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Author Spotlight: Exploring Intrinsically Disordered Protein Dynamics Through NMR Relaxation Experiments
Published on: November 1, 2024
Hydration-controlled excited-state relaxation in protonated dopamine studied by cryogenic ion spectroscopy
Keisuke Hirata1, Ken-Ichi Kasai1, Gilles Grégoire2
1Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsu-ta-cho, Midori-ku, Yokohama 226-8503, Japan.
Abstract:
Ultraviolet (UV) and infrared (IR) spectra of protonated dopamine (DAH+) and its hydrated clusters DAH+(H2O)1-3 are measured by cryogenic ion spectroscopy. DAH+ monomer and hydrated clusters with up to two water molecules show a broad UV spectrum, while it turns to a sharp, well-resolved one for DAH+-(H2O)3. Excited state calculations of DAH+(H2O)3 reproduce these spectral features. The conformer-selected IR spectrum of DAH+(H2O)3 is measured by IR dip spectroscopy, and its structure is assigned with the help of quantum chemical calculations. The excited state lifetime of DAH+ is much shorter than 20 ps, the cross correlation of the ps lasers, revealing a fast relaxation dynamics. The minimal energy path along the NH → π proton transfer coordinate exhibits a low energy barrier in the monomer, while this path is blocked by the high energy barrier in DAH+(H2O)3. It is concluded that the excited state proton transfer in DAH+ is inhibited by water-insertion.
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