Theoretical aspects of the enhancement of metal binding affinity by intramolecular hydrogen bonding and modulating pKa valuesElectronic supplementary information (ESI) available: Tables of the comparison of the calculated and experimental minimum bond lengths available in two of the studied complexes, selected bond lengths for different studied complexes, NBO charges for different metals in AL3 complexes, dissociation energies (ΔE), enthalpies (ΔH) and free energies (ΔG) of the studied metal cat

• Main Authors: Motahari, Ahmad, Fattahi, Alireza
• Format: Journal Article
• Language: English
• Published: 04.12.2017
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/c7nj02693e

Polyols were used as model ligands for Mg 2+ , Ca 2+ , and Zn 2+ complexes to study the role of the hydrogen bond network on the metal binding affinity and modulation of successive p K a values using density functional theory. The results confirm that the acidity of polyols dramatically increases upon metal complexation in the order Zn 2+ > Mg 2+ > Ca 2+ . For example, the three H-site positions in the hydroxyl groups of the heptaol, bound to Zn 2+ , are 11.2, 29.9, and 30.9 p K a units (in methanol) more acidic than those of pure heptaol. This acidity enhancement leads to making polyols as good ligands toward complexation. For instance, the formation constants of the heptaol in the presence of Zn 2+ , Mg 2+ , and Ca 2+ in methanol were 5.67 × 10 71 , 6.46 × 10 66 , and 1.26 × 10 53 times lower than those in its third deprotonation state, respectively. The natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), and reduced density gradient (RDG) analyses show that the intramolecular hydrogen bond network and increment of carbon chain length lead to the enhancement of metal binding affinity. These findings can be used for the manipulation of ligands and metal cations in designing metalloproteins. The stability balance shows that the hydrogen bond network and modulation of p K a values can enhance the metal binding affinity.