Low Transition Temperature Mixtures Research Articles

The effect of 2-hydroxypropyl β-cyclodextrin on the stability of polyphenolic compounds from Moringa oleifera Lam leaf extracts in a natural low-transition temperature mixture

Abstract Polyphenol extracts from Moringa oleifera leaves (MoL) were obtained with a glycerol-based low-transition temperature mixture (LTTM) and a combination of LTTM with 2-hydroxypropyl β-cyclodextrin (HP-β-CD). The extracts were maintained at 4, 22 and 50 °C for 18 days and the antiradical activity (AAR) was recorded to detect modifications in the antioxidant activity of the extracts. AAR displayed a constant decline at every temperature tested, following pseudo first-order kinetics and the decay constants suggested that the presence of HP-β-CD had a protective action, slowing down AAR decline. The analysis of the polyphenolic profiles using liquid chromatography-diode array-mass spectrometry revealed that after storage for 18 days at 50 °C, the major quercetin glycosides occurring in MoL were extensively degraded. Based on the detection of protocatechuic acid in the stored extracts, putative pathways of flavonol glycoside degradation were proposed. It was concluded that the decomposition of these components was mainly responsible for the AAR decline observed.

Liquid–Liquid Extraction of Benzene and Cyclohexane Using Sulfolane-Based Low Transition Temperature Mixtures as Solvents: Experiments and Simulation

The separation of benzene and cyclohexane is considered to be one of the most challenging processes in the petrochemical industry. In this paper, low transition temperature mixtures (LTTMs) were used as solvents for the separation of benzene and cyclohexane. The selected LTTMs were sulfolane–tetrabutylammonium bromide 5:1 and ethylene glycol–trimethylamine hydrochloride 5:1, and liquid–liquid equilibrium (LLE) data of benzene–cyclohexane–LTTMs were experimentally determined at 40 °C under a normal atmosphere. Moreover, the effects of the mole ratio of hydrogen bond donor (HBD) sulfolane and hydrogen bond acceptor (HBA) tetrabutylammonium bromide on extraction performance were also observed based on the LLE data. It is found that, when the mole ratio of sulfolane to tetrabutylammonium bromide is 5:1, LTTM has the best extraction performance. In addition, the LLE data of the benzene–cyclohexane–LTTMs ternary system were used to fit parameters of the NRTL activity coefficient model. Based on the NRTL model the continuous extraction process was simulated and the operating parameters were obtained, and high product purity (cyclohexane 0.997) and high recovery efficiency (cyclohexane 93.28% and benzene 98.25%) can be achieved. In conclusion, the LTTM sulfolane–tetrabutylammonium bromide 5:1 is a promising solvent for the extractive separation of benzene–cyclohexane mixtures.

Incorporation of 2-hydroxypropyl β-cyclodextrin in a biomolecule-based low-transition temperature mixture (LTTM) boosts efficiency of polyphenol extraction from Moringa oleifera Lam leaves

A novel LTTM composed of glycerol and sodium acetate was used to assess the effect of 2-hydroxypropyl β-cyclodextrin (CD) on the effectiveness of polyphenol extraction from M. oleifera leaves (MoL). The extraction process was based on a 23-full factorial design and response surface methodology, to evaluate simultaneously the effect of CD concentration (CCD), liquid-to-solid ratio (RL/S) and temperature (T). By employing optimized conditions (CCD = 1%, RL/S = 40 mL g−1, T = 40 °C), the yield in total polyphenols (YTP) was 67.18 ± 5.04 mg gallic acid equivalents per g dry weight. This yield was significantly higher than that achieved with the extraction performed with LTTM alone or 80% aqueous ethanol. The extraction kinetics suggested that the extraction rate was slowed down in the presence of CD, without compromising the higher extraction capacity of the LTTM/CD. Extract characterization by means of liquid chromatography-mass spectrometry showed that there was no selective extraction of any particular polyphenol, indicating that CD acted only as an extraction booster.

