| Abstract
| - Cyclic voltammetry and chronoamperometry at micropipetelectrodes were applied to study the phase transfer ofpolypeptide protamine facilitated by complexation withcharged ionophore dinonylnaphthalenesulfonate (DNNS)at polarized water/1,2-dichloroethane (DCE) interfaces,i.e., sDNNS- (DCE) + protaminen+ (aq) ⇌ protamine−DNNS complex (DCE). Well-defined current responsesbased on the selective protamine transfer were obtainedreproducibly even in the presence of 0.12 M NaCl. Theselective and reproducible responses make this voltammetric/amperometric approach an attractive alternativeto the traditional potentiometric counterpart based onmixed potential responses, for which both protamine andNa+ need to be transferred simultaneously. Using bothorganic- and water-filled micropipet electrodes, the reaction mechanism was studied under different mass-transferconditions controlled by diffusion of protamine, DNNS,and the complex in the outer solution of the pipets. Bothcharge number of transferred protamine, n, and complexation stoichiometry, s, were determined to be ∼20by chronoamperometry. With these parameters, the electrochemically irreversible voltammograms were analyzedby assuming a one-step transfer model to obtain experimental transfer coefficients, which represent apparentdependence of the transfer rate on the interfacial potential.The analysis showed that the transfer coefficients aremuch larger or smaller than a normal value of ∼0.5 andstrongly depend on the diffusion-limiting species, i.e.,0.088 ± 0.005, 0.89 ± 0.01, and 0.065 ± 0.008 forprotamine, DNNS, and the complex, respectively. Theapparently anomalous transfer coefficients were explainedconsistently by a phenomenological model based onadsorption and transfer processes.
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