Characterization and activity analysis of catalytic water oxidation induced by hybridization of [(OH(2))(terpy)Mn(mu-O)(2)Mn(terpy)(OH(2))](3+) and clay compounds

Hybridization of [(OH(2))(terpy)Mn(mu-O)(2)Mn(terpy)(OH(2))](3+) (terpy= 2,2':6',2' '-terpyridine) (1) and mica clay yielded catalytic dioxygen (O(2)) evolution from water using a CeIV oxidant. The reaction was characterized by various spectroscopic measurements and a kinetic analysis of O(2) evolution. X-ray diffraction (XRD) data indicates the interlayer separation of mica changes upon intercalation of 1. The UV-vis diffuse reflectance (RD) and Mn K-edge X-ray absorption near-edge structure (XANES) data suggest that the oxidation state of the di-mu-oxo Mn(2) core is Mn(III)-Mn(IV), but it is not intact. In aqueous solution, the reaction of 1 with a large excess Ce(IV) oxidant led to decomposition of 1 to form MnO(4-) ion without O(2) evolution, most possibly by its disproportionation. However, MnO(4-) formation is suppressed by adsorption of 1 on clay. The maximum turnover number for O(2) evolution catalyzed by 1 adsorbed on mica and kaolin was 15 and 17, respectively, under the optimum conditions. The catalysis occurs in the interlayer space of mica or on the surface of kaolin, whereas MnO(4-) formation occurs in the liquid phase, involving local adsorption equilibria of adsorbed 1 at the interface between the clay surface and the liquid phase. The analysis of O(2) evolution activity showed that the catalysis requires cooperation of two equivalents of 1 adsorbed on clay. The second-order rate constant based on the concentration (mol g(-1)) of 1 per unit weight of clay was 2.7 +/- 0.1 mol(-1) s(-1) g for mica, which is appreciably lower than that for kaolin (23.9 +/- 0.4 mol(-1) s(-1) g). This difference can be explained by the localized adsorption of 1 on the surface for kaolin. However, the apparent turnover frequency ((kO(2))app/s(-1)) of 1 on mica was 2.2 times greater than on kaolin when the same fractional loading is compared. The higher cation exchange capacity (CEC) of mica statistically affords a shorter distance between the anionic sites to which 1 is attracted electrostatically, making the cooperative interaction between adsorbed molecules of 1 easier than that on kaolin. The higher CEC is important not only for attaining a higher loading but also for the higher catalytic activity of adsorbed 1.     

Cloning of a New Xylanase Gene from <Emphasis Type="Italic">Streptomyces</Emphasis> sp. TN119 Using a Modified Thermal Asymmetric Interlaced-PCR Specific for GC-Rich Genes and Biochemical Characterization

A bacterial strain, Streptomyces sp. TN119, was isolated from the gut of Batocera horsfieldi larvae and showed xylanolytic activity. A degenerate primer set was designed based on the base usage of G and C in Actinobacteria xylanase-coding sequences belonging to the glycosyl hydrolases family 10 (GH 10), and used to clone the partial xylanase gene from Streptomyces sp. TN119. A modified thermal asymmetric interlaced (TAIL)-PCR specific for high-GC genes, named GC TAIL-PCR, was developed to obtain the full-length xylanase gene (xynA119; 1089 bp). Rich in GC content (67.8%), xynA119 encodes a new GH 10 xylanase (XynA119), which shares highest identity (48.8%) with an endo-1,4-β-xylanase from Cellulosimicrobium sp. HY-12. Recombinant XynA119 was expressed in Escherichia coli BL21 (DE3) and purified to electrophoretic homogeneity. The enzyme showed maximal activity at pH 6.5 and 60 °C, was stable at pH 4.0 to 10.0 and 50 °C, was resistant to most chemicals (except for Cu²⁺, Mn²⁺, Ag⁺, Hg²⁺ and SDS) and trypsin, and produced simple products. The specific activity, K _m, V _max, and k _cat using oat-spelt xylan as substrate were 57.9 U mg⁻¹, 1.0 mg ml⁻¹, 74.8 μmol min⁻¹ mg⁻¹, and 49.2 s^–1, respectively.     

Synthesis, characterization, and detailed electrochemistry of binuclear ruthenium(III) complexes bridged by bisacetylacetonate. Crystal and molecular structures of [[Ru(acac)2]2(tae)] (acac = 2,4-pentanedionate ion, tae = 1,1,2,2-tetraacetylethanate dianion)

Binuclear beta-diketonatoruthenium(III) complexes [[Ru(acac)(2)](2)(tae)], [[Ru(phpa)(2)](2)(tae)], and [(acac)(2)Ru(tae)Ru(phpa)(2)] and binuclear and mononuclear bipyridine complexes [[Ru(bpy)(2)](2)(tae)](PF(6))(2) and [Ru(bpy)(2)(Htae)]PF(6) (acac = 2,4-pentanedionate ion, phpa = 2,2,6,6-tetramethyl-3,5-heptanedionate ion, tae = 1,1,2,2-tetraacetylethanate dianion, and bpy = 2,2'-bipyridine) were synthesized. The new complexes have been characterized by (1)H NMR, MS, and electronic spectral data. Crystal and molecular structures of [[Ru(acac)(2)](2)(tae)] have been solved by single-crystal X-ray diffraction studies. Crystal data for the meso isomer of [[Ru(acac)(2)](2)(tae)] have been confirmed by the dihedral angle result that two acetylacetone units of the bridging tae ligand are almost perpendicular to one another. A detailed investigation on the electrochemistry of the binuclear complexes has been carried out. The electrochemical behavior details of the binuclear complexes have been compared with those of the mononuclear complexes obtained from the half-structures of the corresponding binuclear complexes. Studies on the effects of solvents on the mixed-valence states of Ru(II)-Ru(III) and Ru(III)-Ru(IV) complexes have been carried out by various voltammetric and electrospectroscopic techniques. A correlation between the comproportionation constant (K(c)) and the donor number of the solvent has been obtained. The K(c) values for the binuclear complexes have been found to be low because of the fact that two acetylacetone units of the bridging tae ligand are not in the same plane, as revealed by the crystal structure of [[Ru(acac)(2)](2)(tae)].     

