Enantioselective synthesis of cyclohexenone derivatives by a chemicoenzymatic approach: stereo- and regioselective route to potential intermediates of compactin (ML 236B) and mevinolin

As a synthetic application of the chiral monoester 2, prepared by pig liver esterase (PLE)-catalyzed hydrolysis of the corresponding meso diester 1, conversion of 2 into various cyclohexenone derivatives was examined. This paper describes the preparation of the isomeric cyclohexenones 6 and 7, potential intermediates for the synthesis of anti-hypercholesmic compactin (ML 236B) and mevinolin, under stereo- and regioselective control.     

CO-retentive addition reactions of fluorinated acid chlorides to alkynes

[reaction: see text]. The reaction of perfluorinated acid chlorides with terminal alkynes is efficiently catalyzed by rhodium complexes and proceeds with retention of the CO moiety in the acid chloride to afford (Z)-1-perfluoroacyl-2-chloro-1-alkenes selectively in high yields.     

Use of an adjustable soft segment as an effective molecular design for crystal engineering of hydrogen-bonded tape motifs

From all the 11 alkylsilylated guanosine and adenosine derivatives having different numbers and types of nonpolar and flexible alkylsilyl side chains, 13 crystals were obtained from appropriate solvents in spite of their low molecular symmetry, and their crystal structures were studied by X-ray crystallography and thermal analysis. In these crystals, a clear structural hierarchy was observed, and one-dimensional tape motifs were preferentially formed by multiple inter-base hydrogen bonds. The tape motifs were arranged in lamellar-like (L), herringbone (H) or widened lamella (WL) structures in the crystals. However, the alkylsilylated ribose unit adopted a variety of conformations with notable disorders at the alkylsilyl moiety. These results suggested that role of the adjustable and nonpolar alkylsilyl ribose unit was to provide cushioning or a filling effect as a molecular pad, which assisted the crystal packing of the robust tape motifs. The packing mode of the tape motifs could be understood from the size instead of the shape of the adjustable alkylsilyl ribose moiety, offering a novel approach to their crystal engineering.     

Opacity effect on extreme ultraviolet radiation from laser-produced tin plasmas

Opacity effects on extreme ultraviolet (EUV) emission from laser-produced tin (Sn) plasma have been experimentally investigated. An absorption spectrum of a uniform Sn plasma generated by thermal x rays has been measured in the EUV range (9-19 nm wavelength) for the first time. Experimental results indicate that control of the optical depth of the laser-produced Sn plasma is essential for obtaining high conversion to 13.5 nm-wavelength EUV radiation; 1.8% of the conversion efficiency was attained with the use of 2.2 ns laser pulses.     

Generation of a self-chirped few-cycle optical pulse in a FEL oscillator

We study the generation of a self-chirped optical pulse in a free-electron laser (FEL) oscillator. In a high-gain FEL oscillator, the frequency chirp is induced in the slippage region as a result of superradiant FEL resonance, and this time-frequency correlation evolves continuously into a few-cycle regime, if the optical cavity length is perfectly synchronized to the electron bunch interval. Numerical simulations based on the slowly evolving wave approximation and experimental results are presented.     

Magnetic properties of Mn3B4 under high magnetic field

The magnetic properties of antiferromagnetic compound Mn₃B₄ were examined using pulsed magnetic field up to 470 kOe. It was found that Mn₃B₄ shows a clear metamagnetic transition under 360 kOe at 4.2K. The present results are not explained by the magnetic structure proposed by Neov and a modified magnetic structure is proposed to understand the present magnetization curve. The magnetic phase diagram in the H-T plane is shown.     

Photoluminescence excitation spectroscopy of GaP1−xNx alloys: conduction-band-edge formation by nitrogen incorporation

We have investigated the conduction-band-edge formation in GaP_1−xN_x alloys by nitrogen incorporation into GaP using photoluminescence excitation (PLE) spectroscopy. The PLE spectra of GaP_1−xN_x alloys with various nitrogen concentrations show that the absorption edge shifts to lower energies with increasing nitrogen concentration. From the nitrogen concentration dependence of the absorption edge energy we found that the conduction-band-edge formation in GaP_1−xN_x alloys originates from the formation of the A line.