Intrinsic carrier doping in antiferromagnetically interacted supramolecular copper complexes with (pyrazino)tetrathiafulvalene (pyra-TTF) as the ligand, [CuIICl2(pyra-TTF)] and (pyra-TTF)2[CuI3Cl4(pyra-TTF)

New supramolecular copper complexes with pyrazinotetrathiafulvalene (pyra-TTF) as the ligand, [Cu(II)Cl2(pyra-TTF)] (1) and (pyra-TTF) 2[Cu(I)3Cl4(pyra-TTF)] (2), have been synthesized by the diffusion method. Complex 1 is a black block crystal with a three-dimensional (3-D) supramolecular network; the linear chain [-Cu(II)Cl2-(pyra-TTF)-] n extends along the b axis, where the coordinated pyra-TTF donors are stacked in a head-to-tail and ring-over-bond configuration to construct two-dimensional (2-D) sheets, and between the sheets, there are C...Cl(-) or H...Cl(-) contacts. Even though the electron spin resonance (ESR) measurement reveals the nearly Cu(II) state, complex 1 is a semiconductor with sigmaRT=1.0 x 10(-4) S cm(-1) and Ea=0.33 eV. The high-frequency conductivity measurement also confirmed the intrinsic slight carrier doping from Cu(II) to the pyra-TTF donor. This slight doping enhances not only the real and imaginary dielectric constants but also the antiferromagnetic interaction between Cu(II) spins following the 2-D Heisenberg model with 2J=-20 K. In contrast, complex 2 is a very thin black needle. This needle crystal has two crystallographically independent pyra-TTF molecules, which are coordinated and noncoordinated donors. The coordinated donors composed a supramolecular chain [Cu(I)3Cl4(pyra-TTF)(0)]n , whereas the noncoordinated donors formed conducting alpha'-type pyra-TTF(+0.5) sheets. This complex is semiconducting with sigmaRT=0.1 S cm(-1) and Ea=0.15 eV. Both complexes 1 and 2 demonstrate that the pyra-TTF molecule works not only as an oxidized donor by Cu(II) to construct conducting sheets but also as a ligand coordinated to a Cu cation to form supramolecuar chains.     

Photoinduced hydrogen production by direct electron transfer from photosystem I cross-linked with cytochrome c3 to [NiFe]-hydrogenase

The photosynthetic reaction center is an efficient molecular device for the conversion of light energy to chemical energy. In a previous study, we synthesized the hydrogenase/photosystem I (PSI) complex, in which Ralstonia hydrogenase was linked to the cytoplasmic side of Synechocystis PSI, to modify PSI so that it photoproduced molecular hydrogen (H2). In that study, hydrogenase was fused with a PSI subunit, PsaE, and the resulting hydrogenase-PsaE fusion protein was self-assembled with PsaE-free PSI to give the hydrogenase/PSI complex. Although the hydrogenase/PSI complex served as a direct light-to-H2 conversion system in vitro, the activity was totally suppressed by adding physiological PSI partners, ferredoxin (Fd) and ferredoxin-NADP+-reductase (FNR). In the present study, to establish an H2 photoproduction system in which the activity is not interrupted by Fd and FNR, position 40 of PsaE from Synechocystis sp. PCC6803, corresponding to the Fd-binding site on PSI, was selected and targeted for the cross-linking with cytochrome c3 (cytc3) from Desulfovibrio vulgaris. The covalent adduct of cytc3 and PsaE was stoichiometrically assembled with PsaE-free PSI to form the cytc3/PSI complex. The NADPH production by the cytc3/PSI complex coupled with Fd and FNR decreased to approximately 20% of the original activity, whereas the H2 production by the cytc3/PSI complex coupled with hydrogenase from Desulfovibrio vulgaris was enhanced 7-fold. Consequently, in the simultaneous presence of hydrogenase, Fd, and FNR, the light-driven H2 production by the hydrogenase/cytc3/PSI complex was observed (0.30 pmol Hz/mg chlorophyll/h). These results suggest that the cytc3/PSI complex may produce H2 in vivo.     

Reversible Sodium Metal Electrodes: Is Fluorine an Essential Interphasial Component?

