Synthesis and healing properties of poly(arylether sulfone)–poly(alkylthioether) multiblock copolymers containing disulfide bonds

Thermoplastic elastomers composed of soft and hard segments are important elastic and processable synthetic polymers. The microphase‐separated soft domains show low glass transition temperature and possess sufficient chain mobility at room temperature. In this study, we report the synthesis and healing properties of multiblock copolymers containing disulfide bonds as dynamic covalent bonds. The multiblock copolymers composed of poly(arylether sulfone) and poly(alkylthioether) segments were synthesized by oxidative coupling polymerization of the corresponding thiol‐terminated oligomers. Atomic force microscopy phase images, differential scanning calorimetry, and dynamic mechanical analysis curves indicated the microphase‐separated morphology of the multiblock copolymer. Self‐healing properties of the polymer were evaluated by changes in the elongation at break of the cut/adhered samples. The elongation recovery increased with UV irradiation time, and the multiblock copolymer showed a 93% recovery after UV irradiation for 5 h. The healing efficiency induced by UV irradiation, determined by subtracting the recovery without UV irradiation, was calculated to be 51%. According to the UV spectra and solubility changes after UV irradiation, the main healing factor in this study was the crosslinking reactions caused by thiyl radicals generated from UV irradiation instead of disulfide exchange reactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3545–3553     

On computational proofs of the existence of solutions to nonlinear parabolic problems

This paper is an extension of the preceding study (Nakao, this journal, 1991) in which we described a numerical verification method of the solution for one-space dimensional parabolic problems, to the several-space dimensional case. Here, numerical verification means the automatic proof of the existence of solutions to the problems by some numerical techniques on a computer. We reformulate the verification condition for nonlinear parabolic initial boundary value problems using the fixed-point problem of a compact operator on certain function spaces. As in the preceding study based upon a simple C⁰ finite-element approximation and its constructive a priori error estimates, a numerical verification procedure is presented with some numerical examples.     

Nuclear resonance vibrational spectroscopy reveals the FeS cluster composition and active site vibrational properties of an O2-tolerant NAD+-reducing [NiFe] hydrogenase

Hydrogenases are complex metalloenzymes that catalyze the reversible splitting of molecular hydrogen into protons and electrons essentially without overpotential. The NAD⁺-reducing soluble hydrogenase (SH) from Ralstonia eutropha is capable of H₂ conversion even in the presence of usually toxic dioxygen. The molecular details of the underlying reactions are largely unknown, mainly because of limited knowledge of the structure and function of the various metal cofactors present in the enzyme. Here, all iron-containing cofactors of the SH were investigated by ⁵⁷Fe specific nuclear resonance vibrational spectroscopy (NRVS). Our data provide experimental evidence for one [2Fe2S] center and four [4Fe4S] clusters, which is consistent with the amino acid sequence composition. Only the [2Fe2S] cluster and one of the four [4Fe4S] clusters were reduced upon incubation of the SH with NADH. This finding explains the discrepancy between the large number of FeS clusters and the small amount of FeS cluster-related signals as detected by electron paramagnetic resonance spectroscopic analysis of several NAD⁺-reducing hydrogenases. For the first time, Fe–CO and Fe–CN modes derived from the [NiFe] active site could be distinguished by NRVS through selective ¹³C labeling of the CO ligand. This strategy also revealed the molecular coordinates that dominate the individual Fe–CO modes. The present approach explores the complex vibrational signature of the Fe–S clusters and the hydrogenase active site, thereby showing that NRVS represents a powerful tool for the elucidation of complex biocatalysts containing multiple cofactors.     

Scrambled Self‐Assembly of Bacteriochlorophylls c and e in Aqueous Triton X‐100 Micelles

Bacteriochlorophyll (BChl) e was coassembled with BChl c in Triton X‐100 micelles in aqueous solutions. The Q_y absorption bands of the coaggregates were positioned between those of aggregates consisting solely of BChl c or e. The electronic absorption spectra of the coaggregates could not be reproduced by linear combinations of the spectra of the aggregates consisting solely of each pigment, but they were in line with the simulated spectra for the self‐aggregates in which both BChls were randomly distributed. These suggest that BChls c and e are not spatially separated; they are homogenously distributed over the self‐aggregates to give electronic spectra that are different from those of the aggregate consisting solely of each pigment. Deaggregation of the scrambled self‐aggregates by excess Triton X‐100 did not produce any spectral components assigned to an aggregate consisting solely of either BChl c or e. Acid‐induced decomposition of the scrambled aggregates showed different kinetics from those of the aggregates consisting solely of each pigment. These also support the homogeneous distribution of BChls c and e in the scrambled self‐aggregates. These results will be useful to investigate the major light‐harvesting antenna systems of green photosynthetic bacteria that contain two kinds of chlorosomal BChls.     

