Porphyrins carotenoids

The carotenoids, trans-3 carotene (Sigma), I canthaxanthin (Fluka), II 3-8 -apocarotenal (Fluka), III and crocetin (Sigma), IV were used in this study (see structure). Of the above four carotenoids, only crocetin is water soluble. The porphyrins 5,10,15,20-tetra-phenyl-21H,23H-porphine (TPP) and 5,10,15,20-tetra-(4-sodiumsulfonato-phenyl)-21H,23H-porphine, TPPS were obtained from Aldrich, TPPS is a water soluble porphyrin. Carotenoids I-III were used as supplied, however crocetin was purified according to published methods (15) just prior to use. 

What is the role of energy or electron transfer in the quenching of tetrapyrrole fluorescence by carotenoids In other model studies the redox levels of a porphyrin-carotenoid dyad have been shown to influence the quenching mechanism to the extent that electron transfer from the carotenoid to the excited porphyrin was shown to occur (Hermant et al., 1993). However, in a series of carotenoid-porphyrin dyads in which the number of conjugated carbon-carbon double bonds in the carotenoid moiety was systematically increased from 7 to 11, quenching... 

Moore, Gust, and coworkers synthesized the quinone-porphyrin-carotenoid (Figme 5) triad molecule. Upon excitation of the porphyrin moiety, initial charge separation occurred between porphyrin and quinone. Hole shift from porphyrin to carotenoid formed the final charge-separated state, that is, quinone radical anion and carotene radical cation, with a lifetime of 170 ns. These processes were confirmed by means of the picosecond and nanosecond laser flash photolysis. Their covalent bonding system was extended to tetrad and pentad using similar chromophores. 

Figure 5 Molecular structure of the quinone-porphyrin-carotenoid triad. (Reproduced from Ref. 83. Nature Publishing Group, 1984.)...

Red wine, for example, contains porphyrins, carotenoids, anthocyanins, flavones, and tannins as the principal colorants, and the relative proportion of these determines the color and hue of the wine [1]. As the wine matures, the color gradually changes to a more browny hue as the anthocyanins link together and to other chemicals in the wine, forming polymers. Research has shown that approximately 90% of the color of some wines after maturing for a year is due to such polymers [2]. 

The main use of carotenoids in dmgs is to correct the levels of vitamin A in patients with hypovitaminosis or requiring an extra supply of vitamins. However, other applications have been developed not related with the provitamin A character but rather with photochemical and antioxidant properties. For many years, these pigments have been used in therapy to reduce the effects of erythropoietic protoporphyria, a skin disease related with metabolism of the porphyrins. Carotenoids have also been considered as protectors in certain cancer treatments, above all those requiring radiotherapy. Carotenoid pigments are used in cosmetic products in the form of suspensions, emulsions, or lotions, lipsticks, and makeup foundations. 

A major trend in organic synthesis, however, is the move towards complex systems. It may happen that one needs to combine a steroid and a sugar molecule, a porphyrin and a carotenoid, a penicillin and a peptide. Also the specialists in a field have developed reactions and concepts that may, with or without modifications, be applied in other fields. If one needs to protect an amino group in a steroid, it is advisable not only to search the steroid literature but also to look into publications on peptide synthesis. In the synthesis of corrin chromophores with chiral centres, special knowledge of steroid, porphyrin, and alkaloid chemistry has been very helpful (R.B. Woodward, 1967 A. Eschenmoser, 1970). 

In the second oxidation method, a metalloporphyrin was used to catalyze the carotenoid oxidation by molecular oxygen. Our focus was on the experimental modeling of the eccentric cleavage of carotenoids. We used ruthenium porphyrins as models of cytochrome P450 enzymes for the oxidation studies on lycopene and P-carotene. Ruthenium tetraphenylporphyrin catalyzed lycopene oxidation by molecular oxygen, producing (Z)-isomers, epoxides, apo-lycopenals, and apo-lycopenones. 

Carotenoid/ curcumin/porphyrin Water dispersion without using compositions surface-active substance... 

