Issue 41, 2018

Mechanistic insight into the photodynamic effect mediated by porphyrin-fullerene C60 dyads in solution and in Staphylococcus aureus cells

Abstract

The photodynamic action mechanism sensitized by a non-charged porphyrin-fullerene C60 dyad (TCP-C60) and its tetracationic analogue (TCP-C604+) was investigated in solution and in Staphylococcus aureus cells. The ability of both dyads to form a photoinduced charge-separated state was evidenced by the reduction of methyl viologen in N,N-dimethylformamide (DMF). Moreover, the formation of superoxide anion radicals induced by these dyads was detected by the reduction of nitro blue tetrazolium. Also, photosensitized decomposition of L-tryptophan (Trp) was investigated in the presence of reactive oxygen species (ROS) scavengers. The addition of β-carotene and sodium azide had a slight effect on reaction rate. However, photooxidation of Trp mediated by TCP-C60 was negligible in the presence of D-mannitol, while no protection was found using TCP-C604+. In a polar medium, these dyads mainly act by a contribution of type I pathway with low generation of singlet molecular oxygen, O2(1Δg). In S. aureus cell suspensions, an aerobic atmosphere was required for the photokilling of this bacterium. The photocytotoxicity induced by TCP-C60 was increased in D2O with respect to water, while a small effect was found using TCP-C604+. Furthermore, photoinactivation of microbial cells was negligible in the presence of sodium azide. The addition of D-mannitol did not affect the photoinactivation induced by TCP-C60. In contrast, S. aureus cells were protected by D-mannitol when TCP-C604+ was used as a photosensitizer. Also, generation of O2(1Δg) in the S. aureus cells was higher for TCP-C60 than TCP-C604+. Therefore, TCP-C60 appears to act in microbial cells mainly through the mediation of O2(1Δg). Although, a contribution of the type I mechanism was found for cell death induced by TCP-C604+. Therefore, these dyads with high capacity to produce photoinduced charge-separated state represent interesting photosensitizers to inactivate microorganisms by type I or type II mechanisms. In particular, TCP-C60 may be located in a non-polar microenvironment in the cells favoring a type II pathway, while a contribution of the type I mechanism was produced using the cationic TCP-C604+.

Graphical abstract: Mechanistic insight into the photodynamic effect mediated by porphyrin-fullerene C60 dyads in solution and in Staphylococcus aureus cells

Supplementary files

Article information

Article type
Paper
Submitted
29 maj 2018
Accepted
13 jun 2018
First published
21 jun 2018
This article is Open Access
Creative Commons BY license

RSC Adv., 2018,8, 22876-22886

Mechanistic insight into the photodynamic effect mediated by porphyrin-fullerene C60 dyads in solution and in Staphylococcus aureus cells

M. B. Ballatore, M. B. Spesia, M. E. Milanesio and E. N. Durantini, RSC Adv., 2018, 8, 22876 DOI: 10.1039/C8RA04562C

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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