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Fu D, Habtegabir SG, Wang H, Feng S, Han Y. Understanding of protomers/deprotomers by combining mass spectrometry and computation. Anal Bioanal Chem 2023:10.1007/s00216-023-04574-1. [PMID: 36737499 DOI: 10.1007/s00216-023-04574-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 01/19/2023] [Accepted: 01/27/2023] [Indexed: 02/05/2023]
Abstract
Multifunctional compounds may form different prototropic isomers under different conditions, which are known as protomers/deprotomers. In biological systems, these protomer/deprotomer isomers affect the interaction modes and conformational landscape between compounds and enzymes and thus present different biological activities. Study on protomers/deprotomers is essentially the study on the acidity/basicity of each intramolecular functional group and its effect on molecular structure. In recent years, the combination of mass spectrometry (MS) and computational chemistry has been proven to be a powerful and effective means to study prototropic isomers. MS-based technologies are developed to discriminate and characterize protomers/deprotomers to provide structural information and monitor transformations, showing great superiority than other experimental methods. Computational chemistry is used to predict the thermodynamic stability of protomers/deprotomers, provide the simulated MS/MS spectra, infrared spectra, and calculate collision cross-section values. By comparing the theoretical data with the corresponding experimental results, the researchers can not only determine the protomer/deprotomer structure, but also investigate the structure-activity relationship in a given system. This review covers various MS methods and theoretical calculations and their devotion to isomer discrimination, structure identification, conformational transformation, and phase transition investigation of protomers/deprotomers.
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Affiliation(s)
- Dali Fu
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China
| | - Sara Girmay Habtegabir
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China
| | - Haodong Wang
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China
| | - Shijie Feng
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China
| | - Yehua Han
- State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum-Beijing, Beijing, 102249, People's Republic of China.
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2
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Tureček F. UV-vis spectroscopy of gas-phase ions. MASS SPECTROMETRY REVIEWS 2023; 42:206-226. [PMID: 34392556 DOI: 10.1002/mas.21726] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 06/07/2021] [Accepted: 06/08/2021] [Indexed: 06/13/2023]
Abstract
Photodissociation action spectroscopy has made a great progress in expanding investigations of gas-phase ion structures. This review deals with aspects of gas-phase ion electronic excitations that result in wavelength-dependent dissociation and light emission via fluorescence, chiefly covering the ultraviolet and visible regions of the spectrum. The principles are briefly outlined and a few examples of instrumentation are presented. The main thrust of the review is to collect and selectively present applications of UV-vis action spectroscopy to studies of stable gas-phase ion structures and combinations of spectroscopy with ion mobility, collision-induced dissociation, and ion-ion reactions leading to the generation of reactive intermediates and electronic energy transfer.
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Affiliation(s)
- František Tureček
- Department of Chemistry, University of Washington, Seattle, Washington, USA
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3
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Vogt E, Langeland J, Kjær C, Lindkvist TT, Kjaergaard HG, Nielsen SB. Effect of Freezing out Vibrational Modes on Gas-Phase Fluorescence Spectra of Small Ionic Dyes. J Phys Chem Lett 2021; 12:11346-11352. [PMID: 34780698 DOI: 10.1021/acs.jpclett.1c03259] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
While action spectroscopy of cold molecular ions is a well-established technique to provide vibrationally resolved absorption features, fluorescence experiments are still challenging. Here we report the fluorescence spectra of pyronin-Y and resorufin ions at 100 K using a newly constructed setup. Spectra narrow upon cooling, and the emission maxima blueshift. Temperature effects are attributed to the population of vibrational excited levels in S1, and that frequencies are lower in S1 than in S0. This picture is supported by calculated spectra based on a Franck-Condon model that not only predicts the observed change in maximum, but also assigns Franck-Condon active vibrations. In-plane vibrational modes that preserve the mirror plane present in both S0 and S1 of resorufin and pyronin Y account for most of the observed vibrational bands. Finally, at low temperatures, it is important to pick an excitation wavelength as far to the red as possible to not reheat the ions.
