Distinguishing Biologically Relevant Hexoses by Water Adduction to the Lithium-Cationized Molecule

Study of Mono and Di-O-caffeoylquinic Acid Isomers in Acmella oleracea Extracts by HPLC-MS/MS and Application of Linear Equation of Deconvolution Analysis Algorithm for Their Characterization

Chlorogenic acids, the esters of caffeic and quinic acids, are the main phenolic acids detected in Acmella oleracea extracts and have gained increasing interest in recent years due to their important biological activities. Given their structural similarity and instability, the correct analysis and identification of these compounds in plants is challenging. This study aimed to propose a simple and rapid determination of the A. oleracea caffeoylquinic isomers, applying an HPLC-MS/MS method supported by a mathematical algorithm (Linear Equation of Deconvolution Analysis (LEDA)). The three mono- and the three di-caffeoylquinic acids in roots of Acmella plants were studied by an ion trap MS analyzer. A separation by a conventional chromatographic method was firstly performed and an MS/MS characterization by energetic dimension of collision-induced dissociation mechanism was carried out. The analyses were then replicated using a short HPLC column and a fast elution gradient (ten minutes). Each acquired MS/MS data were processed by LEDA algorithm which allowed to assign a relative abundance in the reference ion signal to each isomer present. Quantitative results showed no significant differences between the two chromatographic systems proposed, proving that the use of LEDA algorithm allowed the distinction of the six isomers in a quarter of the time.

Isomers Recognition in HPLC-MS/MS Analysis of Human Plasma Samples by Using an Ion Trap Supported by a Linear Equations-Based Algorithm

The tandem mass spectrometry (MS/MS) approach employing an ion trap mass analyzer (IT) was evaluated in isomers recognition. The proposed approach consists of sole, simple, and rapid liquid chromatographic separation (HPLC) without requiring resolution between the analytes. Then, the MS/MS properties were optimized to solve the signal assignment using post-processing data elaboration (LEDA). The IT-MS/MS experiment uses the same site, helium as collision gas, and different time steps to modify the applied conditions on the studied ions. Nevertheless, helium cannot ensure the quick energization of the precursor ion due to its small cross-section. Then, different combinations between excitation amplitude (ExA) and excitation time (ExT) were tested to achieve the activation of the fragmentation channels and the formation of the MS/MS spectrum. Usually, the IT-MS/MS acquisition cycle is longer for other multistage instruments, decreasing the frequency of sample data collection and influencing the chromatographic profile. To solve these problems, two time segments were set up, and the elution conditions were optimized with a compromise between peaks distinction and run time reduction. The developed HPLC-MS/MS method was checked and applied to analyze a series of human plasma samples spiked with an equimolar mixture of pair of isomers.

Tandem mass spectrometry approaches for recognition of isomeric compounds mixtures

The present review aims to collect the published literature pertaining the recognition of isobaric compounds (isomers or stereoisomers) using the features of tandem mass spectrometry (MS) experiments without any chromatographic separation or chemical modification (derivatization or isotopic enrichment) of the analytes. MS/MS methods possess high selectivity, wide dynamic range and high throughput capabilities. Generally, tandem MS has limited capability for distinguishing isomers that fragment similarly. However, some MS/MS methods have been developed and positively applied to isomers discrimination. Among the literature on this topic, the applications that fit on the review subject can be summarized as follow: (1) chiral discrimination by the kinetic method, (2) the use energy-resolved tandem mass spectra and the survival yield (SY) representation, (3) the kinetics evaluation of the ion-molecule interaction and (4) the postprocessing mathematical algorithm to resolve the isomers in MS/MS signal.

Gas-Phase Behavior of Galactofuranosides upon Collisional Fragmentation: A Multistage High-Resolution Ion Mobility Study

Carbohydrates are ubiquitous in nature but are among the least conserved biomolecules in life. These biopolymers pose a particular challenge to analytical chemists because of their high diversity and structural heterogeneity. In addition, they contain many isomerisms that complicate their structural characterization, notably by mass spectrometry. The tautomerism of the constitutive subunits is of particular interest. A given cyclized monosaccharide unit can take two forms: a most common 6-membered ring (pyranose, p) and a more flexible 5-membered ring (furanose, f). The tautomers impact the biological properties of polysaccharides, resulting in interesting properties of the derived oligosaccharides. From an analytical point of view, the impact of tautomerism on the gas-phase behavior of ions has scarcely been described in the literature. In this work, we study the behavior of Galf-containing oligosaccharides, ionized as [M+Li]⁺ species, under collisional dissociation (CID) conditions using high-resolution and multistage ion mobility (IMS) on a Cyclic IMS platform. In the first part of this work, we studied whether disaccharidic fragments released from Galf-containing (Gal)₁(Man)₂ trisaccharides (and their Galp counterpart) would match the corresponding disaccharide standards, and─despite the fragments generally being a good match─we showed the possibility of Galf migrations and other unidentified alterations in the IMS profile. Next, we expanded on these unknown features using multistage IMS and molecular dynamics, unveiling the contributions of additional gas-phase conformers in the profile of fragments from a Galf-containing trisaccharide compared with the corresponding disaccharides.

