Bilayer to micelle transition of DMPC and alcohol ethoxylate surfactants as studied by isoperibol calorimetry.
The interaction of dimyristoylphosphatidylcholine (DMPC) with non-ionic surfactants has been studied using isoperibol calorimetry. Phospholipid-surfactant systems were formed in the isoperibol calorimeter with varying amounts of surfactant and the change in enthalpy on formation was measured. Solubilization of the phospholipid lamellae was assessed as a decrease in the enthalpy of reaction of co-films containing DMPC and increasing amounts of three linear alcohol ethoxylate surfactants: C(10)H(21)(OCH(2)CH(2))(3)OH, C(10)H(21)(OCH(2)CH(2))(5)OH, or C(12)H(25)(OCH(2)CH(2))(7)OH. The isoperibol calorimetry data for DMPC/surfactant/water systems were consistent with a theoretical three-stage model for the solubilization of phospholipids by surfactants, whereby phospholipid bilayers are transformed into mixed micelles with increasing amounts of surfactant. The results indicate that: (i) the interaction between phospholipid and surfactants results in a non-linear correlation between the enthalpy of reaction and the surfactant concentration; (ii) the structural stage of the lamellar to micelle transition (mixed bilayers, mixed micelles, or both) can be determined from calorimetric data; (iii) phase boundaries in the solubilization process (bilayer saturation, micelle saturation) can be identified as break points in the enthalpy-concentration curve; and (iv) increasing the hydrophilicity of the surfactant results in a decrease of the surfactant concentration producing the onset of solubilization.
Department of Pharmaceutics, School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX, United Kingdom.
Leticia
L
Barriocanal
Kevin M G
KM
Taylor
Graham
G
Buckton
D000438:Alcohols / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry; D008823:Micelles; D046529:Microscopy, Electron, Transmission; D012995:Solubility; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics; D013997:Time Factors; D014867:Water / Q000737:chemistry
D000438:Alcohols; D008051:Lipid Bilayers; D008563:Membrane Lipids; D008823:Micelles; D013501:Surface-Active Agents; D014867:Water; D004134:Dimyristoylphosphatidylcholine