Carotenoids spectra

Fig. 4.5. Raman spectra of tree pollen that is rich in carotenoid. Spectra of pollen from horse-chestnut (a, b), sallow (c, d), large-leaved linden (e, f) before irradiation with laser light of 633 nm wavelength for photodestruction of carotenoids (traces a, c and e) and after 1 h photodestruction with 633 nm. All spectra were excited with 785 nm, 10 s accumulation time and laser power of 18mW ( 1.8 x 106 W/cm2)...

Carotenoids (pg) = 3.92(A445 - A550) volume [diethyl ether (mL)] Determination of chlorophyll / carotenoids spectra by HPLC... 

ON THE EFFECT OF PROTEINASES,PHOSPHOLIPASES AND GROUP-SPECIFIC REACTANTS ON CAROTENOID SPECTRA AND ELECTROCHROMIC RESPONSE OF MEMBRANE PREPARATIONS OF PHOTOSYNTHETIC PURPLE BACTERIA. 

It is therefore important to bear in mind the dependency of the carotenoid spectrum upon properties of the environment for in vivo analysis, which is based on the application of optical spectroscopies. This approach is often the only way to study the composition, structure, and biological functions of carotenoids. Spectral sensitivity of xanthophylls to the medium could be a property to use for gaining vital information on their binding sites and dynamics. The next sections will provide a brief introduction to the structure of the environment with which photosynthetic xanthophylls interact—light harvesting antenna complexes (LHC). 

The HPLC analysis of milkweed, the food-plant source for Monarch butterflies, demonstrates that it contains a complex mixture of carotenoids including lutein, several other xanthophylls, xanthophyll epoxides, and (3-carotene, Figure 25.3b. There is a component in the leaf extract that is observed to elute near 8min, which has a typical carotenoid spectrum but is not identical to that of the lutein metabolite observed at near the same retention time in the extracts from larval tissue. 

Carotenoids also assist chlorophylls in harvesting light. Carotenoids absorb wavelengths of blue light which chlorophylls do not. The energy that carotenoids harvest in the blue range of the spectrum and transfer to chlorophyll contributes... 

Natural pigment production for food coloration includes the entire spectrum of biotechnologies. For example, biological production of carotenoid pigments has medical implications because carotenoids are nutritive (pro-vitamin A), antioxidant, and photoprotective. Carotenoids are produced alternately in agricultural systems (plants), industrial bioreactors (bacterial and fungi), and marine systems (cyanobacteria and algae). 

Solvent — The transition energy responsible for the main absorption band is dependent on the refractive index of the solvent, the transition energy being lower as the refractive index of the solvent increases. In other words, the values are similar in petroleum ether, hexane, and diethyl ether and much higher in benzene, toluene, and chlorinated solvents. Therefore, for comparison of the UV-Vis spectrum features, the same solvent should be used to obtain all carotenoid data. In addition, because of this solvent effect, special care should be taken when information about a chromophore is taken from a UV-Vis spectrum measured online by a PDA detector during HPLC analysis. 

NMR spectrum identification is very demanding and requires training because carotenoids have great numbers of protons (most have 56 protons), and many of them are chemically similar but not exactly equivalent. 

The determination of the absolute configuration of a carotenoid is only possible by circular dichroism (CD) measurement. The spectrum interpretation can only be done by comparison with reference or model compounds with known chiralities. The sample requirement is as low as 5 to 50 pg, but CD facilities are not so commonly available. Buchecker and Noack reported experimental aspects and discussion of the relationships of carotenoid structures and CD spectra. 

NPQ (Rakhimberdieva et al. 2004) exactly matches the absorption spectrum of the carotenoid, 3 -hydrox yech i nenone (Polivka et al. 2005) in the OCP. The OCP is now known to be specifically involved in the phycobilisome-associated NPQ and not in other mechanisms affecting the levels of fluorescence such as state transitions or D1 damage (Wilson et al. 2006). Studies by immunogold labeling and electron microscopy showed that most of the OCP is present in the interthylakoid cytoplasmic region, on the phycobilisome side of the membrane, Figure 1.2 (Wilson et al. 2006). The existence of an interaction between the OCP and the phycobilisomes and thylakoids was supported by the co-isolation of the OCP with the phycobilisome-associated membrane fraction (Wilson et al. 2006, 2007). 

The pattern of the II-NMR spectrum of lycopene differs from the spectra of the other carotenoids because lycopene consists of conjugated double bonds. At 6.6ppm the multiplet of protons 11/11 (6.63ppm) and of proton pairs 15/15 (6.60ppm) resonate adjacent to the doublet of proton pair 7/7 (6.44 ppm), the doublet of proton pair 12/12 (6.29 ppm), the doublet of proton pair 14/14 (6.22 ppm), the doublet of proton pairs 8/8 (6.15ppm), and finally the doublet of proton pair 10/10. The resonance of proton pairs 6/6 and 2/2 are shifted to a higher field at 5.85 and 5.00 ppm due to their position in the conjugated system. 

The (13-Z) isomer of astaxanthin is a noncentrosymmetric carotenoid, thus the proton shifts of both sides of the chain are not equal any longer. For example, this causes proton 15 to have a spectrum of higher order, while it exhibits a doublet in the all-E compound. The largest shift differences... 

In order to obtain nearly absolute purity of the spectra of these xanthophylls, it was necessary to calculate the difference Raman spectra. Therefore, for zeaxanthin, two spectra of samples, one containing violaxanthin and the other enriched in zeaxanthin, were measured at 514.5 nm excitation. After their normalization using chlorophyll a bands at 1354 or 1389 cm-1, a deepoxidized-minus-epoxidized difference spectrum has for the first time been calculated to produce a pure resonance Raman spectrum of zeaxanthin in vivo (Figure 7.10b). A similar procedure was used for the calculation of the pure spectrum for violaxanthin. The only difference is that the 488.0nm excitation wavelength and epoxidized-minus-deepoxidized order of spectra have been applied in the calculation. The spectra produced using this approach have remarkable similarity to the spectra of xanthophyll cycle carotenoids in pure solvents (Ruban et al., 2001). The v, peaks of violaxanthin and zeaxanthin spectra are 7 cm 1 apart and in correspondence to the maxima of this band for isolated zeaxanthin and violaxanthin, respectively. The v3 band for zeaxanthin is positioned at 1003 cm-1, while the one for violaxanthin is upshifted toward 1006 cm-1. 

The v4 region enhancement and structure in the resonance Raman spectra of xanthophylls reviewed in this chapter shows that it can be used for the analysis of carotenoid-protein interactions. Figure 7.8 summarizes the spectra for all four major types of LHCII xanthophylls. Lutein 2 possesses the most intense and well-resolved v4 bands. The spectrum for zeaxanthin is very similar to that of lutein with a slightly more complex structure. This similarity correlates with the structural similarity between these pigments. It is likely that they are both similarly distorted. The richer structure of zeaxanthin spectrum may be explained by the presence of the two flexible P-end rings... 

Besides the main band, H-aggregates also exhibit weaker bands in the red part of the absorption spectrum (marked by in Figure 8.5). Although in some cases the position of these bands coincides with the vibrational bands of the monomeric carotenoid and can be therefore assigned to nonaggregated carotenoid molecules, certain spectral features do not match the vibrational bands... 

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