Protons in liquid water posses an anomalously high mobility compared to other ions. This high mobility results from the fact that hydrated protons are not transported as intact units, i.e. by so called mass transport, but rather form defects that diffuse “structurally” through the water hydrogen-bond network. As such, aqueous proton transfer strongly relies on the structure and dynamics of the water network. Many natural and technologically relevant proton transfer reactions occur in the direct presence of ions, proteins or in geometrically confined volumes (e.g. nanopools, nanochannels). We propose to study how the nature and concentration of ionic co-solutes affects the dominant hydration patterns, conversion time-scales and local reactivity of the proton. We will also study how the structuring of the water network in nanopools and nanochannels affects the rate and mechanism of proton transfer. This will be experimentally realized by powerful spectroscopic techniques including femtosecond mid-infrared pump-probe spectroscopy and time-domain terahertz spectroscopy, which are available at the proposed host organization AMOLF (FOM) in Amsterdam, The Netherlands. Compared to conventional linear spectroscopies, these non-linear techniques are ideally suited to discriminate between the large number of sub-ensembles of local hydration patterns of the aqueous proton present in solution. The techniques will allow the measurement of the evolution of these sub-ensembles in time. The researcher, Dr. Ottosson, has a strong background in X-ray spectroscopic investigations of aqueous solutions from his Ph.D. work at Uppsala University, Sweden, making him an ideal candidate for this challenging project. With the guidance of the host scientist, Prof. H.J. Bakker – a world-leading expert in time-resolved studies of water and aqueous solutions – we believe that the chances for success are high.