Metal chelating monomers

Alternatively a non-metallated chelating monomer such as (227) or (228) may be copolymerized with (223) and the metal introduced post-polymerization. Using this strategy nanoclusters of silver,615 gold,616 ZnS617 and CdS618 have been prepared. A related approach has recently been adopted with the ROMP of norbornenes functionalized with crown ether, (229),619 and triazacy-clononane, (230),620 substituents. 

HPMA [36] and a vinyl metal-chelating monomer A-(A/, A/ -dicarboxy-methylaminopropyl)methacrylamide synthesized [35]. Chemical structures of HPMA and DAMA are given in Figure 4. Poly(HPMA-co-DAMA) was prepared by free radical copolymerization in methanol with AIBN as initiator. Molecular weight distribution was determined by size exclusion chromatography and content of side-chain carboxylic group by acid-base titration. 

Template Polymers. Template effects in chelating polymers constitute an interesting development in the field of metal containing polymers. The Template effects are interpreted by the fact that the small molecule is templating a pattern in the macromolecule which can be recognized by the same molecule in a subsequent process. The idea is to prepare a polymer from the metal-chelated monomer, to remove the metal ion, and then to measure the selectivity of the prepared polymer for the metal ion of the template [36]. Typical examples of template systems are 4-vinyl-4 -methylbipyridine (Neckers [36]) and 1-vinyl-imidazole (Tsuchida [37]). These are polymerized in presence of divinylbenzene [36] and appropriate metal salts (Co2+, Cu2+, Ni2+, Zn2+). The template metal ions are removed by acid leaching and the polymer subsequently used for metal ion absorption studies (Fig. 16). 

In contrast to these approaches based on nonspecific interactions, Zhang and coworkers described a molecularly imprinted hydrogel based on the ther-moresponsive PNIPAM [184], This hydrogel was prepared by copolymerization of a metal chelate monomer iV-(4-vinyl)-benzyl iminodiacetic acid, which formed a coordination complex with the template protein in the presence of Cu ions, A-isopropylacrylamide, acrylamide, and IV.lV-methylenebisacrylamide as crosslinker. The interaction of the imprinted thermoresponsive hydrogel with the protein could be switched between coordination effects and electrostatic attraction by addition or omission of Cu ions. Furthermore, this imprinted hydrogel allowed switching of lysozyme adsorption by changing the temperature. 

Metal-chelate monomers with 5- and 6-membered heterocyclic fragments 91UK1532. 

Figure 4 Representation of functional monomers that can serve as building blocks in noncovalent molecular imprinting. The first row represents acidic functional monomers with methacrylic acid as the most widely used functional monomer. In the second row, a selection of basic functional monomers is shown. Neutral monomers are lined up in the third row and the last row contains monomers that were designed and synthesized for a specific purpose. For example, 4-vinylbenzyl-iminodiacetic acid serves as a metal chelating monomer [89], methyl-a-D-glucopyranoside-6-acrylate was used in the imprinting of a protected amino acid [90]. As the last example, a monomer that would fluorescence upon rebinding of the template is depicted [91].

Studies in the photoinitiation of polymerization by transition metal chelates probably stem from the original observations of Bamford and Ferrar [33]. These workers have shown that Mn(III) tris-(acety]acetonate) (Mn(a-cac)3) and Mn (III) tris-(l,l,l-trifluoroacetyl acetonate) (Mn(facac)3) can photosensitize the free radical polymerization of MMA and styrene (in bulk and in solution) when irradiated with light of A = 365 at 25°C and also abstract hydrogen atom from hydrocarbon solvents in the absence of monomer. The initiation of polymerization is not dependant on the nature of the monomer and the rate of photodecomposition of Mn(acac)3 exceeds the rate of initiation and the initiation species is the acac radical. The mechanism shown in Scheme (14) is proposed according to the kinetics and spectral observations ... 

Metal chelates afford a better initiating system as compared to other redox systems since the reactions can be carried out at low temperatures, thus avoiding wastage reactions due to chain transfer. Homopolymer formation is also minimum in these systems. It was observed by Misra et al. [66,67] that the maximum percentage of grafting occurs at a temperature much below the decomposition temperature of the various metal chelates indicating that the chelate instead of undergoing spontaneous decomposition receives some assistance either from the solvent or monomer or from both for the facile decomposition at lower temperature. The solvent or monomer assisted decomposition can be described as ... 

