Cooperativity and Site-Selectivity of Intramolecular Hydrogen Bonds on the Fluorescence Quenching of Modified GFP Chromophores
Journal
Journal of Organic Chemistry
Journal Volume
80
Journal Issue
24
Pages
12431-12443
Date Issued
2015
Author(s)
Chang, D.-H.
Ou, C.-L.
Hsu, H.-Y.
Huang, G.-J.
Kao, C.-Y.
Liu, Y.-H.
Diau, E.W.-G.
Yang, J.-S.
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.
Type
journal article