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Spectroscopic Studies and Photodynamic Actions of Hypocrellin B in Liposomes ¶
Author(s) -
Yu Cailan,
Chen Shen,
Zhang Manhua,
Shen Tao
Publication year - 2001
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2001)0730482ssapao2.0.co2
Subject(s) - chemistry , liposome , photochemistry , photooxygenation , photosensitizer , quantum yield , aqueous solution , superoxide , disproportionation , singlet oxygen , fluorescence , oxygen , organic chemistry , catalysis , biochemistry , physics , quantum mechanics , enzyme
Hypocrellin B (HB), a lipid‐soluble natural pigment of perylenequinone derivative, is considered as potential photosensitizer for photodynamic therapy. Liposomes loaded with HB can constitute a simple model system, appropriate for better understanding the photodynamic action of HB in vivo. The steady‐state absorption and emission spectra, quantum yield and lifetime of fluorescence of HB incorporated into egg l ‐a‐phosphatidyl‐choline (EPC) liposome were examined. The photochemical properties (Type I and/or Type II) of HB have also been studied in aqueous dispersions of small unilamellar liposomes of EPC using electron paramagnetic resonance and spectrophotometric methods, respectively. The quantum yield of 1 O 2 generated by HB is ca 0.76 in chloroform solution and it did not change upon the incorporation of HB into liposomes of EPC. The superoxide anion radical was generated by the electron transfer from the anion radical of HB (HB ·− ) to oxygen. The disproportionation of O 2 ·− can generate H 2 O 2 and ultimately the highly reactive · OH via the Fenton reaction. It could be that the disproportionation proceeded too fast, so we could not detect O 2 ·− directly in aqueous dispersions of liposome EPC. Moreover, the self‐sensitized photooxygenation of HB embedded in liposomes was studied, and almost fully (87%) inhibiting this reaction of HB by p ‐benzoquinone (as the quencher of O 2 ·− ) in aqueous dispersion of liposome EPC indicated that the radical mechanism (Type I) might be mainly involved in this oxygenation. All these findings suggested that the photodynamic action of HB proceeded via both Type‐I and ‐II mechanisms, but Type‐I mechanism might play a more important role in the aqueous dispersion.