Stereochemical recognition of doubly functional aminotransferase in 2-deoxystreptamine biosynthesis

The doubly functional aminotransferase BtrS in the 2-deoxystreptamine (DOS) biosynthesis, in which two transaminations are involved, was characterized by a genetic as well as a chemical approach with the heterologously expressed enzyme. The gene disruption study clearly showed that BtrS is involved, in addition to the previously confirmed first transamination, in the second transamination as well. This dual function of BtrS for the DOS biosynthesis was further confirmed by the structural determination of the reverse reaction product from DOS. Enantiospecific formation of the reverse reaction product from DOS clearly showed that BtrS distinguishes the enantiotopic amino groups of DOS, but in contrast, both enantiomers of 2-deoxy-scyllo-inosose (DOI) were efficiently accepted by BtrS to give a racemic product. This unique stereochemical recognition of DOI chirality and DOS prochirality by BtrS is mechanistically explained by a specific hydrogen-bond donating force in the enzyme active site as a particular feature of this doubly functional enzyme.     

Metallic Ni nanoparticles confined in hexagonally ordered mesoporous silica material

Single nanometer-sized metallic Ni particles have been successfully deposited inside a hexagonally ordered mesoporous silica material by using a liquid-phase reductive deposition method.     

Tribochemical reaction dynamics of phosphoric ester lubricant additive by using a hybrid tight-binding quantum chemical molecular dynamics method

To study the atomistic behavior of the phosphoric ester molecule on the nascent Fe surface under boundary lubrication conditions, we adopted a hybrid tight-binding quantum chemical molecular dynamics method. First, we investigated chemical interactions between phosphoric ester and the nascent Fe surface. Phosphoric ester was shown to interact with the nascent Fe surface, forming both covalent and ionic bonds. Formation and dissociation dynamics of covalent bonds during tribochemical reaction was clearly observed during the simulation. The effect of friction condition on the tribochemical reaction dynamics was then studied, and it was indicated that friction would influence the formation and the dissociation of covalent bonds. By using a hybrid tight-binding quantum chemical molecular dynamics method, we obtained insights on initial tribochemical reaction processes for the formation of tribofilm from the phosphoric ester molecule on the nascent Fe surface.     

Neural stem cells and strategies for the regeneration of the central nervous system

The adult mammalian central nervous system (CNS), especially that of adult humans, is a representative example of organs that do not regenerate. However, increasing interest has focused on the development of innovative therapeutic methods that aim to regenerate damaged CNS tissue by taking advantage of recent advances in stem cell and neuroscience research. In fact, the recapitulation of normal neural development has become a vital strategy for CNS regeneration. Normal CNS development is initiated by the induction of stem cells in the CNS, i.e., neural stem cells (NSCs). Thus, the introduction or mobilization of NSCs could be expected to lead to CNS regeneration by recapitulating normal CNS development, in terms of the activation of the endogenous regenerative capacity and cell transplantation therapy. Here, the recent progress in basic stem cell biology, including the author’s own studies, on the prospective identification of NSCs, the elucidation of the mechanisms of ontogenic changes in the differentiation potential of NSCs, the induction of neural fate and NSCs from pluripotent stem cells, and their therapeutic applications are summarized. These lines of research will, hopefully, contribute to a basic understanding of the nature of NSCs, which should in turn lead to feasible strategies for the development of ideal “stem cell therapies” for the treatment of damaged brain and spinal cord tissue.     

Design of New Reaction Fields for Spherical Polypyrrole Particle Synthesis

Summary: Polypyrrole conducting polymers have been investigated widely for various applications because of their thermal and environmental stability and good electrical conductivity. Using chemical oxidative polymerization for the synthesis of polypyrrole particles, the reaction rate is very fast. In this study, we designed two new reaction fields for the synthesis of spherical polypyrrole nanoparticles. In the first system, oxidative polymerization of monomer droplets infused in a water/oil (W/O) emulsion reaction field was investigated. The second system employed dispersed monomer in an aqueous solution with a low concentration of oxidant in which polymerization was augmented by ultrasonic irradiation. Effective control of the reaction rate was important for enabling the synthesis of fine spherical polypyrrole particles.     

Growth and characterization of GaSb/AlGaSb multi-quantum well structures on Si (0 0 1) substrates

GaSb/AlGaSb multi-quantum well (MQW) structures with an AlSb initiation layer and a relatively thick GaSb buffer layer grown on Si (0 0 1) substrates were prepared by molecular beam epitaxy (MBE). Transmission electron microscopy (TEM) images and high-resolution X-ray diffraction (XRD) patterns indicated definite MQW structures. The photoluminescence (PL) emission around 1.55 μm wavelength was observed for 10.34 nm GaSb/30 nm Al_0.6Ga_0.4Sb MQW structure at room temperature. Dependence of PL emission energy on GaSb well width was well explained by finite square well potential model.     

Towards single biomolecule handling and characterization by MEMS

Applications of microelectromechanical systems (MEMS) technology are widespread in both industrial and research fields providing miniaturized smart tools. In this review, we focus on MEMS applications aiming at manipulations and characterization of biomaterials at the single molecule level. Four topics are discussed in detail to show the advantages and impact of MEMS tools for biomolecular manipulations. They include the microthermodevice for rapid temperature alternation in real-time microscopic observation, a microchannel with microelectrodes for isolating and immobilizing a DNA molecule, and microtweezers to manipulate a bundle of DNA molecules directly for analyzing its conductivity. The feasibilities of each device have been shown by conducting specific biological experiments. Therefore, the development of MEMS devices for single molecule analysis holds promise to overcome the disadvantages of the conventional technique for biological experiments and acts as a powerful strategy in molecular biology. Figure Towards single bio molecular handling and characterization by MEMS     

Total synthesis of mycestericin A

The first total synthesis of mycestericin A (1) starting from tartrates is described. The Overman rearrangement of an allylic trichloroacetimidate generated a tetra-substituted carbon with nitrogen, and subsequent stereoselective transformations afforded the highly functionalized vinyl iodide. The cross-coupling of the vinyl iodide with a chiral organozinc species under Negishi conditions, followed by deprotection, completed the total synthesis of 1.