Carbon nanotube assisted water self-diffusion across lipid membranes in the absence and presence of electric fields

Electric-Field and Friction Effects on Carbon Nanotube-Assisted Water Self-Diffusion Across Lipid Membranes

“…While the fields employed in this work were relatively weak vis-à-vis fields generated by charge distributions, it was observed that the permeation of water for the (5,5) SWCNT embedded in a lipid membrane is enhanced by static electric fields due to a decrease in the fluctuations of the number of water molecules inside the SWCNT. In the larger single-file (6,6) CNT pore, dipole alignment with the imposed external field is more easily achieved due to a greater degree of rotational freedom of the water molecules and this was observed to result in a significant reduction in the water self-diffusion flux 26 . In this work it was also observed that the non-field (6,6) flux results were much higher than those reported by Zhu and Schulten 14 , even though the same potential/force field was used in both studies.…”

“…Electric-Field and Friction Effects on Carbon Nanotube-Assisted Water Self-Diffusion Across Lipid Membranes 519 them due to a decrease in the fluctuations of the number of water molecules within the pores, arising from the water molecules' dipole orientation with the field 26 . Although it is difficult to reach a conclusion for the (more statistically accurate vis-à-vis [27]) slightly larger static-field rate in the case of this work for (6,6) CNTs, due to overlapping error bars with respect to the zero-field result, the single-file nature of water transport in (6,6) CNTs, similar to the (5,5) case, suggests that a more minor decrease in the fluctuations of the number of water molecules inside is at play in the static field.…”

“…In [26,27], a more general model was developed for the diffusive permeability (which is not restricted in application to single-file pores) and this more general approach is described below. In addition, the collective transport permeability is analysed in this chapter in greater detail using the generalized linear transport theory for slip flow in pores developed in earlier work 42,43 .…”

“…This was confirmed in [27] where it was demonstrated that in these CNT-arrays there is a significant friction effect that retards movement of the single files of water. In this chapter, we report further studies of non-equilibrium MD simulations of water permeation within (6,6) SWCNT's across a lipid bilayer under the influence of both static and alternating electric fields, taking advantage of GPU-accelerated MD 28 to extend the simulation timescales to longer than was previously possible 26,27 , while also investigating single-molecule translational and rotational frequency modes, collective properties and friction in tube-arrays in greater detail, allied with straightforward, mechanistic models to interpret our results.…”

“…Water channels made of double-walled carbon nanotubes embedded in a lipid membrane, where the inner tube is modeled as a (6,6) CNT with a charge distribution emulating the NPA motif of aquaporins 19 , have also been investigated, and anomalous observations relating to the dynamics, configurational states and apparent pore-length dependence of the properties of water confined within CNTs have received attention [20][21][22] . In [26,27], molecular simulations were reported for unidirectional single-file diffusion of water within (5,5) and (6,6) single-walled carbon nanotubes (SWCNT) and normal diffusion in (8,8) and (11,11) SWCNT's across a lipid membrane. These studies employed both equilibrium MD simulation techniques and an adaptation of MD to investigate conditions involving the influence of both static and alternating electric fields.…”