Ionic liquid-induced aggregate formation and their applications
Received: 15 February 2018 /Accepted: 22 February 2018 /Published online: 8 March 2018
International Union for Pure and Applied Biophysics (IUPAB) and Springer-Verlag GmbH Germany, part of Springer Nature 2018
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.
In the year 1999, Thomas Welton first published a review on
the topic room temperature ionic liquid (RTIL) (Welton 1999).
However, ionic liquids (ILs) are not new; some of them are
known for many years. One of the earliest well-known RTIL
is ethylammonium nitrate (EAN), ([EtNH
]) which has
its melting pointat 12 °C, reported in 1914 by Paul Walden
(1914). However, Rây and Sen have worked with different
alkylammonium nitrate salts in 1911 (Rây and Sen 1911).
Since then, a significant number of literature is available in
this area. EAN is a colorless, odorless protic ionic liquid (PIL)
and can form three-dimensional hydrogen bonding networks
very similar to that of water. The ethyl chain of PIL, EAN, is
sufficient to form a self-assembled structure, and thus, EAN
shows nanoscale heterogeneity unlike water. Atkin et al. have
demonstrated that the nitrate ion of EAN strongly interacts
with the ammonium groups via electrostatic as well as hydro-
gen bonding interaction whereas the cationic alkyl groups are
aggregated together due to the solvophobic interactions (Atkin
and Warr 2008). Russina et al. have shown that in the mixture
of amphiphilic molecules methanol and EAN, a wide distri-
bution of clusters exist in the region (0.10 ≤ χ
≤ 0.15) and
EAN molecules retain their bulk-sponge-like morphology.
This microheterogeneous mixture can influence the solute’s
motion and shows some interesting results in comparison with
other PIL-cosolvent mixtures (Russina et al. 2014, 2015;
Kundu et al. 2016). Though there are some reviews available
with the phrase Bionic liquid(s)^ in the title, this review mainly
focuses on the aggregation phenomena induced or improved
by ILs (Welton 1999; Pârvulescu and Hardacre 2007;Hallett
and Welton 2011;Kuchlyanetal.2016).
In the last two decades, surfactant-based self-assemblies have
been investigated with a great interest due to the wide variety
of application of their nanostructures (Kaler et al. 1989;Kaler
et al. 1992; Tondre and Caillet 2001). In 1989, Kaler et al.
have reported that, when the catanionic single-tailed surfac-
tants are taken at the right mixing ratio, they can
This article is part of a Special Issue on BIonic Liquids and Biomolecules^
edited by Antonio Benedetto and Hans-Joachim Galla.
* Nilmoni Sarkar
Department of Chemistry, Indian Institute of Technology,
Kharagpur, WB 721302, India
Biophysical Reviews (2018) 10:861–871