bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined bond polarization function basis sets for accurate ab initio calculation of the dissociation energies of AHn molecules (A=LI to F)
Authors: Martin J. M. L. , François J. P. , Gijbels R.
Published: January 2005

An alternative route toward developing basis sets for post‐Hartree‐Fock calculations, the hybrid bond polarization function method, is investigated. Two new basis sets, denoted 6‐31G(d, p)+ B and 6‐31 + G(d,p)+B, are defined for the first‐row hydrides. The dissociation energies of the first‐row hydride species in their respective ground states are computed using full fourth‐order Møller‐Plesset theory, and compared with results obtained with large polarized basis sets containing no bond functions. It is shown that results are competitive even with basis sets as large as 6‐311++G(3df,3pd), while computation times are reduced by a factor of 4 to 20. On empirical grounds, the basis set superposition error should be neglected entirely.
Extrapolation of the time‐step bias in diffusion quantum Monte Carlo by a differential sampling technique
Authors: Garmer David R.
Published: January 2005

A new method of eliminating the finite‐time‐step error inherent in diffusion quantum Monte Carlo is presented, utilizing an improved version of the existing differential techniques. An implementation is described and results of several small but representative calculations are discussed. The pertinent computation requirements on these systems were reduced by up to a factor of five by the new algorithm. It is speculated that this method may be easily applied to other quantum Monte Carlo and discretized path integral Monte Carlo techniques having related finite step‐size errors with a possibility of obtaining similar good results.
Optimization of parameters for semiempirical methods I. Method
Authors: Stewart James J. P.
Published: January 2005

A new method for obtaining optimized parameters for semiempirical methods has been developed and applied to the modified neglect of diatomic overlap (MNDO) method. The method uses derivatives of calculated values for properties with respect to adjustable parameters to obtain the optimized values of parameters. The large increase in speed is a result of using a simple series expression for calculated values of properties rather than employing full semiempirical calculations. With this optimization procedure, the rate‐determining step for parameterizing elements changes from the mechanics of parameterization to the assembling of experimental reference data.
Optimization of parameters for semiempirical methods II. Applications
Authors: Stewart James J. P.
Published: January 2005

MNDO/AM1‐type parameters for twelve elements have been optimized using a newly developed method for optimizing parameters for semiempirical methods. With the new method, MNDO‐PM3, the average difference between the predicted heats of formation and experimental values for 657 compounds is 7.8 kcal/mol, and for 106 hypervalent compounds, 13.6 kcal/mol. For MNDO the equivalent differences are 13.9 and 75.8 kcal/mol, while those for AM1, in which MNDO parameters are used for aluminum, phosphorus, and sulfur, are 12.7 and 83.1 kcal/mol, respectively. Average errors for ionization potentials, bond angles, and dipole moments are intermediate between those for MNDO and AM1, while errors in bond lengths are slightly reduced.
Spatial geometric arrangements of disulfide‐crosslinked loops in nonplanar proteins
Authors: Kikuchi Takeshi , Némethy George , Scheraga Harold A.
Published: January 2005

The method presented earlier [T. Kikuchi, G. Némethy, and H.A. Scheraga, (1986) J. Comput. Chem. 7, 67] for the classification of patterns of the three‐dimensional folding of a covalently crosslinked polypeptide chain has been extended to nonplanar proteins. The procedure described earlier was applicable only to proteins termed planar, i.e., with a connexity of the crosslinks (e.g., disulfide bonds) that can be represented in a planar diagram. The procedure described in the present work is applicable to any (planar or nonplanar) pattern of crosslinking. The classification is based on a systematic and objective method of enumeration of spatial geometric arrangements of loops (SGAL) using no information other than the location of the disulfide bonds in the amino acid sequence. Various SGAL classes correspond to the presence of different ways of mutual penetration of loops, called thrustings and entanglements. Information on SGAL classes can be of use in structural predictions of folding patterns of proteins.
On the computation of matrix elements between numerical wave functions: The canonical functions method
Authors: Kobeissi H. , Dagher M. , El‐Hajj A. , Kobeissi M.
Published: January 2005

The problem of the computation of the matrix elements

is considered when Ψv(r) and Ψv(r) are eigenfunctions related to a diatomic potential of the RKR type (defined by the coordinates of its turning points Pi with polynomial interpolations). The eigenfunction Ψ(r) is computed by the canonical functions method making use of the abscissas ri of Pi uniquely. This limited number of points allows the storage of ψv(ri) for all the required levels v, and reduces greatly the computational effort when v, ν′, and k are varying. The present method maintains all the advantages of a highly accurate numerical method (even for levels near the dissociation), and reduces greatly the computing time. Furthermore, it is shown that it may be extended to analytical potentials like Morse and Lennard‐Jones functions, to vibrational‐rotational eigenfunctions and to matrix elements between eigenfunctions related to two different potentials. Numerical applications are presented and discussed.
The effect of electron correlation on the topological and atomic properties of the electron density distributions of molecules
Authors: Boyd Russell J. , Wang Liang‐Chen
Published: January 2005

