Critical to the applications of proteins in non-aqueous enzymatic processes is their structural dynamics in relation to solvent polarity. A pool of mutants derived from Geobacillus zalihae T1 lipase was screened in organic solvents (methanol, ethanol, propanol, butanol and pentanol) resulting in the selection of six mutants at initial screening (A83D/K251E, R21C, G35D/S195 N, K84R/R103C/M121I/T272 M and R106H/G327S). Site-directed mutagenesis further yielded quadruple mutants A83D/M121I/K251E/G327S and A83D/M121I/S195 N/T272 M, both of which had improved activity after incubation in methanol. The km and kcat values of these mutants vary marginally with the wild-type enzyme in the methanol/substrate mixture. Thermally induced unfolding of mutants was accompanied with some loss of secondary structure content. The root mean square deviations (RMSD) and B-factors revealed that changes in the structural organization are intertwined with an interplay of the protein backbone with organic solvents. Spatially exposed charged residues showed correlations between the solvation dynamics of the methanol solvent and the hydrophobicity of the residues. The short distances of the radial distribution function provided the required distances for hydrogen bond formation and hydrophobic interactions. These dynamic changes demonstrate newly formed structural interactions could be targeted and incorporated experimentally on the basis of solvent mobility and mutant residues.
With the rise of antibiotic resistance globally, coupled with evolving and emerging infectious diseases, there is an urgent need for the development of novel antimicrobials. Deep eutectic solvents (DES) are a new generation of eutectic mixtures that depict promising attributes with several biological implications. DES exhibit unique properties such as low toxicity, biodegradability, and high thermal stability. Herein, the antimicrobial properties of DES and their mechanisms of action against a range of microorganisms, including bacteria, amoebae, fungi, viruses, and anti-cancer properties are reviewed. Overall, DES represent a promising class of novel antimicrobial agents as well as possessing other important biological attributes, however, future studies on DES are needed to investigate their underlying antimicrobial mechanism, as well as their in vivo effects, for use in the clinic and public at large.
The reactions of 2-chloropyrimidine with methylamine, ethylamine and piperidine gave the corresponding 2-N-methylamino-, 2-N-ethylamino- and 2N- piperidinopyrimidines, respectively. The fluorescence properties of these alkylamino derivatives in chloroform, ethyl acetate, carbon tetrachloride, acetone, ether, ethanol and methanol were studied. All the alkylamino derivatives showed the highest fluorescence intensity in polar protic solvents; thus 2-N-methylaminopyrimidine (highest fluorescence intensity at 377 nm when excited at 282 nm) and 2-N-ethylaminopyrimidine (highest fluorescence intensity at 375 nm, when excited at 286 nm) showed the highest fluorescence in methanol. In ethanol, 2-N-piperidinopyrimidine showed a fluorescence peak at 403 nm when excited at 360 nm and in chloroform it fluoresced at 392 nm when excited at 356 nm.
Deep eutectic solvents (DESs) have been touted recently as potential alternatives to ionic liquids (ILs). Although they possess core characteristics that are similar to those of ILs (e.g., low volatility, non-flammability, low melting points, low vapor pressure, dipolar nature, chemical and thermal stability, high solubility, and tuneability), DESs are superior in terms of the availability of raw materials, the ease of storage and synthesis, and the low cost of their starting materials. As such, they have become the subject of intensive research in various sectors, notably the chemical, electrochemical, and biological sectors. To date, the applications of DESs have shown great promise, especially in the medical and biotechnological fields. In spite of these various achievements, the safety concern for these mixtures must be sufficiently addressed. Indeed, in order to exploit the vast array of opportunities that DESs offer to the biological industry, first, they must be established as safe mixtures. Hence, the biotechnological applications of DESs only can be implemented if they are proven to have negligible or low toxicity profiles. This review is the first of its kind, and it discusses two current aspects of DES-based research. First, it describes the properties of these mixtures with ample focus on their toxicity profiles. Second, it provides an overview of the breakthroughs that have occurred and the foreseeable prospects of the use of DESs in various biotechnological and biological applications.
