Akimasa Nakamura

Significant species-dependence of P700 redox potential as verified by spectroelectrochemistry: Comparison of spinach and Theromosynechococcus elongatus

The redox potentials of P700, the primary electron donor of photosystem (PS) I, of spinach and Thermosynechococcus elongatus were determined by means of spectroelectrochemistry with an error range of ±2–3 mV, to find that the redox potential of P700 in T. elongatus is lower by ca. 50 mV as compared with spinach. The shift in the P700 redox potential of PS I core particles prepared by harsh detergent treatments remained to within 10 mV for both organisms. These results show that the 50 mV difference in the P700 redox potential between the two organisms is not a detergent‐induced artifact but reflects an intrinsic property of each PS I.

Species-Dependence of the Redox Potential of the Primary Electron Donor P700 in Photosystem I of Oxygenic Photosynthetic Organisms Revealed by Spectroelectrochemistry

The redox potential of the primary electron donor P700, E(m)(P700/P700(+)), of Photosystem I (PSI) has been determined for 10 oxygenic photosynthesis organisms, ranging from cyanobacteria, red algae, green algae to higher plants, by spectroelectrochemistry with an optically transparent thin-layer electrode (OTTLE) cell to elucidate the scattering by as much as 150 mV in reported values of E(m)(P700/P700(+)). The E(m)(P700/P700(+)) values determined within error ranges of ± 1-4 mV exhibited a significant species dependence, with a span >70 mV, from +398 to +470 mV vs. the standard hydrogen electrode (SHE). The E(m)(P700/P700(+)) value appears to change systematically in going from cyanobacteria and primitive eukaryotic red algae, then to green algae and higher plants. From an evolutionary point of view, this result suggests that the species believed to appear later in evolution of photosynthetic organisms exhibit higher values of E(m)(P700/P700(+)). Further, the species dependence of E(m)(P700/P700(+)) seems to originate in the species-dependent redox potentials of soluble metalloproteins, Cyt c(6) and plastocyanin, which re-reduce the oxidized P700 in the electron transfer chain.

HPLC determination of photosynthetic pigments during greening of etiolated barley leaves. Evidence for the biosynthesis of chlorophyll a

The temporal evolution of pigment composition during greening of etiolated barley leaves was investigated by reversed‐phase HPLC with particular attention to chlorophyll (Chl) a′ (C132 epimer of Chl a), which had been detected by ourselves in photosystem (PS) I particles. At early stages of greening, the Chl a′/Chl a molar ratio rapidly increased to a level more than twice that in mature leaves, then gradually leveled off, accompanied by a growth of the Chl b/Chl a ratio, to the mature level. After 3 h of illumination, the temporal evolution of the Chl a′/Chl a molar ratio nearly paralleled that of the P700/Chl a ratio with a stoichiometry Chl a′/P700≅2: this strongly suggests that Chl a′ is biosynthesized as a constituent of the PS I reaction center complex.

Photoacid generating ligands for development of positive-tone directly photopatternable metal complexes.

Photoacid generating ligands, 4-(2-nitrobenzy-loxycarbonyl)catechol and 4-(6-nitroveratryloxycarbonyl)catechol, and indium tin and titanium complexes thereof, were synthesized. These metal complexes perform as positive-tone, directly photopatternable indium tin oxide (ITO) or titanium oxide film precursors. After exposure, acid-bearing selectively soluble complexes could be removed to give patterned films upon developing in aqueous base, which were transformable to the corresponding pattern-preserving metal oxide film. Micropatterning of ITO and titanium oxide films was accomplished with the photoreactivity of the 2-nitrobenzyloxycarbonyl (NBOC) and 6-nitroveratryloxycarbonyl (NVOC) moiety bearing ligands.

Metallic film formation using direct micropatterning with photoreactive metal complexes.

Palladium, cobalt, and nickel in complex with photoacid-generating ligands, 4-(2-nitrobenzyloxycarbonyl)catechol and 4-(6-nitroveratryloxycarbonyl)catechol, were prepared in solution. Films formed from the metal complex solutions perform as positive-tone, directly photopatternable palladium, cobalt, nickel oxide, or composite film precursors. After exposure, acid-bearing selectively soluble complexes could be removed to give patterned films upon developing in aqueous base, which were transformable to the corresponding pattern-preserving metal/metal oxide film. The photodynamics of photoinduced solubility and direct micropatterning of palladium, cobalt, nickel, and palladium/nickel oxide composite films were investigated. Employing palladium as the initiator for autocatalytic chemical plating, selective direct copper plating on palladium film on polyethylene naphthalate and palladium/nickel oxide composite film on glass was accomplished.

