Intermediate Cu(II) Thiolate Species in the Reduction of Cu(II)GHK by Glutathione: A Handy Chelate for Biological Cu(II) Reduction Inorganic Chemistry Intermediate Cu(II) Thiolate Species in the Reduction of Cu(II)GHK by Glutathione: A Handy Chelate for Biological Cu(II) Reduction Inorganic Chemistry 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 2021A12 Define the terms tolerance and tachyphylaxis. Discuss the different mechanisms by which tolerance can develop, giving examples where appropriate.