Unravelling the stabilization mechanism of mono-, di- and tri-cholinium citrate-ethylene glycol DESs towards α-chymotrypsin for preservation and activation of the enzyme

Deep eutectic solvents (DESs) are considered as designer solvents that serve as alternatives to traditional solvents. Numerous favourable properties and advantageous characteristics promote their utility in bio-catalysis. Therefore, they have emerged as attractive sustainable media for different biomacromolecules. In the present work, we have synthesized cholinium-based DESs having a hydrogen bond acceptor (HBA) : hydrogen bond donor (HBD) molar ratio of 1 : 2 by varying the cationic ratio in the HBA, which led to the formation of the DESs such as monocholinium citrate ([Chn][Cit]), dicholinium citrate ([Chn]2[Cit]) and tricholinium citrate ([Chn]3[Cit]), keeping the HBD ethylene glycol (EG) constant to study their suitability for α-chymotrypsin (α-CT). Herein, we have systematically evaluated the influence of DES-1 ([Chn][Cit]-[EG]), DES-2 ([Chn]2[Cit]-[EG]) and DES-3 ([Chn]3[Cit]-[EG]) on the structural and thermal stability, thermodynamic profile, colloidal stability and enzymatic activity of α-CT using different spectroscopic techniques. The spectroscopic results explicitly show enhanced structural stability and activity of the enzyme as the cationic ratio in the HBA increases. Fascinatingly, temperature-dependent studies through both fluorescence and activity measurements showed that DES-2 and DES-3 have highly beneficial effects on α-CT stability. The transition temperature (Tm) of α-CT was augmented by 12.0 °C in DES-2, 10.0 °C in DES-3 and 9.1 °C in DES-1 when compared to the enzyme in buffer. Furthermore, transmission electron microscopy (TEM) analysis revealed that the morphology of α-CT in DES-2 and DES-3 closely mirrored the structure of α-CT, while DES-1 exhibited only minor structural deviations. These findings were corroborated by hydrodynamic size (dH) measurements and average decay time analysis, which confirmed the observed morphological similarities and perturbations. The long-term preservation ability and kinetics of DES-3 were eventually confirmed by Michaelis-Menten kinetics. Ultimately, these outcomes demonstrate that increasing the molar ratio of the cholinium cation in the HBA can enhance the ability of DESs to stabilize the α-CT structure. Our results also suggest that the effect imparted by DESs was due to DESs themselves rather than their constituent elements. Altogether, the present investigation provides a new insight into the dependence of protein's stability and conformational alterations on DES composition. Also, the biocompatibility of DESs towards enzymes can be varied by changing the molar ratios of the constituent components of DESs to facilitate the expansion of applicability of DESs in biocatalysis.

Suitability of Adenosine Derivatives in Improving the Activity and Stability of Cytochrome c under Stress: Insights into the Effect of Phosphate Groups

It is well known that adenosine and its phosphate derivatives play a crucial role in biological phenomena such as apoptosis and cell signaling and act as the energy currency of the cell. Although their interactions with various proteins and enzymes have been described, the focus of this work is to demonstrate the effect of the phosphate group on the activity and stability of the native heme metalloprotein cytochrome c (Cyt c), which is important from both biological and industrial aspects. In situ and in silico characterizations are used to correlate the relationship between the binding affinity of adenosine and its phosphate groups with unfolding behavior, corresponding peroxidase activities, and stability factors. Interaction of adenosine (ADN), adenosine monophosphate (AMP), adenosine 5'-diphosphate (ADP), and adenosine 5'-triphosphate (ATP) with Cyt c increases peroxidase-like activity by up to 1.8-6.5-fold compared to native Cyt c. This activity is significantly maintained even after multiple stress conditions such as oxidative stress and the presence of a chaotropic agent such as guanidine hydrochloride (GuHCl). With binding affinities on the order of ADN < AMP < ADP < ATP, adenosine derivatives were found to stabilize Cyt c by varying the secondary structural features of the protein. Thus, in addition to being a fundamental study, the current work also proposes a way of stabilizing protein systems to be used for real-time biocatalytic applications.

