Physics (Internal)

Ion transport in biological ion channels and silicon nanopores: No life without entropy

This event is part of the Biophysics/Condensed Matter Seminar Series.

Joint Condensed Matter/Biophysics Seminar

This talk deals with ion charge transport via a protein ion channel in a lipid membrane or a water filled nanopore in a silicon film. It is known that due to the large ratio of dielectric constants of water filling the channel and of the surrounding channel walls, the electric field of an ion placed inside the channel is confined inside the channel, so that the ion has to cross a large electrostatic self-energy barrier. Two oppositely charged ions can easily enter the channel but they do not conduct because they are connected by interaction potential linearly growing with the distance between them similarly to two quarks. This should lead to negligible conductance of the channel. Nevertheless, ion channels function.

I will talk about two mechanisms employed by Nature for elimination of the electrostatic barrier in ion channels, namely effects of salt ions dissolved in water and of immobile charges on the channel internal walls. Both type of charges lead to insulator-metal crossover. The first transition resembles Mott transition in the exciton gas with increasing density of excitons; the second one resembles Mott transition in a doped semiconductor with growing concentration of impurities. Of course, I talk about completely classical phenomenon (happening in water at room temperature), where the entropy plays the role of quantum mechanics.

Our transition is also similar to the thermal deconfinement of quarks in heavy nuclei collisions leading to quark–gluon plazma.