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

Abstract

We report a molecular dynamics study of the halide inclusion complexes X(-) subset L(4+) of a macrotricyclic tetrahedral receptor L(4+) built from four quaternary ammonium sites connected by six (CH(2))(n) chains. The hydrophilic/hydrophobic character of the complexes is investigated at a water/chloroform interface, represented explicitly and, despite their +3 charge and "spherical" shape, they are found to display amphiphilic behavior and to concentrate at the interface. The more lipophilic N-substituted CH(2)phi derivative, as well as less charged models are more surface active than the N-Me substituted host. In relation with the Hofmeister series, I(-) exo neutralizing counterions are compared with Cl(-) anions and are found to sit closer to the interface, which becomes more neutral. The "macrocyclic interfacial effect" is investigated by a comparison of L(4+) complexes with their acyclic counterparts. Finally, we address the question of anion binding selectivity by L(4+) and its L(1) (4+) and L(2) (4+) topological isomers. F(-) is too small for these three hosts, while I(-) is too big. According to free energy perturbation calculations, Cl(-) is preferred to Br(-), but somewhat more by L(1) (4+) than by L(4+).

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

“…According to simulations, smaller anions like ClO,i or quaternary ammonium NRt cations are also surface active [32], leading to a decrease in INTERFACIAL ACTIVITY OF 222 2 + 141 surface tension [51][52][53][54]. Even tetracharged tetrahedral ammonium hosts and their anion complexes are surface active, as shown by MD simulations [55], in keeping with the experimental observations of their transport properties through hydrophobic membranes [56]. The results obtained with the protonated 222 2 + cryptand agree with these features.…”

Rapid on-site detection of paraquat in biologic fluids by iodide-facilitated pinhole shell-isolated nanoparticle-enhanced Raman spectroscopy

“…22 The direct and selective detection of analytes in complicated matrix without any pretreatment is still a critical challenge in the on-site detection eld. [23][24][25] As some of the anions are basic and S 2À is the most basic with a pH of 11.7 when added to the sample at the concentration of 100 mM, we tested the inuence of pH and found that it didn't have an obvious effect on the SERS signal of paraquat in the range from 6.0 to 12.0 (Fig. Herein, we examined different common anions, and found that iodide is the most effective kind (Fig.…”

Theoretical Studies on Hydrogen Bonds in Anions Encapsulated by an Azamacrocyclic Receptor

“…Among the various anions, halides play an important role in environments and life [5]. Interactions between halides and synthetic receptors have been broadly investigated both experimentally and theoretically [2,[6][7][8][9][10][11][12]. Studies indicate that these interactions are mainly attributed to hydrogen bonding and electrostatic attractions.…”