Francesc Comelles

Self-aggregation and antimicrobial activity of imidazolium and pyridinium based ionic liquids in aqueous solution.

Two series of long-chain imidazolium and pyridinium based ionic liquids (1-alkyl-3-methylimidazolium and 1-alkylpyridinium bromides) were synthesised and the effect of the alkyl chain length and the nature of the cationic head group on micellization and antimicrobial activity of the ionic liquids (ILs) were investigated. Tensiometry, conductometry, spectrofluorimetry and PGSE-NMR were applied to study the self-aggregation of the amphiphilic ILs in aqueous solution. The ILs investigated displayed surface activity and the characteristic chain length dependence of the micellization process of surfactants. The antimicrobial activity was evaluated against Gram-negative and Gram-positive bacteria and fungi. ILs containing more than eight carbon atoms in the alkyl chain showed antimicrobial activity. Their efficiency as antimicrobial agents increased with the hydrophobicity of the amphiphilic cation being the C(14) homologous the most active compounds.

Aggregation Behavior and Antimicrobial Activity of Ester-Functionalized Imidazolium- and Pyridinium-Based Ionic Liquids in Aqueous Solution

Two series of long chain imidazolium- and pyridinium-based ionic liquids containing an ester functional group in the alkyl side chain, 3-methyl-1-alkyloxycarbonylmethylimidazolium bromides (C(n)EMeImBr) and 1-alkyloxycarbonylmethylpyridinium bromides (C(n)EPyrBr), were synthesized and their thermal stability, aggregation behavior in aqueous medium, and antimicrobial activity investigated. The introduction of an ester group decreased the thermal stability of the functionalized ILs compared to simple alkyl chain containing ILs (1-alkyl-3-methylimidazolium bromides and 1-alkylpyridinium bromides). Tensiometry, conductimetry, and spectrofluorimetry were applied to study the self-aggregation of the amphiphilic ILs in aqueous solution. The ILs investigated displayed surface activity and the characteristic chain length dependence of the micellization process of surfactants. As compared to simple alkyl chain containing ILs bearing the same hydrocarbon chain, ester-functionalized ILs possess higher adsorption efficiency (pC(20)) and significantly lower critical micelle concentration (cmc) and surface tension at the cmc (γ(cmc)), indicating that the incorporation of an ester group promotes adsorption at the air/water interface and micelle formation. The antimicrobial activity was evaluated against Gram-negative and Gram-positive bacteria and fungi. ILs containing more than eight carbon atoms in the alkyl chain showed antimicrobial activity. Their efficiency as antimicrobial agents increased with the hydrophobicity of the amphiphilic cation being the C(12) homologous the most active compounds. The incorporation of an ester group particularly increased the biological activity against fungi.

Self-assembly and antimicrobial activity of long-chain amide-functionalized ionic liquids in aqueous solution

Surface active amide-functionalized ionic liquids (ILs) consisting of a long alkyl chain (C6C14) connected to a polar head group (methylimidazolium or pyridinium cation) via an amide functional group were synthesized and their thermal stability, micellar properties and antimicrobial activity in aqueous solution investigated. The incorporation of an amide group increased the thermal stability of the functionalized ionic liquids compared to simple alkyl chain substituted ionic liquids. The surface activity and aggregation behaviour in aqueous solution of amide-functionalized ionic liquids were examined by tensiometry, conductivity and spectrofluorimetry. Amide-functionalized ILs displayed surface activity and their critical micelle concentration (cmc) in aqueous media decreased with the elongation of the alkyl side chain as occurs for typical surfactants. Compared to non-functionalized ILs bearing the same alkyl chain, ionic liquids with an amide moiety possess higher surface activity (pC20) and lower cmc values. The introduction of an amide group in the hydrophobic chain close to the polar head enhances adsorption at the air/water interface and micellization which could be attributed to the H-bonding in the headgroup region. The antimicrobial activity was evaluated against a panel of representative Gram-negative and Gram-positive bacteria and fungi. Amide-functionalized ILs with more than eight carbon atoms in the side chain showed broad antimicrobial activity. Antibacterial activities were found to increase with the alkyl chain length being the C12 homologous the most effective antimicrobial agents. The introduction of an amide group enhanced significantly the antifungal activity as compared to non-functionalized ILs.

