Toward understanding metal-binding specificity of porphyrin: a conceptual density functional theory study

Porphyrin is a key cofactor of hemoproteins. The complexes it forms with divalent metal cations such as Fe, Mg, and Mn compose an important category of compounds in biological systems, serving as a reaction center for a number of essential life processes. Employing density functional theory (DFT) and conceptual DFT approaches, the structural properties and reactivity of (pyridine)(n)-M-porphyrin complexes were systematically studied for the following selection of divalent metal cations: Mg, Ca, Cr, Mn, Co, Ni, Cu, Zn, Ru, and Cd with n varying from 0, 1, to 2. Metal selectivity and porphyrin specificity were investigated from the perspective of both structural and reactivity properties. Quantitative structural and reactivity relationships have been discovered between bonding interactions, charge distributions, and DFT chemical reactivity descriptors. These results are beneficial to our understanding of the chemical reactivity and metal cation specificity for heme-containing enzymes and other metalloproteins alike.