Hidemine Furuya

Molecular dynamics simulation of cis-1,4-polybutadiene. 1. Comparison with experimental data for static and dynamic properties

Molecular dynamics (MD) calculations of cis-1,4-polybutadiene in bulk amorphous phase were performed under constant pressure and constant temperature conditions. The static and dynamic properties were evaluated from the results of MD calculations. The obtained density and coefficient of thermal expansion are in good agreement with experimental data. The feature of the calculated static structure factor is similar to the observed one. Molecular motion is examined with mean square displacements and intermediate scattering functions. An onset of a new motion, which corresponds to so-called fast process, was clearly observed in the temperature dependence of the mean square displacement above 100 K. The dynamic structure factors obtained by the Fourier transformation of the intermediate scattering functions are compared with those obtained from quasielastic neutron scattering measurements. The peaks corresponding to the elastic scattering and the low energy excitation at around 2 meV are reproduced in the dynamic structure factors. The excessive intensity observed in the dynamic structure factor, which corresponds to the fast process, is also reproduced above 140 K in our simulation.

Spatial configurations, transformation, and reorganization of mesophase structures of polyaspartates—A highly intelligent molecular system

Poly(β-phenethyl L-aspartate) (PPLA) takes the right-handed α-helical form in 1,1,2,2-tetrachloroethane at moderate temperatures. The transition to the left-handed α-helix occurs at around 85°C in the isotropic solution as well as in the lyotropic liquid crystalline state. In the presence of a denaturant acid, PPLA also exhibits a transformation to the left-handed form by lowering temperature. Accordingly, a ternary mixture such as PPLA trifluoroacetic acid/chloroform possibly exhibits as many as five phases above certain concentration. The primary cause responsible for such a highly cooperative helix-helix transition was found to reside in a small free-energy difference in the conformational states of the side chain flanking the spiral backbone of the two opposite handedness.

Molecular Ordering in Dimer Liquid Crystals as Estimated by the Analysis of D-NMR Spectra of Deuterated Flexible Spacers

Abstract An attempt has been made to elucidate molecular conformations of ether-and ester-type dimer liquid crystals (DLC) carrying deuterated soft-spacers by utilizing the information provided by the D-NMR method. The analysis has been carried out according to the following steps: 1. All possible configurations are enumerated for a free molecule within the framework of the RIS approximation. 2. Configurations which do not conform to the nematic ordering are discarded. 3. For the nematic ensemble thus selected, conformational statistical weight factors assigned to the individual bond rotations are adjusted so as to reproduce the observed profile of the D-NMR spectrum. In this treatment, following the scheme established in the preceding paper, the molecular axis of a conformer is defined along the line connecting the centers of the terminal mesogenic cores. The results of the analysis indicate that conformations permitted in the nematic state amount to 10 to 15% of the free molecule near the N—I transition...

Screw-sense inversion characteristic of α-helical poly(β-p-chlorobenzyl L-aspartate) and comparison with other related polyaspartates†

This is one of a series of studies on the reversal of the helix sense of polyaspartates originated from the pioneering work of Goodman and his associates in 1960s. Poly(β‐p‐chlorobenzyl L‐aspartate) (PClBLA) is one of the well‐studied polyaspartate derivatives in both solution and the solid state. The chemical structure of PClBLA differs from those of poly(β‐benzyl L‐aspartate) (PBLA) and poly(β‐phenethyl L‐aspartate) (PPLA) only at the terminal of the relatively long side chain. PBLA takes a left‐handed form (L) in conventional helicoidal solvents and does not exhibit any screw‐sense inversion. In contrast to PBLA, both PClBLA and PPLA form a right‐handed helix (R) in chlorinated alkane solvents and exhibits a reversal of α‐helix sense at higher temperatures. Yet the transition behaviors in the presence of denaturant acid are quite different between these two polymers. While PPLA exhibits transitions such as R → L → coil by lowering temperature, PClBLA directly goes into the coil state without showing the reentrant L form. The cause of these phenomenological differences among these polymers has been investigated by constructing the phase diagram.

Deuterium NMR analysis of main-chain polymer liquid crystals

SummaryDeuterium NMR measurements have been performed for main-chain polymer liquid crystals having structures such as {Ø-OC(O)-Ø-O(CD2)nO-Ø-C(O)O-Ø-O(CH2)nO}x with n = 9, 10. D-NMR spectra obtained in the nematic mesophase are compared with those previously reported for the dimer liquid crystals of the type NC-φ-φ-O(CD2)nO-φ-φ-CN with n = 9, 10, Although resolutions are relatively poor in the polymer spectrum, the general profiles of the spectra were found to be similar to those of the corresponding dimer. The results of the RIS analysis suggest that the spatial configurations of the spacer are nearly identical between the dimer and polymer. It has been concluded that the observed enhancement in the quadru-polar splittings should arise largely from a higher orientational ordering of the molecular axis in the polymeric system.

