Author(s): Jaren Meikle, Samuel Archer
Mentor(s): Jacob Dean
Institution SUU
Dipyrroles are a class of heterocyclic molecules ubiquitous in nature. The extensive conjugated network and heterocyclic nature of dipyrroles enable unique characteristics such as metal ion ligation and high absorptive capacity. Such characteristics are foundational to its incorporation into molecules such as chlorophyll, heme, and bilirubin. The structure of dipyrroles, while highly functional in its natural environment, also facilitate unique photochemistry when probed in vitro. Dipyrroles have demonstrated unique pH-dependent reactions when irradiated with high-intensity blue light. In acidic conditions, dipyrroles exhibit exceptional photostability characterized by rapid internal conversion upon electronic excitation. In basic conditions, dipyrroles undergo a complex photooxidation reaction distinguished by solvent addition. Time-resolved UV-visible spectroscopy reveals the decrease of the reactant peak and the emergence of a blue-shifted product peak during the course of photooxidation. Characterization studies of the product indicate the addition of a solvent molecule at the junction of a pyrrole ring and methine bridge, thereby reducing the conjugated π system and blue-shifting the product spectrum. Oxygen-dependence studies also demonstrated decreased rates in an anoxic environment. Although oxygen’s role in the photooxidation mechanism is clear, the specific type of photooxidation—type I or type II—remains unknown. Current research focuses around the involvement of oxygen sensitizers and radical scavengers to determine the method of oxidation. Such research will elucidate the reason behind the design of proteins that employ dipyrrole-containing molecules and inform future applications of dipyrrolic systems.