Highly Efficient and Stable Molecular-Based TiO₂ Photoanodes for Photoelectrochemical Water Splitting Achieved by Pyridyl Anchoring Technique

Photoelectrochemical overall water splitting by semiconductor electrodes modified with functional molecules has attracted considerable attention in recent years. Various kinds of molecular-based photoanodes consisting of a semiconductor thin film modified with both a photosensitizer (PS) and a water oxidation catalyst (WOC) have been developed thus far, and overall water splitting is achieved by using such a molecular-based photoanode and a Pt cathode. Nevertheless, due to the desorption of a PS and/or a WOC from the semiconductor surfaces, almost all the reported molecular-based photoanodes lose their photoelectrocatalytic activity within an hour. Thus, there is a strong demand to greatly improve the long-term stability of the molecular-based photoanodes toward practical applications. Here, we demonstrate the effectiveness of the “pyridyl anchoring technique” developed by us, leading to the long-term stability of our molecular-based photoanodes owing to the high strength of the Ti–N (pyridyl) bonding. A molecular-based TiO2 photoanode modified with both a polypyridyl ruthenium PS, [Ru(dpbpy)2(qpy)]2+ (dpbpy = 4,4′-diphenyl-2,2′-bipyridine, qpy = 4,4′:2′,2″:4″,4‴-quaterpyridine) (Ru-qpy), and a Ru(bda)-type WOC, Ru(bda)(4,4′-bpy)2 (bda = 2,2′-bipyridine-6,6′-dicarboxylic acid, 4,4′-bpy = 4,4′-bipyridine) (Ru(bda)-py) by our technique promotes water oxidation with an almost quantitative Faradaic efficiency (94 ± 6%) at the applied potential of 0.05 V versus SCE over 3 h under solar light irradiation (λ > 410 nm). Moreover, a photoelectrochemical cell (PEC) consisting of this molecular-based photoanode and a Pt cathode promotes overall water splitting only by giving an extra bias of 0.4 V. Our PEC achieves the second highest solar-to-hydrogen (STH) conversion efficiency (0.07%) among such applied bias-compensating PECs, successfully demonstrating the usefulness of the stable anchoring of molecular components in order to fabricate highly efficient PECs for solar water splitting

Synthesis of the MN Ring of Caribbean Ciguatoxin C‑CTX‑1 via Desymmetrization by Acetal Formation

The MN ring of Caribbean ciguatoxin C-CTX-1 was synthesized from a meso-syn-2,7-dimethyloxepane derivative corresponding to the M ring via desymmetrization by acetal formation with a camphor derivative, followed by construction of the N ring via the Horner–Wadsworth–Emmons reaction and acetal formation. The meso-syn-2,7-dimethyloxepane derivative was synthesized via photoinduced electrocyclization of a conjugated exo-diene under flow conditions, giving a cyclobutene derivative, followed by ring expansion via oxidative cleavage and diastereoselective reduction of a β-hydroxy ketone

Heterobimetallic Coordination Polymers Based on the [Pt(SCN)₄]^2– and [Pt(SeCN)₄]^2– Building Blocks

New complexes and the first coordination polymers containing [Pt­(SCN)₄]^2– of the type [M­(L)_<i>x</i>]­[Pt­(SCN)₄] (where L = 2,2′-bipyridine (bipy), <i>x</i> = 2, M = Co­(II), Ni­(II), Cu­(II); L = ethylenediamine (en), <i>x</i> = 2, M = Ni­(II), Cu­(II); L = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine (tmeda), <i>x</i> = 1, M = Cu­(II); L = 2,2′;6′,2″-terpyridine (terpy), <i>x</i> = 1, M = Mn­(II), Co­(II); L = 1,10-phenanthroline (phen), <i>x</i> = 2, M = Pb­(II)) were prepared by reacting the appropriate metal–ligand cations with K₂[Pt­(SCN)₄] and structurally characterized. [M­(bipy)₂Pt­(SCN)₄]₂·2MeOH (M = Co (<b>1</b>), Cu (<b>4</b>)) consist of supramolecular tetranuclear distorted squares containing two [M­(bipy)₂]²⁺ and two [Pt­(SCN)₄]²⁺ units. [Cu­(bipy)₂(NCS)]₂[Pt­(SCN)₄] (<b>6</b>) is a double salt of the [Pt­(SCN)₄]^2– anion and two [Cu­(bipy)­(NCS)]⁺ cations. [Cu­(en)₂Pt­(SCN)₄] (<b>7</b>, <b>8</b>) are 1-D coordination polymers that are coordinated in either cis or trans fashion at the [Pt­(SCN)₄]^2– unit, for <b>7</b> and <b>8</b>, respectively. Complexes [Cu­(en)₂Pt­(SeCN)₄] (<b>9</b>) and [Ni­(en)₂Pt­(SCN)₄] (<b>10</b>) are similar to <b>8</b> and <b>7</b>, respectively, but complex <b>9</b> (prepared using (ⁿBu₄N)₂[Pt­(SeCN)₄]) also presents intermolecular Se–Se interactions which resulted in an increased dimensionality. Compounds [M­(terpy)­Pt­(SCN)₄] (M = Mn (<b>11</b>), Co (<b>13</b>)) involve 2-D sheets of [M­(terpy)]²⁺ and [Pt­(SCN)₄]^2– units, whereas [Mn­(terpy)₂]­[Pt­(SCN)₄] (<b>12</b>) is a double salt of one [Mn­(terpy)₂]²⁺ unit and one [Pt­(SCN)₄]^2–. [Cu­(tmeda)­Pt­(SCN)₄] (<b>14</b>) contains a five-coordinate Cu²⁺ metal center coordinated to one tmeda ligand and three different [Pt­(SCN)₄]^2– units, resulting in 2-D sheets. [Pb­(phen)₂Pt­(SCN)₄] (<b>15</b>) contains an 8-coordinate Pb²⁺ metal center coordinated to two phen ligands and four [Pt­(SCN)₄]^2–, generating a 3-D network in the solid state. Structural correlations were established between the ancillary ligand, the choice of metal, the structure of the [Pt­(SCN)₄]^2– building block, and the resulting dimensionality of the coordination polymers