Thermogravimetric analysis and kinetic modeling of low-transition-temperature mixtures pretreated oil palm empty fruit bunch for possible maximum yield of pyrolysis oil

The impacts of low-transition-temperature mixtures (LTTMs) pretreatment on thermal decomposition and kinetics of empty fruit bunch (EFB) were investigated by thermogravimetric analysis. EFB was pretreated with the LTTMs under different duration of pretreatment which enabled various degrees of alteration to their structure. The TG-DTG curves showed that LTTMs pretreatment on EFB shifted the temperature and rate of decomposition to higher values. The EFB pretreated with sucrose and choline chloride-based LTTMs had attained the highest mass loss of volatile matter (78.69% and 75.71%) after 18 h of pretreatment. For monosodium glutamate-based LTTMs, the 24 h pretreated EFB had achieved the maximum mass loss (76.1%). Based on the Coats-Redfern integral method, the LTTMs pretreatment led to an increase in activation energy of the thermal decomposition of EFB from 80.00 to 82.82–94.80 kJ/mol. The activation energy was mainly affected by the demineralization and alteration in cellulose crystallinity after LTTMs pretreatment.

Electrodeposition of zinc from low transition temperature mixture formed by choline chloride + lactic acid

Electrodeposition of zinc from low transition temperature mixture (LTTM) formed by choline chloride + lactic acid is studied in this work. Electrochemical techniques were used to characterize the deposition process and scanning electron microscopy was used to study the deposit morphology. Phase and chemical composition were determined by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). It has been shown that zinc can be directly deposited on steel in LTTM formed by choline chloride + lactic acid. The surface morphology of Zn deposits is dense and the corrosion current densities (Ecorr) of Zn shifts to more negative than that of substrate.

Simulation and experiment for ethanol dehydration using low transition temperature mixtures (LTTMs) as entrainers

In this work, the separation of ethanol-water azeotrope which was choosing low transition temperature mixtures (LTTMs) as entrainers was investigated through process simulation and batch extractive distillation experiment. Based on the vapor-liquid equilibrium (VLE) curves of ethanol-water with LTTMs and the residual curves of LTTMs-ethanol-water, glycolic acid–choline chloride 3:1(GC3:1) was selected as the entrainer to simulate ethanol-water mixtures separation, and the sensitive analysis was performed in order to determine the main design variables. On this basis, the traditional process was further improved through the optimization of heat exchanger network, and the energy consumption was reduced by 46.24% and 37.00% compared with the ethylene glycol and 1-Ethyl3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), respectively. In addition, GC3:1 was synthesized and used as solvent to separate the mixture of ethanol-water in the batch extractive distillation, which can obtain high-purity ethanol at the top of distillation column. Fourier Transform Infrared Spectrum (FT-IR) was used to analyze the recycled GC3:1, and it suggested that the chemical properties of GC3:1 were stable and GC3:1 could be reused depending on the infrared spectrum of used GC3:1. The advantage of GC3:1 as entrainer for the separation of ethanol-water azeotrope was proved through the combination of process simulation and experiment.

Choline chloride (ChCl) and monosodium glutamate (MSG)-based green solvents from optimized cactus malic acid for biomass delignification

This work aimed to develop an efficient microwave-hydrothermal (MH) extraction of malic acid from abundant natural cactus as hydrogen bond donor (HBD) whereby the concentration was optimized using response surface methodology. The ideal process conditions were found to be at a solvent-to-feed ratio of 0.008, 120°C and 20min with 1.0g of oxidant, H2O2. Next generation environment-friendly solvents, low transition temperature mixtures (LTTMs) were synthesized from cactus malic acid with choline chloride (ChCl) and monosodium glutamate (MSG) as hydrogen bond acceptors (HBAs). The hydrogen-bonding interactions between the starting materials were determined. The efficiency of the LTTMs in removing lignin from oil palm biomass residues, empty fruit bunch (EFB) was also evaluated. The removal of amorphous hemicellulose and lignin after the pretreatment process resulted in an enhanced digestibility and thermal degradability of biomass.

