Reaction mechanisms inorganic substrates

Adhesion of polyimides to inorganic substrates is of great importance to the microelectronics industry [1, 2]. The polyimide films are deposited most often by spin coating the polyamic acid (PAA) usually from a TV-methylpyrrolidone (NMP) solution onto the substrate surface followed by thermal imidization at temperatures up to 400<>C. The most studied polyimide is the pyromellitic dianhydride-oxydianiline (PMDA-ODA), which exhibits excellent mechanical and dielectric properties, but not so good adhesion characteristics. The latter has been generally overcome by application of an adhesion promoter, such as y-aminopropyltriethoxysilane [3-7]. The reactions of APS (coated from water solution) with the silicon dioxide surface as well as with polyamic acid have been well characterized by Linde and Gleason [4] however, we do not have such detailed information available on APS interaction with other ceramic surfaces. 

Other examples of SIMS for surface analyses are studies of CU2S-CdS solar-cell samples (101) and the study of chemisorbed species on inorganic substrates such as methanol on Cu (100) and titania (102). De Pauw s studies of such adsorbed systems may prove to be valuable in determining the mechanism of catalytic reactions on surfaces (103). Winograd and co-workers (104-6) have studied chemisorption on metal surfaces, using SIMS. In a related study (107), Unger et al. have used molecular SIMS to study the reactions of thiophene on a silver surface. They observed the self-hydrogenation of thiophene on the sur-... 

Fig. 17 The two typical reaction mechanisms employed by phosphatases. In (a), the phos-phoryl group is transferred directly to a water molecule, which is typically bound to one or two metal ions if the substrate is made chiral at phosphorus, the stereochemical outcome is inversion. In (b), the phosphoryl group is first transferred to an enzymatic residue. In a subsequent step the phosphoenzyme intermediate is hydrolyzed. Since each step occurs with inversion of configuration at phosphorus, the net outcome is retention. Pi inorganic phosphate.

Peroxidase reacts by mechanisms similar to catalase, but the reaction catalyzed is the oxidation of a wide variety of organic and inorganic substrates by hydrogen peroxide (Reaction 5.83). 

The mechanism of laccase has been reported as a two-step reaction. The first step in the oxidation of quinol by laccase was the formation of the semiquinone, with the transfer of an electron from the substrate to the copper in the enzyme. The second step was a nonenzymatic disproportionation reaction between two semiquinone molecules to give one molecule of quinone and one of quinol. The function of copper and electron transfer in the reaction mechanism has been studied by using inorganic ions, electron paramagnetic resonance, and spectrophotometric methods [14]. 

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