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Ni Z, Arevalo R, Bardyn A, Willhite L, Ray S, Southard A, Danell R, Graham J, Li X, Chou L, Briois C, Thirkell L, Makarov A, Brinckerhoff W, Eigenbrode J, Junge K, Nunn BL. Detection of Short Peptides as Putative Biosignatures of Psychrophiles via Laser Desorption Mass Spectrometry. ASTROBIOLOGY 2023; 23:657-669. [PMID: 37134219 DOI: 10.1089/ast.2022.0138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Studies of psychrophilic life on Earth provide chemical clues as to how extraterrestrial life could maintain viability in cryogenic environments. If living systems in ocean worlds (e.g., Enceladus) share a similar set of 3-mer and 4-mer peptides to the psychrophile Colwellia psychrerythraea on Earth, spaceflight technologies and analytical methods need to be developed to detect and sequence these putative biosignatures. We demonstrate that laser desorption mass spectrometry, as implemented by the CORALS spaceflight prototype instrument, enables the detection of protonated peptides, their dimers, and metal adducts. The addition of silicon nanoparticles promotes the ionization efficiency, improves mass resolving power and mass accuracies via reduction of metastable decay, and facilitates peptide de novo sequencing. The CORALS instrument, which integrates a pulsed UV laser source and an Orbitrap™ mass analyzer capable of ultrahigh mass resolving powers and mass accuracies, represents an emerging technology for planetary exploration and a pathfinder for advanced technique development for astrobiological objectives. Teaser: Current spaceflight prototype instrument proposed to visit ocean worlds can detect and sequence peptides that are found enriched in at least one strain of microbe surviving in subzero icy brines via silicon nanoparticle-assisted laser desorption analysis.
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Affiliation(s)
- Ziqin Ni
- University of Maryland, College Park, Maryland, USA
| | | | - Anais Bardyn
- University of Maryland, College Park, Maryland, USA
| | | | - Soumya Ray
- University of Maryland, College Park, Maryland, USA
| | | | - Ryan Danell
- Danell Consulting, Winterville, North Carolina, USA
| | - Jacob Graham
- NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Xiang Li
- NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Luoth Chou
- NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
- Georgetown University, Washington, DC, USA
| | - Christelle Briois
- Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, Orléans, France
| | - Laurent Thirkell
- Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, Orléans, France
| | | | | | | | - Karen Junge
- University of Washington, Seattle, Washington, USA
| | - Brook L Nunn
- University of Washington, Seattle, Washington, USA
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2
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Robinson KN, Steven RT, Race AM, Bunch J. The Influence of MS Imaging Parameters on UV-MALDI Desorption and Ion Yield. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2019; 30:1284-1293. [PMID: 30949969 DOI: 10.1007/s13361-019-02193-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 02/12/2019] [Accepted: 03/11/2019] [Indexed: 06/09/2023]
Abstract
Ultraviolet matrix-assisted laser desorption/ionization mass spectrometry imaging (UV-MALDI MSI) is a widely used technique for imaging molecular distributions within biological systems. While much work exists concerning desorption in UV-MALDI MS, the effects of commonly varied parameters for imaging applications (repetition rate, use of continuous raster mode and raster speed), which determine spatial resolution and limits of detection for the technique, remain largely unknown. We use multiple surface characterization modalities to obtain quantitative measurements of material desorption and analyte ion yield in thin film model systems of two matrix compounds, arising from different UV-MALDI MSI sampling conditions. Observed changes in resulting ablation feature point to matrix-dependent spatial resolution and laser-induced matrix modification effects. Analyte ion yields of 10-9 to 10-6 are observed. Complex changes in ion yield, between spot and raster sampling and arising from varied laser repetition rate and raster speed, are observed. Graphical Abstract.
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Affiliation(s)
- Kenneth N Robinson
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory, Teddington, UK
- Advanced Materials and Healthcare Technologies Division (AMHT), University of Nottingham, Nottingham, UK
| | - Rory T Steven
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory, Teddington, UK.
| | - Alan M Race
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory, Teddington, UK
| | - Josephine Bunch
- National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), National Physical Laboratory, Teddington, UK.
- Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, London, UK.
