Consecutive loss of two benzyl radicals from the [M + Na]+ adduct ions of pyrogallol tribenzyl ether and its derivatives.

The electrospray ionization-collision-induced dissociation mass spectra of nine pyrogallol tribenzyl ethers, 2-10, and a catechol dibenzyl ether, 11, that bear various functional groups or larger structural extensions have been studied with respect to the occurrence of a highly characteristic consecutive loss of two benzyl radicals from the sodiated molecular ions, [M + Na]+. It is shown that this specific fragmentation reaction strongly dominates other fragmentation routes, such as loss of carbon monoxide, formaldehyde and water. In addition, elimination of benzaldehyde occurs as a minor fragmentation channel in most cases. In contrast to these aryl-benzyl ethers, the consecutive two-fold loss of C7H7• is suppressed in the [M + Na]+ ions of dibenzyl ethers derived from multiply benzylated gallocatechin and catechin, where the elimination of benzyl alcohol prevails the primary fragmentation almost completely. The secondary fragmentation of the [M + Na]+ ions, which also comprises the two-fold loss of C7H7•, as well as a remarkable primary fragmentation of a flavene-based congener leading to particularly stable sodium-free chromylium product ions is also presented. † Deceased.

Orthogonal Click Postfunctionalization of Alternating Copolymers Prepared by Nitroxide-Mediated Polymerization.

Nitroxide-mediated polymerization (NMP) was applied to prepare alternating copolymers using 1,1,1,3,3,3-hexafluoroisopropyl acrylate (HFIPA) 1 and ((6-trimethylsilyl)-hex-5-yn-1-yl)vinyl ether (THVE) 2 as monomers. The alternating sequence of the resulting poly(HFIPA-alt-THVE) 3 was proved by using tandem mass spectrometry (MS/MS) and further supported by 1 H NMR spectroscopy. Alternating alkyne and activated ester moieties of copolymer 3 were further functionalized with organic azides and amines using sequential Cu-catalyzed azide-alkyne click (CuAAC) and amidation reactions, providing dually functionalized poly(acrylamide-alt-triazole) polymers 5. Water-soluble alternating poly(acrylic acid-alt-triazole) copolymers 9 were obtained by saponification of HFIP esters. 1 H and 19 F NMR spectroscopy, IR spectroscopy as well as gel permeation chromatography (GPC) were used to characterize the polymers before and after functionalization.

Diastereoselective anodic hetero- and homo-coupling of menthol-, 8-methylmenthol- and 8-phenylmenthol-2-alkylmalonates.

Diastereoselective radical coupling was achieved with chiral auxiliaries. The radicals were generated by anodic decarboxylation of five malonic acid derivatives. These were prepared from benzyl malonates and four menthol auxiliaries. Coelectrolyses with 3,3-dimethylbutanoic acid in methanol at platinum electrodes in an undivided cell afforded hetero-coupling products in 22-69% yield with a diastereoselectivity ranging from 5 to 65% de. Electrolyses without a coacid led to diastereomeric homo-coupling products in 21-50% yield with ratios of diastereomers being 1.17:2.00:0.81 to 7.03:2.00. The stereochemistry of the new stereogenic centers was confirmed by X-ray structure analysis and 13C NMR data.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry imaging of ochratoxin A and fumonisins in mold-infected food.

RATIONALE: Mycotoxins are toxic secondary metabolites produced by various fungi. Their distribution within contaminated material is of high interest to obtain insight into infection mechanisms and the possibility of reducing contamination during food processing. METHODS: Various vegetable foodstuffs were infected with fungi of the genera Fusarium and Aspergillus. The localization of the produced mycotoxins was studied by matrix-assisted laser desorption/ionization time-of flight mass spectrometry imaging (MALDI-MSI) of cryosections obtained from infected material. The results were confirmed by high-performance liquid chromatography/electrospray ionization triple quadrupole mass spectrometry (HPLC/MS/MS). RESULTS: The mycotoxins ochratoxin A (OTA) and fumonisins of the B- and C-series (FB1 , FB2 , FB3 , FB4 , FC1 , FC2/3 , and FC4 ) as well as partially hydrolyzed fumonisins (pHFB1 , pHFB2 , pHFB3 , pHFC1 , and pHFC2/3 ) could successfully be detected by MALDI-MSI in mold-infested foodstuffs. The toxins are distributed differently in the material: OTA is co-localized with visible fungal spoilage while fumonisins could be detected throughout the whole sample. CONCLUSIONS: This work shows the applicability of MALDI-MSI to mycotoxin analysis. It has been demonstrated that the analyzed mycotoxins are differently distributed within moldy foodstuffs. These findings show the potential of MALDI-MSI for the localization of these hazardous compounds in various plant tissues. Copyright © 2016 John Wiley & Sons, Ltd.

