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The oxidation of substrates, such as alkenes, with H2O2 and the catalyst [MnIV2(μ‐O)3(tmtacn)2]2+ (1; tmtacn = 1,4,7‐trimethyl‐1,4,7‐triazacyclononane) is promoted by the addition of carboxylic acids through the in situ formation of bis(carboxylato) complexes of the type [MnIII2(μ‐O)(μ‐RCO2)2(tmtacn)2]2+. The conversion of 1 to these complexes requires a complex series of redox reactions coupled with the overall exchange of μ‐oxido ligands for μ‐carboxylato ligands. Here, we show that the mechanism by which this conversion occurs holds implications with regard to the species that is directly engaged in the catalytic oxidation of alkenes. Through a combination of UV/Vis absorption, Raman, resonance Raman and electron paramagnetic resonance (EPR) spectroscopy, it is shown that the conversion proceeds by an autocatalytic mechanism and that the species that engages in the oxidation of organic substrates also catalyses H2O2 decomposition, and the former process is faster.

The aqueous and non-aqueous chemistry of the complex [Mn2(III,IV)(μ-CH3COO)(μ-O)2(Me4dtne)](PF6)2 (where Me4dtne = 1,2-bis(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)ethane), which has been demonstrated as an exceptionally active catalyst in the bleaching of raw cotton and especially wood pulp at high pH (>11), is explored by UV/vis absorption, Raman and EPR spectroscopies and cyclic voltammetry. The data indicate that dissociation of the μ-acetato bridge is essential to the catalyst activity and rationalises the effect of sequestrants such as DTPA on its performance.

This is an open access article under the terms of the Creat ive Commo ns Attri butio n-NonCo mmercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. AbstractObjectives: Functional loading and low-temperature degradation may give rise to impaired clinical long-term service of zirconia implant abutments. The aim of this study was to compare the fracture strength (primary outcome measure) and the volume percentage of monoclinic surface zirconia (m-ZrO 2 ) of stock and CAD/CAM-customized zirconia implant abutments that functioned clinically for 1 year with geometrically identical pristine controls in an ex vivo experiment. Material and methods:Twenty-three stock (ZirDesign™) and 23 CAD/CAM-customized (Atlantis™) zirconia implant abutments were retrieved after 1 year of clinical service. They were compared with pristine copies with respect to the volume fraction of the monoclinic phase using Raman spectroscopy and their fracture load by means of a single load-to-fracture test. Failure analysis was performed using optical and SEM microscopy. After verification of normal distribution, paired t tests were used for comparison of fracture loads between pristine and clinically aged specimen. All statistical tests employed a level of significance of α = 0.05. Results:The fracture loads of the stock zirconia abutments were significantly (p < 0.05) reduced to 78.8% (SD 29.5%) after one year of clinical function. For the CAD/CAM abutments, no reduction in fracture load was found. No m-ZrO 2 volume percentages beyond the detection threshold of 5% were observed in any of the samples. Conclusions: After 1 year of clinical service, no difference in fracture strength of the CAD/CAM-customized zirconia implant abutments could be demonstrated, whereas the stock zirconia abutments decreased considerably in fracture strength. No substantial tetragonal-to-monoclinic transformation was observed. K E Y W O R D S biomaterials, clinical research, clinical trials, material sciences, prosthodontics, surface chemistry S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Schepke U, Gresnigt MMM, Browne WR, Abdolahzadeh S, Nijkamp J, Cune MS. Phase transformation and fracture load of stock and CAD/CAMcustomized zirconia abutments after 1 year of clinical function.

Manganese-based oxidation catalysis plays a central role both in nature, in the oxidation of water in photosystem II (PSII) and the control of reactive oxygen species, as well as in chemical processes, in the oxidation of organic substrates and bleaching applications. The focus of this review is on efforts made to explore and elucidate the redox-dependent coordination chemistry of these manganese-based systems in solution and the mechanisms by which their catalytic redox 3432reactions proceed. We also examine the behaviour and activity of complexes that have been developed and used as models for the active sites of the corresponding enzymes, or used as catalysts in the oxidation of organic substrates. Given the current concern over the environmental and economic impact of chemical processes, manganese catalysts that use H 2 O 2 as oxidant are the primary focus of this review.