Molybdenum/Tungsten-Based Heteropoly Salts in Oxidations

Oxidation represents one of the most important and practical chemical transformations for both organic synthesis, material science and pharmaceutical area. Among the existing strategies, molybdenum/tungsten-based heteropoly salts involved oxidations with low-cost and environmentally benign terminal oxidant and thus have attracted considerable attention in recent years. In this review, we have summarized the recent development of heteropoly salts utilized in oxidations, mainly the peroxomolybdates and peroxotungstates. We wish to highlight the progress made in the past 20 years of this field. Three categories are classified according to the aggregation state of metal oxides. Special attention is paid to the catalytically active peroxometalate species generated during the oxidation process. It is helpful to shed light on the common features that enable highly efficient and selective oxidations. We aim to inspire fellow chemists to explore more functional metalates for catalytic oxidations, especially asymmetric versions. Meanwhile, we attempt to understand the design principles for the discovery of more efficient, selective and economical catalytic systems.

Effective Synergistic Effect of Dipeptide-Polyoxometalate-Graphene Oxide Ternary Hybrid Materials on Peroxidase-like Mimics with Enhanced Performance

Dipeptide-polyoxometalates (POMs)-graphene oxide (GO) ternary hybrid is an excellent peroxidase-like mimic, exhibiting enhanced peroxidase-like activity compared to POMs alone. The hybrid was readily prepared through a reprecipitation method involving electrostatic encapsulation of H3PW12O40 (PW12) by cationic diphenylalanine (FF) peptide and coassembly of FF@PW12 spheres with graphene oxide (GO). Using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate, the peroxidase-like activity of FF@PW12 was evaluated in the heterogeneous phase, and it is 13 times higher than that of pristine PW12 in the homogeneous phase. Furthermore, ternary hybrids of FF@PW12@GO containing 5 wt % GO could enhance the activity 1.7 times higher than that of FF@PW12. The noncovalent interactions of hydrogen bonding and ionic interaction between GO and POMs are speculated to result in the synergistic effect for the enhancement of peroxidase-like performance. The strong interactions between rGO and PW12 are evaluated by a four-probe Hall measurement via the van der Pauw method, and rGO is significantly p-doped by the doping effect of PW12 with lower LUMO energy than that of the energy level of rGO and also due to the electron reservoir feature of PW12. Cyclic voltammogram measurements also suggest that GO causes significant influence on the electronic structure of the reduced forms of the redox couples of PW12. The nature of the TMB catalytic reaction may originate from the generation of the hydroxyl radical ((•)OH) from the decomposition of H2O2 by ternary hybrids and the formation of peroxo species of POM. Taking advantage of the UV-vis signals of TMB being correlated to the concentration of H2O2, FF@PW12@GO can be used to detect H2O2 within the limit of detection of 0.11 μM, and the detection range is 1-75 μM. The present method indeed opens up a promising route in constructing heterogeneous peroxidase-like mimics through the use of POMs via the introduction of GO for building H2O2 sensors.

Polymeric ionic liquid nanogel-anchored tungstate anions: a robust catalytic system for oxidation of sulfides to sulfoxides

A new heterogeneous catalytic system was prepared by immobilization of tungstate ions on a cross-linked poly(ionic liquid) nanogel.