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Sohn WY, Kim JJ, Jeon M, Aoki T, Ishiuchi SI, Fujii M, Kang H. Entropic effects make a more tightly folded conformer of a β-amino acid less stable: UV-UV hole burning and IR dip spectroscopy of l-β3-homotryptophan using a laser desorption supersonic jet technique. Phys Chem Chem Phys 2018; 20:19979-19986. [DOI: 10.1039/c8cp02106f] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Gas-phase spectroscopy of homotryptophan was done to understand conformations of β-peptides.
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Affiliation(s)
- Woon Yong Sohn
- Department of Applied Chemistry
- Faculty of Science and Engineering
- Chuo University
- Tokyo 112-8551
- Japan
| | - Jeong Jin Kim
- Department of Chemistry
- Department of Energy Systems Research
- Ajou University
- Suwon 16499
- Korea
| | - Myeongwon Jeon
- Department of Chemistry
- Department of Energy Systems Research
- Ajou University
- Suwon 16499
- Korea
| | - Takuma Aoki
- Laboratory for Chemistry and Life Science
- Institute of Innovative Research
- Tokyo Institute of Technology
- Yokohama 226-8503
- Japan
| | - Shun-ichi Ishiuchi
- Laboratory for Chemistry and Life Science
- Institute of Innovative Research
- Tokyo Institute of Technology
- Yokohama 226-8503
- Japan
| | - Masaaki Fujii
- Laboratory for Chemistry and Life Science
- Institute of Innovative Research
- Tokyo Institute of Technology
- Yokohama 226-8503
- Japan
| | - Hyuk Kang
- Department of Chemistry
- Department of Energy Systems Research
- Ajou University
- Suwon 16499
- Korea
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2
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Shirota T, Tsuge M, Hikosaka Y, Soejima K, Hoshina K. Detection of Neutral Species in the MALDI Plume Using Femtosecond Laser Ionization: Quantitative Analysis of MALDI-MS Signals Based on a Semiequilibrium Proton Transfer Model. J Phys Chem A 2016; 121:31-39. [PMID: 27935303 DOI: 10.1021/acs.jpca.6b09591] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We investigated neutral species in the matrix-assisted laser desorption and ionization (MALDI) plume using femtosecond laser ionization spectrometry with simultaneous measurement of the standard MALDI spectrum of the identical MALDI event induced by pulsed UV laser irradiation. The ratio of neutral species in the plume [A]p/[M]p (A = phenylalanine (Phe) or alanine (Ala), M = 2,5-dihydroxybenzoic acid (DHB)) was confirmed to be the same as that of the sample mixture in the range of [A]0/[M]0 = 4 × 10-4-1, indicating the validity of the widely adopted approximation [A]p/[M]p = [A]0/[M]0 in the reaction quotient of the proton transfer reaction MH+ + A ⇄ M + AH+. An effective parameter representing the extent of thermal equilibrium in the thermal proton transfer model is introduced for the first time. Numerical simulation based on this semiequilibrium model successfully reproduced variations of MALDI signal intensities AH+ and MH+ with two parameters: the fraction of ionized matrix a ≤ 10-5 and an effective temperature T = 1200 and 1100 K for Phe/DHB and Ala/DHB systems, respectively. These values show good agreement with those determined previously by different experimental approaches. The extent of thermal equilibrium was determined to be 95% and 98% for Phe/DHB and Ala/DHB systems, respectively, suggesting that the proton transfer reactions almost proceed to their thermal equilibrium.
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Affiliation(s)
- Tatsuro Shirota
- Faculty of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences , 265-1, Higashijima, Akiha-ku, Niigata 956-8603, Japan
| | - Masashi Tsuge
- Department of Applied Chemistry, National Chiao Tung University , 1001 Ta-Hsueh Road, Hsinchu 30010, Taiwan
| | - Yasumasa Hikosaka
- Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama , 2630 Sugitani, Toyama 930-0194, Japan
| | | | - Kennosuke Hoshina
- Faculty of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences , 265-1, Higashijima, Akiha-ku, Niigata 956-8603, Japan
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3
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Moskovets E, Misharin A, Laiko V, Doroshenko V. A comparative study on the analytical utility of atmospheric and low-pressure MALDI sources for the mass spectrometric characterization of peptides. Methods 2016; 104:21-32. [DOI: 10.1016/j.ymeth.2016.02.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Revised: 12/19/2015] [Accepted: 02/16/2016] [Indexed: 11/16/2022] Open
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4
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Kirmess KM, Knochenmuss R, Blanchard GJ, Kinsel GR. MALDI ionization mechanisms investigated by comparison of isomers of dihydroxybenzoic acid. JOURNAL OF MASS SPECTROMETRY : JMS 2016; 51:79-85. [PMID: 26757075 DOI: 10.1002/jms.3725] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2015] [Revised: 10/23/2015] [Accepted: 10/24/2015] [Indexed: 06/05/2023]
Abstract
Matrix-assisted laser desorption/ionization (MALDI) ion formation mechanisms were investigated by comparison of isomers of dihydroxybenzoic acid (DHB). These exhibit substantially different MALDI performance, the basis for which was not previously understood. Luminescence decay curves are used here to estimate excited electronic state properties relevant for the coupled chemical and physical dynamics (CPCD) model. With these estimates, the CPCD predictions for relative total ion and analyte ion yields are in good agreement with the data for the DHB isomers. Predictions of a thermal equilibrium model were also compared and found to be incompatible with the data. Copyright © 2015 John Wiley & Sons, Ltd.
