title: Bilayer vesicles of amphiphilic cyclodextrins: host membranes that recognize guest molecules.
abstract: A family of amphiphilic cyclodextrins (6, 7) has been prepared through 6-S-alkylation (alkyl=n-dodecyl and n-hexadecyl) of the primary side and 2-O-PEGylation of the secondary side of alpha-, beta-, and gamma-cyclodextrins (PEG=poly(ethylene glycol)). These cyclodextrins form nonionic bilayer vesicles in aqueous solution. The bilayer vesicles were characterized by transmission electron microscopy, dynamic light scattering, dye encapsulation, and capillary electrophoresis. The molecular packing of the amphiphilic cyclodextrins was investigated by using small-angle X-ray diffraction of bilayers deposited on glass and pressure-area isotherms obtained from Langmuir monolayers on the air-water interface. The bilayer thickness is dependent on the chain length, whereas the average molecular surface area scales with the cyclodextrin ring size. The alkyl chains of the cyclodextrins in the bilayer are deeply interdigitated. Molecular recognition of a hydrophobic anion (adamantane carboxylate) by the cyclodextrin vesicles was investigated by using capillary electrophoresis, thereby exploiting the increase in electrophoretic mobility that occurs when the hydrophobic anions bind to the nonionic cyclodextrin vesicles. It was found that in spite of the presence of oligo(ethylene glycol) substituents, the beta-cyclodextrin vesicles retain their characteristic affinity for adamantane carboxylate (association constant K(a)=7.1 x 10(3) M(-1)), whereas gamma-cyclodextrin vesicles have less affinity (K(a)=3.2 x 10(3) M(-1)), and alpha-cyclodextrin or non-cyclodextrin, nonionic vesicles have very little affinity (K(a) approximately 100 M(-1)). Specific binding of the adamantane carboxylate to beta-cyclodextrin vesicles was also evident in competition experiments with beta-cyclodextrin in solution. Hence, the cyclodextrin vesicles can function as host bilayer membranes that recognize small guest molecules by specific noncovalent interaction.
authors.affiliation: Centre for Synthesis and Chemical Biology of the Conway Institute, Department of Chemistry, National University of Ireland, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Patrick
authors.initials: P
authors.lastname: Falvey
authors.forename: Choon Woo
authors.initials: CW
authors.lastname: Lim
authors.forename: Raphael
authors.initials: R
authors.lastname: Darcy
authors.forename: Tobias
authors.initials: T
authors.lastname: Revermann
authors.forename: Uwe
authors.initials: U
authors.lastname: Karst
authors.forename: Marcel
authors.initials: M
authors.lastname: Giesbers
authors.forename: Antonius T M
authors.initials: AT
authors.lastname: Marcelis
authors.forename: Adina
authors.initials: A
authors.lastname: Lazar
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Coleman
authors.forename: David N
authors.initials: DN
authors.lastname: Reinhoudt
authors.forename: Bart Jan
authors.initials: BJ
authors.lastname: Ravoo
mesh_terms: D000388:Air; D003505:Cyclodextrins / Q000138:chemical synthesis / Q000737:chemistry*; D005898:Glass / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008567:Membranes, Artificial; D013499:Surface Properties; D013501:Surface-Active Agents / Q000138:chemical synthesis / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D003505:Cyclodextrins; D008051:Lipid Bilayers; D008567:Membranes, Artificial; D013501:Surface-Active Agents; D014867:Water