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Absorption and luminescence spectroscopy of mass-selected flavin adenine dinucleotide mono-anions
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0003-0471-3844
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Number of Authors: 62018 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 21, article id 214309Article in journal (Refereed) Published
Abstract [en]

We report the absorption profile of isolated Flavin Adenine Dinucleotide (FAD) mono-anions recorded using photo-induced dissociation action spectroscopy. In this charge state, one of the phosphoric acid groups is deprotonated and the chromophore itself is in its neutral oxidized state. These measurements cover the first four optical transitions of FAD with excitation energies from 2.3 to 6.0 eV (210-550 nm). The S-0 -> S-2 transition is strongly blue shifted relative to aqueous solution, supporting the view that this transition has a significant charge-transfer character. The remaining bands are close to their solution-phase positions. This confirms that the large discrepancy between quantum chemical calculations of vertical transition energies and solution-phase band maxima cannot be explained by solvent effects. We also report the luminescence spectrum of FAD mono-anions in vacuo. The gas-phase Stokes shift for S-1 is 3000 cm(-1), which is considerably larger than any previously reported for other molecular ions and consistent with a significant displacement of the ground and excited state potential energy surfaces. Consideration of the vibronic structure is thus essential for simulating the absorption and luminescence spectra of flavins.

Place, publisher, year, edition, pages
2018. Vol. 148, no 21, article id 214309
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:su:diva-158273DOI: 10.1063/1.5024028ISI: 000434837600018PubMedID: 29884035OAI: oai:DiVA.org:su-158273DiVA, id: diva2:1236601
Available from: 2018-08-03 Created: 2018-08-03 Last updated: 2020-02-06Bibliographically 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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