The geometry of TPPFe(II) and L-Thr-TPPFe(II) were optimized using density functional theory (DFT) at the B3LYP level with the mixed basis sets: Lan2dz for Fe(II), 6-31G(d) for C and H atoms, and 6-311++G(2d, p) for N and O atoms. To simulate real conditions, the solvent effects of CHCl3 and H2O were studied using the polarized continuum model (PCM). The electron density at the bond critical point was calculated using the topology analysis of the Multiwfn software. Based on the calculated data of electrostatic potential obtained by quantitative analysis of molecular surface using the Multiwfn software, the molecular electrostatic potential maps were illustrated using VMD software. The bond length and electron density at the bond critical point indicate the coordination bond between the Fe(II) atom and the O atom of carbonyl group in L-threonine and the intramolecular hydrogen bond between H(7) atom and N(1) atom. The porphin ring is warped by the effect of the coordination bond and the intramolecular hydrogen bond. The coordination effect between the Fe(II) atom and carbonyl group may weaken the bond strength between Fe(II) atom and O2, but it is beneficial for the reversible oxygen carrying functions. The solvent effects of CHCl3 and H2O may attenuate the intramolecular hydrogen bond and the coordination effect between the Fe(II) atom and carbonyl group, and enhance the warping of porphin ring and the coordination effect between Fe(II) atom and O2. The computation of molecular electrostatic potential show that the more negative?value outside the O atom, N atom and benzene ring are contributed by lone-pair electrons and π-electrons,?respectively. The?electrostatic?potential?outside the H atom of the benzene ring and the Fe(II) atom is?positive. The most positive value is outside the Fe(II) atom which is the most?probable?active?sites?in coordination?reactions between the Fe(II) atom and O2.
