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Halide Anion Recognition in Water by an Hexaprotonated Octaaza‐Cryptand: A Molecular Dynamics Investigation
Author(s) -
Jost Pierre,
Schurhammer Rachel,
Wipff Georges
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20001201)6:23<4257::aid-chem4257>3.0.co;2-7
Subject(s) - cryptand , chemistry , counterion , solvation , halide , molecular dynamics , aqueous solution , ion , electrostatics , computational chemistry , chemical physics , inorganic chemistry , organic chemistry
Based on molecular dynamics simulations, we describe the F − versus Cl − complexation by an hexaprotonated cryptand L 6+ in aqueous solution, in order to elucidate their structures, solvation properties and the status of external halide counterions. In water, F − and Cl − simulated inclusive complexes adopt a structure somewhat different from the solid state structure of the F − complex: The anion binding involves two diammonium bridges only, and the accompanying counterions are dissociated from the +5 charged complex. A remarkable result is obtained for the dissociated L 6+ ,3F − ,3Cl − system, where spontaneous complexation of F − (the anion which forms the most stable complex with L 6+ ) takes place during the dynamics. The resulting complex is of facial type; this suggests that the equilibrium involves multiple binding modes and structures in aqueous solution. The question of F − /Cl − binding selectivity is investigated by free energy perturbations simulations which nicely reproduce the spectacular preference for F − over Cl − . Two different methodologies used for the treatment of electrostatics (standard versus Ewald calculations) yield similar conclusions.