176 research outputs found
Random Walks on a Fluctuating Lattice: A Renormalization Group Approach Applied in One Dimension
We study the problem of a random walk on a lattice in which bonds connecting
nearest neighbor sites open and close randomly in time, a situation often
encountered in fluctuating media. We present a simple renormalization group
technique to solve for the effective diffusive behavior at long times. For
one-dimensional lattices we obtain better quantitative agreement with
simulation data than earlier effective medium results. Our technique works in
principle in any dimension, although the amount of computation required rises
with dimensionality of the lattice.Comment: PostScript file including 2 figures, total 15 pages, 8 other figures
obtainable by mail from D.L. Stei
Solvent viscosity dependence for enzymatic reactions
A mechanism for relationship of solvent viscosity with reaction rate constant
at enzyme action is suggested. It is based on fluctuations of electric field in
enzyme active site produced by thermally equilibrium rocking (cranckshaft
motion) of the rigid plane (in which the dipole moment lies) of
a favourably located and oriented peptide group (or may be a few of them). Thus
the rocking of the plane leads to fluctuations of the electric field of the
dipole moment. These fluctuations can interact with the reaction coordinate
because the latter in its turn has transition dipole moment due to separation
of charges at movement of the reacting system along it. The rocking of the
plane of the peptide group is sensitive to the microviscosity of its
environment in protein interior and the latter is a function of the solvent
viscosity. Thus we obtain an additional factor of interrelationship for these
characteristics with the reaction rate constant. We argue that due to the
properties of the cranckshaft motion the frequency spectrum of the electric
field fluctuations has a sharp resonance peak at some frequency and the
corresponding Fourier mode can be approximated as oscillations. We employ a
known result from the theory of thermally activated escape with periodic
driving to obtain the reaction rate constant and argue that it yields reliable
description of the preexponent where the dependence on solvent viscosity
manifests itself. The suggested mechanism is shown to grasp the main feature of
this dependence known from the experiment and satisfactorily yields the upper
limit of the fractional index of a power in it.Comment: 36 LaTex pages, 9 Eps figures, final versio
Model for solvent viscosity effect on enzymatic reactions
Why reaction rate constants for enzymatic reactions are typically inversely
proportional to fractional power exponents of solvent viscosity remains to be
already a thirty years old puzzle. Available interpretations of the phenomenon
invoke to either a modification of 1. the conventional Kramers' theory or that
of 2. the Stokes law. We show that there is an alternative interpretation of
the phenomenon at which neither of these modifications is in fact
indispensable. We reconcile 1. and 2. with the experimentally observable
dependence. We assume that an enzyme solution in solvent with or without
cosolvent molecules is an ensemble of samples with different values of the
viscosity for the movement of the system along the reaction coordinate. We
assume that this viscosity consists of the contribution with the weight
from cosolvent molecules and that with the weight from protein matrix and
solvent molecules. We introduce heterogeneity in our system with the help of a
distribution over the weight . We verify the obtained solution of the
integral equation for the unknown function of the distribution by direct
substitution. All parameters of the model are related to experimentally
observable values. General formalism is exemplified by the analysis of
literature experimental data for oxygen escape from hemerythin.Comment: 16 LaTex pages, 5 eps figure
Temperature-dependent macromolecular X-ray crystallography
The dynamical behaviour of crystalline macromolecules and their surrounding solvent as a function of cryo-temperature is reviewed
UPON THE OPTIMAL GRAPHICAL REPRESENTATION OF FLASH DATA FROM PHOTOCHEMICAL SYSTEMS OBEYING FIRST ORDER KINETICS
Kinetics of thermal denaturation of met-hemoglobin in perturbed solvent: Relevance of bulk-electrostatic and hydrophobic interactions
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