DNA Targeting Long-Chain Alkoxy Appended Tin(IV) Porphyrin Scaffolds: Photophysical and Antimicrobial PDT Investigations

Abstract

Tin(IV) porphyrin scaffolds having long-chain (C₈ and C₁₆) alkoxyphenyl group at one <i>meso</i> position were synthesized with axial dichloro and dihydroxo ligands. Modifications with respect to the alkoxy chain length and the axial ligands were investigated using UV-vis and fluorescence spectroscopy as well as cyclic voltammetry. Significantly higher molar absorption coefficients were noted with dichloro axial ligands whereas higher fluorescence quantum yields were observed for C₈ alkoxy chain substituents. Electrochemical redox data revealed that the porphyrin ring became difficult to reduce consequent to the presence of electron donating alkoxy chain. Evaluation of the aggregation behavior in different organic solvents and DMF-water mixture has been carried out. The singlet oxygen production and photostability data are supportive of their suitability for antibacterial photodynamic therapy. The antibacterial studies carried out in Gram negative (<i>E. coli</i>) and Gram positive (<i>B. subtilis</i>) bacteria using agar well diffusion and LB broth assay revealed selective toxicity in <i>B. Subtilis</i> cells. Fluorescence microscopy and competitive DNA binding studies with Hoechst 33342 revealed DNA binding at the minor groove which was further substantiated with molecular docking studies.