Spectroelectrochemistry of P700 in native photosystem I particles and diethyl ether-treated thylakoid membranes from spinach and Thermosynechococcus elongatus

The redox potentials (E ∘′) of P700 in intact and diethyl ether‐treated thylakoid membranes as well as native photosystem (PS) I particles from spinach and Thermosynechococcus elongatus have been measured by a spectroelectrochemistry with an error range of ±2–3 mV. Stepwise removal of antenna pigments by ether treatment caused distinct shifts of the E ∘′ value with increasing degree of water saturation in ether; negatively from +471 to +428 mV for spinach, but positively from +423 to +436 mV for T. elongatus. Such a contrasting behavior is discussed by invoking the mode of action of ether on the microenvironments around P700.

Unexpected Difference in the P700 Redox Potential Among Oxygenic Photosynthetic Organisms Revealed by Spectroelectrochemistry

The redox potential of the primary electron donor P700 of photosystem (PS) I has been determined for diverse organisms by spectroelectrochemistry with an optically transparent thin-layer electrochemical cell (OTTLE) to explore reasons for heavy scattering seen in the reported values of the P700 redox potential. The organisms submitted to examination were seven different organisms, four cyanobacteria including a primitive cyanobacteria Gloeobacter violaceus PCC7421, a red alga, a green algae and a higher plant. The P700 redox potential, determined within an error range of ±4 mV, showed a strong speciesdependence with a span over 70 mV. The causes for the strong species-dependence of the P700 redox potential are discussed in terms of the redox potentials of in vivo electron donors, cytochrome (cyt) c 6 and plastocyanin (PC).

Formation of Micrometer Scale Metal Structures on Glass by Selective Electroless Plating on Photopatterned Titanium and Copper Containing Films

A procedure for formation of catalytic SiO2 substrate adhesive layer patterns and selective electrochemical metal deposition on the catalyst images was investigated. A photoreactive solution containing a diazonaphthoquinone sulfonate ester and Ti and Cu complexes was developed to deposit Cu catalyst-TiO2 adhesive layer latent images on glass. Sub-micrometer/micrometer scale positive tone photoactive TiCu complex film patterns were formed using a conventional photolithography technique. The Cu ions in 40-50 nm thick Ti and Cu oxide layers formed by pyrolysis of the TiCu complex films were reduced, residual Cu displaced with Pd then the porous Ti oxide structure filled and plated with Cu by selective electroless then electrolytic plating. Annealing the Cu plating filled TiO2 layers on glass resulted in formation of a smooth Ti3+/Cu1+ oxide interface that enabled formation of 20 μm thick Cu deposits on glass substrate with up to 1 kN/m adhesion strength. The adhesion strength was attributed to chemical bonding of Ti3+ and Cu1+ oxides to the glass and Ti4+ oxide to the Cu plating that was formed upon annealing the Cu filled TiO2 interlayer. Furthermore, a dip coating procedure was adapted that allowed copper film deposition on the entire surface of a 300 μm thick glass substrate with 50 μm in diameter holes enabling formation of electrically conductive through glass substrate interconnects.

Sensitization of Light-Induced Charge Separation in Photosystem I by Synthetic Fluorescent Dyes

An attempt has been made to sensitize the photochemical process within photosystem (PS) I to green light using artificial fluorescent dyes. Rhodamine (Rh) derivatives, which exhibit intense light absorption for green light, were introduced to PS I surfaces as an additional light-harvesting antenna. To mimic the soluble extrinsic light- harvesting antenna such as phycobilisomes in cyanobacteria, XRh was introduced covalently to stroma and lumenal surfaces of PS I through an amide linkage. Further, an amphiphilic polymer bearing Rh6G moieties was complexed with the hydrophobic membrane integral regions of PS I. Under preferential excitation of the Rh derivatives, Rh-modified PS I exhibited a larger absorbance change attributed to the photooxidation of the primary electron donor P700 than that observed in native PS I. These results show that Rh derivatives function as artificial light-harvesting antennae to drive successfully PS I photochemistry by green light.

Biosyntheses of Chlorophyll a’ and Pheophytin a During Greening of Etiolated Barley Leaves

We detected two molecules of chlorophyll (Chl) a’ the C132-epimer of Chi a, in the vicinity of photosystem (PS) I reaction center (RC), P700, and suggested its possible involvement in the RC photochemistry [1]. If Chi a’ exists at the core part of the PS I RC complex, we could expect that biosynthesis of Chi a’ parallels the appearance of P700 activity during greening of etiolated leaves. However, biosyntheses of minor functional pigments such as Chi a’ and pheophytin (Pheo) a, the primary electron acceptor of PS II, have been largely unknown and their accumulation during greening has not been studied. Recently, our HPLC analysis showed that Chl a’ was biosynthesized during greening of etiolated leaves [2]. In this work, we examined the relationship between the biosynthesis of Chl a’ and accumulation of P700 during greening under two different conditions, namely the greening by continuous light (CL) and the CL greening after intermittent light (IML) growth (IML + CL). Normal-phase HPLC separation of C173 isoprenoid isomers, possible biosynthetic intermediates of Pheo a and Chl a’ is also briefly described.