The Meta-Substituted Isomer of TMPyP Enables More Effective Photodynamic Bacterial Inactivation than Para-TMPyP In Vitro

Abstract

Porphyrinoid-based photodynamic inactivation (PDI) provides a promising approach to treating multidrug-resistant infections. However, available agents for PDI still have optimization potential with regard to effectiveness, toxicology, chemical stability, and solubility. The currently available photosensitizer TMPyP is provided with a para substitution pattern (para-TMPyP) of the pyridinium groups and has been demonstrated to be effective for PDI of multidrug-resistant bacteria. To further improve its properties, we synthetized a structural variant of TMPyP with an isomeric substitution pattern in a meta configuration (meta-TMPyP), confirmed the correct structure by crystallographic analysis and performed a characterization with NMR-, UV/Vis-, and IR spectroscopy, photostability, and singlet oxygen generation assay. Meta-TMPyP had a hypochromic shift in absorbance (4 nm) with a 55% higher extinction coefficient and slightly improved photostability (+6.9%) compared to para-TMPyP. Despite these superior molecular properties, singlet oxygen generation was increased by only 5.4%. In contrast, PDI, based on meta-TMPyP, reduced the density of extended spectrum β-lactamase-producing and fluoroquinolone-resistant Escherichia coli by several orders of magnitude, whereby a sterilizing effect was observed after 48 min of illumination, while para-TMPyP was less effective (p < 0.01). These findings demonstrate that structural modification with meta substitution increases antibacterial properties of TMPyP in PDI.

Photodynamic inactivation of multidrug-resistant strains of Klebsiella pneumoniae and Pseudomonas aeruginosa in municipal wastewater by tetracationic porphyrin and violet-blue light: The impact of wastewater constituents

“…Compared to TMPyP4, TMPyP3 also proved to be a better singlet oxygen producer in all three tested water samples (DEMI, tap water and wastewater) ( 1B and S3 Table). This is consistent with the results described in the literature, especially those in a recent analysis in which TMPyP3 compared to TMPyP4 proved to be a more stable, better 1 O 2 producer (by 5.4%), and also significantly more PDI efficient PS on Escherichia coli in vitro [29]. It must be noted, that counterion for both porphyrins was 4-methylbenzenesulfonate, while in our study chloride salts were used.…”

“…Furthermore, tri- and tetracationic pyridinium porphyrins seem to have stood out as promising for a variety of possible PDI applications [ 27 ], including photoinactivation of bacteria in wastewater [ 28 ]. Although 5,10,15,20-(pyridinium-3-yl)porphyrin tetrachloride (TMPyP3) and its more researched regioisomer 5,10,15,20-(pyridinium-4-yl)porphyrin tetrachloride (TMPyP4) ( Fig 1 ), are both water soluble and excellent 1 O 2 producers, in some reports TMPyP4 has been shown to be less stable than other tested PSs, and less PDI efficient than TMPyP3 [ 15 , 29 ]. In our previous work we examined the PDT effect and inactivation potential of tetracationic symmetric TMPyP3, and two asymmetric tricationic pyridinium porphyrins, one hydrophilic (TMPyP3-CH 3 ) and one amphiphilic with a long alkyl chain (TMPyP3-C 17 H 35 ) ( Fig 1 ), against Legionella pneumophila , an environmental Gram-negative bacterium that is difficult to treat with currently used water disinfection methods [ 30 , 31 ].…”

One A3B Porphyrin Structure—Three Successful Applications

“…Starting from the knowledge that the design for obtaining porphyrins with the desired non-planar conformation relies on core, peripheral and electronic modifications [ 50 , 51 ], and that a larger reduction in the band gap is noticed in the case of porphyrins grafted with hydroxyphenyl groups in comparison with those substituted with carboxy or nitro groups, [ 52 ] we decided to synthesise a hydroxy-substituted porphyrin. In addition, due to the fact that recent reports concluded that the Q(0,0), as well as the Soret band, has maximum intensity in the meta isomer and decreases in the series meta > para > ortho , and structural modification with meta substitution also increases antibacterial properties [ 53 ], the second decision was made to obtain an A 3 B porphyrin with all substituents in a meta position. The third guiding thought was that metalloporphyrins adopt various intermediate conformations besides the four main nonplanar conformations, namely: ruffled, saddled, domed and waved [ 54 ], and that although the hydroxyl group is generally electron donating, when it is in a meta position, it behaves as an electron-withdrawing group.…”