![]() ![]() This approach is in fact an alternative to the one previously proposed (Zhang et al. ![]() Such an isomerization explains competitive dissociations mainly based on internal proton transfer into ion/neutral complex responsible of the complementary product ions. In certain cases, as a consequence, molecular isomerization into ion–dipole as intermediate of stepwise dissociation pathways is considered (Afonso et al. They interpreted formation of these product ions using exclusively mechanisms based on charge-promoted dissociations. 2016) investigated the detected fragment ions of protonated LpAA ( +) resonantly excited under low-energy collisional activation conditions. However, they occur when the dissociative process is exothermic and/or the residual internal energy carried by the produced ions is sufficient to drive consecutive dissociations (Darii et al. Therefore, since the produced ions are not excited, their consecutive dissociations are inhibited unlike competitive dissociations (Bennaceur et al. In this mode, only the parent ion is excited by its own frequency. 2009) or a possible rationalization of ion dissociations under low-energy collision conditions in resonant excitation mode. First, using low-resolution instrumentation based on linear ion trap quadrupole, an encouraging study of ornithine and glutamine lipids (from Rhodobacter sphaeroides) proposed mechanisms (Zhang et al. 2019) especially, using ion collisional activation (i.e. Furthermore, it may be a powerful method for structural elucidation of do novo compounds (Thomas et al. Indeed, this mode is suitable for ionization of a broad variety of more or less polar metabolites. This method is characterized by a large selectivity, specificity and sensitivity when it is combined to desorption/ionization as electrospray (ESI). 2017).Īnalysis of these metabolites by hyphenated methods as liquid chromatography–tandem high-resolution mass spectrometry LC-HRMS/MS is especially versatile for complex mixture analysis. In a previous study, identification of LpAA and lipopeptides produced by Escherichia coli Nissle 1917, such as the N-lauroyl acyl group linked to asparagine (C12Asn), has been done in negative ESI mode yielding abundant ¯ anions (Pérez-Berezo et al. ![]() The major technical barrier for the identification of bacterial LpAA or lipopeptides is the difficulty or even the impossibility to isolate a sufficient sample amount to make the analysis either by NMR or/and by X-ray, which would require more than several tens of μg and several mg, respectively. 2014) have been described for their capacity to regulate host homeostasis. 2017) and lipo-amino acids (LpAA) (Vizcaino et al. Modeling allow to confirm the proposed mechanisms explaining the unexpected behavior of this glutamate conjugate.Īmong intestinal microbiota metabolites, lipopeptides (Pérez-Berezo et al. Such regeneration is comparable to that occurred from dissociation to peptides containing acid amino-acid. By this pathway, surprising regeneration of deprotonated fatty acid takes place. This complex dissociated by partner splitting either directly or after inter-partner proton transfer. Specific to glutamic moiety, they were formed by a stepwise dissociation via molecular isomerization through ion–dipole formation prior to dissociation. ![]() In contrast, instead of the expected product ions due to CONH-CH bond cleavage, an abundant complementary dehydrated glutamic acid and fatty acid anion pair were observed. The singular behavior of ¯ towards CID showed tenth product ions, eight were described by expected fragment ions. To find specific processes that help structural assignment, the negative ion dissociations have been scrutinized for an LpAA: the N-palmitoyl acyl group linked to glutamic acid (C16Glu). The negative ions were used for their advantages of yielding only few fragment ions sufficient to specify each part of LpAA with sensitivity. Structural elucidation of few of them was performed by high-resolution tandem mass spectrometry based on electrospray combined with selective ion dissociations reach by collision-induced dissociation (CID). Among them, lipo-amino acids (LpAA), which are able to cross the epithelial barrier and to act on the host, are poorly identified. The identification of bacterial metabolites produced by the microbiota is a key point to understand its role in human health. ![]()
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