123 research outputs found
Decomposing metabolomic isotope patterns
No full textBöcker S, Pervukhin A, Lipták Z, Letzel M. Decomposing metabolomic isotope patterns. In: Bücher P, ed. Proc. WABI. Lecture notes in computer science ; 4175 : Lecture notes in bioinformatics. Vol 4175. Berlin, Heidelberg: Springer Berlin Heidelberg; 2006: 12-23
Enantioselective supramolecular devices in the gas phase. Resorcin[4] arene as a model system
No full textFraschetti C, Letzel M, Filippi A, Speranza M, Mattay J. Enantioselective supramolecular devices in the gas phase. Resorcin[4] arene as a model system. Beilstein Journal of Organic Chemistry. 2012;8:539-550.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
Cyclochiral resorcin[4]arenes as effective enantioselectors in the gas phase
No full textFraschetti C, Letzel M, Paletta M, et al. Cyclochiral resorcin[4]arenes as effective enantioselectors in the gas phase. Journal of Mass Spectrometry. 2012;47(1):72-78.The effect of cyclochirality of rccc-2,8,14,20-tetra-n-decyl-4,10,16,22-tetra-O-methylresorcin[4]arene (C) on the enantiodiscrimination of a number of chiral bidentate and tridentate aromatic and aliphatic biomolecules (G) has been investigated by nano-electrospray ionization (nano-ESI)-Fourier transform ion cyclotron resonance mass spectrometry. The experimental approach is based on the formation of diastereomeric proton-bound [C center dot H center dot G](+) complexes by nano-ESI of solutions containing an equimolar amount of quasi-enantiomers (C) together with the chiral guest (G) and the subsequent measurement of the rate of the G substitution by the attack of several achiral and chiral amines. In general, the heterochiral complexes react faster than the homochiral ones, except when G is an aminoalcoholic neurotransmitter whose complexes, beyond that, exhibit the highest enantioselectivity. The kinetic results were further supported by both collision-induced dissociation experiments on some of the relevant [C-2 center dot H center dot G](+) three-body species and Density functional theory (DFT) calculations performed on the most selective systems. Copyright (C) 2012 John Wiley & Sons, Ltd
Unprotected Galactosamine as a Dynamic Key for a Cyclochiral Lock.
No full textFraschetti C, Letzel MC, Paletta M, et al. Unprotected Galactosamine as a Dynamic Key for a Cyclochiral Lock. Journal of the American Society for Mass Spectrometry. 2021.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
A kinetic study of guest displacement reactions on a host-guest complex with a photoswitchable calixarene
No full textLetzel M, Schäfer C, Novara FR, et al. A kinetic study of guest displacement reactions on a host-guest complex with a photoswitchable calixarene. Journal of Mass Spectrometry. 2008;43(11):1553-1564.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 photos-witch 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). Copyright (C) 2008 John Wiley & Sons, Ltd
Calibration of electrospray mass spectrometers with rccc-2,8,14,20-tetra-n-octyl-5,11,17,23-tetrahydroxyresorc[4]arene in the high mass range up to m/z 6000
No full textLetzel M, Agena C, Mattay J. Calibration of electrospray mass spectrometers with rccc-2,8,14,20-tetra-n-octyl-5,11,17,23-tetrahydroxyresorc[4]arene in the high mass range up to m/z 6000. EUROPEAN JOURNAL OF MASS SPECTROMETRY. 2001;7(1):35-38.rccc-2,8,14,20-Tetra-n-octyl-5,11,17,23-tetrahydroxyresorc[4]arene has the property to form cluster ions in both positive- and negative-ion mode with good intensity without the addition of any modifiers such as cesium. These cluster ions may be used for the calibration of electrospray mass spectrometers in the mass range up to m/z 6000
Inhibition of furin by serpin Spn4A from Drosophila melanogaster
No full textOley M, Letzel M, Ragg H. Inhibition of furin by serpin Spn4A from Drosophila melanogaster. FEBS Letters. 2004;577(1-2):165-169.The serpin gene Spn4 from Drosophila melanogaster encodes multiple isoforms with alternative reactive site loops (RSL). Here, we show that isoform Spn4A inhibits human furin with an apparent k(assoc) of 5.5 x 10(6) M-1 s(-1). The serpin forms SDS-stable complexes with the enzyme and the RSL of Spn4A is cleaved C-terminally to the sequence -Arg-Arg-Lys-Argdown arrow in accord with the recognition/cleavage site of furin. Immunofluorescence studies show that Spn4A is localized in the endoplasmic reticulum (ER), suggesting that the inhibitor is an interesting tool for investigating the cellular mechanisms regulating furin and for the design of agents controlling prohormone convertases. (C) 2004 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved
A self-assembling metallosupramolecular cage based on cavitand-terpyridine subunits
No full textSchröder T, Brodbeck R, Letzel M, et al. A self-assembling metallosupramolecular cage based on cavitand-terpyridine subunits. TETRAHEDRON LETTERS. 2008;49(41):5939-5942.Metal-directed self-assembly of a terpyridyl-functionalized cavitand yields a large hexameric coordination cage. (C) 2008 Elsevier Ltd. All rights reserved
Calixarenes as hosts for ammonium cations: A quantum chemical study and mass-spectrometric investigations
No full textRozhenko AB, Schoeller W, Letzel M, Decker B, Agena C, Mattay J. Calixarenes as hosts for ammonium cations: A quantum chemical study and mass-spectrometric investigations. Chemistry. A European Journal. 2006;12(35):8995-9000.Host-guest complexes of tetramethylcavitand with different ammonium cations were investigated by using a quantum chemical method at the density func tional level (BP86, B3LYP). The NH4+ cation is strongly bound to the host. Increasing creasing methyl substitution at the cation decreases its inclination towards the complex formation. The calculated data are in line with results from electrospray ionization mass spectrometry (ESI-MS) experiments. They reveal stable aggregates only for the NH4+ cation and for the primary alkylammonium cations
Chiral discrimination on the host-guest complexation of resorc[4]arenes with quarternary amines
No full textMehdizadeh A, Letzel M, Klaes M, Agena C, Mattay J. Chiral discrimination on the host-guest complexation of resorc[4]arenes with quarternary amines. EUROPEAN JOURNAL OF MASS SPECTROMETRY. 2004;10(1):649-655.The interaction of inherently chiral resorc[4]arenes with different chiral ammonium ions was measured by electrospray ionization mass spectrometry. For this purpose, one enantiomer of the ammonium guests was labeled with deuterium to distinguish the enantiomers by their mass. We synthesized the ammonium salts by the reaction of chiral primary amines with either CH3I or CD3I and analyzed the resulting ammonium iodides by nuclear magnetic resonance and optical rotation. The complexation experiments were performed by mixing the chiral host with various ratios of the unlabeled guest and its labeled enantiomer. By analyzing the integrals of the host-guest complexes, we observed a chiral discrimination effect and a secondary isotope effect as well
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