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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.

The electronic effects on O-H bond dissociation energy (BDE) of phenolic compounds have been investigated by a density functional theory (DFT) calculation on 6-31G(d, p) basis set. For para substituted phenols, the stability of phenoxy radical (SPR), the stability of parent molecule (SPM) and the relative O-H BDE correlate well with Hammett-type parameter s þ p and resonance parameter R þ .Therefore, the O-H BDE is mainly governed by the resonance effect. But, only the resonance effect of electron-donating group reduces the O-H BDE, and on the contrary, the resonance effect of electron-withdrawing group increases the O-H BDE. Accordingly, the existing structure-activity relationship (SAR) for flavonoids to scavenge free radicals were questioned.

Specific hydrogen bond breakage by fluoride anions was observed in a simple FRET system formed by thioglycolic acid modified CdTe quantum dots and citrate-capped gold nanoparticles.

Noble-gas hydrides HNgY are frequently described as a single ionic form (H-Ng)(+)Y(-). We apply natural bond orbital (NBO) and natural resonance theory (NRT) analyses to a series of noble-gas hydrides HNgY (Ng = He, Ne, Ar, Kr, Xe, Rn; Y = F, Cl, Br, I) to gain quantitative insight into the resonance bonding of these hypervalent molecules. We find that each of the studied species should be better represented as a resonance hybrid of three leading resonance structures, namely, H-Ng(+ -):Y (I), H:(- +)Ng-Y (II), and H^Y (III), in which the "ω-bonded" structures I and II arise from the complementary donor-acceptor interactions nY → σ*HNg and nH → σ*NgY, while the "long-bond" ([small sigma, Greek, circumflex]-type) structure III arises from the nNg → [small sigma, Greek, circumflex]*HY/[small sigma, Greek, circumflex]HY interaction. The bonding for all of the studied molecules can be well described in terms of the continuously variable resonance weightings of 3c/4e ω-bonding and [small sigma, Greek, circumflex]-type long-bonding motifs. Furthermore, we find that the calculated bond orders satisfy a generalized form of "conservation of bond order" that incorporates both ω-bonding and long-bonding contributions [viz., (bHNg + bNgY) + bHY = bω-bonding + blong-bonding = 1]. Such "conservation" throughout the title series implies a competitive relationship between ω-bonding and [small sigma, Greek, circumflex]-type long-bonding, whose variations are found to depend in a chemically reasonable manner on the electronegativity of Y and the outer valence-shell character of the central Ng atom. The calculated bond orders are also found to exhibit chemically reasonable correlations with bond lengths, vibrational frequencies, and bond dissociation energies, in accord with Badger's rule and related empirical relationships. Overall, the results provide electronic principles and chemical insight that may prove useful in the rational design of noble-gas hydrides of technological interest.