Resonance Raman Spectra of Carotenoid Molecules: Influence of Methyl Substitutions

Abstract

We report here the resonance Raman spectra and the quantum chemical calculations of the Raman spectra for β-carotene and 13,13'-diphenyl-β-carotene. The first aim of this approach was to test the robustness of the method used for modeling β-carotene, and assess whether it could accurately predict the vibrational properties of derivatives in which conjugated substituents had been introduced. DFT calculations, using the B3LYP functional in combination with the 6-311G(d,p) basis set, were able to accurately predict the influence of two phenyl substituents connected to the β-carotene molecule, although these deeply perturb the vibrational modes. This experimentally validated modeling technique leads to a fine understanding of the origin of the carotenoid resonance Raman bands, which are widely used for assessing the properties of these molecules, and in particular in complex media, such as binding sites provided by biological macromolecules.

Triplet–triplet energy transfer in artificial and natural photosynthetic antennas

“…The Raman spectra and relative intensities of Raman peaks were simulated at the same levels of theory on corresponding optimized geometries. This approach was successfully applied in previous studies to model substituent effects on the Raman spectra of carotenoid molecules (45,46). The ultrafine grid keyword was specified for all DFT calculations and the Raman and Wiberg bond order calculations (47) were carried out in Gaussian 09.…”

Chiral Amplification in Nature: Studying Cell‐Extracted Chiral Carotenoid Microcrystals via the Resonance Raman Optical Activity of Model Systems

“…Theo utlined ECD vibrational structure (maxima at 518, 485, 454 nm), the position of the RROA n 1 band (1519 cm À1 ), and the ratio of the integral intensities of n 1 /n 2 (1.12) may be recognized as typical for bCi nt he aggregated form and may be considered as achiral response of bCatthe supramolecular level. [22,23] To confirm that the chiral signal of the bC/AXT model is not aresult of the chirality of AXT itself,w eh ighlight some spectral differences between these two aggregates.F or the AXT J-aggregate,t he n 1 /n 2 intensity ratio equals 1.72, and the 1217 cm À1 RROAb and, assigned to the C À Cs tretching combined with the ring methylene twist vibration, [31][32][33] is significantly weaker compared with this band (at 1211 cm À1 )i nt he bC/AXT model spectrum. Thered-shift of the UV/Vis band and the frequency decrease of the Raman C = Cmode (1525!…”

“…TheECD spectrum reveals quite strong negative-positive bands (from longer to shorter wavelengths), known as bisignate Cotton effects,w ith ac learly accentuated vibrational structure,which was also seen in the UV/Vis spectrum and is typical for carotenoids without conjugated carbonyl groups (such as bC). [30,31] In addition, the RROA shoulder at 967 cm À1 is associated with the symmetric C À H and Cout-of-plane wagging, [32] with asmall contribution due to the b-ring deformations [31] and the CÀCs tretching vibrations. [29] We observed characteristic RROA bands due to typical carotenoid vibrations,namely, n 1 at 1519 cm À1 , n 2 at 1159 cm À1 , n 3 at 1009 cm À1 , and n 4 at 956 cm À1 ,which were assigned to the C=Cstretching, the CÀCs tretching, the in-plane CH 3 rocking,a nd the CÀH out-of-plane wagging motions coupled with the C = Co ut-ofplane torsion modes,respectively.…”

Side Methyl Groups Control the Conformation and Contribute to Symmetry Breaking of Isoprenoid Chromophores

“…[8] In this study we address several fundamental questions concerning the isoprenoid pigments:Why is isoprene and not butadiene the building block of retinals and carotenoids? [9][10][11][12][13][14][15] Furthermore,t oe xamine how the structural effects of the methyl groups compare to other factors,wehave modeled the structures of several endoperoxides of b-Car (Scheme 1). How is it related to the intriguing fact that their molecules in native systems are always helically twisted?W eh ave applied an ab initio DFT approach to analyze the influence of methyl substituents on the structure and symmetry of all-trans retinal, lycopene (Lyc), and b-carotene (b-Car), which are the major natural isoprenoid (achiral) chromophores,a nd lutein (Lut), arepresentative chiral chromophore (Scheme 1).…”

“…Thes ame computational approach has been applied in many other studies of structural effects in Crts. [9][10][11][12][13][14][15] Furthermore,t oe xamine how the structural effects of the methyl groups compare to other factors,wehave modeled the structures of several endoperoxides of b-Car (Scheme 1). [16] Thep redicted structures were compared to the high-resolution crystallographic structures of protein-bound Crts (Protein Data Bank (PDB), entries 5F6B, 3WU2, 1LGH, 5L8R, and 4LCZ, and CCDC 1120466, 1120467, and 253816).…”