FRESH Lecture: Proton Transport in Aqueous and Biomolecular Systems: A Remarkably Complex and Collective Phenomenon
- Prof. dr. Gregory Voth (University of Chicago)
- Thursday 3 September 2015
- FRESH Lectures
- Gorlaeus Building
2333 CC Leiden
- Lecture room C06
The hydrated excess proton plays a critical role in many areas of chemistry, biology, and materials science. Despite playing the central role in fundamental chemical (e.g., acid-base) and biological (e.g., bioenergetics) processes, the nature of the excess proton remains mysterious, surprising, and sometimes misunderstood. In this seminar my group’s longstanding efforts to characterize proton solvation and transport will be described. Theses studies employ a novel multiscale reactive molecular dynamics method combined with large scale computer simulation. The method allows for the treatment of explicit (Grotthuss) proton shuttling and charge defect delocalization, which strongly influences proton solvation and transport in numerous environments including bulk water, water interfaces, and biomolecular systems. One particular focus of my talk will be on the process of protons passing into and through transmembrane biological proton channels. The unique electrostatics related to the dynamic delocalization of the excess proton charge defect in water chains and amino acid residues will be elaborated, as well as the effects of these complex electrostatics on the channel proton transport and selectivity properties. The often opposing and asymptotic viewpoints related to electrostatics on one hand and Grotthuss proton shuttling on the other will be reconciled and unified into a single conceptual framework. Specific simulation results will be given for the important M2 proton channel of influenza A and a comparison to experimental results will be discussed where possible. Another example will be given for a remarkable process that has been recently observed in our computer simulations of proton transport through a hydrophobic carbon nanotube.
Surprisingly, before the hydrated proton enters the tube, it starts shuttling water molecules into the otherwise dry tube via Grotthuss shuttling, effectively creating its own water wire where none existed before. If this behavior is universal, then a prior existing “water wire”, e.g., one seen in an x-ray crystal structure, may not be necessary for excess protons to transport through hydrophobic spaces via water mediated Grotthuss shuttling. They can create their own water wires as needed.