Alternating copolymerization by nitroxide-mediated polymerization and subsequent orthogonal functionalization.

A novel method for the preparation of functionalized alternating copolymers is presented. Nitroxide-mediated polymerization of hexafluoroisopropyl acrylate with 7-octenyl vinyl ether provides the corresponding alternating polymer, which can be chemically modified using two orthogonal polymer-analogous reactions. A thiol-ene click reaction followed by amidation provides dual-functionalized alternating copolymers. The potential of this method is illustrated by the preparation of a small library (15 examples) of functionalized alternating copolymers.

Analysis of free fatty acids by ultraviolet laser desorption ionization mass spectrometry using insect wings as hydrophobic sample substrates.

Physiologically relevant free fatty acids (FFAs) were analyzed by UV-laser desorption/ionization orthogonal extracting time-of-flight mass spectrometry (LDI-oTOF-MS). Dissected wings from Drosophila melanogaster fruit flies were used as the hydrophobic, laser energy strongly absorbing sample substrates. Using untreated substrates produces predominantly molecular [M + K](+) ions of the FFAs, whereas other alkali metal adducts can be generated by treating the wings with the corresponding alkali hydroxide before spotting of analyte. Limits of detection for the positive ion mode were determined for mixtures of isolated FFAs to values in the low 10 pmol range. Specific values depend on chain length and degree of unsaturation. R(2) coefficients for the analysis of saturated FFAs were found to be generally close to 0.98 over about 3 orders of magnitude if an internal standard (15:0 FFA) was added. Semiquantitative analyses of mixtures containing unsaturated FFAs are also possible but require more effort on the calibration strategy. Notably, both saturated and (poly-)unsaturated FFAs are detected sensitively in the presence of relatively high concentrations of other physiologically abundant lipids (phospholipids and triacyclglycerols). This simplifies screening of the FFA composition in crude tissue extracts. This feature is demonstrated by the analysis of a crude liver extract and that of fingermarks.

Unidirectional triple hydrogen rearrangement in the radical cations of electron-rich 3-aryl-1-propanols: further evidence and limitation.

The unidirectional triple-hydrogen (3H) rearrangement of the radical cations of 3-aryl-1-propanols bearing an electron-rich substitutent in the para-position was investigated for the diastereomeric 2-(4-dimethylamino)benzylcyclohexanols and 2-(4-dimethylamino)-benzylcyclopentanols and confirmed to be a highly stereospecific feature. Whereas the standard electron ionization (EI) (70 eV) mass spectra of the trans-isomers exhibit very minor (approximately 2%-3%) albeit stereospecific peaks for the relevant C8H13N*+ ions (m/z 123), the metastable ion [mass-analyzed ion kinetic energy (MIKE)] spectra show these peaks with significant relative intensity (8%-17%). The respective cis-isomers do not undergo the 3H rearrangement, be it under standard or under metastable-ion conditions. The stereospecific 3H rearrangement is suppressed in the radical cations of cis- and trans-3-(4-dimethylamino)phenylcyclohexanol, the mass and MIKE spectra of which are governed by cleavage processes of the cyclohexane ring, which impedes the stereochemical assignment of the isomers by mass spectrometry. A multistep mechanism for the unidirectional 3H rearrangement is discussed in view of the present and previous experimental data.

