Aqueous Hydrotropic Solution Research Articles

Effect of anionic and nonionic hydrotropes on the clouding behavior and thermodynamic properties of nonionic surfactant and ciprofloxacin hydrochloride drug mixture

In the present study, the cloudy development of nonionic triton X-100 (TX-100) and an antibiotic drug ciprofloxacin hydrochloride (CFH) mixture has been conducted by applying the cloud point (CP) measurements method. The CP of TX-100 + CFH mixture was examined in aqueous solutions of hydrotropes (HDTs) (sodium benzoate (NaBenz), sodium salicylate (NaSal), 4-amino benzoic (4-ABA), polyethylene glycol (PGE) and Caffeine (CAF)). The TX-100 and CFH concentration were conserved constant at 50 and 1 mmol kg−1 correspondingly throughout the investigation. The CP values of TX-100 + CFH solution were augmented in the existence of NaBenz, NaSal, CAF along with PEG but diminished in aq. 4-ABA solution; the effects were obtained to be augmented with the enhancing hydrotropes contents. The CP values for TX-100 + CFH mixture in aq. hydrotropes media follow the pattern: CP(aq.4-ABA)<CPaq.CAF≈CPaq.PEG<CPaq.NaBenz<CPaq.NaSal. Therefore, the solubility of TX-100 + CFH mixture is achieved to be decreased in aq. solutions of 4-ABA while the solubility experienced an enhancement in aq. NaSal, NaBenz, PEG and CAF solutions. Among hydrotropes used in the present study, NaSal is the most effective solubility enhancer. The free energy (ΔGc0) were achieved to be positive in all the solvent media used in the study which exposes that the cloudy development process isnot spontaneous. The enthalpy (ΔHc0) and the entropy (ΔSc0) of clouding were obtained to be positive in hydrotropes media. The ΔHc0 and ΔSc0 values imply that the main forces of the cloudy formation in TX-100 and CFH system are hydrophobic interaction, hydrogen bonding, and electrostatic interactions. The compensation temperature (Tc) along with the intrinsic enthalpy gain (ΔHc0,∗) were also calculated and discussed. It is probable that the knowledge gained from these types of studies will be quite helpful in both pharmaceutics formulations and drug delivery system.

Advanced Fractionation of Kraft Lignin by Aqueous Hydrotropic Solutions

Lignin is an underutilized high-potential biopolymer that has been extensively studied over the past few decades. However, lignin still has drawbacks when compared with well-known petroleum-based equivalents, and the production of tailored lignin fractions is highly in demand. In this work, a new method for the fractionation of Lignoboost Kraft Lignin (LKL) is proposed by using two different hydrotropes: sodium xylenesulfonate (SXS) and sodium cumenesulfonate (SCS). The different fractions are obtained by sequentially decreasing the hydrotropic concentration with the addition of water. Four and three different fractions were retrieved from the use of SXS and SCS, respectively. The LKL and respective fractions were analysed, and compared by GPC, FTIR-ATR, 1H-NMR, 13C-NMR, 31P NMR, 2D HSQC and SEM. The fractions showed different molecular weights, polydispersity, and amount of functional groups. Our water-based lignin fractionation platform can potentially be combined with different lignin extraction and processing technologies, with the advantage of hydrotrope recycling.

Hydrotrope assisted green synthesis of dicoumarols and in silico and in vitro antibacterial, antioxidant and xanthine oxidase inhibition studies

