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Journal ArticleDOI

Molecular-dynamics simulation of structural and conformational properties of poly(propylene oxide)

07 Jun 2000-Journal of Chemical Physics (American Institute of PhysicsAIP)-Vol. 112, Iss: 23, pp 10669-10679
TL;DR: In this paper, the dihedral and bond angle distributions obtained from the present MD study are more closely related to experiments than those that have been achieved previously by combining experimental data with reverse Monte Carlo modeling.
Abstract: Molecular-dynamics simulations of poly(propylene oxide) (PPO) have been performed in the temperature range 300 K⩽T⩽450 K using a newly developed atomistic force field. Chains with 1, 11 and 45 repeat units have been considered. We find excellent agreement for the short and intermediate range order as deduced from x-ray and neutron diffraction measurements with deviations (excluding quantum mechanical effects for the nuclear motion) lying within experimental uncertainties. The static structure factor S(q) shows a first sharp diffraction peak due to interchain correlations which is shifted to smaller wave vectors with increasing temperature. The molecular weight dependence of the short and intermediate range order is found to be weak and the obtained density and thermal expansivity compare favorably with experimental data. The backbone dihedral angle distributions are essentially identical for PO11 and PO45, but deviate slightly from those for PO1, and the probability for gauche conformations is quite large resulting in a small characteristic ratio. The dihedral and bond angle distributions obtained from the present MD study are more closely related to experiments than those that have been achieved previously by combining experimental data with reverse Monte Carlo modeling.
Citations
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Journal ArticleDOI
TL;DR: The dependence of the electron correlation contribution to the dimer binding energy on basis-set size and level of theory was investigated as a function of molecular separation for a number of alkane, ether, and ketone dimers.
Abstract: Classical many-body polarizable force fields were developed for n-alkanes, perflouroalkanes, polyethers, ketones, and linear and cyclic carbonates on the basis of quantum chemistry dimer energies of model compounds and empirical thermodynamic liquid-state properties. The dependence of the electron correlation contribution to the dimer binding energy on basis-set size and level of theory was investigated as a function of molecular separation for a number of alkane, ether, and ketone dimers. Molecular dynamics (MD) simulations of the force fields accurately predicted structural, dynamic, and transport properties of liquids and unentangled polymer melts. On average, gas-phase dimer binding energies predicted with the force field were between those from MP2/aug-cc-pvDz and MP2/aug-cc-pvTz quantum chemistry calculations.

161 citations

Journal ArticleDOI
TL;DR: The computational studies suggest that the hydrophilic blocks in these copolymers interact with the polar head groups of lipid molecules, resulting in a predicted modification of the structure of the membranes, and suggest some new structure–function relationships at the nanoscale that are likely to be of importance in determining the biological activity of these otherwise inertCopolymers.
Abstract: Poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) block co-polymers (PEO–PPO–PEO, sold as Pluronics, Poloxamers, Tetronics) are a widely used class of amphiphilic materials for different biological applications. In fact for certain members of the Pluronics series, the interactions of block segments with living cells alter the lipid membrane properties and facilitate the permeation of drugs. A fuller understanding of the molecular mechanisms underpinning these interactions is essential for ensuring their safety and efficacy in biomedical applications and to inform the design of new amphiphilic copolymers for potential use in a clinical setting. In this paper, by means of atomistic molecular dynamics simulations and membrane lysis assays, we investigate the relationship between the molecular conformations of a subset of the Pluronic copolymers (L31, L61, L62 and L64) and their haemolytic activity. Our computational studies suggest that the hydrophilic blocks in these copolymers interact with the polar head groups of lipid molecules, resulting in a predicted modification of the structure of the membranes. Parallel membrane lysis assays in human erythrocytes indicate differences in the rates of haemolysis, as a result of incubation with these polymers, that correlate well with the predicted interactions from the atomistic simulations. The computational data thus provide a putative mechanism to rationalize the available experimental data on membrane lysis by these copolymers and quantitatively agree with haemoglobin release endpoints measured when copolymers with the same molecular weight and structure as of those modelled are incubated with erythrocytes. The data further suggest some new structure–function relationships at the nanoscale that are likely to be of importance in determining the biological activity of these otherwise inert copolymers.

67 citations

Journal ArticleDOI
TL;DR: The conformation and dynamics properties of polyethylene oxide (PEO) and polypropylene oxide (PPO) polymer chains at 298 K have been studied in the melt and at infinite dilution condition in water, methanol, chloroform, carbon tetrachloride, and n-heptane using molecular dynamics simulations.
Abstract: In this paper, the conformation and dynamics properties of polyethylene oxide (PEO) and polypropylene oxide (PPO) polymer chains at 298 K have been studied in the melt and at infinite dilution condition in water, methanol, chloroform, carbon tetrachloride, and n-heptane using molecular dynamics simulations. The calculated density of PEO melt with chain lengths of n = 2, 3, 4, 5 and, for PPO, n = 7 are in good agreement with the available experimental data. The conformational properties of PEO and PPO show an increasing gauche preference for the O–C–C–O dihedral in the following order water>methanol>chloroform>carbon tetrachloride = n-heptane. On the contrary, the preference for trans conformation has a maximum in carbon tetrachloride and n-heptane followed in the order by chloroform, methanol, and water. The PEO conformational preferences are in qualitative agreement with results of NMR studies. PEO chains formed different types of hydrogen bonds with polar solvent molecules. In particular, the occurrence of bifurcated hydrogen bonding in chloroform was also observed. Radii of gyration of PEO chains of length larger than n = 9 monomers showed a good agreement with light scattering data in water and in methanol. For the shorter chains the observed deviations are probably due to the enhanced hydrophobic effects caused by the terminal methyl groups. For PEO the fitting of end-to-end distance distributions with the semi-flexible chain model at 298 K provided persistence lengths of 0.375 and 0.387 nm in water and methanol, respectively. Finally, the radius of gyration of Pluronic P85 turned out to be 2.25 ± 0.4 nm at 293 K in water in agreement with experimental data.

