Stability and reactivity of hydrated magnesium cations

Berg, Christian; Beyer, Martin K.; Achatz, Uwe; Joos, Stefan; Niedner‐Schatteburg, Gereon; Bondybey, V. E.

doi:10.1016/s0301-0104(98)00278-x

Cited by 106 publications

(183 citation statements)

References 37 publications

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“…The activation energy barrier for loss of H is higher than that for the loss of water from M(H 2 O) n ϩ , n ϭ 1-5, but loss of a H atom is more energetically favorable for n ϭ 6 and 7. This result is reasonably consistent with the results of BIRD experiments of Bondybey and coworkers [57] where the loss of water was the exclusive loss channel observed for clusters with n Ͻ 7, but H atom loss occurred for n ϭ 7-21. For smaller clusters, only the loss of water was observed indicating that the activation barrier for loss of an H atom is higher than that for loss of a water molecule for clusters with six or fewer water molecules.…”

Section: Ecd Energetics For Small Mg(h 2 O) N 2ϩ Clusterssupporting

confidence: 92%

“…As discussed previously, thermal activation of Mg(H 2 O) n ϩ , n Ͻ 7 results in loss of water molecules (Pathway I); loss of H is only observed for n between 7 and 21 (Pathway II) [57]. In contrast, Mg(H 2 O) n ϩ , n ϭ 4 -6, when formed by EC by the corresponding Mg(H 2 O) n 2ϩ dissociates exclusively by Pathway II.…”

Section: Evidence For Nonergodic Dissociationmentioning

confidence: 76%

“…Reactions of hydrated magnesium monocations have been investigated previously [55][56][57]. Using an expansion source, it was demonstrated that Mg(H 2 O) n ϩ clusters were formed for n ϭ 1-5 and n Ն 15 whereas MgOH(H 2 O) n ϩ was observed for n ϭ 6 -14 [56].…”

Section: Electron Capture Fragmentation Pathwaysmentioning

confidence: 99%

“…Using an expansion source, it was demonstrated that Mg(H 2 O) n ϩ clusters were formed for n ϭ 1-5 and n Ն 15 whereas MgOH(H 2 O) n ϩ was observed for n ϭ 6 -14 [56]. In elegant BIRD experiments by Bondybey and coworkers who investigated solvent evaporation from singly charged hydrated magnesium cations, loss of water molecules rapidly occurred at room-temperature for large clusters, but below about 21 water molecules, MgOH(H 2 O) n ϩ was formed [57]. Another transition was noted for clusters with n Յ 6, where water loss was again the only dissociation pathway observed [57].…”

Section: Electron Capture Fragmentation Pathwaysmentioning

confidence: 99%

“…The second piece of evidence in support of a nonergodic dissociation process for the smaller clusters is the different dissociation pathways of the precursor ions when thermally activated by BIRD [57] or by collisions with Xe [60] and when formed in an activated state by EC from the doubly charged precursor. As discussed previously, thermal activation of Mg(H 2 O) n ϩ , n Ͻ 7 results in loss of water molecules (Pathway I); loss of H is only observed for n between 7 and 21 (Pathway II) [57].…”

Section: Evidence For Nonergodic Dissociationmentioning

confidence: 99%

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Nonergodicity in electron capture dissociation investigated using hydrated ion nanocalorimetry

Leib

Donald

Bush

et al. 2007

J. Am. Soc. Mass Spectrom.

118

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Hydrated divalent magnesium and calcium clusters are used as nanocalorimeters to measure the internal energy deposited into size-selected clusters upon capture of a thermally generated electron. The infrared radiation emitted from the cell and vacuum chamber surfaces as well as from the heated cathode results in some activation of these clusters, but this activation is minimal. No measurable excitation due to inelastic collisions occurs with the low-energy electrons used under these conditions. Two different dissociation pathways are observed for the divalent clusters that capture an electron: loss of water molecules (Pathway I) and loss of an H atom and water molecules (Pathway II). For Ca(H 2 O) n 2ϩ , Pathway I occurs exclusively for n Ն 30 whereas Pathway II occurs exclusively for n Յ 22 with a sharp transition in the branching ratio for these two processes that occurs for n Ϸ 24. The number of water molecules lost by both pathways increases with increasing cluster size reaching a broad maximum between n ϭ 23 and 32, and then decreases for larger clusters. From the number of water molecules that are lost from the reduced cluster, the average and maximum possible internal energy is determined to be ϳ4.4 and 5.2 eV, respectively, for Ca(. This value is approximately the same as the calculated ionization energies of M(H 2 O) n ϩ , M ϭ Mg and Ca, for large n indicating that the vast majority of the recombination energy is partitioned into internal modes of the ion and that the dissociation of these ions is statistical. For smaller clusters, estimates of the dissociation energies for the loss of H and of water molecules are obtained from theory. For Mg(H 2 O) n 2ϩ , n ϭ 4 -6, the average internal energy deposition is estimated to be 4.2-4.6 eV. The maximum possible energy deposited into the n ϭ 5 cluster is Ͻ7.1 eV, which is significantly less than the calculated recombination energy for this cluster. There does not appear to be a significant trend in the internal energy deposition with cluster size whereas the recombination energy is calculated to increase significantly for clusters with fewer than 10 water molecules. These, and other results, indicate that the dissociation of these smaller clusters is nonergodic. . The effectiveness of the bottom-up method for complex samples can be enhanced by using multidimensional separations. Clemmer and coworkers elegantly demonstrated that combining on-line liquid chromatography (LC) with ion mobility spectrometry and MS can greatly improve separations without increasing analysis times over LC/MS alone [2][3][4]. In contrast, the "top-down" approach to protein characterization has the advantage that de novo sequencing, including the identification and structural localization of labile posttranslational modifications, can be done directly on protein mixtures without proteolysis [5,6]. This top-down approach has greatly benefited from the development of electron capture dissociation (ECD), a method pioneered by McLafferty and coworkers [6][7][8][9]. In a typical ECD experim...

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Section: Ecd Energetics For Small Mg(h 2 O) N 2ϩ Clusterssupporting

confidence: 92%

Section: Evidence For Nonergodic Dissociationmentioning

confidence: 76%

Section: Electron Capture Fragmentation Pathwaysmentioning

confidence: 99%

Section: Electron Capture Fragmentation Pathwaysmentioning

confidence: 99%

Section: Evidence For Nonergodic Dissociationmentioning

confidence: 99%

See 3 more Smart Citations

Nonergodicity in electron capture dissociation investigated using hydrated ion nanocalorimetry

Leib

Donald

Bush

et al. 2007

J. Am. Soc. Mass Spectrom.

118

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Aqueous Chemistry of Transition Metals in Oxidation State (I) in Nanodroplets

et al. 2002

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Round numbers: A gold‐catalyzed 2,7‐cycloaromatization of captodative dienyne carboxylic acids has been developed that occurs at room temperature with low catalyst loading and total regioselective control (see scheme). The reaction is totally dependent on the electronic properties of the dienyne acid: if a strong electron‐donating group is not directly linked to the triple bond, a 1,6‐cyclization/decarboxylation sequence takes place.

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