Aqueous hydrotrope has been employed for the first time to synthesize heteroaryl dicoumarols by condensation of 4-hydroxycoumarin and different heterocyclic aldehydes. This method is highly efficient and green, and the same aqueous hydrotropic solution can be used up to five times without any considerable loss of yield in the product. The synthesized compounds showed good antibacterial potential against Gram-positive (Staphylococcus aureus/NTCC 0997 and B. oceanisediminis) and Gram-negative (Escherichia coli/D0157:H7 and E. coli rosetta) bacterial strains using the Resazurin microtiter plate visual method. The MIC value of 312 µg/ml for compounds 3b, 3k and 3l for S. aureus while 39 µg/ml for compounds 3a, 3b and 3k for E. coli and 625 µg/ml for 3a and 3b for B. oceanisediminis was observed. The compounds were screened via computational methods like molecular docking studies and molecular dynamic simulations with PDB Id’s 2W9S and 2EX6. Antioxidant activity was assessed using DPPH and H2O2 assays. Five compounds with the best binding score in molecular docking with XO (PDB ID: 1FIQ) have been tested in an in-vitro study using an enzyme inhibition assay. Novel compound 3b gave the IC50 value of 0.28 µg/ml, comparable to the standard drug Allopurinol. Communicated by Ramaswamy H. Sarma

Selection of hydrotropes for enhancing the solubility of artemisinin in aqueous solutions

Artemisinin is an antimalarial substance very sparingly soluble in water. In the attempt to identify environmental-friendly and non-toxic aqueous-based solvents to extract it from Artemisia annua L., the solubility of artemisinin in aqueous solutions of different hydrotropes was measured at 303.2 K, for hydrotrope concentrations up to 5 M. The ability of the studied hydrotropes for enhancing the artemisinin solubility increases in the following order: Na[N(CN)2] < Na[SCN] < [Chol][Van] < [Chol][Gal] < [N4,4,4,4]Cl < [Chol][Sal] < [P4,4,4,4]Cl < Na[Sal], with Na[Sal] allowing an increase in the solubility of 750 fold compared to pure water.The COSMO-RS model and experimental Kamlet-Taft solvatochromic parameters were applied to connect the solubility enhancement with solvent properties. At low hydrotrope concentration, the solubility increases with the decreasing of the difference between the Apolar Factors of the hydrotrope and artemisinin, while for higher hydrotrope concentration, the hydrogen-bond acceptor character of the hydrotrope seems to have an impact on the solubility enhancement. Even if some mechanistic understanding is still to unfold, quantitatively the empirical correlations of solubility enhancement with the hydrotrope concentration and the solvatochromic parameters show very high accuracy. In particular, 93% of the change on the artemisinin solubility enhancement could be explained using the hydrotrope concentration and two combined solvatochromic parameters (αβ and π*2) as explaining variables.

An aqueous hydrotropic solution as environmentally benign reaction medium for organic transformations: a short review

An aqueous hydrotropic solution as environmentally benign reaction medium for organic transformations: a short review

Aggregation structure in {water + tert-butanol + benzyl alcohol} ternary solution: Measurements of density and conductivity

In this work, the densities of {water + tert-butanol (TBA) + benzyl alcohol (BA)} ternary solutions were measured, from which the formation and structure transition in {water + TBA + BA} ternary solutions were investigated and discussed. In {water + TBA + BA} ternary solution, at fixed mole number of BA molecules, the BA molecules in the system first present as free BA molecules and BA/TBA dimers, while further increase of TBA concentration would result in the interactions of BA molecules with different types of TBA/water aggregates that was directly reflected by the change of the volumetric properties. Moreover, the change of molar conductivity Λm(NaBr) of NaBr and the maximum absorbance length of methyl orange λmax in ternary system have been determined at different fixed values of TBA concentrations, where various changes of Λm(NaBr) and λmax with BA mass fraction were displayed due to the formation and transition of different microstructures. The results reported herein suggested that the fine structure transitions in hydrotrope solutions can be well reflected by the variance of thermodynamic properties, which may provide an efficient way to investigate the structure change in aqueous hydrotrope solution.