The topological properties of the electron density and the properties of an atom in a molecule are calculated by means of second‐order Møller‐Plesset perturbation theory (MP2) and compared with the results of configuration interaction calculations (C12) which include all single and double substitutions from the Hartree‐Fock reference configuration. A software package for analyzing the effects of electron correlation on the topological properties of the electron density of molecules is described. H2CO is used to provide a numerical example and to indicate that the number of bond critical points is unaffected by the inclusion of electron correlation. Correlation leads to only a small shift in the positions of bond critical points and a small change in the electron density at bond critical points. It is further shown that the energy of an atom in a molecule can be calculated to an accuracy of 1 kcal/mol and the electron population of an atom to about 0.001e. A statistical method is used to show that the deviation of the MP2 correlation correction relative to the CI2 correlation correction for a variety of atomic properties is about 25%.
Algorithm for rapid calculation of excluded volume of large molecules
Authors: Higo Jun'Ichi , Gō Nobuhiro
Published: January 2005

An algorithm is described for rapid calculation of excluded volume of large molecules. The excluded volume is defined based on coordinates of constituent atoms as the volume of overlapping spheres, each standing for a space around an atom inaccessible for a solvent molecule. A computer program based on the algorithm has been tested on a protein, ovomucoid. The accuracy of the numerical calculation is discussed.
Topological electron density analysis of phosphines, phosphaalkenes and phosphaalkynes
Authors: Bachrach Steven M.
Published: January 2005

A general survey of the topological properties of various phospines, phosphaalkenes, and phosphaalkynes is presented. Fifteen compounds containing carbon‐phosphorus single, aromatic, double, and triple bonds were optimized at the Hartree‐Fock‐self‐consistent field (HF‐SCF) level using the 3‐21G, 3‐21G(*) and 6‐31G* basis sets. Inclusion of d‐orbitals was necessary to obtain reasonable structures. The electron densities of these compounds were analyzed using the topological method of Bader, revealing a number of trends. The value of the electron density at the PC bond critical point correlates strongly with the bond distance and bond order. Integrated electron populations correlate with coordination number. The integrated charge indicates a strongly polarized CP bond in all compounds. Comparisons with five CN compounds are made.
Conformational analysis. 48. A molecular mechanics (MMP2) approach to the conformational analysis of methyl‐, dimethyl‐ and trimethylisochromanes
Authors: Olefirowicz Edward M. , Eliel Ernest L.
Published: January 2005

Conformational equilibria of mono‐, di‐, and trimethylisochromanes substituted in the heterocyclic ring are calculated by the MMP2(85) force field program. The results are in generally good agreement with the experimental findings of Pihlaja et al. The accuracy of experimental studies based on vicinal coupling constants is examined.
The tautomerism of 1,2,3‐triazole, 3(5)‐methylpyrazole and their cations
Authors: Catalán Javier , Sánchez‐Cabezudo Marta , De Paz José Luis G. , Elguero José , Taft Robert W. , Anvia Frederick
Published: January 2005

The annular tautomerism of 1,2,3‐triazole and 3(5)‐methylpyrazole is discussed by means of a combination of theoretical calculations and experimental (ICR) gas‐phase basicities and acidities. In the gas phase 1,2,3‐triazole exists as the 2H‐tautomer, whereas both tautomers of 3(5)‐methylpyrazole are of similar energy. The solvent effects on these prototropic equilibria are discussed taking into account solvent properties as polarity/polarizability, acidity, and basicity. In nonhydrogen bonding solvents, the difference in dipole moments between both tautomers plays a role that has usually been underestimated.
Basis set quality versus size II. Approximate GTO wave functions for second row transition metal atoms
Authors: Faegri Knut , Biran Gil
Published: January 2005

Basis sets ranging in size from (16, 10, 7) to (20, 14, 11) have been derived for the atoms Y–Cd. Separate sets represent the energy optimized wave functions for each of the s2dn, s1dn+1, and s0dn+2 configurations. The energies from the largest sets are within 3 mhartrees of the values obtained in numerical Hartree–Fock calculations. Reasonable Hartree–Fock s2dn– s1dn+1 and s2dn– s0dn+2 excitation energies may be obtained either using the largest basis sets, or using d‐orbitals optimized for the s0dn+2 configurations. The basis sets are slightly unbalanced in favor of the s‐functions and in disfavor of the d‐functions, but various alternative basis sets may be derived by combining parts of the five parent sets. The convergence of radial expectation values is discussed.
Application of various population methods to some oxygenated compounds
Authors: Bachrach Steven M. , Streitwieser Andrew
Published: January 2005

The charge on oxygen for a series of compounds was obtained using Mulliken population, natural population analysis (NPA), integrated projected electron population (IPP) analysis, and Bader's topological density analysis, “integrated Bader populations” (IBP). The orbital‐based methods (Mulliken and NPA) predict oxygen charges of about –0.6 whereas the spatial‐based methods (IPP and IBP) predict charges of about – 1.2 to – 1.3. The differences are ascribed primarily to the nuclear‐centered basis sets used in the orbital methods that minimize local atomic polarization effects. Accordingly, such population analyses should be used for electronic structure considerations only with due circumspection. The IPP method as an approximation to IBP shows gross similarities; small but significant differences vary in a nonsystematic manner and IPP values must also be used with care.
An MNDO molecular orbital study of the reactions of protonated oxirane derivatives (XCHCH2OH+, X = CN, Cl, CH3, Ph) with simple nucleophiles. Implications for regioselectivity in the reactions of electrophiles with nucleic acid bases
Authors: Ford George P. , Smith Christopher T.
Published: January 2005