A practical and facile synthesis of various coumarin derivatives was conducted using a liquid phase of 4,4'-trimethylenedipiperidine as a safe and greener dual-task reagent under catalyst-free and solvent-free conditions. This reagent is a commercially available solid and can be handled easily, having a liquid phase over a vast temperature range, high thermal stability, low toxicity, and good solubility in green solvents such as water and ethanol. It is worth mentioning that 4,4'-trimethylenedipiperidine could be completely recovered and regenerated after a simple process. The current method has other merits, including (a) minimizing the use of high-risk and toxic reagents and solvents; (b) the use of a secure and recoverable medium-organocatalyst instead of metal-based catalysts, (c) avoid tedious processes, harsh conditions, and a multi-step process for the preparation of catalysts, (d) transform phenol and salicyladehyde derivatives into the corresponding coumarin derivatives in good to high yields, (e) minimize hazardous waste generation. TMDP could be easily recovered and reused several times with no change in its activity. Furthermore, the current work demonstrated that the liquid phase of 4,4'-trimethylenedipiperidine can be a promising medium in organic reaction at higher temperatures due to its broad liquid range temperature, thermal stability, acceptor/donor hydrogen bond property, and other unique merits. New methodology for the synthesis of coumarines using liquid phase of TMDP under mild conditions.
With rising consumer demand for natural products, a greener and cleaner technology, i.e., ultrasound-assisted extraction, has received immense attention given its effective and rapid isolation for nanocellulose compared to conventional methods. Nevertheless, the application of ultrasound on a commercial scale is limited due to the challenges associated with process optimization, high energy requirement, difficulty in equipment design and process scale-up, safety and regulatory issues. This review aims to narrow the research gap by placing the current research activities into perspectives and highlighting the diversified applications, significant roles, and potentials of ultrasound to ease future developments. In recent years, enhancements have been reported with ultrasound assistance, including a reduction in extraction duration, minimization of the reliance on harmful chemicals, and, most importantly, improved yield and properties of nanocellulose. An extensive review of the strengths and weaknesses of ultrasound-assisted treatments has also been considered. Essentially, the cavitation phenomena enhance the extraction efficiency through an increased mass transfer rate between the substrate and solvent due to the implosion of microbubbles. Optimization of process parameters such as ultrasonic intensity, duration, and frequency have indicated their significance for improved efficiency.
The critical challenge being faced by our current modern society on a global scale is to reduce the surging effects of climate change and global warming, being caused by anthropogenic emissions of CO2 in the environment. Present study reports the surface driven adsorption potential of deep eutectic solvents (DESs) surface functionalized cerium oxide nanoparticles (CeNPs) for low pressure CO2 separation. The phosphonium based DESs were prepared using tetra butyl phosphoniumbromide as hydrogen bond acceptor (HBA) and 6 acids as hydrogen bond donors (HBDs). The as-developed DESs were characterized and employed for the surface functionalization of CeNPs with their subsequent utilization in adsorption-based CO2 adsorption. The synthesis of as-prepared DESs was confirmed through FTIR measurements and absence of precipitates, revealed through visual observations. It was found that DES6 surface functionalized CeNPs demonstrated 27% higher adsorption performance for CO2 capturing. On the contrary, DES3 coated CeNPs exhibited the least adsorption progress for CO2 separation. The higher adsorption performance associated with DES6 coated CeNPs was due to enhanced surface affinity with CO2 molecules that must have facilitated the mass transport characteristics and resulted an enhancement in CO2 adsorption performance. Carboxylic groups could have generated an electric field inside the pores to attract more polarizable adsorbates including CO2, are responsible for the relatively high values of CO2 adsorption. The quadruple movement of the CO2 molecules with the electron-deficient and pluralizable nature led to the enhancement of the interactive forces between the CO2 molecules and the CeNPs decorated with the carboxylic group hydrogen bond donor rich DES. The current findings may disclose the new research horizons and theoretical guidance for reduction in the environmental effects associated with uncontrolled CO2 emission via employing DES surface coated potential CeNPs.
According to the 12 principles of green chemistry, surface functionalization was performed using glutaric anhydride under solvent-free and catalyst-free conditions. FTIR spectra and DS analyses demonstrated the functionalization of HCl-hydrolyzed cellulose. The influence of two parameters, i.e., the glutaric anhydride concentration and the reaction time, on the functionalization of HCl-hydrolyzed cellulose was investigated. Protocol efficiency was studied by a degree of substitution (DS). It was found that higher concentrations of glutaric anhydride cause an enhancement of DS to 0.75 and 0.87 for GA3-12 and GA9-12, respectively. In addition, the longer reaction time increased zeta potential from -12.2 ± 1.7 for G9-6 to -34.57 ± 2.2 for GA9-12. Morphology analysis by SEM showed a decrease in fiber length for the functionalized cellulose. DSC profiles confirmed dehydration at a range of 17 to 134 °C. A glass transition was revealed at -30 to -20 °C for all studied samples. The fusion, the depolymerization of cellulose chains, the cleavage of glycosidic linkages, and the decomposition of the crystalline parts of cellulose occur at 195 to 374 °C. Therefore, an efficient and greener process was developed to functionalize the HCl-hydrolyzed cellulose by glutaric anhydride, a safe and non-toxic anhydride, in the absence of the solvent and catalyst.
