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The modification of the phosphonium-type ionic liquid onto the TiO2 electrode reduced the amount of dye adsorbed on the electrode and showed significant aggregation effect, thereby improving the photovoltaic performance of DSSCs.

We previously reported the preparation and characterization of a Ni(II) complex capable of electrocatalytic hydrogen generation. The complex [Ni(LNH2)2Cl]Cl (1) includes a 6-((diphenylphosphino)methyl)pyridin-2-amine ligand (LNH2), which has an amino group as a base that acts as a proton transfer site by virtue of its location near the metal center. In order to study the effect of counteranions in hydrogen generation, two additional NiII(LNH2) complexes with weakly coordinating/noncoordinating counteranions, [Ni(LNH2)2](OTs)2 (OTs- = p-toluenesulfonate) (2) and [Ni(LNH2)2](BF4)2 (3), were synthesized. Their X-ray crystal structures reveal that the Ni(II) ion is coordinated with two bidentate LNH2 ligands in both complexes. Complex 2 contains both trans and cis isomers in the unit cell. The former is in an axially elongated square-pyramidal geometry (τ5 = 0.17), and the latter is in a nearly square planar geometry (τ4 = 0.11) with two weakly interacting OTs- anions at the axial sites. Complex 3 has only the cis isomer in the solid state, which is in a nearly square planar geometry (τ4 = 0.10). These complexes are slightly different from 1, which has a distorted-square-pyramidal geometry (τ5 = 0.25) with a coordinated chloride anion. UV-vis spectra of 2 and 3 in MeCN show a spectral pattern characteristic of a square-planar Ni(II) complex. These spectra are slightly different from the unique spectrum of 1, which is typical of an axially coordinating Ni(II) species as a result of having a Cl- anion at the apical position. Electrocatalytic hydrogen generation promoted by these three Ni(II) complexes (1.0 mmol) demonstrates an increase in the catalytic current induced by stepwise addition of HOAc (pKa = 22.3 in MeCN) as a proton source. The complexes demonstrate turnover frequencies (TOF) of 3800 s-1 for 1, 5400 s-1 for 2, and 8800 s-1 for 3 in MeCN (3 mL) containing 0.1 M [n-Bu4N](ClO4) in the presence of HOAc (145 equiv) at overpotentials of ca. 530, 490, and 430 mV, respectively.

Cu electrode-based electrochemical CO2 reduction using renewable energy is a promising method for conversion of CO2 to useful compounds such as methane, ethylene, and ethanol. Heteroatom-doped and/...

To develop low-cost and efficient dye-sensitized solar cells (DSSCs), we designed and prepared three homoleptic Cu(I) complexes with asymmetric ligands, M1, M2, and Y3, which have the advantages of heteroleptic-type complexes and compensate for their synthetic challenges. The three copper(I) complexes were characterized by elemental analysis, UV-vis absorption spectroscopy, and electrochemical measurements. Their absorption spectra and orbital energies were evaluated and are discussed in the context of TD-DFT calculations. The complexes have high VOC values (0.48, 0.60, and 0.66 V for M1, M2, and Y3, respectively) which are similar to previously reported copper(I) dyes with symmetric ligands, although their energy conversion efficiencies are relatively low (0.17, 0.64, and 2.66%, respectively).

A N2 coordination to titanocene monochloride, [Cp2TiCl], in an ionic liquid (IL), 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate (Pyr4FAP), was detected by frozen solution E...

It has been before reported that, in addition to hydration of nitriles, the Fe-type nitrile hydratase (NHase) also catalyzes the hydrolysis of tert-butylisocyanide (tBuNC). In order to investigate the unique isocyanide hydrolysis by NHase, we prepared three related Co(III) model complexes, PPh4[Co(L)] (1), PPh4[Co(L-O3)] (2), and PPh4[Co(L-O4)] (3), where L is bis(N-(2-mercapto-2-methylpropionyl)aminopropyl)sulfide. The suffixes L-O3 and L-O4 indicate ligands with a sulfenate and a sulfinate and with two sulfinates, respectively, instead of the two thiolates of L. The X-ray analyses of 1 and 3 reveal trigonal bipyramidal and square pyramidal structures, respectively. Complex 2, however, has five-coordinate trigonal-bipyramidal geometry with η2-type S–O coordination by a sulfenyl group. Addition of tBuNC to 1, 2, and 3 induces an absorption spectral change as a result of formation of an octahedral Co(III) complex. This interpretation is also supported by the crystal structures of PPh4[Co(L-O4)(tBuNC)] (4) ...

