Effect of solution concentration on the structured order and optical properties of short-chain polyene biomolecules

Abstract

We have measured the Raman spectra and UV-Vis absorption spectra of linear polyene biomolecules (β-carotene and lycopene) in CS 2 at low concentrations (10 −6 -10 −10 mol/L). With decreasing concentration, all the carbon-carbon vibrations form a coherent mode in ordered β-carotene and lycopene due to extended π-conjugation that gives strong electron-phonon coupling, which leads to an anomalous experimental phenomenon. We observed an extremely high Raman scattering cross section(RSCS) and the Raman activities in β-carotene and lycopene are characterized by intensive overtones and combinations. Further, the UV-Vis absorption bands become narrower. molecular structured order, Raman spectroscopy, Raman scattering cross section

Quantitative Raman Analysis of Carotenoid Protein Complexes in Aqueous Solution

“…The longest wavelength absorption maximum of Beta Carotene has been shown to be shifted from ~476 nm in ethanol to ~515 nm in 1:1 ethanol water solution due to J aggregation [ 35 , 38 , 39 , 40 ]. Similar spectral shifting in a range of solvents has been documented, depending on polarisability [ 37 , 61 , 62 ], and the UV-Vis spectrum of Beta Carotene in solution is also pressure-dependent, the longest wavelength absorption maximum shifting as low as ~580 nm in carbon disulphide solution at 0.96 GPa [ 63 ]. In H aggregates of Zeaxanthin, prepared in Ethanol:Water mixtures, the UV-vis spectrum is dominated by a strong feature at 370 nm, while in 1:9 THF:Water solutions, the longest wavelength absorption maximum is shifted from 485 nm to ~510 nm [ 64 , 65 ].…”

“…As a result of the spectral shifts, the carotenoid BSA samples had strong orange colour, rather than the typical yellow colour of human serum, as shown in the Supplemental Materials, Figure S1 . Similar shifts in the absorbance features of carotenoid compounds have been extensively explored and reported [ 20 , 36 , 37 , 38 , 39 , 40 ], and can be caused by factors such as aggregation and solvatochromism [ 41 ], as a result of changes to the local electronic environment of each molecule due to intermolecular interactions. The degree of aggregation can also influence the molar absorbance values, as evidenced, for example, by studies of Beta Carotene in ethanol:water solutions, in which the peak absorbance was seen to decrease significantly as the ethanol content was reduced to <67% [ 38 ], and therefore, although the measured solutions of the three carotenes in Figure 1 A were prepared at the same concentration of 1 mg/mL, the resultant absorbance maxima are quite different.…”