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3
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Greco V, Piras C, Pieroni L, Urbani A. Direct Assessment of Plasma/Serum Sample Quality for Proteomics Biomarker Investigation. Methods Mol Biol 2018; 1619:3-21. [PMID: 28674873 DOI: 10.1007/978-1-4939-7057-5_1] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Blood proteome analysis for biomarker discovery represents one of the most challenging tasks to be achieved through clinical proteomics due to the sample complexity, such as the extreme heterogeneity of proteins in very dynamic concentrations, and to the observation of proper sampling and storage conditions. Quantitative and qualitative proteomics profiling of plasma and serum could be useful both for the early detection of diseases and for the evaluation of pathological status. Two main sources of variability can affect the precision and accuracy of the quantitative experiments designed for biomarker discovery and validation. These sources are divided into two categories, pre-analytical and analytical, and are often ignored; however, they can contribute to consistent errors and misunderstanding in biomarker research. In this chapter, we review critical pre-analytical and analytical variables that can influence quantitative proteomics. According to guidelines accepted by proteomics community, we propose some recommendations and strategies for a proper proteomics analysis addressed to biomarker studies.
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Affiliation(s)
- Viviana Greco
- Proteomics and metabonomics unit, Fondazione Santa Lucia, IRCCS, Rome, Italy
| | - Cristian Piras
- Department of Veterinary Medicine, University of Milan, Milan, Italy
| | - Luisa Pieroni
- Proteomics and metabonomics unit, Fondazione Santa Lucia, IRCCS, Rome, Italy
| | - Andrea Urbani
- Proteomics and metabonomics unit, Fondazione Santa Lucia, IRCCS, Rome, Italy. .,Institute of Biochemistry and Clinical Biochemistry, Catholic University of Sacred Heart, Rome, Italy.
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Lai YH, Wang YS. Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry: Mechanistic Studies and Methods for Improving the Structural Identification of Carbohydrates. Mass Spectrom (Tokyo) 2017; 6:S0072. [PMID: 28959517 PMCID: PMC5610957 DOI: 10.5702/massspectrometry.s0072] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Accepted: 08/03/2017] [Indexed: 12/21/2022] Open
Abstract
Although matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is one of the most widely used soft ionization methods for biomolecules, the lack of detailed understanding of ionization mechanisms restricts its application in the analysis of carbohydrates. Structural identification of carbohydrates achieved by MALDI mass spectrometry helps us to gain insights into biological functions and pathogenesis of disease. In this review, we highlight mechanistic details of MALDI, including both ionization and desorption. Strategies to improve the ion yield of carbohydrates are also reviewed. Furthermore, commonly used fragmentation methods to identify the structure are discussed.
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Mirabelli MF, Zenobi R. Observing Proton Transfer Reactions Inside the MALDI Plume: Experimental and Theoretical Insight into MALDI Gas-Phase Reactions. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2017; 28:1676-1686. [PMID: 28451953 DOI: 10.1007/s13361-017-1677-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 03/24/2017] [Accepted: 03/25/2017] [Indexed: 06/07/2023]
Abstract
We evaluated the contribution of gas-phase in-plume proton transfer reactions to the formation of protonated and deprotonated molecules in the MALDI process. A split sample holder was used to separately deposit two different samples, which avoids any mixing during sample preparation. The two samples were brought very close to each other and desorbed/ionized by the same laser pulse. By using a combination of deuterated and non-deuterated matrices, it was possible to observe exclusively in-plume proton transfer processes. The hydrogen/deuterium exchange (HDX) kinetics were evaluated by varying the delayed extraction (DE) time, allowing the desorbed ions and neutrals to interact inside the plume for a variable period of time before being extracted and detected. Quantum mechanical calculations showed that the HDX energy barriers are relatively low for such reactions, corroborating the importance of gas-phase proton transfer in the MALDI plume. The experimental results, supported by theoretical simulations, confirm that the plume is a very reactive environment, where HDX reactions could be observed from 0 ns up to 400 ns after the laser pulse. These results could be used to evaluate the relevance of previously proposed (and partially conflicting) ionization models for MALDI. Graphical Abstract ᅟ.