Incorporation of the tridentate phosphine-enamidoiminophosphorane onto cobalt(II) produces tetrahedral Co(NpNPiPr)Cl, 1, which upon reduction under dinitrogen generates the T-shaped, paramagnetic Co(I) complex Co(NpNPiPr), 2. This paramagnetic T-shaped derivative is in equilibrium with the paramagnetic dinitrogen derivative Co(NpNPiPr)(N2), 3, which can be detected by IR and low-temperature UV–vis spectroscopy. Both 1 and 2 act as homogeneous catalysts for the conversion of molecular nitrogen into tris(trimethylsilyl)amine (N(SiMe3)3) (∼200 equiv, quantified as NH4Cl after hydrolysis) in the presence of excess KC8 and Me3SiCl at low temperatures.

The catalytic conversion of CO2 to useful compounds is of great importance from the viewpoint of global warming and development of alternatives to fossil fuels. Electrochemical reduction of CO2 using aromatic N-heterocylic molecules is a promising research area. We describe a high performance electrochemical system for reducing CO2 to formate, methanol, and CO using imidazole incorporated into a phosphonium-type ionic liquid-modified Au electrode, imidazole@IL/Au, at a low onset-potential of −0.32 V versus Ag/AgCl. This represents a significant improvement relative to the onset-potential obtained using a conventional Au electrode (−0.56 V). In the reduction carried out at −0.4 V, formate is mainly generated and methanol and CO are also generated with high efficiency at −0.6 ∼ −0.8 V. The generation of methanol is confirmed by experiments using 13CO2 to generate 13CH3OH. To understand the reaction behavior of CO2 reduction, we characterized the reactions by conducting potential- and time-dependent in situ ...

Heat-treatment of nano-boehmite intercalated with monoethanolamine derivatives (NBM-MEA) affects its photoluminescence properties. The photoluminescence band of NBM-MEA undergoes a red-shift with an increase in temperature. On the basis of IR and ESR spectroscopic behavior and analysis of time-resolved photoluminescence decay, it is concluded that the emission band originates from the F+ center as singly ionized oxygen vacancies in the boehmite structure and from carbon impurities due to decomposition of monoethanolamine derivatives.

Coordination of N2 to [(Cp2TiCl)2] in a non-coordinating ionic liquid, Pyr4FAP, was studied by UV-vis/NIR and EPR spectroscopies. [(Cp2TiCl)2] is in equilibrium between monomeric [Cp2TiCl] and dimeric species [(Cp2TiCl)2]. The frozen solution EPR spectrum revealed the coordination of N2 to [Cp2TiCl], suggesting that Pyr4FAP promotes N2 coordination to the Ti(III) center.

Reported here is the N2 cleavage of a one-electron oxidation reaction using trans-[Mo(depe)2 (N2 )2 ] (1) (depe=Et2 PCH2 CH2 PEt2 ), which is a classical molybdenum(0)-dinitrogen complex supported by two bidentate phosphine ligands. The molybdenum(IV) terminal nitride complex [Mo(depe)2 N][BArf4 ] (2) (BArf4 =B(3,5-(CF3 )2 C6 H3 )4 ) is synthesized by the one-electron oxidation of 1 upon addition of a mild oxidant, [Cp2 Fe][BArf4 ] (Cp=C5 H5 ), and proceeds by N2 cleavage from a MoII -N=N-MoII structure. In addition, the electrochemical oxidation reaction for 1 also cleaved the N2 ligand to give 2. The dimeric Mo complex with a bridging N2 is detected by in situ resonance Raman and in situ UV-vis spectroscopies during the electrochemical oxidation reaction for 1. Density-functional theory (DFT) calculations reveal that the unstable monomeric oxidized MoI species is converted into 2 via the dimeric structure involving a zigzag transition state.

