Ca2+- and Mg2+-induced molecular interactions in a dehydrocholic acid/didodecyldimethylammonium bromide mixed monolayer

Abstract

The aim of this article is the evaluation of Ca2+ and Mg 2+ subphases presence effect on mixed monolayers composed by dehydrocholic acid (HDHC) and didodecyldimethylammonium bromide (DDAB). The monolayer stability was analyzed by the evaluation of thermodynamic parameters, ΔGmix E and α. At all calcium ion-tested concentration, the mixed systems XHDHC=0.6 and 0.8 at π=30 mJ m-2 were always the most favored proportions. The X HDHC=0.6 system was also stable in magnesium presence, and the X HDHC=0.2-mixed monolayer went through a stable to an unstable state as the content of Ca2+ or Mg2+ augment. Finally, the XHDHC=0.4 monolayer showed a particular behavior, i.e., remained stable at low cation concentration, unstable at intermediate concentration and stable again at high concentration. The effect was similar at Mg2+ presence. © Springer-Verlag 2009.