Molecular complexes of IQ and 4-hydroxy-coumarin: a mutagen–anti-mutagen system

Molecular complexes formed between a cooked food mutagen-carcinogen (2-amino-3-methylimidazo[4,5-f] quinoline, IQ) and a potent anti-mutagen (4-hydroxy-coumarin, 4HC) were synthesized and crystallized from a solution. The active functional groups in IQ and in 4HC that may involve in the formation of these complexes are investigated by UV–visible, infrared, and NMR spectroscopy. The geometrical conformations and heat of formation of IQ:4HC complexes were optimized by semi-empirical molecular orbital calculations. The experimental and theoretical results indicate that the complexes exist in multiple conformations. The energetically favorable ones are formed via hydrogen-bonding type of interactions between amino group in IQ and carbonyl group in 4HC, and also between quinoline-nitrogen (and imidazole-nitrogen) in IQ and hydroxyl group in 4HC. The observed complex formation could serve as a model for understanding the active molecular sites responsible for the initial mutagenic activity in cooked-food mutagens as well as the anti-mutagenic activity in coumarins.