title: Hydrogen bond-assisted macrocyclic oligocholate transporters in lipid membranes.
abstract: Three macrocyclic oligocholates containing a carboxyl group, a guanidinium ion, and a Cbz-protected amine, respectively, were studied as membrane transporters for hydrophilic molecules. To permeate glucose across lipid bilayers, the macrocycles stacked over one another to form a transmembrane nanopore, driven by a strong tendency of the water molecules in the internal cavities of the amphiphilic macrocycles to aggregate in a nonpolar environment. To transport larger guests such as carboxyfluorescein (CF), the macrocycles acted as carriers to shuttle the guest across the membrane. Hydrogen-bonds between the side chains of the macrocycles strongly affected the transport properties. Surprisingly, the carboxyl group turned out to be far more effective at assisting the aggregation of the oligocholate macrocycles in the membrane than the much stronger carboxylate-guanidinium salt bridge, likely due to competition from the phosphate groups of the lipids for the guanidinium.
authors.affiliation: Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111, USA.
authors.forename: Lakmini
authors.initials: L
authors.lastname: Widanapathirana
authors.forename: Xueshu
authors.initials: X
authors.lastname: Li
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
mesh_terms: D001692:Biological Transport; D002264:Carboxylic Acids / Q000737:chemistry / Q000378:metabolism; D020355:Cholates / Q000737:chemistry / Q000378:metabolism*; D005452:Fluoresceins / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D019791:Guanidine / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding; D047028:Macrocyclic Compounds / Q000737:chemistry / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000378:metabolism*; D053835:Unilamellar Liposomes / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002264:Carboxylic Acids; D020355:Cholates; D005452:Fluoresceins; D047028:Macrocyclic Compounds; D026901:Membrane Transport Proteins; D053835:Unilamellar Liposomes; C024098:6-carboxyfluorescein; D005947:Glucose; D019791:Guanidine