Self-Assembled Molecular Fibers Aligned by Compression in Water.

Molecular self-assembly has attracted much attention as a potential approach for fabricating nanostructured functional materials. To date, energy-efficient fabrication of nano-objects such as nanofibers, nanorings, and nanotubes is achieved using well-designed self-assembling molecules. However, the application of molecular self-assembly to industrial manufacturing processes remains challenging because regulating the positions and directions of self-assembled products is difficult. Non-covalent molecular assemblies are also too fragile to allow mechanical handling. The present work demonstrates the macroscopic alignment of self-assembled molecular fibers using compression. Specifically, the macroscopic bundling of self-assembled nanofibers is achieved following dispersion in water. These fiber bundles can also be chemically crosslinked without drastic changes in morphology via trialkoxysilyl groups. Subsequently, vertically oriented porous membranes can be produced rapidly by slicing the bundles. This technique is expected to be applicable to various functional self-assembled fibers and can lead to the development of innovative methods of producing anisotropic nanostructured materials.

Hybrid Surface Design of Organosilica Films for Laser Desorption/Ionization Mass Spectrometry: Low Free Energy Surface with Interactive Sites.

Laser desorption/ionization mass spectrometry (LDI-MS) assisted by solid substrates is useful for the facile and rapid analysis of low-molecular-weight compounds. The LDI performance of solid substrates depends on not only a surface morphology but also the surface functionalities dominating the surface-analyte interactions. In this study, we propose a hybrid surface design for LDI substrates, realizing both weak surface-analyte interaction and homogeneous distribution of analytes. The hybrid surface consisted of a mixture of fluoroalkylsilane (FAS), SiO2, and TiO2 and was formed on organosilica substrates containing UV-laser-absorbing naphthalimide moieties. To investigate the surface interactions, the hybrid surface as well as conventional hydrophobic surfaces treated with FAS only were prepared on flat organosilica films. Contact angle measurements and surface free energy analysis showed that the hybrid surface exhibited the highest hydrophobicity, while the contribution of the polar and hydrogen bonding terms in the surface free energy was clearly observed. The organosilica film with the hybrid surface demonstrated significant LDI performance for the detection of biorelated compounds (e.g., peptides, phospholipids, and medicines), and a high detection ability was particularly observed for peptides. The substrate surface promoted the desorption/ionization of analytes through a low surface free energy and uniform distribution of the analytes due to the interactive sites. The hybrid surface design was then applied to a nanostructured organosilica substrate consisting of a base film and a nanoparticle layer. The signal intensity of a peptide was further improved approximately 3-fold owing to the increased surface area of the nanostructured substrate, and the limit of detection reached the subfemtomole order. Our hybrid surface design is expected to improve the LDI performance of various nanostructured solid substrates.

TiN nanopillar-enhanced laser desorption and ionization of various analytes.

The present paper reports on the use of TiN nanopillars as a robust analytical substrate for laser desorption/ionization mass spectrometry (LDI-MS). TiN nanopillars were fabricated on silicon wafers through the dynamic oblique deposition of titanium, followed by thermal treatment in an ammonia atmosphere. The TiN nanopillars were readily applicable to a simple "dried-droplet" method in the LDI-MS without surface modification or pre-treatment. A broad range of analytes were investigated, including a small drug molecule, a synthetic polymer, sugars, peptides, and proteins. Intact molecular signals were detected with low noise interference and no fragmentation. The developed TiN-nanopillar-based approach extends the applicable mass limit to 150 kDa (immunoglobulin G) and was able to detect trypsinogen (24 kDa) at levels as low as 50 fmol µL-1 with adequate shot-to-shot signal reproducibility. In addition, we carried out MS analysis on biomolecule-spiked human blood plasma and a mixture of standard samples to investigate the promise of the TiN nanopillars for clinical research. The experimental observations are validated using electromagnetic and heat-transfer simulations. The TiN nanopillars show a reduced reflection and exhibit surges in the TiN surface temperature upon irradiation with electromagnetic radiation. Localization of thermal energy at the tips of the TiN pillars is likely to be responsible for the superior LDI performance. Our results suggest that the development of nanostructured TiN substrates will contribute to the widespread implementation of nanostructured solid substrates for biomedical and clinical applications with simple processes.

Amphiphilic Polymer Mediators Promoting Electron Transfer on Bioanodes with PQQ-Dependent Glucose Dehydrogenase.

