Pentadentate and Hexadentate Pyridinophane Ligands Support Reversible Cu(II)/Cu(I) Redox Couples.

Two new ligands were synthesized with the goal of copper stabilization, N,N'-(2-methylpyridine)-2,11-diaza[3,3](2,6)pyridinophane (N4) and N-(methyl),N'-(2-methylpyridine)-2,11-diaza[3,3](2,6)pyridinophane (N4), by selective functionalization of N4 and N4. These two ligands, when reacted with various copper salts, generated both Cu(II) and Cu(I) complexes. These ligands and Cu complexes were characterized by various methods, such as NMR, UV-Vis, MS, and EA. Each compound was also examined electrochemically, and each revealed reversible Cu(II)/Cu(I) redox couples. Additionally, stability constants were determined via spectrophotometric titrations, and radiolabeling and cytotoxicity experiments were performed to assess the chelators relevance to their potential use in vivo as Cu PET imaging agents.