Charge State Dependence Research Articles

Impact of Charge State on Characterization of Large Middle-Down Sized Peptides by Tandem Mass Spectrometry.

Fragmentation trends of large peptides were characterized by five activation methods, including HCD, ETD, EThcD, 213 nm UVPD, and 193 nm UVPD. Sequence coverages and scores were assessed based on charge site, peptide sequence, and peptide size. The effect of charge state and peptide size on sequence coverage was explored for a Glu-C digest of E. coli ribosomal proteins, and linear regression analysis of the collection of peptides indicated that HCD, ETD, and EThcD have a higher dependence charge state than 193 and 213 nm UV. Four model peptides, neuromedin, glucagon, galanin, and amyloid β, were characterized in greater detail based on charge site analysis and showed a charge state dependence on sequence coverage for collision and electron-based activation methods.

CO2 activation by copper oxide clusters: size, composition, and charge state dependence.

The interaction of CO2 with copper oxide clusters of different size, composition, and charge is investigated via infrared multiple-photon dissociation (IR-MPD) spectroscopy and density functional theory (DFT) calculations. Laser ablation of a copper target in the presence of an O2/He mixture leads to the preferred formation of oxygen-rich copper oxide cluster cations, CuxOy+ (y > x; x ≤ 8), while the anionic cluster distribution is dominated by stoichiometric (x = y) and oxygen-deficient (y < x; x ≤ 8) species. Subsequent reaction of the clusters with CO2 in a flow tube reactor results in the preferred formation of near-stoichiometric CuxOy(CO2)+/- complexes. IR-MPD spectroscopy of the formed complexes reveals the non-activated binding of CO2 to all cations while CO2 is activated by all anions. The great resemblance of spectra for all sizes investigated demonstrates that CO2 activation is largely independent of cluster size and Cu/O ratio but mainly determined by the cluster charge state. Comparison of the IR-MPD spectra with DFT calculations of the model systems Cu2O4(CO2)- and Cu3O4(CO2)- shows that CO2 activation exclusively results in the formation of a CO3 unit. Subsequent CO2 dissociation to CO appears to be unfavorable due to the instability of CO on the copper oxide clusters indicating that potential hydrogenation reactions will most likely proceed via formate or bicarbonate intermediates.

Exploring the influence of target atomic number (Z2) on mean equilibrium charge state (q¯: A comprehensive study

We have investigated the effect of the target atomic number Z2 on the mean charge state (q¯ using various model predictions such as the Shima–Ishihara –Mikumo, Ziegler–Biersack–Littmark, Schiwietz, Schiwietz–Grande , Fermi-gas-models and theoretical codes with experimental data available in the literature. This investigation makes it possible to determine the best-fit model to calculate q¯. In this work, we discuss the post-collision charge state distribution in different targets used as thin films and projectile beams (Fq+, Siq+, Clq+, and Cuq+) with different charge states (available in literature). A detailed overview of such collision experiments has been explored over a wide energy range of 1.07–3.93 MeV/u. In this contribution, an overview of the mean charge state dependence on the Fermi velocity of target materials is provided. Finally, the influence of the non-radiative electron capture at the target exit surface on the projectile charge state distribution for fast projectiles in different targets is shown, and a comparison is made with experimental data.

Emission of x rays in collisions of xenon ions with metal surfaces

X-ray spectra emitted in collisions of 1500 ∼ 3500-keV projectile Xeq+ (q = 12–29) ions with medium-Z Fe, Ni, and Cu targets as well as higher-Z Ta targets are reported. Interestingly, the lines from the collisions with higher-Z targets are mainly composed of characteristic x rays of target atoms, while those from the collisions with medium-Z targets consist mainly of characteristic x rays of projectile ions and broad molecular-orbital x rays. The origins of all these lines and their charge-state dependence are analyzed in detail within the framework of the transient quasi-molecular states which are formed in the collisions. By analyzing the fluorescence yields and vacancy lifetimes of the collision partners, the reasons for the differences in producing x rays between medium-Z and higher-Z targets are discussed in detail for the first time.

