CID Experiments Research Articles

Very Low-Pressure CID Experiments: High Energy Transfer and Fragmentation Pattern at the Single Collision Regime.

We have performed CID experiments on a triple quadrupole instrument, lowering the collision gas pressure by 50 times compared to its conventional value. The results show that at very low-collision gas pressure, single collisions dominate the spectra. Indirectly, these results suggest that under conventional conditions, 20-50 collisions may be typical in CID experiments. The results show a marked difference between low- and high-pressure CID spectra, the latter being characterized in terms of 'slow heating' and predominance of consecutive reactions. The results indicate that under single collision conditions, the collisional energy transfer efficiency is very high: nearly 100% of the center of mass kinetic energy is converted to internal energy.

Free Radical-Based Sequencing for Native Top-Down Mass Spectrometry.

Native top-down proteomics allows for both proteoform identification and high-order structure characterization for cellular protein complexes. Unfortunately, tandem MS-based fragmentation efficiencies for such targets are low due to an increase in analyte ion mass and the low ion charge states that characterize native MS data. Multiple fragmentation methods can be integrated in order to increase protein complex sequence coverage, but this typically requires use of specialized hardware and software. Free-radical-initiated peptide sequencing (FRIPS) enables access to charge-remote and electron-based fragmentation channels within the context of conventional CID experiments. Here, we optimize FRIPS labeling for native top-down sequencing experiments. Our labeling approach is able to access intact complexes with TEMPO-based FRIPS reagents without significant protein denaturation or assembly disruption. By combining CID and FRIPS datasets, we observed sequence coverage improvements as large as 50% for protein complexes ranging from 36 to 106 kDa. Fragment ion production in these experiments was increased by as much as 102%. In general, our results indicate that TEMPO-based FRIPS reagents have the potential to dramatically increase sequence coverage obtained in native top-down experiments.

Structural Insights from Tandem Mass Spectrometry, Ion Mobility-Mass Spectrometry, and Infrared/Ultraviolet Spectroscopy on Sphingonodin I: Lasso vs Branched-Cyclic Topoisomers.

Lasso peptides form a class of ribosomally synthesized and post-translationally modified peptides (RiPPs) characterized by a mechanically interlocked topology, where the C-terminal tail of the peptide is threaded and trapped within an N-terminal macrolactam ring. Sphingonodin I is a lasso peptide that has not yet been structurally characterized using the traditional structural biology tools (e.g., NMR and X-ray crystallography), and its biological function has not yet been elucidated. In the present work, we describe structural signatures characteristic of the class II lasso peptide sphingonodin I and its branched-cyclic analogue using a combination of gas-phase ion tools (e.g., tandem mass spectrometry, MS/MS, trapped ion mobility spectrometry, TIMS, and infrared, IR, and ultraviolet, UV, spectroscopies). Tandem MS/MS CID experiments on sphingonodin I yielded mechanically interlocked species with associated bi and yj fragments demonstrating the presence of a lasso topology, while tandem MS/MS ECD experiments on sphingonodin I showed a significant increase in hydrogen migration in the loop region when compared to the branched-cyclic analogue. The high-mobility resolving power of TIMS permitted the separation of both topoisomers, where sphingonodin I adopted a more compact structure than its branched-cyclic analogue. Cryogenic and room-temperature IR spectroscopy experiments evidenced a different hydrogen bond network between the two topologies, while cryogenic UV spectroscopy experiments clearly demonstrated a distinct phenylalanine environment for the lasso peptide.

Surprising Homolytic Gas Phase Co-C Bond Dissociation Energies of Organometallic Aryl-Cobinamides Reveal Notable Non-Bonded Intramolecular Interactions.

