Amphiphilic behavior of two phosphonium based ionic liquids

Investigation of the vesicle-to-micelle transition of 11-amino undecanoic acid derived sulphonamide and a comprehensive study of its interaction with protein

In the present manuscript, an amphiphile sulphonamide based surfactant benzenesulphonyl-11-amino sodium undecanoate (BASU) is designed and synthesized. The surface activity of the amphiphile in the solutions is studied at neutral pH so that the resulting amphiphile self-organizes and transfers from large unilamellar vesicles to small micelles from dilute to concentrated solutions. During the aggregate transitions, the common surfactants tend to form the small aggregate at low concentrations; but BASU shows the large vesicle structure at low concentration of ~3 mM and converts into the small micelle at ~9 mM. Therefore, different techniques have been used, such as, tensiometry, conductometry, fluorimetry and DLS and some microscopic characterization, e.g., confocal fluorescence microscopy to reveal the aggregate assembly and transition mechanism. The isothermal titration calorimetry is used for quantitative measurement of thermodynamic properties of self-assembly formation and the process is found spontaneous and entropically favorable. The permeability of the vesicle membrane bilayer is explored by a kinetic study. Effects of salt and cholesterol on the aggregate of respective amphiphile are also investigated. The interaction of surfactant with both human and bovine serum albumin is analyzed through UV-visible and fluorescence techniques to draw a comparative study. Antibacterial activity is tested by both spectral and zone inhibition methods and its application for mixed amphiphiles (e.g., BASU/CTAB) is found. Therefore, according to the ability of formation of unilamellar vesicles (ULV) and its stability, permeability and antibacterial activity, the amphiphile can have potential applications in the medicinal field.

Alkyl triphenylphosphonium surfactants as nucleic acid carriers: complexation efficacy toward DNA decamers, interaction with lipid bilayers and cytotoxicity studies

Herein, for the first time the complexation ability of a homological series of triphenylphosphonium surfactants (TPPB-n) toward DNA decamers has been explored. Formation of lipoplexes was confirmed by alternative techniques, including dynamic light scattering, indicating the occurrence of nanosized complexes (ca. 100-150 nm), and monitoring the charge neutralization of nucleotide phosphate groups and the fluorescence quenching of dye-intercalator ethidium bromide. The complexation efficacy of TPPB-surfactants toward an oligonucleotide (ONu) is compared with that of reference cationic surfactants. Strong effects of the alkyl chain length and the structure of the head group on the surfactant/ONu interaction are revealed, which probably occur via different mechanisms, with electrostatic and hydrophobic forces or intercalation imbedding involved. Phosphonium surfactants are shown to be capable of disordering lipid bilayers, which is supported by a decrease in the temperature of the main phase transition, T_m. This effect enhances with an increase in the alkyl chain length, indicating the integration of TPPB-n with lipid membranes. This markedly differs from the behavior of typical cationic surfactant cetyltrimethylammonium bromide, which induces an increase in the T_m value. It was demonstrated that the cytotoxicity of TPPB-n in terms of the MTT-test on a human cell line 293T nonmonotonically changes within the homological series, with the highest cytotoxicity exhibited by the dodecyl and tetradecyl homologs.

Interaction of Hydrophobic Ionic Liquids with Lipids in Langmuir Monolayers

The interaction of two ionic liquids, trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)-imide and trihexyl(tetradecyl)phosphonium dicyanamide, [P_6 6 6 14][Ntf₂] and [P_6 6 6 14]/[N(CN)₂], with several long-chained lipids with a different net charge at the hydrophilic group, a cationic surfactant, dioctadecyldimethylammonium bromide (DODAB), a zwitterionic phospholipid (DPPC), an anionic phospholipid (DPPG), and the neutral stearic acid (SA), was investigated at the air-water interface using the Langmuir trough technique. The experimental surface pressure-area (π- A) isotherms obtained for selected compositions of each binary system reveal distinct interfacial behavior. The degree and the nature of the IL-lipid interaction strongly depend on the charge distribution in the lipid polar group. Miscibility, or immiscibility, at the monolayer was inferred from the comparison of the experimental π- A isotherm with the theoretical curve calculated for the corresponding ideal mixture based on the π- A isotherms of the pure components. Phase separation and partial miscibility occurred in IL/DODAB and IL/DPPC systems, respectively. In both the IL/DPPG and the IL/SA systems, a new catanionic complex was found. For the IL/SA system, the catanionic complex formation varies with the subphase pH.

