In the last twenty years, the "roaming atom" mechanism emerged and gained enormous interest thanks to its success in explaining experimental results that are not accounted for by the widely accepted statistical transition state theory. However, despite intense efforts for describing this new mechanism, intriguing questions remain. A crucial one is: does it play a role in molecular systems larger than 25 atoms, in particular those relevant to life sciences and pharmacology? Here, we present data on HCl transfer within a noncovalent complex built upon vancomycin, an antibiotic containing more than 170 atoms, and a tripeptide, following UV-VUV photoabsorption in the gas phase. In this molecular system, the experimental energetics of HCl formation is incompatible with the values obtained by quantum-chemical calculations, assuming a straightforward mechanism governed by the transition state. Instead, our results are consistent with a roaming mechanism.

So-called grandPAH molecules are proposed to be omnipresent in various interstellar regions as they are large enough to be photostable against strong interstellar radiation fields. They are also notoriously difficult to synthesize and sublimate. Measuring their gas phase spectra and molecular properties is thus very difficult. We report on the experimental photoionization of a defined grandPAH cation (C_60H_18(C_12H_25)_4 1415 amu). The molecule consists of a large PAH containing 60 sp^2 carbon atoms and four long alkyl groups (-C_12H_25) attached to peripheral positions. The alkyl chains wrap around the aromatic core and stabilize the dication leading to a lowering of the ionization energy. m/z The ion yield spectrum of the grandPAH was recorded from 8.1 to 25 eV using an ion trap coupled to vacuum-ultraviolet (VUV) synchrotron radiation. To accurately extrapolate the experimental results toward the unsubstituted grandPAH itself, we perform a series of calculations to quantify this lowering of the ionization energy. The adiabatic ionization energy of the grandPAH cation was determined as 8.50 ± 0.35 eV. This dual experimental and theoretical methodology can be used to perform other spectroscopic measurements of large, alkylated PAHs to extract properties of the unsubstituted PAH. The implications of these results are discussed in the context of the behavior of large PAHs in interstellar and/or interplanetary dust particles as well as PAH units embedded in insoluble organic material which are found in meteorites.

Photon activation is a powerful means of inducing controlled fragmentation in mass spectrometry, but the simultaneous activation of multiple precursor ions may produce multiplexed tandem mass spectra that are difficult to interpret. In this work, we show that such photon-activated multiple precursor spectra can be decomposed into individual precursor contributions using correlation-based and information-theoretic approaches. We propose a general, data-driven framework for the statistical resolution of multiplexed photon-activated MS/MS spectra based on the statistical treatment of the spectra followed by clustering analysis. This approach allows statistical tandem mass spectra to be obtained without prior knowledge of the precursor identities.

RATIONALE:Poly (acrylates)s can be distinguished from one another by the nature of their side chains. From model poly (acrylates)s, the purpose of this work was to evaluate the contribution of alternative activation techniques to the collisional activation, based on ion-ion and ion-photon interactions. METHODS:Sodiated poly (acrylate)s produced by electrospray were isolated in an ion trap and then submitted to interactions with fluoranthene anions (by electron transfer dissociation) or with UV photons (from a synchrotron UV source, 16 eV) to induce gas-phase decomposition. The resulting fragmentation pathways were investigated and compared with collision-induced dissociation (CID). Ion mobility spectrometry was coupled to UV photoactivation for some isobaric species. RESULTS:Electron capture from fluoranthene anions or electron loss under synchrotron UV irradiation induced dissociation that differs from CID. A coupling of ion mobility with UV photoactivation allowed the fragmentation of two isobaric species separately. CONCLUSIONS:The decomposition products (ETD, UV-PD) stand out from those coming from classical low-energy CID by inducing specific side-chain fragmentations. These particular fragmentations make them easy to identify.

