18 research outputs found
Influence of sequence correlations on the adsorption of random copolymers onto homogeneous planar surfaces
Using a reference system approach, we develop an analytical theory for the
adsorption of random heteropolymers with exponentially decaying and/or
oscillating sequence correlations on planar homogeneous surfaces. We obtain a
simple equation for the adsorption-desorption transition line. This result as
well as the validity of the reference system approach is tested by a comparison
with numerical lattice calculations
Polymer adsorption onto random planar surfaces: Interplay of polymer and surface correlation
We study the adsorption of homogeneous or heterogeneous polymers onto
heterogeneous planar surfaces with exponentially decaying site-site
correlations, using a variational reference system approach. As a main result,
we derive simple equations for the adsorption-desorption transition line. We
show that the adsorption threshold is the same for systems with quenched and
annealed disorder. The results are discussed with respect to their implications
for the physics of molecular recognition
Random copolymer adsorption: Morita approximation compared to exact numerical simulations
We study the adsorption of ideal random lattice copolymers with correlations
in the sequences on homogeneous substrates with two different methods: An
analytical solution of the problem based on the constrained annealed
approximation introduced by Morita in 1964 and the generating functional (GF)
technique, and direct numerical simulations of lattice chains averaged over
many realizations of random sequences. Both methods allow to calculate the free
energy and different conformational characteristics of the adsorbed chain. The
comparison of the results for random copolymers with different degree of
correlations and different types of nonadsorbing monomers (neutral or repelling
from the surface) shows not only qualitative but a very good quantitative
agreement, especially in the cases of Bernoullian and quasi-alternating random
sequences.Comment: 19 pages, 9 figure
Dependence of the Critical Adsorption Point on Surface and Sequence Disorders for Self-Avoiding Walks Interacting with a Planar Surface
The critical adsorption point (CAP) of self-avoiding walks (SAW) interacting
with a planar surface with surface disorder or sequence disorder has been
studied. We present theoretical equations, based on ones previously developed
by Soteros and Whittington (J. Phys. A.: Math. Gen. 2004, 37, R279-R325), that
describe the dependence of CAP on the disorders along with Monte Carlo
simulation data that are in agreement with the equations. We also show
simulation results that deviate from the equations when the approximations used
in the theory break down. Such knowledge is the first step toward understanding
the correlation of surface disorder and sequence disorder during polymer
adsorption.Comment: 29 pages, 8 figure
Theory of mechanical unfolding of homopolymer globule: all-or-none transition in force-clamp mode vs phase coexistence in position-clamp mode
Equilibrium mechanical unfolding of a globule formed by long flexible
homopolymer chain collapsed in a poor solvent and subjected to an extensional
force f (force-clamp mode) or extensional deformation D (position-clamp mode)
is studied theoretically. Our analysis, like all previous analysis of this
problem, shows that the globule behaves essentially differently in two modes of
extension. In the force-clamp mode, mechanical unfolding of the globule with
increasing applied force occurs without intramolecular microphase segregation,
and at certain threshold value of the pulling force the globule unfolds as a
whole ("all-or-none" transition). The value of the threshold force and the
corresponding jump in the distance between the chain ends increase with a
deterioration of the solvent quality and/or with an increase in the degree of
polymerization. In the position-clamp mode, the globule unfolding occurs via
intramolecular microphase coexistence of globular and extended microphases
followed by an abrupt unraveling transition. Reaction force in the microphase
segregation regime demonstrates an "anomalous" decrease with increasing
extension. Comparison of deformation curves in force and position-clamp modes
demonstrates that at weak and strong extensions the curves for two modes
coincide, differences are observed in the intermediate extension range. Another
unfolding scenario is typical for short globules: in both modes of extension
they unfold continuously, without jumps or intramolecular microphase
coexistence, by passing a sequence of uniformly elongated configurations.Comment: 19 pages, 13 figures, 1 tabl
Collapse-to-Swelling Transitions in pH- and Thermoresponsive Microgels in Aqueous Dispersions: The Thermodynamic Theory
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Developing and analyzing idealized models for molecular recognition
Behringer H, Bogner T, Polotsky A, Degenhard A, Schmid F. Developing and analyzing idealized models for molecular recognition. Journal of Biotechnology. 2007;129(2):268-278.We study equilibrium aspects of molecular recognition of two biomolecules using idealized model systems and methods from statistical physics. Starting from the basic experimental findings we demonstrate exemplarily how an idealized coarse-grained model for the investigation of molecular recognition of two biomolecules can be developed. In addition we provide details regarding two model systems for the recognition of a flexible and a rigid biomolecule respectively, the latter taking into account conformational changes. We focus particularly on the interplay and influence of the correlations of the residue distributions of the biomolecules on the recognition process. (c) 2007 Elsevier B.V. All rights reserved