Acid Radical Anions

The present results confirm that the doublets observed in the e.s.r. spectra of several carboxylic acids immediately after X- or y-irradiation at 77°K are due to the radical anions of the acid. Further it is reasonable to assume that a similar sequence of reactions to that postulated above occurs in the formation of radicals in carboxylic acids by high energy irradiation. Thus the radical anion is the primary product and the more stable free radicals are formed subsequently by hydrogen abstraction by the anion from a neighbouring acid molecule. 

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Following this mechanism, luciferase-bound reduced FMN (FMNH intermediate I) reacts with oxygen to form the 4a-hydroperoxy-4a,5-dihydroFMN intermediate II (HF-OCT). The addition of a long-chain aliphatic aldehyde generates the 4a-peroxyhemiacetal-4a,5-dihydroFMN intermediate III (HF-OOCH(OH)R), which is subsequently converted to a radical pair of 4a-hydroxy-4a,5-dihydroFMN radical cation (IV+ HF-OH+ ) and a carboxylic acid radical anion RC(0H)0" A 1-e transfer from RC(0H)0- to IV+ produces the excited 4a-hydoxy-4a,5-dihydroFMN intermediate IV. Relaxation of IV to the ground state produces bio luminescence ( max 490 nm) with a quantum yield of about 0.16. Finally, IV decays to form FMN and water. The present report addresses several key issues of this mechanism with respect to the identity of the proposed excited emitter HF-OH, the energetics of its formation, and the requirement of a hydrophobic luciferase active site for a high quantum yield of the emitter. 

It can be seen that most of amino acids, common metal ions and acid radical anions do not interfere the determination except Ni2+, Co2+, and DL-a-amino acid. It is concluded that the method had good selectivity. 

As stated above, the background current density observed for diamond electrodes was lower than those for the other types of carbon-based electrodes in non-aqueous as well as aqueous electrolytes. Utilizing this characteristic, the electrochemical sensing processes have been investigated. For example, the Ceo molecule, which shows five reversible reductions at the GC electrode, has been reported to exhibit six waves at the diamond electrode [ll]. Moreover, ascorbic acid, an essential vitamin, has been shown to exhibit a particular reaction in non-aqueous electrolytes. A quasi-reversible redox reaction to produce the ascorbic acid radical anion occurs in non-aqueous electrolytes, while only an irreversible anodic oxidation reaction occurs in aqueous electrolytes [12]. 

M.p. 296 C. Accepts an electron from suitable donors forming a radical anion. Used for colorimetric determination of free radical precursors, replacement of Mn02 in aluminium solid electrolytic capacitors, construction of heat-sensitive resistors and ion-specific electrodes and for inducing radical polymerizations. The charge transfer complexes it forms with certain donors behave electrically like metals with anisotropic conductivity. Like tetracyanoethylene it belongs to a class of compounds called rr-acids. tetracyclines An important group of antibiotics isolated from Streptomyces spp., having structures based on a naphthacene skeleton. Tetracycline, the parent compound, has the structure ... 

Weak to moderate chemiluminescence has been reported from a large number of other Hquid-phase oxidation reactions (1,128,136). The Hst includes reactions of carbenes with oxygen (137), phenanthrene quinone with oxygen in alkaline ethanol (138), coumarin derivatives with hydrogen peroxide in acetic acid (139), nitriles with alkaline hydrogen peroxide (140), and reactions that produce electron-accepting radicals such as HO in the presence of carbonate ions (141). In the latter, exemplified by the reaction of h on(II) with H2O2 and KHCO, the carbonate radical anion is probably a key intermediate and may account for many observations of weak chemiluminescence in oxidation reactions. 

The ESR spectrum of the pyridazine radical anion, generated by the action of sodium or potassium, has been reported, and oxidation of 6-hydroxypyridazin-3(2//)-one with cerium(IV) sulfate in sulfuric acid results in an intense ESR spectrum (79TL2821). The self-diffusion coefficient and activation energy, the half-wave potential (-2.16 eV) magnetic susceptibility and room temperature fluorescence in-solution (Amax = 23 800cm life time 2.6 X 10 s) are reported. 

