An approximate cooperativity analysis by DSC of phase transitions of DPPC-DOCNa dispersions

The effect of solute, sodium deoxycholate bile salt (DOCNa), on the cooperativity of ordered-fluid, fosfolipid phase transition has been investigated by determining of the transition widths in multibilayer dispersions of the dipalmitoylphosphatidylcholine (DPPC)-DOCNa mixtures. The DT1/2 values were determined by differential scanning calorimetry. The van't Hoff values of the main transition enthalpies were calculated using an approximative expression, deduced from Zimm and Bragg theory [Sturtevant,J.M.(1982), Proc.Natl.Acad.Sci.USA,79:3963-3967]. The bile salt decreases the cooperativity (size of cooperative unit) of DPPC bilayers.