Chemical enthalpy-entropy compensation effect in the hydrolysis of p-nitrophenyl carboxylates catalyzed by alkaline mesentericopeptidase

Abstract The temperature dependence of the hydrolysis of p -nitrophenyl carboxylates with general formula H(CH 2 ) n COOC 6 H 4 NO 2 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 ( Δ G 3 ≠ , Δ H 3 ≠ , and Δ S 3 ≠ 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 k 3 T 1 vs log k 3 T 2 : (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 . (Δ H ≠ vs Δ G T hm ≠ ). 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.