Hiromi Kitano

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.

Anticancer gelatin microspheres with multiple functions

Biodegradable, hydrophilic gelatin microspheres (GM) with an average diameter of 70 microns were prepared by cross-linking gelatin with glutaraldehyde for hepatic intra-arterial infusion. An anticancer agent, mitomycin C (MMC), together with a radioisotope, 131I, were bound to the GM for chemotherapy and local internal radiotherapy. The 131I-labelled MMC-GM (131I-MMC-GM) could accumulate in the specific site and embolize the hepatic arteries after the hepatic intra-arterial infusion, while it caused various effects to the liver cells. The 131I-MMC-GM remained within the hepatic arteries for at least one month. In vitro release of drugs from the GM was also quantified using a dynamic dialysis method.

Hollow fiber enzyme reactors

Abstract Recently there have been some exciting developments in techniques to encapsulate enzymes into hollow fiber membranes. This entrapment protects enzymes from proteolytic and immunochemical attacks and makes possible industrial and medical applications of the immobilized enzymes.

Conductance stopped-flow study on the micellar equilibria of ionic surfactants

Rapid ionic equilibria of solutions of cationic and anionic surfactants were studied by the concentration-jump method with the use of the conductance stopped-flow technique. The slow relaxation times (⊺2) assigned to the micellization-dissolution process were obtained from the traces of the conductance changes in a much wider concentration range than in the previous methods. The ⊺2 of sodium dodecyl sulphate (SLS) observed coincided fairly well with those obtained from the temperature-jump technique by Folger et al. (1974) and by Aniansson et at. (1976), when comparison was possible. In a wide concentration range above c. m. c. ⊺2-1 of SLS sharply decreased with increasing concentration, increased with temperature, and decreased with addition of foreign salts. The ⊺2-1 of sodium tetradecyl sulphate (STS) and sodium hexadecyl sulphate (SCS) showed similar trends. The magnitudes of the ⊺2-1 were in the order SLS > STS > SCS. The ⊺2-1 of hexadecyl trimethylammonium bromide solution, which was much smaller than those of the anionic micelles studied, also showed similar dependence on concentration (above c. m. c.) and temperature.

Kinetic study of the effects of solvation on the dimerization process of α-chymotrypsin

Abstract The dimeric association process of α-chymotrypsin has been studied with the aid of a stopped-flow spectrophotometer at various temperatures and pH values. From the temperature dependences of the forward reaction rate constant ( k f ) and the equilibrium dimerization constant ( K D ), the reaction system observed here is concluded to be entropy-driven. The increase in entropy can be attributed to the release of water molecules from both the active site and the surface part of the protein molecule during the course of dimerization. From the pH dependences of the reaction rate constants and the equilibrium constant, the reaction is concluded to depend strongly on the dissociations of the site between the carboxyl group of the aspartic acid and imidazolyl group of the histidine residues (in the higher pH region), and the site between the imidazolyl group of the histidine and the carboxyl group of the tyrosine residue (in the lower pH region), respectively.

Mutual recognition between polymerized liposomes: enzyme and enzyme inhibitor system

In order to examine the usefulness of polymerized liposomes as a model for cell membranes, a mutual recognition phenomenon between different liposomes on which complementary ligands were attached was examined. We used trypsin- and soybean trypsin inhibitor (STI)-carrying polymerized liposomes to attain high sensitivities. The STI which was immobilized on the polymerized mono-dienoylphosphatidylcholine liposome showed a definite inhibitory effect on the catalytic activity of the trypsin which was immobilized on another polymerized liposome, whereas the inhibitory effect of the STI which was immobilized on the di-dienoylphosphatidylcholine liposome was much smaller than that of the mono-dienoylphosphatidylcholine system because of the larger rigity of the di-dienoylphosphatidylcholine liposome. These results suggest that the mutual recognition between complementary ligands can be realized by using polymerized liposomes with a physical stability and moderate deformability as their carriers.

Conductance stopped-flow study on biological complexations: hapten-antibody and enzyme-inhibitor systems

SummaryConductance stopped-flow (CSF) technique is used to investigate the complexations of proteins with complementary ligands. Hapten-antibody and trypsin-trypsin inhibitor systems are adopted as typical complexation reactions containing protein molecules. Clear and rapid conductance changes are observed in both systems and the reaction rate constants evaluated from the observed curves are in a good agreement with the literature values obtained by other methods, which clearly shows a usefulness of the CSF technique for the kinetic analysis of biological systems.

Coenzyme model reaction in lipid bilayers

Abstract Coenzyme model reactions, such as the H − (H + + 2e − ) transfer from NADH models to triphenyl methane dyes, were investigated in the presence of lipid bilayers, for example, l -α-dimyristoyl phosphatidyl choline and egg yolk lecithin. In the temperature dependence of the acceleration effect by the lipid bilayer, discontinuous points were observed, corresponding to the phase transition point such as gel-liquid crystal ( T c ) or the segregation point ( T s ). The T c and T s values of the bilayers varied with the reactant as a result of the difference of perturbing effect on the structure of the bilayers. The pressure effect on the transition point was also studied. Transition points such as T c or T s became higher with increasing pressure, and dT c dP or dT s dP was different for various bilayers. In the gel phase of the membrane, stereospecific reduction of malachite green was observed by chiral nicotinamide: the difference in the catalytic effect on the reduction rate between ( R )- and ( S )-dihydronicotinamides was larger in the gel phase than that in the liquid crystal phase or in the phase separated state, which suggests that the gel-state molecule can recognize the molecular structure better than the liquid-crystal state molecule.

Raman spectroscopic study of hydrogen bonding of N-alkyl-2-pyrrolidinones in heavy water☆

Abstract The Raman spectra of D 2 O solutions of N -methyl-2-pyrrolidinone, N -ethyl-2-pyrrolidinone, and N-n -butyl-2-pyrrolidinone under diverse conditions were measured. Using a computer fitting of the band shape of the carbonyl stretching mode at various temperatures, an enthalpy difference for the inversion motion at the nitrogen atom due to hydrogen bonding with deuterium was estimated for these compounds. The enthalpy difference of hydrogen bond formation to the nitrogen atom of N -methyl-2-pyrrolidinone at 30 wt% in D 2 O (mole fraction 0.080) was greater than that of N -methyl-2-pyrrolidinone in an aqueous solution at a mole fraction of 0.406. Furthermore, the enthalpy difference of N -alkyl-2-pyrrolidinones increased with the alkyl chain length. This is interepreted as a result of the change of the hydrophobic hydration of D 2 O molecules around the solute molecules.

Pulse injection analysis of the binding of serum proteins to porous polymer gels modified with formyl groups

Highly porous spherical polymer gels were modified with formyl groups by a modified Friedel-Crafts reaction and the interaction of serum proteins with the modified gels were examined by pulse injection analysis. The introduction of formyl groups into the polymer greatly increases its protein-binding capacity, and the protein bound to the gel is not eluted by washing with acid, alkali or urea solution. The effects of temperature and the percentage of formyl group substitution on the binding capacity indicate that the binding process can be interpreted as initial approach of the protein to the polymer surface, caused by the hydrophobic interaction, followed by formation of a stable Schiff base between the polymer gel and the protein. Theoretical treatment of the elution behaviour of the protein from the polymer-packed column is also examined, with the assumption that there are three kinds of binding site in the polymer gel: surface, macropore and micropore regions. These polymers are shown to be useful for the removal of proteins from biological samples in clinical assays using immobilized enzymes.