Aerobic reaction mechanism

The reaction mechanism for the aerobic oxidation of the pz to seco-pz can be attributed to a formal 2 + 2 cycloaddition of singlet oxygen to one of the pyrrole rings, followed by cleavage (retro 2 + 2) of the dioxetane intermediate to produce the corresponding seco-pz (160). This mechanism is shown in Scheme 29 for an unsymmetrical bis(dimethylamino)pz. Further photophysical studies show that the full reaction mechanism of the photoperoxidation involves attack on the reactant by singlet oxygen that has been sensitized by the triplet state of the product, 159. As a consequence, the kinetics of the process is shown to be autocatalytic where the reactant is removed at a rate that increases with the amount of product formed. 

Misonidazole [27 l-methoxy-3-(2-nitroimidazol-l-yl)-2-propanol] and the model compound l-methyl-2-nitroimidazole have been used as radiosensitizers in the treatment of certain types of human tumors. One important property of these compounds is that they are more toxic to hypoxic cells than to aerobic cells, indicating that reductive metabolism of the drug is involved in the toxicity. Results of a number of studies suggest that intracellular thiols play a significant role in the hypoxic cell toxicity, and it was found that reduction products formed stable thio ethers with GSH (for literature see References 181-183). The reaction mechanism of thio ether formation has not been fully established. It has been suggested that the 4-electron reduction product was involved in thio ether formation181,184,185, and that the hydroxylamine rather than the nitroso derivative was the reactant. On the other hand, an intermediate nitroso derivative is expected to give a sulfenamide cation (see Scheme 1) which easily allows thio ether formation. 

The enantioselective oxidative coupling of 2-naphthol itself was achieved by the aerobic oxidative reaction catalyzed by the photoactivated chiral ruthenium(II)-salen complex 73. 2 it reported that the (/ ,/ )-chloronitrosyl(salen)ruthenium complex [(/ ,/ )-(NO)Ru(II)salen complex] effectively catalyzed the aerobic oxidation of racemic secondary alcohols in a kinetic resolution manner under visible-light irradiation. The reaction mechanism is not fully understood although the electron transfer process should be involved. The solution of 2-naphthol was stirred in air under irradiation by a halogen lamp at 25°C for 24 h to afford BINOL 66 as the sole product. The screening of various chiral diamines and binaphthyl chirality revealed that the binaphthyl unit influences the enantioselection in this coupling reaction. The combination of (/f,f )-cyclohexanediamine and the (R)-binaphthyl unit was found to construct the most matched hgand to obtain the optically active BINOL 66 in 65% ee. 

Scheme 47 Proposed mechanism of aziridine ring opening under aerobic reaction conditions catalyzed by NHC...

Very recently we have developed a new, easier, and selective metal-free NHPTcatalyzed aerobic epoxidation of primary olefins [19] based on the in situ generation of peracetic acid from acetaldehyde. In this chapter, we will discuss the reaction mechanism in order to explain the significant differences in selectivity with respect to the epoxidation by peracids and we will show preliminary successful results in the synthesis of propylene oxide. 

We turn now to the synthesis of deoxyribonucleotides. These precursors of DNA arc formed by the reduction ot ribonucleotides specifically the 2 -hydroxyl group on the ribose moiety is replaced by a hydrogen atom. The substrates are ribonucleoside diphosphates, and the ultimate reduclant is NADPH. The enzyme ribonucleotide reductase is responsible for the reduction reaction for all four ribonucleotides. The ribonucleotide reductases of different organisms are a remarkably diverse set of enzymes. Yet detailed studies have revealed that they have a common reaction mechanism, and their three-dimensional structural features indicate that these enzymes are homologous. We will focus on the best understood of these enzymes, that of E. coli living aerobically. 

The incorporation of the 0-labeled oxygen atoms derived from 02 (K 02) was not quantitative (not 100%) and the fractions of the 0-labeled oxygen atoms of all the oxygen atoms incorporated into the products were about 49 and 77% under aerobic and anaerobic conditions, respectively (27). In order further to understand the reaction mechanism of indoleamine... 

Through subtle modification of the reaction mechanism, the scope of o-quinone-catalyzed aerobic oxidations has been expanded to secondary amines and JV-heterocyclic compounds as well [45-47]. For example, aerobic oxidation of secondary amines and iV-heterocycles has been achieved by using 10-phenanthroline-5,6-dione (phd) as a catalyst (Scheme 14.10a). Using phd and cocatalytic Znl2, a diverse range of iV-heterocyclic compounds undergo... 

The analytical data show that gold catalysis and enzymatic catalysis allow fast and selective aerobic oxidation of glucose according to the same stoichiometry characterized by the formation of hydrogen peroxide as the by-product (Eq. (21.1)) [8]. However, it is not surprising that completely different catalytic systems adopt different reaction mechanisms as shown by the kinetic studies on commercial enzymatic preparations containing /wcose oxidase and catalase [13]. The results of the research support a Michaelis-Menten type mechanism where the kinetic... 

Elucidating the Reaction Mechanism of Aerobic Oxidation of Benzyl Alcohol 381... 

Nie J, Liu H (2012) Aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran on supported vanadium oxide catalysts structural effect and reaction mechanism. Pure Appl Chem 84 765-777... 

Microsensors and CV can be coupled to assess ORR in cathodic biofilms operating in aerobic environments and to investigate cathodic reaction mechanisms operating in biocathodes in SMFCs and other bioelectrochemical systems. 

Gomez-Hortiguela L, CoraF, SankarG, Zicovich-Wilson CM, CatlowCRA(2010)Catalytie reaction mechanism of Mn-doped nanoporous aluminophosphates for the aerobic oxidation of hydrocarbons. Chem Eur J 16 13638-13645 (and references cited therein)... 

Further research into the reaction mechanism revealed that the reaction rate was correlated with the electron structure of the sulfoxide the more electropositive sulfoxides were the better oxygen donors. Excellent correlation of the reaction rates with the heterolytic benzylic carbon-hydrogen bond dissociation energies indicated a hydride abstraction mechanism in the rate-determining step to yield a carbocation intermediate. The formation of 9-phenylfluorene as by-product in the oxidation of triphenylmethane supports this suggestion. Further kinetic experiments and NMR showed the formation of a polyoxometalate-sulfoxide complex before the oxidation reaction, this complex being the active oxidant in these systems. Subsequently, in a similar reaction system, sulfoxides were used to facilitate the aerobic oxidation of alcohols [29]. In this manner, benzylic, allyUc, and aliphatic alcohols were all oxidized to aldehydes and ketones in a reaction catalyzed by Ke jn-type... 

Isotopic-labeling experiments and evidence of a dimeric intermediate in the transition-metal-free aerobic oxidative C-C bond cleavage of a-hydroxy ketones and their esterification, on reaction with O2 as the ideal oxidant in the presence of K2CO3, have disclosed the reaction mechanism. ... 

Nikaidou, F., Ushiyama, H., Yamaguchi, K., et al. (2010). Theoretical and Experimental Studies on Reaction Mechanism for Aerobic Alcohol Oxidation by Supported Ruthenium Hydroxide Catalysts, J. Phys. Chem. C, 114, pp. 10873-10880. 

The reaction mechanisms of the various aerobic oxidases active in the dissimilation of tryptophan have been reviewed by Mason (338). 

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