Resolution of problems in soft matter dynamics by combining calorimetry and other spectroscopies

Abstract

In several current important problems in different areas of soft matter physics, controversy persists in interpreting the molecular dynamics observed by various spectroscopies including dielectric relaxation, light scattering, nuclear magnetic resonance, and neutron scattering. Outstanding examples include: (1) relaxation of water in aqueous mixtures, in molecular sieves and silica-gel nanopores, and in hydration shell of proteins; and (2) dynamics of each component in binary miscible polymer blends, in mixtures of an amorphous polymer with a small molecular glassformer, and in binary mixtures of two small molecular glassformers. We show the applications of calorimetry to these problems have enhanced our understanding of the dynamics and eliminated the controversies

The role of primitive relaxation in the dynamics of aqueous mixtures, nano-confined water and hydrated proteins

“…From this, the dynamics of proteins is coupled to that of water or other solvents surrounding the protein molecules. However, in the literature, different views of this coupling and explanation of the dynamics have been offered [10,17,19,35,.…”

“…In the past, the neutron scattering data of hydrated biomolecules were interpreted without the benefit of the knowledge gained using other techniques with longer time windows in the same systems or simpler systems of aqueous mixtures and confined water. By taking advantage of these other relevant experimental facts now available [19,35,84,85], a definitive interpretation of the Mössbauer spectroscopic and neutron scattering data can be given, which traces the so-called 'dynamic transition' observed in the MSD to the dynamics of the primitive relaxation of hydration water or other solvents including aqueous mixtures and anhydrous hydrophilic substances. From the results and conclusions, the role of hydration water or other solvents for protein dynamics and function is given a new interpretation.…”

“…The presence of bulk water in addition to hydration water in hydrated biomolecules makes the observed dynamics by dielectric relaxation [19,35,86,90,91] and calorimetry [84] more complicated than aqueous mixtures and confined water. Notwithstanding, these extraneous contributions were identified and separated out from the relevant structural relaxation of the hydrated biomolecule and the relaxation of water in the hydration shell.…”

“…At least two relaxation processes were always reported, both can be detected by the highly sensitive adiabatic calorimetry or by broadband dielectric spectroscopy [8,19]. There is a slower process coming from the structural relaxation of the solute molecules hydrogen bonded to water or from motion of molecules of the confining wall that are hydrogen bonded to water in the case of confined water.…”

Dynamics and Glass Transition of Aqueous Solutions of Molecular Liquid, Polymer, and Protein Studied by Broadband Dielectric Spectroscopy

“…We applied the theoretical interpretation of a mixture of van der Waals liquids using the coupling model to more complicated aqueous solutions [56,86] and successfully explained the behavior of more complicated partially crystallized aqueous protein solutions [84]. Specifically, it has been demonstrated that the correlation between the α-and the JG relaxations observed in various amorphous substances mimics that between the relaxation processes of hydrated protein and water molecules in protein-water systems [84,[87][88][89][90]. This means that the local motion of water molecules serves as the elementary process of the cooperative motion of water and protein molecules that undergo local structural fluctuation and is expected to be related to the expression of the functions of proteins.…”