Nobuhide Tatsumoto

A simple preparation of half N-acetylated chitosan highly soluble in water and aqueous organic solvents

A simple and improved method of preparing highly soluble chitosan (half N-acetylated chitosan) was developed using a series of chitosan samples of low molecular weights, and the solubility of the half N-acetylated chitosan in water and organic solvents was investigated in detail. To reduce the molecular weight, chitosan was treated with NaBO3 under the condition that chitosan was homogeneously dissolved in aqueous acetic acid. Weight-average molecular weights of the obtained chitosan samples were determined using a size-exclusion chromatography system equipped with a low-angle laser light-scattering photometer. Each chitosan sample was then N-acetylated with acetic anhydride under the condition that chitosan was homogeneously dissolved in aqueous acetic acid again. The water solubility of the half N-acetylated chitosan thus prepared increased with decreasing molecular weight. From 1H NMR spectroscopy, it was suggested that the sequence of N-acetylglucosamine and glucosamine residues was random. The solubility of the half N-acetylated chitosan of low molecular weight was rather high even in aqueous dimethylacetamide and dimethylsulfoxide.

Ultrasonic Absorption in Propionic Acid

The ultrasonic relaxational absorption in methyl propionate solutions of propionic acid has been studied in the frequency range 0.5–95 Mc/sec at concentrations varying from 0 to 1 mole fraction. The relaxation frequencies are 1.8, 2.2, 2.8, and 3.4 Mc/sec independent of the concentration at 20°, 25°, 30°, and 35°C, respectively. The independence of fmax on the concentration indicates that the ultrasonic relaxational absorption is associated with the uni—unimolecular reaction. The kinetic values have been calculated for the uni—unimolecular reaction by Tabuchis theoretical equations. The forward and backward rate constants are 2.3×105 and 1.06×107 sec−1 at 20°C for pure propionic acid, respectively, and the heat of reaction is 4.7 kcal/mole of dimer. The value of Cpr is equal to that of Cvr, since the volume change resulting from reaction is absent. The consideration for the type of reaction, the magnitude of heat of reaction, and no volume change associated with reaction have led us to the conclusion tha...

Kinetic study on solubilization of pinacyanol chloride into the micelle of sodium dodecyl sulfate by a stopped-flow technique

Abstract The process of the solubilization of pinacyanol chloride into the micelle of sodium dodecyl sulfate (SDS) was observed by a stopped flow technique applying the specific absorption bands. The transmittance change observed was attributed to the pseudo-unimolecular reaction DS x → k DS m+x ( in excess of S m ) where D is the dye molecule, DS x is the salt of dye with the detergent anion, S m is the micelle, DS m + x is the micelle solubilizing the salt, and k is the rate constant. The rate constant, k , was calculated to be 30 sec −1 at 50°C. The mechanism of the solubilization of dye into the micelle is discussed.

Temperature-responsive properties of poly(acrylic acid-co-acrylamide)-graft-oligo(ethylene glycol) hydrogels

A series of temperature- and pH-responsive hydrogels were prepared from acrylic acid (AAc), acrylamide (AAm), oligo(ethylene glycol)monoacrylate (OEGMA), and oligo(ethylene glycol)diacrylate by varying the AAc:AAm molar ratio and the OEGMA content. Phase-transition temperatures and swelling ratios of the obtained poly(AAc-co-AAm)-graft-OEG gels were measured as a function of temperature and pH. At pH < 5, the obvious transition temperatures ranging from 5 to 35°C were obtained as the AAc: AAm molar ratio was varied. The highest transition temperature was obtained at the AAc: AAm ratios of 5: 5 and 6: 4, and the sharp transition curves were observed at the AAc: AAm ratios from 5: 5 to 8: 2. The transition temperature further increased with increasing OEGMA content. It was suggested that OEG graft chains with a large mobility played an important role for the formation of hydrogen bonding in the hydrogels. The gels prepared here showed obvious reproducibility of the phase transition in response to temperature changes, which suggests the feasibility of their practical applications.

Ultrasonic Absorption in Sodium Metaborate Solution

The kinetics of reaction in the dilute aqueous solution of sodium metaborate have been studied by ultrasonic absorption measurements over the frequency range from 50 kc/sec to 75 Mc/sec. Single relaxation frequencies have been observed in 0.05, 0.1, and 0.2M at 25°C and in 0.1M at 35°C, and the absorption mechanism has been assigned to be due to the hydrolysis of metaborate ion. The corresponding forward and backward rate constants calculated for the reaction BO2−+H2O⇌HBO2+OH− are 4.11×103 sec−1 and 2.36×108M−1 sec−1 at 25°C for 0.05M solution, respectively. From the magnitude of the relaxational acoustic absorption per wavelength, the partial molal volume change ΔV° for the process is calculated to be 6.83 cm3/mole at 25°C for the 0.05M solution. The temperature dependence of the relaxation frequency indicates that the energies of activation for the reaction are 12.6 and 1.31 kcal/mole for the forward and backward reactions, respectively.

Relaxation Studies of the Adsorption-Desorption Equilibrium of Surfactants on the Gas-Liquid Interface. II. Experimental Studies

A general theory for the propagation characteristics of the capillary wave on the gas-liquid interface, where the physicochemical equilibrium exists, is proposed. The theory is developed on the basis of the two-dimensional relaxation theory and the surface thermodynamics. The relaxation parameters in the equations are closely related to the dynamic behavior of the equilibrium. As an example, the theory was applied to the surfactant solution, taking account of the adsorption-desorption and diffusion processes of the surfactant. The derived equations revealed that the adsorption-desorption process plays an important role in the surfactant transfer between the surface and the bulk phase in a concentrated surfactant solution, while the diffusion process plays such a role in a dilute solution.

Pressure‐jump apparatus suitable for repetitive experiments

A repetitive pressure-jump apparatus has been devised and used for the measurement of a small relaxation effect in solution. Although the pressure rise time of the apparatus is inferior to the usual method, signal averaging has enhanced signal-to-noise ratio of the relaxation spectrum.

Kinetic Studies of the Rapid Reactions in n-Alkyl Sulfate Solution

The kinetics of micellization have been studied using the various relaxation techniques on several detergent micelles1–16. Synthetically speaking, the relaxation times obtained by means of the ultrasonic absorption techniques1–7 are above two order of magnitude faster than those by means of the temperature-jump or the pressure-jump techniques8–15. In the latter case, all of the published papers containing ours12,13 have reported that the reciprocal relaxation times increase with the total detergent concentration in the concentration range larger than the critical micellar concentration (c.m.c.) except two papers14,15 which also indicate the apparent concentration dependences of the relaxation times in the lower concentration range. More recently, however, we have obtained the relaxation times independent of the total detergent concentration on sodium dodecyl sulfate (SDS) by means of the pressure-jump technique.