β-Carotene as a lipophilic scavenger of nitric oxide

TY - JOUR

T1 - β-Carotene as a lipophilic scavenger of nitric oxide

AU - Han, Rui-Min

AU - Cheng, Hong

AU - Feng, Ruopei

AU - Li, Dan-Dan

AU - Lai, Wenzhen

AU - Zhang, Jian-Ping

AU - Skibsted, Leif Horsfelt

PY - 2014/10/9

Y1 - 2014/10/9

N2 - The efficient bleaching following continuous bubbling of gaseous nitric oxide (NO∗) to β-carotene (β-Car) dissolved in n-hexane under anaerobic conditions results from an initial addition of two NO∗ followed by fragmentation coupled with further NO∗ addition as shown by mass spectrometry (MS). Density functional theory (DFT) calculations demonstrated that hydrogen atom transfer (HAT) and electron transfer (ET) from β-Car to NO∗ 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∗ at C7 with an activation free energy of δG≠ = 74.40 kJ mol-1 and a rate constant of 0.56 s-1, followed by trans-addition of a second NO∗ at C8 with δG≠ = 55.51 kJ mol-1. MS confirmed the formation of a dinitrosyl-β-Car (596.6 m/z), and of a β-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∗ to the initially formed fragment forming nitroxides. Continuous wave photolysis of sodium nitroprusside (SNP) as a NO∗ source dissolved together with β-Car in 4:1 (v/v) methanol:tetrahydrofuran gradually bleached β-Car. Nanosecond laser flash photolysis at 355 nm followed by transient absorption spectroscopy showed a β-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 β-Car. The NO∗ adduct of β-Car decays with a rate constant of ∼107 s-1 at 25 °C.

AB - The efficient bleaching following continuous bubbling of gaseous nitric oxide (NO∗) to β-carotene (β-Car) dissolved in n-hexane under anaerobic conditions results from an initial addition of two NO∗ followed by fragmentation coupled with further NO∗ addition as shown by mass spectrometry (MS). Density functional theory (DFT) calculations demonstrated that hydrogen atom transfer (HAT) and electron transfer (ET) from β-Car to NO∗ 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∗ at C7 with an activation free energy of δG≠ = 74.40 kJ mol-1 and a rate constant of 0.56 s-1, followed by trans-addition of a second NO∗ at C8 with δG≠ = 55.51 kJ mol-1. MS confirmed the formation of a dinitrosyl-β-Car (596.6 m/z), and of a β-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∗ to the initially formed fragment forming nitroxides. Continuous wave photolysis of sodium nitroprusside (SNP) as a NO∗ source dissolved together with β-Car in 4:1 (v/v) methanol:tetrahydrofuran gradually bleached β-Car. Nanosecond laser flash photolysis at 355 nm followed by transient absorption spectroscopy showed a β-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 β-Car. The NO∗ adduct of β-Car decays with a rate constant of ∼107 s-1 at 25 °C.

U2 - 10.1021/jp5075626

DO - 10.1021/jp5075626

M3 - Journal article

C2 - 25226353

SN - 1520-6106

VL - 118

SP - 11659

EP - 11666

JO - The Journal of Physical Chemistry B

JF - The Journal of Physical Chemistry B

IS - 40

ER -