Density functional theory study of the β-carotene radical cation and deprotonated radicals
Density functional theory study of the β-carotene radical cation and deprotonated radicals
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DOI：
10.1021/jp0643707
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发表时间：
2006-12-07
影响因子：
3.3
通讯作者：
Dixon, David A.
中科院分区：
文献类型：
--
作者：
Gao, Yunlong;Focsan, A. Ligia;Dixon, David A.
在密度泛函理论（DFT）水平上，采用B3 LYP/3- 21 G，SVWN 5/6- 31 G *，BPW 91/DGDZVP 2和B3 LYP/6- 31 G ** 对β-胡萝卜素自由基阳离子和去质子化中性自由基进行了研究.计算了这些物种的几何结构、总能量、自旋分布以及各向同性和各向异性超精细耦合常数。在类胡萝卜素自由基阳离子的环己烯环的双键处的甲基在5或5'处的去质子化产生最稳定的中性自由基，因为保留了π-共轭体系，而在链甲基的9或9'和13或13'处的不太稳定的去质子化导致共轭的显著畸变。预测的甲基超精细耦合常数为13-16 MHz的中性自由基是在良好的协议与以前的电子核双共振（ENDOR）光谱的光解β-胡萝卜素的固体支持。在极性水环境中的β-胡萝卜素自由基阳离子的DFT计算表明，极性环境不会引起显着的变化，从那些在孤立的气相分子的质子超精细常数。DFT计算的甲基质子超精细耦合常数小于7.2 MHz的协议与报道的自由基阳离子在光系统II（PS II）和那些发现在紫外光的情况下，自由基阳离子的二氧化硅-氧化铝基质。
The beta-carotene radical cation and deprotonated neutral radicals were studied at the density functional theory (DFT) level using different density functionals and basis sets: B3LYP/3-21G, SVWN5/6-31G*, BPW91/DGDZVP2, and B3LYP/6-31G**. The geometries, total energies, spin distributions, and isotropic and anisotropic hyperfine coupling constants of these species were calculated. Deprotonation of the methyl group at the double bond of the cyclohexene ring of the carotenoid radical cation at 5 or 5' produces the most stable neutral radical because of retention of the pi-conjugated system while less stable deprotonation at 9 or 9' and 13 or 13' of the chain methyl groups causes significant distortion of the conjugation. The predicted methyl hyperfine coupling constants of 13-16 MHz of the neutral radicals are in good agreement with the previous electron nuclear double resonance (ENDOR) spectrum of photolyzed beta-carotene on a solid support. DFT calculations on the beta-carotene radical cation in a polar water environment showed that the polar environment does not cause significant changes in the proton hyperfine constants from those in the isolated gas-phase molecule. DFT calculated methyl proton hyperfine coupling constants of less than 7.2 MHz are in agreement with those reported for the radical cation in photosystem II (PS II) and those found in the absence of UV light for the radical cation on a silica alumina matrix.