Modification of Hydroxyl Group

Modification of hydroxyl groups with such compounds can be done in 3-10 M NaOH by reacting from 25°C to 40°C for 1.5-4 hours. 

There has been a variety of approaches for imparting antimicrobial activity to cellulosic fibers, many of them developed as part of a weather-resistant finish (Table I). Metal salts, organometallics, resins, sulfur and nitrogen compounds, and chemical modification of hydroxyl groups by acetylation or cyanoethylation are typical methods used to impart antimicrobial activity (125). A survey made in 1966 lists all commercial products available for protecting materials against biodeterioration— trade names, active ingredients, end uses, and names of manufacturers are tabulated (126). 

When highly water-soluble CyD derivatives are investigated for application in drug formulations, random modifications of hydroxyl groups to hydroxypropyl, sulfo-propyl, carboxymethyl, or silyl groups can be easily achieved [14]. On the other hand, if a supramolecular behavior is to be investigated using CyD derivatives, the... 

Takasu A, Niwa T, Itou H, Inal Y, Hirabayashi T (2000) Chemical modification of hydroxyl groups of poly(vinyl alcohol) by a glycosidation reaction. Macromol Rapid Commun 21(ll) 764-769... 

Concerning starch derivatives, their domains of applications is sensibly the same as those of other natural polymers, but their hydrophilicity could be modulated by the partial chemical modification of hydroxyl groups. Like cellulose derivatives, they can even be used as plastics. 

Figure 21.14 Scheme illustrating the one-pot cellulose modification of hydroxyl groups. Reprinted with permission from Braun, B., Dorgan, J. R., Single-step method for the isolation and surface functionalization of cellulosic nanowhiskers, Biomacromolecules, 10, 334-341. Copyright (2009) American Chemical Society [31]. 

Figure 8.2 Selective primary modification of hydroxyl group on...

Another successhil strategy for derivatization of erythromycin employed modification of functional groups involved in intramolecular cyclizations. The C-9 ketone, C-6 hydroxyl group, C-8 proton, and/or C-ll,12-diol of erythromycin were converted into functional groups which participate poorly, if at all, in intramolecular cyclizations. Some derivatives which have been extensively evaluated in preclinical and clinical trials exhibit such desirable properties as better stabiUty under acidic conditions, greater oral bioavadabihty, and higher and more prolonged concentrations of antibiotic in semm and tissues. 

It is usually difficult to discuss unambiguously on the role of the formation of sulphate, which may explain the deactivation. Their formation can equally occur on the support and on the noble metals. The poisoning effect of S02 has been reported by Qi el al. on Pd/Ti02/Al203 [112], However, in the presence of water, the stabilisation of hydroxyl groups could inhibit the adsorption of S02 [113], Burch also suggested a possible redispersion of palladium oxide promoted by the formation of hydroxyl species [114], Such tentative interpretations could correctly explain the tendencies that we observed irrespective to the nature of the supports, which indicate an improvement in the conversion of NO into N2 at high temperature. Nevertheless, the accentuation of those tendencies particularly on prereduced perovskite-based catalysts could be in connection with structural modifications associated with the reconstruction of the rhombohedral structure of... 

Table 7 includes many structurally unique nonprotein amino acids with heterocyclic units as part of the structure. These amino acids are isolated from various sources and exhibit interesting bioactivities. In most cases, enzymatic modification of proline occurs through installation of hydroxyl groups, halogenated side chains, and alkyl side chains to give rise to the observed structural diversity. 

The selective protection of hydroxyl groups is obviously most frequent in carbohydrate synthesis and, in fact, photosensitive protecting groups have been used to this effect in oligosaccharide synthesis, nucleotide synthesis, and saccharide modification. Here, as well as in other Sections, special attention will be devoted to 2-nitrobenzyl derivatives, whose re-... 

Covalent modification by phosphorylation and dephosphorylation of hydroxyl groups on amino acid side chains. 

The chemical structure of UP oligomers is more complex than might be expected from the chemistry of the reactions, Eqs. (2.13) and (2.14). The addition of hydroxyl groups to the activated double bonds is one of the most important side reactions - Eqs. (2.16) and (2.17) (Table 2.4) - called Ordelt reactions. It leads to the formation of side chains and to a modification of the COOH/OH stoichiometry due to diol consumption. 

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