Redox-active phenazinium salts bonded to amphiphilic polymer backbones are demonstrated to function as high-performance electron-transfer mediators in enzymatic bioanodes applicable to biofuel cells. The redox-active moieties could be easily tethered to the electrodes by physical adsorption of the hydrophobic regions of the polymer backbones onto the electrode surface. On the other hand, long hydrophilic chains were essential to ensure high mobility of the redox-active moieties in aqueous solutions and to enhance their electron-transfer properties. We found that an amphiphilic mediator with a linear polymer backbone exhibited stable adsorption behavior on the electrode surface and generated high bioelectrocatalytic current (>1.8 ± 0.32 mA/cm2) in the presence of pyrroloquinoline quinone-dependent glucose dehydrogenase and an aqueous solution of glucose fuel. This current was more than two times higher than that of an electrode treated with a low-molecular-weight phenazinium salt. Moreover, the bioelectrode modified with the polymer mediator retained the high electrocatalytic current after 10 exchanges of the glucose fuel. The mediator-modified bioelectrodes are expected to be useful for various bio-related energy and electronic devices.

Periodic mesoporous organosilica with molecular-scale ordering self-assembled by hydrogen bonds.

Nanoporous materials with functional frameworks have attracted attention because of their potential for various applications. Silica-based mesoporous materials generally consist of amorphous frameworks, whereas a molecular-scale lamellar ordering within the pore wall has been found for periodic mesoporous organosilicas (PMOs) prepared from bridged organosilane precursors. Formation of a "crystal-like" framework has been expected to significantly change the physical and chemical properties of PMOs. However, until now, there has been no report on other crystal-like arrangements. Here, we report a new molecular-scale ordering induced for a PMO. Our strategy is to form pore walls from precursors exhibiting directional H-bonding interaction. We demonstrate that the H-bonded organosilica columns are hexagonally packed within the pore walls. We also show that the H-bonded pore walls can stably accommodate H-bonding guest molecules, which represents a new method of modifying the PMO framework.

A solid chelating ligand: periodic mesoporous organosilica containing 2,2'-bipyridine within the pore walls.

Synthesis of a solid chelating ligand for the formation of efficient heterogeneous catalysts is highly desired in the fields of organic transformation and solar energy conversion. Here, we report the surfactant-directed self-assembly of a novel periodic mesoporous organosilica (PMO) containing 2,2'-bipyridine (bpy) ligands within the framework (BPy-PMO) from a newly synthesized organosilane precursor [(i-PrO)3Si-C10H6N2-Si(Oi-Pr)3] without addition of any other silane precursors. BPy-PMO had a unique pore-wall structure in which bipyridine groups were densely and regularly packed and exposed on the surface. The high coordination ability to metals was also preserved. Various bipyridine-based metal complexes were prepared using BPy-PMO as a solid chelating ligand such as Ru(bpy)2(BPy-PMO), Ir(ppy)2(BPy-PMO) (ppy = 2-phenylpyridine), Ir(cod)(OMe)(BPy-PMO) (cod = 1,5-cyclooctadiene), Re(CO)3Cl(BPy-PMO), and Pd(OAc)2(BPy-PMO). BPy-PMO showed excellent ligand properties for heterogeneous Ir-catalyzed direct C-H borylation of arenes, resulting in superior activity, durability, and recyclability to the homogeneous analogous Ir catalyst. An efficient photocatalytic hydrogen evolution system was also constructed by integration of a Ru-complex as a photosensitizer and platinum as a catalyst on the pore surface of BPy-PMO without any electron relay molecules. These results demonstrate the great potential of BPy-PMO as a solid chelating ligand and a useful integration platform for construction of efficient molecular-based heterogeneous catalysis systems.

Perfluoroalkyl Group-Covered Organosilica Films for the Sensitive Detection of Sulfonylurea Herbicides in Laser Desorption/Ionization Mass Spectrometry.

Simple and rapid screening of agrochemicals greatly contributes to food and environmental safety. Matrix-free laser desorption/ionization mass spectrometry (LDI-MS) is an effective tool for high-throughput analysis of low-molecular-weight compounds. In this study, we report a UV-laser-absorbing organosilica film for the sensitive detection of various sulfonylurea herbicides using LDI-MS. Organosilica films with fluoroalkyl groups on the organic part are fabricated, followed by additional modification of the silica moiety with a fluoroalkyl coupling agent to cover the film surface with hydrophobic fluoroalkyl groups. Nanoimprinting is conducted to impart nanostructures on the film surface to enhance the LDI performance. The fabricated nanostructured organosilica films accomplish sensitive detection of cyclosulfamuron and azimsulfuron at concentrations as low as 1 fmol µL-1. The applicability of the nanostructured organosilica films is confirmed by the recovery of cyclosulfamuron and ethametsulfuron-methyl from pea sprouts (Pisum sativum) hydroponically grown in herbicide-spiked water at concentrations of 0.5 ppm.

