Spin-dependent hopping in cytochromes: role of geometric reorganization and non-collinear effects

Multi-heme cytochromes form nanoscale molecular wires that support electron transport, with recent experimental studies observing spin filtering effects under an applied magnetic field. The mechanisms for spin-dependent conductance are critical for integration into spin-active bioelectronics, but gaps remain in the current models for spin transport in cytochromes. This work builds on previous work, first applying spin dependent hopping models to the coordinated heme group found in cytochromes. The developed mechanisms focus on higher spin states and spin-allowed transitions, focusing on reorganization of the heme centers. These mechanisms yield several distinct pathways for spin dependent conduction and can account for a four order of magnitude difference in hopping rate in ambient conditions. We further explore non-collinear effects to describe inter-heme coupling and coherent transport, which were found to have a negligible effect on spin alignment and electron transport within the cytochrome. The resulting models provide a framework for spin transport modeling in cytochromes, which will focus on multiple spin states and electrode-cytochrome interactions.