Ortho Green Fluorescence Protein Synthetic Chromophore; Excited-State Intramolecular Proton Transfer via a Seven-Membered-Ring Hydrogen-Bonding System

Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, R.O.C.
Journal of the American Chemical Society (Impact Factor: 12.11). 05/2007; 129(15):4534-5. DOI: 10.1021/ja070880i
Source: PubMed


A structural isomer of the core chromophore (p-HBDI) in green fluorescence protein, o-HBDI, is synthesized. o-HBDI possesses a seven-membered-ring hydrogen bond, from which the excited-state intramolecular proton transfer takes place, resulting in a remarkable tautomer emission of similar to 605 nm.

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Available from: Kew-Yu Chen, Jan 04, 2014
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    • "The ortho-derivative, 4-(2-hydroxybenzylidene)-1,2-dimethyl- 1H-imidazol-5(4H)-one, exhibited an absorption maximum at 385 nm and emission at 605 nm with an anomalously large Stokes shift and an increased fluorescence quantum yield, suggesting an efficient ESPT reaction. In contrast, an o-methoxy derivative, which does not display ESPT, showed an absorbance at 370 nm and an emission with a normal Stokes shift at 425 nm (Chen et al., 2007). To test the impact of chromophore rotation on a fluorescence quantum yield, Wu and Burgess prepared synthetic analogs of a GFP chromophore in which rotation about the bond connecting the two cycles was suppressed by complexation with a BF 2 entity. "
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    ABSTRACT: We have synthesized dimethyl derivatives of the GFP chromophore (p-HOBDI) and several of its derivatives, and their photochemistry and photophysics were investigated using various steady-state and time-resolved techniques as follows. We first consider the effect of the £]-barrel on the optical properties of the GFP chromophore (p-HOBDI) experimentally by selective variation of the protonation state of chromophores and different solvents. Each of these forms shows a complex solvatochromic behavior and is governed by both polar and acid/base properties of the solvents. In contrast to their solution behavior, some O-alkyl GFP chromophore (alkoxy-BDI) derivatives exhibit large fluorescent enhancement in the solid state. The color of the crystalline BDI is tuned by substituent-mediated crystal packing, showing the potential applications in optoelectronic devices. Using femtosecond polarization-sensitive infrared (IR) spectrosceopy of the C=O stretching mode of the HOBDI, we have then discovered a near complete twisting around the ethylenic bridge between the phenolate and imidazolidinone groups upon electronic excitation. Cis/trans isomerization induced by the rotation around the bridge is thought to be responsible for the behavior of blinking in fluorescent protein; however, the mechanism of the thermal reverse isomerization is more problematic. Thus we synthesized BDI derivatives with decreasing para-donating ability, HO, CH3O, CH3, H, and Cl, and used a Hammett plot for the rate study. With a positive â value, we conceived, for the first time, a novel nucleophilic addition/elimination mechanism. Finally, the GFP chromophore falls into the general category of hydroxyarene photoacids, which exhibit high excited-state acidities but neutral ground states. A hydroxyl substituent at the meta position shows enhanced charge transfer and greater acidity in the excited state. As a result, we have demonstrated that the fast quenching of the excited state by internal conversion to the ground state is much slower in meta- than in para-HOBDI derivatives. This allows studies of this ultrafast intermolecular ESPT that competes with isomerization. The photoinduced dynamics of the meta isomer of GFP chromophore was further investigated using femtosecond transient absorption and fluorescence upconversion spectroscopies. Ph.D. Committee Chair: Laren M. Tolbert; Committee Member: Andreas S. Bommarius; Committee Member: Bridgette Barry; Committee Member: Donald F. Doyle; Committee Member: Uwe H. F. Bunz
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