Atsushi Hyono

Electrostatic interaction between two cylindrical soft particles

An expression for the potential energy of electrostatic interaction between two soft cylinders (i.e., polyelectrolyte-coated cylindrical particles) in an electrolyte solution is derived by applying Derjaguins approximation to the corresponding interaction energy between two parallel soft plates for the case where the density of fixed charges within the polyelectrolyte layer is low. The interaction between two parallel cylinders and that between two crossed cylinders are considered. The obtained expression covers various limiting cases that include hard cylinder/hard cylinder interaction, cylindrical polyelectrolyte/cylindrical polyelectrolyte interaction, soft cylinder/cylindrical polyelectrolyte interaction, soft cylinder/hard cylinder interaction, and cylindrical polyelectrolyte/hard cylinder interaction.

The van der Waals interaction between two torus-shaped colloidal particles.

An expression for the van der Waals interaction energy between two parallel torus-shaped colloidal particles is derived. It is shown that for small particle separations the torus-torus interaction energy is well approximated by the interaction energy between two parallel cylinders, each being produced by cutting a torus and unrolling it. In particular, in the limit of very small particle separations, the interaction energy between two parallel tori and that between the corresponding two parallel cylinders tend to the same limiting value. This limiting value also agrees with the result of applying Derjaguins approximation to the interaction between two parallel cylinders.

Impacts of papain and neuraminidase enzyme treatment on electrohydrodynamics and IgG-mediated agglutination of type A red blood cells.

The stability of native and enzyme-treated human red blood cells of type A (Rh D positive) against agglutination is investigated under conditions where it is mediated by immunoglobuline G (IgG) anti-D antibody binding. The propensity of cells to agglutinate is related to their interphasic (electrokinetic) properties. These properties significantly depend on the concentration of proteolytic papain enzyme and protease-free neuraminidase enzyme that the cells are exposed to. The analysis is based on the interpretation of electrophoretic data of cells by means of the numerical theory for the electrokinetics of soft (bio)particles. A significant reduction of the hydrodynamic permeability of the external soft glycoprotein layer of the cells is reported under the action of papain. This reflects a significant decrease in soft surface layer thickness and a loss in cell surface integrity/rigidity, as confirmed by nanomechanical AFM analysis. Neuraminidase action leads to an important decrease in the interphase charge density by removing sialic acids from the cell soft surface layer. This is accompanied by hydrodynamic softness modulations less significant than those observed for papain-treated cells. On the basis of these electrohydrodynamic characteristics, the overall interaction potential profiles between two native cells and two enzyme-treated cells are derived as a function of the soft surface layer thickness in the Debye-Hückel limit that is valid for cell suspensions under physiological conditions (approximately 0.16 M). The thermodynamic computation of cell suspension stability against IgG-mediated agglutination then reveals that a decrease in the cell surface layer thickness is more favorable than a decrease in interphase charge density for inducing agglutination. This is experimentally confirmed by agglutination data collected for papain- and neuraminidase-treated cells.

Effect of Counterion and Configurational Entropy on the Surface Tension of Aqueous Solutions of Ionic Surfactant and Electrolyte Mixtures

In order to clarify the adsorption behavior of cationic surfactants on the air/aqueous electrolyte solution surface, we derived the theoretical equation for the surface tension. The equation includes the electrical work required for charging the air/water surface and the work attributable to the configurational entropy in the adsorbed film. By fitting the equation to the experimental data, we determined the binding constant between adsorbed surfactant ion and counterion, and found that the bromide ions, rather than the chloride ions, are preferentially adsorbed by the air/water surface. Furthermore, it was suggested that the contribution of configurational entropy to the surface tension is predominant in the presence of electrolytes because of the increase in the surface density of surfactant molecules associated with decreasing the repulsive interaction between their hydrophilic groups.

Chemical modification to suppress metal ions elution of dental orthodontic wire surface

ABSTRACT In this study, we investigated on suppression of metal ions elution on dental orthodontic wire. To suppress metal ion elution from stainless wire, two types of surface chemical modifications were carried out. The obtained wire were immersed into several aqueous solution then the eluted ions (Cr and Ni, which are well known to cause a metal allergy) were determined using coupled plasma mass spectrometry (ICP-MS). By both electropolymerization and self-assembly monolayer formation, the ion elution was effectively reduced. These results suggested that these surface modifications succeeded to suppress the metal ions.