Lipophilic 1,4-naphthoquinone derivatives: synthesis and redox properties in solution and entrapped in the aqueous cubic liquid-crystalline phase of monoolein

1,4-Naphthoquinone derivatives (NQD) containing lipophilic alkyl chains, i.e. 2-((Z)-heptadec-8-enyl)-3-methyl 1,4-naphthoquinone (QMe), 2-((Z)-heptadec-8-enyl)-3-hydroxy-1,4-naphthoquinone (QOH) and (Z)-octadec-9-enyl 1,4-naphthoquinone-2-carboxylate (QE) were synthesized. The redox behavior of these NQD was studied in ethanol and entrapped in the reversed bicontinuous cubic phase of space group type Pn3m (Q224) of aqueous monoolein. In ethanol, cyclic voltammetry curves exhibit two pairs of oxidation–reduction peaks arising from the redox processes controlled by adsorption and molecular diffusion. The NQD molecules are also electrochemically active in the cubic phase, indicating the participation in the 2e−, 2H+-redox cycle at pH < 9. Therefore, it was concluded that the head group of the entrapped NQD reaches the lipid bilayer interface of cubic phase during the process.