High-yield production of hydrogen by Enterobacter aerogenes mutants with decreased alpha-acetolactate synthase activity

To enhance hydrogen (H2) production from glucose by Enterobacter aerogenes HU-101, two mutants, strains VP-1 and VP-2, with decreased alpha-acetolactate synthase activity, were isolated using the Voges-Proskauer (VP) test. In pH-uncontrolled batch culture, both mutants showed a lower 2,3-butanediol yield for the glucose consumed than that shown by the wild-type strain, although glucose remained in the medium after 12 h of culture. In the same cultures, compared to the H2 yield of 0.80 mol/mol-glucose of the wild-type strain, strain VP-1 showed a high H2 yield of 1.8 mol/mol-glucose with decreased lactate and increased succinate yields, while strain VP-2 showed an H2 yield of 1.0 mol/mol-glucose with an increased lactate yield. Increasing the phosphate buffer concentration, which contributes to maintaining the pH in the medium, increased the glucose consumption by both strains. However, in a pH-controlled batch culture at neutral pH, the H2 yield of strain VP-1 was decreased to 1.2 mol/mol-glucose due to the accumulation of formate, an intermediate of the H2-producing pathway, with the yield of H2 plus formate being 1.7 mol/mol-glucose.     

Cloning of a novel tyrosinase-encoding gene (melB) from Aspergillus oryzae and its overexpression in solid-state culture (Rice Koji)

We have cloned a novel tyrosinase-encoding gene (melB) specifically expressed in solid-state culture of Aspergillus oryzae. A tyrosinase-encoding gene (melO) from A. oryzae was already cloned and the protein structures of its catalytic and copper binding domains were investigated. However, our recent results revealed that the melO gene was highly expressed in submerged culture but not in solid-state culture. Because tyrosinase activity was also detected in solid-state culture, we assumed that another tyrosinase gene other than melO is expressed in solid-state culture. Another tyrosinase gene was screened using the expressed sequence tag (EST) library. One redundant cDNA clone homologous with the tyrosinase gene was found in the collection of wheat bran culture. Northern blot analysis revealed that the gene corresponding to the cDNA clone was specifically expressed in solid-state culture (koji making), but not in submerged culture. Molecular cloning showed that the gene carried six exons interrupted by five introns and had an open reading frame encoding 616 amino acid residues. This gene was designated as melB. The deduced amino acid sequence of the gene had weak homology (24%-33%) with MelO and other fungal tyrosinases but the sequences of the copper binding domains were highly conserved. When the melB gene was expressed under the control of the glaB promoter in solid-state culture, tyrosinase activity was markedly enhanced and the culture mass was browned with the melanization by MelB tyrosinase. These results indicated that the melB gene encodes a novel tyrosinase associated with melanization in solid-state culture.     

Application of Fourier transform near-infrared spectroscopy to optimization of green tea steaming process conditions

In this study, we constructed prediction models by metabolic fingerprinting of fresh green tea leaves using Fourier transform near-infrared (FT-NIR) spectroscopy and partial least squares (PLS) regression analysis to objectively optimize of the steaming process conditions in green tea manufacture. The steaming process is the most important step for manufacturing high quality green tea products. However, the parameter setting of the steamer is currently determined subjectively by the manufacturer. Therefore, a simple and robust system that can be used to objectively set the steaming process parameters is necessary. We focused on FT-NIR spectroscopy because of its simple operation, quick measurement, and low running costs. After removal of noise in the spectral data by principal component analysis (PCA), PLS regression analysis was performed using spectral information as independent variables, and the steaming parameters set by experienced manufacturers as dependent variables. The prediction models were successfully constructed with satisfactory accuracy. Moreover, the results of the demonstrated experiment suggested that the green tea steaming process parameters could be predicted on a larger manufacturing scale. This technique will contribute to improvement of the quality and productivity of green tea because it can objectively optimize the complicated green tea steaming process and will be suitable for practical use in green tea manufacture.     

