title: Probing self assembly in biological mixed colloids by SANS, deuteration, and molecular manipulation.
abstract: Small-angle neutron scattering was used to obtain information on the form and molecular arrangement of particles in mixed colloids of bile salts with phosphatidylcholine, and bile salts with monoolein. Both types of systems showed the same general characteristics. The particle form was highly dependent on total lipid concentration. At the highest concentrations the particles were globular mixed micelles with an overall size of 50A. As the concentration was reduced the mixed micelles elongated, becoming rodlike with diameter about 50A. The rods had a radial core-shell structure in which the phosphatidylcholine or monoolein fatty tails were arranged radially to form the core with the headgroups pointing outward to form the shell. The bile salts were at the interface between the shell and core with the hydrophilic parts facing outward as part of the shell. The lengths of the rods increased and became more polydispersed with dilution. At sufficiently low concentrations the mixed micelles transformed into single bilayer vesicles. These results give insight on the physiological function of bile and on the rules governing the self assembly of bile particles in the hepatic duct and the small intestine.
authors.affiliation: Los Alamos Neutron Scattering Center, Los Alamos National Laboratory, New Mexico 87545, USA. Hjelm@LANL.GOV
authors.forename: R P
authors.initials: RP
authors.lastname: Hjelm
authors.forename: P
authors.initials: P
authors.lastname: Thiyagarajan
authors.forename: A
authors.initials: A
authors.lastname: Hoffman
authors.forename: C
authors.initials: C
authors.lastname: Schteingart
authors.forename: H
authors.initials: H
authors.lastname: Alkan-Onyuksel
mesh_terms: D001647:Bile Acids and Salts / Q000737:chemistry*; D003102:Colloids; D003903:Deuterium; D006000:Glycocholic Acid / Q000737:chemistry; D008433:Mathematics; D008823:Micelles; D008958:Models, Molecular; D008968:Molecular Conformation; D009502:Neutrons; D010713:Phosphatidylcholines / Q000737:chemistry*; D012542:Scattering, Radiation; D014961:X-Ray Diffraction
chemical_list: D001647:Bile Acids and Salts; D003102:Colloids; D008823:Micelles; D010713:Phosphatidylcholines; D003903:Deuterium; D006000:Glycocholic Acid