PcpA is a hydroquinone ring cleaving dioxygenase (RCDO) involved in the enzymatic pathway used to break down the normally toxic chemical pentachlorophenol for metabolic use in Sphingobium chlorophenolicum. This enzyme utilizes a mononuclear nonheme Fe(II) active site with a two His/one Glu facial capping geometry around the Fe(II) center. Model complexes provide a means for better understanding the substrate specificity and mechanistic details of this enzyme and similar RCDOs. A family of tetradentate ligands that incorporate a tethered hydroquinone moiety and that are soluble in protic solvents were synthesized in order to mimic the substrate-bound Fe(II) active site of RCDOs. Upon incorporation of these ligands with divalent metal ions, the resulting coordination compounds provide a flexible platform for structural and spectroscopic studies of how protons control the reactivity of the metal-coordinated hydroquinone moiety.