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Affiliation(s)
- Kristopher M Kirmess
- Department of Chemistry and Biochemistry, Southern Illinois University Carbondale, Carbondale, IL, 62901, USA
| | | | - Gary J Blanchard
- Department of Chemistry, Michigan State University, East Lansing, MI, 48824, USA
| | - Gary R Kinsel
- Department of Chemistry and Biochemistry, Southern Illinois University Carbondale, Carbondale, IL, 62901, USA
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5
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Moon JH, Park KM, Ahn SH, Lee SH, Kim MS. Investigations of Some Liquid Matrixes for Analyte Quantification by MALDI. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:1657-1664. [PMID: 26122519 DOI: 10.1007/s13361-015-1202-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Revised: 05/16/2015] [Accepted: 05/19/2015] [Indexed: 06/04/2023]
Abstract
Sample inhomogeneity is one of the obstacles preventing the generation of reproducible mass spectra by MALDI and to their use for the purpose of analyte quantification. As a potential solution to this problem, we investigated MALDI with some liquid matrixes prepared by nonstoichiometric mixing of acids and bases. Out of 27 combinations of acids and bases, liquid matrixes could be produced from seven. When the overall spectral features were considered, two liquid matrixes using α-cyano-4-hydroxycinnamic acid as the acid and 3-aminoquinoline and N,N-diethylaniline as bases were the best choices. In our previous study of MALDI with solid matrixes, we found that three requirements had to be met for the generation of reproducible spectra and for analyte quantification: (1) controlling the temperature by fixing the total ion count, (2) plotting the analyte-to-matrix ion ratio versus the analyte concentration as the calibration curve, and (3) keeping the matrix suppression below a critical value. We found that the same requirements had to be met in MALDI with liquid matrixes as well. In particular, although the liquid matrixes tested here were homogeneous, they failed to display spot-to-spot spectral reproducibility unless the first requirement above was met. We also found that analyte-derived ions could not be produced efficiently by MALDI with the above liquid matrixes unless the analyte was sufficiently basic. In this sense, MALDI processes with solid and liquid matrixes should be regarded as complementary techniques rather than as competing ones.
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Affiliation(s)
- Jeong Hee Moon
- Functional Genomics Research Center, KRIBB, Daejeon, 305-806, Korea
| | - Kyung Man Park
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Sung Hee Ahn
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Seong Hoon Lee
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
| | - Myung Soo Kim
- Seoul National University Research Institute for Basic Sciences, Seoul, 151-747, Korea.
- Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul, 151-742, Korea.
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Moon JH, Yoon S, Bae YJ, Kim MS. Formation of gas-phase peptide ions and their dissociation in MALDI: insights from kinetic and ion yield studies. MASS SPECTROMETRY REVIEWS 2015; 34:94-115. [PMID: 24863621 DOI: 10.1002/mas.21427] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 03/17/2014] [Indexed: 06/03/2023]
Abstract
Insights on mechanisms for the generation of gas-phase peptide ions and their dissociation in matrix-assisted laser desorption ionization (MALDI) gained from the kinetic and ion yield studies are presented. Even though the time-resolved photodissociation technique was initially used to determine the dissociation kinetics of peptide ions and their effective temperature, it was replaced by a simpler method utilizing dissociation yields from in-source decay (ISD) and post-source decay (PSD). The ion yields for a matrix and a peptide were measured by repeatedly irradiating a region on a sample and collecting ion signals until the sample in the region was completely depleted. Matrix- and peptide-derived gas-phase cations were found to be generated by pre-formed ion emission or by ion-pair emission followed by anion loss, but not by laser-induced ionization. The total number of ions, that is, matrix plus peptide, was found to be equal to the number of ions emitted from a pure matrix. A matrix plume was found to cool as it expanded, from around 800-1,000 K to 400-500 K. Dissociation of peptide ions along b/y channels was found to occur statistically, that is, following RRKM behavior. Small critical energy (E0 = 0.6-0.7 eV) and highly negative critical entropy (ΔS(‡) = -30 to -25 eu) suggested that the transition structure was stabilized by multiple intramolecular interactions.
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Affiliation(s)
- Jeong Hee Moon
- Medical Proteomics Research Center, KRIBB, Daejeon, 305-806, Korea
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Bae YJ, Kim MS. A Thermal Mechanism of Ion Formation in MALDI. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2015; 8:41-60. [PMID: 26161971 DOI: 10.1146/annurev-anchem-081413-024102] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
An important recent discovery concerning the fundamentals of matrix-assisted laser desorption/ionization (MALDI) is that the abundance of each ion appearing in a spectrum is fixed, regardless of the experimental condition, when an effective temperature associated with the spectrum is fixed. We describe this phenomenon and the thermal picture for the ion formation in MALDI derived from it. Accepting that matrix-to-analyte proton transfer is in quasi-equilibrium as supported by experimental data, the above thermal determination occurs because the primary (matrix) ion formation processes are thermally governed. We propose that the abundances of the primary ions are limited by the autoprotolysis-recombination process regardless of how they are initially produced. Finally, we note that primary ion formation, secondary (analyte) ion formation, and their dissociations occur sequentially while the effective temperature of the matrix plume falls steadily due to cooling associated with expansion.
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul 151-742, Korea;
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Lu IC, Lee C, Lee YT, Ni CK. Ionization Mechanism of Matrix-Assisted Laser Desorption/Ionization. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2015; 8:21-39. [PMID: 26132345 DOI: 10.1146/annurev-anchem-071114-040315] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
In past studies, mistakes in determining the ionization mechanism in matrix-assisted laser desorption/ionization (MALDI) were made because an inappropriate ion-to-neutral ratio was used. The ion-to-neutral ratio of the analyte differs substantially from that of the matrix in MALDI. However, these ratios were not carefully distinguished in previous studies. We begin by describing the properties of ion-to-neutral ratios and reviews early experimental measurements. A discussion of the errors committed in previous theoretical studies and a comparison of recent experimental measurements follow. We then describe a thermal proton transfer model and demonstrate how the model appropriately describes ion-to-neutral ratios and the total ion intensity. Arguments raised to challenge thermal ionization are then discussed. We demonstrate how none of the arguments are valid before concluding that thermal proton transfer must play a crucial role in the ionization process of MALDI.
