DFT and TD-DFT Studies of Mg-Substitution in Chlorophyll by Cr(II), Fe(II) and Ni(II)

Abstract

Electronic contributions in electronic transitions and energetic data associated to the Mg-substitution in chlorophyll by three transition metals: chrom (Cr2+), iron (Fe2+) and nickel (Ni2+) have been studied theoretically using density functional theory and time dependent density functional theory (TD-DFT) methods. The binding energies are stronger than for Mg2+ in the case of all three cations especially in the case of Ni2+. The Mg-substitution process is found to be exergonic for all title elements in gas phase and in acetonitrile using both implicit and explicit models of solvation. The natural population analysis results, which estimated by natural bond orbital analysis, showed significant charge transfer from pheophytin ligand to the central cation. The UV–visible proprieties of the different substitution compounds have been studied using the TD-DFT method evidencing that substitution of Mg by Cr, Fe or Ni is associated to a blue shift of the Q-band for the three cations.