SUBJECTS chemical modification

A Acetylation, O-Phosphorylation, and O-Adenylylation. A/-Acetylation, O-phosphorjiation, and O-adenyljiation provide mechanisms by which therapeutically valuable aminocyclitol antibiotics, eg, kanamycia [8063-07-8] gentamicin [1403-66-3] sisomicin [32385-11-8], streptomycia [57-92-1], neomycin, or spectinomycin are rendered either partially or completely iaactive. Thus, eg, kanamycia B [4696-78-8] (50) can be iaactivated by modification at several sites, as shown. The elucidation of these mechanisms has allowed chemical modification of the sites at which the iaactivation occurs. Several such bioactive analogues, eg, dibekacia and amikacin have been prepared and are not subject to the iaactivation hence, they inhibit those organisms against which the parent antibiotics are iaeffective (96) (see Antibacterial agents, synthetic). 

In the present chapter, we will start to briefly summarize all the aspects of this subject, which have been covered in previous specialized reviews, allowing for a broad and general discussion on the subject. Then we will focus on the chemical modification of PS in the presence of cationic catalysts. 

In their original form these cements came as a zinc oxide powder and a concentrated solution of poly(acrylic acid) (Wilson, 1975b). Since then they have been subject to a number of chemical modifications. 

Chromatographic use of monolithic silica columns has been attracting considerable attention because they can potentially provide higher overall performance than particle-packed columns based on the variable external porosity and through-pore size/skeleton size ratios. These subjects have been recently reviewed with particular interests in fundamental properties, applications, or chemical modifications (Tanaka et al., 2001 Siouffi, 2003 Cabrera, 2004 Eeltink et al., 2004 Rieux et al., 2005). Commercially available monolithic silica columns at this time include conventional size columns (4.6 mm i.d., 1-10 cm), capillary columns (50-200 pm i.d., 15-30 cm), and preparative scale columns (25 mm i.d., 10 cm). 

Whenever a polymer is subjected to a chemical modification (here dendro-nization), its degree of polymerization (DP, Pn number average DP, Pw weight average DP) has considerable impact. Normally modifications become increas-... 

Any system in stable chemical equilibrium, subjected to the influence of an external cause which tends to change either its temperature or its condensation (pressure, concentration, number of molecules in unit volume), either as a whole or in some of its parts, can only undergo such internal modifications as would, if produced alone, bring about a change of temperature or of condensation of opposite sign to that resulting from the external cause. 

Surface Modification of Cellulose and PVA Films. Cellulose, as well as PVA,is known to be a typical non-ionic, hydrophilic polymer possessing hydroxyl groups. As this group has a high reactivity,chemical modification of these polymers is relatively easy and, in fact, has been the subject of extensive research. However, so far as we know, no work has been reported concerned with reactions occurring only at the surface of films or fibers from these polymers. 

Proteins are subject to a variety of chemical modification/degradation reactions, viz. deamidation, isomerization, hydrolysis, disulfide scrambling, beta-elimination, and oxidation. The principal hydrolytic mechanisms of degradation include peptide bond... 

The subject of protein chemistry is too large to be surveyed systematically in one chapter. Various examples of chemical modifications are covered nonsystem-atically throughout this volume in discussions of individual enzymes and methods. To aid in locating these examples, some are listed in Table 9.1. 

Amino acid analysis is fraught with literally dozens of pitfalls. For novel protein ingredients, those that have undergone chemical modification, or ones that have been subjected to high heat, conventional methods for protein hydrolysis may or may not be effective. It may be necessary to evaluate different hydrolysis methods to determine which provides the best recovery. 

Another chemical modification is the beta-hydroxy analogue of DMPEA. It has been explored separately, and is the subject of its own recipe, in its own rights. See DME. 

Ionizing radiation can act in two distinct ways on organic substances. In the absence of water, in condensed systems or in concentrated solution, the predominant effects occur directly on the organic molecule and produce electronic excitations or ionizations which may lead to chemical modification. In dilute solution (1% or less) the major effects are the result of reactions between the solute and reactive species produced by the radiolysis of water. These indirect effects are the subject of this article. 

A large amount of research has been done on chemical modification of electrodes. The authoritative treatment of this subject can be found in Bard and Faulkner (2001). Because it is a very active area of electrochemistry, this subject is being periodically reviewed. From the sensing point of view, the motivation for electrode modification has been to introduce additional flexibility in the design of, and additional control over, the electrochemical processes taking place at the electrodes. We have seen one example of such a modification already (Section 7.3 Soukharev et al., 2004). 

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