Physicochemical properties of L-carnitine in aqueous solution and its interaction with trimethylamine N-oxide, sodium chloride and dextrose: Volumetric and calorimetric insights

Abstract

Abstract L -carnitine plays physiologically important roles specifically to decrease triglycerides, very low density lipoprotein (VLDL) and cholesterol. Considering these facts, it is believed to be helpful in the reduction of cardiovascular diseases and diabetes. Physicochemical properties of L -carnitine in aqueous or mixed aqueous solutions are scarcely available in literature. Such properties will be useful in understanding the interactions of L -carnitine with other cellular components like trimethylamine-N-oxide (TMAO), dextrose ( D -glucose) and NaCl. The values of densities (ρ) and speeds of sound (u) of L -carnitine were measured over the molality range of m = 0.05 mol·kg−1 to m = 0.3 mol·kg−1 at temperature T = 293.15 K to T = 313.15 K in water and in aqueous solutions of TMAO, dextrose, and NaCl. Using these data, values of apparent molar volume (V2,m,φ) and apparent molar adiabatic compressibility (Ks,2,m,φ) have been determined. The results obtained from these measurements have been used to derive the standard partial molar volume ( V 2 , m o ), standard partial molar adiabatic compressibility ( K s , 2 , m o ), standard partial molar volume of transfer ( Δ tr V 2 , m o ) and standard partial molar isentropic compressibilities of transfer ( Δ tr K S , 2 , m o ) from water to aqueous solutions of TMAO, dextrose, and NaCl. Through Isothermal Titration Calorimetry (ITC), the enthalpies of dilution ( Δ dil H m ) of L -carnitine in water (over a temperature range of T = 293.15 K to T = 313.15 K) and in aqueous solutions of TMAO, dextrose, and NaCl have been determined. The values of standard molar enthalpy of dilution ( Δ dil H m o ) and their transfer values ( Δ tr Δ dil H m o ) have been derived from these measurements. The results have been discussed in terms of possible intermolecular interactions. The data suggest that there is overall balancing of hydrophobic and hydrophilic interactions in system containing L -carnitine and TMAO in aqueous solution, but hydrophobic effect dominates when the co-solute is NaCl or dextrose.