Abstract
Calix[4]pyrrole and modified calix[4]pyrrole derivatives have been synthesized and characterized, namely calix[4] pyrrole [meso-octamethyl-calix [4] pyrrole], 1, meso-tetramethyl-tetrakis-(4-hydroxyphenyl) calix[4] pyrrole, 2, meso-tetramethyl-tetrakis-(3-hydroxyphenyl) calix[4] pyrrole, 3, mesotetramethyl-tetrakis-[(4-N, N-diethylacetamide) phenoxymethyl]calix[4] pyrrole, 4 and new mesotetramethyl-bis (diethylamino) ethoxybis-(4-hydroxyphenyl) calix[4] pyrrole, 5. Several analytical techniques (1H NMR, conductance measurements, and titration calorimetry) have been used to assess the interaction of calix[4]pyrrole derivatives and acid herbicides in acetonitrile. Chlorophenoxy acids have been selected out of groups of herbicides to carry out this investigation. 1H NMR investigations seem to indicate that the receptor 5 interacts with acid herbicides. Complexation studies in CD3CN show that NH and OH functionalities of the receptor 5 are the active sites of its interaction with herbicides. The composition of the anion complexes was established through conductance measurements. In all cases, 1: 2 (ligand: herbicides) complexes are formed between the receptor 5 with chlorophenoxy acids. The thermodynamics of anion complexation in acetonitrile is discussed. Excellent agreement was found between the data derived from nano-isothermal titration calorimetry and those derived by 1H NMR investigations and conductance measurements. For all the systems investigated, the complexation process between these acid herbicides and the receptor 5 was enthalpically controlled. The enthalpic and entropic contributions to the Gibbs energy associated with these processes are analysed.
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