Wang J C, Patel B
J Pharm Sci. 1986 Feb;75(2):204-7. doi: 10.1002/jps.2600750222.
The degradation kinetics of nicotinyl 6-aminonicotinate in aqueous buffer solutions were studied over the pH range from 4.0 to 10.0. In all cases, pseudo-first-order kinetics were observed at constant hydronium ion concentration. The pH-rate profile indicated that the hydrolysis of nicotinyl 6-aminonicotinate may be described by at least two catalytic terms. In alkaline solution the hydrolysis is catalyzed primarily by hydroxyl ions. In acidic solution the hydrolysis may be attributed to either the water-catalyzed reaction of the protonated species or the hydronium ion catalyzed reaction of the free base. The resulting catalytic profile afforded a sharp pH minimum of approximately 5.90 at 65 degrees C. An activation energy of 16 Kcal/mol was obtained in a phosphate buffer solution at a pH of approximately 5.90 +/- 0.2. The first- and second-order reaction constants for water and hydroxyl ion catalysis were determined, and the temperature dependency of the reaction was studied. The buffer effect and solvent effect on the hydronium and hydroxyl ion catalysis was also investigated.
在pH值为4.0至10.0的范围内，研究了烟酰基6 - 氨基烟酸酯在水性缓冲溶液中的降解动力学。在所有情况下，在恒定的水合氢离子浓度下观察到准一级动力学。pH - 速率曲线表明，烟酰基6 - 氨基烟酸酯的水解至少可以用两个催化项来描述。在碱性溶液中，水解主要由氢氧根离子催化。在酸性溶液中，水解可能归因于质子化物种的水催化反应或游离碱的水合氢离子催化反应。在65℃下，所得的催化曲线在约5.90处出现明显的pH最小值。在pH约为5.90±0.2的磷酸盐缓冲溶液中获得了16千卡/摩尔的活化能。测定了水和氢氧根离子催化的一级和二级反应常数，并研究了反应的温度依赖性。还研究了缓冲效应和溶剂效应对水合氢离子和氢氧根离子催化的影响。
