Riichirô Chûjô

Medium effects on the molecular electronic structure. I. The formulation of a theory for the estimation of a molecular electronic structure surrounded by an anisotropic medium

A theory has been developed for estimation of the electronic structure of molecules embedded in an anisotropic (inhomogeneous) medium. It is assumed that the medium surrounding a solute molecule is composed of more than two polarizable dielectrics with different dielectric constants and that the dielectrics contact each other through arbitrary shaped boundaries. Then, the charge distribution in the solute molecule interacts with the dielectrics through a reaction field. The boundary element method is introduced to obtain a numerical solution to the Poisson equation with necessary boundary conditions. The expressions for the total energy of the molecule and the Helmholtz free energy of the system are given under the Hartree–Fock–Roothaan approximation. The Fock matrix is derived by taking into account nonlinearity of the Schrodinger equation in wave function. The present theory is generally applicable to the problem of medium effects when the medium surrounding a molecule is inhomogeneous and could be appr...

Thermal behaviour and miscibility of poly(3-hydroxybutyrate)/poly(vinyl alcohol) blends

Abstract Thermal behaviour and miscibility of poly(3-hydroxybutyrate) (P(3HB)/poly(vinyl alcohol) (PVA) blend films prepared by casting have been analysed by d.s.c., n.m.r. and density measurements. Blends containing glycerine were also analysed by d.s.c. Melting temperature (Tm) of the P(3HB) crystalline phases decreased as PVA content increased, whereas Tm of the PVA phase remained almost unchanged. The crystallinity of P(3HB) in the blends also decreased with increase of PVA content. These results indicated that the thermal behaviour of the P(3HB) phase was influenced by the existence of PVA. Glycerine had no effect on the thermal properties of the blend, except for depression of Tm of the PVA phase. Miscibility in the amorphous phase of the blend has been analysed by density measurement. If P(3HB) is completely immiscible with PVA, the crystallinity of PVA can be estimated from the crystallinity of P(3HB) and the density of the sample. However, the crystallinities of the PVA phase estimated for some blend samples were greater than unity. This behaviour can be accounted for when these blends are partially miscible in the amorphous phase. In order to investigate the miscibility in detail, we have determined the 1H spin-lattice relaxation times in the laboratory frame (T1) and in the rotating frame (T1ϱ). Both T1 and T1ϱ values for the P(3HB) and PVA phases tend to approach those of blend partners with increase of PVA content. That is to say, the increase of PVA content in a blend enhances the miscibility.

N.m.r. studies of cycloamylose inclusion-complexes with p-substituted phenols

Abstract Aqueous solutions of inclusion complexes of host cyclomaltohexa- and cyclomaltohepta-ose (cyclohexa- and cyclohepta-amylose) with guest phenols p -substituted with Br, Cl, CN, NO 2 , CH 3 , CHO, and COOH have been studied by 1 H- and 13 C-n.m.r. spectroscopy. The stability of the complexes depends on the guests, the cycloamyloses, and the ionisation states of the host hydroxyl groups. The 1 H data for the host protons in the complexes show that the guests are more deeply inserted into the cavity of cyclomaltoheptaose than into that of cyclomaltohexaose.

Studies of the stereospecific polymerization mechanism of propylene by a modified Ziegler-Natta catalyst based on 125 MHz 13C n.m.r. spectra

Abstract The mechanism of stereospecific polymerization of propylene (catalysed by a modified Ziegler-Natta system, TiCl 4 /MgCl 2 /C 6 H 5 COOC 2 H 5 /Al(C 2 H 5 ) 3 ), has been analysed using the values of triad and pentad tacticity determined using 125 MHz 13 C n.m.r. spectroscopy. The well-known single active-site models, such as the Bernoullian, first- and second-Markovian, and enantiomorphic models, were found to be inadequate to describe the observed tacticity. A two-sites model, in which at one site the stereospecific polymerization proceeds in obedience to the Bernoullian model and at the other proceeds under the control of enantiomorphic-site model, is proposed. It was found that the pentad tacticities of both soluble and insoluble (in boiling heptane) fractions of polypropylene agreed well with the two-sites model.

