Proton transport and the topology of hydrogen bond networks: The case of phosphoric acid and water systems

Abstract

Long-range proton transport is a process by which protonic charge carriers move over distances larger than molecular dimensions under the gradient of an electrochemical potential. It is one of the most fundamental processes in physics, chemistry and biology ranging from electrochemical to biological energy conversion machinery. The topology of hydrogen bond network comprising network dimensionality, structure or connectivity is known to play a major role in the proton transporting as well as many other properties of materials. Phosphoric acid and water mixtures represent a very special case in the field of proton conducting systems due to their transport mechanisms. It has been recently suggested that these properties might arise purely from the topology of their hydrogen bond network. The special properties (e.g. small-worldness) of these networks might hold one of the crucial keys in explaining the role, ubiquitous presence and robustness of phosphates in biological structures as well as their unique charge transport properties.