Chemical properties of inner and surficial regions of hydrogen-bonded clusters of biological molecules: ultraviolet photodissociation and water adsorption analyses in the gas phase

The chemical and physical properties of cold, gas-phase hydrogen-bonded clusters of L-alanine (L-Ala), L-trialanine (L-Ala₃), L-tetraalanine (L-Ala₄), and tryptophan (Trp) enantiomers were investigated using tandem mass spectrometry with an electrospray ionization source and cold ion trap. From the ultraviolet (UV) photodissociation spectra at 265-290 nm, the electronic structures of homochiral H⁺(L-Trp)(L-Ala) at 8 K were found to be different from those of heterochiral H⁺(D-Trp)(L-Ala) and protonated Trp. The number of water molecules adsorbed on the surface of gas-phase H⁺(D-Trp)(L-Ala) was larger than that of H⁺(L-Trp)(L-Ala), indicating stronger intermolecular interactions of L-Ala with H⁺(L-Trp) than those with H⁺(D-Trp). The product ion spectrum obtained by 265 nm photoexcitation of H⁺(L-Trp)(L-Ala₃)(H₂O)_n formed via gas-phase water adsorption on H⁺(L-Trp)(L-Ala₃) showed that the evaporation of water molecules was the main photodissociation process. In the case of H⁺(L-Trp)(L-Ala₄)(H₂O)_n, signals of H⁺(L-Ala₄) (H₂O)_n formed via L-Trp evaporation were observed in the product ion spectra, and the cross-section for UV photoinduced L-Trp evaporation became larger as the number of adsorbed water molecules increased. This observation indicates that water molecules were selectively adsorbed on the H⁺(L-Ala₄) side of H⁺(L-Trp)(L-Ala₄) and weakened the intermolecular interactions between L-Trp and H⁺(L-Ala₄) in the hydrogen-bonded cluster.

Application of LEDA algorithm for the recognition of P-glycoprotein and Carbonic Anhydrase hybrid inhibitors and evaluation of their plasma stability by HPLC-MS/MS analysis

Design and synthesis of new candidate drugs produces a large number of compounds that must be qualified and tested to evaluate their characteristics and potential applications. Therefore, many studies will be scheduled and, consequently, it will be necessary to arrange specific, reliable, fast and relatively cheap analytic methods to support this research. The manuscript proposes a new approach in the HPLC-MS/MS analysis by using a sole chromatographic set up, tuned to minimize the run time, without requiring high efficiency or resolution between the analytes. The chromatographic column was used only to avoid or limit the interference of sample matrix towards the analyte ionization process (matrix-effects). Then, the MS/MS properties were explored to solve the signal assignment, by performing a series of energy resolved experiments to optimize the parameters and applying an interesting post-processing data elaboration tool (LEDA). The reliability of the new approach was evaluated in a chemical stability study in PBS and human plasma samples of a series of isomeric compounds P-glycoprotein/Carbonic Anhydrase (P-gp/CA) hybrid inhibitors. The obtained results demonstrated the effectiveness (reliability 97%-100%) of the LEDA algorithm to recognize and to separate the possible isomers present in the samples. The obtained matrix-effects values (ME 96%-106%) established that the chromatographic set up (short column and fast elution gradient) was proper to avoid the matrix interferences, while recovery values (RE 88%-108%) indicate a suitable sample preparation, despite only a protein precipitation was carried out. The quantitative performances of proposed HPLC-MS/MS methods showed an accuracy ranging between 92% and 108% and a precision lower than 13% that allows to be confident on the determination of new P-gp/CA hybrid inhibitors in the degradation study. Therefore, the general procedure proposed was found adequate to study a series of isomeric compounds without their chromatographic separation but only by applying and developing the MS/MS features.

Molecular Adsorption on Cold Gas-Phase Hydrogen-Bonded Clusters of Chiral Molecules

Gas-phase molecular adsorption was investigated as a model for molecular cloud formation. Molecular adsorption on cold gas-phase hydrogen-bonded clusters containing protonated tryptophan (Trp) enantiomers and monosaccharides such as methyl-α-D-glucoside, D-ribose, and D-arabinose was detected using a tandem mass spectrometer equipped with an electrospray ionization source and cold ion trap. The adsorption sites on the surface of cold gas-phase hydrogen-bonded cluster ions were quantified using gas-phase N₂ adsorption-mass spectrometry. The gas-phase N₂ adsorption experiments indicated that the number of adsorption sites on the surface of the hydrogen-bonded heterochiral clusters containing L-Trp and D-monosaccharides exceeded the number of adsorption sites on the homochiral clusters containing D-Trp and D-monosaccharides. H₂O molecules were preferentially adsorbed on the heterochiral clusters, and larger water clusters were formed in the gas phase. Physical and chemical properties of cold gas-phase hydrogen-bonded clusters containing biological molecules were useful for investigating enantiomer selectivity and chemical evolution in interstellar molecular clouds.

