Desolvation of ions and molecules in thermospray mass spectrometry

Schmelzeisen‐Redeker, G.; Bütfering, L.; Röllgen, F. W.

doi:10.1016/0168-1176(89)85004-9

Cited by 147 publications

(78 citation statements)

References 33 publications

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“…In a series of pioneering experiments, Kebarle and co-workers 5 demonstrated that gas-phase hydrated metal dications can be readily produced by electrospray ionization, extending the earlier thermospray work by Schmelzeisen-Redeker et al 9 Ions of the composition M 2+ (H 2 O) n , (n = 0-15) were observed for the group II metals Mg, Ca, Sr, and Ba as well as for most first-row transition metals. However, only singly charged hydrated metal hydroxide species, MOH + (H 2 O) n , were observed with both Be and Cu.…”

Section: Introductionmentioning

confidence: 89%

Unimolecular Reactions of Dihydrated Alkaline Earth Metal Dications M²⁺(H₂O)₂, M = Be, Mg, Ca, Sr, and Ba: Salt-Bridge Mechanism in the Proton-Transfer Reaction M²⁺(H₂O)₂ → MOH⁺ + H₃O⁺

Beyer

Williams²,

Bondybey³

1999

J. Am. Chem. Soc.

151

198

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The unimolecular reactivity of M 2+ (H 2 O) 2 , M = Be, Mg, Ca, Sr, and Ba, is investigated by density functional theory. Dissociation of the complex occurs either by proton transfer to form singly charged metal hydroxide, MOH + , and protonated water, H 3 O + , or by loss of water to form M 2+ (H 2 O) and H 2 O. Charge transfer from water to the metal forming H 2 O + and M + (H 2 O) is not favorable for any of the metal complexes. The relative energetics of these processes are dominated by the metal dication size. Formation of MOH + proceeds first by one water ligand moving to the second solvation shell followed by proton transfer to this second-shell water molecule and subsequent Coulomb explosion. These hydroxide formation reactions are exothermic with activation energies that are comparable to the water binding energy for the larger metals. This results in a competition between proton transfer and loss of a water molecule. The arrangement with one water ligand in the second solvation shell is a local minimum on the potential energy surface for all metals except Be. The two transition states separating this intermediate from the reactant and the products are identified. The second transition state determines the height of the activation barrier and corresponds to a M 2+ -OH − -H 3 O + "saltbridge" structure. The computed B3LYP energy of this structure can be quantitatively reproduced by a simple ionic model in which Lewis charges are localized on individual atoms. This salt-bridge arrangement lowers the activation energy of the proton-transfer reaction by providing a loophole on the potential energy surface for the escape of H 3 O + . Similar salt-bridge mechanisms may be involved in a number of proton-transfer reactions in small solvated metal ion complexes, as well as in other ionic reactions.

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Section: Introductionmentioning

confidence: 89%

Unimolecular Reactions of Dihydrated Alkaline Earth Metal Dications M²⁺(H₂O)₂, M = Be, Mg, Ca, Sr, and Ba: Salt-Bridge Mechanism in the Proton-Transfer Reaction M²⁺(H₂O)₂ → MOH⁺ + H₃O⁺

Beyer

Williams²,

Bondybey³

1999

J. Am. Chem. Soc.

151

198

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“…Both thermospray [21] and electrospray ionization (ESI) [10][11][12][13][14][22][23][24] have been used to produce hydrated divalent metal ion clusters. Kebarle and coworkers [11][12][13] first used ESI to form and study a plethora of previously inaccessible, hydrated doubly charged clusters.…”

Section: Introductionmentioning

confidence: 99%

Formation of hydrated triply charged metal ions from aqueous solutions using nanodrop mass spectrometry

Bush

Saykally

Williams

2006

International Journal of Mass Spectrometry

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Forming hydrated clusters containing triply charged metal ions is challenging due to the competing process of dissociation by forming the metal hydroxide with one less net charge and a protonated water molecule. It is demonstrated for the first time that it is possible to form such clusters using a method we call "nanodrop mass spectrometry". Clusters of the form [M(H 2 O) n ] 3+ , where M = Ce, Eu, and La, are generated using electrospray ionization and are mass analyzed in a Fourier-transform ion cyclotron resonance mass spectrometer with an ion cell cooled to −140 °C. Clusters containing trivalent La with n ranging from 16 to over 160 can be readily produced. These clusters are stable at this temperature for many seconds, enabling all standard methods to probe structure and reactivity of these unusual species. Photodissociation experiments on extensively hydrated clusters of trivalent lanthanum using resonant infrared radiation indicate that a minimum of 17 water molecules is necessary to stabilize these trivalent clusters under the low-energy ion excitation conditions and long time frame of these experiments. These results indicate that a minimum droplet size of approximately a nanometer is necessary for these trivalent species to survive intact. This suggests that elemental speciation of trivalent metal ions from aqueous solutions should be possible using nanodrop mass spectrometry.

