title: Differences in the interactions of a monoglyceride with cholesterol and with a bile salt.
abstract: The differences in the interaction of monoglycerides with bile acids or cholesterol have been investigated from a physico-chemical point of view. A Langmuir trough and fluorescence microscope was used to study mixed monolayers of DL-α-palmitin (a monoglyceride) and cholesterol or deoxycholic acid (a bile acid) at the air/aqueous interface. The surface pressure-area per molecule isotherms of the monolayers were analyzed to give the thermodynamic properties. The deoxycholic acid-DL-α-palmitin monolayer showed stronger repulsions between the film components than was observed with the cholesterol acid-DL-α-palmitin monolayer. Mixed monolayers containing DL-α-palmitin and cholesterol or deoxycholic acid phase separated at high surface pressures and high fractions of DL-α-palmitin, the conditions that resulted in the most repulsions between the two components of the monolayer. The mixed cholesterol and DL-α-palmitin monolayer phase separated in a random pattern. The deoxycholic acid and DL-α-palmitin mixed monolayer gave smaller domains that were distributed in a homogeneous fashion within the monolayer at high molecular packing densities. The difference in the cholesterol and deoxycholic acid interactions with DL-α-palmitin were explained by the fact that while both cholesterol and deoxycholic acid molecules do not pack efficiently with the DL-α-palmitin molecules, the attractive interactions between the alcohol groups on DL-α-palmitin and the carboxylic groups on deoxycholic acid cause attractive interactions between the deoxycholic acid and DL-α-palmitin domains, which causes the interaction abilities of deoxycholic acid with DL-α-palmitin to be higher than cholesterol.
authors.affiliation: Faculty of Textile Science and Technology, Shinshu University, Tokida 3-15-1, Ueda, Nagano 386-8567 Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Sato
authors.affiliation: Faculty of Textile Science and Technology, Shinshu University, Tokida 3-15-1, Ueda, Nagano 386-8567 Japan. Electronic address: mcnamee@shinshu-u.ac.jp.
authors.forename: Cathy E
authors.initials: CE
authors.lastname: McNamee
mesh_terms: D000388:Air; D001647:Bile Acids and Salts / Q000737:chemistry*; D002784:Cholesterol / Q000737:chemistry*; D003840:Deoxycholic Acid / Q000737:chemistry; D008856:Microscopy, Fluorescence; D050178:Monoglycerides / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D001647:Bile Acids and Salts; D050178:Monoglycerides; D003840:Deoxycholic Acid; D014867:Water; D002784:Cholesterol
keywords: Deoxycholic acid; Fluorescence microscopy; Langmuir trough; Lipid; Mixed Langmuir monolayers; dl-α-Palmitin