Electrochemical synthesis of NH3 from dinitrogen and protons from water by using Cp2TiCl2 supported in a hydrophobic ionic liquid, 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate ([C9H20N]+[(C2F5)3PF3]−), was achieved in a solid polymer electrolyte (SPE) cell under ambient conditions. The yield of NH3 per Cp2TiCl2 and current efficiency are 27% and 0.2%, respectively, which are improved in comparison with those reported previously. Keywords: Dinitrogen fixation, Ionic liquid, Transition metal complex, Ammonia

A novel nickel(II) complex [Ni(L)2 Cl]Cl with a bidentate phosphinopyridyl ligand 6-((diphenylphosphino)methyl)pyridin-2-amine (L) was synthesized as a metal-complex catalyst for hydrogen production from protons. The ligand can stabilize a low Ni oxidation state and has an amine base as a proton transfer site. The X-ray structure analysis revealed a distorted square-pyramidal Ni(II) complex with two bidentate L ligands in a trans arrangement in the equatorial plane and a chloride anion at the apex. Electrochemical measurements with the Ni(II) complex in MeCN indicate a higher rate of hydrogen production under weak acid conditions using acetic acid as the proton source. The catalytic current increases with the stepwise addition of protons, and the turnover frequency is 8400 s(-1) in 0.1 m [NBu4 ][ClO4 ]/MeCN in the presence of acetic acid (290 equiv) at an overpotential of circa 590 mV.

An unstable diiron(II,II) complex possessing O2 binding ability at low temperature was encapsulated and stabilized in an ammonium-type ionic liquid layer polymerized on an electrode. The encapsulated complex revealed catalytic reactivity for four-electron reduction of O2 at an ambient temperature in aqueous solution.

A blue photoluminescent nano boehmite was prepared by a solvothermal reaction of aluminum hydroxide gel in monoethanolamine (MEA) at a low temperature of 120 °C for 6 h; it shows a photoluminescence emission at 420 nm with excitation of 360 nm that is attributed to the formation of the carbamate derivative of MEA.

It has been before reported that, in addition to hydration of nitriles, the Fe-type nitrile hydratase (NHase) also catalyzes the hydrolysis of tert-butylisocyanide ( tBuNC). In order to investigate the unique isocyanide hydrolysis by NHase, we prepared three related Co(III) model complexes, PPh

A new tridentate cyclopentane-bridged iminophosphorane ligand, N-(2-diisopropylphosphinophenyl)-P,P-diisopropyl-P-(2-(2,6-diisopropylphenylamido)cyclopent-1-enyl)phosphoranimine (NpNPiPr), was synthesized and used in the preparation of a diiron dinitrogen complex. The reaction of the iron complex FeBr(NpNPiPr) with KC8 under dinitrogen yielded the dinuclear dinitrogen Fe complex [Fe(NpNPiPr)]2(μ-N2), which was characterized by X-ray analysis and resonance Raman and NMR spectroscopies. The X-ray analysis revealed a diiron complex bridged by the dinitrogen molecule, with each metal center coordinated by an NpNPiPr ligand and dinitrogen in a trigonal-monopyramidal geometry. The N–N bond length is 1.184(6) Å, and resonance Raman spectra indicate that the N–N stretching mode ν(14N2/15N2) is 1755/1700 cm–1. The magnetic moment of [Fe(NpNPiPr)]2(μ-N2) in benzene-d6 solution, as measured by 1H NMR spectroscopy by the Evans method, is 6.91μB (S = 3). The Mössbauer spectrum at 78 K showed δ = 0.73 mm/s and ΔEQ = 1.83 mm/s. These findings suggest that the iron ions are divalent with a high-spin configuration and that the N2 molecule has (N═N)2– character. Density functional theory calculations performed on [Fe(NpNPiPr)]2(μ-N2) also suggested that the iron is in a high-spin divalent state and that the coordinated dinitrogen molecule is effectively activated by π back-donation from the two iron ions (dπ) to the dinitrogen molecule (πx* and πy*). This is supported by cooperation between a large negative charge on the iminophosphorane ligand and strong electron donation and effective orbital overlap between the iron dπ orbitals and N2 π* orbitals supplied by the phosphine ligand.