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Affiliation(s)
- I-Chung Lu
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan; , , ,
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9
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Al-Abadleh HA. Review of the bulk and surface chemistry of iron in atmospherically relevant systems containing humic-like substances. RSC Adv 2015. [DOI: 10.1039/c5ra03132j] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The current state of knowledge and future research directions of the bulk and surface chemistry of iron relevant to atmospheric surfaces are reviewed.
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Affiliation(s)
- Hind A. Al-Abadleh
- Department of Chemistry and Biochemistry
- Wilfrid Laurier University
- Waterloo
- Canada
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10
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Kirmess KM, Knochenmuss R, Blanchard GJ, Kinsel GR. Excited state dynamics in the matrix-assisted laser desorption/ionization matrix 2,4,6-trihydroxyacetophenone: evidence for triplet pooling charge separation reactions. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2014; 28:2134-2140. [PMID: 25156603 DOI: 10.1002/rcm.7000] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 07/25/2014] [Accepted: 07/26/2014] [Indexed: 06/03/2023]
Abstract
RATIONALE Excited state pooling reactions are a central part of some models of ultraviolet matrix-assisted laser desorption/ionization (MALDI) mechanisms. Evidence has been found for pooling in several matrix materials, but a recent report of pure exponential fluorescence decay at MALDI-relevant laser fluences suggested that 2,4,6-trihydroxy-acetophenone (THAP) may be an example of a matrix in which pooling does not occur (Lin et al., Rapid Commun. Mass Spectrom. 2014, 28, 77). However, those data were instrumentally limited in dynamic range and signal/noise ratio, and the conclusion does not take into account several aspects of THAP excited state dynamics. METHODS Using time-correlated single photon counting, and absorption and emission spectroscopies, the excited state dynamics of THAP are reexamined. RESULTS Like many other aromatic ketones and acetophenone, isolated THAP molecules undergo very efficient intersystem crossing. No fluorescence is observed in dilute solution. In the solid state, efficient fluorescence reappears, but is non-exponential even at very low excitation intensity. The solvent used for sample preparation was found to have a large effect on the spectra and decay curves. Needle-like crystals seem to be correlated with reduced intersystem crossing. CONCLUSIONS THAP solid state fluorescence is entirely due to intermolecular interactions. Activation of fluorescence, instead of quenching, is a clear indicator of delocalized excited state phenomena in THAP. Contrary to the conclusions of Lin et al., the greatly increased singlet lifetime in the solid state substantially increases the probability that pooling-type reactions are indeed involved in ionization processes. The sensitivity of fluorescence and phosphorescence on sample morphology appears to reflect changes in intermolecular interactions due to crystal packing. Pooling charge separation pathways based on known triplet-triplet ionization reactions of aromatic ketones are proposed.
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Affiliation(s)
- Kristopher M Kirmess
- Department of Chemistry and Biochemistry, Southern Illinois University at Carbondale, Carbondale, IL, 62901, USA
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Knochenmuss R. Energetics and kinetics of thermal ionization models of MALDI. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:1521-1527. [PMID: 24912435 DOI: 10.1007/s13361-014-0931-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Revised: 04/10/2014] [Accepted: 05/12/2014] [Indexed: 06/03/2023]
Abstract
Thermal models of ultraviolet MALDI ionization based on the polar fluid concept are re-examined. Key components are very high solvating power of the fluidized matrix and consequent low reaction-free energy, attainment of thermal equilibrium in the fluid, and negligible recombination losses. None of these are found to hold in a MALDI event. The reaction-free energy in the hot matrix must be near the gas phase value, ion formation is too slow to approach equilibrium, and geminate recombination of autoprotolysis pairs greatly increases the initial loss rate. The maximum thermal ion yield is estimated to be many orders of magnitude below experimental values.
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Bae YJ, Park KM, Ahn SH, Moon JH, Kim MS. Spectral reproducibility and quantification of peptides in MALDI of samples prepared by micro-spotting. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:1502-1505. [PMID: 24845358 DOI: 10.1007/s13361-014-0919-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2013] [Revised: 04/23/2014] [Accepted: 04/23/2014] [Indexed: 06/03/2023]
Abstract
Previously, we reported that MALDI spectra of peptides became reproducible when temperature was kept constant. Linear calibration curves derived from such spectral data could be used for quantification. Homogeneity of samples was one of the requirements. Among the three popular matrices used in peptide MALDI [i.e., α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxybenzoic acid (DHB), and sinapinic acid (SA)], homogeneous samples could be prepared by conventional means only for CHCA. In this work, we showed that sample preparation by micro-spotting improved the homogeneity for all three cases.
