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Kinlein Z, Clowers BH. Altering Conformational States of Dynamic Ion Populations using Traveling Wave Structures for Lossless Ion Manipulations. Anal Chem 2024; 96:6450-6458. [PMID: 38603648 DOI: 10.1021/acs.analchem.4c00692] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/13/2024]
Abstract
With its capacity to store and translate ions across considerable distances and times, traveling wave structures for lossless ion manipulations (TW-SLIM) provide the foundation to expand the scope of ion mobility spectrometry (IMS) experiments. While promising, the dynamic electric fields and consequential ion-neutral collisions used to realize extensive degrees of separation have a considerable impact on the empirical results and the fundamental interpretation of observed arrival time distributions. Using a custom-designed set of TW-SLIM boards (∼9 m) coupled with a time-of-flight mass spectrometer (SLIM-ToF), we detail the capacity to systematically alter the gas-phase distribution of select peptide conformers. In addition to discussing the role charge-transfer may play in TW-SLIM experiments that occur at extended time scales, the ability of the SLIM-ToF to perform tandem IMS was leveraged to confirm that both the compact and elongated conformers of bradykinin2+ undergo interconversion within the SLIM. Storage experiments in which ions are confined within SLIM using static potential wells suggest that factors aside from TW-induced ion motion contribute to interconversion. Further investigation into this matter suggests that the use of radio frequency (RF) fields to confine ions within SLIM may play a role in ion heating. Aside from interconversion, storage experiments also provide insight into charge transfer behavior over the course of extended periods. The results of the presented experiments suggest that considerations should be taken when analyzing labile species and inform strategies for the TW-SLIM design and method development.
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Affiliation(s)
- Zackary Kinlein
- Department of Chemistry, Washington State University, Pullman, Washington 99164, United States
| | - Brian H Clowers
- Department of Chemistry, Washington State University, Pullman, Washington 99164, United States
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2
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Pierson NA, Clemmer DE. An IMS-IMS threshold method for semi-quantitative determination of activation barriers: Interconversion of proline cis↔trans forms in triply protonated bradykinin. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2015; 377:646-654. [PMID: 25838788 PMCID: PMC4378547 DOI: 10.1016/j.ijms.2014.07.012] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Collisional activation of selected conformations by multidimensional ion mobility spectrometry (IMS-IMS), combined with mass spectrometry (MS), is described as a method to determine semi-quantitative activation energies for interconversion of different structures of the nonapeptide bradykinin (BK, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg). This analysis is based on a calibration involving collision-induced dissociation measurements of ions with known dissociation energies (i.e., "thermometer" ions) such as leucine enkephalin, BK, and amino acid-metal cation systems. The energetic barriers between six conformations of [BK+3H]3+ range from 0.23 ±0.01 to 0.55 ±0.03 eV. Prior results indicate that the major peaks in the IMS distributions correspond to specific combinations of cis and trans configurations of the three proline residues in the peptide sequence. The analysis allows us to directly assess pathways for specific transitions. The combination of structural assignments, experimentally determined barrier heights, onset of the quasi-equilibrium region, and dissociation threshold are used to derive a semi-quantitative potential energy surface for main features of [BK+3H]3+.
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Affiliation(s)
- Nicholas A. Pierson
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405 United States
| | - David E. Clemmer
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405 United States
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3
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Ahmed A, Kim S. Atmospheric pressure photo ionization hydrogen/deuterium exchange mass spectrometry--a method to differentiate isomers by mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:1900-1905. [PMID: 24014151 DOI: 10.1007/s13361-013-0726-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Revised: 07/20/2013] [Accepted: 07/25/2013] [Indexed: 06/02/2023]
Abstract
In this report, a method for in-source hydrogen/deuterium (H/D) exchange at atmospheric pressure is reported. The method was named atmospheric pressure photo ionization hydrogen/deuterium exchange mass spectrometry (APPI HDX MS). H/D exchange was performed by mixing samples dissolved in toluene with CH3OD solvent and analyzing the mixture using atmospheric pressure photo ionization mass spectrometry (APPI-MS). The APPI HDX spectra obtained with contact times between the analyte solution and methanol-OD (CH3OD) of < 0.5 s or 1 h showed the same pattern of H/D exchange. Therefore, it was concluded that APPI HDX occurred in the source but not in the solution. The proposed method does not require a specific type of mass spectrometer and can be performed at atmospheric pressure. H/D exchange can be performed in any laboratory with a mass spectrometer and a commercial APPI source. Using this method, multiple H/D exchanges of aromatic hydrogen and/or H/D exchange of active hydrogen were observed. These results demonstrated that H/D exchange can be used to distinguish between isomers containing primary, secondary, and tertiary amines, as well as pyridine and pyrrole functional groups.
