Halide Anion Recognition in Water by an Hexaprotonated Octaaza-Cryptand: A Molecular Dynamics Investigation

Abstract

Based on molecular dynamics simulations, we describe the F- versus Cl- complexation by an hexaprotonated cryptand L6+ 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 L6+,3F- ,3Cl- system, where spontaneous complexation of F- (the anion which forms the most stable complex with L6+) 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.

Macrotricyclic quaternary tetraammonium receptors: Halide anion recognition and interfacial activity at an aqueous interface. A molecular dynamics investigation

“…Useful references can be found in ref. 54, and in more recent work concerning, for example, halide anion binding by calixarenes in organic solution,39 or halide anion complexation by an hexaprotonated cryptand in water 55. Here, we report the first simulation at a liquid liquid interface, which point to the importance of interfacial phenomena in anion recognition, extraction, and transport processes by hydrophobic receptors.…”

M3+ Lanthanide Chloride Complexes in “Neutral” Room Temperature Ionic Liquids: A Theoretical Study

“…39 For Cl -, we used the same van der Waals parameters as for the Cl(TCA) atoms (R* ) 1.943 Å, ) 0.265 kcal/mol), 22 for all chlorine atoms potentially coordinated to a given M 3+ cation have the same size. Tests with a somewhat bigger anion (noted Cl hyd ; R* ) 2.495 Å, ) 0.107 kcal/mol) developed for free energies of hydration 40,41 were performed on the LaCl 6 3complex in solution. The 1-4 van der Waals interactions were scaled down by 2.0 and the 1-4 Coulombic interactions were scaled down by 1.2, as recommended by Cornell et al 42 The pure liquids and solutions were simulated with 3D-periodic boundary conditions.…”

Proton-Coupled Electron Transfer

“…The decay mechanism involves excitedstate intramolecular proton transfer (ESIPT) through a conical intersection. [548][549][550][551][552][553][554] Complete active space self-consistent-field (CASSCF) calculations on 2-(2′-hydroxyphenyl)benzotriazole without the fused benzo group, BZT2, reinforce a mechanism involving (1) excitation to give an internal charge transfer state (ICT), ( 2) intramolecular proton transfer involving twisted geometries, and (3) rapid decay from the keto state following proton transfer (Figure 38). on the ketone and the phenol, pointing to HAT at the ketone and EPT at the phenol in the quenching step.…”