Aurophilic Interactions in Multi-Radical Species: Electronic-Spin and Redox Properties of Bis- and Tris-[(Nitronyl Nitroxide)-Gold(I)] Complexes with Phosphine-Ligand Scaffolds.

Multinuclear Au complexes with two or three nitronyl nitroxide-2-ide radical anion and phosphine-ligand scaffolds, (NN-Au) -1 o, (NN-Au) -1 m, and (NN-Au) -1 p, have been synthesized to investigate the influence of Au -Au (aurophilic) interactions on the properties of multispin molecular systems. The desired complexes were successfully prepared in moderate yields in a one-pot synthesis from the corresponding phosphine ligand, Au source, parent NN, and sodium hydroxide. Among the prepared complexes, (NN-Au) -1 o, in which an aurophilic interaction was clearly observed by crystal structure analysis, showed characteristic spin-spin interactions, electrochemical properties, and solvatochromic behavior.

Formation of Single Double-Layered Coacervate of Poly(-diethylacrylamide) in Water by a Laser Tweezer.

We demonstrate liquid-liquid phase separation involving both coacervation and coil-to-globule phase transition of a thermoresponsive polymer. By focusing a near-infrared laser beam into an aqueous solution of poly(-isopropylacrylamide) (PNIPAM), a single phase-separated polymer microdroplet can be formed and stably trapped at the focal point. Such droplet formation is induced by a local elevation in temperature (induced by a photothermal effect) and an optical force.

Syntheses and Properties of (Nitronyl nitroxide)-substituted Tri-phenylamine ortho-Bridged by Two Oxygen and Sulfur Atoms.

A nitronyl nitroxide unit (NN) was linked with a triphenylamine-based condensed polycyclic skeleton DOTT to form a radical substituted donor NN-DOTT. X-ray crystal structure analysis demonstrated a flat bowl shape of the DOTT unit. EPR spectra showed the localization of electron spin on the NN unit.

Condensed Phenoxazine Dimer and Its Radical Cation.

A condensed phenoxazine dimer was synthesized and characterized. X-ray crystallographic analysis of the dimer shows a double-butterfly structure, in which the nitrogen atoms are located above and below the molecular plane. A radical cation salt of the dimer was obtained using tris(4-bromophenyl)aminium hexafluoroantimonate as the oxidant.

Spectral tuning mediated by helix III in butterfly long wavelength-sensitive visual opsins revealed by heterologous action spectroscopy.

Absorption spectra of opsin-based pigments are tuned from the UV to the red regions by interactions of the chromophore with surrounding amino acid residues. Both vertebrates and invertebrates possess long-wavelength-sensitive (LWS) opsins, which underlie color vision involving "red" sensing. The LWS opsins have independently evolved in each lineage, which suggests the existence of diverse mechanisms in spectral tuning.

TiO N /TiO Photocatalyst for Hydrogen Evolution under Visible Light Irradiation II Degradation of Photocatalytic Activity of TiO N /TiO with Mild Oxidation.

We have studied degradation of photocatalytic activity of TiO N for water splitting under visible light irradiation with heat treatment in O/N mixed gas. The reduction of the N content by oxidation through the formation of O-N-O species (NO ) was confirmed as the result of the reduction of the catalytic activity. The catalytic activity is not simply related to the amount of N remained but that of N taking the chemical state of O-Ti-N in TiO N , which is the active species for visible light responsiveness on hydrogen evolution.

TiO N /TiO Photocatalyst for Hydrogen Evolution under Visible-Light Irradiation. I: Characterization of N in TiO N /TiO Photocatalyst.

TiO N /TiO was synthesized by nitriding of TiO in NH gas. TiO N /TiO generated hydrogen from methanol aqueous solution under visible-light irradiation. It was revealed by N K-edge XANES and N 1s XPS measurements that the N species contributing to visible-light responsiveness was the O-Ti-N species.

Synthesis and Properties of Nitrogen-Containing Pyrenes.

