Computational and experimental investigations of supramolecular assemblies of p-sulfonatocalix[4]arene organized by weak forces

Thermodynamics of Supramolecular Associations with Macrocyclic Water-Soluble Hosts

The thermodynamic study of the complexation of the β-cyclodextrins and p-sulfonatocalix[n]arenes (CnS) with the 4-aminoazobenzene was reported and was carried out by molecular dynamics simulations. We determined the whole thermodynamic properties (K, Δr G°, Δr H°, and TΔr S°) using the potential of mean force (PMF) technique and more precisely the adaptive biasing force method. Depending on both the nature of the host molecule and the pH of the solution, the PMF profiles present different shapes and energy minima. Considering the complexity of these PMF profiles, we are also interested in the structural properties of these associations. Hence, we calculated hydrogen bonds, Lennard-Jones and electrostatic energies, the number of atoms of the guest molecule inserted inside the cagelike host molecule, and the number of water molecules expelled from the cavity.

Associations of Water-Soluble Macrocyclic Hosts with 4-Aminoazobenzene: Impact of pH

An investigation of the pH effect on the inclusion complexes of β-cyclodextrins and calixarenesulfonates with 4-aminoazobenzene was conducted both by experiments and molecular simulations. The whole thermodynamic characterizations of the association between hosts and 4-aminoazobenzene ( K, Δ_r G⁰, Δ_r H⁰, and TΔ_r S⁰) were determined by UV-visible spectroscopy. β-Cyclodextrin inclusion complexes are not affected by pH change unlike those obtained with calixarenes. All the studied systems were enthalpically favored. Nevertheless, the entropic behavior is different depending on the host. In order to interpret these experimental results, molecular simulations were used to calculate the number of atoms inserted into the cage-like host compounds and the number of water molecules expelled from the cavity.

Determining the effects of salt, buffer, and temperature on the complexation of methylated ammonium ions and methyllysines by sulfonated calixarenes

Sulfonated calixarenes have long been used as effective binders of ammonium ions in aqueous solution. Recently, the utility of sulfonated calix[4]arenes and calix[6]arenes as specific agents for binding biologically important ammonium ions, and especially post-translationally methylated amino acids, peptides, and proteins, has suggested that they might have important roles to play in the control and understanding of biological pathways. We report here binding data in various buffer systems that attempt to shed light on the roles of buffer and salt in the recognition processes of these hosts. We also report studies on trimethyllysine binding that explore the effects of near physiological salt concentrations and temperatures. These studies provide an understanding of disparate data on these systems and also demonstrate the ability of a sulfonated calixarene to bind trimethyllysine strongly under aqueous conditions that closely replicate the salt concentrations, pH, and temperature of the human body.

A B3LYP and MP2 theoretical investigation into host-guest interaction between calix[4]arene and Li(+) or Na (+)

The DFT-B3LYP and MP2 methods with 6-311G** and 6-311++G** basis sets have been applied to study the complexation energies of the host-guest complexes between the cone calix[4]arene and Li(+) or Na(+) on the B3LYP optimized geometries. A comparison of the complexation energies obtained from the MP2(full) with those from MP2(fc) method is also carried out. The result shows that it is essential to introduce the diffuse basis set into the geometry optimizations and complexation energy calculations of the alkali-metal cation-pi interaction complexes of calix[4]arene, and the D (e) values show a maximum of 21.13 kJ mol(-1) (14.45% of relative error) between the MP2(full)/6-311++G** and MP2(fc)/6-311++G** method. For Li(+) cation, the complexation is mainly energetically stabilized by the lower rim/cation (namely O-Li(+)) interaction. However, binding energies and NBO analyses confirm that Na(+) cation prefers to enter the calix[4]arene cavity and the cation-pi interaction is predominant, which contradicts the previous low-level theoretical studies. Furthermore, the complexation with Li(+) is preferred over that with Na(+) by at least 12.70 kJ mol(-1) at MP2(full)/6-311++G**//B3LYP/6-311++G** level.