We report the synthesis and luminescent properties of halide-bridged tricopper(I) complexes with a polyaza cryptand having three 2,6-bis(aminomethyl)pyridyl spacers. The asymmetric {Cu3X3} structur...

A Co(III) complex possessing selective nitric oxide (NO) capturing ability was immobilized onto a bulky phosphonium type ionic liquid-modified Au electrode, IL/Au, (Co@IL/Au), which was confirmed b...

Solvothermal reaction of aluminum hydroxide gel (AHG) in monoethanolamine (MEA) was studied at several temperatures (100, 120, 150, and 200 °C) in several reaction times (2, 3, 4, 5, 6, and 13 h). The reaction product prepared at a low temperature of 120 °C in the reaction time more than 6 h gave a blue photoluminescence nanoboehmite intercalated with monoethanolamine derivatives (BM-MEA) in the colloidal solution, which showed a photoluminescence emission centered at 420 nm with an excitation of 360 nm. The powdery samples recovered from the reaction products were characterized by using elemental analysis, XRD analysis, IR spectroscopy, thermogravimetric (TG)-DTA, 13C and 27Al CP/MAS NMR spectroscopies, N2 gas adsorption/desorption isotherm, SEM and TEM images, and photoluminescence spectroscopy. The X-ray diffraction revealed that the basal space in BM-MEA was expanded from 0.61 to 1.2 nm by intercalation of MEA derivatives to boehmite, and the IR and 13C CP/MAS NMR spectra determined that the intercalated MEA derivatives are protonated- and carbamate-substituted MEAs, which are formed in the layers through a covalent bond with Al–OH groups on boehmite surface. The empirical formula of BM-MEA was estimated to be AlO(OH)0.82(OCH2CH2NH3 +)0.05(OCH2CH2NHCOO−)0.13 on the basis of the elemental TG-DTA and IR spectral analyses. We discuss the reaction mechanism of a unique blue photoluminescence BM-MEA formed by proceeding in CO2–H2O–alkanolamine system.

Coordination of N

The role of the amide carbonyl oxygens in the nitrile hydratase (NHase) active site for the nitrile coordination to the metal center was studied using a distorted square-pyramidal N2S3-type Co(III)...

Properties of newly developed Ru(II)-complex dye, cis -bis(isothiocyanato) (2,2′-bipyridyl-4,4′-dicarboxylato) ( N -(4-butoxyphenyl)- N -2-pyridinyl-2-pyridinamine)-ruthenium(II) (J13), having a triarylamine ligand have been studied in comparison with cis -bis(isothiocyanato) bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) (N3), as photosensitizers for solar cells employing electrodeposited porous ZnO thin films. Quantification of dye loading as well as change of the film morphology on extension of the soaking time in solutions of these dyes indicated spontaneous monolayer formation of the J13 dye, in contrast to the strongly aggregating N3 dye. Overloading of the N3 dye molecules not directly bound to ZnO caused decreased J sc as well as worsening of F.F. , so that the efficiency of the N3 cell created a peak with a moderate dipping time. On the other hand, the efficiency of the J13 cells simply saturated to a value of ca. 4% as the dye monolayer was formed, indicating its better chemical match with ZnO.

Artificial siderophore–Fe3+ complexes were prepared and modified with Au nanoparticles. These nanoparticles were found to selectively adsorb onto microbes and initiate selective aggregation. The ag...