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Affiliation(s)
- Arif Ahmed
- Department of Chemistry, Kyungpook National University, Daegu, Republic of Korea
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4
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Pierson NA, Chen L, Russell DH, Clemmer DE. Cis-trans isomerizations of proline residues are key to bradykinin conformations. J Am Chem Soc 2013; 135:3186-92. [PMID: 23373819 PMCID: PMC3624761 DOI: 10.1021/ja3114505] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
A recent ion mobility-mass spectrometry (IM-MS) study of the nonapeptide bradykinin (BK, amino acid sequence Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)) found evidence for 10 populations of conformations that depend upon the solution composition [J. Am. Chem. Soc. 2011, 133, 13810]. Here, the role of the three proline residues (Pro(2), Pro(3), and Pro(7)) in establishing these conformations is investigated using a series of seven analogue peptides in which combinations of alanine residues are substituted for prolines. IM-MS distributions of the analogue peptides, when compared to the distribution for BK, indicate the multiple structures are associated with different combinations of cis and trans forms of the three proline residues. These data are used to assign the structures to different peptide populations that are observed under various solution conditions. The assignments also show the connectivity between structures when collisional activation is used to convert one state into another.
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Affiliation(s)
| | - Liuxi Chen
- Department of Chemistry, Texas A&M University, College Station, TX 77843
| | - David H. Russell
- Department of Chemistry, Texas A&M University, College Station, TX 77843
| | - David E. Clemmer
- Department of Chemistry, Indiana University, Bloomington, IN 47405
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Papadopoulos G, Svendsen A, Boyarkin OV, Rizzo TR. Conformational distribution of bradykinin [bk + 2 H]2+ revealed by cold ion spectroscopy coupled with FAIMS. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:1173-81. [PMID: 22528205 DOI: 10.1007/s13361-012-0384-0] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2012] [Revised: 03/22/2012] [Accepted: 03/23/2012] [Indexed: 05/25/2023]
Abstract
We employ cold ion spectroscopy (CIS) in conjunction with high-field asymmetric waveform ion mobility spectrometry (FAIMS) to study the peptide bradykinin in its doubly protonated charge state ([bk + 2 H](2+)). Using FAIMS, we partially separate the electrosprayed [bk + 2 H](2+) ions into two conformational families and selectively introduce one of them at a time into a cold ion trap mass spectrometer, where we probe them by UV photofragment spectroscopy. Although the two conformational families have distinct electronic spectra, some cross-conformer contamination can be observed under certain conditions. We demonstrate that this contamination comes from isomerization of ions energized during and/or after their separation and not from incomplete separation of the initially electrosprayed conformations in the FAIMS stage. By varying the injection voltage of the ions into our mass spectrometer, we can intentionally induce isomerization to produce what seems to be a gas phase equilibrium distribution of conformers. This distribution is different from the one produced initially by electrospray, indicating that some of the conformers are kinetically trapped and may be related to conformers that are more favored in solution.
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Affiliation(s)
- Georgios Papadopoulos
- Laboratoire de Chimie Physique Moléculaire, École Polytechnique Fédérale de Lausanne, CH-1015, Lausanne, Switzerland
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Somuramasami J, Duan P, Amundson LM, Archibold E, Winger BE, Kenttämaa HI. Differentiation of protonated aromatic regioisomers related to lignin by reactions with trimethylborate in a Fourier transform ion cyclotron resonance mass spectrometer. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2011; 22:1040-1051. [PMID: 21953045 DOI: 10.1007/s13361-011-0099-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2010] [Revised: 02/01/2011] [Accepted: 02/01/2011] [Indexed: 05/31/2023]
Abstract
Several lignin model compounds were examined to test whether gas-phase ion-molecule reactions of trimethylborate (TMB) in a FTICR can be used to differentiate the ortho-, meta-, and para-isomers of protonated aromatic compounds, such as those formed during degradation of lignin. All three regioisomers could be differentiated for methoxyphenols and hydroxyphenols. However, only the differentiation of the ortho-isomer from the meta- and para-isomers was possible for hydroxyacetophenones and hydroxybenzoic acids. Consideration of the previously reported proton affinities at all basic sites in the isomeric hydroxyphenols, and the calculated proton affinities at all basic sites in the three methoxyphenol isomers, revealed that the proton affinities of the analytes relative to that of TMB play an important role in determining whether and how they react with TMB. The loss of two methanol molecules (instead of one) from the adducts formed with TMB either during ion-molecule reactions, or during sustained-off resonance irradiated collision-activated dissociation of the ion-molecule reaction products, revealed the presence of two functionalities in almost all the isomers. This finding supports earlier results suggesting that TMB can be used to count the functionalities in unknown oxygen-containing analytes.
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Bohrer BC, Atlasevich N, Clemmer DE. Transitions between elongated conformations of ubiquitin [M+11H]11+ enhance hydrogen/deuterium exchange. J Phys Chem B 2011; 115:4509-15. [PMID: 21449553 PMCID: PMC3091505 DOI: 10.1021/jp2008495] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Hydrogen/deuterium (H/D) exchange reactions between different elongated conformations of [M + 11H](11+) ions of ubiquitin and D(2)O are studied by a combination of ion mobility spectrometry (IMS) and mass spectrometry techniques. Three conformers (B, C, and D), resolved in the IMS separation, each exchange ∼27 hydrogens upon exposure to 0.06 Torr of D(2)O vapor for ∼35 to 40 ms. However, a region of the IMS spectrum that appears between the C and D states (corresponding to ions that undergo a structural transition during the mobility separation) undergoes substantially more exchanges (∼39 total sites, 44% more than the B, C, and D states). Selection and activation of the individual B, C, and D states reveals that the increased H/D exchange occurs during the transition between structures. Overall, these studies suggest a key process in establishing the maximum exchange levels involves structural transitions, which allow protected sites to be exposed for some fraction of the reaction time. Analysis of changes in exchange levels upon structural transitions can provide insight about common regions of structure that exist in the B, C, and D conformations.
