[Microorganism Immobilization Device Using Artificial Siderophores].

Inspired by the mechanism by which microorganisms utilize siderophores to ingest iron, four different FeIII complexes of typical artificial siderophore ligands containing catecholate and/or hydroxamate groups, K3[FeIII-LC3], K2[FeIII-LC2H1], K[FeIII-LC1H2], and [FeIII-LH3], were prepared. They were modified on an Au substrate surface (Fe-L/Au) and applied as microorganism immobilization devices for fast, sensitive, selective detection of microorganisms, where H6LC3, H5LC2H1, H4LC1H2, and H3LH3 denote the tri-catecholate, biscatecholate-monohydroxamate, monocatecholate-bishydroxamate, and tri-hydroxamate type of artificial siderophores, respectively. Their adsorption properties for the several microorganisms were investigated using scanning electron microscopy (SEM), quartz crystal microbalance (QCM), and electric impedance spectroscopy (EIS) methods. The artificial siderophore-iron complexes modified on the Au substrates Fe-LC3/Au, Fe-LC2H1/Au, Fe-LC1H2/Au, and Fe-LH3/Au showed specific microorganism immobilization behavior with selectivity based on the structure of the artificial siderophores. Their specificities corresponded well with the structural characteristics of natural siderophores that microorganisms release from the cell and/or use to take up an iron. These findings suggest that release and uptake are achieved through specific interactions between the artificial siderophore-FeIII complexes and receptors on the cell surfaces of microorganisms. This study revealed that Fe-L/Au systems have specific potential to serve as effective immobilization probes of microorganisms for rapid, selective detection and identification of a variety of microorganisms.

Catalytic Oxidation of Methanol to Formaldehyde Catalyzed by Iron Complex with N3S3-type Tripodal Ligand.

A Fe3+ complex with N3S3-type tripod ligand, 1, reacts with O2 in CH3OH to generate formaldehyde, which has been studied structurally, spectroscopically, and electrochemically. Complex 1 crystallizes as an octahedral structure with crystallographic C3 symmetry around the metal, with Fe-N=2.2917(17) Å and Fe-S=2.3574(6) Å. UV-vis spectrum of 1 in CH3OH under Ar shows an intense band at 572 nm (ϵ 4,100 M-1cm-1), which shifts to 590 nm (ϵ 2,860 M-1cm-1) by the addition of O2, and a new peak appeared at 781 nm (ϵ 790 M-1cm-1). Such a spectral change is not observed in CH2Cl2. Cyclic voltammogram (CV) of 1 in CH2Cl2 under Ar gives reversible redox waves assigned to Fe2+/Fe3+ and Fe3+/Fe4+ couples at -1.60 V (ΔE=69 mV) and -0.53 V (ΔE=71 mV) vs Fc/Fc+, respectively. In contrast, in CH3OH, the reversible redox waves, albeit accompanied by a positive shift of the Fe2+/Fe3+ couple, are observed at -1.20 V (ΔE=85 mV) and -0.53 V (ΔE=64 mV) vs Fc/Fc+ under Ar. Interestingly, a catalytic current was observed for the CV of 1 in CH3OH in the presence of CH3ONa under Ar, when the sweep rate was slowed down.

Detection of Microorganisms Using Artificial Siderophore-FeIII Complex-Modified Substrates.

Four FeIII complexes of typical artificial siderophore ligands containing catecholate and/or hydroxamate groups of tricatecholate, biscatecholate-monohydroxamate, monocatecholate-bishydroxamate, and trihydroxamate type artificial siderophores (K3[FeIIILC3], K2[FeIIILC2H1], K[FeIIILC1H2], and [FeIIILH3]) were modified on Au substrate surfaces. Their abilities to adsorb microorganisms were investigated using scanning electron microscopy, quartz crystal microbalance, and AC impedance methods. The artificial siderophore-iron complexes modified on Au substrates (FeLC3/Au, FeLC2H1/Au, FeLC1H2/Au, and FeLH3/Au) showed the selective immobilization behavior for various microorganisms, depending on the structural features of the artificial siderophores (the number of catecholate and hydroxamate arms). Their specificities corresponded well with the structural characteristics of natural siderophores released by microorganisms and used for FeIII ion uptake. These findings suggest that they were generated via specific interactions between the artificial siderophore-FeIII complexes and the receptors on microorganism surfaces. Our observations revealed that the FeL/Au systems may be potentially used as effective microbe-capturing probes that can enable rapid and simple detection and identification of various microorganisms.