Understanding the competing processes that govern far ultraviolet photodissociation (FUV-PD) of biopolymers such as proteins is a challenge. Here, we report a combined experimental and theoretical investigation of FUV-PD of protonated leucine-enkephalin pentapeptide ([YGGFL + H]+) in the gas-phase. Time-dependent density functional theory (TD-DFT) calculations in combination with experiments and previous results for amino acids and shorter peptides help in rationalizing the evolution of the excited states. The results confirm that fragmentation of [YGGFL + H]+ results mainly from vibrationally excited species in the ground electronic state, populated after internal conversion. We also propose fragmentation mechanisms for specific photo-fragments such as tyrosine side chain loss (with an extra hydrogen) or hydrogen loss. In general, we observe the same mechanisms as for smaller peptides or protonated Tyr and Phe, that are not quenched by the presence of other amino acids. Nevertheless, we also found some differences, as for H loss, in part due to the fact that the charge is solvated by the peptide chain and not only by the COOH terminal group.

The present work combines the near edge X-ray absorption mass spectrometry of a protonated adenosine 5 '-triphosphate (ATP) molecule isolated in an ion trap with (time-dependent) density functional theory calculations. Our study unravels the effect of protonation on the ATP structure and its spectral properties, providing structure-property relationships at atomistic resolution for protonated ATP (ATPH) isolated in the gas-phase conditions. On the other hand, the present C and N K-edge X-ray absorption spectra of isolated ATPH appear closely like those previously reported for solvated ATP at low pH. Therefore, the present work should be relevant for further investigation and modeling of structure-function properties of protonated adenine and ATP in complex biological environments.

In a recent work, we have shown that photon absorption can cause a chemical bond to be created between the two monomers within a protonated serine dimer, a process known as intra-cluster bond formation, despite this process not occurring following thermal excitation via low energy collision-induced dissociation (LE-CID). Here we show further evidence for non-statistical photon-induced dissociation (PID) of the protonated serine dimer. In addition we discuss LE-CID and PID studies of the protonated serine octamer, showing that in this case as well, PID leads to non-statistical fragmentation and to the formation of two bonds between three neighboring monomers.

Correction for 'UV and VUV-induced fragmentation of tin-oxo cage ions' by Jarich Haitjema et al., Phys. Chem. Chem. Phys., 2021, 23, 20909-20918, https://doi.org/10.1039/D1CP03148A.

The two inseparable companions, tropylium (Tr+) and benzylium (Bz+), were interrogated by vacuum ultraviolet (VUV) radiation from 4.5 to 7.0 eV in an ion trap. These new fingerprints provide a new means of distinguishing these two intertwined C7H7+ isomers. In particular, the singular spectral signature of Tr+ in the VUV consists of a single strong electronic transition at ≈6 eV. To illustrate this diagnostic tool, we shed light on the structure of the C7H7+ intermediate that is ubiquitous when using commercial atmospheric pressure photoionization (APPI) sources. We have identified its structure as the 7-membered ring Tr+, which contradicts some previous beliefs.

Correction for 'UV and VUV-induced fragmentation of tin-oxo cage ions' by Jarich Haitjema et al., Phys. Chem. Chem. Phys., 2021, 23, 20909-20918, https://doi.org/10.1039/D1CP03148A.

