From penicillin to penem and carbapenem. VI1) : Synthesis of dethiathienamycin

A new C₃-unit substitution reaction at C-4 position of 4- acetoxyazetidinone derivative ($\text{1}$ and $\text{5}$) by tetraallyltin ($\text{2}$) in the presence of 1/10 eq. of BF₃-ether in methylene chloride is described. From 4-allylazetidinone derivative ($\text{3}$) via ylid intermediate ($\text{14}$) dethiathienamycin ($\text{16}$) was synthesized.     

W(CO)5(L)-catalyzed formal cope rearrangement of allenyl silyl enol ethers

[reaction: see text] On treatment of 5-siloxyhexa-1,2,5-trienes with a catalytic amount of W(CO)(6) under photoirradiation, formal Cope rearrangement proceeded to give 2-siloxyhex-1-en-5-ynes in good yield. The electrophilic activation of the allenyl moiety by W(CO)(5) triggers the intramolecular attack of the silyl enol ether in a 6-endo manner to produce a cyclohexenyl tungsten species. Carbon-carbon bond cleavage occurs by electron donation from the anionic W(CO)(5) into the silyloxonium moiety to afford the products with regeneration of the W(CO)(5)(L).     

A study of the alumina-silica gel adsorbent for the removal of silicic acid from geothermal water: increase in adsorption capacity of the adsorbent due to formation of amorphous aluminosilicate by adsorption of silicic acid

Two kinds of adsorbents (Si adsorbent and Al adsorbent) for the removal of silicic acid from geothermal water to retard the formation of silica scales were prepared using silicic acid contained in geothermal water. The Si adsorbent was prepared by evaporating geothermal water, and the Al adsorbent was prepared by evaporating geothermal water after the addition of aluminum chloride. The specific surface area of the Si adsorbent was small and it's adsorption capacity of silicic acid was low. Although the specific surface area of the Al adsorbent was also small, it was significantly increased by the adsorption of silicic acid and it's adsorption capacity was high. Based on the change in the local structure of aluminum ion by the adsorption of silicic acid, the Al adsorbent was considered to be silica particles covered with crystalline aluminum hydroxide. Moreover, it was concluded that the increase in the specific surface area of the Al adsorbent and the decrease in the zeta potential were due to the formation of an amorphous aluminosilicate with a large surface area and a negative charge (one 4-coordinated Al) by the reaction between aluminum ions and silicic acids.     

Stereospecific polymerization of isobutyl vinyl ether. III. Polymerization with VCl3 • LiCl

The polymerization of isobutyl vinyl ether by vanadium trichloride in n-heptane was studied. VCl₃ ? LiCl was prepared by the reduction of VCl₄ with stoichiometric amounts of BuLi. This type of catalyst induces stereospecific polymerization of isobutyl vinyl ether without the action of trialkyl aluminum to an isotactic polymer when a rise in temperature during the polymerization was depressed by cooling. It is suggested that the cause of the stereospecific polymerization might be due to the catalyst structure in which LiCl coexists with VCl₃, namely, VCl₃ ? LiCl or VCl₂ ? 2LiCl as a solid solution in the crystalline lattice, since VCl₃ prepared by thermal decomposition of VCl₄ and a commercial VCl₃ did not produce the crystalline polymer and soluble catalysts such as VCl₄ in heptane and VCl₃ ? LiCl in ether solution did not yield the stereospecific polymer. It was found that some additives, such as tetrahydrofuran or ethylene glycol diphenyl ether, to the catalyst increased the stereospecific polymerization activity of the catalysts. Influence of the polymerization conditions such as temperature, time, monomer and catalyst concentrations, and the kind of solvent on the formed polymer was also examined.     

Theoretical study of molecular conduction: I. Effective Green's function based on perturbation theory

There have been many experimental and theoretical studies on molecular conduction, as it is a fundamental parameter in the study of molecular‐scale electronics. We have investigated the features of molecular conduction using a Green's function method, which has often been used to solve problems in quantum transport and is also effective in elucidating electron transport in molecules. We have obtained the novel effective Green's functions, including the first‐order energy corrections, by accommodating the self‐energy of the electrodes as perturbation terms. Although these approximate Green's functions only provide information on the first‐order energy corrections, they can involve the elementary properties of molecular conduction. We propose a scheme for the analysis of the relations between molecular orbitals and their roles in molecular conduction and present analytical calculations for normal and cyclic polyenes. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Development of a cooled He*(23S) beam source for measurements of state-resolved collision energy dependence of Penning ionization cross sections: Evidence for a stereospecific attractive well around methyl group in CH3CN

A low-temperature discharge nozzle source with a liquid-N(2) circulator for He*(2(3)S) metastable atoms has been developed in order to obtain the state-resolved collision energy dependence of Penning ionization cross sections in a low collision energy range from 20 to 80 meV. By controlling the discharge condition, we have made it possible to measure the collision energy dependence of partial ionization cross sections (CEDPICS) for a well-studied system of CH(3)CN+He*(2(3)S) in a wide energy range from 20 to 350 meV. The anisotropic interaction potential energy surface for the present system was obtained starting from an ab initio model potential via an optimization procedure based on classical trajectory calculations for the observed CEDPICS. A dominant attractive well depth was found to be 423 meV (ca. 10 kcal/mol) at a distance of 3.20 A from the center of mass of CH(3)CN in the N-atom side along the CCN axis. In addition, a weak attractive well (ca. 0.9 kcal/mol) surrounding the methyl group (-CH(3)) has been found and ascribed to the interaction between an unoccupied molecular orbital of CH(3)CN and 2s atomic orbital of He*(2(3)S).     

