Labadie M, Debord J, Breton J C
Biochimie. 1979;61(9):1091-4.
A "Batch" microcalorimeter is used at 30 degrees C for the study of the hydrolysis of 4-nitro-phenylphenylphosphonate with a calf-intestinal phosphonate esterase, in a tris buffer, pH 8. The yield of enzymatic hydrolysis is estimated by spectrophotometric determination of the p--nitrophenol evolved; we have then calculated the apparent molar enthalph of the reaction. (delta Happ = -72,2 kj. mol-1). Phenylphosphonic acid, the second reaction product, is not transphosphonylated on tris. The second acidity of phenylphosphonic acid was studied at 30 degrees C by sodium hydroxide electrotitration (pKa2 = 7,13) and by "Flow" microcalorimetry (delta Hionization = 19,8 kj.mol-1). In the same manner at 30 degrees C, we measured the heat of ionization of p-nitrophenol (delta Hionization = 26,75 kj.mol-1). These findings allow a calculation for the actual heat of hydrolysis of 4-nitro-phenyl-phenylphosphonate (delta Hrho = -29,7 kj.mol-1).
使用“批量”微量热计在30℃下，于pH 8的三羟甲基氨基甲烷缓冲液中，研究小牛肠磷酸酯酶催化4-硝基苯基苯基膦酸酯的水解反应。通过分光光度法测定反应生成的对硝基苯酚来估算酶促水解的产率；然后我们计算了该反应的表观摩尔焓（ΔHapp = -72.2 kJ·mol⁻¹）。反应的第二个产物苯基膦酸不会在三羟甲基氨基甲烷上发生转膦酰化反应。通过氢氧化钠电位滴定法（pKa2 = 7.13）和“流动”微量热法（ΔH电离 = 19.8 kJ·mol⁻¹）在30℃下研究了苯基膦酸的二级酸度。同样在30℃下，我们测量了对硝基苯酚的电离热（ΔH电离 = 26.75 kJ·mol⁻¹）。这些结果使得我们能够计算出4-硝基苯基苯基膦酸酯的实际水解热（ΔHρ = -29.7 kJ·mol⁻¹）。
