Proton transfer and regulation across chemical interfaces by small-molecule assemblies

Area of Science:

• Interfacial electrochemistry
• Biophysical chemistry
• Membrane biophysics

Background:

• Biological membranes facilitate crucial proton transport processes.
• Artificial interfaces offer model systems to study membrane-mimetic phenomena.
• Understanding interfacial proton dynamics is key to bioenergetics and sensor development.

Purpose of the Study:

• To quantify and control proton gradients across water/dichloroethane interfaces.
• To investigate the influence of pH and specific molecules on interfacial proton transfer.
• To differentiate between uncoupled proton transfer and proton-coupled electron transfer (PCET) mechanisms.

Main Methods:

• Electrochemical impedance spectroscopy (EIS) was employed to measure interfacial proton gradients.
• EIS data were modeled to extract the reciprocal of the time constant (τ -1) as a descriptor of proton transport.
• The effects of pH and proton shuttling molecules (dinitrophenol, quinone/ferrocene systems) on τ -1 were systematically studied.

Main Results:

• Interfacial proton gradient and τ -1 were found to correlate with aqueous phase pH, decreasing from ~1 s -1 at pH 1 to 0.2 s -1 at pH 7.
• Dinitrophenol acted as a pH-activated proton coupler, primarily active near neutral pH.
• Quinone-type cofactors, in conjunction with decamethylferrocene (DMFc), exhibited PCET, significantly altering τ -1.
• The CoQ10-DMFc system demonstrated a τ -1 of 3.5 s -1 at pH 7, highlighting the impact of small-molecule assemblies on proton availability.

Conclusions:

• Electrochemical impedance spectroscopy is a viable method for quantifying interfacial proton gradients and transfer rates.
• The study demonstrates distinct proton transfer mechanisms (uncoupled vs. PCET) at artificial interfaces.
• Small-molecule assemblies can effectively modulate interfacial proton transport, offering potential for designing proton-transfer systems.