A regio- and stereoselective alpha-methylation of gamma,delta-epoxy-alpha,beta-unsaturated esters with a Me2Zn-CuCN reagent

A highly regio- and stereoselective alpha-methylation reaction of gamma,delta-epoxy-alpha,beta-unsaturated esters was achieved by using a Me2Zn-CuCN reagent.     

Silica sol-gel/organic hybrid material for protein encapsulated column of capillary electrochromatography

A new-type of sol-gel/organic hybrid composite material using gelatin or chitosan with tetramethoxysilane was developed for the bovine serum albumin (BSA)-encapsulated monolithic column for capillary electrochromatography (CEC). The composite monolith was used to immobilize BSA in a fused-silica capillary. The addition of gelatin and chitosan to the alkoxysilane enabled the enantioseparation of Trp. A very small amount of these polymers were effective for the enantioseparation. Especially, the monolithic column prepared from chitosan with tetramethoxysilane showed a high enantioselectivity for Trp enantiomers and the value (alpha' = t2/t1, t1: fast eluted enantiomer, t2: second eluted enantiomer) reached 1.15 on CEC mode. Furthermore, the composite materials exhibited a higher stability compared to the silica sol-gel column. These results showed that the sol-gel/organic hybrid composite was useful as a monolithic matrix for the BSA-encapsulated column for CEC.     

Bifunctional organocatalysts for enantioselective aza-Morita-Baylis-Hillman reaction

The efficient and novel bifunctional organocatalyst for the enantioselective aza-Morita-Baylis-Hillman (aza-MBH) reaction has been established with (S)-3-(N-isopropyl-N-3-pyridinylaminomethyl)BINOL for the first time. The reaction proved to be deeply influenced by the position of the Lewis base attached to BINOL. The acid-base-mediated functionalities for the activation of the substrate and the fixing of conformation of the organocatalyst are harmoniously performed to promote the reaction with high enantiocontrol.     

Separation and purification of uridine diphosphate-glucuronosyltransferases by chromatofocusing on a high-performance liquid chromatograph

A rapid method for the separation and purification of uridine diphosphate-glucuronosyltransferases (GT) was developed with the use of chromatofocusing on a high-performance liquid chromatograph. GT isoenzymes solubilized from hepatic microsomes of Wistar rats were separated on a Mono P column, a pre-packed column for chromatofocusing. Using 4-nitrophenol, testosterone and androsterone as substrates, four fractions with different GT activities were separated in a pH gradient from 9.5 to 7.0. Two isoenzymes, testosterone GT and androsterone GT were purified to apparent homogeneity. They were eluted at pH 8.9 and 8.0 and had subunit molecular weight values of 50000 and 52000, respectively. Approximately 10 mg of solubilized microsomal proteins was applied and the elution was completed within 2 h. Addition of N-nitrodiethylamine, an in vitro activator of GT activity, enhanced the GT activity toward 4-nitrophenol in the three fractions. This chromatographic analysis confirmed the absence of androsterone GT isoenzyme in LA Wistar rats, a mutant strain in terms of androsterone glucuronidation.     

Fabrication of polymer Langmuir-Blodgett films containing regioregular poly(3-hexylthiophene) for application to field-effect transistor

Semiconducting thin films consisting of regioregular poly(3-hexylthiophene) (RR-PHT) and poly(N-dodecylacrylamide) (pDDA) were constructed by the Langmuir-Blodgett (LB) technique. A mixture of RR-PHT and pDDA spread from a chloroform solution on a water surface forms a stable monolayer, which can be transferred onto solid substrates by the LB method, yielding a well-defined polymer LB film. Surface morphology studies of the LB film indicate that the RR-PHT is dispersed uniformly throughout the surface. The polymer thin film was chemically doped by contacting with FeCl3 acetonitrile solution, and a conductivity of 5.6 S/cm was achieved. Further, the LB film was utilized as the semiconducting film in the field-effect transistor (FET), and mobilities of 2.2 x 10(-4) and 4.4 x 10(-4) cm2 V(-1) s(-1) were obtained by analyzing the saturated and linear regions of the current-voltage characteristic, respectively.     

