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Quantum Effects on Proton Transfer in Biomolecular Environments

Subject Area Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
Term from 2009 to 2018
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 160077467
 
Final Report Year 2018

Final Report Abstract

Proton transfer belongs to the most fundamental chemical reactions not only in core chemistry but also in biomolecular environments. In particular, vectorial proton transduction in proteins plays a crucial role in photosynthesis, enzymatic reactions, or in pH regulation of the cell. However, the small mass of the proton allows for quantum effects, such as zero point motion and tunnelling, which are well documented by large measured isotope effects. Experiments together with simulations indicate since long that such effects have a major impact on the kinetics of bacteriorhodopsin being a photon–driven proton pump transporting protons through cell membranes to the extracellular medium. Simulation methods that are able to tackle such complex biomolecular processes must include nuclear quantum effects at the first place while treating the electronic structure currently in order to allow for chemical or enzymatic reactions to occur. Secondly, these methods must provice practical access to multi-dimensional free energy landscapes which include not only thermal activation, but also quantum effects on nuclear motion in chemically complex environments. Within this project, the path integral formulation of quantum mechanics has been combined with mixed quantum/classical treatments of the interactions (also known as QM/MM methods), which enables realistic investigations of biomolecular processes which rigorously include nuclear quantum effects such as proton tunneling. Secondly, path integrals have be used to generalize ab initio metadynamics sampling, being a well-established acceleration method, to involve quantum nuclei. The resulting ab initio path integral metadynamics technique allows one to map multi-dimensional quantum free energy landscapes involving high barriers such as those that govern biochemical reactions, e.g. proton or hydride transfer in enzymes, where nuclear quantum effects are rigorously taken into account.

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