Gas-Phase Mechanism of O^.-/Ni²⁺-Mediated Methane Conversion to Formaldehyde

The gas-phase reaction of NiAl2O4+ with CH4 is studied by mass spectrometry in combination with vibrational action spectroscopy and density functional theory (DFT). Two product ions, NiAl2O4H+ and NiAl2O3H2+, are identified in the mass spectra. The DFT calculations predict that the global minimum-energy isomer of NiAl2O4+ contains Ni in the +II oxidation state and features a terminal Al−O.- oxygen radical site. They show that methane can react along two competing pathways leading to formation of either a methyl radical (CH3⋅) or formaldehyde (CH2O). Both reactions are initiated by hydrogen atom transfer from methane to the terminal O.- site, followed by either CH3⋅ loss or CH3⋅ migration to an O2- site next to the Ni2+ center. The CH3⋅ attaches as CH3+ to O2- and its unpaired electron is transferred to the Ni-center reducing it to Ni+. The proposed mechanism is experimentally confirmed by vibrational spectroscopy of the reactant and two different product ions

Gas-Phase Mechanism of O^.-/Ni²⁺-Mediated Methane Conversion to Formaldehyde

The gas-phase reaction of NiAl2O4+ with CH4 is studied by mass spectrometry in combination with vibrational action spectroscopy and density functional theory (DFT). Two product ions, NiAl2O4H+ and NiAl2O3H2+, are identified in the mass spectra. The DFT calculations predict that the global minimum-energy isomer of NiAl2O4+ contains Ni in the +II oxidation state and features a terminal Al−O.- oxygen radical site. They show that methane can react along two competing pathways leading to formation of either a methyl radical (CH3⋅) or formaldehyde (CH2O). Both reactions are initiated by hydrogen atom transfer from methane to the terminal O.- site, followed by either CH3⋅ loss or CH3⋅ migration to an O2- site next to the Ni2+ center. The CH3⋅ attaches as CH3+ to O2- and its unpaired electron is transferred to the Ni-center reducing it to Ni+. The proposed mechanism is experimentally confirmed by vibrational spectroscopy of the reactant and two different product ions

Cryogenic infrared spectroscopy provides mechanistic insight into the fragmentation of phospholipid silver adducts

Tandem mass spectrometry is arguably the most important analytical tool for structure elucidation of lipids and other metabolites. By fragmenting intact lipid ions, valuable structural information such as the lipid class and fatty acyl composition are readily obtainable. The information content of a fragment spectrum can often be increased by the addition of metal cations. In particular, the use of silver ions is deeply rooted in the history of lipidomics due to their propensity to coordinate both electron-rich heteroatoms and C = C bonds in aliphatic chains. Not surprisingly, coordination of silver ions was found to enable the distinction of sn-isomers in glycerolipids by inducing reproducible intensity differences in the fragment spectra, which could, however, not be rationalized. Here, we investigate the fragmentation behaviors of silver-adducted sn- and double bond glycerophospholipid isomers by probing fragment structures using cryogenic gas-phase infrared (IR) spectroscopy. Our results confirm that neutral headgroup loss from silver-adducted glycerophospholipids leads to dioxolane-type fragments generated by intramolecular cyclization. By combining high-resolution IR spectroscopy and computational modelling of silver-adducted fragments, we offer qualitative explanations for different fragmentation behaviors of glycerophospholipid isomers. Overall, the results demonstrate that gas-phase IR spectroscopy of fragment ions can significantly contribute to our understanding of lipid dissociation mechanisms and the influence of coordinating cations

Inelastic Diffraction and Spectroscopy of Very Weakly Bound Clusters

We study the coherent inelastic diffraction of very weakly bound two body clusters from a material transmission grating. We show that internal transitions of the clusters can lead to new separate peaks in the diffraction pattern whose angular positions determine the excitation energies. Using a quantum mechanical approach to few body scattering theory we determine the relative peak intensities for the diffraction of the van der Waals dimers (D_2)_2 and H_2-D_2. Based on the results for these realistic examples we discuss the possible applications and experimental challenges of this coherent inelastic diffraction technique.Comment: 15 pages + 5 figures. J. Phys. B (in press

