Effect of the Structure of Cholesterol‐Based Tethered Bilayer Lipid Membranes on Ionophore Activity

Abstract

Tethered bilayer lipid membranes (tBLM) are formed on 1) pure tether lipid triethyleneoxythiol cholesterol (EO(3)C) or on 2) mixed self-assembled monolayers (SAMs) of EO(3)C and 6-mercaptohexanol (6MH). While EO(3)C is required to form a tBLM with high resistivity, 6MH dilutes the cholesterol content in the lower leaflet of the bilayer forming ionic reservoirs required for submembrane hydration. Here we show that these ionic reservoirs are required for ion transport through gramicidin or valinomycin, most likely due to the thermodynamic requirements of ions to be solvated once transported through the membrane. Unexpectedly, electrochemical impedance spectroscopy (EIS) shows an increase of capacitance upon addition of gramicidin, while addition of valinomycin decreases the membrane resistance in the presence of K(+) ions. We hypothesise that this is due to previously reported phase separation of EO(3)C and 6MH on the surface. This results in ionic reservoirs on the nanometre scale, which are not fully accounted for by the equivalent circuits used to describe the system.

Voltage-dependent structural changes of the membrane-bound anion channel hVDAC1 probed by SEIRA and electrochemical impedance spectroscopy

“…0.64 mF cm À2 . This value is in line with literature data for lipid membranes 28 and, hence, proves the formation of the tBLM also in the presence of hVDAC1. The tBLM resistance can be estimated using the equivalent circuit R Solution (R Spacer C Spacer )(R Bilayer C Bilayer )Q accounting for the resistance and the capacitance of the two dispersions of the electrode-facing spacer and the solution-exposed bilayer region (see ESI, † Fig.…”

Tethered Membrane Architectures—Design and Applications

“…The choice of anchoring group can significantly impact that quality of the resulting tethering layer. For example, changing the anchoring group from a single thiol (DPhyTT) to a disulfide DPhyTL (Schiller et al, 2003;Atanasov et al, 2006;Vockenroth et al, 2007Vockenroth et al, , 2008aZieleniecki et al, 2016) DPhySL ( (Valincius et al, 2008;McGillivray et al, 2009;Kibrom et al, 2011) TEG-DP (Basit et al, 2011) CPEO3 (also EO3-cholesterol; Boden et al, 1997;Kendall et al, 2010;Wiebalck et al, 2016;Forbrig et al, 2018) (DPhyTL) while using the same length of the spacer molecule, improved the electrical resistance of the resulting bilayer from up to 15 M ·cm 2 to 55 M ·cm 2 (Junghans and Koper, 2010). This is possibly because the size of the anchor group more closely matches that of the hydrophobic chains, resulting in improved packing density as the anchorlipid.…”

“…The EO3-cholesterol based tether shown in Table 1 has also been mixed with mercaptohexanol to create a sparsely tethered lipid bilayer membrane (Kendall et al, 2010). This membrane had a good electrical resistance of around 1 M cm 2 which was reduced by up to four orders of magnitude upon incorporation of valinomycin and other ion transporters.…”

Supramolecular electrode assemblies for bioelectrochemistry

“…Although cation transfer can in principle be detected with impedance spectroscopy, 52–57 it can be difficult to deconvolute electron and cation transport in bioelectrochemical systems. Recently, several alternatives have been reported.…”