Brönsted acid hydrotrope combined catalysis in water: a green approach for the synthesis of indoloquinoxalines and bis-tetronic acids

The present work describes the applications of Bronsted acid hydrotrope combined catalyst (BAHC) as a mild, efficient and reusable catalyst for synthesis of indoloquinoxalines and bis-tetronic acids in water. Using BAHC, we synthesized many indoloquinoxaline derivatives from isatins and o-phenylene diamine using 10 mol% PTSA in 40% aqueous hydrotropic (NaPTS) solution at room temperature with 83–90% yields. On the other hand, the reaction of tetronic acid with the aldehydes/isatins forms bis-tetronic acids with 83–88% yields through Knoevengel condensation-Michael addition pathway in same BHAC. Moreover, the BAHC can be recycled upto 5th cycles with slight decrease in product yields. The extremely simple operational methodology, green solvent, ambient reaction conditions and high yields render this approach extremely appealing for the synthesis of different heterocyclic compounds.

Green preparation of lignin nanoparticles in an aqueous hydrotropic solution and application in biobased nanocomposite films

Abstract Lignin nanoparticles (LNPs) from lignocellulosic biomass are expected to become promising basic building blocks for various applications in the development of multifunctional nanocomposites. Facile green preparation of LNPs and their application in polyvinyl alcohol (PVA) composite films were studied in this paper. LNPs were produced by performing fractionation of wheat straws at less than 80 °C with a recyclable hydrotropic, aqueous p-toluene sulfonic acid (p-TsOH). The dissolved lignin could be simply separated as LNPs by diluting the spent liquor (SL) to below the minimal hydrotropic concentration (MHC) of 11.5%. The resulting LPNs exhibited an oblate spheroid morphology and a uniform particle size distribution. After introducing the available LNPs into the PVA matrix at 6% loading, the nanocomposite products could block 100 and 95% of UV light at 315 and 400 nm, respectively, and exhibited 80% antioxidant activity. In addition, the respective maximum TS and TM were 59.7 MPa and 2.07 GPa, respectively, which were increases of approximately 36 and 104% compared with those of pure PVA film. The LNPs/PVA nanocomposite films displayed improved UV resistance, mechanical properties, thermal stability and antioxidant activity and could be used as additional multifunctional agents in the fields of biodegradable plastics, tissue engineering and UV-protective biobased materials.

Thermodynamic properties and structure transition in {water + tert-butanol} and {water + tert-butanol + iso-butanol} solutions

Different microscopic and thermodynamic properties like the resonance light scattering intensity, microenvironment polarity, the density and heat capacity of {water + TBA} binary solution and the density of {water + TBA + IBA} ternary solution were precisely measured. Formation and structure transitions of alcohol-water aggregate in TBA aqueous solution and {water + TBA + IBA} ternary solutions at different compositions were investigated by analysis of both microscopic and thermodynamic properties. It is indicated from the results that the fine structure transitions in hydrotrope solutions can be well reflected by the variance of thermodynamic properties, which provides an efficient way to give deeper insight into the structure changes in aqueous hydrotrope solutions.

Aqueous hydrotropic solution: green reaction medium for synthesis of pyridopyrimidine carbonitrile and spiro-oxindole dihydroquinazolinone derivatives

From the green chemistry point of view, water is one of the most sustainable solvents for chemical transformations, but there are some limitations to its use as a reaction medium due to the lack of solubility of organic compounds. To overcome this difficulty, we used aqueous hydrotropic solution, which increases the solubility of organic compounds in water by 200-fold. We report an environmentally efficient method for synthesis of pyridopyrimidine carbonitriles and spiro-oxindole dihydroquinazolinones by using 50 % aqueous sodium p-toluene sulfonate (NaPTS) solution at ambient reaction condition. The merits of the present protocol include short reaction time, excellent product yield with high purity, easy workup procedure and reusability of reaction medium.