Stable dispersion of water-insoluble and/or hydrophobic natural pigment such as carotenoid, curcumin, porphyrin pigment, or vegetable carbon black in form of bodies of average size of 10 ram Addition of 0.5 ppm P-carotene to yogurt containing 200 ppm riboflavin color did not change after 40 days at 6°C compared with control (decoloration at 1 day)... 

Chapter 13 is devoted to the PLC of namral pigments, which encompass fla-vonoids, anthocyanins, carotenoids, chlorophylls and chlorophyll derivatives, porphyrins, quinones, and betalains. Chromatography of pigments is especially difficult because many are photo- and air-sensitive and can degrade rapidly unless precautions are taken. 

The chemically catalyzed oxidation of carotenoids by metalloporphyrins has also been described in the literature. In 2000, French et al. described a central cleavage mimic system (ruthenium porphyrin linked to cyclodextrins) that exhibited a 15,1 S -regiosclectivity of about 40% in the oxidative cleavage of [3-carotene by tert-butyl hydroperoxide in a biphasic system (French et al. 2000). 

These results produce an ordering of the one-electron reduction potentials as shown in Figure 14.9. This order is consistent with results on the reactions of oxygen and porphyrins with carotenoids (McVie at al. 1979, Conn et al. 1992), for example, p-CAR - reacts much more efficiently with oxygen than LYC - and DECA -. Comparative studies have been made in benzene due to the decreased solubility of XANs in hexane and Table 14.8 gives the corresponding bimolecular rate constants for electron transfer. Overall, the one-electron reduction potentials increase in the order ZEA < P-CAR LUT < LYC < APO - CAN < ASTA. 

McVie, J., Sinclair, R.S., Tait, D., Truscott, T.G., and Land E.J. 1979. Electron transfer reactions involving porphyrins and carotenoids. J. Chem. Soc. Faraday Trans. 775 2869-2872. 

Li and coworkers49 reported a molecular motion of /1-carotene and a carotenopor-phyrin dyad (composed of a porphyrin, a trimethylene bridge and a carotenoid polyene) in solution. Internal rotational motions in carotenoid polyenes and porphyrins are of interest because they can mediate energy and electron transfer between these two moieties when the pigments are joined by covalent bonds. Such internal motions can affect the performance of synthetic model systems which mimic photosynthetic antenna function,... 

A possible mechanism for this transformation, similar to the proposed enzymatic cleavage of carotenoids (Fig. 3), involves 0 = Ru = 0 porphyrin 21 catalyzed epoxidation of 17 to 22, followed by nucleophilic attack of TBHP and ring opening with assistance of 23. Subsequent fragmentation yields the aldehydes (Fig. 8). 

Porphyrins and Plant Pigments Chiorophyii Hemin Carotenes and Xanthophyiis > Chlorin Phaeophytin hydrocarbons Phytane, pristane, carotenoids, isoprenoids, alcohols, ketones, acids, porphyrins... 

A few examples to render tetrapyrrolic compounds less phototoxic can be found in the hterature. In one approach, carotenoid structures were employed for the synthesis of some carotenoporphyrin derivatives [92-94]. Figure 8 shows two stuctures by way of example. Due to similar photophysical properties of the two structural components, the excited triplet state of the porphyrin is quenched by the carotenoid moiety, thus inhibiting the formation of singlet oxygen, while its fluorescence capabilities are still preserved. Biodistribution studies revealed enhanced uptake into tumour tissue [39,93,95]. However, microscopy studies have shown that such compounds are associated with connective tissues in the tumors rather than with cancerous cells indicating low specificities for mahgnant transformation [96]. 

Triplet-State Decay Rate Constants of Porphyrin in the Presence of Carotenoids... 

Recently it has been reported (3 ) that in a triad molecule where a porphyrin is juxtaposed between a carotenoid and a quinone, a charge transfer donor-acceptor pair with a lifetime similar to that found experimentally in biological systems was produced on light irradiation. It was suggested that an electrical potential similar to the type developed in this donor-acceptor pair may be important in driving the chemical reactions in natural photosynthesis. 

Porphyrin Medium None Carotenoids 3-carotene Apocarotenal Crocetin... 

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