Chemical modification oxidative methods

The properties of polythiophenes can be influenced by the structure and the substituents of the starting materials, the synthetic methods, physical treatment (e.g. stretching, annealing, pressing, synthesis on oriented surfaces) and chemical modification (oxidation and reduction reactions, doping, dedoping). Therefore materials with tailor-made properties can be designed for selective applications. 

Unfortunately, there are no universal methods to detect all types of protein oxidation, because the products formed can be so diverse in nature. However, some forms of protein oxidation can be assayed using chemical modification (Davies et al., 1999 Shacter, 2000). In particular, the formation of carbonyl groups on proteins can be targeted using the reagent 2,4-dinitrophenyl-hydrazine (DNPH). This compound reacts with aldehydes to form 2,4-dinitrophenylhydrazone derivatives, which create chromogenic modifications that can be detected at high sensitivity in microplate assays or Western blot analysis (Buss et al., 1997 Winterbourn et al., 1999). 

The catalysts are predominantly modified ZSM-5 zeolite. In general, the modifications are intended to restrict pore mouth size to promote the shape selective production of para-xylene within the microporous structure. The same modifications also serve to remove external acid sites and eliminate the consecutive isomerization of para-xylene. Methods used to modify the zeolite pore openings have included silation [50], incorporation of metal oxides such as MgO, ZnO and P2O5 [51, 52], steaming and the combination of steaming and chemical modification [53]. 

Starch (amylose and amylopectin) hydrolysis along with ester-fication, etherification or oxidation have been previously discussed as available methods for producing starch derivatives with improved water dispersibilities and reduced retrogradation potential (, ). Since oxidative and hydrolytic reactions are simple, easily controlled chemical modifications, starch-derived polymers made by hydrolysis alone or oxidative and hydrolytic processes were developed and tested. 

Physical trapping dye molecules in sol-gel materials are reviewed elsewhere in this chapter. A comparatively recent approach is to have the dye molecules chemically bonded to the oxide matrix. This approach requires the chemical modification of the dye molecules by Si(OR )3-containing groups, i.e. the preparation of compounds (R 0)3Si—X—A, in which A is a chromophore, by the methods shown in equations 3-7. This is mostly not a trivial task, since the chromophore has to remain undisturbed. 

Hydrogenation is an important method of chemical modification of elastomers. Because of the absence of carbon-carbon unsaturation, hydrogenated elastomers have good resistance to oxidative and thermal degradation, improved weatherability and good resistance towards chemicals and fluids [5-7]. Nitrile rubber (NBR) is a specialty rubber, and because of its oil resistance properties, it has been used in oil-wells and the automotive industry. Hydrogenation of NBR has been studied extensively because of its technological importance [16-19]. 

IR spectroscopy can be used to characterise not only different rubbers, but also to understand the structural changes due to the chemical modification of the rubbers. The chemical methods normally used to modify rubbers include hydrogenation, halogenation, hydrosilylation, phosphonylation and sulfonation. The effects of oxidation, weathering and radiation on the polymer structure can be studied with the help of infrared spectroscopy. Formation of ionic polymers and ionomeric polyblends behaving as thermoplastic elastomers can be followed by this method. Infrared spectroscopy in conjunction with other techniques is an important tool to characterise polymeric materials. 

Properties of rice starches are changed by chemical modification in the same way as the properties of other starches (see Chapter 18). Starches prepared via the alkali method have been modified to provide additional pH and shear stability. In general, hypochlorite-oxidized rice starch has a lower gelatinization temperature and lower maximum paste viscosity producing a softer, clearer gel. Hydroxypropylated rice starches have lower gelatinization temperatures, whereas crosslinked rice starch has an increased gelatinization temperature, increased shear resistance and acid stability. 

Chemical modifications of the antigens were achieved by oxidation of the monosaccharide residues with periodate and reduction of the carboxyl groups of the uronic acid residues by the carbodiimide and borohydride methods, Fig. (IOC). The periodate oxidation was performed by a procedure described in the literature [37]. The reduction of the uronic acid residues of the antigen was performed by the carbodiimide (CMC) and sodium borohydride method [38], The oxidized and reduced types of antigens no longer reacted with the antibodies, Fig. (IOC). 

The problem with sulfide catalysts (hydrotreatment) is to determine the active centres, which represent only part of their total surface area. Chemisorption of O2, CO and NO is used, and some attempts concern NIL, pyridine and thiophene. Static volumetric methods or dynamic methods (pulse or frontal mode) may be used, but the techniques do not seem yet reliable, due to the possible modification (oxidation) of the surface or subsurface regions by O2 or NO probe molecules or the kinetics of adsorption. CO might be more promising. Infrared spectroscopy, especially FTIR seems necessary to characterise co-ordinativcly unsaturated sites, which are essential for catalytic activity. CO and NO can also be used to identify the chemical nature of sites (sulfided, partially reduced or reduced sites). For such... 

Gorton and coworkers have been particularly active in this field and produced an excellent review of the methods and approaches used for the successful chemical modification of electrodes for NADH oxidation [33]. They concentrated mainly on the adsorption onto electrode surfaces of mediators which are known to oxidise NADH in solution. The resulting systems were based on phenazines [34], phenoxazines [35, 36] and pheno-thiazines [32]. To date, this approach has produced some of the most successful electrodes for NADH oxidation. However, attempts to use similar mediators attached to poly(siloxane) films at electrode surfaces have proved less successful. Kinetic analysis of the results indicates that this is because of the slow charge transfer between the redox centres within the film so that the catalytic oxidation of NADH is restricted to a thin layer nearest the electrode surface [37, 38]. This illustrates the importance of a charge transfer between mediator groups in polymer modified electrodes. 

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