Flat and roll-type translucent anodic porous alumina molds anodized in oxalic acid for UV nanoimprint lithography.

There is much interest in UV nanoimprinting as a fabrication method for various functional devices because of its suitability for efficient fine patterning. To form patterns on opaque substrates by UV nanoimprinting, it is essential to use molds through which UV light can pass. In this study, translucent anodic porous alumina (APA) molds for UV nanoimprinting were fabricated by the anodization of an Al substrate. To fabricate a translucent APA mold, an ordered APA film used as a mold for UV nanoimprinting was formed on the surface side of the Al substrate, and then anodization was continued from the back surface of the Al substrate to increase its transparency in the UV spectral range. A gradient change of Al thickness is necessary for the production of a large-area translucent mold, since it lowers the thickness of opaque defects remaining in the mold. The resulting translucent mold was effective for UV nanoimprinting to prepare ordered polymer nanopillar arrays on the surfaces of opaque substrates because the transmittance of the resulting translucent APA mold was 40% at a wavelength of 365 nm, which was confirmed to be sufficiently translucent to polymerize the photocurable monomer used in this study. In addition, it was possible to fabricate roll-type translucent APA molds by using Al pipes as a starting material. A seamless ordered nanopillar array can be effectively formed on a substrate by continuous UV nanoimprinting using the resulting roll-type translucent APA molds. Ordered nanopillar arrays formed on opaque substrates by UV nanoimprinting using translucent APA molds have various potential applications, such as those for forming antireflective and water-repellent surfaces.

Iron(III) Complexes with Hybrid-Type Artificial Siderophores Containing Catecholate and Hydroxamate Sites.

Two hybrid-type artificial siderophore ligands containing both catecholate and hydroxamate groups as iron-capturing sites, bis(2,3-dihydroxybenzamidepropyl)mono[2-propyl]aminomethane (H5LC2H1) and mono(2,3-dihydroxybenzamide-propyl)bis[2-propyl]aminomethane (H4LC1H2), were designed and synthesized. Iron(III) complexes, K2[FeIIILC2H1] and K[FeIIILC1H2], were prepared and characterized spectroscopically, potentiometrically, and electrochemically. The results were compared with those previously reported for iron complexes with non-hybridized siderophores containing either catecholate or hydroxamate groups, K3[FeIIILC3] and [FeIIILH3]. Both K2[FeIIILC2H1] and K[FeIIILC1H2] formed six-coordinate octahedral iron(III) complexes. Evaluation of the thermodynamic properties of the complexes in an aqueous solution indicated high log ß values of 37.3 and 32.3 for K2[FeIIILC2H1] and K[FeIIILC1H2], respectively, which were intermediate between those of K3[FeIIILC3] (44.2) and [FeIIILH3] (31). Evaluation of the ultraviolet-visible and Fourier transform infrared spectra of the two hybrid siderophore-iron complexes under different pH or pD (potential of dueterium) conditions showed that the protonation of K2[FeIIILC2H1] and K[FeIIILC1H2] generated the corresponding protonated species, [FeIIIHnLC2H1](2-n)- and [FeIIIHnLC1H2](1-n)-, accompanied by a significant change in the coordination mode. The protonated hybrid-type siderophore-iron complexes showed high reduction potentials, which were well within the range of those of biological reductants. The results suggest that the hybrid-type siderophore easily releases an iron(III) ion at low pH. The biological activity of the four artificial siderophore-iron complexes against Microbacterium flavescens and Escherichia coli clearly depends on the structural differences between the complexes. This finding demonstrates that the changes in the coordination sites of the siderophores enable close control of the interactions between the siderophores and receptors in the cell membrane.

Dehydrogenative Annulation of Silylated 1H-Indoles with Alkynes via Silyl Migration.

We investigated the dehydrogenative annulation of silylated 1H-indole derivatives with alkynes to synthesize a silole-fused indole. The addition of the in situ generated silylium ion to alkynes was followed by the sila-Friedel-Crafts reaction via silyl migration, realizing regioselective dehydrogenative annulation controlled by the steric bulkiness of a base. The optical properties of the obtained siloloindoles indicated fluorescence of which the intensity depends on the location of the fused silole.

Preparation of size-controlled LiCoPO4 particles by membrane emulsification using anodic porous alumina and their application as cathode active materials for Li-ion secondary batteries.

