Stability of Like and Oppositely Charged Organic Ion Pairs in Aqueous Solution

Abstract

To investigate the stability of ionic pairs in aqueous solution, polarizable continuum-model (PCM) ab initio molecular orbital calculations were carried out. Ion pairs formed from three organic ions, methylacetate, methylammonium, and guanidinium, were treated. The methylacetate ion pair forms a stable complex when the two methyl groups are in contact. When the charged groups of methylacetate and methylammonium are in contact, this pair does not form a stable complex in aqueous solution. When the methyl group of methylacetate is in contact with that of methylammonium, the ionic groups are far apart, and a stable complex is not formed, even though the complex involves a strong attractive electrostatic interaction. The guanidinium pair forms a stable complex in aqueous solution at all conformations investigated in this work even though a strong repulsive electrostatic interaction is present in this complex.

Variations on the (3,4)-Net Motif in Organo-Zincophosphite Chemistry: Syntheses and Structures of (CN3H6)2·Zn3(HPO3)4·H2O and H3N(CH2)3NH3·Zn3(HPO3)4·H2O

“…The C12C1 separation of 3.37 A > is exceptionally small and compares well to the situation predicted by molecular dynamic studies (22) Selected bond distance/angle data are presented in Table 3. (Table 3).…”

Cation-cation contact pairing in water: Guanidinium

“…7 Recently, like-charge ion pairing of Gdm + , a counterintuitive analogue of ion-specific effects, has received considerable attention. Various computational methods, including ab initio, 8,9 Monte Carlo, 10 molecular dynamics (MD) simulations, 9,11,12 and quantum chemical calculations 13,14 have all indicated the existence of contact ion pairing between Gdm + ions in water. However, the direct experimental detection of this ion pairing remains elusive: neutron diffraction with isotopic substitution (NDIS) saykally@berkeley.edu geometry, 11 but subsequent investigation using broadband dielectric relaxation spectroscopy revealed only weak pairing for Gdm 2 CO 3(aq) solutions and no signs of ion-pairing with GdmCl (aq).…”

UV Resonance Raman and DFT Studies of Arginine Side Chains in Peptides: Insights into Arginine Hydration

“…This is consistent with previous reports on the hydration of the gdn compounds. 23-27 The formation of gdn dimers 23-25,50 possibly accounts for this low hydration level.…”