Antioxidants, adsorption

Antioxidants often contain functional groups that are capable of interaction with the filler surface. This can result in antioxidant adsorption depending upon the surface chemistry of the filler and the type of antioxidant. Once adsorbed, the antioxidant becomes ineffective because it is unable to diffuse to, and react with, the radicals that cause polymer degradation. The amount of deactivated antioxidant can he significant, and the usual response in industry is to add more antioxidant to attain the required level of stability. However, that approach raises the cost of the compound significantly. Another commercial approach is to use an epoxy additive that preferentially adsorbs onto the filler surface, physically blocking antioxidant adsorption. That helps to reduce cost, but the epoxy additive is itself still a relatively expensive chemical. 

Electrophoresis fraction No. 4 was chosen for further chemical characterization, in spite of the fact that it was not as antioxidative as the precipitate. It was, however, considered to be more homogeneous. At least it was purified from the fluorescent material. Still, its purity is uncertain. The fact that no well defined bands were obtained in the electrophoresis indicates that the fractions consisted of more than one compound, possibly differing slightly in molecular weight and/or content of charged groups. Another explanation to the lack of distinct bands could be unselective adsorption between the compound and the paper. This is supported by the fact that rechromatography of the five electrophoresis fractions failed to reproduce the same fractions distinctly. 

Official quality parameters comprise acidity, peroxide value, halogenated solvents, ultraviolet adsorption and sensory assessment. In addition to these official parameters important roles and high values are attributed to the content of the chlorophyll and carotene pigments and phenol antioxidants, as well as to the correlated induction time value. The significance of olive oil quality parameters is explained in Table 2.1. The phenol content and the related induction period, defined as the delay in the commencement of oxidation in an oil , merits particular comment the longer the induction period, the better the oil. Resistance... 

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... 

Highly disperse silica is widely used in pharmaceutical formulations as a filler, adsorbent, thickener etc.5 Their high hydrophilicity and the absence of emulsifying ability restrict their application. In contrast to hydroxylated silica, partially or fully hydrophobized silica may exhibit improved properties as a drug carrier. The main goal of this work is to study hydrophobized silica nanocomposites with immobilized vitamins C and E. Investigations of adsorption-desorption processes which involve silica nanoparticles and the antioxidants are described. Factors affecting the antioxidant stability have also been carefully considered. 

Antioxidant activity of silica nanocomposites with immobilized vitamin C was tested using the polyphenolic activity index.8 After adsorption of ascorbic acid on the silica surface and centrifugation, the excess solution was removed to obtain the suspension of a fixed volume (2 ml). Distilled water, sodium carbonate solution, and Folin-Ciocalteu s phenol reagent were subsequently added to suspensions and to the reference Vitamin C solution. The suspensions were then stored for 30 min, and the optical density of supernatant was measured at X = 750 nm. The reference solution of ascorbic acid was used to compare antioxidant activity of vitamin-containing nanocomposites with the activity of dissolved vitamin C. 

Partial silylation of the highly disperse silica surface enhances the adsorption of vitamin E from ethanol solution, and provides the ability to obtain water-soluble nanocomposites containing vitamin E. Immobilization of vitamin C on the silica surface prevents its oxidation. Its interaction with the adsorbent surface leads to a decrease in proton-donor ability of the OH-groups involved in the oxidation of ascorbic acid. Elydrophobized silica nanocomposites are characterized by a prolonged desorption of immobilized vitamins. It has been shown that vitamin C does not lose its antioxidant properties after desorption. 

Oil (Aa 4-38) determines oil content in a dried sample of oil-bearing material by extraction with petroleum ether. This method is specific for cottonseed, which first must be fumed with hydrochloric acid to prevent oil adsorption to the fiber. Additional methods exist for other oilseeds. Oxygen Stability Index (OSI) (Cd 12b-92) measures the oxidation induction period of fat sample (essentially the time for a sample to exhaust its antioxidant properties) under conditions of the test. 

Further examples reported in Table 40 arc given by the alkyl ketone moieties deriving from oxidation of polyenes, which arc subjected to Mannich aminomethylation in order to produce compounds 559 having dispersant properties for lubricating oils, by benzotriazoles 557, capable of forming, due to physical adsorption, thin layers over the surfaces subjected to friction, and by S-Mannich bases 558, combining antifriction and antioxidant properties. 

Adsorptive purihcation, in its most general sense, involves the use of adsorbents to remove undesirable constiments and contaminants from fats and oils by adsorptive mechanisms. It must be noted, however, that although different adsorbents do exhibit some degree of selectivity for certain adsorbates (see Section 4.3), none exhibit specific selectivity for a single compound or chemical. Some trace constituents that are desirable (e.g., tocopherols) will also be removed. According to Boki et al. (106), 20-40% of the tocopherols present in most alkali-refined oils are removed by bleaching with acid-activated bleaching clay the exception is soybean oil, which only loses 3-5% (71, 105). Buxton has reported (107) that activated carbon removes antioxidants from fish hver oils and renders the vitamin A in the oil unstable. 

Phenol-ketone novolacs 1487, 1488 Phenol-nitrile complexes 377 Phenol radical cations 1101 fragmentation of 289-291 Phenols—see also Biphenols, Bis-phenols, Hydroxybenzenes, Polyphenols acidities of, gas-phase 310-312 acylation of 629-632, 933, 934 Lewis acid catalyzed 631 montmoriUonite-catalyzed 632 pyridine-catalyzed 631 adsorption of 944 alkylation of 606-629, 941 Brdnsted acid catalyzed 612 Lewis acid catalyzed 607-611 solid acid catalyzed 612-621 stereoselective 621-626 under supercritical conditions 621 as antioxidants 139-143, 840-901 ort/io-substituted 845 thermochemistry of 139, 140, 179 autoxidation of 1118, 1119 bromination of 649-651 jr-cation interaction of 322 chlorination of 649 comparison with isoelectronic methyl, amino and fluoro aromatic derivatives 226... 

Microbiological preservatives and/or antioxidants may be necessary, especially if a multi-dose product is envisaged, or the oil used in the formulation is contaminated with peroxide. Care must be taken with both types of additive, as it is often the case that it partitions between the two phases and some of the required activity is lost. Activity may be also lost if there is incompatibility with other excipients, or there is adsorption onto the container/closure system. The choice of either component must therefore be checked thoroughly by effectiveness testing of the final product during the pharmaceutical development process. 

This volume is including information about thermal and thermooxidative degradation of polyolefine nanocomposites, modeling of catalytic complexes in the oxidation reactions, modeling the kinetics of moisture adsorption by natural and synthetic polymers, new trends, achievements and developments on the effects of beam radiation, structural behaviour of composite materials, comparative evaluation of antioxidants properties, synthesis, properties and application of polymeric composites and nanocomposites, photodegradation and light stabilization of polymers, wear resistant composite polymeric materials, some macrokinetic phenomena, transport phenomena in polymer matrix, liquid crystals, flammability of polymeric materials and new flame retardants. 

Modifeation of alumina surfaee to enhance selective adsorption of particular compounds is an area of rapid development. The activated alumina surface contains a range of surface sites differing in their chemical structure and reactivity. Modification of the surface to contain a greater proportions of surface fuctionalities that enhance the desired separtion or reaction which reducing undesired sites, is a powerful tool in the design of selective adsorption process. In the present study the modification of alumina surface is effected by treatment with acid and base to enhance the adsorption of an antioxidant (tert-butyl catechol) from aromatic hydrocarbon (styrene). 

Antioxidants Butylated hydroxytoluene, Adsorption MicroPak Hexane-dichlorome-... 

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