|Topology discrimination of saponin ions by Hyphenated Mass Spectrometry techniques and computational chemistry
|Ion Mobility - Mass Spectrometry (BMSS)
|Mr Corentin Decroo
|Prof Pascal Gerbaux
Dr Patrick Flammang
Dr Jerome Cornil
Abstract Information :
Because of their huge biological and pharmacological activities, saponins arouse nowadays an increasing interest. When deciphering the biological activities or the potential applications of natural products, the structural characterization of the targeted molecules must be performed with great many details. Generally, the structural characterization of biomolecules, like saponins, is realized based on NMR measurements on purified and isolated molecules. Nowadays, mass spectrometry coupled with liquid chromatography appears to be an inescapable tool for the determination of molecular structures since no extreme purification nor isolation is mandatory to identify molecules. The structure of saponin is often derived from tandem mass spectrometry experiments, with a special interest in collision-induced dissociation experiments. Unfortunately, for saponin ions, MSMS appears to be not sufficient because of similar decomposition pathways between isomers and even between congeners. In the present work, we consider ion mobility spectrometry (IMS) as an orthogonal tool for the gas phase separation of saponin isomers. Indeed, this technique allows for the separation of gas-phase ions based on their mobilities in an electric field when submitted to collision against a countercurrent inert gas. IMS can go far beyond ion separation when considering the measurement of the collision cross sections (CCS) of the saponin ions. In first approximation, the CCS data is highly related to the 3D structure of the gaseous ions and is then intrinsically related to the molecular structures of the ionized molecules. Nevertheless, CCSexp measurements only become relevant from a structure analysis point of view upon the direct comparison with the CCS calculated for candidate ion structures generated upon theoretical calculations - CCSth. In the present study, we submitted to the IMS/theoretical chemistry combination selected saponins presenting model structures. The different molecules are extracted from different plants such as soy (Glycine max) and quinoa (Chenopodium quinoa) but also from marine animals like sea cucumbers, Holothuria forskali. By this selection, we get access to different structures such as monodesmosidic and polydesmositic saponins. We here present our experimental and theoretical results revealing the potentialities and the weaknesses of IMS for the structural characterization of saponins.