Experimental Techniques in Gas-Phase Ion Thermochemistry

Ervin, Kent M.

doi:10.1021/cr990081l

Cited by 235 publications

(269 citation statements)

References 490 publications

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“…The energetics of cationic An oxides is less well established. For singly charged AnO and AnO 2 species, most of the available experimental ionization energy (IE) determinations of AnO and AnO 2 [2,3a] are based on electron-impact measurements whose reliability is known to be variable and unpredictable [22]. Highly reliable spectroscopic data for IEs are only available for ThO, UO, and UO 2 from recent determinations by Heaven and coworkers Table S9 for a compilation of the previously available bond dissociation enthalpies of singly charged An oxides, and [24] was the object of controversy related to the experimental approach [25].…”

Section: Methodsmentioning

confidence: 99%

Gas-Phase Energetics of Actinide Oxides: An Assessment of Neutral and Cationic Monoxides and Dioxides from Thorium to Curium

2009

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An assessment of the gas-phase energetics of neutral and singly and doubly charged cationic actinide monoxides and dioxides of thorium, protactinium, uranium, neptunium, plutonium, americium, and curium is presented. A consistent set of metal-oxygen bond dissociation enthalpies, ionization energies, and enthalpies of formation, including new or revised values, is proposed, mainly based on recent experimental data and on correlations with the electronic energetics of the atoms or cations and with condensed-phase thermochemistry. IntroductionThe thermodynamic properties of actinide (An) oxides are of paramount importance to nuclear science at both the fundamental and applied levels. In the most recent, comprehensive overview of the thermodynamics of actinides and actinide compounds [1], the history of the field and the most reliable current data can be found. As concerns the actinide oxides, that work appropriately indicates that, while a significant number of studies of the solid compounds have been undertaken, gas-phase data are still incomplete. An earlier compilation devoted to the gas-phase thermochemistry of the actinides [2], as well as others of a more general nature [3], are now more than twenty years old and do not reflect the experimental data gathered since then. For instance, recent high-quality spectroscopic studies of thorium and uranium oxides [4] ], which showed significant differences relative to the older accepted values included in the compilations. In recent years, we have carried out a systematic study of the gas-phase thermochemistry of neutral and cationic actinide oxides from thorium to curium using Fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS) [5,6]. This experimental work was based on the observation of exothermic reactions of An metal or metal-oxide cations with various inorganic and organic molecules. Reactions of singly or doubly charged An cations with oxidizing reagents with a large range of oxygen dissociation energies provided metal-oxygen bond dissociation enthalpies, D[An

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Section: Methodsmentioning

confidence: 99%

Gas-Phase Energetics of Actinide Oxides: An Assessment of Neutral and Cationic Monoxides and Dioxides from Thorium to Curium

2009

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“…31 Por fim, na tentativa de se identificar a estrutura de moléculas cationizadas e anionizadas, geralmente não se leva em consideração que as conformações adquiridas em presença de solvente comumente diferem daquelas em fase gasosa. 32 Neste contexto, os modelos quími-co-quânticos embasados na teoria de orbitais moleculares podem ser de grande valia para a identificação dos sítios reativos mais favorecidos para a produção dos íons gasosos.…”

Section: Aspectos Mecanísticos Das Reações De Fragmentaçãounclassified

Aplicação da química quântica computacional no estudo de processos químicos envolvidos em espectrometria de massas

Vessecchi¹,

Galembeck²,

Lopes³

et al. 2008

Quím. Nova

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Recebido em 4/7/07; aceito em 14/11/07; publicado na web em 19/3/08 APPLICATION OF COMPUTATIONAL QUANTUM CHEMISTRY TO CHEMICAL PROCESSES INVOLVED IN MASS SPECTROMETRY. The field of application of mass spectrometry (MS) has increased considerably due to the development of ionization techniques. Other factors that have stimulated the use of MS are the tandem mass spectrometry (MS/MS) and sequential mass spectrometry (MS n ) techniques. However, the interpretation of the MS/MS and MS n data may lead to speculative conclusions. Thus, various quantum chemical methods have been applied for obtaining high quality thermochemical data in gas phase. In this review, we show some applications of computational quantum chemistry to understand the formation and fragmentation of gaseous ions of organic compounds in a MS analysis.Keywords: theoretical calculations; fragmentation studies; protonation site. INTRODUÇÃONo século passado, vários métodos e técnicas para obtenção de parâmetros moleculares aplicando a química quântica a sistemas multi-eletrônicos foram desenvolvidos. Este desenvolvimento foi fortemente impulsionado pelo aumento do poder computacional, conforme previsto pela Lei de Moore, 1 bem como pelo desenvolvimento de novos métodos computacionais e aperfeiçoamento daqueles já existentes. Atualmente, parâmetros como a energia de um sistema em uma dada geometria e freqüências vibracionais podem auxiliar na determinação da estrutura e das propriedades químicas de intermediários e de possíveis estados de transição para um dado caminho de reação, além de assistirem na obtenção de correlações entre as entalpias de reação e a temperatura, efeitos isotópicos e energias de dissociação. Comumente, nos estudos químico-quântico computacionais utiliza-se como modelo uma molécula isolada no vácuo. Há, portanto, certas similaridades entre estas condições e as condições de baixas pressões no interior de um espectrômetro de massas, onde ocorrem vários fenômenos em fase gasosa.3 Neste contexto, é possível utilizar estes métodos para se estimar uma série de parâmetros de interesse de um espectroscopista de massas, auxiliando na compreensão tanto dos fenômenos de geração de íons como nos processos de fragmentação dos mesmos.Em processos de ionização, por exemplo, é possível obter parâmetros como a energia de ionização adiabática, basicidade e afinidade protônica, entre outros. 4 No caso de substâncias que apresentam vários grupos funcionais ácidos e/ou básicos em suas estruturas, muitas vezes é difícil se identificar qual é o sítio mais suscetível à protonação ou à desprotonação, 5 mesmo existindo na literatura extensas compilações sobre acidez e basicidade em fase gasosa.6 Em princípio, a suscetibilidade à protonação apresentada por dois grupos funcionais diferentes em uma mesma estrutura quími-ca pode ser estimada a partir da diferença entre suas basicidades em fase gasosa. Entretanto, quando os grupos funcionais são parecidos, tal como os nitrogênios de cadeia lateral e de anel de histamina ou pirimidinas, a identificação do sítio m...

