Norio Ise

On the electrostatic interaction in macroionic solutions

A general theory on the electrostatic interaction in macroionic solution is developed. It is assumed that the motion of macroions is adiabatically cut off from that of simple ions and the distribution of simple ions is determined by the Boltzmann distribution. A generalized Poisson–Boltzmann equation is solved with the linearization approximation. The total electrostatic energy of the solution is obtained, from which the Helmholtz free energy of interaction is calculated. The Gibbs free energy is derived by the use of its additivity relation with respect to the number of the ionic species. The two free energies are demonstrated not to be equal to each other for highly charged macroions, in contrast with widely accepted view. It is shown that the electrostatic potential for a pair of macroions predicts strong attraction between the macroions, as was the case with the Levine–Dube treatment, and the Helmholtz pair potential results in purely repulsive interaction, in accordance with the DLVO theory. However,...

Void structure in colloidal dispersions

The time evolution of void structures in highly purified polymer latex dispersions was studied with a confocal laser scanning microscope. In such dispersions, which were initially homogeneous, the voids grew with time when the dispersions were kept standing and formed more quickly in the internal material than in material close to the glass-dispersion interface. Void formation is thus not an artifact arising from the presence of the interface. A similar structural inhomogeneity, in apparently homogeneous systems, is discussed for simple ionic solutions, ionic polymer solutions, and Langmuir-Blodgett films.

Ordered structure in dilute solutions of highly charged polymer lattices as studied by microscopy. I. Interparticle distance as a function of latex concentration

The coexistence of ordered and disordered regions has been observed in dilute solutions of highly charged monodisperse latex particles, a copolymer of styrene and styrenesulfonate, by using a metallurgical microscope. Unlike latex particles of low charge numbers, the interparticle distances (2Dexp) in the hexagonal ordered regions are smaller than the calculated average values for a face‐centered‐cubic distribution (2D0,h) at low polymer concentrations (0.2–2 vol %). However, at high concentrations, up to 12%, the 2Dexp value approaches 2D0,h. The results are consistent with a ‘‘two‐state structure’’ containing ordered and disordered regions and indicate the existence of ‘‘attractive’’ interactions between the charged solutes. The findings are also consistent with those for other species of high charge densities such as synthetic macroions and simple ions.

‘‘Ordered’’ structure in dilute solutions of sodium polystyrenesulfonates as studied by small‐angle x‐ray scattering

The small angle x‐ray scattering measurements were performed for aqueous solutions of sodium polystyrenesulfonates having relatively narrow molecular weight distributions. As was observed for other synthetic macroions, polynucleotide and proteins, a single, broad peak was observed. The scattering vector at the peak position (Sm) was shifted toward larger values with increasing polymer concentration and toward lower values with increasing salt concentration, which confirmed earlier observations with polyacrylate and poly‐L‐lysine. The molecular weight dependence of the scattering behavior, which was earlier observed, was confirmed to be true for samples with Mw of 74 000, 18 000, and 4600. The mixture of two fractions with different Mw’s gave a scattering curve which was again different from the composite curve obtained with the parent curves before mixing. A similar situation was observed for the mixture of polystyrenesulfonate and polyacrylate. Thus, it was concluded that the observed single peak indicat...

Pressure dependence of trypsin-catalyzed hydrolyses of specific substrates

The effects of pressure on the trypsin-catalyzed hydrolyzed hydrolyses of three specific substrates, N-benzoyl-L-arginine ethyl ester (BzArgOEt), amide (BzArgNH2) and p-nitroanilide (BzArgNA), have been examined. The volume of the activation (delta V++) for kcat was -2.4 ml/mol for BzArgOEt and +3 - +6 ml/mol for BzArgNH2. Because of different rate-determining steps in the steady-state kinetics, the delta V++ value for BzArgOEt would indicate the activation volume of the deacylation step, whereas that for BzArgNH2 the delta V++ for the acylation step. The activation volumes were accounted for in terms of the difference in the mechanisms on the formation and decomposition of the tetrahedral-like intermediates during the acylation and deacylation steps. The delta V values for the formation of BzArgNH2- and thionine-trypsin complexes were several ml/mol, consistent with the fact that the main driving force of the substrate binding to this enzyme is electrostatic interaction, and in contrast to the delta V values of alpha-chymotrypsin complex formation with indole (approximately 0 ml/mol) or 2-furylacryloyl-D-tryptophan methyl ester (approximately 0 ml/mol), for which the hydrophobic interaction is the dominant force of the substrate binding. For the hydrolysis of BzArgNA, which showed a distinct substrate activation at high substrate concentrations, the pressure dependence of the four parameters, ks, Ks, (the catalytic rate and dissociation constant of the normal enzyme-substrate complex, respectively), Kss and Kss (those of the complex activated by the binding of the second substrate molecule), were measured at 1 atm and 1000 atm (25 degrees C). All of the four parameters increased with increase in pressure.