Enhanced fluorescence detection of metal ions using light-harvesting mesoporous organosilica.

Enhanced fluorescence detection of metal ions was realized in a system consisting of a fluorescent 2,2'-bipyridine (BPy) receptor and light-harvesting periodic mesoporous organosilica (PMO). The fluorescent BPy receptor with two silyl groups was synthesized and covalently attached to the pore walls of biphenyl (Bp)-bridged PMO powder. The fluorescence intensity from the BPy receptor was significantly enhanced by the light-harvesting property of Bp-PMO, that is, the energy funneling into the BPy receptor from a large number of Bp groups in the PMO framework which absorbed UV light effectively. The enhanced emission of the BPy receptor was quenched upon the addition of a low concentration of Cu(2+) (0.15-1.2×10(-6) M), resulting in the sensitive detection of Cu(2+). Upon titration of Zn(2+) (0.3-6.0×10(-6) M), the fluorescence excitation spectrum was systematically changed with an isosbestic point at 375 nm through 1:1 complexation of BPy and Zn(2+) similar to that observed in BPy-based solutions, indicating almost complete preservation of the binding property of the BPy receptor despite covalent fixing on the solid surface. These results demonstrate that light-harvesting PMOs have great potential as supporting materials for enhanced fluorescence chemosensors.

Energy and electron transfer from fluorescent mesostructured organosilica framework to guest dyes.

Energy and electron transfer from frameworks of nanoporous or mesostructured materials to guest species in the nanochannels have been attracting much attention because of their increasing availability for the design and construction of solid photofunctional systems, such as luminescent materials, photovoltaic devices, and photocatalysts. In the present study, energy and electron-transfer behavior of dye-doped periodic mesostructured organosilica films with different host-guest arrangements were systematically examined. Fluorescent tetraphenylpyrene (TPPy)-silica mesostructured films were used as a host donor. The location of guest perylene bisimide (PBI) dye molecules, acting as an acceptor, could be controlled on the basis of the molecular design of the PBI substituent groups. PBI dyes with bulky substituents and polar anchoring groups were located at the pore surface with low self-aggregation, which induced efficient energy or electron transfer because of the close host-guest arrangement. However, PBI dye with bulky and hydrophobic substituents was located in the center of template surfactant micelles; the fluorescence emission from the host TPPy groups was hardly quenched when the host-guest distance was longer than the critical Förster radius (ca. 4.5 nm). The relationship between the energy or electron-transfer efficiency and the location of guest species in the channels of mesostructured organosilica was first revealed by molecular design of the PBI substituents.

Syntheses, properties and applications of periodic mesoporous organosilicas prepared from bridged organosilane precursors.

Periodic mesoporous organosilicas (PMOs) prepared by surfactant-directed polycondensation of bridged organosilane precursors are promising for a variety of next-generation functional materials, because their large surface areas, well-defined nanoporous structures and the structural diversity of organosilica frameworks are advantageous for functionalization. This critical review highlights the unique structural features of PMOs and their expanding potential applications. Since the early reports of PMOs in 1999, various synthetic approaches, including the selection of hydrolytic reaction conditions, development of new precursor compounds, design of templates and the use of co-condensation or grafting techniques, have enabled the hierarchical structural control of PMOs from molecular- and meso-scale structures to macroscopic morphology. The introduction of functional organic units, such as highly fluorescent π-conjugates and electroactive species, into the PMO framework has opened a new path for the development of fluorescent systems, sensors, charge-transporting materials and solid-state catalysts. Moreover, a combinational materials design approach to the organosilica frameworks, pore wall surfaces and internal parts of mesopores has led to novel luminescent and photocatalytic systems. Their advanced functions have been realized by energy and electron transfer from framework organics to guest molecules or catalytic centers. PMOs, in which the precise design of hierarchical structures and construction of multi-component systems are practicable, have a significant future in a new field of functional materials (93 references).

Nanoporous Substrates with Molecular-Level Perfluoroalkyl/Alkylamide Surface for Laser Desorption/Ionization Mass Spectrometry of Small Proteins.