We developed a short-step synthesis of 2,4,10-triazapyrenes involving two sequential C-H substitutions: Pd-catalyzed cross-coupling reactions via C-H arylation followed by intramolecular Cu-catalyzed C-H functionalization. This method was successfully applied to the preparation of 4,10-diaza-, 1,4,10-triaza-, and 1,3,4,10-tetraazapyrenes. Crystal structure analysis of 5,9-di(4-methylphenyl)-2,4,10-triazapyrene showed that planar triazapyrene cores have π-stack packing.

Synthesis and Magnetic Properties of (Pyrrolidin-1-oxyl)-(Nitronyl Nitroxide)/(Iminonitroxide)-Dyads.

Unlike extensively studied diradicals linked by π-conjugated systems, only a few studies have investigated weakly coupled diradicals linked by an sp carbon atom. Herein, we prepared pyrrolidin-1-oxyl-(nitronyl nitroxide)-dyad 5 and pyrrolidin-1-oxyl-iminonitroxide-dyad 6. From the observed temperature dependence of the magnetic susceptibility, 5 and 6 were determined to be in singlet ground states with 2J /k =-35.

Color opponency with a single kind of bistable opsin in the zebrafish pineal organ.

Lower vertebrate pineal organs discriminate UV and visible light. Such color discrimination is typically considered to arise from antagonism between two or more spectrally distinct opsins, as, e.g.

Preparation and Properties of a Polycyclic p-Quinodimethane with Two Oxygen Bridges and its Radical Cation in Comparison with the Isomeric o-Quinodimethane.

We prepared an electron-rich p-quinodimethane compound, 2,9-dibromo-7,14-dimesityl-5,12-dioxapentacene (1). The quinoidal character was clarified by bond-length alternation in the central ring. Clear vibrational structures in both absorption and emission bands and small Stokes shift indicate the rigid dioxapentacene framework.

Ligand-Binding Ability of a Porphyrin Core in a Dendrimer with Rigid Branched Terminal Components.

A dendrimer with rigid branched terminal components was prepared by a copper-catalyzed Hüisgen 1,3-dipolar cycloaddition reaction. A zinc 5,15-diethynyl-10,20-bis(3,5-di- tert-butylphenyl)porphyrin unit was incorporated at the core of the dendrimer as a receptor site for an added pyridyl ligand. The appearance of an absorption band characteristic of the planar conformer of conjugated chains in the terminal components suggested that the dendrimer adopts a folded higher order structure in dichloromethane at 25 °C.

(Azulene-1,3-diyl)-bis(nitronyl nitroxide) and (Azulene-1,3-diyl)-bis(iminonitroxide) and Their Copper Complexes.

In contrast to diradicals connected by alternant hydrocarbons, only a few studies on those connected by nonalternant hydrocarbons have been reported. The syntheses, structures, and magnetic properties of azulene-1,3-diyl linked bis(nitronyl nitroxide) (NN Az) and bis(iminonitroxide) (IN Az) diradicals and their Cu(hfac) (hfac=hexafluoroacetylacetonate) complexes were investigated. NN Az was shown to have an intramolecular ferromagnetic interaction with J /k =+10.

Carotenoids and Photosynthesis.

Carotenoids are ubiquitous and essential pigments in photosynthesis. They absorb in the blue-green region of the solar spectrum and transfer the absorbed energy to (bacterio-)chlorophylls, and so expand the wavelength range of light that is able to drive photosynthesis. This is an example of singlet-singlet energy transfer, and so carotenoids serve to enhance the overall efficiency of photosynthetic light reactions.

Fuzzy nanostructure growth on Ta/Fe by He plasma irradiation.

In this study, we show from helium (He) plasma irradiation to tantalum and iron surfaces that morphology changes in nanoscale occur on the both metals. In particular, from systematic irradiation experiments, it is identified that fuzzy nanostructures are grown on the both metals. The necessary conditions for the morphology changes are discussed based on the experimental results in terms of the helium migration, the physical sputtering, and the shear modulus of materials.

Novel Features of Eukaryotic Photosystem II Revealed by Its Crystal Structure Analysis from a Red Alga.

Photosystem II (PSII) catalyzes light-induced water splitting, leading to the evolution of molecular oxygen indispensible for life on the earth. The crystal structure of PSII from cyanobacteria has been solved at an atomic level, but the structure of eukaryotic PSII has not been analyzed. Because eukaryotic PSII possesses additional subunits not found in cyanobacterial PSII, it is important to solve the structure of eukaryotic PSII to elucidate their detailed functions, as well as evolutionary relationships.

