Water mediated attraction between repulsive ions: A cluster-based simulation approach

Abstract

Could two like ions be attractive to each other in the presence of water? To address this question and to further interrogate the intriguing solvent effects at a molecular level on multiply charged species, a "bottom-up" simulation approach was formulated, from which the inter-ionic potential of mean force and other properties were monitored closely with the gradual addition of the water molecules. This approach was first tested on a commonly studied ion pair (namely, Na+ and Cl-), where excellent agreement with the published bulk-phase data was found. Further application of this approach to the like-ion pair indicated that an attractive interaction between two anions or two cations can be induced by the addition of an appropriate number of water molecules. This result corroborates a recent experimental report of an intriguing folding of a dianionic polymer into a more compact structure with the addition of water molecules in gas phase as well as previous theoretical findings of possible attraction between like-ion pairs in bulk aqueous phases.

Ion Pairing of the Neurotransmitters Acetylcholine and Glutamate in Aqueous Solutions

“…Nevertheless, one could consider a water-mediated attraction between repulsive ions as it is discussed in the literature. 85,100 However, as found, 60,106 in the case of NH 3 + −NH 3 + interaction, such an attraction is also impossible because both the hydration of the ammonium group and the formed N−H•••OH 2 hydrogen bonds are weak. Thus, the obtained As to the Glu − −Glu − binding via the COO − groups, this could be realized by means of the interactions of "backbone" carboxylate oxygen with "backbone" or "side-chain" carboxylate oxygen, and "side-chain" carboxylate oxygen with "sidechain" carboxylate oxygen.…”

“…One of the issues debated actively in the literature is a possibility of cation–cation or anion–anion pairing. − Despite the obvious Coulomb repulsion of like-charged ions, an effective attraction between some of the like-charged ions is discussed in these papers. This phenomenon was detected in the diffraction experiments, − computer simulations, − and from the results of calculations in the framework of the integral equation theory. , The attraction between the like-charged ions was established for monovalent and multivalent ions in water, including the biologically relevant ions such as the amino acid arginin, , guanidinium ion, − , or zwitterionic dipeptides . Attempts are made to explain this “illogical” ion behavior.…”

“…These PMF features are an indicator for impossibility of the attractive Glu – –Glu – interactions by means of the NH 3 + groups, that is, these Coulomb interactions can be only repulsive. Nevertheless, one could consider a water-mediated attraction between repulsive ions as it is discussed in the literature. , However, as found, , in the case of NH 3 + –NH 3 + interaction, such an attraction is also impossible because both the hydration of the ammonium group and the formed N–H···OH 2 hydrogen bonds are weak. Thus, the obtained data does not indicate a possibility for anion–anion pairing via the ammonium groups.…”

Interactions between Keggin Anions in Water: The Higher Their Charge, the Higher Their Condensation? A Simulation Study

“…A key stabilizing feature of the Cl – ··· Cl – contact ion pair stems from bridging water molecules, which form Cl – (HOH) n Cl – clusters in aqueous solution and in solid structures 41. Even in the gas phase, the stabilization brought about by a few H 2 O molecules overcomes the Coulomb repulsion between the anions, according to quantum mechanics (QM) calculations41 and to recent simulations on gradually hydrated dimers 42. The smaller F – anions display stronger hydrogen bonds with water and form a more stable F – (HOH) m F – aggregate in water43 and in the gas phase 41.…”

An innovative simulation approach for water mediated attraction based on grid computing

“…To further this theoretical research, a new technique was proposed in [13], which enables an efficient and quantitatives evaluation of the solvation effects as well as the effective interactions or potentials of mean force (PMFs) between ions with respect to their seperation and the number of water molecules added. It allows the calculation of nucleation properties over a wide range of thermodynamic conditions but the simulation is computation expensive.…”