Aryl‐cobalamins are a new class of organometallic structural mimics of vitamin B12 designed as potential ‘antivitamins B12’. Here, the first cationic aryl‐cobinamides are described, which were synthesized using the newly developed diaryl‐iodonium method. The aryl‐cobinamides were obtained as pairs of organometallic coordination isomers, the stereo‐structure of which was unambiguously assigned based on homo‐ and heteronuclear NMR spectra. The availability of isomers with axial attachment of the aryl group, either at the ‘beta’ or at the ‘alpha’ face of the cobalt‐center allowed for an unprecedented comparison of the organometallic reactivity of such pairs. The homolytic gas‐phase bond dissociation energies (BDEs) of the coordination‐isomeric phenyl‐ and 4‐ethylphenyl‐cobinamides were determined by ESI‐MS threshold CID experiments, furnishing (Co−Csp2 )‐BDEs of 38.4 and 40.6 kcal mol−1, respectively, for the two β‐isomers, and the larger BDEs of 46.6 and 43.8 kcal mol−1 for the corresponding α‐isomers. Surprisingly, the observed (Co−Csp2 )‐BDEs of the Coβ‐aryl‐cobinamides were smaller than the (Co−Csp3 )‐BDE of Coβ‐methyl‐cobinamide. DFT studies and the magnitudes of the experimental (Co−Csp2 )‐BDEs revealed relevant contributions of non‐bonded interactions in aryl‐cobinamides, notably steric strain between the aryl and the cobalt‐corrin moieties and non‐bonded interactions with and among the peripheral sidechains.

Phenyl-Group Exchange in Triphenylphosphine Mediated by Cationic Gold-Platinum Complexes-A Gas-Phase Mimetic Approach.

The PPh3 ligands in the heterodinuclear AuPt complex [(Ph3P)AuPt(PPh3)3][BAr4F] (BAr4F = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) exhibit a high fluxionality on the AuPt core. Fast intramolecular and slow intermolecular processes for the reversible exchange of the PPh3 ligands have been identified. When [(Ph3P)AuPt(PPh3)3][BAr4F] is heated in solution, the formation of benzene is observed, and a trinuclear, cationic AuPt2 complex is generated. This process is preceded by reversible phenyl-group exchange between the PPh3 ligands present in the reaction mixture as elucidated by deuterium-labeling studies. Both the elimination of benzene and the preceding reversible phenyl-group exchange have originally been observed in mass-spectrometry-based CID experiments (CID = Collision-Induced Dissociation). While CID of mass-selected [Au,Pt,(PPh3)4]+ results exclusively in the loss of PPh3, the resulting cation [Au,Pt,(PPh3)3]+ selectively eliminates C6H6. Thus, the dissociation of a PPh3 ligand from [Au,Pt,(PPh3)3]+ is energetically not able to compete with processes which result in C-H- and C-P-bond cleavage. In both media, the heterobimetallic nature of the employed complexes is the key for the observed reactivity. Only the intimate interplay of the gas-phase investigations, studies in solution, and thorough DFT computations allowed for the elucidation of the mechanistic details of the reactivity of [(Ph3P)AuPt(PPh3)3][BAr4F].

Intramolecular Hydrogen Transfer from the Alpha-Carbon (Cα) and Backbone Amide Nitrogen (Nb) to Form c- and y-Ions in Negative-Ion CID of Peptides.

The source of hydrogen in the formation of c- and y-ions produced by intramolecular hydrogen transfer in negative-ion CID experiments with peptides has been examined using Cα-, Cβ-, and backbone amide (Nb)-deuterated peptides AAA(d3)AA, AAG(d2)AA, AAAG(d2)A, and AAAAA-d7, as well as five other peptides. The c- and y-ions produced by deuterium transfer from the deuterated residues were detected and identified by the exact m/z values obtained with a high-resolution orbitrap mass spectrometer. The rate of deuterium transfer obtained indicates that over 50% of the hydrogen was originated from the backbone amide nitrogen, with the residual hydrogen coming from the backbone Cα. It is clear that the hydrogen does not originate from the side chain Cβ. It is hypothesized that the intramolecular hydrogen transfer to form negative c- and y-ions takes place via 3-, 4-, 6-, 7-, 8-, and 9-membered ring transition states.

Evaluation of the Katsuki-Sharpless Epoxidation Precatalysts by ESI-FTMS, CID, and IRMPD Spectroscopy.