Ultrasound-assisted solvent extraction (UAE) was applied to extract underutilized Madhuca longifolia seed oil. The effect of extraction time, temperature, solvent type, solvent/sample ratio, and amplitude on the oil yield and recovery were investigated. Approximately 56.97% of oil yield and 99.54% of oil recovery were attained using mild conditions of 35 min, 35 °C, 40% amplitude, isopropanol to acetone (1:1), and solvent to sample (20 mL/g). UAE oil yield and recovery were comparable with Soxhlet extraction (SXE) whilst mechanical pressing (ME) yielded
Among wide range of membrane-based operations, membrane contactors, as they reify comparatively modern membrane-based mechanism are gaining quite an attention in both pilot and industrial scales. In recent literature, carbon capture is one of the most researched applications of membrane contactors. Membrane contactors have the potential to minimize the energy consumption and capital cost of traditional CO2 absorptions columns. In a membrane contactor, CO2 regeneration can take place below the solvent boiling point, resulting into lower consumption of energy. Various polymeric as well as ceramic membrane materials have been employed in gas liquid membrane contactors along with several solvents including amino acids, ammonia, amines etc. This review article provides detailed introduction of membrane contactors in terms of CO2 removal. It also discusses that the main challenge that is faced by membrane contactors is membrane pore wetting caused by solvent that in turn can reduce the mass transfer coefficient. Other potential challenges such as selection of suitable solvent and membrane pair as well as fouling are also discussed in this review and are followed by potential ways to reduce them. Furthermore, both membrane gas separation and membrane contactor technologies are analysed and compared in this study on the basis of their characteristics, CO2 separation performances and techno economical transvaluation. Consequently, this review provides an opportunity to thoroughly understand the working principle of membrane contactors along its comparison with membrane-based gas separation technology. It also provides a clear understanding of latest innovations in membrane contactor module designs as well as challenges encountered by membrane contactors along with possible solutions to overcome these challenges. Finally, semi commercial and commercial implementation of membrane contactors has been highlighted.
Density, viscosity and ionic conductivity data sets of deep eutectic solvents (DESs) formed by tetrabutylammonium bromide (TBABr) paired with ethlyene glycol, 1,3-propanediol, 1,5-pentanediol and glycerol hydrogen bond donors (HBDs) are reported. The properties of DES were measured at temperatures between 303 K and 333 K for HBD percentages of 66.7% to 90%. The effects of HBDs under different temperature and percentages are systematically analyzed. As expected, the measured density and viscosity of the studied DESs decreased with an increase in temperature, while ionic conductivity increases with temperature. In general, DESs made of TBABr and glycerol showed the highest density and viscosity and the lowest ionic conductivity when compared to other DESs. The presence of an extra hydroxyl group on glycerol in a DES affected the properties of the DES.
Utilizing lignocellulosic biomass wastes to produce bioproducts is essential to address the reliance on depleting fossil fuels. However, lignin is often treated as a low-value-added component in lignocellulosic wastes. Valorization of lignin into value-added products is crucial to improve the economic competitiveness of lignocellulosic biorefinery. Monomers obtained from lignin depolymerization could be upgraded into fuel-related products. However, lignins obtained from conventional methods are low in β-O-4 content and, therefore, unsuitable for monomer production. Recent literature has demonstrated that lignins extracted with alcohol-based solvents exhibit preserved structures with high β-O-4 content. This review discusses the recent advances in utilizing alcohols to extract β-O-4-rich lignin, where discussion based on different alcohol groups is considered. Emerging strategies in employing alcohols for β-O-4-rich lignin extraction, including alcohol-based deep eutectic solvent, flow-through fractionation, and microwave-assisted fractionation, are reviewed. Finally, strategies for recycling or utilizing the spent alcohol solvents are also discussed.
