Ichiro Okura

Light-driven Hydrogen Production by a Hybrid Complex of a [NiFe]-Hydrogenase and the Cyanobacterial Photosystem I

Abstract In order to generate renewable and clean fuels, increasing efforts are focused on the exploitation of photosynthetic microorganisms for the production of molecular hydrogen from water and light. In this study we engineered a ‘hard-wired’ protein complex consisting of a hydrogenase and photosystem I (hydrogenase–PSI complex) as a direct light-to-hydrogen conversion system. The key component was an artificial fusion protein composed of the membrane-bound [NiFe] hydrogenase from the β-proteobacterium Ralstonia eutropha H16 and the peripheral PSI subunit PsaE of the cyanobacterium Thermosynechococcus elongatus. The resulting hydrogenase-PsaE fusion protein associated with PsaE-free PSI spontaneously, thereby forming a hydrogenase–PSI complex as confirmed by sucrose-gradient ultracentrifuge and immunoblot analysis. The hydrogenase–PSI complex displayed light-driven hydrogen production at a rate of 0.58 μmol H2·mg chlorophyll−1·h−1. The complex maintained its accessibility to the native electron acceptor ferredoxin. This study provides the first example of a light-driven enzymatic reaction by an artificial complex between a redox enzyme and photosystem I and represents an important step on the way to design a photosynthetic organism that efficiently converts solar energy and water into hydrogen.

Optical sensor for oxygen using a porphyrin-doped sol-gel glass

Organic dye-doped glasses, viz., platinum octaethylporphyrin incorporated in silica matrices by the sol–gel method, were prepared and their photochemical properties were investigated. The optical sensing of oxygen using these materials is based on the change in the phosphorescence intensity of the oxygen-sensitive dye. This approach allows the development of a photostable, chemically durable optical oxygen sensor with a fast response time (5 s). There was no significant bleaching after 5 months in the absence of light.

Optical oxygen sensor devices using metalloporphyrins

Oxygen-monitoring techniques are applied to various fields, such as chemicals, deep sea environment, fluid dynamics, clinical analysis and environmental monitoring. Recently, a variety of devices and sensors based on phosphorescence or photoexcited state quenching of porphyrin molecules have been developed to measure oxygen concentration on the solid surface. Many optical oxygen sensors are composed of porphyrins (platinum(II), palladium(II), zinc(II), metal-free, etc.) dispersed in oxygen-permeable polymer film or directly immobilized onto solid surface via chemical or physical adsorption. Oxygen-sensing systems are classified into four types: (1) phosphorescence intensity change, (2) phosphorescence lifetime change, (3) change of lifetime of photoexcited triplet state, and (4) intensity change of absorption of photoexcited triplet state. In this review, the properties of various optical oxygen-sensing devices using porphyrins and sensing system are introduced.

Intercalator-linked cisplatin: synthesis and antitumor activity of cis-dichloroplatinum(II) complexes connected to acridine and phenylquinolines by one methylene chain

Abstract Three novel intercalator-linked cisplatin-type platinum complexes, cis-[ PtCl 2 (9−(2- aminoethyl)aminomethylacridine )/ ( 1 ) , cis-[PtCl2(4−(2-aminoethyl)aminomethyl-2-phynylquinoline)] (2), and cis-[PtCl2(8−(2-aminoethyl)aminomethl-2-phenylquinoline)] (3) were synthesized. The structure of 1 was determined by X-ray crystallography (triclinic, space group P l with a = 15.007(b), b = 15.597(4), c = 10.398(3), A , a = 98.51°, β = 96.79(3)°, γ = 114.61(2)°, Z = 4, R = 0.053, R w = 0.063 ). The antitumor activity of the platinum complexes was investigated against the HeLa cell. Compound 3 was the most cytotoxic among the complexes synthesized here and was more effective than cisplatin. It was suggested from microscopic analysis that the acridine complex 1, which had no cytotoxicity against the HeLa cell, was not incorporated in the nucleus of the cell. Against the P388 cell, however, complex 1 gave a more therapeutic result than 3. The covalent binding ability of the cisplatin moiety was suppressed significantly in these compounds. The results of molecular mechanics showed that interculation and covalent binding could be compatible. The cytotoxicity and DNA binding ability of phenylquinoline-type ligands were also studied to evaluate the intrinsic cytotoxicity of the intercalator. From the duplex DNA denaturation experiment and fluorescent ethidium displacement assay, the DNA binding affinities of the ligands are in agreement with the cytotoxicity of these compounds and the corresponding platinum complexes.

Cellular Uptake and Photocytotoxicity of Glycoconjugated Porphyrins in Hela Cells.

