Polar Solvents Water Research Articles

A DFT study on protic solvent assisted tautomerization of heterocyclic thiocarbonyls

Thione-thiol tautomerization is biologically and synthetically significant proton transfer reaction. Current study analyses the effect of protic solvents on this reaction involving heterocyclic thiocarbonyl compounds having potent bioactivities such as 1,3-dihydroimidazole-2-thione, 2-thiohydantoin and 2-thiouracil. The computed catalytic effect of polar protic solvents water and methanol is explained by the favorable lone pair – antibonding orbital interactions which facilitates the required proton transfer. Microhydration study up to six water molecules has been carried out to get more insight into the explicit water-solute interaction. It has been concluded that four water molecules are enough to model explicit water-solute interaction that favorably affects the tautomerism of heterocyclic thiocarbonyl compounds. Moreover, the thione formation step of the equilibrium gets relatively more facilitated by the polar protic solvents. The results are further validated by considering a reported thiol-thione conversion in enzymatic decarboxylation reaction of 4′-phosphopantothenoylcysteine.

Graphene Oxide: A Smart (Starting) Material for Natural Methylxanthines Adsorption and Detection.

Natural methylxanthines, caffeine, theophylline and theobromine, are widespread biologically active alkaloids in human nutrition, found mainly in beverages (coffee, tea, cocoa, energy drinks, etc.). Their detection is thus of extreme importance, and many studies are devoted to this topic. During the last decade, graphene oxide (GO) and reduced graphene oxide (RGO) gained popularity as constituents of sensors (chemical, electrochemical and biosensors) for methylxanthines. The main advantages of GO and RGO with respect to graphene are the easiness and cheapness of synthesis, the notable higher solubility in polar solvents (water, among others), and the higher reactivity towards these targets (mainly due to π–π interactions); one of the main disadvantages is the lower electrical conductivity, especially when using them in electrochemical sensors. Nonetheless, their use in sensors is becoming more and more common, with the obtainment of very good results in terms of selectivity and sensitivity (up to 5.4 × 10−10 mol L−1 and 1.8 × 10−9 mol L−1 for caffeine and theophylline, respectively). Moreover, the ability of GO to protect DNA and RNA from enzymatic digestion renders it one of the best candidates for biosensors based on these nucleic acids. This is an up-to-date review of the use of GO and RGO in sensors.

DFT study of the antiradical properties of some aromatic compounds derived from antioxidant essential oils: C–H bond vs. O–H bond

This paper describes a theoretical comparative study of the antiradical properties of six aromatic compounds namely eugenol (EUG), safrole (SAF), myristicin (MYR), carvacrol (CAR), cinnamaldehyde (CIN), and isoeugenol (ISO) found in antioxidant essential oils. Using density functional theory (DFT) calculations, some structural characteristics such as molecular descriptors, frontier molecular orbitals, and molecular electrostatic potential have been studied. Three main antiradical mechanisms, hydrogen atom transfer (HAT), single electron transfer proton transfer (SETPT, and sequential proton loss electron transfer (SPLET) have been also investigated. In addition, the Gibbs free energies related to the reactions of the studied compounds with two reactive oxidant species (HO• and HOO•) have been computed. Throughout the study, the implicitly of polar and nonpolar solvents (water and benzene) has been taken into account. It was found that EUG, SAF, CIN, and ISO scavenge free radicals by means of a CH bond, while CAR and ISO by means of an OH bond. In the gas and benzene phases, all the studied compounds prefer to undergo HAT mechanism, while in water, SPLET is more favoured for CIN, CAR, and ISO and both HAT and SPLET are possible for EUG, SAF, and MYR. In all the studied mediums, the sequence of the antiradical potential is: MYR ≈ SAF ≈ ISO ≈ EUG > CAR > CIN. This order is in line with the available experimental results.

Inclusion Complexes of Some Substituted 4-Thiazolidinones with Activating and Deactivating Group

Some substituted 4-thiazolidinones have been prepared by taking 2-hydrazinobenzothiazole as a staring material. Polar solvent water makes less solubility of these compounds. Hence inclusions of compounds are prepared by taking suitable ratio of compound and β-cyclodextrin. The purpose of this work is to synthesize more soluble and more bioaccesible compounds. The synthesized compounds and their inclusions are known from the study of their thermodynamic properties and spectral characteristics (UV, IR and NMR). Pharmaceutical activity of the compounds and inclusion can be performed by using the bacteria namely E. coli, S. aureus and P. vulgaris. Considering and discussing all the matters, it has been found that inclusion formation shows more antibacterial activity than simple compound.

Bistable colloidal orientation in polar liquid near a charged wall

We examine the translation and rotation of an uncharged spheroidal colloid in polar solvents (water) near a charged flat surface. We solve the nonlinear Poisson-Boltzmann equation outside of the colloid in two dimensions for all tilt angles θ with respect to the surface normal. The colloid’s size is assumed to be comparable to the Debye’s length and hence field gradients are essential. The Maxwell stress tensor, including the ideal gas pressure of ions, is integrated over the colloid’s surface to give the total force and torque on the colloid. From the torque we calculate the effective angular potential Ueff(θ). The classical behavior where the colloid tends to align in the direction perpendicular to the surface (parallel to the field, θ=0) is retrieved at large colloid-surface distances or small surface potentials. We find a surprising transition whereby at small separations or large potentials the colloid aligns parallel to the surface (θ=90°). Moreover, this colloid orientation is amplified at a finite value of the aspect ratio. This transition may have important consequences to flow of colloidal suspensions or as a tool to switch layering of such suspensions near a surface.