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Affiliation(s)
- Emil Vogt
- Department of Chemistry, University of Copenhagen, 2100 Copenhagen Ø, Denmark
| | - Jeppe Langeland
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus, Denmark
| | - Christina Kjær
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus, Denmark
| | | | - Henrik G Kjaergaard
- Department of Chemistry, University of Copenhagen, 2100 Copenhagen Ø, Denmark
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4
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Wong NGK, Rhodes C, Dessent CEH. Photodegradation of Riboflavin under Alkaline Conditions: What Can Gas-Phase Photolysis Tell Us about What Happens in Solution? Molecules 2021; 26:6009. [PMID: 34641554 PMCID: PMC8512791 DOI: 10.3390/molecules26196009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Revised: 09/25/2021] [Accepted: 09/30/2021] [Indexed: 11/16/2022] Open
Abstract
The application of electrospray ionisation mass spectrometry (ESI-MS) as a direct method for detecting reactive intermediates is a technique of developing importance in the routine monitoring of solution-phase reaction pathways. Here, we utilise a novel on-line photolysis ESI-MS approach to detect the photoproducts of riboflavin in aqueous solution under mildly alkaline conditions. Riboflavin is a constituent of many food products, so its breakdown processes are of wide interest. Our on-line photolysis setup allows for solution-phase photolysis to occur within a syringe using UVA LEDs, immediately prior to being introduced into the mass spectrometer via ESI. Gas-phase photofragmentation studies via laser-interfaced mass spectrometry of deprotonated riboflavin, [RF - H]-, the dominant solution-phase species under the conditions of our study, are presented alongside the solution-phase photolysis. The results obtained illustrate the extent to which gas-phase photolysis methods can inform our understanding of the corresponding solution-phase photochemistry. We determine that the solution-phase photofragmentation observed for [RF - H]- closely mirrors the gas-phase photochemistry, with the dominant m/z 241 condensed-phase photoproduct also being observed in gas-phase photodissociation. Further gas-phase photoproducts are observed at m/z 255, 212, and 145. The value of exploring both the gas- and solution-phase photochemistry to characterise photochemical reactions is discussed.
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Affiliation(s)
| | | | - Caroline E. H. Dessent
- Department of Chemistry, University of York, Heslington YO10 5DD, UK; (N.G.K.W.); (C.R.)
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5
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Giacomozzi L, Kjær C, Brøndsted Nielsen S, Ashworth EK, Bull JN, Stockett MH. Non-statistical fragmentation in photo-activated flavin mononucleotide anions. J Chem Phys 2021; 155:044305. [PMID: 34340366 DOI: 10.1063/5.0056415] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The spectroscopy and photo-induced dissociation of flavin mononucleotide anions in vacuo are investigated over the 300-500 nm wavelength range. Comparison of the dependence of fragment ion yields as a function of deposited photon energy with calculated dissociation energies and collision-induced dissociation measurements performed under single-collision conditions suggests that a substantial fraction of photo-activated ions decompose through non-statistical fragmentation pathways. Among these pathways is the dominant photo-induced fragmentation channel, the loss of a fragment identified as formylmethylflavin. The fragment ion specific action spectra reveal electronic transition energies close to those for flavins in solution and previously published gas-phase measurements, although the photo-fragment yield upon excitation of the S2 ← S0 transition appears to be suppressed.
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Affiliation(s)
| | - Christina Kjær
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | | | - Eleanor K Ashworth
- School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, United Kingdom
| | - James N Bull
- School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, United Kingdom
| | - Mark H Stockett
- Department of Physics, Stockholm University, Stockholm, Sweden
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6
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Mal M, Mandal D. Double proton transfer in a polar nano-droplet: Phototautomerization of alloxazine in AOT/alkane reverse micelles containing water or glycerol. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2021; 255:119708. [PMID: 33784597 DOI: 10.1016/j.saa.2021.119708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 03/09/2021] [Accepted: 03/10/2021] [Indexed: 06/12/2023]
Abstract
Alloxazine phototautomerization is believed to occur through an excited state double proton transfer (ESDPT) mechanism involving cyclic intermolecular H-bonded complexes between Alloxazine and hydroxylic solvents like water and alcohols. In AOT/alkane dispersions in the absence of any polar liquid, Alloxazine molecules reside inside the polar core of the AOT reverse micelle nanoparticles, where they involve in H-bonding with the anionic sulfonate head-groups of the AOT molecules, but are unable to generate the appropriate cyclic intermolecular H-bonded complexes conducive to ESDPT. However, tautomerization is switched on with addition of water and formation ofwater nano-droplet at the core of reverse micelle. Evidently, the Alloxazine⋅⋅⋅⋅AOT H-bonds are now replaced by Alloxazine⋅⋅⋅⋅Water H-bonds, promotingESDPT. On the other hand, Alloxazine phototautomerization is hindered in Glycerol, irrespective of whether the latter is in the bulk liquid state or in the form of a polar nano-droplet. This may be explained by steric considerations.
