Interactions of copper(II) and zinc(II) with chlorophyll: Insights from density functional theory studies

The reaction of chlorophyll (a) with Cu or Zn in the presence of acetonitrile has been studied on a slightly simplified model using DFT computations of three potential processes: the substitution of the central Mg cation, the chelation of the peripheral keto-ester, associated or not with deprotonation. Mg-substitution is found to be highly favored in the case of copper, whereas chelation without deprotonation is proposed to occur for zinc. It is proposed that chelation associated with deprotonation could become competitive if water is present in the reaction medium. The resulting compounds are shown to have interesting electronic properties as metal → ligand spin transfer is observed in the case of Cu.