Context. The vacuum ultraviolet (VUV) photoprocessing of polycyclic aromatic hydrocarbons (PAHs) has been established as a key piece of the puzzle to understand the life cycle of carbon-based molecules in space. The recent detection of cyano (CN) aromatic species, with unexpectedly high abundance, motivated the current study of investigating their interaction with UV/VUV radiation.Aims. The aims were to investigate the fate, after VUV photoexcitatation, of medium-size (three rings) CN-PAH radical cations and of their protonated analogs, and thus to assess the effect of protonation on the photostability of the CN-PAHs. Photoproducts (ionic fragments and dications) were mass-analyzed and measured as a function of photon energy. The results were also compared with those for the bare anthracene radical cation to assess the influence of the added CN group.Methods. The positively charged CN-PAHs were stored in a quadrupole ion trap prior to interrogation by UV/VUV radiation, with photon energies between 4.5 and 13.6 eV, delivered by the DESIRS beamline from the synchrotron SOLEIL.Results. The HCN/HNC loss channel is present for both radical cations and protonated species, but H-2 loss is only apparent for the radical cations. Based on comparison with quantum chemical calculations, radiative and/or collisional processes should be relevant at energies lower than 8 eV, with a stronger propensity for radical cation than protonated CN-PAHs. The cata-condensed 9-CN-anthracene has a nearly two-fold larger photoionization yield at 13.6 eV than peri-condensed 9-CN-phenanthrene.Conclusions. The photoionization yield of singly and doubly ionized CN-PAHs is greater for radical cations than for protonated analogs. The photoionization yields of CN-PAHs is diminished by protonation and, in the future, similar investigations should target larger protonated CN-PAHs to support a general model for the photo-processing of these relevant molecular systems. Similar processes to those for the bare PAH radical cations may involve the radical cations of CN-PAHs, making their addition important in models that describe the photoelectric heating of interstellar gas.

Angewandte ChemieVolume 135, Issue 15 e202381511 Graphisches InhaltsverzeichnisFree Access Graphisches Inhaltsverzeichnis: Angew. Chem. 15/2023 First published: 26 March 2023 https://doi.org/10.1002/ange.202381511AboutPDF ToolsRequest permissionAdd to favorites ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume135, Issue15April 3, 2023e202381511 This is the German version of Angewandte Chemie. Note for articles published since 1962: Do not cite this version alone. Take me to the International Edition version with citable page numbers, DOI, and citation export. We apologize for the inconvenience. RelatedInformation

Possible routes for intra-cluster bond formation (ICBF) in protonated serine dimers have been studied. We found no evidence of ICBF following low energy collision-induced dissociation (in correspondence with previous works), however, we do observe clear evidence for ICBF following photon absorption in the 4.6-14 eV range. Moreover, the comparison of photon-induced dissociation measurements of the protonated serine dimer to those of a protonated serine dipeptide provides evidence that ICBF, in this case, involves peptide bond formation (PBF). The experimental results are supported by ab initio molecular dynamics and exploration of several excited state potential energy surfaces, unraveling a pathway for PBF following photon absorption. The combination of experiments and theory provides insight into the PBF mechanisms in clusters of amino acids, and reveals the importance of electronic excited states reached upon UV/VUV light excitation.

Context. The recent detection in pre-stellar sources of cyano-substituted and pure hydrocarbon cycles has emphasized the importance of aromatic chemistry in the earliest stages of star formation. Ultraviolet (UV) and vacuum-UV (VUV) radiation is ubiquitous in space and thus the photo-processing of small cyclic ions may open a window onto rich chemical networks and lead to the formation of larger aromatics in space. Aims. The aim is to investigate the fate of protonated benzonitrile species after UV and VUV photoexcitation and the subsequent potential impact on stellar and interstellar chemistry. Methods. Protonated benzonitrile was isolated in a linear ion trap prior to irradiation with UV and VUV radiation (4.5–13.6 eV) from the DESIRS beamline at synchrotron SOLEIL. The study was extended down to 3.5 eV using a cryogenic Paul ion trap coupled to an OPO laser at the PIIM laboratory. Photodissociation action spectra were obtained by monitoring the photofragment yields as a function of photon energy. Results. The UV/VUV photodissociation action spectra of protonated benzonitrile show structured bands from 3.8 to 9 eV. The primary dissociation channel of protonated benzonitrile corresponds to HCN/HNC loss and formation of the phenylium cation (C6H5+); whereas at high energies, a minor channel is observed that correlates with HC3N loss and formation of C4H5+. Conclusions. The UV and VUV photodestruction of protonated benzonitrile leads to the formation of a highly reactive cationic species, C6H5+, predicted to be an important precursor of larger aromatic molecules in space, such as polycyclic aromatic hydrocarbons. The inclusion of C6H5+ – a precursor of benzene and, by extension, of benzonitrile – as the result of formation via the photodissociation of protonated benzonitrile in current astrochemical models could improve the predicted abundance of benzonitrile, which is currently underestimated.

