Reduction of Acetonitrile by Hydrated Magnesium Cations Mg+(H2O)n (n≈20–60) in the Gas Phase

Lam, Tim-Wai; Linde, Christian van der; Akhgarnusch, Amou; Hao, Qiang; Beyer, Martin K.; Siu, Chi‐Kit

doi:10.1002/cplu.201300170

Cited by 22 publications

(26 citation statements)

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“…Especially, the hydrated magnesium ion has attracted considerable attention over the years 15 and is certainly among the best studied of these systems. 16 First ab initio calculations to optimize structures and determine binding energies, electronic transition energies, and vibrational frequencies of Mg + (H 2 O) were done by Bauschlicher, Jr. in the early 1990s. 17 Shortly afterwards, Duncan and co-workers measured vibrationally resolved electronic and partially resolved rotational structures in the photodissociation spectrum of Mg + (H 2 O).…”

Section: Introductionmentioning

confidence: 99%

“…32 They also explained the switch off for the hydrogen loss process for larger clusters due to the barrier increase when the solvated electron moves beyond the third solvation shell. 15 Our group has a long history in studying the reactivity of hydrated metal ions, 13,16,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) which is well suited for this task as it allows highest mass resolution coupled with long storage times to allow multiple collisions with reactant gases. In the present study, we couple the mass spectrometer with a tunable optical parametric oscillator (OPO)/amplifier system to conduct photodissociation experiments.…”

Section: Introductionmentioning

confidence: 99%

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Photochemistry and spectroscopy of small hydrated magnesium clusters Mg+(H2O)n, n = 1–5

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Barwa

et al. 2018

The Journal of Chemical Physics

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Hydrated singly charged magnesium ions Mg(HO), n ≤ 5, in the gas phase are ideal model systems to study photochemical hydrogen evolution since atomic hydrogen is formed over a wide range of wavelengths, with a strong cluster size dependence. Mass selected clusters are stored in the cell of an Fourier transform ion cyclotron resonance mass spectrometer at a temperature of 130 K for several seconds, which allows thermal equilibration via blackbody radiation. Tunable laser light is used for photodissociation. Strong transitions to D states (correlating with the 3s-3p transitions of Mg) are observed for all cluster sizes, as well as a second absorption band at 4-5 eV for n = 3-5. Due to the lifted degeneracy of the 3p energy levels of Mg, the absorptions are broad and red shifted with increasing coordination number of the Mg center, from 4.5 eV for n = 1 to 1.8 eV for n = 5. In all cases, H atom formation is the dominant photochemical reaction channel. Quantum chemical calculations using the full range of methods for excited state calculations reproduce the experimental spectra and explain all observed features. In particular, they show that H atom formation occurs in excited states, where the potential energy surface becomes repulsive along the O⋯H coordinate at relatively small distances. The loss of HO, although thermochemically favorable, is a minor channel because, at least for the clusters n = 1-3, the conical intersection through which the system could relax to the electronic ground state is too high in energy. In some absorption bands, sequential absorption of multiple photons is required for photodissociation. For n = 1, these multiphoton spectra can be modeled on the basis of quantum chemical calculations.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Photochemistry and spectroscopy of small hydrated magnesium clusters Mg+(H2O)n, n = 1–5

Ončák

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Barwa

et al. 2018

The Journal of Chemical Physics

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“…On the other hand, the C ␣ -C bond is relatively nonpolar and homolytic cleavage of which can transfer the unpaired electron from the ␤-carbon atom to the incipient [x] • fragment in which the spin can delocalize between its amide carbon and oxygen atoms in an orbital with a significant CO * character, similar to the isoelectronic RCN •-analog. 46,47 …”

Section: [Ac(ala)nhme -H] •mentioning

confidence: 98%

Theoretical examination of competitive β-radical-induced cleavages of N–C_α and C_α–C bonds of peptides

et al. 2015

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Selective cleavages of N-C ␣ and C ␣ -C bonds of ␤-radical tautomers of amino acid residues in radical peptides have been examined theoretically by means of the density functional theory at the M06-2X/6-311++G(d,p) level. The majority of the bond cleavages are homolytic via ␤-scission. Their energy barriers depend largely on the ability of the radical being stabilized in the transition structures and the availability of a mobile proton in the vicinity of the ␤-radical center. The N-C ␣ bond is less favorably cleaved than the C ␣ -C bond (except Ser and Thr) for systems without a mobile proton. It is because, firstly, the homolytic cleavage is less favorable for the more polar N-C ␣ bond than for the less polar C ␣ -C bond. Secondly, a less stable -radical localized on the amide nitrogen atom of the incipient N-terminal fragment is formed for the former, while a more stable radical delocalized in a *(CO)-like orbital of the incipient C-terminal fragment is formed for the latter. In the presence of a mobile proton N-terminal to the ␤-radical center, some degrees of heterolytic cleavage character, as preferred by the polar N-C ␣ bond, are observed. Consequently, its barrier is reduced. If the mobile proton is located at the C-terminal amide oxygen of the ␤-radical center, the C ␣ -C bond cleavage will be significantly suppressed. It is because the radical in the incipient C-terminal fragment becomes more localized as a -radical on the carbon atom of its protonated amide group. With basic amino acid residues, the C ␣ -C bond cleavage can be reactivated. Heterolytic cleavage of the polar N-C ␣ bond can be largely facilitated if a mobile proton N-terminal to the ␤-radical center is available and the radical in the incipient C-terminal fragment is sufficiently stabilized, for instance, by the aromatic side chain of Trp and Tyr. Therefore, cleavages of the N-C ␣ bond induced by the ␤-radical tautomer of Trp and Tyr are often preferred as compared with cleavages of the C ␣ -C bond in peptide radical cations containing mobile protons.Résumé : Nous avons modélisé les clivages sélectifs des liaisons N-C ␣ et C ␣ -C des tautomères ␤-radicalaires de résidus d'acides aminés dans des peptides radicalaires au niveau M06-2X/6-311++G(d,p) de la théorie de la fonctionnelle de la densité. La majorité des clivages de liaison sont homolytiques et se produisent par scission ␤. Leurs barrières énergétiques dépendent fortement de l'aptitude du radical à être stabilisé dans les structures de transition et de la présence d'un proton labile à proximité du centre ␤-radicalaire. Le clivage de liaison N-C ␣ est moins favorable que celui de la liaison C ␣ -C (sauf dans les résidus Ser et Thr) dans les systèmes sans proton labile. Ce phénomène s'explique premièrement par le fait que le clivage homolytique des liaisons N-C ␣ plus polaires est moins favorable que celui des liaisons C ␣ -C moins polaires. Deuxièmement, un radical moins stable, localisé sur l'atome d'azote de l'amide du fragment N-terminal naissant, se forme dans le premier cas, alor...

