Interior segment regrowth configurational-bias algorithm for the efficient sampling and fast relaxation of coarse-grained polyethylene and polyoxyethylene melts on a high coordination lattice.

We demonstrate the application of a modified form of the configurational-bias algorithm for the simulation of chain molecules on the second-nearest-neighbor-diamond lattice. Using polyethylene and poly(ethylene-oxide) as model systems we show that the present configurational-bias algorithm can increase the speed of the equilibration by at least a factor of 2-3 or more as compared to the previous method of using a combination of single-bead and pivot moves along with the Metropolis sampling scheme [N. Metropolis, A.

Calculation of pressure using the virtual-volume-variation method and the virial method from chain conformations obtained by Monte Carlo simulations on the second nearest neighbor diamond lattice.

For a model system of polyethylene of chain lengths 40 and 100 carbon atoms, we calculated the pressure at different densities and compared them with the experimental values. The simulation was conducted on the second nearest neighbor diamond lattice, and the pressure was calculated using the virtual-volume-variation method after the system was reverse mapped to its fully atomistic form in continuous space and energy minimized. In addition, the pressure was also calculated from the virial route by conducting a short molecular dynamics simulation starting from the energy minimized structure.

Molecular origin of demixing, prior to crystallization, of atactic polypropylene/isotactic polypropylene blends upon cooling from the melt.

An amorphous 50/50 atactic polypropylene (aPP)/isotactic polypropylene (iPP) mixture at 125 degrees C was simulated using a second nearest neighbor diamond lattice and a three states rotational isometric state model. The result suggests that at the liquidlike density that corresponds to the atmospheric pressure, aPP prefers to interact with other aPP chains rather than with iPP chains. The result is consistent with the inference of Keith and Padden [J.

Modification of statistical threading in two-component pseudorotaxane melts using the amphiphilic approach and variations in the confinement geometry.

Recently we described a coarse-grained model of poly(ethylene oxide) and then employed that model to study the amount of spontaneous threading of cyclic molecules by linear chains in the melt [C. A. Helfer, G.

Molecular Mechanics Study of the Inclusion Complexes of 2-Methyl Naphthoate with alpha- and beta-Cyclodextrins.

Molecular mechanics calculations were employed to study the inclusion of 2-methyl naphthoate in alpha- and beta-cyclodextrin in vacuo and in the presence of water as a solvent. The driving forces for complexation are dominated by nonbonded van der Waals host:guest interactions in both environments. The 2-methyl naphthoate penetrates completely into the cavity of beta-cyclodextrin, but there is only partial penetration by the same molecule into the smaller cavity of alpha-cyclodextrin.

Intramolecular energy transfer in compounds with two 1-pyrenoate groups separated by methylene spacers.

Steady-state fluorescence anisotropy (r) and fluorescence lifetime (τ) measurements have been used to study the efficiency of nonradiative singlet energy transfer as a function of alkane size in 1-pyrenecarboxylic acid alkanediyl esters (as a function ofm in Py-COO-(CH2) m -OOC-Py, where Py denotes pyrene substituted in the 1-position, andm=2-6). Experiments were performed in media of different viscosity, η, obtained by changing the temperature (from -20 to 40°C) of dilute solutions in ethylene glycol and by examination of the compounds in a solid matrix of poly(methyl methacrylate) (PMMA) at ambient temperature. The Py-COO-(CH2)m-OOC-Py exhibit intramolecular excimer emission in ethylene glycol at these temperatures, but the intensity of this emission is much lower than when these compounds are placed in common solvents of lower η.

Range of the influence of the carbohydrate moiety on the conformation of the poly(amino acid) backbone in glycosylated mucins.

The influence of glycosylation on the conformational properties of porcine submaxillary gland mucin has been investigated using rotational isomeric state theory. The specific objective was to determine the conditions under which the polypeptide has the relatively large mean square unperturbed radius of gyration mean value of s2(0), demanded by the measurements of Shogren et al., while retaining the overall architecture of a random coil.

Influence of L-cystinyl side-chain configurations on the melting of crosslinked alpha-tropomyosin dimers.

The experimental melting profile reported by Holtzer, M.E., Holtzer, A.

Helix formation upon acidification of protein-dodecyl sulfate complexes.

The pH dependence of circular dichroism spectra has been studied for dodecyl sulfate complexes formed by 25 proteins and for a random copolypeptide of glutamic acid and alanine. The pH range covered is that in which titration of side-chain carboxyl groups is to be expected. Circular dichroism spectra signify an increase in helical content upon acidification, although in many cases the increase is quite small.

Effects of temperature, pH and detergents on the molecular conformation of the enterotoxin of Clostridium perfringens.

The effects of temperature, pH and sodium dodecyl sulfate on the conformation of the enterotoxin from Clostridium perfringens type A were followed by circular dichroism in both the peptide and aromatic regions. At near-physiological conditions (35 degrees C, pH 6.7) the enterotoxin exhibited a conformation consisting of approximately 60% pleated sheet, 40% non-periodic, and essentially no helix.