Biophysical Society Conference | Tahoe 2023

Proton Reactions: From Basic Science to Biomedical Applications

Poster Abstracts

3-POS Board 3 PROTON ABSTRACTION FROM METHANOL BY PHOTOBASES Dina Pines 1 ; Evyatar Ben Haim 1 ; Ehud Pines 1 ; 1 Ben-Gurion University of the Negev, Chemistry, Beer Sheva, Israel

We have investigated the thermodynamic and dynamic properties of three photobases, namely 5 methoxyquinoline (5MQ), 6-aminoquinoline (6AQ) and the naturally occurring harmine. These compounds are known for their strong basicity in the electronic excited state, capable of abstracting protons from water and simple alcohols. Studying these molecules can provide insight into the proton transfer processes that occur in acid-base reactions, which play a crucial role in many biological systems. In particular, a cyclic imine group is common to all three photobases and is the site of protonation both in the ground and the excited electronic state of these photobases. Our measurements of the electronic ground and excited states of these photobases reveal the kinetic parameters of their proton abstraction reactions. In addition, we examined the effect of different solvents on the excited-state basicity of these photobases using the Kamlet-Taft correlation, which allowed us to investigate the intermolecular solvent-solute interactions of these compounds. To gain further understanding of the proton abstraction reaction of these bases, we studied the effect of adding metal cations to the solvent on the proton abstraction rate of excited 5MQ in methanol. We use steady-state measurements and high resolution time-correlated single photon counting (TCSPC) techniques. Our findings suggest that metal cations can significantly impact the proton transfer abstraction processes in methanol but do it to a lesser extent than in water. Our findings are relevant for comprehending cation-assisted water-splitting to proton and hydroxide such as in the carbonic anhydrase water splitting. assisted by a Zinc cation, which is part of the enzyme's reactive center.

49