Parent Ion Charge State Research Articles

Coulomb explosion imaging for gas-phase molecular structure determination: An ab initio trajectory simulation study.

Coulomb explosion velocity-map imaging is a new and potentially universal probe for gas-phase chemical dynamics studies, capable of yielding direct information on (time-evolving) molecular structure. The approach relies on a detailed understanding of the mapping between the initial atomic positions within the molecular structure of interest and the final velocities of the fragments formed via Coulomb explosion. Comprehensive on-the-fly ab initio trajectory studies of the Coulomb explosion dynamics are presented for two prototypical small molecules, formyl chloride and cis-1,2-dichloroethene, in order to explore conditions under which reliable structural information can be extracted from fragment velocity-map images. It is shown that for low parent ion charge states, the mapping from initial atomic positions to final fragment velocities is complex and very sensitive to the parent ion charge state as well as many other experimental and simulation parameters. For high-charge states, however, the mapping is much more straightforward and dominated by Coulombic interactions (moderated, if appropriate, by the requirements of overall spin conservation). This study proposes minimum requirements for the high-charge regime, highlights the need to work in this regime in order to obtain robust structural information from fragment velocity-map images, and suggests how quantitative structural information may be extracted from experimental data.

Analysis of multiply charged monomers and dimers of human islet amyloid polypeptide by collision-induced dissociation with electrospray ionization mass spectrometry

Collision-induced dissociation (CID) with ESI-MS was used to obtain structural information on early-stage aggregation of hIAPP (human islet amyloid polypeptide) monomers and oligomers. MS analysis showed that the hIAPP monomers and oligomers were multiply charged. MS/MS analysis indicated that the hIAPP monomers adopt different structures depending on the parent ion charge state. The fragmentation patterns indicated structural similarity of M2+ & M3+ and M4+ & M5+ (M = monomer). MS/MS analysis of the dimers showed that D5+ (D = dimer) comprised M2+ and M3+ subunits, and the peptide bond dissociated in the 15–37 residue region of the monomer subunit.

Reactivity of self-assembled supramolecular complexes in the gas phase: A supramolecular neighbor group effect

Infrared multi-photon dissociation (IRMPD) spectra of mass-selected, self-assembled supramolecular squares and their gas-phase fragments have been recorded in a Fourier-transform ion-cyclotron resonance (FT-ICR) mass spectrometer. The squares have been transferred into the gas phase by electrospray ionization (ESI) under very soft ionization conditions resulting in a series of signals for intact squares in different charge states by stripping off two or more counter ions. The fragmentation patterns of the squares strongly depend on the parent ion's charge state. For species with a lower number of charges, expulsions of edge ligands prevail, whereas charge separation pathways dominate the dissociation pathways of more highly charged species.

Ion Trap versus Low-Energy Beam-Type Collision-Induced Dissociation of Protonated Ubiquitin Ions

The beam-type and ion trap collision-induced dissociation (CID) behaviors of protonated bovine ubiquitin ions were studied for charge states ranging from +6 to +12 on a modified triple quadrupole/linear ion trap tandem mass spectrometer. Both beam-type CID and ion trap CID were conducted in a high-pressure linear ion trap, followed by proton-transfer ion/ion reactions to reduce the charge states of product ions mostly to +1. The product ions observed under each activation condition were predominantly b- and y-type ions. Fragmentation patterns showed a much stronger dependence on parent ion charge state with ion trap CID than with beam-type CID using nitrogen as the collision gas, with preferential cleavages C-terminal to aspartic acid at relatively low charge states, nonspecific fragmentation at moderate charge states, and favored cleavages N-terminal to proline residues at high charge states. In the beam-type CID case, extensive cleavage along the protein backbone was noted, which yielded richer sequence information (77% of backbone amide bond cleavages) than did ion trap CID (52% of backbone amide bond cleavages). Collision gas identity and collision energy were also evaluated in terms of their effects on the beam-type CID spectrum. The use of helium as collision gas, as opposed to nitrogen, resulted in CID behavior that was sensitive to changes in collision energy. At low collision energies, the beam-type CID data resembled the ion trap CID data with preferential cleavages predominant, while at high collision energies, nonspecific fragmentation was observed with increased contributions from sequential fragmentation.

