Thermodynamic investigation of L-carnitine

In the present work temperature dependence of heat capacity of L-carnitine has been measured for the first time over the range from 6 K to 346 K by precision adiabatic vacuum calorimetry. Based on the experimental data, the thermodynamic functions of the L-carnitine, namely, the heat capacity, enthalpy H degrees(T) - H degrees(0), entropy S degrees(T) - S degrees(0) and Gibbs function G degrees(T) - H degrees(0) have been determined for the range from T -> 0 to 350 K. The value of the fractal dimension D in the function of multifractal generalization of Debye's theory of the heat capacity of solids was estimated and the character of heterodynamics of structure was detected. Enthalpy of combustion (-4142.1 +/- 2.3) kJ mol(-1 )of the L-carnitine was measured for the first time using high-precision combustion calorimeter. The standard molar enthalpy of formation in the crystalline state (-756.2 +/- 2.5) kJ mol(-1) of L-carnitine at 298.15 K was derived from the combustion experiments. Using combination of the adiabatic and combustion calorimetry results the thermodynamic functions of formation of the L-carnitine at T = 298.15 K and p = 0.1 MPa have been calculated. The low-temperature X-ray diffraction was used for the determination of coefficients of thermal expansion. (C) 2018 Elsevier Ltd.