Biomimetic Membranes as a Tool to Study Competitive Ion-Exchange Processes on Biologically Active Sites (original) (raw)

2011, Advances in Biomimetics

at al., 2000). In particular, ATP takes part in active membrane potential formation, Hep in the anticoagulation process (Desai, 2004) and Asn and Gln in the voltage-ligand gated influx on calcium ions via the NMDA channels (McBain & Mayer, 1994). The following methodology is accepted for applying CPs as biomimetic membranes. In order to obtain the membranes (CP-BL-Y, where Y = K + , Na + , Li + , Ca 2+ , Mg 2+), first ATP, ADP, Hep, Asn or Gln are introduced into the CP matrix during electropolymerization. Next, the calcium, magnesium, lithium, sodium or potassium potentiometric sensitivity is induced by soaking in an alkaline solution of one of these ions until close-to-Nernstian sensitivity for the films is obtained. The films are then used to monitor the equilibration processes induced by the change in bulk concentration of magnesium/calcium or lithium/potassium/sodium ions or stimulation with external electrical signal (Paczosa-Bator at al., 2009). The resulting transitory potential response is recorded and characteristic potential transients observed are theoretically interpreted. 2. Conducting polymers used and their properties It is well known that conducting polymers (CPs) such as poly(pyrrole) (PPy), poly(Nmethylpyrrole) (PMPy) or poly(3,4-ethylenedioxythiophene) (PEDOT) in the oxidation process during electrodeposition are easily doped with small inorganic anions and in consequence exhibit anionic open-circuit sensitivity. Cationic sensitivity can be observed if the CP films are doped with cations during reduction. This happens when the CP film is doped with bulky immobile anions, for instance naphthalenesulphonate, indigo carmine or methylene blue (Gao at al., 1994; Bobacka et al., 1994). The ionic sensitivity induced in this way is dependent on the redox status of the polymer film and is rather nonselective (Lewenstam at al., 1994). As we shown, the cationic sensitivity may be enhanced and stabilized with use of bulky, metal-complexing ligands from the group of metallochromic indicators as dopants. This happens because the bulky dopants retain in the polymer film their complexing properties known from water chemistry and the selective cationic sensitivity results from the complex formation inside CP films (Migdalski et al., 1996). This provides the unique possibility of forming CP films doped with bulky and biologically active anions such as adenosinotriphosphate (ATP), adenosinodiphosphate (ADP), heparin (Hep) or amino acids-asparagine (Asn) and glutamine (Gln). These films may be used as biomimetic membranes to inspect processes important for membrane potential formation or membrane transport (Paczosa-Bator at al., 2007). Our observations have shown that the conducting polymer designed for biomimetic membranes should have smooth surface morphology (a. Paczosa-Bator at al., 2006). It is well known that the morphology of conducting polymer films depends on many experimental parameters, such as substrate used, electrodeposition method, kind of monomer and doping anions, kind of solvent, pH and post deposition treatment of the film. Depending on the further application of conducting polymer layers, different surface morphology (rough or smooth) and different structure are required (