Spectral and structural properties of carotenoids - DFT and thermochemical calculations

Revealing the chemical synergism in coloring tomatoes by Raman spectroscopy

“…It is suggested that these differences are due to the simultaneous increase in the anharmonicity of vibrations. [ 27 ]…”

“…It is suggested that these differences are due to the simultaneous increase in the anharmonicity of vibrations. [27] 3.4 | Raman spectroscopy applied to the characterization of tomato color markers…”

“…These vibrational stretching modes have been used to distinguish between conjugated polyenes according to the length of their conjugated unsaturated chains. [27,28] In this context, the Raman technique is suitable to characterize the biosynthetic precursor of lycopene, which starts with the tetraterpene phytoene containing three conjugated double bonds (n = 3), and stepwise desaturation (dehydrogenation) reactions convert phytoene to phytofluene (n = 5), ζ-carotene (n = 7), neurosporene (n = 9), lycopene (n = 11), and other carotenes and xanthophylls (n = 9). [29,30] Regarding the conjugated systems in hydroxycinnamic acids and flavonoids, characteristic Raman bands are attributed to the phenyl ring in the range between 1630 and 1550 cm À1 and phenol C-OH bending modes around 1360-1300 cm À1 , [31,32] which are distinct from carotenoids and therefore can be also identified in complex matrices such as that provided in a tomato.…”

“…[33] The combination of Raman spectroscopy and density functional theory (DFT) has provided reliable data on the electronic structure of molecules as a basis for vibrational assignments; it has already been used to analyze structural and spectral properties of the main carotenoids, such as lycopene (n = 11) and β-carotene (n = 9). [27,34] However, there is a gap in the literature concerning the application of vibrational spectroscopy in the characterization of biosynthetic precursors with less than nine carbon-carbon double bond conjugation, such as phytoene (n = 3), phytofluene (n = 5), [27] and ζ-carotene…”

Deciphering the Color Origin of Pink Conch Pearl Using Nondestructive Spectroscopies and DFT Calculations

“…It can be found that the peaks at 1516, 1298, 1204, 1128, and 1017 cm −1 vary with the different intensities of the colors and the intensity of these peaks will be stronger at the locations where the pink color is relatively intense. Due to the very high intensity of C=C and C-C stretching vibrations (as the result of numerous conjugated double bonds), the corresponding Raman peaks at 1516 cm −1 and 1128 cm −1 are clearly visible [26,27]. Especially, there is a relatively direct relationship between the Raman shifts of the two peaks and the chain length of polyene [26].…”