Bilayer to micelle transition of DMPC and alcohol ethoxylate surfactants as studied by isoperibol calorimetry
✍ Scribed by Leticia Barriocanal; Kevin M.G. Taylor; Graham Buckton
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 324 KB
- Volume
- 94
- Category
- Article
- ISSN
- 0022-3549
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✦ Synopsis
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.