Interaction of cationic 5,10,15,20-tetra(N-methylpyridyl)porphyrin and its Co(III) complex with premicellar SDS aggregates: Structure and properties

The study explores the interactions between 5,10,15,20-tetra(N-methylpyridyl)porphyrin (H2P) and sodium dodecyl sulfate (SDS) at concentrations below the critical micelle concentration (CMC) in aqueous solutions employing spectrophotometric and fluorescence methods. The composition and structure of the complexes involved in the association of H2P with premicellar SDS aggregates of varying compositions denoted as [H2P-5·SDS], [H2P-10·SDS] and [H2P-20·SDS] were characterized using mass spectrometry, DOSY, and 1D NOESY techniques. Possible reasons for the decrease in the intensity of absorption and emission of porphyrin in micellar aggregates of SDS compared to porphyrin in an aqueous environment are analyzed. The research has revealed that SDS can act as both a catalyst and an inhibitor, depending on its concentration in the reaction of complexation of H2P with metal cations (Co2+). The spectrophotometric approach examined interaction processes between 5,10,15,20-tetra(N-methylpyridyl)porphyrinate Co(III) and premicellar SDS aggregates, which proceed similarly to the processes with the porphyrin ligand. The study demonstrated the impact of premicellar aggregates on the binding capacity of Co(III) porphyrinate with electron-donating molecules using imidazole as an illustrative example.