We synthesized a new amine-type host molecule 2 by 2 steps, using 1,3,5-tris(aminomethyl)-2,4,6-trimethylbenzene and 2,6-pyridinedicarboxaldehyde as starting materials. Recrystallization of 2·6H2O from hot acetonitrile, hot propionitrile and hexane/benzonitrile solutions gave colorless crystals of MeCN@2·MeCN·2H2O, EtCN@2·EtCN, and 8H2O@2·PhCN. In the former two crystals, the nitrile compounds were captured inside of the cavity of 2. On the other hand, in the latter one, the benzonitrile was laid outside 2. Infrared spectral measurements of MeCN@2·MeCN·2H2O, EtCN@2·EtCN, and 8H2O@2·PhCN showed that absorption bands assignable to the C ≡ N stretching vibrations of nitrile compounds were observed at 2240, 2241, and 2226 cm−1 for MeCN@2·MeCN·2H2O, EtCN@2·EtCN, and 8H2O@2·PhCN, respectively. The former two peaks shifted to a lower energy region by 6–13 and 21–26 cm−1 than those of liquid and gas phases of MeCN and EtCN, respectively. That for 8H2O@2·PhCN shifted to a slightly lower region by 2 and 12 cm−1 those of liquid and gas states of PhCN, respectively, indicating that the outer benzonitrile molecule dose not so much interact with 2 in the crystal.

Square planar Co(III) complexes,1 and 2, were synthesized and characterized. The structure kept in any other organic solution and even in an aqueous one, indicating that Lewis acidity of the metal center is rather small. Introduction of NO gas into CH3OH solutions of 1 and 2 caused a decrease of the absorption band in a visible region. This result indicates that NO molecule interacted to the Co(III) center. Reduction potential corresponding to Co(III)/(II) also shifted from -1.24 V to -1.65 V for 2 (vs. Ag/Ag+ in CH3CN) by addition of NO. On the other hand, addition of the other ions or molecules such as O2, Cl-, CO, and NO2- that is producible by reacting NO gas and O2 in an aqueous solution did not show any changes for the chemical properties.

Siderophores, which are secreted by microorganism for iron uptake, strongly bind Fe(III) ions and permeate the cell membrane through the receptor and/or binding protein. Our aim is the development devices based on the substrates modifying Fe(III)-artificial siderophore complexes for adsorbing and sensing microorganisms. The key point of our strategy is the interaction between the artificial siderophore complexes on the substrates and the siderophore receptor proteins at the cell membrane. We report the construction of the Au films modified by the artificial siderophore complexes and their adsorption ability for microbes.

The hydroxamate-type artificial siderophore, tris[2-{3-( N -acetyl- N -hydroxamino)propylamido}propyl]aminomethane (TAPPA) and its Fe III complex, Fe III -TAPPA were prepared and characterized by several spectroscopic methods. Fe III -TAPPA exhibits biological activity for the hydroxamate-type siderophore auxotrophic microorganism, Microbacterium flavescens , suggesting that Fe III -TAPPA can permeate the cell membrane of the microorganism. The adsorption of the Fe III -siderophore complex onto a deposited Au substrate was achieved by a stepwise self-assembling method. The modification of Fe III -TAPPA on the surface was confirmed from the cyclic voltammogram of the resultant Au electrode, Fe III -TAPPA/Au. The adsorption experiments of M. flavescens with Fe III -TAPPA/Au were monitored by optical, scanning electron, and atomic force microscopy and quartz crystal microbalance (QCM) measurements. These results clearly indicate that Fe III -TAPPA/Au can immobilize M. flavescens . This adsorption characteristic is due to the interaction between Fe III -TAPPA on an Au electrode and a receptor/binding protein within the cell membrane.

The hydroxamate-based artificial siderophore that contains terminated-amine group was newly synthesized. This artificial siderophore formed stable complex with FeIII ion and high bio-activities. The FeIII-artificial siderophore complex was attached onto the glass substrate surface by stepwise self-assembling method. The obtained artificial siderophore-modified glass substrate adsorbed the Gram-positive bacterium Microbacterium. flavescens. The Gram-negative bacterium Escherichia. coli was not adsorbed. The artificial siderophore-modified glass substrates indicated the selective adsorption of microorganisms.

Novel ruthenium(II) polypyridyl complexes with diethynylphenanthrolines containing acetylthiophenyl unit(s) have been prepared and characterized by photophysical measurements. These complexes showe...

