Antioxidants study

Stephens, N.G., Parsons, A., Schodiel, P.M., Kelly, F., Cheeseman, K., and Mitchinson, M.J. 1996. Randomised controlled trial of vitamin E in patients with coronary disease Cambridge heart antioxidant study (CHAOS). Lancet 347, 781-786. 

Cambridge Heart Antioxidant Study DATATOR Deprenyl and Tocopherol Antioxidative Therapy of Rarkinsonism FMC, Finnish Mobile Clinic Health Examination Survey GISSI, Gruppo Italiano Studio Soprawivenza Infarto HOPE, Heart Outcome Prevention Evaluation HPFS, Health Professional Follow-up Study NHS, Nurses Health Study PPR Primary Prevention Project SPACE, Secondary Prevention with Antioxidants of Cardiovascular disease in End-stage renal disease VEAPS, Vitamin E Atherosclerosis Prevention Study VECAT Vitamin E Cataract Age-related maculopathy Trial. 

Stephens NG, Parsons A, Schofield PM, Kelly F, Cheeseman K, and Mitchinson MJ (1996) Randomised controlled trial ofvitaminE inpatients with coronary disease Cambridge Heart Antioxidant Study (CHAOS). Lancet 347,781-6. 

The antioxidants studied can be classified into two broad types phenolic antioxidants and non-phenolic antioxidants. Phenolic antioxidants have been found to be more promising as they are obtained from dietary sources.Vitamin E (a-tocopherol), the first known chainbreaking antioxidant, is also an o-methoxy phenol. Pulse radiolysis studies of vitamin E and its water-soluble analogue, trolox C, have been reported several years ago. a-tocopherol reacts with almost all the oxidizing free radicals, and the phenoxyl radicals produced during oxidation reactions absorb at -460 nm (Fig. 1). The regeneration reaction of a-tocopherol phenoxyl radicals back to a-tocopherol by water-soluble antioxidant ascorbic acid was also first reported by pulse radiolysis method. The one-electron reduction potential of vitamin E is -0.48 V vs. NHE. Both a-tocopherol and trolox C are used as standards for evaluating the antioxidant ability of new compounds. 

Stephens N G et al 1996 Randomised controlled trial of vitamin E in patients with coronary disease Cambridge heart antioxidant study. Lancet 347 781-786. 

In considering that vitamin C is an important dietary antioxidant, studies were conducted on the effects of the addition of vitamin C upon selected actions of L-tryptophan and on its ability to bind to a specific hepatic nuclear receptor for L-tryptophan and to stimulate protein synthesis.190 The results indicated that the addition of ascorbic acid at 106 to 10-4 M to hepatic nuclei in vitro inhibited 3H-tryptophan binding to the nuclei and nuclear envelopes. Also, the in vivo administration of ascorbic acid before or along with L-tryp-tophan decreased the tryptophan-induced stimulation of hepatic protein synthesis (measured in vitro using microsomes). 

Acronyms and abbreviations PHSl, Physician s Health Study I CHAOS, Cambridge Heart Antioxidant Study ATBC, Alpha-Tocopherol, Beta-Carotene Cancer Prevention Stirdy NHS, Nurses Healtli Study CVD, cardiovascular disease ALS, amyotrophic lateral sclerosis NMD A, A-methyl-D-aspartate glutamate receptors. 

Shirwaikar, A., Shirwaikar, A., Rajendran, K., Punitha, I.S.R. (2006). In vitro antioxidant studies on the benzyl tetra isoquinoline alkaloid berberine. Biol Pharm. Bull, 29(9), 1906-1910. 

For all the antioxidants studied, the 266 nm photoionisation mass spectra are dominated by the molecular ion peak very little fragmentation is observed. In contrast, at 193 nm, the molecular ion peak is usually absent from the photoionisation mass spectra. Similar behaviour is exhibited by the UV stabilisers (Tinuvin) in their photoionisation mass spectra. This wavelength-dependent fragmentation can be exploited for unambiguous identification of many polymer additives. For example, it is shown that the isomeric UV stabilisers Tinuvin 320, Tinuvin 343, and Tinuvin 329 can be differentiated on the basis of... 

In 1960 Hilton [80] published a method for the determination of phenolic antioxidants in polymers based on the preparation of a methanol or ethanol extract of the polymer, followed by coupling the extracted phenol with diazotised p-nitroaniline in strongly acidic medium. The solution is then made alkaline and the visible absorption spectrum determined. Many of the antioxidants studied have an absorption maximum at a characteristic wavelength. Hence, in some instances, it is possible to both identify and determine the antioxidant, provided a pure specimen of the compound in question is available for calibration purposes. Table 2.13 shows absorptivity and wavelength maxima data taken from Hilton s paper. The methods are summarised next. 

