9 research outputs found
Highly Efficient and Stable Molecular-Based TiO<sub>2</sub> 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 âpyridyl anchoring techniqueâ developed by us,
leading to the long-term stability of our molecular-based photoanodes
owing to the high strength of the TiâN (pyridyl) bonding. A
molecular-based TiO2 photoanode modified with both a polypyridyl
ruthenium PS, [Ru(dpbpy)2(qpy)]2+ (dpbpy = 4,4â˛-diphenyl-2,2â˛-bipyridine,
qpy = 4,4â˛:2â˛,2âł:4âł,4â´-quaterpyridine)
(Ru-qpy), and a Ru(bda)-type WOC, Ru(bda)(4,4â˛-bpy)2 (bda = 2,2â˛-bipyridine-6,6â˛-dicarboxylic acid,
4,4â˛-bpy = 4,4â˛-bipyridine) (Ru(bda)-py) by our technique promotes water oxidation with an almost quantitative
Faradaic efficiency (94 Âą 6%) at the applied potential of 0.05
V versus SCE over 3 h under solar light irradiation (Îť >
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 CâCTXâ1 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 HornerâWadsworthâEmmons 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)<sub>4</sub>]<sup>2â</sup> and [Pt(SeCN)<sub>4</sub>]<sup>2â</sup> Building Blocks
New complexes and
the first coordination polymers containing [PtÂ(SCN)<sub>4</sub>]<sup>2â</sup> of the type [MÂ(L)<sub><i>x</i></sub>]Â[PtÂ(SCN)<sub>4</sub>] (where L = 2,2â˛-bipyridine (bipy), <i>x</i> = 2, M = CoÂ(II), NiÂ(II), CuÂ(II); L = ethylenediamine (en), <i>x</i> = 2, M = NiÂ(II), CuÂ(II); L = <i>N</i>,<i>N</i>,<i>N</i>â˛,<i>N</i>â˛-tetramethylethylenediamine
(tmeda), <i>x</i> = 1, M = CuÂ(II); L = 2,2â˛;6â˛,2âł-terpyridine
(terpy), <i>x</i> = 1, M = MnÂ(II), CoÂ(II); L = 1,10-phenanthroline
(phen), <i>x</i> = 2, M = PbÂ(II)) were prepared by reacting
the appropriate metalâligand cations with K<sub>2</sub>[PtÂ(SCN)<sub>4</sub>] and structurally characterized. [MÂ(bipy)<sub>2</sub>PtÂ(SCN)<sub>4</sub>]<sub>2</sub>¡2MeOH (M = Co (<b>1</b>), Cu (<b>4</b>)) consist of supramolecular tetranuclear distorted squares
containing two [MÂ(bipy)<sub>2</sub>]<sup>2+</sup> and two [PtÂ(SCN)<sub>4</sub>]<sup>2+</sup> units. [CuÂ(bipy)<sub>2</sub>(NCS)]<sub>2</sub>[PtÂ(SCN)<sub>4</sub>] (<b>6</b>) is a double salt of the [PtÂ(SCN)<sub>4</sub>]<sup>2â</sup> anion and two [CuÂ(bipy)Â(NCS)]<sup>+</sup> cations. [CuÂ(en)<sub>2</sub>PtÂ(SCN)<sub>4</sub>] (<b>7</b>, <b>8</b>) are 1-D coordination polymers that are coordinated
in either cis or trans fashion at the [PtÂ(SCN)<sub>4</sub>]<sup>2â</sup> unit, for <b>7</b> and <b>8</b>, respectively. Complexes
[CuÂ(en)<sub>2</sub>PtÂ(SeCN)<sub>4</sub>] (<b>9</b>) and [NiÂ(en)<sub>2</sub>PtÂ(SCN)<sub>4</sub>] (<b>10</b>) are similar to <b>8</b> and <b>7</b>, respectively, but complex <b>9</b> (prepared using (<sup>n</sup>Bu<sub>4</sub>N)<sub>2</sub>[PtÂ(SeCN)<sub>4</sub>]) also presents intermolecular SeâSe interactions
which resulted in an increased dimensionality. Compounds [MÂ(terpy)ÂPtÂ(SCN)<sub>4</sub>] (M = Mn (<b>11</b>), Co (<b>13</b>)) involve
2-D sheets of [MÂ(terpy)]<sup>2+</sup> and [PtÂ(SCN)<sub>4</sub>]<sup>2â</sup> units, whereas [MnÂ(terpy)<sub>2</sub>]Â[PtÂ(SCN)<sub>4</sub>] (<b>12</b>) is a double salt of one [MnÂ(terpy)<sub>2</sub>]<sup>2+</sup> unit and one [PtÂ(SCN)<sub>4</sub>]<sup>2â</sup>. [CuÂ(tmeda)ÂPtÂ(SCN)<sub>4</sub>] (<b>14</b>) contains a five-coordinate
Cu<sup>2+</sup> metal center coordinated to one tmeda ligand and three
different [PtÂ(SCN)<sub>4</sub>]<sup>2â</sup> units, resulting
in 2-D sheets. [PbÂ(phen)<sub>2</sub>PtÂ(SCN)<sub>4</sub>] (<b>15</b>) contains an 8-coordinate Pb<sup>2+</sup> metal center coordinated
to two phen ligands and four [PtÂ(SCN)<sub>4</sub>]<sup>2â</sup>, 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 [PtÂ(SCN)<sub>4</sub>]<sup>2â</sup> building
