Copper ions radicals

Dialkyl peroxydicarboaates are used primarily as free-radical iaitiators for viayl monomer po1ymeri2ations (18,208). Dialkyl peroxydicarboaate decompositioas are accelerated by certaia metals, coaceatrated sulfuric acid, and amines (44). Violent decompositions can occur with neat or highly concentrated peroxides. As with most peroxides, they Hberate iodine from acidified iodides. In the presence of copper ions and suitable substrates, dialkyl peroxydicarbonates have been used to synthesi2e alkyl carbonates (44) ... 

Apparently the alkoxy radical, R O , abstracts a hydrogen from the substrate, H, and the resulting radical, R" , is oxidized by Cu " (one-electron transfer) to form a carbonium ion that reacts with the carboxylate ion, RCO - The overall process is a chain reaction in which copper ion cycles between + 1 and +2 oxidation states. Suitable substrates include olefins, alcohols, mercaptans, ethers, dienes, sulfides, amines, amides, and various active methylene compounds (44). This reaction can also be used with tert-huty peroxycarbamates to introduce carbamoyloxy groups to these substrates (243). 

The concentration of copper(II) has a pronounced effect on the course of the reaction. In the presence of very low copper(II) concentrations, oxidation of allyl radical 69 is slow and major amounts of allyl radical dimer are formed. In the presence of very high concentrations of copper(II), radical 68 is oxidized rapidly before addition to diene can take place. An optimum yield of product 71 can therefore only be achieved at certain copper(II) concentrations. The metal-ion-promoted addition of chloramines to butadiene appears to follow the same mechanism93. 

Superoxide dismutase enzymes are functional dimers of molecular weight (Mr) of approximately 32 kDa. The enzymes contain one copper ion and one zinc ion per subunit. Superoxide dismutase (SOD) metalloenzymes function to disproportionate the biologically harmful superoxide ion-radical according to the following reaction ... 

Copper ions bind to and inhibit many enzymes. Of more importance, perhaps, is that in free solution or when bound to proteins, copper ions catalyse the Fenton reaction which produces the highly dangerous hydroxyl radical, OH (Appendix 9.6). 

In summary, the copper ion transfers an electron from the unsaturated substrate to the diazo-nium cation, and the newly formed diazonium radical quickly loses nitrogen. The aryl radical formed attacks the ethylenic bond within the active complexes that originated from aryldiazo-nium tetrachlorocuprate(II)-olefin or initial arydiazonium salt-catalyst-olefln associates and yields >C(Ar)-C < radical. The latter was detected by the spin-trap ESR spectroscopy. The formation of both the cation-radical [>C=C<] and radical >C(Ar)-C < as intermediates indicates that the reaction involves two catalytic cycles. In the other case, radical >C(Ar)-C < will not be formed, being consumed in the following reaction ... 

The data shown in Figures 1-4 support the suggestion that PM2 5 contains radicals that, like those in cigarette tar, can reduce oxygen to superoxide, which then forms hydrogen peroxide and, ultimately, the hydroxyl radical, as shown in reactions 1-3. Iron and copper ions, which are the transition metals most frequently found in combustiongenerated particles (44) and also are ubiquitous in biological systems, could be involved in reaction 3 ... 

This mechanism is of importance in radical induced amino acid damage catalyzed by copper ions. The study of the decomposition of transients with a metal-carbon -bond containing two potential leaving groups (both an amine and a carboxylate group) at the p position of the carbon centered radical is of special interest. It was reported that the intermediate formed with the amino acid 2-methylalanine with cupric ions decomposes via p-carboxyl elimination whereas the intermediate formed with cuprous ions decomposes via p-amine elimination (102). 

There are numerous reports on the chemical synthesis of models for the active site of galactose oxidase both in the reduced Cu(l) and the oxidized Cu(II) form. We mention only a selection in which EPR is at least used to characterize the complex either on the phenoxy radical or on the copper part, typically in conjunction with X-ray data.48,49 50 A review on structural, spectroscopic and redox aspects of galactose oxidase models is available.51 More important with respect to EPR is the report on the 3-tensor calculation of the thioether substituted tyrosyl radical by ab initio methods but this is borderline to the aspects treated in this review since the copper ion is not involved.52... 

This screening work shows the selective nature of E D D S for transition metal ions in the presence of hardness ions, as compared with other chelants. Moreover, the reduced dye damage demonstrates how well EDDS prevents the formation of hydroxyl radicals from peroxy species and copper ions [32]. 

How is the reduced cofactor reoxidized Presumably the copper ion adjacent to the TPQ functions in this process, passing electrons one at a time to the next carrier in a chain. There is no copper in the TTQ-containing subunits. Electrons apparently must jump about 1.6 ran to the copper ion of amicyanin, then another 2.5 nm to the iron ion of the cytochrome c.472 Reoxidation of the aminoquinol formed in Eq. 15-53, step d, yields a Schiff base whose hydrolysis will release ammonia and regenerate the TTQ. Intermediate states with Cu+ and a TTQ semiquinone radical have been observed.4833... 

The ability of copper ions to undergo reversible changes in oxidation state permits them to function in a variety of oxidation-reduction processes. Like iron, copper also provides sites for reaction with 02, with superoxide radicals, and with nitrite ions. 

Mira L, Tereza Fernandez M, Santos M, Rocha R, Helena Flore ncio M, Jennings KR. 2002. Interactions of flavonoids with iron and copper ions A mechanism for their antioxidant activity. Free Radic Res 36 1199-1208. 

The C(l )-radical does not give rise to frank SSB as such, at least not in remarkable yields (see above), but cationic polyamines and divalent metal cations (Roginskaya et al. 2005) as well as transition metal ions such as 1,10-phenanth-roline-copper ion are capable of catalyzing p-elimination processes from 2-dRL that lead to an SSB and eventually to 5-MF. These reactions are discussed in some detail below (Sect. 12.9.4). 5-MF is also produced by desferal-copper ion (Joshi et al. 1994) or oxoruthenium(IV) (Neyhart et al. 1995 Cheng et al. 1995). 

Figure 8.3 Pomegranate juice consumption reduces serum and LDL oxidation in humans and in atherosclerotic E° mice. Mean ( SD) effect of 2 and 9 weeks of PJ supplementation to 13 healthy men and to E° mice (A and B, respectively) on the susceptibility of serum to radical-induced lipid peroxidation and copper ion-induced LDL oxidation (C and D, respectively) is shown. = p < 0.01 (after vs. before PJ consumption in humans, and PJ vs. control in mice).

---