PHENYLBUTAZONE ACTION ON DIMIRISTOYL PHOSPHATIDYLCHOLINE LIPOSOME PHASE-TRANSITION AND 8-ANILINO-1-NAPHTHALENE SULFONATE BINDING

Phenylbutazone (PhB), a powerful anti-inflammatory drug, is able to modify the phase transition of phospholipid bilayers without changing its calorimetric enthalpy (DELTA-H(cal)), as can be shown by differential scanning calorimetry (DSC) experiments. Under PhB interaction, dimiristoyl phosphatidylcholine (DMPC) multilamellar liposomes (MLV) undergo lateral phase separation as a result of immiscibility in the bilayer plane. On the other hand, the binding of the anionic fluorescent probe 8-anilino-1-naphthalene sulfonate (ANS) to the surface of DMPC liposomes is altered by PhB. Even though the quantum efficacy of the probe fluorescence emission remains unaffected, the negative cooperativity of the binding process disappears, with the intrinsic dissociation constant showing only a minor variation. From these results it is concluded that PhB would be most likely located close to the lipid:water interface.