Azide reduction potential

The aqueous solution chemistiy of nitrous acid and nitrites has been extensively studied. Some reduction potentials involving these species are given in Table 11.4 (p. 434) and these form a useful summaiy of their redox reactions. Nitrites are quantitatively oxidized to nitrate by permanganate and this reaction is used in titrimetric analysis. Nitrites (and HNO2) are readily reduced to NO and N2O with SO2, to H2N2O2 with Sn(II), and to NH3 with H2S. Hydrazinium salts yield azides (p. 432) which can then react with further HNO2 ... 

Faraggi M, Klapper MH (1993) Reduction potentials determination of some biochemically important free radicals. Pulse radiolysis and electrochemical methods. J Chim Phys 90 711-744 Faraggi M, Klapper MH (1994) One electron oxidation of guanine and 2 -deoxyguanosine by the azide radical in alkaline solutions. J Chim Phys 91 1062-1069 Faraggi M, Broitman F, Trent JB, Klapper MH (1996) One-electron oxidation reactions of some purine and pyrimidine bases in aqueous solutions. Electrochemical and pulse radiolysis studies. J Phys Chem 100 14751-14761... 

The first experimental evidence that Met in j8-APl-42 is more easily oxidized than in other peptides and proteins comes from one-electron oxidation of /3AP1-40 using azide radicals (Nj) produced by pulse radiolysis.Thermodynamic considerations indicate that Nj should not oxidize Met residues unless the one-electron reduction potential of Met is lowered because of favorable environment. It was shown that Met is the target in /3-AP(l-40) oxidation. Conversely the oxidation of /3-AP(40-l) with a reversed sequence of amino acids has shown that Tyr is the target of Nj radicals. These observations are the first experimental evidences that (i) Met in AP(l-40) is more easily oxidized than in other peptides or proteins, and (ii) a change in a primary sequence drastically affects the one-electron reduction potential of Met, even in a small peptides. 

Complex IV - Complex IV is also known as cytochrome oxidase, because it takes electrons from cytochrome c. Complex IV contains cytochromes a and a3. Cytochromes a and a3 evidently represent two identical heme A moieties, attached to the same polypeptide chain. They are within different environments in the inner membrane, however, so they have different reduction potentials. Each of the hemes is associated with a copper ion, located close to the heme iron. Electrons that pass through complex IV can be blocked by cyanide, azide, and carbon monoxide and the artificial electron carrier, ferricyanide, can accept electrons from cytochrome a in the complex (Figure 15.9). A model for the final stages in proton pumping by cytochrome oxidase is shown in Figure... 

Figure 13.30 Biocatalytic azide reduction-cyclization sequence for the synthesis of various pyrrolo[2,l-c][l,4]benzodiazepines, potential antitumor antibiotics.

Exposure of ferri-heme-hemopexin to imidazole or KCN can displace one or both of the heme coordinating His residues, but millimolar concentrations are required (138). Other potential ligands such as azide or fluoride are inactive. This coordination stability of the ferri-heme-hemopexin bis-histidyl complex, despite the exposed heme site, is home out by thermal imfolding studies (Section IV,F). Reduction of the heme-hemopexin complex, however, has dramatic effects on its stability. 

There is one method of direct alkylation of a nitrogen nucleophile. Preliminary FGI (with reduction in mind again) to an alkyl azide 52 allows C-N disconnection to the alkyl halide and azide ion 54. This interesting species is linear and can slip into crowded molecules like a tiny dart. But there is a drawback all azides are toxic and POTENTIALLY EXPLOSIVE. 

The synthetic potential of reductions by formate has been extended considerably by the use of ammonium formate with transition metal catalysts like palladium and rhodium. This forms a safe alternative to use of hydrogen. In this fashion it is possible to reduce hydrazones to hydrazines, azides and nitro groups to amines, to dehalogenate chloro-substituted aromatics, and to carry out various reductive removals of functional groups. For example, phenol triflates are selectively deoxygenated to the aromatic derivatives using triethylammonium formate as reductant and a palladium catalyst. - These recent af li-cations have been reviewed. 

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