The Interaction of the Dipeptide Carnosine with Alkali Metal Ions Studied by Ion Trap Mass Spectrometry

The complexation of alkali metal ions and the proton X+ (X = H, Li, Na, K. Rb, Cs) by beta-alanyl-L-histidine (carnosine, Car) was investigated by electrospray ionization mass spectrometry (ESI-MS) and MS/MS fragmentation studies. Collision-induced dissociation (CID) breakdown curves were recorded and the resulting apparent activation energies were compared to DFT calculations of binding energies at the B3LYP/cc-pVDZ level of theory. Additionally, the influence of metal complexation on hydrogen/deuterium exchange of CarX(+) with D2O was tested. Our investigations characterize the structures of Car-alkali complexes and elucidate the interaction with the differently sized solvated metal cations.