Phase behavior of fully hydrated DMPC-amphiphilic cyclodextrin systems.
With the aim of exploring relationships between the chemical structure and the physico-chemical properties of amphiphilic beta-cyclodextrin, a reappraisal of the obtaining of pure heptakis (2,3-di-O-hexanoyl)-beta-cyclodextrin (beta-CDC(6)) was undertaken. In this paper the chemical characterization of the newly synthesized beta-CDC(6) and its ability to form mixed structures with dimyristoylphosphatidylcholine (DMPC) are reported. Miscibility of the two amphiphiles is examined: (i) in monolayers formed at the air-water interface by analyzing the surface pressure-area isotherms; and (ii) in fully hydrated mixtures by differential scanning calorimetry (DSC) and X-ray diffraction at small and wide angles. Results demonstrate that the beta-cyclodextrin derivative is partially miscible to the phospholipid: intimate mixing occurs at beta-CDC(6) molar ratios smaller than 7-15 mol%, depending on the dimensional scale considered, while beyond these compositions phase separation is observed. At the air-water interface, the miscibility region of the two compounds shows non-ideal behavior characterized by the non-additivity of the molecular areas in the mixed monolayers. At the three-dimension level, the formation of a beta-CDC(6)/DMPC mixed lamellar phase occurs except at beta-CDC(6) molar ratios close to 5 mol% at which a highly ordered structure is depicted below the solid-to-liquid state transition of the DMPC hydrocarbon chains. At beta-CDC(6) contents higher than 7 mol%, the mixed assemblies coexist with excess amphiphilic cyclodextrin which then forms a separated hexagonal structure.
Laboratoire de Physico-Chimie-Pharmacotechnie-Biopharmacie, UMR CNRS 8612, Université Paris-Sud, Faculté de Pharmacie, 5 rue J. B. Clément, F-92296 cedex, Châtenay-Malabry, France. sylviane.lesieur@cep.u-psud.fr
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D002152:Calorimetry, Differential Scanning; D003505:Cyclodextrins / Q000737:chemistry*; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
D003505:Cyclodextrins; D014867:Water; D004134:Dimyristoylphosphatidylcholine