration and composition on protein dynamics: 13 C MAS NMR studies of elastin in glycerol–water mixtures

“…On the other hand, 2 H NMR provides straightforward access to the solvent dynamics. We exploited this capability to determine the rates and mechanisms of water and glycerol motions in elastin matrices over broad time and temperature ranges [39][40][41][42][43].…”