Colloid vibration potential in a suspension of spherical colloidal particles

When a sound wave is applied to a suspension of colloidal particles in an electrolyte solution, the colloid vibration potential (CVP) is produced in the suspension. The CVP is proportional to the difference between the mass density of the particles and that of the electrolyte solution. For a suspension of biological colloids such as cells, whose mass density is only slightly different from the electrolyte solution, its CVP becomes very small so that the magnitude of the ion vibration potential (IVP) of the electrolyte solution exceeds that of CVP. This causes difficulty in analyzing the CVP in biological systems. In the present paper, we show that even in such cases the phase of CVP becomes much greater than that of IVP.     

A model for binding of inhalation anesthetics to membranes: two dose-dependent distinctly different binding modes

Inhalation anesthetics currently in clinical use, such as halothane, methoxyflurane, enflurane, isoflurane, etc., are polar hydrophobic molecules, except nitrous oxide, which is an apolar and weak anesthetic, incapable of inducing surgical stage anesthesia. Experimental data are accumulating that these potent amphipathic inhalation anesthetics preferentially bind membranes and macromolecules on the surface at clinical concentrations. The anesthetic binding to lipid membranes in the low concentration range is characterized by a saturable curve approaching to a limiting value. When the anesthetic concentration s greatly increased above the clinical range, the binding starts to exceed the limiting saturation value. Our model for anesthetic binding to membranes consists of two parts: Langmuir-type adsorption to the membrane surface at the low concentration range and penetration into the hydrophobic core at the high concentration range. The present communication provides a statistical-thermodynamic basis to analyze this twostep interaction. An expression is derived for membrane capacitance as a function of anesthetic concentration, which explains the experimental data well. Binding parameters of anesthetics are estimated according to the theory.This study was supported by NIH grants GM 25716 and GM 26950, and by the Medical Research Service of the Veterans Administration.     

Flavin mononucleotide chemiluminescence in cationic micellar media for determination of chromium(III + VI) by flow injection

The flavin mononucleotide chemiluminescence system, originally developed for the determination of copper(II), is modified with cationic surfactant micelles for the determination of chromium(III + VI). In order for chromium to be detected predominantly, the copper-induced luminescent reaction is significantly suppressed by virtue of the cationic micellar effect. The limit of detection (signal-to-noise ratio = 2) is 5 × 10^?8 M chromium (50-μl sample injection).     

Distribution of local anesthetics in lipid membranes

Absorption of local anesthetics into lipid membranes and adsorption onto their surfaces were studied as a function of the pH of aqueous bulk solutions by measuring lipid vesicle electrophoretic mobility, the partition of the anesthetics between the aqueous and membrane phases by the use of fluorescence and radioactive tracer methods, and the effect of the anesthetics on interfacial tension of lipid monolayers formed at the oil/aqueous interface.

At a pH much lower than the pK_a value of the local anesthetic, the charged form of the local anesthetic was only adsorbed onto the membrane surface, as determined from vesicle electrophoretic mobility, radioisotope tracer and the monolayer surface tension studies. Surface partition coefficients of the charged form of the local anesthetics on phosphatidylcholine and phosphatidylserine membranes were obtained from the data of electrophoretic mobilities for lipid vesicles. The surface partition coefficients of various local anesthetics paralleled those of the bulk partition coefficients.

As the pH of the solutions increased, the adsorbed amount of the charged form of the anesthetic at the membrane interface decreased, while the absorption of the uncharged form of the local anesthetic into the membrane increased. The total amount of local anesthetic adsorbed per unit area of the membrane generally increased as the pH of the solution increased. This was also observed from the measurements of the fluorescence of local anesthetics adsorbed into the membranes. At lower pH than that corresponding to the pK_a value of the local anesthetic, the amount of anesthetic adsorbed depended greatly upon the membrane surface charge. At a higher pH than its pK_a, it did not depend appreciably on the surface charge density of the membrane but did depend on the bulk partition coefficients between the aqueous and oil phases.     

Electrophoresis of soft particles: analytic approximations

An approximate analytic expression is derived for the electrophoretic mobility of a weakly charged spherical soft particle (i.e., a hard particle covered with a weakly charged polyelectrolyte layer) on the basis of the general mobility expression for soft particles (Ohshima, H., J. Colloid Interface Sci. 2000, 228, 190-193). The obtained mobility expression, which reproduces various approximate results so far derived and gives some new mobility formulas, covers all types of weakly charged soft particles with arbitrary values of the thickness of polymer layer, the radius of the particle core, the electrophoretic softness, and the Debye length, including spherical polyelectrolytes with no particle core as well as spherical hard particles with no polyelectrolyte layer.     

The kinetic deuterium isotope effect in the thermal dehydration of boric acid

The kinetic deuterium isotope effect in the thermal dehydration process from H₃BO₃ to HBO₂(III) was determined using simultaneous TG and DSC. The rate constant ratio of H₃BO₃ to D₃BO₃ obtained by the analysis of isothermal TG and DSC curves was found to be smaller than unity. Both activation energy, E, and frequency factor, A, for the dehydration of H₃BO₃ proved to be larger than those of D₃BO₃, using non-isothermal TG and DSC. The origin of the deuterium kinetic isotope effect in the thermal dehydration of boric acid is also briefly discussed.     

Functional modification of cytochrome c by peroxynitrite in an electron transfer reaction.

The redox reaction of cytochrome c after modification with peroxynitrite under physiological conditions was investigated. Cytochrome c was treated with a bolus of synthetic peroxynitrite at a sub-millimolar concentration, and then subjected to reduction by superoxide and oxidation by hydrogen peroxide. The ability for the membrane potential formation in the mitochondrial respiratory chain was also evaluated. After the treatment with peroxynitrite, the cytochrome c molecule was mono-nitrated mainly at a tyrosine residue, using liquid chromatography-electrospray ionizing mass spectrometry (LC-ESI-MS) and HPLC. Although the redox capacity of cytochrome c was not affected by the peroxynitrite treatment, the oxidation of ferrocytochrome c to ferricytochrome c by hydrogen peroxide was accelerated. When cytochrome c was treated with peroxynitrite in the presence of 5-methoxytryptamine, an inhibitor for the tyrosine nitration by peroxynitrite, the acceleration of hydrogen peroxide-mediated oxidation was suppressed. It was also found that the formation of membrane potential in the rat liver mitochondria was suppressed when peroxynitrite-treated cytochrome c was used instead of the intact cytochrome c in vitro. From these results, we concluded that the peroxynitrite-treated cytochrome c was nitrated at a tyrosine residue and became more susceptible to oxidation by hydrogen peroxide, concomitantly losing the ability to transfer electrons in the mitochondrial respiratory chain. It is suggested that the peroxynitrite-induced modification of cytochrome c increases the susceptibility to non-physiological oxidants, and may cause dysfunction of mitochondria by suppressing of membrane potential.