“…A value of 2.89 mM was obtained for the cmc from fluorescence intensities of 2-(4‘-piridil)bencimidazol (see Figure ). The value is in the range of most published values at 0.1−0.2 M Na + (2 to 3 mM 13f,, ). 2 Critical micelle concentration determination for NaDC at 20 °C by fluorescence of 2-(4‘-piridil)bencimidazol at 380 nm.…”
Section: Methodssupporting
confidence: 65%
“…Here we present the experimental results for the aggregation kinetics obtained from static light scattering measurements. Although static light scattering has been extensively used to measure physicochemical properties of bile salt−aqueous solutions systems, , it has not been applied to study the NaDC gelation process. It is also important that it is not an invasive technique and that the system remains unperturbed.…”
The aggregation kinetics of sodium deoxycholate in aqueous solution has been studied at pH values close to neutrality. An induction time is observed and taken as inversely proportional to the rate constant for the aggregation of two small aggregates to form a larger one but one that is smaller than a critical size. When the critical size is reached, the length of the polymer-like structure allows the entanglement of the aggregates, accounting for the gel behavior of the solution. After the induction time, it is observed that the weight average aggregation number increases linearly with time for more than 50% of the aggregation. This is analyzed through the Smoluchowski equation in its simplest form. The influence of the temperature on the kinetics suggests the existence of a kinetic-thermodynamic relationship. It is deduced that the aggregation rate is limited by physical interactions, and the role of hydrogen bond in the aggregation rate is discussed. The influences of pH and phosphate concentration are also studied and discussed.
“…A value of 2.89 mM was obtained for the cmc from fluorescence intensities of 2-(4‘-piridil)bencimidazol (see Figure ). The value is in the range of most published values at 0.1−0.2 M Na + (2 to 3 mM 13f,, ). 2 Critical micelle concentration determination for NaDC at 20 °C by fluorescence of 2-(4‘-piridil)bencimidazol at 380 nm.…”
Section: Methodssupporting
confidence: 65%
“…Here we present the experimental results for the aggregation kinetics obtained from static light scattering measurements. Although static light scattering has been extensively used to measure physicochemical properties of bile salt−aqueous solutions systems, , it has not been applied to study the NaDC gelation process. It is also important that it is not an invasive technique and that the system remains unperturbed.…”
The aggregation kinetics of sodium deoxycholate in aqueous solution has been studied at pH values close to neutrality. An induction time is observed and taken as inversely proportional to the rate constant for the aggregation of two small aggregates to form a larger one but one that is smaller than a critical size. When the critical size is reached, the length of the polymer-like structure allows the entanglement of the aggregates, accounting for the gel behavior of the solution. After the induction time, it is observed that the weight average aggregation number increases linearly with time for more than 50% of the aggregation. This is analyzed through the Smoluchowski equation in its simplest form. The influence of the temperature on the kinetics suggests the existence of a kinetic-thermodynamic relationship. It is deduced that the aggregation rate is limited by physical interactions, and the role of hydrogen bond in the aggregation rate is discussed. The influences of pH and phosphate concentration are also studied and discussed.
“…In most papers in Figure 1 and Table 1, the reported values of N pertain to those at the CMC, but in a few reports the values refer to some concentrations above the CMC (39, 44, 49) (points b, g and 1). In several papers, pH of solutions was not indicated nor was it controlled (43,44,47,48) (points f, g, j, k). The temperature effects on N cannot explain the discrepancies in Figure 1.…”
The current state of the knowledge of the size and the aggregation numbers of micelles formed in solutions of bile salts was evaluated. The experimental techniques considered include static light scattering, sedimentation equilibrium, membrane osmometry, sedimentation velocity and transla‐tional diffusion. The theoretical background of each method is briefly discussed, the working equations are summarized, and the limitations of each technique are enumerated. Various interaction parameters and their effects on the measured micellar size are discussed. A brief survey of the recent experimental results from the author's laboratory is presented.
“…Here it should be noted that when some dif-ferent types of aggregates are formed by protonated SMDP molecules, the aggregates can gather together to form a bigger aggregate, or a huge molecular assembly, depending on the situation given. These aggregates can be formed and become large even in very lower concentration range, as has been observed for aqueous solution of sodium deoxycholate having two hydroxyl groups and a carboxyl group (22)(23)(24)(25) . Such large size aggregates composed of many protonated SMDP molecules can be suspended (dispersed) in bulk solution.…”
Section: Aggregates Formation Suggested By Ph and Light Scattering mentioning
confidence: 62%
“…A similar situation is shown below with respect to the concentration dependence in pH. In the case of a bile salt, sodium deoxycholate being a surfactant present in living bodies, the molecules are highly polymerized through hydrogen bonding to form huge aggregates below CMC, or result in gelation throughout the solution (22)(23)(24)(25). Similar to the case of the bile salt, a large aggregate may be transformed into smaller aggregates again by further increased concentration; the frown huge particles or polymerized fibril aggregates which are regarded as being in a state between dissolution and precipitation can be solubilized by the further added surfactant.…”
Section: Aggregates Formation Suggested By Ph and Light Scattering mentioning
Aggregation behavior of sodium salt of mono-n-dodecyl phosphoric acid ester i.e. a species of mono-alkyl phosphate (MAP) surfactants, in pure water was investigated as a function of surfactant concentration (C S) by means of surface tension (g), electroconductivity (measuring both specific (k) and molar (L) conductivities), pH and UV-Vis spectra measurements. The Krafft temperature was determined as 40 by observing the change of k with raised temperature. Although the curve of g vs. log C S plot gave only one break which corresponds to critical micellization concentration(CMC) in common theory, different relations of k vs. C S , L vs. √ C S , or k vs. log C S , and pH vs. C S resulted in several breaks suggesting the occurrence of various transitions of aggregates or micelles over the concentration range not only above, but also below CMC. The CMC determined by surface tension measurement was referred to as the first CMC (CMC 1). The critical concentrations of the transitions observed by various methods were termed as CAC i (i=1,2,3) for three-step aggregate formation below CMC 1 and as CMC j (j=1 5) for five-step transitions in micellar form. From the temperature study on CAC i and CMC j , the estimated standard Gibbs energy changes were estimated, which showed us that the primary driving force of aggregate/micelle formation at any step comes from the entropy term, since the energy term (enthalpy) in this case was found to be positive. This supports our interpretation that the aggregates/micelles are mainly composed of hydrolyzed (protonated) mono-dodecyl phosphate molecules so that they behave as if they were nonionic surfactant micelles. A light scattering measurement verified the existence of aggregates formed below CMC. The experiment of catalytic activity assay revealed that SMDP aggregates formed in the low concentration range (ten times lower than CMC 1) were found to act as catalysts for the hydrolysis reaction of p-nitrophenyl acetate (pNPA).
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