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“…[14,15,21] For Zn + (H 2 O) n , uptake of two HCl molecules is required to induce elimination of atomic hydrogen. [22] In reactions with acetonitrile, a hydrogen atom is transferred from Mg + (H 2 O) n , again removing the upper size limit for the formation of MgOH + (H 2 O) n-1 species, [23] which replicates the chemistry of the hydrated electron. [24] A similar observation was made with CO 2 and O 2 , which scavenge the hydrated electron present in the hydration shell of Mg + (H 2 O) n , [25] while hydrated transition metal ions exhibit a more complex behavior.…”

Section: Introductionmentioning

confidence: 99%

Photochemical Hydrogen Evolution at Metal Centers Probed with Hydrated Aluminium Cations, Al⁺(H₂O)_n, n=1–10

Heller

Pascher

Linde

et al. 2021

Chemistry A European J

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Hydrated aluminium cations have been investigated as a photochemical model system with up to ten water molecules by UV action spectroscopy in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Intense photodissociation was observed starting at 4.5 eV for two to eight water molecules with loss of atomic hydrogen, molecular hydrogen and water molecules. Quantum chemical calculations for n = 2 reveal that solvation shifts the intense 3s-3p excitations of Al + into the investigated photon energy range below 5.5 eV. During the photochemical relaxation, internal conversion from S 1 to T 2 takes place, and photochemical hydrogen formation starts on the T 2 surface, which passes through a conical intersection, changing to T 1 . On this triplet surface, the electron that was excited to the Al 3p orbital is transferred to a coordinated water molecule, which dissociates into a hydroxide ion and a hydrogen atom. If the system remains in the triplet state, this hydrogen radical is lost directly. If the system returns to singlet multiplicity, the reaction may be reversed, with recombination with the hydroxide moiety and electron transfer back to aluminium, resulting in water evaporation. Alternatively, the hydrogen radical can attack the intact water molecule, forming molecular hydrogen and aluminium dihydroxide. Photodissociation is observed for up to n = 8. Clusters with n = 9 or 10 occur exclusively as HAlOH + (H 2 O) n-1 and are transparent in the investigated energy range. For n = 4-8, a mixture of Al + (H 2 O) n and HAlOH + (H 2 O) n-1 is present in the experiment.

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Reduction of Acetonitrile by Hydrated Magnesium Cations Mg⁺(H₂O)_n (n≈20–60) in the Gas Phase

Cited by 22 publications

References 98 publications

Photochemistry and spectroscopy of small hydrated magnesium clusters Mg+(H2O)n, n = 1–5

Photochemistry and spectroscopy of small hydrated magnesium clusters Mg+(H2O)n, n = 1–5

Theoretical examination of competitive β-radical-induced cleavages of N–C_α and C_α–C bonds of peptides

Photochemical Hydrogen Evolution at Metal Centers Probed with Hydrated Aluminium Cations, Al⁺(H₂O)_n, n=1–10

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Reduction of Acetonitrile by Hydrated Magnesium Cations Mg+(H2O)n (n≈20–60) in the Gas Phase

Cited by 22 publications

References 98 publications

Photochemistry and spectroscopy of small hydrated magnesium clusters Mg+(H2O)n, n = 1–5

Photochemistry and spectroscopy of small hydrated magnesium clusters Mg+(H2O)n, n = 1–5

Theoretical examination of competitive β-radical-induced cleavages of N–Cα and Cα–C bonds of peptides

Photochemical Hydrogen Evolution at Metal Centers Probed with Hydrated Aluminium Cations, Al+(H2O)n, n=1–10

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Reduction of Acetonitrile by Hydrated Magnesium Cations Mg⁺(H₂O)_n (n≈20–60) in the Gas Phase

Theoretical examination of competitive β-radical-induced cleavages of N–C_α and C_α–C bonds of peptides

Photochemical Hydrogen Evolution at Metal Centers Probed with Hydrated Aluminium Cations, Al⁺(H₂O)_n, n=1–10