The Katsuki-Sharpless epoxidation reaction is one of the most recognized chiral catalytic reactions, allowing for chiral epoxides to be used as starting materials for a series of synthetic pathways. The complete understanding of this reaction mechanism depends on the identification and description of species formed from Ti(IV) alkoxides and alkyl tartrates precatalysts. Despite previous reports on the nature of a bimetallic catalyst based on IR spectroscopy and NMR analysis, some debate remains. Therefore, we carried out mass spectrometry analysis by direct extraction of the ions from the reaction media by ESI(-)-FT-ICR and evaluated the observed ions by CID and IRMPD experiments. These techniques allowed us to detect carboxylates that correlate to the species in the reaction media and to confirm the actual presence of the titanium-tartrate complexes in solution. Our IRMPD results suggest the carboxylate dimer as an asymmetric species with two tartrates coordinated to a single Ti atom, while the other Ti center is coordinated by labile alkoxydes that could be easily exchanged by the organic peroxide and the substrate, allowing the epoxidation reaction to take place.

C–H Bond Activation by a Ruthenium(II) β‐Diketonate Complex: A Mechanistic Study

Ruthenium(II)‐catalysed C–H bond activation of arenes containing a functional directing group depends on the ligand coordinated to ruthenium(II). In this study, 2‐phenylpyridine C–H activation catalysed by a “piano‐stool“ ruthenium(II) complex containing a fluorinated β‐diketonate ligand was examined by ESI‐MS in combination with CID experiments. [Ru(β‐diketonate)(CTPhPy)Cl]+ was identified as an active intermediate, and its collisional activation leads to C–H activation. CID analysis indicates proton transfer from the phenylpyridine to the chlorine anion, showing HCl elimination, while the β‐diketonate ligand is retained in the complex together with the activated phenylpyridine. Furthermore, DFT calculations were performed for the neutral analogue [Ru(β‐diketonate)(PhPy)Cl] to identify all ruthenium intermediates along the C–H activation reaction pathway. The results suggest that the most stable structure of [Ru(β‐diketonate)(PhPy)Cl] has pre‐activated 2‐phenylpyridine with a partly developed Ru–H bond. Further, we show that K2CO3 is not directly involved in the C–H activation step and it serves in the reaction as a base.

Entrapment of amino acids in gas phase surfactant assemblies: The case of tryptophan confined in positively charged (1R,2S)-dodecyl (2-hydroxy-1-methyl-2-phenylethyl) dimethylammonium bromide aggregates.

The ability of positively charged aggregates of the surfactant (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB) to incorporate D-tryptophan or L-tryptophan in the gas phase has been investigated by electrospray ion mobility mass spectrometry (ESI-IM-MS). Strongly impacted by the pH of the electrosprayed solutions, both protonated (T+ ) and deprotonated (T- ) tryptophan are effectively included into the aggregates, whereas, tryptophan in zwitterionic (T0 ) form is practically absent in singly charged DMEB aggregates but can be found in multiply charged ones. The ability to incorporate tryptophan increases with the aggregation number and charge state of aggregates. More than 1 tryptophan species can be entrapped (aggregates including up to 5 tryptophan are observed). Collision induced dissociation experiments performed on the positively singly charged DMEB hexamer containing 1 T- show that at low collision energies the loss of a DMEB molecule is preferred with respect to the loss of the DMEB cation plus T- species which, in turn, is preferred with respect to the loss of mere tryptophan, suggesting that the deprotonated amino acid is preferentially located in proximity of a DMEB head group and with the ionic moiety pointing towards the core of the aggregate. The analysis of the collision cross sections (CCS) of bare and tryptophan containing aggregates allowed evaluating the contributions of tryptophan and bromide ions to the total aggregate CCS. No significant discrimination between D-tryptophan and L-tryptophan by the chiral DMEB aggregates has been evidenced by mass spectra data, CID experiments, and CCS values.

Forced degradation studies of lansoprazole using LC-ESI HRMS and 1 H-NMR experiments: in vitro toxicity evaluation of major degradation products.

