title: Retention properties of hydrophobically end-capped poly(ethylene glycol)s on a beta-cyclodextrin support.
abstract: High-performance liquid chromatography (HPLC) was used to examine the retention behavior of monomethoxypoly(ethylene glycol)s bearing one hydrophobic naphthyl end group (Nap-MPEG) on beta-cyclodextrin polymer (poly-beta-CD) immobilized on a silica support, under isocratic elution conditions and using water as mobile phase. Studies of retentions and theoretical plate heights H were conducted at infinite dilution by comparing the behavior of Nap-MPEGs having different molecular weight (750, 1000 and 5000 g/mol). The larger is its molecular size, the lower is the retention of the polymer. The linear increase of H with mobile phase velocity reveals slow mass-transfer kinetics arising from the restricted diffusion into the pores of the support. The complexation constants between the Nap-MPEGs and beta-CD in solution (around 500M(-1)) were determined from the decrease of retention observed by adding increasing concentrations of hydroxypropyl beta-CD into the eluent. The peak profiles in mass-overload conditions were studied by fitting a model based upon bi-Langmuir kinetics which assumes a non-uniform support having two types of binding sites and apparent adsorption rate constants are used to describe mass-transfer kinetics. A three-parameter adsorption equilibrium isotherm was sufficient to account for the modifications of peak shapes observed when increasing amounts of polymer were injected. This result indicates an interaction with a heterogeneous poly-beta-CD support mainly composed of low affinity groups, non-saturable in the range of polymer concentration studied. An upper limit was estimated for the equilibrium constant (<1000 M(-1)) characterizing the affinity of Nap-MPEG for the non-saturable sites of the poly-beta-CD support. Large affinity constants (8-9 x 10(4)M(-1)) were found for the interaction of Nap-MPEGs with a small percentage of active sites.
authors.affiliation: Laboratoire de Recherche sur les Polymères, CNRS-Université Paris 12, 2 rue Henry Dunant, 94320 Thiais, France.
authors.forename: Carole
authors.initials: C
authors.lastname: Karakasyan
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Millot
authors.forename: Alain
authors.initials: A
authors.lastname: Jaulmes
authors.forename: Claire
authors.initials: C
authors.lastname: Vidal-Madjar
mesh_terms: D000327:Adsorption; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003198:Computer Simulation; D008962:Models, Theoretical; D011092:Polyethylene Glycols / Q000737:chemistry / Q000302:isolation & purification*; D047392:beta-Cyclodextrins
chemical_list: D047392:beta-Cyclodextrins; D011092:Polyethylene Glycols; C031215:betadex