Interactions of uracil and its derivatives with polyfunctional acids

The previously obtained experimental and quantum chemical data on the composition, structure, stability, and thermodynamic properties of complexes of uracil and a series of its derivatives with different high- and low-molecular-weight carboxylic acids are summarized and analyzed. Interactions of uracil derivatives with polyfunctional acids (apple pectin, the oxidized fraction of apple pectin, the oxidized fraction of arabinogalactan from Siberian larch, as well as succinic, fumaric, 4- and 5-aminosalicylic acids) were studied by spectroscopic methods. The compositions and stability constants of the resulting complexes were determined. Electron-donating substituents at position 5 of 6-methyluracil increase the stability of its complexes with polyfunctional acids. The temperature dependence (293–323 K) of stability constants was studied using eleven complexes, and the thermodynamic parameters of the complexation were calculated. Quantum chemical calculations demonstrated that COOH groups of acids are involved in complexation with uracils. The H—N(1)—C(2)—O(7) moiety of uracil molecules is the most preferable for complexation with polyfunctional acids.