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We present the application of one-dimensional (1D) and two-dimensional (2D) electron spin resonance imaging (ESRI) for the study of photo- and thermal degradation of polymers containing hindered amine stabilizers (HAS). The method is based on the formation of stable nitroxide radicals derived from HAS during polymer treatment, and on encoding spatial information in the ESR spectra via magnetic field gradients. The imaging technique allowed nondestructive profiling of the HAS-derived nitroxide radicals. The intensity profile in the sample depth was deduced by 1D ESRI, and the spatial variation of the ESR line shapes (‘spectral profiling’) was determined by 2D spectral-spatial ESRI. Application of this approach to the photodegradation of polypropylene and to the photo- and thermal degradation of poly(acrylonitrile–butadiene–styrene) will be described. The method can be used to detect spatial heterogeneities in the degradation process and to identify morphological domains that are selectively degraded. [Copyright &y& Elsevier]

Abstract: Irradiation of N-triphenylmethyloxy- or N-diphenylmethyloxy phthalimide is reported to result in the formation of phthalimide N-oxyl radical (PINO), which is able to initiate and propagate oxidative radical chain reactions of hydrocarbons. [Copyright &y& Elsevier]

Abstract: Chalcone, flavone, and arylideneflavanone derivatives bearing one or two 3,5-di-tert-butyl-4-hydroxyphenyl groups were synthesized from 2′,4′-dihydroxyacetophenone and 3,5-di-tert-butyl-4-hydroxybenzaldehyde. These flavonoids were converted into the corresponding malonates and then reacted with C60 to yield the title compounds. The O–H bond dissociation enthalpies (BDE) and the chain-breaking antioxidant activity of the flavonoid derivatives and the corresponding C60 conjugates were evaluated. These results are consistent with the phenolic moiety being the main responsible for the reaction with peroxyl radicals, while the C60 part of the molecule acts synergically by trapping alkyl radicals under reduced O2 partial pressure. These novel C60–flavonoid conjugates are therefore promising leads for broad-spectrum radical scavengers. [Copyright &y& Elsevier]

Abstract: Halogen-bonded complexes between aliphatic and aromatic iodoperfluorocarbons and persistent nitroxide radicals have been detected by ESR spectroscopy in solution. Quantitative data indicate that nitroxides behave as strong electron donors in halogen bonding, giving rise to interactions whose strength is close to that of strong hydrogen bonds. These results point to a novel design of supramolecular paramagnetic species. [Copyright &y& Elsevier]

Abstract: Epidemiological and animal studies linking high fruit and vegetable consumption to lower cancer risk have strengthened the belief that long-term administration of isolated naturally occurring dietary constituents could reduce the risk of cancer. In recent years, metabolites derived from phytoalexins, such as glucoraphanin found in broccoli and other cruciferous vegetables (Brassicaceae), have gained much attention as potential cancer chemopreventive agents. The protective effect of these micronutrients is assumed to be due to the inhibition of Phase-I carcinogen-bioactivating enzymes and/or induction of Phase-II detoxifying enzymes, an assumption that still remains uncertain. The protective effect of glucoraphanin is thought to be due to sulforaphane, an isothiocyanate metabolite produced from glucoraphanin by myrosinase. Here we show, in rat liver, that while glucoraphanin slightly induces Phase-II enzymes, it powerfully boosts Phase-I enzymes, including activators of polycyclic aromatic hydrocarbons (PAHs), nitrosamines and olefins. Induction of the cytochrome P450 (CYP) isoforms CYP1A1/2, CYP3A1/2 and CYP2E1 was confirmed by Western immunoblotting. CYP induction was paralleled by an increase in the corresponding mRNA levels. Concomitant with this Phase-I induction, we also found that glucoraphanin generated large amount of various reactive radical species, as determined by electron paramagnetic resonance (EPR) spectrometry coupled to a radical-probe technique. This suggests that long-term uncontrolled administration of glucoraphanin could actually pose a potential health hazard. [Copyright &y& Elsevier]

Evidence from both epidemiological and experimental observations have fueled the belief that the high consumption of fruits and vegetables rich in carotenoids may help prevent cancer and heart disease in humans. Because of its well-documented antioxidant and antigenotoxic properties, the carotenoid β-carotene (βCT) gained most of the attention in the early 1980s and became one of the most extensively studied cancer chemopreventive agents in population-based trials supported by the National Cancer Institute. However, the results of three randomized lung cancer chemoprevention trials on βCT supplementation unexpectedly contradicted the large body of epidemiological evidence relating to the potential benefits of dietary carotenoids. Not only did βCT show no benefit, it was associated with significant increases in lung cancer incidence, cardiovascular diseases, and total mortality. These findings aroused widespread scientific debate that is still ongoing. It also raised the suspicion that βCT may even possess co-carcinogenic properties. In this review, we summarize the current data on the co-carcinogenic properties of βCT that is attributed to its role in the induction of carcinogen metabolizing enzymes and the over-generation of oxidative stress. The data presented provide convincing evidence of the harmful properties of this compound if given alone to smokers, or to individuals exposed to environmental carcinogens, as a micronutrient supplement. This has now been directly verified in a medium-term cancer transformation bioassay. In the context of public health policies, while the benefits of a diet rich in a variety of fruits and vegetables should continue to be emphasized, the data presented here point to the need for consideration of the possible detrimental effects of certain isolated dietary supplements, before mass cancer chemoprevention clinical trials are conducted on human subjects. This is especially important for genetically predisposed individuals who are environmentally or occupationally exposed to mutagens and carcinogens, such as those found in tobacco smoke and in industrial settings. [Copyright &y& Elsevier]

Reactions of alkanes with different halogenating systems are compared in order to explore the reactivity of phthalimido-N-oxyl radical in hydrogen abstraction; the importance of polar effects is emphasised. [Copyright &y& Elsevier]