Theoretical Assessment of Hinge-Type Models for Electron Donors in Reaction Centers of Photosystems I and II as well as of Purple Bacteria

Hinge-type molecular models for electron donors in reaction centers of Photosystems I and II and purple bacteria were investigated using a two-state computational approach based on frozen-density embedding (FDE). This methodology, dubbed FDE-diab, is known to avoid consequences of the self-interaction error as far as intermolecular phenomena are concerned, which allows a prediction of qualitatively correct spin densities for large biomolecular systems. The calculated spin density distributions are in a good agreement with available experimental results and demonstrated a very high sensitivity to changes in the relative orientation of cofactors and amino acid protonation states. This allows a validation of the previously proposed hinge-type models providing hints on possible protonation states of axial histidine molecules.

Automated summary

In this study, hinge-type molecular models for electron donors in reaction centers of Photosystems I and II and purple bacteria were investigated using a two-state computational approach based on frozen-density embedding (FDE). The calculated spin density distributions were in good agreement with experimental results and demonstrated high sensitivity to changes in the relative orientation of cofactors and amino acid protonation states. This validation of previously proposed hinge-type models provides insights into possible protonation states of axial histidine molecules.