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 standard molecular 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-bronnouracil, respectively