The phenomenon of molecular recognition including further function is common in nature. Host-guest complexation occurring at Langmuir monolayers has been investigated in detail similarly to molecular recognition in solutions. Langmuir monolayers at the air-water interface provide a unique environment for molecular recognition. Characteristic binding efficiency and selectivity of water-soluble substrates by specific pairing of hydrogen bonding have been found for functionalized monolayers at the air-water interface. Hydrogen bonding network formation between a functionalized monolayer and a substrate enables cleavage of the head group of an amphiphile forming the monolayer by hydrolysis of a C=C double bond that links the head group to the hydrophobic tail. Molecular organization termed “molecular recognition-directed self-assembly” has been demonstrated through complementary base-pairing in monolayers at the air-water interface. Controlling of molecular arrangement of nucleobase amphiphiles in Langmuir monolayers has been attempted by using complementary base-pairing with sequence-designed oligonucleotides as a molecular template. This unique molecular recognition should be useful for nanotechnology.
We have developed a quartz-crystal microbalance (QCM), in which fundamental frequency decreases with increasing mass on the electrode in aqueous solution. When a 27 MHz QCM is employed, a mass of 0.62 ng/cm2 deposited on the electrode decreases the frequency by 1 Hz. Thus, when the host molecule is immobilized on the QCM electrode, the binding behavior of guest molecules could be observed in nanogram level in aqueous solution. In this review, we report that the biomolecular recognitions and reactions at the water-substrate interface by using the QCM technique, such as 1) protein binding to a sugar lipid monolayer at the air-water interface, and 2) oligo nucleotides biding to a nucleolipids monolayer at the air-water interface.
Solution surface can be studied by using X-ray Absorption Fine Structure (XAFS) method. To obtain surface sensitivity, the X-rays are introduced onto the solution surface at a very small grazing incidence angle to meet the total-reflection condition. This new spectroscopic method was successfully applied to the surfaces of aqueous solutions covered with monolayers of alkylammonium bromide, zinc stearate, and also zinc porphyrine complex. The spectra from these surfaces indicated quite interesting but not yet known facts such as, dehydration of anions adsorbed onto the alkylammonium monolayer and coordination change of zinc ions from the octahedral to tetrahedral when the metal ions come to the stearate monolayer from the bulk solution. The XAFS experiments were also performed with linearly polarized X-rays to elucidate the selective orientation of the planar Zn porphyrine complex on the solution surface.
The orientation of liquid crystal molecules is crucially influenced by the surface properties of substrates. Surface-mediated photoalignment now occupies one of the important areas of liquid crystal technologies. Development of photoalignment for many types of materials other than liquid crystals may open new opportunities in the materials science and technology. This article introduces our recent results on the photoalignment of polymer materials (polysilanes) and mesoporous silica materials based on the orientational transfer from a photoresponsive monolayer irradiated with linearly polarized light.
Distribution of normal alcohol (n-alcohol) on water and its stability were investigated using molecular dynamics simulation for three types of n-alcohol (n-propanol, C3H7OH; n-heptanol, C7H15OH; and n-undecanol, C11H23OH) of five differrent concentrations. The simulation reveals that the distribution of n-propanol on water is homogeneous for all the concentrations examined here, but the distribution is heterogeneous for n-heptanol and n-undecanol on water. The n-alcohol concentration at which fluctuation in the distribution begins to increase is related to the length of the hydrocarbon chain of n-alcohol.
Observation of ultrathin silicon nitride surfaces by using ultrahigh vacuum scanning tunneling microscopy (STM) and atomic force microscopy (AFM) was performed. The ultrathin silicon nitride was prepared on Si(111) and (001) surfaces by novel thermal nitridation method using N2/H2 gas mixture at 780−1100oC. On Si(111) surface, the STM and AFM images show clear step-and-terrace structure and well-ordered atomic arrangement showing 8/3×8/3 superstructure. On Si(001), atomic arrangement showing 2×2 superstructure was observed on the surface. The structural models were proposed for these observed surface superstructures.
TiO2 films were prepared using RF magnetron sputtering with a variety of parameters such as sputtering pressure, substrate temperature, the kind of target, and atmosphere. Crystal structures and photocatalytic activities of these films under UV light irradiation were compared with sputtering conditions. In general, rutile phases were formed at low sputtering pressure and anatase phases became predominant at high pressure. Highest activities were obtained at high pressures irrespective of substrate temperatures in Ar + O atmosphere. Similar high activities were also achieved at high temperatures and high pressures when TiO2 target was sputtered in pure Ar. Although the films were produced under various conditions, it was indicated that decomposition rate of methylene blue (MB) was almost solely determined by anatase content.
Hybridized nanocrystals, which were composed of polydiacetylene (PDA) nanocrystal as a shell layer and silver nano-particle as a core part, were successfully fabricated by means of the “co-reprecipitation method” and the subsequent UV-irradiation to convert the shell layer of solid-state polymerizable diacetylene into PDA. The hybridized core-shell type structure was investigated using both SEM and TEM observations. Interestingly, the plasmon absorption peak of silver nanoparticle decreased and apparently disappeared during UV-irradiation for solid-state polymerization, while the excitonic absorption peak from π-conjugation of PDA was remarkably red-shifted at the same time, compared with only PDA nanocrystal having the same crystal size as the hybridized nanocrystal. These facts suggest that silver nanoparticle of core part may interact optoelectronically with the shell layer of PDA in hybridized nanocrystals to provide different electron states from the original materials.
Application of carbon nanotubes (CNTs) as field emitters for large-area field emission display (FED) panels is described. In 1998, we presented the first experimental devices: light-source tubes for outdoor large area displays and a diode-type flat panel display, both with screen-printed CNT cathodes. The first practical high-luminance color CNT-FED panel was built in 1999. It employed a new triode-structure panel that was x-y addressable. The CNT-FED structure was further optimized for large-area display panels by improving the luminous uniformity. The CNT-FED will be a valuable high-luminance and low-power-consumption technology in light-source tube and large-screen-sized display applications.