Water-soluble polyol-methanofullerenes as mitochondria-targeted antioxidants: Mechanism of action.

The mechanism of an antioxidant action of water-soluble polyol - methanofullerenes C60[C9H10O4(OH)4]6 and C60[C13H18O4(OH)4]6 as the mild uncouplers of an oxidative phosphorylation and respiration is postulated. According to this mechanism, hydroxyl group of methanofullerenols can be protonated under excess of protons in the intermembrane space of hyperpolarized mitochondria. Protonation of fullerene derivatives is confirmed by the decrease in their negative Zeta potential in the pH below 5.4. Heavily protonated methanofullerenols become positively charged and move into the mitochondrial matrix. As a consequence, the proton gradient is dissipated, which causes a decrease in mitochondrial transmembrane potential (ΔΨm) and reduction in ROS production.

Novel water-soluble methanofullerenes C60[C13H18O4(OH)4]6 and C60[C9H10O4(OH)4]6: Promising uncouplers of respiration and phosphorylation.

Here, we report for the first time on two novel water-soluble polyol-methanofullerenes which uncouple respiration and oxidative phosphorylation. A cytofluorimetric JC-1-based ratiometric assay was used to quantify mitochondrial potential Ψm in Yarrowia lipolytica cells exposed to the fullerenes tested. Both methanofullerenes significantly downregulated Ψm, thereby decreasing the subset of cells with high mitochondrial potential compared with intact control cells. The Ψm-low subset of Yarrowia lipolytica cells resulted from methanofullerenes exposure preserved physiological cell size and granularity patterns.

W-band transient EPR and photoinduced absorption on spin-labeled fullerene derivatives.

We investigated by W-band (94 GHz) transient electron paramagnetic resonance (TREPR) and photoinduced absorption (PIA) spectroscopy two fullerene derivatives bearing a nitroxide radical unit. After pulsed laser photoexcitation of the molecules in liquid toluene solution, complex EPR spectra are recorded, with lines in absorption and emission. The intrinsic higher spectral and temporal resolution of the W-band frequency leads to the assignment of all the lines in the spectrum and the determination of the sign and the absolute value of the exchange coupling between the fullerene in its photoexcited triplet state (S(T) = 1) and the radical (S(R) = 1/2). The two compounds with different fullerene-nitroxide spacers show opposite-ferromagnetic and antiferromagnetic-exchange couplings. The time evolution of the spectra and the polarization of the lines are interpreted in terms of several possible spin polarization mechanisms. The EPR measurements are complemented with PIA experiments.

Synthesis, structure and biological activity of nitroxide malonate methanofullerenes.

Two nitroxide methanofullerenes was synthesized for the first time, and their structures and biological activities studied. It was shown by X-ray single crystal analysis that the methanofullerene with two nitroxide groups forms a 1 : 2 inclusion complex with chloroform and has a nearly tetrahedral (diamond-like) arrangement of fullerene-fullerene interactions in the crystal. For the first time, it has been found that malonate nitroxide methanofullerene in combination with the known anticancer drug cyclophosphamide (CPA) shows high antitumor activity against leukemia P-388.

First observation of the hyperfine structure of an excited quintet state in liquid solution.

After pulsed photoexcitation of a new fullerene-linked bisnitroxide, a well resolved transient EPR spectrum is detected which is assigned to an excited quintet spin state generated by spin coupling of the nitroxides and the fullerene excited triplet.