Synthesis of the P-cluster inorganic core of nitrogenases

The [8Fe-7S] core of the P-clusters in nitrogenases is unique among the known [Fe-S] clusters which are essential to electron-transfer processes in nature. The [8Fe-7S] cluster has been thought unstable and to exist only in protein environments. We found that this unusual [8Fe-7S] structure can be self-assembled from the reaction of Fe(II) bis-amide, tetramethylthiourea, 2,4,6-triisopropylbenzenethiol, and elemental sulfur in a specific mole ratio. The structure of the complex isolated therefrom closely resembles that of the reduced form (PN) of the P-clusters, while the 6Fe(II)2Fe(III) oxidation state was manifested by the M?ssbauer study.     

Microscopically controlled oxidation of H/Si(1 0 0) by lateral surface electric field studied by emission electron microscopies

The ultrathin oxidation of a H/Si(1 0 0) surface with microfabricated pn-junctions was studied by photoemission electron microscopy (PEEM), mirror electron microscopy (MEM) and microscopic X-ray photoelectron spectroscopy (μ-XPS). The ultrathin oxidation inverts the contrast of the junctions in PEEM images. It is found by analyzing the intensity profiles of images that the potential distribution across the pn-junctions is also inverted by the oxidation. The charging of the oxide by ultraviolet irradiation from a light source of PEEM is attributed as the cause of the inversion of the contrast shown by μ-XPS and MEM.     

Influence of intramolecular vibrations in charge redistribution at the pentacene-graphite interface

We have investigated the relation between the intramolecular vibrational modes of pentacene and the charge redistribution at the pentacene-graphite interface by using high-resolution electron-energy-loss-spectroscopy. The three main vibrational peaks shift to lower energies as the pentacene film thickness decreases. In order to discuss this energy shift, we have calculated the vibrational energies of a free pentacene molecule by changing its charge state. We have also calculated the vibrational energies of a pentacene molecule adsorbed on a graphite sheet by changing the pentacene-graphite distance. Taking the experimental and calculation results into account, we conclude that the observed energy shifts result from an intramolecular charge redistribution. The present results indicate that the effect of an intramolecular charge redistribution is essential to discuss the origin of an energy shift observed in a vibrational study of an organic molecule/substrate interface.     

Tailoring D‐Amino Acid Oxidase from the Pig Kidney to R‐Stereoselective Amine Oxidase and its Use in the Deracemization of α‐Methylbenzylamine

The deracemization of racemic amines to yield enantioenriched amines using S‐stereoselective amine oxidases (AOx) has recently been attracting attention. However, R‐stereoselective AOx that are suitable for deracemization have not yet been identified. An R‐stereoselective AOx was now evolved from porcine kidney D ‐amino acid oxidase (pkDAO) and subsequently use for the deracemization of racemic amines. The engineered pkDAO, which was obtained by directed evolution, displayed a markedly changed substrate specificity towards R amines. The mutant enzyme exhibited a high preference towards the substrate α‐methylbenzylamine and was used to synthesize the S amine through deracemization. The findings of this study indicate that further investigations on the structure–activity relationship of AOx are warranted and also provide a new method for biotransformations in organic synthesis.     

A novel redox system consisting of π-conjugated polymers and transition metals

Coordination of π-conjugated polymers to transition metals constructs a novel redox system due to interchangeable various oxidation states of the polymers, which permits transition metals to interact with each other through a π-conjugate chain. The redox characteristics were found to depend on the electronic interaction with metals and the doping. A combination of copper(II) or iron(III) chloride and polyanilines afforded the complex catalysts with the higher oxidation capability for dehydrogenative oxidation. A catalytic system was also realized in the transition-metal-induced oxidation reaction, in which π-conjugated polymers serve as redox-active ligands participating in the reversible redox cycle. The Wacker oxidation of terminal olefins proceeded catalytically in the presence of a catalytic amount of polyaniline or polypyrrole derivative under oxygen.     

Novel syntheses of enantiopure hexahydroimidazo[1,5-b]isoquinolines and tetrahydroimidazo[1,5-b]isoquinolin-1(5H)-ones via iminium cation cyclizations

Condensations of chiral diamines 11a-c with benzotriazole and formaldehyde gave benzotriazolyl intermediates 12a-c; similar condensations of alpha-amino-amides 10a-c with benzotriazole and paraformaldehyde gave 14a-c. Subsequent treatment of 12a-c and 14a-c with AlCl(3) led to enantiopure tricyclic 1,2,3,5,10,10a-hexahydroimidazo[1,5-b]isoquinolines 1a-c and 2,3,10,10a-tetrahydroimidazo[1,5-b]isoquinolin-1(5H)-ones 15a-c, respectively, via Lewis acid promoted iminium cation cyclizations.     

Synthesis of syn‐2,4‐Dimercapto‐1,3,2,4‐dithiadigermetane and Its Application to Ge2PdS4 Cluster Synthesis

The sulfurization of DmpGeH₃ (Dmp=2,6‐dimesitylphenyl) afforded the trinuclear germanium sulfide [DmpGe(μ‐S)]₂(μ‐S)₂Ge(SH)‐Dmp and a series of polythiadigermabicyclo[x.1.1]alkanes (x=3, 4, 5). The reduction of the S? S bonds of these germabicycloalkanes by NaBH₄ at 0 °C afforded the dinuclear mercaptogermane syn‐[DmpGe(SH)(μ‐S)₂Ge(SH)‐Dmp] ( 5 ) in good yield. The reaction of [Pd(dppe)Cl₂] (dppe=1,2‐bis(diphenylphosphanyl)ethane) and the dilithium salt of 5 prepared in situ by the addition of nBuLi (2 equiv) gave the Ge₂PdS₄ cluster [DmpGe(μ‐S)]₂[(μ‐S)₂Pd(dppe)], in which the dithiadigermetanedithiolate is bound to the Pd atom at the two thiolato sulfur atoms. The same reaction with [Pd(PPh₃)₂Cl₂] gave another Ge₂PdS₄ cluster, [DmpGe(μ‐S)]₂[(μ‐S)₂Pd(PPh₃)], but with the dithiadigermetanedithiolate and the Pd center conjoined through a μ‐S atom between the two germanium atoms in addition to the two thiolato sulfur atoms to form a highly distorted cluster core. The formation of two different types of Ge₂PdS₄ clusters represents the usefulness of 5 in the synthesis of various polynuclear complexes composed of germanium and transition metals.     

Controllable photoinduced optical attenuation in a single-mode optical fiber by irradiation of a femtosecond pulse laser

Novel optical attenuation fibers were fabricated by the irradiation of a focused infrared femtosecond pulsed laser onto the core of a silica glass single-mode optical fiber. Optical attenuation at a wavelength of 1.55 microm proportionally increased with increasing numbers of irradiation points and was controllable under laser irradiation conditions. The single-mode property of the waveguide and the mode-field diameter of the optical fiber were maintained after irradiation of the femtosecond laser. It is suggested that the attenuation results from optical scattering at photoinduced spots formed inside the fiber core.     

Direct synthesis of 1,3-diketones by Rh-catalyzed reductive alpha-acylation of enones

1,3-Diketones were synthesized from alpha,beta-unsaturated ketones by treatment with acid chlorides and Et(2)Zn in the presence of RhCl(PPh(3))3. This is a very simple and extremely chemoselective reaction to give the adduct at the alpha-position of alpha,beta-unsaturated ketones.