Assessing the compatibility of choline-based deep eutectic solvents for the structural stability and activity of cellulase: Enzyme sustain at high temperature

As a new generation of 'green solvents' deep eutectic solvents (DESs) represents a promising alternative to the conventional solvents. Their environmental-benign nature and designer properties promote their utility in biocatalysis. Enzymes are marginally stable when exposed to physical/chemical disturbances. One such enzyme is cellulase which is a propitious catalyst for the depolymerization of cellulose under mild conditions. Therefore, their stability is a prerequisite condition to match demands of biorefineries. To address this issue of low stability, activity and thermal denaturation of cellulase, there is a need to find a sustainable and suitable co-solvent that is biocompatible with enzymes ultimately to facilitate their application in bio-industries. In this regard, we synthesized three choline-based DESs, choline chloride (ChCl)-glycerol, ChCl-ethylene glycol and ChCl-lactic acid and employed them to analyze their suitability for cellulase. The present study systematically evaluates the influence of the mentioned DESs on stability, activity and thermal stability of cellulase with the help of various spectroscopic techniques. The spectroscopic analysis revealed that the structural stability and activity of the enzyme were improved in presence of ChCl-glycerol and ChCl-ethylene glycol. The thermal stability was also very well maintained in both the DESs. Interestingly, the relative activity of cellulase was >80 % even after incubation at 50 °C after 48 h for both the DESs. This activity preservation behaviour was more pronounced for ChCl-ethylene glycol than ChCl-glycerol. Moreover, temperature variations studies also reveal promising results by maintain conformational intactness. On the other side, ChCl-lactic acid showed a deleterious effect on the enzyme both structurally as well as thermally. The dynamic light scattering (DLS) analysis provides more specific information about the negative influence of ChCl-lactic acid towards cellulase native structure. This DES induces unavoidable alterations in the enzyme structure which leads to the unfolding of enzyme, ultimately, destabilizing it. Overall, our results present a physical insight into how the enzyme stability and activity depend on the nature of DES. Also, the findings will help to facilitate the development and application of DESs as biocatalytic process.

Deep eutectic solvents induced changes in the phase transition behavior of smart polymers: a sustainable future approach

Deep eutectic solvents (DESs) are considered "green" and "sustainable" alternatives to conventional organic solvents and ionic liquids (ILs) due to their characteristic properties and relatively low costs. DESs are considered IL analogs and have attracted consideration as benign media formulations for the synthesis of novel polymers because they satisfy the principle of sustainability. Over the past few years, the use of DESs has resulted in novel pathways for the synthesis of novel materials, biomaterials, functional materials, and ionic soft materials. Furthermore, DESs have been widely applied in the science, industrial, engineering, and technological fields. On the other hand, stimulus-responsive (smart) polymers have been widely utilized in intelligent devices owing to their virtues of good processibility, stimuli and environmental sensitivity, responsivity, and so on. With the introduction of a DES into the smart polymeric matrices, their potential characteristics, biocompatibility, and flexibility endow the corresponding DES-based polymeric materials with intriguing properties, which in turn will broaden their applications in various domains of polymer science and material chemistry. Substantial research has been done in the fabrication of DES-based polymeric materials. Numerous studies have extensively investigated the effects of DESs on biomolecules such as proteins/enzymes and nucleic acids, whereas few have addressed the impact of DESs on the aggregation and phase transition behaviors of smart polymers. This review focuses on mechanistic insights, aggregation behavior, and interactions between smart polymers and DESs. Opportunities and future research perspectives in this blossoming arena are also discussed. It is hoped that this review will pave futuristic pathways for the design and development of advanced DES-based polymeric materials and biomaterials for various applications.

The attenuating ability of deep eutectic solvents towards the carboxylated multiwalled carbon nanotubes induced denatured β-lactoglobulin structure

