In this study, we improved the hydrogen production efficiency by combining photosystem I with an artificial light harvesting dye, Lumogen Red. In the reaction system, Lumogen Red allows light absorption and energy transfer to photosystem I by Förster resonance energy transfer; therefore, the Pt nanoparticles act as active sites for hydrogen generation.

25. J. M. Brown and C. A. Bunton, J. C. S. Chem. Comm., 969 (1974). 26. Y. Ihara, M. Nango and N. Kuroki, J. Org. Chem., 45, 5009 (1979). 27. Y. Kimura, A. Tanaka, M. Nango and N. Nuwki, J. Polym. Soc. Polym. Chem. Ed., 22, 407 (1984). 28. Y. Murakami, A. Nakano, A. Yoshimatsu and K. Fukuya,/. Am. Chem. Soc., 103, 728 (1981). 29. R. Andriamanampisoa, B. Boyer, G. Lamaty and J. P. Roque, J. C. S. Chem. Comm.f 597 (1986). 30. S. Sakaki, Y. Nakano and K. Ohkubo, Chem. Lett., 413 (1983). 31. D. Kippenberger, K. Rosenquist, L. Odberg, P. Tundo and J. H. Fendler,/ Am. Chem. Soc.f 1Q5, 1129(1983).

Photosynthesis is a process used by algae and plants to convert light energy into chemical energy. Due to their uniquely natural and environmentally friendly nature, photosynthetic proteins have attracted attention for use in a variety of artificial applications. Among the various types, biophotovoltaics based on dye-sensitized solar cells have been demonstrated in many studies. Although most related works have used n-type semiconductors, a p-type semiconductor is also a significant potential component for tandem cells. In this work, we used mesoporous NiO as a p-type semiconductor substrate for Photosystem I (PSI) and demonstrated a p-type PSI-biophotovoltaic and tandem cell based on dye-sensitized solar cells. Under visible light illumination, the PSI-adsorbed NiO electrode generated a cathodic photocurrent. The p-type biophotovoltaic cell using the PSI-adsorbed NiO electrode generated electricity, and the IPCE spectrum was consistent with the absorption spectrum of PSI. These results indicate that the PSI-adsorbed NiO electrode acts as a photocathode. Moreover, a tandem cell consisting of the PSI-NiO photocathode and a PSI-TiO2 photoanode showed a high open-circuit voltage of over 0.7 V under illumination to the TiO2 side. Thus, the tandem strategy can be utilized for biophotovoltaics, and the use of other biomaterials that match the solar spectrum will lead to further progress in photovoltaic performance.

To examine the applicability of fluorinated membrane-forming phospholipids to reconstitution matrices for functional membrane proteins, the membrane properties of a synthetic ether-type phosphatidylcholine (PC) bearing partially fluorinated C18-monoacetylenic (9-octadecynyl) chains, DF8CCH8PC, were compared with those of its non-fluorinated counterpart, DH8CCH8PC. Light-harvesting complex 2 (LH2) and the light-harvesting 1‒reaction center core complex (LH1-RC) isolated from purple photosynthetic bacteria were employed as probe membrane proteins to evaluate the extent to which their reconstitution into DF8CCH8PC membranes could proceed. DF8CCH8PC formed more expanded and more stable fluid monolayers than DH8CCH8PC at the air-water interface at 25 °C; the former PC molecule occupied an area of ca. 0.70 nm2 at a collapse pressure, πc, of 52 mN/m, while the latter occupied an area of ca. 0.55 nm2 at a πc of 45 mN/m. In contrast, the molecular motion detected using fluorescent probes was much more restricted in DF8CCH8PC bilayers than in DH8CCH8PC ones. Although the reconstitution efficiencies of both LH2 and LH1-RC into DF8CCH8PC bilayers were lower than those into DH8CCH8PC bilayers, the membrane proteins incorporated into DF8CCH8PC bilayers showed increased thermostability. The increased thermostability of these proteins in fluorinated PC membranes might be due to the restricted molecular motion in the hydrophobic chains. The results of this study suggest that partially fluorinated PCs can be useful materials for the construction of lipid‒functional membrane protein assemblies including large membrane protein complexes, such as LH1-RC, for biotechnological applications.

