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Re: WSN: residence time in the hydration shell (fwd)
Sender: bruce_bush@merck.com (Bruce Bush)
Subject: Re: WSN: residence time in the hydration shell
There should be a huge literature in this area, coming from neutron
scattering, NMR, hydrodynamics, fluorescence polarization relaxation,
perhaps electrophoresis. I have a few references provided by speakers
at the 1994 Water Gordon Research Conference. They may lead you to
real experts in the field:
M-C Bellisent-Funel et al, Physica B 180&181 740-44 (1992)
Single-particle dynamics of hydration water in protein (expt)
S.H.Lee & P.J.Rossky, J Chem Phys 100, 3334 (1994)
Comparison of structure and dynamics of liquid water at hydrophobic
and hydrophilic surfaces -- MD simulation
W. Doster et al, Phys Rev Letts 65:1080-2 (1990)
Instability of liquidlike motions in a globular protein observed
by inelastic neutron scattering
[This reference may not be the best; Doster spoke in 1994 about
neutron difference spectroscopy of confined water near myoglobin.
He mentioned molecular dynamics simulations by **Peter Steinbach**
which you may want to look up.
Kurt Wuethrich [ETH, Zurich] has written frequently on NMR relaxation
times of water near proteins. Very few waters are different from
bulk water, by this measure. That says something about residence
times compared with rotational relaxation times and NMR time scale.
I would be very careful in interpreting all-atom computer simulations
to get time scales ('residence times'). A simulation cannot accurately
sample ong time scales, unless one cleverly knows the transition state
geometry in advance. Even then, the force field used in the simulation
may not contain good information about distorted states, only about
the ground state. For both reasons, a simulation could easily be
many orders of magnitude "off". Empirical models fit to experimental
data may be much more useful.
A fine article in recent _Science_ about glassy states and time scales
may apply in some way to the interface between water and solute or protein:
Frank H Stillinger Science 267 1935 (31 March 95)
A topographic view of supercooled liquids and glass formation
He doesn't talk specifically about water or water structure, but he does
show why it is that when structure-energies and system entropies are evenly
balanced, around the "glass temperature", time scales can change rapidly
for small changes in condition. For uniform systems, the changing factor is
temperature and perhaps pH or ionic strength. Around a solute surface,
features such as exposed peptide or hydrophobic patches could have equally
large effects on time scale of nearby waters.
I suspect that changes in time scale do not help much to *explain*
equilibrium energy differences -- rather the other way around: tiny
energy-level changes can greatly modify time scales. This includes
time scales of enzyme kinetics when water is involved in the rate-
limiting steps. So enzyme kinetics studies are also experimental probes
of water residence times.
Best wishes,
/ Bruce /
bruce_bush@merck.com Merck Research Labs, Rahway NJ USA 07065
>
> I'm interested in the residence time of water molecules around hydrophilic
> or hydrophobic solutes. I am searching for references on experimental
> and theoretical studies, and especially those with computer simulation of
> this feature of aqueous solutions.
>
> Grazia Cottone
>
>