Investigation of UV and Visible Light Effects on Kinetic and Thermodynamic Properties of Metal-Binding Aroylhydrazone Photoswitches

Abstract

The use of light as a controlled stimulus for chemical reactions has many advantages over stimuli, such as physical or chemical stimuli, that include its high specificity, resolution, and non-invasiveness. HAPI and its 16 easily synthesized derivatives studied here have the unique ability of shifting between ground and excited state equilibria in response to different wavelengths of light. They also possess E isomer-specific metal binding abilities, furthering its ability for application. UVC, UVA, and Blue Light centered on 254, 371, and 395 nm, respectively, were used as the different light sources for sample stimulation. Different derivatives possess a wide range of isomer compositions in the ground and excited state equilibria depending on which wavelength is used for stimulation. Each derivative had a unique response to any of the three wavelengths used. Once these compounds were stimulated long enough, they reach a photostationary state (PSS) where any more stimulation with light does not produce a change in equilibrium monitored by UV-visible spectroscopy. From this state, the compounds thermally relax back to the ground state equilibrium at different rates, allowing for calculations of half-lives for the PSS of each compound. These half-lives range from 26 min to 216 min. A competitive binding assay is used to assess relative Fe3+ affinity for each compound in its ground and excited states. It was observed that altering certain functional groups on HAPI could dramatically inhibit or enhance iron chelating ability. These data suggest a wide range of effects that simple molecular changes can produce. Thus, further study into this class of compounds may yield optimizations for various potential applications.