Density functional studies of iron-porphyrin cation with small ligands X (X: O, CO, NO, O2, N2, H2O, N2O, CO2).

Molecular structure of the iron porphyrin cation [FeP]+ with small ligands X (X: O, CO, NO, O2, N2, H2O, N2O, CO2) are studied employing density functional theory (DFT) methods with the exchange-correlation (XC) functionals OPBE and B3LYP using the LANL2DZ basis set. The relative spin state energies and bond dissociation energies of all of the complexes are presented at their optimized geometries. The low-spin (S = 1/2, S = 0) state is found to be the lowest energy states for the [FePO]+, [FePCO]+, and [FePNO]+ complexes whereas the high-spin (S = 5/2) state has the lowest energy for the [FePO2]+ complex.

Alpha-helices direct excitation energy flow in the Fenna Matthews Olson protein.

In photosynthesis, light is captured by antenna proteins. These proteins transfer the excitation energy with almost 100% quantum efficiency to the reaction centers, where charge separation takes place. The time scale and pathways of this transfer are controlled by the protein scaffold, which holds the pigments at optimal geometry and tunes their excitation energies (site energies).