Interaction between amphiphilic ionic liquid 1-butyl-3-methylimidazolium octyl sulfate and anionic polymer of sodium polystyrene sulfonate in aqueous medium

Comprehensive NMR Investigation of Imidazolium-Based Ionic Liquids [BMIM][OSU] and [BMIM][Cl] Impact on Binding and Dynamics of the Anticancer Drug Doxorubicin Hydrochloride

For the design of an efficient drug delivery system utilizing an ionic liquid (IL) as a carrier, it is prudent to gain molecular/atomistic level insights of a drug with IL in terms of binding and dynamics. In this scenario, the influence of anionic counterpart of imidazolium-based ILs, namely, 1-butyl-3-methyl-imidazolium octyl sulfate [BMIM][OSU] and 1-butyl-3-methyl-imidazolium chloride [BMIM][Cl] in their submicellar region ([IL] = 20 mM) on the model water-soluble anticancer drug doxorubicin hydrochloride (DOX) was probed by employing an arsenal of nuclear magnetic resonance (NMR) approaches. The salient feature of the present study includes the significant interaction of DOX with [BMIM][OSU], whereas the lack of such an interaction with [BMIM][Cl] is gauged by 1H NMR translation self-diffusometry and is further corroborated by 13C chemical shift perturbation. The two-step model was utilized to estimate the bound fraction (pb) and equivalent partition coefficient (K) of DOX with [BMIM][OSU]. A combination of selective and nonselective spin-lattice relaxation rates (R1SEL and R1NS, respectively) enables to gauze the significant interaction of DOX with [BMIM][OSU] over [BMIM][Cl]. Furthermore, 1D transient and truncated driven nuclear Overhauser enhancement (NOE) data analyses in the initial rate limit permits the evaluation of the cross-relaxation efficacy of DOX with the investigated ILs. An Arrhenius-type temperature dependence of the drug's self-diffusion was observed for DOX, DOX-[BMIM][OSU], and DOX-[BMIM][Cl] aqueous mixtures and the corresponding activation energies were evaluated.

pH-Induced Biophysical Perspectives of Binding of Surface-Active Ionic Liquid [BMIM][OSU] with HSA and Dynamics of the Formed Complex

The influence of pH on the human serum albumin (HSA) interaction with ionic liquid (IL)1-butyl 3-methylimidazolium octyl sulfate ([BMIM][OSU]) at its sub-micellar concentration of 5 mM (well below CMC ∼31 mM at 25 °C) in aqueous solution has been monitored employing different methods, viz., circular dichroism (CD), fluorescence, electrokinetic determination of the zeta potential (ZP), nuclear magnetic resonance (NMR), small-angle neutron scattering (SANS), and molecular docking (MD). CD analysis indicated a noticeable reduction of the α-helical content of HSA by IL at pH 3. A significant interaction of the anionic part of IL with HSA was evident from the ¹H chemical shifts and saturation transfer difference (STD) NMR. A strong binding between IL and HSA was observed at pH 3 relative to pH 5, revealing the importance of electrostatic and hydrophobic interactions assessed from global binding affinities and molecular correlation times derived from STD NMR and a combined selective/nonselective spin-relaxation analysis, respectively. ZP data supported the electrostatic interaction between HSA and the anionic part of IL. The nature of IL self-diffusion with HSA was assessed from the translational self-diffusion coefficients by pulse field gradient NMR. SANS results revealed the formation of prolate ellipsoidal geometry of the IL-HSA complex. MD identified the preferential binding sites of IL to the tryptophan centers on HSA. The association of IL with HSA was supported by fluorescence measurements, in addition to the structural changes that occurred in the protein by the interaction with IL. The anionic part of IL contributed a major interaction with HSA at the pH levels of study (3, 5, 8, and 11.4); at pH > 8 (effectively 11.4), the protein also interacted weakly with the cationic component of IL.

New ternary water-soluble support from self-assembly of β-cyclodextrin-ionic liquid and an anionic polymer for a dialysis device

We developed a new hybrid material resulting from an innovative supramolecular tripartite association between an ionic liquid covalently immobilized on primary β-cyclodextrins rim and an anionic water-soluble polymer. Two hydrophilic ternary complexes based on native and permethylated β-cyclodextrins substituted with an ionic liquid and immobilized on poly(styrene sulfonate) (CD-IL⁺PSS^- and CD(OMe)IL⁺PSS^-) were obtained by simple dialysis with a cyclodextrin maximal grafting rate of 25% and 20% on the polymer, respectively. These polyelectrolytes are based on electrostatic interactions between the opposite charges of the imidazolium cation of the ionic liquid and the poly(styrene sulfonate) anion. The inclusion properties of the free cavities of the cyclodextrins and the synergic effect of the polymeric matrix were studied with three reference guests such as phenolphthalein, p-nitrophenol, and 2-anilinonaphthalene-6-sulfonic acid using UV-visible, fluorescent, and NMR spectroscopies. The support has been applied successfully in dialysis device to extract and concentrated aromatic model molecule. This simple and flexible synthetic strategy opens the way to new hybrid materials useful for fast and low-cost ecofriendly extraction techniques relevant for green analytical chemistry.

