| Description |
This thesis is concerned with the study of the nature of self-association of the trihydroxy and dihydroxy bile salts in aqueous electrolyte solutions. Most often the pattern of this association has be described by using a nonomer-millar modal borrowed from flexible chain surfactants. One of the characteristics of this model is the existence of the critical micelle concentration (CMC). Based on this model, it is assumed that there is not higher aggregate in the dilute concentrations somewhat below the CMC. Utilizing the light scattering technique, the turbidity as a function of concentration wa obtained for sodium cholate, sodium taurocholate and sodium glycocholate over the concentration range from 0-25 mg/ml. For the bile salt sodium cholate, the concentration of the supporting electroyte, NaC1, was varied over the range fro 0-0.5 M. For sodium glycocholate, the turbidity was determined in 0.15 M NaF, NaC1, and Na1 and for sodium cholate and sodium taurocholate the turbidity was determined in the above systems plus NaBr. Comparison of the light scattering data with the monmermicelle equilibrium model shows qualitative agreement; hovever, quantitative agreement cannot be achieved. Further examination of the data has shown that the light scattering results are excellent agreement with a model which includes dimers, trimers and a higher aggregate containing an average of about 8 monomeric units. For the dihydroxy bile salts, the turbidity is a function of concentrations was determined for sodium deoxycholate, sodium taurodeoxycholate and sodium glycodeoxycholate over the concentration range from 0-20 mj/ml. For sodium deoxycholate, the turbidity was obtained in 0.15 M NaCl. On comparison of the light scattering data obtained from these dihydroxy bile salt with the monomermicelle model, qualitative agreement with the experimental results was obtained for the above systems utilizing a model whtich assumes the existence of dimers, trimers, tetramers and a much higher aggreagate. The average aggregation number for the higher aggreagate was found to be 25 for sodium taurocholate, while values of 17.6 and 18 were found for sodium deoxycholate and sodium glycodeoxycholate. From the study of the ionic strength effects on the self-association of sodium cholate, and increasing tendency in the values of the association constants for the small oligomers and in the aggregation numbers for the high aggregates was indicated. However, this effect is hard to confirm from the present results. For the purpose of comparison of the model for the trihydoxy bile salts obtained from the light scattering results, the equilibrium solubility of naphthalene in 0.15 M NaC1 was determined. Based on the analysis, the light scattering results who excellent agreement with the naphthalene solubility data. This is a further proof of the validity of the model obtained from the light scattering results for the self-association of the trihydroxy bile salts. |
