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Native mass spectrometry of membrane proteins relies on non-ionic detergents which protect the protein during transfer from solution into the gas phase. Once in the gas phase, the detergent micelle must be efficiently removed, which is usually achieved by collision-induced dissociation (CID). Recently, infrared multiple photon dissociation (IRMPD) has emerged as an alternative activation method for the analysis of membrane proteins, which has led to a growing interest in detergents that efficiently absorb infrared light. Here we investigate whether the absorption properties of synthetic detergents can be tailored by merging structural motifs of existing detergents into new hybrid detergents. We combine gas-phase infrared ion spectroscopy with density functional theory to investigate and rationalize the absorption properties of three established detergents and two hybrid detergents with fused headgroups. We show that, although the basic intramolecular interactions in the parent and hybrid detergents are similar, the three-dimensional structures differ significantly and so do the infrared spectra. Our results outline a roadmap for guiding the synthesis of tailored detergents with computational chemistry for future mass spectrometry applications., (© 2024 The Authors. ChemPlusChem published by Wiley-VCH GmbH.)

Mirrors for atoms and molecules are essential tools for matter-wave optics with neutral particles. Their realization has required either a clean and atomically smooth crystal surface, sophisticated tailored electromagnetic fields, nanofabrication, or particle cooling because of the inherently short de Broglie wavelengths and strong interactions of atoms with surfaces. Here, we demonstrate reflection of He atoms from inexpensive, readily available, and robust gratings designed for light waves. Using different types of blazed gratings with different periods, we study how microscopic and macroscopic grating properties affect the mirror performance. A holographic grating with 417 nm period shows reflectivity up to 47% for He atoms, demonstrating that commercial gratings can serve as mirrors for thermal energy atoms and molecules. We also observe reflection of He 2 and He 3 which implies that the grating might also function as a mirror for other breakable particles that, under typical conditions, do not scatter nondestructively from a solid surface such as, e.g. , metastable atoms or antihydrogen atoms.

Rotationally resolved vibrational spectra of DyO and DyO + in a molecular beam are obtained by IR excitation from the X8 ground state and from high- n Rydberg states of DyO using an infrared free electron laser. Vibrational excitation is detected either by resonance enhanced multiphoton ionisation from X8( v = 1) or by autoionisation of Rydberg states converging to DyO + ( v = 1). For most heavy molecules, the large spectral width of an infrared free electron laser does not allow for rotational resolution. In DyO and DyO + the P, Q, and R transitions can be resolved due to the high angular momentum in their ground states. For 164 DyO a vibrational constant of ω e = 847.5(2) cm -1 and a vibrational anharmonicity of ω e χ e = 2.9(1) cm -1 are deduced. For the 161 DyO + cation a transition frequency of Δ G 1/2 = 907(1) cm -1 is found.

Tandem mass spectrometry is routinely used for the structural analysis of organic molecules, but many fragmentation reactions are not well understood. Because several potential structures can correspond to a measured mass, the assignment of product ions is ambiguous using mass spectrometry alone. Here, we combine mass spectrometry with high-resolution gas-phase infrared spectroscopy and computational chemistry tools to identify product ion structures and derive collision-induced fragmentation mechanisms of the chromane derivatives Trolox and Methyltrolox. We find that protonated Trolox and Methyltrolox fragment identically via dehydration and decarbonylation, while deprotonated ions display substantially diverging reactivities. For deprotonated Methyltrolox, we observe unusual radical fragmentation reactions and suggest a [1,2]-Wittig rearrangement involving aryl migration in the gas phase. Overall, the combined experimental and theoretical approach presented here revealed complex proton dynamics and intramolecular rearrangement reactions, which expand our understanding on structure-reactivity relationships of isolated molecules in different protonation states.

A series of saturated ruthenium cluster carbonyls (Ru(CO) 5 + , Ru 2 (CO) 9 + , Ru 3 (CO) 12 + , Ru 4 (CO) 14 + , Ru 5 (CO) 16 + and Ru 6 (CO) 18 + ) have been synthesized in the gas phase and subsequently characterized by infrared spectroscopy. Their size-specific IR spectra in the region of the carbonyl stretch vibration (1900-2150 cm -1 ) and in the region of the Ru-C-O bending modes (420-620 cm -1 ) are obtained by infrared multiple photon dissociation spectroscopy. The structures of these cluster carbonyls are assigned by comparison with results from density functional calculations. A multitude of differently activated CO ligands are identified in these cationic cluster carbonyls, reaching from terminal, over non-symmetrically bridging (semi-bridging) ligands with varying degrees of interaction to additional Ru atoms towards symmetrically bridging CO ligands.

Hydrogen bonding interactions are essential in the structural stabilization and physicochemical properties of complex molecular systems, and carboxylic acid functional groups are common participants in these motifs. Consequently, the neutral formic acid (FA) dimer has been extensively investigated in the past, as it represents a useful model system to investigate proton donor-acceptor interactions. The analogous deprotonated dimers, in which two carboxylate groups are bound by a single proton, have also served as informative model systems. In these complexes, the position of the shared proton is mainly determined by the proton affinity of the carboxylate units. However, very little is known about the nature of the hydrogen bonding interactions in systems containing more than two carboxylate units. Here we report a study on the deprotonated (anionic) FA trimer. IR spectra are recorded in the 400-2000 cm -1 spectral range by means of vibrational action spectroscopy of FA trimer ions embedded in helium nanodroplets. Characterization of the gas-phase conformer and assignment of the vibrational features is achieved by comparing the experimental results with electronic structure calculations. To assist in the assignments, the 2 H and 18 O FA trimer anion isotopologues are also measured under the same experimental conditions. Comparison between the experimental and computed spectra, especially the observed shifts in spectral line positions upon isotopic substitution of the exchangeable protons, suggests that the prevalent conformer, under the experimental conditions, exhibits a planar structure that resembles the crystalline structure of formic acid.

