title: Separable cooperative and localized translational motions of water confined by a chemically heterogeneous environment.
abstract: We report quasi-elastic neutron scattering experiments at two resolutions that probe timescales of picoseconds to nanoseconds for the hydration dynamics of water, confined in a concentrated solution of N-acetyl-leucine-methylamide (NALMA) peptides in water over a temperature range of 248 K to 288 K. The two QENS resolutions used allow for a clean separation of two observable translational components, and ultimately two very different relaxation processes, that become evident when analyzed under a combination of the jump diffusion model and the relaxation cage model. The first translational motion is a localized beta-relaxation process of the bound surface water, and exhibits an Arrhenius temperature dependence and a large activation energy of approximately 8 kcal mol(-1). The second non-Arrhenius translational component is a dynamical signature of the alpha-relaxation of more fluid water, exhibiting a glass transition temperature of approximately 116 K when fit to the Volger Fulcher Tamman functional form. These peptide solutions provide a novel experimental system for examining confinement in order to understand the dynamical transition in bulk supercooled water by removing the unwanted interface of the confining material on water dynamics.
authors: Department of Bioengineering, University of California, Berkeley, CA 94720, USA.
authors: Cecile
authors: C
authors: Malardier-Jugroot
authors: Teresa
authors: T
authors: Head-Gordon
mesh_terms: D007930:Leucine / Q000031:analogs & derivatives; D008956:Models, Chemical; D033363:Neutron Diffraction; D012212:Rheology; D013057:Spectrum Analysis; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: C492360:N-acetyl-leucine-methylamide; D014867:Water; D007930:Leucine