Tamm-Horsfall protein in humane urine: sex-dependent differences in the excretion and N-glycosylation pattern.

Tamm-Horsfall protein (THP) is a highly N-glycosylated protein from epithelial cells of the ascending limb of Henle loop. It is secreted into the urine as part of the innate immune response against uropathogenic pathogens. As women are more likely to suffer from urinary tract infections, biomedical studies were conducted to investigate sex-differences in THP excretion, as well as differences in the THP N-glycosylation pattern. A total of 238 volunteers (92 men, 146 women, 69 with hormonal contraceptives) participated in this study, providing urine samples. Women showed a clear tendency to have higher THP concentration and excretion rates than men (p < 0.16). Regular intake of hormonal contraceptives had no significant influence on urinary THP concentration compared to no regular intake. The individual N-glycosylation pattern of THP in urine samples from randomly selected individuals (10 female, 10 male) was investigated after enzymatic release and MS analysis of the oligosaccharides. Female subjects tended to have an increased proportion of oligomannose type N-glycans and non-fucosylated glycans, whereas men had an increased proportion of fucosylated complex-type glycans. The higher level of oligomannose-type glycans in THP from women might be explained by a self-defence mechanism to overcome the higher infections pressure by the female anatomical properties.

Enantioselective supramolecular devices in the gas phase. Resorcin[4]arene as a model system.

This review describes the state-of-art in the field of the gas-phase reactivity of diastereomeric complexes formed between a chiral artificial receptor and a biologically active molecule. The presented experimental approach is a ligand-displacement reaction carried out in a nano ESI-FT-ICR instrument, supported by a thermodynamic MS-study and molecular-mechanics and molecular-dynamics (MM/MD) computational techniques. The noncovalent ion-molecule complexes are ideal for the study of chiral recognition in the absence of complicating solvent and counterion effects.

Unprecedented gas-phase chiroselective logic gates.

The gas-phase encounters between 2-aminobutane and proton-bound chiral resorcin[4]arene/nucleoside complexes behave in the gas phase as supramolecular "chiroselective logic gates" by releasing the nucleoside depending on the resorcin[4]arene and the 2-aminobutane configurations.

Unprotected Galactosamine as a Dynamic Key for a Cyclochiral Lock.

The discrimination of d-galactosamine (G), representative of the amino-sugar class of compounds, has been probed through nano-ESI-FT-ICR mass spectrometry by isolating the relevant [C·H·G]+ proton-bound complexes with the enantiomers of the cyclochiral resorcin[4]arene C and allowing them to react toward three primary amines (B = EtNH2, iPrNH2, and (R)- and (S)-sBuNH2). The system under investigation presents several features that help to unveil the behavior of unprotected G in such a supramolecular architecture: (i) the hydrophobic derivatization of the C convex side forces the polar guest G to be coordinated by the cyclochiral concave region; (ii) protonated d-galactosamine exists as an anomeric mixture, dynamically interconverting throughout the experimental time-window; and (iii) different basicities of B allow the experiment to subtly tune the reactivity of the [C·H·G]+ complexes. Three [C·H·G]+ aggregate-types were found to exist, differing in both their origin and reactivity. The most reactive adducts ([C·H·G]ESI+), generated in the electrospray environment, undergo a G-to-B ligand exchange in competition with a partial isomerization to the unreactive [C·H·G]GAS+-type complexes. Finally, the poorly reactive [C·H·G]SOL+ aggregates are formed in solution over an hours-long time scale. A cyclochirality effect on the reactivity was found to depend on the considered [C·H·G]+ aggregate-type.

SIRIUS: decomposing isotope patterns for metabolite identification.

MOTIVATION: High-resolution mass spectrometry (MS) is among the most widely used technologies in metabolomics. Metabolites participate in almost all cellular processes, but most metabolites still remain uncharacterized. Determination of the sum formula is a crucial step in the identification of an unknown metabolite, as it reduces its possible structures to a hopefully manageable set. RESULTS: We present a method for determining the sum formula of a metabolite solely from its mass and the natural distribution of its isotopes. Our input is a measured isotope pattern from a high resolution mass spectrometer, and we want to find those molecules that best match this pattern. Our method is computationally efficient, and results on experimental data are very promising: for orthogonal time-of-flight mass spectrometry, we correctly identify sum formulas for >90% of the molecules, ranging in mass up to 1000 Da.

