An investigation on calcium taurodeoxycholate micellar aggregates

Abstract

The formation of micellar aggregates in the presence of calcium(II) ions in solutions containing sodium and taurodeoxycholate ions and their composition at 25 C and in 0.5 mol dm À 3 N(CH 3 ) 4 Cl as constant ionic medium was studied. The study was carried out by means of two different procedures. In the first one, solid calcium oxalate was equilibrated with taurodeoxycholate, sodium and hydrogen ions and the free concentration of sodium and hydrogen ions was determined. After filtration, the calcium(II) (by atomic absorption spectrophotometry) and oxalate concentration were also determined. In the second approach, hydrogen and sodium ions free concentrations were obtained by electromotive force measurements carried out in solutions containing taurodeoxycholate. The results of both procedures could be explained by assuming the presence of aggregates of different composition with the participation of sodium, calcium(II) and taurodeoxycholate ions, depending on the concentration of the reagents. Protonated species were even present in appreciable concentrations. All the found species have taurodeoxycholate aggregation numbers in multiples of three. A mechanism for the micellar aggregates containing calcium and sodium is proposed. Sodium taurodeoxycholate in the presence of calcium(II) forms larger aggregates than does taurocholate in the presence of calcium(II); the building block of the former is a trimer whereas the latter system has lower aggregation numbers and its building block is a dimer or an octamer.

Solubility and the Solubility Product of Some Calcium(II) Salts of Bile Acids

“…Previous , studies carried out on solutions containing calcium(II) and taurocholate and taurodeoxycholate showed that no precipitate is formed in a wide range of concentration, but only aggregates with different compositions.…”

“…The protonation constants, k 1 , of the bile anions investigated here was previously determined in the same experimental conditions. 27 Previous 31,32 studies carried out on solutions containing calcium(II) and taurocholate and taurodeoxycholate showed that no precipitate is formed in a wide range of concentration, but only aggregates with different compositions.…”

“…Calcium(II) chloride (RP C. Erba) was used to prepare the calcium(II) bile salts and to prepare standards for AA spectrometry. It was analyzed as described previously . A solution of EDTA (as disodium salt) was prepared from a C. Erba RP reagent and analyzed using a CaCO 3 standard.…”

“…It was analyzed as described previously. 32 A solution of EDTA (as disodium salt) was prepared from a C. Erba RP reagent and analyzed using a CaCO 3 standard. The final point of the titration was obtained by using a magnesium(II) EDTA complex, ammonia buffer at Àlog[H] = 10, and Eriochrom black T as an indicator.…”

“…The formation of micellar aggregates of calcium(II), taurocholate (TC) and taurodeoxycholate (TDC), was investigated in previous papers. , It was found that both these salts are soluble and the composition of premicellar and micellar aggregates was found.…”