Ion Mobility Measurements and their Applications to Clusters and Biomolecules

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A challenging aspect of structural elucidation of carbohydrates is gaining unambiguous information for anomers, linkage, and position isomers. Such isomers with identical mass can't be easily distinguished in mass spectrometry and a separation step is required prior to mass spectrometry identification. In our laboratory, gas-phase separation and differentiation of anomers, linkage, and position isomers of disaccharides was achieved using High-Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS). The FAIMS method responds to changes in ion mobility at high field rather than absolute values of ion mobility, and was shown to provide efficient separation and identification of disaccharide isomers at high sensitivity. Separation of analyzed disaccharide isomers can be accomplished at low nM level in a matter of seconds without sample purification or fractionation. Capability for examining a large population of ionic species of disaccharides by this method allowed for correlating structural details of disaccharide isomers with their separation properties in FAIMS. Results for disaccharide isomers indicate that this method could be applied to a larger group of carbohydrates. ( Mass spectrometry has shown a unique ability to resolve certain structural ambiguities. Permethylation is a well developed but time-consuming GC-MS method in linkage analysis of oligosaccharides [1,2]. Other methods implementing the derivatization of saccharides have been used to obtain their structural information [3][4][5][6][7][8][9][10][11]. The soft mass spectrometry ionization techniques such as fast atom bombardment (FAB) [12][13][14][15][16], liquid secondary ionization mass spectrometry (LSIMS) [17,18], along with matrix-assisted laser desorption ionization (MALDI) [19 -23], and electrospray ionization (ESI) [24 -28] have gained attention as approaches to investigate underivatized oligosaccharides. Collision-induced dissociation (CID) offers the possibility to assign details of carbohydrate structure such as sugar sequence for linear oligosaccharides [12], linkage position [12,[15][16][17]29], and differentiation of anomers [25,30]. In addition to analyzing protonated or deprotonated molecular ions of saccharides in CID, alkali metal adduct ions have been used to promote fragmentation of ligand-carbohydrate complexes. In the positive ion mode, calcium and magnesium adducts of oligosaccharides were investigated for the elucidation of the linkage position of trisaccharides [26] and cobalt complexes have been used to differentiate the anomeric configuration of disaccharides [30]. In the negative ion mode, decomposition of chloride adducts was investigated for differentiation of the linkage position of disaccharides [31].Despite recent advances in tandem mass spectrometry of carbohydrates, the spectral differences for some isomers are very small and they do not provide unambiguous identification. This is especially true when a mixture of isomers with the same m/z has to be analyzed. In such applications a separation step is required ...

Section: Considerations Related To the Separation Mechanism Of Disaccmentioning

confidence: 83%

Rapid and sensitive differentiation of anomers, linkage, and position isomers of disaccharides using High-Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS)

Gabryelski

Froese

2003

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“…The drift tube contains 2.0 torr of 300 K He buffer gas. The pulse of ions drifts through the gas under the influence of a uniform electric field and different conformations (for a specific charge state selected by the quadrupole mass spectrometer) are separated because of differences in their collision cross sections with the buffer gas [20]. Compact conformers have smaller cross sections (and thus shorter drift times) than elongated conformers.…”

Section: Methodsmentioning

confidence: 99%

Evidence for unfolding and refolding of gas-phase cytochrome c ions in a Paul trap

Badman

Myung

Clemmer

2005

Self Cite

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The folding pathways of gas-phase cytochrome c ions produced by electrospray ionization have been studied by an ion trapping/ion mobility technique that allows conformations to be examined over extended timescales (10 ms to 10 s). The results show that the ϩ9 charge state emerges from solution as a compact structure and then rapidly unfolds into several substantially more open structures, a transition that requires 30-60 ms; over substantially longer timescales (250 ms to 10 s) elongated states appear to refold into an array of folded structures. The new folded states are less compact than those that are apparent during the initial unfolding. Apparently, unfolding to highly open conformations is a key step that must occur before ϩ9 ions can sample more compact states that are stable at longer times. . Recently, structural studies of ions in the gas phase have attracted significant attention as a means of studying intrinsic interactions of biomolecules in the absence of solvent to further understand fundamental aspects of protein folding. Examination of gas-phase structure/ conformations of protein ions has primarily been studied by ion mobility [4, 5] and gas-phase hydrogendeuterium exchange [6-10] methods, with some recent studies [11,12] using the "gentle" dissociation process of electron capture dissociation (ECD) [13]. In addition, unfolding and folding transitions of gas-phase ions have been studied by exciting the ions via laser irradiation [8,11,12] or energetic collisions [5,8,9] followed by analysis of structure/conformation by the aforementioned methods. The advantages of studying gas-phase ions is that one is able to study not only "naked" ions' intrinsic physical and chemical properties, but also the stepwise solvation of these ions [14 -16].We have recently developed a new method for studying the time-dependent behavior of gas-phase protein ions. In this approach we store ions in a Paul geometry ion trap for variable amounts of time and follow the structural transitions by analyzing the conformations of electrosprayed ions by a combined ion mobility/time-of-flight analysis [17,18]. In this study we show evidence for structural transitions of the ϩ9

“…Our original goal was to use mass spectrometry and ion mobility methods [37,38] to examine the gas-phase conformations of the above-mentioned T/G tetranucleotides to determine whether dTGTT Ϫ and dTTGT Ϫ form zwitterions as predicted. However, since so little data is available on the conformations of oligonucleotides in the gas phase, we began with the more straightforward dinucleotides [39,40].…”

mentioning

confidence: 99%

Gas-phase conformations of deprotonated trinucleotides (dGTT⁻, dTGT⁻, and dTTG⁻): the question of zwitterion formation

Gidden

Bowers

2003

The gas-phase conformations of a series of trinucleotides containing thymine (T) and guanine (G) bases were investigated for the possibility of zwitterion formation. Deprotonated dGTT Ϫ , dTGT Ϫ , and dTTG Ϫ ions were formed by MALDI and their collision cross-sections in helium measured by ion mobility based methods. dTGT Ϫ was theoretically modeled assuming a zwitterionic and non-zwitterionic structure while dGTT Ϫ and dTTG Ϫ were considered "control groups" and modeled only as non-zwitterions. In the zwitterion, G is protonated at the N7 site and the two neighboring phosphates are deprotonated. In the non-zwitterion, G is not protonated and only one phosphate group is deprotonated. Two conformers, whose cross-sections differ by 17 Ϯ 2 Å 2 , are observed for dTGT Ϫ in the 80 K experiments. Multiple conformers are also observed for dGTT Ϫ and dTTG Ϫ at 80 K, though relative cross-section differences between the conformers could not be accurately obtained. At higher temperatures (Ͼ200 K), the conformers rapidly interconvert on the experimental time scale and a single "time-averaged" conformer is observed in the ion mobility data. Theory predicts only one low-energy conformation for the zwitterionic form of dTGT Ϫ with a cross-section 8% smaller than experimental values. Additionally, the extra H ϩ on G does not bridge both phosphates. Thus, dTGT Ϫ does not appear to be a stable zwitterion in the gas-phase. Theory does, however, predict two low-energy conformers for the non-zwitterionic form of dTGT Ϫ that differ in cross-section by 18 Ϯ 3 Å 2 , in good agreement with the experiment. In the smaller cross-section form (folded conformer), G and one of the T bases are stacked while the other T folds towards the stacked pair and hydrogen bonds to G. In the larger cross-section form (open conformer), the unstacked T extends away from the T/G stacked pair. Similar folded and open conformers are predicted for all three trinucleotides, regardless of which phosphate is