5,525 research outputs found
Structure and stability of chiral beta-tapes: a computational coarse-grained approach
We present two coarse-grained models of different levels of detail for the
description of beta-sheet tapes obtained from equilibrium self-assembly of
short rationally designed oligopeptides in solution. Here we only consider the
case of the homopolymer oligopeptides with the identical sidegroups attached,
in which the tapes have a helicoid surface with two equivalent sides. The
influence of the chirality parameter on the geometrical characteristics, namely
the diameter, inter-strand distance and pitch, of the tapes have been
investigated. The two models are found to produceequivalent results suggesting
a considerable degree of universality in conformations of the tapes.Comment: 24 pages, 5 PS figures. Accepted to J. Chem. Phy
On the conformational structure of a stiff homopolymer
In this paper we complete the study of the phase diagram and conformational
states of a stiff homopolymer. It is known that folding of a sufficiently stiff
chain results in formation of a torus. We find that the phase diagram obtained
from the Gaussian variational treatment actually contains not one, but several
distinct toroidal states distinguished by the winding number. Such states are
separated by first order transition curves terminating in critical points at
low values of the stiffness. These findings are further supported by
off-lattice Monte Carlo simulation. Moreover, the simulation shows that the
kinetics of folding of a stiff chain passes through various metastable states
corresponding to hairpin conformations with abrupt U-turns.Comment: 9 pages, 16 PS figures. Journal of Chemical Physics, in pres
Monte Carlo simulations of infinitely dilute solutions of amphiphilic diblock star copolymers
Single-chain Monte Carlo simulations of amphiphilic diblock star copolymers
were carried out in continuous space using implicit solvents. Two distinct
architectures were studied: stars with the hydrophobic blocks attached to the
core, and stars with the polar blocks attached to the core, with all arms being
of equal length. The ratio of the lengths of the hydrophobic block to the
length of the polar block was varied from 0 to 1. Stars with 3, 6, 9 or 12
arms, each of length 10, 15, 25, 50, 75 and 100 Kuhn segments were analysed.
Four distinct types of conformations were observed for these systems. These,
apart from studying the snapshots from the simulations, have been
quantitatively characterised in terms of the mean-squared radii of gyration,
mean-squared distances of monomers from the centre-of-mass, asphericity
indices, static scattering form factors in the Kratky representation as well as
the intra-chain monomer-monomer radial distribution functions.Comment: 12 pages, 11 ps figures. Accepted for publication in J. Chem. Phy
Conformations of dendrimers in dilute solution
Conformations of isolated homo- dendrimers of G=1-7 generations with D=1-6
spacers have been studied in the good and poor solvents, as well as across the
coil-to-globule transition, by means of a version of the Gaussian
self-consistent (GSC) method and Monte Carlo (MC) simulation in continuous
space based on the same coarse-grained model. The latter includes harmonic
springs between connected monomers and the pair-wise Lennard-Jones potential
with a hard core repulsion. The scaling law for the dendrimer size, the degrees
of bond stretching and steric congestion, as well as the radial density, static
structure factor, and asphericity have been analysed. It is also confirmed that
while smaller dendrimers have a dense core, larger ones develop a hollow domain
at some separation from the centre.Comment: RevTeX, 14 pages, 19 PS figures, Accepted for publication in J. Chem.
Phy
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