A. J. Hopfinger

Polymorphism of poly(vinylidene fluoride): potential energy calculations of the effects of head‐to‐head units on the chain conformation and packing of poly(vinylidene fluoride)

Potential‐energy calculations have been used to investigate the effects of head‐to‐head defects on the chain conformation and packing of poly(vinylidene fluoride). The calculations have demonstrated that such positional isomerism can contribute to the polymorphism exhibited by PVF2. We have shown that increased concentration of head‐to‐head defects or tetrafluoroethylene comonomer can cause the phase‐I form to become the favored structure for poly(vinylidene fluoride). The calculations have also proven capable of reflecting some of the subtle changes arising from the insertion of such defects. Packing calculations have shown that isomorphous replacement significantly affects the way in which PVF2 chains pack into a crystalline array. The differences in the structures proposed by Tadokoro and by Doll and Lando for phase II of poly(vinylidene fluoride) have been attributed to the inclusion of head‐to‐head defects in the polymer chains. In general, the potential‐energy functions have proven useful qualitativ...

Molecular mechanics and the camseq processor

Abstract The CAMSEQ processor used to carry out molecular mechanics as well as other molecular structure calculations is described in detail. General comments concerning potential energy functions, exploration of conformational space, and optimizing, with respect to size and speed, structure and coding of various subroutines of a molecular mechanics package are inserted at appropriate positions in the CAMSEQ description. Size, speed and reliability benchmarks for different versions of CAMSEQ on different computers are also provided.

Dynamics of the field‐induced transition to the polar α phase of poly(vinylidene fluoride)

A mechanism for the poling of α‐phase poly(vinylidene fluoride) into its polar form is studied in which a 180° twist or kink is propagated along a chain. Results are obtained by analytical approximation and by computer experiment for the field and temperature dependence of the poling time. Intrachain and interchain potentials used in this calculation are obtained by conformational analysis. The results are compared with experimental data.

Conformational analysis of glycosaminoglycans. I. Charge distributions, torsional potentials, and steric maps

Abstract An initial study of the charge distributions and torsional potentials for (1→4)-linked disaccharides, and a steric energy-map for (1→4)-linked disaccharides is reported for six acidic glycosaminoglycans. The charge distributions have been computed by the CNDO quantum-mechanical procedure, together with a molecular-decomposition technique. The intrinsic torsional potential has been computed by using CNDO energies and empirical potential-energies. The intrinsic torsional potential is two-dimensional. The general steric-map for a (1→4)-linked disaccharide will be useful for simplifying future conformational analyses of glycosaminoglycans. Wherever possible, comparisons between theory and experiment are presented or cited.

Theory of structural phase transitions in crystalline poly(vinylidene fluoride)

A mean‐field theory capable of predicting structural phase transitions in a linear polymer is presented. The intrachain and interchain potentials, derived from conformational analysis based upon molecular mechanics, are combined in a transfer–integral approach to calculate free energies as a function of temperature and applied uniaxial stress. The theory is applied to poly(vinylidene fluoride) and is successful in yielding several observed phases of this material and in predicting the effect of uniaxial stress on the most stable phase. There are no adjustable parameters in the theory.

An extended conformational analysis of doxorubicin

The antibiotic doxorubicin (tig.la) is a highly active anticancer agent in current clinical use [ 11. It is believed that the inhibitory effect of this compound on both normal and tumour cell growth is due to its interference with RNA synthesis by binding directly to the double-stranded DNA template [2]. X-Ray fiber diffraction studies are believed to support a binding model in which intercalation between DNA base pairs, with consequent helix unwinding, plays an important role [3]. The crystallographic analysis of doxorubicin has not been determined. However, the crystal structures of daunomycin (fig.lb) as pyridine [4] and butanol [S] adducts, the N-bromoacetyl derivative of daunomycin [6] and 4hydroxydaunomycin (carminomycin) [7-91 have been determined by X-ray analysis. Neidle and Taylor have reported in this yournal [lo] an intramolecular conformational analysis of daunomycin and some corresponding congeners. Their work was prompted by the observation that the apparently flexible sugar-chromophore system, characterized by the bond rotations

Longitudinal polarization of α‐poly(vinylidene fluoride) by kink propagation

r and & defined in flg.2, adopts similar conformations in the crystals mentioned above. This preferred crystal conformation has been suggested to be the active biological conformation as well as a minimum energy conformation [4,11]. Neidel and Taylor have specifically calculated the conformational energy associated with rotations

Field‐induced phase transitions in phase‐II poly(vinylidene fluoride)

r and

Hybrid Ising mean‐field treatment of melt transitions: Application to polymethylene

2 using molecular mechanics [ 121. The particular set of potential functions, e g., atomic charge densities, used in these calculations are not given. The remainder

Computer graphics and the generation of DNA confirmations for intercalation studies

The α‐ phase chain of poly(vinylidene fluoride) has a component of dipole moment parallel to the chain axis which can be reversed by propagation of a solitary wave along the chain. Calculations of the energy required to create such a wave in a perfect chain yield larger values than are implied by experiment. This suggests that either head‐to‐tail defects or regions of stress at the lamellar boundary might play an important role in causing the observed dielectric behavior.