A TIMS-TOF mass spectrometry study of disaccharides from in situ ESI derivatization with 3-pyridinylboronate

Mobilograms of in situ ESI 3-pyridinylboronic acid tagging of isomaltose in the positive or negative mode.

Hybrid 213 nm photodissociation of cationized Sterol lipid ions yield [M]+. Radical products for improved structural characterization using multistage tandem mass spectrometry

Sterols are a class of lipid molecules that include cholesterol, oxysterols, and sterol esters. Sterol lipids play critical functional roles in mammalian biology, including the dynamic regulation of cell membrane fluidity, as precursors for the synthesis of bile acids, steroid hormones and vitamin D, as regulators of gene expression in lipid metabolism, and for cholesterol transport and storage. The most common method employed for sterol analysis is high performance liquid chromatography coupled with tandem mass spectrometry (MS/MS). However, conventional collision induced dissociation (CID) methods used for ion activation during MS/MS typically fail to provide sufficient structural information for unambiguous assignment of sterol species based on their fragmentation behaviour alone. This places a significant burden on the efficiency of the chromatographic separation methods for the effective separation of isomeric sterols. Here, toward developing an improved analysis strategy for sterol lipids, we have explored the novel use of 213 nm photodissociation MS/MS and hybrid multistage-MS/MS (i.e., MSⁿ) data acquisition approaches for the improved structural characterization of cholesterol, representative isomeric oxysterols, and cholesteryl esters. Most notably, UVPD-MS/MS of ammoniated, lithiated and sodiated adducts of cholesterol, several representative oxysterol species, and an oxosterol lipid, are shown to give rise to abundant [M]^+. radical cation products, that subsequently fragment during collision induced MS³ to yield extensive structurally informative product ions, similar to those observed by Electron Ionization, and that enable their unambiguously assignment, including isomeric differentiation of oxysterols. For cholesterol esters, a reversed hybrid collision induced-MS/MS and UVPD-MS³ approach is shown to enable assignment of the sterol backbone, and localization of the site(s) of unsaturation within esterified fatty acyl chains.

A Comparative Analysis of Methods for Quantitation of Sugars during the Corn-to-Ethanol Fermentation Process

The quantitation of sugars, including glucose, the primary fermentable sugar; maltose (DP2); and maltotriose (DP3), is a standard procedure during the corn-to-ethanol fermentation process. The quantitation of glucose by the Megazyme Assay utilizing glucose oxidase and peroxidase enzymes (GOPOD) and UV-Vis detection, high-performance liquid chromatography with refractive index detection (HPLC-RID), and liquid chromatography mass spectrometry (LC-MS) with electrospray ionization (ESI) and selected ion monitoring (SIM) was studied. Three biological flask fermentation replicates were analyzed every 12 h beginning at 14 h of fermentation (T14) until near completion of fermentation (T62).The method comparison results for glucose quantitation showed that the LC-MS SIM analysis had the lowest limit of quantitation (LOQ) at 2 ppm and the widest dynamic range of 2.7 orders of magnitude. The HPLC-RID analysis had a linear dynamic range (LDR) of 1.5 orders of magnitude with an LOQ of 1500 ppm. The Megazyme GOPOD analysis had an LDR of 0.9 orders of magnitude with an LOQ of 120 ppm.The HPLC-RID method was ideal for glucose quantitation when it was present in high concentrations. In contrast, maltose and maltotriose components were found to be present in lower concentrations, such that simultaneous quantitation of the three analytes is difficult during fermentation. The LC-MS method was the only method able to quantify the concentration of glucose successfully and simultaneously with DP2 and DP3 in all the fermentation broth samples collected from T14 through T62 during the corn-to-ethanol fermentation process.