Nuclear-stopping-induced fast multifragmentation inAr+−C60collisions

Ionization and multifragmentation of C{sub 60} in Ar{sup +} impact at 7 keV, 14 keV, and 20 keV have been investigated. Fragment mass spectra differentiated according to the C{sub 60}{sup r+} parent ion charge state are interpreted in terms of a transition from the nonstatistical fast multifragmentation in a time range of about 500 fs induced by nuclear interaction at low collision velocity (v<0.1 a.u.) to the statistical multifragmentation induced by nuclear and electronic interaction at higher collision velocities. Prompt ejection of a carbon atom due to the direct momentum transfer is observed.

Targeted biomarker detection via whole protein ion trap tandem mass spectrometry: thymosin ?4 in a human lung cancer cell line

N-Terminally acetylated thymosin beta4, a species implicated for use as a cancer biomarker, was identified in a human lung cancer cell line using ion trap tandem mass spectrometry at the whole protein level. Ion-ion proton transfer reactions were used for parent ion concentration/manipulation and to simplify interpretation of product ion spectra. Dissociation data for the +6 to +3 charge states are reported. As is usually the case, structural information available from the ion trap collisional activation of the protein is sensitive to parent ion charge state. Each parent ion charge state selected, however, provided sufficient information to make a confident identification. Furthermore, each charge state provided relatively rich fragmentation. Therefore, any of the charge states can be used to detect with high specificity thymosin beta(4) in a complex protein mixture. There are advantages associated with the rapid detection of protein biomarkers at the whole protein level, as opposed to the peptide level following protein digestion, particularly for relatively small protein and polypeptide biomarkers. Having identified and characterized the protein, product ion spectra obtained directly, without recourse to ion-ion proton transfer reactions, can be used for library matching. However, ion-ion proton transfer reactions for parent ion concentration and charge state purification are advantageous in addressing relatively complex mixtures.

Effects of single amino acid substitution on the collision-induced dissociation of intact protein ions: Turkey ovomucoid third domain.

Expanded understanding of the factors that direct polypeptide ion fragmentation can lead to improved specificity in the use of tandem mass spectrometry for the identification and characterization of proteins. Like the fragmentation of peptide cations, the dissociation of whole protein cations shows several preferred cleavages, the likelihood for which is parent ion charge dependent. While such cleavages are often observed, they are far from universally observed, despite the presence of the residues known to promote them. Furthermore, cleavages at residues not noted to be common in a variety of proteins can be dominant for a particular protein or protein ion charge state. Motivated by the ability to study a small protein, turkey ovomucoid third domain, for which a variety of single amino acid variants are available, the effects of changing the identity of one amino acid in the protein sequence on its dissociation behavior were examined. In particular, changes in amino acids associated with C-terminal aspartic acid cleavage and N-terminal proline cleavage were emphasized. Consistent with previous studies, the product ion spectra were found to be dependent upon the parent ion charge state. Furthermore, the fraction of possible C-terminal aspartic acid cleavages observed to occur for this protein was significantly larger than the fraction of possible N-terminal proline cleavages. In fact, very little N-terminal proline cleavage was noted for the wild-type protein despite the presence of three proline residues in the protein. The addition/removal of proline and aspartic acids was studied along with changes in selected residues adjacent to proline residues. Evidence for inhibition of proline cleavage by the presence of nearby basic residues was noted, particularly if the basic residue was likely to be protonated.

Thermal decomposition of a gaseous multiprotein complex studied by blackbody infrared radiative dissociation. Investigating the origin of the asymmetric dissociation behavior.