What is the role of acid-acid interactions in asymmetric phosphoric acid organocatalysis? A detailed mechanistic study using interlocked and non-interlocked catalysts.

Organocatalysis has revolutionized asymmetric synthesis. However, the supramolecular interactions of organocatalysts in solution are often neglected, although the formation of catalyst aggregates can have a strong impact on the catalytic reaction. For phosphoric acid based organocatalysts, we have now established that catalyst-catalyst interactions can be suppressed by using macrocyclic catalysts, which react predominantly in a monomeric fashion, while they can be favored by integration into a bifunctional catenane, which reacts mainly as phosphoric acid dimers. For acyclic phosphoric acids, we found a strongly concentration dependent behavior, involving both monomeric and dimeric catalytic pathways. Based on a detailed experimental analysis, DFT-calculations and direct NMR-based observation of the catalyst aggregates, we could demonstrate that intermolecular acid-acid interactions have a drastic influence on the reaction rate and stereoselectivity of asymmetric transfer-hydrogenation catalyzed by chiral phosphoric acids.

Reactions of an anionic chelate phosphane/borata-alkene ligand with [Rh(nbd)Cl]2, [Rh(CO)2Cl]2 and [Ir(cod)Cl]2.

Borata-alkenes can serve as anionic olefin equivalent ligands in transition metal chemistry. A chelate ligand of this type is described and used for metal coordination. Deprotonation of the Mes2P(CH2)2B(C6F5)2 frustrated Lewis pair in the α-CH[B] position gave the methylene-bridged phosphane/borata-alkene anion. It reacted with the [Rh(nbd)Cl] or [Rh(CO)2Cl] dimers to give the respective neutral chelate [P/C[double bond, length as m-dash]B][Rh] complexes. The reaction of the [P/C[double bond, length as m-dash]B]- anion with [Ir(cod)Cl]2 proceeded similarly, only that the complex underwent a subsequent oxidative addition reaction at the mesityl substituent. Both the resulting Ir(iii)hydride complex 15 and the P/borata-alkene Rh system 12 were used as hydrogenation catalysts. The [P/C[double bond, length as m-dash]B(C6F5)2]Rh(nbd) complex 12 served as a catalyst for arylacetylene polymerization.

Interactions of vinca alkaloid subunits with chiral amido[4]resorcinarenes: a dynamic, kinetic, and spectroscopic study.

The stereoselectivity of the reaction between (R)-(-)-2-butylamine and the diastereomeric proton-bound complexes of (+)-catharanthine (C) or (-)-vindoline (V) with some chiral amido[4]resorcinarenes has been investigated in the gas phase by ESI-FT-ICR-MS. The reaction stereoselectivity (0.56 < k(homo)/k(hetero) < 16.9) is found to depend critically on the functional groups present in the chiral pendants of the hosts. Rationalisation of the kinetic results is based on careful computational and spectroscopic studies of the most stable conformations of (+)-catharanthine and its protonated form in the isolated state and in water, as well as in a representative host structure. The emerging picture points to the relevant diastereomeric proton-bound complexes as quasi-degenerate, thus suggesting that their stereoselectivity in the guest exchange reaction is mostly due to kinetic factors. The results of this study may represent a starting point for a deeper comprehension of the intrinsic factors that endow these molecules, and their dimeric forms, with their biochemical properties.

Gas-phase enantioselectivity of chiral N-linked peptidoresorc[4]arene isomers toward dipeptides.

