The Role of the Primitive Relaxation in the Dynamics of Aqueous Mixtures, Nano-confined Water and Hydrated Proteins
Abstract
The relaxation scenario in aqueous systems, such as mixtures of water with hydrophilic solutes, nano-confined water and hydrated biomolecules, has been shown to exhibit general features, in spite of the huge differences in structure, chemical composition and complexity. Dynamics, in all these systems, invariably shows at least two relaxations: (i) a slower process, related to cooperative and structural motions of the water and solute molecules (in the case of mixtures) or related to interfacial processes in the case of confined water and (ii) a faster process, with non-cooperative character originating from water. The latter has properties including timescale and temperature dependence similar or related in all the aqueous systems. This water-specific relaxation can be identified as the primitive relaxation, or the Johari-Goldstein beta-relaxation in glass-forming substances. The primitive process is the precursor of the many-body relaxation process which increases in length-scale with time until the terminal α-relaxation is reached. Using new experimental data (at atmospheric and high pressure) along with a revision of most of the recent literature on the dynamics of confined water and aqueous mixtures, we show that the two above-mentioned relaxation processes are inter-related as evidenced by correlations in their properties. For instance, both relaxation time and dielectric strength of the water-specific relaxation exhibit a crossover from a stronger to a weaker dependence with decreasing T, at the temperature where the slow process attains a very long timescale (> 1ks) and becomes structurally arrested, exactly analogous to that found for beta-relaxation in van der Waals liquids. Moreover, the primitive relaxation of water is shown to play a pivotal role in determining the dynamics of hydrated biomolecules in general, including the "dynamic transition" observed by neutron scattering and Mossbauer spectroscopy.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2010
- Accession Number
- ADA530800
Entities
People
- K. L. Ngai
- N. Shinyashiki
- P. A. Rolla
- S. Ancherbak
- S. Capaccioli
Organizations
- United States Naval Research Laboratory