Composition of Sodium Cholate Micellar Solutions

Abstract

To study the composition of sodium cholate solutions, an investigation was carried out at 25 degrees C and in N(CH3)4Cl, as a constant ionic medium, at three different concentrations (W = 0.100; 0.500 and 0.800 mol dm(-3)). Electromotive force measurements of three different galvanic cells, the first involving a glass electrode for hydrogen ions, the second an electrode for sodium ions and the third a lead amalgam electrode, were performed. Independently, lead (II) cholate solubility measurements in the presence of sodium ions were performed, as well. The experimental results obtained from both approaches were explained by assuming the formation of aggregates in cholate and sodium of different composition depending on W and on the cholate concentration. The maximum aggregation found number for cholate was 24 and even aggregation numbers were markedly predominant. Only two species with odd aggregation number were found, but at a low percentage. The assumed species and the relative constants were compared with those found for the other sodium salt of cholanic acids.

Composition of Aqueous Solutions Containing Sodium Glycocholate and Glycodeoxycholate

“…21 As in the solutions S, lead (II) was in equilibrium both with c GC and c GDC , from the knowledge of c Pb it was possible to calculate c GC and c GDC , by means of the equilibria previously studied. 26 Solutions where the concentrations of the reagents varied within wide ranges were investigated, so that when W = 0.100 mol dm -3 , the following ranges were investigated: 0.5 x 10 -3 ≤ C Na ≤ 0.040 mol dm -3 ; 1.0 x 10 -3 ≤ C GC ≤ 0.020 mol dm -3 ; 1.0 x 10 -3 ≤ C GDC ≤ 0.020 mol dm -3 ; while when W = 0.500 mol dm -3 , the following ranges were investigated: 0.5 x 10 -3 ≤ C Na ≤ 0.100 mol dm -3 ; 1.0 ≤ x 10 -3 C GC ≤ 0.050 mol dm -3 ; 1.0 x 10 -3 ≤ C GDC ≤ 0.050 mol dm -3 ; and in the case of W = 0.750 mol dm -3 , the following ranges were investigated: 0.5 x 10 -3 ≤ C Na ≤ 0.150 mol dm -3 ; 1.0 x 10 -3 ≤ C GC ≤ 0.080 mol dm -3 ; 1.0 x 10 -3 ≤ C GDC ≤ 0.080 mol dm -3 .…”

“…2 -16 Earlier investigations carried out on solutions of sodium salts of dihydroxycholanic (deoxycholate and its conjugates) 17 -19 and trihydroxycholanic (cholate and its conjugates) 14,[20][21][22] showed a very different behaviour with regard to the aggregation number, the participation of hydrogen ions to the aggregate formation and the basic unit constituent of the micelles of the two kinds of cholanic salts.…”

“…More recently, sodium taurocholate (NaTC), 14,20 sodium glycocholate (NaGC) 14,21 and sodium cholate (NaCol), 22 containing three OH groups in the positions 3α, 7α and 12 α, showed a very different behaviour, because the experimental data obtained in their solutions were explained by assuming the presence of a dimeric species constituent the building block of the micellar aggregates, which always have aggregation numbers that are multiples of two. Furthermore, aggregates formed by dihydroxycholanic salts reach bigger dimensions than those formed by trihydroxycholanic ones.…”

The Influence of the Ionic Medium on the Behaviour of Sodium Glycocholate and Cholate Aqueous Solutions

“…measurements as a function of hydrogen ion and reagent concentration. [6][7][8][9][10][11] Reagent activity coefficients were kept constant, in spite of a wide change of concentrations, adopting the constant ionic medium method. 12 N(CH 3 ) 4 Cl at different concentrations was selected as an ionic medium considered inert.…”

“…In the investigations on the dihydroxycholanic salts, 6-8 W was 0.100, 0.200, 0.300, 0.400, 0.500, 0.600 and 0.750 mol dm -3 , while in the case of the trihydroxycholanic salts [9][10][11] , W was only 0.100, 0.500 and 0.800 mol dm -3 .…”