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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-C₆₀ ⁴⁺) 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-C₆₀ ⁴⁺. In a polar medium, these dyads mainly act by a contribution of type I pathway with low generation of singlet molecular oxygen, O₂(¹Δ_g). 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-C₆₀ ⁴⁺. 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-C₆₀ ⁴⁺ was used as a photosensitizer. Also, generation of O₂(¹Δ_g) in the S. aureus cells was higher for TCP-C₆₀ than TCP-C₆₀ ⁴⁺. Therefore, TCP-C₆₀ appears to act in microbial cells mainly through the mediation of O₂(¹Δ_g). Although, a contribution of the type I mechanism was found for cell death induced by TCP-C₆₀ ⁴⁺. 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-C₆₀ ⁴⁺.

SUBMITTER: Ballatore MB

PROVIDER: S-EPMC9081455 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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

Ballatore M Belén MB Spesia Mariana B MB Milanesio M Elisa ME Durantini Edgardo N EN

RSC advances 20180621 41

The photodynamic action mechanism sensitized by a non-charged porphyrin-fullerene C60 dyad (TCP-C60) and its tetracationic analogue (TCP-C60 4+) 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 d ...[more]

PMID: 35540123

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Project description:The effect of molecular topology, and conformation on the dynamics of photoinduced electron transfer (ET) processes has been studied in interlocked electron donor-acceptor systems, specifically rotaxanes with zinc(II)-tetraphenylporphyrin (ZnP) electron donor and [60]fullerene (C(60)) as the electron acceptor. Formation or cleavage of coordinative bonds was used to induce major topological and conformational changes in the interlocked architecture. In the first approach, the tweezers-like structure created by the two ZnP stopper groups on the thread was used as a recognition site for complexation of 1,4-diazabicyclo[2.2.2]octane (DABCO), which creates a bridge between the two ZnP moieties on the rotaxane, generating a catenane structure. The photoinduced processes in the DABCO-complexed (ZnP)(2)-[2]catenate-C(60) system were compared with those of the (ZnP)(2)-rotaxane-C(60) precursor and the previously reported ZnP-[2]catenate-C(60). Steady-state emission and transient absorption studies showed that a similar multistep ET pathway emerged for rotaxanes and catenanes upon photoexcitation at various wavelengths, ultimately resulting in a long-lived ZnP(•+)/C(60) (•-) charge separated radical pair state. However, the decay kinetics of the latter states clearly reflect the topological differences between the rotaxane, the catenate, and DABCO-complexed-catenate architectures. The lifetime of the long-distance ZnP(•+)-[Cu(I)phen(2)](+)-C(60) (•-) charge separated state is more than four times longer in 3 (1.03 µs) than in 1 (0.24 µs) and approaches that in catenate 2 (1.1 µs). The results clearly showed that adoption of a catenane from a rotaxane topology inhibits the charge recombination process. In a second approach, the Cu(I) ion used as template to assemble the (ZnP)(2)-[Cu(I)phen(2)](+)-C(60) rotaxane was removed, and structural analysis suggested a major topographical change occurred, such that charge separation between the chromophores was no longer observed upon photoexcitation in nonpolar as well as polar solvents. Only ZnP and C(60) triplet excited states were observed upon laser excitation. These results highlighted the critical importance of the central Cu(I) ion for long range ET processes in these large interlocked electron donor-acceptor systems.

Dataset Information

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

Publications

Mechanistic insight into the photodynamic effect mediated by porphyrin-fullerene C<sub>60</sub> dyads in solution and in <i>Staphylococcus aureus</i> cells.

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