摘要
The molecular structural and Raman spectroscopic characteristics of fl-carotene and lycopene are investigated by density functional calculations. The effects of molecular structure and solvent environment on the Raman spectra are analyzed by comparing the calculated and measured results. It is found that the B3LYP/6-31G（d） method can predict the reasonable result for β-carotene, but the vl Raman activities of lycopene overflow at all the used theo- retical methods because of the longer conjugation length in β-carotene impedes the delocalization of ~r-electrons The calculated results indicate that the rotation of β-rings shortens the effective conjugation length, and results in higher frequency and lower activity of the vl mode in /q-carotene than lycopene. The measured vl bands of β-carotene and lycopene shift respectively to higher and lower frequencies in solution compared with that in crystals since the crystal packing forces can lead to different conformational variations in the carotenoids molecules. The polarized continuum model theoretical analysis suggests that solvent has slight （significant） effects on the Raman frequencies （intensities） of both carotenoids.
The molecular structural and Raman spectroscopic characteristics of fl-carotene and lycopene are investigated by density functional calculations. The effects of molecular structure and solvent environment on the Raman spectra are analyzed by comparing the calculated and measured results. It is found that the B3LYP/6-31G（d） method can predict the reasonable result for β-carotene, but the vl Raman activities of lycopene overflow at all the used theo- retical methods because of the longer conjugation length in β-carotene impedes the delocalization of ~r-electrons The calculated results indicate that the rotation of β-rings shortens the effective conjugation length, and results in higher frequency and lower activity of the vl mode in /q-carotene than lycopene. The measured vl bands of β-carotene and lycopene shift respectively to higher and lower frequencies in solution compared with that in crystals since the crystal packing forces can lead to different conformational variations in the carotenoids molecules. The polarized continuum model theoretical analysis suggests that solvent has slight （significant） effects on the Raman frequencies （intensities） of both carotenoids.
基金
This work was supported by the National Natural Science Foundation of China （Nos. 21003033, 11004076, 10774034 and 21173063）, the China Post- doctoral Science Foundation （No. 20100481006）, the Guangxi Natural Science Foundation （No. 2012GXNSFBA053012）, and the Research Foundation of Education Bureau of Guangxi （No. 200103YB 140）.
