Plasticity in the copper-thioether bond: manifestation in blue Cu proteins and in synthetic analogs.

The binding of thioethers to transition metals in biological and biomimetic systems is reviewed with a focus on copper. Literature data show that copper(I) ions have a stronger tendency to bind thioethers, e.g. methionine-like ligands, than the isoelectronic Zn(II) ions. The plasticity in the Cu(II) coordination sphere, and the diffuseness of the lone pair electrons of a thioether sulfur, allow Cu(II)-S(thioether) bond distances to vary from 2.4 to 3.2 Å, as shown by an in-depth analysis of protein structures (Protein Structure Database, PDB) and molecular structures of copper coordination compounds (Cambridge Structural Database, CSD).