Scientific Reports (Jul 2017)

Origin of proton affinity to membrane/water interfaces

  • Ewald Weichselbaum,
  • Maria Österbauer,
  • Denis G. Knyazev,
  • Oleg V. Batishchev,
  • Sergey A. Akimov,
  • Trung Hai Nguyen,
  • Chao Zhang,
  • Günther Knör,
  • Noam Agmon,
  • Paolo Carloni,
  • Peter Pohl

DOI
https://doi.org/10.1038/s41598-017-04675-9
Journal volume & issue
Vol. 7, no. 1
pp. 1 – 8

Abstract

Read online

Abstract Proton diffusion along biological membranes is vitally important for cellular energetics. Here we extended previous time-resolved fluorescence measurements to study the time and temperature dependence of surface proton transport. We determined the Gibbs activation energy barrier ΔG ‡ r that opposes proton surface-to-bulk release from Arrhenius plots of (i) protons’ surface diffusion constant and (ii) the rate coefficient for proton surface-to-bulk release. The large size of ΔG ‡ r disproves that quasi-equilibrium exists in our experiments between protons in the near-membrane layers and in the aqueous bulk. Instead, non-equilibrium kinetics describes the proton travel between the site of its photo-release and its arrival at a distant membrane patch at different temperatures. ΔG ‡ r contains only a minor enthalpic contribution that roughly corresponds to the breakage of a single hydrogen bond. Thus, our experiments reveal an entropic trap that ensures channeling of highly mobile protons along the membrane interface in the absence of potent acceptors.