Synthesis and Structure Revision of the C43–C67 Part of Amphidinol 3

Stereoselective synthesis of the C43–C67 part of amphidinol 3 (AM3) and its C51-epimer was achieved starting from a common intermediate corresponding to the tetrahydropyran moiety of AM3, via asymmetric oxidations and Julia–Kocienski olefination. By comparing NMR data of the synthetic specimens with those of AM3, the absolute configuration at C51 of AM3 was revised from <i>R</i> to <i>S</i>

Prognostic value of the 7-year protocol biopsy of adult kidney allografts: impact of mesangiosclerosis and proteinuria

The aim of the present study was to clarify the relationship between the Banff score of the 7-year protocol biopsy and the allograft outcome. One-hundred-and-eighty-four patients received kidney transplantation from 2002 to 2008. We excluded patients aged n = 24), those who did not undergo a 7-year protocol biopsy (n = 66), and those who underwent for-cause biopsy (n = 5). Consequently, 89 patients who underwent a 7-year protocol biopsy were enrolled. We analyzed the relationship between the clinicopathological findings 7 years after transplantation and the estimated glomerular filtration rate (eGFR) change per year and allograft survival. Histological evaluation was performed using the Banff 2015 classification. Among the clinicopathological findings, each Banff mesangial matrix increase (mm) score ≥1 and proteinuria ≥1+ was independently associated with the eGFR decline per year during a median follow-up of 73 months. Furthermore, in the model of the clinicopathological findings including the presence of mm with proteinuria, mm ≥1 alone and mm ≥1 with proteinuria were each independently associated with the eGFR decline. The graft survival was significantly worse for those with mm ≥1 with proteinuria than those with mm ≥1 without proteinuria. Among the 7-year protocol biopsy findings, the presence of mm alone and mm with proteinuria were each significant predictors of eGFR decline. The presence of both proteinuria and mm had a negative impact on graft survival. These results underscore the significance of the Banff mm score and proteinuria at the time of the 7-year protocol biopsy to predict the allograft outcome.</p

Tuning of Redox Potentials by Introducing a Cyclometalated Bond to Bis-tridentate Ruthenium(II) Complexes Bearing Bis(<i>N</i>-methylbenzimidazolyl)benzene or -pyridine Ligands

A series of asymmetrical bis-tridentate cyclometalated complexes including [Ru­(Mebib)­(Mebip)]⁺, [Ru­(Mebip)­(dpb)]⁺, [Ru­(Mebip)­(Medpb)]⁺, and [Ru­(Mebib)­(tpy)]⁺ and two bis-tridentate noncyclometalated complexes [Ru­(Mebip)₂]²⁺ and [Ru­(Mebip)­(tpy)]²⁺ were prepared and characterized, where Mebib is bis­(<i>N</i>-methylbenzimidazolyl)­benzene, Mebip is bis­(<i>N</i>-methylbenzimidazolyl)­pyridine, dpb is 1,3-di-2-pyridylbenzene, Medpb is 4,6-dimethyl-1,3-di-2-pyridylbenzene, and tpy is 2,2′:6′,2″-terpyridine. The solid-state structure of [Ru­(Mebip)­(Medpb)]⁺ is studied by X-ray crystallographic analysis. The electrochemical and spectroscopic properties of these ruthenium complexes were studied and compared with those of known complexes [Ru­(tpy)­(dpb)]⁺ and [Ru­(tpy)₂]²⁺. The change of the supporting ligands and coordination environment allows progressive modulation of the metal-associated redox potentials (Ru^II/III) from +0.26 to +1.32 V vs Ag/AgCl. The introduction of a ruthenium cyclometalated bond in these complexes results in a significant negative potential shift. The Ru^II/III potentials of these complexes were analyzed on the basis of Lever’s electrochemical parameters (<i>E</i>_L). Density functional theory (DFT) and time-dependent DFT calculations were carried out to elucidate the electronic structures and spectroscopic spectra of complexes with Mebib or Mebip ligands