Light-harvesting complex of photosystem II (LHCII) is the most abundant membrane protein-chlorophyll complex in chloroplasts. Here, we evaluated the photocatalytic activity of the native trimer and the enzymatically treated monomer forms of LHCII. Upon white light irradiation using a solar simulator, photocatalytic reduction of methylviologen revealed that the activity of monomeric LHCII was higher than that of the trimer form. Fluorescence of the monomeric LHCII was more significantly quenched by methylviologen than that of the trimer form. In the presence of Pt nanoparticles in a catalytic solution system, photoinduced hydrogen production was observed for the LHCII monomer. The difference in photocatalytic activities of LHCII trimer and monomer are briefly discussed in terms of an interaction between LHCII and methylviologen.

With the aim of understanding the excitation energy transfer mechanism in natural photosynthetic membranes, light-harvesting (LH)2 and LH1-reaction center, which are pigment-protein complexes separated from Rhodobacter sphaeroides, were aligned on a planar electrode surface in stripe patterns at 5 urn intervals. Observation of the absorption spectrum and fluorescence microphotographs revealed selective immobilization and conservation of the pigments. Photocurrent signals were obtained when the electrode was illuminated at either 880 or 800 nm. The fabricated structure was confirmed to function as a natural photosynthetic membrane with the highest photocurrent signal being obtained when using a co-immobilized substrate under excitation at 800 nm.

In this study, we demonstrated the conversion of CO2 to formic acid under ambient conditions in a photoreduction nanoporous reactor using a photosensitizer, methyl viologen (MV2+), and formate dehydrogenase (FDH). The overall efficiency of this reactor was 14 times higher than that of the equivalent solution. The accumulation rate of formic acid in the nanopores of 50 nm is 83 times faster than that in the equivalent solution. Thus, this CO2 photoreduction nanoporous glass reactor will be useful as an artificial photosynthesis system that converts CO2 to fuel.

Photosynthetic light-harvesting polypeptide/pigment complexes (LH) play an essential role in the primary process of an efficient solar energy-transduction in photosynthetic membrane. In our research, we aim to use the LH complex and control its direction and orientation on electrodes for the development of nanobiodevices from solar to fuel. Specifically, we focus on the construction of an array of the LH on electrodes using a modified photosynthetic protein complex prepared from modern biosynthetic manufacturing methods and in lipid membranes.

To develop efficient systems for light-energy conversion, monomeric and dimeric zinc chlorin derivatives were synthesized. These derivatives act as photosensitizers for light-induced hydrogen production with methylviologen as the electron mediator and Pt nanoparticles as the hydrogen-evolution catalyst. The monomeric derivative exhibited ~1.5-times higher activity than the dimeric derivative. The photocurrent-generating activity of the Zn chlorin derivatives assembled on a chemically modified indium tin oxide electrode was investigated; the dimeric derivative exhibited significant activity compared to the monomeric derivative. The photosensitizing activity of the derivatives in dye-sensitized solar cells was also investigated. The dimeric derivative exhibited two-fold higher performance than the monomeric derivative. The dimerization effect on the photosensitizing activities is briefly discussed in terms of stacking conformations based on the results of absorption and fluorescence spectroscopies.

Morphology of dipalmitoyl phosphatidyl choline (DPPC)-cholesterol (Chol) mixed monolayer formed on water surface by dropping method was investigated using surface tension measurement (STm), Brewster angle microscopy (BAM), and fluorescence microscopy (FM). STm showed strong condensation effect of Chol in fluidic DPPC monolayer. Excess area (Sex) from mean mixing state of DPPC and Chol was about twice larger than that by general compression method in the range from xC = 0.2 to 0.4 (xC: mole fraction of Chol). BAM and FM images showed clearly that the fluidic DPPC monolayer changed to condensed rigid monolayer due to the condensation effect of Chol. At more than xC = 0.3 DPPC-Chol mixed monolayer changed to condensed state similar to the Chol monolayer. These results support previous reports by compression method that Chol molecule demonstrates the strong condensation effect to the fluidic monolayer and also indicate that dropping method enables to form unique monolayer on the water surface.