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Affiliation(s)
- Brian C. Bohrer
- Department of Chemistry, Indiana University, Bloomington, IN 47405
| | | | - David E. Clemmer
- Department of Chemistry, Indiana University, Bloomington, IN 47405
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8
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Shvartsburg AA, Smith RD. Ultrahigh-resolution differential ion mobility spectrometry using extended separation times. Anal Chem 2011; 83:23-9. [PMID: 21117630 PMCID: PMC3012152 DOI: 10.1021/ac102689p] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Ion mobility spectrometry (IMS), and particularly differential IMS or field asymmetric waveform IMS (FAIMS), is emerging as a versatile tool for separation and identification of gas-phase ions, especially in conjunction with mass spectrometry. For over two decades since its inception, the utility of FAIMS was constrained by resolving power (R) of less than ∼20. Stronger electric fields and optimized gas mixtures have recently raised achievable R to ∼200, but further progress with such approaches is impeded by electrical breakdown. However, the resolving power of planar FAIMS devices using any gas and field intensity scales as the square root of separation time (t). Here, we extended t from the previous maximum of 0.2 s up to 4-fold by reducing the carrier gas flow and increased the resolving power by up to 2-fold as predicted, to >300 for multiply charged peptides. The resulting resolution gain has enabled separation of previously "co-eluting" peptide isomers, including folding conformers and localization variants of modified peptides. More broadly, a peak capacity of ∼200 has been reached in tryptic digest separations.
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Affiliation(s)
- Alexandre A Shvartsburg
- Biological Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
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9
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Papadopoulos G, Svendsen A, Boyarkin OV, Rizzo TR. Spectroscopy of mobility-selected biomolecular ions. Faraday Discuss 2011; 150:243-55; discussion 257-92. [DOI: 10.1039/c0fd00004c] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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10
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Fu M, Duan P, Li S, Eismin RJ, Kenttämaa HI. An ion/molecule reaction for the identification of analytes with two basic functional groups. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2009; 20:1251-1262. [PMID: 19345113 DOI: 10.1016/j.jasms.2009.02.020] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Revised: 02/13/2009] [Accepted: 02/13/2009] [Indexed: 05/27/2023]
Abstract
A mass spectrometric method is presented for the identification of analytes with two basic functionalities and PA between 222 and 245 kcal/mol, including diamines. This method utilizes gas-phase ion-molecule reactions of protonated analytes with neutral 1,1-diethoxyethene (DEE) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR). A variety of protonated mono-, bi-, and trifunctional analytes containing different functional groups, namely, amido, amino, N-oxide, hydroxy, carboxylic acid, keto, thio, thioether, alkene, phosphite, and phosphonate, were tested in the FT-ICR. The results demonstrate that basic protonated bifunctional compounds (PA between 222 and 245 kcal/mol) react selectively with DEE by forming a specific addition/elimination product ion (adduct - EtOH) (this product was also observed for lysine with three functionalities). The diagnostic reaction sequence involves proton transfer from the protonated analyte to the basic vinyl group in DEE, followed by addition of one of the functional groups of the analyte to the electrophilic alpha-carbon in protonated DEE. The next step involves proton transfer from this functionality to the other analyte functionality, followed by proton transfer to DEE and elimination of ethanol. Since the mechanism involves proton transfer between two functional groups of the analyte, the reaction does not occur for analytes where the two functionalities cannot be in close proximity (i.e., meta-phenylenediamine), and where no proton is available (i.e., dimethylaminoketone).
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Affiliation(s)
- Mingkun Fu
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, USA
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11
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Rodriquez CF, Orlova G, Guo Y, Li X, Siu CK, Hopkinson AC, Siu KWM. Gaseous bradykinin and its singly, doubly, and triply protonated forms: a first-principles study. J Phys Chem B 2007; 110:7528-37. [PMID: 16599534 DOI: 10.1021/jp046015r] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The conformers of gaseous bradykinin, BK, (Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)) and its protonated forms, [BK + H](+), [BK + 2H](2+), and [BK + 3H](3+), were examined theoretically using a combination of the Merck molecular force field, Hartree-Fock, and density functional theory. Neutral BK, [BK + H](+), and [BK + 2H](2+) exist in zwitterionic forms that are stabilized by internal solvation and have compact structures; [BK + 3H](3+) differs by the absence of a salt bridge and adopts an elongated form. The common structural feature in all four BK species is a beta-turn in the Ser(6)-Pro(7)-Phe(8)-Arg(9) sequence. The gas-phase basicity of [BK + H](+) estimated from the calculated protonation energy is in accord with published experimental basicity; population-weighted collision cross-sections of the three ionic forms are in agreement with experimental cross-sections in the literature.
