Carotenoids spectral properties

In the carotenoid radicals, the unpaired electron is highly delocalized over the conjugated polyene chromophore. This has a stabilizing effect and also allows subsequent reactions. The cation and anion radicals can be detected by their characteristic spectral properties, with intense absorption in the near-infrared region. 

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). 

Detection can be performed using UV, UV-Vis, DAD, fluorometric detector (ELD) or ED. Gatti et al. [444] report an on-line photochemical derivatization to enhance the selectivity. A photo reactor system was inserted on-line between the column and the ELD. The eluate was irradiated at 254 and 366 nm inducing alterations that modified spectral properties of the analytes. Recently an increasing number of studies have reported the use of LC-MS for the identification of both retinoids and carotenoids [426,433,445-447],... 

Chapter 13 Role of Carotenoids in Photosynthesis II. B. 1. Spectral Properties... 

As described above, different cA-isomers are formed during oxidation. The carotenoid stractnre makes a c/x-tranx-isomerisation possible around the double bonds (Fig. 8.2). In vegetables, the carotenoids are predominantly the aS -trans isomers, which may be converted to the cix-isomers. Cis-trans isomerisation resnlts in colonr changes in vegetable products as the spectral properties of the cA-carotenoids are different from the corresponding frawx-carotenoids. Insertion of one or more cA-double bonds in an aH-trans conjugated system results in a... 

Heterologous reconstitution experiments show some structural restraints Spheroidene from Rb. sphaeroides can be reconstituted into a complex with LHl polypeptides from Rhodospirillum rubrum, restoring spectral properties of native Rs. rubrum LHl and carotenoid-BChl energy transfer whereas spirilloxanthin is unable to incorporate into a reconstituted complex with LHl apoproteins from Rb. sphaeroides (Davis et al., 1995). 

Yamamoto HY and Bangham AD (1978) Carotenoid organization in membranes. Thermal transition and spectral properties of carotenoid-contaimng liposomes. Biochim Biophys Acta 507 ... 

While excited-state properties of monomeric carotenoids in organic solvents have been the subject of numerous experimental and theoretical studies (Polfvka and Sundstrom 2004), considerably less is known about excited states of carotenoid aggregates. Most of the knowledge gathered so far stems from studies of aggregation-induced spectral shifts of absorption bands of carotenoid aggregates that are explained in terms of excitonic interaction between the molecules in the aggregate. 

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