title: Characteristics of CO3(2-)-water hydrogen bonds in aqueous solution: insights from HF/MM and B3LYP/MM MD simulations.
abstract: Two combined quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations, namely HF/MM and B3LYP/MM, have been performed to investigate the local hydration structure and dynamics of carbonate (CO(3)(2-)) in dilute aqueous solution. With respect to the QM/MM scheme, the QM region, which contains the CO(3)(2-) and its surrounding water molecules, was treated at HF and B3LYP levels of accuracy, respectively, using the DZV+ basis set, while the rest of the system is described by classical MM potentials. For both the HF/MM and B3LYP/MM simulations, it is observed that the hydrogen bonds between CO(3)(2-) oxygens and their nearest-neighbor waters are relatively strong, i.e., compared to water-water hydrogen bonds in the bulk, and that the first shell of each CO(3)(2-) oxygen atom somewhat overlaps with the others, which allows migration of water molecules among the coordinating sites to exist. In addition, it is observed that first-shell waters are either "loosely" or "tightly" bound to the respective CO(3)(2-) oxygen atoms, leading to large fluctuations in the number of first-shell waters, ranging from 1 to 6 (HF/MM) and 2 to 7 (B3LYP/MM), with the prevalent value of 3. Upon comparing the HF and B3LYP methods in describing this hydrated ion, the latter is found to overestimate the hydrogen-bond strength in the CO(3)(2-)-water complexes, resulting in a slightly more compact hydration structure at each of the CO(3)(2-) oxygens.
authors.affiliation: School of Chemistry, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima , Thailand. anan_tongraar@yahoo.com
authors.forename: Anan
authors.initials: A
authors.lastname: Tongraar
authors.forename: Pathumwadee
authors.initials: P
authors.lastname: Yotmanee
authors.forename: Apirak
authors.initials: A
authors.lastname: Payaka
mesh_terms: D002254:Carbonates / Q000737:chemistry*; D006860:Hydrogen Bonding; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D012996:Solutions; D014867:Water / Q000737:chemistry*
chemical_list: D002254:Carbonates; D012996:Solutions; D014867:Water