In this lecture I will discuss recent developments from our lab in the areas of biomimetic metalloporphyrin catalysts and those of novel, heme-thiolate APO biocatalysts with active sites similar to that of cytochrome P450. Both platforms are able to functionalize unactivated C-H bonds. Ferryl porphyrins, P-FeIV=O, are central reactive intermediates in the catalytic cycles of numerous heme proteins and a variety of model systems. There has been considerable interest in elucidating factors, such as terminal oxo basicity and porphyrin redox potential, that may control ferryl reactivity. In particular there are lively discussions regarding the roles of driving force and electron configuration in determining C-H bond cleavage. I will compare and contrast data for C-H hydroxylation by heme-thiolate enzymes such as the aromatic peroxygenases (APO) to results from a family of synthetic ferryl and manganyl porphyrin complexes. Results with the model system reveal a novel internal electromeric equilibrium, P-FeIV=O &lt;=&gt; P+-FeIII(OH2)2 with reversible pKa values in the range of 4-6.3. Ferryl protonation could have important ramifications for C-H bond cleavage reactions mediated by oxoiron(IV) porphyrin cation radicals. The solvent-derived proton adds significantly to the driving force for C-H bond scission. The extent to which enzymes also employ this strategy and how that strategy may be implemented will also be discussed. Supported by the National Institutes of Health (2R37 GM036298) and the National Science Foundation (1004436). References: 1. Proc. Nat. Acad. Sci. U.S.A., 2015, 112, 3686. 2. Angew. Chem. Int. Ed., 2015, 54, 5241-5245. 3. Science, 2012, 337, 1322. 4. J. Am. Chem. Soc. 2014, 136, 6842. 5. J. Am. Chem. Soc. 2015, 137, 5300. 6. Acc. Chem. Res. 2015, 48, 1727.

C-H bond cleavage by metalloenzymes and metalloporphyrins

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.