Stimuli-Responsive Cerium(III) Complex with a Merocyanine-Based Surfactant to Potentially Treat Viral Infections

Spiropyrans are a class of molecules that present different physicochemical properties according to the response to stimuli in the medium (such as light, temperature, and pH). This switching is related to the interconversion between non-ionic closed-form isomers (spiropyran isomers) and ionic open-form isomers (merocyanine isomers).1 The zwitterionic merocyanine isomer can also form metal complexes.2 The cation could be released in response to a molecule switching to another different isomer. Considering the promising activity of cerium oxide nanoparticles against viral infections3, we proposed to complex Ce3+ with a merocyanine-based surfactant as a potential antiviral system. We expected that Ce3+ would be released at a low pH only and subsequently form cerium oxide nanoparticles in situ. We studied the stoichiometry of the Ce3+-merocyanine complex using a Job plot strategy. We also investigated the cerium release triggered by pH and its subsequent oxidation in situ by H2O2 at a biological concentration to form cerium oxide nanoparticles, using ultraviolet-visible spectroscopy and transmission electron microscopy.