A simple and reproducible testing method for dialkyl phthalate migration from polyvinyl chloride products into saliva simulant

We describe a method of mechanical agitation to determine rates of dialkyl phthalate migration from polyvinyl chloride (PVC) products into saliva simulant. The method consists of rotary shaking of a sample with 30 mL of saliva simulant (pH 7.0) at 35 degrees C in a 50 mL glass tube at 300 rpm for 15 min, then measuring the amount of dialkyl phthalate in the saliva simulant by HPLC with a UV detector. The migration rates of diisononyl phthalate (DINP), di-2-ethylhexyl phthalate (DEHP) and di-n-butyl phthalate (DBP) from PVC plates containing about 45% (w/w) plasticizer (molded in our laboratory) were identical. However, the migration rates from molded plates containing 13% (w/w) DBP were almost double those of DINP and DEHP at the same ratios. In addition, the amounts of DINP that migrated in vitro after rotary shaking for 15 min were equivalent to those in vivo determined in saliva from volunteers who chewed plates for 60 min. The migration rates of dialkyl phthalates from 11 commercially available toys ranged from 15.6 to 85.2 micrograms/cm2/h [relative standard deviation (RSD), 3 to 12%].     

Role of chlorine in combustion field in formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during waste incineration

Combustion experiments performed in the presence of hydrogen chloride (HCl) in a laboratory-scale fluidized-bed reactor were carried out to elucidate the role of chlorine in the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs; together: PCDD/Fs) in various sections of a municipal waste incinerator. We first demonstrated that the homologue profile and the pattern of the congener proportions of PCDD/Fs for a model waste containing poly(vinyl chloride) (PVC) combusted in the absence of HCl were similar to those for a PVC-free waste combusted in the presence of HCl. This showed no difference between PVC in the waste and injected HCl in the role as a chlorine source in PCDD/F formation during incineration. Next, to investigate PCDD/F formation in each section of the incinerator, we carried out combustion experiments with the PVC-free waste, injecting HCl at different locations of the incinerator. The amounts of PCDDs and PCDFs formed were significantly reduced when HCI was not supplied to the main combustion section. The presence of HCI in the main combustion section was essential for the formation of PCDD/Fs, even in the downstream sections. This finding indicates that compounds that were able to form PCDD/Fs in the downstream sections were mainly formed in the main combustion section in the presence of HCl.     

Electrochemical oxidation of ethylene glycol on Pt-based catalysts in alkaline solutions and quantitative analysis of intermediate products

Electrocatalytic activities of Pt/C, Pt-Ru/C, and Pt-Ni/C for the oxidation of ethylene glycol in a basic solution are evaluated by cyclic voltammetry and quasi-steady state polarization. Based on the results of Tafel slopes from quasi-steady state polarization, the catalytic activities for ethylene glycol oxidation are in the order of Pt-Ru/C > Pt-Ni/C > Pt/C. The analysis of intermediate products for ethylene glycol oxidation by higher performance liquid chromatograph (HPLC) demonstrates that the degree of ethylene glycol oxidation is dependent on catalysts. Pt-Ru/C shows the highest current densities for ethylene glycol oxidation, but shows lower fuel utilization. On the other hand, Pt-Ni/C shows higher ability to cleavage C–C bonds, but is suffered from catalyst poisoning. To improve the tolerance for catalyst poisoning, we construct a novel Pt-Ni-SnO₂/C catalyst, compare its catalytic activities, and evaluate the intermediates. Pt-Ni-SnO₂/C shows superior catalytic activities for ethylene glycol oxidation, resulting in the highest degree of complete electro-oxidation of ethylene glycol to CO₂.     

Structural aspects of the LCST phase behavior of poly(benzyl methacrylate) in room-temperature ionic liquid

The structure and lower critical solution temperature (LCST) phase behavior of well-defined poly(benzyl methacrylate) (PBnMA) solution using 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide, [C₂mim][NTf₂] ionic liquid (IL) as a solvent have been studied by dynamic light scattering (DLS) and small-angle neutron scattering (SANS) at various temperatures. The SANS profiles observed for fully deuterated IL ([C₂mim]-d₁₁[NTf₂]) containing PBnMA were kept practically unchanged in the temperature range between 298 and 363 K, while they suddenly changed at 363 K. This indicates that the LCST behavior of PBnMA-IL solution is a first-order phase transition, which is consistent with the DLS results. The SANS profiles below 363 K were well represented by the theoretical Debye scattering function with inter-molecular interaction and the radius of gyration, R_g was estimated to be almost constant, i.e., ∼45 Å. The SANS result obtained here was compared with those in aqueous PNIPAm solutions as a typical LCST system, and some differences between IL and aqueous solution systems are pointed out. It is found that thermodynamic quantities (ΔH_demix, ΔS_demix and ΔG_demix) from the homogeneous solution to the phase separation states strongly depend on the solvation of the PBnMA polymer by the IL ([C₂mim] cation and [NTf₂] anion). We propose an LCST phase separation mechanism in the polymer-IL solution.     

