Photodynamic potentiality of hypocrellin B and its lanthanide complexes

Abstract

The search for new photosensitizers with strong absorption bands, fast elimination from the body and high singlet oxygen generation quantum yield has been the subject of intensive research over the past two decades. Perylenequinonoid pigments, such as hypocrellins and hypericin, stand out among other photosensitizers due to their remarkable properties, which fulfil these requirements. Besides, it was shown that hypocrellin B complexes with metal ions possess even more notable optical and photodynamic properties. In this work, a study of the photosensitizer hypocrellin B and its complexes formed with the lanthanide ions europium, lanthanum and terbium, in ethanol and dimethyl sulfoxide solutions, was carried out by spectroscopic methods, with the purpose of verifying its potentiality for use in photodynamic therapy. The photobleaching of this molecule was also investigated, and our results show that, under experimental conditions, there is a significant decrease in HB emission intensity after about 30 min of exposure to white light. Moreover, lanthanide ions are able to modify hypocrellin B energy levels, as well as its radioactive decay probabilities. Infrared emission revealed the capacity of these complexes for generating singlet oxygen. Hypocrellin B complex with lanthanum in ethanol showed the best results among the studied complexes regarding optical characteristics of ideal photosensitizers, since it induced the larger redshift of about 30 nm, as well as enhanced HB singlet oxygen generation quantum yield of about 32%.