| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 92 === Abstract
The migration behavior of cationic solutes and influences of the interactions of cationic solutes with sodium dodecyl sulfate (SDS) on the formation of micelles and its critical micelle concentration (CMC) were investigated by capillary electrophoresis at neutral/acidic pH. Catecholamines and structurally related compounds, including epinephrine, norepinephrine, dopamine, norephedrine, and tyramine, which involve different extents of hydrophobic, ionic and hydrogen bonding interactions with SDS surfactant, are selected as cationic solutes. The dependence of the effective electrophoretic mobility of cationic solutes on the concentration of SDS monomers in the premicellar region provides direct evidence of the formation of ion-pairs between cationic solutes and SDS monomers. Three different approaches, based on the variations of either the effective electrophoretic mobility or the retention factor as a function of SDS concentration in the premicellar and micellar regions, and the linear relationship between the retention factor and the product of a distribution coefficient and the phase ratio, were considered to determine the CMC value of SDS micelles. The suitability of the methods used for the determination of the CMC of SDS with these cationic solutes was discussed. Depending on the structures of cationic solutes and electrophoretic conditions, the CMC value of SDS determined varies in a wide concentration range. The results indicate that, in addition to hydrophobic interaction, both ionic and hydrogen bonding interactions have pronounced effects on the formation of SDS micelles. Ionic interaction between cationic solutes and SDS surfactant stabilizes the SDS micelles, whereas hydrogen bonding interactions weakens the solubilization of the attractive ionic interaction. The elevation of the CMC of SDS depends heavily on hydrogen bonding interactions between cationic solutes and SDS surfactant. Thus the CMC value of SDS is remarkably elevated with catecholamines, such as epinephrine and norepinephrine, as compared with norephedrine. In addition, the effect of methanol content in the sample solution of these cationic solutes on the CMC of SDS was also examined. The binding constant of cationic solutes with SDS monomers and those of cationic solutes to SDS micelles are evaluated.
The influence of ��-cyclodextrin (��-CD) on the critical micelle concentration (CMC) of sodium dodecyl sulfate (SDS) was investigated by capillary electrophoresis using cationic solutes as probe molecules at pH 7.0. The variations of the electrophoretic mobility of probe molecules as a function of surfactant concentration in both premicellar and micellar regions in the absence and presence of ��-CD was analyzed.
The results indicate that, as a consequence of a strong inclusion complexation between ��-CD and SDS, the encapsulation of ��-CD with probe molecules is greatly diminished, or even vanished, in the presence of SDS. The complexes formed between ��-CD and SDS monomers exist predominantly in the form of a 1:1 stoichiometry, while complexes with a 2:1 stoichiometry reported previously in the literature as a minor component is indicative at a concentration of ��-CD exceeding about 7mM. The elevation of the CMC value of SDS depends on the concentration of ��-CD in the buffer electrolyte . The binding constants of probe molecules to ��-CD, to surfactant molecules, and to the complexes formed between ��-CD and SDS are reported.
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