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Affiliation(s)
- Christopher F Rodriquez
- Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario M3J 1P3, Canada
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12
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Kjeldsen F, Silivra OA, Zubarev RA. Zwitterionic States in Gas-Phase Polypeptide Ions Revealed by 157-nm Ultra-Violet Photodissociation. Chemistry 2006; 12:7920-8. [PMID: 16871505 DOI: 10.1002/chem.200600248] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
A new method of detecting the presence of deprotonation and determining its position in gas-phase polypeptide cations is described. The method involves 157-nm ultra-violet photodissociation (UVPD) and is based on monitoring the losses of CO2 (44 Da) from electronically excited deprotonated carboxylic groups relative to competing COOH losses (45 Da) from neutral carboxylic groups. Loss of CO2 is a strong indication of the presence of a zwitterionic [(+)...(-)...(+)] salt bridge in the gas-phase polypeptide cation. This method provides a tool for studying, for example, the nature of binding within polypeptide clusters. Collision-activated dissociation (CAD) of decarboxylated cations localizes the position of deprotonation. Fragment abundances can be used for the semiquantitative assessment of the branching ratio of deprotonation among different acidic sites, however, the mechanism of the fragment formation should be taken into account. Cations of Trp-cage proteins exist preferentially as zwitterions, with the deprotonation position divided between the Asp9 residue and the C terminus in the ratio 3:2. The majority of dications of the same molecule are not zwitterions. Furthermore, 157-nm UVPD produces abundant radical cations M*+ from protonated molecules through the loss of a hydrogen atom. This method of producing M*+ ions is general and can be applied to any gas-phase peptide cation. The abundance of the molecular radical cations M*+ produced is sufficient for further tandem mass spectrometry (MS/MS), which, in the cases studied, yielded side-chain loss of a basic amino acid as the most abundant fragmentation channel together with some backbone cleavages.
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Affiliation(s)
- Frank Kjeldsen
- Biomedical Center Laboratory for Biological and Medical Mass Spectrometry Box 583, Uppsala University, 75123 Uppsala, Sweden.
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Herrmann KA, Kuppannan K, Wysocki VH. Fragmentation of doubly-protonated peptide ion populations labeled by H/D exchange with CD(3)OD. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2006; 249-250:93-105. [PMID: 18802500 PMCID: PMC2542902 DOI: 10.1016/j.ijms.2005.12.047] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Doubly-protonated bradykinin (RPPGFSPFR) and an angiotensin III analogue (RVYIFPF) were subjected to hydrogen/deuterium (H/D) exchange with CD(3)OD in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. A bimodal distribution of deuterium incorporation was present for bradykinin after H/D exchange for 90 s at a CD(3)OD pressure of 4 x 10(-7) Torr, indicating the existence of at least two distinct populations. Bradykinin ion populations corresponding to 0-2 and 5-11 deuteriums (i.e., D(0), D(1), D(2), D(5), D(6), D(7), D(8), D(9), D(10), and D(11)) were each monoisotopically selected and fragmented via sustained off-resonance irradiation (SORI) collision-induced dissociation (CID). The D(0)-D(2) ion populations, which correspond to the slower exchanging population, consistently require lower SORI amplitude to achieve a similar precursor ion survival yield as the faster-reacting (D(5)-D(11)) populations. These results demonstrate that conformation/protonation motif has an effect on fragmentation efficiency for bradykinin. Also, the partitioning of the deuterium atoms into fragment ions suggests that the C-terminal arginine residue exchanges more rapidly than the N-terminal arginine. Total deuterium incorporation in the b(1)/y(8) and b(2)/y(7) ion pairs matches very closely the theoretical values for all ion populations studied, indicating that the ions of a complementary pair are likely formed during the same fragmentation event, or that no scrambling occurs upon SORI. Deuterium incorporation into the y(1)/a(8) pseudo-ion pair does not closely match the expected theoretical values. The other peptide, doubly-protonated RVYIFPF, has a trimodal distribution of deuterium incorporation upon H/D exchange with CD(3)OD at a pressure of 1 x 10(-7) Torr for 600 s, indicating at least three distinct ion populations. After 90 s of H/D exchange where at least two distinct populations are detected, the D(0)-D(7) ion populations were monoisotopically selected and fragmented via SORI-CID over a range of SORI amplitudes. The precursor ion survival yield as a function of SORI amplitude falls into two distinct behaviors corresponding to slower- and faster-reacting ion populations. The slower-reacting population requires larger SORI amplitudes to achieve the same precursor ion survival yield as the faster exchanging population. Total deuterium incorporation into the y(2)/b(5) ion pairs matches closely the theoretical values over all ion populations and SORI amplitudes studied. This result indicates the y(2) and b(5) ions are likely formed by the same mechanism over the SORI amplitudes studied.