High density polyethylene Olive oil Benzopbenone and benzotriazole UV stabilizers, antioxidant Study of migration models [169]... 

The results of the TEARS antioxidant study remain perplexing, specifically the apparent switch from antioxidant to pro-oxidant activities displayed by the pyrone molecules upon moving from higher to lower concentrations. Antioxidant activity, particularly in biological systems, is a very complex matter [13]. Indeed, many studies have shown that various compounds have the ability to act both as antioxidants and pro-oxidants, dependent on various conditions including concentration, metal ions, and presence/absence of co-antioxidants. This includes, but is not limited to, flavonoids [3], carotenoids [14, 15] and ascorbate itself [14, 16, 17]. 

Lafontaine, R. H. (1979). Decreasing the yellowing rate of dammar varnish using antioxidants. Studies in Conservation, 24, 14-22. 

Manojlovic NT, Vasiljevic PJ, Gritsanapan W et al (2010) Phytochemical and antioxidant studies of Laurera benguelensis growing in Thailand. Biol Res 43 169-176 Manojlovic N, Rankovic B, Kosanic M et al (2012) Chemical composition of three Parmelia lichens and antioxidant, antimicrobial and cytotoxic activities of some their major metabolites. Phytomedicine 19 1166-1172... 

Cranberries (Vaccinium macrocarpon) are potentially an excellent dietary source of phenolic confounds such as flavonoids, anthocyanins and caffeic acid derivatives which are potent antioxidants. Studies also link a lowered incidence of breast cancer to cranberry juice consumption. In this study, cranberry fruits were fractionated by several methods and tested for radical-scavenging activity in an effort to begin establishing a link between chemical composition and antioxidant activity. The strongest activity was observed in flavonoid-rich extracts. Cytotoxicity assays in several tumor cell lines showed some specificity for HT-29 tumor cells and K562 cells from a methanolic cranberry extract containing several phenolic compounds. 

Despite these negative attributes, there are opportunities for these phenolic compounds to be extracted using pure or aqueous solvents like ethanol to be further utilized as natural antioxidants. Studies showed that the extracts obtained from the oilseed residues displayed remarkable antioxidant activity, the extent of which depends on the type of residue and the solvent used for the extraction (Amarowicz et al 2000). Wanasundara et al. (1994) reported that the best antioxidant activity was exhibited by a fraction of canola meal phenolics that contained only 34 mg of phenolic compounds/g of sample. On the other hand, Amarowicz et al. (1996) observed that the antioxidant activity of ethanolic extracts of mustard correlated well with the total content of phenolic... 

The concentration of an initiator was 2 x 10 M and the concentration of antioxidants was varied in the range 0.5-10.0 x 10 M. All the antioxidants studied inhibit initiation of cumene oxidation by reacting with cumylperoxide radicals. Figure 9.1 presents the typical kinetic curves for cumene oxidation in the presence of sulphur-containing antioxidants. The rate constants for reaction of the antioxidants with cumylperoxide radicals (kj) was calculated by absorption kinetics of oxygen,... 

It is established that all sulphur-containing antioxidants decompose cumyl hydroperoxide. The kinetic curves of decomposition of cumyl hydroperoxide under the action of these antioxidants are S shaped (Fig. 9.4, curve 1), which is indicative of autocatalysis. There is always some induction period during which a negligible amount of CHP is consumed, followed by a rapid catalytic decomposition of CHP and then a decrease in this rate as the CHP concentration approaches zero. This indicates that catalytic decomposition of CHP in the presence of the antioxidants studied here proceeds not by reaction with the initial antioxidant but with its transformation products formed during the induction period. 

The values of a catalytic factor v showed that the transformation products of one molecule of antioxidant, depending on the structure, are able to decompose from several hundred to several thousand CHP molecules. The value v increases directly proportional to the increase of the ratio of CHP and the initial antioxidant concentrations (Fig. 9.6). This indicates that the antioxidants studied are more efficient in the decomposition of hydroperoxides than other known organic compounds. 

Measurement of the reaction rate constant at various temperatures facilitated determination of the activation energy for the catalytic decomposition of CHP by the antioxidants studied. Depending on the structure of sulphur-containing antioxidant, the activation energy values varied in the range 40-90 kJ/mol. 

It was known that the reaction of phenolic and amine antioxidants with peroxide radicals proceeds in the presence of hydroxy and amine groups. The fact that the reaction products of sulphur-containing antioxidants studied with peroxide radicals do not catalytically decompose CHP indicates that participation of hydroxy and amine groups in the formation of an effective catalyst for the decomposition of hydroperoxides. 

The investigations showed that the introduction of pyridine either at the beginning of the process or at the stage of catalytic CHP decomposition, fully inhibits the reaction of sulphur-containing antioxidants studied with CHP. Hence, the transformation products of the antioxidants catalytically decomposing CHP are acidic in character. 

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