Investigation of spin-charge-structure in human heme using the DFT method

Abstract

The enzyme heme oxygenase (HO) plays an essential role in the destruction of heme molecules. Heme oxygenase uses dioxygen to open the specific orientation of the porphyrin ring at the position of the [Formula: see text]-meso carbon. This reaction is called mesohydroxylation, which produces [Formula: see text]-bilirubin, and the [Formula: see text]-bilirubin produced by the second enzyme bilirubin reductase is converted into bilirubin. The destruction of heme is carried out by a special enzymatic process, and the enzymes heme oxygenase and bilirubin reductase are responsible for the enzymatic role of this process. All calculations were done using Gaussian 2003 and Gaussian 2009 on an Asus NW522 computer and with the help of the Gaussian viewer, and Hyperchem software. Calculation and optimization of different configurations of molecules using the quantum computing method from the beginning of B3LYP were performed using the 631G-basis set using the FOPT keyword. The calculation of charge and spin was done based on Mulliken’s charge and spin. The analysis of bonding orbitals (NBO) was done to fully investigate the distribution of [Formula: see text] and [Formula: see text] spins in d orbitals of iron and ring. The molecule is optimized using the quantum calculation method from the beginning, B3LYP with the basis set 6-31G. The results of DFT studies showed that the LUMO-HOMO energy gap values reflect the chemical activity of the molecule. The higher the HOMO-LUMO energy gap, the harder and more stable the molecule is and the less reactive it is. The reduction of the HOMO and LUMO energy gap explains the final charge transfer interaction that occurs inside the molecule due to the ability to accept electrons in the electron acceptor group.