Aurora Pinazo

“Green” amino acid-based surfactants

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. Amino acid-based surfactants, which have an amino acid residue as a hydrophilic moiety, are reviewed with respect to their synthesis, properties and some applications. The review covers three main categories of amino acid-based surfactants: Nα-acyl, N-alkyl amide and O-alkyl ester derivatives among the linear or single chain amino acid-based surfactants; Nα, Nω-bis(Nα-acylarginine)α,ω-alkylendiamides, which are gemini amino acid-based surfactants; and 1-monoacyl-rac-glycero-3-O-(Nα-acetyl-L-amino acid) and 1,2-diacyl-rac-glycero-3-O-(Nα-acetyl-L-amino acid), both amino acid-based surfactants with glycerolipid-like structures.

Cationic Surfactants Derived from Lysine: Effects of Their Structure and Charge Type on Antimicrobial and Hemolytic Activities

Three different sets of cationic surfactants from lysine have been synthesized. The first group consists of three monocatenary surfactants with one lysine as the cationic polar head with one cationic charge. The second consists of three monocatenary surfactants with two amino acids as cationic polar head with two positive charges. Finally, four gemini surfactants were synthesized in which the spacer chain and the number and type of cationic charges have been regulated. The micellization process, antimicrobial activity, and hemolytic activity were evaluated. The critical micelle concentration was dependent only on the hydrophobic character of the molecules. Nevertheless, the antimicrobial and hemolytic activities were related to the structure of the compounds as well as the type of cationic charges. The most active surfactants against the bacteria were those with a cationic charge on the trimethylated amino group, whereas all of these surfactants showed low hemolytic character.

Non-conventional surfactants from amino acids and glycolipids: Structure, preparation and properties

Due to current trends, such as energy savings and the increase in environmental and toxicological concerns, at present there is a strong industrial need for high performance chemicals such as surfactants with biodegradable and biocompatible properties. One interesting and practical strategy concerns the preparation of surfactant molecules based on the design of molecular mimics of natural compounds such as lipoaminoacids, phospholipids and glycolipids. They are characterized by a non-conventional structure derived from amino acids, oligisaccarides and glycerols. This paper reviews the research results on structure, chemical preparation, properties and uses of lipoaminoacids and glycerolipids.

Cationic surfactants from lysine: Synthesis, micellization and biological evaluation

Biocompatible cationic surfactants from the amino acid lysine (hydrochloride salts of N(epsilon)-lauroyl lysine methyl ester, N(epsilon)-myristoyl lysine methyl ester and N(epsilon)-palmitoyl lysine methyl ester) have been prepared in high yields by lysine acylation in epsilon position with three natural saturated fatty acids. The micellization process of these surfactants has been studied using the PGSE-NMR technique. The compounds were tested as antimicrobial agents against Gram-positive and Gram-negative bacteria. The surfactants show moderate antimicrobial activity against the Gram-positive bacteria but Gram-negative bacteria are resistant to these surfactants in the concentration range tested. The haemolytic activity is considerably lower than those reported for other cationic N(alpha)-acyl amino acid analogues. The acute toxicity against Daphnia magna and biodegradability was studied. The toxicity is clearly lower than that reported for conventional cationic surfactants from quaternary ammonium and the three surfactants from lysine can be classified as ready biodegradable surfactants.

Gemini surfactants from natural amino acids

In this review, we report the most important contributions in the structure, synthesis, physicochemical (surface adsorption, aggregation and phase behaviour) and biological properties (toxicity, antimicrobial activity and biodegradation) of Gemini natural amino acid-based surfactants, and some potential applications, with an emphasis on the use of these surfactants as non-viral delivery system agents. Gemini surfactants derived from basic (Arg, Lys), neutral (Ser, Ala, Sar), acid (Asp) and sulphur containing amino acids (Cys) as polar head groups, and Geminis with amino acids/peptides in the spacer chain are reviewed.

Synthesis, surface active properties and antimicrobial activity of new bis quaternary ammonium compounds

New dimeric surfactants 1 and 2 containing two saturated hydrocarbon chains and two quaternary ammonium salts linked through an alkene spacer chain with amide and disulfide bonds have been prepared from a betaine type amphoteric surfactant. They show a high effectiveness of adsorption in comparison with their single chain homologues. Surfactants 1 and 2 are very water soluble compounds with extraordinary micelle-forming properties. Both are very active against a wide range of microorganisms including gram negative bacteria.

