Prof. Dr Lubomir Rulíšek

Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, Prague, CZ-16610, Czech Republic

The metalloenzymatic activity is often intimately related to a redox chemistry. To fully understand details how the nature fine-tunes the reduction potentials of active sites, computational electrochemistry is involved. Over the past two decades, a reliable and yet simple methodology for the calculation of a key electrochemical quantity one-electron reduction potential, has been developed. The same holds true for acidobasic equilibria. The key ingredients of the computational methodology (performance of quantum chemical methods for one-electron ionization energies, accuracy of solvation models, etc.) will be described in the first part of the talk. Few specific examples from the recent literature will be included.  For smaller molecules, including transition metal complexes, the accuracy of the computed reduction potentials is quite remarkable, often within 0.2 V from the experimental values whereas the acidity constants (pKa values) often match experimental data within 1-2 pKa units accuracy. A little bit more complicated is the situation with metalloproteins. There are various approaches to treat computationally the complex enzymatic systems - when it comes to the reduction potentials and/or acidity constants - and they will be covered in the second part of the talk. 

The talk will be finalized by discussing the thermodynamic driving force in CEPT (coupled electron and proton transfer) reactions that, per se, involves reduction potentials and acidity constants. I will describe the concept of asynchronicty in CEPT reactions and description of its effect on CEPT reactivity and selectivity. According to this concept, pioneered by Srnec and coworkers, a more pronounced disparity between redox and acidobasic thermodynamic driving forces leads to a larger reduction of CEPT reaction barrier (considering the non-tunneling regime) and hence an increased reaction rate. This effect is quantifiable through the implementation of the asynchronicity factor into the Marcus-type reaction barrier.

Keywords: reduction potentials, acidity constants, solvation methods, theoretical bioinorganic chemistry, thermodynamic driving force

References:

Tomaník, L.; Rulíšek, L.; Slavíček, P.*: Redox Potentials with COSMO-RS: Systematic Benchmarking with Different Databases. J. Chem. Theor. Comput. 2023, 19, 1014–1022.

Bím, D.; Chalupský, J.; Culka, M.; Solomon, E. I.; Rulíšek, L.*; Srnec, M.*: Proton-Electron Transfer to the Active Site Is Essential for the Reaction Mechanism of Soluble Δ⁹-Desaturase. J. Am. Chem. Soc. 2020, 142, 10412−10423.

Bím, D.; Maldonado-Domínguez, M.; Rulíšek, L.; Srnec, M.*: Beyond the Classsical Thermodynamic Contributions to Hydrogen Atom Abstraction Reactivity. Proc. Natl. Acad. Sci. 2018, 115, E10287-E10294. 

Bím, D.; Rulíšek, L.; Srnec, M.*: Computational Electrochemistry as a Reliable Probe of Experimentally Elusive Mononuclear Nonheme Iron Species. J. Phys. Chem. C 2018, 122, 10773‑10782.

Recording:

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