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Affiliation(s)
- Mario F Mirabelli
- ETH Zurich, Department of Chemistry and Applied Biosciences, CH-8093, Zurich, Switzerland
| | - Renato Zenobi
- ETH Zurich, Department of Chemistry and Applied Biosciences, CH-8093, Zurich, Switzerland.
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6
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Lu IC, Pophristic M, Inutan ED, McKay RG, McEwen CN, Trimpin S. Simplifying the ion source for mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2016; 30:2568-2572. [PMID: 27520740 DOI: 10.1002/rcm.7718] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2016] [Revised: 08/09/2016] [Accepted: 08/10/2016] [Indexed: 06/06/2023]
Affiliation(s)
- I-Chung Lu
- Department of Chemistry, Wayne State University, Detroit, MI, 48202, USA
| | - Milan Pophristic
- Department of Chemistry & Biochemistry, University of the Sciences, Philadelphia, PA, 19104, USA
- MSTM LLC, Newark, DE, 19711, USA
| | - Ellen D Inutan
- Department of Chemistry, Wayne State University, Detroit, MI, 48202, USA
- MSTM LLC, Newark, DE, 19711, USA
| | | | - Charles N McEwen
- Department of Chemistry & Biochemistry, University of the Sciences, Philadelphia, PA, 19104, USA
- MSTM LLC, Newark, DE, 19711, USA
- M&M Mass Spec Consulting, LLC, Harbeson, DE, 19951, USA
| | - Sarah Trimpin
- Department of Chemistry, Wayne State University, Detroit, MI, 48202, USA
- MSTM LLC, Newark, DE, 19711, USA
- Cardiovascular Research Institute, Wayne State University School of Medicine, Detroit, MI, 48202, USA
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7
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Wang CC, Lai YH, Ou YM, Chang HT, Wang YS. Critical factors determining the quantification capability of matrix-assisted laser desorption/ionization- time-of-flight mass spectrometry. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2016; 374:rsta.2015.0371. [PMID: 27644968 PMCID: PMC5031637 DOI: 10.1098/rsta.2015.0371] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/17/2016] [Indexed: 05/03/2023]
Abstract
Quantitative analysis with mass spectrometry (MS) is important but challenging. Matrix-assisted laser desorption/ionization (MALDI) coupled with time-of-flight (TOF) MS offers superior sensitivity, resolution and speed, but such techniques have numerous disadvantages that hinder quantitative analyses. This review summarizes essential obstacles to analyte quantification with MALDI-TOF MS, including the complex ionization mechanism of MALDI, sensitive characteristics of the applied electric fields and the mass-dependent detection efficiency of ion detectors. General quantitative ionization and desorption interpretations of ion production are described. Important instrument parameters and available methods of MALDI-TOF MS used for quantitative analysis are also reviewed.This article is part of the themed issue 'Quantitative mass spectrometry'.
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Affiliation(s)
- Chia-Chen Wang
- Department of Biochemistry, National Yang-Ming University, No. 155, Section 2, Linong Street, Taipei 112, Taiwan, Republic of China Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Taipei 115, Taiwan, Republic of China
| | - Yin-Hung Lai
- Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Taipei 115, Taiwan, Republic of China
| | - Yu-Meng Ou
- Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Taipei 115, Taiwan, Republic of China Department of Chemistry, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan, Republic of China
| | - Huan-Tsung Chang
- Department of Chemistry, National Taiwan University, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan, Republic of China
| | - Yi-Sheng Wang
- Department of Biochemistry, National Yang-Ming University, No. 155, Section 2, Linong Street, Taipei 112, Taiwan, Republic of China Genomics Research Center, Academia Sinica, 128 Academia Road, Section 2, Taipei 115, Taiwan, Republic of China
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8
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Quantitative profiling of O-glycans by electrospray ionization- and matrix-assisted laser desorption ionization-time-of-flight-mass spectrometry after in-gel derivatization with isotope-coded 1-phenyl-3-methyl-5-pyrazolone. Anal Chim Acta 2016; 935:187-96. [DOI: 10.1016/j.aca.2016.06.032] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Revised: 06/02/2016] [Accepted: 06/16/2016] [Indexed: 11/19/2022]
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9
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Knochenmuss R. The Coupled Chemical and Physical Dynamics Model of MALDI. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2016; 9:365-385. [PMID: 27070182 DOI: 10.1146/annurev-anchem-071015-041750] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The coupled physical and chemical dynamics model of ultraviolet matrix-assisted laser desorption/ionization (MALDI) has reproduced and explained a wide variety of MALDI phenomena. The rationale behind and elements of the model are reviewed, including the photophysics, kinetics, and thermodynamics of primary and secondary reaction steps. Experimental results are compared with model predictions to illustrate the foundations of the model, coupling of ablation and ionization, differences between and commonalities of matrices, secondary charge transfer reactions, ionization in both polarities, fluence and concentration dependencies, and suppression and enhancement effects.
