Absence of kinetic barrier for transfer of protons from aqueous phase to membrane-water interface

The kinetics of interfacial proton transfer reaction is an important factor in proton transport across membranes. The following experimental system was designed in order to measure this kinetics. Sonicated liposomes having the protonophore SF6847 was suspended in Tris buffer. Application of a temperature jump (in ∼ 3 μs) caused a drop in the aqueous phase pH which was subsequently sensed by the membrane-bound SF6847. The kinetics of this interfacial proton transfer reaction was monitored on μs timescales. The estimated bimolecular rate constant of 2×10¹¹ M⁻¹ s_#x2212;1 for this process show that there is no kinetic barrier for the transfer of protons from the aqueous phase to the membrane-water interface.