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Visible‐Light‐Induced Photodimerization of a Photoactive Yellow Protein (PYP) Chromophore Model in a Single Crystal
Author(s) -
Nath Naba K.,
Manoj Kochunnoonny,
Gâz Andrei Şerban,
Naumov Panče
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201300427
Subject(s) - chromophore , chemistry , photochemistry , photoisomerization , crystal structure , isomerization , deprotonation , excited state , residue (chemistry) , crystallography , stereochemistry , organic chemistry , catalysis , ion , physics , nuclear physics
Abstract The chromophore of the photoactive yellow protein (PYP), the photoreceptor in the photomotility of the bacterium Halorhodospira halophila , is a deprotonated para ‐coumaric thioester linked to the side residue of a cysteine residue. The photophysics of the PYP chromophore is conveniently modeled with para ‐hydroxycinnamic thiophenyl esters. Herein, we report the first direct evidence, obtained with X‐ray diffraction, of photodimerization of a para ‐hydroxycinnamic thiophenyl ester in single crystalline state. This result represents the first direct observation of [2+2] dimerization of a model PYP chromophore, and demonstrates that even very weak light in the visible region is capable of inducing parallel radical reactions in PYP from the excited state of the chromophore, in addition to the main reaction pathway ( trans–cis isomerization). This PYP model system adds an interesting example to the known solid‐state photodimerizations, because unlike the anhydrous crystal (which is not capable of sustaining the stress and disintegrates in the course of photodimerization), a single water molecule “dilutes” the structure to the extent sufficient for single‐crystal‐to‐single‐crystal reaction.