The impact of pH on packing in tethered lipid bilayers

Abstract

We report that increasing the H3O+ concentration when lowering the pH reduces the intrinsic ionic conduction through phospholipid bilayers (Fig 1A), which is counter to what might be expected from increasing the H3O+ concentration. We attribute the conduction decrease to a reduction of the molecular area per lipid (ao)[1]. These effects are seen at H3O+ concentrations in the range nM to µM despite these being very low concentrations compared to that of a typical bathing electrolyte solution of 135mM ionic concentration. We present a model, in which the pH dependent reduction in ao favours an increase in lipid packing. To support this model, we provide evidence of the effects of the hydronium ion on lipid geometry using neutron reflectometry (Fig 1C). Further examples will be given of the impact of the H3O ion concentration on the hydrogen bonding within the polar groups of lipid.