The involvement of free radicals in the mechanism of -Carotene Degradation

-Carotene, a pro-vitamin A carotenoid, was reacted with oxygen in benzeneas solvent, in the dark. The products of oxidation were characterised by HPLC with aUV photodiode detector and LC-MS, EI mode. The products identified were oxygencontainingcompounds of the type epoxides, aldehydes and ketones. ESR study ofretinyl- and ionyl-derivatives revealed that the secondary sites C7 and C9 were the mostreactive towards radical generation. Both the results of product analysis and the ESRstudy enabled us to propose that the products of -carotene autoxidation were obtainedby a free radical mechanism involving initial formation of a biradical during the transto-cis isomerisation at the 15,15' bond and attack by oxygen.Keywords: Carotene, Carotenoids, Apo-carotenoids, ESR, Degradation, Autoxidation,Free radicals

Electron spin resonance study of free radicals generated from retinyl- and ionyl-derivatives

Free radicals generated from α- and β-ionyl bromides gave well resolved ESR spectra, but retinyl bromide and chloride gave only broad signals. Delocalised radicals were also spectrosopically observed on hydrogen abstraction from α-ionane, α-ionyltrimethylsilylether and buten-3-ynyl-2,6,6-trimethyl-2-cyclohexene. Retinyl and β-ionyl radicals, derived from the corresponding xanthates, were successfully spin trapped with nitrosodurene. The results suggested that the secondary sites C(7) and C(9) were the most reactive in the β-ionyl radicaland that the secondary sites C(7) and C(11) and probably the primary site C(15) were the most reactive in the retinyl radical

Identification of products from canthaxanthin oxidation

John C. Walton and Raphael C. Mordi acknowledge the financial support of EaStCHEM.Canthaxanthin is a carotenoid that lacks pro-vitamin A activity but is known to have antioxidant activity. The products of its oxidation in oxygen were found to be mainly substituted apo-carotenals and apo-carotenones. The product profile resembles that obtained in the oxidation of β-carotene, except that with canthaxanthin these products are the 4-oxo-β-apo-carotenals and 4-oxo-β-apo-carotenones. Epoxides and diepoxides were clearly identified from β-carotene oxidation but in contrast, with canthaxanthin, apart from 5,6-epoxy-canthaxanthin, which was detected at the early stage of oxidation and minor quantities of 5,6-epoxy-β-ionone and 5,6-epoxy-4-oxo-β-apo-11-carotenal, no other epoxides were detected. The identities of these products lead us to suggest that the mechanism of canthaxanthin oxidation bears significant similarity to that of β-carotene.PostprintPeer reviewe

Gasoline range chemicals from zeolite-catalysed thermal degradation of polypropylene

The thermal degradation of polypropylene over zeolite catalysts (H-ZSM-5, H-mordenite and H-theta-1) has been studied; GC analysis of the product fractions revealed that 70–80% were of the gasoline range hydrocarbons

Zeolite Catalyzed Aldol Condensation Reactions

The review is based on the description of zeolite structure, uses, synthesis, and catalytic aldol reaction in aldol condensation. An internal aldol condensation reaction has been achieved over ZSM-5 zeolite with high silica-alumina ratio at 350°C. It therefore follows that zeolite can function as a catalyst in aldol type condensation reactions and that weak acid sites as well as a small number of active sites favor the aldol condensation reaction of carbonyl compounds. However, the mixed condensation product was found to be favored at temperatures above 300°C and the self-condensation of ethanal to crotonaldehyde was favored at temperatures below 3000C. It has also been suggested that both Broosted and Lewis acids are involved in aldol reactions with Lewis acid sites the most probable catalytic sites. The zeolite group of minerals has found use in many chemical and allied industries

Prevalence of Otitis Media in Okada Community, Edo State, Nigeria

Aim. To determine the prevalence of otitis media in Okada, a rural community in Nigeria, and the effect of age and gender on its prevalence as well as susceptibility profile of the bacterial agents in the community.Material and Methods. Ear discharge from 500 (240 males and 260 females) patients with signs and symptoms of otitis media were processed to recover bacterial agents. Susceptibility test was performed on all bacterial isolates. Results. Male gender was a significant (P = 0.011) risk factor for acquiring otitis media (male Vs female; 36.25% Vs 25.38%. OR = 1.671 95 CI = 1.139, 2.454). Age significantly (P < 0.0001) affected the prevalence of otitis media with children within the age range of 0 – 5years having the highest prevalence of 78.41%. Pseudomonas aeruginosa was the predominant bacteria isolate causing otitis media generally and in both gender. All bacterial isolates showed were poorly susceptible to the antibacterial agents used as less than 50 percent of any bacteria genera were susceptible to any antibacterial agent.Conclusion. An overall prevalence of 30.6% of bacteriologically proven otitis media was observed in this study. The prevalence were higher in males and in children 5 years and younger. Following the high level resistance observed, rational use of antibacterial agents is advocated

HOFMANN-MARTIUS REARRANGEMENT REACTIONS CATALYSED BY ZEOLITE

N-Methylaniline was reacted over HZSM-5, H-Theta-1 and HY zeolites and was found to rearrange to give the toluidines, aniline and N,N-dimethylaniline. Percentage conversion to these products was found to be highest over HY zeolite with a higher selectivity to p-toluidine, whereas over HZSM-5 and H-Theta-1 selectivity was to N,N-dimethylaniline. The conversion to these products is in line with Hofmann-Martius and the Reilly-Hickin bottom rearrangement reactions. However the selectivity to N,N-dimethylaniline as observed over HZSM-5 and H-Theta-1 (medium pore zeolites) is ne

Experimental appraisal of solvent effects on internal rotation barriers and stabilization energies of disubstituted methyl radicals

The EPR spectra of aminopropynyl and aminocyanomethyl radicals were recorded in a variety of solvents with different dielectric constants. For the former radical the spectra showed exchange broadening due to restricted rotation about the H2NC˙ bond. Arrhenius parameters for the bond rotation, i.e. for the interconversion of the two rotamers, were obtained by computer simulation of the exchange-broadened spectra. The rotational barrier height was found to change only marginally in solvents with dielectric constants ranging from 2.1 to 37.5. For both radicals the temperature dependences of the α(NH2) values also indicated little change in their H2NC˙ rotation barriers in solvents of differing polarity. Because rotation barriers are directly related to the stabilization energies (SE) of the radicals, it was concluded that solvent polarity has little effect on the SE of a capto-datively substituted radica

Identification of products from canthaxanthin oxidation

a b s t r a c t Canthaxanthin is a carotenoid that lacks pro-vitamin A activity but is known to have antioxidant activity. The products of its oxidation in oxygen were found to be mainly substituted apo-carotenals and apocarotenones. The product profile resembles that obtained in the oxidation of b-carotene, except that with canthaxanthin these products are the 4-oxo-b-apo-carotenals and 4-oxo-b-apo-carotenones. Epoxides and diepoxides were clearly identified from b-carotene oxidation but in contrast, with canthaxanthin, apart from 5,6-epoxy-canthaxanthin, which was detected at the early stage of oxidation and minor quantities of 5,6-epoxy-b-ionone and 5,6-epoxy-4-oxo-b-apo-11-carotenal, no other epoxides were detected. The identities of these products lead us to suggest that the mechanism of canthaxanthin oxidation bears significant similarity to that of b-carotene