We report on cluster-mediated C-N bond formation in the gas phase using N 2 as a nitrogen source. The V 3 C + +N 2 reaction is studied by a combination of ion-trap mass spectrometry with infrared photodissociation (IRPD) spectroscopy and complemented by electronic structure calculations. The proposed reaction mechanism is spectroscopically validated by identifying the structures of the reactant and product ions. V 3 C + exhibits a pyramidal structure of C 1 -symmetry. N 2 activation is initiated by adsorption in an end-on fashion at a vanadium site, followed by spontaneous cleavage of the N≡N triple bond and subsequent C-N coupling. The IRPD spectrum of the metal nitride product [NV 3 (C=N)] + exhibits characteristic C=N double bond (1530 cm -1 ) and V-N single bond (770, 541 and 522 cm -1 ) stretching bands., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Fatty acids are an abundant class of lipids that are characterised by wide structural variation including isomeric diversity arising from the position and configuration of functional groups. Traditional approaches to fatty acid characterisation have combined chromatography and mass spectrometry for a description of the composition of individual fatty acids while infrared (IR) spectroscopy has provided insights into the functional groups and bond configurations at the bulk level. Here we exploit universal 3-pyridylcarbinol ester derivatization of fatty acids to acquire IR spectra of individual lipids as mass-selected gas-phase ions. Intramolecular interactions between the protonated pyridine moiety and carbon-carbon double bonds present highly sensitive probes for regiochemistry and configuration through promotion of strong and predictable shifts in IR resonances. Gas-phase IR spectra obtained from unsaturated fatty acids are shown to discriminate between isomers and enable the first unambiguous structural assignment of 6 Z -octadecenoic acid in human-derived cell lines. Compatibility of 3-pyridylcarbinol ester derivatization with conventional chromatography-mass spectrometry and now gas-phase IR spectroscopy paves the way for comprehensive structure elucidation of fatty acids that is sensitive to regio- and stereochemical variations and with the potential to uncover new pathways in lipid metabolism., Competing Interests: SJB holds patents on ozone-induced dissociation technology (A method for the determination of the position of unsaturation in a compound, US8242439 and US7771943). The work presented in this publication was supported in-part through funding from Waters Corporation and the Australian Research Council through the Linkage Partnership Scheme (LP18010023)., (This journal is © The Royal Society of Chemistry.)

We report on a method of enhanced elastic and coherent reflection of 4 He 2 and 4 He 3 from a micro-structured solid surface under grazing incidence conditions. The van der Waals bound ground-state helium clusters exhibit fundamental quantum effects: 4 He 2 , characterized by a single ro-vibrational bound state of 10 -7 eV dissociation energy, is known to be a quantum halo state; and 4 He 3 is the only electronic ground-state triatomic system possessing an Efimov state in addition to the ro-vibrational ground state. Classical methods to select and manipulate these clusters by interaction with a solid surface fail due to their exceedingly fragile bonds. Quantum reflection under grazing incidence conditions was demonstrated as a viable tool for elastic scattering from a solid surface but suffers from small reflection probabilities for typical conditions. Here we demonstrate that multiple-edge diffraction enables enhanced elastic scattering of the clusters from a solid. A dual-period reflection grating, where the strips consist of micro-structured edge arrays, shows an up to ten fold increased reflection probability as compared to its conventional counterpart where the strips are plane patches enabling quantum reflection of the clusters. The observed diffraction patterns of the clusters provide evidence of the coherent and elastic nature of scattering by multiple-edge diffraction.

The gas-phase reaction of NiAl 2 O 4 + with CH 4 is studied by mass spectrometry in combination with vibrational action spectroscopy and density functional theory (DFT). Two product ions, NiAl 2 O 4 H + and NiAl 2 O 3 H 2 + , are identified in the mass spectra. The DFT calculations predict that the global minimum-energy isomer of NiAl 2 O 4 + 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 (CH 3 ⋅) or formaldehyde (CH 2 O). Both reactions are initiated by hydrogen atom transfer from methane to the terminal O .- site, followed by either CH 3 ⋅ loss or CH 3 ⋅ migration to an O 2- site next to the Ni 2+ center. The CH 3 ⋅ attaches as CH 3 + to O 2- 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., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Single-atom (SA) catalysis presently receives much attention with its promise to decrease the cost of the active material while increasing the catalyst's performance. However, key details such as the exact location of SA species and their stability are often unclear due to a lack of atomic level information. Here, we show how vibrational spectra measured with surface action spectroscopy (SAS) and density functional theory (DFT) simulations can differentiate between different adatom binding sites and determine the location of Ni and Au single atoms on Fe 3 O 4 (001). We reveal that Ni and Au adatoms selectively bind to surface oxygen ions which are octahedrally coordinated to Fe ions. In addition, we find that the Ni adatoms can activate O 2 to superoxide in contrast to the bare surface and Ni in subsurface positions. Overall, we unveil the advantages of combining SAS and DFT for improving the understanding of single-atom catalysts., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)