New Surfactant Phosphine Ligands and Platinum(II) Metallosurfactants. Influence of Metal Coordination on the Critical Micelle Concentration and Aggregation Properties

We have prepared the first platinum(II) metallosurfactants from a new family of linear surfactant phosphines Ph(2)P(CH(2))(n)SO(3)Na {1 (n = 2), 2 (n = 6), and 3 (n = 10)}, which were synthesized by reaction between the halosulfonates X(CH(2))(n)SO(3)Na and sodium diphenylphosphide. The metallosurfactants cis-[PtCl(2)L(2)] (L = 1-3) were obtained after reaction between the phosphines and PtCl(2) in dimethylsulfoxide. All compounds were fully characterized by the usual methods {NMR ((1)H, (13)C, (31)P, (195)Pt), IR, MS-ESI and HRMS}. By exploring the surfactant properties of phosphines 1-3 and their respective platinum metallosurfactants cis-[PtCl(2)L(2)] (L = 1-3) through surface tension measurements, dynamic light scattering spectroscopy, and cryo-TEM microscopy, we were able to analyze the influence of the metal coordination on the critical micelle concentration (cmc) and the aggregation properties. The cmc values of platinum metallosurfactants were considerably lower than those obtained for the free phosphines 1-3. This behavior could be understood by an analogy between the structure of cis-[PtCl(2)L(2)] complexes and bolaform surfactants. The calculated values of area per molecule also showed different tendencies between 1-3 and cis-[PtCl(2)L(2)] complexes, which could be explained on the basis of the possible conformations of these compounds in the air-water interface. The study of aggregates by dynamic light scattering spectroscopy and cryo-TEM microscopy showed the formation of spherical disperse medium size vesicles in all cases. However, substantial differences were observed between the three free phosphines (the population of micellar aggregates increased with long chain length) and also between phosphines and their respective metallosurfactants.

Interaction of Nonionic Surfactants and Hydrophilic Ionic Liquids in Aqueous Solutions: Can Short Ionic Liquids Be More Than a Solvent?

The interaction between an ethoxylated nonionic surfactant (C(12-14)EO(8)) and three conventional hydrophilic imidazolium-based ionic liquids (bmim-octyl SO(4), bmim-methyl SO(4), and bmim-BF(4)) in aqueous solution has been investigated. In most of the reported studies where a surfactant is dissolved in an ionic liquid aqueous solution, conventional ionic liquids are merely considered to be solvents. Consequently, the resulting critical micelle concentration (cmc) is considered to be that of the surfactant. However, given that the three ionic liquids selected showed the typical shape of a surface-active compound when the surface tension was plotted against concentration, the role of these compounds as secondary surfactants and consequently the possibility of mixed-micelle formation have been investigated. Different series of experiments where a surfactant and an ionic liquid were combined in a wide range of mole ratios have been performed and treated as typical binary surfactant systems in aqueous solution. It has been found for the three surfactant/ionic liquid systems that depending on the surfactant mole fraction, α(1), attractive or repulsive interactions in mixed-micelle formation are produced. Therefore, when we select the appropriate α(1) these systems can be adjusted to a given application, depending on whether monomers or micelles are mainly required.

