title: Chlorophyll-Derived Yellow Phyllobilins of Higher Plants as Medium-Responsive Chiral Photoswitches.
abstract: The fall colors are signs of chlorophyll breakdown, the biological process in plants that generates phyllobilins. Most of the abundant natural phyllobilins are colorless, but yellow phyllobilins (phylloxanthobilins) also occur in fall leaves. As shown here, phylloxanthobilins are unique four-stage photoswitches. Which switching mode is turned on is controlled by the molecular environment. In polar media, phylloxanthobilins are monomeric and undergo photoreversible Z/E isomerization, similar to that observed for bilirubin. Unlike bilirubin, however, the phylloxanthobilin Z isomers photodimerize in apolar solvents by regio- and stereospecific thermoreversible [2+2] cycloadditions from self-assembled hydrogen-bonded dimers. X-ray analysis revealed the first stereostructure of a phylloxanthobilin and its hydrogen-bonded self-templating architecture, helping to rationalize its exceptional photoswitch features. The chemical behavior of phylloxanthobilins will play a seminal role in identifying biological roles of phyllobilins.
authors.affiliation: Institute of Organic Chemistry and Centre of Molecular Biosciences, University of Innsbruck, 6020, Innsbruck, Austria.
authors.forename: Chengjie
authors.identifier: 0000-0001-5602-6566
authors.initials: C
authors.lastname: Li
authors.affiliation: Institute of General, Inorganic & Theoretical Chemistry, University of Innsbruck, Austria.
authors.forename: Klaus
authors.identifier: 0000-0002-8774-9051
authors.initials: K
authors.lastname: Wurst
authors.affiliation: Department of Chemistry, Columbia University, New York, USA.
authors.forename: Steffen
authors.identifier: 0000-0002-4592-5280
authors.initials: S
authors.lastname: Jockusch
authors.affiliation: Institute of Molecular Biosciences, University of Graz, Austria.
authors.forename: Karl
authors.identifier: 0000-0002-3485-9740
authors.initials: K
authors.lastname: Gruber
authors.affiliation: Institute of General, Inorganic & Theoretical Chemistry and Centre of Molecular Biosciences, University of Innsbruck, Austria.
authors.forename: Maren
authors.identifier: 0000-0001-7256-1219
authors.initials: M
authors.lastname: Podewitz
authors.affiliation: Institute of General, Inorganic & Theoretical Chemistry and Centre of Molecular Biosciences, University of Innsbruck, Austria.
authors.forename: Klaus R
authors.identifier: 0000-0002-0985-2299
authors.initials: KR
authors.lastname: Liedl
authors.affiliation: Institute of Organic Chemistry and Centre of Molecular Biosciences, University of Innsbruck, 6020, Innsbruck, Austria.
authors.forename: Bernhard
authors.identifier: 0000-0002-2222-0587
authors.initials: B
authors.lastname: Kräutler
keywords: cycloaddition; hydrogen bonds; photoisomerization; plant pigments; self-assembly