Synergism example

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 ... 

Synergism can also arise from cooperative effects between mechanistically different classes of antioxidants, e.g., the chain breaking antioxidants and peroxide decomposers (heterosynergism) [42]. For example, the synergism between hindered phenols (CB—D) and phosphites or sulphides (PD) is particularly important in thermal oxidation (Table 2). Similarly, effective synergism is achieved between metal dithiolates (PD) and UV-ab-sorbers (e.g., UV 531), as well as between HALS and UV-absorbers, (Table 3). 

Polypropylene block and graft copolymers are efficient blend compatibilizers. These materials allow the formation of alloys, for example, isotactic polypropylene with styrene-acrylonitrile polymer or polyamides, by enhancing the dispersion of incompatible polymers and improving their interfacial adhesion. Polyolefinic materials of such types afford property synergisms such as improved stiffness combined with greater toughness. 

A redox mechanism. An oxidized form of a more efficient component of a synergic mixture is reduced by the presence of a less reactive component. Example aromatic amines + phenols. 

Expert systems represent a branch of artificial intelligence that has received enormous publicity in the last two to three years. Many companies have been formed to produce computer software for what is predicted to be a substantial market. This paper describes what is meant by the term expert system and the kinds of problems that currently appear amenable to solution by such systems. The physical sciences and engineering disciplines are areas for application that are receiving considerable attention. The reasons for this and several examples of recent applications are discussed. The synergism of scientists and engineers with machines supporting expert systems has important implications for the conduct of chemical research in the future some of these implications are described. 

Manufacturers have acknowledged the use of hundreds of chemical additives in tobacco products (Lefifingwell et al. 1972 Philip Morris 1994). Some of these additives may synergize with nicotine or demonstrate other reinforcing effects. Cocoa, for example, contains alkaloids, which may themselves have pharmacological effects when inhaled, or may modify the effects of nicotine. Pyridine is chemically a portion of the nicotine molecule, acting as a CNS depressant similar to nicotine, although it is less potent. 

Rh, are the base of active catalysts for CO hydrogenation and the hydroformylation of olefins. The presence of several promoters modifies their catalytic behavior and synergic effects on the base-metal have been observed Table 8.5 illustrates several examples in which homonuclear or heteronuclear carbonyl compounds have been used in the preparation of Co- or Co-Rh-based catalysts for the CO hydrogenation and/or hydroformylation reactions. 

When two compounds exert the same action by acting at different sites, their interaction will often result in a synergistic effect but a simple additive effect is also a possibility (the synergism between smoking and asbestos exposure is the classical example). 

Another excellent example of synergism is the activation of a soluble adenylyl cyclase by forskolin and the a-... 

Abrupt temperature changes are easier to appreciate than long-term changes. El Nino events, which are the best examples of the first type, occur in Indonesian forests in synergisms with threatening by human activities (Curran 1999). The same probably occurs on coral reefe too, where El Nino warming causes the death of seaweeds and invertebrates, in particular corals, which are extremely sensitive to temperature variations. 

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