Chemical modification of functional groups

The diverse chemical reactivity of HAs makes them potential toxic compounds, either directly, by chemical modification of functional groups of a variety of biological systems, or indirectly, by their conversion to toxic metabolites. In some cases their metabolites are considered to be toxic in humans, animals and plants even at relatively modest levels of exposure. 

In order to overcome this drawback, there are two main approaches for the surface modification of carbon nanostructures that reoccur in the literature. The first one is covalent functionalization, mainly by chemical bonding of functional groups and the second one is noncovalent functionalization, mainly by physical interactions with other molecules or particles. Both strategies have been used to provide different physical and chemical properties to the carbon nanostructures. Those that will be presented here are only a few examples of the modifications that can be achieved in carbon nanostructure surfaces and composite fabrication. 

The second route to postsynthetic modification of SAMs is the chemical transformation of functional groups present on their outermost surface this approach mostly relies on chemistries already established for the functionalization of solid supports (Fig. 4.3). Two important points to bear in mind are (1) it is essentially impossible to extensively characterize the structure of the reaction products or purify them without destroying the SAM and (2) many solution-phase reactions may be very difficult when carried out on a surface because of the steric hindrance due to the very closely packed end groups. 

Modification of functional groups to control the level of chemical reactivity. 

Upon X-ray exposure of a NPPTMS multilayer film (Mg K emitting at 1253.6 eV operated at 15 kV and 20 pA), X-ray photoelectron spectroscopy (XPS) elemental composition data suggested chemical modification of nitro groups to primary amine functions. The N (Is) XPS profile of NPPTMS SAMs as a function of irradiation time is shown in Fig. lb. It can be observed that the pristine peak with a binding energy at 405.6 eV, characteristic of the NO2 moiety [13], diminishes in intensity with elapsed time. Concomitantly, a new peak... 

Film-forming biocidal polymers useful in marine antifouling compositions selected from trialkyltin groups chemically bound to homo- and copolymeric chains of organotin acrylate were prepared by various methods such as (1) the polymerization of trialkyltin acrylate or methacrylate monomers, (2) chemical modification of functionalized polymer as P(S-MA) with bis(tributyltm) oxide, (3) grafting or blending of the polymers, e.g., PVC, with trialkyltin acrylate (Scheme 3.23) [262]. 

IR absorption bands in amorphous solids are rather broad, with extensive overlap. Direct identification and quantification of the numerous oxidation products, most often of similar chemical structures, in a degraded polymer are difficult. More precise conclusions about the nature of absorbing species can be obtained by selective chemical derivatization. Selective modification of functional groups with reactive gases, such as SF4, NH3, SO2, or NO, results in a shift in absorption band positions, which can then be compared with model compounds to allow for a better chemical assignment of the absorbing species (Table 15.3) [13]. 

Treatments with Chemicals or Resins. Resin treatments are divided into topical or chemical modifications of the fiber itself. Most chemical treatments of synthetic fibers are topical because of the inert character of the fiber itself and the general resistance of the fiber to penetration by reagents. By contrast, ceUulosics and wool possess chemical functionality that makes them reactive with reagents containing groups designed for such purchases. Natural fibers also provide a better substrate for nonreactive topical treatments because they permit better penetration of the reagents. 

Chemical Modification. The chemistry and synthetic strategies used in the commercial synthesis of cephalosporins have been reviewed (87) and can be broadly divided into ( /) Selection of starting material penicillin precursors must be rearranged to the cephalosporin nucleus (2) cleavage of the acyl side chain of the precursor (2) synthesis of the C-7 and C-3 side-chain precursors (4) acylation of the C-7 amino function to introduce the desked acylamino side chain (5) kitroduction of the C-3 substituent and 6) protection and/or activation of functional groups that may be requked. 

In the chemical modification of PS with MA, AA, EC, butadiene, and isoprene using cationic catalysis caused either destruction of macromolecules or the binding of functional groups to the aromatic ring. 

Broadening of the optimal pH range for reactive dye biosorption by chemical modification of surface functional groups of Corynebacterium glutamicum biomass... 

Owing to multi-functionahty, physical properties such as solubihty and the glass transition temperature and chemical functionahty the hyperbranched (meth) acrylates can be controlled by the chemical modification of the functional groups. The modifications of the chain architecture and chemical structure by SCV(C)P of inimers and functional monomers, which may lead to a facile, one-pot synthesis of novel functionahzed hyperbranched polymers, is another attractive feature of the process. The procedure can be regarded as a convenient approach toward the preparation of the chemically sensitive interfaces. 

There is rather a small number of functional groups or structural motifs that have the ability to carry out efficient modification of cellular DNA. ° These molecules are of chemical and biological interest because they successfully execute a difficult balancing act—they possess sufficient reactivity to make and break covalent bonds... 

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