Gouterman’s four-orbital model

Gouterman’s four-orbital model explains the colors of heme proteins by focusing on four key electron orbitals in the iron atom’s environment. When light hits these molecules, electrons move between these orbitals, producing absorption at specific wavelengths. The model identifies two pairs of orbitals whose interactions cause the characteristic colors of different states (like oxygen-bound or unbound). By understanding how these orbitals interact, scientists can predict and explain the molecule’s color changes, which are essential for biological functions like oxygen transport.