10-Oct-2019 - Max-Born-Institut (MBI) im Forschungsverbund Berlin e.V

Forward or backward? New pathways for protons in water or methanol

A collaborative ultrafast spectroscopy and ab initio molecular dynamics simulations study, as recently published by scientists of the Max Born Institute of Nonlinear Optics and Short Pulse Spectroscopy (MBI) and the Martin-Luther-University Halle-Wittenberg (MLU) in the Journal of the American Chemical Society, shows that proton vacancies in the form of hydroxide/methoxide ions are as relevant for proton transfer between acids and bases as hydrated excess protons (H3O+, H5O2+), thus pointing for a clear demand for refinement of the microscopic picture for aqueous proton transport – in solution as well as in hydrogen fuel cells or transmembrane proteins – away from currently often assumed dominant role of hydrated excess protons. 

The exchange of protons between two chemical groups (acid-base neutralization) is a textbook chemistry problem for many years. Surprisingly, up to this date new fundamental insight about the elementary steps of proton transport is being obtained. This may well lie in the fact that the elementary steps (by protons or proton vacancies) take place on extremely short time scales, that are not accessible with conventional laboratory techniques (Figure 1). Observation of these elementary reaction steps, as achieved by the research teams of MBI and MLU thus requires direct access to time scales of 1-100 picoseconds, necessitating an experimental set-up with an accordingly high time resolution as well as high performance computer systems.

The research teams have jointly studied a particular model system (7-hydroxyquinoline in water/methanol mixtures), where an ultrashort laser pulse triggers the deprotonation of an OH-group and the protonation of a nitrogen atom. The precise chronology of the elementary steps with these class of chemical reactions have remained elusive, leading to numerous speculations. The scientists of the MBI and MLU have now been able to determine that the release of a proton from the OH-group to the solvent is indeed ultrafast, yet the pick-up of a proton by the nitrogen atom is even faster. This results in a transport mechanism of proton vacancies, i.e. of hydroxide/methoxide ions. The elementary reaction steps have been elucidated with time-resolved IR spectra and detailed quantum chemical calculations (see Figure 2).

Facts, background information, dossiers
More about MBI
  • News

    Atom-Billiards with X-Rays

    In 1921, Albert Einstein received the Nobel Prize in physics for the discovery that light is quantized, interacting with matter as a stream of particles called photons. Since these early days of quantum mechanics, it is known that photons also possess momentum. The photon’s ability to trans ... more

    Self-imaging of a molecule by its own electrons

    One of the long-standing goals of research on the light-induced dynamics of molecules is to observe time-dependent changes in the structure of molecules, which result from the absorption of light, as directly and unambiguously as possible. To this end, researchers have developed and applied ... more

    How to generate and steer electrons in liquid water

    Water molecules undergo ultrafast dithering motions at room temperature and generate extremely strong electric fields in their environment. New experiments demonstrate how in presence of such fields free electrons are generated and manipulated in the liquid with the help of an external tera ... more

More about MLU
More about Forschungsverbund Berlin
  • News

    Atom-Billiards with X-Rays

    In 1921, Albert Einstein received the Nobel Prize in physics for the discovery that light is quantized, interacting with matter as a stream of particles called photons. Since these early days of quantum mechanics, it is known that photons also possess momentum. The photon’s ability to trans ... more

    Self-imaging of a molecule by its own electrons

    One of the long-standing goals of research on the light-induced dynamics of molecules is to observe time-dependent changes in the structure of molecules, which result from the absorption of light, as directly and unambiguously as possible. To this end, researchers have developed and applied ... more

    How to generate and steer electrons in liquid water

    Water molecules undergo ultrafast dithering motions at room temperature and generate extremely strong electric fields in their environment. New experiments demonstrate how in presence of such fields free electrons are generated and manipulated in the liquid with the help of an external tera ... more