Chemical enthalpy-entropy compensation effect in the hydrolysis of p-nitrophenyl carboxylates catalyzed by alkaline mesentericopeptidase |
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Authors: | Victoria Dorovska-Taran Diana Raykova Sava Tishkov Blagoy Blagoev |
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Affiliation: | Institute of Organic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria |
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Abstract: | The temperature dependence of the hydrolysis of p-nitrophenyl carboxylates with general formula H(CH2)nCOOC6H4NO2 catalyzed by alkaline mesentericopeptidase has been studied (n varying from 1 to 7, temperature range 2–30°C, pH 8.80, 5 vol% dimethylsulfoxide). The activation parameters of the deacylation step depend on the length of the hydrophobic side chain of the substrate molecule (, , and decrease by 2.0 kcal/mol, 4.9 kcal/mol, and 10 eu, respectively, as the length of the acyl carbon chain increases from n = 1 to n = 4). The following criteria were applied to establish a chemical enthalpy-entropy compensation effect: (a) Exner's plot of log vs : (b) Petersen's plot of log, k/T vs 1/T; (c) Exner's statistical treatment in coordinates log k vs 1/T; (d) according to Krug et al. (ΔH≠ vs ΔGThm≠). By use of all the above-mentioned criteria the existence of a chemical enthalpy-entropy compensation effect was proved with an isokinetic temperature β of about 470°K, which is significantly higher than the average experimental temperature. |
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