Michael J. Zdilla
B.S. Millersville University (2000)
PhD. Princeton (2005)
Figure 1. OEC complex of photosystem II (left) and FeMoco of nitrogenase (right)
My research interests are focused at the interfaces of inorganic chemistry and biology. In particular, I I am interested in the role of metalloclusters in biochemical transformations. Metal clusters mediate some of the most difficult reactions in nature. For example, the manganese water oxidizing complex of photosystem II harvests electrons from water for photosynthesis, forming dioxygen in the process. Additionally, the nitrogenase enzyme, which contains several structurally unique Fe-S clusters, mediates the reductive cleavage of the N-N triple bond, the strongest in nature. Metalloclusters are able to achieve these intensive redox reaction by the action of multiple metal sites localized in the active site, which allows the storage of multiple oxidizing or reducing equivalents. The storage of charge in this way facilitates these multi-electron reactions without large overpotentials. The application of these principles in the laboratory has very important implications for the development of renewable energy technology.
My research interests in this field can be divided into 3 areas:
Preparation of low-coordinate clusters of Manganese
The water-oxidizing center in photosynthesis contains a unique calcium-manganese-oxo cluster. This cluster is oxidized by photoexcitation of the nearby chlorophyll molecule, and is the location for the binding and oxidation of water to form O2. The nature of binding and oxidation of water remains unknown, and all manganese cluster models to date contain inaccurate 6-coordinate ligation of manganese. Synthesis of unusual 4-coordinate manganese clusters are therefore sought using core imide ligands as surrogates for the core oxos of the manganese cluster. Mechanisms of cluster rearrangement and substrate binding upon oxidation may offer insights into the mechanism of biological water oxidation, and may pave the way to the development of catalysts for the light-driven oxidation of water.
Rational synthesis of nitrogenase cofactor analogues
The field of Fe-S chemistry has been explored for decades using traditional self-assembly techniques. However, no accurate analogue of the nitrogenase cofactor have been prepared to date. The sophisticated preparation of the nitrogenase cofactor by nitrogenous bacteria suggests that this cluster cannot form using simple self assembly methods, but that a well-controlled kinetic pathway is required to arrive at the desired cluster geometry. Rational synthetic strategies for cluster preparation will therefore be sought via the targeted preparation of smaller fragment clusters, and subsequent assembly into larger molecules. Careful terminal ligation choice will facilitate the controlled joining of smaller clusters in the proper configuration to give the desired products.
Figure 2. A proposed assembly of a nitrogenase cofactor model from cluster fragments.
Design of protein scaffolds for the assembly of metalloclusters
With the field of de novo protein design well developed and understood, the opportunity to design protein scaffolds to stabilize metalloclusters will be explored. The design of protein active sites to constrain metal and ligand groups in desired positions will limit the structure types which can be adopted in a given protein, and lead to the generation of unique, water-soluble metallocluster species. In addition to the generation and study of biologically relevant clusters (photosystem II, nitrogenase), the mechanism of cluster assembly in metalloproteins can be examined by kinetic and spectroscopic methods, a field of research which is little explored due to the proprietary fashions in which biological systems prepare their proteins. The availability of abiological small metalloproteins offers the opportunity to gain simple mechanistic insight into metallocluster formation in proteins.
Sandeep K. Kondaveeti, Shivaiah Vaddypally, Carol Lam, Ni Ni, Robert J. Cava, Michael J. Zdilla. “Low-coordinate manganese-oxygen cluster chemistry: An unchelated, 5-coordinate octanuclear manganese cluster with water-derived oxo ligands.” Inorg. Chem. 2012, 51, 10095
Imler, G. H.; Lu, Z.; Kistler, K. A.; Carroll, P. J.; Wayland, B. B.; Zdilla, M. J. “Complexes of 2,5-bis(a-pyridyl)pyrrolate with Pd(II) and Pt(II): A mono-anionic iso-p-electron analog of terpyridine.” Inorg. Chem. 2012, 51, 10122
Kondaveeti, S. K.; Vaddypally,
S.; McCall, J. D.; Zdilla, M. J. “Electronic
structure and solution behavior of a tris(N,N′-diphenylhydrazido)
Vaddypally, S.; Kondaveeti, S. K.; Zdilla, M. J. “Synthesis of a high-valent, four-coordinate manganese cubane cluster with a pendant manganese atom: Photosystem II-inspired manganese-nitrogen clusters.” Inorg. Chem. 2012, 51, 3950.
Vaddypally, S.; Kondaveeti, S. K.; Zdilla, M. J. “An isolable, metastable, geometrically unique manganese(IV) trihydrazide complex poised for reactivity.” Chem. Commun. 2011, 47, 9696.
Hamilton, C. R.: Baglia, R. A.; Gordon, A. D.; Zdilla, M. J. “Synthesis of Tetranuclear, Four-Coordinate Manganese Clusters with “Pinned Butterfly” Geometry Formed by Metal-Mediated N-N Bond Cleavage in Diphenylhydrazine.” J. Am. Chem. Soc. 2011, 133, 4208.