Structural characterization of self-assembled monolayers (SAMS) by means of surface-enhanced Raman spectroscopy (SERS) was reviewed. It was concluded that SERS provides important information not only about conformation and orientation of molecules in SAM, but also about interaction between SAM and other molecules.

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Cryo-transmission electron microscopy at the liquid helium temperature was applied to visualize the micellar structure of perfluorooctylsulfonates (FOS) and surfactin. The micellar system of tetraethylammonium (TEA) perfluorooctyl-sulfonate showed the formation of threadlike micelles. At a high concentration of FOSTEA, threadlike micelles evolved to form a randomly dense loop structure, which correlated with an increase in bulk viscosity. On the other hand, lithium perfluorooctylsulfonate (FOSLi) only showed the formation of spherical micelles with no loop structures, which indicated no change in the bulk viscosity. The different influence between TEA and Li ions on the formation of threadlike and spherical micelles was discussed in terms of the hydrophobic and hydrophilic nature of these ions. For surfactin, a biosurfactant, micelles were spherical, ellipsoidal, and rod-shaped structures with an in- homogeneous size distribution at pH 7, 9.5, and 12. The disappearance of a characteristic FT-IR band of a lactone group in surfactin at pH 12 suggested that the micelles with different structure of a linear head group are formed. At pH 9.5, the addition of 100 mM NaCl and 20 mMCaCl₂ to a surfactin solution transformed the rod-shaped micelles into small sized spherical micelles. The samll sized micellles were explained by a common understanding model with a high or low degree of internal order in the structure of alkyl chains. The large sized spherical, ellipsoidal, and rod-shaped micelles were explained in terms of bilayered unilamellar or multilamellar structures.

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We have performed direct observation on a single large deoxyribonucleic acid (DNA) molecule in PEG (polyethylene glycol) solution to study the mechanism for conformational change of a DNA molecule. We have found the followings: (1) An individual single double stranded DNA chain undergoes first-order phase transition between unfolded coil and compact globule states. (2) Around the transition point, there exists a coexistence region of coil and globule states. (3) In the transition from coil to globule, “nucleation and growth” along a single DNA chain is observed. The speed of the growth of the globule state is almost constant. (4) As for the reverse transition, the time process of the unfolding is slow at the initial period and then accelerated.

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Preparations of an organic-inorganic nano-composite film based on the synthesis of nano-sized inorganic materials in molecuar assembly films have been described. Exposure of metal stearate Langmuir-Blodgett (LB) films to H2S and HI gases results in the formation of size-quantized metal sulfides (CdS, ZnS, PbS) and PbI₂, respectively, in the stearate LB films. When the metal sulfide-bearing composite film was subjected repeatedly to a cycle of immersion in aqueous solutions of the corresponding metal ion (I) and the exposure to H₂S gas (S), a nano-order increase in the size of the metal sulfide was observed. The dimension of size-quantized CdS formed in LB films was also controlled precisely by the occupied molecular area of amphiphiles which regulates the concentration of Cd²⁺ ions introduced in the hydrophilic interlayers. When the CdS-bearing stearate LB film was subjected alternately to the intercalation of Pb²⁺ ions and sulfidation, a composite film in which size-quantized CdS and PbS coexisted was produced. On the structure of CdS bearing stearate LB films, the existence of an ordered (crystalline) region consisting of a layered structure of stearic acid and CdS sheets was suggested from IR and X-ray diffraction results. Third-order optical nonlinearity of the PbS-bearing composite system was relatively large and was optimizedby the amount and size of PbS.

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Development of low-molecular-mass gelling agents to harden organic fluids and their gelation mechanism are described. The previously reported gelling agents were briefly outlined, and then the properties and gelation mechanism for our gelling agents were mentioned. The examined gelling agents are i) amino acid derivatives, ii) equimolar mixtures of barbituric acid derivatives and 2, 4, 6-triaminopyrimidine derivatives, iii) cyclo (dipeptide) s, and iv) oligo (α-amino acid) s. The gelation mechanism is as follows; fiber-like aggregates are formed from numerous molecules by intermolecular hydrogen bonding, then they are juxtaposed and interlocked by van der Waals interaction, and finally immobilized organic fluids. The concluded three features that are important in the development of gelling agents are the existence of intermolecular interactions to build up macromolecule-like aggregates, the occurrence of intertwining of the aggregates, and the presence of some factor to prevent the transformation from a metastable gel to a crystalline mass.

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The role of ESR spectroscopy in the characterization of functional LB films is discussed. Unpaired electrons in LB films are associated with isolated radical molecules produced by charge transfer, paramagnetic metallic ions such as Cu²⁺, strongly interacting spins in the mixed valence states in charge-transfer salts, and so on. These spins often manifest the functions of materials. They can also act as microscopic probes in the ESR analysis devoted for the elucidation of characteristic properties of LB films. In structural studies, ESR is of particular importance in the analysis of molecular orientation of LB films. ESR can unambiguously determine the orientation of molecules through g-value anisotropy: different g value, different resonance field. Two types of new control methods of molecular orientation in LB films originated from the ESR analysis: study of in-plane orientation in dye LB films which led to the discovery of flow-orientation effect, and observation of drastic change of orientation of Cu-porphyrin in LB films using the trigger molecule, n-hexatriacontane. In the studies of electronic properties, hyperfine interactions between electron and nuclear spins provide information about molecular orbitals and local structures. Stable isotopes have been successfully applied to the stable radicals in merocyanine LB films to identify hyperfine couplings. In conducting LB films composed of charge-transfer salts, quasi-one-dimensional antiferromagnetism in semiconducting films and spin resonance of conduction electrons in metallic films are observed. Results provide microscopic evidence for the development of columnar structures of constituent molecules. Development of new functional LB films may provide more cases where ESR spectroscopy will clarify the nature of such films.

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Polypeptides embedded in phospholipid bilayer membranes were designed and synthesized to mimic functions of membrane proteins. Artificial functional groups such as Ru-trisbipyridine complex, tetraphenylporphyrin, anthraquinone, methylviologen, and flavin were deployed into the constructed three-dimensional super-structures of polypeptides: 2α-helix peptide bearing Ru-trisbipyridine complex, 4α-helix bundle peptides on atropisomers of Zn- and Mn- tetraphenylporphyrins as super-structural templates and reaction centers. These membrane-penetrating polypeptides acted as an electron migration path across the bilayer membranes. The artificial membrane proteins would provide important information for the development of biomimetic super-molecular devices.

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Irradiation of visible light and introduction of hydrogen into aqueous solutions of noble metal salts in the presence of surfactants gave stable colloidal dispersions of nanoscopic noble metal clusters protected by surfactant micelles with relatively narrow size distributions. The concentration of the surfactant had to be higher than the corresponding critical micelle concentration (CMC). These clusters can be used as active catalysts for hydrogenation of olefins or visible-light-induced hydrogen-evolution from water. In the case of hydrogenation of unsaturated fatty acids and their salts, some regio-selectivity is observed, probably because the substrates are aligned in the organized media surrounding the metal clusters. The protective structures of noble metal cluster particles protected by surfactants are analyzed by the chemical shifts of surfactant molecules in ¹³C and ¹H NMR. The Stokes' radii of the surfactant-protected particles measured by a Taylor dispersion method were also helpful.

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