Organic supramolecular architectures and their sol-gel transcription to Silica nanotubes

A Tautoleptic Approach to Chiral Hydrogen-Bonded Supramolecular Tubular Polymers with Large Cavity

A new strategy towards tubular hydrogen-bonded polymers based on the self-assembly of isocytosine tautomers in orthogonal directions is proposed and experimentally verified, including by 1 H fast magic-angle spinning (MAS) solid-state NMR. The molecular tubes obtained possess large internal diameter and tailor-made outer functionalities rendering them potential candidates for a number of applications.

Left-handed helical polymer resin nanotubes prepared by using N-palmitoyl glucosamine

Although the preparation of single-handed helical inorganic and hybrid organic-inorganic nanotubes is well developed, approaches to the formation of single-handed organopolymeric nanotubes are limited. Here, left-handed helical m-phenylenediamine-formaldehyde resin and 3-aminophenol-formaldehyde resin nanotubes were prepared by using N-palmitoyl glucosamine that can self-assemble into left-handed twisted nanoribbons in a mixture of methanol and water. In the reaction mixture, the helical pitch of the nanoribbons decreased with increasing reaction time. The resin nanotubes were obtained after removing the N-palmitoyl glucosamine template, and circular dichroism spectroscopy indicated that the organopolymeric nanotubes had optical activity. Carbonaceous nanotubes were then prepared by carbonization of the 3-aminophenol-formaldehyde resin nanotubes.

Hybrid bicelles as a pH-sensitive nanocarrier for hydrophobic drug delivery

Stabilized disc-like hybrid bicelles provide pH-sensitive release, preferable cellular uptake, tumor accumulation and therapeutic effect in vitro and in vivo.

Lighting up silica nanotubes transcribed from the submicron structure of a metal-peptide hybrid

Fluorescent silica nanotubes are attracting increasing interest because of their versatile applicability in a range of diverse fields. By using sol-gel transcription of tetraethylorthosilicate (TEOS) from various soft templates, silica nanotubes can be conveniently prepared. Metal-peptide hybrids with well-defined nanostructures and outstanding functionalities are very interesting candidates to serve as templates. Herein, we demonstrate that glutathione (GSH) can act as a building block for a bioinspired structure with dimensions down to the nanoscale, based on specific interactions between metal ions and the peptide. Congo red is able to selectively stain the nanofibres obtained, and appears apple-green in colour, implying that Congo red is promising to serve as an effective and convenient probe for determining the self-assembly of GSH and copper ions. Furthermore, silica nanotubes are synthesized using the nanofibres as a template in a very simple way. The silica nanotubes can be lit up by biomolecule-templated metal nanoparticles or nanoclusters and emit bright fluorescence. This work will certainly open up new opportunities in fabricating a broad range of nanostructured materials with versatile functionalities.

Luminescent alkynylplatinum(II) terpyridyl metallogels stabilized by Pt...Pt, pi-pi, and hydrophobic-hydrophobic interactions

A series of luminescent alkynylplatinum(II) terpyridyl complexes have been synthesized and characterized by 1H NMR, IR, FAB-mass spectrometry, and elemental analysis; one of the platinum(III) complexes has also been structurally characterized by X-ray crystallography. Their electrochemical and photophysical properties have also been investigated. A majority of the complexes were able to form stable thermoreversible metallogels in organic solvents, tested by the "stable-to-inversion of a test tube" method. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of the xerogels showed typical fibrous structures on the micrometer scale. Interestingly, whereas 2-OTf, 3-OTf, and 5-PF6 formed thermotropic metallogels mainly through van der Waals' forces with different emission colors, 1-X (X = OTf, BF4, PF6, and ClO4) showed additional Pt...Pt and pi-pi interactions to stabilize the resultant metallogels and showed drastic color changes during the gel-to-sol phase transition. The metallogels of 1-X were also different colors, depending on the nature of the counter anions, which governs the degree of aggregation and the extent of Pt...Pt and pi-pi interactions involved in the gelation process. This property may be utilized to serve as an effective reporter for microenvironmental changes.

Unusual luminescence enhancement of metallogels of alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine complexes upon a gel-to-sol phase transition at elevated temperatures

A series of alkynylplatinum(II) complexes of 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine has been synthesized and characterized by (1)H NMR, IR, FAB mass spectrometry, and elemental analysis; the photophysical properties have also been investigated. All the complexes have been shown to exhibit interesting gelation properties. Scanning electron microscopy (SEM) of the xerogels showed a network of fibrous structures, typical of morphologies of organogels/metallogels. Interestingly, two of the complexes were found to show strong luminescence enhancement upon a gel-to-sol phase transition upon increasing the temperature. This unusual behavior is rarely encountered, as it represents a sharp contrast to that exhibited by other typical thermotropic organogels and metallogels reported so far. Variable-temperature UV-vis and luminescence spectroscopies were performed to probe the gel-to-sol phase transition. Concentration-dependent, variable-temperature, and time-resolved emission studies in dilute benzene solution have also been made to provide further insights into the spectroscopic origin in the sol forms. A quantitative treatment of the system based on the Birks scheme has been performed.

