Thermodynamic investigation of l-carnitine

Abstract

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°(T) − H°(0), entropy S°(T) − S°(0) and Gibbs function G°(T) − H°(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.