Ionization from catalytic oxidation

Ionization from the Heterogeneous Catalytic Oxidation of Hydrocarbons in the Vapor Phase... 

The marked influence of hydrocarbon structure on the ionization from catalytic oxidation prompted extension of this study to other selected hydrocarbons. In addition, the effect of the oxygen content of the gas mixture has been explored. The results have led to certain suggestions in regard to the processes involved in these examples of catalytic oxidation. 

Effect of Hydrocarbon Molecular Structure on Ionization from Catalytic Oxidation in Air. Figure 1 shows the data for the ion yields obtained for several hydrocarbons during oxidation in air over a platinum filament in the approximate temperature range of 400° to 900°C. The hydrocarbons fall into two broad categories those which produced about 0.04 coulomb per mole of hydrocarbon oxidized, and those which produced about 1.0 coulomb or more per mole. The latter yield is similar to that obtained during combustion of hydrocarbons in a hydrogen flame... 

The catalytic cysteine-215 of PTP-1B is highly reactive toward oxidation and electrophiles and as such it is a tempting target for fragment discovery. Ockey and Gadek assembled a set of 19 reversible electrophiles, such as aldehydes, nitriles and boronic acids.1271 They then used electrospray ionization mass spectrometry to look for one-to-one complexes and three of the compounds were found to form covalent complexes. The dissociation constants ranged from 25 to 150 p,M and one of the compounds was also able to inhibit PTP-1B with an IC50 of 60 xM. 

With both the Fu and the Denmark catalysts it can be assumed that catalysis is effected by formation of a highly electrophilic silicon cation D from tetrachlorosi-lane and the nucleophilic catalyst C, i.e. by attack of the pyridine N-oxide or of the phosphoramide O-atom on silicon, followed by ionization (Scheme 13.38). The latter cation can then activate the epoxide toward nucleophilic attack by the chloride ion. Exchange of the product silane for another molecule of tetrachlorosilane completes the catalytic cycle [75],... 

Fig. 9. Correlation between the catalytic activity and the parameter Y in propylene oxidation. Y = 10 (/ // + i )(r 12). where / is the nth ionization potential, r is the ionic radius of the metal ion, and n is its formal charge. (Reproduced from Ref. 43 with permission from the authors.)...

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