Sodium glyco- and taurodeoxycholate: possible helical models for conjugated bile salt micelles

Abstract

supported on alumina. The appearance of all of the products and the disappearance of one of the reactants (OH-) can be simultaneously followed by FTIR.RhC13 has been shown to react with surface O H groups on alumina at 180 "C. The product of this reaction is believed to be Rh3+ bonded to a surface oxygen on alumina. This species is an intermediate in the room-temperature oxidation of CO listed above.Removal of the surface O H groups by reaction with RhC1, dramatically suppresses the reaction of COz with alumina.Acknowledgment. This work has been funded in part by the Office of Naval Research, and the University of Richmond Faculty Research Committee. We thank Dr. John Yates for his helpful comments and for his assistance in designing the experimental setup and Hampton Rexrode for his work on the apparatus construction. Previously a helical model was satisfactorily verified for sodium (NaDC) and rubidium (RbDC) deoxycholate micelles in aqueous solutions by means of SAXS, EXAFS, NMR, ESR, and CD measurements. Here we report the beginning of an analogous study carried out on sodium glycodeoxycholate (NaGDC) and taurodeoxycholate (NaTDC) following the strategy applied to NaDC and RbDC. The crystal structure of NaGDC sesquihydrate, solved by X-ray analysis, provides again a helical model that is compared with those of NaDC, RbDC, and NaTDC. Since it was previously observed that bilirubin-IXa (BR) exhibits a bisignate CD Cotton effect in NaDC aqueous solutions, and it was suggested that the chiral micelles of NaDC interact preferentially or exclusively with one of the two enantiomeric conformers of BR, we have recorded CD spectra of BR in aqueous micellar solutions of the bile salts in order to check the helical models. The spectra show in all cases two large and proximate bands of opposite sign between 400 and 500 nm, which support both our chiral models and the selection of the BR left-handed enantiomer. Moreover, we have accomplished van der Waals energy calculations for the system formed by a NaGDC helix and the left-or right-handed BR molecule to test if the interaction energy is lower for one of the two BR enantiomeric conformers. The results of the calculations seem to indicate that the NaGDC helix binds preferentially the BR molecule with left-handed chirality. Interaction models are proposed. IntroductionStudies carried out on sodium and rubidium deoxycholate (NaDC and RbDC, respectively) following a strategy previously reported' showed that a helical model, observed in the crystal structures of NaDC and RbDC,2v3 describes very satisfactorily the behavior of their micellar aggregates in aqueous solutions.'*e7 The helical structure of the NaDC and RbDC micelles was verified unambiguously by nuclear magnetic resonan~e,'.~ circular dichroism! electron spin resonance! small-angle X-ray scattering,6 and extended X-ray absorption fine structure7 measurements.Subsequently, the investigation of the structure of the sodium taurodeoxycholate (NaTDC) micellar aggregates was undert a k e~? +~ and other helical models were...

Capillary zone electrophoresis and micellar electrokinetic chromatography, with taurodeoxycholate as micellar agent, of protein kinase A peptide substrates

“…In the present study, the anionic surfactant taurodeoxycholate (TDC) was used primarily to study its impact on the separation selectivity of some series of PKA peptide substrates, and to identify the structural features of the peptides that determine their distribution to the micelles. TDC forms small (up to ten monomers) reversed micelles of helical structure [28], it contains asymmetric carbon atoms, and has mainly been used in MEKC for chiral separations of derivatized amino acids [29-321 and local anaesthetics [33], but also in nonchiral separations of phthalates [34] and of small peptides [35].…”

Direct Measurement of the Thermodynamics of Chiral Recognition in Bile Salt Micelles

“…2,6 Although it is well known that bile salts form micelles, the precise structure and dynamics of micellization is still poorly understood. Several models of micelle formation have been proposed in the literature 2,[7][8][9][10][11] and the study of these systems remains an active endeavor. In 1968, Small et al 2 proposed a two-step model of bile salt aggregation, and this model remains one of the more prominent hypotheses in the bile salt literature.…”

“…9 Alternative models for bile salt aggregation have been suggested, such as by Kawamura et al, 10 who proposed a disk-like micellar model where the hydrophilic surfaces of the bile salt monomer are exposed to the solvent and the hydrophobic surfaces are orientated towards the interior of the micelle. Also, Giglio et al 11 have suggested aggregation that results in a helical micellar structure.…”

Spectral investigation of the conformation of primary and secondary micelles of sodium cholate and the impact of pH and salt concentration.

“…Perhaps because humans do not have fur to protect the skin from ultraviolet radiation, we have adapted to have SQ produced in our sebum as a source of protection. It is noteworthy that sebum from most animals do not contain SQ except the otter, beaver, mole and kinkajou which contain up to 94 % SQ in their sebum [32][33][34][35]. All of these species inhabit wet environments suggesting a water repellant function for SQ.…”

“…34,35 The structure of the crystalline state suggests a helical arrangement for bile salt micelles. Association of In this model, the head and tail of the bile salt are also labeled to show the anti-parallel arrangement.…”