Autoxidation aqueous model system

The speed of autoxidation was compared for different carotenoids in an aqueous model system in which the carotenoids were adsorbed onto a C-18 solid phase and exposed to a continnons flow of water saturated with oxygen at 30°C. Major products of P-carotene were identified as (Z)-isomers, 13-(Z), 9-(Z), and a di-(Z) isomer cleavage prodncts were P-apo-13-carotenone and p-apo-14 -carotenal, and also P-carotene 5,8-epoxide and P-carotene 5,8-endoperoxide. The degradation of all the carotenoids followed zero-order reaction kinetics with the following relative rates lycopene > P-cryptoxanthin > (E)-P-carotene > 9-(Z)-p-carotene. 

Hydroxylation Induced during the Autoxidation of N-benzyl-1,4-dihydronicotinamide. Oxygen was bubbled through the aromatic compound suspended in an aqueous solution of N-benzyl-l,4-dihydronico-tinamide and ferric chloride. Four compounds were oxidized by this model system benzene to phenol and no biphenyl toluene to benzyl alcohol, cresols, phenol, and no bibenzyl anisole to phenol and methoxyphenols fluorobenzene to phenol and fluorophenols. Even under optimum... 

Figure 1.7 Typical zero-order and corresponding second-derivative electronic absorption spectra of ethanol-reconstituted lipid/chloroform extracts of autoxidized model polyunsaturated fatty-acid compounds and inflammatory synovial fluid obtained after (1) reduction with NaBH4 and (2) dehydration with alcoholic H2S04- (a) Methyl linoleate subsequent to autoxidation in air at ambient temperature for a period of 72 h (—), or exposure to a Fenton reaction system containing EDTA (5.75 x 10 mol/dm ), H2O2 (1.14 X 10 mol/dm ) and Fe(ll) (5.75 x IO mol/dm ) as an aqueous suspension (—) (b) as (a) but with methyl linolenate (c) untreated rheumatoid knee-joint synovial fluid.

The first model proposed for the drug monooxygenase stem in liver microsomes was described by Udenfnend et al. ) and since then referred to as the Udenfriend system . It consists of ferrous iron, EDTA and ascorbate which are incubated aerobically in an aqueous buffer of pH 5—8. Aromatic compounds were hydroxylated in this mixture to phenols and the substitution pattern pointed to an electrophilic mechanism. Breslow and Lukens argued that the Udenfriend system was not different from the Fenton stem since the autoxidation of ascorbate provides hydrogen peroxide, which by the reduction with ferrous ions forms hydroxyl radicals as hydroxylating agent ... 

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