title: Topochemistry and photomechanical effects in crystals of green fluorescent protein-like chromophores: effects of hydrogen bonding and crystal packing.
abstract: To obtain insight into the effects of the environment on the photophysics and photochemistry of the green fluorescence protein (GFP), eight crystal structures of six synthetic aryl-substituted analogues (2-fluoro, 2-methyl, 3-hydroxy, 3-methoxy, 2,4-dimethyl and 2,5-dimethyl) of the GFP chromophore (4-hydroxy-benzylidenedimethylimidazolinone) were determined and correlated with their two-dimensional steady-state and time-resolved solid-state excitation-emission spectra. The stacking between the molecules greatly affected the emission energy and the lifetime of the emission of the chromophore, implying that pi-pi interactions could be critical for the photophysics of GFP. The reaction pathways were dependent on the excitation energy, resulting either in [2 + 2] photodimerization at the bridging double bond (UV excitation) or flipping of the imidazolone ring (visible excitation). The meta-hydroxy chromophore (3-HOBDI) was the only GFP-chromophore analogue that was obtained as more than one stable polymorph in the pure state thus far. Due to the asymmetric substitution with hydrogen bond donors and acceptors, 3-HOBDI is tetramorphic, the forms showing distinctly different structure and behavior: (1) while one of the polymorphs (3-HOBDI-A), having multilayer structure with alternating stereochemistry of linear hydrogen-bonded motifs, undergoes photodimerization under UV light, (2) another (3-HOBDI-C), which has dimeric head-to-tail structure, shows Z-to-E isomerization via tau-one-bond flip of the imidazolone ring by excitation in the visible region. X-ray diffraction analysis of a partially reacted single crystal of 3-HOBDI-C provided the first direct evidence of tau-one-bond flip occurring in a GFP-like compound. Moreover, the cooperative action of the photodimerization of 3-HOBDI-A appears as a photomechanical effect of unprecedented magnitude for a single crystalline specimen, where photoexcited single crystals bend to more than 90 degrees without breaking.
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita 565-0871, Osaka, Japan. npance@wakate.frc.eng.osaka-u.ac.jp
authors.forename: Pance
authors.initials: P
authors.lastname: Naumov
authors.forename: Janusz
authors.initials: J
authors.lastname: Kowalik
authors.forename: Kyril M
authors.initials: KM
authors.lastname: Solntsev
authors.forename: Anthony
authors.initials: A
authors.lastname: Baldridge
authors.forename: Jong-Seok
authors.initials: JS
authors.lastname: Moon
authors.forename: Christine
authors.initials: C
authors.lastname: Kranz
authors.forename: Laren M
authors.initials: LM
authors.lastname: Tolbert
mesh_terms: D001593:Benzyl Compounds / Q000737:chemistry*; D018360:Crystallography, X-Ray; D049452:Green Fluorescent Proteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D048288:Imidazolines / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D055668:Photochemical Processes; D012399:Rotation; D013237:Stereoisomerism
chemical_list: D001593:Benzyl Compounds; D048288:Imidazolines; C533767:p-hydroxybenzylidenedimethylimidazolinone; D049452:Green Fluorescent Proteins