CALORIMETRIC AND UV SPECTROSCOPIC STUDY OF THE INTERACTION OF PARAQUAT WITH PHOSPHOLIPIDS

Paraquat (PQ) is a popular herbicide and its main effect is the modifi cation of the membrane integrity, The PQ-dipalmitoylphosphatidic acid (DPPA) and PQ-dipalmitoylphosphatydilcholine (DPPC) water suspension s ystems at pH 7 have been investigated in order to determine the kind o f the molecular interaction that exists between PQ and phospholipids ( PL) with different charges, and the influence of the presence of Ca+ions on this interaction. The experimental results demonstrate that th e interaction between PQ and PL is mainly electrostatic; PQ strongly b inds to DPPA, which bears one negative charge at pH 7, but only weakly to DPPC, which, unlike DPPA, is uncharged. The presence of Ca++, in a n amount sufficient to completely bind the lipid (1 M), strongly alter s the DPPA-PQ interactions, thus inhibiting the binding of PQ to lipid . On the contrary, the DPPC-PQ interactions are not modified by the pr esence of calcium ions.