Thermodynamic characteristics of the formation of α- and β-cyclodextrin complexes with lumichrome, lumazine, and uracil in aqueous solution

Interactions of α- and β-cyclodextrins with lumichrome and its structural fragments, lumazine and uracil, were studied by means of solubility and 1H NMR spectroscopy. α-Cyclodextrin was found to have a weak complexing ability toward the studied compounds. It was established that β-cyclodextrin forms stable complexes with lumichrome and does not complex with lumazine and uracil. It was shown that only the benzene ring of lumichrome penetrates the β-cyclodextrin cavity, leading to a substantial increase in the solubility of lumichrome in water. We concluded that β-cyclodextrin complexation with lumichrome is highly exothermic due to the van der Waals interactions and hydrogen bonding between polar groups of the reagents.