Auswirkung der EMV-Anforderungen auf den Netzteilentwurf für Modellbahnsysteme

Klassische Modellbahnsysteme werden mittels eines Streufeldtransformators zur Netztrennung versorgt. Für Systeme mit Gleichspannung wird ein Gleichrichter zwischen dem regelbaren Trafoausgang geschaltet, für Wechselspannungssysteme entfällt dieser. Der Transformator dient gleichzeitig zur Stellung der Ausgangsspannung und damit der Fahrgeschwindigkeit sowie zur Versorgung von weiteren Lasten (Weichenantrieb, Beleuchtung). An den entsprechenden Ausgängen wird die Gleisanlage angeschlossen, auf der eine oder mehrere Lokomotiven durch Kleinmaschinen mit Bürsten angetrieben werden. Die auftretenden EMV-Störungen werden hierbei vom Strom über die Bürsten des Motors, dem Stromfluss innerhalb der Lokomotive über sich drehende Teile des Getriebes oder des Gestänges sowie dem Stromfluss über den Rad-Schiene-Kontakt erzeugt. Der Transformator selbst erzeugt, den Einfluss des Gleichrichters ausgenommen, keine EMV-Störungen. Er dient vielmehr als Filterelement zum Netz hin. Diese Rundfunkstörungen sorgen seit der Existenz des Modellbahnsystems zu Komplikationen mit dem Rundfunk im Frequenzbereich der Mittelwelle, der in Deutschland jedoch an Bedeutung verloren hat. Aus diesem Grund wurde im letzten Jahrhundert eine Messung der Funkstörspannungen am Gleis gegenüber PE mit einem Tastkopf in den EMV-Normen aufgenommen, die immer noch Bestand hat (1). In der Norm ist nicht spezifiziert, an welcher Stelle am Gleis oder auf welchem Leitungsabschnitt die Störspannung erfasst werden muss. Der Messpunkt wird vom jeweiligen Prüfer bestimmt

Unveiling Glycerolipid Fragmentation by Cryogenic Infrared Spectroscopy

Mass spectrometry is routinely employed for structure elucidation of molecules. Structural information can be retrieved from intact molecular ions by fragmentation; however, the interpretation of fragment spectra is often hampered by poor understanding of the underlying dissociation mechanisms. For example, neutral headgroup loss from protonated glycerolipids has been postulated to proceed via an intramolecular ring closure but the mechanism and resulting ring size have never been experimentally confirmed. Here we use cryogenic gas-phase infrared (IR) spectroscopy in combination with computational chemistry to unravel the structures of fragment ions and thereby shed light on elusive dissociation mechanisms. Using the example of glycerolipid fragmentation, we study the formation of protonated five-membered dioxolane and six-membered dioxane rings and show that dioxolane rings are predominant throughout different glycerolipid classes and fragmentation channels. For comparison, pure dioxolane and dioxane ions were generated from tailor-made dehydroxyl derivatives inspired by natural 1,2- and 1,3-diacylglycerols and subsequently interrogated using IR spectroscopy. Furthermore, the cyclic structure of an intermediate fragment occurring in the phosphatidylcholine fragmentation pathway was spectroscopically confirmed. Overall, the results contribute substantially to the understanding of glycerolipid fragmentation and showcase the value of vibrational ion spectroscopy to mechanistically elucidate crucial fragmentation pathways in lipidomics

Decoherence in a Talbot Lau interferometer: the influence of molecular scattering

We study the interference of C70 fullerenes in a Talbot-Lau interferometer with a large separation between the diffraction gratings. This permits the observation of recurrences of the interference contrast both as a function of the de Broglie wavelength and in dependence of the interaction with background gases. We observe an exponential decrease of the fringe visibility with increasing background pressure and find good quantitative agreement with the predictions of decoherence theory. From this we extrapolate the limits of matter wave interferometry and conclude that the influence of collisional decoherence may be well under control in future experiments with proteins and even larger objects.Comment: 8 pages, 5 figure

The size of two-body weakly bound objects : short versus long range potentials

The variation of the size of two-body objects is investigated, as the separation energy approaches zero, with both long range potentials and short range potentials having a repulsive core. It is shown that long range potentials can also give rise to very extended systems. The asymptotic laws derived for states with angular momentum l=1,2 differ from the ones obtained with short range potentials. The sensitivity of the asymptotic laws on the shape and length of short range potentials defined by two and three parameters is studied. These ideas as well as the transition from the short to the long range regime for the l=0 case are illustrated using the Kratzer potential.Comment: 5 pages, 3 figures, submitted to Physical Review Letter

Studying the Key Intermediate of RNA Autohydrolysis by Cryogenic Gas-Phase Infrared Spectroscopy

Over the course of the COVID-19 pandemic, mRNA-basedvaccineshave gained tremendous importance. The development and analysis of modified RNA moleculesbenefit from advanced mass spectrometry and require sufficient understanding of fragmentation processes.Analogous tothe degradation of RNA in solution by autohydrolysis,backbone cleavage of RNA strands wasequally observedin the gas phase; however, the fragmentation mechanism remained elusive.In this work,autohydrolysis-like intermediates weregenerated from isolated RNA dinucleotidesin the gas phaseand investigatedusing cryogenic infrared spectroscopy in helium nanodroplets.Data from both experiment and density functional theory provide evidence forthe formation of a five-membered cyclic phosphateintermediateand rule outlinear orsix-membered structures. Furthermore, the experiments show that another prominent condensed-phase reactionof RNA nucleotides can be induced in the gas phase: the tautomerization of cytosine.Both observed reactions aretherefore highlyuniversal and intrinsic properties of the investigated molecules