Experimental Determination of Proton-Cation Exchange Equilibrium Constants at Water-Membrane Interface Fundamental to Bioenergetics
Haitham A. Saeed and James W. Lee*
Department of Chemistry and Biochemistry, Old Dominion University, Physical Sciences Building 3100, 4541 Hampton Blvd, Norfolk, VA 23529
*Corresponding Author email: [email protected]
Keywords: water thixotropy, viscosity, conductivity, ions, hydrophilic surfaces, laser light scattering, luminescence, ultraviolet absorption, proton-electrostatic localization model, cation exchange equilibrium constant, corrected pmf equation, salinity tolerance, bioenergetics, proton conductor.
Received: October 11, 2017; Revised: March 16, 2018; Accepted: March 23, 2018; Published: May 2, 2018; Available Online: May 2, 2018
Abstract
Recently the Lee proton electrostatic localization hypothesis has successfully elucidated the decades-longstanding energetic conundrum of ATP synthesis in alkalophilic bacteria. According to the Lee proton electrostatic localization model, the equilibrium constant KPi for non-proton cations such as Na+ to delocalize the localized protons from the membrane-water interface should be much smaller than unity. Through the experimental study reported here, it has now been determined for the first time that the equilibrium constant KPi is indeed far much less than one. The equilibrium constant KPNa +for sodium (Na+) cations to exchange with the electrostatically localized protons was determined to be (5.07 ± 0.46) x 10-8 while the equilibrium constant KPK+ for potassium (K+) cations to exchange with localized protons was determined to be (6.93 ± 0.91) x 10-8. These results mean that the localized protons at the water-membrane interface are so stable that it requires ten million more sodium (or potassium) cations than protons in the bulk liquid phase to even partially delocalize them at the water-membrane interface. This provides a logical experimental support of the proton electrostatic localization theory. The finding reported here may have fundamental implications in understanding the importance of water to life not only as a solvent and substrate but also as a proton conductor for proton coupling energy transduction. It may also have fundamental implications in understanding the salinity tolerance in biological systems in relation to localized proton coupling bioenergetics.