Synergistic action

Localised attack or fracture due to the synergistic action of a mechanical factor and corrosion... 

There are in addition several other factors that accelerate corrosion and must betaken into account these include crevices, galvanic coupling, tensile stress, aeration, presence of impurities, surface finish, etc. If these were also taken into consideration then several million experiments would have to be performed to compile such data. There are many instances where two or more chemicals exert a marked synergistic action such that low dissolution rates obtained in either environment become much greater in the presence of both. Further, the corrosiveness of a chemical will be affected by the presence of certain impurities, which may act as either accelerators or inhibitors. To take all these factors into account would add to an already impossible task and as Evans has remarked, There are not enough trained investigators in the world to obtain the empirical information to cover all combinations of conditions likely to arise . Unfortunately corrosion science has not yet reached the stage where prediction, based on a few well established laws, allows selection of materials to be made without recourse to a vast amount of data. 

Thus, effectiveness of basic (alkaline) additives has been greatly improved by increasing their solubility in base stocks, by exploiting synergistic action between two similar additive types and by the use of a third additive to enhance (catalyse) the performance of the other two. Similar principles have been used to augment the performance of oxidation inhibitors. 

That the synergistic action of an electron donor (Na8+) and electron acceptor (O5") promoter can cause dramatic enhancement in rate and selectivity. This is very likely due to the increase in the field strength, E, of the effective double layer discussed in Chapters 5 and 6 and to the concomitant enhanced interaction with the adsorbate dipoles, leading to more pronounced promotional behaviour (Chapter 6). 

Kostarelos K, Teknetzis A, Lefaki I, loannides D, Minas A (2000) Double-blind clinical study reveals synergistic action between alpha-hydroxy acid and betamethasone lotions towards topical treatment of scalp psoriasis. J Eur Acad Dermatol Venereol 14(1) 5-9... 

Meled, M., Thrasyvoulou, A., and Belzunces, L.P. (1998). Seasonal variation in susceptibility of Apis mellifera to the synergistic action of prochloraz and deltamethrin. Environmental Toxicology Chemistry 17, 2517-2520. 

Stabilizers bind at a site separate from those of traditional activators and of ciguatoxin-brevetoxin, but they exert a synergistic action on both types of activators (J5, 42). This action potentiates the activators and generally increases their efficacy, yielding larger depolarizations at lower doses 42) it occurs uniquely with the peptide stabilizers and not with ions or oxidants that also slow the inactivation of Na current 37). 

KAJiMOTO G (1963) On the antioxidative components and antiseptic components in tea. Part 111. The synergistic action of caffeine to catechin components , Nihon Shokuhin... 

BisHov s J, MASUOKA Y and KAPSALis J G (1977) Antioxidant effect of spices, herbs and protein Hydrolyzates in freeze-dried model systems Synergistic action with synthetic phenolic antioxidants, J Foot/ Processing Preservation, 1, 153-66. 

Table 2 Mechanisms of synergistic action towards currently used antibiotics hypothesized for catechins and proanthocyanidins...

Bronson F. and Maruniak J.A. (1975). Male-induced puberty in female mice evidence for a synergistic action of social cues. Biol Reprod 13, 94-98. 

The relative toxicity, especially of the newer compounds, to various pests and species is of practical importance, as are also differences in species tolerance to DDT and other sprays. This is also of direct concern in relation to parasites and predators. There is interest in synergistic action and the effect of spreaders, stickers, and related products. The effect and use of repellents and attractants have received attention. 

The synergistic action of these four effects may explain why trivinylborane (24) shows no sign of B—C 7r-bonding but vinylboron fluorides (e.g., 25a) do. 

K Osann, P Sweet, LM Slater. (1992). Synergistic action of cyclosporin A and verapamil on vincristine and daunorubicin resistance in multidrug-resistant human leukemia cells in vitro. Cancer Chemother Pharmacol 30 152-154. 

A mathematical model has been proposed to account for the mutual synergistic action of either particle component on the other in increasing the value of the dimensionless time 0 as shown in Fig. 53, in terms of the mass fraction x2 of fines, and two empirical parameters n, and n2 ... 

T. Handa, T. Nagashima and N. Ebihara, Synergistic Action of Sb2(>3 with Bromine-Containing Flame Retardants in Polyolefins. II. Structure-Effect Relationships in Flame Retardant Systems," J. of Fire Retardant Chemistry,, 37 (1981). ... 

