Electrochemistry and electrochemical assessment of host-guest complexation of substituted pillar[m]arene[n]quinones

Electrochemical behavior of pillar[n]arene[m]quinone (n + m = 5, n = 2-4) has been for the first time inves-tigated in aqueous media on the glassy carbon electrode. All the compounds studied showed quasi-reversible redox conversion to hydroquinone derivatives. The reaction was not complicated with ionization of hydroxy groups or by the formation of intramolecular hydrogen bonds. In the whole pH region tested (2.0 - 9.0) the stoichiometry of electron and hydrogen ions transfer was found the same (1:1). The peak currents changed with no respect of the number of quinone units in the macrocycle molecule and were probably more affected by steric factors and self-aggregation confirmed by scanning electron microscopy. Adsorption of the macrocy-cles on the electrode covered with carbon black resulted in remarkable improvement of the conditions of elec-tron exchange and of the peak currents on voltammograms. Screening of possible guest molecules showed that among amino acids, tyrosine formed complexes with pillarquinones both in solution and on the electrode inter-face. Complexation resulted in decrease of the peak currents on voltammograms due to steric hindrance of elec-tric wiring. This made it possible to determine 5-100 mu M tyrosine in the solution and 1-100 mu M tyrosine with pillar[3]arene[2]quinone adsorbed in the carbon black layer. No interferences were established in normal human serum and Ringer-Locke's solution. The approach to supramolecular detection of small molecules by intrinsic redox activity of the macrocyclic hosts can be extended to other analytes by modification of the macro-cyclic components of the reaction.

Automated summary

For the first time, the electrochemical behavior of pillar[n]arene[m]quinone (n + m = 5, n = 2-4) was investigated in aqueous media on a glassy carbon electrode. The compounds showed quasi-reversible redox conversion to hydroquinone derivatives, with the stoichiometry of electron and hydrogen ions transfer being consistent. The peak currents were affected by steric factors and self-aggregation, and the adsorption of the macrocycles on the electrode improved the electron exchange conditions.