It is essential to investigate the physicochemical and thermal properties of choline chloride (ChCl)-based deep eutectic solvents (DESs) as hydrogen bond acceptor (HBA) with various hydrogen bond donor (HBD) functional groups, such as α-hydroxy acid (lactic acid) or polyol (glycerol). It is important to consider how molar ratios impact these properties, as they may be altered for particular applications. This study aimed to examine the physicochemical and thermal properties of ChCl-based DESs with lactic acid (LA) or glycerol (Gly) at different molar ratios (1:2-1:10). The pH of ChCl:LA (0-1.0) is lower than that of ChCl:Gly (4.0-5.0) because of the hydrogen bonds between ChCl and LA. A higher amount of LA/Gly resulted in higher densities of ChCl:Gly (1.20-1.22 g cm-3) and ChCl:LA (1.16-1.19 g cm-3) due to the stronger hydrogen bonds and tighter packing of the molecules. The refractive index of ChCl:Gly (1.47-1.48) was higher than ChCl:LA (1.44-1.46), with a trend similar to density. The viscosities of ChCl:Gly (0.235-0.453 Pa s) and ChCl:LA (0.04-0.06 Pa s) increased with increasing LA/Gly molar ratio but decreased with temperature due to the high kinetic energy from heating, lowering the attractive forces between molecules. The activation energy for ChCl:LA (15.29-15.55 kJ mol-1) is greater than for ChCl:Gly (7.77-8.78 kJ mol-1), indicating that ChCl:LA has a greater viscosity-temperature dependence than ChCl:Gly. The DESs decomposition temperatures are 179.73-192.14 °C for ChCl:LA and 189.69-197.41 °C for ChCl:Gly. Freezing temperatures are correlated with the molecular weight of HBDs, with lower values causing a larger decrease in freezing temperatures. The interactions of polyols with anions were stronger than those of α-hydroxy acids with anions. The variations in HBA to HBD molar ratios affected DESs properties, providing a fundamental understanding of the properties critical for their diverse applications.
Pretreatment is an essential upstream process to deconstruct oil palm empty fruit bunch fiber (OPEFBF) prior to sugars production. This study aimed to investigate the efficiency of OPEFBF pretreatment using palm oil mill effluent (POME) as solvent. The effect of alkali catalyst (5%w/w NaOH and ammonia), temperature (90,120,135 °C) and time (60,120,180 min) on the efficiency of pretreatment (OPEFBF-to-solvent ratio of 1:25) was also investigated. The results indicated that POME-pretreatment (135 °C, 180 min) enhanced glucose yield by only ~56%. Glucose production was increased about 5.8-fold to 495.3 ± 5.9 mg g-1 OPEFBF when NaOH was added in POME-pretreatment (Na-P). The xylose production from OPEFBF was increased about 3.7-fold after ammonia-catalyzed POME-pretreatment. About 12.1 ± 0.2 g L-1 of ethanol was produced from Na-P-hydrolysate at molar conversion of 59.4 ± 1.4%. This research provides new insight into the use of POME as a cost-effective pretreatment solvent of OPEFBF to reduce upstream process cost by cutting down water usage.
Biomass wastes exhibit a great potential to be used as a source of non-depleting renewable energy and synthesis of value-added products. The key to the valorization of excess lignocellulosic biomass wastes in the world lies on the pretreatment process to recalcitrant barrier of the lignocellulosic material for the access to useful substrates. A wide range of pretreatment techniques are available and advances in this field is continuously happening, in search for cheap, effective, and environmentally friendly methods. This review starts with an introduction to conventional approaches and green solvents for pretreatment of lignocellulosic biomass. Subsequently, the mechanism of actions along with the advantages and disadvantages of pretreatment techniques were reviewed. The roles of choline chloride (ChCl) in green solvents and their potential applications were also comprehensively reviewed. The collection of ideas in this review serve as an insight for future works or interest on biomass-to-energy conversion using green solvents.
Since the introduction of deep eutectic solvent (DES) in biomass processing field, the efficiency of DES in lignocellulosic biopolymer model compounds' (cellulose, hemicellulose and lignin) solubilisation and conversion was widely recognized. Nevertheless, DES's potential for biorefinery application can be reflected more accurately through their performance in raw lignocellulosic biomass processing rather than model compound conversion. Therefore, this review examines the studies on raw lignocellulosic biomass fractionation using DES and the subsequent conversion of DES-fractionated products into bio-based products. The review stresses on three key parts: performance of varying types of DESs and pretreatment schemes for biopolymer fractionation, properties and conversion of fractionated saccharides as well as DES-extracted lignin. The prospects and challenges of DES implementation in biomass processing will also be discussed. This review provides a front-to-end view on the DES's performance, starting from pretreatment to DES-fractionated products conversion, which would be helpful in devising a comprehensive biomass utilization process.
