A study of the conformational changes of β-lactoglobulin in the vicinity of critical point of binary mixed solvents

Most of the protein is entangled in the upper IB rich phase.

Interactions of ionic liquids with hydration layer of poly(N-isopropylacrylamide): comprehensive analysis of biophysical techniques results

Here, we report comprehensive analysis of biophysical technique results for the influence of ionic liquids (ILs) containing the same cation, 1-butyl-3-methylimidazolium (Bmim(+)), and commonly used anions such as SCN(-), BF4(-), I(-), Br(-), Cl(-), CH3COO(-) and HSO4(-) on the phase transition temperature of poly(N-isopropylacrylamide) (PNIPAM) aqueous solution. Further, the effect of these ILs on bovine serum albumin (BSA) has also been studied. The modulations in UV-visible (UV-vis) absorption spectra, fluorescence intensity spectra, viscosity (η), hydrodynamic diameter (dH), Fourier transform infrared (FTIR) spectra and scanning electron microscopy (SEM) micrographs clearly reflect the change in the hydration state of PNIPAM in the presence of ILs. The observed single phase transition of PNIPAM aqueous solution at higher concentration of IL is the result of weak ion-ion pair interactions in IL.

Does the stability of proteins in ionic liquids obey the Hofmeister series?

Understanding the behavior of Hofmeister anions of ionic liquids (ILs) on protein stability helps to shed light on how the anions interact with proteins in aqueous solution and is a long standing object for chemistry and biochemistry. Ions effects play a major role in understanding the physicochemical and biological phenomenon that undertakes the protein folding/unfolding and refolding process. Despite the generality of these effects, our understanding of ions at the molecular-level is still limited. This review offers a tour through past successful investigations and presents a challenge in current research in the field to reassess the possibilities of ions and to apply new strategies. This review highlights on the stability behavior of the proteins and also comparisons of our past research work in the Hofmeister series of ILs. Furthermore, we specifically focus on the critical discussion on the recent findings with existing results and their implications, along with our understanding of the Hofmeister series of anions of ILs on biomolecular stability. A detailed examination of the difference between selective proteins can provide a better understanding of the molecular mechanism of protein folding/unfolding in the presence of the Hofmeister series of ions of ILs.

Evaluation of thermophysical properties of ionic liquids with polar solvent: a comparable study of two families of ionic liquids with various ions

In this work, we explore and compare the role of the ion effect on the thermophysical properties of two families of ionic liquids (ILs), namely, tetra-alkyl ammonium cation [R4N](+) with hydroxide [OH](-) anion and 1-alkyl-3-methyl imidazolium cation [amim](+) with different anions (chloride, methyl sulfate, and tetrafluoroborate), with polar solvent such as dimethylsulfoxide (DMSO) in the temperature range from 25 to 40 °C and over the whole concentration range of ILs. Two families of ILs, namely, tetramethyl ammonium hydroxide [(CH3)4N][OH] (TMAH), tetraethyl ammonium hydroxide [(C2H5)4N][OH] (TEAH), tetrapropyl ammonium hydroxide [(C3H7)4N][OH] (TPAH), and tetrabutyl ammonium hydroxide [(C4H9)4N][OH] (TBAH) from ammonium-based ILs and 1-ethyl-3-methylimidazolium chloride [Emim][Cl], 1-ethyl-3-methylimidazolium methylsulfate [Emim][MeSO4], 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4], and 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) from imidazolium family of ILs, are used in the present study. To address the molecular interactions of ILs with DMSO, densities (ρ), ultrasonic sound velocities (u), and viscosities (η) have been measured over the entire composition range and at four temperatures, 25, 30, 35, and 40 °C, under atmospheric pressure. From these experimental data, the excess molar volume (V(E)), the deviation in isentropic compressibility (Δκs), and the deviation in viscosity (Δη) were calculated and were adequately correlated by using the Redlich-Kister polynomial equation. The measured and predicted data were interpreted on the basis of intermolecular interactions and structural effects between like and unlike molecules upon mixing. The hydrogen-bonding features between ammonium-based ILs and DMSO were analyzed using molecular modeling program by HyperChem 7.

Phase transition of poly(N-isopropylacrylamide) in aqueous protic ionic liquids: kosmotropic versus chaotropic anions and their interaction with water

We have investigated the influence of a series of triethylammonium-based protic ionic liquid-water solutions on the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAM). We find that kosmotropic anions lower the LCST of PNIPAM more dramatically when compared with chaotropic anions. In addition, we have probed the solvent properties of the hydrated protic ionic liquid solutions using (1)H NMR, polarity measurements, and solvatochromic analysis of the Kamlet-Taft parameters, β and π*. We find that the hydrogen bond character--more specifically, the interactions between water and pIL--is the dominant parameter responsible for lowering the LCST of PNIPAM. We have added choline dihydrogen phosphate (choline dhp) into this study on the basis of positive results from previously reported protein folding studies using this ionic liquid.