Construction of Thermophilic Xylanase and Its Structural Analysis

The glycoside hydrolase family 11 xylanase has been utilized in a wide variety of industrial applications, from food processing to kraft pulp bleaching. Thermostability enhances the economic value of industrial enzymes by making them more robust. Recently, we determined the crystal structure of an endo-β-1,4-xylanase (GH11) from mesophilic <i>Talaromyces cellulolyticus</i>, named XylC. Ligand-free XylC exists to two conformations (open and closed forms). We found that the “closed” structure possessed an unstable region within the N-terminal region far from the active site. In this study, we designed the thermostable xylanase by the structure-based site-directed mutagenesis on the N-terminal region. In total, nine mutations (S35C, N44H, Y61M, T62C, N63L, D65P, N66G, T101P, and S102N) and an introduced disulfide bond of the enzyme contributed to the improvement in thermostability. By combining the mutations, we succeeded in constructing a mutant for which the melting temperature was partially additively increased by >20 °C (measured by differential scanning calorimetry) and the activity was additively enhanced at elevated temperatures, without loss of the original specific activity. The crystal structure of the most thermostable mutant was determined at 2.0 Å resolution to elucidate the structural basis of thermostability. From the crystal structure of the mutant, it was revealed that the formation of a disulfide bond induces new C–C contacts and a conformational change in the N-terminus. The resulting induced conformational change in the N-terminus is key for stabilizing this region and for constructing thermostable mutants without compromising the activity

Synthesis and Properties of Sulfonated Block Copolymers Having Fluorenyl Groups for Fuel-Cell Applications

A series of sulfonated poly(arylene ether sulfone)s (SPEs) block copolymers containing fluorenyl groups were synthesized. Bis(4-fluorophenyl)sulfone (FPS) and 2,2-bis(4-hydroxy-3,5-dimethylpheny)propane were used as comonomers for hydrophobic blocks, whereas FPS and 9,9-bis(4-hydroxyphenyl)fluorene were used as hydrophilic blocks. Sulfonation with chlorosulfonic acid gave sulfonated block copolymers with molecular weight (Mw) higher than 150 kDa. Proton conductivity of the SPE block copolymer with the ion exchange capacity (IEC) = 2.20 mequiv/g was 0.14 S/cm [80% relative humidity (RH)] and 0.02 S/cm (40% RH) at 80 °C, which is higher or comparable to that of a perfluorinated ionomer (Nafion) membrane. The longer hydrophilic and hydrophobic blocks resulted in higher water uptake and higher proton conductivity. Scanning transmission electron microscopy observation revealed that phase separation of the SPE block copolymers was more pronounced than that of the SPE random copolymers. The SPE block copolymer membranes showed higher mechanical properties than those of the random ones. With these properties, the SPE block copolymer membranes seem promising for fuel-cell applications

Hydrolytically Stable Polyimide Ionomer for Fuel Cell Applications

Hydrolytically Stable Polyimide Ionomer for Fuel Cell Application

Sulfonated Poly(arylene ether sulfone ketone) Multiblock Copolymers with Highly Sulfonated Block. Synthesis and Properties

Poly(arylene ether sulfone ketone) (SPESK) multiblock copolymer membranes having highly sulfonated hydrophilic blocks were synthesized. The degree of polymerization of hydrophobic blocks (X) was controlled to be 15, 30, and 60 and that of hydrophilic blocks (Y) to be 4, 8, 12, and 16. Morphological observation by scanning transmission microscopy (STEM) and small-angle X-ray scattering (SAXS) showed that high local concentration of sulfonic acid groups within the hydrophilic blocks enhanced phase separation between the hydrophobic and hydrophilic blocks. Rodlike hydrophilic aggregates were found to be interconnected very well, which resulted in high proton conductivity even at low relative humidity (RH). The ionomer membrane with X30Y8 and 1.86 mequiv/g of ion exchange capacity (IEC) showed 0.03 S/cm at 80 °C and 40% RH, which was a comparable or higher proton conductivity than that of the state-of-the-art perfluorinated ionomer (Nafion) membrane. The longer blocks induced higher proton conductivity; however, excessively long block length offset mechanical properties. Low hydrogen and oxygen permeability was also observed

Novel Sulfonated Poly(arylene ether): A Proton Conductive Polymer Electrolyte Designed for Fuel Cells

Novel Sulfonated Poly(arylene ether):  A Proton Conductive Polymer Electrolyte Designed for Fuel Cell

Temperature Dependence of CO-Tolerant Hydrogen Oxidation Reaction Activity at Pt, Pt−Co, and Pt−Ru Electrodes

The temperature dependence of CO-tolerant H2 oxidation reaction (HOR) activity at Pt, Pt−Co, and Pt−Ru electrodes in 0.1 M HClO4 solution was examined with a channel flow electrode at 30 to 90 °C. The kinetically controlled current density (jK) for the HOR at Pt decreased seriously at CO overage (θCO) >0.6 in the whole temperature range examined. In contrast, the Pt−Ru alloy exhibited an excellent CO tolerance:  only 15% reduction in jK even at θCO = 0.6 and 30 °C. The Pt−Co alloy also showed moderate CO tolerance up to 70 °C. It was found for these alloys that the CO adsorption rate was much slower than that of Pt and the HOR sites were not so rigidly blocked by adsorbed CO due to its enhanced mobility, resulting from their modified electronic structure of surface Pt sites. The activation energies for the apparent rate constants for the HOR were as low as 3.0 and 5.3 kJ mol-1 at Pt and Pt−Ru, respectively, indicating that the high-temperature operation increases CO-free HOR sites as well as enhancing the HOR kinetics

