Hydrogen peroxide is produced from hydrogen gas and air in industry by using the anthraquinone process. The mechanism for the production of hydrogen peroxide in this process is studied by using DFT calculations and reaction rate measurements. A hydrogen atom of anthrahydroquinone (AHQ) is directly abstracted by triplet dioxygen to produce a hydroperoxide radical (HOO·) and a 10‐hydroxy‐9‐anthroxyl radical (AQH·), followed by subsequent hydrogen atom abstraction that leads to the formation of hydrogen peroxide and anthraquinone (AQ). Hydrogen atom abstraction was found to be the rate‐determining step in this process. Tetrahydroanthrahydroquinone (THAHQ) is also used in this process in a similar way to AHQ, but a higher activation energy is required for the rate‐determining step when THAHQ is used, which would lead to a 25‐fold rate deacceleration compared with AHQ at 27 °C. The reactivities of AHQ and THAHQ are not significantly influenced by effects of side alkyl chain that is used in the industrial process for increasing the solubility of AHQ and AQ in working solution. The relative reaction rate of AHQ and THAHQ is measured under laboratory conditions. The computational results are consistent with an observed lower rate of the oxidation process of THAHQ.

The structure, electronic properties, and catalytic activity toward oxygen activation of gold nanoclusters with size between 10 and 42 atoms were investigated with first principle methods. Nanoparticle symmetry, bond lengths, and surface charge distribution were analyzed and compared to those of macroscopic gold surfaces. Irregular charge distribution was found on the surfaces of nanoparticles consisting of fewer than 30 gold atoms. Nanoparticles with more than 30 atoms were characterized with core–shell charge separation, e.g, positively charged core and negatively charged surface. The charge distribution on those nanoparticles significantly differs from the charge distribution on macroscopic gold surface. The structure and electronic properties of the gold nanoparticles were related to their catalytic activity toward the aerobic oxidation of organic molecules, e.g., cyclohexane. It was found that oxygen is activated by partially negatively charged surface gold atoms. Nanoparticles with sizes between 10 and 30 gold atoms could only activate oxygen over the negatively charged surface active sites, whereas larger nanoparticles could activate oxygen over the whole surface. The results are in good agreement and provide detailed understanding of recently published experimental data of aerobic oxidation on subnanometer gold nanoparticles (ACS Catal. 2011, 1, 2–6).

A copper(II) complex bearing a pentadentate ligand, [Cu(II)(N4Py)(CF(3)SO(3))(2)] (1) (N4Py = N,N-bis(2-pyridylmethyl)bis(2-pyridyl)methylamine), was synthesized and characterized with various spectroscopic techniques and X-ray crystallography. A mononuclear Cu(II)-hydroperoxo complex, [Cu(II)(N4Py)(OOH)](+) (2), was then generated in the reaction of 1 and H(2)O(2) in the presence of base, and the reactivity of the intermediate was investigated in the oxidation of various substrates at -40 degrees C. In the reactivity studies, 2 showed a low oxidizing power such that 2 reacted only with triethylphosphine but not with other substrates such as thioanisole, benzyl alcohol, 1,4-cyclohexadiene, cyclohexene, and cyclohexane. In theoretical work, we have conducted density functional theory (DFT) calculations on the epoxidation of ethylene by 2 and a [Cu(III)(N4Py)(O)](+) intermediate (3) at the B3LYP level. The activation barrier is calculated to be 39.7 and 26.3 kcal/mol for distal and proximal oxygen attacks by 2, respectively. This result indicates that the direct ethylene epoxidation by 2 is not a plausible pathway, as we have observed in the experimental work. In contrast, the ethylene epoxidation by 3 is a downhill and low-barrier process. We also found that 2 cannot be a precursor to 3, since the homolytic cleavage of the O-O bond of 2 is very endothermic (i.e., 42 kcal/mol). On the basis of the experimental and theoretical results, we conclude that a mononuclear Cu(II)-hydroperoxo species bearing a pentadentate N5 ligand is a sluggish oxidant in oxygenation reactions.

Heme metabolism by heme oxygenase (HO) is investigated with quantum mechanical/molecular mechanical (QM/MM) calculations. A mechanism assisted by water is proposed: (1) an iron-oxo species and a water molecule are generated by the heterolytic cleavage of the O-O bond of an iron-hydroperoxo species in a similar way to P450-mediated reactions, (2) a hydrogen atom abstraction by the iron-oxo species from the generated water molecule and the C-O bond formation between the water molecule and the α-meso carbon take place simultaneously. The water molecule is hydrogen-bonded to the oxo ligand and to the water cluster in the active site of HO. The water cluster can control the position of the generated water molecule to ensure the regioselective oxidation of heme at the α-meso position, at the same time, can facilitate the oxidation by stabilizing a positive charge on the water molecule in the transition state. A key difference between HO and P450 is observed in the structure of the active site; Thr252 in P450 blocks the access of the water molecule to the α-meso position, and can thus suppress the undesired heme oxidation for P450.