Coupling of cationic porphyrins on manganese ferrite nanoparticles: A potential multifunctional nanostructure for theranostics applications

Abstract

We present here the coupling of cationic meso-tetrakis(N-methylpyridinium-4-yl) porphyrin (TMPyP) and their zinc complex (ZnTMPyP) with magnetic nanoparticles (MNPs) of manganese ferrite (MnFe2O4) covered with citric acid (CA), dimercaptosuccinic acid (DMSA), and tripolyphosphate (TPP). In the presence of MNPs, the fluorescence emission of porphyrins was suppressed through static fluorescence quenching. Stern-Volmer method was employed to determine the binding constants (Kb) between porphyrins and MNPs. These interactions were described based on the coating layer properties and the unfunctionalized metallic sites on the surface of MNPs. The higher binding constants (Kb) were observed for TPP and CA MNPs (KbTPP < KbCA), which possess a poor recovery coefficient. In this case, the residuals unfunctionalized Fe3+/Mn2+ atomic sites on the MNPs surface can interact with nitrogen atoms of macrocyclic ring of free base porphyrin and the free oxygens from carboxylate and phosphate groups interact with amino hydrogens of porphyrin ring through hydrogen bonds. For ZnTMPyP, can occur a coordination of zinc atoms by the carboxylate or phosphate groups that are able to form strong and stable interactions. Furthermore, it was observed that while porphyrins are bound to MNPs, fluorescence emission and singlet oxygen production are reduced. However, such properties were recovered after the release of porphyrins from MNPs. To investigate the molecules release, a proof-of-concept photothermal experiment was designed and performed, where temperatures higher than 50 °C were reached. These results show that this system combines properties which can be employed for development of drug delivery system, magnetic tracers for alternating current biosusceptometry (ACB), as well as application of photodynamic (PDT), photothermal therapy (PTT) and magnetic hyperthermia (MHT) therapies.