The stabilization of proteins has been a major challenge for their practical utilization in industrial applications. Proteins can easily lose their native conformation in the presence of denaturants, which unfolds the protein structure. Since the introduction of deep eutectic solvents (DESs), there are numerous studies in which DESs act as promising co-solvents that are biocompatible with biomolecules. DESs have emerged as sustainable biocatalytic media and an alternative to conventional organic solvents and ionic liquids (ILs). However, the superiority of DESs over the deleterious influence of denaturants on proteins is often neglected. To address this, we present the counteracting ability of biocompatible DESs, namely, choline chloride-glycerol (DES-1) and choline chloride-urea (DES-2), against the structural changes induced in β-lactoglobulin (Blg) by carboxylated multiwalled carbon nanotubes (CA-MWCNTs). The work is substantiated with various spectroscopic and thermal studies. The spectroscopic results revealed that the fluorescence emission intensity enhances for the protein in DESs. Contrary to this, the emission intensity extremely quenches in the presence of CA-MWCNTs. However, in the mixture of DESs and CA-MWCNTs, there was a slight increase in the fluorescence intensity. Circular dichroism spectral studies reflect the reappearance of the native band that was lost in the presence of CA-MWCNTs, which is a good indicator of the counteraction ability of DESs. Further, thermal fluorescence studies showed that the protein exhibited extremely great thermal stability in both DESs as well as in the mixture of DES-CA-MWCNTs compared to the protein in buffer. This study is also supported by dynamic light scattering and zeta potential measurements; the results reveal that DESs were successfully able to maintain the protein structure. The addition of CA-MWCNTs results in complex formation with the protein, which is indicated by the increased hydrodynamic size of the protein. The presence of DESs in the mixture of CA-MWCNTs and DESs was quite successful in eliminating the negative impact of CA-MWCNTs on protein structural alteration. DES-1 proved to be superior to DES-2 over counteraction against CA-MWCNTs and maintained the native conformation of the protein. Overall, both DESs act as recoiling media for both native and unfolded (denatured by CA-MWCNTs) Blg structures. Both the DESs can be described as potential co-solvents for Blg with increased structural and thermal stability of the protein. To the best of our knowledge, this study for the first time has demonstrated the role of choline-based DESs in the mixture with CA-MWCNTs in the structural transition of Blg. The DESs in the mixture successfully enhance the stability of the protein by reducing the perturbation caused by CA-MWCNTs and then amplifying the advantages of the DESs present in the mixture. Overall, these results might find implications for understanding the role of DES-CA-MWCNT mixtures in protein folding/unfolding and pave a new direction for the development of eco-friendly protein-protective solvents.

Designing protein nano-construct in ionic liquid: a boost in efficacy of cytochrome C under stresses

Herein, we present a simple approach to fabricate protein nanoconstructs by complexing cytochrome C (Cyt C) with silk nanofibrils (SNF) and choline dihydrogen phosphate ionic liquid (IL). The peroxidase activity of the IL modified Cyt C nanoconstruct (Cyt C + SNF + IL) increased significantly (2.5 to 10-fold) over unmodified Cyt C and showed enhanced catalytic activity and stability under harsh conditions, proving its potential as a suitable protein packaging strategy.

Unprecedented enhancement and preservation of the peroxidase activity of cytochrome-c packaged with ionic liquid-modified gold nanoparticles by offsetting temperature and time stresses

Inspired by the biocompatibility of ionic liquids and their dexterousness for the preservation of enzyme structure and activity, herein, the interactions of Cyt-c with naked AuNPs and four IL-mediated AuNPs, which were formed by the fabrication of ILs with common cation 1-ethyl-3-methyl-imidazolium (EMIM) and different anions, to obtain AuNP-IL1 [(BF4)^-1 anion], AuNP-IL2 [(CH₃OSO₃)^-1 anion], AuNP-IL3 [(CH₃CH₂OSO₃)^-1 anion], and (AuNP-IL4) [Cl^-1 anion], were studied. Through this work, the peroxidase activity observed in the presence of a lower concentration IL-AuNPs is exceptionally increased (16 fold). IL-AuNPs preferentially counteract the temperature gradient change and long-term solvent preservation effects while persistently maintaining the Cyt-c peroxidase activity without much depreciation. The hydrodynamic diameter (d_H) of the Cyt-c-AuNP system was obtained, which supported the TEM results. Furthermore, to evaluate the effect of Cyt-c interaction with the AuNPs, a Zeta potential analysis was performed. Taken together, the binding of IL-AuNPs with Cyt-c, diameter size analysis, zeta potential, structural integrity evaluation using the DichroWeb software and morphology results suggest the interaction order of the IL-AuNPs to be in a sequence of AuNP-IL2 > AuNP-IL3 > AuNP- IL4 > AuNP-IL1 > Naked AuNPs. Moreover, results indicate that the IL anions play a dominating role in the modulation of interactions between IL-mediated AuNPs and Cyt-c. The study strongly supports the promising character of sulfur-containing IL-mediated AuNPs for Cyt-c immobilization simultaneously opening new avenues for the application of greener and biocompatible nanoparticles with drug delivery and therapeutic applications.