Charge State Dependence of Phase Transition Catalysis of Dynamic Cu Clusters in CO2 Dissociation

Charge State Dependence of Phase Transition Catalysis of Dynamic Cu Clusters in CO₂ Dissociation

Size and charge-state dependence of detachment energies of polyanionic silver clusters.

The electronic properties of silver clusters (N up to 800) charged by attachment of up to z = 7 excess electrons are investigated. As an essential preparation step, the technique of in-trap electron attachment to size-selected monoanions within a linear Paul trap is applied. By taking advantage of tunable laser pulses, the photoelectron spectra allow us to evaluate details of the electronic structure of polyanionic metal clusters, giving a multidimensional dataset. The subsequent analysis based on the liquid drop model provides information about the atomic structure and the bulk work function at a hitherto unknown quality.

Dynamic charge-changing processes in highly charged ions colliding with Ar atoms near the Bohr velocity

The average charge states of $^{20}\mathrm{Ne}^{7+}$ and $^{131}\mathrm{Xe}^{20+}$ ions penetrating through the gaseous argon targets with different areal densities are measured, and the velocities of projectile is close to the Bohr velocity regime ($v\ensuremath{\sim}1$ a.u.). The results show that, with the increase of target density, the dynamic evolution of average charge occurs in three different stages. The dependence of the average charge state on the charge-changing cross section from the nonequilibrium stage to the equilibrium stage is revealed by the theoretical predictions that consider single-electron and additional double-electron processes. It is found that the multi-electron charge-changing process needs to be properly considered in the equilibrium stage. In addition, an analysis model is proposed to predict the average charge state of the projectile in the event of significant energy loss and to quantitatively evaluate the dependence of energy loss on the charge-changing cross section.

Velocity and charge-state dependence on the Coulomb explosion of N2, under the impact of highly-charged ions at intermediate velocities

We report the comprehensive measurement of the Coulomb explosion of the double and triple ionization of N2 in collisions with slow highly-charged ions. The experiments are carried out with ion beams of different charge states for a given velocity (1 a.u.) and at three different velocities for a given charge state (O6+). By analyzing the kinetic energy release distributions of and molecular ions, the effects of projectile velocity and charge state on the population of different molecular states are inferred. We explain such a systematic variation in the population of different molecular states considering the energy deposition to N2 by the projectile ions.

Charge State Dependence of Amino Acid Propensity at Water Surface: Mechanisms Elucidated by Molecular Dynamics Simulations.

Atmospheric aerosols contain a variety of compounds, among them free amino acids and salt ions. The pH of the aerosol droplets depends on their origin and environment. Consequently, compounds like free amino acids found in the droplets will be at different charge states, since these states to a great extent depend on the surrounding pH condition. In droplets of marine origin, amino acids are believed to drive salt ions to the water surface and a pH-dependent amino acid surface propensity will, therefore, indirectly affect many processes in atmospheric chemistry and physics such as for instance cloud condensation. To understand the surface propensity of glycine, valine, and phenylalanine at acidic, neutral, and basic pH, we used molecular dynamics (MD) simulations to investigate them at three different charge states in water. Their respective surface propensities were obtained by the means of a potential of mean force (PMF) in an umbrella sampling approach. Glycine was found to have no preference for the surface, while both valine and phenylalanine showed high propensities. Among the charge states of the surface-enriched ones, the cation, representing the amino acids at low pH, was found to have the highest affinity. Free energy decomposition revealed that the driving forces depend strongly on the nature of the amino acid and its charge state. In phenylalanine, the main factor was found to be a substantial entropy gain, likely related to the side chain, whereas in valine, hydrogen bonding to the functional groups leads to favorable energies and, in turn, affects the surface propensity. A significant gain in water–water enthalpy was seen for both valine and phenylalanine.

