Mass Spectrometry of Self-Assembled Supramolecular Structures of Glycyrrhetic Acid with Benzimidazole

Mass spectrometry with electrospray ionization (ESI-MS) was used for the first time to study the formation of supramolecular complexes of glycyrrhetic acid (GLA) with benzimidazole (BMZ) derivatives (9-diethylaminoethyl-2,3-dihydroimidazo[1,2-a]benzimidazole dihydrochloride). ESI-MS spectra showed peaks for non-covalent complexes of GLA with BMZ that contained from 3 to 7 GLA molecules and one BMZ molecule (3:1, 4:1, 5:1, 6:1, and 7:1). Peaks for non-covalent complexes corresponding to ions containing one or two GLA molecules and one BMZ molecule (1:1 and 2:1) were not observed. Increasing the GLA mole fraction in the samples increased the peak intensities of the GLA–BMZ complexes. GLA self-assembly and GLA complexation with BMZ occurred simultaneously and were competitive.