Tatsuya Yasunaga

Acoustic study on the kinetics for the dissociation-recombination reaction between micelle and counterion in sodium dodecyl sulfate solution

Abstract The ultrasonic absorption of sodium dodecyl sulfate (SDS) in aqueous solution was measured at 30°C. in the range of frequency between 70 kc. and 95 Mc. and of concentration from 6.5 to 100 mM. The excess absorption was observed only in the solutions the concentration of which was higher than the critical micellar concentration. The excess absorption of sound and the relaxation frequencies obtained from the absorption curves show a discontinuity with the variation of the concentration of SDS in the neighborhood of 50 mM. Other properties like viscosity, conductivity, and velocity of sound also exhibit such a change near the same concentration. It is concluded that a change in the properties of the micelles of SDS occurs in the neighborhood of this concentration. The mechanism of the observed ultrasonic absorption is considered and attributed to the reaction M″ ⇌ M′ + 2Na+, where M′ and M″ are two types of micelles. The rate constants of the forward and backward reactions are found to be 1.5 × 105 sec.−1 and 8.4 × 109 mole−2 sec.−1, respectively, and the partial molal volume change between the initial and final states in the reaction is 29.4 cm.3 mole−1.

Kinetic study of sodium dodecyl sulfate micelle dissociation by a stopped-flow method

The process of the micelle dissociation of sodium dodecyl sulfate (SDS) was observed by a stopped-flow method applying the specific absorption band. The absorbance change observed in the dilution from above the CMC to below the CMC was attributed to the next reaction nDSn→k+mS, (n>m) nwhere DSn is the micelle solubilizing the dye, D′ is the salt of the dye cation with the detergent anion, S is the detergent monomer, and k is the overall micelle dissociation rate constant. The micelle dissociation rate constant was calculated to be 5.5 sec−1 at 42°C.

Kinetics of proton adsorption-desorption at TiO2-H2O interface by means of pressure-jump technique

Abstract Single relaxation was found in TiO2 (anatase) suspension by means of the pressure-jump technique with electrical conductance detection. The reciprocal relaxation time observed changed markedly with pH to show a minimum at pH 3.5. The relaxation was attributed to proton adsorption-desorption on the surface of TiO2 particle. It was well expressed by a Langmuir-type adsorption-desorption rate equation. The adsorption and desorption rate constants were 4 × 10−4 dm3 cm−2 sec−1 and 8 × 10−9 mole cm−2 sec−1, respectively. The experimental value of adsorption energy was in agreement with the theoretical one calculated on the basis of Ficks first law.

Acoustic study of the kinetics of the dissociation-recombination reaction between micelle and counterion in solutions of sodium salts of fatty acids—sodium caprylate and sodium caprate

Abstract The ultrasonic absorption has been measured in aqueous solutions of sodium caprylate and sodium caprate at 30°C over the frequency range of 5–95 mc. As in the case of sodium dodecyl sulfate, the excess absorption was observed only in solutions in which the concentration was higher than the critical micellar concentration (CMC), both in the presence and absence of salt. The mechanism for these features was attributed to the reaction M ″→M′ + 3 N a + for sodium caprylate and M ″→M′ + 2.5 N a + for sodium caprate, where M′ and M″ are two types of micelle. The rate constants of the forward and backward reactions were 3.8 × 107 sec−1, 3.3 × 109 mole−3 sec−1 for sodium caprylate and 1.1 × 107 sec−1, 2.8 × 109 mole−2.5 sec−1 for sodium caprate, respectively. Some kinetic characteristics including the free energy, enthalpy, and entropy were calculated.

Kinetic study of sodium decyl sulfate micelle dissociation by the relaxation method

Abstract The micelle dissociation rate of sodium decyl sulfate was studied with an addition of salt by a temperature-jump technique and without it by a pressure-jump technique. The relaxation phenomena were observed only above the critical micelle concentration and were attributed to the perturbation of the monomer-micelle equilibrium. From the concentration-dependent relaxation time, the rate constants of micelle dissociation were determined to be 22–30 sec−1 at 30°C. The effects of the hydrocarbon chain length and the addition of salt on the rate constants were discussed.

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.

Kinetics of helix-coil transition of polypeptides in solution by the relaxation methods

Relaxation phenomena were studied in aqueous solutions of poly (alpha-L-glutamic acid) (Glu)n and poly (alpha-L-lysine) (Lys)n under various conditions using the electric field pulse method with detection by conductivity change. The relaxation time for the (Glu)n has a maximum value at the midpoint of the helix-coil transition. Some possible mechanisms are discussed and the observed relaxation phenomenon is attributed to the helix-coil transition. In the case of (Lys)n, the relaxation time as a function of pH exhibits two maxima. One is assigned to a proton transfer reaction and the other to the helix-coil transition. Using the Schwarzs theory the rate constants of the helix growth step for both (Glu)n and (Lys)n are estimated. The difference in the activation parameters for (Glu)n and (Lys)n is discussed.

Unusually fast ligand exchange rate in horseradish peroxidase as studied by temperature-jump method

A kinetics of azide binding by horseradish peroxidase was studied by temperature-jump method. It was found that the reaction of the enzyme with azide is quite rapid, occuring in microsecond time range. This rate is unusually rapid in contrast to the usual hemoprotein ferric iron-ligand interactions so far reported. The resulting value for the apparent association and dissociation rate constants were k1=6.8×106 M−1 s−1 and k1=3.5×105 s−1 at 23°C and pH 5.0 for the reaction. The pH dependence of the rate constants was also studied to show a strong linkage of the ligand binding with a proton uptake of a dissociable group on the enzyme.

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.

Mechanism of the binding of 2-(4′-hydroxyphenylazo)benzoic acid to bovine serum albumin

The mechanism of the binding of 2-(4-hydroxyphenylazo)benzoic acid (HABA) to bovine serum albumin was studied by relaxation methods as well as the binding isotherm using gel chromatography. A single relaxation was observed over a wide range of HABA concentration except at the extremes of high concentration where another slow process was observed. The concentration dependence of the reciprocal relaxation time of the fast process decreased monotonically with increase in concentration of HABA at constant polymer concentration. The data were analyzed on the basis of Browns domain structure model and were found to be consistent with a sequential binding mechanism. The azohydrazon tautomerism of HABA was identified with the intramolecular step of the complex. The activation parameters of the step, determined from the temperature dependence of the relaxation time of the fast process, showed that this step is rate limited by an enthalpy barrier in both forward and backward directions. Comparison of the activation parameters with those of other serum albumin-ligand systems suggests that there is an enthalpy-entropy compensation in the activation process of the intramolecular step with the compensation temperature at about 270 K; the enthalpy-entropy compensation is thought to be related to the hydrophobic nature of the ligand.