Double layer (biospecific)

Double Layer in biological system has several peculiar features that distinguish it from typical Double Layer (interfacial)

• First of all surface of biological cells carry many different types of chemical groups. This groups have different dissociation constants. Some of them can be positively charged, others - negatively, at the given pH. This indicates that bio-surfaces are chemically heterogeneous. This biospecific feature is typical for all bio-surfaces, including proteins, bio-macromolecules, and various biological cells, living and dead.

• Second biospecific feature is peculiar for biological cells. These objects covered with so-called glycocalix layer, which can be modeled as polyelectrolyte layer with volume spread electric charge. This means that notion of surface charge that is located on certain flat surface is not valid for these biological objects. Instead, surface of these objects is a finite thickness polyelectrolyte layer with volume charge. There is a special term for describing equilibrium between such polyelectrolyte layers and fluid bulk - Donnan equilibrium. The polyelectrolyte volume charge creates equilibrium electric potential that is called Donnan potential^[1]. Part of Donnan potential is located inside of the polyelectrolyte layer, the other part is associated with external Double Layer that is located in the dispersion medium. This external part is Double Layer {biospecific). There is large literature on this subject initiated by work of H.Ohshima ^[2], and following by other groups ^[3].

• Third biospecific feature is peculiar for living biological cells only. These object are not equilibrium with the fluid bulk, in definition of life. There is constant ion exchange between living cells and fluid. Consequently, there is difference in electric potentials between cell interior and fluid bulk. This potential is called transmembrane potential ^[4]. This non-equilibrium potential should affect structure of the Double Layer. This is confirmed with several experiments, for instance, ^{[5] [6]}, ^[7] . These experiments are theoretically interpreted in the paper ^[8]

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