Thermodynamic studies of the solubilization of dipalmitoylphosphatidylcholine in various physical states with an anionic, cationic, and nonionic surfactant
Long, Hussain Bin
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The enthalpy changes accompanying the solubilization of dipalmitoylphosphatidyicholine (DPPC) in three different states, small unilamellar (SUV), large unilamellar (LUV), and large multilamellar (MLV) by four surfactants, DTAB, DTAC, SDS and TRITON X-100, were determined at 25°C using continuous enthalpy titrations. A dye solubilization method was employed for the determination of critical micellar concentrations (cmc) of the surfactants in buffer. Thermodynamic functions of transfer were used to interpret the results following the paper by Roux et al., J. Solution Chemistry, 13, 1-25 (1984). The relative molal heat contents of DPPC vesicles is in the descending order of MLV, LUV, and SUV determined by continuous enthalpy titrations with SDS, DTAB and DTAC. Differential scanning Calorimetry was used for the determination of transition temperature, T , enthalpy and the entropy of the DPPC vesicles. From this study, the transition enthalpies of DPPC vesicles are in the descending order of MLV, LUV, and SUV in agreement with the literature.