The gas‐phase analogs of the classical SN1 and SN2 reactions of nucleophiles with a series of protonated oxiranes bearing the substituents CN, Cl, Me, and Ph were studied using MNDO semiempirical molecular orbital theory. The transition states for nucleophilic attack on the intact rings are calculated to become progressively more “SN1‐like,” as the ability of the substituent group to stabilize the corresponding ring opened carbenium ion increases. At the same time the activation barriers become progressively smaller and their relative values for different nucleophiles approach the order expected on the basis of a purely electrostatic attraction between the reacting moieties. Exactly the opposite trends are calculated for the transition states for nucleophilic attack on the intermediate carbenium ions. As the stabilities of the latter increase the extent of bond formation, and transfer of charge to the incoming nucleophile also increase. Here, the relative barriers for attack by different nucleophiles approach the order expected on the basis of a superposition of both covalent and electrostatic interactions in which the former dominate. These results support a previously suggested rationalization for the enhanced reactivities of certain alkylating agents towards the exocyclic oxygen atoms, rather than the ring nitrogens, of the nucleic acid bases. They also suggest a new explanation for the tendencies of aralkylating electrophiles to modify the exocyclic amino groups of the nucleic acid bases: sites which are unreactive towards simple alkylating agents.
Theoretical studies in molecular recognition: Rebek's cleft
Authors: Lipkowitz Kenny B. , Zegarra Richard
Published: January 2005

Molecular recognition in Rebek's cleft was studied with the MM2 force field. A new computational protocol was used to determine the free energies of substrate binding to this topologically unique model receptor. The energies and structural features of substrate‐receptor complexes reveal that molecular recognition involves ammonium ion binding to the interior of the cleft and aromatic π‐stacking on the exterior of the cleft.
Evaluation of the dispersion contribution to the solvation energy. A simple computational model in the continuum approximation
Authors: Floris F. , Tomasi J.
Published: January 2005

We present a simple computational method for the evaluation of solute‐solvent dispersion energy contributions in dilute isotropic solutions, supplementing the method with an analysis of its sensitivity with respect to several parameters (or features of the solvation model) which are left free in the general formulation. The method is a natural complement of the electrostatic solvation procedure described in preceding articles.
An algorithm for the representation and computation of supermolecular surfaces and volumes
Authors: Karfunkel Heinrich R. , Eyraud Veronique
Published: January 2005

An algorithm for the computation and representation of van der Waals surfaces and volumes of supermolecules (several overlapping molecules) by a set of grid points originating from an equidistant lattice is described in detail. The grid points in this set belong either to the “outer” surface of the van der Waals body or to a layer just below that outer surface. By means of this double layer (outer and inner) it is possible to represent the volume via the surface without referring to grid points lying inside the body. The algorithm is based on the octree concept, which means that the final relevant lattice points are derived by the successive refinement of an initial coarse lattice. The main features of the algorithm are the automatic elimination of inner atoms irrelevant for the surface definition and the association of any surface point with only those atoms which define the surface in the vicinity of these points. The most remarkable consequence of these features is that the amount of computation is almost independent of the number of atoms in the supermolecule. The algorithm can be used in solving problems arising in drug design, protein folding, molecular graphics, etc.
On the construction of the matching polynomial for unbranched catacondensed benzenoids
Authors: Randić Milan , Hosoya Haruo , Polansky Oskar E.
Published: January 2005

An algorithm for obtaining the matching polynomial of an arbitrary catacondensed unbranched benzenoid molecule is presented. It is based on multiplication of only three 5 x 5 transfer matricesI,J,K, and an appropriate terminal vector. The choice of the matrices is dictated by the history of the growth of the hexagonal “animals” (i.e., by the pattern of the successive fusions of the benzene rings). The approach also gives the number of Kekule valance structures, the count of conjugated circuits, the values of the topological indexZ, and the characteristic polynomials.
Theoretical studies in molecular recognition: Enantioselectivity in chiral chromatography
Authors: Lipkowitz Kenny B. , Baker Brian , Zegarra Richard
Published: January 2005

The enantioselective binding of optical analytes on chiral stationary phases used in column chromatography is investigated with molecular modeling techniques. By rolling the analytes over the van der Waals surface of the phase, configurations are sampled and free energies of transient diastereomeric complexes are computed. These free energies allow us to compute chromatographic separability factors and a linear relationship between computed and observed values is found. The intermolecular potential energy surfaces of these diastereomeric complexes are flat with gentle rolling hills and multiple minima. The binding sites are ill‐defined and the analytes are found to freely slide over the chiral stationary phases. An energy partitioning algorithm is used to determine how much of the total binding energy is attributable to a given molecular fragment on the phase. It is found that the fragments of the phase bearing the stereogenic carbons are the least cognizant of differences between optical antipodes.
Methods for the Fourier‐series expansion of torsional energies
Authors: Chung‐Phillips Alice
Published: January 2005

Several general procedures for the derivation and analysis of a Fourier‐series expansion V(ϕ) over computed torsional energies E(ϕi) are formulated. STO‐3G energy values in n‐butane, 1‐chloropropane, and 1,2‐dichloroethane are used as test data for deriving V(ϕ) with the numerical methods of interpolation and least squares. The accuracy of each derived V(ϕ) is assessed on the basis of calculated conformational properties, mean and rms deviations, and an error curve, V(ϕ)–V(ϕ)ref, where V(ϕ)ref represents a reference set of E(ϕi). Results indicate that given the same number of expansion terms, interpolation and least squares yield functions of comparable accuracy; however, interpolation is a more efficient procedure for monitoring the accuracy of a function in regions of interest. In cases where there are too few input energies to achieve the desired accuracy, energy derivatives can be employed effectively for expanding the input set. In designing special‐purpose functions, the error curve can be used meaningfully as a guide; an example for producing functions that are especially well behaved in regions for gauche conformations is provided. The present study continues to add systematics and rigor to the fitting of an internal rotation potential function from energy data.
Force related atomic multipoles in planar molecules. Derivation of atomic quadrupole and octupole moments
Authors: Dinur Uri
Published: January 2005

