Tomohiro Hiraishi

Photoinduced hydrogen evolution with viologen-linked ruthenium(II) complexes and hydrogenase

Abstract Bisviologen-linked ruthenium(II) complexes with different methylene chain length between ruthenium complex and viologen, Ru(bpy)2(dcbpy)CmVACnVB(m=2, n=3; m=3, n=4), were synthesized and characterized. From luminescence spectra, the photoexcited state of Ru(bpy)2(dcbpy) moiety is oxidatively quenched by the bound viologen, and an intramolecular electron transfer occurs. Luminescence lifetime measurements show that the electron transfers from the photoexcited state of ruthenium(II) complex moiety to the bound bisviologen more rapidly than that of monoviologen-linked ruthenium(II) complexes. Ru(bpy)2(dcbpy)CmVACnVB were applied to the photoinduced hydrogen evolution in the system containing nicotinamide-adenine dinucleotide phosphate (reduced form, NADPH), Ru(bpy)2(dcbpy)CmVACnVB and hydrogenase under steady state irradiation. In the case of Ru(bpy)2(dcbpy)C3VAC4VB, the efficient photoinduced hydrogen evolution was observed.

Photoinduced hydrogen evolution using water soluble viologen-linked trisulfonatophenylporphyrins (TPPSCnV) with hydrogenase

Abstract A series of water soluble viologen-linked trisulfonatophenylporphyrins with different methylene chain lengths (n = 3–6) between porphyrin and viologen, TPPSCnV, were synthesized and were characterized. The intramolecular electron transfer rate constants from the porphyrin moiety of TPPSCnV to viologen were measured by using fluorescence lifetime and laser flash photolysis. The photoexcited singlet state of the porphyrin was quenched by the bonded viologen. These compounds were applied to photoinduced hydrogen evolution in the system containing nicotinamide-adenine dinucleotide phosphate (reduced form NADPH), TPPSCnV and hydrogenase under steady state irradiation.

Photoinduced hydrogen evolution with cytochrome c3-viologen-ruthenium(II) triad complex and hydrogenase

Abstract Cytochrome c 3 -viologen-ruthenium(II) triad complex, Ru-V-cyt. c 3 , was prepared and characterized by using spectroscopic techniques. Effective quenching of the photoexcited state of ruthenium complex moiety by the bound viologen was observed in Ru-V-cyt. c 3 . When the system containing Ru-V-cyt. c 3 and hydrogenase was irradiated by visible light, photoinduced hydrogen evolution was observed, showing the effective two-step electron transfer from the photoexcited state of ruthenium complex moiety to cytochrome c 3 via bound viologen.

Preparation and characterization of water soluble viologen-linked trisulfonatophenylporphyrin (TPPSCnV)

Abstract A series of water soluble viologen-linked trisulfonatophenylporphyrins (TPPSC n V; n = 3–6) were synthesized. Viologen is connected with the trisulfonatophenylporphyrin via a methylene chain (-(CH 2 ) n )-: n = 3–6) in these compounds. The photochemical and electrochemical properties of TPPSC n V were investigated by using the absorption spectra, the fluorescence spectra and the cyclic voltammetric measurement. The photoexcited singlet state of the porphyrin moiety of TPPSC n V was quenched by the bonded viologen.

Lysine-linked viologen for substrate of hydrogenase on hydrogen evolution

Lysine-linked viologen was synthesized and was applied for hydrogen evolution with hydrogenase. The lysine-linked viologen has high affinity for hydrogenase than methyl viologen, resulting the high hydrogen evolution rate.

Kinetic studies of electron transfer on photoinduced hydrogen evolution with hydrogenase

Abstract The kinetic properties of the elementary processes of electron transfer on photoinduced hydrogen evolution with hydrogenase, using cytochrome c 3 and methyl viologen as electron carriers, were studied. The electron transfer from reduced methyl viologen to cytochrome c 3 was monophasic and proceeded with a rate constant of 1.5 × 10 7 mol −1 dm 3 s −1 . The rate constants for hydrogenase reduction with reduced cytochrome c 3 were determined to be k 2 = 154 s −1 and K m = 5.4 × 10 −7 mol dm −3 , and were more efficient than that of reduced methyl viologen. These results indicate that cytochrome c 3 reduction with reduced methyl viologen occurs, followed by rapid electron transfer from reduced cytochrome c 3 to hydrogenase.

Purification and properties of intact hydrogenase from Desulfovibrio vulgaris (Miyazaki)

Abstract The intact hydrogenase from Desulfovibrio vulgaris (Miyazaki) was purified and characterized. The purified hydrogenase had a molecular weight of 92.0 kDa, with two different subunits (Mw = 62.5 kDa and 29.5 kDa). The molecular weight of the large subunit of the intact hydrogenase was 2 kDa larger than the tryptic digested hydrogenase. The absorption spectrum and the EPR spectrum of the intact hydrogenase were identical to those of tryptic digested hydrogenase. Phase separation study indicated the detergent solubilized hydrogenase was more hydrophobic than tryptic digested hydrogenase.

The role of specific lysine in cytochrome c3 on the electron transfer with hydrogenase

Abstract Modification of specific lysine residue of cytochrome c 3 with 2,4,6-trinitorobenzenesulfonic acid sodium salt dehydrate (TNBS) was carried out. By comparing the hydrogen evolution rate with modified cytochrome c 3 and native cytochrome c 3 catalyzed by hydrogenase, the role of lysine residue of cytochrome c 3 was discussed. The modified lysine residue was responsible for the intermolecular electron transfer from cytochrome c 3 to hydrogenase.

Preparation and characterization of bisviologen-linked ruthenium(II) complexes

Abstract Bisviologen linked ruthenium(II) complexes with different methylene chain length between ruthenium complex and viologen, Ru(bpy)2(dcbpy)CmVACnVB(m = 2, n = 3; m = 3, n = 4), were synthesized and characterized by using spectroscopic and electrochemical techniques. UV spectra of Ru(bpy)2(dcbpy)CmVACnVB are similar to that of Ru(bpy)2(dcbpy), indicating no interaction between ruthenium(II) complex moiety and binding bisviologen in the ground state. The photoexcited state of Ru(bpy)2(dcbpy) moiety is oxidatively quenched by binding bisviologen and the intramolecular electron transfer occurs. Electrochemical properties of bisviologen linked ruthenium complexes show that photoinduced two step electron transfer from ruthenium complex moiety to bisviologen can occur to yield the longlived charge separated states. Luminescence lifetime measurements show that the electron transfers from the photoexcited state of ruthenium(II) complex moiety to the binding bisviologen more rapidly than that of viologen free ruthenium(II) complexes, indicating the intramolecular electron transfer from photoexcited ruthenium(II) complex moiety to bisviologen.

Effect of Hg(II) on hydrogenase activity from Desulfovibrio vulgaris (Miyazaki)

Abstract Effect of Hg(II) on the intact hydrogenase activity from Desulfovibrio vulgaris (Miyazaki) was studied kinetically. When the hydrogenase was incubated with Hg(II), the hydrogen evolution rate was strongly inhibited. From the absorption spectra of the iron-sulfur cluster(s) and the EPR spectra of [3Fe4S] cluster and Ni center, reaction mechanism is discussed.