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Despite being a very strong oxidizing agent, most organic molecules are not oxidized in the presence of O2 at room temperature because O2 is a diradical whereas most organic molecules are closed‐shell. Oxidation then requires a change in the spin state of the system, which is forbidden according to non‐relativistic quantum theory. To overcome this limitation, oxygenases usually rely on metal or redox cofactors to catalyze the incorporation of, at least, one oxygen atom into an organic substrate. However, some oxygenases do not require any cofactor, and the detailed mechanism followed by these enzymes remains elusive. To fill this gap, here the mechanism for the enzymatic cofactor‐independent oxidation of 3,5‐dihydroxyphenylacetyl‐CoA (DPA‐CoA) is studied by combining multireference calculations on a model system with QM/MM calculations. Our results reveal that intersystem crossing takes place without requiring the previous protonation of molecular oxygen. The characterization of the electronic states reveals that electron transfer is concomitant with the triplet–singlet transition. The enzyme plays a passive role in promoting the intersystem crossing, although spontaneous reorganization of the water wire connecting the active site with the bulk presets the substrate for subsequent chemical transformations. The results show that the stabilization of the singlet radical‐pair between dioxygen and enolate is enough to promote spin‐forbidden reaction without the need for neither metal cofactors nor basic residues in the active site. [ABSTRACT FROM AUTHOR]

Sub‐nanometer metal clusters have special physical and chemical properties, significantly different from those of nanoparticles. However, there is a major concern about their thermal stability and susceptibility to oxidation. In situ X‐ray Absorption spectroscopy and Near Ambient Pressure X‐ray Photoelectron spectroscopy results reveal that supported Cu5 clusters are resistant to irreversible oxidation at least up to 773 K, even in the presence of 0.15 mbar of oxygen. These experimental findings can be formally described by a theoretical model which combines dispersion‐corrected DFT and first principles thermochemistry revealing that most of the adsorbed O2 molecules are transformed into superoxo and peroxo species by an interplay of collective charge transfer within the network of Cu atoms and large amplitude "breathing" motions. A chemical phase diagram for Cu oxidation states of the Cu5‐oxygen system is presented, clearly different from the already known bulk and nano‐structured chemistry of Cu. [ABSTRACT FROM AUTHOR]

The impact of the number and positions of Rb ions in the RbCo[Fe(CN)6] Prussian blue analogue is analyzed by means of complete active space self-consistent field (CASSCF) and subsequent second-order perturbation theory (CASPT2) calculations performed upon embedded cluster models. It is shown that the geometries and corresponding electronic structures of the monomeric [CoIII(NC)5(OH2)]2- and [CoII(NC)5(OH2)]3- units are differently affected when the apical cyanide ligand is substituted by a water molecule. The CoIII ion moves away from the equatorial plane by ca. 0.15 Å, whereas the CoII is almost not sensitive to the environmental change. Furthermore, we find that this phenomenon is rather independent of the positions and numbers of the nearest-neighbour alkali ions. The Co ion displacement directly controls the overlap between the bridging cyanide and metal ion orbitals, a scenario which might be favorable to trigger electron transfer in the photomagnetic dimeric CoFe units of the CoFe Prussian blue analogues. [ABSTRACT FROM AUTHOR]

In-situ XPS and XANES spectroscopy experiments, along with theoretical characterizations of Cu5-(O SB 2 sb ) SB I n i sb complexes, provide direct evidence of the Cu SB 5 sb clusters' O SB 2 sb stability. Keywords: density functional calculations; nanotechnology; oxidation; photoelectron spectroscopy; X-ray absorption spectroscopy EN density functional calculations nanotechnology oxidation photoelectron spectroscopy X-ray absorption spectroscopy 1 1 1 09/05/23 20230901 NES 230901 B Bare clusters of five Cu atoms b , synthesized electrochemically, display remarkable oxidation stability on highly oriented pyrolytic graphite. Density functional calculations, nanotechnology, oxidation, photoelectron spectroscopy, X-ray absorption spectroscopy. [Extracted from the article]