10 research outputs found
Insights into Hydration Dynamics and Cooperative Interactions in Glycerol-Water Mixtures by Terahertz Dielectric Spectroscopy.
We report relaxation dynamics of glycerol-water mixtures as probed by megahertz-to-terahertz dielectric spectroscopy in a frequency range from 50 MHz to 0.5 THz at room temperature. The dielectric relaxation spectra reveal several polarization processes at the molecular level with different time constants and dielectric strengths, providing an understanding of the hydrogen-bonding network in glycerol-water mixtures. We have determined the structure of hydration shells around glycerol molecules and the dynamics of bound water as a function of glycerol concentration in solutions using the Debye relaxation model. The experimental results show the existence of a critical glycerol concentration of ∼7.5 mol %, which is related to the number of water molecules in the hydration layer around a glycerol molecule. At higher glycerol concentrations, water molecules dispersed in a glycerol network become abundant and eventually dominate, and four distinct relaxation processes emerge in the mixtures. The relaxation dynamics and hydration structure in glycerol-water mixtures are further probed with molecular dynamics simulations, which confirm the physical picture revealed by the dielectric spectroscopy
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Insights into Hydration Dynamics and Cooperative Interactions in Glycerol-Water Mixtures by Terahertz Dielectric Spectroscopy.
We report relaxation dynamics of glycerol-water mixtures as probed by megahertz-to-terahertz dielectric spectroscopy in a frequency range from 50 MHz to 0.5 THz at room temperature. The dielectric relaxation spectra reveal several polarization processes at the molecular level with different time constants and dielectric strengths, providing an understanding of the hydrogen-bonding network in glycerol-water mixtures. We have determined the structure of hydration shells around glycerol molecules and the dynamics of bound water as a function of glycerol concentration in solutions using the Debye relaxation model. The experimental results show the existence of a critical glycerol concentration of ∼7.5 mol %, which is related to the number of water molecules in the hydration layer around a glycerol molecule. At higher glycerol concentrations, water molecules dispersed in a glycerol network become abundant and eventually dominate, and four distinct relaxation processes emerge in the mixtures. The relaxation dynamics and hydration structure in glycerol-water mixtures are further probed with molecular dynamics simulations, which confirm the physical picture revealed by the dielectric spectroscopy
High-Precision Megahertz-to-Terahertz Dielectric Spectroscopy of Protein Collective Motions and Hydration Dynamics
The
low-frequency collective vibrational modes in proteins as well
as the protein–water interface have been suggested as dominant
factors controlling the efficiency of biochemical reactions and biological
energy transport. It is thus crucial to uncover the mystery of the
hydration structure and dynamics as well as their coupling to collective
motions of proteins in aqueous solutions. Here, we report dielectric
properties of aqueous bovine serum albumin protein solutions as a
model system using an extremely sensitive dielectric spectrometer
with frequencies spanning from megahertz to terahertz. The dielectric
relaxation spectra reveal several polarization mechanisms at the molecular
level with different time constants and dielectric strengths, reflecting
the complexity of protein–water interactions. Combining the
effective-medium approximation and molecular dynamics simulations,
we have determined collective vibrational modes at terahertz frequencies
and the number of water molecules in the tightly bound and loosely
bound hydration layers. High-precision measurements of the number
of hydration water molecules indicate that the dynamical influence
of proteins extends beyond the first solvation layer, to around 7
Ã… distance from the protein surface, with the largest slowdown
arising from water molecules directly hydrogen-bonded to the protein.
Our results reveal critical information of protein dynamics and protein–water
interfaces, which determine biochemical functions and reactivity of
proteins