Redox behaviors of monomeric and dimeric titanocenes, [Cp2TiCl2] (1) and [(Cp2TiCl)2] (2), were investigated in two different types of ionic liquid (IL) with non-coordinating and coordinating anions, 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)- trifluorophosphate (Pyr4FAP) and 1-butyl-1-methylpyrrolidinium triflate (Pyr4OTf), respectively. UV-vis/NIR spectra obtained during the electrochemical reduction of 1 revealed that it was converted to 2 in the ILs through the formation of [Cp2TiCl] (3). In Pyr4OTf, 3 was coordinated with the OTf anion in the η1-O mode, during the electrochemical reductions of Ti(IV/III) process, whereas 3 was not coordinated by the FAP anion in Pyr4FAP. Additionally, electrochemical NH3 synthesis was carried out in a solid polymer electrolyte cell by using a gas diffusion electrode coated with Pyr4FAP or Pyr4OTf containing titanocenes. The electrochemical reduction using 2 in Pyr4FAP at −1.5 V (vs. Ag/AgCl) gave a high yield (34 % at 29.9 C) of NH3 per Ti ion. The electrochemical reduction using 1 in Pyr4OTf gave a 6.8 % yield of NH3 per Ti ion at 20 °C. These findings indicate that the use of an IL with a non-coordinating anion such as FAP contributes to the coordination and reduction of N2 to titanocenes.

The previously reported monochelate iron complex with κ(3) SNS thioamide pincer ligand, 2,6-bis(N-2,6-bis(diphenylmethyl)-4-isopropylphenyliminothiolate)pyridine (L(DPM)), [Fe(THF)2(κ(3)-L(DPM))], gave novel complexes, [Fe(NHC)(κ(3)-L(DPM))] and [Fe(NO)2(κ(3)-L(DPM))], by substitution reactions with N-heterocyclic carbene (NHC) and NO molecules, respectively. The X-ray crystal structure of the [Fe(NHC)(κ(3)-L(DPM))] complex revealed a unique square planar iron(ii) complex, which was determined to be in an intermediate spin state (S = 1) in benzene from the Evans method. The [Fe(NO)2(κ(3)-L(DPM))] complex was determined to have a trigonal bipyramidal geometry from X-ray analysis and was indicated to be diamagnetic from the (1)H NMR spectrum. The ν(NO) stretching vibration of this complex showed two peaks at 1840 cm(-1) and 1790 cm(-1), and also the Fe-N-O bond angles were 168.9(2)° and 168.03(19)°. These findings suggest that the two coordinated NO molecules have neutral radical character, and they are antiferromagnetically coupled with the high-spin iron center.

A terminal ligand-substitution reaction at triruthenium redox centres within monolayer films is investigated. For this purpose, a new redox-active trinuclear ruthenium complex containing one carbonyl ligand at a terminal site, [Ru3(O)(CH3COO)6(CO)(mpy)(C10PY)] (mpy = 4-methylpyridine, C10PY = {(NC5H4)CH2NHC(O)(CH2)10S–}2) 1, has been chemically adsorbed onto a gold electrode surface with a disulfide-alkyl spacer C10PY. Densely packed monolayers of complex 1 on Au electrodes (surface coverage, Γ(Ru3) = 1.8 × 10−10 mol cm−2) display the {RuII–CO}RuIIIRuIII/{RuIII–CO}RuIIIRuIII couple at E1/2 = + 0.61 V s. Ag–AgCl in a 0.1 mol dm−3 HClO4 aqueous solution. Upon electrochemical oxidation of the adsorbed complex at + 0.80 V, where the triruthenium carbonyl complex is in the oxidized form {RuIII–CO}RuIIIRuIII, the coordinated CO is replaced by an aqua ligand present in the bulk phase, which is followed by cyclic voltammetry at appropriate electrolysis time intervals. During 8000 s of electrolysis, ca. 67% of the initially assembled carbonyl complexes are converted to the triruthenium aqua complexes, while ca. 25% desorbed from the electrode surface.