Ethylene and propylene polymerization behavior of a series of bis(phenoxy–imine)titanium complexes

This contribution reports ethylene and propylene polymerization behavior of a series of Ti complexes bearing a pair of phenoxy–imine chelate ligands. The bis(phenoxy–imine)Ti complexes in conjunction with methylalumoxane (MAO) can be active catalysts for the polymerization of ethylene. Unexpectedly, this C₂ symmetric catalyst produces syndiotactic polypropylene. ¹³C NMR spectroscopy has revealed that the syndiotacticity arises from a chain-end control mechanism. Substitutions on the phenoxy–imine ligands have substantial effects on both ethylene and propylene polymerization behavior of the complexes. In particular, the steric bulk of the substituent ortho to the phenoxy–oxygen is fundamental to obtaining high activity and high molecular weight for ethylene polymerization and high syndioselectivity for the chain-end controlled propylene polymerization. The highest ethylene polymerization activity, 3240 kg/mol-cat h, exhibited by a complex having a t-butyl group ortho to the phenoxy–oxygen, represents one of the highest reported to date for Ti-based non-metallocene catalysts. Additionally, the polypropylene produced exhibits a T_m, 140 °C, and syndioselectivity, rrrr 83.7% (achieved by a complex bearing a trimethylsilyl group ortho to the phenoxy–oxygen) that are among the highest for polypropylenes produced via a chain-end control mechanism. Hence, the bis(phenoxy–imine)Ti complexes are rare examples of non-metallocene catalysts that are useful for the polymerization of not only ethylene but also propylene.     

Crystal structure of the parent misfit-layered cobalt oxide [Sr2O2]qCoO2

The crystal structure of our newly discovered Sr-Co-O phase is investigated in detail through high-resolution electron microscopy (HREM) techniques. Electron diffraction (ED) measurement together with energy dispersive X-ray spectroscopy (EDS) analysis show that an ampoule-synthesized sample contains an unknown Sr-Co-O ternary phase with monoclinic symmetry and the cation ratio of Sr/Co=1. From HREM images a layered structure with a regular stacking of a CdI₂-type CoO₂ sheet and a rock-salt-type Sr₂O₂ double-layered block is observed, which confirms that the phase is the parent of the more complex “misfit-layered (ML)” cobalt oxides of [M_mA₂O_m+2]_qCoO₂ with the formula of [Sr₂O₂]_qCoO₂, i.e. m=0. It is revealed that the misfit parameter q is 0.5, i.e. the two sublattices of the CoO₂ sheet and the Sr₂O₂ block coexist to form a commensurate composite structure. We propose a structural model with monoclinic P2₁/m symmetry, which is supported by simulations of ED patterns and HREM images based on dynamical diffraction theory.     

Aromaticity of planar boron clusters confirmed

Low-energy boron clusters are characterized by two-dimensional geometry. Aromaticity of these planar boron clusters was established in terms of topological resonance energy (TRE). All planar boron clusters were found to be highly aromatic with large positive TREs even if they have 4n pi-electrons. Aromaticity must therefore be the origin of unusual planar or quasi-planar geometry. Thus, the aromaticity concept is as useful in boron chemistry as it is in general organic chemistry. It is evident that the Hückel 4n + 2 rule of aromaticity should not be applied to such polycyclic pi-systems. Some of the boron clusters are in the triplet electronic state to attain higher aromaticity. Multivalency and electron deficiency of boron atoms are responsible for lowering the energies of low-lying pi molecular orbitals and then for enhancing aromaticity. For polycyclic pi-systems, paratropicity does not always indicate antiaromaticity.     

High enantioselectivity in rhodium-catalyzed allylic alkylation of 1-substituted 2-propenyl acetates

[reaction: see text] Rhodium-catalyzed asymmetric allylic alkylation of 1-substituted 2-propenyl acetates with dimethyl malonate proceeded with high enantioselectivity in the presence of cesium carbonate as a base and a rhodium catalyst generated from Rh(dpm)(C(2)H(4))(2) (dpm = dipivaloylmethanato) and a chiral phosphino-oxazoline whose basic skeleton is axially chiral binaphthyl to give branch alkylation products in greater than 90% ee.     

Molecular orientation of azobenzene chromophores in ultrathin polymer nanosheets studied by attenuated total reflection spectroscopy

This paper describes characterization of molecular orientation for azobenzene moieties in a polymer nanosheet. Copolymers of N-[4-(phenylazo)phenyl] acrylamide (PAZoA) with tert-pentyl acrylamide (tPA) were synthesized and the monolayers deposited on tapered quartz waveguides by Langmuir–Blodgett (LB) technique. Spectroscopic properties of the copolymer (p(tPA/PAZoA)) monolayers were monitored by integrated optical waveguide technique on the molecular level. Molecular orientation of the azobenzene was precisely determined by polarized absorption spectra. It was found that the azobenzene groups took a horizontal orientation and distributed uniformly in the p(tPA/PAZoA) monolayer without significant PAZoA aggregation. Photoisomerization process from trans to cis form was also investigated. More than half of the trans form (60–70%) was photoisomerized under unpolarized light irradiation, and the photoisomerization rate was independent on the PAZoA contents. This implies that the microenvironment of PAZoA moieties was almost the same in three different p(tPA/PAZoA) monolayers.