The Calotropis procera Transformed Green NiO and Fe‐NiO Nanoparticles for Diaryl Pyrimidinones Synthesis in Hydrotropic Medium at Room Temperature

AbstractWe report the synthesis of NiO and Fe doped NiO nanoparticles by simple and cost effective Calotropis procera leaf extract assisted green co‐precipitation method. The leaf extract of Calotropis procera acts as reducing as well as capping agent for the synthesis of NiO and Fe doped NiO. The presence of –OH and aldehydic group (‐CHO) on synthesized nanoparticle imparts their strong interaction with synthesized nanoparticles, conveying efficient catalyst for heterocycle synthesis. The proficient catalytic application of biogenic NiO and Fe doped NiO NPs were explored in aqueous hydrotropic solution for syntheses of diaryl pyrimidinones at room temperature. The synthesized catalysts are efficient in terms of yield, reaction time and reusability. The NiO or Fe doped NiO/NaPTS/27°C is efficient, highly sustainable catalytic system for heterocycle synthesis at room temperature. Accordingly, Fe doped NiO/NaPTS proved to be a better catalytic system than NiO/NaPTS in water.

Green synthesis of lignin nanoparticle in aqueous hydrotropic solution toward broadening the window for its processing and application

To exploit a green way to produce polymer nanoparticles using biodegradable and renewable macromolecules instead of petroleum-based ones, we initiated a novel and facile method to synthesize lignin nanoparticles (LNPs). The LNPs, having a hydrodynamic diameter ranging from ca. 80 to 230 nm, were formed by self-assembly in a recyclable and non-toxic aqueous sodium p-toluenesulfonate (pTsONa) solution at room temperature, with a lowest concentration of up to 48 g/L. We eliminated the unfavorable factors of restricted processing pH and lignin species by taking advantage of the hydrotropic chemistry and the synergistic dissociation of the entrapped pTsONa and intrinsic phenolic hydroxyl and carboxylic acid moieties of the LNPs. Because of the hydrotropic system, various water-soluble or water-insoluble drugs can be dissolved and encapsulated in the LNPs with an encapsulation efficiency of up to 90%. The drug-encapsulated LNPs also showed great properties, with sustained drug-releasing capability and biocompatibility. Furthermore, the unloaded drugs and free pTsONa could be easily recycled for multiple use, thereby achieving environmental sustainability. This synthesis approach with broad processing window could realize the industrial scale-up production of LNPs and have wide potential applications, including but not limited to versatile drug/bioactive macromolecule loading in the biomedical field.

Novel catalytic application of Ni@ZnO nanoparticles and ZnO nanoflakes in aqueous solution of NaPTS hydrotrope at room temperature via a green synthesis of 3,4-dihydropyrimidin-2(1H)-ones

We investigated a novel catalytic application of nickel-doped zinc oxide (Ni-ZnO) nanoparticles and zinc oxide (ZnO) nanoflakes at room temperature in an aqueous hydrotropic solution for the synthesis of biologically active dihydropyrimidones (DHPMs). Ni-ZnO is a stable, recyclable, green, efficient heterogeneous catalyst which shows maximum yield in a shorter reaction time than ZnO nanoflakes in very mild conditions of hydrotropic aqueous medium for DHPMs syntheses.

Crystallization of Curcumin and Cinnamic Acid from Aqueous Solutions of Hydrotropes

Batch crystallization studies of curcumin from hydrotropic solutions of sodium cumenesulphonate (NaCS) and of cinnamic acid from a photosensitive hydrotropic medium of sodium cinnamate (Na-CIN) were carried out, in an agitated reactor for the effect of alternate heating and cooling cycles on crystal morphology. The crystal characterization by Scanning electron microscopy (SEM) and crystal size distribution (CSD) showed formation of spheroidal curcumin crystals while cinnamic acid formed porous aggregates when subjected to thermal cycles. The UV irradiation of cinnamic acid however showed no formation of the aggregates. The type of hydrotrope used and the initial crystal morphologies of curcumin and cinnamic acid are shown to be important factors to result in a different behaviour of the crystal morphology upon thermal cycles. The CSD data were effectively used for estimation of nucleation and growth rate parameters.

