Weak Interactions of the Isomers of Phototrexate and Two Cavitand 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.

Anodic Polymerization of Phenylphenols in Methyl Isobutyl Ketone and Mesityl Oxide: Incorporation of a Cavitand into the Layers Formed for Sensing Phenols in Organic Media

The electropolymerization of three phenylphenol isomers was studied in methyl isobutyl ketone and mesityl oxide, and the remarkable differences highlighted the importance of the carbon–carbon double bond in mesityl oxide. In the case of each substrate, a brownish deposit formed during the electrooxidation. The obvious difference between the polymers formed from the two solvents was recognized via voltammetric signal enhancement of 4-methoxyphenol and 4-chlorophenol, and it was only observed in the case of mesityl oxide. The experiments highlighted that incorporation of a cavitand with biphenyl groups on the upper rim of the polymers of phenylphenols improved the results to a small extent. The cavitand was, itself, electroactive without any fouling effect. As 2-phenylphenol is by far the cheapest of the three isomers, a cavitand was incorporated into its polymer, which was exploited to solve analytical problems while mesityl oxide was used as solvent. Useful quantifications were achieved in organic solvents; however, it failed under aqueous conditions due to the high hydrophobicity of the deposit. Application of differential pulse voltammetry for 4-methoxyphenol and 4-chlorophenol gave detection limits of 9.28 and 50.8 μM in acetonitrile, respectively. This procedure resulted in the immobilization of cavitand derivatives onto the electrode’s surface, and the layer formed offered selective sensing of phenols by electrochemical methods.