Izumi Nishio

Quasielastic light scattering study of the formation of inhomogeneities in gels

The inhomogeneities in gels, in particular the mechanism of the formation of the inhomogeneities, were studied. The gels used in this report are water based poly(acrylamide) gels (AA gels) and poly(N‐isopropylacrylamide) gels (N‐IPA gels). It is known that the cross linkers in AA gels are water insoluble at low temperature and that the linear components in N‐IPA gels are water insoluble at high temperature. By changing the gelation temperature at which gels are made, we can control the formation of the inhomogeneous structure in the samples. In order to investigate the inhomogeneities in the gels, two experiments were performed by using the standard laser light scattering method. For the characterization of the degree of inhomogeneities in gels, the position dependence of scattered light intensity from homogeneous and inhomogeneous gels were measured. It was found that the position dependence was a very good indicator of gel inhomogeneities. We also observed the change of the autocorrelation function of s...

The behaviour of red cells in narrow tubes in vitro as a model of the microcirculation

To investigate the behaviour of red cells in the microcirculation, we established a new capillary method using narrow fluorinated ethylenepropylene copolymer tubes with internal diameters of 12.5 and 25.0 μm. Red cell flow in the tubes under a given range of pressure was analysed through a video system connected to a microscope. The experimental condition was adjusted so that the velocity of the control normocytes would be compatible with that in corresponding vessels in vivo, 0.5–1.5 mm/s. In the 12.5 μm tube, normocytes obtained from 12 young normal volunteers ran in an axisymmetric edge‐on orientation with a folded shape at higher pressures, but rolled along freely without deformation at lower pressures. Deformation during the passage of the microcytes obtained from four patients with polycythaemia vera complicated with iron‐deficient microcytosis and 10 patients with iron deficiency anaemia was relatively mild, whereas that of the macrocytes obtained from eight patients with refractory anaemia was marked. Even after the screening effect at the tube entrance was taken into consideration, the velocities of both microcytes and macrocytes were found to be significantly lower than the control normocytes. Therefore this method may be a new way to investigate the flow properties of red cells in the microcirculation.

Change in phase transition behavior of an NIPA gel induced by solvent composition: hydrophobic effect

Abstract We carried out the measurements of the equilibrium size of N-isopropylacrylamide (NIPA) gel immersed in a dilute aqueous solution of hydroquinone (HQ) as a function of temperature. It was found that, by embedding a small amount of HQ molecules into the gel fluid, volume phase transition behavior of the NIPA gel changed qualitatively depending on the HQ concentration. Moreover, the change in phase transition from continuous to discontinuous was observed without permanent alteration of polymer networks such as hydrolysis. This fact suggests that, by changing HQ concentration, we will be able to find a critical isobar without changing the gel structure.

Colloidal crystal: bead–spring lattice immersed in viscous media

We present a report about a new approach that can be used to describe the single-particle dynamics of colloidal crystals. This approach regards the colloidal crystal as a classical bead–spring lattice immersed in viscous fluid. In this model, the mean square displacement of a particle (MSD) and the mean product of displacement of a particle and that of another particle (x-MSD) are obtained exactly using the Langevin treatmentlike method. In other words, MSD and x-MSD are, respectively, an autocorrelation function of a particle and a cross-correlation function of two particles. As the first-order approximation of hydrodynamic interaction, effective Stokes’ viscous drag coefficient γeff is introduced to the model that includes all of the hydrodynamic effects due to the presence of all other particles. As a result of the viscous media, traveling phonon modes are transformed into relaxation modes, and the motion of a particle is comprehended as a superposition of these relaxation modes. The predicted MSD for ...

A study on the structure of water in an aqueous solution by the solvent effect on a volume phase transition of N-isopropylacrylamide gel and low-frequency Raman spectroscopy

We introduce a new technique to investigate the effect of residual substances on the hydrogen-bonded network structure of water molecules. We have characterized the effect of very low concentrations of several alcohol and phenol compounds on the structure of water from observations of their effect on the volume phase transition of N-isopropylacrylamide (NIPA) gels. The alteration of the volume phase transition was observed as a remarkable drop of the transition temperature associated with the change in entropy of the gel fluid. In addition, we have investigated the effect of these same compounds on water structure using low-frequency Raman spectroscopy, the results verify quantitatively the increase in entropy of the gel fluid with the addition of the residual substances. We found the effect of phenols on the structure of water clusters was remarkably large compared to the effect of alcohols. We demonstrate there is a strong correlation between the measurements of the drop in transition temperature of the...

