The Role of Nonheme Transition Metal-Oxo, -Peroxo, and -Superoxo Intermediates in Enzyme Catalysis and Reactions of Bioinspired Complexes

Transition metals are common cofactors in enzymes and enable catalysis to take place via reaction barriers that are accessible at room temperature. Oxygen-activating metalloenzymes are versatile species in Nature involved in vital processes ranging from biodegradation to biosynthesis. Since oxygen-activating intermediates are not readily amenable to experimental study, research has started to focus on biomimetic model systems that have the active site coordination sphere and structural features, but react in solution. In our research group, we have been involved in computational modeling of heme and nonheme iron dioxygenases as well as biomimetic models of these complexes. In this contribution, an overview is given on recent results of the characterization and reactivity patterns of metal-oxo, metal-peroxo, and metal-superoxo complexes. In particular, in recent studies attempts were made to trap and characterize the short-lived oxygen-bound intermediate in the catalytic cycle of cysteine dioxygenase. Many suggested structures could be ruled out by theoretical considerations, yet these also provided suggestions of possible candidates for the experimentally observed spectra. In addition, we review recent studies on the nonheme iron(III)-hydroperoxo species and how its reactivity patterns with arenes are dramatically different from those found for heme iron(III)-hydroperoxo species. In the final two sections there is a description, with illustrations, of a series of computational studies on manganese(V)-oxo and side-on manganese(III)-peroxo moieties that identify a unique spin-state reactivity pattern with a surprising product distribution.</p

Epoxidations Catalyzed by Manganese(V) Oxo and Imido Complexes: Role of the Oxidant−Mn−Oxo (Imido) Intermediate

The manganese(V) oxo complex (TBP8Cz)MnV(O) (1) is shown to catalyze the epoxidation of alkenes with a series of iodosylarenes (ArIO) as oxidants. Competition experiments reveal that the identity of ArIO influences the product ratios, implicating an unusual coordinated oxo−metal−ArIO intermediate (1-OIAr) as the active catalytic species. The isoelectronic manganese(V) imido complex (TBP8Cz)MnV(NMes) (2) does not participate in NR transfer but does catalyze epoxidations with ArIO as the O-atom source, suggesting a mechanism similar to that seen for 1. Direct evidence (ESIMS) is obtained for 1-OIMes

Combining vitamin B₁₂ and cisplatin-loaded porous silica nanoparticles via coordination: a facile approach to prepare a targeted drug delivery system

In this work, a novel drug delivery system for targeted therapy is developed based on noncovalent interactions.</p

Cycloalkane Oxidation Catalyzed by Copper-based Catalysts with H2O2 under Mild Conditions

Copper-catalyzed cycloalkane oxidation using H2O2 as an oxidant was investigated under mild conditions. The copper catalysts studied in this work ranged from commercially-available copper(II) salts to copper(II) complexes containing polypyridyl ligands. Various factors that affected catalytic activity of copper catalysts were elucidated. It was found that geometry of the copper complex in solution and coordinated anions played important roles in catalytic activity. The copper(II) complex generated in-situ by mixing Cu(OAc)(2) and TMPA ligand (TMPA=tris(2-pyridylmethyl)amine) adopted trigonal bipyramidal geometry and was competent to catalyze cyclohexane oxidation with higher yields, compared to those of other Cu2+ species used in this work. The optimal catalytic condition was achieved using 1.0 % mol of Cu(OAc)(2)/TMPA and 10 equivalents of H2O2 with respect to cyclohexane in CH3CN at 33-35 degrees C for 3 hours, resulting in the total product yield of 44 %. Moreover, since cyclohexyl hydroperoxide was detected as a major product, the Fenton-like mechanism via one electron process was proposed as a plausible mechanism in this cycloalkane oxidation. In addition, our catalytic system was further demonstrated to be applicable for oxidation of various cycloalkane substrates with moderate yields and relatively short time.LIMN