The rapid detection of biomolecules greatly contributes to health management, clinical diagnosis, and prevention of diseases. Mass spectrometry (MS) is effective for detecting and analyzing various molecules at high throughput. However, there are problems with the MS analysis of biological samples, including complicated separation operations and essential pretreatments. In this study, a nanostructured organosilica substrate for laser desorption/ionization mass spectrometry (LDI-MS) is designed and synthesized to detect peptides and small proteins efficiently and rapidly. The surface functionality of the substrate is tuned by perfluoroalkyl/alkylamide groups mixed at a molecular level. This contributes to both lowering the surface free energy and introducing weak anchoring sites for peptides and proteins. Analyte molecules applied onto the substrate are homogeneously distributed and readily desorbed by the laser irradiation. The organosilica substrate enables the efficient LDI of various compounds, including peptides, small proteins, phospholipids, and drugs. An amyloid ß protein fragment, which is known as a biomarker for Alzheimer's disease, is detectable at 0.05 fmol µL-1. The detection of the amyloid ß at 0.2 fmol µL-1 is also confirmed in the presence of blood components. Nanostructured organosilica substrates incorporating a molecular-level surface design have the potential to enable easy detection of a wide range of biomolecules.

Self-assembled single-crystal bimodal porous GaN exhibiting a petal effect: application as a sensing platform and substrate for optical devices.

This paper investigates the petal effect (hydrophobicity and strong adhesion) observed on single-crystal bimodal porous GaN (porous GaN), which has almost the same electrical properties as bulk GaN. The water contact angles of porous GaN were 100°-135° despite the intrinsic hydrophilic nature of GaN. Moreover, it was demonstrated that the petal effect of porous GaN leads to the uniform attachment of water solutions, enabling highly uniform and aggregation-free attachment of chemicals and quantum dots. These results indicate that porous GaN can be applied in quantum dot light-emitting diodes and as an analytical substrate.

Theoretical studies on Si-C bond cleavage in organosilane precursors during polycondensation to organosilica hybrids.

Molecular orbital theory calculations were carried out to predict the occurrence of Si-C bond cleavage in various organosilane precursors during polycondensation to organosilica hybrids under acidic and basic conditions. On the basis of proposed mechanisms for cleavage of the Si-C bonds, the proton affinity (PA) of the carbon atom at the ipso-position and the PA of the carbanion generated after Si-C cleavage were chosen as indices for Si-C bond stability under acidic and basic conditions, respectively. The indices were calculated using a density functional theory (DFT) method for model compounds of organosilane precursors (R-Si(OH)(3)) having organic groups (R) of benzene (Ph), biphenyl (Bp), terphenyl (Tph), naphthalene (Nph), N-methylcarbazole (MCz), and anthracene (Ant). The orders for the predicted stability of the Si-C bond were Ph > Nph > Bp > Ant > Tph > MCz for acidic conditions and Ph > MCz > Bp > Nph > Tph > Ant for basic conditions. These behaviors were primarily in agreement with experimental results where cleavage of the Si-C bonds occurred for Tph (both acidic and basic), MCz (acidic), and Ant (basic). The Si-C bond cleavage of organosilane precursors during polycondensation is qualitatively predicted from these indices based on our theoretical approach.

Direct nanoimprinting of nanoporous organosilica films consisting of covalently crosslinked photofunctional frameworks.

Nanoimprinting methods have been used widely to prepare various patterned or nanostructured thin films from inorganic or organic components. However, the accumulation of large functional aromatic groups in covalently crosslinked nanoimprints is challenging, due to the difficulty in controlling the fluidity and reactivity of the precursor films. In this work, nanoimprinting of naphthalimide-silica sol-gel films results in vertically oriented nanoporous structures consisting of covalently crosslinked UV-absorbing frameworks. The nanoimprinted films demonstrate potential as robust analytical substrates for laser desorption/ionization mass spectrometry (LDI-MS). The sol-gel polycondensation behavior of the precursors is examined using 29Si NMR spectroscopy to determine reaction conditions suitable for nanoimprinting. The inorganic-organic hybrid frameworks containing a high density of naphthalimide groups exhibit small volume shrinkage during the polycondensation reactions, which leads to desired nanoimprinting. Various bio-related compounds on the order of picomole to femtomole quantities are detectable by LDI-MS measurements using the nanoimprinted substrates. To improve their user-friendliness and signal intensity in LDI-MS analysis, the nanoimprinted substrates are patterned with surface-modified silica nanoparticles. The direct formation of surface nanostructures by nanoimprinting of functional organosilica films may open a new path to developing optically and electronically functional materials, thereby widening their utility.

Hole-transporting periodic mesostructured organosilica.

Hole-transporting framework is formed by surfactant-templated sol-gel polycondensation of an electroactive phenylenevinylene-based organosilane precursor. Molecular geometry of the three-armed precursor contributes to both formation of periodic mesostructures and introduction of hole conductivity in the organosilica hybrids. Electroactive organosilicas with mesopores and large surface areas have great potentials for novel photovoltaic and photocatalytic systems.

