Using choline as a counterion in fatty acid surfactants substantially increases their water solubility as compared to classical sodium and potassium soaps, and thereby enables the application of desirable longer-chain derivatives at ambient temperature. Since choline can be decomposed both physiologically and environmentally, corresponding fatty acid soaps are considered to be highly biocompatible. Recent toxicity and biodegradability studies of choline ionic liquids, including anions such as short- and middle-chain alkanoates, have verified the expected low toxic impact. However, according to the European Cosmetic Directive 76/768/EEC, all salts of choline are forbidden in cosmetic products, mainly just due to its classification as a quaternary ammonium ion. In order to facilitate their application in the future, we have investigated the biodegradability of choline soaps (ChCm) with alkyl chain lengths of m = 12–18 according to the OCDE 301F standard. Further, the cytotoxicity of ChCm surfactants with m = 8–16 was determined, both for odd- and even-numbered fatty acids. Studies were carried out using two different human cell lines, namely cervix carcinoma cells (HeLa) and keratinocytes (SK-Mel-28). For a better comparability to common soaps and to shed light on the influence of the cation, sodium and potassium homologues were also investigated. Results reveal an unexpected non-linear relationship between the hydrophobic chain length and the IC₅₀ value. Most importantly, the presented data show that IC₅₀ values of ChCm surfactants coincide with those of the widely applied sodium and potassium soaps. This demonstrates that choline carboxylate surfactants are harmless and thus strongly supports their applicability in customer end products.

Objectives: A tacrine-silibinin codrug showed promising results in pharmacological and toxicity testing, superior to an equimolar mixture of tacrine and silibinin. The aim of this study was to get more information about its stability, possible degradation products, metabolites, and especially its active principle in vitro and in vivo. Methods: The stability of the codrug was analysed under in-vitro assay conditions. Additionally, its metabolism was investigated using pooled human liver microsomes. Metabolites were identified via liquid chromatography-high resolution electrospray ionization mass spectrometry. Furthermore, the influence of one of the main cleavage products, tacrine hemi succinamide, on viability and mitochondria of hepatic stellate cells was analysed. Key findings: The codrug remained stable in culture medium (Dulbecco's modified Eagle's medium) over an incubation period of 24 h, whereas exposition to microsomal enzymes led to rapid cleavage of the ester bond to form silibinin and a tacrine hemi succinamide. In addition, glucuronidated metabolites of both silibinin and the codrug were detected. For the tacrine hemi succinamide, no effects were observed with regard to cell viability and mitochondrial impairment. Conclusions: This study helps understand and interpret previous results concerning the effects and the absence of toxicity of the tacrine–silibinin codrug and supplies important information for further identification of the active principles of the codrug in vivo.