Intermediate Cu(II) Thiolate Species in the Reduction of Cu(II)GHK by Glutathione: A Handy Chelate for Biological Cu(II) Reduction Inorganic Chemistry Ghk Cu Copper Peptide: Uncover Its Full Potential GHK Cu 50mg Third Kind Your copper peptide product should be this exact blue. If it isn't, you already have your answer. GHK Cu is blue because of coordination chemistry, not dye. The Cu ion at the center