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Relative Ground and Excited-State pKa Values of Phytochromobilin in the Photoactivation of Phytochrome: A Computational StudyRelative Ground and Excited-State pKa Values of Phytochromobilin in the Photoactivation of Phytochrome: A Computational Study
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Quantum Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Quantum Chemistry.
2007 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 111, no 39, 11554-11565 p.Article in journal (Refereed) Published
Abstract [en]

The conversion of the plant photoreceptor phytochrome from an inactive (Pr) to an active form (Pfr) is accomplished by a red-light induced Z→ E photoisomerization of its phytochromobilin chromophore. In recent years, the question whether the photoactivation involves a change in chromophore protonation state has been the subject of many experimental studies. Here, we have used quantum chemical methods to calculate relative ground and excited-state pKa values of the different pyrrole moieties of phytochromobilin in a protein-like environment. Assuming (based on experimental data) a Pr ZaZsZa chromophore and considering isomerizations at C15 and C5, it is found that moieties B and C are the strongest acids both in the ground state and in the bright first singlet excited state, which is rationalized in simple geometric and electronic terms. It is also shown that neither light absorption nor isomerization increases the acidity of phytochromobilin relative to the reference Pr state with all pyrrolenic nitrogens protonated. Hence, provided that the subset of chromophore geometries under investigation is biologically relevant, there appears to be no intrinsic driving force for a proton-transfer event. In a series of benchmark calculations, the performance of ab initio and time-dependent density functional theory methods for excited-state studies of phytochromobilin is evaluated in light of available experimental data.

Place, publisher, year, edition, pages
2007. Vol. 111, no 39, 11554-11565 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96764DOI: 10.1021/jp0727953ISI: 000249838600031OAI: oai:DiVA.org:uu-96764DiVA: diva2:171445
Available from: 2008-02-26 Created: 2008-02-26 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Theoretical Photochemistry: Halogenated Arenes, Phytochromobilin, Ru(II)polypyridyl complexes and 6-4 photoadducts
Open this publication in new window or tab >>Theoretical Photochemistry: Halogenated Arenes, Phytochromobilin, Ru(II)polypyridyl complexes and 6-4 photoadducts
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents Quantum Chemical calculations on the Photochemistry of Halogenated benzenes, Phytochromobilin, Ruthenium Polypyridyl complexes and 6-4 photoadducts in DNA. The work is focused on improving the understanding of a number of experimentally observed photochemical processes in these systems. New results regarding the mechanism of photodissociation of halogenated arenes, photointerconversion of phytochromobilin are presented, as well as of the photoprocesses of Ruthenium Polypyridyl complexes and new mechanistic insights in the repair of 6-4 photoadducts in DNA.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 61 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 394
Keyword
Quantum chemistry, Quantum Chemistry, Halogenated Arenes, Phytochromobilin, Phytochrome, Ruthenium, 6-4 photoadducts, Photochemistry, Kvantkemi
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:uu:diva-8469 (URN)978-91-554-7096-8 (ISBN)
Public defence
2008-03-19, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2008-02-26 Created: 2008-02-26 Last updated: 2011-03-14Bibliographically approved

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