Quantum Effects on Proton Transfer in Biomolecular Environments

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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. Recent experiments together with simulations indicate 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. Most crucial is the experimental finding that deuteration, i.e. the exchange of H by D, basically stops the pumping process, which is a most dramatic quantum effect. Our very recent progress in developing novel quantum simulation methods now allows for an accurate investigation of such phenomena by being able to treat quantum effects within molecularly complex environments such as proteins, which is the focus of this proposal. However, in view of a multitude of experimental reports of very significant isotope effects in enzymatic reactions, e.g. on hydride transfer, the ultimate goal of this line of research is to assess the role of quantum effects in biomolecular environments transcending the specific case.