Electrochemical generation of Cu(I) complexes in aqueous solutions studied by on-line mass spectrometry

Abstract

Taking advantage of the electrochemical aspects of electrospray ionization (ESI) sources in positive ionization mode mass spectrometry (MS), aqueous copper complexes are electrogenerated using sacrificial copper electrodes. When using 8-hydroxyquinoline or bathocuproine, two chelating agents for Cu 2+ and Cu + ions, respectively, the electrodissolution of copper leads to the formation of the respective complexes that are then analyzed by MS. This electrochemical generation of copper(I) complexes offers a direct route to synthesize Cu + complexes in aqueous solutions.

The role of copper in cysteine oxidation: study of intra- and inter-molecular reactions in mass spectrometry

“…Second, copper metal atoms are oxidized to copper(I) ions that react with specific ligands, such as cysteine, according to a Mattsson and Bockris mechanism, 45 as discussed previously. 37 We can conclude that, with a copper electrode, both copper(I) and copper(II) ions are electrogenerated. 37 Copper(II) catalyzes the oxidation of cysteines to cystine as corroborated by the high abundance of 2M 1 (in different charged states) and copper(I) binds to free cysteines or other residues specific to this ion, such as lysine.…”

“…37 We can conclude that, with a copper electrode, both copper(I) and copper(II) ions are electrogenerated. 37 Copper(II) catalyzes the oxidation of cysteines to cystine as corroborated by the high abundance of 2M 1 (in different charged states) and copper(I) binds to free cysteines or other residues specific to this ion, such as lysine.…”

“…This abundant dimer is present as multiply charged species: [2M 1 The electrooxidation of the Cu electrode produces either Cu 2+ or Cu + cations in solution. 13,37 These cations can here react with M 1 and 2M 1 . The addition of Cu + on M 1 (m/z = 872.2 Th) and on 2M 1 (m/z = 840.3 Th for z = 2 and m/z = 1679.3 Th for z = 1z) were the most abundant metal complexes observed.…”

“…Metal ion on-line complexation was carried out using a microspray interface 36,37 with a microchannel of 45 mm  120 mm  1 cm, made in polyimide and developed by DiagnoSwiss SA (Monthey, Switzerland). 38,39 A reservoir of polycarbonate (ø = 6.5 mm, h = 5 mm) was glued at the inlet of the microchannel.…”

“…36 In particular, sacrificial copper electrodes lead to the electrogeneration of either copper(I) or copper(II) ions depending on the ligands present in aqueous solution. 13,37 Taking advantage of the electrochemical aspects of ESI, the complexation of copper ions, in different oxidation states, with non-cysteinyl peptides have been previously studied by using a sacrificial copper electrode. 13 Herein we study, with the same device, cysteine oxidation of peptides containing, one, two or three cysteines to compare the different oxidation pathways.…”