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Biophys J, June 2002, p. 3081-3088, Vol. 82, No. 6

Hydrophobic Ion Hydration and the Magnitude of the Dipole Potential

Jens Schamberger and Ronald J. Clarke

School of Chemistry, University of Sydney, Sydney NSW 2006, Australia

The magnitude of the dipole potential of lipid membranes is often estimated from the difference in conductance between the hydrophobic ions, tetraphenylborate, and tetraphenylarsonium or tetraphenylphosphonium. The calculation is based on the tetraphenylarsonium-tetraphenylborate hypothesis that the magnitude of the hydration energies of the anions and cations are equal (i.e., charge independent), so that their different rates of transport across the membrane are solely due to differential interactions with the membrane phase. Here we investigate the validity of this assumption by quantum mechanical calculations of the hydration energies. Tetraphenylborate (Delta Ghydr = -168 kJ mol-1) was found to have a significantly stronger interaction with water than either tetraphenylarsonium (Delta Ghydr = -145 kJ mol-1) or tetraphenylphosphonium (Delta Ghydr = -157 kJ mol-1). Taking these differences into account, literature conductance data were recalculated to yield values of the dipole potential 57 to 119 mV more positive in the membrane interior than previous estimates. This may partly account for the discrepancy of at least 100 mV generally observed between dipole potential values calculated from lipid monolayers and those determined on bilayers.

Biophys J, June 2002, p. 3081-3088, Vol. 82, No. 6
© 2002 by the Biophysical Society   0006-3495/02/06/3081/08  $2.00


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