Hiromichi Kurosu

A study on dynamics of water in crosslinked poly (N-isopropylacrylamide) gel by n.m.r. spectroscopy

Abstract The dynamics of crosslinked poly ( N -isopropylacrylamide) gel have been studied by means of pulsed-gradient spin-echo (PGSE) 1 H nuclear magnetic resonance (n.m.r.), pulse 1 H n.m.r. and 1 H n.m.r. imaging. The self-diffusion coefficients of HDO ( D HDO ) in D 2 O (containing a small amount of HDO) in the gels with various degree of swellings were determined by the PGSE 1 H n.m.r. method. From these experimental results, it was found that the D HDO is decreased as the degree of swelling is decreased, and D HDO in the gels with a constant degree of swelling in going from 20 to 45°C is transitionally decreased at about 32°C, which corresponds to the phase transition temperature. From the detailed analysis of proton spin-spin relaxation time T 2 determined by the pulse 1 H n.m.r. method, the process of the volume phase transition of the gel has been elucidated. Furthermore, spatial information about the molecular motion of water in the gel sample was obtained by T 2 enhanced 1 H n.m.r. imaging.

Chemical modification of monolithic poly(styrene–divinylbenzene) polyHIPE® materials

Monolithic samples of highly porous poly(styrene/DVB) PolyHIPE® have undergone a number of electrophilic aromatic substitution reactions, namely sulfonation, nitration and bromination. Mild, hydrophobic reagents and homogeneous reaction conditions were sought in an effort to achieve uniform chemical modification, to a reasonable degree of substitution, throughout the large polymeric structures. Thus, sulfonation was carried out with lauroyl sulfate in cyclohexane, nitration with tetrabutylammonium nitrate-trifluoroacetic anhydride (TBAN–TFAA) in dichloromethane and bromination with bromine–stannic chloride in dichloromethane. An average degree of sulfonation of 2.4 mmol g–1 was achieved, with a drop in sulfonic acid content of approximately 1 mmol g–1 from surface to centre. Nitration occurred to a lesser extent, with similar differences in substitution between surface and centre being observed. PolyHIPE® monolithic samples were brominated to an extent of 3.6 mmol g–1 furthermore, this was uniform across the entire substrate. The differences in extent of each reaction are explained by consideration of such factors as the nature of the solvent, polarity of the reagents and compatibility between the reagents and the polymer matrix throughout the reactions.

Hydrogen-bonded structure and 13C NMR chemical shift tensor of amino acid residue carbonyl carbons of peptides and polypeptides in the crystalline state. Part I

Abstract 13 C chemical shift tensor components ( δ 11 δ 22 and δ 33 ) of glycine (Gly), l -valine (Val), l -leucine (Leu), and l -asparagine (Asp) residue carbonyl carbons (C  O) of peptides and polypeptides covering a wide range of hydrogen-bond lengths ( R N…O ) in the crystalline state have been measured by slow magic-angle-spinning solid-state 13 C NMR. From these experiments, it is found that δ 22 , which lies approximately along the amide C  O bond, moves linearly downfield with a decrease in R N…O and the slope and intercept of the variation of δ 22 against R N…O depend on the amino acid residue. Using this relationship, the R N…O values for polypeptides were determined by observation of the δ 22 of the guest Gly residue incorporated into host polypeptides. δ 11 , and δ 33 are found to be insensitive to the change in R N…O and amino acid residues. Moreover, it is found that the sum of δ 11 and δ 33 is almost constant (337.5 ± 3.5 ppm) and is independent of the amino acid residue. The quantum-chemical calculation on the 13 C shielding constant for a peptide model compound was carried out by the finite perturbation theory within the INDO framework. This calculation acceptably explains the experimental results.

Structure of peptides and polypeptides in the solid state as elucidated by NMR chemical shift

Abstract It is reviewed that through the observation of solid-state 13 C NMR chemical shift, the main-chain conformation and hydrogen-bonded structure of peptides, polypeptides and proteins in the solid state have been successfully elucidated, and the combination of solid state 13 C NMR and chemical shift calculation by quantum chemistry is a powerful means for the structural characterization. Furthermore, it is briefly introduced that solid state NMR of 15 N and 17 O nuclei is very useful for obtaining information about hydrogen-bonded structure. This review article is communicated on the basis of our recent works on structural characterization of peptides and polypeptides including proteins in the solid state by high-resolution solid-state NMR spectroscopy and its combination with quantum chemical calculation.