Aggregation Behavior of Polyether Based Siloxane Surfactants in Aqueous Solutions: Effect of Alkyl Groups and Steric Hindrance

A series of polyether based siloxane surfactants with different branched chain and alkyl groups were synthesized by thiol-ene reaction and Piers-Rubinsztajn reaction. The effect of the siloxane structures (alkyl groups and branched chains) on the adsorption and aggregation behavior in aqueous solution was investigated by surface tension, fluorescence, dynamic light scattering (DLS), freeze-fracture transmission electron microscopy (TEM), and TEM. The molecular structures of siloxane can obviously influence their surface activities and thermodynamics. Replacing the methyl of trimethylsiloxyl groups with longer alkyl groups (ethyl, propyl, and butyl) and branching trimethylsiloxyl resulted in an obvious decrease of the values of critical micelle concentration (CMC) and surface tension at CMC (γ_CMC). Dense surface films packed with CH₃ groups result in the lower surface tensions being disordered by longer alkyl groups or branched chains of siloxane hydrophobic groups. And the minimum surface area per surfactant molecule ( A_min) values of Si₃-PG, Et-Si₃-PG, Pro-Si₃-PG, and But-Si₃-PG successively decrease about 3.5 Å with each increasing -CH₂- group. All polyether based siloxane surfactants can form nonuniform size spheroidal aggregates in aqueous solution. Concerning the driving force, the micellization process was spontaneous but less spontaneous compared with adsorption.

Self-assembly of a short-chain ionic liquid within deep eutectic solvents

Ionic liquids (ILs) and deep eutectic solvents (DESs) are receiving increased attention from both academic and industrial research due to their immense application potential. These designer solvents are environmentally friendly in nature with tunable physicochemical properties. In the present investigation, we have studied the aggregation behavior of a short-chain IL 1-butyl-3-methylimidazolium octylsulphate [Bmim][OS] within aqueous DESs using fluorescence, UV-vis, dynamic light scattering (DLS) and FT-IR spectroscopic techniques. We have prepared two DESs, ChCl–urea and ChCl–Gly, which are obtained by heating a mixture of an ammonium salt choline chloride with hydrogen bond donor urea or glycerol, respectively, in 1 : 2 molar ratios. The local microenvironment and size of the aggregates are obtained from steady state fluorescence (using pyrene and pyrene-1-carboxaldehyde as polarity probes) and DLS measurements, respectively. DLS results shows that IL [Bmim][OS] forms relatively larger micelles within the aqueous solution of DES ChCl–urea (avg. hydrodynamic radii = 209 nm) than compared to ChCl–Gly (avg. hydrodynamic radii = 135 nm). A significant decrease in the critical micelle concentration and increase in the aggregation number (N_agg) are observed within DES solutions as compared to that in water, thus indicating that the micellization process of the IL [Bmim][OS] is much favored in the DES solutions. Molecular interactions of [Bmim][OS] in DESs are revealed from FT-IR spectroscopic investigation. Furthermore, these systems were applied to study the IL-drug binding of the antidepressant drug promazine hydrochloride (PH).

Self-assembly of short-chain imidazolium-based ILs within DESs have been investigated by fluorescence, UV-Vis, DLS and FT-IR spectroscopy. Further, these micellar systems [Bmim][OS]-DESs are utilized to study the IL-drug binding of an antidepressant drug (PH).

How ionic species structure influences phase structure and transitions from protic ionic liquids to liquid crystals to crystals

Phase behaviour of n-alkylammonium (C6 to C16) nitrates and formates was characterised using synchrotron small angle and wide angle X-ray scattering, differential scanning calorimetry, cross polarised optical microscopy and FTIR.

Self-assembly of a short-chain ionic liquid within deep eutectic solvents

Self-assembly of short-chain imidazolium-based ILs within DESs have been investigated by fluorescence, UV-Vis, DLS and FT-IR spectroscopy. Further, these micellar systems [Bmim][OS]-DESs are utilized to study the IL-drug binding of an antidepressant drug (PH).

Host–guest complexation of ionic liquid with α- and β-cyclodextrins: a comparative study by 1H-NMR, 13C-NMR and COSY

The inclusion complexation of 1-butyl-3-methylimidazolium octylsulphate [Bmim][OS] with host α- and β-cyclodextrins (CDs) has been explored by ¹H NMR, ¹³C NMR and COSY methods. The insertion of a guest molecule into the cavity of CD is clearly reflected by changes in ¹H-NMR and ¹³C-NMR chemical shift values and COSY NMR suggest that both H-bonding and electrostatic interactions involved to the complexation.