Biomass-derived carbon helices induced phase transition in poly(N-ispropylacrylamide): A sustainable tailoring of coil-globule transition in thermoresponsive polymer.

Functional carbon helices (FCHs) containing various oxygenated functionalities derived directly from lignocellulosic biomass is proved to be a potential eco friendly candidate for biomolecules. No study reports the effect of biomass derived platform molecules on the thermoresponsive behavior of polymers, which have been proved potential candidates in carrying various drug delivery applications, gels, and tissue engineering in this vast area of research. Poly(N-isopropylacrylamide) (PNIPAM) is a thermoresponsive polymer that has been found to be a prevailing tool in carrying various aforesaid applications. This study reports a powerful impact on the thermoresponsive behavior of PNIPAM by a non-hazardous alternative form of a herbecious plant Parthenium hysterophorus. Fluorescence spectroscopy was deployed to study the microenvironment provided by carbon helices around the polymer structure. The results obtained are directly correlating with the increased polarity with higher concentration of FCHs and further confirmed a decrease in fluorescence intensity. Moreover, for better understanding of interactions between PNIPAM and FCHs, Fourier transform infrared spectroscopy (FTIR) was employed. The analysis of hydrodynamic diameter (dH) was carried out by dynamic light scattering (DLS) and the aggregate size of PNIPAM was found to increase in higher concentration of FCHs. A decrease from 34.7 °C to 29.0 °C in the lower critical solution temperature (LCST) of PNIPAM in FCHs was further confirmed by differential scanning calorimetry (DSC). Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM) were also taken into account to understand the morphological changes of PNIPAM in presence of biomass derived carbon helices. The micrographs of PNIPAM-biomass are representing a perturbed morphology of PNIPAM during interaction with FCHs. In this study, high degree of oxygenated functionalities on the carbon helices has a meaningful impact on the conformational phase behavior of PNIPAM. The tendril like functional carbon helices (TLFCHs) are uniquely causing a decrease in the lower critical solution temperature (LCST) of PNIPAM. Our combined study indicates that biomass derived carbon helices significantly decrease the LCST of PNIPAM by 5 °C. Ultimately, the polymer achieves compact globule conformational and complete aggregated state.

Effect of Imidazolium-Based Ionic Liquids on the Structure and Stability of Stem Bromelain: Concentration and Alkyl Chain Length Effect.

In the present work, changes in the structure and stability of stem bromelain (BM) are observed in the presence of a set of four imidazolium-based ionic liquids (ILs) such as 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]), 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]), 1-hexyl-3-methylimidazolium chloride ([Hmim][Cl]), and 1-decyl-3-methylimidazolium chloride ([Dmim][Cl]), using various biophysical techniques. Fluorescence spectroscopy is used to observe the changes taking place in the microenvironment around the tryptophan (Trp) residues of BM and its thermal stability because of its interactions with the ILs at different concentrations. Near-UV circular dichroism results showed that the native structure of BM remained preserved only at lower concentrations of ILs. In agreement with these results, dynamic light scattering revealed the formation of large aggregates of BM at higher concentrations of ILs, indicating the unfolding of BM. In addition to this, the results also show that higher alkyl chain length imidazolium-based ILs have a more denaturing effect on the BM structure as compared to the lower alkyl chain length ILs because of the increased hydrophobic interaction between the ILs and the BM structure. Interestingly, it is noted that low concentrations (0.01-0.10 M) of short alkyl chain ILs only alter the structural arrangement of the protein without any significant effect on its stability. However, high concentrations of all five ILs are found to disrupt the structural stability of BM.

Long-term protein packaging in bio-ionic liquids: Improved catalytic activity and enhanced stability of cytochrome C against multiple stresses.

There is a considerable interest in the use of structurally stable and catalytically active enzymes, such as cytochrome C (Cyt C), in the pharmaceutical and fine chemical industries. However, harsh process conditions, such as temperature, pH, and presence of organic solvents, are the major barriers to the effective use of enzymes in biocatalysis. Herein, we demonstrate the suitability of bio-based ionic liquids (ILs) formed by the cholinium cation and dicarboxylate-based anions as potential media for enzymes, in which remarkable enhanced activity and improved stability of Cyt C against multiple stresses were obtained. Among the several bio-ILs studied, an exceptionally high catalytic activity (> 50-fold) of Cyt C was observed in aqueous solutions of cholinium glutarate ([Ch][Glu]; 1g/mL) as compared to the commonly used phosphate buffer solutions (pH 7.2), and > 25-fold as compared to aqueous solutions of cholinium dihydrogen phosphate ([Ch][Dhp]; 0.5g/mL) -the best known IL for long term stability of Cyt C. The catalytic activity of the enzyme in presence of bio-ILs was retained against several external stimulus, such as chemical denaturants (H2O2 and GuHCl), and temperatures up to 120 °C. The observed enzyme activity is in agreement with its structural stability, as confirmed by UV-Vis, circular dichroism (CD), and Fourier transform infrared (FT-IR) spectroscopies. Taking advantage of the multi-ionization states of di/tri-carboxylic acids, the pH was switched from acidic to basic by the addition of the corresponding carboxylic acid and choline hydroxide, respectively. The activity was found to be maximum at a 1:1 ratio of [Ch][carboxylate], with a pH in the range from 3 to 5.5. Moreover, it was found that the bio-ILs studied herein protect the enzyme against protease digestion and allow long-term storage (at least for 21 weeks) at room temperature. An attempt by molecular docking was also made to better understand the efficacy of the investigated bio-ILs towards the enhanced activity and long term stability of Cyt C. The results showed that dicarboxylates anions interact with the active site's amino acids of the enzyme through H-bonding and electrostatic interactions, which are responsible for the observed enhancement of the catalytic activity. Finally, it is demonstrated that Cyt C can be successfully recovered from the aqueous solution of bio-ILs and reused without compromising its yield, structural integrity and catalytic activity, thereby overcoming the major limitations in the use of IL-protein systems in biocatalysis.

