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BackgroundThe urgent need for cheap and easy-to-use protection against both unwanted pregnancies and sexually transmitted diseases has stimulated considerable interest in the use of surfactants as microbicides, anti-viral, and contraceptive agents in recent years. In the present study we report a systematic in vitro evaluation of the microbicidal, anti-viral and contraceptive potential of cationic, anionic, zwitterionic, and non-ionic surfactants.Methodology/Principal FindingsToxicity was evaluated in mammalian columnar epithelial (MDCK) cells, human sperm cells, Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Neisseria gonorrhoeae, Streptococcus agalactiae and Enterococcus faecalis. The inhibition of adenovirus and lentivirus infection of MDCK cells was also tested. A homologous series of cationic surfactants, alkyl-N,N,N-trimethylammonium bromides (CnTAB), with varying alkyl chains were shown to be bactericidal and fungicidal at doses that were related to the surfactant critical micelle concentrations (CMC), all of them at concentrations significantly below the CMC. In general, bacteria were more susceptible to this surfactant group than C. albicans and this organism, in turn, was more susceptible than MDCK cells. This suggests that the CnTAB may be useful as vaginal disinfectants only in so far as bacterial and fungal infections are concerned. None of the surfactants examined, including those that have been used in pre-clinical studies, showed inhibition of adenovirus or lentivirus infection of MDCK cells or spermicidal activity at doses that were sub-toxic to MDCK cells.Conclusions/SignificanceThe results of this study lead us to propose that systematic analysis of surfactant toxicity, such as we report in the present work, be made a mandatory pre-condition for the use of these substances in pre-clinical animal and/or human studies.

Understanding the mechanisms of toxicity of ionic liquids at the molecular level is crucial for their conscious design as to promote higher acceptability as green solvents in a wide range of applications. In this systematic study, we investigated the effects of three families of ionic liquids on the plasma membrane of the filamentous fungus Aspergillus nidulans. Using fluorescence microscopy and gene expression analysis, we were able to demonstrate that the widely studied 1-alkyl-3-methylimidazolium chlorides with long alkyl substituents cause membrane permeabilisation. In opposition, the biocompatibility of cholinium alkanoates was reinforced here, even though their toxicity also increases with the elongation of the anion.Further investigating the effects of charge on membrane permeabilisation, we observed that a series of alkyl-(2-hydroxyethyl)-dimethylammonium bromides led to permeabilisation of the fungal plasma membrane by increasing the length of one alkyl substituent in the cholinium cation. We hypothesise that the chemical nature of the plasma membrane, which presents a heterogeneous charge distribution along its surface, is pivotal for the membrane permeabilising effects of ionic liquids. This study may inspire a new trend in the ionic liquid field: to give preference for the development of compounds carrying functionalised anions as greener alternatives to those carrying functionalized cations. † Electronic supplementary information (ESI) available. See