Ether formation on the tridentate Schiff base ligands of copper(II) complexes

Abstract

A series of copper(II) complexes, CuL·imidazole, where L 2− are tridentate Schiff base ligands formed by condensation of salicylaldehyde with a series of amino acids, have been synthesized. Visible spectral data indicate that copper(II) in these complexes are five coordinate in the solid state and in solution. Electrospray mass spectrometry has been used to show how these complexes react in alcohol/NaOH solutions with and without the presence of D-galactose. In the absence of D-galactose where the amino acid in the ligand is serine, the alcohol group on the ligand is converted to its alkyl ether after sonication of the solution for up to 4 h. In the presence of D-galactose, an alkoxy group is added to the ligands except for the ligand containing serine after sonication of the solutions for up to 4 h. At the same time, D-galactose is oxidized to its aldehyde. Where the ligand contains methionine, oxygen is also added to the ligand, most likely to the thioether sulfur.

The crystal and molecular structures of three copper-containing complexes and their activities in mimicking galactose oxidase

“…The use of mass spectrometry has been reported in a study of the oxidation of d-galactose (Gal) by Cu II complexes of a series of tridentate Schiff base ligands in alcohol/NaOH solutions (Butcher et al, 2014). The change in the color of the solutions from blue-green to yellow and the appearance of a negative-ion electrospray mass spectral peak at m/z = 195 [Oxidized Gal + OH] showed that the copper complexes had oxidized the galactose while being reduced to a Cu I species.…”