block, and the resulting dimensionality of the coordination polymers
Synthesis and Structure Revision of the C43âC67 Part of Amphidinol 3
Stereoselective synthesis of the C43âC67 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 JuliaâKocienski 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 nâ=â24), those who did not undergo a 7-year protocol biopsy (nâ=â66), and those who underwent for-cause biopsy (nâ=â5). Consequently, 89 patients who underwent a 7-year protocol biopsy were enrolled. We analyzed the relationship between the clinicopathological findings 7âyears 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 âĽ1 and proteinuria âĽ1+ was independently associated with the eGFR decline per year during a median follow-up of 73âmonths. Furthermore, in the model of the clinicopathological findings including the presence of mm with proteinuria, mm âĽ1 alone and mm âĽ1 with proteinuria were each independently associated with the eGFR decline. The graft survival was significantly worse for those with mm âĽ1 with proteinuria than those with mm âĽ1 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 [RuÂ(Mebib)Â(Mebip)]<sup>+</sup>, [RuÂ(Mebip)Â(dpb)]<sup>+</sup>, [RuÂ(Mebip)Â(Medpb)]<sup>+</sup>, and [RuÂ(Mebib)Â(tpy)]<sup>+</sup> and two bis-tridentate noncyclometalated complexes [RuÂ(Mebip)<sub>2</sub>]<sup>2+</sup> and [RuÂ(Mebip)Â(tpy)]<sup>2+</sup> were prepared
and characterized, where Mebib is bisÂ(<i>N</i>-methylbenzimidazolyl)Âbenzene,
Mebip is bisÂ(<i>N</i>-methylbenzimidazolyl)Âpyridine, dpb
is 1,3-di-2-pyridylbenzene, Medpb is 4,6-dimethyl-1,3-di-2-pyridylbenzene,
and tpy is 2,2â˛:6â˛,2âł-terpyridine. The solid-state
structure of [RuÂ(Mebip)Â(Medpb)]<sup>+</sup> 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 [RuÂ(tpy)Â(dpb)]<sup>+</sup> and [RuÂ(tpy)<sub>2</sub>]<sup>2+</sup>. The change of the supporting ligands and coordination environment
allows progressive modulation of the metal-associated redox potentials
(Ru<sup>II/III</sup>) 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<sup>II/III</sup> potentials
of these complexes were analyzed on the basis of Leverâs electrochemical
parameters (<i>E</i><sub>L</sub>). 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 MetalâMetal 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)ÂMÂ(BL)ÂMÂ(L)] (where M = Ru, Os; L = bisÂ(<i>N</i>-methylbenzimidazolyl)Âpyridine,
-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 MÂ(II/III) (M = Ru, Os) or ligand reduction
waves. In addition, an MÂ(III/IV) couple was observed in cyclometalated
[M<sub>2</sub>(bisÂ(benzimidazolyl)Âbenzene)<sub>2</sub>(BL)] complexes
(M = Ru, Os). Effects of the cyclometalated bonds on the redox behaviors
and the accessibility to the mixed-valence MÂ(II)âMÂ(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 â1.0 to â1.2 V for the bridging sites and â0.65
to â0.7 V for the ancillary ones. This large negative potential
shift arises from the strong electron-donating property of the phenyl
anion in a metalâC bond. Replacing the ruthenium by osmium
in the dinuclear complexes with the same bridging ligand results in
an increase of the potential separation (Î<i>E</i>(1)) and the comproportionation constant (<i>K</i><sub>com</sub>) of the mixed-valence complexes having the tppz bridging
ligand (Î<i>E</i>(1) and <i>K</i><sub>com</sub> values: Os > Ru); however, complexes having the tpb bridging
ligand
showed the opposite trend (Î<i>E</i>(1) and <i>K</i><sub>com</sub>: 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 dĎ
orbitals and bridging-ligand Ď or Ď<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 JuliaâKocienski 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 JuliaâKocienski 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