Anchoring copper–amino acid complexes on silica or in montmorillonite—an FT-IR study

Cu(amino acid) complexes were immobilised in mommorillonite or on silica gel by two methods (i) cation exchange first followed by ligation (two-step method) or (ii) depositing the ligands onto/into the support, then introducing the metal ion and, finally, filling the empty coordination sites of the central ions by added ligands (three-step method). The amino acids were L-tyrosine, L-histidine or L-aspartic acid. Immobilisation was followed by infrared spectroscopy. Host-guest substances were formed in every Cu2+- amino acid- montmorillonite system, however, significant anchoring occurred on silica gel only when tyrosine was the ligand. The heat stabilities of these host-guest substances were appreciable, complete decomposition only occurred at 673 K

Covalent grafting of copper–amino acid complexes onto chloropropylated silica gel—an FT-IR study

Cu(amino acid) complexes were immobilised on silica gel by covalent anchoring. The amino acids were L-histidine and L-tyrosine and their BOC-(tert-butoxycarbonyl) or methyl ester protected derivatives. To gain control over the synthesis the appropriately protected amino acid was reacted with chloropropylated silica gel first. This modified material as is, or after deprotecting the anchored amino acids, was used in further steps of building the immobilised Cu(II) complex. The covalently grafted complexes were studied by FT-IR spectroscopy and computer modelling. Materials containing protected histidine ligands showed catalase activity (decomposition of H2O2), those containing protected or unprotected tyrosine ligands displayed tyrosinase activity (the decomposed H2O2 oxidised the tyrosine skeleton to a quinoidal structure)