Alkaline metals are an ideal negative electrode for rechargeable batteries. Forming a fluorine‐rich interphase by a fluorinated electrolyte is recognized as key to utilizing lithium metal electrodes, and the same strategy is being applied to sodium metal electrodes. However, their reversible plating/stripping reactions have yet to be achieved. Herein, we report a contrary concept of fluorine‐free electrolytes for sodium metal batteries. A sodium tetraphenylborate/monoglyme electrolyte enables reversible sodium plating/stripping at an average Coulombic efficiency of 99.85 % over 300 cycles. Importantly, the interphase is composed mainly of carbon, oxygen, and sodium elements with a negligible presence of fluorine, but it has both high stability and extremely low resistance. This work suggests a new direction for stabilizing sodium metal electrodes via fluorine‐free interphases.     

Superionic Conduction in Co‐Vacant P2‐NaxCoO2 Created by Hydrogen Reductive Elimination

The layered P2‐Na_xMO₂ (M: transition metal) system has been widely recognized as electronic or mixed conductor. Here, we demonstrate that Co vacancies in P2‐Na_xCoO₂ created by hydrogen reductive elimination lead to an ionic conductivity of 0.045 S cm^?1 at 25 °C. Using in situ synchrotron X‐ray powder diffraction and Raman spectroscopy, the composition of the superionic conduction phase is evaluated to be Na_0.61(H₃O)_0.18Co_0.93O₂. Electromotive force measurements as well as molecular dynamics simulations indicate that the ion conducting species is proton rather than hydroxide ion. The fact that the Co‐stoichiometric compound Na_x(H₃O)_yCoO₂ does not exhibit any significant ionic conductivity proves that Co vacancies are essential for the occurrence of superionic conductivity.     

Five‐State Molecular Shuttling of a Pair of [2]Rotaxanes: Distinct Outputs in Response to Acid and Base Stimuli

In this study we synthesized two acid‐/base‐controllable [2]rotaxanes featuring aminodiazobenzene and aminocoumarin units, respectively, as chromophores and dibenzo[24]crown‐8 and dibenzo[25]crown‐8 units, respectively, as their macrocyclic components. Each [2]rotaxane contained N‐alkylarylamine (ammonium) and N,N‐dialkylamine (ammonium) centers as binding sites for their crown ether components. The absorption patterns of the chromophores were dependent on the position of the encircling macrocyclic component and the degree of protonation, with three distinct states (under acidic, neutral, and basic conditions) evident for each [2]rotaxane. The mixed [2]rotaxane system displayed stepwise and independent molecular shuttling behavior based on the degree of protonation of the amino groups in response to both the amount and strength of added acids or bases; as such, the system provided five different absorption signals as outputs that could be read using UV/Vis spectroscopy.     

Biosynthetic Conclusions from the Functional Dissection of Oxygenases for Biosynthesis of Actinorhodin and Related Streptomyces Antibiotics

1. Download : Download high-res image (332KB)
2. Download : Download full-size image

Highlights? ActVA-ORF5 is a flavin-dependent monooxygenase required for actinorhodin biosynthesis ? ActVA-ORF5 and its three close homologs were functionally dissected ? ActVA-ORF5 and Gra-21 are bifunctional at C-6/C-8, while Med-7 acts only for C-6 ? AlnT exhibits different regiospecificity for oxidation of tricyclic substrates     

