Takayuki Narita

Nanomosaic : Formation of Nanodomains Confined in a Two-Dimensional Molecular Plane

Atomic force microscopy observations of a (hydrocarbon guanidinium/fluorocarbon carboxylic acid) mixed monolayer revealed that a nanoscopic phase-separated structure was formed by a combination of attractive interaction between the oppositely charged head groups and repulsive phase separation of the hydrocarbon and fluorocarbon chains.

Promotion of cell adhesion by low-molecular-weight hydrogel by Lys based amphiphile

Hydrogels formed by low-molecular hydrogelators have been used as anti-microbial agents and cell-attachment materials. However the biomedical application of low-molecular gelators is slowly progressing compared to the hydrogels formed by polymer hydrogelator that is applied to biomedical application such as tissue engineering and biomedical regions. To obtain a simple molecular model for potent and prospective usage of low-molecular hydrogelators, we designed a Lys-based hydrogelator which was mimic to the poly cationic poly-l-lysine that promotes cells to attach to a plastic plate nonspecifically. The gel-coating led to cause 10-fold cell attachment compared to no-coating well. Also five-time cells were attached to the well compared to the poly-l-lysine coating. From the competitive assay, these hydrogels could interact with cells through electrostatic interaction between positive charge from -NH3(+) in the hydrogelator and negative charge from substances on the cell surface such as glycosaminoglycans. This strong adhesive ability can be useful for the tissue engineering and molecular glue regions using low-molecular hydrogels in the future.

Phase behaviors of agarose gel

We present evidence for the existence of phase separation in the gel state of agarose having the mixture of water and methanol as the gel solvent. Firstly, the sol-gel transition line and the cloud point line are determined independently as a function of the concentration of agarose as well as the concentration of methanol in the mixed solvent by the quasi-equilibrium cooling of the solutions. Then the spinodal line is determined by quenching the solutions below the sol-gel transition line. We find that the spinodal line appears below the cloud point line and both lines are entirely buried below the sol-gel transition line in the aqueous agarose system. The concentration fluctuations are, therefore, frozen into the polymer network of agarose gel that promotes the opacity of the resultant gel. The structure of agarose gel is observed by the confocal laser scanning microscope (CLSM) imaging technique that reveals that the density fluctuations are grown up to micrometer scale in space. The phase separation boundary is found to shift to the higher temperature region than the sol-gel transition line when the concentration of methanol in the mixed solvent is increased. The results indicate that the position of the phase separation boundary in relative to the sol-gel transition line varies with the quality of solvent. These results are in agreement with the theory of the sol-gel transition in which both the divergence of the connectivity and the thermodynamic instability are taken into account.

A novel preparation method of lead-based layered perovskite Langmuir films with a negligible amount of PbBr2

The addition of halide salts into the subphase has caused formation of the layered perovskite structure in a Langmuir monolayer on the subphase containing lead bromide at a concentration three orders of magnitude lower than that in the conventional methods.

Phase Separation for Langmuir Monolayer in Binary System Based on a π-A Isotherm Measurement

The mixing behavior of binary monolayer of fatty acid was investigated on the basis of π-A isotherm measurements. The (palmitic acid(C16)/arachidic acid(C20)) and (C20/lignoceric acid(C24)) mixed monolayers were in a miscible state, whereas the (C16/C24) mixed monolayer was an immiscible state. The (C16/behenic acid(C22)) and (stearic acid(C18)/C24) mixed monolayers were in an incomplete miscible state. The dependence of mixing behavior on the difference in the number of methylene group between components in monolayer is probably due to an enthalpic contribution based on the difference in cohesive energy between the monolayer components.

Liposome Deformation by Imbalance of pH and Ionic Strength Across the Membrane

The deformation of giant dioleoylphosphatidylcholine (DOPC) liposomes in solution and the properties of DOPC monolayers were investigated by florescence microscopy and surface pressure-area (π-A) isotherm measurements, respectively. These measurements were taken as functions of pH and ionic strength. When the ionic strength was changed from 0.001 to 0.6 at constant pH of 5.6, the coverage of the DOPC monolayer expanded by 10%, and the liposomes formed small protrusions. When the pH was changed from 5.6 to 3.5 at a constant ionic strength of 0.001, the monolayer coverage shrank by 10 %. During this process the external liposome morphology remained the same, but new, smaller vesicles appeared within the interior of the liposomes. Simultaneously changing the pH and the ionic strength to their final values (3.5 and 0.6, respectively), resulted in an expanded monolayer and produced long, protruded liposomes. Our results suggest that the deformation of liposomes is not only driven by osmotic pressure but also the condensed states in each monolayers composing liposome membrane.