skip to main content

SciTech ConnectSciTech Connect

Title: Depolarized light scattering and dielectric response of a peptide dissolved in water

The density and orientational relaxation of bulk water can be separately studied by depolarized light scattering (DLS) and dielectric spectroscopy (DS), respectively. Here, we ask the question of what are the leading collective modes responsible for polarization anisotropy relaxation (DLS) and dipole moment relaxation (DS) of solutions involving mostly hydrophobic solute-water interfaces. We study, by atomistic molecular dynamics simulations, the dynamics and structure of hydration water interfacing N-Acetyl-leucine-methylamide dipeptide. The DLS response of the solution is consistent with three relaxation processes: bulk water, rotations of single solutes, and collective dipole-induced-dipole polarizability of the solutes, with the time-scale of 130–200 ps. No separate DLS response of the hydration shell has been identified by our simulations. Density fluctuations of the hydration layer, which largely contribute to the response, do not produce a dynamical process distinct from bulk water. We find that the structural perturbation of the orientational distribution of hydration waters by the dipeptide solute is quite significant and propagates ∼3−5 hydration layers into the bulk. This perturbation is still below that produced by hydrated globular proteins. Despite this structural perturbation, there is little change in the orientational dynamics of the hydration layers, compared to the bulk, as probed by both single-particlemore » orientational dynamics and collective dynamics of the dipole moment of the shells. There is a clear distinction between the perturbation of the interfacial structure by the solute-solvent interaction potential and the perturbation of the interfacial dynamics by the corresponding forces.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Department of Physics, Arizona State University, PO Box 871604, Tempe, Arizona 85287-1604 (United States)
  2. Dipartimento di Fisica, Universita di Perugia, via Pascoli, 06123 Perugia (Italy)
  3. Department of Physics and Department of Chemistry and Biochemistry, Arizona State University, PO Box 871604, Tempe, Arizona 85287-1604 (United States)
Publication Date:
OSTI Identifier:
22255240
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 3; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANISOTROPY; DENSITY; DIPOLE MOMENTS; DIPOLES; HYDRATION; INTERACTIONS; LAYERS; LEUCINE; LIGHT SCATTERING; MOLECULAR DYNAMICS METHOD; PEPTIDES; PERTURBATION THEORY; POLARIZABILITY; RELAXATION; SIMULATION; SOLUTES; SOLUTIONS; SPECTROSCOPY; WATER