On the Micellar Aggregates of Alkali Metal Salts of Deoxycholic Acid

Abstract

The X-ray patterns of lithium (LiDC) and potassium (KDC) deoxycholate fibers, drawn from aqueous micellar solutions, have been interpreted by means of a packing of 8/1 helices formed by trimers. Previously, these helices satisfactorily represented the structure of the sodium (NaDC) and rubidium (RbDC) deoxycholate micellar aggregates. Dielectric measurements show that the trend of the average electric dipole moment µ of a NaDC monomer as a function of temperature and concentration supports a two-structure equilibrium. The high µ values (32-58 D) can be explained by the remarkable hydration of the NaDC micellar aggregates. The µ moderate decrease when the size of the aggregates increases can agree with the presence of small helices but disagrees with the existence of aggregates that are disordered or have a center (or a pseudocenter) of symmetry. Formerly, it was observed that sodium taurodeoxycholate (NaTDC) micellar aggregates, represented by 7/1 helices, formed by trimers, behave similarly. The contribution to the electrical conductivity of NaDC and NaTDC in aqueous solutions containing NaCl tends to zero by increasing the NaCl concentration, denoting strong interactions between Na + ions and anion aggregates. According to the similar 7/1 and 8/1 helices, which have the Na + ions in their inner part, the micellar size and the fraction of Na + ions trapped inside the helices increase together. The aggregate apparent hydrodynamic radius (R h ) increases by increasing the ionic strength in the order LiDC > NaDC > KDC > RbDC. Fibers drawn from solutions containing two cations at the same concentration show that the affinity for the anionic structure seems to follow the order Li + > Na + > K + > Rb + at high ionic strength. The R h values vs the mole fractions of Li + and Rb + or Na + and K + at lower ionic strength are fitted by straight lines. Probably, the free energy gains, associated with the cation and anion transfer from the bulk solution to the micellar aggregates, are almost equal for the four salts at lower ionic strength.

Composition of Aqueous Solutions Containing Sodium Glycocholate and Glycodeoxycholate

“…Structural studies showed that helical models described satisfactorily aqueous solutions of micellar aggregates of dihydroxycholanic salts (DC, GDC, TDC). [12][13][14] The hypothesis can be formulated that GDC increases along a cylinder and GC tends to block the increasing of the helical of GDC by positioning at the two bases of the cylinder. On the other side, aggregation numbers of GC are smaller than 24 (value observed in solutions where GC was the alone bile salt), because it is probable that the excess of GC increases the percentage of monomer or dimer.…”

“…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.…”

Composition of Sodium Cholate Micellar Solutions

“…were studied by many researchers. [4][5][6][7][8][9][10][11][12][13][14][15][16] The results obtained from e.m.f. measurements, carried out as a function of hydrogen ions, reagents and ionic medium 17 concentrations on aqueous sodium salt solution of dihydroxycholanic acids (deoxycholate = NaDC 18 , glycodeoxycholate = NaGDC 19 and taurodeoxycholate = NaTDC 20 ), were explained by assuming the presence of several species with different odd high aggregation numbers and also formed with the uptake of protons.…”

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

“…[1][2][3][4][5] Prevailing aggregation numbers, stability of the formed species and their range of existence were studied in aqueous solutions by means of electromotive force (e.m.f.) measurements as a function of hydrogen ion and reagent concentration.…”