In situ X-ray measurements to probe a new solid-state polycondensation mechanism for the design of supramolecular organo-bridged silsesquioxanes

A long-range ordered organic/inorganic material is synthesized from a bis-silane, (EtO)(3)Si-(CH(2))(3)-NHCONH-C(6)H(4)-NHCONH-(CH(2))(3)-Si(OEt)(3). This crosslinked sol-gel solid exhibits a supramolecular organization via intermolecular hydrogen bonding interactions between urea groups (-NHCONH-) and covalent siloxane bonding, triple bond Si-O-Si triple bond. Time-resolved in situ X-ray measurements (coupling small- and wide-angle X-ray scattering techniques) are performed to follow the different steps involved in the synthetic process. A new mechanism based on the crystallization of the hydrolyzed species followed by their polycondensation in solid state is proposed.

Preparation and characterization of a novel organic-inorganic nanohybrid "cerasome" formed with a liposomal membrane and silicate surface

A novel class of organic-inorganic hybrids, the so-called cerasomes, which have a bilayer vesicular structure and a silicate surface, has been synthesized by combination of sol-gel reaction and self-assembly of organoalkoxysilanes with a molecular structure analogous to lipids. We have synthesized two cerasome-forming organoalkoxysilanes, N-[N-(3-triethoxysilyl)propylsuccinamoyl]dihexadecylamine (1) and N,N-dihexadecyl-N (alpha)-[6-[(3-triethoxysilyl)propyldimethylammonio]hexanoyl]glycinamide bromide (2), and investigated the synthetic conditions of the cerasomes and their structural characteristics. For the proamphiphilic 1, the cerasome was obtained under restricted pH conditions where acid-catalyzed hydrolysis of the triethoxysilyl moiety proceeded without disturbing the vesicle formation. In contrast, the amphiphilic 2, additionally having a hydrophilic quaternary ammonium group, formed stable dispersions of the cerasome in a wide pH range. The hydrolysis behavior of the triethoxysilyl groups was monitored by (1)H NMR spectroscopy. Morphology of the cerasomes having the liposomal vesicular structure was confirmed by TEM observations. Extent of the development of siloxane networks through condensation among the silanol groups on the cerasome surface was evaluated by using MALDI-TOF-MS spectrometry. Formation of oligomers of the cerasome-forming lipids in the vesicle was clearly confirmed. Due to the siloxane network formation, the cerasome showed remarkably high morphological stability compared with a reference liposome, as evaluated by surfactant dissolution measurements.

Control of Mesoporous Silica Nanostructures and Pore-Architectures Using a Thickener and a Gelator

A chiral cationic thickener l-ValPyBr, which was able to enhance the viscosity of water and form loosely physical gel in mixtures of water and alcohols, was synthesized. Sol-gel polymerization of TEOS was carried out in mixtures of water and alcohols under basic conditions using the self-assemblies of l-ValPyBr as template. The left-handed twisted mesoporous silica nanoribbons, which were constructed by nanotubes in monolayer, were obtained, and they tended to self-assemble into bundle structure. Stirring under the preparation process played an important role in the formation of this bundle structure. The obtained silica nanoribbons were uniform in width, thickness, and helical pitch without combining amorphous particles. The helical pitch and pore size of the mesoporous silica nanoribbons sensitively depended on the volume ratio of alcohols to water in the reaction mixtures. With increasing volume ratio of alcohols to water in the reaction mixture, the morphologies of the obtained silica changed from left-handed twisted ribbon to coiled ribbon, then to tubular structure. A compound l-ValPyPF6, structurally related to thickener l-ValPyBr, was able to form physical gel in ethanol, THF, acetonitrile, and the mixtures of ethanol and water. Left-handed multiple helical mesoporous silica nanofibers were prepared by using the self-assemblies of l-ValPyPF6 as template in mixtures of water and alcohols under basic conditions. By controlling both the volume ratio of ethanol to water and the weight ratio of l-ValPyPF6 to TEOS, two- or three-dimensional pore-architecture constructed by porous chiral nanotubes was obtained.

Fabrication of TiO2usingl-lysine-based organogelators as organic templates: control of the nanostructures

Using uncharged or negatively charged L-lysine-based organogelators as templates, the nanostructures of TiO2 are controllable.