Structure and stability of the N-hydroxyurea dimer: Post-Hartree–Fock quantum mechanical study

Abstract

The potential energy surface (PES) search of the N-hydroxyurea dimer was searched with second-order Møller–Plesset perturbation theory (MP2) and the 6-31G(d,p) basis set. Eight local minimum energy structures have been found. Four of them have relatively strong (ΔE∼−10 to −13 kcal/mol) intermolecular interactions and the others are moderately strongly interacting species (ΔE∼−3 to −7 kcal/mol). Final estimation of interaction energies was performed using the larger 6-311G(df,pd) and 6-311G(2df,2pd) basis sets. The predicted interaction energies are ΔE=−14.26 kcal/mol and −3.43 kcal/mol for the strongest and the weakest interacting forms of the studied complex, respectively, at the MP2/6-311G(2df,2pd)//MP2/6-31G(d,p) level of theory. The self-consistent field (SCF) interaction energy decomposition indicates the important influence of the deformation term magnitude on ΔE(SCF). The calculated electron correlation contribution to ΔE(MP2) depends on the geometry of the system and varies from −0.5 to −5 kcal/mol. The estimated influence of water on the stability (free energy of hydration) of N-hydroxyurea dimers using the self-consistent isodensity polarized continuum (SCI-PCM) model of solvation varies from ∼−11 kcal/mol to ∼−21 kcal/mol. The forms predicted to be more strongly interacting species in gas phase are less influenced by hydration than the more weakly interacting ones.