Superoxide dismutase inspired immobilised Ni(II)–protected amino acid catalysts—Synthesis, characterisation, and catalytic activity

• Constructing biomimetic Ni(II)–amino acid complexes over silica gel via covalent grafting.
• Full structural characterisation with a range of methods.
• Testing with a superoxide dismutase biochemical test reaction.
• Oxidation of cyclohexane with high epoxide selectivity.

Covalently anchored Ni(II)–C-protected amino acid (l-histidine, l-cysteine, and l-cystine) complexes inspired by the active site of the Ni-superoxide dismutase enzyme were synthesised using chloropropylated silica gel as support. The structural features of the surface complexes were studied by the Kjeldahl method and ICP-MS, mid/far IR, UV–vis diffuse reflectance, and X-ray absorption spectroscopies. The enzyme-like activities of the materials were determined in a biochemical test reaction. Covalent grafting and building the complex onto the surface of the support were successful in all cases. It was found that in many instances the structures obtained and the coordinating groups substantially varied upon changing the conditions of the syntheses. All the covalently immobilised Ni(II)-complexes displayed enzyme-like activity. They also were active in the liquid-phase oxidation of cyclohexene, providing the epoxide with high selectivity.

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