Peptide Isomerization is Suppressed at the Air-Water Interface

TL;DR

This study uses molecular dynamics simulations to analyze how the air-water interface affects alanine dipeptide isomerization, revealing suppressed reaction rates and altered solvent interactions at the interface.

Contribution

It provides new insights into the thermodynamics and kinetics of peptide isomerization specifically at the air-water interface using advanced simulation techniques.

Findings

Isomerization rate is suppressed at the interface by a factor of 3.

Dipeptide shows affinity for the interface due to intramolecular interactions.

Water's mediating role in intramolecular interactions is reduced near the interface.

Abstract

We use molecular dynamics simulations to study the thermodynamics and kinetics of alanine dipeptide isomerization at the air-water interface. Thermodynamically, we find an affinity of the dipeptide to the interface. This affinity arises from stablizing intramolecular interactions that become unshielded as the dipeptide is desolvated. Kinetically, we consider the rate of transitions between the alpha-L and beta conformations of alanine dipeptide and evaluate it as a continuous function of the distance from the interface using a recent extension of transition path sampling, TPS+U. The rate of isomerization at the Gibbs dividing surface is suppressed relative to the bulk by a factor of 3. Examination of the ensemble of transition states elucidates the role of solvent degrees of freedom in mediating favorable intramolecular interactions along the reaction pathway of isomerization. Near the air-water interface, water is less effective at mediating these intramolecular interactions.