Competitive thermodynamic and kinetic processes during dissociation of some host-guest complexes of calix[4]arene derivatives

Voltammetric and Fluorimetric Studies of Dibenzoylmethane on Glassy Carbon Electrodes and Its Interaction with Tetrakis (3,5-Dicarboxyphenoxy) Cavitand Derivative

Due to the medical importance of dibenzoylmethane, one of the aims of the study was to find an appropriate packing material and a biologically friendly co-solvent to help its introduction into living systems. Accordingly, redox properties of dibenzoylmethane were investigated on glassy carbon electrodes in acetonitrile and in 1-propanol with cyclic voltammetry, and showed a diffusion-controlled process. In the anodic window, an oxidation peak appeared at around 1.9 V in both solvents. Cycling repeatedly between 0 and 2 V, the reproducibility of this peak was acceptable, but when extending the window to higher potentials, the electrode deactivated, obviously due to electrode material. The addition of the investigated tetrakis(3,5-dicarboxyphenoxy) cavitand did not significantly change the voltammograms. Further electrochemical experiments showed that the coexistence of water in acetonitrile and 1-propanol drastically reduces the solubility of dibenzoylmethane. Moreover, very rapid electrode deactivation occurred and this fact made the use of electrochemical methods complicated. Considering that both the cavitand and dibenzoylmethane are soluble in dimethyl sulfoxide, the interaction of these species was investigated and formation of stable complexes was detected. This observation was verified with fluorescence quenching studies. The mixture of water and dimethyl sulphoxide also dramatically improved the solubility of the cavitand-dibenzoylmethane complex at high excess of water. The addition of cavitand improved the solubility of dibenzoylmethane, a property which supports the application of dibenzoylmethane in therapy.

Thermodynamic description of bis-urea self-assembly: competition between two supramolecular polymers

Supramolecular polymers are chains of small molecules held together through reversible noncovalent interactions. In general, a given monomer self-assembles into a single type of supramolecular polymer. However, in a few cases, two different self-assembled structures can coexist; this yields interesting responsive systems. To improve the understanding of these systems, we report an association model describing the self-assembly of a supramolecular polymer into two competing forms. The parameters controlling the system were measured by high sensitivity differential scanning calorimetry and isothermal titration calorimetry in the case of a hydrogen-bonded bis-urea supramolecular polymer solution in toluene. The model enables us to compute the proportion and length of all components in the system at any temperature and concentration. The results of these calculations are in agreement with the experimental phase diagram and with independent viscosity measurements.