Fig. 1. Proposed coordination modes of Cu(ii),¹⁰ Cu(i),¹⁰ Zn(ii)³⁴ and the mixed metal Cu(ii),Zn(ii) or Cu(i),Zn(ii) complexes^52,53 based on experimental results and bibliographic data. Affinity constant values (K_a) at pH 7.4 for Cu(ii),⁵⁷ Cu(i)^58,59 and Zn(ii)⁴⁹ are given in M^–1 (bold, purple).