Acid Dissociation Behavior of 8-Hydroxyquinoline-5-Sulfonic Acid in Molecular Crowding Environment Modeled Using Polyethylene Glycol

The thermodynamics and kinetics of biomolecular reactions in a molecular crowding environment are different from those in dilute solutions. Although biomolecular reactions in crowding solutions have received extensive attention from many researchers, fundamental thermodynamic reactions, such as acid dissociation, are not yet understood. Herein, we investigated the thermodynamic behavior of acid dissociation of 8-hydroxyquinolin-5-sulfonic acid in the molecular crowding. Two acid dissociation constants, K-a1 and K-a2, in polyethylene glycol (PEG) of different molecular weights were determined by pH titration. The K-a change was analyzed based on the change in osmotic pressure. The temperature dependences of K-a1 and K-a2 allowed us to obtain the enthalpy (Delta H) and entropy changes (Delta S) . The Delta H and Delta S values suggest that dehydration of the dissociated species was induced by the decrease in water activity upon the addition of PEG. The results show that the acid dissociation in the PEG solution can be explained by dehydration. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the thermodynamic behavior of acid dissociation of 8-hydroxyquinolin-5-sulfonic acid in a molecular crowding environment and finds that it is influenced by the presence of polyethylene glycol (PEG), which leads to dehydration of the dissociated species, explaining the process of acid dissociation.