Spontaneous formation of complementary hydrogen-bond pairs and their hierarchical self-assembly (reconstitution) into chiral supramolecular membranes are achieved in water by mixing amphiphilic pairs of glutamate-derived melamine 6 and ammonium-derivatized azobenzene cyanuric acid 4. Electron microscopy is used to observe formation of helical superstructures, which are distinct from the aggregate structures observed for each of the single components in water. In addition, a spectral blue-shift and induced circular dichroism (ICD) with exciton coupling are observed for the pi-pi* absorption of the azobenzene chromophores. These observations are consistent with the reconstitution of the hydrogen-bond-mediated supramolecular membrane 6-4. Spectral titration experiments indicate the stoichiometric integration of the complementary subunits with an association constant of 1.13 x 10(5) M(-1). This value is considerably larger than those reported for the artificial hydrogen-bonding complexes in aqueous media. The remarkable reconstitution efficiency is ascribed to the hydrophobically driven self-organization of the amphiphilic, linear hydrogen-bond networks in water. Molecular structure of the complementary subunits plays an important role in the complexation process since it is restricted by the photoisomerized cis-azobenzene subunit. On the other hand, thermally regenerated trans-isomer 4 undergoes facile complexation with the counterpart 6. The present reconstitution of supramolecular membranes provides the first example of complementary hydrogen-bond-directed formation of soluble, mesoscopic supramolecular assemblies in water.

Amphiphilic hydrogen bond networks consisting of alkylated melamines and ammonium headgroup-appended cyanuric acids are stably dispersed in water as supramolecular membranes. Electron micrographs of these aqueous dispersions indicated the formation of supramolecular assemblies of mesoscopic dimension. Their aggregate morphologies, molecular orientation, and thermal characteristics are markedly dependent on the chemical structure of constituent molecules. Self-supporting multilayer films were obtainable by casting the aqueous dispersions, like the conventional aqueous bilayer. X-ray diffraction of the cast films indicated that hydrogen bonded pairs of ammonium-appended cyanuric acid and double-chained melamine adopted the bilayer structure. On the other hand, complementary pairs formed from single-chained melamines adopted partially or completely interdigitated bilayers. The long period of the former cast film (ca. 9 nm) is in good agreement with the thickness of disklike aggregates observed in electron microscopy, indicating that bilayer structures mediated by complementary hydrogen bonds are maintained in water. Thermal characteristics of aqueous dispersions were investigated by differential scanning calorimetry and spectroscopically by using 1,6-diphenyl-1,3,5-hexatriene as a fluorescence probe. The observed spectral characteristics indicate that supramolecular membranes display phase transition from a highly ordered state to a liquid crystalline phase. In addition, reversible dissociation and irreversible segregation of complementary pairs proceeded at higher temperatures. These supramolecular membranes are the first example of water-soluble supermolecules directed by complementary hydrogen bonds and constitute a new family of amphiphilically designed supramolecular assemblies.

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We describe herein self-assembly of ordered bilayer membranes from amphiphilic complexes of complementary hydrogen bond pairs as an aqueous dispersion and as a cast film.Synthetic bilayer membranes are two-dimensionally organized molecular assemblies. The mode of packing of component amphiphiles plays a crucial role in determining physical properties of these bilayers and consequently their functiom2 In addition to alignment of hydrophobic alkyl chains, the intermolecular stacking of rigid segments3 and multiple hydrogen bonds among neighboring amphiphiles4 promote ordered bilayer assemblies.Molecular recognition and self-assembling processes directed by complementary hydrogen bonding have received a great deal of attention5-' Construction of bilayer membranes via complementary hydrogen bonding would provide a new class of selfassembly in which novel molecular control is achieved. In general, hydrogen bonding in artificial molecular systems is most effective in solid states or in noncompetitive (aprotic) organic media. However, our recent finding that molecular recognition via hydrogen bonding is effective at the air-water interface8 prompted us to investigate molecular recognition-directed bilayer assembly in bulk water.Substituted melamines 1 and 2 and isocyanuric acid derivatives 3 and 49 (shown in Chart I) were used as molecular components because they form extended arrays of complementary hydrogen bond^.^.^ Molecular complexes of 1,2 and 3,4 were prepared by mixing equimolar amounts of each component in ethanol and removing the solvent under reduced pressure. This procedure was repeated 3 times, and the resultant complexes were finally dried at 60 "C in vacuo. Among the prepared equimolar complexes of 1-3,1-4, 2-3, and 2-4, only 1-3 gave a transparent dispersion in water (ca. 30 mM) upon ultrasonication (Branson Sonifier Model 185, sonic power 45 W, 10 min at 0 "C). The aqueous dispersion was stable over a period of 1 month. In contrast, the other complexes (1) Contribution No. 973 from the Department of Chemical Science and (2) Kunitake, T. Angew. Chem., Znt. Ed. Engl. 1992,31,709 and references (3) Kunitake, T.; Okahata, Y .; Shimomura, M.; Takarabe, K. J. Am. Chem. (4) Kunitake, T.; Yamada, N.; Fukunaga, N. Kunitake, T. J. Am. Chem. SOC. 1991, 113, 9685 and references cited therein. (9) Substituted melamines 1 and 2 were synthesized by aminoalkylation of 2-amino-4,6-dichlorotriazine. Isocyanuric acid derivatives 3 and 4 were prepared according to the modified method of Hagemann.'" All new compounds gave satisfactory 'H NMR data (60 MHz) and elemental analysis. Detailed description of the synthetic procedures will be reported elsewhere. Technology. therein.Figure 1. Electron micrograph of an aqueous dispersion of 1-3 (1.5 mM).Stained by uranyl acetate. and components 1, 2, and 3 displayed poor solubilities in water even at a lower concentration of 5 mM. From comparisons of the component structures, we suggest that improved molecular orientation by the phenyl group in 3 and facilitated alkyl chain alignment...

Effects of ultrasound irradiation on DNA polymerase (Klenow fragment, KF) reactions were studied on the template/primer DNA-immobilized quartz crystal microbalance (QCM). Under ultrasound irradiation, binding of KF to the DNA was suppressed due to the decrease of the binding rate constant (k(1)) and the increase of the dissociation rate constant (k(-)(1)). The catalytic elongation rate (k(cat)) was increased, but the stability of the KF/DNA/monomer ternary complex (K(m)) was decreased by the ultrasound irradiation. Ultrasound effects are discussed in correlation with the conformation changes of domain structures in KF.