There are now well-established examples of carriers and pores which facilitate the transfer of ions across thin lipid membranes. In the absence of such agents, lipid bilayer membranes are extremely impermeable to the common inorganic ions. Thus, the conductance of a pure lecithin + decane or glyceryl mono-oleate + decane membrane in M/10 NaCl is less than10−9Ω −1 cm−2. However, on the addition of small lipid-soluble molecules such as valinomycin, or surface-active polypeptides such as gramicidin A, the conductance may become so high (> 10−1 ω−l cm−2) that the resistance of the membrane merges into that of the aqueous phase. This review is concerned with the extent to which we now understand how these added substances transfer ions across lipid membranes. Attention has been concentrated on the simpler systems, i.e. the lipid-soluble ions, the 1–1 carriets, a simple pore and, with some loss of simplicity, a substance which prodeces interacting pores. Only molecules of known primary structure are discussed.

Ion transport across thin lipid membranes: a critical discussion of mechanisms in selected systems.

Nonelectrolyte partition coefficients (K's) and free energies of solution (ΔF

 l
 's) in dimyristoyl lecithin liposomes and in bulk nonpolar solvents were compared. Individual substituent groups tend to have consistent effects onK, permitting the extraction of incremental free energies (δΔF), enthalpies (δΔH), and entropies (δΔS) of partition and of solution. Values of the selectivity constants and of δΔF

 l
 for the −CH2−and −OH groups in lecithin suggest that partitioned solutes are mainly located in a region slightly less hydrophobic than octanol and similar to C5H11OH in its solvent properties. Lecithin discriminates against branched solutes more than does a bulk solvent with the sames value. Below the endothermic phase-transition temperature (i.e., when the hydrocarbon tails “freeze”), ΔS and ΔH of partition increase 10-fold,K jumps down slightly, ΔS and ΔH of solution reverse in sign from negative to positive, and the Barclay-Butler constants become more positive. Partition in lecithin and in erythrocytes is similar, except for the absence of surface charge effects in lecithin. Resistance to nonelectrolyte permeation is inhomogeneously distributed through the bilayer, and the region of maximum partition does not provide the rate-limiting barrier. An appendix derives a simple general expression for the nonelectrolyte permeability of a membrane that may be asymmetrical, may have position-dependent partition coefficients and diffusion coefficients, and may have significant interfacial resistances.

Interpretation of nonelectrolyte partition coefficients between dimyristoyl lecithin and water.

Biomimetic membranes: A review

https://science.sciencemag.org/content/sci/178/4056/24.full.pdf

Carrier-mediated ion transport.

Tethered lipid bilayers (tBLMs) were obtained by the fusion of liposomes from diphytanoylphosphatidylcholine (DPhyPC) with self-assembled monolayers (SAMs) of a newly designed archaea analogue thiolipid, 2,3-di-O-phytanyl-sn-glycerol-1-tetraethylene glycol-d,l-α-lipoic acid ester (DPTL) on template stripped gold (TSG) films from silicon wafer as a template. SAMs, as characterized by reflection absorption infrared spectroscopy (RAIRS), show a mixture of different conformations of the tetraethylene segment in air, which appears to rearrange into the fully extended conformation when the SAM is immersed into an aqueous electrolyte solution, as deduced from thickness measurements by surface plasmon resonance spectroscopy (SPR). The fusion of liposomes was followed by SPR, quartz crystal microbalance (QCM), and fluorescence microscopy. Highly resistive tBLMs were obtained, as demonstrated by electrochemical impedance spectroscopy (EIS) results, which are equivalent to those for the BLM. This large resistivity i...

B. Ketterer

Papers

The Rate Constants of Valinomycin-Mediated Ion Transport through Thin Lipid Membranes