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Affiliation(s)
- Madhushree Mal
- Department of Chemistry, University of Calcutta, 92, APC Road, Kolkata 700009, India
| | - Debabrata Mandal
- Department of Chemistry, University of Calcutta, 92, APC Road, Kolkata 700009, India.
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7
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Müller D, Dopfer O. Interaction of Alkali Ions with Flavins: Infrared and Optical Spectra of Metal–Riboflavin Complexes. J Phys Chem A 2021; 125:3146-3158. [DOI: 10.1021/acs.jpca.1c01846] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- David Müller
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstr. 36, D-10623 Berlin, Germany
| | - Otto Dopfer
- Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstr. 36, D-10623 Berlin, Germany
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8
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9
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Insińska-Rak M, Prukała D, Golczak A, Fornal E, Sikorski M. Riboflavin degradation products; combined photochemical and mass spectrometry approach. J Photochem Photobiol A Chem 2020. [DOI: 10.1016/j.jphotochem.2020.112837] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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10
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Müller D, Dopfer O. Optical spectroscopy of cryogenic metalated flavins: The O2(+) isomers of M+lumiflavin (M=Li–Cs). JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY 2020. [DOI: 10.1016/j.jpap.2020.100009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
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11
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Marlton SJP, McKinnon BI, Ucur B, Bezzina JP, Blanksby SJ, Trevitt AJ. Discrimination between Protonation Isomers of Quinazoline by Ion Mobility and UV-Photodissociation Action Spectroscopy. J Phys Chem Lett 2020; 11:4226-4231. [PMID: 32368922 DOI: 10.1021/acs.jpclett.0c01009] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The influence of oriented electric fields on chemical reactivity and photochemistry is an area of increasing interest. Within a molecule, different protonation sites offer the opportunity to control the location of charge and thus orientation of electric fields. New techniques are thus needed to discriminate between protonation isomers in order to understand this effect. This investigation reports the UV-photodissociation action spectroscopy of two protonation isomers (protomers) of 1,3-diazanaphthalene (quinazoline) arising from protonation of a nitrogen at either the 1- or 3-position. It is shown that these protomers are separable by field-asymmetric ion mobility spectrometry (FAIMS) with confirmation provided by UV-photodissociation (PD) action spectroscopy. Vibronic features in the UVPD action spectra and computational input allow assignment of the origin transitions to the S1 and S5 states of both protomers. These experiments also provide vital benchmarks for protomer-specific calculations and examination of isomer-resolved reaction kinetics and thermodynamics.
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Affiliation(s)
- Samuel J P Marlton
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Benjamin I McKinnon
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Boris Ucur
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - James P Bezzina
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
| | - Stephen J Blanksby
- Central Analytical Research Facility, Institute for Future Environments, Queensland University of Technology, Brisbane 4001, Australia
| | - Adam J Trevitt
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, New South Wales 2522, Australia
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12
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Müller D, Dopfer O. Vibronic optical spectroscopy of cryogenic flavin ions: the O2+ and N1 tautomers of protonated lumiflavin. Phys Chem Chem Phys 2020; 22:18328-18339. [DOI: 10.1039/d0cp03650a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The electronic structure of cryogenic protonated lumiflavin ions probed by photodissociation spectroscopy and density functional theory calculations reveals the presence of the two most stable tautomers protonated at the O2+ and N1 positions.
