Formation of stoichiometric complexes between dibenzo-30-crown-10 and guanidinium moiety containing compounds

Inclusion complexes between protonated guanidinium moiety and a large crown ether, dibenzo-30-crown-10, have been studied by electrospray ionization mass spectrometry (ESI-MS). In order to determine which solvent is the most suitable for generation of these complexes, methanol, water, acetonitrile and their mixtures (most common solvents for ESI) have been tested. Acetonitrile/water (1/1) has been found the best choice. In acetonitrile/water solution, the formation of stoichiometric complexes has been established (stoichiometric means that a peptide attaches the number of crown ether molecules equal to the number of guanidinium moieties it contains). For example, for the peptide containing three arginine residues the peak of the respective complex with three crown ether molecules is clearly seen.