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Published on: October 4, 2024
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Controlling Light-Induced Proton Transfer from the GFP Chromophore
Jeppe Langeland1, Natascha W Persen1, Elisabeth Gruber1
1Department of Physics and Astronomy, Aarhus University, DK-8000, Aarhus C, Denmark.
Summary
Green Fluorescent Protein (GFP) exhibits excited-state proton transfer (ESPT). Its mechanism and quantum nature are influenced by hydrogen bonds, with chemical modifications altering proton transfer probability and wavelength dependence.
Area of Science:
- Photochemistry
- Quantum Chemistry
- Biophysics
Background:
- Green Fluorescent Protein (GFP) is known for excited-state proton transfer (ESPT).
- Ultrafast ESPT is favored by short hydrogen bonds in GFP-like proteins.
- The detailed mechanism and quantum nature of ESPT in GFP remain incompletely understood.
Purpose of the Study:
- To investigate light-induced proton transfer in the GFP chromophore complexed with anionic proton acceptors (iodide and TCA-).
- To elucidate the role of strong hydrogen bonds and excited-state quantum mechanical proton distribution on transfer probability.
- To explore how chemical modifications and microenvironment affect ESPT.
Main Methods:
- In vacuo study of light-induced proton transfer.
- Utilizing anionic proton acceptors: iodide (I-) and deprotonated trichloroacetic acid (TCA-).
- High-level ab initio calculations to analyze the S1 excited state and proton dynamics.
Main Results:
- Proton transfer probability is significantly altered by chemical modifications and becomes wavelength-dependent.
- Proton-transfer branching ratios were 60% for TCA- and 10% for I-, with iodide complex showing high photon energy dependence.
- Light-induced proton transfer occurs in the S1 state, revealing photoacid properties of the isolated GFP chromophore in H-bonded complexes.
Conclusions:
- ESPT in GFP is highly sensitive to the anharmonic potential topography in the S1 state, influenced by quantum proton density.
- The S1 potential-energy surface and ESPT can be tuned by modifying the chromophore's microenvironment.
- The study reveals intrinsic photoacid characteristics of the GFP chromophore under specific H-bonding conditions.
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