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Affiliation(s)
| | | | - Vicki H. Wysocki
- University of Arizona, Department of Chemistry, 1306 E. University Blvd., Tucson, AZ 85721-0041, USA
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15
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Sawyer HA, Marini JT, Stone EG, Ruotolo BT, Gillig KJ, Russell DH. The structure of gas-phase bradykinin fragment 1-5 (RPPGF) ions: an ion mobility spectrometry and H/D exchange ion-molecule reaction chemistry study. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2005; 16:893-905. [PMID: 15878286 DOI: 10.1016/j.jasms.2005.03.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2004] [Revised: 02/28/2005] [Accepted: 03/05/2005] [Indexed: 05/02/2023]
Abstract
Ion mobility-mass spectrometry (IM-MS) data is interpreted as evidence that gas-phase bradykinin fragment 1-5 (BK1-5, RPPGF) [M + H](+) ions exist as three distinct structural forms, and the relative abundances of the structural forms depend on the solvent used to prepare the matrix-assisted laser desorption ionization (MALDI) samples. Samples prepared from organic rich solvents (90% methanol/10% water) yield ions having an ion mobility arrival-time distribution (ATD) that is dominated by a single peak; conversely, samples prepared using mostly aqueous solvents (10% methanol/90% water) yield an ATD composed of three distinct peaks. The BK1-5 [M + H](+) ions were also studied by gas-phase hydrogen/deuterium (H/D) exchange ion-molecule reactions and this data supports our interpretation of the IM-MS data. Plausible structures for BK1-5 ions were generated by molecular dynamics (MD). Candidate MD-generated structures correlated to measured cross-sections suggest a compact conformer containing a beta-turn whereas a more extended, open form does not contain such an interaction. This study illustrates the importance of intra-molecular interactions in the stabilization of the gas-phase ions, and these results clearly illustrate that solution-phase parameters (i.e., MALDI sample preparation) greatly influence the structures of gas-phase ions.
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Affiliation(s)
- Holly A Sawyer
- Laboratory for Biological Mass Spectrometry, Department of Chemistry, Texas A&M University, College Station, TX 77843, USA
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16
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Sudha R, Kohtani M, Jarrold MF. Non-Covalent Interactions between Unsolvated Peptides: Helical Complexes Based on Acid−Base Interactions. J Phys Chem B 2005; 109:6442-7. [PMID: 16851718 DOI: 10.1021/jp045490m] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have used ion-mobility mass spectrometry to examine the conformations of the protonated complex formed between AcA(7)KA(6)KK and AcEA(7)EA(7), helical alanine-based peptides that incorporate glutamic acid (E) and lysine (K). Designed interactions between the acidic E and basic K residues help to stabilize the complex, which is generated by electrospray and studied in the gas phase. There are two main conformations: (1) a coaxial linear arrangement where the helices are tethered together by an EKK interaction between the pair of lysines at the C-terminus of the AcA(7)KA(6)KK peptide and a glutamic acid at the N-terminus of the AcEA(7)EA(7) peptide and (2) a coiled-coil arrangement with side-by-side antiparallel helices where there is an additional EK interaction between the E and K residues in the middle of the helices. The coiled-coil opens up to the coaxial linear structure as the temperature is raised. Entropy and enthalpy changes for the opening of the coiled-coil were derived from the measurements. The enthalpy change indicates that the interaction between the E and K residues in the middle of the helices is a weak neutral hydrogen bond. The EKK interaction is significantly stronger.
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Affiliation(s)
- Rajagopalan Sudha
- Chemistry Department, Indiana University, Bloomington, Indiana 47405-7102, USA
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17
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Wells JM, Chrisman PA, McLuckey SA. Formation and characterization of protein-protein complexes in vacuo. J Am Chem Soc 2003; 125:7238-49. [PMID: 12797797 DOI: 10.1021/ja035051l] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Gas-phase reactions between multiply charged positive and negative protein ions are carried out in a quadrupole ion trap mass spectrometer. The ions react with one another by proton transfer and complex formation. Proton transfer products and complexes are formed via competitive processes in single ion/ion encounters. The relative contributions of proton transfer versus complex formation are dependent upon the charges of the ions as well as other characteristics of the ions yet to be clearly delineated. No fragmentation of covalent bonds of the protein reactants is observed. A model that considers the trajectories associated with ion/ion interactions appears to hold the most promise in accounting for the results. The formation of bound ion/ion orbits appears to play an important role in determining overall reaction kinetics as well as the distribution of ion/ion reaction products. Tandem mass spectrometry is used to compare protein complexes formed in the gas-phase with those formed initially in solution and subsequently liberated by electrospray; it is shown that both forms of complex dissociate similarly, but the complexes formed in the gas phase can retain a "memory" of their method of formation.
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Affiliation(s)
- J Mitchell Wells
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA
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Hartings MR, Kinnear BS, Jarrold MF. The energy landscape of unsolvated peptides: the role of context in the stability of alanine/glycine helices. J Am Chem Soc 2003; 125:3941-7. [PMID: 12656629 DOI: 10.1021/ja020610u] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ion mobility measurements have been used to examine the conformations present for unsolvated Ac-(AG)(7)A+H(+) and (AG)(7)A+H(+) peptides (Ac = acetyl, A = alanine, and G = glycine) over a broad temperature range (100-410 K). The results are compared to those recently reported for Ac-A(4)G(7)A(4)+H(+) and A(4)G(7)A(4)+H(+), which have the same compositions but different sequences. Ac-(AG)(7)A+H(+) shows less conformational diversity than Ac-A(4)G(7)A(4)+H(+); it is much less helical than Ac-A(4)G(7)A(4)+H(+) at the upper end of the temperature range studied, and at low temperatures, one of the two Ac-A(4)G(7)A(4)+H(+) features assigned to helical conformations is missing for Ac-(AG)(7)A+H(+). Molecular dynamics simulations suggest that the different conformational preferences are not due to differences in the stabilities of the helical states, but differences in the nonhelical states: it appears that Ac-(AG)(7)A+H(+) is more flexible and able to adopt lower energy globular conformations (compact random looking three-dimensional structures) than Ac-A(4)G(7)A(4)+H(+). The helix to globule transition that occurs for Ac-(AG)(7)A+H(+) at around 250-350 K is not a direct (two-state) process, but a creeping transition that takes place through at least one and probably several intermediates.
