Direct fission versus sequential evaporation mechanism of sputtered caesium iodide cluster ions

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Abstract. Singly and doubly charged adducts of LiCl with β-cyclodextrin (βCD) of the type (βCD)(LiCl) n Li + and (βCD) 2 (LiCl) p Li 2 2+ were studied using electrospray ionization mass spectrometry (ESI-MS). Insight into their structural composition was gained by analysis of their collision-induced dissociation (CID) mass spectra. The conditions the ions experience in the transfer region interfacing the ESI source and the mass analyzer were found to have a marked influence on the nature of the detected ions. In one instrument incorporating a single skimmer, individually attached LiCl ion pairs were observed, whereas the dual funnel ion guides of the second instrument allow the detection of previously unknown labile inclusion complexes of (LiCl) n clusters in βCD.

Section: Fragmentation Behaviorsupporting

confidence: 77%

Section: Fragmentation Behaviormentioning

confidence: 99%

Influence of Single Skimmer Versus Dual Funnel Transfer on the Appearance of ESI-Generated LiCl Cluster/ß-Cyclodextrin Inclusion Complexes

Kellner

Drewello

2015

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“…Although our work with ionic liquid clusters [4] did not actively excite ion fragmentation, the mass spectra of DMA-selected ions showed a diversity of product ions along with the parent ion, clearly revealing individual neutral ion-pair evaporation events of the form (CA) n C ϩ ¡(CA) n-1 C ϩ ϩCA. Metastable evaporation events from ionic clusters have been previously observed for hot ions formed by highenergy processes, in particular sputtering from CsI surfaces [5,6]. However, these are the first direct observations of single molecule evaporation events with ionic liquids, and therefore warrant the present more detailed account.…”

mentioning

confidence: 76%

Ion-pair evaporation from ionic liquid clusters

Hogan

Mora

2010

A differential mobility analyzer (DMA) is used in atmospheric pressure N 2 to select a narrow range of electrical mobilities from a complex mix of cluster ions of composition (CA) n (C ϩ ) z . The clusters are introduced into the N 2 gas by electrospraying concentrated (ϳ20 mM) acetonitrile solutions of ionic liquids (molten salts) of composition CA (C ϩ ϭ cation, A -ϭ anion). Mass analysis of these mobility-selected ions reveals the occurrence of individual neutral ion-pair evaporation events from the smallest singly charged clusters:Although bulk ionic liquids are effectively involatile at room temperature, up to six sequential evaporation events are observed. Because this requires far more internal energy than available in the original clusters, substantial heating (ϳ10 eV) must take place in the ion guides leading to the mass analyzer. The observed increase in IL evaporation rate with decreasing size is drastic, in qualitative agreement with the exponential vapor pressure dependence predicted by Kelvin's formula. A single evaporation event is barely detectable at n ϭ 13, while two or more are prominent for n Յ 9. Magic number clusters (CA) 4 C ϩ with singularly low volatilities are found in three of the four ionic liquids studied. Like their recently reported liquid phase prenucleation cluster analogs, these magic number clusters could play a key role as gas-phase nucleation seeds. All the singularly involatile clusters seen are cations, which may help understand commonly observed sign effects in ion-induced nucleation. No other charge-sign asymmetry is seen on cluster evaporation. (J Am Soc Mass Spectrom 2010, 21, 1382-1386

“…In this case however, covalent cleavage of the protein appears to be a competitive process to noncovalent subunit ejection. This is evident from the observation of complementary fragment ions between 5300 and 6600 m/z that correspond to [pentamer-y 40 . This process, summarized in Scheme 2, is an unusual example of backbone fragmentation from oligomeric proteins by CID, while preserving some of the noncovalent interactions between subunits as well as the covalently bound saccharide.…”

Section: Protein Complexesmentioning

confidence: 95%

Surface-induced dissociation shows potential to be more informative than collision-induced dissociation for structural studies of large systems

Wysocki

Jones

Galhena

et al. 2008

103

The ability to preserve noncovalent, macromolecular assemblies intact in the gas phase has paved the way for mass spectrometry to characterize ions of increasing size and become a powerful tool in the field of structural biology. Tandem mass spectrometry experiments have the potential to expand the capabilities of this technique through the gas-phase dissociation of macromolecular complexes, but collisions with small gas atoms currently provide very limited fragmentation. One alternative for dissociating large ions is to collide them into a surface, a more massive target. Here, we demonstrate the ability and benefit of fragmenting large protein complexes and inorganic salt clusters by surface-induced dissociation (SID), which provides more extensive fragmentation of these systems and shows promise as an activation method for ions of increasing size. ver the past two to three decades, mass spectrometry (MS) has expanded significantly, from its early use as a technique for measuring the isotopes of elements and analyzing volatile compounds, to a technique that is now routinely used to study nonvolatile molecules and large macromolecular complexes. Increasingly, mass spectrometry and ion mobility/mass spectrometry are described as structural biology tools. Mass spectrometry has recently provided insights on posttranslational modifications [1], mono-and polydisperse subunit stoichiometry [2], subunit organization [3,4], and noncovalent protein-ligand binding sites [5]. In addition to revealing structural information, mass spectrometry can be used to monitor dynamic processes, such as protein complex assembly [6], protein-substrate and protein-protein interactions [7,8], and substratespecific conformational changes [9].One of the limitations of current technology, however, is the fact that commercial instrumentation is still hampered by the amount of dissociation that can be induced from large biomolecular complexes. Often, MS has to be combined with many solution-based experiments (H/D exchange plus digestion, chemical crosslinking plus digestion, limited proteolysis, solution disruption by changes in ionic strength) because the MS instruments commercially available do not provide extensive dissociation of these massive complexes. A typical dissociation result that is achieved is ejection of a monomer subunit as illustrated here (Figure 1) for a small heat shock protein (sHSP) dodecamer, consisting of 12 subunits each weighing 16.9 kDa [8,10,11]. The 16.9 kDa monomer typically carries away a large percentage of the charge of the original complex with the remainder of the charge on the 11-mer that weighs 186 kDa. Investigators have concluded that this behavior, which has been observed by several research groups for many different noncovalent protein complexes, happens because the low-energy collisions with a gas initiate unfolding of one of the protein subunits [12][13][14]. As this subunit unfolds, it gains surface area, thus allowing it to accept more charge. Eventually, when the unfolding protein and the remainde...