Synthesis of novel nicotinamide susbstituted phthalocyanine and photodynamic antomicrobial chemotherapy evaluation potentiated by potassium iodide against the gram positive S. aureus and gram negative E. coli

Restricting Bond Rotations by Ring Fusion: A Novel Molecular Design Strategy to Improve Photodynamic Antibacterial Efficacy of AIE Photosensitizers

In recent years, aggregation-induced emission photosensitizers (AIE-PSs) for antibacterial photodynamic therapy (aPDT) have received increasing attention because of their ability to increase reactive oxygen species (ROS) generation in the aggregation state. However, their antibacterial effect still has great room for improvement. Herein, we propose that if the rotation of some bonds in AIE-PSs is restricted, the nonradiative decay could be further suppressed to boost the generation of fluorescence and ROS, so as to improve their antibacterial efficacy. Following this molecular design strategy, we developed a new class of carbazole group-based AIE-PSs (CPVBA, CPVBP, CPVBP2, and CPVBP3), in which the rotation of phenyl-N bonds is restricted in the carbazole ring. Compared with diphenylamine group-based AIE-PSs with free rotation of phenyl-N bonds, carbazole group-based AIE-PSs showed stronger fluorescence, ROS generation, and antibacterial abilities, demonstrating the feasibility of this new design strategy. Notably, CPVBP3 can enter the entire cell of E. coli to exert its antibacterial effect, and there are few reports of photosensitizers with similar functions. Furthermore, to the best of our knowledge, the light dose (1.2 J/cm²) we used for CPVBP2 to kill Staphylococcus aureus is much lower than that of many reported photosensitizers, indicating great prospects for AIE antimicrobial photosensitizers.

Conjugation of Antimicrobial Peptide to Zinc Phthalocyanine for an Efficient Photodynamic Antimicrobial Chemotherapy

Photodynamic antimicrobial chemotherapy is an attractive and novel therapeutic approach to treat microbial infections. Antimicrobial peptides (AMPs) have the potential to specifically target and kill the microorganism while showing no effect toward mammalian cells. In the current study, antimicrobial peptide (GGG(RW)3), an analogue of MP-196, was conjugated to a zinc phthalocyanine (ZnPc) photosensitizer (PS) for photoinactivation assay to enhance the bacterial killing efficacy of the peptide. The AMPs showed selectivity toward the Gram-positive strain of bacteria. We observed that the conjugate ZnPc-GGG(RW)3 also displayed a photoinactivation effect against the Gram-positive strains of S. aureus. The results showed that ZnPc-GGG(RW)3 induced a 6-log reduction (i.e., 99.999% cell killing) in Gram-positive S. aureus at a light dose of 22 J/cm2 upon illumination under red light, while the peptide did not exhibit such a significant effect when tested alone at the same concentration. The conjugate also showed 50% inhibition of the bacterial strain in the dark at a higher concentration. Furthermore, the addition of potassium iodide salt to the PS at lower concentrations also significantly killed the Gram-negative E. coli strain and killed the E. coli strain with up to a 5-log reduction at a light dose of 22 J/cm2 under red light illumination. We demonstrated the efficacy of antimicrobial peptide (GGG(RW)3 enhanced by conjugation to a ZnPc photosensitizer.