Photoprotection vs. Photoinhibition of Photosystem II in Transplastomic Lettuce (Lactuca sativa) Dominantly Accumulating Astaxanthin.

Transplastomic (chloroplast genome-modified; CGM) lettuce that dominantly accumulates astaxanthin grows similarly to a non-transgenic control with almost no accumulation of naturally occurring photosynthetic carotenoids. In this study, we evaluated the activity and assembly of PSII in CGM lettuce. The maximum quantum yield of PSII in CGM lettuce was <0.

An endogenous protein inhibitor, YjhX (TopAI), for topoisomerase I from Escherichia coli.

Almost all free-living bacteria contain toxin-antitoxin (TA) systems on their genomes and the targets of toxins are highly diverse. Here, we found a novel, previously unidentified TA system in Escherichia coli named yjhX-yjhQ. Induction of YjhX (85 amino acid residues) causes cell-growth arrest resulting in cell death, while YjhQ (181 residues) co-induction resumes cell growth.

Stark absorption spectroscopy on the carotenoids bound to B800-820 and B800-850 type LH2 complexes from a purple photosynthetic bacterium, Phaeospirillum molischianum strain DSM120.

Stark absorption spectroscopy was applied to clarify the structural differences between carotenoids bound to the B800-820 and B800-850 LH2 complexes from a purple photosynthetic bacterium Phaeospirillum (Phs.) molischianum DSM120. The former complex is produced when the bacteria are grown under stressed conditions of low temperature and dim light.

Ultrafast time-resolved vibrational spectroscopies of carotenoids in photosynthesis.

This review discusses the application of time-resolved vibrational spectroscopies to the studies of carotenoids in photosynthesis. The focus is on the ultrafast time regime and the study of photophysics and photochemistry of carotenoids by femtosecond time-resolved stimulated Raman and four-wave mixing spectroscopies. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.

Elucidation and Control of an Intramolecular Charge Transfer Property of Fucoxanthin by a Modification of Its Polyene Chain Length.

Fucoxanthin is an essential pigment for the highly efficient light-harvesting function of marine algal photosynthesis. It exhibits excited state properties attributed to intramolecular charge transfer (ICT) in polar environments due to the presence of the carbonyl group in its polyene backbone. This report describes the excited state properties of fucoxanthin homologues with four to eight conjugated double bonds in various solvents using the femtosecond pump-probe technique.

Ultrafast intramolecular relaxation dynamics of Mg- and Zn-bacteriochlorophyll a.

Ultrafast excited-state dynamics of the photosynthetic pigment (Mg-)bacteriochlorophyll a and its Zn-substituted form were investigated by steady-state absorption∕fluorescence and femtosecond pump-probe spectroscopic measurements. The obtained steady-state absorption and fluorescence spectra of bacteriochlorophyll a in solution showed that the central metal compound significantly affects the energy of the Qx state, but has almost no effect on the Qy state. Photo-induced absorption spectra were recorded upon excitation of Mg- and Zn-bacteriochlorophyll a into either their Qx or Qy state.

Excitation Energy-Transfer Dynamics of Brown Algal Photosynthetic Antennas.

Fucoxanthin-chlorophyll-a/c protein (FCP) complexes from brown algae Cladosiphon okamuranus TOKIDA (Okinawa Mozuku in Japanese) contain the only species of carbonyl carotenoid, fucoxanthin, which exhibits spectral characteristics attributed to an intramolecular charge-transfer (ICT) property that arises in polar environments due to the presence of the carbonyl group in its polyene backbone. Here, we investigated the role of the ICT property of fucoxanthin in ultrafast energy transfer to chlorophyll-a/c in brown algal photosynthesis using femtosecond pump-probe spectroscopic measurements. The observed excited-state dynamics show that the ICT character of fucoxanthin in FCP extends its absorption band to longer wavelengths and enhances its electronic interaction with chlorophyll-a molecules, leading to efficient energy transfer from fucoxanthin to chlorophyll-a.