Atomic multipoles as defined by current methods generally do not account for forces in molecules that arise from external electrostatic fields. It is pointed out that such forces and the electrostatic potential that the molecule itself generates are both determined by the molecular multipolar tensors. The latter constitute therefore the fundamental molecular constants that determine the molecular electrostatics apart from polarization. In general the multipolar tensors include contributions from the atomic multipoles and their fluxes. In planar molecules, however, the perpendicular charge flux is zero by symmetry. This gives rise to a (previously introduced) formalism that extracts analytical, force‐related, atomic multipoles from the molecular multipolar tensors. This formalism is extended in this work to include force‐related (FR) atomic quadrupoles and octupoles in planar molecules. The properties of the FR atomic multipoles, including their perpendicular fluxes, are discussed and some formal theoretical and computational advantages that characterize them are indicated. As an example, the electrostatics of OCS, including the molecular electrostatic potential and the forces on the nuclei due to an external point charge, is discussed.
Theoretical calculation of the steric effects of ortho substituents by the AM1 method
Authors: Sotomatsu Tomoko , Murata Yoshiyuki , Fujita Toshio
Published: January 2005

The AM1 calculation was done for ortho‐substituted toluenes (o‐X‐C6H4‐CH3) and ortho‐substituted tert‐butylbenzenes (o‐X‐C6H4‐t‐Bu). The difference in the calculated heat of formation between o‐X‐C6H4‐CH3 and o‐X‐C6H4‐t‐Bu was used as a theoretical steric index for ortho‐X. The correlation of this theoretical steric index with the empirical steric parameter sets such as our recently defined Es(AMD) and the Taft–Kutter–Hansch (TKH) Es was examined. In spite of the simplicity of the model system, the theoretical index was linear with the Es(AMD) constant with a correlation coefficient of r = 0.972 for 17 substituents of various structures. Including the phenyl group, the correlation with the TKH Es constant was r = 0.948. The theoretically calculated index was shown to serve as a measure of the ortho steric effect.
Upregulation of clusterin/apolipoprotein J in lactacystin‐treated SH‐SY5Y cells
Authors: Carreras Isabel , Garrett‐Young Rosemary , Ullman M. David , Eisenhauer Patricia B. , Fine Richard E. , Wells John M. , Conn Kelly J.
Published: January 2005

Clusterin (apolipoprotein J) is a highly conserved, multifunctional, vertebrate glycoprotein. Several isoforms of clusterin have been described including the predominant secreted isoform (sCLU) and several nuclear isoforms (nCLU) associated with cell death. sCLU has been shown to bind a variety of partly unfolded, stressed proteins including those associated with Lewy bodies (LBs) in patients with Parkinson's disease (PD). The development of familial and sporadic PD has been associated with the ubiquitin‐proteasome system (UPS) dysfunction and aberrant protein degradation. This suggests that failure of the UPS to degrade abnormal proteins may underlie nigral degeneration and LB formation in PD. The effects of toxin‐mediated proteasomal impairment on changes in gene expression and cell viability were studied in differentiated SH‐SY5Y cells. Clusterin expression was increased in cells exposed for 24 hr to the proteasomal inhibitor lactacystin (10 μM) as determined by gene microarray analysis. RT‐PCR showed that sCLU, not nCLU, was the major clusterin isoform expressed in both control and lactacystin‐treated cells. Western blot analysis identified statistically significant increases in sCLU in total cell lysates after 24 hr of lactacystin exposure and showed that sCLU fractionates with the endoplasmic reticulum. Time‐course studies demonstrated that maximal decreases in proteasome activity (4 hr) preceded maximal increases in clusterin expression (24 hr). Together these data suggest that proteasome impairment results in the upregulation of sCLU in SH‐SY5Y cells, supporting the hypothesis that the association of clusterin with LBs in PD may be related to UPS failure. © 2005 Wiley‐Liss, Inc.
Mitogen‐ and stress‐activated protein kinase 1: Convergence of the ERK and p38 pathways in Alzheimer's disease
Authors: Webber Kate M. , Smith Mark A. , Lee Hyoung‐gon , Harris Peggy L. , Moreira Paula , Perry George , Zhu Xiongwei
Published: January 2005

Two of the earliest manifestations of the selective neurodegeneration that occurs in Alzheimer's disease (AD) involve the oxidative modification of various biomacromolecules and the reexpression of a multitude of cell cycle‐related proteins. Taken together with the proximal and ectopic increases in activated components of the ERK and p38 pathways, involved in mitotic and cellular stress signaling, respectively, there is a clear and important role for mitotic and oxidative insults in the pathogenesis of AD. Despite the mounting evidence, however, for the causal role of mitogenic abnormalities and oxidative stress in AD pathogenesis, the effect of the converging relevant pathways due to chronic stimulation in AD remains largely unknown. To delineate further the mechanism by which mitogenic and stress signaling cascades converge, we focused on one of the downstream effectors of activated ERK and p38, mitogen‐ and stress‐activated kinase 1 (MSK1). Activated MSK1, phosphorylated at residues Ser376 and Thr581, was upregulated in vulnerable neurons in AD when compared to that in age‐matched controls, whereas MSK1 phosphorylated at residue Ser360 was not increased in AD. Furthermore, activated MSK1 phosphorylated at Thr581 colocalized strongly with activated p38 but only weakly with activated ERK, whereas MSK1 phosphorylated at Ser376 colocalized strongly with activated ERK but only weakly with activated p38, suggesting potential preferential phosphorylation sites for the two upstream effectors. © 2005 Wiley‐Liss, Inc.
Age‐related expression of σ1 receptors and antidepressant efficacy of a selective agonist in the senescence‐accelerated (SAM) mouse
Authors: Phan Vân‐Ly , Miyamoto Yoshiaki , Nabeshima Toshitaka , Maurice Tangui
Published: January 2005