Membrane emulsification using anodic porous alumina is an effective method for preparing monodisperse droplets with controlled sizes. In this study, membrane emulsification using anodic porous alumina was applied to the preparation of size-controlled particles composed of composite metal oxides. To obtain size-controlled composite metal oxide particles, membrane emulsification was performed using an aqueous solution containing a water-soluble monomer and metal salts as a dispersed phase. After the membrane emulsification, composite metal oxide particles were obtained by solidifying the droplets in a continuous phase and subsequent heat treatment. Here, as a demonstration of this process, the fabrication of size-controlled LiCoPO4 particles, which are considered high-potential cathode active materials for Li-ion secondary batteries (LIBs), was investigated. The application of the obtained LiCoPO4 particles as cathode active materials for LIBs was also investigated. The results of this study showed that LiCoPO4 particles with controlled sizes could be fabricated on the basis of this process and that their cathode properties could be improved by optimizing the heat treatment conditions and particle sizes. According to this process, size-controlled particles composed of various metal oxides can be fabricated by changing the metal salt in the dispersed phase, and the resulting size-controlled particles are expected to be applied not only as cathode active materials for LIBs but also as components of various functional devices.

Structure and Optical Anisotropy of Spider Scales and Silk: The Use of Chromaticity and Azimuth Colors to Optically Characterize Complex Biological Structures.

Herein, we give an overview of several less explored structural and optical characterization techniques useful for biomaterials. New insights into the structure of natural fibers such as spider silk can be gained with minimal sample preparation. Electromagnetic radiation (EMR) over a broad range of wavelengths (from X-ray to THz) provides information of the structure of the material at correspondingly different length scales (nm-to-mm). When the sample features, such as the alignment of certain fibers, cannot be characterized optically, polarization analysis of the optical images can provide further information on feature alignment. The 3D complexity of biological samples necessitates that there be feature measurements and characterization over a large range of length scales. We discuss the issue of characterizing complex shapes by analysis of the link between the color and structure of spider scales and silk. For example, it is shown that the green-blue color of a spider scale is dominated by the chitin slab's Fabry-Pérot-type reflectivity rather than the surface nanostructure. The use of a chromaticity plot simplifies complex spectra and enables quantification of the apparent colors. All the experimental data presented herein are used to support the discussion on the structure-color link in the characterization of materials.

Syntheses, Characterizations, Crystal Structures, and Protonation Reactions of Dinitrogen Chromium Complexes Supported with Triamidoamine Ligands.

A novel dinitrogen-dichromium complex, [{Cr(LBn)}2(µ-N2)] (1), has been prepared from reaction of CrCl3 with a lithiated triamidoamine ligand (Li3LBn) under dinitrogen. The X-ray crystal structure analysis of 1 revealed that it is composed of two independent dimeric Cr complexes bridged by N2 in the unit cell. The bridged N-N bond lengths (1.188(4) and 1.185(7) Å) were longer than the free dinitrogen molecule. The elongations of N-N bonds in 1 were also supported by the fact that the ν(N-N) stretching vibration at 1772 cm-1 observed in toluene is smaller than the free N2. Complex 1 was identified to be a 5-coordinated high spin Cr(IV) complex by Cr K-edge XANES measurement. The 1H NMR spectrum and temperature dependent magnetic susceptibility of 1 indicated that complex 1 is in the S = 1 ground state, in which two Cr(IV) ions and unpaired electron spins of the bridging N22- ligand are strongly antiferromagnetically coupled. Reaction of complex 1 with 2.3 equiv of Na or K gave chromium complexes with N2 between the Cr ion and the respective alkali metal ion, [{CrNa(LBn)(N2)(Et2O)}2] (2) and [{CrK(LBn)(N2)}4(Et2O)2] (3), respectively. Furthermore, the complexes 2 and 3 reacted with 15-crown-5 and 18-crown-6 to form the respective crown-ether adducts, [CrNa(LBn)(N2)(15-crown-5)] (4) and [CrK(LBn)(N2)(18-crown-6)] (5). The XANES measurements of complexes 2, 3, 4, and 5 revealed that they are high spin Cr(IV) complexes like complex 1. All complexes reacted with a reducing agent and a proton source to form NH3 and/or N2H4. The yields of these products in the presence of K+ were higher than those in the presence of Na+. The electronic structures and binding properties of 1, 2, 3, 4, and 5 were evaluated and discussed based on their DFT calculations.

Preparations of trans- and cis-µ-1,2-Peroxodiiron(III) Complexes.

