title: Microsolvation of Mg²⁺, Ca²⁺: strong influence of formal charges in hydrogen bond networks.
abstract: A stochastic exploration of the quantum conformational spaces in the microsolvation of divalent cations with explicit consideration of up to six solvent molecules [Mg (H₂O)n)](2+), (n=3, 4, 5, 6) at the B3LYP, MP2, CCSD(T) levels is presented. We find several cases in which the formal charge in Mg²⁺ causes dissociation of water molecules in the first solvation shell, leaving a hydroxide ion available to interact with the central cation, the released proton being transferred to outer solvation shells in a Grotthus type mechanism; this particular finding sheds light on the capacity of Mg²⁺ to promote formation of hydroxide anions, a process necessary to regulate proton transfer in enzymes with exonuclease activity. Two distinct types of hydrogen bonds, scattered over a wide range of distances (1.35-2.15 Å) were identified. We find that in inner solvation shells, where hydrogen bond networks are severely disturbed, most of the interaction energies come from electrostatic and polarization+charge transfer, while in outer solvation shells the situation approximates that of pure water clusters.
authors.affiliation: Instituto de Química, Universidad de Antioquia, AA 1226, Medellín, Colombia.
authors.forename: Juan David
authors.initials: JD
authors.lastname: Gonzalez
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Florez
authors.forename: Jonathan
authors.initials: J
authors.lastname: Romero
authors.forename: Andrés
authors.initials: A
authors.lastname: Reyes
authors.forename: Albeiro
authors.initials: A
authors.lastname: Restrepo
mesh_terms: D002118:Calcium / Q000737:chemistry*; D002413:Cations, Divalent; D006860:Hydrogen Bonding; D008274:Magnesium / Q000737:chemistry*; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011522:Protons; D011789:Quantum Theory; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D002413:Cations, Divalent; D011522:Protons; D014867:Water; D008274:Magnesium; D002118:Calcium