The gas-phase enantioselectivity of cone N-linked peptidoresorc[4]arenes (generally symbolized as M) toward the homologue dipeptides (generally symbolized as A) has been evaluated by measuring the kinetics of the A release from the diastereomeric [M x H x A](+) complexes induced by (R)-(-)-2-butylamine (B). In most cases investigated, the heterochiral [M x H x A](+) complexes, namely those wherein the configuration of the A guest is opposite to that of the host M pendants, react faster (up to 5 times) than the homochiral analogues, wherein guest A guest has the same configuration of the host M pendants. The kinetic results, discussed in the light of previous MS and NMR evidence, indicate that both the efficiency and the enantioselectivity of the guest exchange reaction depend essentially on the structure and the relative stability of the diastereomeric [M x H x A](+) complexes. These, in turn, depend on the functional groups and the configuration of both the guest and the host pendants. The absence of any significant effects of the B configuration indicates that, in all systems investigated, the dipeptide guest A is predominantly located outside the host chiral cavity.

Energetics and reaction mechanisms for the competitive losses of H2, CH4 and C2H4 from protonated methylbenzenes--implications to the methanol- to-hydrocarbons (MTH) process.

We report the unimolecular decomposition following collisional activation of protonated mono-, di- and trimethylbenzenes as a function of collision energy. The resulting energy-resolved mass spectra are then used for the quality control of high-level quantum chemical models of the respective potential energy surfaces. Distinction is made between direct dissociation products (CH(4) or H(2)) and indirect products (alkenes), since formation of the latter requires extensive rearrangement of the molecular skeleton. Very good consistency was found between model and experiment. The models thereby provide a solid foundation for discussing the reaction mechanisms of the industrial methanol-to-hydrocarbon process. The losses of CH(4), C(2)H(4) and C(3)H(6) from mesitylenium ions have been studied by (13)C and (2)H labelling and the alkene losses were found to occur via irreversible isomerisation pathways.

A kinetic study of guest displacement reactions on a host-guest complex with a photoswitchable calixarene.

The displacement processes of several guests, incorporated in a calixarene host system, were investigated in the gas phase by electrospray ionization-Fourier transform-ion cyclotron resonance (ESI-FT-ICR) mass spectrometry. The complexes resulting from a resorcin[4]arene host with ammonia and sec-butylamine guests were isolated in an ICR-cell, separately using both states of the photoswitch as well as two reference systems for the open and closed forms of the photoswitchable host. The isolated complexes were forced to exchange the guest by using methylamine, ethylamine and sec-butylamine, resulting in different reaction rates for all the measured systems. Especially, the reaction rates of both states of the photoswitch are dependent on the provided guest. Potential side effects like proton exchanges were examined by an H/D-exchange experiment. The results were investigated and supported by quantum chemical calculations (DFT).

Chemical Modification and Detoxification of the Pseudomonas aeruginosa Toxin 2-Heptyl-4-hydroxyquinoline N-Oxide by Environmental and Pathogenic Bacteria.

2-Heptyl-4-hydroxyquinoline N-oxide (HQNO), a major secondary metabolite and virulence factor produced by the opportunistic pathogen Pseudomonas aeruginosa, acts as a potent inhibitor of respiratory electron transfer and thereby affects host cells as well as microorganisms. In this study, we demonstrate the previously unknown capability of environmental and pathogenic bacteria to transform and detoxify this compound. Strains of Arthrobacter and Rhodococcus spp. as well as Staphylococcus aureus introduced a hydroxyl group at C-3 of HQNO, whereas Mycobacterium abscessus, M. fortuitum, and M. smegmatis performed an O-methylation, forming 2-heptyl-1-methoxy-4-oxoquinoline as the initial metabolite. Bacillus spp. produced the glycosylated derivative 2-heptyl-1-(ß-d-glucopyranosydyl)-4-oxoquinoline. Assaying the effects of these metabolites on cellular respiration and on quinol oxidase activity of membrane fractions revealed that their EC50 values were up to 2 orders of magnitude higher than that of HQNO. Furthermore, cellular levels of reactive oxygen species were significantly lower in the presence of the metabolites than under the influence of HQNO. Therefore, the capacity to transform HQNO should lead to a competitive advantage against P. aeruginosa. Our findings contribute new insight into the metabolic diversity of bacteria and add another layer of complexity to the metabolic interactions which likely contribute to shaping polymicrobial communities comprising P. aeruginosa.