尾-Carotene As a Lipophilic Scavenger of Nitric Oxide
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- 作者：Rui-Min Han ; Hong Cheng ; Ruopei Feng ; Dan-Dan Li ; Wenzhen Lai ; Jian-Ping Zhang ; Leif H. Skibsted
- 刊名：Journal of Physical Chemistry B
- 出版年：2014
- 出版时间：October 9, 2014
- 年：2014
- 卷：118
- 期：40
- 页码：11659-11666
- 全文大小：443K
- ISSN：1520-5207
文摘
The efficient bleaching following continuous bubbling of gaseous nitric oxide (NO鈥?/sup>) to 尾-carotene (尾-Car) dissolved in n-hexane under anaerobic conditions results from an initial addition of two NO鈥?/sup> followed by fragmentation coupled with further NO鈥?/sup> addition as shown by mass spectrometry (MS). Density functional theory (DFT) calculations demonstrated that hydrogen atom transfer (HAT) and electron transfer (ET) from 尾-Car to NO鈥?/sup> are strongly energetically unfavorable in contrast to radical adduct formation (RAF) followed by degradation. The results indicated the lowest energy for addition of the first NO鈥?/sup> at C7 with an activation free energy of 螖G鈮?/i> = 74.40 kJ mol鈥? and a rate constant of 0.56 s鈥?, followed by trans-addition of a second NO鈥?/sup> at C8 with 螖G鈮?/i> = 55.51 kJ mol鈥?. MS confirmed the formation of a dinitrosyl-尾-Car (596.6 m/z), and of a 尾-Car fragment (400.4 m/z) formed by C7/C8 bond cleavage and suggested to be of importance for progression of bleaching. Up to eight reaction products with increasing mass of 28 m/z are assigned to continuous addition of NO鈥?/sup> to the initially formed fragment forming nitroxides. Continuous wave photolysis of sodium nitroprusside (SNP) as a NO鈥?/sup> source dissolved together with 尾-Car in 4:1 (v/v) methanol:tetrahydrofuran gradually bleached 尾-Car. Nanosecond laser flash photolysis at 355 nm followed by transient absorption spectroscopy showed a 尾-Car derived intermediate with an absorption maximum around 420 nm in agreement with a prediction (425 nm) from time-dependent DFT (TDDFT) for the trans-C7,8 dinitrosyl adduct of 尾-Car. The NO鈥?/sup> adduct of 尾-Car decays with a rate constant of 鈭?07 s鈥? at 25 掳C.