Solvolysis of p-nitrophenyl esters catalyzed by oligo-4(5)-vinylimidazoles

Abstract

The preparation of low molecular weight poly-4(5)-vinylimidazole is described. Oligomer fractions with molecular weight ranges from a few hundred to two thousand, five hundred were obtained by fractionation through a Sephadex LH-20 column. The apparent dissociation constant of the imidazolium ion in oligo-4(5)vinylimidazole decreases rapidly as the average molecular weight increases from 390 to 626. At an average molecular weight greater than 626, the apparent dissociation-constant value plateaus. The imidazole group in oligo-4(5)-vinylimidazole with ca. 5 imidazole units per oligomer molecule shows 71% of the solvolytic rate of the imidazole groups which are located in the oligomer with an average molecular weight of 2460 during the solvolysis of p-nitrophenyl acetate. The results indicate that short-range imidazole groups are interacting with each other to catalyze the solvolysis ofp-nitrophenyl acetate. Solvolysis ofp-nitrophenyl heptanoate catalyzed by oligomer fractions in 21% (v/v) n-propanol-water solutions indicates that the solvolysis rate ofp-nitrophenyl heptanoate increases with an increase of oligomer's molecular weight.

Binding and biomimetic cleavage of the RNA poly(U) by synthetic polyimidazoles

“…Overberger et al had extensively examined them as catalysts for the hydrolysis of phenyl esters (15,16). We had previously seen that they are good catalysts with our reversibly bound pyridoxamine coenzyme mimic for the transamination of phenylpyruvate to form phenylaniline (14).…”