Imidazole groups, polymeric

There are some side reactions that may occur when using EDC with proteins. In addition to reacting with carboxylates, EDC itself can form a stable complex with exposed sulfhydryl groups (Carraway and Triplett, 1970). Tyrosine residues can react with EDC, most likely through the phe-nolate ionized form of its side chain (Carraway and Koshland, 1968). The imidazolyl group of histidine may react with sulfo-NHS esters, resulting in an active carbonyl imidazole group which subsequently hydrolyzes (Cuatrecasas and Parikh, 1972). Finally, EDC may promote unwanted polymerization due to the usual abundance of both amines and carboxylates on protein molecules. 

The effect of mixtures of surfactants and polyelectrolytes on spontaneous, water-catalysed hydrolysis (Fadnavis and Engberts, 1982) was mentioned in Section 4, but mixtures of functionalized polyelectrolytes and cationic surfacants are effective deacylating agents (Visser et al., 1983). Polymerized isocyanides were functionalized with an imidazole group and the deacylation of 2,4-dinitrophenyl acetate in the polyelectrolyte was speeded by addition of single or twin chain quaternary ammonium ion surfactants, up to a plateau value. Anionic surfactants had essentially no effect. It is probable that the cationic surfactants accelerate the reaction by increasing the deprotonation of the imidazole groups. 

The paramagnetic nature of Cu ion was utilised to characterise these polymeric receptors by studying the interaction between the Cu centres and imidazole groups using ESR spectroscopy [17]. Results from the ESR experiments indicate that Cu -imidazole coordination bonds formed during the assembly of the monomer and template are conserved upon polymerisation. Furthermore, analysis of the ESR data obtained for different polymers suggested a defined arrangement of metal ion sites in the templated materials, which is absent in the non-templated control polymers. 

The peptide-based isocyanides 50a-e were successfully polymerized by Ni(II) catalysts under an inert atmosphere [63-66]. An alanine-derived isocyanide, whose isocyano group was labeled using 13C and 15N, was prepared and successfully polymerized for structure elucidation [67]. Several solvent systems were used in the polymerization of the peptide-based isocyanides, depending upon the solubility of the isocyanides. As mentioned earlier, the use of alcohols as a solvent or co-solvent can accelerate the polymerization. The protective groups on the ester, hydroxy, and imidazole groups were removed after polymerization by treatment with aqueous NaOH to yield poly(isocyanide)s bearing unprotected peptide side chains. 

Esterolytic Reactions of Active Esters Using Heterogeneous Polymeric Catalysts Containing Imidazole Groups... 

The hydrophobic effect can be described in a broad sense as a type of non-specific apolar bonding between catalyst and substrate. These hydrophobic interactions, especially in an aqueous environment, have been predominant in determining the efficiency of the catalysts.(8,10,12) Toward this end, considerable effort on our part has been directed toward the preparation of polymeric catalysts that contain pendant imidazole groups and apolar bonding sites that are soluble in highly aqueous solvent systems. 

The catalytic action of polyvinylimidazole 1 is undoubtedly dependent on its molecular weight. This problem was taken up by the Overbei er group (52). 4-Vinyl-imidazole was polymerized by using large amounts of the initiator, and the resulting oligomer fractionated through a Sephadex LH-20 column. 

Important chemical reactions mediated by enz3rmes, which are proteins, are often controlled by the interaction of a nucleophile with an electrophile. Proteins are polymeric structures made of amino acids units (called amino acid residues). Important nucleophilic groups include the hydroxyl (OH) group of the amino acid serine (72), the thiol unit (SH) of cysteine (73 see Chapter 27) and the nitrogen of the imidazole group of histidine (74). Note that the term nucleophilic in this biochemical context does not necessarily indicate reaction at carbon, but rather indicates a two-electron donor. The electron-deficient center (called an electrophilic site or electrophilic group) may be a metal such as Mg, Mn+2, Fe", or an ammonium unit (-NH3+). In some cases, the electron-deficient center is a carbonyl group (C=0) in which the electron donor is indeed a nucleophile because the reaction occurs at the carbonyl carbon. 

Vinyl group polymerization has been used to prepare polymers incorporating heterocyclic systems such as pyridine, quinoline, and imidazole rings. They have been prepared by polymerization of the respective monomers either alone or as copolymers with DVB (Table 2-5). These... 

Another example of multiresponsive brushes shows response to magnetic fields and pH (Yu et al., 2013). Imidazole group-modified PEG-polypeptides were grafted onto silica-coated Fe304 NPs. The Fe304 responded to external magnetic fields while the polymeric shell responded to pH. SPB assembled by PEO-g-PDMAEMA, a copolymer synthesized by ATRP, responded to shear, ionic strength, and pH (Fig. 4.14) (Sui et al., 2011). 

Cooperative interactions between catalytically active imidazole groups and other functional groups has been well documented (6). The total rate equation for the polymeric catalyst can be expressed by the following equation ... 

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