LIGHT INDUCED FLUORESCENCE SPECTRAL CHANGES IN NATIVE PHYTOCHROME FROM Secale cereale L. AT LIQUID NITROGEN TEMPERATURE

Abstract— Fluorescence spectra of native rye phytochrome were determined under different light conditions at liquid nitrogen temperature. Fluorescence spectrum of the red-light-absorbing form (Pr) had a major peak at about 685 nm (14 600 cm⁻¹) and a broad sub-peak at about 515 nm (19 400 cm⁻¹). The peak height at 685 nm was reduced by irradiation with monochromatic light of 640 nm, and a new peak became obvious at about 702 nm (14250 cm⁻¹). This spectral change was almost completely reversed by subsequent irradiation with 700-nm light. Fluorescence spectrum of the photoequilibrium mixture of Pr and far-red-light absorbing form under continuous red light showed a sharp peak at about 685 nm having a peak height ca. 12% of Pr, and a broad sub-peak at about 508 nm (19 700 cm⁻¹). Light of 730 nm did not reduce the peak height at about 685 nm but induced a new shoulder at about 699 nm (14300 cm⁻¹). Monochromatic light of 640 and 700 nm given following the light of 730 nm could not reverse the spectral change at 699 nm induced by the irradiation with 730-nm light. Fluorescence spectrum of Pr in partially degraded phytochrome was similar to that in native phytochrome but the peak position in the red region was shifted by about 5 nm (100 cm⁻¹) to the blue.     

Hydrochlorothiazide Enhances UVA‐Induced DNA Damage

The UVA is currently thought to be carcinogenic because, similar to UVB, it induces the formation of cyclobutane pyrimidine dimers (CPDs). Various drugs have been reported to cause photosensitive drug eruptions as an adverse effect. Although the precise mechanism of photosensitive drug eruption remains to be elucidated, it is generally accepted that free radicals and other reactive molecules generated via UV‐irradiated drugs play important roles in the pathogenesis of photosensitive drug eruptions. The waveband of concern for photo‐reactive drugs is UVA‐visible light, but some extend into the UVB region. We tested whether photosensitive drugs could enhance CPD formation after UVA exposure by using isolated DNA in the presence of several reported photosensitive drugs using high‐performance liquid chromatography. We found that the diuretic agent hydrochlorothiazide (HCT) significantly enhanced the production of TT dimers over a wide range of UVA. Furthermore, we investigated whether UVA plus HCT could enhance CPD production in xeroderma pigmentosum model mice defective in nucleotide excision repair. Immunofluorescence studies showed that CPD formation in the skin significantly increased after 365 nm narrow‐band UVA irradiation in the presence of HCT, compared with that in wild‐type mice. HCT could be used with caution because of its enhancement of UVA‐induced DNA damage.     

Modern synthetic methods for fluorine-substituted target molecules

Fluorine has come to be recognized as a key element in materials science: in heat-transfer agents, liquid crystals, dyes, surfactants, plastics, elastomers, membranes, and other materials. Furthermore, many fluorine-containing biologically active agents are finding applications as pharmaceuticals and agrochemicals. Progress in synthetic fluorine chemistry has been critical to the development of these fields and has led to the invention of many novel fluorinated molecules as future drugs and materials. As a result of the electronic effects of fluorine substituents, fluorinated substrates and reagents often exhibit unusual and unique chemical properties, which often make them incompatible with established synthetic methods. Thus, the problem of how to control the unusual properties of compounds with fluorine substituents deserves much attention, so as to promote the design of facile, efficient, and environmentally benign methods for the synthesis of valuable organofluorine targets.     

Lactococcus lactis catalyses electricity generation at microbial fuel cell anodes via excretion of a soluble quinone

Lactococcus lactis is a gram-positive, normally homolactic fermenter that is known to produce several kinds of membrane associated quinones, which are able to mediate electron transfer to extracellular electron acceptors such as Fe³⁺, Cu²⁺ and hexacyanoferrate. Here we show that this bacterium is also capable of performing extracellular electron transfer to anodes by utilizing at least two soluble redox mediators, as suggested by the two-step catalytic current developed. One of these two mediators was herein suggested to be 2-amino-3-dicarboxy-1,4-naphthoquinone (ACNQ), via evaluation of standard redox potential, ability of the bacterium to exploit the quinone when exogenously provided, as well as by high performance liquid chromatography coupled with UV spectrum analysis. During electricity generation, L. lactis slightly deviated from its normal homolactic metabolism by excreting acetate and pyruvate in stoichiometric amounts with respect to the electrical current. In this metabolism, the anode takes on the role of electron sink for acetogenic fermentation. The finding that L. lactis self-catalyses anodic electron transfer by excretion of redox mediators is remarkable as the mechanisms of extracellular electron transfer by pure cultures of gram-positive bacteria had previously never been elucidated.