Abstract
Proton transfer is important for chemistry in general and for protein function in particular. Water is often involved as a donor, a receptor, or an element in a chain of concerted transfers. Recently we have shown that the amphiprotic behavior of water can be captured by a simple model that is inspired by the traditional Lewis construct. The model comprises explicit and fully charged oxygen cores, valence electron pairs, and protons, all interacting via pair-wise pseudo-potentials that reflect Heisenberg uncertainty and Pauli exclusion. These independently mobile particles produce stable neutral, protonated and deprotonated water clusters. They also exhibit transport of protons and proton-holes through water chains. A self-consistent extension of the model to nitrogen hydrides provides a description of ammonia that forms hydrogen bonds and transports protons. Further generalization to include carbon allows us to build “Lewis” amino acids. In in vacuo simulations, initially zwitterionic forms of the amino acids evolve to non-ionic forms via an intramolecular proton transfer. The intermediate in this process is a 5-member ring with the migrating hydrogen bridging the amine nitrogen and a carboxyl oxygen.