Heptad configurational analysis of 13C n.m.r. spectra in highly isotactic polypropylene

Abstract 13C nuclear magnetic resonance (n.m.r.) spectra were obtained at 67.8 MHz for highly isotactic polypropylene polymerized with a Ziegler-Natta catalyst. The tactic heptad peaks observed in the methyl region of the spectrum were assigned on the basis of the gamma effect of chemical shift and by using the Suter-Flory RIS model of polypropylene conformations. The mechanisms of propylene polymerization were analysed from the values of triad and pentad tacticities. The analysis of the propylene polymerization mechanism was based on the two-site model, where polymerization at one site proceeds according to the Bernoullian model of selection between meso and racemo configurations, and at the other site according to selection between dextro and laevo. As a result, the two-site model, with its three parameters optimized, reproduced well the observed relative areas of pentad and heptad peaks in the region of methyl carbon resonances.

A molecular orbital study of cyclodextrin (cyclomalto-oligosaccharide) inclusion complexes. III, dipole moments of cyclodextrins in various types of inclusion complex

Abstract Large values (10–20 D) of the dipole moments were calculated for cyclomalto-hexaose, -heptaose, and -octaose (αCD, βCD, and γCD) and also two types of methylated CD by means of the CNDO/2 MO method, using the X-ray structures of various inclusion complexes. The relative strengths of the dipole moments were αCD

Heme methyl hyperfine shift pattern as a probe for determining the orientation of the functionally relevant proximal histidyl imidazole with respect to the heme in hemoproteins

Heme methyl 1H and 13C resonances of met‐cyano form of myoglobin from the shark, Geleorhinus japonicus (GJMbCN), have been assigned via 1H‐13C heteronuclear shift correlated spectroscopy (COSY) connectivities and their hyperfine shifts were compared with those of the corresponding resonances of some hemoproteins. Variation of the heme methyl 1H hyperfine shift pattern correlates well with the angle (Φ) between the projection of the proximal histidyl imidazole plane onto the heme plane and the NII‐Fe‐Niv vector. The alteration of the interaction of the heme peripheral side‐chains and/or the iron‐bound ligand with the surrounding amino acid residues cannot account for large differences in the shifts of the corresponding heme methyl resonances between GJMbCN and sperm whale MbCN. Since the heme methyl 1H shifts for GJMbCN fall in between those of the corresponding resonances for sperm whale Mb and Aplysia limacma Mb in which the Φ values have been reported to be 19° and 29°, respectively, the Φ value in GJMb is estimated to be slightly larger than 19°.

A high-resolution c.p.-m.a.s. 13C-n.m.r. study of solid-state cyclomaltohexaose inclusion-complexes: Chemical shifts and structure of the host cyclomaltohexaose

Abstract High-resolution, solid-state 13 C-n.m.r. spectra were obtained for several crystalline cyclomaltohexaose inclusion-complexes. The resonances of C-1, C-4, and C-6 of the host were dispersed. The averaged 13 C shifts of these resonances were in good agreement with the 13 C shifts observed in solution, where the dispersion due to conformational diversity is expected to be averaged by rapid interconversion of the conformers. This result indicates that the most plausible source of the solid-state 13 C-shift dispersions of the resonances of C-1 and C-4 is the diversity of conformations about the glycosidic linkage. The molecular origins of conformation-dependent 13 C shifts are discussed.

N.m.r. study of interaction between sugar and peptide moieties in mucin-type model glycopeptides.

In order to investigate the structural properties of the sugar and peptide linkage region in glycoprotein, some glycopeptides were synthesized as a model for AFGP (antifreeze glycoprotein), which is one of the mucin-type glycoproteins. The results from n.m.r. measurements in DMSO and aqueous conditions revealed that the glycopeptides form an intramolecular hydrogen bond between the amide proton of N-acetylgalactosamine (GalNAc) and the carbonyl oxygen of threonine (Thr) to which the GalNAc is covalently linked. This intramolecular hydrogen bond may play an important role in determining the orientation of the sugar moiety relative to the protein backbone. The roles for the activity of the proline (Pro) residue in AFGP were also discussed.

13C n.m.r. studies on the microstructure of poly(vinylidene cyanide/vinyl benzoate) and poly(vinylidene cyanide/styrene)

Abstract The microstructure of vinylidene cyanide-vinyl benzoate and vinylidene cyanide-styrene copolymers, both of which were prepared by radical copolymerization, were studied by 125 MHz 13 C n.m.r. spectroscopy. The former shows high piezoelectricity, while the latter has low piezoelectricity. It was found that the compositional sequence distribution and tacticity of both copolymers were not largely different from each other, namely, both were highly alternating copolymers with a non-stereoregular structure. Possible origins of piezoelectricity were suggested for vinylidene cyanide copolymers.