ABSTRACTN-heterocycles are suspected to play an important role in the chemical origin of life. Despite their detection in meteorites and in Titan’s atmosphere, their extra-terrestrial chemical formation networks remain elusive. Furthermore N-heterocyclics are undetected in the interstellar medium. This paper assesses the photostability of protonated N-hetero(poly)acenes after ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. It provides information on their ability to retain the N atom into the cycle to generate larger N-containing species or functionalized N-heterocyles. Protonated N-hetero(poly)acenes were generated using electrospray ionization and injected into a linear ion trap where they were irradiated by radiation of 4.5 to 10 eV using the DESIRS beamline at the synchrotron SOLEIL. The photodissociation action spectra of protonated pyridine, quinoline, isoquinoline, and acridine were measured by recording the photofragment yields as a function of photon energy. The four systems exhibit dissociation channels associated with H2 and HCN/HNC loss but with different branching ratios. The results indicate that increasing the size of the N-hetero(poly)acenes increases the chance of retaining the N atom in the larger fragment ion after photodissociation but it remains that all the protonated N-hetero(poly)acenes studied lose their N atom at part of a small neutral photofragment, with high propensity. Therefore, protonated N-hetero(poly)acenes in interstellar space are unlikely precursors to form larger N-containing species. However, protonated pyridine, quinoline, isoquinoline, and acridine are most likely to retain their N atoms in planetary atmospheres where UV radiation at the planet’s surface is typically restricted to wavelengths greater than 200 nm – suggesting such environments are possible substrates for prebiotic chemistry.

Context. The recent detection in pre-stellar sources of cyano-substituted and pure hydrocarbon cycles has emphasized the importance of aromatic chemistry in the earliest stages of star formation. Ultraviolet (UV) and vacuum-UV (VUV) radiation is ubiquitous in space and thus the photo-processing of small cyclic ions may open a window onto rich chemical networks and lead to the formation of larger aromatics in space. Aims. The aim is to investigate the fate of protonated benzonitrile species after UV and VUV photoexcitation and the subsequent potential impact on stellar and interstellar chemistry. Methods. Protonated benzonitrile was isolated in a linear ion trap prior to irradiation with UV and VUV radiation (4.5-13.6 eV) from the DESIRS beamline at synchrotron SOLEIL. The study was extended down to 3.5 eV using a cryogenic Paul ion trap coupled to an OPO laser at the PIIM laboratory. Photodissociation action spectra were obtained by monitoring the photofragment yields as a function of photon energy. Results. The UV/VUV photodissociation action spectra of protonated benzonitrile show structured bands from 3.8 to 9 eV. The primary dissociation channel of protonated benzonitrile corresponds to HCN/HNC loss and formation of the phenylium cation (C6H5+); whereas at high energies, a minor channel is observed that correlates with HC3N loss and formation of C4H5+. Conclusions. The UV and VUV photodestruction of protonated benzonitrile leads to the formation of a highly reactive cationic species, C6H5+, predicted to be an important precursor of larger aromatic molecules in space, such as polycyclic aromatic hydrocarbons. The inclusion of C6H5+ - a precursor of benzene and, by extension, of benzonitrile - as the result of formation via the photodissociation of protonated benzonitrile in current astrochemical models could improve the predicted abundance of benzonitrile, which is currently underestimated.

