Bulletin of the Chemical Society of Japan

Yamashita, Makoto

doi: 10.1246/bcsj.20110123pmid: N/A

A series of anionic boron compounds, possessing a polarized boron–metal bond, were synthesized and structurally characterized. Detailed analyses of these boryl anions using NMR spectroscopy, X-ray crystallography, reactivity with electrophiles, and DFT calculations revealed that these compounds have anionic and nucleophilic character on the boron center in contrast to conventional boron-containing molecules with a Lewis acidic character. Some applications of boryl anions toward organic synthesis, organometallic chemistry, and main group chemistry are also described.

Abe, Ryu

doi: 10.1246/bcsj.20110132pmid: N/A

Photocatalytic water splitting using semiconductor materials has attracted considerable interest due to its potential for clean production of H2 from water by utilizing abundant solar light. The developments of water-splitting systems that can efficiently use visible light have been a major challenge for many years in order to realize efficient conversion of solar light. We have developed a new type of photocatalysis system that can split water into H2 and O2 under visible light irradiation, which was inspired by the two-step photoexcitation (Z-scheme) mechanism of natural photosynthesis in green plants. In this system, the water-splitting reaction is broken up into two stages: one for H2 evolution and the other for O2 evolution; these are combined by using a shuttle redox couple (Red/Ox) in the solution. The introduction of a Z-scheme mechanism reduces the energy required to drive each photocatalysis process, extending the usable wavelengths significantly (≈660 nm for H2 evolution and ≈600 nm for O2 evolution) from that in conventional water splitting systems (≈460 nm) based on one-step photoexcitation in single semiconductor material.

Tsujimoto, Yuya; Ie, Machiko; Ando, Yasunari; Yamamoto, Taiki; Tsuda, Akihiko

doi: 10.1246/bcsj.20110178pmid: N/A

In a vortex generated by mechanical rotary stirring in an optical cell, DNA molecules in pure water temporarily align helically to the spiral flow, and dynamically display strong induced circular dichroism (CD) and linear dichroism (LD) responses. Although a sample solution without stirring provided the characteristic CD spectral pattern of DNA, an entirely different macroscopic CD spectral pattern with a much larger intensity and LD spectrum appeared upon mechanical rotary stirring of the sample solution. Clockwise (CW) and counterclockwise (CCW) stirring resulted in mirror-image CD spectral profiles and virtually the same LD profiles with different intensities. The CW stirring of the sample solution in LD spectroscopy always resulted in larger spectral intensities than CCW stirring, but the differences became negligible upon addition of NaCl or ethidium bromide. The observed CD and LD responses of the stirred sample solution decreased simultaneously as the double-stranded structure denatures with increasing temperatures. The results obtained in this study indicate that DNA, when it forms a double-stranded structure, can effectively align in the vortex flows, and show hydrodynamic preference to a right-handed vortex than to a left-handed vortex.

Li, Jun; Yoshizawa, Kazunari

doi: 10.1246/bcsj.20110128pmid: N/A

A reaction mechanism for the hydrogenation of CO2 to formate catalyzed by an Ir(III)–pincer trihydride complex has been investigated with density functional theory calculations. Two routes for the formation of formate were considered: (I) the insertion of CO2 into the Ir–H bond with the assistance of the metal center, and (II) the direct addition of hydride to CO2 via nucleophilic attack. Route II is energetically more favorable than route I. Molecular orbital and natural bond orbital analyses showed that this trihydride complex consists of two kinds of hydrides with distinct Ir–H bond properties, and the hydride in the plane vertical to the pyridine moiety is highly active. The whole catalytic cycle for CO2 hydrogenation to formate is exothermic by 30.3 kcal mol−1, and the rate-limiting step is the regeneration of the active complex, which involves a barrier of 15.6 kcal mol−1. The theoretical results are in good agreement with and give a reasonable explanation to the experimental observations. Moreover, the results imply that the type of a metal–hydride bond might determine which route the CO2 insertion takes, route I or route II.

Kojima, Hirotaka; Mori, Takehiko

doi: 10.1246/bcsj.20110176pmid: N/A

The herringbone structure is a representative molecular packing in organic semiconductors, but there are some modifications with largely different dihedral angles ranging from 40 to 130°. Dihedral angle θ dependence of the transfer integrals is systematically investigated on the basis of the molecular orbital calculations for various organic semiconductors including pentacene, picene, oligothiophene, fused thiophene, tetrathiafulvalenes (TTF), and benzothienobenzothiophene (BTBT). In the conventional organic semiconductors such as pentacene and oligothiophene, the transfer integral is a monotonously decreasing function of θ starting from the stacking geometry, and smaller θ provides more two-dimensional bands. When the molecules are slipped along the molecular long axis D, these compounds show characteristic oscillating structure of the transfer integrals depending on D, which is called D-modulation. Contrarily, TTF derivatives show oscillating structure of the transfer integrals depending on θ (θ-modulation) due to interaction at the side position. BTBT exhibits a pattern much different from the conventional organic semiconductors, and a considerable magnitude of transfer integrals is expected in the large θ region. These systematic investigations demonstrate that the θ-dependence of the charge transport largely depends on the original molecular orbital symmetry.

