Biophysical Society Conference | Tahoe 2023

Proton Reactions: From Basic Science to Biomedical Applications

Sunday Speaker Abstracts

THE MANY-FACES NATURE OF PROTON TRANSFER REACTIONS  M. GUTMAN AND ESTHER NACHLIEL LASER LABORATORY FOR FAST REACTIONS BIOCHEMISTRY TEL AVIV UNIVERSITY. TEL AVIV ISRAEL Menachem Gutman ; menachem gutman 1 ; 1 Tel Aviv university, biochemistry, Tel Aviv, Israel In 1979 we published a manuscript titled “Rapid pH and deltamuH+ jump by short laser pulse” describing how pulse excitation of naphthol derivatives can perturb the acid-base equilibrium of aqueous solutions and even build a proton motive force across a lipid membrane. Now, with the hindsight of ~40 years, we can evaluate the various aspects and significance of the photo-ejection of protons from excited molecules. The most initial event is the discharge of the proton to the solvent, a reaction that reflects the nature of the excited molecule ΦOH* and the composition of the solvent. The time constant of the proton ejection depends on the pK* of the excited molecule and the availability of the acceptor. Once the proton was released into the solvent, it can ei ther recombine with the parent molecule ΦO -* or diffuse to the bulk. The recombination reaction is observed as a slowdown of the ΦOH* emission decay -reflecting the re-protonation of ΦO -*. This reaction takes place in the ps-ns time frame. The quantitative analysis reflects the reaction space's geometry, diffusion coefficient, ionic strength, and the dielectric constant of the immediate environment. Once the perturbation expands beyond the Coulomb Cage (ns-µs), the system is in a state of acid-base disequilibrium. Equilibrium is regained by a large number of parallel diffusion-controlled reactions among all reactants present in the system. A set of differential rate equations that includes all possible interactions among all components of the system, together with the Genetic Algorithm assures the uniqueness of the derived rate constants. This analysis yields the rate constants of all first and second-order reactions that participate in the perturbed system.

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