Complexation of cyclofrunctans with transition metal ions studied by electrospray ionization mass spectrometry and collision-induced dissociation

Abstract

Interactions between transition metal ions (Fe2+, Co2+, Ni2+, Cu2+ and Zn2+) and cyclofrunctans (CFs) in different solvents were investigated using positive electrospray ionization mass spectrometry (ESI-MS). ESI mass spectral analysis revealed that the 1:1 complexes were formed stably in ion trap and Fourier transform ion cyclotron resonance mass spectrometers (or in solution). The transition metal ion affinities of CFs were influenced by different solvents. In methanol and acetone, the complexation of CFs with transition metal ions was weak and the complexes of CFs with alkali metal ions were dominant. In contrast, the complexes of CFs with transition metal ions were the most abundant species in the presence of acetonitrile. The stability of inclusion complexes between cyclofructans and transition metal ions were tested by collision-induced dissociation through determining the CE50 values. The gas phase stability of cyclofructans in binding with transition metal cations was found to be in the order of Ni2+>Fe2+>Co2+>Zn2+>Cu2+, which did not follow the size of ionic radius. An experimental approach based on ESI-MS is therefore established to study the host–guest interactions between cyclofructans and transition metal ions.