A rapid method for the preparation of silica-coated ZrO2 nanoparticles by microwave irradiation

A novel synthesis of silica-coated ZrO₂ nanoparticles is reported based on microwave irradiation (MW) method. The synthesis of silica-coated ZrO₂ nanoparticles was realized by a rapid uniform hydrolysis and subsequent copolymerization of the precursor tetraethoxysilane (TEOS) on ZrO₂ surface. One of the advantages of this MW irradiation method is the very short coating time and uniform heating in comparison to the conventional ones, allowing the synthesis of uniformly coated ZrO₂ nanoparticles with silica. The XPS analysis revealed the shifts in binding energies for Zr 3d5/2 and Zr 3d3/2 peaks after coating confirming the formation of silica layer on the surface of ZrO₂ nanoparticles. Characteristic silica peaks were observed in the FTIR spectra of coated nanoparticles. The shift in the isoelectric point measured by dynamic light scattering method was indicator of silica coverage of the ZrO₂ surface. The coatings formed at 70 °C were thin and uniform and extended up to 2 nm from the ZrO₂ surface as confirmed by the HR-TEM images.     

Local structural analysis of a-SiCx:H films formed by decomposition of tetramethylsilane in microwave discharge flow of Ar

Hydrogenated amorphous silicon carbide (a-SiC_x:H) films were prepared by the decomposition of tetramethylsilane (TMS) with microwave discharge flow of Ar. When radio-frequency (RF) bias voltage (− V_RF) was applied to the substrate, the film hardness increased as (2.39 ± 1.12)-(9.15 ± 0.55) GPa for − V_RF = 0-100 V. The a-SiC_x:H films prepared under various − V_RF conditions were analyzed by the carbon-K near edge X-ray absorption fine structure (NEXAFS), by the elastic recoil detection analysis (ERDA), and by the X-ray photoelectron spectroscopy (XPS). From a quantitative analysis of NEXAFS, the sp²/(sp²+ sp³) ratios of C atoms were evaluated as 67.9 ± 2.0, 55.4 ± 2.7, and 51.7 ± 0.7% for − V_RF = 0, 60, and 100 V, respectively. From ERDA, hydrogen content of the film prepared under the condition of − V_RF = 100 V was found to decrease 28% comparing with that under − V_RF = 0 V. It is suggested that the cause of the increase of the film hardness when applying − V_RF is predominantly the growth of the sp³-hybridized structure of C atoms accompanied by the decrease of hydrogen terminations.     

Self-assembled fabrication of a polycrystalline boron-doped diamond surface supporting Pt (or Pd)/Au-shell/core nanoparticles on the (111) facets and Au nanoparticles on the (100) facets

Modified boron-doped diamond (BDD) surfaces supporting different, carefully selected types of metal nanoparticles on different types of crystal facets were fabricated via a self-assembly method. A hydrogen plasma-treated BDD surface was treated with UV/ozone for 10 s followed by immersion in a Au nanoparticle (AuNP) solution to fabricate a BDD surface selectively and densely supporting AuNPs on the (111) facet (AuNP₁₁₁-BDD). The AuNP₁₁₁-BDD sample was then immersed in H₂PtCl₆/ascorbic acid or H₂PdCl₄/sodium citrate to cover the AuNP surface with Pt or Pd (Pt/AuNP₁₁₁-BDD or Pd/AuNP₁₁₁-BDD). These samples were treated with UV/ozone for 40 s followed by re-immersion in the AuNP solution to immobilize AuNPs on the (100) facets (Pt/AuNP₁₁₁-AuNP₁₀₀-BDD or Pd/AuNP₁₁₁-AuNP₁₀₀-BDD). The metal nanoparticles supported on the BDD surface were confirmed by cyclic voltammetry to be electrochemically active. The crystal-facet-selective support of the metal nanoparticles was also confirmed by two-dimensional elemental mapping via field emission Auger electron spectroscopy. The macro procedures used for the crystal-facet-selective immobilization of the AuNPs was reproducible, and this technique should be applicable to the creation of a new class of advanced materials in such fields as optics, electronics, sensing, and (electro)catalysis.