title: Cooperativity and Site-Selectivity of Intramolecular Hydrogen Bonds on the Fluorescence Quenching of Modified GFP Chromophores.
abstract: This paper provides the first example of experimentally characterized hydrogen-bond cooperativity on fluorescence quenching with a modified green fluorescence protein (GFP) chromophore that contains a 6-membered C═N···H-O and a 7-membered C═O···H-O intramolecular H-bonds. Variable-temperature (1)H NMR and electronic absorption and emission spectroscopies were used to elucidate the preference of intra- vs intermolecular H-bonding at different concentrations (1 mM and 10 μM), and X-ray crystal structures provide clues of possible intermolecular H-bonding modes. In the ground state, the 6-membered H-bond is significant but the 7-membered one is rather weak. However, fluorescence quenching is dominated by the 7-membered H-bond, indicating a strengthening of the H-bond in the excited state. The H-bonding effect is more pronounced in more polar solvents, and no intermediates were observed from femtosecond fluorescence decays. The fluorescence quenching is attributed to the occurrence of diabatic excited-state proton transfer. Cooperativity of the two intramolecular H-bonds on spectral shifts and fluorescence quenching is evidenced by comparing with both the single H-bonded and the non-H-bonded counterparts. The H-bond cooperativity does not belong to the conventional patterns of σ- and π-cooperativity but a new type of polarization interactions, which demonstrates the significant interplay of H-bonds for multiple H-bonding systems in the electronically excited states.
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Deng-Hsiang
authors.initials: DH
authors.lastname: Chang
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Chun-Lin
authors.initials: CL
authors.lastname: Ou
authors.affiliation: Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University , Hsinchu 30010, Taiwan.
authors.forename: Hung-Yu
authors.initials: HY
authors.lastname: Hsu
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Guan-Jhih
authors.initials: GJ
authors.lastname: Huang
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Chen-Yi
authors.initials: CY
authors.lastname: Kao
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Yi-Hung
authors.initials: YH
authors.lastname: Liu
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Shie-Ming
authors.initials: SM
authors.lastname: Peng
authors.affiliation: Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University , Hsinchu 30010, Taiwan.
authors.forename: Eric Wei-Guang
authors.initials: EW
authors.lastname: Diau
authors.affiliation: Department of Chemistry, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: Jye-Shane
authors.initials: JS
authors.lastname: Yang