Delignification of cotton stalks using sodium cumene sulfonate for bioethanol production

ABSTRACTThe objective of this study was to evaluate the effect of hydrotropic delignification of cotton stalk on sugar release performance for bioethanol production. In this study, different alkyl benzene sulfonates were screened to select the best pretreatment agent, and the effectiveness of pretreatment was evaluated by enzymatic saccharification. Sodium cumene sulfonate was found to be the best hydrotropic agent in terms of reducing sugar yield. Parameters such as hydrotrope concentration, biomass loading and incubation time were optimized by adopting a central composite design. Under optimized pretreatment conditions, 0.211 g reducing sugar/g of dry biomass was obtained. Reusability of aqueous hydrotrope solution was also demonstrated.

ChemInform Abstract: Ligand‐Free Pd Catalyzed Cross‐Coupling Reactions in an Aqueous Hydrotropic Medium.

A simple, efficient and ligand-free protocol for the Suzuki–Miyaura reaction and base-free Heck–Matsuda reactions under mild reaction conditions have been developed over palladium supported on activated carbon (Pd/C) in an aqueous hydrotropic solution. The catalyst Pd/C was fully characterized by TG-DTA, SEM, EDS, XRD, XPS, BET and ICP-AES analyses. This green methodology represents a cost-effective and operationally convenient method for the synthesis of a variety of biaryls, prochiral ketones, and acrylates under the conditions that are tolerant for a broad range of functional groups with good to excellent yields. The developed Pd/C–aqueous hydrotrope combined catalytic system is well suited for the 3R approach (reducible, robust, and recyclable) for different cross-coupling reactions without an appreciable loss of its activity.

Hydrotropic pretreatment on rice straw for bioethanol production

The aim of this study was to investigate the effect of hydrotrope as a pretreatment process on rice straw for bioethanol production. Sodium cumene sulfonate and sodium xylene sulfonate (Na–X) were used as hydrotropes to delignify rice straw. Effects of biomass loading, time, temperature and hydrotrope concentration were studied for both the hydrotropes. There was no loss of cellulose & hemicellulose in the hydrotrope solution. Sodium cumene sulfonate could remove more than 50% of lignin from rice straw with 5% biomass loading at 121 °C for 1 h. Reusability of aqueous hydrotrope solution was demonstrated. Enzymatic digestibility of the hydrotrope pretreated rice straw was studied and evaluated for subsequent bioethanol production. The use of the hydrotrope for biomass pretreatment has the potential to mitigate the environmental impact of chemical pretreatment.

Ligand-free Pd catalyzed cross-coupling reactions in an aqueous hydrotropic medium

A simple, efficient and ligand-free protocol for the Suzuki–Miyaura reaction and base-free Heck–Matsuda reactions under mild reaction conditions has been developed over palladium supported on activated carbon (Pd/C) in an aqueous hydrotropic solution.

Aqueous hydrotrope: an efficient and reusable medium for a green one-pot, diversity-oriented synthesis of quinazolinone derivatives.

A library of quinazolinones was prepared by the one-pot three-component reaction of isatoic anhydride, ammonium salts/amines, and various electrophiles using aqueous hydrotropic solution as an efficient, economical, reusable, and green medium giving good to excellent yields of products in very short time. The method offers a versatile way for the development of diversity-oriented synthesis of quinazolinones.

Aza-Micheal Reaction in Glycerol as a Sustainable Hydrotropic Medium

The organic transformation carried out in suitable solvent as well as in presence of catalyst is more important due to its environmental impact. We try to optimize the organic transformation in aqueous hydrotropic solution because of it is a sustainable technique. Now days, the glycerine used as hydrotrope and it shows excellent hydrotropic properties. Glycerine has been show combine advantages of water like non-toxic, colourless, odourless liquid, large availability, renewability due to this important properties it recently proposed as a valuable green solvent.