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
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Park KM, Moon JH, Kim KP, Lee SH, Kim MS. Relative Quantification in Imaging of a Peptide on a Mouse Brain Tissue by Matrix-Assisted Laser Desorption Ionization. Anal Chem 2014; 86:5131-5. [DOI: 10.1021/ac500911x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Kyung M. Park
- Department
of Chemistry, Seoul National University, Seoul 151-747, Korea
| | - Jeong H. Moon
- Medical Proteomics Research Center, KRIBB, Daejeon 305-806, Korea
| | - Kwang P. Kim
- Department
of Applied Chemistry, Kyunghee University, Yongin 446-701, Korea
| | - Seong H. Lee
- Department
of Chemistry, Seoul National University, Seoul 151-747, Korea
| | - Myung S. Kim
- Department
of Chemistry, Seoul National University, Seoul 151-747, Korea
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14
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Bae YJ, Moon JH, Kim MS. Dual track time-of-flight mass spectrometry for peptide quantification with matrix-assisted laser desorption/ionization. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2014; 28:787-792. [PMID: 24573810 DOI: 10.1002/rcm.6845] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 01/18/2014] [Accepted: 01/18/2014] [Indexed: 06/03/2023]
Abstract
RATIONALE Previously, we reported a method (Anal. Chem. 2012, 84, 10332) for peptide quantification based on matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS). In the method, the peptide-to-matrix ion abundance ratio was utilized. Implementation of the method with a commercial MALDI-TOF can be somewhat inconvenient because matrix-derived ions are routinely deflected away to avoid detector saturation. A solution for this inconvenience is required. METHODS We installed a detector to acquire the TOF spectrum of the ions thrown away to avoid detector saturation. By sending the matrix- and peptide-derived ions along two different tracks and detecting them with different detectors, the inconvenience mentioned above could be avoided. RESULTS Excellent linearity of the calibration curves obtained by the dual track TOF spectrometry is demonstrated. The method also allows for the acquisition of the tandem mass spectrum of a selected peptide, which can be useful for its identification. CONCLUSIONS We devised the dual track MALDI-TOF MS method to avoid detector saturation and demonstrated that the quantification and identification of peptides can be performed simultaneously.
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
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Chu KY, Lee S, Tsai MT, Lu IC, Dyakov YA, Lai YH, Lee YT, Ni CK. Thermal proton transfer reactions in ultraviolet matrix-assisted laser desorption/ionization. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:310-8. [PMID: 24395022 DOI: 10.1007/s13361-013-0792-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2013] [Revised: 11/24/2013] [Accepted: 11/25/2013] [Indexed: 05/20/2023]
Abstract
One of the reasons that thermally induced reactions are not considered a crucial mechanism in ultraviolet matrix-assisted laser desorption ionization (UV-MALDI) is the low ion-to-neutral ratios. Large ion-to-neutral ratios (10(-4)) have been used to justify the unimportance of thermally induced reactions in UV-MALDI. Recent experimental measurements have shown that the upper limit of the total ion-to-neutral ratio is approximately 10(-7) at a high laser fluence and less than 10(-7) at a low laser fluence. Therefore, reexamining the possible contributions of thermally induced reactions in MALDI may be worthwhile. In this study, the concept of polar fluid was employed to explain the generation of primary ions in MALDI. A simple model, namely thermal proton transfer, was used to estimate the ion-to-neutral ratios in MALDI. We demonstrated that the theoretical calculations of ion-to-neutral ratios exhibit the same trend and similar orders of magnitude compared with those of experimental measurements. Although thermal proton transfer may not generate all of the ions observed in MALDI, the calculations demonstrated that thermally induced reactions play a crucial role in UV-MALDI.
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Affiliation(s)
- Kuan Yu Chu
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
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16
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Knochenmuss R. MALDI mechanisms: wavelength and matrix dependence of the coupled photophysical and chemical dynamics model. Analyst 2014; 139:147-56. [DOI: 10.1039/c3an01446k] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Knochenmuss R. MALDI ionization mechanisms: the coupled photophysical and chemical dynamics model correctly predicts 'temperature'-selected spectra. JOURNAL OF MASS SPECTROMETRY : JMS 2013; 48:998-1004. [PMID: 24078239 DOI: 10.1002/jms.3248] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 05/30/2013] [Accepted: 06/14/2013] [Indexed: 06/02/2023]
Abstract
A number of possible ultraviolet MALDI ionization mechanisms based on different fundamental phenomena have been proposed. Recently, it has been argued, based on 'temperature'-selected spectra, that photoionization models should be rejected in favor of thermal ones. Here, one non-thermal photoionization model, the coupled photophysical and chemical dynamics model, is shown to be fully consistent with the data.
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Affiliation(s)
- Richard Knochenmuss
- Research and Development, Tofwerk AG, Uttigenstrasse 22, 3600 Thun, Switzerland
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Ahn SH, Park KM, Bae YJ, Kim MS. Efficient methods to generate reproducible mass spectra in matrix-assisted laser desorption ionization of peptides. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:868-876. [PMID: 23595259 DOI: 10.1007/s13361-013-0612-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2013] [Revised: 03/01/2013] [Accepted: 03/06/2013] [Indexed: 06/02/2023]
Abstract
In our previous matrix-assisted laser desorption ionization (MALDI) studies of peptides, we found that their mass spectra were virtually determined by the effective temperature in the early matrix plume, Tearly, when samples were rather homogeneous. This empirical rule allowed acquisition of quantitatively reproducible spectra. A difficulty in utilizing this rule was the complicated spectral treatment needed to get Tearly. In this work, we found another empirical rule that the total number of particles hitting the detector, or TIC, was a good measure of the spectral temperature and, hence, selection of spectra with the same TIC resulted in reproducible spectra. We also succeeded in obtaining reproducible spectra throughout a measurement by controlling TIC near a preset value through feedback adjustment of laser pulse energy. Both TIC selection and TIC control substantially reduced the shot-to-shot spectral variation in a spot, spot-to-spot variation in a sample, and even sample-to-sample variation in MALDI using α-cyano-4-hydroxycinnamic acid or 2,5-dihydroxybenzoic acid as matrix. Based on the utilization of acquired data, TIC control was more efficient than TIC selection by an order of magnitude. Both techniques produced calibration curves with excellent linearity, suggesting their utility in quantification of peptides.
