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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.

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.

In this paper, a systematic investigation into the structure-property relationship of long-chain N-alkyl amide 1, O-alkyl ester arginine 2, and N-acyl arginine methyl ester analogues 3 is reported. The surface properties were studied by adsorption isotherm curves. Biological properties such as antimicrobial activity, hemolysis, ocular irritation, aquatic toxicity, and biodegradability are discussed and correlated with some specific parameters of the surfactants. These surfactants constitute a novel class of bio-based materials of low toxicity, excellent surface properties, and a wide antimicrobial activity. They selectively disrupt bacteria membranes at submicellar concentrations, but not erythrocytes or skin cell membranes. The presence of two positive cationic charges enhances the antimicrobial activity. The incorporation of ester functionality accelerates biodegradation. From the data obtained, it was concluded that the hydrophobicity is a negative parameter for the toxicity and biodegradability of these surfactants.

Abstract:We report the synthesis of a series of aglucosyl derivatives of resveratrol (3,5,4'-trihydroxy-A C H T U N G T R E N N U N G stilbene) by a transglycosylation reaction catalyzed by the enzyme cyclodextrin glucanotransferase (CGTase) using starch as glucosyl donor. Several reaction parameters (temperature, solvent composition, enzyme concentration and starch/resveratrol ratio) were optimized. The yield of a-glucosylated products reached 50% in 24 h. The structures of the derivatives were determined by a combination of amyloglucosidase-hydrolysis tests, MS and 2D-NMR. Three families of products were obtained: glucosylated at 3-OH, at 4'-OH and at both 3-OH and 4'-OH. The bonds between glucoses were basically aA C H T U N G T R E N N U N G (1!4). Interestingly, the water solubilities of the a-glucosylated derivatives were at least 65-and 5-fold higher than those of resveratrol and the natural b-glucosylated derivative (piceid), respectively. In contrast with piceid, the synthesized a-glucosylated compounds exhibited surfactant activity, with critical micelle concentration (CMC) values in the range 0.5-3.6 mM. Although the incorporation of a glucosyl moiety caused a loss of antioxidant activity (more pronounced in the position 3-OH compared with 4'-OH), the fact that the glycosides need to be converted into the aglycones before they are absorbed minimizes such an effect. In contrast, the modification of physicochemical properties such as solubility and partition coefficient by glycosylation could exert a positive influence on the bioavailability of resveratrol.

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Imidazolium-based ionic liquids (ILs) containing cleavable carbonate linkages, 1-alkyloxycarbonyloxyethyl-3-methylimidazolium chlorides with alkyl chains of 10, 12, and 14 carbon atoms, were synthesized, and their self-assembly behavior and antimicrobial activity were investigated. Differential scanning calorimetry and polarized optical microscopy studies reveal that carbonate-functionalized ILs form stable thermotropic smectic liquid-crystalline phases over a wide range of temperature. The surface activity and aggregation behavior of these new ILs were investigated by tensiometry, conductometry, potentiometry, and spectrofluorimetry. The size of aggregates was examined by dynamic light scattering (DLS). Carbonate-functionalized ILs display a higher adsorption efficiency and a lower critical micelle concentration (cmc) than simple alkyl-chain-substituted ILs. The insertion of a carbonate ester moiety in the alkyl side chain favors adsorption at the air-water interface and micellization in the bulk solution when compared to nonfunctionalized ILs. DLS measurements show that small micellelike aggregates are spontaneously formed above the cmc. Furthermore, carbonate-functionalized ILs were examined for their antimicrobial activity against a panel of clinically relevant microorganisms. Biological activity was found to increase with hydrophobicity. The presence of a carbonate ester moiety significantly enhances the antimicrobial efficiency as compared to nonfunctionalized ILs, with the susceptibility of Staphylococcus sp. toward the action of these compounds being particularly remarkable. It has been demonstrated that the functionalization of the alkyl side chain of the imidazolium salts can not only modify the aggregation behavior but also lead to differences in both efficiency and the spectrum of antimicrobial activity of amphiphilic ILs.

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