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Overgeneration of reactive oxygen species (ROS) is closely associated with cellular damage and diseases. As superoxide anion (O2(•-)) is the precursor of other ROS, exploring O2(•-) fluctuations in cells and in vivo is of great significance. To address this critical need, we have developed a novel reversible fluorescent probe with one-photon and two-photon fluorescence properties, which is well suited for monitoring O2(•-) fluxes selectively and dynamically. Imaging results substantiate dynamic and reversible fluorescence responses of this probe to intracellular O2(•-) under apoptotic stimuli. Moreover, this probe can conveniently visualize changes in O2(•-) concentration during reperfusion injury in hepatocytes, zebrafish, and mice, by means of one-photon or two-photon imaging according to depths of various samples. The present study provides a powerful fluorescent imaging tool for dynamic tracking of O2(•-) in live cells and in vivo.

[reaction: see text] Bond dissociation enthalpies (BDEs) for the curcumin-related compounds have been calculated using density functional theory (DFT) methods. It was found that the antioxidant mechanism of curcumin was a H-atom abstraction from the phenolic group, not from the central CH2 group in the heptadienone link. Curcumin, methylcurcumin, and half-curcumin had similar O-H BDEs, indicating that the two phenolic groups in curcumin were independent of each other.

Density functional theory calculations have been performed to investigate the detailed mechanism of the carbonyl hydrogenation catalyzed by the first well-defined bifunctional iron catalyst. The catalytic reaction proceeds by hydrogen transfer and dihydrogen activation. The hydrogen transfer reaction occurs via the bifunctional mechanism in which the two hydrogen atoms attached on the Fe and O of the catalyst are transferred to the oxygen and carbon atom of the carbonyl compound concertedly. Both the alcohol-mediated and nonalcohol-mediated dihydrogen activation processes are explored.