Fluorescence emission from 2,6-naphthylene-bridged mesoporous organosilicas with an amorphous or crystal-like framework.

We report that 2,6-naphthylene-bridged periodic mesoporous organosilicas exhibit unique fluorescence behavior that reflects molecular-scale periodicities in the framework. Periodic mesoporous organosilicas consisting of naphthalene-silica hybrid frameworks were synthesized by hydrolysis and condensation of a naphthalene-derived organosilane precursor in the presence of a template surfactant. The morphologies and meso- and molecular-scale periodicities of the organosilica materials strongly depend on the synthetic conditions. The naphthalene moieties embedded within the molecularly ordered framework exhibited a monomer-band emission, whereas those embedded within the amorphous framework showed a broad emission attributed to an excimer band. These results suggest that the naphthalene moieties fixed within the crystal-like framework are isolated in spite of their densely packed structure, different from conventional organosilica frameworks in which only excimer emission was observed for both the crystal-like and amorphous frameworks at room temperature. This key finding suggests a potential to control interactions between organic groups and thus the optical properties of inorganic/organic hybrids.

Self-assembled fibers photopolymerized in nematic liquid crystals: stable electrooptical switching in light-scattering mode.

Liquid-crystalline (LC) gels showing stable light-scattering electrooptical properties have been prepared by the photopolymerization of a gelator forming self-assembled fibers in a room-temperature nematic liquid crystal. A polymerizable gelator having methacryloyl moieties self-assembles into finely dispersed fibers in the nematic liquid crystal, resulting in the formation of LC physical gels. Photopolymerization of the gelator in the gel states leads to the preparation of cross-linked fibrous networks. The LC polydomain structures effective for light-scattering electrooptical switching are kept after polymerization. The polymerized LC gels show stable reversible switching of electrooptical responses with enhanced threshold properties between 0 and 70 V.

Charge Separation in a Multifunctionalized Framework of Hydrogen-Bonded Periodic Mesoporous Organosilica.

Integration of functional molecular parts into nanoporous materials in a state that allows intermolecular charge or energy transfer is one of the key approaches to the development of photofunctional and electroactive materials. Herein, we report charge separation in a functionalized framework of a periodic mesoporous organosilica (PMO) self-assembled by hydrogen bonds. Electroactive π-conjugated organic species with different electron-donating and electron-accepting properties were selectively fixed onto the external surface of a nanoparticulate PMO, within the pore wall, and onto the surface of the internal mesopore. UV irradiation of the modified PMO resulted in photoinduced electron transfer and charge separation from the external surface to the pore wall and from the pore wall to the surface of the internal mesopores. These results suggest the high potential of multifunctionalized PMOs in the construction of photocatalytic reaction fields.

Organised structures of flexible bolaamphiphiles with trisiloxane spacers: three- and two-dimensional molecular assemblies with different molecular conformation.

We designed and synthesised new bolaamphiphiles consisting of hydrophobic rigid cores, flexible trisiloxane spacers, and terminal ammonium groups. Organised structures of the bolaamphiphiles with biphenyl and azobenzene cores were examined in the bulk and in the monolayer states. In the bulk states, these molecules exhibited layered liquid crystal phases with an extended molecular conformation. The biphenyl derivative showed only lyotropic liquid crystallinity in the presence of water. In contrast, the azobenzene derivative exhibited both thermotropic and lyotropic liquid crystal behaviour. UV-vis spectroscopy for the materials indicated that the association of the azobenzene cores contributed to the formation of the stable mesomorphic structures. On the other hand, when these molecules were spread on the water surface, monolayer films were formed with both hydrophilic ends on the water surface. The compression of the monolayer films induced the conformational changes in the bolaamphiphiles from a flat-lying extended state to a reverse U-shaped folded state and the core parts were lifted up to the uppermost film surface, maintaining their flat orientation. The cores integrated to the film surface were shown to be monomeric species by UV-vis spectroscopy, whereas the azobenzene cores tend to associate in the bulk and on the water surface at low surface pressures. The - photoisomerisation and - thermal isomerisation of the azobenzene cores occurred efficiently in the compressed monolayer films, which is available to tune the surface properties of the monolayer films. For these monolayer films with two-dimensional core arrays, we can expect novel surface-mediated functionalities as photo- and electro-active surfaces, alignment layers for materials synthesis, and molecular sensors due to their tunabilities in core density and polarity.