Solute-Solvent Interactions from Impedance Measurements: 'π-way' Conduction and Water Structure-Enforced Ion Pair Formation in Aqueous Lidocaine Hydrochloride

Admittance measurements of aqueous 0.01, 0.02, 0.05, 0.10, 0.40, and 0.80 M solutions of lidocaine hydrochloride and 0.10 M solution of lidocaine sulfate were investigated using a mercury working electrode. These measurements indicated an increase or decrease in admittance with decreasing frequency depending on the concentration of lidocaine hydrochloride. As the potential changes from negative to less negative, to zero and finally to positive, the admittance increased and passed through a maximum. There was also a slight anodic shift in the maximum with decreasing frequencies suggesting the role of solute-water interactions and orientation effects of water near the double layer changeover potential. To explain the admittance data, we have used the concept of "potential induced and water structure-enforced ion pair formation", at or near the double layer. The impedance data indicate negative differential resistance at negative potentials, suggesting the role of pi electrons in the conduction process, similar to the 'pi-way' in DNA. Sodium chloride affects the lidocaine hydrochloride double layer and impedes the 'pi-way' conduction process, while lidocaine sulfate admittance data suggest a more complex self-assembly process near the double layer.