This is the first study to provide a preliminary investigation into the recovery of protein from wheat germ and the prediction of their extraction conditions in microwave cavity using a novel DES solvent. The response surface methodology was used to predict the microwaved protein extraction conditions of the DWG. The effects of DES buffer-concentration (X1: 0.01-1.00 g/mL), microwave power (X2: 50-250 W), irradiation time (X3: 1-5 min) and sample-to-buffer ratio (X4: 1:10-1:50) were tested using a single factor and Box-Behnken experimental design. Under the optimized conditions (X1 = 0.52 g/mL, X2 = 186 W, X3 = 3.28 min, and X4 = 1:39) protein yield and absorbed microwave were obtained at the optimal value of 33.00 % and 677 J/min, respectively with no denaturation of the protein as validated from the SDS-PAGE gel electrophoresis profile. Consequently, this investigation provides a practical approach for the extraction of bioactive protein from DWG using a novel deep eutectic solvent.
In the present work, the synthesis of cellulose nanowhiskers (CNW)/chitosan nanocomposite films via deep eutectic solvents (DES) changing the chemical structures were carried out. It was observed that a pure chitosan film has broadband at 3180-3400 cm-1, indicating amide and hydroxyl groups. Upon CNW incorporation, the peak gets sharper and stronger and shifts to a greater wavelength. Further, the addition of DES infuses more elements of amide into the nanocomposite films. Moreover, the mechanical properties incorporating CNW filler into a chitosan matrix show an enhancement in tensile strength (TS), Young's modulus (YM), and elongation at break. The TS and YM increase while the elongation decrease as the CNW concentration increases. The YM of biocomposite films is increased to 723 MPa at 25% CNW into chitosan films. Besides, the TS has enhanced to 11.48 MPa at 15% CNW concentration in the biocomposite films. The elongation at break has decreased to 11.7% at 25% CNW concentration. Hence, incorporating CNW into the chitosan matrix via DES can still improve the mechanical properties of the nanocomposite films. Therefore, the application of DES results in a lower YM and TS as the films are hygroscopic. In conclusion, DES can be considered the new green solvent media for synthesizing materials. It has the potential to replace ionic liquids due to its biodegradability and non-toxic properties while preserving the character of low-vapour pressure. Besides that, chitosan can be used as potential material for applications in process industries, such as the biomedical and pharmaceutical industries. Thus, DES can be used as a green solvent and aim to reduce the toxic effect of chemicals on the environment during chemical production.
The temperature dependence of the density, dynamic viscosity and ionic conductivity of several deep eutectic solvents (DESs) containing ammonium-based salts and hydrogen bond donvnors (polyol type) are investigated. The temperature-dependent electrolyte viscosity as a function of molar conductivity is correlated by means of Walden's rule. The oxidation of ferrocene (Fc/Fc+) and reduction of cobaltocenium (Cc+/Cc) at different temperatures are studied by cyclic voltammetry and potential-step chronoamperometry in DESs. For most DESs, chronoamperometric transients are demonstrated to fit an Arrhenius-type relation to give activation energies for the diffusion of redox couples at different temperatures. The temperature dependence of the measured conductivities of DES1 and DES2 are better correlated with the Vogel-Tamman-Fulcher equation. The kinetics of the Fc/Fc+ and Cc+/Cc electrochemical systems have been investigated over a temperature range from 298 to 338 K. The heterogeneous electron transfer rate constant is then calculated at different temperatures by means of a logarithmic analysis. The glycerol-based DES (DES5) appears suitable for further testing in electrochemical energy storage devices.
Ionic liquids (ILs), a potentially attractive "green," recyclable alternative to environmentally harmful volatile organic compounds, have been increasingly exploited as solvents and/or cosolvents and/or reagents in a wide range of applications, including pretreatment of lignocellulosic biomass for further processing. The enzymatic delignification of biomass to degrade lignin, a complex aromatic polymer, has received much attention as an environmentally friendly process for clean separation of biopolymers including cellulose and lignin. For this purpose, enzymes are generally isolated from naturally occurring fungi or genetically engineered fungi and used in an aqueous medium. However, enzymatic delignification has been found to be very slow in these conditions, sometimes taking several months for completion. In this chapter, we highlight an environmentally friendly and efficient approach for enzymatic delignification of lignocellulosic biomass using room temperature ionic liquids (ILs) as (co)solvents or/and pretreatment agents. The method comprises pretreatment of lignocellulosic biomass in IL-aqueous systems before enzymatic delignification, with the aim of overcoming the low delignification efficiency associated with low enzyme accessibility to the solid substrate and low substrate and product solubilities in aqueous systems. We believe the processes described here can play an important role in the conversion of lignocellulosic biomass-the most abundant renewable biomaterial in the world-to biomaterials, biopolymers, biofuels, bioplastics, and hydrocarbons. Graphical Abstract.