Antioxidant properties chemical methods

Abstract. Adsorption of antioxidants (vitamins C and E) from aqueous and ethanol solutions on unmodified and partially hydrophobized nanosilica A-200 was studied using UV spectroscopy and quantum chemical methods with consideration for the solvent effects. Antioxidant power of silica nanocomposites with immobilized vitamins was evaluated by measuring the total polyphenolic index following the Folin-Ciocalteu method. It has been shown that immobilization of vitamins on silica surface leads to their stabilization. Being released from the carrier molecules of vitamins do not lose their antioxidant properties... 

For the assessment of antioxidant properties of the isolated compounds from these four spices, we used two other systems as well as the OSI method. The electron-donating ability of chemical substances results in their antioxidant activity toward lipid oxidation. Therefore the radical scavenging activity against l,l-diphenyl-2-picrylhydra2yl (DPPH) was measured as one of the antioxidant assay (7). The inhibitory effect on autoxidation of linoleic acid in an ethanol-buffer system was adopted as another method. This assay system is one of the simple conditions of lipid oxidation in multiple phases like food for evaluation of effects of antioxidants (8). 

Another approach was developed by Scott in the 1970 s (7.8) which utilises the same mechanochemistry used previously by Watson to initiate the Kharacsh-type addition of substituted alkyl mercaptans and disulphides to olefinic double bonds in unsaturated polymers. More recently, this approach was used to react a variety of additives (both antioxidants and modifiers) other than sulphur-containing compounds with saturated hydrocarbon polymers in the melt. In this method, mechanochemically formed alkyl radicals during the processing operation are utilised to produce polymer-bound functions which can either improve the additive performance and/or modify polymer properties (Al-Malaika, S., Quinn, N., and Scott, 6 Al-Malaika, S., Ibrahim, A., and Scott, 6., Aston University, Birmingham, unpublished work). This has provided a potential solution to the problem of loss of antioxidants by volatilisation or extraction since such antioxidants can only be removed by breaking chemical bonds. It can also provide substantial improvement to polymer properties, for example, in composites, under aggresive environments. 

Selecting the correct combination of antioxidants is specific to the elastomer polymer type as well as the compound formulation and the end use application. It is important to note that many of these materials may be considered toxic or hazardous in nature. Chemical specific Material Safety Data Sheets (MSDS) should be consulted for safe handling practices. Particular attention should be given to the proper selection and use of personal protective equipment, including proper ventilation and/or the use of respiratory protection. The MSDS will also provide information on how to handle spills and proper disposal procedures. Disposal methods should not be overlooked since these chemicals are all regulated, and hence waste disposal must conform to EPA and local disposal regulations. Refer to Rubber Oxidation. (Source Handbook of Polymer Science and Technology Volume 2 - Performance Properties of Plastics and Elastomers, N. P. Cheremisinoff - editor, Marcel Dekker Inc., New York, 1989). 

The numerical determination of the value quantities as a function of time allows explaining the chemical reason of the antioxidant s effectiveness. Also the value method has been used to analyze the mechanisms for the liquid phase oxidation of ethylbenzene and model lipids methyl linoleate, in the presence of antioxidants in the reaction mixture - butylated hydroxytoluene and a-tocopherol, respectively. The dominant steps responsible for the antioxidant and pro-oxidant properties of cMn reaction inhibitors are identified. 

The most contemporary chemical physics methods and principles are applied to the characterization of these ten properties. The coverage is broad, ranging from the study of biopolymers to the analysis of antioxidant and medicinal chemical activity, on the one hand, to the determination of the chemical kinetics of not chemical systems and the characterization of elastic properties of novel nanometer scale material systems, on the other. 

Advances in Kinetics and Mechanism of Chemical Reactions describes the chemical physics and/or chemistiy of 10 novel material or chemical systems. These 10 novel material or chemical systems are examined in the context of issues of stmeture amd bonding, and/or reactivity, and/or transport properties, and/or polymer properties, and/ or biological characteristics. This eclectic survey thus encompasses a special focus on the associated kinetics, reaction mechanisms and/or other chemical physics properties, of these 10 broadly chosen material or chemical systems. Thus, the most contemporary chemical physics methods and principles are applied to the characterization of the properties of these 10 novel material or chemical systems. The coverage of these novel systems is thus broad, ranging fiom the study of biopolymers to the analysis of antioxidant and medicinal chemical activity, on the one hand, to the determination of the chemical kinetics of novel chemical systems, and the characterization of elastic properties of novel nanometer scale material systems, on the other hand. 

Structural differences between different polyphenols decide their chemical properties and thus affect their extractability. Antioxidant effect, which is one of the most commonly smdied effects of polyphenols, has been found to generally increase with the amount of polyphenols in the extracts [23-25]. However, the factors such as solvents and the reactivity and solubility of different polyphenols in different solvents also affect the extraction efficiency and antioxidant activity of the different polyphenols. Hence, the extraction processes and the solvents to be chosen are very much dependent on the type of polyphenols to be extracted, and the processes are chosen to obtain the highest amotmt of polyphenols possible. Study of the mechanisms of different extraction methods, their basic principles, and factors affecting the extraction processes can be helpful in deciding the best method for the extraction of different polyphenols from different sources. 

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