Kun Li,Qin Zhang,Mei Wang,Rongrong Zhu,Xiaoyu Sun,Xianzheng Wu,Shi-Long Wang
Tanshinone IIA (Tan IIA) has the properties of cardiovascular protection, anti-inflammation, antioxidation and anticancer. Its light-induced instability has drawn our interests in its photochemistry. Therefore, laser flash photolysis herein was used to investigate the transient photochemistry of Tan IIA. Our results show that direct photoexcitation by 355 nm laser pulses or photosensitization by energy transfer can lead to the formation of the triplet state of Tan IIA ( 3 Tan IIA*). The triplet absorption spectrum and molar absorption coefficient, and ISC quantum yield were determined. Self-quenching of 3 Tan IIA* by its ground state was identified as an autooxidation reaction. 3 Tan IIA* was proved to react quickly with N , N -dimethylaniline, tert-butylhydroquinone and propyl gallate via electron transfer with the diffusion-controlled rate constants. One of the products with maximum absorption around 390 nm was assigned to the radical anion of Tan IIA. Our results indicate that 3 Tan IIA* is a reactive transient species and can be generated by photosensitization or direct photoexcitation. According to our results, the possible role of Tan IIA as a photosensitizer to induce potential phototoxicity via Type-II pathway in the presence of O 2 can be predicted.
Yixuan An,Lingdong Kong,Beibei Liu,Jiandong Shen,Yu Lu,Yuwen Wang,Jie Tan,Lin Wang
The heterogeneous conversion of SO 2 plays a crucial role in atmospheric sulfate formation. In recent years, it has been recognized that light-absorbing brown carbon can generate reactive oxygen species and enhance the oxidative capacity of the atmosphere. However, the influence of atmospheric brown carbon on the heterogeneous conversion of SO 2 on mineral oxide surfaces has not yet achieved sufficient attention. In this study, the impact of imidazole-2-carboxaldehyde (2-IC), a ubiquitous atmospheric brown carbon, on the heterogeneous conversion of SO 2 on hematite particle surfaces was investigated in the absence and presence of simulated solar irradiation by using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results indicated that 2-IC can significantly influence the heterogeneous reactivities of hematite. Under dry conditions, the heterogeneous reactivities decreased with the increase of the loaded 2-IC mass fraction in the absence of light, but in the presence of light, the higher reactivities were observed at an appropriate mass fraction range of 2-IC when compared to pure hematite, showing the promoting effects in this mass fraction range. Under the condition of 58% relative humidity, the heterogeneous reactivities in the absence of light decreased with the increasing mass fractions of 2-IC, and pure hematite showed the highest reactivity. However, in the presence of light, the heterogeneous reactivities increased first and then decreased with the increasing mass fractions of 2-IC, and the mixture containing 1×10 -4 % 2-IC showed the highest reactivity. Water molecules can renew surface reactive sites and facilitate the photosensitization reaction of 2-IC, and further enhance sulfate formation. A possible mechanism for the impact of 2-IC on the heterogeneous conversion of SO 2 on hematite is proposed. This study reveals a new pathway for brown carbon to enhance SO 2 conversion and sulfate formation in the atmosphere, providing new insights into its atmospheric impact.
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