62 citations

Journal ArticleDOI
TL;DR: In this paper, a force field for poly(dimethylsiloxane) and its oligomers was derived on the basis of intermolecular binding energies, molecular geometries, molecular electrostatic potentials, and conformational energies obtained from quantum chemistry calculations on model compounds.
Abstract: A classical force field for poly(dimethylsiloxane) (PDMS) and its oligomers has been derived on the basis of intermolecular binding energies, molecular geometries, molecular electrostatic potentials, and conformational energies obtained from quantum chemistry calculations on model compounds. The force field accurately reproduces the molecular properties of the model compounds obtained from quantum chemistry, including the Si−O−Si bond linearization energy. Molecular dynamics simulations performed on PDMS of various molecular weights between 310 and 1571 using the quantum chemistry based force field yielded good agreement with experiment for their densities, enthalpies of vaporization, and X-ray structure factors. The characteristic ratio of PDMS was also found to be in good agreement with experimental values. Molecular dynamics as represented by the melt self-diffusion coefficient and viscosity at 298 K as a function of molecular weight were also found to be in reasonable agreement with experimental value...

53 citations

Journal ArticleDOI
TL;DR: In this paper, the authors characterize the conformational and structural relaxations of poly(ethylene oxide) and poly(propylene oxide) melts, and show that correlated forward-backward motion is an important aspect of conformational relaxation, leading to strongly nonexponential distributions for the waiting times of the dihedrals in the various conformational states.
Abstract: Performing molecular dynamics simulations for all-atom models, we characterize the conformational and structural relaxations of poly(ethylene oxide) and poly(propylene oxide) melts. The temperature dependence of these relaxation processes deviates from an Arrhenius law for both polymers. We demonstrate that mode-coupling theory captures some aspects of the glassy slowdown, but it does not enable a complete explanation of the dynamical behavior. When the temperature is decreased, spatially heterogeneous and cooperative translational dynamics are found to become more important for the structural relaxation. Moreover, the transitions between the conformational states cease to obey Poisson statistics. In particular, we show that, at sufficiently low temperatures, correlated forward–backward motion is an important aspect of the conformational relaxation, leading to strongly nonexponential distributions for the waiting times of the dihedrals in the various conformational states.

33 citations

References
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Journal ArticleDOI
TL;DR: In this paper, a method is described to realize coupling to an external bath with constant temperature or pressure with adjustable time constants for the coupling, which can be easily extendable to other variables and to gradients, and can be applied also to polyatomic molecules involving internal constraints.
Abstract: In molecular dynamics (MD) simulations the need often arises to maintain such parameters as temperature or pressure rather than energy and volume, or to impose gradients for studying transport properties in nonequilibrium MD A method is described to realize coupling to an external bath with constant temperature or pressure with adjustable time constants for the coupling The method is easily extendable to other variables and to gradients, and can be applied also to polyatomic molecules involving internal constraints The influence of coupling time constants on dynamical variables is evaluated A leap‐frog algorithm is presented for the general case involving constraints with coupling to both a constant temperature and a constant pressure bath

25,256 citations

Journal ArticleDOI

23,110 citations

Book
01 Jan 1953
TL;DR: In this paper, the Hartree-Fock Approximation of many-body techniques and the Electron Gas Polarons and Electron-phonon Interaction are discussed.
Abstract: Mathematical Introduction Acoustic Phonons Plasmons, Optical Phonons, and Polarization Waves Magnons Fermion Fields and the Hartree-Fock Approximation Many-body Techniques and the Electron Gas Polarons and the Electron-phonon Interaction Superconductivity Bloch Functions - General Properties Brillouin Zones and Crystal Symmetry Dynamics of Electrons in a Magnetic Field: de Haas-van Alphen Effect and Cyclotron Resonance Magnetoresistance Calculation of Energy Bands and Fermi Surfaces Semiconductor Crystals I: Energy Bands, Cyclotron Resonance, and Impurity States Semiconductor Crystals II: Optical Absorption and Excitons Electrodynamics of Metals Acoustic Attenuation in Metals Theory of Alloys Correlation Functions and Neutron Diffraction by Crystals Recoilless Emission Green's Functions - Application to Solid State Physics Appendix: Perturbation Theory and the Electron Gas Index.

21,954 citations

Journal ArticleDOI
TL;DR: In this paper, a numerical algorithm integrating the 3N Cartesian equations of motion of a system of N points subject to holonomic constraints is formulated, and the relations of constraint remain perfectly fulfilled at each step of the trajectory despite the approximate character of numerical integration.

18,394 citations