Poly(arylene ether)s Containing Superacid Groups as Proton Exchange Membranes

A series of poly(arylene ether)s containing pendant superacid groups on fluorenyl groups were synthesized and their properties were investigated for fuel cell applications. Poly(arylene ether)s containing iodo groups were synthesized by the polymerization of 2,7-diiodo-9,9-bis(4-hydroxyphenyl)fluorene with difluorinated compounds such as decafluorobiphenyl, bis(4-fluorophenyl)sulfone, and bis(4-fluorophenyl)ketone, under nucleophilic substitution conditions. The iodo groups on the fluorenyl groups were converted to perfluorosulfonic acid groups via the Ullmann coupling reaction. The degree of perfluorosulfonation was controlled to be up to 92%, which corresponds to an ion exchange capacity (IEC) of 1.52 meq/g. The ionomers yielded flexible, ductile membranes by solution casting. The ionomer membranes exhibited a characteristic hydrophilic/hydrophobic phase separation, with small interconnected hydrophilic clusters (2−3 nm), which is similar to that of the benchmark perfluorinated membrane (Nafion). The aromatic ionomers containing superacid groups showed much higher proton conductivities than those of the conventional sulfonated aromatic ionomers with similar main chain structures. Fuel cell performance with the superacidic ionomer membranes was also tested

Sulfonated Poly(arylene ether phosphine oxide ketone) Block Copolymers as Oxidatively Stable Proton Conductive Membranes

The introduction of triphenylphosphine oxide moiety into the hydrophilic segments of aromatic multiblock copolymers provided outstanding oxidative stability and high proton conductivity. Our designed multiblock copolymers are composed of highly sulfonated phenylene ether phosphine oxide ketone units as hydrophilic blocks and phenylene ether biphenylene sulfone units as hydrophobic blocks. High molecular weight block copolymers (<i>M</i>_w = 204–309 kDa and <i>M</i>_n = 72–94 kDa) with different copolymer compositions (number of repeat unit in the hydrophobic blocks, <i>X</i> = 30, and that of hydrophilic blocks, <i>Y</i> = 4, 6, or 8) were synthesized, resulting in self-standing, transparent, and bendable membranes by solution-casting. The block copolymer membranes exhibited well-developed hydrophilic/hydrophobic phase separation, high proton conductivity, and excellent oxidative stability due to the highly sulfonated hydrophilic blocks, which contained phenylene rings with sulfonic acid groups and electron-withdrawing phosphine oxide or ketone groups

Carbon Segregation-Induced Highly Metallic Ni Nanoparticles for Electrocatalytic Oxidation of Hydrazine in Alkaline Media

The important roles of Ni in electrocatalytic reactions such as hydrazine oxidation are limited largely by high oxidation states because of its intrinsically high oxophilicity. Here, we report the synthesis and properties of highly metallic Ni nanoparticles (NPs) on carbon black supports. We discovered that the heat treatment of as-prepared Ni NPs with an average particle size of 5.8 nm produced highly metallic Ni NPs covered with thin carbon shells, with negligible particle coarsening. The carbon shells were formed by the segregation of carbons in the Ni lattice to the surface of the Ni NPs, leaving highly metallic Ni NPs. X-ray photoelectron spectroscopic analyses revealed that the atomic ratio of metallic Ni increased from 19.2 to 71.7% as a result of the heat treatment. The NPs exhibited higher electrocatalytic activities toward the hydrazine oxidation reaction in alkaline solution, as compared to those of the as-prepared Ni NPs and commercial Ni powders

Electrochemical Quartz Crystal Microbalance Analysis of the Oxygen Reduction Reaction on Pt-Based Electrodes. Part 1: Effect of Adsorbed Anions on the Oxygen Reduction Activities of Pt in HF, HClO₄, and H₂SO₄ Solutions

The effects of anion adsorption on the activities for the oxygen reduction reaction (ORR) at a Pt film electrode in electrolyte solutions (HClO4 and HF at various concentrations) were analyzed using an electrochemical quartz crystal microbalance (EQCM) and a rotating disk electrode (RDE). With an increasing HClO4 concentration [HClO4], the onset potential for the Pt oxide formation in the voltammogram shifted in the positive direction, accompanied by a compression of the hydrogen adsorption/oxidation wave to less positive potentials. This is ascribed to a specific adsorption of the ClO4− anion, because the [HClO4] dependence of the mass change Δm detected by EQCM in the double-layer region was found to be fitted well by a Frumkin−Temkin adsorption isotherm. The potential dependencies of Δm in both 0.1 and 0.5 M HClO4 solutions accord well with those of the ν(Cl−O) intensities observed by in situ Fourier transform infrared (FTIR) spectroscopy in the potential range from 0.3 to 0.6 V. The kinetically controlled current densities jk for the ORR at the Pt−RDE were found to decrease with increasing [HClO4], because of the blocking of the active sites by specifically adsorbed ClO4−. The values of jk in the non-adsorbing 0.1 M HF electrolyte solution, however, were smaller than those in 0.1 M HClO4. It was found that the low ORR activity could be ascribed to the low H+ activity in the weak acid solution of HF. We, for the first time, detected a reversible mass change for one or more adsorbed oxygen species on the Pt−EQCM in O2-saturated and He-purged HF and HClO4 solutions. The coverages of oxygen species θO on Pt were found to increase in the O2-saturated solution. High values of θO in O2-saturated 7 mM HF suggest that the ORR rate was limited by the very low H+ activity in the solution, and the adsorbed oxygen species remained on the surface because of a slow consumption rate