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Affiliation(s)
- Sung Hee Ahn
- Department of Chemistry, Seoul National University, Seoul, 151-742, Korea
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19
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Knochenmuss R. MALDI and Related Methods: A Solved Problem or Still a Mystery? Mass Spectrom (Tokyo) 2013; 2:S0006. [PMID: 24349925 DOI: 10.5702/massspectrometry.s0006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2012] [Accepted: 01/22/2013] [Indexed: 11/23/2022] Open
Abstract
MALDI ionization mechanisms remain a topic of controversy. Some of the major modern models are compared, with emphasis on those of the author. Primary formation, secondary reaction, and loss mechanisms are considered.
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Park KM, Ahn SH, Bae YJ, Kim MS. Efficiency of Gas-Phase Ion Formation in Matrix-Assisted Laser Desorption Ionization with 2,5-Dihydroxybenzoic Acid as Matrix. B KOREAN CHEM SOC 2013. [DOI: 10.5012/bkcs.2013.34.3.907] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Ahn SH, Park KM, Bae YJ, Kim MS. Quantitative reproducibility of mass spectra in matrix-assisted laser desorption ionization and unraveling of the mechanism for gas-phase peptide ion formation. JOURNAL OF MASS SPECTROMETRY : JMS 2013; 48:299-305. [PMID: 23494784 DOI: 10.1002/jms.3155] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2012] [Revised: 12/07/2012] [Accepted: 12/11/2012] [Indexed: 06/01/2023]
Abstract
In a previous study on matrix-assisted laser desorption ionization (MALDI) of peptides using α-cyano-4-hydroxycinnamic acid (CHCA) as a matrix, we found that the patterns of single-shot spectra obtained under different experimental conditions became similar upon temperature selection. In this paper, we report that absolute ion abundances are also similar in temperature-selected MALDI spectra, even when laser fluence is varied. The result that has been obtained using CHCA and 2,5-dihydroxybenzoic acid as matrices is in disagreement with the hypothesis of laser-induced ionization of matrix as the mechanism for primary ion formation in MALDI. We also report that the total number of ions in such a spectrum is unaffected by the identity, concentration and number of analytes, i.e. it is the same as that in the spectrum of pure matrix. We propose that the generation of gas-phase ions in MALDI can be explained in terms of two thermal reactions, i.e. the autoprotolysis of matrix molecules and the matrix-to-analyte proton transfer, both of which are in quasi-equilibrium in the early matrix plume.
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Affiliation(s)
- Sung Hee Ahn
- Department of Chemistry, Seoul National University, Seoul 151-742, Korea
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22
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Seo J, Suh MS, Yoon HJ, Shin SK. N-Acylated Dipeptide Tags Enable Precise Measurement of Ion Temperature in Peptide Fragmentation. J Phys Chem B 2012; 116:13982-90. [DOI: 10.1021/jp308697v] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Jongcheol Seo
- Bio-Nanotechnology Center, Department
of Chemistry, Pohang University of Science and Technology, San 31
Hyoja-dong Nam-gu, Pohang, 790-784, Korea
| | - Min-Soo Suh
- Bio-Nanotechnology Center, Department
of Chemistry, Pohang University of Science and Technology, San 31
Hyoja-dong Nam-gu, Pohang, 790-784, Korea
| | - Hye-Joo Yoon
- Bio-Nanotechnology Center, Department
of Chemistry, Pohang University of Science and Technology, San 31
Hyoja-dong Nam-gu, Pohang, 790-784, Korea
| | - Seung Koo Shin
- Bio-Nanotechnology Center, Department
of Chemistry, Pohang University of Science and Technology, San 31
Hyoja-dong Nam-gu, Pohang, 790-784, Korea
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Bae YJ, Shin YS, Moon JH, Kim MS. Degree of ionization in MALDI of peptides: thermal explanation for the gas-phase ion formation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:1326-35. [PMID: 22653466 DOI: 10.1007/s13361-012-0406-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2012] [Revised: 04/24/2012] [Accepted: 04/27/2012] [Indexed: 05/20/2023]
Abstract
Degree of ionization (DI) in matrix-assisted laser desorption ionization (MALDI) was measured for five peptides using α-cyano-4-hydroxycinnanmic acid (CHCA) as the matrix. DIs were low 10(-4) for peptides and 10(-7) for CHCA. Total number of ions (i.e., peptide plus matrix) was the same regardless of peptides and their concentration, setting the number of gas-phase ions generated from a pure matrix as the upper limit to that of peptide ions. Positively charged cluster ions were too weak to support the ion formation via such ions. The total number of gas-phase ions generated by MALDI, and that from pure CHCA, was unaffected by the laser pulse energy, invalidating laser-induced ionization of matrix molecules as the mechanism for the primary ion formation. Instead, the excitation of matrix by laser is simply a way of supplying thermal energy to the sample. Accepting strong Coulomb attraction felt by cations in a solid sample, we propose three hypotheses for gas-phase peptide ion formation. In Hypothesis 1, they originate from the dielectrically screened peptide ions in the sample. In Hypothesis 2, the preformed peptide ions are released as part of neutral ion pairs, which generate gas-phase peptide ions via reaction with matrix-derived cations. In Hypothesis 3, neutral peptides released by ablation get protonated via reaction with matrix-derived cations.