Role of aggregate size in the hemolytic and antimicrobial activity of colloidal solutions based on single and gemini surfactants from arginine

Cationic colloidal systems composed of arginine based surfactants (single or gemini structures) and membrane additive compounds such as DLPC or cholesterol have been characterized by means of size distribution and zeta-potential measurements. The single or monocatenary surfactant (LAM) as well as the gemini with the shortest spacer chain (C6(LA)2) formed micelles, while aqueous solutions of pure gemini surfactants with longer spacers (C9(LA)2 and C12(LA)2) formed very big aggregates. The addition of phospholipids or cholesterol changed drastically the aggregation behaviour. In the case of LAM and C6(LA)2, the incorporation of additives gave rise to the formation of cationic vesicles. For C9(LA)2 and C12(LA)2, this type of additives promoted the formation of smaller aggregates. All the formulations had positive zeta-potential values and in general exhibited high colloidal stability. We also evaluated the hemolysis and the antimicrobial activity of these systems. The capability of disrupting erythrocyte membranes depends on the hydrophobicity of the molecules and the size of aggregates in the solution. Gemini surfactants with short spacer chains are more hemolytic than their single chain homologue, while gemini surfactants with long spacers are much less hemolytic than their single chain counterpart. Moreover, for the same formulation, the hemolysis depends on the initial concentration of the stock solution used to set up the hemolysis/concentration curve. Results show that small aggregates interact easily with these biological membranes. The alkyl spacer chain and the presence of additives also play an important role in the antimicrobial activity, and, in general, the interaction with bacteria and erythrocytes is affected by the same parameters. The physico-chemical and biological characterization of these systems might be important for several biotechnological applications in which cationic vesicular systems are involved.

The physicochemical properties and chemical composition of trehalose lipids produced by Rhodococcus erythropolis 51T7

This study analyzed the chemical and physical properties of a biosurfactant synthesized by Rhodococcus sp. 51T7. The biosurfactant was a trehalose tetraester (THL) consisting of six components: one major and five minor. The hydrophobic moieties ranged in size from 9 to 11 carbons. The critical micelle concentration (CMC) was 0.037g L(-1) and the interfacial tension against hexadecane was 5mN m(-1). At pH 7.4 the glycolipid CMC/critical aggregation concentration (CAC) was 0.05g L(-1) and at pH 4 it was 0.034g L(-1). A phase diagram revealed effective emulsification with water and paraffin or isopropyl myristate. A composition of 11.3-7.5-81.8 (isopropyl myristate-THL-W) was stable for at least 3 months. The HLB was 11 and the phase behaviour of the glycolipid revealed the formation of lamellar and hexagonal liquid-crystalline textures.

Unconventional vesicle-to-ribbon transition behaviour of diacyl glycerol amino acid based surfactants in extremely diluted systems induced by pH-concentration effects

A vesicle-to-ribbon transition has been observed in extremely dilute 1-O-(L-arginyl)-2, 3-O-di-decanoyl-sn-glycerol dichlorohydrate (1010R) surfactant systems by means of static light scattering. At concentration as low as 0.005 mM the solutions scattered significantly. From the angular dependence and molecular weight of the aggregates a vesicular structure is suggested. Increasing surfactant concentration in water induces the vesicle-to-ribbon transition at concentrations as low as 0.5 mM. This transition is accompanied by a strong decrease of scattered intensity and change in angular dependence. Lowering the pH at a fixed concentration can induce the same transition. Both parameters change the protonation of the surfactant, inducing an increase in preferred surfactant head-group area. Those findings are congruent with the observed surface tension behaviour as a function of surfactant concentration and suggests an explanation for the widely different critical micellar concentration (c.m.c.) as determined by different techniques.

Synthesis and biological properties of dicationic arginine–diglycerides

A novel family of dicationic arginine–diglyceride surfactants, 1,2-diacyl-3-O-(L-arginyl)-rac-glycerol·2HCl (XXR) with alkyl chain lengths in the range of C8–C14 was prepared. These new surfactants can be regarded as analogues of lecithins. They have two hydrophobic tails of identical fatty acid chains attached to the glycerol through ester bonds and a dicationic polar head from arginine instead of the zwitterionic on the lecithins. These new compounds can be classified as multifunctional surfactants with self-aggregation behaviour comparable to that of short-chain lecithins. They have antimicrobial activity similar to that of the conventional cationic surfactants and are as harmless as amphoteric betaines.