Complexation of water-soluble phosphorylated calixarenes with uracils. Stability constants and DFT study of the supramolecular complexes

Modification of the upper rim of the lipophilic cone-shaped tetrapropoxycalix [ 4 ]arene with hydrophilic phosphine oxide groups or phosphinic acid groups yielded nano-sized water-soluble calixarenes that form supramolecular complexes with uracils, including active pharmaceutical ingredients of 5-Fluorouracil and 5-Methyluracil drugs. Stability constants of the formed complexes in an aqueous-organic medium were determined by the HPLC method. The most favored structures of the calixarenes and their uracil complexes were optimized at the DFT level of approximation. In the most favored structures of all adducts, the uracil molecules coordinate via hydrogen bonding with the phosphorus-containing groups on the upper rim of the calixarene ligands.