Interplay between spin proximity effect and charge-dependent exciton dynamics in MoSe2/CrBr3 van der Waals heterostructures

Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. Here, we report a charge-state dependency of the magnetic proximity effects between MoSe2 and CrBr3 in photoluminescence, whereby the valley polarization of the MoSe2 trion state conforms closely to the local CrBr3 magnetization, while the neutral exciton state remains insensitive to the ferromagnet. We attribute this to spin-dependent interlayer charge transfer occurring on timescales between the exciton and trion radiative lifetimes. Going further, we uncover by both the magneto-optical Kerr effect and photoluminescence a domain-like spatial topography of contrasting valley polarization, which we infer to be labyrinthine or otherwise highly intricate, with features smaller than 400 nm corresponding to our optical resolution. Our findings offer a unique insight into the interplay between short-lived valley excitons and spin-dependent interlayer tunneling, while also highlighting MoSe2 as a promising candidate to optically interface with exotic spin textures in van der Waals structures.

Coupling 193 nm Ultraviolet Photodissociation and Ion Mobility for Sequence Characterization of Conformationally-Selected Peptides.

Ultraviolet photodissociation (UVPD) has emerged as a useful technique for characterizing peptide, protein, and protein complex primary and secondary structure. 193 nm UVPD, specifically, enables extensive covalent fragmentation of the peptide backbone without the requirement of a specific side chain chromophore and with no precursor charge state dependence. We have modified a commercial quadrupole-ion mobility-time-of-flight (Q-IM-TOF) mass spectrometer to include 193 nm UVPD following ion mobility. Ion mobility (IM) is a gas-phase separation technique that enables separation of ions by their size, shape, and charge, providing an orthogonal dimension of separation to mass analysis. Following instrument modifications, we characterized the performance of, and information that could be generated from, this new setup using the model peptides substance P, melittin, and insulin chain B. These experiments show extensive fragmentation across the peptide backbone and a variety of ion types as expected from 193 nm UVPD. Additionally, y-2 ions (along with complementary a+2 and b+2 ions) N-terminal to proline were observed. Combining the IM separation and mobility gating capabilities with UVPD, we demonstrate the ability to accomplish both mass- and mobility-selection of bradykinin des-Arg9 and des-Arg1 peptides followed by complete sequence characterization by UVPD. The new capabilities of this modified instrument demonstrate the utility of combining IM with UVPD because isobaric species cannot be independently selected with a traditional quadrupole alone.

A Modified Drift Tube Ion Mobility-Mass Spectrometer for Charge-Multiplexed Collision-Induced Unfolding.

Collision-induced unfolding (CIU) of protein ions and their noncovalent complexes offers relatively rapid access to a rich portfolio of biophysical information, without the need to tag or purify proteins prior to analysis. Such assays have been characterized extensively for a range of therapeutic proteins, proving exquisitely sensitive to alterations in protein sequence, structure, and post-translational modification state. Despite advantages over traditional probes of protein stability, improving the throughput and information content of gas-phase protein unfolding assays remains a challenge for current instrument platforms. In this report, we describe modifications to an Agilent 6560 drift tube ion mobility-mass spectrometer in order to perform robust, simultaneous CIU across all precursor ions detected. This approach dramatically increases the speed associated with typical CIU assays, which typically involve mass selection of narrow m/ z regions prior to collisional activation, and thus their development requires a comprehensive assessment of charge-stripping reactions that can unintentionally pollute CIU data with chemical noise when more than one precursor ion is allowed to undergo simultaneous activation. By studying the unfolding and dissociation of intact antibody ions, a key analyte class associated with biotherapeutics, we reveal a predictive relationship between the precursor charge state, the amount of buffer components bound to the ions of interest, and the amount of charge stripping detected. We then utilize our knowledge of antibody charge stripping to rapidly capture CIU data for a range of antibody subclasses and subtypes across all charge states simultaneously, demonstrating a strong charge state dependence on the information content of CIU. Finally, we demonstrate that CIU data collection times can be further reduced by scanning fewer voltage steps, enabling us to optimize the throughput of our improved CIU methods and confidently differentiate antibody variant ions using ∼20% of the data typically collected during CIU. Taken together, our results characterize a new instrument platform for biotherapeutic stability measurements with dramatically improved throughput and information content.

Impact of charge state on 193 nm ultraviolet photodissociation of protein complexes.

