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Qi Y, Hu X, Yang X, Jia S, Zhong H. Competing Deprotonation and Electron Capture Dissociation in MALDI Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2021; 32:322-329. [PMID: 33200938 DOI: 10.1021/jasms.0c00344] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
A protonation/deprotonation mechanism has been established for the interpretation of ions in MALDI. We show herein that negative ions can be generated in different ways. Molecules with different electron affinities have been spotted on surfaces of TiO2, ZnO, and a stainless steel plate for the investigation of electron capture dissociation in comparison with photo- or thermal-induced deprotonation upon irradiation of the third harmonic of Nd3+:YAG (355 nm) laser pulses. Detection of C60•- and Fe (II) (porph•-) radical anions unambiguously demonstrates the electron-transfer process and the exothermic capture of electrons. Radical anions of fatty acids were difficult to observe because of electron-directed ultrafast homolytic cleavage of O-H bonds unless there is a conjugated system as that in C60 and porphyrin for the delocalization and stabilization of acquired changes. The surface basicity of substrate materials was found to determine the competition of the electron-capture dissociation with deprotonation processes. Multiple electron transfers to pyrrole, -COOH, and Fe2+ of the heme were observed on TiO2 and the stainless steel plate but not on ZnO. When the heme was deprotonated by proton sponge 1,8-bis(dimethylamino)naphthalene, the occurrence of electron transfer on TiO2 was also not observed. It is proposed that negative charges of deprotonated ions prevent electron transfer due to the repulsive force. When both deprotonation and electron transfer are inhibited, adsorbed fatty acids on TiO2 undergo dehydration reactions to form titanium esters. In contrast, ZnO generates gaseous micelles composed of positive metal ions and negative fatty acid ions through either deprotonation or electron-capture dissociation.
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Affiliation(s)
- Yinghua Qi
- Laboratory of Mass Spectrometry, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079, P.R. China
- Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, Wuhan, Hubei 430079, P.R. China
| | - Xuewen Hu
- Laboratory of Mass Spectrometry, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079, P.R. China
- Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, Wuhan, Hubei 430079, P.R. China
| | - Xiaojie Yang
- Laboratory of Mass Spectrometry, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079, P.R. China
- Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, Wuhan, Hubei 430079, P.R. China
| | - Shanshan Jia
- Laboratory of Mass Spectrometry, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079, P.R. China
- Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, Wuhan, Hubei 430079, P.R. China
| | - Hongying Zhong
- Laboratory of Mass Spectrometry, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079, P.R. China
- Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, Wuhan, Hubei 430079, P.R. China
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Zeegers GP, Günthardt BF, Zenobi R. Target Plate Material Influence on Fullerene-C60 Laser Desorption/Ionization Efficiency. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2016; 27:699-708. [PMID: 26894888 DOI: 10.1007/s13361-016-1333-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Revised: 12/03/2015] [Accepted: 12/30/2015] [Indexed: 06/05/2023]
Abstract
Systematic laser desorption/ionization (LDI) experiments of fullerene-C60 on a wide range of target plate materials were conducted to gain insight into the initial ion formation in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The positive and negative ion signal intensities of precursor, fragment, and cluster ions were monitored, varying both the laser fluence (0-3.53 Jcm(-2)) and the ion extraction delay time (0-950 ns). The resulting species-specific ion signal intensities are an indication for the ionization mechanisms that contribute to LDI and the time frames in which they operate, providing insight in the (MA)LDI primary ionization. An increasing electrical resistivity of the target plate material increases the fullerene-C60 precursor and fragment anion signal intensity. Inconel 625 and Ti90/Al6/V4, both highly electrically resistive, provide the highest anion signal intensities, exceeding the cation signal intensity by a factor ~1.4 for the latter. We present a mechanism based on transient electrical field strength reduction to explain this trend. Fullerene-C60 cluster anion formation is negligible, which could be due to the high extraction potential. Cluster cations, however, are readily formed, although for high laser fluences, the preferred channel is formation of precursor and fragment cations. Ion signal intensity depends greatly on the choice of substrate material, and careful substrate selection could, therefore, allow for more sensitive (MA)LDI measurements. Graphical Abstract ᅟ.
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Affiliation(s)
- Guido P Zeegers
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, CH-8093, Zürich, Switzerland
| | - Barbara F Günthardt
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, CH-8093, Zürich, Switzerland
| | - Renato Zenobi
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, CH-8093, Zürich, Switzerland.
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Zakrzewski VG, Dolgounitcheva O, Ortiz JV. Electron propagator calculations on C60 and C70 photoelectron spectra. J Chem Phys 2008; 129:104306. [DOI: 10.1063/1.2976789] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Hishida Y, Nishi M, Baba Y, Ikeuchi H. Diffusion Coefficients of C60 and C60- in Benzonitrile and Dichloromethane Solutions Containing Tetrabutylammonium Perchlorate, Measured by Potential-step Chronoamperometry. ANAL SCI 2006; 22:931-5. [PMID: 16837741 DOI: 10.2116/analsci.22.931] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The diffusion coefficients of C(60) in dichloromethane and benzonitrile solutions containing 0.1 M tetrabutylammonium perchlorate were determined by single potential-step chronoamperometry at small disk electrodes. The diffusion coefficients of C(60) were obtained by curve fitting of the chronoamperograms to a theoretical equation by Shoup and Szabo. The values were (1.4 +/- 0.3) x 10(-9) and (4.1 +/- 0.3) x 10(-10) m(2) s(-1), respectively (the errors are 95% confidence limits). The diffusion coefficients of C(60)(-) in these solutions were measured by double potential-step chronoamperometry. The ratios of the diffusion coefficients of C(60) to those of C(60)(-) were obtained from theoretical curves of the ratios of the current at the second potential step to the current at the first one. The values of the ratios were 1.2 +/- 0.2 and 1.0 +/- 0.3, respectively.
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Affiliation(s)
- Yukihiro Hishida
- Department of Chemistry, Faculty of Science and Technology, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan
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