Formation of Micelles of Acylcarnitines in Glycerol

Acylcarnitine chlorides form micelles in water and polyprotic solvents such as glycerol, ethylene glycol; 1,3-propanediol and 1,4-butanediol. The effect of the acyl chain on the formation of micelles was studied for compounds with chain lengths of 2 to 16 carbon atoms. The critical micellar concentration in glycerol was determined at 25 °C by means of difference spectroscopy using phenol as a probe. The acylcarnitine chlorides with chains containing less than 8 C atoms do not form micelles in glycerol. The critical micellar concentration varies from 0.060 mol dm−3 for octanoylcarnitine to 0.011 mol dm−3 for palmitoylcarnitine. The free energy of micellization, ΔGmic°, varies linearly with chain length in the range of −6.95 kJ mol−1 to −11.2 kJ mol−1. The “hydrophobic” or “solvophobic” effect was more pronounced in water than in glycerol and the free energy change per metylene group was −2.89 kJ mol−1 and −0.75 kJ mol−1, respectively. The formation of micelles of acylcarnitine chlorides in glycerol is important in terms of the metabolism of fatty acids and their transport across biological membranes.