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Ion mobility action spectroscopy of flavin dianions reveals deprotomer-dependent photochemistry
Stockholm University, Faculty of Science, Department of Physics.
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Number of Authors: 52018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 29, p. 19672-19681Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2018. Vol. 20, no 29, p. 19672-19681
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-162058DOI: 10.1039/c8cp03244kISI: 000448132600043PubMedID: 30014081OAI: oai:DiVA.org:su-162058DiVA, id: diva2:1266457
Available from: 2018-11-28 Created: 2018-11-28 Last updated: 2019-03-14Bibliographically approved
In thesis
1. Collision- and photon-induced dynamics of complex molecular ions in the gas phase
Open this publication in new window or tab >>Collision- and photon-induced dynamics of complex molecular ions in the gas phase
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, I report experiments probing collision- and photon-induced molecular dynamics in the gas phase. Excited molecules formed in such interactions may relax by emitting electrons or photons, isomerization or fragmentation. For complex molecular systems, these processes typically occur on timescales exceeding picoseconds following statistical redistribution of the excitation energy across the internal degrees of freedom. However, energy transfer to molecules through ion/atom impact may in some cases lead to prompt atom knockout in Rutherford-type scattering processes on much faster timescales. Another example of such a non-statistical process is photon-induced excited-state proton transfer, a structural rearrangement occurring on the femtosecond timescale.

In this work, I investigate the competition between statistical and non-statistical fragmentation processes for a range of molecules colliding with He at center-of-mass energies in the sub-keV range. I show that heavy atom knockout is an important process for systems containing aromatic rings such as Polycyclic Aromatic Hydrocarbons (PAHs) or porphyrins, while statistical fragmentation processes dominate for less stable and/or smaller systems such as adenine or hydrogenated PAHs. Furthermore, I present the first measurements of the threshold energies for prompt single atom knockout from isolated molecules. The experimental results are interpreted with the aid of Molecular Dynamics (MD) simulations which allow us to extract the energy deposited into the system during a collision, knockout cross sections, fragmentation pathways and the structures of the fragments. The results presented in this work may be important for understanding the response of complex molecules to energetic processes in e.g. astrophysical environments.

Furthermore, I present the results of photodissociation and luminescence experiments probing flavin mono-anions in the gas phase. These are compared against calculations and previously measured spectra in solution. The discrepancies between the present results and the theoretical values suggest that more consideration of the vibronic structure is needed to model the photoabsorption and emission in flavins. Finally, I present the results of photoisomerisation experiments of flavin di-anions where two different isomers have been found and I discuss the proton transfer mechanisms which govern the structural changes.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2019. p. 70
Keywords
PAHs, Porphyrins, Adenine, Flavins, Biomolecules, Collisions, Experiments, Reactions, Non-Statistical Fragmentation, Molecular Dynamics, Photon-Induced Fragmentation, Luminescence, Photoisomerization, Proton Transfer
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-167001 (URN)978-91-7797-632-5 (ISBN)978-91-7797-633-2 (ISBN)
Public defence
2019-04-25, FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
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Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 1: Manuscript.

Available from: 2019-04-02 Created: 2019-03-12 Last updated: 2019-03-21Bibliographically approved

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