Determination of Relative Stabilities of Metal‐Peptide Bonds in the Gas Phase

Understanding binding site preferences in biological systems as well as affinities to binding partners is a crucial aspect in metallodrug development. We here present a mass spectrometry‐based method to compare relative stabilities of metal‐peptide adducts in the gas phase. Angiotensin 1 and substance P were used as model peptides. Incubation with isostructural N‐heterocyclic carbene (NHC) complexes of Ru(II), Os(II), Rh(III), and Ir(III) led to the formation of various adducts, which were subsequently studied by energy‐resolved fragmentation experiments. The gas‐phase stability of the metal‐peptide bonds depended on the metal and the binding partner. Of the four complexes used, the Os(II) derivative bound strongest to Met, while Ru(II) formed the most stable coordination bond with His. Rh(III) was identified as the weakest peptide binder and Ir(III) formed peptide adducts with intermediate stability. Probing these intrinsic gas‐phase properties can help in the interpretation of biological activities and the design of site‐specific protein binding metal complexes.