Oligomycin A complex structures with some divalent metal cations studied by ESI MS and PM5 semiempirical methods

The ability of Oligomycin A (OLA) to form complexes with monovalent cations was studied by the ESI mass spectrometry and PM5 semiempirical method. At low cone voltage values the ESI MS spectra indicate that OLA formes stable 1:1 complexes with Mg2+, Ca2+, Sr2+, Ba2+, Zn2+ divalent cations irrespective of the stoichiometry. With increasing cone voltages the formation of the [OLA + M + (ClO4 or Cl)]+ complexes was preferred. This process occurred simultaneously with the formation of fragmentary metal cation complexes with the exception of Pb2+ ions which does not form complexes with OLA molecule. PM5 semiempirical calculations allowed the visualizations of all structures of (OLA + M)2+ and [OLA + M + (ClO4or Cl)]+ complexes as well as the fragmentary cations.