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Affiliation(s)
- Matthew R Hartings
- Chemistry Department, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405-7102, USA
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19
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Mao D, Douglas DJ. H/D exchange of gas phase bradykinin ions in a linear quadrupole ion trap. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2003; 14:85-94. [PMID: 12586457 DOI: 10.1016/s1044-0305(02)00818-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The gas phase H/D exchange reaction of bradykinin ions, as well as fragment ions of bradykinin generated through collisions in an orifice skimmer region, have been studied with a linear quadrupole ion trap (LIT) reflectron time-of-flight (rTOF) mass spectrometer system. The reaction in the trap takes only tens of seconds at a pressure of few mTorr of D2O or CD3OD. The exchange rate and hydrogen exchange level are not sensitive to the trapping q value over a broad range, provided q is not close to the stability boundary (q = 0.908). The relative rates and hydrogen exchange levels of protonated and sodiated +1 and +2 ions are similar to those observed previously by others with a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer system. The doubly and triply protonated ions show multimodal isotopic distributions, suggesting the presence of several different conformations. The y fragment ions show greater exchange rates and levels than a or b ions, and when water or ammonia is lost from the fragment ions, no exchange is observed.
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Affiliation(s)
- Dunmin Mao
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
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20
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Reid GE, McLuckey SA. 'Top down' protein characterization via tandem mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2002; 37:663-675. [PMID: 12124999 DOI: 10.1002/jms.346] [Citation(s) in RCA: 180] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Technological and scientific advances over the past decade have enabled protein identification and characterization strategies to be developed that are based on subjecting intact protein ions and large protein fragments directly to tandem mass spectrometry. These approaches are referred to collectively as 'top down' to contrast them with 'bottom up' approaches whereby protein identification is based on mass spectrometric analysis of peptides derived from proteolytic digestion, usually with trypsin. A key step in enabling top down approaches has been the ability to assign tandem mass spectrometer product ion identities, which can be done either via high resolving power or through product ion charge state manipulation. The ability to determine product ion charge states has permitted studies of the reactions, including dissociation, ion-molecule reactions, ion-electron reactions and ion-ion reactions of high-mass, multiply charged protein ions. Electrospray ionization combined with high magnetic field strength Fourier transform ion cyclotron resonance has proven to be particularly powerful for detailed protein characterization owing to its high mass resolution and mass accuracy and its ability to effect electron capture-induced dissociation. Other types of tandem mass spectrometers are also beginning to find increasing use in top down protein identification/characterization studies. Charge state manipulation via ion-ion reactions in electrodynamic ion traps, for example, enables top down strategies to be considered using instruments with relatively modest mass resolution capabilities. Precursor ion charge state manipulation techniques have also recently been demonstrated to be capable of concentrating and charge-state purifying proteins in the gas phase. Advances in technologies applied to the structural analysis of whole protein ions and in understanding their reactions, such as those described here, are providing new options for the study of complex protein mixtures.
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Affiliation(s)
- Gavin E Reid
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, USA
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21
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Wells JM, Chrisman PA, McLuckey SA. "Dueling" ESI: instrumentation to study ion/ion reactions of electrospray-generated cations and anions. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2002; 13:614-622. [PMID: 12056562 DOI: 10.1016/s1044-0305(01)00364-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Novel instrumentation has been developed which allows for the sequential injection and subsequent reaction of oppositely-charged ions generated via electrospray ionization (ESI) in a quadrupole ion trap mass spectrometer. The instrument uses a DC turning quadrupole to sequentially direct the two ion polarities into the ion trap from ESI sources which are situated 90 degrees from the axial (z) dimension of the trap, and 180 degrees from one another. This arrangement significantly expands the range of ionic reactants amenable to study over previously-used instrumentation. For example, ion/ion reactions of multiply-charged positive ions with multiply-charged negative ions can be studied. Also, reactions of multiply-charged ions with singly-charged ions of opposite polarity that could not be generated by previously used ionization methods, or that could not be efficiently injected through the ion trap ring electrode, can be studied with the new instrument. This capability allows, for example, the charge state manipulation of negatively-charged precursor and product ions derived from proteins and oligonucleotides via proton transfer reactions with singly-charged cations generated by ESI.
