Performance of a dual-stage semiconductor laser amplifier for optical transmission repeater system

The performance of a dual-stage semiconductor laser amplifier consisting of a preamplifier and a power amplifier is evaluated theoretically and experimentally. The dual-stage optical amplifier can offer high-gain amplification with low noise figure by using a low-noise amplifier as a preamplifier. Using the dual-stage amplifier, 2.4 Gbits^–1 193 km optical fibre transmission was demonstrated. In addition, by applying an automatic power control system to the dual-stage amplifier, output power stabilization with wide dynamic range was obtained.     

Quantum beat between two excitonic levels split by spin--orbit interactions in the oxychalcogenide LaCuOS

Degenerate four-wave mixing signals excited by femtosecond laser pulses were measured in LaCuOCh (Ch = S and Se) at 4 K. The signals for LaCuOS exhibit a beat structure with a period of 480 fs just at the exciton peak energy, indicating that the lowest exciton states are split by 9 meV, but no beat structure was observed in LaCuOSe, regardless of the laser's energy. The spin--orbit interaction of the Ch ion accompanied by the hybridization of Cu 3d orbitals causes splitting of the exciton levels. Furthermore, the contribution of Ch p orbitals in the valence band maximum is larger in LaCuOSe owing to increased covalency in the Cu--Ch bond when S is replaced with Se.     

Synthetic studies on pseudolaric acid B: Construction of the trans-fused [5–7] ring system via Dieckmann condensation

Pseudolaric acids A (1) and B (2) are diterpene acids isolated from the root bark of Pseudolarix kaempferi as the main biologically active constituents of tujinpi, a traditional Chinese medicinal herb. Studies toward the total synthesis of 2 are described. The unusual trans-fused [5–7] ring system in the core structure of 2 was successfully synthesized via Dieckmann condensation.     

Enantioselective catalysis of carbonyl-ene and Friedel–Crafts reactions with trifluoropyruvate by ‘naked’ palladium(II) complexes with SEGPHOS ligands

Chiral dicationic SEGPHOS–Pd(II) complex gives high chemical yield, (E)-olefin selectivity, anti-diastereoselectivity, along with high enantioselectivity even with less reactive mono- and 1,2-disubstituted olefins in this much less reactive ketone-ene reactions. The high levels of enantioselectivity not only in carbonyl-ene but also in Friedel–Crafts reactions stem from the effective shielding with diphenyl groups on phosphines caused by the narrow dihedral angle of metal complexes with SEGPHOS.     

A new isoflavone glycoside from Ceiba pentandra (L.) Gaertner

From the 80% EtOH extract of the bark of Ceiba pentandra (L.) Gaertner, a new isoflavone glycoside was isolated along with known isoflavones, vavain and vavain glucoside. The structure was elucidated by spectroscopic analysis as 5-hydroxy-7,4',5'-trimethoxyisoflavone 3'-O-alpha-L-arabinofuranosyl(1-->6)-beta-D-glucopyranoside.     

Why do the second row transition metal atoms prefer 5s14dm+1 to 5s24dm?

Numerical Hartree-Fock (NHF) calculations have been performed for 332 ground and low-lying excited states of the fifth period atoms Rb through Xe, with our special interest in the states arising from the 5s ²4d ^m , 5s ¹4d ^m +1, and 5s ⁰ 4d ^m +2 configurations of the second row transition metal atoms. Among various properties, orbital energies and mean values ofr of the outermost orbitals of each symmetry are presented as well as total energies. It is discussed in some detail why the second row transition metal atoms have a tendency to prefers ¹ d ^m +1 as the ground configuration in contrast to the preferreds ² d ^m configuration in the first row transition metal atoms. Our systematic NHF computations reported in this and the previous papers conclude that the Hartree-Fock method correctly predicts the experimental ground state of the atoms He through Xe with the sole exception for Zr.     

Addition of stable nitroxide radical to stable divalent compounds of heavier group 14 elements

The reactions of stable cyclic dialkylgermylene 2 and dialkylstannylene 3 with 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical (2 equiv) gave the corresponding 1:2 adducts 4 and 5, respectively, which were characterized by NMR, MS, and X-ray analyses. The kinetics of the stepwise addition of two TEMPO molecules to germylene 2 revealed that the initial addition of TEMPO to 2 was 1010 times slower than the second TEMPO addition to the resulting germyl radical. The origin of the rate difference was discussed on the basis of the qualitative perturbation theory. In contrast to the reactions of 2 and 3, the reaction of dialkylsilylene 1 with TEMPO gave an interesting 1,3-dioxadisiletane derivative.     

Peroxidase-like catalytic activity of Mn-octabromo-tetrakis(4-sulfophenyl)porphine on linoleate hydroperoxide and its analytical application

To reveal an enzyme-like catalytic activity of metal-octabromo-tetrakis(sulfophenyl)porphines (M-OBPSs), their peroxidease-like catalytic activity on linoleate hydroperoxide (LOOH) were evaluated on the basis of dye-formation in the coloring reaction between N,N-diethylaniline and 4-aminoantipyrine that yields a quinoid-type dye. Among M-OBPSs tested, Mn³⁺-OBPS allowed to produce the largest amount of dye. The optimal conditions of the coloring reaction catalyzed by Mn³⁺-OBPS for the determination of LOOH were determined. A good linear calibration curve was obtained in the concentration range of 0.025-0.4 μmole LOOH with good reproducibility (coefficient of variance = 1.23%), suggesting that Mn³⁺-OBPS is a good artificial mimesis of the peroxidase for LOOH. In addition, Mn³⁺-OBPS was highly specific for LOOH even in the presence of cumene hydroxyperoxide or hydrogen peroxide. It was revealed that the peroxidase-like activity of Mn³⁺-OBTP is attributable to the redox cycle of Mn³⁺ ↔ Mn⁴⁺.     

First diastereoselective chiral synthesis of (-)-securinine

[reaction: see text] A diastereoselective total synthesis of securinine in optically pure form was achieved by employing ring-closing metathesis of the corresponding dienyne compound as a key step.     

A new synthesis of serricornin [(4s,6s,7s)-7-hydroxy-4,6-dimethyl-3-nonanone], the sex pheromone of the cigarette beetle

Serricornin, the sex pheromone of Lasioderma serricorne F, was synthesised in 7.6% overall yield starting from methyl (R)-3-hydroxypentanoate of microbial origin. Its (4R,6S,7S)-isomer was also synthesised.