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Affiliation(s)
- Richard Knochenmuss
- Departement für Chemie und Biochemie, Universität Bern, CH-3012 Bern, Switzerland;
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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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Moskovets E. Ghost peaks observed after atmospheric pressure matrix-assisted laser desorption/ionization experiments may disclose new ionization mechanism of matrix-assisted hypersonic velocity impact ionization. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2015; 29:1501-12. [PMID: 26212165 PMCID: PMC4518465 DOI: 10.1002/rcm.7248] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Revised: 05/28/2015] [Accepted: 06/09/2015] [Indexed: 05/12/2023]
Abstract
RATIONALE Understanding the mechanisms of matrix-assisted laser desorption/ionization (MALDI) promises improvements in the sensitivity and specificity of many established applications in the field of mass spectrometry. This paper reports a serendipitous observation of a significant ion yield in a post-ionization experiment conducted after the sample had been removed from a standard atmospheric pressure (AP)-MALDI source. This post-ionization is interpreted in terms of collisions of microparticles moving with a hypersonic velocity into a solid surface. Calculations show that the thermal energy released during such collisions is close to that absorbed by the top matrix layer in traditional MALDI. The microparticles, containing both the matrix and analytes, could be detached from a film produced inside the inlet capillary during the sample ablation and accelerated by the flow rushing through the capillary. These observations contribute some new perspective to ion formation in both laser and laser-less matrix-assisted ionization. METHODS An AP-MALDI ion source hyphenated with a three-stage high-pressure ion funnel system was utilized for peptide mass analysis. After the laser had been turned off and the MALDI sample removed, ions were detected during a gradual reduction of the background pressure in the first funnel. The constant-rate pressure reduction led to the reproducible appearance of different singly and doubly charged peptide peaks in mass spectra taken a few seconds after the end of the MALDI analysis of a dried-droplet spot. RESULTS The ion yield as well as the mass range of ions observed with a significant delay after a completion of the primary MALDI analysis depended primarily on the background pressure inside the first funnel. The production of ions in this post-ionization step was exclusively observed during the pressure drop. A lower matrix background and significant increase in relative yield of double-protonated ions are reported. CONCLUSIONS The observations were partially consistent with a model of the supersonic jet from the inlet capillary accelerating detached particles to kinetic energies suitable for matrix-assisted hypersonic-velocity impact ionization.
