Amphiphiles self-assemble in water to form molecular bilayers. Their head-group arrangements can be considered to be fluidlike. This character is quite different from that of usual 3-D crystals. In this paper, self-assembling properties and morphologies of synthetic dumbbell-shaped amphiphiles (bolaamphiphiles) have been discussed. In particular, the effect of multiple hydrogen bonds on the supramolecular structures were commented. The D-glucose-and oligoglycine-based bolaamphiphiles self-assembled in water to form well-defined fibrous and vesicle-encapsulated tubular assemblies, respectively. The formation strongly depends on the length and even or odd carbon numbers of the spacer alkylene chains. FT-IR spectroscopy, X-ray diffraction and crystal analyses showed that the utilization of multiple hydrogen bonds provides the assemblies with an interesting self-assembling morphology and crystalline surfaces. These crystalline assemblies can rearrange to form 3-D crystals by converting the hydrogen-bonded scheme. Possible selfassembling models for the molecular arrangements within the fibers and tubes were proposed as a result of various solid analyses.
Liquid-crystalline supramolecular networks have been obtained by self-assembly through the formation of hydrogen bonds. Hydrogen-bonded networks built from 4, 4'-bipyridine and polyacrylates containing a side-chain benzoic acid show smectic A phases. The complexation of poly(acrylic acid) and bis(imidazolyl) mesogenic compounds also leads to mesomorphic networks. Self-assembly of multifunctional small molecules having benzoic acids and pyridyl moieties affords H-bonded networks which exhibit nematic and smectic phases. Liquid-crystalline polymer alloys have been prepared from a thermotropic polyester containing a lateral pyridyl group and poly(4-vinylphenol). The interaction through H bonds between these polymers results in the formation of the miscible blends that show nematic phases. These networks exhibit thermoreversible phase transitions due to the dynamic nature of H bond.
Self-organization of amphiphilic supermolecules consisted of complementary hydrogen bonds provide supramolecular assemblies of higher hierarchy, which are soluble in water or in organic media (mesoscopic supramolecular assemblies). When ammonium-derivatized cyanuric acids and dialkylmelamines were mixed in water, complementary hydrogen bond-mediated bilayer assembly were spontaneously formed. This “reconstitution” in water is achieved as a result of interplaying hydrophobic interaction and hydrogen bond formation. The hydrogen bond-mediated bilayers displayed unique bilayer characteristics as exemplified by dynamic aggregate separation process, which was observed for ternaly complimentary mixtures. On the other hand, an equimolar mixture of dialkyl-melamine and naphthalenediimide formed stable dispersions in cyclohexanes. Electron microscopy observations indicated the presence of flexible rods with a diameter of ca. 100Å, and is most probably composed of circularly hydrogen-bonded units of the two components. In addition, an equimolar mixtures of dialkyl-melamine and alkylated cyanuric acid provided linear hydrogen bond-mediated bilayer structures both in cyclohexanes and in chloroform, in which thermal phase transition characteristics were preserved in organic media.
There has been increasing research interest in the study of molecular-based magnetism. A rational design of nitroxisides with magnetic cooperativity using the intermolecular magnetic coupling is described. Introducing the hydrogen bonding site into nitroxides is a useful way of controlling magnetic interaction and/or molecular arrangement in crystal. Nitronyl nitroxide with imidazole (Im-NN) and benzimidazole (BIm-NN) were designed and their self-assembled structures and magnetic properties were characterized according to McConnell's theorem. BIm-NN were assembled in a columnar structure with N-H…O-N motif and formed a 1-D ferromagnetic chain due to the overlap of magnetic orbitals. The effect of hydrogen bonding on the molecular packing was also observed with nitronyl nitroxides having hydrophobic chain. Spectroscopic property of nitronyl nitroxides at air-water interface was discussed in terms of their electronic structure.
Scanning tunneling microscopic observations at room temperature and 70 K have revealed that the DNA and RNA base molecules which are randomly dispersed on Cu(111) surfaces self-assemble to form two dimensional superstructure through the interaction of hydrogen bonding.
We have calculated the desorption curves of molecular hydrogen from hydrogenated diamond surfaces as the rate-determining step is the bondbreaking between carbon and hydrogen atoms at CHχ(χ=1, 2, 3) species on surfaces. We can simulate the broad curve of H2 desorption by assuming the normal distribution of activation energies of desorption even though a simple rate equation of first-order desorption can not reproduce.
Characterization of surface and thin films is one of the most essential fields in the research and development of functional materials. Recently, we developed a new X-ray diffraction system, namely an energy dispersive-total reflection Xray diffraction (ED-TXRD) for the surface and thin film studies. In order to demonstrate the capabilities of this system for the structural and orientational characterizations of thin films, organic thin films (perfluoro-n-alkane, n-alkane) vacuum-evaporated on alkali halide single crystals were evaluated by the ED-TXRD system. Moreover, the potential calculation was conducted based on van der Waals interaction between thin films and substrate, and the most energetically preferable molecular arrangement was estimated by the simulation. The epitaxial growth of the long chain molecules are especially discussed in detail through their experimental and theoretical results.
Wet Air Oxidation (WAO) of industrial wastewater in the presence of catalysts provides a potential method for removing high concentration organic chemical wastes from industrial effluents. The oxidation of nitrogen-containing organics tends to form ammonia, oxidation of which is a hardest step among the total oxidation of such chemicals. In this study, an alumina supported ruthenium catalyst was found to exhibit remarkable activities for the oxidation of ammonia. Under a milder operating condition of 453 K, 3.0 MPa, 99% of ammonia (1500 ppm) was removed. The product was dinitrogen exclusively with a small amount of nitrate, which was found to be produced through the nitrite intermediate. The selectivity is significantly affected by the set of reaction conditions such as pH, air feed pressure, temperature and catalyst loading. Based on the result of an optimal experiment, the best set of reaction conditions was found that the selectivity for N2 was 98%. The practical application of this WAO technology was reviewed.