Copper–Oxygen Dynamics in the Tyrosinase Mechanism

The dinuclear copper enzyme, tyrosinase, activates O₂ to form a (μ-η²:η²-peroxido)dicopper(II) species, which hydroxylates phenols to catechols. However, the exact mechanism of phenolase reaction in the catalytic site of tyrosinase is still under debate. We herein report the near atomic resolution X-ray crystal structures of the active tyrosinases with substrate l -tyrosine. At their catalytic sites, CuA moved toward l -tyrosine (CuA1 → CuA2), whose phenol oxygen directly coordinates to CuA2, involving the movement of CuB (CuB1 → CuB2). The crystal structures and spectroscopic analyses of the dioxygen-bound tyrosinases demonstrated that the peroxide ligand rotated, spontaneously weakening its O−O bond. Thus, the copper migration induced by the substrate-binding is accompanied by rearrangement of the bound peroxide species so as to provide one of the peroxide oxygen atoms with access to the phenol substrate's ϵ carbon atom.     

Effect of electropolymerization duration on the structure and performance of polypyrrole/graphene nanoplatelet counter electrode for dye-sensitized solar cells

Journal of Solid State Electrochemistry - Despite their potential for use as a low-cost energy-conversion device, dye-sensitized solar cells (DSSCs) have not been widely utilized because they apply...     

On the characteristics of two-dimensional double cellular detonations with two successive reactions model

Double cellular detonations were numerically investigated using two-dimensional Euler equations with two successive chemical reactions, whose reaction lengths differ one order of magnitude. Simulated soot track images showed the double cellular structure with two cell widths that differ one order of magnitude, as well as previous experiments and numerical simulations. We successfully divided the double cellular detonation with two successive exothermic reactions into two detonations, primary and secondary detonations, with a single exothermic reaction, based on p–v relation of Rayleigh line and Hugoniot curves with the addition of the hypothetical condition of intermediate initial state. The ratio of cell widths of primary and secondary detonations showed good agreement with that caused by the first and second reactions of double cellular detonation, and there was no interaction between two successive chemical reactions. The linear stability analysis of planar detonation and the soot rack images of double, primary and secondary detonations showed that instabilities of primary and secondary detonations are dominant to that of double cellular detonation with two successive reactions. We confirmed the validity of division of two successive reactions to clarify the detonation instability and its cellular structure.     

Efficient Nonlinear Optical Properties of Dyes Confined in Interlayer Nanospaces of Clay Minerals

Nonlinear optical (NLO) responses from organic dyes can be maximized when the dyes are aligned in appropriate manners in bulk materials. The use of restricted nanospaces provided by interlayer spacing of inorganic layered materials is a promising strategy for imposing suitable molecular alignments for NLO materials on dyes. The hybrid materials thus obtained exhibit salient NLO responses owing to the improved molecular orientation. In some cases, extension of the π‐electron system as a consequence of improved molecular planarity, obtained by the intercalation of a dye into the 2‐dimensional interlayer space of an inorganic layered material, is also observed as a factor that enhances NLO responses of chromophores at the molecular level. This review focuses on recent progress in the strategies for controlling the molecular orientation of NLO‐phores by employing clay minerals, which are one of the typical inorganic layered materials. In addition, development of a means for fabricating composites that satisfy the properties of an optical material, such as a sufficient size and thickness, a flat surface, and low light‐scattering characteristics is required to utilize the superior NLO properties observed for clay/dye hybrid materials for practical applications. A novel means for obtaining such a hybrid material is also outlined.