Regulatory agencies from all over the world have set up stringent guidelines with regard to drug degradation products due to their toxic effects or carcinogenicity. Lansoprazole, a proton-pump inhibitor, was subjected to forced degradation studies as per ICH guidelines Q1A (R2). The drug was found to degrade under acidic, basic, neutral hydrolysis and oxidative stress conditions, whereas it was found to be stable under thermal and photolytic conditions. The chromatographic separation of the drug and its degradation products were achieved on a Hiber Purospher, C18 (250×4.6mm, 5μ) column using 10mM ammonium acetate and acetonitrile as a mobile phase in a gradient elution mode at a flow rate of 1.0ml/min. The eight degradation products (DP1-8) were identified and characterized by UPLC/ESI/HRMS with in-source CID experiments combined with accurate mass measurements. DP-1, DP-2 and DP-3 were formed in acidic, DP-4 in basic, DP-5 in neutral and DP-1, DP-6, DP-7 and DP-8 were in oxidation stress condition Among eight degradation products, five were hitherto unknown degradation products. In addition, one of the major degradation products, DP-2, was isolated by using semi preparative HPLC and other two, DP-6 and DP-7 were synthesized. The cytotoxic effect of these degradation products (DP-2, DP-6 and DP-7) were tested on normal human cells such as HEK 293 (embryonic kidney cells) and RWPE-1(normal prostate epithelial cells) by MTT assay. From the results of cytotoxicity, it was found that lansoprazole as well as its degradation products (DP-2, DP-6 and DP-7) were nontoxic up to 50-μM concentrations, and the latter showed slightly higher cytotoxicity when compared with that of lansoprazole. DNA binding studies using spectroscopic techniques indicate that DP-2, DP-6 and DP-7 molecules interact with ctDNA and may bind to its surface. Copyright © 2017 John Wiley & Sons, Ltd.

Chemical characterization of synthetic cannabinoids by electrospray ionization FT-ICR mass spectrometry

The synthetic cannabinoids (SCs) represent the most recent advent of the new psychotropic substances (NPS) and has become popularly known to mitigate the effects of the ο9-THC. The SCs are dissolved in organic solvents and sprayed in a dry herbal blend. However, little information is reported on active ingredients of SCs as well as the excipients or diluents added to the herbal blend. In this work, the direct infusion electrospray ionization Fourier transform ion cyclotron mass spectrometry technique (ESI-FT-ICR MS) was applied to explore the chemical composition of nine samples of herbal extract blends, where a total of 11 SCs (UR-144, JWH-073, XLR-11, JWH-250, JWH-122, AM-2201, AKB48, JWH-210, JWH-081, MAM-2201 and 5F-AKB48) were identified in the positive ionization mode, ESI(+), and other 44 chemical species (saturated and unsaturated fatty acids, sugars, flavonoids, etc.) were detected in the negative ionization mode, ESI(⿿). Additionally, CID experiments were performed, and fragmentation pathways were proposed to identify the connectivity of SCs. Thus, the direct infusion ESI-FT-ICR MS technique is a powerful tool in forensic chemistry that enables the rapid and unequivocal way for the determination of molecular formula, the degree of unsaturation (DBE⿿double bond equivalent) and exact mass (<1ppm) of a total of 55 chemical species without the prior separation step.

Characterization of the ultraviolet–visible photoproducts of thiophanate-methyl using high performance liquid chromatography coupled with high resolution tandem mass spectrometry—Detection in grapes and tomatoes

UV–visible irradiation of thiophanate-methyl (TM) led to the formation of nine photoproducts that were characterized by high performance liquid chromatography coupled with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Although carbendazime has been reported in the literature to be the major metabolite and photoproduct of thiophanate-methyl, it was not detected in this study. However, an isomer of carbendazime referred as PP2, which was unambiguously characterized owing to CID experiments, was found in great abundance. Grape berries and cherry tomatoes treated with aqueous solutions of thiophanate-methyl were submitted to irradiation under laboratory conditions. TM and PP2 were detected in both peel and flesh of berries. The ability of TM and PP2 to pass through the fruit skin has been shown to be highly compound and matrix dependent. In vitro bioassays on Vibrio fischeri bacteria showed that the global ecotoxicity of the TM solution increases significantly with the irradiation time. PP2 should likely contribute to this ecotoxicity enhancement since in silico estimations for Daphnia magna provide a LC50 value seven times lower for PP2 than for the parent molecule.

