Effect of a water structure modifier on the aqueous electrochemistry of supramolecular systems: Redox-active versus conventional surfactants

Aqueous electrochemistry of a redox-active nonionic surfactant, α-phenothiazinylhexyl-ω-hydroxy-oligo(ethylene oxide) (PCPEG) and phenothiazine (PT) and its derivative, PT-labeled poly(ethylene oxide) (PT-PEO) in aqueous solution of a conventional surfactant, cetyltrimethylammonium bromide (CTAB) above its critical micelle concentration (CMC) has been studied. Cyclic voltammetric results at a glassy carbon electrode in absence and presence of urea were compared to investigate the influence of water structure modification by urea on the micellization behavior of the surfactants. The addition of urea raises the CMC of CTAB by water structure breaking effect which influences the electrochemical behavior of PT and PT-PEO in aqueous solution. The electrochemical behavior on the other hand, does not exhibit any noticeable change with added urea in aqueous solution of PCPEG. This is due to the fact that water structure modification by urea is not sufficient to upset enhanced hydrophobic interaction due to aromatic π–π-stacking interaction from PT group to disrupt PCPEG micelles to monomeric PCPEG. The comparative and contrastive features of the effect of urea to influence micellization behavior and consequent electrochemical changes for conventional and redox-active surfactants have been discussed.