Low transition temperature mixtures prompted one-pot synthesis of 5, 10 dihydropyrimido[4,5-b]quinoline-2,4(1H,3H)-dione derivatives

An efficient green protocol has been investigated for the synthesis of pyrimido[4,5-b]quinolines derivatives via one-pot three-component condensation of 4-chloro aniline, aromatic aldehyde and barbituric acid using low transition temperature mixtures as new generation and sustainable solvents. The process was accomplished with the use of greener and recyclable reaction media, simple methodology, easy workup procedures and no chromatographic purification with high yield. This new approach is expected to discover some significance in combinatorial synthesis of biologically active scaffolds.

Low melting oxalic acid dihydrate: proline mixture as dual solvent/catalyst for synthesis of spiro[indoline-3,9′-xanthene]trione and dibarbiturate derivatives

A simple, proficient and an elegant synthetic route for the synthesis of spiroxanthene and dibarbiturate derivatives has been developed under the umbrella of green chemistry. The operational simplicity, good to excellent product yields, easy workup procedures and non-chromatographic purification procedure are remarkable features of this protocol. Furthermore, the use of low transition temperature mixture as green reaction medium reduces burden on environment and makes the present method environmentally sustainable. The calculated values of green chemistry metrics are found to be in well agreement with ideal values signifying greenness of developed protocol.

Enhanced extraction of antioxidant polyphenols from Moringa oleifera Lam. leaves using a biomolecule-based low-transition temperature mixture

In this study, the extraction of polyphenols from Moringa oleifera leaves was investigated, using a biomolecule-based low-transition temperature mixture (LTTM), composed of glycerol and sodium acetate. The first step was to optimise LTTM concentration (C LTTM) and the molar ratio (R mol) of glycerol-to-sodium acetate, by employing a Box–Behnken experimental design. Following this, a kinetic assay was undertaken to assess the effect of temperature. A maximum yield in total polyphenols (Y TP = 53.80 mg gallic acid equivalents per g lyophilised material) was achieved using a C LTTM = 80% (w/v) and a R mol = 6. The extraction followed a second-order model, requiring activation energy (E a) of 55.71 kJ mol−1. Comparative evaluation using 80% ethanol showed that the LTTM used was significantly more efficient in extracting polyphenols and flavonoids, yielding extracts with higher reducing power. However, results concerning the antiradical activity were contradictory. Liquid chromatography–diode array–mass spectrometry examination of both the LTTM and the hydroalcoholic extracts revealed some qualitative differences, which might indicate selectivity of the LTTM towards relatively polar substances.

Ultrasound-Assisted Extraction of Polyphenolic Antioxidants from Olive (Olea europaea) Leaves Using a Novel Glycerol/Sodium-Potassium Tartrate Low-Transition Temperature Mixture (LTTM)

Olive leaves (OLL) represent a major waste generated during the production of olive oil, but there is a great potential for their valorization, because they provide important content in polyphenolic phytochemicals, which possess several bioactivities. In spite of the high number of studies dealing with polyphenol recovery from olive leaves, green processes involving environmentally benign solvents are scarce. In this study, a novel renewable natural low-transition temperature mixture (LTTM), composed of glycerol and sodium-potassium tartrate, was tested for its efficient ability to extract polyphenolic substances from OLL. The extraction process was optimised by using response surface methodology and the maximum yield in total polyphenols was 26.75 ± 3.22 mg caffeic acid equivalents per g dry weight, achieved with 50% (v/v) aqueous LTTM, liquid-to-solid ratio of 45 mL g−1 and at 73 °C. The LTTM was proven to be equally effective with 60% aqueous methanol, but it displayed inferior antioxidant properties. Liquid chromatography-diode array-mass spectrometry analyses revealed no significant qualitative differences between the LTTM and the aqueous methanolic extract.

