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Probing biological interfaces by tracing proton passage across them
Armen Y Mulkidjanian1, Dmitry A Cherepanov
1A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia. AMULKID@UOS.DE
Summary
Surface water properties differ from bulk water, especially at charged interfaces. Experiments suggest an electrostatic barrier at charged membrane surfaces influences proton exchange and interfacial reactions.
Area of Science:
- Physical Chemistry
- Biophysics
- Surface Science
Background:
- Water properties at interfaces, particularly charged ones, diverge significantly from bulk water.
- Understanding these surface properties is crucial for biological processes like energy conversion and transport.
Purpose of the Study:
- To investigate the distinct characteristics of water at charged membrane surfaces.
- To elucidate the nature of the electrostatic barrier at the membrane-water interface.
- To explore the impact of this barrier on interfacial reactions.
Main Methods:
- Proton pulse experiments utilizing light-triggered membrane enzymes.
- Tracing proton movement between the membrane surface and bulk aqueous phase.
- Analyzing the effect of mobile pH-buffers with varying electric charges on proton exchange rates.
Main Results:
- Proton exchange between membrane surface and bulk water is slow (approx. 1 ms) but can be accelerated by mobile pH-buffers.
- The accelerating capacity of pH-buffers decreases with increasing electric charge, indicating an electrostatic barrier.
- This barrier may be explained by dielectric saturation or dielectric overscreening in surface water layers.
Conclusions:
- A significant electrostatic barrier exists at charged membrane surfaces, influencing proton transfer.
- This interfacial potential barrier plays a role in reactions at interfaces, including biological energy conversion and membrane transport.
- The findings contribute to understanding the fundamental physics of water at charged interfaces.