Deuterium NMR analysis of dimer liquid crystals

SummaryDeuterium NMR measurements have been performed for dimer liquid crystals (DLC) having structures such as NCφφ-O(CH2)nO-φφCN (CBA) with n=9, 10. Fully deuterated CBAs with n=9 and 10 exhibit, respectively, three and four splittings in the D-NMR spectra. By using partially deuterated samples, the signals corresponding to the largest splittings were found to include contributions from the α- and β-CD2 groups. The origins of the rest of the signals were elucidated by the RIS method previously established. Characteristic properties of the nematic mesophase were estimated for CBA-10. The results were found to be consistent with those of the previous analysis on Griffin et al.s DLC.

High pressure differential thermal analysis of dimer liquid crystals: α, ω-Bis [(4,4′-cyanobiphenylyl) oxy] alkanes

Abstract The phase behaviour of dimer liquid crystals (DLC), α, ω-bis[(4,4′-cyanobiphenylyl) oxy]alkanes (CBA-n with n = 9,10) has been studied by differential thermal analysis (DTA) over a pressure range from 0.1 to 150 MPa. Both samples exhibit crystal (Cr)↔nematic (N)↔isotropic (I) transitions under all experimental conditions. The slopes of the phase boundary curve (dp/dt)tr were determined from the P tr vs. T tr phase diagram, where the subscript tr designates CrN or NI. Both transition temperatures T CrN and T NI were found to increase almost linearly as a function of pressure; CBA-9: (dp/dt)CrN = 3.92, (dp/dt)NI = 2.03; CBA-10: (dp/dt)CrN = 3.66, (dp/dt)NI = 2.17, the units being MPaK−1. As a consequence, the nematic region defined by the interval between the CrN and NI transitions becomes broader as the applied pressure increases. While the transition enthalpies δS CrN and the associated entropies δS CrN at the CrN transition decrease substantially with increasing pressure, the corresponding quant...

Thermal Neutron Spin-Echo Studies on Dynamics of a Glass-Forming Polymer in a High Q Range

We performed thermal neutron spin echo measurements on a glass-forming polymer, deuterated polybutadiene (–[CD 2 –CD=CD–CD 2 ] n –; PB- d 6 ), in a high Q range up to 3.5 A -1 covering the first an...

Gas phase NMR and ab initio molecular orbital calculations of 5-methoxy-1,3-dioxanes: a critical survey of the Gauche effect

Abstract The gas-phase NMR analysis of 5-methoxy-1,3-dioxanes was carried out. The conformational energies estimated from the observed coupling constant data were compared with the results of ab initio MO calculations using d95 + (2df,p) basis set at the MP2 level. While the energy difference between the axial-out and equatorial-out forms was in a reasonable agreement, the 1,5 interaction energy between the methoxy methyl and the ring oxygens was not in accord.

Quantitative analysis of helix–coil transition of block copolypeptide, Glu12–Ala12, by combined use of CD and NMR spectroscopy

To investigate helix–coil transition mechanisms, conformations of Glu12–Ala12, EA, in aqueous solution have been studied in detail over the pH range from 2 to 8 and the temperature range from 20 to 60°C using CD and NMR spectroscopy. The 750‐MHz NMR spectra displayed excellent dispersion of the backbone amide proton signals, and permitted essentially complete sequence‐specific resonance assignments. These assignments, together with short‐ and medium‐range nuclear Overhauser effect (NOE) constraints and coupling constants, enable us to analyze conformational characteristics of all the residues in the EA peptide individually. A combined use of CD and NMR techniques reveals that the EA peptide assumes a stable α‐helix from Glu12 to Ala19 in 0.1M NaCl solution at 20°C above pH 7. The α‐helix is getting longer as decreasing pH. Below pH 4, the peptide assumes the longest α‐helix from Glu3 to Ala23. The important observation of the present study is that the helix–coil transition occurs stepwise, residue by residue, from both the N‐ and C‐termini of the α‐helix. No conformational equilibrium between the helical and random‐coil states is detected for the residues in the central region of the α‐helix. Quantitative analysis of temperature‐induced helix‐to‐coil transitions at various pHs provides a pH‐independent residual enthalpy change ΔHr = 0.95 kcal res−1. Similar values have been reported for a 50‐residue alanine‐rich peptide (1.2 kcal res−1), poly‐L‐glutamate (1.1 kcal res−1), poly‐L‐lysine (1.1 kcal res−1), and poly‐L‐alanine (0.86 kcal res−1). Those investigations, along with our present result, suggest that ΔHr is mainly determined by the transformation of the backbone associated with the disruption of the intramolecular hydrogen bond. These results should increase our understanding of the helix–coil transition.