Solvent-catalyzed umpolung carbonsulfur bond-forming reactions by nucleophilic addition of thiolate and sulfinate ions to in situ–derived nitrosoalkenes in deep eutectic solvents

The low transition temperature mixture formed by lactic acid and choline chloride proved to be effective for an umpolung carbonsulfur bond formation at the α-position of α-chloro oximes. Aliphatic, aromatic, and heteroaromatic thiolate and sulfinate ions can be smoothly added to in situ–derived nitrosoalkenes affording the corresponding sulfenylated or sulfonylated adducts, respectively, in a very good yield (up to >98%). This methodology offers the advantage of working at room temperature and under air in biodegradable and cost-effective reaction mixtures, which can be used both as solvents and catalysts (20 mol %), thereby avoiding the use of anhydrous, hazardous volatile organic solvents and an inert atmosphere.

Low-Transition Temperature Mixtures (LTTMs) Made of Bioorganic Molecules: Enhanced Extraction of Antioxidant Phenolics from Industrial Cereal Solid Wastes

Several low-transition temperature mixtures (LTTMs), based on l-lactic acid and amino acids but also choline chloride, were synthesized and screened for their effectiveness in extracting antioxidant phenolics from industrial cereal solid wastes. In most cases, highly efficient LTTMs were those composed of l-lactic acid and choline chloride, but LTTMs composed of l-lactic acid and glycine or alanine also exhibited comparable extraction capacity. The extract from barley bran was shown to express powerful antioxidant activity, which was significantly higher than all the other extracts examined. This fact was attributed to the particularly high content in total flavanols. The data suggested that the most effective solvents, as revealed herein, merit further investigation as very promising means of extracting valuable chemicals from industrial agri-food residues. Additionally, barley bran should be more thoroughly examined for its prospect as a waste source of effective antioxidants, which could be used as nutritional supplements and active cosmetic ingredients.

Optimised extraction of antioxidant polyphenols from Satureja thymbra using newly designed glycerol-based natural low-transition temperature mixtures (LTTMs)

The medicinal plant Satureja thymbra (pink savory) has been chosen to study the capacity of three newly designed glycerol-based, natural low-transition temperature mixtures (LTTMs) to extract polyphenolic antioxidants. First, it was assessed the effect of water concentration (CW) and the liquid-to-solid ratio (RL/S), by deploying response surface methodology (Box-Behnken design). As a further step, kinetics was investigated to examine the effect of temperature. It was found that the optimum CW varied from 54.8 to 63.8% (v/v) and RL/S from 29.5 to 36.2mLg−1. Under optimised conditions, all three LTTMs displayed apparent anti-Arrhenius kinetics over a temperature ranging from 40 to 80°C, evidencing peculiar extraction behaviour. The investigation of the polyphenolic composition of the extracts obtained by liquid chromatography-diode array-mass spectrometry showed that the major constituents were apigenin, luteolin, quercetin and rosmarinic acid derivatives, but none of the LTTMs exhibited notable selectivity. However, significant differences were seen with regard to the antiradical activity and reducing power of the extracts, as extract obtained with LTTM1 displayed consistently strong effects, whereas the extract obtained with LTTM3 had rather questionable efficiency.

