Goldberg R N, Tewari Y B, Ahluwalia J C
National Institute of Standard and Technology, Gaithersburg, Maryland 20899.
J Biol Chem. 1989 Jun 15;264(17):9901-4.
A thermodynamic investigation of the hydrolysis of sucrose to fructose and glucose has been performed using microcalorimetry and high-pressure liquid chromatography. The calorimetric measurements were carried out over the temperature range 298-316 K and in sodium acetate buffer (0.1 M, pH 5.65). Enthalpy and heat capacity changes were obtained for the hydrolysis of aqueous sucrose (process A): sucrose(aq) + H2O(liq) = glucose(aq) + fructose (aq). The determination of the equilibrium constant required the use of a thermochemical cycle calculation involving the following processes: (B) glucose 1-phosphate2-(aq) = glucose 6-phosphate2-(aq); (C) sucrose(aq) + HPO4(2-)(aq) = glucose 1-phosphate2-(aq) + fructose(aq); and (D) glucose 6-phosphate2-(aq) + H2O(liq) = glucose(aq) + HPO4(2-)(aq). The equilibrium constants determined at 298.15 K for processes B and C are 17.1 +/- 1.0 and 32.4 +/- 3.0, respectively. Equilibrium data for process D was obtained from the literature, and in conjunction with the data for processes B and C, used to calculate a value of the equilibrium constant for the hydrolysis of aqueous sucrose. Thus, for process A, delta G0 = -26.53 +/- 0.30 kJ mol-1, K0 = (4.44 +/- 0.54) x 10(4), delta H0 = -14.93 +/- 0.16 kJ mol-1, delta So = 38.9 +/- 1.2 J mol-1 K-1, and delta CoP = 57 +/- 14 J mol-1 K-1 at 298.15 K. Additional thermochemical cycles that bear upon the accuracy of these results are examined.
利用微量量热法和高压液相色谱法对蔗糖水解为果糖和葡萄糖的过程进行了热力学研究。量热测量在298 - 316 K的温度范围内，于醋酸钠缓冲液（0.1 M，pH 5.65）中进行。得到了蔗糖水溶液水解（过程A）的焓变和热容变化：蔗糖（水溶液） + H₂O（液体） = 葡萄糖（水溶液） + 果糖（水溶液）。平衡常数的测定需要使用涉及以下过程的热化学循环计算：（B）葡萄糖 - 1 - 磷酸²⁻（水溶液） = 葡萄糖 - 6 - 磷酸²⁻（水溶液）；（C）蔗糖（水溶液） + HPO₄²⁻（水溶液） = 葡萄糖 - 1 - 磷酸²⁻（水溶液） + 果糖（水溶液）；以及（D）葡萄糖 - 6 - 磷酸²⁻（水溶液） + H₂O（液体） = 葡萄糖（水溶液） + HPO₄²⁻（水溶液）。在298.15 K时，过程B和C的平衡常数分别为17.1 ± 1.0和32.4 ± 3.0。过程D的平衡数据取自文献，并与过程B和C的数据相结合，用于计算蔗糖水溶液水解的平衡常数。因此，对于过程A，在298.15 K时，ΔG⁰ = -26.53 ± 0.30 kJ·mol⁻¹，K⁰ = (4.44 ± 0.54) × 10⁴，ΔH⁰ = -14.93 ± 0.16 kJ·mol⁻¹，ΔS⁰ = 38.9 ± 1.2 J·mol⁻¹·K⁻¹，以及ΔCₚ = 57 ± 14 J·mol⁻¹·K⁻¹。还研究了影响这些结果准确性的其他热化学循环。
