Recent studies on the in-situ observation of the monomolecular films at the air-water interface by means of the fluorescence microscopy and the reflection spectroscopy are reviewed. Several kinds of Langmuir trough equipped with fluorescence microscope were constructed. Various morphologies and crystallization process of the surface monolayers were observed. Thermal treatment of the surface monolayer was shown to be effective for the crystal growth. Crystallization of the guest cyanine dye at the well organized charged interface of the monolayer was monitored not only by the fluorescence microscopy but also by the reflection spectroscopy.
Current status of the studies on the instrumentation for LB deposition was reviewed. Techniques used in the current instrumentation for measuring properties of insoluble monolayers and for LB deposition, such as pressure control, temperature control, etc., were summarized. Newly developed instruments for making complex LB films were introduced. The importance of the basic studies on insoluble monolayers was emphasized.
Simulation of photoelectric conversion in the photosynthetic reaction center by monomolecular layer assemblies of a folded or a linear type A-S-D triad carried out in this laboratory is reviewed. The oriented triad molecule acts as a charge separation unit and is named a molecular photodiode. The combined system with the linear triad and an antenna pigment is discussed next in terms of the charge separation and the light harvesting. Finally, electrocatalytic reduction of CO2 by alkyl Ni2+-cyclam derivatives studied is described. This monolayer can be used in artificial photosynthetic LB films as a catalytic layer which is deposited upon the electron-acceptor side of the charge separation layer in series.
In LB films, acceleration or selectivity of chemical reactions and regulation of conformation or configuration of the products can be achieved, because mutual orientation and packing of the functional groups can be easily controlled. This review describes mainly polymerization reactions including both of condensation and addition, and chromic reactions such as cis-trans isomerization in the LB films. Polymers with specific structures can be obtained in the LB films and these are expected to improve the stabilization of functional LB films. Control of chromic reactions in the LB films are promising for the conversion of photoenergy, such as in optical memory.
Enzyme molecular films have been synthesized for biosensors by two different LB film technologies. The one is based on the deposition of a protein LB film which is followed by bioaffinity self assembling to form enzyme films. The other is the two-step method involving the formation of phospholipid monolayer and the adsorption of enzyme molecules. The characteristics of these enzyme molecular films are described. Two biosensors have currently been developed in association with the protein LB film technology. These involve an enzyme sensor fabricated by the two-step LB film technology and an optical sensor for taste. The principles and characteristics of these sensors are presented.
Development of molecules for Langmuir-Blodgett films are reviewed. Typical amphiphilic molecules have long alkyl chains in the hydrophobic parts and functional moieties in the hydrophilic parts. There are two new fashions. Firstly, π-electrons and aromatic moieties are introduced in the hydrophobic part to exhibit new functions and construct highly ordered structures in the molecular assemblies. Secondly, organic metal complexes are employed in addition to the usual organic dye moieties in the hydrophilic parts. Moreover, noncentrosymmetric structures in the LB films are designed not merely fabrication technique but also molecular polarity design.
HLB composition was found to depend on the concentrations of emulsifiers in systems of aqueous/sodium dodecyl sulfate/2 ethylhexylglyceryl ether/aromatic oil. The ratio of lipophilic emulsifier at the HLB composition increased progressively with systems containing aromatic hydrocarbon, alicyclic hydrocarbon and alkane at high emulsifier concentration in this order. This order corresponded to that of HLB temperature in systems of nonionic emulsifiers. In contrast, it increased with systems containing alicyclic hydrocarbon, alkane, aromatic hydrocarbon at low concentration and this finding has practical application. Taking these results into consideration, the monodispersed solubilities of emulsifiers in each oil were examined.
The hydrolysis of monodecyl phosphate (C12MAP) Na and K salts at various degrees of neutralization (DN) in 5.0 wt% aqueous solution was studied by analysis of dodecyl alcohol formed by hydrolysis of C12 MAP. The hydrolysis rate followed a first-order kinetics and the rate constants (kobs) showed Λ-shape dependence on DN (Fig.-2) and the maximum kobs were found at DN=1.08. The extrapolated kobs at DN=0.18 was zero. Under highly alkaline conditions (at DN=4.0) hydrolysis did not occur. In the pH-DN profile in aqueous solution, there were three equivalent points at DN=0.5, 1.0 and 2.0, indicating MAP to have three dissociation equilibria (Scheme-3, pK1=2.45, pK2=5.60, pK3=7.80) including bimolecular aggregates (A0, A1). The Arrhenius activation energy was Ea-29.7 kcal/mol and did not depend on DN. This value is essentially the same as that for monomethyl phosphate (Ea=30.6 kcal/mol). A possible hydrolysis mechanism is proposed and discussed based on the obtained results.
Agar-wood (Jinkoh) has long been used as incense. It is thought to derive from the fungus-infected wood of old aquilaria trees through resignification of the essential oil. The biotransformation of dehydroabietic acid (DHAA) is presently being attempted by fungi considered to have the ability to form “Jinkoh”. To date 2 hydroxydehydroabietic acid, 7 hydroxydehydroabietic acid, and 16 hydroxydehydroabietic acid from DHAA have been obtained.