On-line electrogeneration of copper-peptide complexes in microspray mass spectrometry

The interaction of copper ions with peptides was investigated by electrospray mass spectrometry. Two electrospray micro-emitters were compared, the first one with a platinum electrode using a copper(II) electrolyte solution containing a peptide sample, and the second one with a sacrificial copper anode in a water/methanol solution containing only a peptide (i.e., angiotensin III, bradykinin, or Leu-enkephalin). The former yielded mainly Cu2+ complexes either with histidine residues or with the peptide backbone (Cu+ complexes can be also formed due to gas-phase reactions), whereas the latter can generate a mixture of both Cu+ and Cu2+ aqueous complexes that yield different complexation patterns. This study shows that electrospray emitters with soluble copper anodes enable the study of Cu(l)-peptide complexes in solution.