Evaluation of ultraviolet photodissociation tandem mass spectrometry for the structural assignment of unsaturated fatty acid double bond positional isomers

Fatty acids are a major source of structural diversity within the lipidome due to variations in their acyl chain lengths, branching, and cyclization, as well as the number, position, and stereochemistry of double bonds within their mono- and poly-unsaturated species. Here, the utility of 193 nm UltraViolet PhotoDissociation tandem mass spectrometry (UVPD-MS/MS) has been evaluated for the detailed structural characterization of a series of unsaturated fatty acid lipid species. UVPD-MS/MS of unsaturated fatty acids is shown to yield pairs of unique diagnostic product ions resulting from cleavages adjacent to their C=C double bonds, enabling unambiguous localization of the site(s) of unsaturation within these lipids. The effect of several experimental variables on the observed fragmentation behaviour and UVPD-MS/MS efficiency, including the position and number of double bonds, the effect of conjugated versus non-conjugated double bonds, the number of laser pulses, and the influence of alkali metal cations (Li, Na, K) as the ionizing adducts, has been evaluated. Importantly, the abundance of the diagnostic ions is shown to enable relative quantitation of mixtures of fatty acid isomers across a range of molar ratios. Finally, the practical application of 193 nm UVPD-MS/MS is demonstrated via characterization of changes in the ratios of fatty acid double bond positional isomers in isogenic colorectal cancer cell lines. This study therefore demonstrates the practicality of UVPD-MS/MS for the structural characterization of fatty acid isomers in lipidome analysis workflows.

Development of a Post-Column Liquid Chromatographic Chiral Addition Method for the Separation and Resolution of Common Mammalian Monosaccharides

The first solely MS-based methodology for the identification and resolution of the ten common mammalian monosaccharides is presented. Based on Cooks' fixed ligand kinetic method, this technique is effective on multiple classes of monosaccharides and includes the first example of two fixed ligand combinations used in a single multiplexed experiment. Subsequently, a post-HPLC chiral addition method is used in conjunction with this newly developed MS methodology for the separation and identification of mixtures of common neutral mammalian monosaccharides. This proposed technique is able to overcome a limitation of present carbohydrate analysis methods, namely the simultaneous isomeric resolution of multiple monosaccharides in a mixture. Graphical Abstract.

Distinguishing enantiomeric amino acids with chiral cyclodextrin adducts and structures for lossless ion manipulations

Enantiomeric molecular evaluations remain an enormous challenge for current analytical techniques. To date, derivatization strategies and long separation times are generally required in these studies, and the development and implementation of new approaches are needed to increase speed and distinguish currently unresolvable compounds. Herein, we describe a method using chiral cyclodextrin adducts and structures for lossless ion manipulations (SLIM) and serpentine ultralong path with extended routing (SUPER) ion mobility (IM) to achieve rapid, high resolution separations of d and l enantiomeric amino acids. In the analyses, a chiral cyclodextrin is added to each sample. Two cyclodextrins were found to complex each amino acid molecule (i.e. potentially sandwiching the amino acid in their cavities) and forming host-guest noncovalent complexes that were distinct for each d and l amino acid pair studied and thus separable with IM in SLIM devices. The SLIM was also used to accumulate much larger ion populations than previously feasible for evaluation and therefore allow enantiomeric measurements of higher sensitivity, with gains in resolution from our ultralong path separation capabilities, than previously reported by any other IM-based approach.

Fragmentation Pathways of Lithiated Hexose Monosaccharides

We characterize the primary fragmentation reactions of three isomeric lithiated D-hexose sugars (glucose, galactose, and mannose) utilizing tandem mass spectrometry, regiospecific labeling, and theory. We provide evidence that these three isomers populate similar fragmentation pathways to produce the abundant cross-ring cleavage peaks (^0,2A₁ and ^0,3A₁). These pathways are highly consistent with the prior literature (Hofmeister et al. J. Am. Chem. Soc. 113, 5964-5970, 1991, Bythell et al. J. Am. Soc. Mass Spectrom. 28, 688-703, 2017, Rabus et al. Phys. Chem. Chem. Phys. 19, 25643-25652, 2017) and the present labeling data. However, the structure-specific energetics and rate-determining steps of these reactions differ as a function of precursor sugar and anomeric configuration. The lowest energy water loss pathways involve loss of the anomeric oxygen to furnish B₁ ions. For glucose and galactose, the lithiated α-anomers generate ketone structures at C2 in a concerted reaction involving a 1,2-migration of the C2-H to the anomeric carbon (C1). In contrast, the β-anomers are predicted to form 1,3-anhydroglucose/galactose B₁ ion structures. Initiation of the water loss reactions from each anomeric configuration requires distinct reactive conformers, resulting in different product ion structures. Inversion of the stereochemistry at C2 has marked consequences. Both lithiated mannose forms expel water to form 1,2-anhydromannose B₁ ions with the newly formed epoxide group above the ring. Additionally, provided water loss is not instantaneous, the α-anomer can also isomerize to generate a ketone structure at C2 in a concerted reaction involving a 1,2-migration of the C2-H to C1. This product is indistinguishable to that from α-glucose. The energetics and interplay of these pathways are discussed. Graphical Abstract ᅟ.