Cation–π interactions in competition with cation microhydration: a theoretical study of alkali metal cation–pyrene complexes

Abstract

Cation–π interactions were systematically investigated for the adsorption of H+ and alkali metal cations M+ to pyrene by means of Møller–Plesset perturbation theory (MP2) and density functional theory (DFT). The main aims were to determine the preferred adsorption sites and how the microhydration shell influences the adsorption process. The preferred adsorption sites were characterized in terms of structural parameters and energetic stability. Stability analysis of the M+–pyrene complexes revealed that the binding strength and the barrier to transitions between neighboring sites generally decreased with increasing cation size from Li+ to Cs+. Such transitions were practically barrierless (<<1 kcal/mol) for the large Rb+ and Cs+ ions. Further, the influence of the first hydration shell on the adsorption behavior was investigated for Li+ and K+ as representatives of small and large (alkali metal) cations, respectively. While the isolated complexes possessed only one minimum, two minima—corresponding to an inner and an outer complex—were observed for microhydrated complexes. The small Li+ ion formed a stable hydration shell and preferentially interacted with water rather than pyrene. In contrast, K+ favored cation–π over cation–water interactions. It was found that the mechanism for complex formation depends on the balance between cation–π interactions, cation–water complexation, and the hydrogen bonding of water to the π-system.

Mechanism of Nucleophilic Fluorination Facilitated by a Pyrene‐tagged Ionic Liquids: Synergistic Effects of Pyrene–Metal Cation π‐Interactions

“…These findings are in line with the promotion of S N 2 reaction rates by the O atoms of Lewis base such as bulky alcohols and oligoethylene glycols acting on the counter cation as described in our previous works . It is also worth noting that the metal counter‐cation Cs + lies above pyrene in both pre‐reaction complexes, suggesting that interactions between Cs + and the π electrons in pyrene play an important role in promoting the S N 2 fluorination reaction as discussed below.…”

A constricted opening in Kir channels does not impede potassium conduction

“…6 and Supplementary Movie 1) to replenish their hydration shell as they pass through. A recent study demonstrating that K + favors cation-π over cation-water interactions 50 , suggests that in KirBac3.1 (and in all human Kir3 and Kir6 subfamily members) a weakly bound hydration shell and the aromatic rings at the constriction are particularly favorable for partial dehydration.…”

Co-adsorption and interaction mechanism of cadmium and sulfamethazine onto activated carbon surface

“…Cadmium ions are first adsorbed by cation-π interactions and then diffuse to other adsorption sites. Although the cation-π interaction does not promote the adsorption of SMT, cadmium species adsorbed at other sites may form SMT-Cd 2+ -AC complexes with negatively charged SMT, and Cd 2+ ions at a certain concentration can enhance the adsorption of SMT [55].…”

“…To explore the influence of cadmium on the adsorption of SMT, different Cd 2+ concentrations (0, 25,35,45,55,65,75,100,150,350, 500, and 650 mg•L -1 ) were added to a 50 mg•L -1 SMT solution; then, 20 mg activated carbon was added and the water bath was shaken at a constant temperature (303K). To further explore the adsorption behavior of SMT and cadmium ions in a binary system, we selected a concentration ratio of 1:1 between antibiotic and cadmium ions.…”