(4dk) Understanding Nature's Catalysts: Chemistry of Transition Metal Containing Enzymes

Authors: 
Sharma, S., Massachusetts Institute of Technology



Enzymes with transition metal containing prosthetic groups are found in all forms of life and facilitate some of the most remarkable chemistry on earth. For example, iron-sulfur containing enzymes are able to reduce atmospheric N2 to ammonia at ambient conditions, as compared to Haber-Bosch process that is carried out at 400 C and 200 bar and uses more than 1% of global energy production. Other examples include, nickel and molybdenum containing carbon monoxide dehydrogenase (CODH), iron containing Cytochrome-P450 catalyzes C-H bond functionalization. A deeper understanding of these catalysts is not only central to problems of biology but can also revolutionize the chemical industry.

The common feature of these enzymes is the presence of transition metal atoms, that give rise to multiple low lying electronic states, which is the key to the their rich chemistry. However, determining the details of these states is a highly non-trivial problem. Traditional approaches like Density Functional Theory (DFT), although cheap and usually quite accurate, fail spectacularly when applied to transition metal containing systems. With recent advances in electronic structure theory, in particular with the advent of Density Matrix Renormalizaton Group (DMRG), we now have a method that is able to correctly describe the challenging chemistry of these enzymes. 

In my postdoctoral work I have made significant contributions to the development and application of the DMRG to the quantum chemical systems. To the best of my knowledge I have written the most efficient implementation of DMRG, which is furthermore capable of targeting specific spin states in molecules. I have also demonstrated the power of the DMRG to model small molecules containing FexSy groups, which will be described in greater detail in the poster.

In my phd I studied the complex reaction mechanisms of soot formation and proposed pathways for formation of soot precursors using quantum chemical methods. Here I worked in close collaboration with experimentalists to provide mechanistic insights that were tested against their data. These results were then used in chemical mechanisms to design efficient combustors with higher efficiency and lower emissions.

During my faculty appointment I intend to combine my expertise in advanced electronic structure methods and experience in solving practical problems in collaboration with the experimentalists. In particular, I will work to bridge the gap between the kinds of model problems that new electronic structure methods are developed for, and the challenges of describing kinetics in real materials and biological problems. This will require not only the applications of the current tools, but also development of new methodologies. In conjunction with this I will use our theoretical understanding of biological motifs to collaborate with engineers and experimental chemists to guide the design of synthetic bio-mimetic catalysis.

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