Kano, Taichi; Yamamoto, Akihiro; Song, Sunhwa; Maruoka, Keiji

doi: 10.1246/bcsj.20110155pmid: N/A

Catalytic asymmetric synthesis of various isoxazoline-N-oxides having a tetrasubstituted carbon has been accomplished by asymmetric phase-transfer conjugate addition of bromomalonate to nitroolefins and subsequent ring-closing O-alkylation. The obtained isoxazoline-N-oxide was readily converted to the corresponding oxime, isoxazoline, and lactam without loss of optical purity.

Nitami, Tsuyoshi; Sekine, Akiko; Uekusa, Hidehiro; Ohashi, Yuji

doi: 10.1246/bcsj.20110175pmid: N/A

When a crystal of [(S)-1-cyclohexylethylamine]bis(dimethylglyoximato)[(S)-1-(ethoxycarbonyl)ethyl]cobalt(III) was irradiated with a halogen lamp, the absolute configuration of the (S)-1-(ethoxycarbonyl)ethyl group gradually changed from S to R with retention of the single crystal form. After 24 h exposure, the change became within experimental error and the S:R ratio of the 1-(ethoxycarbonyl)ethyl group was found to be 18:82 by X-ray crystal structure analysis. The crystals with the (R)- and (racemic)-1-(ethoxycarbonyl)ethyl groups instead of the (S)-enantiomer have isomorphous structures to the crystal with the (S)-enantiomer. Both of the crystals were also changed to the same structure as that with the (S)-enantiomer on exposure to the halogen lamp. This marvelous ratio of 18:82 was clearly explained with the shape of the reaction cavity for the photoreactive 1-(ethoxycarbonyl)ethyl group in each crystal structure. A pseudo-isomorphous crystal of the complex with the (S)-enantiomer was obtained under the same conditions but it contains a water molecule as solvate. The (S)-1-(ethoxycarbonyl)ethyl group in the crystal gradually changed to the disordered racemate with retention of the single-crystal form. The different reaction pathway between the pseudo-isomorphous crystals with and without a water molecule was explained with not only the size but also the shape of the reaction cavity for the photoreactive group.

Fuchiwaki, Yusuke; Nagai, Hidenori; Saito, Masato; Tamiya, Eiichi

doi: 10.1246/bcsj.20110130pmid: N/A

Flow-through PCR devices for performing rapid and small-volume DNA amplification on a single chip have attracted great interest. Flow-through DNA amplification was performed by moving PCR solution as a liquid plug through three individual temperature zones. Since precise control of the temperature setting is the most important technique for successful DNA amplification, real-time temperature analyses of the moving fluid were investigated using a polyolefin pressure-sensitive adhesive (PPSA) film to cover the microchannel. The temperature profile at 20 °C during annealing phase was the closest to the recommended conditions for PCR compared to the profile from 55 to 20 °C, and it showed the highest amplification of the tested regimes. The microchannel design was optimized using an infrared (IR) thermal imager to significantly increase the fluorescence intensity of the amplified products. A flow time of five to six seconds per cycle resulted in a temperature profile close to the recommended thermal gradient. These studies resulted in effective findings for simple and rapid amplification by moving a PCR solution as liquid-plug on a single chip.

Takahashi, Saori; Murase, Mami; Hagiwara, Hiroaki; Matsumoto, Naohide; Tsuchimoto, Masanobu

doi: 10.1246/bcsj.20110141pmid: N/A

Three SmIII complexes with tripod heptadentate N7 ligands containing three imidazole groups, [Sm(H3L2-Me)(ac)](ClO4)2·2MeOH·H2O (1), [Sm(H3L2-Me)(ac)](ClO4)2·2EtOH (2), and [Sm(H3L4-Me)(ac)](ClO4)2·MeOH (3), were synthesized and the crystal structures were determined, where H3L2-Me and H3L4-Me are the 1:3 condensation products of tris(2-aminoethyl)amine and either 2-methyl-4-formylimidazole and 4-methyl-5-formylimidazole, respectively, and ac denotes acetate ion. Each SmIII ion is coordinated by a tripod heptadentate N7 ligand and two oxygen atoms of the acetate ion. Due to the screw coordination arrangement of the achiral tripod ligand to the SmIII ion, the complex-cation [SmIII(H3L2- or 4-Me)(ac)]2+ gives Δ- and Λ-enantiomorphs. In compounds 1 and 2, two adjacent [Sm(H3L2-Me)(ac)]2+ species with the same chirality are linked by an intermolecular imidazole···acetate hydrogen bond to form a homochiral 1D chain structure. Adjacent chains with the same chirality are stacked to give a conglomerate crystal in 1, while adjacent chains with opposite chiralities are stacked to give a racemic crystal in 2. In compound 3, two adjacent [Sm(H3L4-Me)(ac)]2+ species with the opposite chiralities are doubly bridged by two intermolecular imidazole···acetate hydrogen bonds to form a heterochiral dimer and the adjacent dimers are connected by ClO4− ion through the hydrogen bonds to form a racemic crystal.

Kojima, Natsuko; Hayashi, Shigenobu

doi: 10.1246/bcsj.20110187pmid: N/A

We have studied the state of adsorbed dichloromethane molecules not removed by evacuation in several H-type zeolites, ZSM5, mordenite, β, and Y, by means of solid-state NMR. The amount of undesorbed dichloromethane was determined by quantitative analysis of 1H MAS NMR spectra. The strength and the amount of Brønsted acid sites could not explain the amount of the undesorbed dichloromethane. The channel size is the most probable to determine the amount. The 1H and 13C MAS NMR spectra as well as the 2H static NMR spectra demonstrated that undesorbed dichloromethane is rather mobile.