Modeling Spin Transport in Multi-Heme Cytochromes

Multi-heme cytochromes have attracted attention due to their conductive properties [1] and, more recently, their spin-selective properties [2]. The small tetraheme cytochrome (STC), a c-type cytochrome prominently found in Shewanella oneidensis, has been experimentally validated to act as a spin filter [3], highlighting its potential integration into the burgeoning field of nano-scale spintronic devices. A spin-dependent transport model was used to model this system, building upon prior work that has proven effective in analyzing similar biomaterials and cytochromes [4]. The improved model incorporates non-collinear effects such as spin-orbit coupling using generalized open shell density functional theory (DFT) in order to analyze the electronic structure of the cytochrome and spin-dependent transport properties. Preliminary findings indicate that collinear effects, arising from electron exchange and spin state, predominantly influence the transport pathway while spin-orbit effects only cause minor shifts in orbital energies. <br/> <br/>To complement our electronic structure and transport studies, we have undertaken a detailed analysis of the role of the peptide backbone, employing hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) modeling methods. The modeling results indicate that the peptide backbone functions primarily as a structural scaffold facilitating heme-to-heme electron transport, rather than directly contributing to electron conduction. Additionally, recognizing the importance of solvation effects in biological systems, we have investigated the impact of solvation on the cytochrome’s properties. The solvent, modeled using an implicit model and counterions, was found to modulate the coupling between heme sites and the overall conductivity of the cytochrome.<br/> <br/>The research was supported by National Science Foundation NSF Grant Number 2317843, NSF Future of Manufacturing Grant No. 2229131 and the NDSEG fellowship.<br/> <br/>References:<br/>[1] Dahl, Peter J., et al. "A 300-fold conductivity increase in microbial cytochrome nanowires due to temperature-induced restructuring of hydrogen bonding networks." <i>Science advances </i>8.19 (2022).<br/>[2] Mishra, Suryakant, et al. "Spin-dependent electron transport through bacterial cell surface multiheme electron conduits." Journal of the American Chemical Society 141.49 (2019): 19198-19202.<br/>[3] Niman, Christina M., et al. "Bacterial extracellular electron transfer components are spin selective." The Journal of Chemical Physics 159.14 (2023).<br/>[4] Livernois, William, and M. P. Anantram. "A Spin-Dependent Model for Multi-Heme Bacterial Nanowires." ACS nano 17.10 (2023): 9059-9068.