Interaction of protoporphyrinix (PPIX) and 5-amino levulinic acid (ALA) in nanoemulsion

Abstract

Nanoemulsion is an interesting and unique fluid system in that it is used to solubilize both ionic and non-ionic molecules. Because of its uniqueness it has been used as a medium for drug delivery. It is therefore used in this work to study the interaction of Protoporphyrin (PPIX) and 5-Amino levulinic acid (ALA). While ALA is a distant precursor of PPIX, PPIX itself is not only a precursor of Heme but also a photosensitizer in the modality of Photodynamic Therapy (PDT). Both compounds are used use in PDT regimen. A steady-state fluorescence technique is used for the study of the interaction of these very important biological compounds. It is found that ALA quenches the fluorescence of PP IX in nanoemulsion. This observed quenching is diffusion controlled. The bimolecular quenching constant, kq, was determined as 2.86x 1010/M-s with an interaction constant, Ka, of 4.48 x 105 with the free energy of interaction, ΔGa of -32.234kJ/mole.