Nayak et al. have also reported grafting of vinyl monomers onto wool [75] and silk [76] using metal chelates as initiators. 

Each step in dendrimer synthesis occurs independent of the other steps therefore, a dendrimer can take on the characteristics defined by the chemical properties of the monomers used to construct it. Dendrimers thus can have almost limitless properties depending on the methods and materials used for their synthesis. Characteristics can include hydrophilic or hydrophobic regions, the presence of functional groups or reactive groups, metal chelating properties, core/shell dissimilarity, electrical conductivity, hemispherical divergence, biospecific affinity, photoactivity, or the dendrimers can be selectively cleavable at particular points within their structure. 

The broad PL emission spectra of some metal chelates match the requirements for white emission. Hamada et al. investigated a series of Zn complexes and found bis(2-(2-hydroxy-phenyl)benzothiazolate)zinc (Zb(BTZ)2, 246) is the best white emission candidate. An OLED with a structure of ITO/TPD/Zn(BTZ)2/OXD-7/Mg In showed greenish-white emission with CIE (0.246, 0.363) with a broad emission spectrum (FWHM 157 nm) consisting of two emission peaks centered at 486 and 524 nm (Figure 3.14) [277], A maximum luminance of 10,190 cd/m2 at 8 V was achieved. The electronic and molecular structure of Zn(BTZ)2 have been elucidated by Liu et al. [278]. There is evidence that the dimeric structure [Zn(BTZ)2]2 in the solid state is more stable than its monomer Zn(BTZ)2. They also found that the electron transport property of Zn(BTZ)2 is better than that of Alq3. 

Examination of the pH dependence of the polymerization process established that the enolate anion of the activator was the species responsible for initiation (46). Metal chelates of the dienones were also found to be effective. Chaberek believed that the semireduced dye radicals were active initiators in his system (47), in contradistinction to the work of Chen (17). Chaberek proposed that an excited dye-enolate complex was produced during the photochemistry and that this adduct reacted with monomer to yield a radical, capable of initiation, and a semireduced dye radical. Figure 4 shows the proposed mechanism. Several aspects of this mechanism should be modified in view of present knowledge. The semireduced radical (D ) has been conclusively shown to be a terminator (17) and not an initiator. 

Frecht [2] prepared Generation-0 polyhydroxyl dendrimeric monomers, (I), for use as diagnostic agents in metal chelate-based contrast materials. 

Although 2,3 QD has been isolated from several fungal species,the enzyme from Aspergillus japonicus has been extensively characterized and will be described herein. A partially deglycosylated form of 2,3QD from A. japonicus has been crystallized in its resting form and in anaerobic complexes with substrates or metal chelators. The enzyme fold is shown in Figure 9. Each 2,3QD monomer... 

When considering the suitability of a bead production technique for imprinting, it is essential to evaluate the compatibility of the conditions used for polymerisation with those required for complex formation between functional monomers and templates. Where covalent imprinting methods are used, the covalent adducts are often highly stable and need quite harsh conditions to disrupt them. Such adducts could be used in most of the procedures described below with reasonable expectation of success. The same can be said for many metal-chelate complexes, which have stabilities approaching covalently bonded structures. The use of cyclic boronate esters is an exception. This adduct is unstable in water and hence cannot be combined efficiently with aqueous suspension polymerisation. 

Only possible for some covalent and metal chelate-based processes Phase partitioning of monomers complicates system... 

A soft contact lens comprises a water-swollen gel of a polymer prepared by polymerising one or more hydrophilic monomers, such as 2-hydroxyethyl methacrylate, one or more crosslinking monomers and a monomer, which contains metal-chelating functionality, such as an aminopolycarboxylic acid containing a polymerisable olefinic group. 

Another metal chelating resin was looked at using CP/MAS [46] (Fig. 15.2.40). This resin was based on an salicylaldehyde acrylate monomer... 

Cross-Linked Polymers. Apart from the soluble polymers, insoluble resins with unusual functional groups are of interest in areas such as metal-chelating resins. The most promising monomers of Table I were studied as potential resins. To obtain cross-linked polymers without adding new interfering groups, 1,6-diallylaminohexane (XVI) was used in 5-10 mol % quantities as the cross-linking monomer. 

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