Jianquan Shen

Active oxygen species (1O2, O2⋅−) generation in the system of TiO2 colloid sensitized by hypocrellin B

TiO2 semiconductor colloids have been successfully employed in environmental clean-up, antibacterial and bactericidal action under ultraviolet light due to its strong redox ability and high yield of active oxygen species (1O2, O2*-), *OOH) generation. Hypocrellin B, isolated from Hypocrella bambusae (B.et.Br) Sacc, a natural pigment with strong and broad absorption over the visible light region, was used in our work in an attempt to extend the photoresponse of TiO2 to visible light and maintain the high generation of active oxygen under visible light illumination. The formation of the HB-TiO2 chelate was characterized by UV-Vis and surface enhanced raman spectroscopy (SERS) and it was found that the chelate still had high efficiency of active oxygen generation. The possible generation mechanism was explored by Electron Paramagnetic Resonance (EPR) and time-resolved transient spectra techniques, showing that singlet oxygen (1O2) and superoxide radical anion (O2*-)) were produced via energy transfer and electron transfer, respectively. The application of HB-TiO2 chelate in environment protection and bacteria sterilization was implied.

Photodynamic action of amino substituted hypocrellins: EPR studies on the photogenerations of active oxygen and free radical species

A novel method has been employed to prepare 2-butylamino-2-demethoxy hypocrellin A (BADMHA) and 2-butylamino-2-demethoxy hypocrellin B (BADMHB). Both compounds exhibit stronger absorption at the phototherapeutic window (600-900 nm). The spin trapping and spin counteraction studies have shown that they are both efficient generators of the active oxygen (1O2, O2*-) in the aerobic condition. Under the anaerobic condition they generate non-oxygen free radical (semiquinone radical anion), and the active oxygen mechanism of photosensitization can be converted into non-oxygen free radical mechanism with the depletion of oxygen. The quantum yields of 1O2 generation of BADMHA and BADMHB are 0.46 and 0.44, respectively. Both are lower than those of their parent compounds HA and HB. But the productions of superoxide anion are enhanced significantly compared with HA and HB, indicating they are both favorable Type I phototherapeutic agents.

Active oxygen generation and photo-oxygenation involving temporfin (m-THPC)

Abstract The active oxygen generating ability of m -THPC, including the formation of singlet oxygen and superoxide anion radical species, was studied via spin trapping ESR spectroscopy. The mechanisms and the products associated with the self-sensitized photo-oxygenation of m -THPC in different solvents were also characterised with the aid of quenching experiments in tandem with UV–visible and HPLC analyses.

Photosensitization of TiO2 colloid by hypocrellin B in ethanol

Abstract Hypocrellin B (HB), a natural pigment, when adsorbed on colloidal TiO 2 can participate in the sensitization process by injecting electrons from its excited singlet and triplet states into the conduction band of the semiconductor. Upon excitation in its absorption band, 80% of the fluorescence emission of HB could be quenched by colloidal TiO 2 . Lifetime measurements and time-resolved absorption spectra gave the rate constant for the electron injection process from the excited singlet and triplet states of HB into the conduction band of the semiconductor as 6×10 8 and 1.3×10 6 s −1 , respectively. Analysis of the electron paramagnetic resonance spectra confirmed the generation of the cation radical of HB.

New long-wavelength perylenequinones: synthesis and phototoxicity of hypocrellin B derivatives

Five new derivatives of hypocrellin B were obtained from the reactions of hypocrellin B with ammonia and ethanolamine. Their photophysical and photochemical properties were investigated. The phototoxicity of one compound on AH cells irradiated with red light (lambda = 600-700 nm) was also studied. Their significantly enhanced red absorptivities at wavelengths longer than 600 nm and singlet oxygen-generating function qualify them as promising photodynamic therapy agents.

EPR investigation of the free radicals generated during the photosensitization of TiO2 colloid by hypocrellin B

The cation radical of dye produced from the interfacial electron transfer from a surface chelated dye to the conduction band of the colloidal TiO2 was studied by laser flash photolysis and electron paramagnetic resonance (EPR) techniques. The study employed hypocrellin B (HB), a natural photodynamic pigment with strong absorption over the visible light region, as a sensitizer and titanium dioxide as a colloid semiconductor. HB formed a chelate with this colloid semiconductor and exhibited a red-shifted and strongly enhanced absorption in the visible spectrum. Laser photolysis indicated that the electron excitation in the visible absorption band of the chelate resulted in extremely rapid and efficient electron injection from the excited triplet state of the dye into the conduction band of the semiconductor. A transient absorption of cation radical of HB at 570 nm was observed. The appearance of cation radical of HB was characterized by EPR spectrometry: the photoinduced EPR signal was not quenched by oxygen and its intensity decreased in the presence of NaI, a typical hole scavenger. The generation of conduction band electrons in HB-sensitized TiO2 system was also verified by the spin elimination of a stable cyclic nitroxide, 2,2, 6,6-tetramethylpiperidine-1-oxyl (TEMPO), and by the reduction of methyl viologen (MV2+) to its radical MV+·.

Chelation of hypocrellin B with zinc ions with electron paramagnetic resonance (EPR) evidence of the photodynamic activity of the resulting chelate.

Hypocrellin B (HB), a perylenequinone derivative, is an efficient phototherapeutic agent. The chelation of HB with Zinc ions (Zn2+) results in a metal chelate (Zn-HB) which exhibits considerable absorption (λmax = 612nm) in the phototherapeutic window. The structure of this chelate has been characterized by UV-Vis, IR and mass spectra. The redox potentials of the Zn-HB chelate were Eox = +1.1V (vs. SCE) and Ere = -0.7V (vs. SCE) as measured using the circle volt curve. The quantum yield of singlet oxygen generated by the Zn-HB chelate was 0.86, which both the electron spin trap (EPR) method and the chemical trap method show to be about 0.1 higher than that of its parent compound HB. In irradiated oxygen-saturated solutions of Zn-HB chelate, superoxide radical anions and hydroxyl radicals were detected by EPR spectroscopy using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping agent.

Langmuir monolayer of hypocrellins and their amino substituted derivatives at the air/water interface: Brewster angle microscopy study

Abstract The monolayer behavior at the air/water interface of the natural pigments hypocrellin A (HA), hypocrellin B (HB) and their butyl-amino derivatives (HAD, HBD) was investigated using Brewster angle microscopy (BAM). The results showed that stable monolayers were established with different phase transitions when the films were compressed. The collapse pressures of HA, HB, HAD and HBD were 30.3, 31.0, 34.8 and 35.5 mN m−1, respectively, which suggests that the butyl-amino substituents and the perylenoquinone rings of HAD and HBD are coplanar. The monolayer morphologies recorded by BAM showed differences among the images of these four compounds. Aggregation of HA, which may be attributed to the intermolecular hydrogen bonds between the two molecules, was observed. No obvious domains in the monolayers of HAD and HBD were observed using BAM, indicating that no large aggregations were formed in the monolayers.

Study of ultrafine particles-organic polymer thin films

Abstract Au ultrafine particles-polyethylene thin films and C 60 -polyethylene thin films have been prepared in an ionized-cluster-beam time-of-flight mass spectrometer system and analysed by transmission electron microscopy. We found that the small Au clusters with a size of 2.0–5.0 nm are suspended randomly in the polyethylene thin films, and the C 60 -polyethylene thin films are f.c.c. structures with a lattice constant a of 1.454 nm.