Interactions of carbendazim and thiabendazole with β-cyclodextrin in aqueous solutions
The article evaluates the thermodynamic parameters (enthalpy, ΔH, entropy, ΔS, Gibbs free energy, ΔG, association constant, K) of formation of the complexes of a number of fungicides with nanomolecules - β-cyclodextrins (β-CD). The introduction describes the object of the study: the biologically active substances, fungicides carbendazim and thiabendazole widely used to reduce losses in agriculture caused by pathogenic microscopic fungi. These fungicides are organic hydrophobic substances, poorly soluble in water. The aim of the work was to find the possibility of replacing the currently used toxic organic solvents by water-soluble “nanocontainers” which due to the inclusion of non-polar fungicides significantly increase their solubility. Natural nontoxic cyclodextrins play a role of these nanocontainers. The incorporation of a fungicide (ligand) molecule in the inner cavity of a cyclodextrin (receptor) macromolecule leads to a significant increase in water solubility and resistance to harmful atmospheric influences, including UV radiation. The main part of the work presents the results of calorimetric titration of carbendazim with β-cyclodextrin in solutions of dimethylformamide and thiabendazole with β-cyclodextrin in aqueous-ethanol solutions. To assess the effect of β-cyclodextrin (β-CD) on the increase in water solubility of carbendazim and thiabendazolein, water solutions of carbendazim and thiabendazole were titrated with β-cyclodextrin in a VP-ITC calorimeter. The results indicate a spontaneous formation of stable inclusion complexes of β-cyclodextrin and fungicides with stoichiometry of 1 (β-CD) : 1 (carbendazim) and 1 (β-CD) : 1 (thiabendazole). The values for the constants of formation of the inclusion complex exceeded 103 M-1.The physical and chemical parameters (complex formation constants K, molar enthalpy ΔH and molar entropy ΔS) of the complexes were determined. The spectroscopic studies confirm the conclusion about a significant increase in the carbendazim and thiabendazole solubilities in water in the presence of β-cyclodextrin. In conclusion, it is noted that the results can be used to obtain new nontoxic nanosized water-soluble forms of fungicides used in medicine and agriculture.