Low-temperature heat capacity of d-glucose and d-fructose

The thermodynamics data of crystalline states of two representative components in blood sugar, d-glucose and d-fructose, are significant in researching artificial synthesis and composition transformation in vivo. The heat capacities of d-glucose and d-fructose over a temperature range of 1.9–300 K were measured and calculated by the heat capacity measurement module of physical property measurement system (PPMS). The heat capacities of two compounds increased steadily with temperature, showing a smooth curve without any thermal anomalies. The heat capacity of d-glucose is greater than that of d-fructose in the range of 0 K < T < 80 K, which is smaller than that of d-fructose between 80 and 300 K. Based on the lattice vibration mode, factors of generating the difference heat capacity data between the two isomers were investigated. Additionally, the heat capacity data were fitted by low-temperature heat capacity theoretical model. The thermodynamic data that molar entropy change and molar enthalpy change over the temperature range of 0–300 K were calculated. The standard molar entropy of d-glucose and d-fructose at 298.15 K was calculated by heat capacity fitting to be 214.64 and 217.56 J K−1 mol−1, all with an error of 0.21.