The iron(II) complex with cis,cis-1,3,5-tris(benzylamino)cyclohexane (Bn3CY) (1) has been synthesized and characterized, which reacted with dioxygen to form the peroxo complex 2 in acetone at -60 °C. On the basis of spectroscopic measurements for 2, it was confirmed that the peroxo complex 2 has a trans-µ-1,2 fashion. Additionally, the peroxo complex 2 was reacted with benzoate anion as a bridging agent to give a peroxo complex 3. The results of resonance Raman and 1H-NMR studies supported that the peroxo complex 3 is a cis-µ-1,2-peroxodiiron(III) complex. These spectral features were interpreted by using DFT calculations.

The Steric Effect in Preparations of Vanadium(II)/(III) Dinitrogen Complexes of Triamidoamine Ligands Bearing Bulky Substituents.

The reactions of newly designed lithiated triamidoamines Li3LR (R = iPr, Pen, and Cy2) with VCl3(THF)3 under N2 yielded dinitrogen-divanadium complexes with a µ-N2 between vanadium atoms [{V(LR)}2(µ-N2)] (R = iPr (1) and Pen (2)) for the former two, while not dinitrogen-divanadium complexes but a mononuclear vanadium complex with a vacant site, [V(LCy2)] (R = Cy2 (3)), were obtained for the third ligand. The V-NN2 and N-N distances were 1.7655(18) and 1.219(4) Å for 1 and 1.7935(14) and 1.226(3) Å for 2, respectively. The ν(14N-14N) stretching vibrations of 1 and 2, as measured using resonance Raman spectroscopy, were detected at 1436 and 1412 cm-1, respectively. Complex 3 reacted with potassium metal in the presence of 18-crown-6-ether under N2 to give a hetero-dinuclear vanadium complex with µ-N2 between vanadium and potassium, [VK(LCy2)(µ-N2)(18-crown-6)] (4). The N-N distance and ν(14N-14N) stretching for 4 were 1.152(3) Å and 1818 cm-1, respectively, suggesting that 4 is more activated than complexes 1 and 2. The complexes 1, 2, 3, and 4 reacted with HOTf and K[C10H8] to give NH3 and N2H4. The yields of NH3 and N2H4 (per V atom) were 47 and 11% for 1, 38 and 16% for 2, 77 and 7% for 3, and 80 and 5% for 4, respectively, and 3 and 4, which have a ligand LCy2, showed higher reactivity than 1 and 2.

Micro-nano hierarchical pillar array structures prepared on curved surfaces by nanoimprinting using flexible molds from anodic porous alumina and their application to superhydrophobic surfaces.

Flexible molds with micro-nano hierarchical structures on the surface were fabricated by a two-step template process using anodic porous alumina as a starting material. The obtained flexible molds could be used to form micro-nano hierarchical pillar arrays on the surface of glass tubes and convex lenses by photo-nanoimprinting. The contact angle characteristics of the surfaces with hierarchical pillar arrays were measured, and it was confirmed that they exhibit superhydrophobic properties with a water-droplet contact angle exceeding 150°. The flexible molds obtained in this study can be used repeatedly and efficiently to form micro-nano hierarchical surfaces with superhydrophobic properties on the surfaces of substrates with various curvatures.

Improvements in photoelectric performance of dye-sensitised solar cells using ionic liquid-modified TiO2 electrodes.

One of the major problems in dye-sensitised solar cells (DSSCs) is the aggregation of dyes on TiO2 electrodes, which leads to undesirable electron transfer. Various anti-aggregation agents, such as deoxycholic acid, have been proposed and applied to prevent dye aggregation on the electrodes. In this study, we designed and synthesised a phosphonium-type ionic liquid that can be modified on the TiO2 electrode surface and used as a new anti-aggregation agent. Although the modification of the ionic liquid onto the electrode reduced the amount of dye adsorbed on the electrode, it showed a significant anti-aggregation effect, thereby improving the photovoltaic performance of DSSCs with N3 and J13 dyes. This finding suggests that ionic liquids are effective as anti-aggregation agents for DSSCs.

Preparation of ordered nanohole array structures by anodization of prepatterned Cu, Zn, and Ni.

Anodic porous oxides with ordered nanohole array structures were prepared by the formation of concave arrays on the surface of Cu, Zn, and Ni substrates and the subsequent anodization of the prepatterned substrates. The concave arrays on the surface of the substrate were formed by Ar ion milling using an alumina mask. Although the anodization of Cu, Zn, and Ni substrates without prepatterning generates spongelike porous structures, ordered arrays of cylindrical nanoholes were obtained by the anodization of prepatterned substrates. The interpore distance of the obtained nanohole arrays was controlled by changing the period of the concave arrays. Crystallized ordered nanohole arrays of Cu2O, ZnO, and NiO were also obtained by heat treatment. The obtained anodic porous oxide with ordered nanohole array structures can be used for various applications such as photocatalysts, solar cells, and sensors.

