DFT Study on Amino-Phospholipids Surface Mediated Decomposition of Hydrogen Peroxide

Abstract

[eng] Hydrogen peroxide molecules play a significant role in controlling certain cellular functions, and its excess causes significant damage to biological systems. There is experimental evidence that its decomposition is accelerated above phospholipids membranes surface. We propose a mechanism for decomposition of hydrogen peroxide on amino-phospholipids surface model based in Dmol3/DFT calculations. The model was built using periodic boundary conditions. Each unit cell contained two phospholipids molecules, two hydrogen peroxide molecules, and nine water molecules. In the studied reaction, two hydrogen peroxide molecules react in a bimolecular reaction to yield an oxygen molecule and two waters. The reaction proceeds by two steps. In the first step, an intermediate hydrogen trioxide from two H2O2 molecules is formed. In the second step, this intermediate is cleaved in O2 and H2O. There are proton exchanges along the interface between water and amine-phospholipids monolayer in all parts of the pathway. A parallel periodic model of pure water was built to compare the free energy variation through the reaction. Our results show that first step, intermediate hydrogen trioxide formation, is the limiting step of the reaction, having a free energy barrier of 8.76 kcal mol<br>1 in the amino-phospholipids surface model and 25.56 kcal mol<br>1 in the case of pure water model. It could be hypothesized that cell membrane surface environment could enhance this reaction by a neighboring catalyst effect.