• hydrogen polyoxide;
  • solvation effects;
  • QM/MM;
  • molecular dynamics;
  • ozone


Hydrogen polyoxides H2On have been theoretically studied in gas phase and in aqueous solution. Structures up to n = 4 have been detected experimentally. Larger systems are speculative till now but previous calculations predicted stable structures. Minimum energy geometries and formation enthalpies for n = 3–10 have been calculated in gas phase using high-level ab initio calculations that include DFT, QCISD, and CCSD(T) methods. Formation enthalpies are negative for n < 5, close to zero for n = 5, and positive for n > 5. They go up by ∼12–16 kcal/mol per O atom although the increase is not regular; it presents an oscillatory behavior that is clearly connected with odd/even effects reported for OO bond lengths. Computations in aqueous solution focus on free energies of solvation, solute–solvent hydrogen bonds strength, and solvent effects on polyoxide structure. We use two solvent models. A dielectric continuum implicit model is used to estimate free energies of solvation at an affordable cost. An explicit model is then used combining a QM/MM description of the solution and molecular dynamics (MD) simulations for polyoxides n = 3–6. The solute is described at the DFT level whereas solvent molecules are treated with an empirical force field. The analysis of the solute dynamics in solution shows that the systems are very good proton donors but poor proton acceptors. The structure with n = 5 exhibits a particular behavior that seems to be related with its larger statistical probability of forming intramolecular hydrogen bonds. Most bonds are lengthened in solution, especially the polar H[BOND]O bonds and the inner O[BOND]O bonds. Remarkably, the amplitude of O[BOND]O bond length fluctuations has been shown to depend primarily on its position along the chain, that is, the distance with respect to the terminal H[BOND]O bond, and less on chain length. For n = 6, the central O[BOND]O bond fluctuates between 1.2 and 1.9 Å. Chains beyond n = 6 should be extremely labile since fluctuations of the central O[BOND]O bonds should be even larger. Hence, if formed, the corresponding lifetimes should be extremely short. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010