Excited state dynamics of protonated dopamine: hydration and conformation effects

Electronic and vibrational spectroscopy in a cryogenic ion trap has been applied to protonated dopamine water clusters and assigned with the help of quantum chemistry calculations performed in the ground and electronic excited states. A dramatic hydration effect is observed when dopamine is solvated by three water molecules. The broad electronic spectra recorded for the bare and small water clusters containing protonated dopamine turn to sharp, well-resolved vibronic transitions in the 1-3 complex. This reflects the change induced by hydration in the photodynamics of protonated dopamine which is initially controlled by an excited state proton transfer (ESPT) reaction from the ammonium group toward the catechol ring. Interestingly, conformer selectivity is revealed in the 1-3 complex which shows two low lying energy conformers for which the ESPT reaction is prevented or not depending on the H-bond network formed between the dopamine and water molecules.

Automated summary

This study investigates protonated dopamine water clusters using electronic and vibrational spectroscopy in a cryogenic ion trap. The spectroscopic results are compared and assigned with quantum chemistry calculations performed in different states. The researchers observe a significant hydration effect when dopamine is solvated by three water molecules. The study also reveals conformer selectivity in the 1-3 complex, where the occurrence of an excited state proton transfer reaction depends on the hydrogen bond network formed between dopamine and water molecules.