Metal deactivation, strategies

A remaining crucial technological milestone to pass for an implanted device remains the stability of the biocatalytic fuel cell, which should be expressed in months or years rather than days or weeks. Recent reports on the use of BOD biocatalytic electrodes in serum have, for example, highlighted instabilities associated with the presence of 02, urate or metal ions [99, 100], and enzyme deactivation in its oxidized state [101]. Strategies to be considered include the use of new biocatalysts with improved thermal properties, or stability towards interferences and inhibitors, the use of nanostructured electrode surfaces and chemical coupling of films to such surfaces, to improve film stability, and the design of redox mediator libraries tailored towards both mediation and immobilization. 

Nuclearity has a strong impact on reactivity, as evidenced by the different reactivity of mono versus binuclear copper oxidation enzymes (aromatic vs aliphatic oxidation) or the specific roles of the different Zn centers in alkaline phosphatase. Some nuclearities (e.g., binuclear metal complexes) correspond to thermodynamic sinks. In that case, preorganization is not required. Less stable nuclearities require a platform in order to be maintained during the catalytic process. Mononuclear systems correspond to this situation. In particular, monocopper centers need to be embedded to be protected. The funnel complex strategy was developed for that purpose. Porphyrin complexes can be protected from deactivation pathways by grafting them... 

This method is specific for metallacyclopentanes. The alkene-coupling process is favored by metal reduction. A typical synthetic strategy is the in situ reduction of a metal halide precursor in the presence of the alkene see, for example, the synthesis of 79 in Scheme 34.1 An alkylidene precursor may also lead to a metallacycle with elimination of the car-bene ligand as in the synthesis of 81, representing a deactivation pathway for alkene metathesis catalysts. Ilie two alkenes may be generated in situ in the coordination sphere by rearrangement processes, such as intramolecular hydrogen transfer from an alkyl-vinyl precursor. I ... 

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