Stabilization of Cu(i) for binding and calorimetric measurements in aqueous solution

Abstract

Conditions have been developed for the comproportionation reaction of Cu²⁺ and copper metal to prepare aqueous solutions of Cu⁺ that are stabilized from disproportionation by MeCN and other Cu⁺-stabilizing ligands. These solutions were then used in ITC measurements to quantify the thermodynamics of formation of a set of Cu⁺ complexes (Cu^I(MeCN)₃⁺, Cu^IMe₆Trien⁺, Cu^I(BCA)₂³⁻, Cu^I(BCS)₂³⁻), which have stabilities ranging over 15 orders of magnitude, for their use in binding and calorimetric measurements of Cu⁺ interaction with proteins and other biological macromolecules. These complexes were then used to determine the stability and thermodynamics of formation of a 1 : 1 complex of Cu⁺ with the biologically important tri-peptide glutathione, GSH. These results identify Me₆Trien as an attractive Cu⁺-stabilizing ligand for calorimetric experiments, and suggest that caution should be used with MeCN to stabilize Cu⁺ due to its potential for participating in unquantifiable ternary interactions.