Tuning of Metal–Metal Interactions in Mixed-Valence States of Cyclometalated Dinuclear Ruthenium and Osmium Complexes Bearing Tetrapyridylpyrazine or -benzene

New dinuclear ruthenium or osmium complexes with cyclometalated bonds in either tridentate bridging (BL) or ancillary ligands (L), [(L)­M­(BL)­M­(L)] (where M = Ru, Os; L = bis­(<i>N</i>-methylbenzimidazolyl)­pyridine, -benzene; BL= tetrapyridylpyrazine (tppz), -benzene (tpb)), were synthesized, and their mixed-valence-state characteristics were investigated. All of the complexes showed successive one-electron redox processes, each of which correspond to M­(II/III) (M = Ru, Os) or ligand reduction waves. In addition, an M­(III/IV) couple was observed in cyclometalated [M₂(bis­(benzimidazolyl)­benzene)₂(BL)] complexes (M = Ru, Os). Effects of the cyclometalated bonds on the redox behaviors and the accessibility to the mixed-valence M­(II)–M­(III) dinuclear complexes are discussed. Introduction of a cyclometalated bond induced a large negative potential shift in the redox potentials of dinuclear ruthenium and osmium complexes, depending on either bridging or ancillary sites of the cyclometalated bonds: the change falls within the range of −1.0 to −1.2 V for the bridging sites and −0.65 to −0.7 V for the ancillary ones. This large negative potential shift arises from the strong electron-donating property of the phenyl anion in a metal–C bond. Replacing the ruthenium by osmium in the dinuclear complexes with the same bridging ligand results in an increase of the potential separation (Δ<i>E</i>(1)) and the comproportionation constant (<i>K</i>_com) of the mixed-valence complexes having the tppz bridging ligand (Δ<i>E</i>(1) and <i>K</i>_com values: Os > Ru); however, complexes having the tpb bridging ligand showed the opposite trend (Δ<i>E</i>(1) and <i>K</i>_com: Os < Ru). In addition to the results of EPR and DFT calculation, it was found that the orbital energy levels of the central metal ion (namely, either Ru or Os) in the mixed-valence complex determines the degree of orbital mixing between metal dπ orbitals and bridging-ligand π or π<b>*</b> orbitals, which leads to either hole- or electron-transfer exchange mechanisms

Synthesis and Complete Structure Determination of a Sperm-Activating and -Attracting Factor Isolated from the Ascidian <i>Ascidia sydneiensis</i>

For the complete structure elucidation of an endogenous sperm-activating and -attracting factor isolated from eggs of the ascidian <i>Ascidia sydneiensis</i> (<i>Assydn</i>-SAAF), its two possible diastereomers with respect to C-25 were synthesized. Starting from ergosterol, the characteristic steroid backbone was constructed by using an intramolecular pinacol coupling reaction and stereoselective reduction of a hydroxy ketone as key steps, and the side chain was introduced by Julia–Kocienski olefination. Comparison of the NMR data of the two diastereomers with those of the natural product led to the elucidation of the absolute configuration as 25<i>S</i>; thus the complete structure was determined and the first synthesis of <i>Assydn</i>-SAAF was achieved

Synthesis and Complete Structure Determination of a Sperm-Activating and -Attracting Factor Isolated from the Ascidian <i>Ascidia sydneiensis</i>

For the complete structure elucidation of an endogenous sperm-activating and -attracting factor isolated from eggs of the ascidian <i>Ascidia sydneiensis</i> (<i>Assydn</i>-SAAF), its two possible diastereomers with respect to C-25 were synthesized. Starting from ergosterol, the characteristic steroid backbone was constructed by using an intramolecular pinacol coupling reaction and stereoselective reduction of a hydroxy ketone as key steps, and the side chain was introduced by Julia–Kocienski olefination. Comparison of the NMR data of the two diastereomers with those of the natural product led to the elucidation of the absolute configuration as 25<i>S</i>; thus the complete structure was determined and the first synthesis of <i>Assydn</i>-SAAF was achieved