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Affiliation(s)
- David Müller
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- D-10623 Berlin
- Germany
| | - Otto Dopfer
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- D-10623 Berlin
- Germany
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13
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Zelenka J, Cibulka R, Roithová J. Flavinium Catalysed Photooxidation: Detection and Characterization of Elusive Peroxyflavinium Intermediates. Angew Chem Int Ed Engl 2019; 58:15412-15420. [PMID: 31364790 PMCID: PMC6852162 DOI: 10.1002/anie.201906293] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 07/08/2019] [Indexed: 12/18/2022]
Abstract
Flavin-based catalysts are photoactive in the visible range which makes them useful in biology and chemistry. Herein, we present electrospray-ionization mass-spectrometry detection of short-lived intermediates in photooxidation of toluene catalysed by flavinium ions (Fl+ ). Previous studies have shown that photoexcited flavins react with aromates by proton-coupled electron transfer (PCET) on the microsecond time scale. For Fl+ , PCET leads to FlH.+ with the H-atom bound to the N5 position. We show that the reaction continues by coupling between FlH.+ and hydroperoxy or benzylperoxy radicals at the C4a position of FlH.+ . These results demonstrate that the N5-blocking effect reported for alkylated flavins is also active after PCET in these photocatalytic reactions. Structures of all intermediates were fully characterised by isotopic labelling and by photodissociation spectroscopy. These tools provide a new way to study reaction intermediates in the sub-second time range.
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Affiliation(s)
- Jan Zelenka
- Department of Spectroscopy and CatalysisInstitute for Molecules and MaterialsRadboud University NijmegenHeyendaalseweg 1356525AJNijmegenThe Netherlands
| | - Radek Cibulka
- Department of organic chemistryFaculty of Chemical TechnologyUniversity of Chemistry and Technology PragueTechnická 5166 28Prague 6Czech Republic
| | - Jana Roithová
- Department of Spectroscopy and CatalysisInstitute for Molecules and MaterialsRadboud University NijmegenHeyendaalseweg 1356525AJNijmegenThe Netherlands
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14
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Zelenka J, Cibulka R, Roithová J. Flavinium Catalysed Photooxidation: Detection and Characterization of Elusive Peroxyflavinium Intermediates. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201906293] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Jan Zelenka
- Department of Spectroscopy and Catalysis Institute for Molecules and Materials Radboud University Nijmegen Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands
| | - Radek Cibulka
- Department of organic chemistry Faculty of Chemical Technology University of Chemistry and Technology Prague Technická 5 166 28 Prague 6 Czech Republic
| | - Jana Roithová
- Department of Spectroscopy and Catalysis Institute for Molecules and Materials Radboud University Nijmegen Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands
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15
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Müller D, Nieto P, Miyazaki M, Dopfer O. Effect of alkali ions on optical properties of flavins: vibronic spectra of cryogenic M+lumiflavin complexes (M = Li–Cs). Faraday Discuss 2019; 217:256-275. [DOI: 10.1039/c8fd00203g] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Cryogenic ion spectroscopy of metal–lumiflavin (M+LF) complexes at the level of vibrational resolution illustrates the large impact of alkali ions on the optical properties of this prototypical flavin molecule.
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Affiliation(s)
- David Müller
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- 10623 Berlin
- Germany
| | - Pablo Nieto
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- 10623 Berlin
- Germany
| | - Mitsuhiko Miyazaki
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- 10623 Berlin
- Germany
- Laboratory for Chemistry and Life Science
| | - Otto Dopfer
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- 10623 Berlin
- Germany
- Tokyo Tech World Research Hub Initiative (WRHI)
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16
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Marlton SJP, McKinnon BI, Ucur B, Maccarone AT, Donald WA, Blanksby SJ, Trevitt AJ. Selecting and identifying gas-phase protonation isomers of nicotineH+ using combined laser, ion mobility and mass spectrometry techniques. Faraday Discuss 2019; 217:453-475. [DOI: 10.1039/c8fd00212f] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Protonation isomers of gas-phase nicotineH+ are separated and assigned using a combination of FAIMS and UV photodissociation action spectroscopy.
