A Simple Additive Potential Model for Simulating Hydrogen Peroxide in Chemical and Biological Systems.

Hydrogen peroxide (HO) has numerous industrial, environmental, medical, cosmetic, and biological applications. Given its importance, we provide a simple model as an alternative to experiment for studying the properties of pure liquid HO and its concentrated aqueous solutions, which are hazardous, and for understanding the biological roles of HO at the molecular level. A four-site additive model is calibrated for HO based on the ab initio and experimental properties of the gaseous monomer and the density and heat of vaporization of liquid HO at 0 °C. Our model together with the TIP3P water model reproduce the ab initio binding energies of (HO) , HO· nHO, and nHO·HO clusters ( m = 2, 3 and n = 1, 2) calculated at the MP2 level using the 6-311++G(d,p) or the 6-311++G(3df,3pd) basis set. It yields structure, the self-diffusion coefficient, heat capacity, and densities at temperatures up to 200 °C of the pure liquid in good agreement with experiment. The model correctly predicts the hydration free energy of HO and reproduces the experimental density of aqueous HO solutions at 0-96 °C. Investigation of the solvation of HO and HO in aqueous HO solutions reveals that, as in the gas phase, HO is a better H-bond donor but poorer acceptor than HO and the bonding stability follows the order O-H···O > O-H···O ≥ O-H···O > O-H···O. Stronger H-bonding in HO/HO mixtures than in the pure liquids is consistent with exothermic heats of mixing and explains why the observed density and vapor pressure of the aqueous solutions are higher and lower, respectively, than expected from ideal mixing. Results also show that HO adopts a skewed equilibrium geometry in gas and liquid phases but more polar cis and nonpolar trans conformations also are accessible and will stabilize HO in environments of different polarity. In sum, our simple model presents a reliable tool for simulating HO in chemistry and biology.