Can deep eutectic solvents be the best alternatives to ionic liquids and organic solvents: A perspective in enzyme catalytic reactions

As a new generation of green solvents, deep eutectic solvents (DESs) have been considered as a promising alternative to classical organic solvents and ionic liquids (ILs). DESs are normally formed by two or more components via various h-bonds interactions. Up to date, four types of DESs are found, namely, type I DESs (formed by MClx, namely FeCl₂, AlCl₃, ZnCl₂, CuCl₂ and AgCl et al., and quaternary ammonium salts); type II DESs (formed by metal chloride hydrates and quaternary ammonium salts); type III DESs (formed by choline chlorides and different kinds of HBDs) and type IV DESs (formed by salts of transition metals and urea). DESs share many advantages, such as low vapor pressure, good substrate solubility and thermal stability, with ILs, and offering a high potential to be the medium of biocatalysis reactions. In this case, this paper reviews the applications of DESs in enzymatic reactions. Lipases are the most widely used enzyme in DESs systems as their versatile applications in various reactions and robustness. Interestingly, DESs can improve the efficiency of these reactions via enhancing the substrates solubility and the activity and stability of enzymes. Therefore, the directed engineering of DESs for special reactions such as degradation of polymers in high temperature or strong acid-base conditions will be one of the future perspectives of the investigation DESs.

Current understanding and insights towards protein stabilization and activation in deep eutectic solvents as sustainable solvent media

Deep eutectic solvents (DESs) have emerged as a new class of green, designer and biocompatible solvents, an alternative to conventional organic solvents and ionic liquids (ILs) which are comparatively toxic and non-biodegradable. DESs are eutectic mixtures that are formed when a hydrogen bond acceptor (HBA) is mixed with a hydrogen bond donor (HBD) at particular molar ratios by mechanical grinding or under mild heating conditions. Very recently, these solvents have been the center of attention for researchers in biotechnology, biomedicine and various scientific applications. These environmentally benign solvents have a close analogy with ILs; however, they offer certain unique merits over traditional ILs. DESs display remarkable properties such as easy preparation, tunable composition, biodegradability, recyclability, inherently low toxicity, sustainability and biocompatibility; these special features validate DESs as new potential solvents/co-solvents for biomolecules. Mechanistically, the biocompatibility and protein friendly nature of DESs depend on various factors, which include the composition of the DES, viscosity and hydration level. Therefore, it becomes an essential task to bring together all the studies related to protein behaviour in DESs to unlock their biomolecular proficiency. This review specifically highlights recent insights into the biomacromolecular functionality in DESs, including outlines of the solubilization and stabilization of proteins, long term protein packaging, different extraction methods and enzyme activation in the presence of DESs. A literature survey reveals that DESs act as green media in which the protein structure and activity are retained. In some cases, proteins refolded and enzymatic activity was enhanced several fold in the presence of DESs. Furthermore, we have reviewed the possible mechanistic behaviour behind protein stabilization, refolding and activation in DESs. Overall, the main objective of this review is to explicate the advantages of the introduction of DESs for biomolecules and to demonstrate the versatility of these eco-friendly solvents for future bio-based applications.

Recent Advances in Ionic Liquids in Biomedicine

The use of ionic liquids and deep eutectic solvents in biomedical applications has grown dramatically in recent years due to their unique properties and their inherent tunability. This review will introduce ionic liquids and deep eutectics and discuss their biomedical applications, namely solubilization of drugs, creation of active pharmaceutical ingredients, delivery of pharmaceuticals through biological barriers, stabilization of proteins and other nucleic acids, antibacterial agents, and development of new biosensors. Current challenges and future outlooks are discussed, including biocompatibility, the potential impact of the presence of impurities, and the importance of understanding the microscopic interactions in ionic liquids in order to design task-specific solvents.

A novel amalgamation of deep eutectic solvents and crowders as biocompatible solvent media for enhanced structural and thermal stability of bovine serum albumin

This study unravels the effect of a novel solvent medium designed by amalgamation of macromolecular crowders and deep eutectic solvents (DESs) on bovine serum albumin (BSA).