Analysis of the conserved P9-G10.1 metal-binding motif in hammerhead ribozymes with an extra nucleotide inserted between A9 and G10.1 residues

Hammerhead ribozymes (Rz) have catalytically important tandem G:A pairs in the core region, and we recently demonstrated that the P9-G10.1 motif (a sheared-type G:A pair with a guanine residue on the 3' side of the adenine residue) with several flanking base pairs is sufficient for capture of divalent cations, such as Mg(2+) and Cd(2+) ions that are important to maintain full activities (Tanaka et al. J. Am. Chem. Soc. 2002, 124, 4595-4601; Tanaka et al. J. Am. Chem. Soc. 2004, 126, 744-752). We also found that mutant hammerhead ribozymes that have an additional G residue inserted between A9 and G10.1 residues (the metal-binding P9-G10.1 motif) have significant catalytic activities. In this study, we demonstrate that the hammerhead ribozymes are capable of maintaining the catalytically competent structure even when the tandem, sheared-type G:A pairs were perturbed by an insertion of an additional nucleotide, whereas the chirality of the phosphorothioate at the P9 position significantly influenced the enzymatic activity for both the natural and G-inserted ribozymes.     

Carbon‐bridged Oligo(phenylenevinylene)s as Light‐harvesting Antenna for Porphyrins

The efficacy of carbon‐bridged oligo(phenylenevinylenes)s (COPVs) as light‐harvesting antenna for porphyrins is demonstrated using a series of 5,15‐di‐COPVn‐substituted free‐base and zinc porphyrins, COPVn‐MP‐COPVn (n=1–3, M=H₂, Zn). These molecules were synthesized by Suzuki–Miyaura cross‐coupling reactions of COPVn‐Bpin and Br‐H₂P‐Br . The absorption spectra of these compounds in solution show a significant expansion of the Soret band region together with a bathochromic shift of the Q band, suggesting a significant interaction between these chromophores in the ground state. The photoluminescence quantum yield of the porphyrin‐COPV conjugates is enhanced up to four times relative to the parent porphyrins. Theoretical calculations also indicated interactions between these chromophores in the HOMO, which suggests that the light‐harvesting ability stems from the expansion of the π‐electron‐conjugation system.     

Relationships between Raman parameters obtained from cyclic indentation impressions on DLC coatings

Diamond-like carbon (DLC) coatings were indented 3000 to 15 000 times cyclically using a Si₃N₄ sphere having a diameter of 10 mm under a normal load of approximately 107 N. DLC coatings were prepared by unbalanced magnetron (UBM) sputtering under substrate bias voltage of −200 on a heat-treated and polished JIS SCM 415 substrates. SEM images and the energy dispersive X-ray spectrometry (EDX) results of the indented impressions showed that a Cr/C layer or substrate surface partially revealed on the impressions. In order to estimate structural alterations in DLC coatings after cyclic indentations, Raman spectroscopy were performed on the impressions. Relationships between Raman parameters such as the intensity ratio I(D)/I(G) of the disorder peak around 1350 cm⁻¹ and the graphitic peak around 1580 cm⁻¹ and full width of half maximum of the G peak (FWHM(G)) were estimated with the Raman spectroscopy on the impressions. Enclosed area by maximum and minimum of I(D)/I(G) and FWHM(G) was defined as “Safety Zone” in this paper, and it can be used to determine integrity of DLC coatings.     

Thermally Stabilized Blue Luminescent Poly(p‐phenylene)s Covered with Polyhedral Oligomeric Silsesquioxanes

A novel series of poly(p‐phenylene)s (PPPs) with polyhedral oligomeric silsesquioxanes (POSSs) on their side chains was prepared. The obtained POSS‐modified PPPs are as follows: 25POSS‐PPP ( 2b , containing 25 mol‐% of POSS units in all side chains), 50POSS‐PPP ( 2c , containing 50 mol‐% of POSS units in all side chains), 100POSS‐PPP ( 2d , containing 100 mol‐% of POSS units in all side chains), and 0POSS‐PPP ( 2a , as a blank polymer). Films polymer 2d showed the same absorption and photoluminescence (PL) spectra as those in CHCl₃ solution, indicating that bulky POSS units strongly suppressed intermolecular aggregation of the PPP backbone. Polymer 2d showed the same PL spectra even after thermal annealing at 150 °C for 6 h. This enhancement of PL stability is due to the significant effect of the bulky POSS units.

     

Simulation of solid–fluid mixture flow using moving particle methods

A new basic framework for solid–fluid mixture flow simulation was developed using moving particle methods. The interactions between solid and fluid were modeled by the finite volume particle (FVP) method. The distinct element method (DEM) together with a multi-time-step algorithm was introduced into the FVP method to calculate the effects of contact between solid bodies and between solid bodies and walls. The introduced DEM model was verified by experimental analyses for the collapse of multiple solid cylinder layers. The proposed algorithm using the optimized DEM model was then applied to a water dam breaking, involving multiple solid cylinder layers. A comparison between experiments and simulations demonstrated the DEM model introduced into the FVP method is effective in representing solid–fluid mixture flows reasonably well.