Spontaneous oxidation method

Finally, radiolysis/EPR results forced the reinterpretation of literature spanning more than 25 years on EPR studies of olefin reactions on zeolites in the presence of Lewis acid sites. " Spontaneous oxidation of olefins and products of their Bronsted acid-catalyzed reactions on dehydroxylated (to form Lewis acid sites) ZSM5 and Mordenite vide infra) provides an alternative method of spin labeling, and the technique gives results mostly consistent with those from radiolysis/EPR. However, in the spontaneous oxidation method, the limited degree of control over the ionization process and progress of the catalysis has led to erroneous conclusions (mainly in the earlier work). Interpretation of the radiolysis/EPR experiments is greatly aided by the ability to methodically vary the relative contribution of different products to the EPR spectrum. 

Figure 10.20 Substrate analogs of dihydroxyacetone phosphate accessible by the CPO oxidation method, and spontaneous, reversible formation of arsenate or vanadate analogs of dihydroxyacetone phosphate/n s/tu for enzymatic aldol additions.

An alternative method of synthesizing the pyrazine compounds was described by Ghosh et al, and the synthesis is shown is Scheme 32 [78]. Reaction of a 1,2-dione (124) with a 1,2-diamine (125) to form an imine intermediate followed by spontaneous oxidation of the dihydropyrazine intermediate, formed the protected pyrazine compound 126. The free phenol 127 was obtained by removal of the methyl-protecting groups with a boron trifluoride-dimethyl sulfide complex. Similar compounds were prepared via the same method by Simoni et al. [79]. 

Once the saturation coverage of Ru on Au(lll) had been achieved, it was possible to increase it further using a multiple spontaneous deposition method.17 After the first deposition, the crystal was held at 0.1 V in H2SO4 to reduce Ru oxide, then the solution was replaced at the OCP with a ruthenium-containing solution and the deposition was performed for another 3 min, without removal of the deposited ruthenium from the previous deposition. STM images obtained after three consecutive depositions of 3 min each are shown in Fig. 8c, d.16 An increase in the number of Ru islands... 

Ruthenium and osmium depositions on platinum are of special interest with reference to methanol anodic oxidation on fuel cells and were first reported in the early 1960s [116,117], Among the different methods of deposition of ruthenium or osmium on platinum [116-121], the spontaneous deposition method is attractive because of its simplicity and the fast achievement of a surface concentration plateau (reached in seconds) [26,122,123]. Contrary to the reversible behavior of the electrochemically deposited ruthenium on noble metal substrates, the films formed by spontaneous deposition normally do not dissolve easily from the metal surface. They are very stable and normally change to stable hydroxides and oxides when the electrode potential is increased. 

Similarly, radiolytically produced radical cations can be stabilized in zeohtes and related materials. This possibility was exploited by spectroscopists to study the EPR of radical cations and some neutral radicals even before the development of inert matrices such as rare gases and freons for radical cation stabilization. Recently, work in our laboratory has developed the use of inert zeolites as microreactors to control radical cation reactions and to study radiation chemistry in heterogeneous systems. In the case of active catalysts, radiolysis can potentially produce radical cations of products as weU as starting material. Thus, like the spontaneous oxidation process described above, radiolysis combined with EPR permits a method of post-reaction analysis of products by in situ spectroscopy. 

Lu Wd, Wang Deming, Chen Ge, etc. Research on Programmed Temperature-rise Oxidation Method Used for Evaluating Performance of Inhibitors of Coal Spontaneous Combustion [J]. Mining Safety Environmental Protection, 2005, 32(6) 12-14. 

An alternative way of NAD" recycling makes use of a three-enzyme cascade with molecular oxygen as the ultimate oxidant (Scheme 3.30) [339]. As in the methods described above, all the enzymes and cofactors have to be precipitated together. Thus, NADH which is produced by HLADH-catalyzed oxidation of a secondary alcohol is re-oxidized by diaphorase at the expense of pyrroloquinoline quinone (PQQ) [340]. The reduced form of the latter (PQQH2) is spontaneously oxidized by molecular oxygen producing hydrogen peroxide, which, in mm, is destroyed by catalase. 

In addition to diazonium salts, there are many other species that are able, once electrochemicaUy activated, to modify the surface with aromatics, unsaturated and saturated groups. These surface modifications can be achieved by (i) oxidation (amines, hydrazines, alcohols, carboxylates, carbamates, carbanions, Grignard reagents) (ii) reduction, some being closely related to diazonium salts (iodoniums, sulfonium) and other different species (vinylics, alkyl halide) (iii) spontaneously, chemically or pho-tochemically (alcenes, azides, peroxides). Note that electrochemical oxidation methods can be applied only to the materials that can withstand quite positive potentials such as carbon or Pt. This section will describe these modifications [357]. 

Although these fluorescence-based methods can increase sensitivity by orders of magnitude over Ellman s assay, there are some significant drawbacks. It is necessary to use a suitable model compound, such as DTT or free cysteine, to generate a standard curve with each assay. This can be complicated by the propensity of these model thiol compounds to undergo spontaneous oxidation reactions in solution. In order for the standard curve to provide an accurate value, the model compounds must be 100% in the reduced state. It is not trivial to determine if the model compounds being used have undergone some amount of oxidation, which may lead to systematic overestimation of the thiol content of a protein. 

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