Structural study of peptides containing L-alanine residues by ab initio chemical shielding calculation

Abstract The correlation between the chemical shifts and the main-chain dihedral angles of peptides containing l -alanine residues are estimated by carrying out chemical shielding calculations using the coupled Hartree—Fock method with the gauge invariant atomic orbitals (GIAO-CHF). This aids understanding of the 13C chemical shift behaviour of the peptides and polypeptides.

Interchain effect of 13C nuclear magnetic resonance chemical shift and electronic structure of polyoxymethylene chains in the solid state

The tight‐binding MO calculations of the 13C NMR chemical shifts and electronic structure for seven polyoxymethylene chains having trigonal and orthorhombic forms were carried out within the CNDO/2 sum‐over‐state framework, taking into account the interchain interactions. The calculation explains reasonably the experimental data. Based on these results, the interchain interactions were discussed.

Ultra-drawing of low molecular weight polyethylene : ultra-high molecular weight polyethylene blend films prepared by gelation/crystallization from semi-dilute solutions

Greatest drawability was studied for blend films with branched low molecular weight polyethylene (B-LMWPE) and ultra-high molecular weight polyethylene (UHMWPE) prepared by gelation/crystallization from solutions. The morphology of B-LMWPE–UHMWPE dry gel film and its deformation mechanism were mainly estimated by using differential scanning calorimeter, small-angle X-ray scattering, wide-angle X-ray diffraction and solid-state 13C NMR. The detailed analysis was carried out for the blend films including large amounts of B-LMWPE. As a result, it was found that the UHMWPE and B-LMWPE were crystallized separately from the mixed solution. The greatest drawability was attributed to a suitable number of entanglements between UHMWPE crystal lamellae that are highly oriented with their large flat faces parallel to the film surface. These entanglements play an important role to transmit the drawing force as intermolecular cross-links and ensured smooth crystal transition of UHMWPE from a folded to a fibrous. In this process, large amount of B-LMWPE is thought to be almost independent of the ultra-drawing behavior of UHMWPE, since the domains of UHMWPE and B-LMWPE within the blend have no interaction and B-LMWPE crystallites take almost a random orientation.

Structural characterization of polypyrrole in the solid state by high resolution 15N NMR spectroscopy combined with quantum chemistry

Abstract The 15 N CP/MAS NMR spectra of doped and undoped 15 N-labeled polypyrroles in the solid state, prepared electrochemical polymerization, were measured by means of high-resolution solid-state NMR and related to electrical conductivity. From these results, it was found that the 15 N signal of polypyrrole consists of at least four peaks which were decomposed by computer-fitting. In order to obtain systematic information on the structure and electronic structure, a quantum chemical calculation was carried out to assist in analyzing the four 15 N peaks.

Effect of interchain interactions on 13C nuclear magnetic resonance chemical shifts and electronic structures of polyacetylene in the solid state as studied by tight‐binding molecular orbital theory

The 13C NMR chemical shifts of undoped cis and trans polyacetylenes in the solid state were calculated using the tight‐binding sum‐over‐state theory within the CNDO/2 framework. In order to investigate the effect of the interchain interactions on the 13C NMR chemical shifts and electronic structures of the polymers, the calculation was carried out using the multichains models. The calculation for the seven‐chains model explains reasonably the experimental data. From this, it was found that the interchain interactions greatly influence the electronic structures of polyacetylene chains.

A structural study of peptides and proteins containing l-alanine residues by 13C NMR spectroscopy combined with ab initio chemical shift calculations

Abstract From the observation of solid-state 13C NMR chemical shifts of l -alanine residues which are contained in some peptides, and the 13C chemical shift calculations employing the coupled-Hartree—Fock method with gauge-invariant-atomic-orbital, it was found that the 13C chemical shift of the Cβ-carbon in the l -alanine residue is related to the main-chain dihedral angles, φψ, but that of the Cα-carbon is affected not only by dihedral angles but also by hodrogen-bonding structure. These results were successfully applied to the structural study of proteins in solution, ribonuclease H from Escherichia coli and basic pancreatic trypsin inhibitor.