Shigenori Kashimura

Electroreductive synthesis of polygermane and germane–silane copolymer

Formation of Ge–Ge and Ge–Si bonds has been achieved by electroreduction with an Mg electrode and this method has been successfully applied to the preparation of polygermane and germane–silane copolymer.

Physicochemical Studies of Demetalation of Light-harvesting Bacteriochlorophyll Isomers Purified from Green Sulfur Photosynthetic Bacteria

Demetalation kinetics of bacteriochlorophylls (BChls) c, d and e from green sulfur photosynthetic bacteria were studied under weakly acidic conditions. Demetalation rate constants of BChl e possessing a formyl group at the 7‐position were significantly smaller than those of BChls c and d, which had a methyl group at this position. The activation energy of demetalation of 31R‐8,12‐diethyl([E,E])‐BChl e was 1.5‐times larger than that of 31R‐[E,E]‐BChl c. 15N‐labeled 31R‐[E,E]‐BChls c and e were purified from cells of green sulfur bacteria grown in a medium containing 15NH4Cl, and their 15N NMR spectra were measured. The chemical shifts of N21, N22 and N23 atoms of 31R‐[E,E]‐BChl e were lower‐field shifted than those of 31R‐[E,E]‐BChl c, respectively, and especially the difference in chemical shifts of N22 was significantly large. These results suggest that the electron‐withdrawing formyl group at the 7‐position of BChl e affected an electronic state of the chlorin macrocycle and caused BChl e to be more tolerant for removal of the central magnesium compared with BChls c and d.

Cathodic coupling of aliphatic esters. Useful reaction for the synthesis of 1,2-diketone and acyloin

Abstract It has been found in this study that electroreduction of aliphatic ester (1) with Mg electrode leads to the formation of the corresponding 1,2-diketone under aprotic conditions, whereas bis(trimethylsilyloxy)alkene is afforded through acyloin condensation when the reduction is carried out in the presence of chlorotrimethylsilane.

Electroreductive synthesis of oligosilanes and polysilanes with ordered sequences

Abstract The stepwise elongation of SiSi or SiGe chain was achieved by the electroreductive cross-coupling reaction of chlorohydrosilanes with dichlorooligosilanes using magnesium electrodes. The electroreductive cross-coupling reaction of chlorodimethylsilane ( 1 ) with dichlorodiphenylsilane ( 2 ) or dichlorodiphenylgermane ( 4 ), for instance, gave 1,3-dihydro-1,1,3,3-tetramethyl-2,2-diphenyltrisilane ( 3 ) or bis(hydrodimethylsilyl)germane ( 5 ) in good yield. Compounds 3 and 5 were readily transformed to the corresponding 1,3-dichlorotrisilane ( 6 ) and bis(chlorosilyl)germane ( 7 ), respectively. The electroreductive polymerization of the resulting dichlorooligosilanes using magnesium electrodes in tetrahydrofuran was successfully applied to the synthesis of sequence-ordered polysilanes.

Electroreductive synthesis of some functionalized polysilanes and related polymers

Abstract Polysilanes having hydroxyl and related functional groups have been synthesized by the electroreduction of appropriate dichlorosilanes with Mg electrode, and a vinyl polymer which has oligosilane unit in the side chain has also been synthesized.

Demetalation kinetics of natural chlorophylls purified from oxygenic photosynthetic organisms: effect of the formyl groups conjugated directly to the chlorin π-macrocycle

Demetalation kinetics of natural chlorophyll (Chl) d purified from Acaryochloris marina was first studied and compared with those of Chls a and b. The demetalation rate constant of Chl d, which possessed a formyl group at the 3-position, was five-fold smaller than that of Chl a possessing a vinyl group at the same position in aqueous acetone at the proton concentration of 1.2 x 10(-3) M at 25 degrees C. In contrast, the demetalation rate constant of Chl b possessing a formyl group at the 7-position was 26 times smaller than that of Chl a. The activation energy of demetalation reaction of Chl d was larger than that of Chl a, but smaller than that of Chl b. These indicate that the substitution effect of 3-formyl group on the acidic removal of central magnesium in Chls was smaller than that of 7-formyl group.

Cathodic intra- and intermolecular couplings of ketones with unsaturated silanes

Abstract The electroreduction of 6-trimethylsilyl-6-hepten-2-one afforded cis -1-methyl-3-trimethylsilyl cyclohexanol, and γ-trimethylsilyl alcohols were yielded as the intermolecular coupling products when the cathodic reduction of ketones was carried out in the presence of unsaturated silanes.

Biosynthesis of unnatural bacteriochlorophyll c derivatives esterified with α,ω-diols in the green sulfur photosynthetic bacterium Chlorobaculum tepidum.

Unnatural bacteriochlorophyll (BChl) c derivatives possessing a hydroxy group at the terminus of a hydrocarbon chain at the 17-propionate were biosynthesized in the green sulfur photosynthetic bacterium Chlorobaculum tepidum. Addition of exogenous 1,8-octanediol, 1,12-dodecanediol, and 1,16-hexadecanediol in acetone to liquid cultures resulted in accumulation of BChl c monoesterified with the corresponding diols. The relative ratios of the novel BChl c derivatives esterified with 1,8-, 1,12-, and 1,16-diols to totally producing BChl c were 8.2, 50.2, and 57.6% in the cells grown with additive α,ω-diols at concentrations of 1.5, 0.06, and 0.06 mM, respectively, at the final concentration. The homologue composition of BChl c derivatives esterified with these α,ω-diols was similar to that of original, coexisting BChl c esterified with farnesol (BChl c(F)), suggesting that esterification of α,ω-diols occurred at the last step of the BChl c biosynthetic pathway by BChl c synthase, BchK, in the same manner as in BChl c(F). Chlorosomes, which were isolated from cells grown in the presence of exogenous α,ω-diols, contained a ratio and a composition of BChl c derivatives esterified with the diols similar to those in the whole cells, indicating that these BChl c derivatives were actually present in chlorosomes. Q(y) absorption bands of C. tepidum cells containing the novel BChl c derivatives were shifted to a shorter wavelength, although their bandwidths were analogous to those of cells obtained by normal cultivation. Circular dichroism spectra of cells that had BChl c derivatives esterified with α,ω-diols exhibited S-shaped signals in the Q(y) region, whose polarities were the reverse of those of cells grown in the normal medium and by supplementation with neat acetone as a control experiment. These spectral features of C. tepidum possessing BChl c derivatives esterified with α,ω-diols imply that the novel BChl c derivatives possessing a hydroxy group at the terminus of a hydrocarbon chain affect their self-assembly in chlorosomes.

Electroreduction of aliphatic esters using new paired electrolysis systems

Electroreduction of aliphatic esters to form 2-alkoxytetrahydrofurans was achieved by using a new paired electrolysis system, that consists of the cathodic reduction of aliphatic esters and the anodic oxidation of the solvent (THF). It was also found that the presence of magnesium ion in the electrolyte promoted the electroreduction of aliphatic esters remarkably. In fact, the electroreduction of aliphatic esters was found to proceed toward 2-alkoxytetrahydrofurans by using a platinum cathode and anode in the presence of anodically dissolved magnesium ions.

Diacylation of activated olefins promoted by electrochemically generated NO3·p1☆

Abstract It has been found in this study that an acyl radical is formed by the reaction of an aldehyde with a radical NO3· generated by the anodic oxidation of NO3− and the reaction of this acyl radical with activated olefins lead to the formation of a diacylated compound.