Intramolecular h-bonding in the bay region of hypericin: an AM1 study

The semi-empirical quantum chemical method AM1 was employed to study intram olecular H-bonding in the bay region of hypericin (HYP). It was found that three isomers of HYP, which correspond to structures with 0.1, and 2 H-bond s in the bay region, readily interconvert, and that the isomer with two H-b onds is the predominant species in polar or nonpolar solvents. It was also shown that the formation of intramolecular H-bonding in the bay region faci litates proton dissociation and intramolecular proton transfer, providing a n alternative explanation for the experimentally observed transient species produced from HYP. (C) 2001 Elsevier Science Ltd. All rights reserved.