The gas phase offers the possibility to analyze organic molecules by ultraviolet-vacuum ultraviolet (UV-VUV) spectroscopy without any solvent effect or limitation in terms of spectral range due to absorption by the solvent. Up to now, the size and chemical composition of neutral molecular systems under study have been limited by the use of vaporization methods based on thermal heating. Soft sources of gas-phase thermolabile molecular systems such as electrospray or matrix-assisted laser desorption ionization are appealing alternatives to heating-based techniques, but they lead to the production of ions. In such cases, UV-VUV action spectroscopy is then the method of choice to study the electronic structure and corresponding photodynamics of these gas-phase molecular ions. However, previous investigations have shown that the UV-VUV action spectrum of a given molecular ion depends on the charge state, which in many cases might be a caveat. Here, by means of synchrotron radiation coupled to mass spectrometry and through the test case of the glycopeptide antibiotic vancomycin noncovalently bound to a deprotonated small peptide, we show that the UV-VUV photofragmentation spectrum of neutral thermally fragile organic molecules can be obtained via charge-tagging action spectroscopy.

Gas-phase decompositions of polymer ions play an important role in mass spectrometry to obtain accurate structural information. In this work, UV photoactivation experiments were performed from two poly(dimethylsiloxane)s bearing different end groups (two trimethylsilyl, or α-sec-butyl and ω- trimethylsilyl). Precursor ions, such as [Polysiloxane+Cation]+ produced by an electrospray source, were stored in a linear ion trap and then submitted to synchrotron UV irradiation during different activation times and over a range of wavelengths (52 to 248 nm) from extreme UV (XUV) to deep UV. Upon photoactivation of a precursor ion from poly(dimethylsiloxane) (PDMS; with two trimethylsilyl end groups, [PDMS25+Na]+), important fragmentations were observed, including the loss of a methyl radical followed by various heterolytic cleavages along the polymer backbone, for photon energies typically >9.5-10 eV (ionization threshold of the neutral oligomer). This report focuses on different aspects: (i) the identification of the UV photodissociation (UV-PD) products of PDMS, (ii) the influence of the irradiation time for two photon energies (10 or 20 eV), (iii) the influence of the energy of the photon for two activation times (100 or 5000 ms), (iv) the influence of the nature of the cation, and (v) the influence of the end groups of PDMS. Synchrotron UV irradiation with a tunable wavelength was a great opportunity to study the effect of the photon energy and to probe the original mechanisms of ion decomposition from poly(dimethylsiloxane).

Mammalian hyaluronidases are endo-N-acetyl-D-hexosaminidases involved in the catabolism of hyaluronic acid (HA) but their role in the catabolism of chondroitin sulfate (CS) is also examined. HA and CS are glycosaminoglycans implicated in several physiological and pathological processes, and understanding their metabolism is of significant importance. Data have been previously reported on the degradation of CS under the action of hyaluronidase, yet a detailed structural investigation of CS depolymerization products remains necessary to improve our knowledge of the CS depolymerizing activity of hyaluronidase. For that purpose, the fine structural characterization of CS oligosaccharides formed upon the enzymatic depolymerization of various CS subtypes by hyaluronidase has been carried out by high-resolution Orbitrap mass spectrometry (MS) and extreme UV (XUV) photodissociation tandem MS. The exact mass measurements show the formation of wide size range of even oligosaccharides upon digestion of CS-A and CS-C comprising hexa- and octa-saccharides among the main digestion products, as well as formation of small quantities of odd-numbered oligosaccharides, while no hyaluronidase activity was detected on CS-B. In addition, slight differences have been observed in the distribution of oligosaccharides in the digestion mixture of CS-A and CS-C, the contribution of longer oligosaccharides being significantly higher for CS-C. The sequence of CS oligosaccharide products determined by XUV photodissociation experiments verifies the selective beta(1 -> 4) glycosidic bond cleavage catalyzed by mammal hyaluronidase. The ability of the mammal hyaluronidase to produce hexa- and higher oligosaccharides supports its role in the catabolism of CS anchored to membrane proteoglycans and in extra-cellular matrix.