Ionic liquid-induced aggregate formation and their applications

Abstract

In the last two decades, researchers have extensively studied highly stable and ordered supramolecular assembly formation using oppositely charged surfactants. Thereafter, surface-active ionic liquids (SAILs), a special class of room temperature ionic liquids (RTILs), replace the surfactants to form various supramolecular aggregates. Therefore, in the last decade, the building blocks of the supramolecular aggregates (micelle, mixed micelle, and vesicular assemblies) have changed from oppositely charged surfactant/surfactant pair to surfactant/SAIL and SAIL/SAIL pair. It is also found that various biomolecules can also interact with SAILs to construct biologically important supramolecular assemblies. The very latest addition to this combination of ion pairs is the dye molecules having a long hydrophobic chain part along with a hydrophilic ionic head group. Thus, dye/surfactant or dye/SAIL pair also produces different assemblies through electrostatic, hydrophobic, and π-π stacking interactions. Vesicles are one of the important self-assemblies which mimic cellular membranes, and thus have biological application as a drug carrier. Moreover, vesicles can act as a suitable microreactor for nanoparticle synthesis.

Keywords: Biomolecules; Dye molecules; SAIL; Supramolecular assembly; Surfactant·RTIL.

Fig. 1

Confocal fluorescent images of single catanionic vesicles immobilized on a positive glass surface obtained by objective scanning at 20 °C. The image size is a 80 μm × 80 μm and b 30 μm × 30 μm. Adapted with permission from (J. Phys. Chem. B 2010, 114, 15506-15511). Copyright (2010) American Chemical Society

Scheme 1

Cationic components of the RTILs

Scheme 2

Structures of different cationic and anionic SAILs

Fig. 2

Variation of size (diameter) of [C₄mim][C₈SO₄]/CTAB solution at different volume fraction values. Adapted with permission from (Langmuir 2013, 29, 10066-10076). Copyright (2013) American Chemical Society

Fig. 3

DLS intensity versus size distribution histograms of a [C₄mim][C₈SO₄] micelles, b mixed micelles (${\chi }_{C_{12}\mathit{\text{mimCl}}}$ = 0.15), c mixed micelles (${\chi }_{C_{12}\mathit{\text{mimCl}}}$ = 0.25), and d mixed SAILs that form vesicles (${\chi }_{C_{12}\mathit{\text{mimCl}}}$ = 0.50). Adapted with permission from (Chemphyschem 2014, 15, 3544-3553)

Fig. 4

TEM images of unilamellar vesicles of C₁₆mimCl-vitamin E (a, b). Adapted with permission from (J. Colloid Interface Sci. 2017, 501, 202-214)

Fig. 5

Change in the turbidity of C₁₆mimCl-5-mS aggregates with change in the concentration of 5-mS and the temperature of the system. Adapted with permission from (Langmuir 2016, 32, 7127-7137). Copyright (2016) American Chemical Society

Fig. 6

Variation of turbidity of [Span 60]/[C₁₆mim]Cl at a fixed concentration of [C₁₆mim]Cl (0.02 M) with varying concentration of span60. Adapted with permission from (Chem. Phys. Lett. 2016, 665, 14-21)

Fig. 7

SEM (a, b) and CLSM (c (bright field), d (dark field)) images of giant vesicles formed by 0.5 mmol L⁻¹ AO/0.5 mmol L⁻¹ C₁₄mimBr. Adapted with permission from (Langmuir 2016, 32, 9548-9556). Copyright (2016) American Chemical Society

Fig. 8

SEM images of 0.5 mmol L⁻¹ MO/C₁₄mimBr at different pHs: a pH = 2; b pH = 4; c pH = 11; d pH = 14. e Fluorescence spectra of 0.5 mmol L⁻¹ MO/C₁₄mimBr at different pHs. CLSM images of 0.5 mmol L⁻¹ MO/C₁₄mimBr at different pHs: f pH = 4; g pH = 11; h pH = 14. i pH-dependent mechanism of the MO molecule. j The digital photo of solutions at different pHs (scale bar = 2 μm). Adapted with permission from (J. Phys. Chem. C 2016, 120, 27533-27540). Copyright (2016) American Chemical Society

Fig. 9

FLIM images of the aggregates formed at a 20 mM MC 540/20 mM C₈mimCl, b 10 mM MC 540/10 mM C₈mimCl, c 5 mM MC 540/5 mM C₈mimCl, d 2 mM MC 540/2 mM C₈mimCl, and e 1 mM MC 540/1 mM C₈mimCl. Adapted with permission from (Langmuir 2017, 33, 9811-9821). Copyright (2017) American Chemical Society.

Fig. 10

TEM microscopic images of vesicles formed by a [CTA][AOT] and b [BHD][AOT] ILs in water at 298 K. Adapted with permission from (J. Phys. Chem. B 2013, 117, 3927-3934). Copyright (2013) American Chemical Society

Fig. 11

FLIM Z stack recording of [C₁₆mim][AOT], excitation at 488 nm, emission above 495 nm. Z step width ± 5 μm; “e” is the optimum position. FLIM data format 256 × 256 pixels. Reproduced from Phys. Chem. Chem. Phys. 2016, 18, 14520-14530 with permission from the PCCP Owner Societies

Fig. 12

TEM images of NaDC aggregates in the presence of a 1.12 wt% [bmim]-BF₄, b 1.68 wt% [bmim]-BF₄ (the inset shows a single rod-like structure and the scale length of the image is 200 nm), and c 11.2 wt% [bmim]-BF₄ (the scale length of the inset image is 0.2 mm). The SEM image of 20 mM NaDC d in the presence of 1.68 wt% [bmim]-BF₄ and e in the presence of 5.6 wt% [bmim]-BF₄. Reproduced from Phys. Chem. Chem. Phys. 2015, 17, 25216-25227 with permission from the PCCP Owner Societies

Fig. 13

FLIM images of OEA vesicle in the presence of 0.1 M Bmim-BF₄ collected in different time scales (time zero indicates the time when the image of the sample is started to record; it does not imply the starting time of the reaction after addition of Bmim-BF₄ into the medium). Adapted with permission from (J. Phys. Chem. B 2017, 121, 8162-8170). Copyright (2017) American Chemical Society