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Affiliation(s)
| | | | - Boris Ucur
- School of Chemistry
- University of Wollongong
- Wollongong
- Australia
| | | | | | - Stephen J. Blanksby
- Central Analytical Research Facility
- Institute for Future Environments
- Queensland University of Technology
- Brisbane
- Australia
| | - Adam J. Trevitt
- School of Chemistry
- University of Wollongong
- Wollongong
- Australia
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17
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Matthews E, Dessent CEH. Observation of Near-Threshold Resonances in the Flavin Chromophore Anions Alloxazine and Lumichrome. J Phys Chem Lett 2018; 9:6124-6130. [PMID: 30277786 DOI: 10.1021/acs.jpclett.8b02529] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Lumichrome (LC) is the chromophore of the flavin family of photoactive biomolecules, where key biochemical activity involves interplay between redox and photophysical events. Questions remain about the relationship between the redox status of the ground and excited states and demand an improved understanding of the intrinsic photochemistry. Using anion photodissociation spectroscopy, we have measured the intrinsic electronic spectroscopy (564-220 nm) and accompanying photodegradation pathways of the deprotonated anionic form of LC. Experiments were also performed on alloxazine (AL), which is equivalent to LC minus two methyl groups. We observe a resonance state close to 3.8 eV for both anions for the first time, which we tentatively assign to dipole-bound excited states. For AL this state is sufficiently long-lived to facilitate dissociative electron attachment. Our results suggest that the presence of methyl group rotors at key positions along the molecular dipole may reduce the lifetime of the resonance state and hence provide a structural barrier to valence electron capture, and ensuing molecular dissociation.
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Affiliation(s)
- Edward Matthews
- Department of Chemistry , University of York , Heslington, York YO10 5DD , U.K
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18
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Matthews E, Cercola R, Dessent CEH. Protomer-Dependent Electronic Spectroscopy and Photochemistry of the Model Flavin Chromophore Alloxazine. Molecules 2018; 23:molecules23082036. [PMID: 30110962 PMCID: PMC6222404 DOI: 10.3390/molecules23082036] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 08/10/2018] [Accepted: 08/11/2018] [Indexed: 12/16/2022] Open
Abstract
Flavin chromophores play key roles in a wide range of photoactive proteins, but key questions exist in relation to their fundamental spectroscopic and photochemical properties. In this work, we report the first gas-phase spectroscopy study of protonated alloxazine (AL∙H⁺), a model flavin chromophore. Laser photodissociation is employed across a wide range (2.34⁻5.64 eV) to obtain the electronic spectrum and characterize the photofragmentation pathways. By comparison to TDDFT quantum chemical calculations, the spectrum is assigned to two AL∙H⁺ protomers; an N5 (dominant) and O4 (minor) form. The protomers have distinctly different spectral profiles in the region above 4.8 eV due to the presence of a strong electronic transition for the O4 protomer corresponding to an electron-density shift from the benzene to uracil moiety. AL∙H⁺ photoexcitation leads to fragmentation via loss of HCN and HNCO (along with small molecules such as CO₂ and H₂O), but the photofragmentation patterns differ dramatically from those observed upon collision excitation of the ground electronic state. This reveals that fragmentation is occurring during the excited state lifetime. Finally, our results show that the N5 protomer is associated primarily with HNCO loss while the O4 protomer is associated with HCN loss, indicating that the ring-opening dynamics are dependent on the location of protonation in the ground-state molecule.
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Affiliation(s)
- Edward Matthews
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
| | - Rosaria Cercola
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK.
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19
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Bull JN, Carrascosa E, Giacomozzi L, Bieske EJ, Stockett MH. Ion mobility action spectroscopy of flavin dianions reveals deprotomer-dependent photochemistry. Phys Chem Chem Phys 2018; 20:19672-19681. [PMID: 30014081 PMCID: PMC6063075 DOI: 10.1039/c8cp03244k] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Photo-induced proton transfer, deprotomer-dependent photochemistry, and intramolecular charge transfer in flavin anions are investigated using action spectroscopy.