Thirty‐two glycoconjugated porphyrins were synthesized by a modification of Lindsey method in the presence of Zn(OAc)2.2H2O as a template. The Zn2+ ion template strategy improved the yield about three‐fold in the case of meta ‐substituted tetraphenylporphyrins. In addition, free‐base porphyrins were obtained almost quantitatively by demetalation with 4 M HCI. Sixteen deacetylated glycoconjugated porphyrins were tested as candidate photodynamic therapy (PDT) drugs using HeLa cells. Most of the deacetylated glycoconjugated porphyrins showed higher cellular uptake than tetraphenylporphyrin tetrasulfonic acid (TPPS), and 5,10,15, 20‐tetrakis[4‐(β‐D‐arabinopyranosyloxy)phenyl]porphyrin p‐5d) in particular showed 18.5‐fold higher uptake than TPPS. The photocytotoxicity of 5,10,15,20‐tetrakis[4‐(β‐D‐glucopyranosyloxy) phenyl]porphyrin (p‐5a), (p‐5d and TPPS was examined with HeLa cells, using a light dose of 16 J/cm2. These photosensitizers had no cytotoxicity in the dark, but their photocytotoxicity increased in the order of TPPS p‐5a p‐5d. These results suggest p‐5d is a good candidate for a PDT drug.

Optical oxygen sensing materials: chemisorption film of ruthenium(II) polypyridyl complexes attached to anionic polymer

Abstract The optical oxygen sensors were prepared using the some Ru(II) polypyridyl complexes, tris(4,7′-diphenyl-1,10′-phenanthroline) ruthenium(II) dichloride (Ru(ph2phen)32+), tris(1,10′-phenanthroline) ruthenium(II) dichloride (Ru(phen)32+) and tris(2,2′-bipyridine) ruthenium(II) dichloride (Ru(bpy)32+), electrostatically attached to anionic polymer, poly(acrylic acid) and poly(sodium-4-styrene sulfonate) chemisorption thin film onto alumina plate. These sensing films were good linearity using modified Stern–Volmer plot based on two-site model (oxygen-accessible site and oxygen-difficult accessible site) in total oxygen concentration region. These results show that Ru(II) polypyridyl complexes attached to anionic polymer films onto alumina plate can be developed for a highly sensitive device for oxygen sensing. Especially, the superior oxygen sensors are developed using Ru(II) polypyridyl complex in poly(sodium 4-styrene sulfonate) film.

Effective photoinduced hydrogen evolution with hydrogenase in surfactant micelles

Abstract Photoinduced hydrogen evolution with hydrogenase from Desulfovibrio vulgaris (Miyazaki) by the combination of three component system consisting of triethanolamine, zinc-tetraphenylporphyrin tetrasulfonate (ZnTPPS 4 ) and methyl viologen was investigated in cationic surfactant, cetyltrimethylammonium bromide (CTAB), anionic surfactant, sodium dodecyl sulfate (SDS) or non ionic surfactant, Triton X-100 micellar solution by steady state irradiation. The rate of photoreduction of methyl viologen increased by the addition of surfactants, especially CTAB. The back electron transfer reaction from reduced methyl viologen to ZnTPPS 4 cation radical was strongly suppressed by the addition of various surfactants, especially ionic surfactant CTAB or SDS. The effective hydrogen evolution from reduced methyl viologen with hydrogenase was accomplished in the presence of CTAB or Triton X-100 micelle.

Photoinduced hydrogen production with the system containing water-soluble viologen-linked porphyrins and hydrogenase

Abstract Water-soluble viologen-linked cationic porphyrins (ZnP(C n V) 4 , n =3–6) and anionic porphyrins (TPPSC n V, n =3–6) were synthesized and their photochemical properties were characterized. The quenching processes of the photoexcited state of porphyrin moiety by the bonded viologen were measured by fluorescence lifetime and laser flash photolysis, and photoinduced hydrogen evolution with ZnP(C n V) 4 or TPPSC n V and hydrogenase from Desulfovibrio vulgaris (Miyazaki) was performed under steady state irradiation.

Improvement of the purification method for retaining the activity of the particulate methane monooxygenase from Methylosinus trichosporium OB3b

The purification method of particulate methane monooxygenase (pMMO) from Methylosinus trichosporium OB3b was improved, and purified pMMO retained its activity with duroquinol as a reductant. n-Dodecyl-β,d-maltoside was used for the solubilization of pMMO and Brij 58 was used for the purification for anion exchange chromatography. Compared to the original pMMO activity in the membrane fraction, 88% of the activity was now retained in the purified material. The purified pMMO monomer (94 kDa) contained only two copper atoms and did not contain iron. Both copper ions showed only a typical type II copper EPR signal with a superhyperfine structure at the g⊥ region, indicating that the type II copper ions play an important role as the active site of methane hydroxylation in pMMO.

Effect of cationic surfactant on photoinduced hydrogen evolution with hydrogenase

Photoinduced hydrogen evolution with hydrogenase by use of a three component system consisting of triethanolamine, zinctetraphenylporphyrin tetrasulfonate (ZnTPPS4) and methyl viologen was investigated in cationic surfactant, cetyltrimethylammonium bromide (CTAB). In the presence of CTAB, the lifetime of reduced methyl viologen and ZnTPPS4 cation radical increased and effective hydrogen evolution from reduced methyl viologen with hydrogenase was accomplished.