In recent years, a number of light-induced hydrogen production systems composed of photosystem I (PSI) and hydrogen production catalysts (e.g. hydrogenases and Pt nanoparticles) have been reported. However, the utility of these systems under aerobic conditions is limited due to their poor stability in the presence of oxygen. The development of light-induced hydrogen production systems that work under aerobic conditions is, therefore, of great importance to establish artificial photosynthetic devices. Ideally, these systems should utilise water as an electron source, via water splitting by photosystem II (PSII). We report the construction of a novel light-induced hydrogen production system composed of PSI-platinum nanoparticle conjugates and cytochrome c (6) (cyt c (6)) immobilised in nanoporous glass plates (PGP50, 50-nm pore diameter). PSI trimer (PSIt) from Thermosynechococcus elongatus and Pt nanoparticles (PtNPs) were conjugated via electrostatic interactions (PSIt-PtNP). PSIt-PtNP and cyt c (6) were spontaneously absorbed in nanopores of PGP50 without denaturation. Upon irradiation in the presence of ascorbate as a sacrificial electron donor, catalytic H-2 evolution was observed for PSIt-PtNP immobilised in the pores of PGP50 (PSIt-PtNP/PGP50) under both anaerobic and aerobic conditions, indicating that an effective photoinduced electron transfer system had been established. PSIt-PtNP/PGP50 was found to exhibit improved oxygen resistivity over the homogeneous solution system consisting of PSIt-PtNP, cyt c (6), and ascorbate, suggesting that the PSIt-PtNP/PGP50 system could be a potential candidate for artificial photosynthetic systems. The distribution of the components, PSIt-PtNP and cyt c (6), in PGP50 was characterised to discuss the efficiency of light-induced hydrogen production.

The development of artificial photosynthesis has focused on the efficient coupling of reaction at photoanode and cathode, wherein the production of hydrogen (or energy carriers) is coupled to the electrons derived from water-splitting reactions. The natural photosystem II (PSII) complex splits water efficiently using light energy. The PSII complex is a large pigment-protein complex (20 nm in diameter) containing a manganese cluster. A new photoanodic device was constructed incorporating stable PSII purified from a cyanobacterium Thermosynechococcus vulcanus through immobilization within 20 or 50 nm nanopores contained in porous glass plates (PGPs). PSII in the nanopores retained its native structure and high photoinduced water splitting activity. The photocatalytic rate (turnover frequency) of PSII in PGP was enhanced 11-fold compared to that in solution, yielding a rate of 50-300 mol e(-)/(mol PSII·s) with 2,6-dichloroindophenol (DCIP) as an electron acceptor. The PGP system realized high local concentrations of PSII and DCIP to enhance the collisional reactions in nanotubes with low disturbance of light penetration. The system allows direct visualization/determination of the reaction inside the nanotubes, which contributes to optimize the local reaction condition. The PSII/PGP device will substantively contribute to the construction of artificial photosynthesis using water as the ultimate electron source.

Introducing appropriate artificial components into natural biological systems could enrich the original functionality. To expand the available wavelength range of photosynthetic bacterial light-harvesting complex 2 (LH2 from Rhodopseudomonas acidophila 10050), artificial fluorescent dye (Alexa Fluor 647: A647) was covalently attached to N- and C-terminal Lys residues in LH2 α-polypeptides with a molar ratio of A647/LH2 ≃ 9/1. Fluorescence and transient absorption spectroscopies revealed that intracomplex energy transfer from A647 to intrinsic chromophores of LH2 (B850) occurs in a multiexponential manner, with time constants varying from 440 fs to 23 ps through direct and B800-mediated indirect pathways. Kinetic analyses suggested that B800 chromophores mediate faster energy transfer, and the mechanism was interpretable in terms of Förster theory. This study demonstrates that a simple attachment of external chromophores with a flexible linkage can enhance the light harvesting activity of LH2 without affecting inherent functions of energy transfer, and can achieve energy transfer in the subpicosecond range. Addition of external chromophores, thus, represents a useful methodology for construction of advanced hybrid light-harvesting systems that afford solar energy in the broad spectrum.

Zinc chlorophyll a derivatives were synthesised for use as photosensitizers. Herein, we report a system for photoinduced hydrogen production with colloidal platinum via photoreduction of methylviologen (MV2+) using the photosensitization of a Zn pyropheophorbide a (ZnPyOH) dimer connected by lysine (ZnPy-K(ZnPy)OH) as a special pair model in the photosynthetic reaction centre in the presence of NADPH as an electron donor.

•Artificial Hybrid photosynthetic membranes were constructed by introducing both LH2 complexes (from Rps. acidophila) and LH1-RC core complexes (from Blc. viridis) to a lipid bilayer system composed of Egg PC.•The architecture of the artificial photosynthetic membranes can be varied by controlling the ratio of added LH2 to LH1-RC core complexes.•The local arrangement of the pigment–protein complexes has been investigated using high-resolution atomic force microscopy.•LH2 to LH1 energy transfer was studied using confocal laser fluorescence microscopy with 400nm spatial resolutions.•A difference in the ratio of the fluorescence intensity emitted from LH2 and LH1 was found depending on the local arrangement of the antenna complexes in the hybrid artificial photosynthetic membranes.

