Solubilisation of stearic acid by the organic base choline hydroxide

Abstract

In a previous study we have shown that the substitution of alkali ions in common fatty acid soaps by choline as a counterion of biol. origin increases the soly. of the resp. soaps without lowering the biocompatibility. Nevertheless, while choline dodecanoate (ChC12), myristate (ChC14), and palmitate (ChC16) have Krafft points below room temp. or even under 0°, choline stearate (ChC18) was not sol. below 40°. In the present contribution we show that an excess of choline hydroxide is able to solubilize choline stearate at temps. as low as 14°. Furthermore, we compare our results to those obtained for the sodium and potassium salts of fatty acids, with molar ratios of base to acid higher than 1:1. In order to elucidate the solubilization process regarding the different ion binding to the carboxylic headgroup, we further investigated the effect of different added chloride salts on the soly. of choline stearate. Our findings indicate that the cation affinity to the carboxylate headgroup follows the trend Na+ > K+ » Ch+. The results are discussed in terms of hydrolysis of the fatty acids in combination with Collins' concept of "matching water affinities". As a feasible application of choline base, we present the sapon. and simultaneous solubilization of butter as an example of a hardly sol. triglyceride