Revisit to the intrinsic viscosity-molecular weight relationship of ionic polymers: I. Viscosity behavior of dilute suspensions of ionic polymer latices

Abstract The viscosity of aqueous suspensions of ionic polymer latices was measured by using a variable shear viscometer, Ubbelohde viscometer, and a rotational viscometer. At variance with previous data, the reduced viscosity showed a strong shear rate dependence in the range between 10 and 1350 s−1 when the concentration of coexisting salt was low. At high-salt conditions, the shear rate dependence became smaller and the Einstein behavior was approached. For low-charge density latices at low- and high-salt conditions, the reduced viscosity ( η sp φ ) increased with increasing latex concentration in the low-concentration range. On the other hand, the η sp φ of highly charged samples decreased with increasing concentration at low-salt concentrations while it monotonically increased at high-salt concentration. The effective charge number of the latices, which was determined in a direct manner (by electric conductivity), was found to be rather insensitive toward the latex concentration in the same concentration range as employed in the viscosity measurements. By using the charge number thus found, we evaluated the first-order electroviscous effect from the viscosity and compared it with Booths theory. A satisfactory agreement was found at relatively high-salt concentrations. Implications of these findings for latex systems in the viscosity properties of linear polyelectrolyte solutions are briefly discussed. The interpretation in terms of the Debye screening length is critically discussed.

Void structure and vapor–liquid condensation in dilute deionized colloidal dispersions

Void formation and vapor–liquid condensation in deionized dilute aqueous colloidal dispersions were studied for the same latex sample. The former was observed under density‐matched conditions, while the latter was observed when the particles were denser than the dispersion medium. The critical concentration for void formation was found by direct observation using a confocal laser scanning microscope. Vapor–liquid condensation was observed for a dispersion of the same latex particles below the critical concentration. The critical concentrations for both phenomena were in agreement. The results clearly suggest an important role of a long‐range electrostatic attractive interaction on the stability of the colloidal dispersion.

Determination of the number of effective charges of colloidal particles by transference measurements

The number of effective charges of colloidal particles was determined for polystyrene‐based polymer latices by transference measurement. The fraction of free counterions (f) was surprisingly low and appeared to decrease with the analytical valency; the f values were about 0.1 for a latex having 1.7×104 SO3H groups per particle. A more highly charged latex (with 7.2×105 sulfonate groups) had f values of about 0.04. These values are definitely smaller than those reported for soluble polyelectrolytes (about 0.4).

‘‘Ordered’’ structure in dilute solutions of biopolymers as studied by small‐angle x‐ray scattering

Dilute aqueous solutions of bovine serum albumin, lysozyme, chondroitin sulfate, and tRNA were measured by small‐angle x‐ray scattering. The scattering curves showed a single, broad peak as was observed for synthetic polyelectrolytes, indicating the presence of an ordered distribution of charged solutes. The intermolecular distance evaluated from the peak position (2Dexpt) increased with decreasing polymer concentration and with increasing salt concentration. Except for chondroitin sulfate, 2Dexpt values were nearly equal to the interparticle distance (2D0) calculated based on the assumption of a uniform distribution. The observed relationship between 2Dexpt and 2D0 was in agreement with the proposal that intermacroion attraction is weak for low‐charge density particles under discussion. This attraction and repulsive interparticle interaction create a ‘‘secondary’’ minimum in the potential curve enabling ordering to take place. For tRNA, the scattering peak became lower with rising temperature. The fact t...

‘‘Ordered’’ structure in dilute suspensions of charged polymer latices as observed in the vertical planes and in mixtures of heavy and light waters

The aqueous suspension of various polystyrene‐based latices was studied by the microscopic method and the interparticle spacing was determined for 100 pairs of particles with the aid of an image data analyzer. The precision of the data was thereby largely improved. By using mixtures of light and heavy waters, the influence of the specific gravity of the solvent was studied. The spacing 2Dexp in the horizontal plane was almost independent of the specific gravity for latices of diameters smaller than about 5000 A, indicating that the inequality relation, 2Dexp<2D0 (average spacing calculated from the concentration), observed in an earlier publication [J. Chem. Phys. 78, 536 (1983)] is not an artifact due to the gravitational effects on latices and solvents. The spacing in the vertical plane was also measured in H2O and H2O–D2O mixtures. The 2Dexp values were hardly dependent on the suspension column height. The spacing was measured after the suspension was left undisturbed for a definite period. Up to 11 da...