Do Picrate Anions Attract Each Other in Solution? Molecular Dynamics Simulations in Water and in Acetonitrile Solutions

Abstract

Molecular dynamics simulations performed on the Pic-···Pic- like-anion pair (Pic- = picrate = 2,4,6-trinitrophenoxide) show that its behavior is strongly dependent on the solvent. In water, the intimately stacked pair is stable, while in acetonitrile it dissociates. The stability of the stacked pair in water is confirmed by several methodological tests (choice of atomic charges; role of starting configuration; Ewald/no-Ewald) and by PMF (potentials of mean force) calculations. Simulations on (K+Pic-)2 and (K+Pic-)4 in water starting with unstacked anions lead to the formation of stacked dimers. The simulation of the dissolution of a (K+Pic-)27 fragment of the crystal also reveals a contrast in the behavior in water (formation of diluted stacks) compared to that in acetonitrile (formation of a “molten salt”). In the solid state, stacking arrangements of Pic- anions are common but diverse in form, supporting this theoretical prediction that the stacking of two like Pic- anions is common and highly environment dependent. Dimerization can be viewed as the primary stage of crystal nucleation. The results also have implications concerning the behavior of Pic- at liquid−liquid interfaces in electrochemical or assisted ion-transfer processes.

Interfacial Activity of the Diprotonated 222 Cryptand at the Water/"Oil" Interface Revealed by Molecular Dynamics Simulations

“…[25] while Pic-was described as in Ref. [26] reaction field (RF) correction, as described in Ref. [29].…”

Interfacial Behavior of Ionophoric Systems: Molecular Dynamics Studies on 18-Crown-6 and Its Complexes at the Water-Chloroform Interface

“…Some of 45 ANALYTICAL SCIENCES FEBRUARY 1998, VOL. 14 the molecules adopted different orientations and conformations.…”

“…14 can "attract each other" in water, due to solvation effects. 45 For the K + cations, distinct behavior can be noticed, in relation with the counterions and the treatment of liquid boundaries. In the no-Ewald calculations, the right side on water (Fig.…”

Dimethylsuphoxide and its roles in the coordination chemistry of the uranyl ion

“…Although this stacking involves various forms of projection of one picrate unit upon another, in a global sense it can be understood in terms of optimising the approaches, typically to within~3.5 Å, of centres of relatively positive charge in one picrate to centres of relatively negative charge on another [33,34]. More specifically, it is often seen to involve the close approach of a nitro-group oxygen atom of one picrate to the nitro-group nitrogen atom of another.…”