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Affiliation(s)
- J Mitchell Wells
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, USA
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22
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Kinnear BS, Hartings MR, Jarrold MF. The energy landscape of unsolvated peptides: helix formation and cold denaturation in Ac-A4G7A4 + H+. J Am Chem Soc 2002; 124:4422-31. [PMID: 11960471 DOI: 10.1021/ja012150v] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ion mobility measurements and molecular dynamics simulations were performed for unsolvated A4G7A4 + H+ and Ac-A4G7A4 + H+ (Ac = acetyl, A = alanine, G = glycine) peptides. As expected, A4G7A4 + H+ adopts a globular conformation (a compact, random-looking, three-dimensional structure) over the entire temperature range examined (100-410 K). Ac-A4G7A4 + H+ on the other hand is designed to have a flat energy landscape with a marginally stable helical state. This peptide shows at least four different conformations at low temperatures (<230 K). The two conformations with the largest cross sections are attributed to - and partial -helices, while the one with the smallest cross section is globular. The other main conformation may be partially helical. Ac-A4G7A4 + H+ becomes predominantly globular at intermediate temperatures and then becomes more helical as the temperature is raised further. This unexpected behavior may be due to the helix having a higher vibrational entropy than the globular state, as predicted by some recent calculations (Ma, B.; Tsai, C.-J.; Nussinov, R. Biophys. J. 2000, 79, 2739-2753).
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Affiliation(s)
- Brian S Kinnear
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA
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23
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Ewing NP, Pallante GA, Zhang X, Cassady CJ. Gas-phase basicities for ions from bradykinin and its des-arginine analogues. JOURNAL OF MASS SPECTROMETRY : JMS 2001; 36:875-881. [PMID: 11523086 DOI: 10.1002/jms.188] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Apparent gas-phase basicities (GB(app)s) for [M + H]+ of bradykinin, des-Arg1-bradykinin and des-Arg9-bradykinin have been assigned by deprotonation reactions of [M + 2H]2+ in a Fourier transform ion cyclotron resonance mass spectrometer. With a GB(app) of 225.8 +/- 4.2 kcal x mol(-1), bradykinin [M + H]+ is the most basic of the ions studied. Ions from des-Arg1-bradykinin and des-Arg9-bradykinin have GB(app) values of 222.8 +/- 4.3 kcal x mol(-1) and 214.9 +/- 2.3 kcal x mol(-1), respectively. One purpose of this work was to determine a suitable reaction efficiency 'break point' for assigning GB(app) values to peptide ions using the bracketing method. An efficiency value of 0.1 (i.e. approximately 10% of all collisions resulting in a deprotonation reaction) was used to assign GB(app)s. Support for this criterion is provided by the fact that our GB(app) values for des-Arg1-bradykinin and des-Arg9-bradykinin are identical, within experimental error, to literature values obtained using a modified kinetic method. However, the GB(app)s for bradykinin ions from the two studies differ by 10.3 kcal x mol(-1). The reason for this is not clear, but may involve conformation differences produced by experimental conditions. The results may be influenced by salt-bridge conformers and/or by conformational changes caused by the use of a proton-bound heterodimer in the kinetic method. Factors affecting the basicities of these peptide ions are also discussed, and molecular modeling is used to provide information on protonation sites and conformations. The presence of two highly basic arginine residues on bradykinin results in its high GB(app), while the basicity of des-Arg1-bradykinin ions is increased by the presence of two proline residues at the N-terminus. The proline residue in the second position folds the peptide chain in a manner that increases intramolecular hydrogen bonding to the protonated N-terminal amino group of the proline at the first position.
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Affiliation(s)
- N P Ewing
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
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24
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Abstract
The conformations of unsolvated Ac-K(AGG)(5)+H(+) and Ac-(AGG)(5)K+H(+) peptides (Ac = acetyl, A = alanine, G = glycine, and K = lysine) have been examined by ion mobility measurements over a wide temperature range (150-410 K). The Ac-K(AGG)(5)+H(+) peptide remains a globule (a compact, roughly spherical structure) over the entire temperature range, while both an alpha-helix and a globule are found for Ac-(AGG)(5)K+H(+) at low temperature. As the temperature is raised the alpha-helix unfolds. Rate constants for loss of the helix (on a millisecond time scale) have been determined as a function of temperature and yield an Arrhenius activation energy and preexponential factor of 38.2 +/- 1.0 kJ mol(-1) and 6.5 +/- 3.7 x 10(9) s(-1), respectively. The alpha-helix apparently does not unfold directly into the globule, but first converts into a long-lived intermediate which survives to a significantly higher temperature before converting. According to molecular dynamics simulations, there is a partially untwisted helical conformation that has both a low energy and a well-defined geometry. This special structure lies between the helix and globule and may be the long-lived intermediate.
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Affiliation(s)
- B S Kinnear
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA
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25
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Levy-Seri E, Koster G, Kogan A, Gutman K, Reuben BG, Lifshitz C. An Electrospray Ionization−Flow Tube Study of H/D Exchange in Protonated Bradykinin. J Phys Chem A 2001. [DOI: 10.1021/jp0037145] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Elchanan Levy-Seri
- Department for Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Grielof Koster
- Department for Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Alexandra Kogan
- Department for Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Karnit Gutman
- Department for Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Bryan G. Reuben
- Department for Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Chava Lifshitz
- Department for Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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26
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Purves RW, Barnett DA, Ells B, Guevremont R. Gas-phase conformers of the [M + 2H](2+) ion of bradykinin investigated by combining high-field asymmetric waveform ion mobility spectrometry, hydrogen/deuterium exchange, and energy-loss measurements. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2001; 15:1453-1456. [PMID: 11507759 DOI: 10.1002/rcm.390] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The continuous separation capability of high-field asymmetric waveform ion mobility spectrometry (FAIMS) was used in combination with complementary techniques for probing biomolecular ions in the gas phase. Gas-phase conformers of the [M + 2H](2+) ion of bradykinin were examined using a combination of FAIMS, H/D exchange, and energy-loss measurements. When FAIMS data and H/D exchange data were analyzed separately, the presence of only two conformers of the [M + 2H](2+) ion of bradykinin could be detected. However, in an experiment in which FAIMS and H/D exchange were combined, at least four different conformers of the gas-phase [M + 2H](2+) ion of bradykinin were detected, including one of very low abundance. Cross sections calculated for the four conformers, based on energy-loss measurements, were 250, 240, 250, and 244 A(2), in order of decreasing abundance.
