On the role of interfacial hydrogen bonds in "on-water" catalysis

TL;DR

This study investigates the microscopic origins of the 'on-water' catalytic effect in organic reactions, specifically examining the role of interfacial hydrogen bonds using advanced molecular dynamics simulations.

Contribution

The paper extends a molecular dynamics method to analyze the role of interfacial hydrogen bonds in 'on-water' catalysis, challenging previous assumptions about their significance.

Findings

Interfacial hydrogen bonds play a smaller role than previously thought.

Transition state stabilization is not primarily due to dangling hydrogen bonds.

The 'on-water' effect involves other mechanisms beyond hydrogen bonding.

Abstract

Numerous experiments have demonstrated that many classes of organic reactions exhibit increased reaction rates when performed in heterogeneous water emulsions. Despite enormous practical importance of the observed "on-water" catalytic effect and several mechanistic studies, its microscopic origins remains unclear. In this work, the second generation Car-Parrinello molecular dynamics method is extended to self-consistent charge density-functional based tight-binding in order to study "on-water" catalysis of the Diels-Alder reaction between dimethyl azodicarboxylate and quadricyclane. We find that the stabilization of the transition state by dangling hydrogen bonds exposed at the aqueous interfaces plays a significantly smaller role in "on-water" catalysis than has been suggested previously.