engleski

THEORETICAL STUDY OF THE COUPLED ELECTRON-ION TRANSFER REACTIONS RELEVANT TO THE CHARGE TRANSFER PROCESSES AT THE LIVING CELL MEMBRANES

Coupled electron-ion transfer reactions are processes of exceptional physiological significance occurring at the living cell membranes where the ion transfers across the aqueous phase | lipid membrane interface is energetically driven by simultaneous redox reactions occurring at the inner side of the membrane. Thin-film electrodes [1] are simple but powerful tool to mimic the charge transfer processes encountered at the cell membranes and provide both thermodynamic and kinetic information on the complex coupled electron-ion transfer reactions. The thin-film electrode consists of a solid graphite electrode (GE) covered with a thin film of an electrochemically inert water immiscible organic solvent (O) of micrometer dimensions. The organic film contains a neutral lipophilic redox probe (R) and a small amount of an organic electrolyte. The thin-film electrode is immersed into an aqueous electrolyte (AQ) and used in a conventional three-electrode electrochemical cell. Electrochemical transformation of the redox probe R to a stable lipophilic cation R+ is accompanied by an appropriate anion X- from AQ to O. Hence, the overall electrochemical process comprises two simultaneous charge transfer reaction occurring at separate interfaces, i.e., electron transfer across the GE|O interface and the ion transfer across the O|AQ interface. Apparently, this system mimics the situation at the real membranes, where the organic film substitutes the lipid membrane and the GE|O and the O|AQ interfaces correspond to the inner and outer sides of the cell membrane, respectively. A kinetically controlled coupled electron-ion transfer reaction at the thin-film electrodes is theoretically modelled under conditions of square-wave voltammetry (SWV). The mass transfer of all electroactive species within the limiting boundaries of the thin film together with the semiinfinite diffusion of the transferring ion in the aqueous phase is considered. In the first part of the study, the process is assumed to be controlled by the electron transfer rate, whereas in the second one, the ion transfer is the rate limiting step. A comparative analysis of the two limiting cases is presented, revealing that SWV is a powerful technique capable to discriminate the electron from the ion transfer kinetics

living cell membranes

nije evidentirano