Sensing the active site properties of enzymes as a function of the size of an effective peptidic environment using DFT reactivity parameters

Abstract

The influence of effective electrostatic potentials of increasing size on the electronic properties of the active sites of superoxide dismutases enzymes of Fe and Mn is evaluated. The probes used to follow the changes are the generalized electronic chemical potentials and condensed Fukui functions defined within the spin-polarized formulation of density functional theory. The effective electrostatic potentials were included within the Kohn–Sham potential during the SCF procedure. It is determined that the sensitivity of the chemical potentials and the Fukui function to the presence of point charges dies off at around 17 a.u. beyond the first coordination sphere. When the reactivity parameters are evaluated with all electron models including the second coordination sphere, the physical meaning of the quantities can be related to the trends of experimental redox potentials. It is found that the use of unbalanced effective electrostatic potentials could give rise to strong changes that modify the relative order of the values; consequently, the use of spherical truncation for the effective potentials is recommended to assure the appropriate description of the reaction capabilities of the active sites in these systems.