Combining Magnetic Spectroscopy and Modern Multireference Methods to Understand the Properties of Bio-Inspired and Enzymatic Multicopper Systems

• Applicant: Professor Dr. Michael Roemelt
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation ; Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2018 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 406697875

Copper active sites play central biological roles, including electron transfer, dioxygen binding, activation and reduction, as well as denitrification processes. Enzymatic copper centers are extremely diverse in geometric and electronic structure, and range from mononuclear sites to dinuclear, trinuclear and tetranuclear clusters. When magnetically active Cu(II) ions are present in proximity or interact through chemical bonds, their unpaired spin moments couple leading to a rich phenomenology in terms of magnetism and spectroscopy. This is mainly probed by electron paramagnetic resonance (EPR) techniques and expressed in terms of spin Hamiltonian parameters such as exchange coupling constants, hyperfine/superhyperfine coupling interactions of metal and ligand sites, and local/global zero-field splitting parameters. If multiple Cu(II) centers are involved, as in the trinuclear site of multicopper oxidases and the tetranuclear CuZ site of N2O reductase, the magnetic interactions and associated spectroscopic behavior can become complex so that a unique assignment of electronic structure may require quantum chemical mapping of structural and spectroscopic features. Single-determinant density functional theory (DFT) methods that are widely applicable often struggle to correctly describe the magnetic interaction between Cu(II) sites, and perform inconsistently in reproducing spindependent observables or predicting non-Heisenberg terms of the spin Hamiltonian. Multireference correlated wave function methods such as Difference-Dedicated Configuration Interaction (DDCI) are more reliable but are limited by their cost to simple, usually dinuclear systems and do not provide access to many spectroscopic observables. Such limitations can be lifted by the Density Matrix Renormalization Group (DMRG), which enables multireference calculations to be conducted with unprecedentedly large active spaces. The project involves a combined experimental and theoretical approach, where the French partners will synthesize and spectroscopically characterize biomimetic multinuclear Cu complexes, including a DFT-based description of their properties using spin-projection methods, while the German partners will develop and apply DMRG-based multireference methods on these synthetic models. A major and novel goal is to establish the applicability of DMRG and novel DMRG based techniques to the magnetism and spectroscopy of multicopper systems. The combination of synthesis, spectroscopy and theory aims to first build the basis for interpreting the electronic structure, magnetism and spectroscopy of multicopper complexes, to apply the proven theoretical methods to models of enzymatic systems in order to understand the properties and function of the bioinorganic sites themselves, and finally to inform the synthesis of improved spectroscopic, and potentially functional, analogues of the biological multicopper sites.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Co-Investigator: Dr. Dimitrios A. Pantazis
• Cooperation Partners: Dr. Sylvain Bertaina; Dr. Maylis Orio; Privatdozentin Dr. Jalila Simaan