Jingjing Jiao

Aggregation Behaviors of Dodecyl Sulfate-Based Anionic Surface Active Ionic Liquids in Water

Halogen-free, low-cost alkyl sulfate-based surface active ionic liquids (SAILs), 1-butyl-3-methylimidazolium dodecyl sulfate ([C(4)mim][C(12)SO(4)]), and N-butyl-N-methylpyrrolidinium dodecyl sulfate ([C(4)MP][C(12)SO(4)]) were easily synthesized through ion exchange reaction. The aggregation behaviors of [C(4)mim][C(12)SO(4)] and [C(4)MP][C(12)SO(4)] in aqueous solution were investigated by surface tension, electric conductivity, and static fluorescence quenching. Both [C(4)mim][C(12)SO(4)] and [C(4)MP][C(12)SO(4)] have rather lower cmc, γ(cmc) values and higher pC(20), π(cmc) values than those reported for the traditional ionic surfactant, sodium dodecyl sulfate (SDS), and imidazolium-based SAIL, 1-dodecyl-3-methylimidazolium bromide ([C(12)mim]Br), with the same hydrocarbon chain length. The thermodynamic parameters evaluated from electric conductivity measurements show that the micelle formation of [C(4)mim][C(12)SO(4)] and [C(4)MP][C(12)SO(4)] is entropy-driven in the temperature range investigated. Lower average aggregation number indicates that the micelles of two SAILs present much looser structure. It is found that both the nature and the ring type of counterions can affect the aggregation behavior in aqueous solution. (1)H NMR results of [C(4)mim][C(12)SO(4)] were used to further verify the mechanism of micelle formation. Hydration ability and steric hindrance of the imidazolium or pyrrolidinium counterion as well as the cooperative hydrophobic interaction of longer alkyl chain of [C(12)SO(4)] anion and comparatively shorter alkyl chain of [C(4)mim] or [C(4)MP] cation are proposed to play critical roles in the aggregation of [C(4)mim][C(12)SO(4)] and [C(4)MP][C(12)SO(4)].

Salt-free catanionic surface active ionic liquids 1-alkyl-3-methylimidazolium alkylsulfate: aggregation behavior in aqueous solution.

A series of salt-free catanionic surface active ionic liquids (SAILs), 1-alkyl-3-methylimidazolim alkyl sulfates (denoted as [Cnmim][CmSO4], n=6, 8, 10; m=12 and n=4; m=10, 14) were synthesized by an ion exchange reaction and their surface properties in aqueous solution were examined systematically by surface tension, fluorescence and electrical conductivity measurements. As catanionic surfactants, these SAILs exhibit notably higher surface activity, compared to the cationic or anionic analogues. Increment in both cationic and anionic alkyl chain lengths for [Cnmim][CmSO4] can both improve the amphiphilic character remarkably. This can be ascribed to cooperative interactions as formation of catanionic pairs between alkyl-substituted imidazolium cations and alkyl sulfate anions. The negative micellization Gibbs free energy values prove that the micellization of all the 1-alkyl-3-methylimidazolim alkyl sulfates investigated is a spontaneous process. Any additional CH2 group makes the micellization process easier regardless if it is on a cation or an anion. When keeping the total carbon atom number constant, we find that the [Cnmim][CmSO4] molecules with greater asymmetric alkyl chains display superior surface activity. This work indicates that the self-assembly of these imidazolium-based salt-free catanionic SAILs can be tailored by adjusting the mismatch of alkyl chains. These SAILs are expected to have potential applications in the fields of colloidal and interface and nanomaterial synthesis.

Interaction of Bovine Serum Albumin with Ester-Functionalized Anionic Surface-Active Ionic Liquids in Aqueous Solution: A Detailed Physicochemical and Conformational Study

Ester-functionalized anionic surface-active ionic liquids (SAILs), 3-methyl-1-(ethoxycarbonylmethyl)imidazolium dodecylsulfate ([C(1)COOC(2)C(1)im][C(12)SO(4)]) and 3-methyl-1-(ethoxycarbonylmethyl)pyrrolidinium dodecylsulfate ([C(1)COOC(2)C(1)Py][C(12)SO(4)]), were synthesized. The tensiometric profiles demonstrate that, in pure water, the studied SAILs exhibit higher surface activity than the traditional anionic surfactant, sodium dodecyl sulfate (SDS), and cationic SAILs, 1-dodecyl-3-methylimidazolium bromide ([C(12)mim]Br) and N-dodecyl-N-methylpyrrolidimium bromide (C(12)MPB), with the same hydrocarbon chain length. The interaction between bovine serum albumin (BSA) and the anionic SAILs in pH 7.4 buffer solution was systematically investigated by various techniques. The results show that the cationic ring has a slight effect on the BSA-SAIL interaction. The binding isotherms of BSA with the SAILs display four characteristic regions with increasing SAIL concentration. The unfolding of BSA occurs in the third region. Fluorescence spectroscopy indicates that the studied SAILs cause the exposure of tryptophan residues to a hydrophobic environment, and [C(1)COOC(2)C(1)im][C(12)SO(4)] can more effectively reduce the fluorescence intensity of BSA at low SAIL concentrations than [C(1)COOC(2)C(1)Py][C(12)SO(4)]. Circular dichroism spectroscopy evidences that the denaturation extent of BSA induced by [C(1)COOC(2)C(1)im][C(12)SO(4)] is higher than that of [C(1)COOC(2)C(1)Py][C(12)SO(4)].

Electrolyte effect on the aggregation behavior of 1-butyl-3-methylimidazolium dodecylsulfate in aqueous solution.

Effect of three inorganic electrolytes (LiCl, NaCl, and MgCl2) and four organic electrolytes, viz. tetraalkylammonium bromides ((CH3)4NBr, (C2H5)4NBr, (C3H7)4NBr, and (C4H9)4NBr) on the aggregation behavior of the anionic halogen-free surface active ionic liquid, 1-butyl-3-methylimidazolium dodecylsulfate ([C4mim][C12SO4]), in aqueous solution was studied by surface tension, steady-state fluorescence quenching, and dynamic light scattering measurements. The results show that all the electrolytes investigated have a salting-out effect, which promotes aggregate formation of [C4mim][C12SO4]. The stronger hydrophobicity of organic electrolytes is crucial for the superior influence on the surface activity of [C4mim][C12SO4]. However, the stabilization energy results obtained by quantum chemical calculations prove that although the promoting effect of organic cations (tetraalkylammonium cations) on the micellization process of [C4mim][C12SO4] is powerful, they mainly act as counterions. For a given electrolyte (i.e., NaCl), critical micelle concentration of [C4mim][C12SO4] decreases with increasing electrolyte concentration. The average aggregation number and aggregate size of [C4mim][C12SO4] were shown to change slightly in the presence of various electrolytes, except for MgCl2. Anyway, hydrophobicity together with bulkiness and hydration ability of cations of the added electrolytes are suggested to play important roles in modifying the aggregation behavior of [C4mim][C12SO4] in aqueous solution.