The σ1 receptor is a unique intracellular receptor whose activation results in an efficient modulation of several neurotransmitter responses. Its role as a target for the rapid nongenomic effects of neuro(active)steroids and the age‐related diminutions in steroid levels suggested that targeting the σ1 receptor might allow alleviation of age‐related neuronal dysfunctions. We examined here the expression and behavioral efficacy of σ1 receptors in the senescence‐accelerated (SAM) mouse model. The σ1 receptor mRNA expression was measured by using comparative RT‐PCR in the olfactory bulb, hippocampus, hypothalamus, cortex, or cerebellum of senescence‐prone SAMP/8 and senescence‐resistant SAMR/1 control animals. No difference was observed between substrains in 6‐, 9‐, and 12‐month‐old (m.o.) mice. The σ1 protein expression was analyzed by using immunohistochemical techniques. Labeling was intense in the olfactory bulb, hippocampus, hypothalamus, and midbrain of both SAMR/1 and SAMP/8 mice, and the distribution appeared unchanged in 6‐, 9‐, and 12‐m.o. animals. The receptor's in vivo availability was examined by using in vivo [3H](+)‐SKF‐10,047 binding. No age‐related difference was observed in the olfactory bulb, hippocampus, hypothalamus, cortex, cerebellum, and brainstem of 6‐ or 12‐m.o. SAMR/1 or SAMP/8 mice. The antidepressant efficacy of the selective agonist igmesine was examined in the forced‐swimming test. The compound decreased significantly the immobility duration at 60 mg/kg in 6‐ and 12‐m.o. SAMR/1 and in 6‐m.o. SAMP/8 mice. In 12‐m.o. SAMP/8 mice, the drug efficacy was facilitated; a significant effect was measured at 30 mg/kg. Decreased neurosteroid levels, particularly of progesterone, were seen in 12‐m.o. SAMP/8 mice that might explain the enhanced efficacy of igmesine. Preserved σ1 receptor expression and enhanced behavioral efficacy of σ1 agonists were measured in SAM animals, confirming the therapeutic opportunies for selective ligands against age‐related mood disorders. © 2005 Wiley‐Liss, Inc.
Stereoblock Poly(lactic acid): Synthesis via Solid‐State Polycondensation of a Stereocomplexed Mixture of Poly(L‐lactic acid) and Poly(D‐lactic acid)
Authors: Fukushima Kazuki , Furuhashi Yukiko , Sogo Kazuaki , Miura Shigenobu , Kimura Yoshiharu
Published: January 2005

Summary: Stereoblock poly(lactic acid) consisting of D‐ and L‐lactate stereosequences can be successfully synthesized by solid‐state polycondensation of a 1:1 mixture of poly(L‐lactic acid) and poly(D‐lactic acid). In the first step, melt‐polycondensation of L‐ and D‐lactic acids is conducted to synthesize poly(L‐lactic acid) and poly(D‐lactic acid) with a medium‐molecular‐weight, respectively. In the next step, these poly(L‐lactic acid) and poly(D‐lactic acid) are melt‐blended in 1:1 ratio to allow formation of their stereocomplex. In the last step, this melt‐blend is subjected to solid‐state polycondensation at temperature where the dehydrative condensation is allowed to promote chain extension in the amorphous phase with the stereocomplex crystals preserved. Finally, stereoblock poly(lactic acid) having high‐molecular‐weight is obtained. The stereoblock poly(lactic acid) synthesized by this way shows a higher melting temperature in consequence of the controlled block lengths and the resulting higher‐molecular‐weight. The product characterization as well as the optimization of the polymerization conditions is described.

Changes in $\overline M _{\rm w}$ of stereoblock poly(lactic acid) (sb‐PLA) as a function of the reaction time.

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Changes in $\overline M _{\rm w}$ of stereoblock poly(lactic acid) (sb‐PLA) as a function of the reaction time.
Comb‐Like Ionic Complexes of Cationic Surfactants with Bacterial Poly(γ‐glutamic acid) of Racemic Composition
Authors: García‐Alvarez Monserrat , Alvarez José , Alla Abdelilah , Martínez de Ilarduya Antxon , Herranz Concepción , Muñoz‐Guerra Sebastián
Published: January 2005

Summary: Comb‐like ionic complexes, nATMA · PG(DL)GA, were prepared from microbial poly(γ‐glutamic acid), with a nearly racemic configuration, and alkyltrimethylammoniun bromides, with linear alkyl chains containing an even number of carbon atoms, n, ranging from 12 to 22. The complexes had a nearly stoichiometric composition, displayed thermal stability up to temperatures above 200 °C and were insoluble in water but soluble in organic solvents. In the solid state, they were arranged in a regularly layered structure with the alkyl side chain crystallized for n ≥ 18. Heating above melting entailed a contraction in the interlayer distance which varied from 1 to 10% depending on the value of n. Comparison with data reported on similar complexes obtained from nearly enantiomerically pure poly(γ‐glutamic acid) revealed an overall behavior very similar for the two series but with specific significant differences concerning side chain crystallinity and dimensional response to temperature.