As applications in mass spectrometry continue to expand into the field of structural biology, there have been an increasing number of studies on noncovalent biological assemblies. Ensuring that protein complexes maintain native-like conformations and architectures during the transition from solution to the gas phase is a key aim. Probing composition and arrangement of subunits of multi-charged complexes via tandem mass spectrometry (MS/MS) may lead to protein unfolding and the redistribution of charges on the constituent subunits, leading to asymmetric charge partitioning and ejection of a high-charged monomer. Additionally, the overall dissociation efficiency of many ion activation methods is often suppressed for low charge states, hindering the effectiveness of MS/MS for complexes that have low charge density. Ultraviolet photodissociation (UVPD) of proteins using 193 nm photons is a high-energy alternative to collisional activation and demonstrates little to no charge state dependence. Here the symmetry of charge partitioning upon UVPD is evaluated for an array of multimeric protein complexes as a function of initial charge state. The results demonstrate that high laser energies (3 mJ) for UVPD induces more symmetric charge partitioning and ejection of low-charged, presumably compact monomers than higher-energy collisional dissociation (HCD).

Ultraviolet Photodissociation of ESI- and MALDI-Generated Protein Ions on a Q-Exactive Mass Spectrometer.

The identification of molecular ions produced by MALDI or ESI strongly relies on their fragmentation to structurally informative fragments. The widely diffused fragmentation techniques for ESI multiply charged ions are either incompatible (ECD and ETD) or show lower efficiency (CID, HCD), with the predominantly singly charged peptide and protein ions formed by MALDI. In-source decay has been successfully adopted to sequence MALDI-generated ions, but it further increases spectral complexity, and it is not compatible with mass-spectrometry imaging. Excellent UVPD performances, in terms of number of fragment ions and sequence coverage, has been demonstrated for electrospray ionization for multiple proteomics applications. UVPD showed a much lower charge-state dependence, and so protein ions produced by MALDI may exhibit equal propensity to fragment. Here we report UVPD implementation on an Orbitrap Q-Exactive Plus mass spectrometer equipped with an ESI/EP-MALDI. UVPD of MALDI-generated ions was benchmarked against MALDI-ISD, MALDI-HCD, and ESI-UVPD. MALDI-UVPD outperformed MALDI-HCD and ISD, efficiently sequencing small proteins ions. Moreover, the singly charged nature of MALDI-UVPD avoids the bioinformatics challenges associated with highly congested ESI-UVPD mass spectra. Our results demonstrate the ability of UVPD to further improve tandem mass spectrometry capabilities for MALDI-generated protein ions. Data are available via ProteomeXchange with identifier PXD011526.

Optical emission from the interaction of highly charged Xeq+ (6 ≤ q ≤ 23) ions with GaAs surface

This paper reports the measurement of visible light emission in the collisions of slow (V ∼ 0.38 VBohr) highly charged Xeq+ (6 ≤ q ≤ 23) ions with GaAs surface. The experimental results include Ga I lines from the 4d 2D3/2 and 5 s 2S1/2 to the 4p 2P1/2,3/2 states and Ga II lines belonged to the electron transitions 4p21D2 → 4s4p 1P1, 4s5s 1S0 → 4s4p 1P1 and 4s4f 1F3 → 4s4d 3D3. The measurement on the projectile charge state dependences of Ga II at 270.20, 277.90, 426.20 nm and Ga I at 287.65, 294.55, 403.55, 417.35 nm lines is presented. It is concluded that the photon yields increase with charge state in the same way as the potential energy increases and the potential energy is the driving force for optical emission of excited Ga atoms and Ga+ ions.

Structural Characterization and Absolute Quantification of Microcystin Peptides Using Collision-Induced and Ultraviolet Photo-Dissociation Tandem Mass Spectrometry.