Screening of Natural Sodium Acetate-Based Low-Transition Temperature Mixtures (LTTMs) for Enhanced Extraction of Antioxidants and Pigments from Red Vinification Solid Wastes

Low-transition temperature mixtures (LTTMs), also known as deep eutectic solvents, are liquid mixtures of natural substances that possess unique properties, not encountered with conventional solvents. Such liquids represent a state-of-the-art means of extracting bioactive plant constituents, yet the plethora of combinations of various substances that form LTTMs dictates detailed comparative testing, to identify LTTMs with high extraction capacity. In this study, a number of combinations of hydrogen bond donors (HBDs) with sodium acetate serving as the hydrogen bond acceptor (HBA), was attempted. The stable LTTMs formed were then used to extract antioxidant polyphenols and pigments from red grape pomace (RGP). The LTTM composed of L-lactic acid and sodium acetate at a molar ratio of 5:1 was found to be the most efficient solvent, giving a total polyphenol yield of 134.54 mg gallic acid equivalents per g of dry weight and a total pigment yield of 3.32 mg malvin equivalents per g of dry weight. The extract obtained with this particular LTTM also possessed the strongest antioxidant activity. The principal compounds in this extract were tentatively identified as phenolic acids, anthocyanin pigment derivatives and a flavonol glycoside.

Extraction of Antioxidant Phenolics from Agri-Food Waste Biomass Using a Newly Designed Glycerol-Based Natural Low-Transition Temperature Mixture: A Comparison with Conventional Eco-Friendly Solvents

A novel natural low transition temperature mixture (LTTM), composed of glycerol and ammonium acetate (molar ratio 3:1), was tested for its efficacy as a solvent in recovering phenolics from chlorogenate-rich agri-food solid wastes, including potato peels (PPs), eggplant peels (EPPs), and spent filter coffee (SFC). The efficacy of this solvent was compared with other eco-friendly solvents, including aqueous glycerol, aqueous ethanol, and water. The LTTM was demonstrated to be by far the most efficient in extracting chlorogenates and superior or equally efficient with the other solvents in recovering flavonoids. LTTM extracts produced from waste were also more potent radical scavengers, but results on the reducing power were inconclusive. Liquid chromatography-diode array-mass spectrometry analysis showed that the polyphenolic profiles of all waste extracts obtained with the LTTM were rich in caffeoylquinic and p-coumaroylquinic acid conjugates.

Oxalic acid dihydrate and proline based low transition temperature mixture: An efficient synthesis of spiro [diindenopyridine-indoline] triones derivatives

The new facile approach has been developed for the synthesis of spiro [diindenopyridine-indoline] triones under the umbrella of green chemistry. The developed protocol is endowed with the use of low transition temperature mixture as a green reaction medium, operational simplicity, easy workup procedures, good to excellent product yields, and non-chromatographic purification procedure. Since indenone fused motifs have a broad spectrum of biological activities, this protocol is expected to find application in the combinatorial synthesis of biologically active compounds.

Synthesis and characterization of phenol–furfural resins using lignin modified by a low transition temperature mixture

An efficient and green method for the modification of lignin by a low transition temperature mixture was used in the synthesis of phenol–furfural resins.

Efficient separation and purification of anthocyanins from saskatoon berry by using low transition temperature mixtures

Separation of anthocyanins from saskatoon berry by using low transition temperature mixtures.

Microwave-assisted hydrothermal extraction of natural malic acid for the synthesis of low transition temperature mixtures

This work describes the utilization of microwave hydrothermal extracted malic acid from cactus, lophatherum herb, papaya and Luffa cylindrica as hydrogen bond donor for the synthesis of natural low transition temperature mixtures (LTTMs) with sucrose as hydrogen bond acceptor. The effects of parameters including reaction temperature, extraction time, mass of sample and oxidant, H2O2 were discussed. The saturation equation was used to fit with the experimental data, observing only a slight loss of the goodness of fit. The optimum conditions for microwave hydrothermal extraction were found to be at 1 g of sample, 200 °C and 45 min in the presence of hydrogen peroxide (H2O2) as oxidant. Consequently, the proposed method was successfully applied to extract malic acid from plants and fruits for the synthesis of LTTMs. The LTTMs prepared from the extracted malic acid have identical physicochemical properties with the LTTMs derived from commercial malic acid due to the existence of hydrogen bond and the ability to dissolve lignin.