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Asakura T.,Tokyo University of Agriculture and Technology | Asakura T.,Japan Institute for Molecular Science | Ohata T.,Tokyo University of Agriculture and Technology | Kametani S.,Mitsui Chemical Analysis and Consulting Service Inc. | And 9 more authors.

We have previously suggested that crystalline Bombyx mori silk in silk II form (the silk structure after spinning) is not a simple antiparallel β-sheet but is intrinsically heterogeneous. Using the peptide (AG)15, we have obtained the first fully assigned high resolution solid state 1H NMR spectrum. Distinct heterogeneity was observed, in both 1H and 13C CP/MAS signals. Based on these results, a new model is proposed that contains two different packing arrangements of antiparallel β-sheets. The structures were energetically minimized by CASTEP calculation and used to calculate the solid state 1H, 13C, and 15N NMR chemical shifts using the GIPAW method. This new model was supported by good agreement between the calculated and observed 1H, 13C, and 15N chemical shifts and relative 1H-1H proximities obtained from 2D 1H DQMAS experiments. We conclude that the intermolecular packing of B. mori silk fibroin has been finally resolved. © 2014 American Chemical Society. Source

Kokufuta M.K.,Mitsui Chemical Analysis and Consulting Service Inc. | Sato S.,University of Tsukuba | Kokufuta E.,University of Tsukuba
Colloid and Polymer Science

The lower critical solution temperature (LCST) behavior of copolymers of N-isopropylacrylamide (NiPA) and N-isopropylmethacrylamide (NiPMA) in water was studied as a function of the copolymer composition, using a combination of turbidity measurements and differential scanning calorimetry (DSC). The copolymers were prepared by free radical polymerization using N,N-dimethylformamide as a solvent and α,α′- azobis(isobutyronitrile) as an initiator. The copolymer composition was determined by elemental analysis. It was found that the temperature (T c) at which the copolymer undergoes a phase transition, i.e., LCST, increases linearly with increasing the mole fraction (f m) of NiPMA in the copolymer, within the T c range from 32 °C (at f m=0; NiPA homopolymer) to 42 °C (at f m=1; NiPMA homopolymer). Also found from heating DSC thermograms were the linear dependencies of the enthalpy (ΔH) and entropy (ΔS) changes at T c upon f m. However, the ΔH (5.5 kJ/unit-mol) at fm01 was slightly smaller than that (5.7 kJ/unit-mol) of poly(N-n-propylacrylamide) but considerably smaller than that (7.8 kJ/unit-mol) of poly(N-n- propylmethacrylamide). The same trend was observed in the f m dependence of ΔS. These results were discussed in terms of the structural effects of the NiPMA monomer unit on the heat-induced phase transition in water of poly(NiPA-co-NiPMA)s. It was suggested that a strong interaction of water with the amide group in the NiPMA would raise the transition temperature, but a local dehydration which occurs around the isopropyl side chain would not lead to large changes in the enthalpy and entropy at T c. © Springer-Verlag 2012. Source

Kokufuta E.,University of Tsukuba | Sato S.,University of Tsukuba | Kokufuta M.K.,Mitsui Chemical Analysis and Consulting Service Inc.

Electrophoretic behavior was studied for N-isopropylacrylamide (NIPA) microgels, into which different amounts of poly(acrylic acid) (PAAc) were physically entrapped. Copolymer microgels of NIPA with acrylic acid (AAc) were also studied as a control. Electrophoretic mobility was measured in 0.1 M NaCl solution at 25 C as a function of pH, using an electrophoretic light scattering technique. The mobility of the copolymer microgel whose COOH groups are fully ionized agreed with that of PAAc when its ionization degree (α n) is close to the mole fraction (fAAc) of the AAc unit in the copolymer gel. There was good agreement between the mobility values of the copolymer microgel and the linear NIPA/AAc copolymer when their AAc contents are very close to each other. However, the mobility of the microgel with immobilized PAAc was higher than that of the copolymer microgel, even when there was no difference in the AAc content for both microgels. Moreover, the immobilized PAAc showed a higher mobility than the free PAAc when its αn is equal to fAAc in the immobilized system. No correlation was observed between the mobility and the hydrodynamic radius. These results were discussed in terms of the free draining model (FDM) for the electrophoresis of polyelectrolytes. It became apparent that the mobility difference depending upon whether (i) the PAAc ions are in the cage of the NIPA network or (ii) the AAc units are copolymerized with the network chain is due to the structural difference of the segments considered in the FDM. © 2013 American Chemical Society. Source

Sasahara T.,Kitasato University | Mase H.,Materials Development, Inc. | Abe M.,Mitsui Chemical Analysis and Consulting Service Inc. | Abe M.,Kitasato University | Saito H.,Japan Copper Development Association
Acta Dermato-Venereologica

Metallic copper has been shown signifcantly to reduce methicillin-resistant Staphylococcus aureus (MRSA) contamination of the ambient surroundings of the beds of MRSA-carrying patients in dermatology wards. The aim of this study was to determine whether a bed sheet made of copper-coated film will reduce the spread of MRSA contamination in the environment of a heavily-colonized patient. The bacterial count was highest on the bed sheet. MRSA cell counts on the surface of the non-film-coated control sheet were high (6,600-11,000 colony forming units (cfu)), but those on the copper film were considerably lower (20-130 cfu). Use of metallic copper on the bed sheets of patients who are likely to be a source of MRSA contamination may help to prevent the spread of MRSA contamination in hospital wards. © 2013 The Authors. Source

Kokufuta M.K.,Mitsui Chemical Analysis and Consulting Service Inc. | Sato S.,University of Tsukuba | Kokufuta E.,University of Tsukuba
Colloids and Surfaces B: Biointerfaces

We synthesized the glutaraldehyde cross-linked hydrogels using four kinds of poly(lysine)s (PLs) and measured the equilibrium swelling ratio (Q) as a function of pH. Also measured was the temperature change of Q at a fixed pH (11.6) in the absence and presence of additives (LiBr, methanol and urea) that affect the secondary structure of PLs. The swelling data were examined using a force balance approach in which the repulsive and attractive interactions among the cross-linked PL chains were considered based on the conformational properties of PLs in aqueous solutions. It was found that the formation of the helical segments in the cross-linked chain has little effect in the gel collapse, but their association acts as the attractive interaction causing the gel to shrink. The formation of the beta-sheet structure within the network also acts as the attractive interaction. These attractive interactions are mainly due to the hydrogen bonding, but hydrophobic interactions between the lysine side chains should be considered. In addition, in the swelling behavior of all the PL gels the polyampholyte nature appears due to electrostatic interactions of the basic groups with the C-terminal carboxyl group. © 2011 Elsevier B.V. Source

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