Absorption and Raman spectra of spheroidene dissolved in various organic solvents and bound to peripheral light-harvesting LH2 complexes from photosynthetic purple bacteria Rhodobacter (Rba.) sphaeroides 2.4.1 were measured. The results showed that the peak energies of absorption and C–C and C=C stretching Raman lines are linearly proportional to the polarizability of solvents, as has already been reported. When comparing these results with those measured on LH2 complexes, it was confirmed that spheroidene is surrounded by a media with high polarizability. However, the change in the spectral width of the Raman lines, which reflect vibrational decay time, cannot be explained simply by a similar dependence of solvent polarizability. The experimental results were analyzed using a potential theoretical model. Consequently, a systematic change in the Raman line widths in the ground state can be satisfactorily explained as a function of the viscosity of the surrounding media. Even when the absorption peaks appear at the same energy, the vibrational decay time of spheroidene in the LH2 complexes is approximately 15–20 % slower than that in organic solvents.

Lipid nanoparticles (LNP) modified with cell-penetrating peptides (CPP) were prepared for the delivery of small interfering RNA (siRNA) into cells. Lipid derivatives of CPP derived from protamine were newly synthesized and used to prepare CPP-decorated LNP (CPP-LNP). Encapsulation of siRNA into CPP-LNP improved the stability of the siRNA in serum. Fluorescence-labeled siRNA formulated in CPP-LNP was efficiently internalized into B16F10 murine melanoma cells in a time-dependent manner, although that in LNP without CPP was hardly internalized into these cells. In cells transfected with siRNA in CPP-LNP, most of the siRNA was distributed in the cytoplasm of these cells and did not localize in the lysosomes. Analysis of the endocytotic pathway indicated that CPP-LNP were mainly internalized via macropinocytosis and heparan sulfate-mediated endocytosis. CPP-LNP encapsulating siRNA effectively induced RNA interference-mediated silencing of reporter genes in B16F10 cells expressing luciferase and in HT1080 human fibrosarcoma cells expressing enhanced green fluorescent protein. These data suggest that modification of LNP with the protamine-derived CPP was effective to facilitate internalization of siRNA in the cytoplasm and thereby to enhance gene silencing.

Photosystems, PSI and PSII isolated from Thermosynechococcus elongatus were successfully immobilized on a TiO2 nanostructured film for use in dye-sensitized biosolar cells (DSBCs). The photosystem complexes were also immobilized on an ITO electrode modified with 3-aminopropyltriethoxysilane by utilizing the interactions between the electrode and the surface of the PSI or PSII polypeptide. Illumination of the PSI and PSII complexes immobilized on the ITO electrode resulted in action spectra in the presence of methyl viologen, which corresponded to the absorption spectra of the complexes. Compared with the ITO electrode, PSI or PSII complexes assembled on the TiO2 electrode had much higher energy-conversion efficiency in the presence of an iodide/triiodide redox system of an ionic-liquid-based electrolyte. This could have interesting applications in the development of DSBCs.

PTEN-positive tumors are not susceptible to the treatment with rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR). Here, we determined the susceptibility of PTEN-positive cells to small interfering RNA for mTOR (si-mTOR) by using a novel liposomal delivery system. We prepared dicetyl phosphate-tetraethylenepentamine-based polycation liposomes (TEPA-PCL) decorated with polyethylene glycol (PEG) grafting Ala-Pro-Arg-Pro-Gly (APRPG), a VRGFR-1-targeting peptide. APRPG-PEG-decorated TEPA-PCL carrying si-mTOR (APRPG-TEPA-PCL/si-mTOR) had an antiproliferative effect against B16F10 murine melanoma cells (PTEN-positive) and significantly inhibited both the proliferation and tube formation of mouse 2H-11 endothelial-like cells (PTEN-positive). APRPG-TEPA-PCL/si-mTOR treatment did not induce Akt phosphorylation (Ser473) in either B16F10 or 2H-11 cells although there was strong phosphorylation of Akt in response to rapamycin treatment. Intravenous injection of APRPG-TEPA-PCL/si-mTOR significantly suppressed the tumor growth compared with rapamycin treatment in mice bearing B16F10 melanoma. These findings suggest that APRPG-TEPA-PCL/si-mTOR is useful for the treatment of PTEN-positive tumors.