Insights into the denaturation of bovine serum albumin with a thermo-responsive ionic liquid

Insights into protein-ionic liquid interaction: A comprehensive overview on theoretical and experimental approaches

Owing to highly tunable nature, ionic liquids are nesting stance in the scientific community for a wide variety of applications ranging from electrochemistry to product purification, from chemical and biomedical applications to biotechnological interventions and proteomics. Proteins are unstable in its native form and several attempts have been made to stabilize them by addition of various additives. This review focusses on the studies conducted to improve protein stability with ionic liquids along with an emphasis on the mechanism of interaction. This review also specifies and discusses about the brief introduction to ionic liquids, evolution of first-, second-, and third generation of liquids over the years and their selection criterion and applications. Though, there are several elegant reviews available on proteins-ionic liquids interaction, this review systematically highlights the effect of ionic liquids viz., imidazolium, ammonium, phosphonium and choline-based ionic liquids (amino acid-based anions & classical anions) on fibrous proteins viz., collagen and keratin and globular proteins viz., bovine serum albumin and cytochrome c. Thus, this review elaborates the thorough investigations conducted to explore the stabilizing properties of ionic liquids over fibrous and globular proteins.

Chemical Tuning of Zwitterionic Ionic Liquids for Variable Thermophysical Behaviours, Nanostructured Aggregates and Dual-Stimuli Responsiveness

The design and synthesis of a series of zwitterionic ionic liquids (ZILs) to understand the structure-property relationship towards an increase of the thermal stability, a variation of the glass transition temperature, the shape-tuning of nanostructured aggregates and the tuning of the stimuli responsiveness are demonstrated. The substitution reaction of imidazole with various aliphatic and aromatic bromides followed by the reaction of the corresponding substituted imidazoles with bromoalkyl carboxylic acids of varying spacer length produces the ZILs. In aqueous solution, a ZIL molecule either exist in its ionic liquid (substituted imidazolium bromide) form or its zwitterionic (substituted imidazolium alkyl carboxylate) form with an isoelectric point (pI) depending on the pH value of the solution. Upon changing the pH to near or above the pI, the aqueous ZIL solution undergoes transition from a transparent to a turbid phase due to the formation of insoluble hierarchical nanostructured aggregates of various morphologies, such as spheres, tripods, tetrapods, fern-like, flower-like, dendrites etc. depending on the pH of the solution and the nature of the alkyl/vinyl/aryl substituents. Upon heating the solution a phase transition occurs from turbid to transparent, exhibiting a distinct reversible upper critical solution temperature (UCST)-type cloud point (T_cp ). It is observed that the cloud point varies with the nature of the substituent, an increase of the concentration of the ZIL as well as with changes of the pH of the solution.

Insights into the thermal phase transition behavior of a gemini dicationic polyelectrolyte in aqueous solution

The thermal-induced phase transition behavior of a LCST-type poly(ionic liquid) (PIL) aqueous solution with gemini-cationic structure, poly[(1,8-octanediyl-bis(tri-n-butylphosphonium)4-styrene sulfonate)] (P[SS-P2]), was investigated in this paper. Based on the calorimetric measurements, a unique dependence of transition points on concentration was found in P[SS-P2] aqueous solution compared to its mono-cationic PIL and [SS-P2] aqueous solution. Optical microscopy showed that globular microscopic droplets were formed during the phase transition, suggesting that gemini dications and the possible dynamic ionic bonds may facilitate the liquid-liquid phase separation (LLPS) in P[SS-P2] aqueous solution. Temperature-variable 1H NMR and FT-IR investigations manifested that the dehydration of anionic chains instead of the dehydration of dications served as the driving force of the phase separation in the P[SS-P2] aqueous solution, implying that the polymerized anions tended to aggregate together first and lay in the core with dications distributed around the globules at the end of the transition process. Notably, considering that the SO3 groups in the gemini-cationic system tended to be distributed around the surface of collapsed anionic main chains rather than be wrapped into the aggregates, it is supposed that dynamic ionic bonding between dication and anionic backbones was distributed in the periphery of the globules and acted as the "cross-linkers", which enhanced the stability of regular droplets after the phase transition in P[SS-P2] aqueous solution.