The blackbody infrared radiative dissociation technique was used to study the thermal decomposition of the gaseous B5 pentamer of the Shiga-like toxin I and its complexes with the Pk trisaccharide and a decavalent Pk-based oligosaccharide ligand (STARFISH, S). Dissociation of the protonated pentamer, (B5 + nH)n+ triple bond B5n+ where n = 11-14, proceeds almost exclusively by the loss of a single subunit (B) with a disproportionately large fraction (30-50%) of the parent ion charge. The degree of charge enrichment of the leaving subunit increases with increasing parent ion charge state. For n = 12-14, a distribution of product ion charge states is observed. The yields of the complementary pairs of product ions are sensitive to the reaction temperature, with higher temperatures favoring greater charge enrichment of the leaving subunit for +13 and +14, and the opposite effect for +12. These results indicate that some of the protons are rapidly exchanged between subunits in the gas phase. Dissociation of B5(14+) x S proceeds exclusively by the loss of one subunit, although the ligand increases the stability of the complex and also reduces the degree of charge enrichment in the ejected monomer. For B5(12+)(Pk)1-3, the loss of neutral Pk competes with loss of a subunit at low temperatures. Linear Arrhenius plots were obtained from the temperature-dependent dissociation rate constants measured for the loss of B from B5n+ and B514+ x S. The magnitude of the Arrhenius parameters is highly dependent on the charge state of the pentamer: Ea = 35 kcal/mol and A = 1,019 s(-1) (+14), 46 kcal/mol and 1,023 S(-1) (+13), 50 kcal/mol and 1026 s(-1) (+12), and 80 kcal/mol and 10(39) (+11). The Ea and A for B5(14+) x S are 59 kcal/mol and 10(30) s(-1), respectively. The reaction pathways leading to greater charge enrichment of the subunit lost from the B5(14+) and B5(13+) ions correspond to higher energy processes, however, these pathways are kinetically preferred at higher temperatures due to their large A factors. A simple electrostatic model, whereby charge enrichment leads to Coulombic repulsion-induced denaturation of the subunits and disruption of the intersubunit interactions, provides an explanation for the magnitude of the Arrhenius parameters and the origin of the asymmetric dissociation behavior of the complexes.

Ion trap collisional activation of protonated poly(propylene imine) dendrimers: generations 1–5

Ions derived from electrospray ionization of poly(propylene imine) dendrimers (generations 1–5, synthesized from a 1,4-diaminobutane core) were subjected to ion trap tandem mass spectrometry. In some cases, ion/ion proton transfer reactions were used to form low charge state parent ions from higher charge state ions generated by electrospray. In addition, ion/ion proton transfer reactions performed on product ions formed by ion trap collisional activation of multiply charged parent ions facilitated interpretation of tandem mass spectrometry (MS/MS) spectra. Almost all of the products derived from dendrimer parent ions could be rationalized based on a set of dissociation processes involving a previously noted intramolecular nucleophilic attack by a nearest-neighbor nitrogen atom on a carbon alpha to a protonation site. For a given protonation site, attack can occur either from the adjacent nitrogen closer to the interior or closer to the exterior of the dendrimer. The processes that lead to the dominant products are highly dependent upon parent ion charge state. Singly charged ions fragment primarily by processes directed by protonation at a diaminobutane nitrogen whereas highly charged parent ions fragment largely by processes directed by protonation closer to the periphery of the dendrimer. MS/MS data for singly charged ions of series of synthesis failure products in the fourth and fifth generation dendrimers were collected. The results show that ion trap tandem mass spectrometry can provide information about the composition of mixtures of isomeric products resulting from side reactions that occur during the course of the multistep syntheses of the dendrimers. The data show, for example, that synthesis failures tend to occur on one side of the dendrimer.

Charge state effects in the decompositions of single-nucleobase oligonucleotide polyanions

A series of anions derived from electrospray ionization of small oligonucleofides, each consisting of a single nucleobase (adenine, thymine, cytidine or guanine), have been subjected to ion trap tandem mass spectrometry. The data set allows for comparisons of dissociation behavior as functions of parent ion charge, oligomer length, and nucleobase identity. Parent ion charge is seen to play a major role in determining the most important dissociation channels. Dramatic changes in the relative contributions of the various possible dissociation channels are observed from one parent ion charge state to the next. Parent ion charge apparently can alter the relative order of the threshold energies required for the various competitive sequence channels. In addition, the ion trap collisional activation experiment is highly sensitive to differences in the energy requirements for the lowest energy dissociation pathways. Nucleobase identity also is an important factor, with each series of single-nucleobase oligomers showing unique dissociation behavior. For example, poly-T anions show an enhanced tendency for the loss of the 5′ thymine relative to the same charge states of oligomers comprised of the other nucleobases whereas the poly-G anions show a lower tendency for the loss of the 5′ guanine. Poly-A anions show consecutive nucleobase loss as a reaction channel that competes with those that provide direct sequence information. This tendency increases with increasing oligomer size and charge.