The multiple conformational charge states of zinc(II) coordination by 2His-2Cys oligopeptide investigated by ion mobility-mass spectrometry, density functional theory and theoretical collision cross sections.

Whether traveling wave ion mobility-mass spectrometry (IM-MS), B3LYP/LanL2DZ density functional theory, and ion size scaled Lennard-Jones (LJ) collision cross sections (CCS) from the B3LYP optimized structures could be used to determine the type of Zn(II) coordination by the oligopeptide acetyl-His -Cys -Gly -Pro -Tyr -His -Cys (amb ) was investigated. The IM-MS analyses of a pH titration of molar equivalents of Zn(II):amb showed that both negatively and positively charged complexes formed and coordination of Zn(II) increased as the His and Cys deprotonated near their pKa values. The B3LYP method was used to generate a series of alternative coordination structures to compare with the experimental results.