Timeframe Dependent Fragment Ions Observed in In-Source Decay Experiments with β-Casein Using MALDI MS.

The fragment ions observed with time-of-flight (TOF) and quadrupole ion trap (QIT) TOF mass spectrometers (MS) combined with matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) experiments of phosphorylated analytes β-casein and its model peptide were compared from the standpoint of the residence timeframe of analyte and fragment ions in the MALDI ion source and QIT cell. The QIT-TOF MS gave fragment c-, z'-, z-ANL, y-, and b-ions, and further degraded fragments originating from the loss of neutrals such as H(2)O, NH(3), CH(2)O (from serine), C2H4O (from threonine), and H(3)PO(4), whereas the TOF MS merely showed MALDI source-generated fragment c-, z'-, z-ANL, y-, and w-ions. The fragment ions observed in the QIT-TOF MS could be explained by the injection of the source-generated ions into the QIT cell or a cooperative effect of a little internal energy deposition, a long residence timeframe (140 ms) in the QIT cell, and specific amino acid effects on low-energy CID, whereas the source-generated fragments (c-, z'-, z-ANL, y-, and w-ions) could be a result of prompt radical-initiated fragmentation of hydrogen-abundant radical ions [M + H + H](+) and [M + H - H](-) within the 53 ns timeframe, which corresponds to the delayed extraction time. The further degraded fragment b/y-ions produced in the QIT cell were confirmed by positive- and negative-ion low-energy CID experiments performed on the source-generated ions (c-, z'-, and y-ions). The loss of phosphoric acid (98 u) from analyte and fragment ions can be explained by a slow ergodic fragmentation independent of positive and negative charges.

Role of gold(I) α-oxo carbenes in the oxidation reactions of alkynes catalyzed by gold(I) complexes.

The gas phase structures of gold(I) complexes formed by intermolecular oxidation of selected terminal (phenylacetylene) and internal alkynes (2-butyne, 1-phenylpropyne, diphenylacetylene) were investigated using tandem mass spectrometry and ion spectroscopy in conjunction with quantum-chemical calculations. The experiments demonstrated that the primarily formed β-gold(I) vinyloxypyridinium complexes readily undergo rearrangement, dependent on their substituents, to either gold(I) α-oxo carbenenoids (a synthetic surrogate of the α-oxo carbenes) or pyridine adducts of gold(I) enone complexes in the condensed phase and that the existence of naked α-oxo carbenes is highly improbable. Isotopic labeling experiments performed with the reaction mixtures clearly linked the species that exist in solution to the ions transferred to the gas phase. The ions were then fully characterized by CID experiments and IRMPD spectroscopy. The conclusions based on the experimental observations perfectly correspond with the results from quantum-chemical calculations.

Glycan Side Reaction May Compromise ETD-Based Glycopeptide Identification

Tris(hydroxymethyl)aminomethane (Tris) is one of the most frequently used buffer ingredients. Among other things, it is recommended and is usually used for lectin-based affinity enrichment of glycopeptides. Here we report that sialic acid, a common 'capping' unit in both N- and O-linked glycans may react with this chemical, and this side reaction may compromise glycopeptide identification when ETD spectra are the only MS/MS data used in the database search. We show that the modification may alter N- as well as O-linked glycans, the Tris-derivative is still prone to fragmentation both in 'beam-type' CID (HCD) and ETD experiments, at the same time--since the acidic carboxyl group was 'neutralized'--it will display a different retention time than its unmodified counterpart. We also suggest solutions that--when incorporated into existing search engines--may significantly improve the reliability of glycopeptide assignments.