Control of separation selectivity in micellar electrokinetic chromatography by modification of the micellar phase with solubilized organic compounds

On the basis of the data on the distribution of various neutral solutes between sodium dodecyl sulfate (SDS) micelles and water, the control of separation selectivity in micellar electrokinetic chromatography (MEKC) by modification of the micellar phase with organic additives has been proposed and applied to the separation of simple model compounds. It was found that the distribution constants between the micelles and water (K_d,mc), which were determined by means of MEKC, of the solutes possessing hydrophilic functional groups are much larger than those between heptane and water (K_d,hep), whereas the K_d,mc values of the solutes possessing no hydropholic groups are comparable to their K_d,hep values. This indicates that the former solutes are preferentially solubilized in the Stern layer of the micelles and that the latter are located in the hydrocarbon core. In MEKC separations of aromatic compounds and metal acetylacetonates, considerable changes in separation selectivity were caused by the addition of compounds possessing both hydrophilic functional groups such as alcohols, phenol and ketones to the SDS micellar solution. The variations of the retention factors of the analytes could be explained in terms of saturation of the solubilization sites in the Stern layer with the modifiers, specific interaction of the modifiers with the analytes via hydrogen bonding in the micelles, and expansion of the core volume with the hydrocarbon parts of the modifiers. Such effects of the micellar modification could improve the resolution as well as the selectivity of MEKC separations.     

Metal-complex assemblies constructed from the flexible hinge-like ligand H2bhnq: structural versatility and dynamic behavior in the solid state

Novel metal-complex assemblies constructed from the flexible hinge-like ligand H(2)bhnq (H(2)bhnq=2,2'-bi(3-hydroxy-1,4-naphthoquinone)) have been synthesized. The X-ray crystal structures of these compounds reveal that four types of architectures are accessible by variation of the metal ions. In copper(II) compounds 1-3, the chelating bhnq(2-) ions bridge copper(II) centers to form one-dimensional zigzag chains. The chains of 1-3 are arranged by hydrogen-bonding interactions and stacking interactions to produce porous structures. Cobalt(II) and zinc(II) compounds 4 and 5 form one-dimensional helical chains. In 4 and 5, the crystal packing induces spontaneous resolution of the helical chains with chiral cavities formed perpendicular to the helices. Nickel(II) compounds 6 and 7 form cyclic tetramers. The fourth architecture, a dimer (compound 8), is obtained by the reaction of zinc(II) and bhnq(2-) in MeOH. In these compounds, changes of the dihedral angles and the metal-coordination mode of the bhnq(2-) ion induce the structural versatility. The assemblies of the zigzag chains of the copper(II) compounds exhibit reversible vapochromic behavior. UV/Vis, powder X-ray diffraction, EPR, and adsorption isotherm measurements indicate that this vapochromic behavior is based on the hinge-like flexibility of the bhnq(2-) ion.     

New efficient route for solid-phase synthesis of benzimidazole derivatives

A simple and efficient method for the solid-phase synthesis of benzimidazole libraries is described. Monoalkylation of various o-phenylenediamines on resin-bound bromoacetamide proceeded smoothly to give the monoalkyl resin-bound o-phenylenediamines in high yields. Subsequent cyclization of the diamines with various aldehydes afforded solid-supported benzimidazoles. Cleavage from the resin gave benzimidazoles in good yields. The present method enabled the introduction of the diversity on the benzene ring of imidazoles. Azabenzimidazoles, such as 4-azabenzimidazoles, 5-azabenzimidazoles, and purines, were also synthesized in good yields with high purities by the same procedure.     

Triple hydrogen bonds direct crystal engineering of metal-assembled complexes: the effect of a novel organic-inorganic module on supramolecular structure

Novel triply hydrogen bonded suprastructures based on [M(tdpd)2(L)2]2- (H2tdpd=1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, L=solvent) and melamine-analogous cations have been synthesized and characterized. The use of anions containing two AAA sets from [M(tdpd)2(L)2]2- together with cations containing one DDD set (A=hydrogen-bond acceptor, D=hydrogen-bond donor) leads to the formation of complementary triply hydrogen bonded modules in the solid state. In all cases, the building module is further extended via additional hydrogen-bonding interactions to produce a tape, and tapes are assembled into sheets. These results show that a hydrogen-bonded module consisting of different kinds of building blocks, one of which is a metal complex that includes hydrogen-bond acceptor sites and the other is a hydrogen-bond donor molecule, will be attractive for constructing metal-containing supramolecular systems by the self-assembly technique.