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Affiliation(s)
- Eugene Moskovets
- MassTech Inc., 6992 Columbia Gateway Dr., Columbia MD, USA, Phone: 443-539-0139
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12
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Lu IC, Chu KY, Lin CY, Wu SY, Dyakov YA, Chen JL, Gray-Weale A, Lee YT, Ni CK. Ion-to-Neutral Ratios and Thermal Proton Transfer in Matrix-Assisted Laser Desorption/Ionization. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:1242-1251. [PMID: 25851654 DOI: 10.1007/s13361-015-1112-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Revised: 02/15/2015] [Accepted: 02/16/2015] [Indexed: 06/04/2023]
Abstract
The ion-to-neutral ratios of four commonly used solid matrices, α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxybenzoic acid (2,5-DHB), sinapinic acid (SA), and ferulic acid (FA) in matrix-assisted laser desorption/ionization (MALDI) at 355 nm are reported. Ions are measured using a time-of-flight mass spectrometer combined with a time-sliced ion imaging detector. Neutrals are measured using a rotatable quadrupole mass spectrometer. The ion-to-neutral ratios of CHCA are three orders of magnitude larger than those of the other matrices at the same laser fluence. The ion-to-neutral ratios predicted using the thermal proton transfer model are similar to the experimental measurements, indicating that thermal proton transfer reactions play a major role in generating ions in ultraviolet-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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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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15
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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: 43] [Impact Index Per Article: 4.8] [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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Lin HY, Hsu HC, Lu IC, Hsu KT, Liao CY, Lee YY, Tseng CM, Lee YT, Ni CK. Fluorescence spectroscopy of UV-MALDI matrices and implications of ionization mechanisms. J Chem Phys 2014; 141:164307. [DOI: 10.1063/1.4898372] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Hou-Yu Lin
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Hsu Chen Hsu
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - I-Chung Lu
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Kuo-Tung Hsu
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Chih-Yu Liao
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Yin-Yu Lee
- National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Chien-Ming Tseng
- Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan
| | - Yuan-Tseh Lee
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Chi-Kung Ni
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
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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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18
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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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19
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Lai YH, Chen BG, Lee YT, Wang YS, Lin SH. Contribution of thermal energy to initial ion production in matrix-assisted laser desorption/ionization observed with 2,4,6-trihydroxyacetophenone. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2014; 28:1716-22. [PMID: 24975252 DOI: 10.1002/rcm.6952] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Revised: 05/01/2014] [Accepted: 05/21/2014] [Indexed: 05/20/2023]
Abstract
RATIONALE Although several reaction models have been proposed in the literature to explain matrix-assisted laser desorption/ionization (MALDI), further study is still necessary to explore the important ionization pathways that occur under the high-temperature environment of MALDI. 2,4,6-Trihydroxyacetophenone (THAP) is an ideal compound for evaluating the contribution of thermal energy to an initial reaction with minimum side reactions. METHODS Desorbed neutral THAP and ions were measured using a crossed-molecular beam machine and commercial MALDI-TOF instrument, respectively. A quantitative model incorporating an Arrhenius-type desorption rate derived from transition state theory was proposed. Reaction enthalpy was calculated using GAUSSIAN 03 software with dielectric effect. Additional evidence of thermal-induced proton disproportionation was given by the indirect ionization of THAP embedded in excess fullerene molecules excited by a 450 nm laser. RESULTS The quantitative model predicted that proton disproportionation of THAP would be achieved by thermal energy converted from a commonly used single UV laser photon. The dielectric effect reduced the reaction Gibbs free energy considerably even when the dielectric constant was reduced under high-temperature MALDI conditions. With minimum fitting parameters, observations of pure THAP and THAP mixed with fullerene both agreed with predictions. CONCLUSIONS Proton disproportionation of solid THAP was energetically favorable with a single UV laser photon. The quantitative model revealed an important initial ionization pathway induced by the abrupt heating of matrix crystals. In the matrix crystals, the dielectric effect reduced reaction Gibbs free energy under typical MALDI conditions. The result suggested that thermal energy plays an important role in the initial ionization reaction of THAP.
