Oxides covalent activations

Davis et al. [89] reported an important work regarding the immobilization of metalloproteins and enzymes on oxidized, purified and vacuum-annealed SWCNTs in aqueous solution. AFM experiments showed that the immobilization is mainly physical, without need for covalent activation or electrostatic interaction. In fact, cytochrome c at pHs below the isoelectric point and ferritin at pHs above the isoelectric point showed an important adsorption obtained just by stirring the nanotubes dispersion (0.03 mg/mL) in dilute protein solutions (50-100 pg/mL) for a given time (2-20 h). GOx could be also adsorbed in a very efficient... 

Oxidation reactions make up an important class of organocatalyzed asymmetric processes, offering some of the most synthetically useful and widely apphcable methods to have emerged from the field [1, 2]. In this chapter we review a subsection of this area, namely, covalently activated organocatalytic asymmetric oxidation reactions. Here, covalent activation will be considered as the catalytic activation of the stoichiometric oxidant through the formation of new covalent bonds between the oxidant and the catalyst. Key developments prior to a similar review [2] are summarized, along with a more detailed account of advances since 2006. Prolinol-and imidazolidinone-catalyzed oxidation reactions, where the substrate rather than the oxidant may be covalently activated, are covered elsewhere in this publication (Chapters 2 and 3). 

Multivalent counterions have also been used as redox mediators for oxidation/ reduction of redox-active sites that are covalently bound to the polyelectrolyte [177]. hi this case, the oxidized redox-active sites are shielded by their interaction with the polyanion. This prevents reduction of the redox polymer, unless a mobile cationic mediator, [Ru(NH3)6], which interacts with the polyelectrolyte, is added. In this example, no real solubility changes were observed. 

Very few examples have been described for the non-covalent immobilization of chiral porphyrin complexes (Fig. 26). In the first case, the porphyrin-dichlororutheninm complex was encapsulated in silica, which was prepared around the complex by a sol-gel method [78], in an attempt to prevent deactivation observed in solution in the epoxidation of different alkenes with 2,6-dichloropyridine N-oxide. In fact, the heterogeneous catalyst is much more active, with TON up to 10 800 in the case of styrene compared to a maximum of 2190 in solution. Enantioselectivities were about the same imder both sets of conditions, with values aroimd 70% ee. 

Previous studies by Sorokin with iron phthalocyanine catalysts made use of oxone in the oxidation of 2,3,6-trimethylphenol [134]. Here, 4 equiv. KHSO5 were necessary to achieve full conversion. Otherwise, a hexamethyl-biphenol is observed as minor side-product. Covalently supported iron phthalocyanine complexes also showed activity in the oxidation of phenols bearing functional groups (alcohols, double bonds, benzylic, and allylic positions) [135]. Besides, silica-supported iron phthalocyanine catalysts were reported in the synthesis of menadione [136]. 

COVALENT COMPOUNDS, METAL IONS OXIDATION-REDUCTION The activation parameters for the oxidations of HC204." and 204 are... 

Liu, J. Li, Q. Yang, X. van Breemen, R. B. Bolton, J. L. Thatcher, G. R. Analysis of protein covalent modification by xenobiotics using a covert oxidatively activated tag raloxifene proof-of-principle study. Chem. Res. Toxicol. 2005, 18, 1485-1496. 

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