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul 151-742, Korea
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24
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Bae YJ, Park KM, Kim MS. Reproducibility of Temperature-Selected Mass Spectra in Matrix-Assisted Laser Desorption Ionization of Peptides. Anal Chem 2012; 84:7107-11. [DOI: 10.1021/ac3014077] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yong Jin Bae
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Kyung Man Park
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Myung Soo Kim
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
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25
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Moon JH, Shin YS, Bae YJ, Kim MS. Ion yields for some salts in MALDI: mechanism for the gas-phase ion formation from preformed ions. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:162-170. [PMID: 22048904 DOI: 10.1007/s13361-011-0278-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Revised: 10/11/2011] [Accepted: 10/12/2011] [Indexed: 05/31/2023]
Abstract
Preformed ion emission is the main assumption in one of the prevailing theories for peptide and protein ion formation in matrix-assisted laser desorption ionization (MALDI). Since salts are in preformed ion forms in the matrix-analyte mixture, they are ideal systems to study the characteristics of preformed ion emission. In this work, a reliable method to measure the ion yield (IY) in MALDI was developed and used for a solid salt benzyltriphenylphosphonium chloride and two room-temperature ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate and trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate. IY for the matrix (α-cyano-4-hydroxycinnamic acid, CHCA) was also measured. Taking 1 pmol salts in 25 nmol CHCA as examples, IYs for three salts were similar, (4-8) × 10(-4), and those for CHCA were (0.8-1.2) × 10(-7). Even though IYs for the salts and CHCA remained virtually constant at low analyte concentration, they decreased as the salt concentrations increased. Two models, Model 1 and Model 2, were proposed to explain low IYs for the salts and the concentration dependences. Both models are based on the fact that the ion-pair formation equilibrium is highly shifted toward the neutral ion pair. In Model 1, the gas-phase analyte cations were proposed to originate from the same cations in the solid that were dielectrically screened from counter anions by matrix neutrals. In Model 2, preformed ions were assumed to be released from the solid sample in the form of neutral ion pairs and the anions in the ion pairs were assumed to be eliminated via reactions with matrix-derived cations.
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Affiliation(s)
- Jeong Hee Moon
- Medical Proteomics Research Center, KRIBB, Daejeon, 305-806, Korea
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26
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Bae YJ, Moon JH, Kim MS. Expansion cooling in the matrix plume is under-recognized in MALDI mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2011; 22:1070-1078. [PMID: 21953048 DOI: 10.1007/s13361-011-0115-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2011] [Revised: 02/20/2011] [Accepted: 02/23/2011] [Indexed: 05/31/2023]
Abstract
Time-of-flight (TOF) mass spectra for a peptide (Y(6)) were obtained by utilizing matrix-assisted infrared laser desorption ionization (IR-MALDI) with glycerol as the matrix and by ultraviolet MALDI with α-cyano-4-hydroxycinnamic acid (CHCA), sinapinic acid (SA), and 2,5-dihydroxybenzoic acid (DHB). Collisional activation during ion extraction and exothermicity in the gas-phase proton transfer were found to be unimportant as the driving forces for in-source (ISD) and post-source (PSD) decays, indicating that the thermal energy acquired during photo-ablation is responsible for their occurrence. The temperatures of [Y(6) + H](+) in the 'early' and 'late' matrix plumes were estimated by the kinetic analysis of the ISD and PSD yields, respectively. The order of the temperatures was glycerol < DHB ≈ SA < CHCA in the early plume and glycerol < DHB < SA < CHCA in the late plume. For each matrix, the temperature in the late plume was lower than in the early plume by 300-400 K, which was attributed to expansion cooling. The model (thermalization followed by expansion cooling) proposed to explain the occurrence of both rapid ISD and slow PSD is not only in sharp contrast with but also mutually exclusive with the prevailing explanation that the exothermicity in proton transfer and in-plume collisional activation are the driving forces for ion fragmentation in MALDI. The model also explains why MALDI is more successful for mass spectrometry of labile molecules than other desorption techniques that do not utilize a matrix. Factors affecting the plume temperature are also discussed.
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul, Korea
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27
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Casey G, Wentworth GR, Hamilton I, Al-Abadleh HA. Quantum chemical calculations on solvation effects for selected photoreactive aromatic organic molecules of atmospheric relevance. COMPUT THEOR CHEM 2011. [DOI: 10.1016/j.comptc.2010.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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28
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Lourantos E, Ramirez OM, Giannakopulos AE, Beran KA, Derrick PJ, Bashir S. The use of a silica-based heat sink to “uncouple” the matrix-assisted laser desorption/ionization (MALDI) mechanism. CAN J CHEM 2011. [DOI: 10.1139/v10-154] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The relationships between ion yield(s) as a function of desorption alone and (or) ionization was investigated using two model systems. In the first model system, a carbohydrate (2,3,6-tri-O-methyl-β-cyclodextrin, TMBCD), which could be directly laser desorbed, was analyzed with and without a silicon-based heat sink compound (HSC). The HSC allowed heat to pass through but obstructed the flow of charge. In the second model system, a peptide (substance P), which ccould not be laser desorbed, was analyzed under similar conditions. The ion yield of TMBCD under either system of heat conductivity was similar, whereas the ion yield of the peptide with the heat sink was negligible. Compounds that are predominately cationized either in the gas phase or preformed in solution give an ion yield that is not dependent upon the surface conditions, whereas compounds that are not ordinarily cationized are affected by the emission of electrons from the metal surface.
