Characterizing and contrasting structural proton transport mechanisms in azole hydrogen bond networks using ab initio molecular dynamics

TL;DR

This study uses ab initio molecular dynamics to compare proton transport mechanisms in imidazole and 1,2,3-triazole, revealing structural factors influencing their differing proton diffusion rates relevant to biological and energy systems.

Contribution

It provides the first detailed computational analysis of proton transport in these azole compounds, identifying key structural factors affecting proton mobility.

Findings

Proton diffusion constants differ by over an order of magnitude between the two compounds.

Hydrogen-bonded chain linearity influences proton transport efficiency.

Central nitrogen atom in 1,2,3-triazole causes blocking mechanisms that reduce proton mobility.

Abstract

Imidazole and 1,2,3-triazole are promising hydrogen-bonded heterocycles that conduct protons via a structural mechanism and whose derivatives are present in systems ranging from biological proton channels to proton exchange membrane fuel cells. Here, we leverage multiple time-stepping to perform ab initio molecular dynamics of imidazole and 1,2,3-triazole at the nanosecond timescale. We show that despite the close structural similarities of these compounds, their proton diffusion constants vary by over an order of magnitude. Our simulations reveal the reasons for these differences in diffusion constants, which range from the degree of hydrogen-bonded chain linearity to the effect of the central nitrogen atom in 1,2,3-triazole on proton transport. In particular, we uncover evidence of two "blocking" mechanisms in 1,2,3-triazole, where covalent and hydrogen bonds formed by the central nitrogen atom limit the mobility of protons. Our simulations thus provide insights into the origins of the experimentally observed 10-fold difference in proton conductivity.