尿嘧啶和5-溴尿嘧啶的低温热容

采用综合物性测量系统(PPMS)的热容测量模块在1.9-300 K温度区间内对两种药物中间体(尿嘧啶和5-溴尿嘧啶)的低温热容进行了测量与研究.结果表明,在测量温区内两种化合物的低温热容随温度的上升而逐步增加,无任何热异常现象产生;在相同温度下,5-溴尿嘧啶的热容数值始终高于尿嘧啶.利用低温热容理论模型对热容数据进行了拟合,并计算得到了0-300 K温区的摩尔熵变、焓变等热力学函数.此外,通过热容拟合数据计算得到的尿嘧啶和5-溴尿嘧啶在298.15 K的标准摩尔规定熵分别为(132.48±1.32)和(165.39±1.65)J·K-1·mol-1.

Low Temperature Heat Capacities of Uracil and 5-Bromouracil

The heat capacities of uracil and 5-bromouracil were measured using a quantum design physical property measurement system (PPMS) in the temperature range of 1.9-300 K. The experimental results indicate that the heat capacities of the two compounds increase with increasing temperature, and no thermal anomalies are observed across the whole temperature range studied. The heat capacity values of 5-bromouracil are larger than those of uracil as it has a higher molecular weight but a similar molecular structure. The heat capacities were fitted to theoretical models and the thermodynamic functions were calculated based on the curve fitting. The standardmolecular entropies at 298.15 K were determined to be (132.48±1.32) and (165.39±1.65) J·K^-1·mol^-1 for uracil and 5-bromouracil, respectively.