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Affiliation(s)
- E. Lourantos
- Institute of Mass Spectrometry, University of Warwick, Coventry CV4 7AL, UK
- Department of Physical Sciences, The University of Texas of the Permian Basin, 4901 E. University Blvd., Odessa, TX 79762, USA
| | - O. M. Ramirez
- Institute of Mass Spectrometry, University of Warwick, Coventry CV4 7AL, UK
- Department of Physical Sciences, The University of Texas of the Permian Basin, 4901 E. University Blvd., Odessa, TX 79762, USA
| | - A. E. Giannakopulos
- Institute of Mass Spectrometry, University of Warwick, Coventry CV4 7AL, UK
- Department of Physical Sciences, The University of Texas of the Permian Basin, 4901 E. University Blvd., Odessa, TX 79762, USA
| | - K. A. Beran
- Institute of Mass Spectrometry, University of Warwick, Coventry CV4 7AL, UK
- Department of Physical Sciences, The University of Texas of the Permian Basin, 4901 E. University Blvd., Odessa, TX 79762, USA
| | - Peter J. Derrick
- Institute of Mass Spectrometry, University of Warwick, Coventry CV4 7AL, UK
- Department of Physical Sciences, The University of Texas of the Permian Basin, 4901 E. University Blvd., Odessa, TX 79762, USA
| | - S. Bashir
- Institute of Mass Spectrometry, University of Warwick, Coventry CV4 7AL, UK
- Department of Physical Sciences, The University of Texas of the Permian Basin, 4901 E. University Blvd., Odessa, TX 79762, USA
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29
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Yoon SH, Moon JH, Kim MS. Changes in dissociation efficiency and kinetics of peptide ions induced by basic residues and their mechanistic implication. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2011; 22:214-220. [PMID: 21472581 DOI: 10.1007/s13361-010-0043-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2010] [Revised: 11/10/2010] [Accepted: 11/15/2010] [Indexed: 05/30/2023]
Abstract
With matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry, total abundance of product ions formed by dissociation inside (in-source decay, ISD) and outside (post-source decay, PSD) the source was measured for peptide ions [Y(5)X + H](+), [XY(5) + H](+), [Y 2)XY(3) + H](+), and [XY(4)X + H](+) (X = tyrosine (Y), histidine (H), lysine (K), and arginine (R) with H for the ionizing proton). α-Cyano-4-hydroxycinammic acid was used as matrix. Product abundance became smaller in the presence of basic residues (H, K, and R), in the order Y > H ≈ K > R. In particular, product abundances in ISD of peptide ions with R were smaller than those with H or K by an order of magnitude, which, in turn, were smaller than that for [Y(6) + H](+) by an order of magnitude. Product abundance was affected by the most basic residue when more than one basic residue was present. A kinetic explanation for the data was attempted under the assumption of quasi-thermal equilibrium for peptide ions in MALDI plume which undergoes expansion cooling. Dramatic disparity in product abundance was found to arise from small difference in critical energy and entropy. Results indicate similar transition structures regardless of basic residues present, where the ionizing proton keeps interacting with a basic site. Further implication of the results on the dissociation mechanism along b-y channels is discussed.
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Affiliation(s)
- So Hee Yoon
- Department of Chemistry, Seoul National University, Seoul, Korea
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30
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Yoon SH, Moon JH, Kim MS. A comparative study of in- and post-source decays of peptide and preformed ions in matrix-assisted laser desorption ionization time-of-flight mass spectrometry: effective temperature and matrix effect. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2010; 21:1876-1883. [PMID: 20696595 DOI: 10.1016/j.jasms.2010.07.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2010] [Revised: 07/01/2010] [Accepted: 07/05/2010] [Indexed: 05/29/2023]
Abstract
In-source decay (ISD) and post-source decay (PSD) of a peptide ion ([Y(6) + H](+)) and a preformed ion (benzyltriphenylphosphonium, BTPP) generated by matrix-assisted laser desorption ionization (MALDI) were investigated with time-of-flight mass spectrometry. α-Cyano-4-hydroxycinammic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB) were used as matrices. For both ions, ISD yield was unaffected by delay time, indicating rapid termination of ISD. This was taken as evidence for rapid expansion cooling of hot "early" plume formed in MALDI. CHCA was hotter than DHB for [Y(6) + H](+) while the matrix effect was insignificant for BTPP. The "early" plume temperature estimated utilizing previous kinetic results was 800-900 K, versus 400-500 K for "late" plume. The results support our previous finding that the temperature of peptide ions interrogated by tandem mass spectrometry was lower than most rough estimates of MALDI temperature.
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Affiliation(s)
- So Hee Yoon
- Department of Chemistry, Seoul National University, Seoul, Korea
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31
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Yoon SH, Moon JH, Kim MS. Dissociation mechanisms and implication for the presence of multiple conformations for peptide ions with arginine at the C-terminus: time-resolved photodissociation study. JOURNAL OF MASS SPECTROMETRY : JMS 2010; 45:806-814. [PMID: 20564416 DOI: 10.1002/jms.1773] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Time-resolved photodissociation (PD) patterns of singly protonated peptides with arginine at the C-terminus (C-arg peptide ions) have been used to classify the dissociation channels into two categories, i.e. high-energy channels generating v, w and x and low-energy ones generating b, y and z. x + 1 formed by C(alpha)-CO cleavage seems to be the intermediate ion in high-energy channels just as a + 1 is for N-arg peptide ions. Difference in time-resolved pattern indicates that the two sets of channels, high- and low-energy ones, are not in direct competition. Noncompetitive dissociation is also indicated by the observation of anomalous effect of matrix used in matrix-assisted laser desorption ionization, a cooler matrix generating more high-energy product ions both in spontaneous dissociation and in PD. Results from detailed investigation suggest that the two sets of channels start from two (or more) different conformations.
