Kinetic Inertness and Electrochemical Behavior of Copper(II) Tetraazamacrocyclic Complexes: Possible Implications for in Vivo Stability

TLDR: In this article, the kinetic inertness of copper(II) complexes of carboxymethyl-armed cyclams and cyclens in 5 M HCl was determined confirming that the complex derived from cross-bridged cyclam (Cu-CB-TE2A) is by far the most resistant to acid decomplexation.

Abstract: The kinetic inertness of copper(II) complexes of several carboxymethyl-armed cyclams and cyclens in 5 M HCl have been determined confirming that the complex derived from cross-bridged cyclam (Cu-CB-TE2A) is by far the most resistant to acid decomplexation. FT-IR studies in D2O solution revealed its unique resistance to full carboxylate protonation and its retention of coordination by both pendant arms even in 1 M DCl. The X-ray structure of its monoprotonated form, [Cu-CB-TE2AH]+, also established full coordination by both COO– and COOH pendant arms in the solid state. Cyclic voltammograms of four carboxymethyl pendant-armed cyclam and cyclen complexes in aqueous solution were obtained with only Cu-CB-TE2A displaying a quasi-reversible CuII/CuI reduction wave. These indicators correlate with the superior in vivo behavior of this complex and its bifunctional conjugate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)