Tools to Simulate Resonance Raman Spectra for in-Situ Studies of Electron Transport Mediators and Bioelectrocatalysts

Abstract

Raman spectroscopy is widely applied as an in-situ probe of electrochemical processes. When the excitation light is resonant with an electronic transition, the detected signal can be enhanced by more than 1,000-fold. Resonance Raman (RR) spectroscopy has broad application in the study of common organic electron transport mediators (i.e., viologens, phenazines, photosynthetic pigments) and active sites of redox proteins (i.e., laccases, peroxidases, flavin-containing enzymes). To support investigations of bioelectrocatalytic membranes, we have been adapting RR spectroscopy to gain insights into the properties of immobilized redox mediators and biocatalyst active sites.1,2 Computational methods can be useful for guiding spectral interpretation. This poster reports on applications of recently advanced time-dependent density functional theory (TDDFT) codes that enable the simulation of RR spectra for small electron transport mediators (e.g., methyl viologen radical anion) and redox protein active site models (e.g., laccase T1 site mimics). The ORCA program suite3 was adapted. A series of Cu-centered compounds that model the T1 active site in laccases was studied along with the methyl viologen radical cation. The T1 site in laccases facilitates direct electron transport to an electrode and is a target for in-situ RR measurements. The reported work demonstrates careful selection of the functional (B3-LYP versus the long-range corrected hybrid exchange functional, ωB97X-D3) results in TDDFT-calculated electronic absorption and RR spectra that have features in excellent agreement with experiment. The results provide a foundation to build from in advancing models of small redox mediators and laccase catalytic active sites in support of sustainable technologies. Ozuguzel, U.; Aquino, A.J.A.; Nieman, R.; Minteer, S.D.; Korzeniewski, C. “Calculation of Resonance Raman Spectra and Excited State Properties for Blue Copper Protein Model Complexes” ACS Sustainable Chem. Eng. 2022, 10, 14614. Xu, J.; Koh, M.; Minteer, S. D.; Korzeniewski, C. “In Situ Confocal Raman Microscopy of Redox Polymer Films on Bulk Electrode Supports” ACS Measurement Science Au 2023 (DOI: 10.1021/acsmeasuresciau.2c00064). Neese, F.; Wennmohs, F.; Becker, U.; Riplinger, C. “ORCA Quantum Chemistry Program Package” J. Chem. Phys. 2020, 152, 224108.