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“…14 Three different types of structures were studied in which the six water molecules are either all in the first shell or distributed between the first and second solvation shells around the metals. By the use of the nomenclature of Pavlov 2 for all of the metals. The energy differences between each of the higher energy structures and the M 2+ (H 2 O) 6 conformation are reported in Table 2.…”

mentioning

confidence: 99%

Binding Energies of Hexahydrated Alkaline Earth Metal Ions, M²⁺(H₂O)₆, M = Mg, Ca, Sr, Ba: Evidence of Isomeric Structures for Magnesium

1999

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One strategy that has commonly been used to gain a more detailed understanding of ion chemistry in bulk solution is to investigate the structure and energetics of solvated ions in the gas phase. While solvation of singly charged metal ions has been studied extensively during the last two decades, 1 significantly less information about doubly and triply charged metal ions is known. Solvated divalent metal ions can now be readily produced using electrospray ionization (ESI). 2-5 This has led to a significant interest in obtaining thermochemical information about these ions with both experiment 3-5 and theory. 6-8 Kebarle and co-workers measured the Gibbs free energies of hydration for water molecules located in the second solvation shell of a variety of divalent metal ions using equilibrium experiments. 3 More recently, Posey and co-workers combined ESI with laser photofragmentation mass spectrometry to study divalent transition metal-ligand complexes with methanol in the second solvation shell. 4 Binding energies of inner solvent shell water molecules around Ni 2+ and Ca 2+ ions have been determined from blackbody infrared radiative dissociation (BIRD) experiments. 5 Here, BIRD kinetics of the hexahydrated alkaline earth metal ions, Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ , are presented. At low temperatures, binding energies obtained from these kinetic data are directly correlated with the radii of the metal ions (Mg 2+ > Ca 2+ > Sr 2+ > Ba 2+ ). In contrast, the binding energies at higher temperatures follow the trend Ca 2+ > Mg 2+ > Sr 2+ > Ba 2+ . This is the first direct evidence for two distinct gas-phase structures for a hydrated divalent metal ion.Experiments were performed using an external electrospray ionization source Fourier transform mass spectrometer that has been described previously. 9 Hydrated alkaline earth M 2+ (H 2 O) n ions were generated from ~10 −4 M aqueous solutions of the metal chloride salts using nanoelectrospray. Ions are loaded into the cell for 5 s during which time N 2 gas (10 −6 Torr) is introduced. Dissociation kinetics of the mass-selected ion are investigated at pressures <10 −8 Torr. At these pressures, ion activation occurs by absorption of blackbody photons emitted by the heated vacuum chamber walls. 9-11 Unimolecular dissociation rate constants in the zero-pressure limit are measured as a function of temperature (22-140 °C) from which Arrhenius activation parameters are obtained. Under these conditions, the ion population does not have a Boltzmann distribution of internal energies. 10 Measured Arrhenius preexponentials and activation energies are smaller than those measured in the rapid energy exchange (REX) limit. To determine the threshold dissociation energies, master equation modeling of the kinetic data is necessary. 12 The application of the master equation model to obtain threshold dissociation energies has been described in detail previously. 11 The reverse activation barriers for these dissociation reactions should be negligible. Thus, the threshold dissociation energy ...

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Desolvation of ions and molecules in thermospray mass spectrometry

Cited by 147 publications

References 33 publications

Unimolecular Reactions of Dihydrated Alkaline Earth Metal Dications M²⁺(H₂O)₂, M = Be, Mg, Ca, Sr, and Ba: Salt-Bridge Mechanism in the Proton-Transfer Reaction M²⁺(H₂O)₂ → MOH⁺ + H₃O⁺

Unimolecular Reactions of Dihydrated Alkaline Earth Metal Dications M²⁺(H₂O)₂, M = Be, Mg, Ca, Sr, and Ba: Salt-Bridge Mechanism in the Proton-Transfer Reaction M²⁺(H₂O)₂ → MOH⁺ + H₃O⁺

Formation of hydrated triply charged metal ions from aqueous solutions using nanodrop mass spectrometry

Binding Energies of Hexahydrated Alkaline Earth Metal Ions, M²⁺(H₂O)₆, M = Mg, Ca, Sr, Ba: Evidence of Isomeric Structures for Magnesium

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Desolvation of ions and molecules in thermospray mass spectrometry

Cited by 147 publications

References 33 publications

Unimolecular Reactions of Dihydrated Alkaline Earth Metal Dications M2+(H2O)2, M = Be, Mg, Ca, Sr, and Ba: Salt-Bridge Mechanism in the Proton-Transfer Reaction M2+(H2O)2 → MOH+ + H3O+

Unimolecular Reactions of Dihydrated Alkaline Earth Metal Dications M2+(H2O)2, M = Be, Mg, Ca, Sr, and Ba: Salt-Bridge Mechanism in the Proton-Transfer Reaction M2+(H2O)2 → MOH+ + H3O+

Formation of hydrated triply charged metal ions from aqueous solutions using nanodrop mass spectrometry

Binding Energies of Hexahydrated Alkaline Earth Metal Ions, M2+(H2O)6, M = Mg, Ca, Sr, Ba: Evidence of Isomeric Structures for Magnesium

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Unimolecular Reactions of Dihydrated Alkaline Earth Metal Dications M²⁺(H₂O)₂, M = Be, Mg, Ca, Sr, and Ba: Salt-Bridge Mechanism in the Proton-Transfer Reaction M²⁺(H₂O)₂ → MOH⁺ + H₃O⁺

Unimolecular Reactions of Dihydrated Alkaline Earth Metal Dications M²⁺(H₂O)₂, M = Be, Mg, Ca, Sr, and Ba: Salt-Bridge Mechanism in the Proton-Transfer Reaction M²⁺(H₂O)₂ → MOH⁺ + H₃O⁺

Binding Energies of Hexahydrated Alkaline Earth Metal Ions, M²⁺(H₂O)₆, M = Mg, Ca, Sr, Ba: Evidence of Isomeric Structures for Magnesium