Ion mobility mass spectrometry of saponin ions

Abstract

Rationale Saponins are natural compounds presenting a high structural diversity whose structural characterization remains extremely challenging. Ideally, saponin structures are best established using nuclear magnetic resonance experiments conducted on isolated molecules. However, saponins are also increasingly characterized using tandem mass spectrometry (MS/MS) coupled with liquid chromatography, even if collision‐induced dissociation (CID) experiments are often quite limited in accurately determining the saponin structure. Methods We consider here ion mobility mass spectrometry (IMMS) as an orthogonal tool for the structural characterization of saponin isomers by comparing the experimental collisional cross sections (CCSs) of saponin ions with theoretical CCSs for candidate ion structures. Indeed, state‐of‐the‐art theoretical calculations perfectly complement the experimental results, allowing the ion structures to be deciphered at the molecular level. Results We demonstrate that ion mobility can contribute to the structural characterization of saponins because different saponin ions present significantly distinct CCSs. Depending on the nature of the cation (in the positive ion mode), the differences in CCSs can also be exacerbated, optimizing the gas‐phase separation. When associated with molecular dynamics simulations, the CCS data can be used to describe the interactions between the cations, i.e. H+, Na+ and K+, and the saponin molecules at a molecular level. Conclusions Our work contributes to resolve the relationship between the primary and secondary structures of saponin ions. However, it is obvious that the structural diversity and complexity of the saponins cannot be definitively unraveled by measuring a single numerical value, here the CCS. Consequently, the structural characterization of unknown saponins will be difficult to achieve based on IMMS alone. Nevertheless, we demonstrated that monodesmosidic and bidesmosidic saponins can be distinguished via IMMS.

Enhancing the Membranolytic Activity of Chenopodium quinoa Saponins by Fast Microwave Hydrolysis

“…The saponin extract from the quinoa husk is analyzed using the MS-based protocol that was described previously [23,24] that combines MALDI-MS, HRMS, LC-MS, LC-MSMS and LC-IMS. Saponin identification is then achieved by comparing our MS data to the quinoa saponins qualitatively described by Madl et al [6] and Kuljanabhagavad et al [27].…”

“…The first group of saponin ions in the m/z 1100-1160 range includes four-saccharide saponins, whereas the saponins detected between m/z 950-1000 are three-saccharide saponins. The MALDI data must be complemented by LC-MS analysis to: (i) evaluate the presence of isomeric saponins, (ii) evaluate the monosaccharide sequence using LC-MSMS [23] and (iii) confirm the bidesmosidic nature of the detected saponins using LC-IMS [24]. In Table 1, we summarize all the MS data including the retention times in LC-MS and the saponin ion collision cross sections ( TW Ω N2->He ) as determined using ion mobility experiments [31].…”

“…Based on LC-MSMS experiments, the distinction between the monodesmosidic and the bidesmosidic topologies is difficult to achieve [6]. In a recent report [ [24]. As a typical example (see Figure 5), the saponin B ions, detected at m/z 973 and 995 for [M + H] + and [M + Na] + ions, respectively, present significantly different collision cross-sections, TW CCS N2→He , at 260 and 243 Å 2 respectively.…”

“…Today, saponin characterization takes more and more advantage of the capabilities of mass spectrometry-based methods and LC-MS experiments are very efficient for saponin mixture characterization [6,9], often using accurate mass measurements (high-resolution MS-HRMS) and tandem mass spectrometry experiments (collision-induced dissociation-CID) [6,9,20]. We have reported the use of ion mobility spectrometry (IMS) [21,22] for saponin characterization [23,24]. We shown that isomeric saponins presenting different connectivities between the glycone and the aglycone moieties can be distinguished using IMS [24].…”

“…We have reported the use of ion mobility spectrometry (IMS) [21,22] for saponin characterization [23,24]. We shown that isomeric saponins presenting different connectivities between the glycone and the aglycone moieties can be distinguished using IMS [24]. More recently, taking advantage of the high ion mobility resolution achieved on the newly-introduced cyclic ion mobility experimental setup [25], we succeeded in distinguishing regioisomeric and steroisomeric saponins from Aesculus hippocastanum [20,25].…”