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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 17: Charged Soft Matter, Polyelectrolytes and Ionic Liquids I

CPP 17.4: Talk

Tuesday, March 19, 2024, 10:30–10:45, H 0107

Anions and Cations Affect Amino Acid Dissociation Equilibria via Distinct Mechanisms — •Varun Mandalaparthy, Madhusmita Tripathy, and Nico van der Vegt — Department of Chemistry, Technical University, Darmstadt

Salts reduce the pKa of weak acids by a mechanism sensitive to ion identity and concentration that involves charge screening of the deprotonated state. In our recently published study [1], we utilize constant pH molecular dynamics simulations to understand the molecular mechanism behind the salt-dependent dissociation of aspartic acid (Asp). We calculate the pKa of Asp in the presence of monovalent salts and investigate Hofmeister ion effects by systematically varying the ionic radii. We observe that an increase in the anion size leads to a monotonic decrease in Asp pKa. Conversely, changes in the cation size affect the pKa nonmonotonically, interpretable in the context of the law of matching water affinity. The net effect of salt on Asp acidity is governed by an interplay of solvation and competing ion interactions. Our proposed mechanism is rather general and can be applicable to several problems in Hofmeister ion chemistry, such as pH effects on protein stability and ion effects on soft matter interfaces.

[1] Mandalaparthy V., Tripathy M., van der Vegt, N.F.A., Anions and Cations Affect Amino Acid Dissociation Equilibria via Distinct Mechanisms, J. Phys. Chem. Lett. 2023, 14, 41, 9250-9256

Keywords: Constant pH MD simulations; Hofmeister chemistry; Ion specific effects; Law of matching water affinities; Solvation thermodynamics