New oxo-centred acetate-bridged triruthenium(III) complexes with a long alkyl-chain disulfide ligand, (NC5H4)CH2NHC(O)(CH2)nSS(CH2)nC(O)NHCH2(C5H4N) (C5H4N represents a 4-pyridyl residue, n = 10; abbreviated as C10PY), have been prepared as a redox-active metal cluster adsorbate on gold electrodes: [Ru3(O)(CH3CO2)6(mpy)2(C10PY)]ClO45a (mpy = 4-methylpyridine), [Ru3(O)(CH3CO2)6(mpy)2(C10PY)]CF3SO35b. The preparation, spectroscopic and electrochemical properties of 5a,5b are presented and are compared with those of triruthenium(III) analogues of a shorter alkyl-chain disulfide ligand (n = 2; abbreviated as C2PY), e.g. [Ru3(O)(CH3CO2)6(mpy)2(C2PY)]ClO43a and [Ru3(O)(CH3CO2)6(MeIm)2(C2PY)]ClO44a (MeIm = 1-methylimidazole). Characterization of all the compounds was accomplished using 1H and 1H–1H COSY NMR, UV-vis and infrared spectroscopy, elemental analysis, fast-atom bombardment (FAB) mass spectrometry and cyclic voltammetry. Compounds 3a, 4a and 5a,5b in 0.1 M [n-Bu4N]PF6–CH3CN exhibit three {Ru3(O)} cluster core-based one-electron redox waves which are all reversible in the applied potential range between +1.2 and –2.0 V vs. Ag–AgCl. The redox potentials are dependent on the basicity of the terminal ligands (mpy and MeIm), but are insensitive to the length of the methylene chains of the disulfide ligand (C10PY and C2PY). Self-assembly of 5b on a gold electrode results in the formation of electrochemically stable monolayers which exhibit one-electron redox wave corresponding to the Ru3 redox process III,III,III–II,III,III in aqueous media containing 0.1 M supporting electrolytes. The redox potentials and the shape of the voltammetric waves of the surface-attached triruthenium complexes are found to be largely dependent upon the nature of anions used (ClO4−, CF3SO3−, NO3−, PF6− and SO42−) and also upon the basicity of terminal ligands on the {Ru3(O)} cluster moiety.

The phenoxo-based dinucleating ligand, 2,6-bis[bis(6-pivalamido-2-pyridylmethyl)amino-methyl]-4-aminophenol (1), and its Fe2(II) complex, [Fe2(II)(1)(PhCOO)2](CF3SO3) (2), were prepared and 2 deposited on the Au surface (2/Au) is much more stable than in solution and exhibits redox behavior in aqueous media as well as reversible adsorption/desorption of oxygen at room temperature.

Electrochemical studies of three c-type cytochromes (cyt c from horse heart, cyt c(2) from Rhodospirillum rubrum, and cyt c(553) from Alcaligenes xylosoxidans GIFU 1051) were performed by using the optically active Co(III) complex-modified Au electrode. Three cytochromes gave different redox behaviors reflected from the respective structural information. From relationship between their redox behaviors and their structural characteristics, we evaluated the solution structure around heme center of cyt c(553).

A catecholate-type artificial siderophore with a terminal-NH2 group (1) and its Fe(3+) complex (2) were prepared. Siderophore 1 was characterized by (1)H NMR, FT-IR, and ESI-TOF MS spectroscopy. The corresponding Fe(3+) complex 2 was obtained by reaction of 1 with Fe(acac)3. The absorption band at 500 nm (ε = 4670 M(-1) cm(-1) at pH 7.0) of the electronic absorption spectrum of 2 is assignable as the LMCT (O(catecholate) → Fe(3+)) absorption band. This band indicates the formation of the Fe(3+) complex of 1. The biological activity of 2 with respect to Escherichia coli was clearly confirmed by observing that it permeates into the cell membrane. The self-assembled monolayer of 2 on an Au substrate, 2/Au, was prepared and its preparation was confirmed by FT-IR reflection-absorption spectroscopy (IR-RAS) and cyclic voltammetry (CV). Furthermore, a quartz crystal microbalance (QCM) chip modified with 2 effectively adsorbed E. coli. M. flavescens, an organism which is incapable of synthesizing siderophores and must therefore use exogenous hydroxamate-type siderophores for growth, did not adsorb on 2/Au. In contrast, E. coli did not adsorb on the hydroxamate-type artificial siderophore-Fe(3+) complex (3)-modified Au substrate, 3/Au. These results provide preliminary evidence that microbes recognized Fe(3+) ion-bound siderophores on the surface. The detection limit of 2/Au was ∼10(4) CFU mL(-1).