Browsing by Author "Huang, Guan-Jhih"

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Cooperativity and Site-Selectivity of Intramolecular Hydrogen Bonds on the Fluorescence Quenching of Modified GFP Chromophores
(2015-12-18)
Chang, Deng-Hsiang
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Ou, Chun-Lin
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Hsu, Hung-Yu
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Huang, Guan-Jhih
;
Kao, Chen-Yi
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 center dot center dot center dot H-O and a 7-membered C=O center dot center dot center dot H-O intramolecular H-bonds. Variable-temperature H-1 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 mu M), 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 sigma- and pi-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.
Effects of Hydrogen Bonding on Internal Conversion of GFP-like Chromophores. I. The para-Amino Systems
(2013-03-07)
Huang, Guan-Jhih
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Cheng, Chi-Wen
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Hsu, Hung-Yu
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Prabhakar, Ch.
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Lee, Yuan-Pern
To understand the effects of solvent-solute hydrogen bonding (SSHB) on the excited-state dynamics of two GFP-like chromophores, p-ABDI and p-CFABDI, we have determined the quantum yields for fluorescence (Phi(f)) and the isomerization Z -> E (Phi(ZE)) and the femtosecond fluorescence and transient infrared absorption in selected solvents. The behavior that Phi(ZE) congruent to 45 0.50 in aprotic solvents, such as CH3CN, indicates that the E-Z photoisomerization adopts a one-bond-flip mechanism through the torsion of the exocyclic C=C bond (the tau torsion) to form a perpendicular species (tau similar to 90 degrees) in the singlet excited state followed by internal conversion (IC) to the ground state and partition to form the E and Z isomers with equal probabilities. The observed Phi(ZE) decreased from 0.50 to 0.15-0.28 when CH3CN was replaced with the protic solvents CH3OH and CF3CH2OH. In conjunction with the solvent-independent rapid (<1 ps) kinetics for the fluorescence decay and the solvent-dependent slow (7-20 ps) kinetics for the ground-state recovery, we conclude that the SSHB modifies the potential energy surface for the tau torsion in a way that the IC occurs also for the twisted intermediates with a tau-torsion angle smaller than 90 degrees, which favors the formation of the Z isomers. The possibility of IC induced by torsion of the exocyclic C-C bond (the phi torsion) is also considered but excluded.
Effects of Hydrogen Bonding on Internal Conversion of GFP-like Chromophores. II. The meta-Amino Systems
(2013-03-07)
Cheng, Chi-Wen
;
Huang, Guan-Jhih
;
Hsu, Hung-Yu
;
Prabhakar, Ch.
;
Lee, Yuan-Pern
To rationalize the efficient quenching of the fluorescence and the Z -> E photoisomerization of m-ABDI, the meta-amino analogue of the green fluorescent protein (GFP) chromophore, in protic solvents, the femtosecond time-resolved fluorescence and transient infrared (TRIR) spectra of m-ABDI in CD3CN, CH3OH, and CD3OD are determined. For solutions in CD3CN, the fluorescence decay lifetime is similar to 7.9 ns and IR absorption lines near 1513, 1531, 1557, and 1613 cm(-1) of m-ABDI in its electronically excited state were observed with a decay time >5 ns. For solutions in CH3OH, the fluorescence decay is double exponential with time constants of similar to 16 and 62 ps. In addition to IR absorption lines of m-ABDI in its electronically excited state with a decay time of similar to 16 ps, new features near 1513, 1532, 1554, and 1592 cm(-1) were observed to have a rise time of similar to 19 ps and a decay constant of similar to 58 ps, indicating formation of an intermediate. The assignments for the IR spectra of the ground and excited states were assisted with DFT and TDDFT calculations, respectively. We conclude that the torsion of the exocyclic C=C bond (the tau torsion) is responsible for the nonradiative decay of electronically excited m-ABDI in CD3CN. However, in CH3OH and CD3OD, the solute-solvent hydrogen bonding (SSHB) interactions diminish significantly the barrier of the tau torsion and induce a new pathway that competes successfully with the tau torsion, consistent with the efficient fluorescence quenching and the diminished yield for Z -> E photoisomerization. The new pathway is likely associated with excited state proton transfer (ESPT) from the solvent to m-ABDI, particularly the carbonyl group, and generates an intermediate (ESPT*) that is weakly fluorescent.
Excited state dynamics of green fluorescence protein chromophore derivatives investigated with time-resolved fluorescence and transient infrared absorption
(2012-08-19)
Cheng, Chi-Wen
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Hsu, Hung-Yu
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Huang, Guan-Jhih
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Diau, Eric Wei-Guang
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Yang, Jye-Shane