Microcystin (MC) peptides produced by cyanobacteria pose a hepatotoxic threat to human health upon ingestion from contaminated drinking water. While rapid MC identification and quantification in contaminated body fluids or tissue samples is important for patient treatment and outcomes, conventional immunoassay-based measurement strategies typically lack the specificity required for unambiguous determination of specific MC variants, whose toxicity can significantly vary depending on their structures. Furthermore, the unambiguous identification and accurate quantitation of MC variants using tandem mass spectrometry (MS/MS)-based methods can be limited due to a current lack of appropriate stable isotope-labeled internal standards. To address these limitations, we have systematically examined here the sequence and charge state dependence to the formation and absolute abundance of both "global" and "variant-specific" product ions from representative MC-LR, MC-YR, MC-RR, and MC-LA peptides, using higher-energy collisional dissociation (HCD)-MS/MS, ion-trap collision-induced dissociation (CID)-MS/MS and CID-MS3, and 193nm ultraviolet photodissociation (UPVD)-MS/MS. HCD-MS/MS was found to provide the greatest detection sensitivity for both global and variant-specific product ions in each of the MC variants, except for MC-YR where a variant-specific product uniquely formed via UPVD-MS/MS was observed with the greatest absolute abundance. A simple methodology for the preparation and characterization of 18O-stable isotope-labeled MC reference materials for use as internal standards was also developed. Finally, we have demonstrated the applicability of the methods developed herein for absolute quantification of MC-LR present in human urine samples, using capillary scale liquid chromatography coupled with ultra-high resolution / accurate mass spectrometry and HCD-MS/MS. Graphical abstract ᅟ.

Research Update: Ab initio study on resistive memory device optimization trends: Dopant segregation effects and data retention in HfO2−x

Segregation energy trends and their charge state dependence were established for Group II to Group VI substitutional metal dopants in HfO2 using density functional theory. Corroborating the segregation energy with dopant-oxygen bond lengths and charge state stability, strong effects are predicted for Group II and Group III p-type dopants, which can easily reverse their segregation trend due to −2 charge state preference. Transitions between segregation and isolation may occur around 1.5 eV above the valence band maximum, with the exception of Al, which remains barely stable in its segregated form. In Al-doped HfOx, the switching characteristics of filaments formed near Al dopants show subtle changes and the OFF state data retention is degraded. A comprehensive assessment on configurational Al-VO interaction, charge state dependence, and migration energy changes points to the fact that to achieve OFF state data retention improvements, it will be necessary to engineer the filament interaction with Al to stabilize configurations that favor vacancy filament dissolution. Another mode of failure can result from subsequent charge trapping during the operation of the device, which ultimately prohibits the filament dissociation.

Transition metal ions in ZnO: Effects of intrashell coulomb repulsion on electronic properties

Electronic structure of the transition metal (TM) dopants in ZnO is calculated by first principles approach. Analysis of the results is focused on the properties determined by the intrashell Coulomb coupling. The role of both direct and exchange interaction channel is analyzed. The coupling is manifested in the strong charge state dependence of the TM gap levels, which leads to the metastability of photoexcited Mn, and determines the accessible equilibrium charge states of TM ions. The varying magnitude of the exchange coupling is reflected in the dependence of the spin splitting energy on the chemical identity across the 3d series, as well as the charge state dependence of spin-up spin-down exchange splitting.

Analysis of the plasma blob formation/transport and its effects on impurity transport in the scrape‐off layer regions

The purpose of this study was to clarify the effects of a plasma blob on the impurity transport in the scrape‐off layer (SOL) and divertor region of fusion devices. As a first step, plasma blob formation and transport were simulated by a two‐dimensional interchange turbulence model. Its effects on impurity transport were studied by the impurity equations of motion in the trace impurity limit. The results show that a blob is produced by the interchange instability and transported radially towards the wall by the E × B drift due to the polarization electric field by the charge separation between ions and electrons inside the blob due to their magnetic drifts. The polarization electric field also induces the impurity radial E × B drift and the resultant impurity radial transport at least for impurities with a small Larmor radius in comparison with the blob size. These first results provide us with a robust basis for a more systematic study (e.g., dependence of impurity mass and charge state) and for a more quantitative evaluation of the effects of the blob on the impurity transport in the SOL and divertor region.

3p-B-4 低速多価イオンによって固体表面から脱離される水素イオンの強い価数依存性

3p-B-4 低速多価イオンによって固体表面から脱離される水素イオンの強い価数依存性