Origin of proton affinity to membrane/water interfaces

Area of Science:

• Biophysics
• Cellular Energetics
• Membrane Transport

Background:

• Proton diffusion along biological membranes is critical for cellular energetics.
• Understanding surface proton transport dynamics is essential for elucidating cellular energy processes.

Purpose of the Study:

• To investigate the time and temperature dependence of surface proton transport.
• To determine the Gibbs activation energy barrier (ΔG‡r) for proton surface-to-bulk release.

Main Methods:

• Utilized time-resolved fluorescence measurements.
• Analyzed Arrhenius plots of proton surface diffusion constants and surface-to-bulk release rate coefficients.
• Quantified the Gibbs activation energy barrier (ΔG‡r).

Main Results:

• The determined Gibbs activation energy barrier (ΔG‡r) was large, disproving quasi-equilibrium between membrane-associated and bulk protons.
• Non-equilibrium kinetics accurately describes proton transport dynamics.
• The activation energy barrier (ΔG‡r) was found to be primarily entropic, with a minor enthalpic contribution.

Conclusions:

• An entropic trap mechanism facilitates the channeling of mobile protons along membrane interfaces.
• This channeling occurs efficiently even without strong proton acceptors.
• The findings provide new insights into proton dynamics at biological membrane surfaces.