A Computational Study of the Hydration of the OH Radical

Abstract

The OH radical is an important species in natural and man made aqueous environments, influencing diverse processes such as the oxidation of atmospheric pollutants or the development of some diseases. Yet, little is known about the solvation thermodynamics and structure of the hydration shell of OH. Here, we present a computational study of the hydration of OH in small H2 n +1O n +1 (n = 1−5) clusters. We begin by comparing three different quantum chemical methods, UMP2, BLYP, and BHLYP. We find that BLYP does not describe correctly the OH−H2O interaction as compared to the current MP2 or other high ab initio calculations found in the literature. BLYP favors the formation of hemibonded H2O−OH structures, whereas MP2 predicts that hydrogen-bonded complexes are more stable. Mixing Becke's exchange functional with 50% Hartree−Fock exchange improves the DFT description, yielding results that are similar to those from MP2. We find that the H2 n +1O n +1 clusters form structures in which all species are donors and acceptors in hydrogen bonded rings similar to those of pure water clusters. OH participates in two or three hydrogen bonds. Structures in which OH forms more than three hydrogen bonds are not favored energetically. We report values of energy, enthalpy, and Gibbs free energy of complexation in the gas phase, OH(g) + H2 n O n (g) → H2 n +1O n +1(g), as a function of cluster size. We also estimate values of thermodynamic parameters of hydration in the liquid phase from OH(g) + H2 n O n (aq) → H2 n +1O n +1(aq), where the energies of the aqueous species, H2 n O n (aq) and H2 n +1O n +1(aq), are calculated by means of a hybrid solvation model in which part of the solvent is treated explicitly and the long-range interactions are added into the Hamiltonian by means of the PCM version of the self-consistent reaction field. The implications of our work as well as the accuracy of the results are also discussed.

The hydration of the OH radical: Microsolvation modeling and statistical mechanics simulation

“…12 Several works have been carried out to analyze the interactions of the OH radical with the water molecule [13][14][15][16] and the microsolvation of the radical in water clusters. 12,17 In the present paper we report a theoretical study of the hydration of the OH radical. To carry out this study two approaches have been adopted: microsolvation modeling and Monte Carlo statistical mechanics simulations.…”

Molecular dynamics study of the hydration of the hydroxyl radical at body temperature

“…2,3 On the other hand, the properties of the hydroxyl radical are commonly exploited by the immune system and prove advantageous in targeted anticancer therapy. [8][9][10][11][12][13][14][15][16][17][18][19] They include ab initio studies of OH in small clusters, mostly consisting of o10 water molecules, density functional theory (DFT) molecular dynamics simulations of OH-(H 2 O) 31 complexes, as well as classical molecular dynamics (MD) and Monte Carlo (MC) simulations. 5,6 Being involved in various chemical and biochemical mechanisms, the hydroxyl radical has become a target of scientific investigations.…”

“…5,6 Being involved in various chemical and biochemical mechanisms, the hydroxyl radical has become a target of scientific investigations. 10,12 The location of OH in clusters of such size is of primary interest for atmospheric chemistry, since the oxidizing activity of OH towards air pollutants, such as volatile organic compounds (VOCs) and methane, determines their lifetime and concentration in the troposphere. 7 The past decade has yielded a lot of computational studies on the hydroxyl radical in liquid water.…”

Classical molecular-dynamics simulation of the hydroxyl radical in water

“…[5][6][7][8][9][10][11][12][13][14][15][16] Hamza et al 5 studied the proton subtraction of the C4 * of a DNA sugar using an ab initio method. In this case, the charge of the OH 0 is 0.44e for the proton, and −0.44e for the oxygen.…”

“…They obtained three structures, in two of them the OH 0 acts as proton donor, and in a third it acts as proton acceptor. Hamad et al 7 studied the hydration of OH 0 in small H 2n+1 -O n ͑n =1-5͒ clusters using different quantumchemical methods. The binding energy is the largest when OH 0 acts as proton donor.…”