Ionic Liquid Modifies the Lower Critical Solution Temperature (LCST) of Poly(N-isopropylacrylamide) in Aqueous Solution

Abstract

The effect of the imidazolium based ionic liquid (IL) 1-benzyl-3-methylimidazolium tetrafluoroborate ([Bzmim][BF(4)]) was investigated on the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAM) in aqueous solution by using fluorescence, viscometric, and dynamic light scattering (DLS) techniques. The measurements were performed at four different [Bmim][BF(4)] concentrations (1-4 mg/mL) in PNIPAM aqueous solution. Our experimental results elucidate that the IL induces the collapsed globular structure of polymer, facilitated by the weakening of hydrogen bonds between the amide group of the polymer and water molecules; therefore, IL destabilizes the hydrated macromolecule structure. We observed that the phase transition of PNIPAM aqueous solution abruptly shifts down with increasing IL concentration mainly due to hydrophobic collapse and aggregation of a macromolecule. These results unambiguously reveal that the imidazolium based IL significantly affected the phase transition of PNIPAM and ruptured the hydrogen bonding between polymer and water molecules, and eventually the hydrated macromolecule structure was destabilized.

Influence of protic ionic liquids on the structure and stability of succinylated Con A

“…The fluorescence spectroscopy instrument used for measuring fluorescence intensity in the present investigation is similar to that depicted in our earlier articles [22,32]. Steady-state fluorescence measurements were carried out in a Cary Eclipse fluorescence spectrofluorimeter (Varian optical spectroscopy instruments, Mulgrave, Victoria, Australia) equipped with an intense Xenon flash lamp as the light source.…”

“…However, these physiological stresses are overcome in the presence of biocompatible ionic liquid (ILs) [15][16][17]. Main advantages of ILs as compared to common molecular organic solvents are negligible vapor pressure, high ionic conductivity, low toxicity, reduced inhalator exposure, absence of flammability and high variability concerning chemical structure of headgroups, substituents and anions [18][19][20][21][22]. Recently, ILs are finding broader scope within the chemical sciences, including pharmaceutical, enzymatic, biosensors and bioanalytical applications [18][19][20][21][22][23].…”

“…Main advantages of ILs as compared to common molecular organic solvents are negligible vapor pressure, high ionic conductivity, low toxicity, reduced inhalator exposure, absence of flammability and high variability concerning chemical structure of headgroups, substituents and anions [18][19][20][21][22]. Recently, ILs are finding broader scope within the chemical sciences, including pharmaceutical, enzymatic, biosensors and bioanalytical applications [18][19][20][21][22][23]. Moreover, ILs were reported to be effective biocompatible media for not only stabilization of the native structure of biomolecules [24][25][26][27][28][29][30][31], but also for refolding additive of denatured protein [7,24].…”

Temperature dependence measurements and molecular interactions for ammonium ionic liquid with N-methyl-2-pyrrolidone

“…Moreover, ILs have become much popular because of the intensified ion densities, good ionic conductivities, and wide electrochemical window, good thermal stability and ILs used as green solvents for biochemistry, polymer chemistry, catalysis reactions, chemical synthesis and separation science [2,7]. The right choice of the cationanion pair allows the modulation of physicochemical properties, such as density (q), speed of sound (u), and viscosity (g) as well as structural properties of the solvent media, which is markedly controlled both by cation-anion and ion-solvent interaction [8][9][10][11][12][13][14][15]. The chemical complexity of the combination of ions of ILs involved in the liquid structure exhibit challenges for theoreticians and chemists to understand the thermophysical properties for mixed solvents of ILs with organic molecular liquids.…”

Well-defined poly(N-isopropylacrylamide) with a bifunctional end-group: synthesis, characterization, and thermoresponsive properties

“…As a result, an ever-increasing interest has been focused on the phase transition behavior of PNIPAM in aqueous solutions during the past decades. Many efforts have been devoted to providing insights into the influence of the factors regarding concentration [6,10], cosolvents [11][12][13], molecular weight, polydispersity [14][15][16][17], and tacticity [18][19][20] as well as end-group [21][22][23][24][25][26] on the thermoresponsive properties of PNIPAM.…”