Mass balance method for purity assay of phthalic acid esters: development of primary reference materials as traceability sources in the Japan Calibration Service System

Purity assay of high-purity materials (HPMs) of phthalic acid esters (PAEs) was carried out by means of a mass balance method. In this method, chromatographic methods such as gas chromatography-flame ionization detector (GC-FID) and/or high-performance liquid chromatography (HPLC) in combination with other methods such as Karl-Fischer (KF) titration and vacuum evaporation (VE) were applied. The sum of the impurities estimated by these methods allowed the estimation of the purity of the main component by difference. Seven PAEs with varying side chain structures and levels of impurities were analysed on a systematic way in which impurities were classified into several groups in terms of their abundance, availability of qualitative information and availability of authentic compounds, etc. The absolute quantity of each impurity was determined by GC-FID and/or HPLC based on the calibration made by the authentic compounds of impurities whenever available. The purities in mass fraction of these PAEs were certified at the National Metrology Institute of Japan (NMIJ), and the PAEs were registered as primary reference materials playing an essential role in linking the metrological traceability of the Japan Calibration Service System (JCSS) to the International System of Units (SI).     

Activity of SiDbCl in the Electrooxidation of Ascorbic Acid,Dopamine, and Uric Acid

Selective electroanalytical responses for ascorbic acid, dopamine and uric acid at a carbon modified electrode based on 3‐n‐propyl‐1‐azonia‐4‐azabicyclo[2.2.2]octane silsesquioxane chloride (SiDbCl) is reported. The overlapped peaks observed at an unmodified electrode are resolved into three well defined voltammetric peaks allowing the simultaneous determination of the three species. Detection limits of 37, 0.3 and 0.1 μmo L⁻¹ of ascorbic acid, dopamine and uric acid, respectively, were calculated from calibration curves based on differential pulse voltammetric experiments performed in Britton ‐ Robinson buffer solution at pH 7.04.     

3]Rotaxane-based dinuclear palladium catalysts for ring-closure Mizoroki-Heck reaction

[3]Rotaxane containing two Pd centers in the cyclic compounds catalyzes a Mizoroki-Heck reaction of substrates with two iodophenyl groups with bisacrylate. Formation of the cyclic products is enhanced by the rotaxane catalyst more smoothly than Pd(OAc)(2).     

Structural study of a series of layered rare-earth hydroxide sulfates

We report structure analysis of a new family of rare-earth hydroxides Ln(2)(OH)(4)SO(4)·2H(2)O (Ln = Pr, Nd, Sm, Eu, Gd, Tb) from synchrotron X-ray and electron diffraction data. Rietveld profile analysis revealed that all members were isostructural and crystallized in a face-centered monoclinic system A2/m (No. 12), in which the monoclinic angles were approximately equal to the right angle, varying from 90.387(1)° for Pr sample to 90.0718(3)° for Tb sample. The structure consisted of LnO(9) polyhedra connected by μ(3)-hydroxyl groups and μ(2)-water molecules, forming a corrugated two-dimensional layer, which was pillared by bidentated sulfate ions. This series of compounds had a supercell a' = 2a, b' = 2b because of the local orientation ordering of SO(4)(2-). Structural features along the series, such as unit-cell parameters and average Ln-O distances, represented a progressive contraction associated with the shrinking radius of the lanthanide cations from Pr to Tb.     

Synthesis of bis(N-heterocyclic carbene) palladium complexes derived from (S,S)-1,2-bis(1-hydroxypropyl)benzene

New o-xylylene-linked bis(benzimidazolium) salts were synthesized in six-steps from C₂-symmetric chiral 1,4-diol, 1,2-bis(1-hydroxypropyl)benzene, as a starting material. The silver complex of bis(benzimidazol-2-ylidene) was obtained on treatment of bis(benzimidazolium) salt with silver oxide. The reaction of the silver bis-NHC with [PdCl₂(PhCN)₂] afforded the bis-NHC complex of palladium. The X-ray diffraction studies on Pd complexes revealed that these complexes have distorted square planar geometry around the Pd center coordinating the NHC ligand in mutually cis-position. The arene ring of o-xylylene unit hanged over the Pd center and thus these complexes showed C₁-symmetric structures. The variable temperature NMR spectroscopy revealed that these Pd complexes showed fluxional behavior between C₁- and C₂-symmetric structures in solution state.     

Characterization of a synthetic peroxodiiron(III) protein model complex by nuclear resonance vibrational spectroscopy

The vibrational spectrum of an η(1),η(1)-1,2-peroxodiiron(III) complex was measured by nuclear resonance vibrational spectroscopy and fit using an empirical force field analysis. Isotopic (18)O(2) labelling studies revealed a feature involving motion of the {Fe(2)(O(2))}(4+) core that was not previously observed by resonance Raman spectroscopy.