Proton Transfer Reactivity of Large Multiply Charged Ions

Williams, Evan R.

doi:10.1002/(sici)1096-9888(199608)31:8<831::aid-jms392>3.0.co;2-7

Cited by 186 publications

(194 citation statements)

References 54 publications

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“…The former process can result in charge reduction of the analyte or metal ion species via proton transfer to solvent [31,36,37]. The ESI mass spectra of the trivalent hydrated metal ions are very sensitive to source conditions.…”

Section: Mechanism Of Ion Formation: Solvent Evaporation Versus Condementioning

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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Section: Mechanism Of Ion Formation: Solvent Evaporation Versus Condementioning

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

Self Cite

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“…As discussed previously [36,39], it is impossible to calculate the total ion energy for all possible charge site assignments for each structure [20a, 36]. Here, we assume formal charges of ϩ3 on the heme iron atom and -1 on each heme carboxylate group [12,40] Added protons from the electrospray process are confined to basic Arg, His, or Lys residues.…”

Section: Charge Placement In Simulated Structuresmentioning

confidence: 99%

Temperature-dependent H/D exchange of compact and elongated cytochrome c ions in the gas phase

Valentine

Clemmer

2002

J. Am. Soc. Mass Spectrom.

109

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Isotopic exchange reactions of compact and elongated conformations of gaseous cytochrome c ions (ϩ5 and ϩ9 states) with D 2 O have been measured as a function of temperature (from 300 to ϳ440 K) using ion mobility techniques. Rate constants for those sites that exchange at high temperatures (Ͼ400 K) are about an order of magnitude smaller than rate constants for sites that exchange at 300 K. Although the exchange rates decrease, the maximum exchange levels for rapidly exchanging sites increase with temperature. At 300 K, exchange levels of 53 Ϯ 3 and 63 Ϯ 3 are measured for the compact and elongated states, respectively. From 300 to 335 K, the exchange levels increase slightly to ϳ60 to 70 hydrogens. Above 335 K, the levels increase to a value of ϳ200 for the ϩ5 state and ϳ190 for the ϩ9 state, near the maximum possible levels, 200 and 204 for these respective charge states. Molecular dynamics simulations have been carried out on structures having calculated cross sections that are near the experimental values in order to explore the exchange process. Overall, it appears that charge site and exchange site proximities are important factors in the exchange profiles for the elongated ϩ9 ion and the compact ϩ5 ion. (J Am Soc Mass Spectrom 2002, 13, 506 -517) © 2002 American Society for Mass Spectrometry I t is well known that the structures of proteins are influenced by environmental factors such as solution composition, pH, and temperature. However, the degree to which environment and intrinsic properties influence structure is not well understood. Structural domains such as ␣-helices, which are stable in a wide range of environments, were predicted theoretically without considering effects of solvation [1]. More subtle features, such as tertiary structure in different environments, are difficult to predict. Recently, efforts have been made to gather information about the degree to which solvent-free protein conformations resemble their native solution structures [2]. Several studies of lyophilized protein powders have shown that removal of solvent can cause structural changes [3], and the extent of differences between lyophilized and solution states is an active area [4]. New ion sources [5,6] make it possible to isolate biomolecules in the gas phase as ions, and a number of mass spectrometry (MS) based strategies for examining solvent-free conformations are being developed . The new information from these technologies is beginning to be evaluated by theoretical methods [33, 34,35]. There is now substantial evidence that, under some experimental conditions, anhydrous protein and peptide ions may retain elements of solution conformation.The conformations of cytochrome c ions have been examined previously by a number of MS techniques [8, 28]. Ion mobility (for reviews of ion mobility studies see [30]) and isotopic exchange studies [7-10, 11, 12] provide information about the overall shape and number of accessible exchange sites, respectively. These studies indicate the presence of multiple conformations within ind...

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“…However, an understanding of the relationship between gas phase structure and solution conformation is still at a very primitive stage, in large part because detailed gas phase structural information is limited. In addition to chemical probes of gas phase ion structure [1][2][3][4][5][6][7][8][9][10][11][12][13][14], a number physical methods are being developed to examine gas-phase peptide and protein ion structure [15][16][17][18][19][20][21][22][23][24][25][26][27], including collisional activation to examine fragmentation pathways [18 -23, 25-27]. A few studies have suggested that ion conformation may influence fragmentation pathways [19,23,27,28].…”

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confidence: 99%