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Affiliation(s)
- Yin-Hung Lai
- Genomics Research Center, Academia Sinica, Taipei, 115, Taiwan
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20
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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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21
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Lu IC, Lee C, Chen HY, Lin HY, Hung SW, Dyakov YA, Hsu KT, Liao CY, Lee YY, Tseng CM, Lee YT, Ni CK. Ion Intensity and Thermal Proton Transfer in Ultraviolet Matrix-Assisted Laser Desorption/Ionization. J Phys Chem B 2014; 118:4132-9. [DOI: 10.1021/jp5008076] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- I-Chung Lu
- Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Chuping Lee
- Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan
| | - Hui-Yuan Chen
- Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Hou-Yu Lin
- Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan
| | - Sheng-Wei Hung
- Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Yuri A. Dyakov
- Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Kuo-Tung Hsu
- National
Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Chih-Yu Liao
- National
Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Yin-Yu Lee
- National
Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
| | - Chien-Ming Tseng
- Department
of Applied Chemistry, National Chiao Tung University, Hsinchu 30010, Taiwan
| | - Yuan-Tseh Lee
- Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
- Department
of Chemistry, National Taiwan University, Taipei 10617, Taiwan
| | - Chi-Kung Ni
- Institute
of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
- Department
of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
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22
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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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23
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Lin HY, Song B, Lu IC, Hsu KT, Liao CY, Lee YY, Tseng CM, Lee YT, Ni CK. Is energy pooling necessary in ultraviolet matrix-assisted laser desorption/ionization? RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2014; 28:77-82. [PMID: 24285392 DOI: 10.1002/rcm.6765] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Revised: 10/06/2013] [Accepted: 10/14/2013] [Indexed: 06/02/2023]
Abstract
RATIONALE Energy pooling has been suggested as the key process for generating the primary ions during ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI). In previous studies, decreases in fluorescence quantum yields as laser fluence increased for 2-aminobenzoic acid, 2,5-dihydroxybenzoic acid (2,5-DHB), and 3-hydroxypicolinic acid were used as evidence of energy pooling. This work extends the research to other matrices and addresses whether energy pooling is a universal property in UV-MALDI. METHODS Energy pooling was investigated in a time-resolved fluorescence experiment by using a short laser pulse (355 nm, 20 ps pulse width) for excitation and a streak camera (1 ps time resolution) for fluorescence detection. RESULTS The excited-state lifetime of 2,5-DHB decreased with increases in laser fluence. This suggests that a reaction occurs between two excited molecules, and that energy pooling may be one of the possible reactions. However, the excited-state lifetime of 2,4,6-trihydroxyacetophenone (THAP) did not change with increases in laser fluence. The upper limit of the energy pooling rate constant for THAP is estimated to be approximately 100-500 times smaller than that of 2,5-DHB. CONCLUSIONS The small energy pooling rate constant for THAP indicates that the potential contribution of the energy pooling mechanism to the generation of THAP matrix primary ions should be reconsidered.
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Affiliation(s)
- Hou-Yu Lin
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan
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24
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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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25
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Bae YJ, Choe JC, Moon JH, Kim MS. Why do the abundances of ions generated by MALDI look thermally determined? JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:1807-1815. [PMID: 23990058 DOI: 10.1007/s13361-013-0717-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 07/23/2013] [Accepted: 07/23/2013] [Indexed: 06/02/2023]
Abstract
In a previous study (J. Mass Spectrom. 48, 299-305, 2013), we observed that the abundance of each ion in a matrix-assisted laser desorption ionization (MALDI) spectrum looked thermally determined. To find out the explanation for the phenomenon, we estimated the ionization efficiency and the reaction quotient (QA) for the autoprotolysis of matrix, M + M → [M + H](+) + [M - H](-), from the temperature-controlled laser desorption ionization spectra of α-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB). We also evaluated the equilibrium constants (KA) for the autoprotolysis at various temperatures by quantum chemical calculation. Primary ion formation via various thermal models followed by autoprotolysis-recombination was compatible with the observations. The upper limit of the effective temperature of the plume where autoprotolysis-recombination occurs was estimated by equating QA with the calculated equilibrium constant. Figure ᅟ
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Affiliation(s)
- Yong Jin Bae
- Department of Chemistry, Seoul National University, Seoul, 151-747, Korea
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26
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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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27
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Ahn SH, Bae YJ, Moon JH, Kim MS. Matrix Suppression as a Guideline for Reliable Quantification of Peptides by Matrix-Assisted Laser Desorption Ionization. Anal Chem 2013; 85:8796-801. [DOI: 10.1021/ac401967n] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sung Hee Ahn
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Yong Jin Bae
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Jeong Hee Moon
- Medical
Proteomics Research Center, KRIBB, Daejeon 305-806, Korea
| | - Myung Soo Kim
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
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28
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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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29
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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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30
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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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31
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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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32
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Park KM, Bae YJ, Ahn SH, Kim MS. A Simple Method for Quantification of Peptides and Proteins by Matrix-Assisted Laser Desorption Ionization Mass Spectrometry. Anal Chem 2012; 84:10332-7. [DOI: 10.1021/ac302807u] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Affiliation(s)
- Kyung Man Park
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Yong Jin Bae
- Department
of Chemistry, Seoul National University, Seoul 151-742, Korea
| | - Sung Hee Ahn
- 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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33
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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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