Matrix‐assisted laser desorption ionization time‐of‐flight/time‐of‐flight tandem mass spectra of biodegradable polybutylenesuccinate

Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight/Time-Of-Flight Tandem Mass Spectrometry (MALDI-TOF MS/MS) was employed to analyze five poly(butylene succinate) (PBSu) oligomers and to investigate their fragmentation pathways. MALDI-TOF MS/MS analysis was performed on cyclic and linear oligomers terminated by dicarboxyl groups, carboxyl and hydroxyl groups, hydroxyl and olefin groups, and dihydroxyl groups. The sodium adduct ions of these oligomers were selected as precursor ions. Experiments were carried out with and without argon as the collision gas. A β-hydrogen transfer rearrangement, leading to the selective cleavage of the -O-CH2- bonds, and cleavage of the -CH2-CO- bonds, the ester bonds, and the -CH2-CH2- bonds in the diol moiety were observed. Two fragmentation mechanisms, correlated to the end-group structure of the precursor ions, were also proposed. The detection of cyclic anhydrides was related to the presence of succinic acid terminal groups. The formation of microcyclic oligoesters probably occurred via an intramolecular transesterification mechanism involving a hydroxyl end group. A β-hydrogen transfer rearrangement has been proposed as the main fragmentation mechanism occurring in PBSu without using the collision gas. Cleavages of almost all types of bonds take place in the MALDI CID experiments. According to the structures of the most abundant product ions, six fragmentation pathways have been proposed when using argon as the collision gas. Two fragmentation mechanisms were suggested as being correlated to the end-group structure of the precursor ions.

Structural analysis and profiling of phenolic secondary metabolites of Mexican lupine species using LC–MS techniques

Flavonoid glycoconjugates from roots and leaves of eight North America lupine species (Lupinus elegans, Lupinus exaltatus, Lupinus hintonii, Lupinus mexicanus, Lupinus montanus, Lupinus rotundiflorus, Lupinus stipulatus, Lupinus sp.), three Mediterranean species (Lupinus albus, Lupinus angustifolius, Lupinus luteus) and one species from South America domesticated in Europe (Lupinus mutabilis) were analyzed using two LC/MS systems: low-resolution ion trap instrument and high-resolution quadrupole-time-of-flight spectrometer. As a result of the LC/MS profiling using the CID/MS(n) experiments structures of 175 flavonoid glycoconjugates found in 12 lupine species were identified at three confidence levels according to the Metabolomic Standard Initiative, mainly at level 2 and 3, some of them were classified to the level 1. Among the flavonoid derivatives recognized in the plant extracts were isomeric or isobaric compounds, differing in the degree of hydroxylation of the aglycones and the presence of glycosidic, acyl or alkyl groups in the molecules. The elemental composition of the glycoconjugate molecules was established from the exact m/z values of the protonated/deprotonated molecules ([M+H](+)/[M-H](-)) measured with the accuracy better than 5 ppm. Information concerning structures of the aglycones, the type of sugar moieties (hexose, deoxyhexose or pentose) and, in some cases, their placement on the aglycones as well as the acyl substituents of the flavonoid glycoconjugates was achieved in experiments, in which collision-induced dissociation was applied. Flavonoid aglycones present in the studied O-glycoconjugates were unambiguously identified after the comparison of the pseudo-MS(3) spectra with the spectra registered for the standards. Isomers of flavonoid glycoconjugates, in which one or two sugar moieties were attached to 4'- or 7-hydroxyl groups or directly to the C-6 or C-8 of the aglycones, could be distinguished on the basis of the MS(2) spectra. However, the collision energy applied in the CID experiments had to be optimized for each group of the compounds and there were no universal settings that allowed the acquisition of structural information for all the compounds present in the sample. Information obtained from the flavonoid conjugate profiling was used for the chemotaxonomic comparison of the studied lupine species. A clear-cut discrimination of the Mediterranean and North American lupines was obtained as a result of this analysis.

