Covalent catalysis bonds, reduction

In transition metal oxides, multiple oxidation states and the propensity for covalent bonding affect both the bulk and surface structures. The change of oxidation state of the anions typically gives these materials a range of possible compositions and is also the basis of much of the catalysis in which they are involved. One example for which there are published calculations is vanadium pentoxide, V2O5. Vanadia-based compounds are used as catalysts for the oxidation of hydrocarbons and other organic molecules under mild conditions and also find application as NOx reduction catalysts by selective reduction with NH3. 

In the transamination process, the pyridoxal coenzyme is transferred from the enzyme-imine intermediate to the substrate-imine. The evidence of an imine function comes from reduction by borohydride which does not yield pyridoxine but shows that a covalent bond is formed with a lysine residue of the enzyme. The protonation of the pyridine ring is also essential for catalysis. 

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