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Cover Picture: Macromol. Mater. Eng. 12/2004
Authors: Sharma Lakshmi , Ogino Yoshino , Kanaya Toshiji
Published: January 2005

Cover: For the first time, a shish kebab structure has been discovered in PHB, using a series of in‐situ rheo SAXS and DPLS methods. This finding changes the fundamentals of this unique biopolymer and creates a ‘new’ PHB macromolecule possessing a range of previously unforeseen chemical and physical properties.

Further details can be found in the Full Paper by L. Sharma,* Y. Ogino, and T. Kanaya on page 1059.
Cover Picture: Macromol. Rapid Commun. 1/2005
Authors: Vyazovkin Sergey , Dranca Ion , Lang Anthony J.
Published: January 2005

Cover: The application of an oscillating tensile load to a nitrocellulose film causes its degradation as detected by mass spectrometry (MS). An isothermal dynamic mechanical analysis (DMA)‐MS run is shown. This combination of DMA with MS provides a new approach to detecting mechanochemical degradation under moderate strain fields.

Further details can be found in the Communication by S. Vyazovkin,* I. Dranca, and A. J. Lang on page 29.
Interface Orientation and Chain Conformation in Simulated Symmetric Diblock Copolymer Lamellar Systems
Authors: Yang Jian , Winnik Mitchell A. , Pakula Tadeusz
Published: January 2005

Summary: We describe the results of Monte Carlo simulations, based on the cooperative motion algorithm, of the lamellar structure generated at finite temperature by a symmetric diblock copolymer. The (70 × 70 × 70) simulation box in which the polymer chains were embedded for each simulation was rotated, based on the interface orientation, to bring the interfacial planes of the simulated structure into parallel. We found that the interface thickness, as defined by the distribution of the junction points, became narrower at lower temperature, and that the interface plane was characterized by a waviness with a maximum peak‐to‐valley distance of 20–30 lattice bonds. Compared with the isotropic state (T/N = ∞), chains at lower temperatures were stretched in the direction perpendicular to the interface; but only modestly compressed in the direction parallel to the interface. Individual block chains within the lamellar domains still behave like random coils. The block copolymer molecules exhibit only a modest tendency to orient themselves with their end‐to‐end vector perpendicular to the plane of the lamellar interface. Considered as an ensemble average, the results we obtained are similar to those reported from small angle neutron scattering measurements for the mean conformation of the PSd blocks of symmetrical PSd‐PVP diblock copolymers.

2‐D projections onto the X‐Z plane of the end beads for the A‐ and B‐chains (gray) and the junction points J (black) at T/N = 0.2. The interface plane is oriented parallel to the Y‐Z plane by rotating the simulation box. The distribution profiles of junction points and the end beads across the system in the direction of interface normal are shown in the lower part of the figure.

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2‐D projections onto the X‐Z plane of the end beads for the A‐ and B‐chains (gray) and the junction points J (black) at T/N = 0.2. The interface plane is oriented parallel to the Y‐Z plane by rotating the simulation box. The distribution profiles of junction points and the end beads across the system in the direction of interface normal are shown in the lower part of the figure.
Properties of stationary states of delay equations with large delay and applications to laser dynamics
Authors: Yanchuk Serhiy
Published: January 2005

We consider properties of periodic solutions of the differential‐delay system, which models a laser with optical feedback. In particular, we describe a set of multipliers for these solutions in the limit of large delay. As a preliminary result, we obtain conditions for stability of an equilibrium of a generic differential‐delay system with fixed large delay τ. We also show a connection between characteristic roots of the equilibrium and multipliers of the mapping obtained via the formal limit τ→∞. Copyright © 2004 John Wiley & Sons, Ltd.
Short‐segment nerve conduction studies in ulnar neuropathy at the elbow
Authors: Visser Leo H. , Beekman Roy , Franssen Hessel
Published: January 2005

The aim of the study was to assess the diagnostic value of short‐segment nerve conduction studies (NCS) at 2‐cm intervals from 4 cm above to 4 cm below the medial epicondyle in a large group of patients with ulnar neuropathy at the elbow (UNE). Furthermore, we wanted to compare electrodiagnostic and clinical findings. We evaluated 73 arms in 70 patients with UNE and observed the following abnormalities on short‐segment NCS: focal conduction block (CB) in 1, focal CB with increased latency change in 34, and increased latency change alone in 25. Short‐segment NCS had an additional localizing value in 28 arms of the 37 patients (76%) with motor conduction velocity (MCV) slowing across the elbow only or with nonlocalizing electrodiagnostic findings. The lesion was located above the elbow in 32 arms (53%), at the epicondyle in 16 arms (27%), and below the epicondyle in 12 (20%) of the 60 arms with focal CB or increased latency change on short‐segment NCS. Patients with CB on routine and short‐segment NCS had muscle weakness significantly more often than patients without CB. Thus, short‐segment NCS are useful in localizing the lesion in patients with UNE and CB on routine NCS and have additional diagnostic value in patients with MCV slowing across the elbow or with nonlocalizing signs on routine nerve conduction studies. We recommend its use in all patients in whom UNE is suspected. Muscle Nerve, 2005
Oxygen infusions (hemoglobin‐vesicles and albumin‐hemes) based on nano‐molecular sciences
Authors: Tsuchida Eishun , Sakai Hiromi , Komatsu Teruyuki , Takeoka Shinji , Huang Yubin , Sou Keitaro , Nakagawa Akito , Teramura Yuji , Kobayashi Koichi
Published: January 2005