Detection of Amine Impurity and Quality Assessment of the MALDI Matrix α-Cyano-4-Hydroxy-Cinnamic Acid for Peptide Analysis in the amol Range

We have studied sample preparation conditions to increase the reproducibility of positive UV-MALDI-TOF mass spectrometry of peptides in the amol range. By evaluating several α-cyano-4-hydroxy-cinnamic acid (CHCA) matrix batches and preparation protocols, it became apparent that two factors have a large influence on the reproducibility and the quality of the generated peptide mass spectra: (1) the selection of the CHCA matrix, which allows the most sensitive measurements and an easier finding of the "sweet spots," and (2) the amount of the sample volume deposited onto the thin crystalline matrix layer. We have studied in detail the influence of a contaminant, coming from commercial CHCA matrix batches, on sensitivity of generated peptide mass spectra in the amol as well as fmol range of a tryptic peptide mixture. The structure of the contaminant, N,N-dimethylbutyl amine, was determined by applying MALDI-FT-ICR mass spectrometry experiments for elemental composition and MALDI high energy CID experiments utilizing a tandem mass spectrometer (TOF/RTOF). A recrystallization of heavily contaminated CHCA batches that reduces or eliminates the determined impurity is described. Furthermore, a fast and reliable method for the assessment of CHCA matrix batches prior to tryptic peptide MALDI mass spectrometric analyses is presented.

Antioxidant, antimicrobial activities and characterization of phenolic compounds from buriti (Mauritia flexuosa L. f.) by UPLC–ESI-MS/MS

Mauritia flexuosa L. f. is a native palm tree from the South American Amazon rainforest commercialized in food, cosmetics and medicine. This paper reported the antioxidant, antimicrobial activities and characterization of phenolics from buriti leafs, trunk and fruit extracts. The total phenolics of the buriti extracts ranged from 378.07±3.12 to 86.89±3.15mg GAEq/100g and flavonoid content ranged from 567.16±1.15 to 246.84±1.11mg QUEREq/100g. The antioxidant activity assays with EC50 of 12.28±0.022 to 19.58±0.064mg/mL revealed the antioxidant capacity of M. flexuosa extracts. Results of the antimicrobial tests against some pathogenic bacteria revealed its strong ability to inhibit the growth of pathogen with low MIC values, where the best results were found with the leaf extract against the pathogen Pseudomonas aeruginosa (MIC 50μg/mL). The characterization of the phenolic compounds using Ultra Performance Liquid Chromatography coupled to Electrospray Ionization Tandem Mass Spectrometry (UPLC–ESI-MS/MS) was based on CID experiments of the observed precursors, thus 13 compounds were tentatively identified ((+)-catechin, caffeic acid hexoside, chlorogenic acid, quercetin, narigenin, myricetin, vitexin, scoparin, rutin, cyanidin-3-rutinoside, cyanidin-3-glucoside, (−)-epicatechin and kaempferol). These results indicate that antioxidant and antimicrobial activities in buriti phenolic extracts are quite potent and implicate the presence of compounds with potent free-radical-scavenging activity.

Intriguing Differences in the Gas-Phase Dissociation Behavior of Protonated and Deprotonated Gonyautoxin Epimers

The aim of this study was to investigate the unusual gas-phase dissociation behavior of two epimer pairs of protonated gonyautoxins (GTX) following electrospray ionization in comparison to their deprotonated counterparts. The chemical structures of the investigated GTX1-4 variants vary in their substitution pattern at N-1 and the stereochemical orientation of the hydroxysulfate group at C-11 (11α for GTX1/2 versus 11β for GTX3/4). The direct comparison of mass spectra in positive and negative ion modes illustrated two distinct features: first, an intriguing difference between protonated 11α and 11β species, where 11α conformations exhibited almost complete dissociation of [M + H](+) ions via facile SO(3) elimination, while 11β species remained mostly intact as [M + H](+); and second, the lack of such differences for the deprotonated counterparts. In this study, we propose an acid-catalyzed elimination mechanism from density functional theory calculations, initiated by a proton transfer of a guanidinium proton to the hydroxysulfate group with simultaneous SO(3) release, which is only possible for the 11α conformation based on intramolecular distances. The same mechanism explains the lack of a comparable SO(3) loss in the negative ion mode. CID experiments supported this proposed mechanism for GTX1 and GTX2. Computational modeling of product ions seen in the CID spectra of GTX3 and GTX4 established that the lowest energy dissociation pathway for the 11β epimers is elimination of water with the possibility for further SO(3) release from the intermediate product. Experimental data for structurally analogous decarbamoyl gonyautoxins confirmed the evidence for the GTX compounds as well as the proposed elimination mechanisms.