Fluorinated sulflnates are prepared from sodium dithionite and liquid per-fluoroalkyl halides [74] (equation 67). For the transformation of the gaseous and poorly reactive trifluoromethyl bromide, it is necessary to use moderate pressure [75] (equation 68) These reactions are interpreted by a SET between the intermediate sulfur dioxide radical anion and the halide The sodium trifluorometh-anesulfinate thus obtained is an intermediate for a chemical synthesis of triflic acid. 

In the case of electron-deficient monomers (e.g, acrylics) it is accepted that reaction occurs by initial addition of the sulfate radical anion to the monomer. Reactions of sulfate radical anion with acrylic acid derivatives have been shown to give rise to the sulfate adduct under neutral or basic conditions but under acidic conditions give the radical cation probahly by an addition-elimination process. 

Hydroxy radical and sulfate radical anion, though they may sometimes give rise to similar products, show quite different selectivity in their reactions with unsaturated substrates. In particular, the sulfate radical anion has a somewhat lower propensity for hydrogen abstraction than the hydroxyl radical. For example, the sulfate radical anion shows little tendency to abstract hydrogen from mcthacrylic acid.232... 

A particular case of a [3C+2S] cycloaddition is that described by Sierra et al. related to the tail-to-tail dimerisation of alkynylcarbenes by reaction of these complexes with C8K (potassium graphite) at low temperature and further acid hydrolysis [69] (Scheme 24). In fact, this process should be considered as a [3C+2C] cycloaddition as two molecules of the carbene complex are involved in the reaction. Remarkable features of this reaction are (i) the formation of radical anion complexes by one-electron transfer from the potassium to the carbene complex, (ii) the tail-to-tail dimerisation to form a biscarbene anion intermediate and finally (iii) the protonation with a strong acid to produce the... 

Nowadays, ultramarine-type pigments are produced synthetically. Inside the zeolite structure the highly reactive sulfur radical anions are well protected which explains the stability of the blue color over thousands of years in air. However, the species responsible for the blue color should not be confused with the sulfur radical cations responsible for the blue color of sulfur solutions in fuming sulfuric acid (oleum) and similar oxidizing mixtures... 

The electrophilic character of sulfur dioxide does not only enable addition to reactive nucleophiles, but also to electrons forming sulfur dioxide radical anions which possess the requirements of a captodative" stabilization (equation 83). This electron transfer occurs electrochemically or chemically under Leuckart-Wallach conditions (formic acid/tertiary amine - , by reduction of sulfur dioxide with l-benzyl-1,4-dihydronicotinamide or with Rongalite The radical anion behaves as an efficient nucleophile and affords the generation of sulfones with alkyl halides " and Michael-acceptor olefins (equations 84 and 85). 

Alpha-l-antiprotease (ai-AP) limits tissue damage arising from the actions of the leucocyte protease, elastase (Carrell and Travis, 1985), and there is much evidence available for the oxidative inactivation of this protein by oxygen-derived free-radical species and hypochlorous acid/hypochlorite anion (HOCl/OCP). The mechanism of this inactivation appears to involve the oxidation of a critical methionine residue (Met-358) to its corresponding sulphoxide and methionine sulphoxide has been detected in ai-AP samples isolated from the lungs of cigarette smokers (Carp et al., 1982) and rheumatoid synovial fluids (Wong and Travis, 1980). 

Dietz and Peover examined the electrochemical reduction of cis and trans stilbene (114) in DMF containing carbon dioxide, 9>. The first electron transfer to trans-114 affords a planar radical anion (115) which then undergoes rapid reaction with carbon dioxide to produce, ultimately, 2,3-diphenylsuc-cinic acid (116) in... 

PMR) trends that correspond to relative rates.179 From an examination of the displacement of chloride from l-chloro-5-nitrofuran by potassium iodide in acetic acid or by sodium sulfide in water it was concluded that the substitution need not be a true nucleophilic substitution. Initially there could be a transfer of one electron from the nucleophile to the furan nucleus the resultant radical anion loses chloride to form a furyl radical and product.179... 

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