Monohydride-Dichloro Rhodium(III) Complexes with Chiral Diphosphine Ligands as Catalysts for Asymmetric Hydrogenation of Olefinic Substrates

We report full details of the synthesis and characterization of monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands, such as (S)-BINAP, (S)-DM-SEGPHOS, and (S)-DTBM-SEGPHOS, producing cationic triply chloride bridged dinuclear rhodium(III) complexes ( 1 a : (S)-BINAP; 1 b : (S)-DM-SEGPHOS) and a neutral mononuclear monohydride-dichloro rhodium(III) complex ( 1 c : (S)-DTBM-SEGPHOS) in high yield and high purity. Their solid state structure and solution behavior were determined by crystallographic studies as well as full spectral data, including DOSY NMR spectroscopy. Among these three complexes, 1 c has a rigid pocket surrounded by two chloride atoms bound to the rhodium atom together with one tBu group of (S)-DTBM-SEGPHOS for fitting to simple olefins without any coordinating functional groups. Complex 1 c exhibited superior catalytic activity and enantioselectivity for asymmetric hydrogenation of exo-olefins and olefinic substrates. The catalytic activity of 1 c was compared with that of well-demonstrated dihydride species derived in situ from rhodium(I) precursors such as [Rh(cod)Cl]₂ and [Rh(cod)₂]⁺[BF₄]⁻ upon mixing with (S)-DTBM-SEGPHOS under dihydrogen.     

Conformational change of H+-ATPase beta monomer revealed on segmental isotope labeling NMR spectroscopy

F1-ATPase has been shown to be a stepwise molecular motor. Its rotation mechanism has been explained by the interaction of the gamma axis with the open and closed forms of the beta subunit. Although NMR should be a powerful method for elucidating its mechanism, its molecular size (473 amino acid residues, 52 kDa) is a major obstacle. We have applied segmental labeling based on intein ligation to the beta subunit, and succeeded in assigning 89% of the NH (402/451), 89% of the Calpha (417/473), 83% of the Cbeta (357/431), and 90% of the CO (425/473) signals of the beta subunit monomer. The secondary structures predicted from the chemical shifts of the main chain atoms and the relative orientations determined from residual dipolar couplings indicated that the subunit beta monomer takes on the open form in the absence of nucleotide. Furthermore, the chemical shift perturbation and the residual-dipolar-coupling changes induced by nucleotide binding show that conformational change from the open to the closed form takes place on nucleotide binding. The intrinsic conformational change of the beta subunit monomer induced by nucleotide binding must be one of the essential driving forces for the rotation of F1-ATPase.     

Integrable discrete time chains for the Frobenius-Stickelberger-Thiele polynomials

The notion of Frobenius-Stickelberger-Thiele (FST) polynomials is introduced. Spectral transformations for these polynomials analogous to the Christoffel and Geronimus transformations for orthogonal polynomials are constructed. They yield an integrable discrete time chain (the FST chain) related to the generalized -algorithm. Relations of the FST polynomials to the Padé interpolation problem and to general and symmetric biorthogonal rational functions are considered in detail. This work is supported in part by the Russian Foundation for Basic Research (RFBR) grant no. 06-01-00191 and the Grant-in-Aid for Scientific Research no. 15540119 from the Ministry of Education, Culture, Sports, Science and Technology, Japan.     

Green Nanocomposites from Renewable Resources: Biodegradable Plant Oil‐Silica Hybrid Coatings

Green nanocomposite coatings based on renewable plant oils have been developed. An acid‐catalyzed curing of epoxidized plant oils with 3‐glycidoxypropyltrimethoxysilane produced transparent nanocomposites. The hardness and mechanical strength improved by incorporating the silica network into the organic polymer matrix, and good flexibility was observed in the nanocomposite. The nanocomposites showed high biodegradability.