A green approach to offset the perturbation action of 1-butyl-3-methylimidazolium iodide on α-chymotrypsin.

Recently, studies have provided evidence for the negative effects of ionic liquids (ILs), "greener solvents," on proteins [Phys. Chem. Chem. Phys., 2014, 16, 5514]. The search to offset the negative effects of ILs on proteins has come into limelight as the maintenance of a "green solvent medium" is a great challenge for chemists and biochemists. As the first step in this search, 1-butyl-3-methylimidazolium bromide ([Bmim][Br]) has been applied to offset the deleterious action of 1-butyl-3-methylimidazolium iodide ([Bmim][I]) on α-chymotrypsin (CT). Fluorescence and circular dichroism (CD) experiments results have indicated that [Bmim][Br] significantly offsets the deleterious action of [Bmim][I] at lower concentrations (0.025 M). Surprisingly, the stabilizing action of [Bmim][Br] turns into a deleterious action for CT at higher concentrations (>0.1 M). On the other hand, [Bmim][I] acted as a destabilizer for CT at all investigated concentrations (0.025-0.6 M). The results obtained from this study lead to valuable insights into the selection of suitable ILs to attenuate the deleterious action of another IL without disturbing the protein structure.

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.

Influence of ionic liquids on the critical micellization temperature of a tri-block co-polymer in aqueous media.

To explore the role of additives in controlling the critical micellization temperature (CMT) of a block copolymer in aqueous solution, in the present work, a series of ionic liquids (ILs) containing the same cation, 1-butyl-3-methylimidazolium, bmim(+) and commonly used anions such as SCN(-), BF4(-), I(-), Cl(-), CH3COO(-) and HSO4(-) were chosen for study with a triblock copolymer, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), (PEG-PPG-PEG) in aqueous solution. The present results suggest that the ability of ILs for decreasing the polymer CMT is mainly a result of not only from charge and size of anions of the ILs, but also due to the weak ion-ion pair interactions within IL. The present study provides important information that can be helpful to tune the IL- or temperature-sensitive copolymer CMT and micelle shapes which are crucial for understanding the drug delivery mechanisms.

Water and a protic ionic liquid acted as refolding additives for chemically denatured enzymes.

In this communication, we present the ability of water and a protic ionic liquid, triethyl ammonium phosphate (TEAP) to act as refolding additives for the urea-induced chemical denaturated state of the two enzymes, α-chymotrypsin and succinylated Con A. We show that the enzymatic activity is regained and in certain circumstances enhanced.

Influence of polymer molecular weight and concentration on coexistence curve of isobutyric acid + water.

We report the influence of variation of molecular weights (MWs = 2, 4, 6, and 9 × 10(5) g mol(-1)) and concentration (C) of a long-chain polymer (polyethylene oxide, PEO) on an upper critical solution temperature (UCST) of isobutyric acid (I) + water (W) using density (ρ) measurements as a function of temperature. The ρ values in each coexisting phase of IW have been measured at three different PEO concentrations (C = 0.395, 0.796, and 1.605 mg/cm(3)) in the near critical composition of IW at temperatures below the system's upper critical point for each molecular weight (MW) of PEO. Further, to ascertain the PEO behavior in IW we have measured the polydispersity values for both coexisting liquid phases by using dynamic light scattering (DLS). The data show that the polymer was significantly affected in the critical region of IW and these various MWs and concentrations of PEO show significant modulation on the critical exponents (ß), the critical temperatures (T(c)), and critical composition (ϕ(c)), which are depicting the shape of the coexistence curve. The values of ß and T(c) increase with increasing PEO MW and concentrations. Besides, the ϕ(c) values slightly decrease with increasing the C values in the mixture of IW. However, the rate of decrease in ϕ(c) is insignificant. Our experimental results explicitly elucidate that most of polymer chain entangles in water rich phase, thereby the polymer monomers strongly interact with neighbor solvent particles and also intra chain interaction between polymer monomers.

Ionic liquid modifies the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) in aqueous solution.

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.

Measurements and molecular interactions for N,N-dimethylformamide with ionic liquid mixed solvents.

To understand the molecular interactions between N,N-dimethylformamide (DMF) with two families of ionic liquids (ILs), we have measured thermophysical properties such as densities (rho) and ultrasonic sound velocities (u) over the whole composition range at 25 degrees C under atmospheric pressure. The excess molar volume (V(E)) and the deviation in isentropic compressibilities (DeltaK(s)) were predicted using these properties as a function of the concentration of IL. These results are fitted to the Redlich-Kister polynomials. The materials investigated in the present study included two families of ILs such as ammonium salts and imidazolium salts. Diethylammonium acetate ([Et(2)NH][CH(3)COO], DEAA), triethylammonium actetate ([Et(3)NH][CH(3)COO], TEAA), triethylammonium dihydrogen phosphate ([Et(3)NH][H(2)PO(4)], TEAP), and triethylammonium sulfate ([Et(3)NH][HSO(4)], TEAS) are ammonium salts and 1-benzyl-3-methylimidazolium chloride ([Bmim][Cl]) belongs to the imidazolium family. The intermolecular interactions and structural effects were analyzed on the basis of the measured and the derived properties. A qualitative analysis of the results is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding between ILs and DMF molecules and their structural factors.