Sorption of Alkyl Benzyl Dimethyl Ammonium Compounds by Activated Sludge

The adsorption isotherms on activated sludge from wastewater treatment plants and the surface properties in aqueous solution of alkyl benzyl dimethyl ammonium compounds have been investigated. Langmuir and Freundlich adsorption isotherms described satisfactorily the equilibrium adsorption of these cationic surfactants on activated sludge. Adsorption on sludge as well as the affinity of these compounds to be adsorbed in the liquid/gas interface increased with increasing the alkyl chain length in the cationic surfactant molecule. Water hardness decreased the critical micelle concentration values of the alkyl benzyl dimethyl ammonium homologues tested and the extent of their sorption to activated sludge.

Self Assembly of pH-Sensitive Cationic Lysine Based Surfactants

Three cationic surfactants of the type N(ε)-acyl lysine methyl ester hydrochloride have been studied with respect to solution behavior and adsorption on the air/water interface, as well as the thermolyotropic behavior. The self-assembly of these surfactants, which have the cationic charge on amine protonated groups, was assessed by different physicochemical methods. Depending on the pH value, these surfactants can dissociate in aqueous solutions, losing the cationic charge. Therefore, knowledge of the pK(a) of these compounds is essential to explain their behavior in aqueous solutions. The bulk techniques, conductivity, and nuclear magnetic resonance diffusion (NMR) obtained similar critical micellar concentration (CMC) values, which were well above those obtained from surface tension. Surface tension measurements were strongly dependent on the technique used, namely, Wilhelmy plate and pendant drop. The phase behavior at medium to high concentrations has been studied by optical polarizing microscopy and small angle x-ray scattering (SAXS). The X-ray studies showed that the lysine-based surfactants at low hydration have rich thermotropic liquid crystalline behavior. The results are discussed in terms of the structure of the compounds and the cationic charge of the molecule. We will show how apparently small changes in molecule structure have a large influence on phase behavior.

MICROEMULSIONS WITH BUTYL LACTATE AS COSURFACTANT

ABSTRACT The use of butyl lactate as cosurfactant on the preparation of microemulsions with anionic surfactant is suggested. A parallel study between the classical system water/sodium dodecyl sulphate/pentanol and the proposed water/sodium dodecyl sulphate/butyl lactate has been carried out on their capacities of incorporating heptane as lipophilic component. The results obtained show the ability of butyl lactate to prepare microemulsions, allowing the incorporation of heptane up to contents of 30–40% at higher dilutions with water than the classical system containing pentanol.

Skin delivery of antioxidant surfactants based on gallic acid and hydroxytyrosol

The aim of this study has been to investigate the dermal absorption profile of the antioxidant compounds gallic acid and hydroxytyrosol as well as their derivatives, hexanoate (hexyl gallate and hydroxytyrosol hexanoate) and octanoate (octyl gallate and octanoate derivative) alkyl esters (antioxidant surfactants). Previously, the scavenging capacity of these compounds, expressed as efficient dose ED50, has also determined.

Micellization of sodium laurylethoxysulfate (SLES) and short chain imidazolium ionic liquids in aqueous solution.

In the present study the interactions between an anionic surfactant sodium laurylethoxysulfate (SLES) and three short chain imidazolium (1-butyl-3-methylimidazolium) based ionic liquids (bmim-octyl SO4, bmim-methyl SO4 and bmim-BF4) in aqueous solution have been investigated. Generally when a surfactant is dissolved in a hydrophilic ionic liquid aqueous solution the critical micelle concentration (cmc) obtained is attributed to the surfactant because the ionic liquid (IL) is considered to be only a cosolvent. However, some short hydrophilic ionic liquids posses surface activity in aqueous solution and behave like a surfactant. In that case mixed aggregates between surfactant and ionic liquid can be formed. The three SLES/IL systems here studied have been treated as typical binary surfactant mixtures in aqueous solution. Surface tension measurements have revealed that mixed aggregates and monolayers of surfactant and ionic liquid instead of single surfactant are responsible for the surface active properties of these aqueous solutions. From the Regular Solution Theory, negative interaction parameters (β) for mixed aggregates and monolayers have been found for all SLES/IL mole ratios indicating synergism between the anionic surfactant and the ionic liquids.