Influence of charge and metal coordination of meso-substituted porphyrins on bacterial photoinactivation

•Were synthesized and characterized 8 meso substituted porphyrins with different substituents.•Effect of charges and metal coordination in their photochemical characteristics was studied.•We performed a detailed study of photoinduced antibacterial structure–activity.•It was obtained a relation among the structural integrity, ROS production and antibacterial activity.

The photodynamic effect of meso-substituted porphyrins with different charges and metal ions: meso-tetraphenylporphyrin tetrasulfonate 1, its nickel 2 and zinc complexes 3; meso-tetranaphthylporphyrin tetrasulfonate 4, and its zinc complex Zn 5; and tetra piridyl ethylacetate porphirins 6 and their nickel 7 and zinc 8 complexes, were synthesized and studied their antimicrobial activity against Escherichia coli. Fluorescence quantum yields (ΦF) were measured in water using reference TPPS4, obtaining higher values for complexes 3 and 4. The singlet oxygen ΦΔ were measured using histidine as trapping singlet oxygen and Rose Bengal as a reference standard. Complexes 1, 2 and 6 have the highest quantum yields of singlet oxygen formation, showing no relation with the peripheral charges and efficiency as Type II photosensitizers. Meanwhile complexes 3, 8 and 4 were the most efficient in producing radical species, determined with their reaction with NADH. The photoinduced antibacterial activity of complex was investigated at different concentrations of the photosensitizers with an irradiation time of 30 min. The higher antibacterial activities were obtained for the complexes 1–3 that are those with greater production of ROS and minor structural deformations. Complexes 7 and 8 had moderate activity, while 4–6 a low activity. Thus, in this work demonstrates that the production of ROS and structural deformations due to peripheral substituents and metal coordination, influence the activity of the complexes studied. Therefore, is important to perform comprehensive study physics and structurally when predicting or explain such activity.

Graphical abstractA: The series of TNPS4 have higher structural deformity, low production of ROS and reduced antibacterial activity. B: The series of TPPS4 have a low structural deformity, high production of ROS and the greater antibacterial activity.Figure optionsDownload full-size imageDownload as PowerPoint slide