Intermediate Cu(II) Thiolate Species in the Reduction of Cu(II)GHK by Glutathione: A Handy Chelate for Biological Cu(II) Reduction Inorganic Chemistry Frontiers Exploring the beneficial effects of GHK Cu on an experimental model of colitis and the underlying mechanisms Not too big. Not too small. Because of their intermediate size, macrocyclic peptides combine the potency and precise targeting of an antibody or biologic therapy with the stability and ease of administration of a Frontiers Exploring the beneficial effects of GHK Cu on an experimental model of colitis and the underlying mechanisms