Synergism more

Synergism is appHed to a situation where the effect of two or more chemicals that have common mechanism of toxicity, given together, is significantly greater than that expected from considerations on the toxicity of each material alone. This differs from potentiation in that both materials contribute to the toxic injury, and the net effect is always greater than additive. 

Antioxidants are today often used in combination. One reason for this is that certain combinations can exhibit in a polymer an effect sometimes found with other additives, that known as synergism. In these circumstances two antioxidants may exhibit a co-operative effect and be more powerful than either antioxidant used alone, even when the total antioxidant concentration is the same. Certain terms are sometimes encountered here and these are defined in Table 7.6. 

In commercially practical terms it may be that although synergism occurs, one additive may be sufficiently less expensive for more to be used to achieve the required stability and still give the lowest overall cost. 

In antioxidants, synergism appears to arise either from one antioxidant effectively regenerating another so that the latter does not become consumed or by the two antioxidants functioning by differing mechanisms. The latter is more important and it is easy to see how effective a combination of peroxide decomposer and chain-breaking antioxidant can be. 

Two final points should be made while considering antioxidant synergism. Firstly, some antioxidants which function by more than one mechanism are in all probability autosynergistic. Secondly, certain additives which appear to act... 

In many of their complexes PF3 and PPI13 (for example) resemble CO (p. 926) and this at one time encouraged the belief that their bonding capabilities were influenced not only by the factors (p. 198) which affect the stability of the a P M interaction which uses the lone-pair of elecU"ons on p and a vacant orbital on M, but also by the possibility of synergic n back-donation from a nonbonding d , pair of electrons on the metal into a vacant 3d , orbital on P. It is, however, not clear to what extent, if any, the a and n bonds reinforce each other, and more recent descriptions are based on an MO approach which uses all (cr and n) orbitals of appropriate symmeU"y on both the phosphine and the metal-containing moiety. To the extent that a and n bonding effects on the stability of metal-phosphorus bonds can be isolated from each otlier and from steric factors (see below) the accepted sequence of effects is as follows ... 

A cooperative interaction between two or more antioxidants (or antioxidant function) that leads to an overall antioxidant effect greater than the sum of the individual effects of each antioxidant is referred to as synergism. Synergism can be achieved in different ways. It may arise from the combined action of two chemically similar antioxidants, e.g., two hindered phenols (homosynergism), or when two different antioxidant functions are present in the same molecule (autosynergism) the latter is exemplified by many commercial antioxidants (e.g., Irgastab 2002, AO 29 Table lb), which have CB and UVA activity. 

Vitamin D3 (VD3) and retinoids synergistically inhibit the growth and progression of squamous cell carcinomas and actinic keratoses in chronically sun exposed skin. One reason for this synergism may be the direct influence of VD3 on the isomerization and the metabolism of RA. Here, VD3 inhibits the isomerization of 13-cis-RA to the more receptor active all-trans and 9-cis-isomers. Moreover, the VD3 derivative secocholestra-trien-l,3,24-triol (tacalcitol), used for the treatment of severe keratinizing disorders inhibits 4-hydroxylation of all-ri ans-RA. 

Synergism Similar to potentiation [q.v.], but some authors use the term in a more restricted way (e.g., where one component of a mixture, the synergist, would not cause toxicity if applied alone at the dose in question). 

The most common natural antioxidants are tocopherols, ascorbic acid and P-carotene (more often synthetic nature-identical compounds than natural products). Their changes were studied in detail in model systems, fats and oils, but experimental evidence is mainly lacking on more complicated systems, such as natural foods and ready dishes. Still less is known on different antioxidants from spices and from essential oils. These data will probably be obtained gradually. Very little is known about synergism of antioxidants in food products other than edible fats and oils or their regeneration from the respective free radicals and quinones. In mixtures, some antioxidants are preferentially destroyed and others are saved. Some data have already been published, but these complex changes should be studied in more detail. 

For more efficient utilization of MOFs sorbents, several hybrid systems based on MOFs with other solid sorbents have been investigated in the literature. The objective of having hybrid materials is to utilize the synergism between the two sorbents and therefore ultimately improve the overall performance in C02 separation. Moreover, sorbents such as activated carbons, graphenes, and CNTs provide the added feature of high surface area and easily functionalized sites which contribute to the tuning of the final properties of the composite... 

Hence, for both of the oxidants, N02 and ONOO-, a marked synergism in cell protection by the antioxidant combination of P-CAR with vitamins E and C was observed for both in vivo and in vitro experiments, although the synergistic effect was more pronounced in protection from N02 . 

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