Raman Tensor Analysis of Crystalline Lead Titanate by Quantitative Polarized Spectroscopy

Recently, the mode splitting of B1+E in PbTiO3-related heterostructures has been attracted wide range of attention because it is considered to represent intrinsic stress in the materials. However, the spectral behaviour of B1+E mods had remained unclear even in the bulk crystal, i.e., they had been often designated as “silent,” even though they should be Raman active. This seems because they does not exhibit a significant mode splitting in the bulk crystal. This work employed an angle-resolved quantitative polarized spectroscopy to clarify the unclarity. The precise measurements revealed that the both two modes are ordinary Raman active modes with a minute energy difference.

Low Frequency Raman Profile of Type II Clathrate Hydrate of THF and Its Application for Phase Identification

Low frequency Raman profiles of type II clathrate hydrate (CH) of various guest molecules have been studied and their common feature, the sharp peak at 60 cm -1 , was identified as the most dominan...

Effect of dibucaine hydrochloride on raft-like lipid domains in model membrane systems

To clarify the biophysical and/or physicochemical mechanism of anaesthesia, we investigated the influence of dibucaine hydrochloride (DC·HCl), a local anaesthetic, on raft-like domains in ternary liposomes composed of dioleoylphosphatidylcholine (DOPC), dipalmitoylphosphatidylcholine (DPPC) and cholesterol (Chol). The large DOPC/DPPC/Chol liposome is directly observable by optical microscopy and is known to be laterally separated into a liquid-ordered (Lo) phase (raft-like domain) and liquid-disordered (Ld) phase under certain conditions. Hence, it is useful for the study of lipid raft domains as a simple model system of cell membranes. We observed ternary liposomes with three concentrations (0, 0.05 and 0.2 mM) of DC·HCl at various temperatures and calculated the angle-averaged two-dimensional autocorrelation functions to confirm the change in miscibility transition temperature (Tc) of ternary liposomes. Furthermore, we calculated the circularity of the Lo domain to confirm the change in line tension of the Lo/Ld phase boundary. The results indicated that the insertion of DC molecules into lipid bilayers induces reduction in Tc of the ternary liposome, accompanied by reduction in line tension of the phase boundary. This suggests that the DC·HCl molecules may disturb ion channel functions by affecting the lipid bilayers surrounding the ion channels.

Deformation of lipid membranes containing photoresponsive molecules in response to ultraviolet light.

Recently, membrane deformation using photoresponsive molecules has been extensively studied toward controlling their shapes because light can supply energy without contacting the vesicles. In this study, photoresponsive pseudogem-bis(diphenylimidazole) [2.2]paracyclophane (pseudogem-bisDPI[2.2]PC) molecules were doped into dioleoylphosphatidylcholine (DOPC) membranes, and the deformation of the DOPC/pseudogem-bisDPI[2.2]PC vesicles was observed under ultraviolet (UV)-light irradiation. It was also found that the volume-to-surface area ratio of spherical vesicles was changed by UV irradiation. Further, we performed high performance liquid chromatography (HPLC) analysis of membrane components in order to clarify the absence of irreversible chemical reactions and UV-irradiation experiments under an osmotic pressure in order to investigate the volume change of the vesicles. Then, we calculated the time-correlation function of membrane fluctuation. Change in the relaxation time of the time-correlation function indicated that the photoisomerization of pseudogem-bisDPI[2.2]PC might decrease the membrane fluidity. We consider that decreasing fluidity is induced by physical entanglement between photochromic compounds and lipids. This technique of membrane deformation may be expected to be applied to various situations such as drug delivery systems (DDS).

Real‐Time Observation of Liposome Bursting Induced by Acetonitrile

We show the bursting process of dioleoylphosphatidylcholine (DOPC) liposomes in response to the addition of acetonitrile, a small toxic molecule widely used in the fields of chemistry and industry. The percentage of destroyed liposomes is reduced upon decreasing the acetonitrile fraction in the aqueous solution and vesicle bursting is not observed at volume ratios of 4:6 and below. This indicates that a high fraction of acetonitrile causes the bursting of liposomes, and it is proposed that this occurs through insertion of the molecules into outer leaflet of the lipid bilayer. The elapsed time between initial addition of acetonitrile and liposome bursting at each vesicle is also measured and demonstrated to be dependent on the volume fraction of acetonitrile and the vesicle size.