The intrinsic optical properties and photochemistry of flavin adenine dinucleotide (FAD) dianions are investigated using a combination of tandem ion mobility spectrometry and action spectroscopy. Two principal isomers are observed, the more stable form being deprotonated on the isoalloxazine group and a phosphate (N-3,PO4 deprotomer), and the other on the two phosphates (PO4,PO4 deprotomer). Ion mobility data and electronic action spectra suggest that photo-induced proton transfer occurs from the isoalloxazine group to a phosphate group, converting the PO4,PO4 deprotomer to the N-3,PO4 deprotomer. Comparisons of the isomer selective action spectra of FAD dianions and flavin monoanions with solution spectra and gas-phase photodissociation action spectra suggests that solvation shifts the electronic absorption of the deprotonated isoalloxazine group to higher energy. This is interpreted as evidence for significant charge transfer in the lowest optical transition of deprotonated isoalloxazine. Overall, this work demonstrates that the site of deprotonation of flavin anions strongly affects their electronic absorptions and photochemistry.
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Affiliation(s)
- James N Bull
- School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Eduardo Carrascosa
- School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia
| | | | - Evan J Bieske
- School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia
| | - Mark H Stockett
- School of Chemistry, University of Melbourne, Melbourne, VIC 3010, Australia and Department of Physics, Stockholm University, Stockholm, Sweden.
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20
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Nieto P, Müller D, Sheldrick A, Günther A, Miyazaki M, Dopfer O. Effect of alkali ions on optical properties of flavins: vibronic spectra of cryogenic M+lumichrome ions (M = Li–Cs) in the gas phase. Phys Chem Chem Phys 2018; 20:22148-22158. [DOI: 10.1039/c8cp03950j] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Cryogenic ion spectroscopy of M+LC (M = Li–Cs) obtained by photodissociation of mass selected ions in a tandem mass spectrometer illustrates the large impact of metalation on the optical properties of the simplest flavin molecule.
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Affiliation(s)
- Pablo Nieto
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- Berlin D-10623
- Germany
| | - David Müller
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- Berlin D-10623
- Germany
| | - Alexander Sheldrick
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- Berlin D-10623
- Germany
| | - Alan Günther
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- Berlin D-10623
- Germany
| | - Mitsuhiko Miyazaki
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- Berlin D-10623
- Germany
- Laboratory for Chemistry and Life Science
| | - Otto Dopfer
- Institut für Optik und Atomare Physik
- Technische Universität Berlin
- Berlin D-10623
- Germany
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21
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Lincke K, Langeland J, Madsen AØ, Kiefer HV, Skov L, Gruber E, Mikkelsen KV, Andersen LH, Nielsen MB. Elucidation of the intrinsic optical properties of hydrogen-bonded and protonated flavin chromophores by photodissociation action spectroscopy. Phys Chem Chem Phys 2018; 20:28678-28684. [DOI: 10.1039/c8cp05368e] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The intrinsic optical properties of the flavin chromophore when engaged in hydrogen bonding or being protonated were elucidated by photo-induced action spectroscopy and computations.
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Affiliation(s)
- Kasper Lincke
- Department of Chemistry, University of Copenhagen
- DK-2100 Copenhagen Ø
- Denmark
| | - Jeppe Langeland
- Department of Physics and Astronomy, Aarhus University
- DK-8000 Aarhus C
- Denmark
| | | | - Hjalte V. Kiefer
- Department of Physics and Astronomy, Aarhus University
- DK-8000 Aarhus C
- Denmark
| | - Louise Skov
- Department of Chemistry, University of Copenhagen
- DK-2100 Copenhagen Ø
- Denmark
| | - Elisabeth Gruber
- Department of Physics and Astronomy, Aarhus University
- DK-8000 Aarhus C
- Denmark
| | - Kurt V. Mikkelsen
- Department of Chemistry, University of Copenhagen
- DK-2100 Copenhagen Ø
- Denmark
| | - Lars H. Andersen
- Department of Physics and Astronomy, Aarhus University
- DK-8000 Aarhus C
- Denmark
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