ESR evidence of the photogeneration of free radicals (GDHB [rad]− , O 2[rad]− ) and singlet oxygen ( 1O 2) by 15-deacetyl-13-glycine-substituted hypocrellin B

• Published in: Biochimica et biophysica acta. General subjects Vol. 1472; no. 1; pp. 307 - 313
• Main Authors: Song, Yu-zhu, An, Jingyi, Jiang, Lijin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 18.10.1999
• Subjects: 15-Deacetyl-13-glycine-substituted hypocrellin B; ESR; Semiquinone anion radical; Singlet oxygen; Spin trapping; Superoxide radical anion; Semiquinone anion radical; 15-Deacetyl-13-glycine-substituted hypocrellin B; Superoxide radical anion; Singlet oxygen; ESR; Spin trapping
• ISSN: 0304-4165; 1872-8006
• DOI: 10.1016/S0304-4165(99)00137-3

15-Deacetyl-13-glycine-substituted hypocrellin B (GDHB) is a new type of hypocrellin derivative with an enhanced red absorption longer than 600 nm and water solubility. Visible light (>470 nm) irradiation of an anaerobic aqueous solution of GDHB, the formation of GDHB − was detected by an ESR method in the absence or presence of electron donor. When exposed to oxygen, superoxide anion radical and singlet oxygen were formed. The superoxide anion radical was generated by GDHB − via electron transfer to oxygen and this process was significantly enhanced by the presence of electron donors. Singlet oxygen ( 1O 2) was also formed in the photosensitization of GDHB in aerobic solution and 1,4-diazabicyclo [2,2,2] octane (DABCO), sodium azide (NaN 3) and histidine inhibited the generation of 1O 2. A 9,10-diphenyl antracene (DPA)-bleaching method was used to determine the quantum yield of 1O 2 generated from GDHB photosensitization. The 1O 2 quantum yield was estimated to be 0.65. With the depletion of oxygen, the accumulation of GDHB − would replace that of 1O 2. Evidence accumulated that the photodynamic action of GDHB may proceed via both type I and type II mechanisms and that a type II mechanism will be transformed into a type I mechanism as oxygen gets depleted.