Photodynamic inactivation of Escherichia coli by novel meso-substituted porphyrins by 4-(3-N,N,N-trimethylammoniumpropoxy)phenyl and 4-(trifluoromethyl)phenyl groups

摘要

The photodynamic effect of novel cationic porphyrins,with different pattern of meso-substitution by 4-(3-N,N,N-trimethylammoniumpropoxy)phenyl (A) and 4-(trifluoromethyl)phenyl (B) groups,have been studied in both solution bearing photooxidizable substrates and in vitro on a typical Gram-negative bacterium Escherichia coli.In these sensitizers,the cationic groups are separated from the macrocycle ring by a propoxy spacer.Thus,the charges have a high mobility and a minimal influence on photophysical properties of the porphyrin.These compounds produce singlet molecular oxygen,O_2(~1 DELTA _g),with quantum yields of approx 0.41-0.53 in N,N-dimethylformamide.In methanol,the L-tryptophan photodecomposition increases with the number of cationic charges in the sensitizer.In vitro investigations show that cationic porphyrins are rapidly bound to E.coli cells in approx 5 min.A higher binding was found for A_3B~(3+) porphyrin,which is tightly bound to cells still after three washing steps.Photosensitized inactivation of E.coli cellular suspensions follows the order: A_3B~(3+) > A_4~(4+) >> ABAB~(2+) > AB_3~+.Under these conditions,a negligible effect was found for 5,10,15,20-tetra(4-sulfonatophenyl)porphyrin (TPPS_4~(4-)) that characterizes an anionic sensitizer.Also,the results obtained for these new cationic porphyrins were compared with those of 5,10,15,20-tetra(4-N,N,N-trimethylammonium phenyl)porphyrin (TTAP~(4+)),which is a standard active sensitizer established to eradicate E.coli.The photodynamic activity of TTAP~(4+) is quite similar to that produced by A_4~(4+).Studies in an anoxic condition indicate that oxygen is necessary for the mechanism of action of photodynamic inactivation of bacteria.The higher photodynamic activity of A_3B~(3+) was confirmed by growth delay experiments.Photodynamic inactivation capacities of these sensitizers were also evaluated in E.coli cells immobilized on agar surfaces.Under these conditions,A_3B~(3+) porphyrin retains a high activity to inactivate localized bacterial cells.Therefore,tricationic porphyrin A_3B~(3+) is an interesting sensitizer with potential applications in photodynamic inactivation of bacteria in liquid suspensions or on surfaces.