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“…However, the conditions that favor the formation and survival of anionic adducts have not been extensively defined and are not fully understood. Moreover, the interactions between neutral analyte molecules and the attaching small inorganic anions have not been fully characterized.Various mass spectrometry methods have been applied to probe the interactions between ions and neutral analyte molecules [13][14][15]. These methods typically evaluate enthalpies of ion-molecule reactions or unimolecular dissociations of ionic adducts to derive gasphase thermodynamic properties such as bond energies and ion affinities.…”

mentioning

confidence: 99%

“…Various mass spectrometry methods have been applied to probe the interactions between ions and neutral analyte molecules [13][14][15]. These methods typically evaluate enthalpies of ion-molecule reactions or unimolecular dissociations of ionic adducts to derive gasphase thermodynamic properties such as bond energies and ion affinities.…”

mentioning

confidence: 99%

Evaluation of the role of multiple hydrogen bonding in offering stability to negative ion adducts in electrospray mass spectrometry

Cai

Concha

Murray

et al. 2002

J. Am. Soc. Mass Spectrom.

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An experimental approach, electrospray mass spectrometry (ES-MS), and a theoretical approach employing computer modeling, have been used to characterize the interaction between small inorganic anions and neutral analyte molecules that form anionic adduct species in negative mode ES mass spectrometry. Certain anionic adducts of small saccharides (e.g., ␣-D-glucose, sucrose) have shown exceptional stability in ES mass spectra even when internal energies are raised at high "cone" voltages. Computer modeling studies reveal that multiple hydrogen bonding strengthens the interaction between these neutral molecules and the attaching anion. The equilibrium structures and stabilization energies of these anionic adducts have been evaluated by semi-empirical, ab initio, and density functional theory (DFT) methods. Chloride anion is found to be capable of forming "bridging" hydrogen bonds between monosaccharide rings of polysaccharides resulting in the stabilization of chloride adducts, thus reducing the tendency for the glycosidic bond to decompose. Moreover, the tendency for various hydroxyl hydrogens on saccharide molecules to dissociate in the form of HA ( [5][6][7][8], have been used to generate anionic adducts for ES-MS studies. The formation and decomposition of chloride adducts have been further investigated from a thermodynamic standpoint [9 -12]. However, the conditions that favor the formation and survival of anionic adducts have not been extensively defined and are not fully understood. Moreover, the interactions between neutral analyte molecules and the attaching small inorganic anions have not been fully characterized.Various mass spectrometry methods have been applied to probe the interactions between ions and neutral analyte molecules [13][14][15]. These methods typically evaluate enthalpies of ion-molecule reactions or unimolecular dissociations of ionic adducts to derive gasphase thermodynamic properties such as bond energies and ion affinities. In some cases, the nature of the ion-molecule interaction could be further elucidated by determining the difference in the entropy changes for competing decomposition pathways [16,17]. To date, the vast majority of ion-molecule interaction studies performed by mass spectrometry focus on positive ion studies of cationic adduct species, especially protonated molecules [14] and alkali metal adducts [18 -21]. Dication adduct species, such as alkaline earth metal [22] and transition metal [23] adducts of oligosaccharides have also been explored. Small inorganic anions attaching to neutral analyte molecules, on the other hand, have received far less research attention. However, a few studies employing anion attachment in negative ion ES-MS have appeared, such as reports on iodide attachment to acetone [24], chloride attachment to saccharides [1, 10 -12], and cyanide attachment (including covalent) to fullerenes [6,8]. In order to gain insight into the exact nature of the interactions between neutral analyte molecules and attaching small inorganic anions that are responsi...

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Experimental Techniques in Gas-Phase Ion Thermochemistry

Cited by 235 publications

References 490 publications

Gas-Phase Energetics of Actinide Oxides: An Assessment of Neutral and Cationic Monoxides and Dioxides from Thorium to Curium

Gas-Phase Energetics of Actinide Oxides: An Assessment of Neutral and Cationic Monoxides and Dioxides from Thorium to Curium

Aplicação da química quântica computacional no estudo de processos químicos envolvidos em espectrometria de massas

Evaluation of the role of multiple hydrogen bonding in offering stability to negative ion adducts in electrospray mass spectrometry

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