文摘
The transfer of a biopolymer, 蔚-poly-L-lysine (蔚PL), at a polarized nitrobenzene (NB) | water (W) interface was studied voltammetrically. Despite the polydispersity of sample (n = 25-35, n being the degree of polymerization), an S-shaped current-potential curve with a well-defined limiting current was observed in normal pulse voltammogram for the transfer of 蔚PL at the NB | W (pH 3.0) interface. In the W-phase, 蔚PL would exist in the fully protonated form, and the limiting current can be explained by the diffusion of the polycationic 蔚PL species. Also a pair of anodic and cathodic peak currents was observed by cyclic voltammetry. The midpoint potential was in agreement with the half-wave potential in the normal pulse voltammogram. The influence of pH and the supporting electrolyte anions in both phases on the voltammograms has been also studied. By the addition of dibenzo-18-crown-6 (DB18C6) to NB, the half-wave potential shifted to negative potentials. This can be interpreted as being due to the 蔚PL-transfer facilitated by the formation of 蔚PL-DB18C6 complex in NB. The concentration dependence of the half-wave potential can be explained by the formation of 1:n 蔚PL-DB18C6 complex. The results suggest the applicability of the voltammetric technique to compare the phase-transfer characteristics of 蔚PL and the derivatives.