Since the discovery of a red‐colored saline solution of a heme derivative that reversibly binds and releases oxygen (1983), significant efforts have been made to realize an oxygen infusion as a red cell substitute based on the sciences of both molecular assembling phenomena and macromolecular metal complexes. The authors have specified that hemoglobin (Hb)‐vesicles (HbV) and recombinant human serum albumin‐hemes (rHSA‐heme) would be the best systems that meet the clinical requirements. (A) Hb is rigorously purified from outdated, donated red cells via pasteurization and ultrafiltration, to completely remove blood type antigen and pathogen. The HbV encapsulates thus purified concentrated Hb solution with a phospholipid bimolecular membrane (diameter, 250 nmϕ), and its solution properties can be adjusted comparable with blood. Surface modification of HbV with a water‐soluble polymer ensures stable dispersion state and storage over a year at 20°C. In vivo tests have clarified the efficacy for extreme hemodilution and resuscitation from hemorrhagic shock, and safety in terms of biodistribution, metabolism in reticuloendothelial system (RES), clinical chemistry, blood coagulation, etc. The HbV does not induce vasoconstriction thus maintains blood flow and tissue oxygenation. (B) rHSA is now manufactured in Japan as a plasma‐expander. The rHSA can incorporate eight heme derivatives (axial base substituted hemes) as oxygen binding sites, and the resulting rHSA‐heme is a totally synthetic O2‐carrier. Hb binds endothelium‐derived relaxation factor, NO, and induces vasoconstriction. The rHSA‐heme binds NO as Hb does, however, it does not induce vasoconstriction due to its low pI (4.8) and the resulting low permeability across the vascular wall (1/100 of Hb). A 5%‐albumin solution possesses a physiologic oncotic pressure. Therefore, to increase the O2‐transporting capacity, albumin dimer is effective. Albumin dimer can incorporate totally 16 hemes with a regulated oncotic pressure. The rHSA‐heme is effective not only as a red cell substitute but also for oxygen therapeutics (e.g. oxygenation for tumor). Significant efforts have been made to produce HbV and rHSA‐heme with a facility of Good Manufacturing Practice (GMP) standard, and to start preclinical and finally clinical trials. Copyright © 2005 John Wiley & Sons, Ltd.
Transient shear rheology and rheo‐optical microstructural characterization of a thermotropic liquid crystalline polymer
Authors: Guo Tianren , Harrison Graham M. , Ogale Amod A.
Published: January 2005

The shear rheology and the corresponding microstructure evolution during transient flow of a thermotropic liquid crystalline polymer (LCP; Vectran V400P) are reported; the polymer does not display a crystalline melting phenomenon. The steady shear viscosity displays three regions that are typical of LCPs. However, the transient shear stress displays a local stress maximum at a strain of ≈ 2, a local minimum at a strain of ≈ 20, and then a stress overshoot at a strain of ≈ 100 before attaining a steady state value. The transient first normal stress difference exhibits a distinct overshoot at ≈ 100 strain units. The steady‐state first normal stress difference is always positive in the tested shear rate range 0.1–10 s–1. In situ rheo‐optical characterization revealed that the melt shows a threaded texture at rest. Upon start up of shear flow, this threaded texture becomes deformed, and the domains initially appear to stretch and align in the shearing direction. Next, the domains break up, and a significant drop in the optical intensity is observed. These microstructural features are used to explain the presence of the first maximum and the minimum observed in the transient shear stress. Polym. Eng. Sci. 45:187–197, 2005. © 2005 Society of Plastics Engineers.
Theoretical model for flash generation
Authors: Higuchi Hiroyuki , Kosaka Wataru , Koyama Kiyohito
Published: January 2005

Reduction of flash generated in a gas vent is of great concern for manufacturers of electronic parts. The present study proposes a theoretical model for flash generation through consideration of flow characteristics in a gas vent. The model predicts the factors controlling flash, i.e., material parameters such as zero‐shear viscosity, crystallization temperature, thermal conductivity, and heat capacity, and process parameters such as injection and mold wall temperatures, packing pressure, and the clearance of a gas vent. On the other hand, we measure the amount of flash generated in the molding of poly(phenylene sulfide) (PPS) composites containing glass fiber and spherical fillers (CaCO3 or Al2O3). Flash reduces with decreasing size of spherical fillers. These experimental data are successfully interpreted using the flash model. Polym. Eng. Sci., 45:198–206, 2005. © 2005 Society of Plastics Engineers
Structural characterization and mass transfer properties of segmented polyurethane: influence of block length of hydrophilic segments
Authors: Hu Jin‐Lian , Mondal Subrata
Published: January 2005

