Synthetic cation-selective nanotube: Permeant cations chaperoned by anions

Abstract

The ability to design ion-selective, synthetic nanotubes which mimic biological ion channels may have significant implications for the future treatment of bacteria, diseases, and as ultrasensitive biosensors. We present the design of a synthetic nanotube made from carbon atoms that selectively allows monovalent cations to move across and rejects all anions. The cation-selective nanotube mimics some of the salient properties of biological ion channels. Before practical nanodevices are successfully fabricated it is vital that proof-of-concept computational studies are performed. With this in mind we use molecular and stochastic dynamics simulations to characterize the dynamics of ion permeation across a single-walled (10, 10), 36 Å long, carbon nanotube terminated with carboxylic acid with an effective radius of 5.08 Å. Although cations encounter a high energy barrier of 7 kT, its height is drastically reduced by a chloride ion in the nanotube. The presence of a chloride ion near the pore entrance thus enables a cation to enter the pore and, once in the pore, it is chaperoned by the resident counterion across the narrow pore. The moment the chaperoned cation transits the pore, the counterion moves back to the entrance to ferry another ion. The synthetic nanotube has a high sodium conductance of 124 pS and shows linear current-voltage and current-concentration profiles. The cation-anion selectivity ratio ranges from 8 to 25, depending on the ionic concentrations in the reservoirs.

Role of spatial ionic distribution on the energetics of hydrophobic assembly and properties of the water/hydrophobe interface

“…Such selectivity can be exploited in the development of filtration/desalination processes and may have general implications for biological ion channels. [79][80][81][82][83][84] It is interesting to note the presence of ions also influenced the critical distance for wetting/dewetting of the interior region. The most pronounced difference (relative to pure water) was observed in the 3 M NaI solution in which the critical distance increased from 10.5 to 10.8 A ˚.…”

The very low number of calcium-induced permeability transition pores in the single mitochondrion

“…The second critical assumption of our approach is that the rates of the water flux through the pore are estimated for the flow with no interactions with the pore wall (e.g., in a pristine carbon nanotube). The structure of PTP is not defined, but according to its weak ion selectivity, we can assume that the walls of the PTP would be polar (Hilder et al, 2010(Hilder et al, , 2011a(Hilder et al, , 2011b. Thus, in our estimates, we should take into account that water flux might be considerably slower than in an uncharged pore.…”

Poly(Rhodamine B) modified carbon paste electrode for the selective detection of dopamine

“…3b that the maximum Ipa for DA is attained at pH 7.0. This is due to the complete ionization of the carboxyl group on the Rhodamine B film [85] which leads to the effective electrostatic attraction of the DA cation towards the electrode surface. This result helps us to maintain the physiological condition throughout our studies.…”