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Affiliation(s)
- R W Purves
- Institute for National Measurement Standards, National Research Council of Canada, Ottawa, K1A 0R6, Canada
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27
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Kinnear BS, Kaleta DT, Kohtani M, Hudgins RR, Jarrold MF. Conformations of Unsolvated Valine-Based Peptides. J Am Chem Soc 2000. [DOI: 10.1021/ja001207v] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Brian S. Kinnear
- Contribution from the Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208
| | - David T. Kaleta
- Contribution from the Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208
| | - Motoya Kohtani
- Contribution from the Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208
| | - Robert R. Hudgins
- Contribution from the Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208
| | - Martin F. Jarrold
- Contribution from the Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208
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28
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Zhu C, Balta B, Aviyente V, Lifshitz C. The Interaction of Protonated Diglycine with Ammonia: A Density Functional Theory Model Study. J Phys Chem A 2000. [DOI: 10.1021/jp994214i] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Chuanbao Zhu
- Department of Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel, and Chemistry Department, Bogaziçi University, 80815, Bebek, Istanbul, Türkiye
| | - Bülent Balta
- Department of Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel, and Chemistry Department, Bogaziçi University, 80815, Bebek, Istanbul, Türkiye
| | - Viktorya Aviyente
- Department of Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel, and Chemistry Department, Bogaziçi University, 80815, Bebek, Istanbul, Türkiye
| | - Chava Lifshitz
- Department of Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel, and Chemistry Department, Bogaziçi University, 80815, Bebek, Istanbul, Türkiye
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29
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Strittmatter EF, Williams ER. Structures of protonated arginine dimer and bradykinin investigated by density functional theory: further support for stable gas-phase salt bridges. J Phys Chem A 2000; 104:6069-76. [PMID: 16604161 PMCID: PMC1434516 DOI: 10.1021/jp000038y] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The gas-phase structures and energetics of both protonated arginine dimer and protonated bradykinin were investigated using a combination of molecular mechanics with conformational searching to identify candidate low-energy structures, and density functional theory for subsequent minimization and energy calculations. For protonated arginine dimer, a good correlation (R = 0.88) was obtained between the molecular mechanics and EDF1 6-31+G* energies, indicating that mechanics with MMFF is suitable for finding low-energy conformers. For this ion, the salt-bridge or ion-zwitterion form was found to be 5.7 and 7.2 kcal/mol more stable than the simple protonated or ion-molecule form at the EDF1 6-31++G** and B3LYP 6-311++G** levels. For bradykinin, the correlation between the molecular mechanics and DFT energies was poor (R = 0.28), indicating that many low-energy structures are likely passed over in the mechanics conformational searching. This result suggests that structures of this larger peptide ion obtained using mechanics calculations alone are not necessarily reliable. The lowest energy structure of the salt-bridge form of bradykinin is 10.6 kcal/mol lower in energy (EDF1) than the lowest energy simple protonated form at the 6-311G* level. Similarly, the average energy of all salt-bridge structures investigated is 13.6 kcal/mol lower than the average of all the protonated forms investigated. To the extent that a sufficient number of structures are investigated, these results provide some additional support for the salt-bridge form of bradykinin in the gas phase.
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Affiliation(s)
- E F Strittmatter
- Department of Chemistry, University of California, Berkeley, California 94720 Received: January 5, 2000; In Final Form: April 11, 2000
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30
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Schaaff TG, Stephenson JL, McLuckey SA. Gas phase H/D exchange kinetics: DI versus D2O. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2000; 11:167-171. [PMID: 10689670 DOI: 10.1016/s1044-0305(99)00137-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The gas phase H/D exchange reactions of bradykinin (M + 3H)3+ ions with D2O and DI were monitored in a quadrupole ion trap mass spectrometer. The H/D exchange kinetics of both chemical probes (D2O and DI) indicate the presence of two noninterconverting reactive gas phase ion populations of bradykinin (M + 3H)3+ at room temperature. The H/D exchange involving DI, however, generally proceeds faster than that involving D2O. The rate observations described here can be rationalized on the basis of the "relay mechanism" (see Campbell et al. J. Am. Chem. Soc. 1995, 117, 12840-12854) recently proposed to account for H/D exchange between D2O and gaseous protonated polypeptides. The higher exchange rate with DI is believed to arise primarily as a result of its lower gas-phase acidity relative to that of D2O and, secondarily, as a result of the longer bond length of DI relative to that of OD in D2O.
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Affiliation(s)
- T G Schaaff
- Chemical and Analytical Sciences Division, Oak Ridge National Laboratory, Tennessee 37831-6365, USA
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