Bioinspired Structure/Function Studies that Leverage Proton-Responsive Secondary Coordination Spheres and Ligand-Based Redox Sites

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Project Summary/Abstract The aim of the research described in this renewal proposal is to continue to develop unique and innovative bioinspired complexes to translate metalloenzyme active site reactivity and selectivity into the realm of synthetic constructs for the study biologically relevant reactions. Many metalloenzymes catalyze reactions that involve either oxidation or reduction of substrate, vital for maintaining human health, and these chemical transformations are generally multi-electron redox processes. One such process is the denitrification of Nitrite (NO2-) and nitrate (NO3-). NO3- and NO2- are known water pollutants and suspected carcinogens, in the case of NO2-. A key step in the denitrification pathway is the N-N bond formation to form N2O. Systems capable of denitrification, and N– N bond-forming reactions in particular, are vital to elucidate the mechanism of N2O formation. We plan to explore key reactions in denitrification through the continued development of bioinspired metal ligand complexes containing secondary coordination spheres capable of enticing anion complexation and merging those with ligand-based redox-active sites within a single metal-ligand construct. We will continue to utilize the redox-active pyridinediimine (PDI) scaffold, as it is possible to uncouple the charge state of the secondary coordination sphere of the complex from the ligand-based redox-active sites. It is possible to independently tune both the structural properties of the metal-ligand scaffolds (secondary coordination sphere) and the redox properties (ligand-based redox active sites) independently. We propose that this approach is an innovative and effective way to model the reactivity of metalloenzymes and provide regulatory control over chemical reactions. A series of structure- function relationships will leverage these novel structural motifs to explore denitrificaiton through NOx- binding and reduction, including N-N coupling to form N2O. These studies will provide a fundamental understanding necessary to provide a blueprint for metal-ligand constructs that can be tuned for denitrification reactions. Ultimately, this research will lead to a new complexes that display the elegant control over reactivity that is inspired by metalloenzymes. Specific Aims include: (1) Develop a class of ditopic H-bond donating receptors for NOx- binding and reduction. (2) Investigate N-N bond formation reactions from NOx- sources. (3) Utilize electric fields in the secondary coordination sphere to entice NOx- reactivity.