The Effect of Benzyl Alcohol on the Voltage-Current Characteristics of Tethered Lipid Bilayers

Abstract

In this study a lipid bilayer membrane model was used in which the bilayer is tethered to a solid substrate with molecular tethers. Voltage–current (V–I) measurements of the tethered bilayer membranes (tBLM) and tBLM with benzyl alcohol (BZA) incorporated in their structures, were measured using triangular voltage ramps of 0–500 mV. The temperature dependence of the conductance deduced from the V–I measurements are described. An evaluation of the activation energies for electrical conductance showed that BZA decreased the activation/ Born energies for ionic conduction of tethered lipid membranes. It is concluded that BZA increased the average pore radius of the tBLM.

Graphical Abstract

Appendix

• 1- The total activation energy for ionic conduction through a pore is given by: ${\mathrm{E}}_{\mathrm{a }= }{\mathrm{E}}_{\mathrm{D}} + {\mathrm{E}}_{\mathrm{B}}$

  Where ${\mathrm{E}}_{\mathrm{a}}$ is the total activation energy, E_B is the Born energy and ${\mathrm{E}}_{\mathrm{D}}$ is the energy required for diffusion through the aqueous medium filling the pore, which is ∼18 kJ/mol.

• 2- The Born energy for inserting an ion into a pore is given by ${\mathrm{E}}_{\mathrm{B}= }\frac{{\mathrm{Z}}^{2} {\mathrm{q}}^{2 }\mathrm{\alpha }}{4\uppi {\upvarepsilon }_{0 }{\upvarepsilon }_{\mathrm{h}}\mathrm{r}}$, where α =  ~ 0.2 for a long cylindrical pore.

• 3- Using the experimentally determined activation energy for conduction, the Born energy could be calculated and from this using Eq. 1, the average pore radius was calculated. The average pore conductivity can then be calculated using the following:

  $$\mathrm{Gp}=\upsigma \frac{\mathrm{A}}{\mathrm{L}}=\upsigma \frac{\uppi {\mathrm{r}}^{2}}{\mathrm{d}}$$

  where Gp is the conductivity of the pore, d is the thickness of the bilayer and $\upsigma$ is the specific conductivity inside the pore. $\upsigma$ is calculated using the following equation:

• 4- $\upsigma$ = ${\upsigma }_{\mathrm{Pbs }*}{\upgamma }_{\mathrm{partition}}$

  Where ${\upsigma }_{\mathrm{Pbs}}$ is the specific conductivity of PBS solution, which was 17 × 10^–3 S/cm and ${\upgamma }_{\mathrm{partition}}$ is the partition coefficient. Therefore:

  $$\mathrm{Gp}=\upsigma \frac{\mathrm{A}}{\mathrm{L}}=\left({\upsigma }_{\mathrm{Pbs}*}{\upgamma }_{\mathrm{partition}}\right)\times \frac{\uppi {\mathrm{r}}^{2}}{\mathrm{d}}$$

  To calculate the partition coefficient ${\upgamma }_{\mathrm{partition}}$, the following equation was used:

• 5- ${\upgamma }_{\mathrm{partition}}= {\mathrm{e}}^{\frac{-{\mathrm{E}}_{\mathrm{B}}}{\mathrm{KT}}}$

• 6- The total membrane conductance ${\mathrm{G}}_{\mathrm{m}}$ is the total number of pores $\mathrm{n}\left(\mathrm{r}\right)$ multiplied by the specific conductance of each pore ${\mathrm{G}}_{\mathrm{p}}:$

  $${\mathrm{G}}_{\mathrm{m }}=\mathrm{ n}\left(\mathrm{r}\right)\times {\mathrm{G}}_{\mathrm{p}}$$