Synergistic Action of Quinone in Combination with Phenol or Amine... 

The synergistic action of a phenol and aromatic amine mixture on hydrocarbon oxidation was found by Karpukhina et al. [16]. A synergistic effect of binary mixtures of some phenols and aromatic amines in oxidizing hydrocarbon is related to the interaction of inhibitors and their radicals [16-26]. In the case of a combined addition of phenyl-A-2-naphthylamine and 2,6-bis(l,l-dimethylethyl)phenol to oxidizing ethylbenzene (v, = const, 343 K), the consumption of amine begins only after the phenol has been exhausted [16], in spite of the fact that peroxyl radicals interact with amine more rapidly than with phenol (7c7 (amine) = 1.3 x 105 and /c7 (phenol) = 1.3 x 104 L mol 1 s respectively 333 K). This phenomenon can be explained in terms of the fast equilibrium reaction [27-30] ... 

The rare example of synergistic action of a binary mixture of 1-naphthyl-A-phcnylaminc and phenol (1-naphthol, 2-(l,l-dimethylethyl)hydroquinone) on the initiated oxidation of cholesterol esters was evidenced by Vardanyan [34]. The mixture of two antioxidants was proved to terminate more chains than both inhibitors can do separately ( > /[xj). For example, 1-naphtol in a concentration of 5 x 10 5 mol L-1 creates the induction period t=170s, 1 -naphthyl-A-phenylamine in a concentration of 1.0 x 10-4 mol L 1 creates the induction period t = 400s, and together both antioxidants create the induction period r = 770 s (oxidation of ester of pelargonic acid cholesterol at 7= 348 K with AIBN as initiator). Hence, the ratio fs/ZfjXi was found equal to 2.78. The formation of an efficient intermediate inhibitor as a result of interaction of intermediate free radicals formed from phenol and amine was postulated. This inhibitor was proved to be produced by the interaction of oxidation products of phenol and amine. 

The combined addition of two phenols, one of which is sterically hindered, for example, 2,6-bis(l,l-dimethylethyl)phenol, and another is sterically nonhindered also leads to a synergistic effect [35-38]. As found by Mahoney [35], 2,4,6-tris(l,l-dimethylethyl)phenol with a concentration of 10 4 L mol 1 does not virtually inhibit the initiated oxidation of 9,10-dihydroan-thracene (333 K), but /)-methoxyphenol, taken in the same concentration, does inhibit oxidation. The induction period doubles if two phenols are added together in equal concentrations, which indicates that both phenols are involved in chain termination. The mechanism of synergistic action can be explained by the following kinetic scheme [35] ... 

One more mechanism responsible for the synergistic action of two phenols has recently been discovered during the study of disproportionation of phenoxyl radicals [42,43], This reaction is possible only for phenoxyls possessing C—H groups in the ortho- or para-position [43], For instance, 2,4,6-tris(l,l-dimethylethyl)phenoxyl is unable to disproportionate, whereas ionol radicals disproportionate. It was found that the cross-disproportionation of ionol and a-tocopherol radicals occurs much more rapidly than homodisproportionation (323 K [42]) ... 

Nitroxyl radicals as alkyl radical acceptors are known to be very weak antioxidants due to the extremely fast addition of dioxygen to alkyl radicals (see Chapter 2). They retard the oxidation of solid polymers due to specific features of free radical reactions in the solid polymer matrix (see Chapter 19). However, the combination of two inhibitors, one is the peroxyl radical acceptor (phenol, aromatic amine) and another is the alkyl radical acceptor (nitroxyl radical) showed the synergistic action [44-46]. The results of testing the combination of nitroxyl radical (>NO ) (2,2,6,6-tetramethyl-4-benzoylpiperidine-l-oxyl) + amine (phenol) in the autoxidation of nonene-1 at 393 K are given here ([>NO ]o + [InH]o = 1.5 x 10 4mol L 1 p02 98 kPa) [44]. 

It is seen that the substitution of the part of amine or phenol by quinone prolongs the induction period by two or three times. The mechanism of synergistic action of quinone is the same as in the case of nitroxyl radicals. Quinone reacts with InH with production of semiquinone radicals. The latter rapidly reacts with peroxyl radicals and provokes the additional rapid chain termination [47],... 

The Synergistic Action of Tyrphostins with Cytotoxic Agents... 

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