Disassembly Control of Saccharide-Based Amphiphiles Driven by Electrostatic Repulsion

According to the design of disassembly using electrostatic repulsion, novel amphiphiles consisting of a lipophilic ion part and a hydrophilic saccharide part were synthesized via the facile copper-catalyzed click reaction, and their molecular assemblies in water and chloroform were studied. The amphiphiles exhibited a molecular orientation opposite to that of the conventional amphiphiles in each case. ζ Potential measurements indicated that the lipophilic ion part is exposed outside in chloroform. The size of a solvophobic part in the amphiphiles dominates the size of an assembling structure; that is, in water, these amphiphiles tethering different lengths of the saccharide part exhibited almost identical assembling size, whereas in chloroform, the size depends on the length of the saccharide part in the amphiphiles.

Transport properties of microemulsions with ionic liquid apolar domains as a function of ionic liquid content

The conductivity, dynamic viscosity and diffusion coefficient of aqueous ionic liquid microemulsions were measured as a function of ionic liquid content. ​The conclusions from transport properties were supported by UV-Vis as well as FTIR measurements.

Crystalline-like structures and multilayering in Langmuir films of ionic liquids at the air–water interface

Langmuir films of [C₁₈mim][NTf₂] ionic liquid exhibited, for the first time, the reversible formation of crystalline-like structures at the surface of water, compatible with the formation of multilayers.

Ionic Liquid Films at the Water-Air Interface: Langmuir Isotherms of Tetra-alkylphosphonium-Based Ionic Liquids

The behavior of ionic liquids trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide and trihexyl(tetradecyl)phosphonium dicyanamide, [P6 6 6 14][Ntf2] and [P6 6 6 14][N(CN)2], respectively, at the water-air interface was investigated using the Langmuir trough technique. The obtained surface pressure versus mean molecular area (MMA) isotherms, π-A, and surface potential versus MMA isotherms, ΔV-A, show distinct interfacial behavior between the two systems. The results were interpreted at a molecular level using molecular dynamics simulations: the different compression regimes along the [P6 6 6 14][Ntf2] isotherm correspond to the self-organization of the ions at the water surface into compact and planar monolayers that coalesce at an MMA value of ca. 1.85 nm(2)/ion pair to form an expanded liquidlike layer. Upon further compression, the monolayer collapses at around 1.2 nm(2)/ion pair to yield a progressively thicker and less organized layer. These transitions are much more subdued in the [P6 6 6 14][N(CN)2] system because of the more hydrophilic nature of the dicyanamide anion. The numerical density profiles obtained from the MD simulation trajectories are also able to emphasize the very unusual packing of the four long alkyl side chains of the cation above and below the ionic layer that forms at the water surface. Such a distribution is also different for the two studied systems during the different compression regimes.

Automated evaluation of pharmaceutically active ionic liquids' (eco)toxicity through the inhibition of human carboxylesterase and Vibrio fischeri

The toxicity of 16 pharmaceutical active ionic liquids (IL-APIs) was evaluated by automated approaches based on sequential injection analysis (SIA). The implemented bioassays were centered on the inhibition of human carboxylesterase 2 and Vibrio fischeri, in the presence of the tested compounds. The inhibitory effects were quantified by calculating the inhibitor concentration required to cause 50% of inhibition (EC50). The EC50 values demonstrated that the cetylpyridinium group was one of the most toxic cations and that the imidazolium group was the less toxic. The obtained results provide important information about the safety of the studied IL-APIs and their possible use as pharmaceutical drugs. The developed automated SIA methodologies are robust screening bioassays, and can be used as a generic tools to identify the (eco)toxicity of the structural elements of ILs, contributing to a sustainable development of drugs.