Reactions of 2-Pyridyl Substituted Phosphine Oxides and Phosphonium Salts with Organometallic Reagents and in Aqueous Media

Phosphine oxides bearing two or three 2-pyridyl groups react with organometallic reagents affording 2,2′-bipyridyl, 2-substituted pyridines and pyridine in good yields. Phosphonium salts and phosphine oxides, bearing at least two 2-pyridyl or substituted 2-pyridyl groups also give the corresponding 2,2′-bipyridyls and pyridines upon treatment with acid or neutral solvents such as water and alcohols in substantial yields. The 2,2′-bipyridyls are considered to be formed by ligand coupling within the pentacoordinated phosphorus intermediate formed incipiently during the reaction.     

Quantum mechanical Monte Carlo approach to electron transport at heterointerface

With the progress of LSI technology, the electronic device size is scaled down to the sub 0.1μ m region. In such an ultrasmall device, it is indispensable to take quantum mechanical effects into account in device modeling. In this paper, we present a newly developed quantum Monte Carlo device simulation applicable to ultrasmall semiconductor devices. In this model, the quantum effects are represented in terms of quantum mechanically corrected potential in the classical Boltzmann equation. It is demonstrated that the quantum transport effects such as tunneling and energy quantization in ultrasmall semiconductor devices are obtained for the first time by using the standard Monte Carlo techniques.     

Biosynthesis of Indole Diterpene Lolitrems: Radical-Induced Cyclization of an Epoxyalcohol Affording a Characteristic Lolitremane Skeleton

Lolitrems are tremorgenic indole diterpenes that exhibit a unique 5/6 bicyclic system of the indole moiety. Although genetic analysis has indicated that the prenyltransferase LtmE and the cytochrome P450 LtmJ are involved in the construction of this unique structure, the detailed mechanism remains to be elucidated. Herein, we report the reconstitution of the biosynthetic pathway for lolitrems employing a recently established genome-editing technique for the expression host Aspergillus oryzae. Heterologous expression and bioconversion of the various intermediates revealed that LtmJ catalyzes multistep oxidation to furnish the lolitrem core. We also isolated the key reaction intermediate with an epoxyalcohol moiety. This observation allowed us to establish the mechanism of radical-induced cyclization, which was firmly supported by density functional theory calculations and a model experiment with a synthetic analogue.     

Chiral bicyclic imidazolium salts as a new class of N-heterocyclic carbene precursors

A N(1)-C(5) bridged chiral bicyclic imidazole with a morpholine framework was synthesized from an enantiopure 2-amino alcohol. The resultant imidazole reacted with various electrophiles, including primary and secondary alkyl halides, benzyne, and an electron-deficient aryl halide, to give the corresponding imidazolium salts. Some of the imidazolium salts were found to have potential as the precursor of a chiral N-heterocyclic carbene catalyst; by the direct annulation of an enal and a ketone through the intermediacy of a homoenolate and an activated carboxylate, the target lactone was obtained in an enantiomerically enriched form (up to 66% ee).     

Computation of the reduction free energy of coenzyme in aqueous solution by the QM/MM-ER method

In a recent development we proposed a quantum chemical approach to compute free energy change for chemical reactions in condensed phases by combining the QM/MM method with the theory of energy representation (QM/MM-ER). We extend in this Letter the novel approach to compute reduction free energy of isoalloxazine ring of FAD (flavin adenine dinucleotide) immersed in water within the framework of the QM/MM-ER method. The characteristic feature of our approach is that the excess electron to be attached on the FAD is identified as a solute. The reduction free energy has been obtained as −80.1 kcal/mol in the aqueous solution.     

Mechanical and tribological properties of DLC coatings deposited by plasma-based ion implantation and deposition method on polyoxymethylene

Polyoxymethylene (POM, polyacetal) is one of the most popular plastics for machine elements, especially in Japan. However, it is difficult to use it under severe operating conditions such as high speed and high contact pressure. Diamond-like carbon (DLC) coatings were well known to be tribological and functional coatings. However, both POM and DLC coatings are difficult to adhere them each other. In the present paper, DLC coatings are deposited by plasma-based ion implantation and deposition (PBIID) method on POM substrate, and validity of DLC coatings on POM was investigated through friction and mechanical tests. When gas pressure was 0.2 and 0.8 Pa, hardness and adhesion properties of DLC coating deposited under gas pressure of 0.5 Pa were lower compared with under 0.2 and 0.8 Pa. For preparing DLC coatings having hard and good adhesion properties, relatively thin substrate was suitable. A correlation between relative humidity in the laboratory and friction coefficient was confirmed while DLC coatings remain on the substrate.     

Synthesis of polymers by use of divalent metal salts of monohydroxyethyl phthalate: Metal-containing isocyanurate-type crosslinked polyurethanes

Divalent metal salts (I) of monohydroxyethyl phthalate have catalytic activity for polymerization of isocyanate groups. The synthesis of novel metal-containing isocyanurate-type crosslinked polyurethanes were investigated by the crosslinking reaction of I in DMF with diisocyanates or urethane prepolymers, that is, diisocyanate adducts of polyethylene glycol. 2,4-Toluene diisocyanate and diphenylmethane diisocyanate were used as diisocyanates, and DMF was the solvent. The crosslinking reactions were followed by determining the gelation time. Gelation time decreased with increasing temperature. The Ca salt was more effective than the Mg salt in the crosslinking reaction. The yields of resulting metal-containing three-dimensional polymers decreased with increasing metal content in the feed. The Ca salt was more easily introduced into the network polymers than the Mg salt was. Decomposition temperatures decreased on introducing metals into the network polymers. Some physical properties of the metal-containing network polymers are also discussed.     

Ishigadine A,a new canthin-6-one alkaloid from an Okinawan marine sponge Hyrtios sp.

A new indole alkaloid with the canthin-6-one skeleton, ishigadine A, has been isolated from an Okinawan marine sponge Hyrtios sp. The structure of ishigadine A was elucidated on the basis of spectroscopic analyses. Ishigadine A is a new canthin-6-one alkaloid possessing a hydroxy group, a 1,3-dimethyl-4-methylthioimidazolium, and a 1-propylguanidine. Ishigadine A is the third canthin-6-one alkaloid from sponges. Ishigadine A might be generated from l-arginine, l-histidine, and l-tryptophan. Ishigadine A exhibited moderate cytotoxicity against L1210 murine leukemia cells.