Efficient fabrication of ordered alumina through-hole membranes using a TiO2 protective layer prepared by atomic layer deposition.

Ordered alumina through-hole membranes were obtained by a combination of the anodization of Al, formation of a TiO2 protective layer, and subsequent etching. Two-layered anodic porous alumina materials composed of TiO2-coated and noncoated alumina were prepared by the combination of the anodization of Al and the formation of a TiO2 protective layer by atomic layer deposition (ALD). The obtained two layers of anodic porous alumina have different solubilities because the TiO2 thin layer formed by ALD acts as a protective layer that prevents the dissolution of the alumina layer during wet etching of the sample in an etchant. After the selective dissolution of the bottom layer of porous alumina without the TiO2 layer, an ordered alumina through-hole membrane could be detached from the Al substrate. This process allows the repeated preparation of ordered alumina through-hole membranes from a single Al substrate. By this process, ordered alumina through-hole membranes with large interhole distances could also be obtained. The obtained alumina through-hole membrane can be used in various applications.

Synthesis of 1-Silabenzo[d,e]isochromanes via Electrophilic Aromatic Substitution of Aldehydes Activated by Silylium Ion.

A strong Lewis acid silylium ion was utilized for dehydrogenative annulation between dialkyl(1-naphthyl)silanes 1 and aldehydes 2. Silane 1a was reacted with [Ph3C][B(C6F5)4] in the presence of 2,6-di-tert-butyl-4-methylpyridine and aldehydes 2 to afford the annulation product, 1-silabenzo[d,e]isochromanes 3, in moderate isolated yields. The annulation occurred only at the 8-position on the 1-naphthyl group. The silylium ion-promoted hydrosilylation proceeded competitively to afford silyl ethers 4 via the same intermediates, silylcarboxonium ions, in the dehydrogenative annulation. The ratio of 3 and 4 was affected by solvents and the electronic properties of aromatic aldehydes; for example, the use of less polar solvents and that of benzaldehydes with an electron-withdrawing group at the para-position predominantly yielded 3. This annulation reaction was applicable to aldehydes bearing a heteroaromatic group and aliphatic alkyl groups. Judging from these results, both the formation of silylcarboxonium ions by in situ-generated silylium ions and the electrophilic aromatic substitution are important for this annulation reaction.

Synthesis and Physico-Chemical Properties of Homoleptic Copper(I) Complexes with Asymmetric Ligands as a DSSC Dye.

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).

Renewable Superhydrophobic Surfaces Prepared by Nanoimprinting Using Anodic Porous Alumina Molds.

Renewable superhydrophobic surfaces based on laminated polymer films with nanopillar array structures were prepared. Polymer nanopillar arrays exhibiting superhydrophobic properties were prepared by nanoimprinting using anodic porous alumina as a mold. The hydrophobic properties of the obtained polymer nanopillar arrays could be controlled and optimized by changing the geometrical structures of anodic porous alumina molds used for nanoimprinting. The polymer films were laminated using a photocurable monomer. The ordered polymer nanopillar array structures could be maintained even after delamination of the films. Renewed polymer nanopillar arrays exposed by peeling off the upper films exhibited a water contact angle higher than 150°. Using this process, superhydrophobic surfaces could be obtained repeatedly by delamination of a film even when superhydrophobicity deteriorated with the collapse of surface patterns. The obtained renewable superhydrophobic surfaces can be used for various applications requiring high durability.

Preparation of Ordered Anodic Porous Alumina with Single-Nanometer-Order-Size Holes by Atomic Layer Deposition.

Ordered anodic porous alumina with controlled-size holes on the order of a single-nanometer scale was obtained by the atomic layer deposition (ALD) of Al2O3 or TiO2. The thin metal oxide layers of uniform thickness were formed successfully on the inner wall of the hole of the ordered anodic porous alumina with high aspect ratios by ALD. The hole diameter of the ordered anodic porous alumina could be controlled precisely by adjusting the number of cycles of ALD. The obtained anodic porous alumina with an ordered hole arrangement of reduced holes will be applied to various application fields requiring uniform-sized holes on the order of a single-nanometer scale, such as the starting material for preparing various types of quantum effect devices.

Effect of Counteranions in Electrocatalytic Hydrogen Generation Promoted by Bis(phosphinopyridyl) Ni(II) Complexes.

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.