There is a pressing need for developing efficiently surfactants that are biodegradable and biocompatible. Surfactant molecules from renewable raw materials that mimic natural lipoamino acids are one of the preferred choices for food, pharmaceutical and cosmetic applications. Given their natural and simple structure they show low toxicity and quick biodegradation. The value of amino acids and vegetable oil derivatives as raw materials for the preparation of surfactants was recognized as soon as they were discovered early in the last century. The combination of polar amino acids/peptides (hydrophilic moiety) and non-polar long-chain compounds (hydrophobic moiety) for building up the amphiphilic structure has produced molecules with high surface activity. Our group has a wide experience in synthesis (chemical, enzymatic or, usually, by a combination of both methodologies) of amino acid-based surfactants obtained from the combination of natural saturated fatty acids, alcohols and amines with different amino acid head groups through ester and amide linkages. Thus, saturated single-chain, double-chain, and gemini surfactants of different ionic character have been found to be in all cases highly biodegradable, with low toxicity, ecotoxicity and irritation effects. Water solubility and self-aggregation properties were directly associated with the chemical structure of the molecule and only cationic lipoamino acids possessed antimicrobial activity. To cite this article:

Cationic surfactants associate strongly to DNA and compact but are often toxic. The interaction of some novel cationic amino acid-based surfactants, which may enhance transfection and appear to be nontoxic, is described. A cationic arginine-based surfactant, ALA, gives in combination with anionic surfactants spontaneously stable vesicles, and special attention is given to the association of these catanionic vesicles, with a net positive charge, to DNA. The ability of this surfactant alone to compact DNA is compared in fluorescence microscopy studies to classical cationic surfactants. Addition of DNA to a solution of the catanionic vesicles results in associative phase separation at very low vesicle concentrations; there is a separation into a precipitate and a supernatant solution, which is first bluish but becomes clearer as more DNA is added. From studies using cryogenic transmission electron microscopy (cryo-TEM) and small angle X-ray scattering it is demonstrated that there is a lamellar structure with DNA arranged within the surfactant bilayers. Analysis of the supernatant by means of proton nuclear magnetic resonance ( 1 H NMR) showed that above the isoelectric point between ALA, anionic surfactant (sodium octyl sulfate, SOS) and DNA, anionic surfactant starts to be expelled from the bilayers on further incorporation of DNA. There appears to be a transition from a lamellar to a hexagonal liquid crystal structure when most of SOS has been expelled from the aggregate bilayers; at higher DNA-to-surfactant ratios, self-assembled SOS micelles and the excess of DNA added seem to coexist in solution. Regarding the phase-separating DNA-surfactant particles, cryo-TEM demonstrates a large and nonmonotonic variation of particle size as the DNA-surfactant ratio is varied, with the largest particles obtained in the vicinity of overall charge neutrality.

A novel family of dicationic arginine-monoglyceride surfactants, 1-acyl-3-O-(L-arginyl)-rac-glycerol Á 2HCl, was synthesised and characterised. They have one alkyl chain of with length in the range of C 10 -C 14 attached to the glycerol though esters bonds and a dicationic polar head from the arginine. Structurally they can be regarded as analogues of the monoglycerides, widely used as emulsifiers in the food and in the pharmaceutical industry. The introduction of the basic amino acid arginine into the monoglycerides increases the solubility of these compounds and improves their antimicrobial activity. Moreover, the acute toxicity of these surfactants against Daphnia magna is clearly lower than the toxicity reported for conventional cationic surfactants. P A P E R NJC www.rsc.org/njc

Understanding nanomaterial interactions within cells is of increasing importance for assessing their toxicity and cellular transport. Here, we developed nanovesicles containing bioactive cationic lysine-based amphiphiles, and assessed whether these cationic compounds increase the likelihood of intracellular delivery and modulate toxicity. We found different cytotoxic responses among the formulations, depending on surfactant, cell line and endpoint assayed. The induction of mitochondrial dysfunction, oxidative stress and apoptosis were the general mechanisms underlying cytotoxicity. Fluorescence microscopy analysis demonstrated that nanovesicles were internalized by HeLa cells, and evidenced that their ability to release endocytosed materials into cell cytoplasm depends on the structural parameters of amphiphiles.The cationic charge position and hydrophobicity of surfactants determine the nanovesicle interactions within the cell and, thus, the resulting toxicity and intracellular behavior after cell uptake of the nanomaterial. The insights into some toxicity mechanisms of these new nanomaterials contribute to reducing the uncertainty surrounding their potential health hazards.

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