Vinylimidazoles

Reaction of the 3,4-dimethyl-1-phenylphosphole (L) complex [PdLjClj] with 1-vinylimidazole in the presence of silver perchlorate carried out in... 

So far, many kinds of nucleophiles active for hydrolysis such as imidazolyl-, amino-, pyridino-, carboxyl- and thiol-groups, have been used for preparation of hydrolase models. Overberger et al.108,1091 prepared copolymers of vinylimidazole and acrylic acid 60 (PVIm AA), by which the cationic substrate, 61 (ANTI), was hydrolyzed. This kind of copolymer is considered to be a model of acetylcholinesterase. With ANTI, the rate of the copolymer catalysis was higher than that of imidazole itself in the higher values of pH, as is seen in Table 9. In this work, important contributions of the electrostatic interactions are clear. The activity of the copolymer was not as high with the negatively charged and neutral substrates. 

Shimidzu etal.111 studied the catalytic activity of poly (4(5)-vinylimidazole-co-acrylic add) 60 (PVIm AA) in hydrolyses of 3-acetoxy-N-trimethylanilinium iodide 61 (ANTI) and p-nitrophenylacetate 44 (PNPA). The hydrolyses of ANTI followed the Michaelis-Menten-type kinetics, and that of PNPA followed the second-order kinetics. Substrate-binding with the copolymer was strongest at an imidazole content of 30 mol%. The authors concluded that the carboxylic acid moiety not... 

Azolides can also be used in amide syntheses with very good results when incorporated into copolymers. For example, reactions with l-acyl-4-vinylimidazole/divinylbenzene (96 4) copolymer in solvents like 1,4-dioxane or acetonitrile provide amides in good yields within 1-4 h [1221... 

Other acylations using the copolymer l-acyl-4-vinylimidazole/divinylbenzene/ styrene (48 4 48) in solvents like 1,4-dioxane, benzene, diethylether, or acetone produce within reaction times of three hours the amide yields listed in Table 4-4.[122]... 

TableE 4-4. Amides from l-acyl-4-vinylimidazole/divinylbenzene/ styrene copolymer.

Similarly, /V-sulfonyl-protected vinylimidazole 597 reacts with PTAD to provide the cycloaddition reaction product 598 which easily undergoes the retro-Diels-Alder reaction upon heating or with acid treatment. The primary product is easily isomerized using a base to the aromatized condensed imidazole 599 (Scheme 95) <1998TL4561>. 

Pd(OAc)2 works well with strained double bonds as well as with styrene and its ring-substituted derivatives. Basic substituents cannot be tolerated, however, as the failures with 4-(dimethylamino)styrene, 4-vinylpyridine and 1 -vinylimidazole show. In contrast to Rh2(OAc)4, Pd(OAe)2 causes preferential cyclopropanation of the terminal or less hindered double bond in intermolecular competition experiments. These facts are in agreement with a mechanism in which olefin coordination to the metal is a determining factor but the reluctance or complete failure of Pd(II)-diene complexes to react with diazoesters sheds some doubt on the hypothesis of Pd-olefin-carbene complexes (see Sect. 11). 

These examples demonstrate that additives can have a beneficial effect on the entrapped biopolymers. Unfortunately, they are generally not universal. The additives need to be found for individual immobilized biopolymers and that is not so easy to do. For instance, lactate oxidase retained its activity in a silica matrix if the enzyme was taken as a complex with poly(N-vinylimidazole) prior to the immobilization, but the polymer did not stabilize glycolate oxidase [87,114], Its stabilization was observed after an exchange of poly(N-vinylimidazole) for poly(ethyleneimine). This is a decisive disadvantage of the approaches because they do not offer a general solution that might be extended to any immobilized biopolymer. 

This strategy was first realized by Lozinsky et al., who studied the redox-initiated free-radical copolymerization of thermosensitive N-vinylcaprolactam with hydrophilic N-vinylimidazole at different temperatures, as well as by Chi Wu and coworkers. Lozinsky presents an extensive review of the experimental approaches, both already described in the literature and potential new ones, to chemical synthesis of protein-like copolymers capable of forming core-shell nanostructures in a solution. 

QPVP = partially quaternized PVP with ethylbromide DBQP = partially crosslinked PVP with dibromobutane PSP = copolymer of styrene and 4-vinyl pyridine PVIm = poly(N-vinylimidazole)... 

In aqueous solvent a hydrophobic environment was constructed by using a water-soluble and hydrophobic tri-block copolymer (Scheme 7). The central block is hydrophobic and composed of the copolymer of styrene and N-vinylimidazole (PSI), to which Cu ions can coordinate. This central block was synthesized by UV-irradia-tion polymerization bytelechelic initiator of bis(4-carbomethoxy-phenyl)-disulfide. The reaction of telechelic block with poly-(ethyleneoxide) gave the block copolymer PE0-PSI-PE0. 

Chlorocyclononatetraene 267 rapidly rearranges in liquid sulfur dioxide to 1-chloro-8,9-dihydroindene 268, which forms the cycloadduct 269 with the triazolinedione 264 (equation 145)137. The vinylimidazole 270 affords the purine analogue 271 (equation 146)138. 

First-Order Observed Rate Constants for 1 1.95 Imidazole-Phenol Copolymer, Poly-4(5)-vinylimidazole, and Imidazole-Catalyzed Solvolyses of PNPA° ... 

Copolymer of 4(5)-vinylimidazole and p-vinylphenol Poly-4(5)-vinylimidazole Imidazole... 

Apolar binding of substrates has been demonstrated with polymers of vinylimidazole. Overberger etal. (77) studied the hydrolysis ofp-nitrophenyl acetate and p-nitrophenylheptanoate by poly[4(5)-vinylimidazole] in ethanol water mixtures. 

As one might expect the rate of p-nitrophenyl heptanoate hydrolysis increased at low ethanol concentrations as a result of apolar binding. The rate of p-nitrophenyl acetate hydrolysis also increased markedly at low ethanol concentration. This finding was explained by a conformational effect on the polymer, that is, lower ethanol concentration brings about a shrinkage of the polymer, which increases concerted interactions of the imidazole residues. The hydrolysis of 3-nitro-4-dodecanoyloxybenzoate was found to be 1700 times faster in the presence of poly[4(5)-vinylimidazole] compared to free imidazole (77). A double-displacement mechanism was demonstrated for this system (75). 

Polymers of 4(5)-vinylimidazole and copolymers containing this monomer are usually studied with ethanol-buffer mixtures as solvent because of their insolubility in water. Overberger and Smith (82) found that poly(l-Me-5-vinylimidazole) was soluble in water. Negatively charged substrates with long apolar side chains were bound very strongly to this polymer. A rate enhancement of 106 over the monomeric analog, 1,5-dimethylimidazole, was observed. 

Azole compounds, poly-N-vinylimidazole (PVI-1) and 2-undecylimidazole (UDI), are studied as alternative inhibitors to benzotriazole (BTA) for copper corrosion in aqueous systems using electrochemical techniques. It is shown that UDI, either as a cast film or dissolved in solution at concentrations as low as 7 X inhibits oxygen reduction on... 

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