     

Crystal structural, magnetic, and transport properties of layered cobalt oxyfluorides, Sr2CoO(3+x)F(1-x) (0 ≤ x ≤ 0.15)

The crystal structure of the layered cobalt oxyfluoride Sr(2)CoO(3)F synthesized under high-pressure and high-temperature conditions has been determined from neutron powder diffraction and synchrotron powder diffraction data collected at temperatures ranging from 320 to 3 K. This material adopts the tetragonal space group I4/mmm over the measured temperature range and the crystal structure is analogous to n = 1 Ruddlesden-Popper type layered perovskite. In contrast to related oxyhalide compounds, the present material exhibits the unique coordination environment around the Co metal center: coexistence of square pyramidal coordination around Co and anion disorder between O and F at the apical sites. Magnetic susceptibility and electrical resistivity measurements reveal that Sr(2)CoO(3)F is an antiferromagnetic insulator with the Néel temperature T(N) = 323(2) K. The magnetic structure that has been determined by neutron diffraction adopts a G-type antiferromagnetic order with the propagation vector k = (1/2 1/2 0) with an ordered cobalt moment μ = 3.18(5) μ(B) at 3 K, consistent with the high spin electron configuration for the Co(3+) ions. The antiferromagnetic and electrically insulating states remain robust even against 15%-O substation for F at the apical sites. However, applying pressure exhibits the onset of the metallic state, probably coming from change in the electronic state of square-pyramidal coordinated cobalt.     

Broadly tunable subterahertz emission from internal branches of the current-voltage characteristics of superconducting Bi2Sr2CaCu2O(8+δ) single crystals

Continuous, coherent subterahertz radiation arises when a dc voltage is applied across a stack of the many intrinsic Josephson junctions in a Bi2Sr2CaCu2O(8+δ) single crystal. The active junctions produce an equal number of I-V characteristic branches. Each branch radiates at a slightly tunable frequency obeying the Josephson relation. The overall output is broadly tunable and nearly independent of heating effects and internal cavity frequencies. Amplification by a surrounding external cavity to allow for the development of a useful high-power source is proposed.     

Fabrication of mesoporous polymer monolith: a template-free approach

Mesoporous polyacrylonitrile (PAN) monolith has been fabricated by a template-free approach using the unique affinity of PAN towards a water/dimethyl sulfoxide (DMSO) mixture. A newly developed Thermally Induced Phase Separation Technique (TIPS) has been used to obtain the polymer monoliths and their microstructures have been controlled by optimizing the concentration and cooling temperature.     

Synthesis of high-performance green nanocomposites from renewable natural oils

This paper describes preparation and properties of green nanocomposites from renewable resources. The nanocomposites were synthesized by an acid-catalyzed curing of epoxidized natural oils in the presence of silane coupling agents. The resulting nanocomposites were transparent and highly glossy. Their hardness and Young's modulus of the nanocomposite coatings improved, as compared with those only from the epoxidized natural oils. Dynamic viscoelasticity analysis and TEM observation showed the homogeneous structure of the nanocomposites. The properties of the nanocomposites were strongly affected by the structure and feed ratio of the monomers.     

Thermogelation of amphiphilic poly(asparagine) derivatives

Thermoresponsive sol–gel transition polymers based on biodegradable poly(amino acid) were synthesized by the reaction of poly(succinimide) with dodecylamine and amino alcohols. The introduction of the hydrophobic amine into the thermoresponsive poly(amino acid)s induced the sol–gel transition in phosphate buffer saline. The effects of the side chain structure, molecular weight, concentration of the polymer, and the additives (inorganic salts and urea) in the solution on the thermoresponsive behaviors were systematically investigated. A relationship between the lowest critical solution temperature (LCST) in the dilute solution and the viscosity reduction of the concentrated solution upon heating was observed. The present poly(amino acid)s showing a thermoresponsive sol–gel transition in aqueous solutions possess immense potential as an injectable biodegradable hydrogel system for various biomedical applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Electron transfer cascade by organic/inorganic ternary composites of porphyrin, zinc oxide nanoparticles, and reduced graphene oxide on a tin oxide electrode that exhibits efficient photocurrent generation

A bottom-up strategy has been developed to construct a multiple electron transfer system composed of organic/inorganic ternary composites (porphyrin, zinc oxide nanoparticles, reduced graphene oxide) on a semiconducting electrode without impairing the respective donor-acceptor components. The hierarchical electron transfer cascade system exhibited remarkably high photocurrent generation with an incident-photon-to-current efficiency of up to ca. 70%.