302Carotenoids are widely distributed in nature where they play an important role in cell protection [1]. Oxygen species including 1 O 2 , 3 O 2 and O 2 · -are capable to damage lipid membranes as well as DNA, and become the cause of mutation of cell material. Carotenoids can play the role of versatile antioxidants because they are effective biological quenchers as well as radical chain breaking agents [2]. Many studies including in vitro, in vivo and epidemiological tests were carried out to investigate these properties of carotenoids [3 -5]. β-Carotene (1a), as the best known carotenoid compound, shows the remarkable effect of changing its antioxidant to a prooxidant behaviour at high concentrations of β-carotene and in the presence of high oxygen partial pressures [2]. Since epidemiological studies can show contradictory and confounding results [3 -5], a more thorough inspection of the anti-and prooxidant functions of carotenoids is needed. Carotenoids with antioxidative properties better than β-carotene (1a), like astaxanthin (5a), have attracted special interest [6a,c].In this study we present an approach to a better understanding of these anti-and prooxidant properties of carotenoids and describe carotenoids, both natural and synthetic, with sole antioxidant efficiency approaching that of α-tocopherol. Anti-and Prooxidant Properties of CarotenoidsHans-Dieter Martin*, Claudia Jäger, Christoph Ruck, and Marcus Schmidt Düsseldorf, Institute of Organic Chemistry and Macromolecular Chemistry, University Robin WalshReading/UK, Department of Chemistry, University Joachim PaustLudwigshafen, BASF AG Received Februar 8th, 1999 Dedicated to Professor Fritz Vögtle on the Occasion of his 60th BirthdayKeywords: Autoxidation, Carotenoids, Oxygen, Antioxidant, Prooxidant Abstract. Carotenoids can be effective singlet oxygen quenchers and inhibit free-radical induced lipid peroxidation. A remarkable property of β-carotene (1a) is the change from an antioxidant to a prooxidant depending on oxygen pressure and concentration. In the present study a considerable number of carotenoids (1a, 2c, 2d, 2e, 3a, 4a, 5a, 6a, 7a, 8a, 8h, 8i, 8j, 9f, 10a, 11a, 12g) was investigated using two independent approaches: 1. Comparison of their effects on inhibition of the free-radical oxidation of methyl linoleate, and 2. The direct study of the effect of oxygen partial pressure upon their rates of oxidation. It is shown that some carotenoids (7a, 8a) are even more effective than the well-known compounds β-carotene (1a) and astaxanthin (5a) and are powerful antioxidants without any prooxidative property. Different carotenoids display different behaviour depending on chain length and end groups. The influence of these functional groups on the antioxidative reactivity is discussed.Scheme 1 Structures of all investigated carotenoid compounds 1-12
Effective chain length / Second-order quenching rate constantsThe bimolecular rate constants k, for quenching of singlet oxygen (lAS state) by 26 different natural and novel synthetic carotenoids were determined at 37 "C in a mixture of chloroform and ethanol. The steady-state technique used involves the generation of by thermal decomposition of disodium 3,3'-naphtalene-l,4-diyl-dipropionate endoperoxide (NDP02) and the detection of its luminescence intensity at 1270 nm.Excitation energies (xJ', llA, -+ llB,) and absorption maxima (430-590 nm) vary in the broadest range. Deeply coloured blue carotenoids are also included in the studies for the first time. An empirical correlation between the X,X* (llA, + llB,) excitation energy and carotenoid structure (effective chain length N,,,) was found: E ( S ) = 12642 cm-l + 92027 cm-l X l/Neff. The quenching ability of the investigated carotenoids depends on the excitation energy of their transition at long wavelengths in a characteristic way showing as limiting factors either the thermal Arrhenius activation or the diffusion-controlled rate. This dependence and the suspected relationship between singlet E ( S ) and triplet E(T) energies, respectively, are discussed.
Acetolysis results for the various (3-methyl-substituted cyclopropyl tosylates are reported. The kinetic results are correlated with a treatment based on electronic and steric effects in ground and transition states, assuming stereospecific ring opening according to the Woodward-Hoffmann-DePuy predictions and considerable progress toward allyl cations in the transition states. The results of the standard mechanistic criteria [m value, (kRa ai J £ « ) , k0TjkBr, and a-methyl/hydrogen rate ratio] for the parent cyclopropyl system indicate that solvolysis is a concerted process. The magnitude of anchimeric assistance in the cyclopropyl system is estimated by two
A series of experiments was conducted to determine the efficacy of 15 synthetic retinoic acid amides (retinamides) as inhibitors of chemical carcinogenesis of the urinary bladder in C57BL/6 x DBA/2F1 mice. Eight of the retinamides tested had significant protective activity when administered at nontoxic levels in the diet. Minor structural alterations, such as the addition of a methyl or hydroxyl group to the terminal amide moiety had a major influence on the anticarcinogenic activity of the retinamides. Although 13-cis retinamides generally were less toxic on a molar basis than were their all-trans isomers, no consistent pattern of differential anticarcinogenic activity was noted among the six pairs of all-trans and 13-cis isomers tested. All-trans-4-hydroxyphenyl retinamide was among the most active and least toxic of the retinoids tested, and appears to be the compound of choice for further study.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.