title: Proton transport at the monolayer-water interface.
abstract: It is shown that when monolayers of stearic acid, palmitic acid, DPPC, or DPPS are compressed above some critical area Ac a lateral conduction mechanism is initiated at the monolayer/water interface. The interfacial conductance increases on further increasing the molecular packing density in the monolayer. All compounds also show major changes in surface potential at Ac the potential becoming more positive in all cases. It is argued that this is a consequence of structural reorganisation at the headgroup/water interface causing a significant reduction in the local permittivity. The critical area, Ac, is approximately double the molecular areas estimated from the pressure-area isotherm, and experiments with stearic acid monolayers show that Ac decreases significantly when the chaotropic ion SCN-, which is known to disrupt the molecular structure of water, is added to the subphase. It is likely, therefore, that the structural changes occurring at Ac involve the formation of a hydrogen bonded network between monolayer headgroups and adjacent water molecules at the monolayer/water interface. It is suggested that the conduction mechanism initiated at Ac arises from proton hopping along this hydrogen-bond network.
authors.affiliation: Institute of Molecular and Biomolecular Electronics, University of Wales, Bangor, Gwynedd, U.K.
authors.forename: H
authors.initials: H
authors.lastname: Morgan
authors.forename: D M
authors.initials: DM
authors.lastname: Taylor
authors.forename: O N
authors.initials: ON
authors.lastname: Oliveira
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D001692:Biological Transport; D004563:Electrochemistry; D008563:Membrane Lipids / Q000737:chemistry*; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000737:chemistry; D010718:Phosphatidylserines / Q000737:chemistry; D011522:Protons; D013229:Stearic Acids / Q000737:chemistry; D013499:Surface Properties; D014867:Water
chemical_list: D008563:Membrane Lipids; D010169:Palmitic Acids; D010718:Phosphatidylserines; D011522:Protons; D013229:Stearic Acids; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; D019308:Palmitic Acid; C038694:dipalmitoylphosphatidylserine; C031183:stearic acid