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Affiliation(s)
- So Hee Yoon
- Department of Chemistry, Seoul National University, Seoul 151-742, Korea
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32
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Moon JH, Yoon SH, Bae YJ, Kim MS. Dissociation kinetics of singly protonated leucine enkephalin investigated by time-resolved photodissociation tandem mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2010; 21:1151-1158. [PMID: 20409731 DOI: 10.1016/j.jasms.2010.03.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2010] [Revised: 03/12/2010] [Accepted: 03/17/2010] [Indexed: 05/29/2023]
Abstract
The yields of post-source decay (PSD) and time-resolved photodissociation (PD) at 193 and 266 nm were measured for singly protonated leucine enkephalin ([YGGFL + H](+)), a benchmark in the study of peptide ion dissociation, by using tandem time-of-flight mass spectrometry. The peptide ion was generated by matrix-assisted laser desorption ionization (MALDI) using 2,5-dihydroxybenzoic acid as the matrix. The critical energy (E(0)) and entropy (DeltaS(++) at 1000 K) for the dissociation were determined by Rice-Ramsperger-Kassel-Marcus fit of the experimental data. MALDI was done for a mixture of YGGFL and Y(6) and the plume temperature determined by the kinetic analysis of [Y(6) + H](+) data were used to improve the precision of E(0) and DeltaS(++) for [YGGFL + H](+). E(0) and DeltaS(++) thus determined (E(0) = 0.67 +/- 0.08 eV, DeltaS(++) = -24.4 +/- 3.2 eu with 1 eu = 4.184 J K(-1)mol(-1)) were significantly different from those determined by blackbody infrared radiative dissociation (BIRD) (E(0) = 1.10 eV, DeltaS(++) = -14.9 eu), and by surface-induced dissociation (SID) (E(0) = 1.13 eV, DeltaS(double dagger) = -10.3 eu). Analysis of the present experimental data with the SID kinetics (and BIRD kinetics also) led to an unrealistic situation where not only PSD and PD but also MALDI-TOF signals could not be detected. As an explanation for the discrepancy, it was suggested that transition-state switching occurs from an energy bottleneck (SID/BIRD) to an entropy bottleneck (PSD/PD) as the internal energy increases.
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Affiliation(s)
- Jeong Hee Moon
- Medical Proteomics Research Center, KRIBB, Daejeon, Korea
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33
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Knochenmuss R, Zhigilei LV. Molecular dynamics simulations of MALDI: laser fluence and pulse width dependence of plume characteristics and consequences for matrix and analyte ionization. JOURNAL OF MASS SPECTROMETRY : JMS 2010; 45:333-346. [PMID: 20301182 DOI: 10.1002/jms.1732] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Molecular dynamics simulations of matrix-assisted laser desorption/ionization were carried out to investigate laser pulse width and fluence effects on primary and secondary ionization process. At the same fluence, short (35 or 350 ps) pulses lead to much higher initial pressures and ion concentrations than longer ones (3 ns), but these differences do not persist because the system relaxes toward local thermal equilibrium on a nanosecond timescale. Higher fluences accentuate the initial disparities, but downstream differences are not substantial. Axial velocities of ions and neutrals are found to span a wide range, and be fluence dependent. Total ion yield is only weakly dependent on pulse width, and consistent with experimental estimates. Secondary reactions of matrix cations with analyte neutrals are efficient even though analyte ions are ablated in clusters of matrix.
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Affiliation(s)
- Richard Knochenmuss
- Novartis Institutes for Biomedical Research, Tofwerk AG, Uttigenstrasse 22, 3600 Thun, Switzerland.
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34
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Bae YJ, Yoon SH, Moon JH, Kim MS. Optimization of Reflectron for Kinetic and Mechanistic Studies with Multiplexed Multiple Tandem (MSn) Time-of-flight Mass Spectrometry. B KOREAN CHEM SOC 2010. [DOI: 10.5012/bkcs.2010.31.01.092] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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35
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Yoon SH, Moon JH, Chung YJ, Kim MS. Influence of basic residues on dissociation kinetics and dynamics of singly protonated peptides: time-resolved photodissociation study. JOURNAL OF MASS SPECTROMETRY : JMS 2009; 44:1532-1537. [PMID: 19753580 DOI: 10.1002/jms.1670] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Product ion yields in postsource decay and time-resolved photodissociation at 193 and 266 nm were measured for some peptide ions with lysine ([KF6 + H]+, [F6K + H]+, and [F3KF3 + H]+) formed by matrix-assisted laser desorption ionization. The critical energy (E0) and entropy (DeltaS(double dagger)) were determined by RRKM fitting of the data. The results were similar to those found previously for peptide ions with histidine. To summarize, the presence of a basic residue, histidine or lysine, inside a peptide ion retarded its dissociation by lowering DeltaS(double dagger). On the basis of highly negative DeltaS(double dagger), presence of intramolecular interaction involving a basic group in the transition structure was proposed.
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Affiliation(s)
- So Hee Yoon
- Department of Chemistry, Seoul National University, Seoul 151-742, Republic of Korea
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36
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Yoon SH, Moon JH, Kim MS. Time-resolved photodissociation study of singly protonated peptides with a histidine residue generated by matrix-assisted laser desorption ionization: dissociation rate constant and internal temperature. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2009; 20:1522-1529. [PMID: 19467884 DOI: 10.1016/j.jasms.2009.04.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2009] [Revised: 04/11/2009] [Accepted: 04/14/2009] [Indexed: 05/27/2023]
Abstract
Product ion yields in post-source decay and time-resolved photodissociation at 193 and 266 nm were measured for some peptide ions with a histidine residue ([HF(6) + H](+), [F(6)H + H](+), and [F(3)HF(3) + H](+)) formed by matrix-assisted laser desorption ionization (MALDI). Compared with similar data for peptide ions without any basic residue reported previously, significant reduction in dissociation efficiency was observed. Internal temperatures (T) of the peptide ions and their dissociation kinetic parameters-the critical energy (E(0)) and entropy (DeltaS(double dagger))-were determined by the method reported previously. Slight decreases in E(0), DeltaS(double dagger), and T were responsible for the histidine effect-reduction in dissociation rate constant. Regardless of the presence of the residue, DeltaS(double dagger) was far more negative than previous quantum chemical results. Based on this, we propose the existence of transition structures in which the nitrogen atoms in the histidine residue or at the N-terminus coordinate to the reaction centers. Reduction in T in the presence of a histidine residue could not be explained based on popular models for ion formation in MALDI, such as the gas-phase proton transfer model.
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Affiliation(s)
- So Hee Yoon
- Department of Chemistry, Seoul National University, Seoul, Korea
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