Interactions of daunorubicin with Langmuir–Blodgett thiolipid monolayers

Interactions of daunorubicin (DNR) with thiolipid membranes composed of 1,2-Dipalmitoyl-sn-Glycero-3-Phosphothioethanol (DPPTE) formed both at the air–water interface and transferred onto gold electrodes were investigated. The drug incorporates into the DPPTE layers during their formation increasing the area per molecule and causing the fluidization of the layers. The interactions of DNR with preformed layers depend on the membrane organization and therefore the dominating type of the driving forces. For less organized layers both electrostatic and hydrophobic interactions take place, while for more condensed layers precompressed to higher surface pressures, electrostatic interactions seem to be prevailing. The drug adsorbs at the layer formed at the air–water interface, which prevents from its further penetration. The DPPTE layers were transferred onto gold electrodes by means of Langmuir–Blodgett and self-assembly method. Cyclic voltammetry experiments revealed that DNR is more easily incorporated into LB layers supported on solid substrate than into SAMs, since the former tend to be less compact and hydrophobic interactions between the acyl chains of the thiolipid and hydrophobic anthraquinone part of DNR is facilitated. The influence of pH changes of the supporting electrolyte on the electrode processes of DNR incorporated into the layers was also investigated in order to verify if the lipid environment affects the mechanism of electron transfer.