The aggregation behavior of two cationic
surfactants, i.e., cetyldimethylethanolammonium
bromide (CDMEAB) and cetyltributylphosphonium bromide (CTBPB), within
an aqueous deep eutectic solvent (DES) is studied. The synthesized
DES is composed of 1:2 mole ratio of choline chloride and glycerol
and is further characterized by Fourier transform infrared (FTIR)
and
1
H NMR spectroscopy techniques. The critical micellar
concentration (CMC), micellar size, and intermolecular interaction
in surfactants within Gly-based DES solutions are investigated by
various techniques including surface tension, conductivity, fluorescence,
dynamic light scattering (DLS), FTIR,
1
H NMR, and two-dimensional
(2D) nuclear Overhauser effect spectroscopy (NOESY). The various interfacial
properties and thermodynamic parameters are determined in the presence
of 5 wt % glyceline (Gly)-based DES in an aqueous solution. The CMC,
aggregation number (
N
agg
), and Stern–Volmer
constant (
K
sv
) have also been determined
by a steady-state fluorescence method. DLS is used to obtain information
regarding the size of the aggregates formed by the cationic surfactants
in DES solutions. FTIR spectroscopy is used to study the surfactant–DES
interactions that tune the micellar structure of the surfactants within
the Gly-based DES solution. The functional groups involved in the
interactions (H-bonding and electrostatic) are the head groups (HO–CH
2
–CH
2
–N
+
ion for CDMEAB
and quaternary phosphonium (P
+
) ion for CTBPB) of the surfactants
with the −OH-containing Gly DES. The hydrophobic moieties are
involved in the hydrophobic interactions. The
1
H NMR data
show that differences in chemical shifts can provide significant information
about the interactions taking place within the system.
1
H NMR and NOESY techniques are further employed to strengthen our
claim on the feasible structural arrangements within the aqueous surfactant–DES
self-assembled structures. It is observed that both the cationic surfactants,
i.e., CDMEAB and CTBPB, form self-assembled nanostructures in the
Gly-based DES solutions. The present results are expected to be useful
for colloidal solutions of DES and their mixtures with water.
Silver nanoparticles (AgNPs) show
immense application potential
in many fields including biomedical sciences owing to their advanced
antimicrobial property (antibacterial, antifungal and anti-inflammatory).
Ionic liquids (ILs) known as designer solvents with a melting point
below 100 °C are a new class of compounds with exclusive properties
and great chemical variety. Since the past decade, ILs are vastly
used in interdisciplinary research including the synthesis and stabilization
of metal nanoparticles. In the present work, we have studied the interaction
between IL 1-butyl-3-methylimidazolium octylsulfate [Bmim][OS] and
AgNPs using a simple and sensitive UV–visible spectroscopic
method via the response obtained from the surface plasmon resonance
(SPR) band of AgNPs. The analysis of the SPR band at the 400–425
nm range and the Fourier transform infrared (FT-IR) spectral results
show a transfer of N–H stretching frequency from 3367 to 3228
cm–1, which clearly suggests the formation of nanoparticles.
FT-IR spectroscopy is systematically applied to explore information
about the intermolecular interactions taking place within AgNPs-[Bmim][OS]
micellar solutions. The critical micelle concentration (CMC) of [Bmim][OS]
is determined using conductivity and UV–visible spectroscopy,
and the size of micellar aggregates is obtained using dynamic light
scattering (DLS) technique. Further, the above system is also utilized
to consider the structural modify of human serum albumin (HSA) and
bovine serum albumin (BSA). UV–vis, fluorescence, FT-IR, 1H nuclear magnetic resonance and DLS spectroscopic investigations
reveal some interesting outcomes. It is observed that modification
in the structures of both the globular proteins HSA and BSA takes
place within the system, thus indicating significant IL–protein
binding. Further, it is noticed that HSA shows more binding affinity
toward [Bmim][OS] than compared to BSA.
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