Proteins in Ionic Liquids: Current Status of Experiments and Simulations

In the last two decades, while searching for interesting applications of ionic liquids as potent solvents, their solvation properties and their general impact on biomolecules, and in particular on proteins, gained interest. It turned out that ionic liquids are excellent solvents for protein refolding and crystallization. Biomolecules showed increased solubilities and stabilities, both operational and thermal, in ionic liquids, which also seem to prevent self-aggregation during solubilization. Biomolecules can be immobilized, e.g. in highly viscous ionic liquids, for particular biochemical processes and can be designed to some extent by the proper choice of the ionic liquid cations and anions, which can be characterized by the Hofmeister series.

The influence of a thermoresponsive polymer on the microdynamic phase transition mechanisms of distinctly structured thermoresponsive ionic liquids

The study of a ternary solution involving a thermoresponsive polymer, a thermoresponsive ionic liquid (IL), and a solvent will not only help with interpreting their distinct phase transition behavior, but also promote the development of novel thermoresponsive systems.

Revealing the distinct thermal transition behavior between PEGA-based linear polymers and their disulfide cross-linked nanogels

Description of the distinct thermal transition behavior between PEGA-based linear polymers and their disulfide cross-linked nanogels at a molecular level.

Unusual Phase Transition Behavior of Poly(N-isopropylacrylamide)-co-Poly(tetrabutylphosphonium styrenesulfonate) in Water: Mild and Linear Changes in the Poly(N-isopropylacrylamide) Part

In this paper, one LCST-type thermoresponsive poly(ionic liquid) (PIL), poly(tetrabutylphosphonium styrenesulfonate) (P[P4,4,4,4][SS]), was introduced to poly(N-isopropylacrylamide) (PNIPAM) by two different ways, mixing and copolymerization. Interestingly, they show distinct thermoresponsive phase transition behaviors, evidenced by temperature-variable (1)H nuclear magnetic resonance and Fourier transform infrared in combination with the perturbation correlation moving window (PCMW) technique. The PNIPAM/P[P4,4,4,4][SS] mixture exhibits a sharp and drastic phase transition, similar to that of pure PNIPAM. In the statistical copolymer, PNIPAM-co-P[P4,4,4,4][SS], the thermosensitivity of P[P4,4,4,4][SS] is largely suppressed, resulting in a linear, mild, and incomplete phase transition, which has never been reported before. This abnormal phenomenon is shown to arise from the outstanding hydration ability of P[P4,4,4,4][SS]. Our findings should be conducive to improving our understanding of the interaction between LCST-type polymers with distinct structures and provide a new perspective for preparing thermoresponsive materials with linear phase transition behavior.

Toward the dynamic phase transition mechanism of a thermoresponsive ionic liquid in the presence of different thermoresponsive polymers

The influence of two thermoresponsive polymers, poly(N-isopropylacrylamide) (PNIPAM) and poly(N-vinylcaprolactam) (PVCL), on the phase transition behavior of a thermoresponsive ionic liquid, tributylhexylphosphonium 3-sulfopropylmethacrylate ([P4,4,4,6][MC3S]), was investigated. An obvious distinction was observed in the LCSTs and morphologies of [P4,4,4,6][MC3S]-PNIPAM and [P4,4,4,6][MC3S]-PVCL aqueous solutions, indicating their large differences in dynamic transition processes. In general, PNIPAM can "break" the water structure of [P4,4,4,6][MC3S] to decrease the transition temperature, while PVCL can "make" the water structure to increase it. Surprisingly, [P4,4,4,6][MC3S] has an unusual over-hydration behavior before dehydration while PNIPAM experiences a two-step transition process in [P4,4,4,6][MC3S]-PNIPAM aqueous solution, which has never been reported so far. Further studies revealed that the formation of strong intra-/inter-molecular hydrogen bonds C[double bond, length as m-dash]OD-N in PNIPAM is the driving force for the LCST phenomenon of [P4,4,4,6][MC3S]-PNIPAM solution, while it is the [P4,4,4,6][MC3S] that dominates the phase separation of [P4,4,4,6][MC3S]-PVCL solution.