An attempt has been made to investigate the effect of the block length of hydrophilic segments on the structure and mass transfer properties of segmented polyurethane (HSPU). Three different block lengths of hydrophilic poly(ethylene glycol) (PEG) segments were used, namely PEG‐200, PEG‐2000 and PEG‐3400, where the numbers indicate the molecular weight of the PEG in g mol−1. The HSPU were characterized using Fourier‐transform infrared (FTIR) spectroscopy, wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and tensile testing. Mass transfer properties were measured by sorption and water vapour flux (WVF) measurements. The control sample polyurethanes without PEG and a sample with PEG‐200 showed amorphous structure and an unclear phase separation as detected by WAXD, DSC and DMTA. There is evidence that the introduction of PEG blocks into the polyurethane matrix aids soft‐segment crystallization. The percentage crystallinity of soft segments was the highest with PEG‐2000 and an increase of PEG block length to 3400 g mol−1 resulted in a decrease in crystallinity. Mechanically, polyurethane without PEG is tough while percentage strain at maximum load increased with increasing block length of PEG. In addition, sorption and WVF increased linearly with increasing PEG block length and with temperature. The permeability of such HSPUs is a function of temperature and showed a good fit to an Arrhenius form. Copyright © 2005 Society of Chemical Industry
Marcus‐grunwald theory and the nitroalkane anomaly
Authors: Albery W. John , Bernasconi Claude F. , Kresge A. Jerry
Published: January 2005

The Disparity reaction proposed in a recent application of Marcus‐Grunwald theory to nitroalkane ionization is shown to put the reaction's transition state in an energy‐diagram region where electronic rearrangement leads proton transfer, contrary to experimental evidence; it is suggested that addition of solvent reorganization to electronic rearrangement as the second reaction progress variable would remedy this situation.
Reaction of triethylsilyl radical with sulfides, a laser flash photolysis study
Authors: Soundararajan N. , Jackson James E. , Platz Matthew S.
Published: January 2005

Triethylsilyl radical was generated by laser flash photolysis of a 1:1 (v/v) solution of triethylsilane and di‐tert‐butyl peroxide. The silicon centered radical was reacted with sulfides to give carbon centered radicals by displacement at sulfur. The carbon radicals were readily detected by their transient absorption spectra. The absolute rate of reaction of triethylsilyl radical with 9‐fluorenylphenylsulfide, di‐n‐butylsulfide, di‐sec‐butyl sulfide, di‐tert‐butyl sulfide and di‐n‐butyl disulfide are 2.40 ± 0.12 × 108 M−1S−1, 1.1 × 107±0.89×106M−1S−1, 8.79± 0.73×106M−1S−1, 3.29±0.18×106 M−1S−1, and 3.41±0.09×108 M−1S−1, respectively.
Reaction of sulfur ylides with elemental sulfur and selenium. Aspects and mechanistic considerations
Authors: Nakayama Juzo , Akimoto Keiichi , Hoshino Masamatsu
Published: January 2005

The reaction of sulfur ylides with elemental sulfur or selenium initially affords thio‐ or seleno‐carbonyl compounds, which then react with starting ylides to give episulfides or episelenides from which the heteroatom (sulfur or selenium) is extruded to give olefins as the final product. In the case of carbonyl‐stabilized ylides, the resulting thio‐ or seleno‐carbonyl compounds react with starting ylides to afford 1,3‐oxathioles or 1,3‐oxaselenoles as previously reported. Supporting evidence for the intermediacy of thio(seleno)‐carbonyl compounds and episulfides (episelenides) is presented.
Non‐planar structures of the pentafluoroallyl and 1,1‐difluoroallyl anions
Authors: Dixon David A. , Fukunaga Tadamichi , Smart Bruce E.
Published: January 2005

The structures of the allyl anion (1) and two fluoro‐substituted derivatives, perfluoro (2) and 1,1‐difluoro (3) have been calculated by ab inito molecular orbital theory. Geometries were gradient optimized, and force fields and an MP‐2 correlation correction were determined at stationary points. The calculations were done with a double zeta basis set augmented by d functions on carbon (DZ + Dc). Final self‐consistent field (SCF) and MP‐2 energy calculations were done with the DZ + Dc basis set augmented by diffuse functions. The ground state of 1 is the planar allyl anion (C2v). The rotation barrier in 1 is 21·1 kcal/mol at the MP‐2 level. The cyclopropyl carbanion is 27·0 kcal/mol higher in energy at the MP‐2 level. The perfluoroallyl anion is not planar, and the rotated structure is 25·7 kcal/mol more stable than the C2v structure at the MP‐2 level. The lowest energy structure on the potential energy surface for 2 is the perfluorocyclopropyl carbanion which is 27·8 kcal/mol more stable than the C2v structure at the MP‐2 level. The 1,1‐difluoroallyl anion is also not planar. Here the most stable structure on the potential energy surface is the rotated allyl anion which is 8·3 kcal/mol more stable than the all‐planar allyl anion structure.
Nonplanar phenyl ring and inverse order of solvolytic reactivity for tertiary benzylic substrates
Authors: Liu Kwang‐Ting , Kuo Mann‐Yan , Wang Yu
Published: January 2005

The rates of solvolysis of l‐aryl‐l‐phenyl‐2,2‐dimethylpropyl(1) p‐nitrobenzoates and of aryldiphenylmethyl‐p‐nitrobenzoates (2) were measured in 80% acetone. An inverse order of reactivity, k/km‐ CF3 > l was observed for 1 but not for 2. The X‐ray crystallogoraphic study of the parent compounds, l,l‐diphenyl‐2,2‐dimethylpropyl‐p‐nitrobenzoate (1b) and triphenylemethyl benzoate (3b), and of 2‐phenyl‐2‐propyl‐p‐nitrobenzoate (4) indicated that in the highly congested system 1 both phenyl rings were nonplanar, whereas the phenyl rings in 3 and 4 were essentially planar.