Carotenoids generation

Lately, LC—MS analysis of carotenoids and retinoids has been reported for food matrices such as fish eggs [104] and infant formula [105,106]. Atmospheric pressure chemical ionization (APCI) is the method of choice for their detection in the positive ion mode Retinol gives an intense dehydrated pseudomolecular ion, [MH—H20], at zzz/z 269 retinyl esters are fragmented in the ion source producing [MH—fatty acid—H20] ions (i.e., retinol dehydrated at zzz/z 269) carotenoids generate several ions such as [M + H]" ", [M]" ", and [M—H]" ". The ESI interface is better for the ionization of xanthophylls when semiaqueous mobile phases are used for their separation. 

Figure 12.17 Computer-generated diagram of the stmcture of light-harvesting complex LH2 from Rhodopseudomonas acidophila. Nine a chains (gray) and nine p chains Bight blue) form two rings of transmembrane helices between which are bound nine carotenoids (yellow) and 27 bacteriochlorophyll molecules (red, green and dark blue). (Courtesy of M.Z. Papiz.)...

Because the carotenoids favour hydrophobic domains they are generally localised in the membranes and lipoproteins of animal cells. In this location they can influence the oxidation of membrane lipids and prevent the passage of free radicals from one cellular compartment to another. Thus, DNA in the nucleus is protected from intracellularly generated ROS by (at least) the nuclear membrane and from extracellular ROS by a number of membranes. Should ROS reach the nucleus, base oxidation can occur. The base most susceptible to oxidation is guanine, although all other bases can also be affected. The cell has the ability to detect damaged bases, excise them. 

Carotenoid radicals — Many of the important oxidations are free-radical reactions, so a consideration of the generation and properties of carotenoid radicals and of carbon-centered radicals derived from carotenoids by addition of other species is relevant. The carotenoid radicals are very short-lived species. Some information has been obtained about them by the application of radiation techniques, particularly pulse radiolysis. Carotenoid radicals can be generated in different ways. "... 

Addition — The addition of a radical species such as a peroxy radical ROO or the hydroxyl radical HO" to the polyene chain could generate a carotenoid-adduct radical CAR + ROO —> CAR - OOR. 

Convincing evidence indicates that ROS generated both endogenously and also in response to diet and lifestyle factors may play a significant role in the etiology of atherosclerosis and CHD. Indeed, free radicals are responsible for LDL oxidation, which is involved in the initiation and promotion of atherosclerosis. Thus, protection from LDL oxidation by antioxidants such as carotenoids may lead to protection against human CHD. 

Carotenoid reactions with ROS or RNS (reactive nitrogen species) would generate prooxidative products. ... 

Studies on carotenoid autoxidation have been performed with metals. Gao and Kispert proposed a mechanism by which P-carotene is transformed into 5,8-per-oxide-P Carotene, identified by LC-MS and H NMR, when it is in presence of ferric iron (0.2 eq) and air in methylene chloride. The P-carotene disappeared after 10 min of reaction and the mechanism implies oxidation of the carotenoid with ferric iron to produce the carotenoid radical cation and ferrous iron followed by the reaction of molecular oxygen on the carotenoid radical cation. Radical-initiated autoxidations of carotenoids have also been studied using either radical generators like or NBS.35... 

In a very recent study in potatoes, inhibition of LCYE accumulation was accomplished by an antisense LcyE driven by the patatin promoter and allowed rechanneling of lycopene toward the P-carotene branch of the pathway to produce up to 14-fold increased levels of P-carotene as well as up to 2.5-fold increased total carotenoids. RNAi and TILLING for manipulation of carotenogenesis have yet to be reported, but these new techniques for suppression of function and generation and selection of allelic diversity are likely to impact future research and production of varieties with enhanced pigment accumulation. 

Carmona, M. et al.. Generation of saffron volatiles by thermal carotenoid degradation, J. Agric. Food Chem. 54, 6825, 2006. 

The origin of many of the components of black tea aroma has been studied. Aldehydes are produced by catechin quinone oxidation of amino acids. Enzymic oxidation of carotenoids during manufacture generates ionones and their secondary oxidation products such as theaspirone and dihydroactinidolide. Oxidation of linoleic acid is responsible for the formation of trans-2-hexenal.82... 

A second highly soluble diphosphate derivate, 3.17, was also produced (solubility 29mg/mL) its efficacy in an in vitro cancer agent was screened, and it proved to be the most active carotenoid ever tested in this system (Hix et al. 2005), and more potent than Cardax, 3.19 (Hix et al. 2004). Overall, the second-generation compounds showed increased promise over the prototypes in certain contexts, particularly those in which immediate radical scavenging by highly potent and soluble compounds are required. 

Gao, F. G., A. J. Bard, and L. D. Kispert. 2000. Photocurrent generated on a carotenoid-sensitized Ti02 nanocrystalline mesoporous electrode. J. Photochem. Photobiol. A 130 49-56. 

Spin trapping EPR technique and UV-Vis spectroscopy have been used (Polyakov et al. 2001b) to determine the relative rates of reaction of carotenoids with OOH radicals formed by the Fenton reaction in organic solvents. The Fe3+ species generated via the Fenton reaction... 

Carotenoid neutral radicals are also formed under irradiation of carotenoids inside molecular sieves. Davies and Mims ENDOR spectra of lutein (Lut) radicals in Cu-MCM-41 were recorded and then compared with the simulated spectra using the isotropic and anisotropic hfcs predicted by DFT. The simulation of lutein radical cation, Lut +, generated the Mims ENDOR spectrum in Figure 9.7a. Its features at B through E could not account for the experimental spectrum by themselves, so contribution from different neutral radicals whose features coincided with those of the experimental... 

Carotenoid radical intermediates generated electrochemically, chemically, and photochemically in solutions, on oxide surfaces, and in mesoporous materials have been studied by a variety of advanced EPR techniques such as pulsed EPR, ESEEM, ENDOR, HYSCORE, and a multifrequency high-held EPR combined with EPR spin trapping and DFT calculations. EPR spectroscopy is a powerful tool to characterize carotenoid radicals to resolve -anisotropy (HF-EPR), anisotropic coupling constants due to a-protons (CW, pulsed ENDOR, HYSCORE), to determine distances between carotenoid radical and electron acceptor site (ESEEM, relaxation enhancement). 

Wu, Y., L. Piekara-Sady et al. (1991). Photochemically generated carotenoid radicals on Nafion film and silica gel An EPR and ENDOR study. Chem. Phys. Lett. 180 573-577. 

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