Physical properties and the ability to disperse into different polar solvents of the new polyurethane–cellulose composites

Novel castor oil (CO)-based polyurethane composites which include polyethylene glycol (PEG) as a polyol and cellulose fillers were prepared. The purpose of this article was to render polyurethane composites that can be dispersed in polar solvents (ethyl alcohol, isopropyl alcohol, and water) using bio-based feedstocks such as CO and cellulose. The chemical structures of the polyurethanes and their cellulose composites were studied by Fourier transform infrared spectroscopy and nuclear magnetic resonance of protons. The atomic force microscopy results showed the surface topography of the cellulose–polyurethane composites matrix. The inclusion of cellulose has been found to improve the thermal stability of the materials and their ability to disperse into the studied polar solvents. Cellulose along with PEG plays an important role in increasing the degree of moisture within the polyurethane composite matrix. Thus, we obtained solutions in polar solvents of polyurethane–cellulose composites without the use of waterborne polyurethanes.

Hybrid Atomistic and Coarse-Grained Model for Surfactants in Apolar Solvents.

Here, we develop and verify the performance of a hybrid molecular modeling approach that combines coarse-grained apolar solvent and atomistic solute or polar solvent description, for example, for description of reverse micellar systems. The coarse-grained solvent model is directly applicable to organic solvents encompassing alkane, alkene, and fatty acid ester functional groups and connects directly to both standard united-atom GROMOS 53A6 and all-atom CHARMM27 force fields, as well as the atomistic detail water models compatible with these force fields. The different levels of description are coupled via explicit, unscaled electrostatics, and scaled mixing rules for dispersive interactions. The hybrid model is in near-quantitative agreement with fully atomistic simulations when combined with the CHARMM27 model but underestimates modestly surfactant aggregation when using GROMOS 53A6 united-atom description. The use of truncated electrostatics affords up to a 9-fold increase in computational speed without significant loss of accuracy. However, long-range electrostatic calculations and load imbalance at high core counts can significantly degrade the performance. We demonstrate the usability of the hybrid model by assessing the reverse micelle formation of a homologous series of nonionic glycerolipids via large-scale self-assembly simulations. The presented model is demonstrated here for accurate description of surfactant systems in apolar solvents, with and without also polar solvent (water) in the system. The formulation can be expected to describe well also other solute species or interfaces with an apolar solvent in an apolar environment.

Russian dandelion (<i>Taraxacum kok-saghyz</i> Rodin): rubber extraction methods and prospects for biotechnological methods application

Natural rubber is a strategic natural raw material, which is used in the production of tires and military equipment, in medicine and other industries. An alternative to Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg. and the most promising rubber plant is the Russian dandelion (Taraxacum kok-saghyz Rodin). The rubber that accumulates in the roots of this dandelion is not inferior in quality to the natural rubber from H. brasiliensis, and its content reaches 27% of the dry weight of roots. The purpose of this paper is to describe the economically important components of T. kok-saghyz roots, the main methods for extracting natural rubber from the roots, as well as the approaches to micropropagation and genetic transformation of kok-saghyz and related species. In the middle of the 20th century, the industrial method of isolating rubber from Russian dandelion in the USSR was based on preliminary treatment of the roots with a 2% solution of alkali, which could negatively affect rubber quality. Therefore, it is important to develop new, rapid, but at the same time, inexpensive methods of rubber extraction from T. koksaghyz. Some of them are considered in this paper. The breeding of Russian dandelion should be aimed at both increasing the root size and the content of rubber. In this regard, the development of laboratory express methods for rubber extraction is also important. The authors have developed and optimized a method for extracting rubber from dry plant tissue using polar solvents (water and acetone), with the final extraction with a non‑polar solvent (hexane). The developed rubber extraction protocol showed results comparable to the literature data. In order to create more productive plant forms, experiments are also being conducted on T. kok-saghyz micropropagation and genetic transformation. However, the number of such works is still very small, probably due to the low regenerative abilities of this dandelion species.

Evaluation of the hypoglycemic effect of seven wild folkloric edible plants from Palestine.

Alfa-amylase inhibitors are used to reduce glucose absorption by suppressing carbohydrate digestion. The current study aimed to evaluate seven wild edible Palestinian plants' hydrophilic and lipophilic fractions against porcine pancreatic α-amylase enzyme. The lipophilic fractions of Arum palaestinum, Malva sylvestris, Plantago major, Centaurea iberica, Cichorium endivia, Bituminaria bituminosa, Sisymbrium irio leaves were sequentially separated with a nonpolar solvent hexane, while the hydrophilic fractions of the studied plants were separated with polar solvents ethanol and water. The activity of α-amylase inhibition was carried out by using α-amylase porcine pancreatic enzyme and 3,5-dinitrosalicylic acid (DNSA) method as well as by using Acarbose as a positive control. Among the studied plant's hydrophilic fractions, C. iberica and C. endivia have the highest porcine pancreatic α-amylase inhibitory effect with an IC50 value of 12.33 µg/mL and 9.96 µg/mL, respectively. In addition, among the studied plant's lipophilic fractions, S. irio and A. palaestinum have the highest porcine pancreatic α-amylase inhibitory effect with an IC50 value of 7.72 µg/mL and 25.3 µg/mL, respectively. In fact, these revealed results were near the values of Acarbose. The hydrophilic fractions of M. sylvestris and the lipophilic fractions of P. major plants exhibit remarkable α-amylase inhibitory activity. Hence, these leaves have a potential for use as regular supplements also; further investigations are required to isolate pure pharmacological molecules and to design suitable pharmaceutical dosage forms with anti-diabetic activity.

The influence of fatty acid chain length on the chemical, physical and morphological properties of the grafted barley husk for application in biocomposites

Abstract The present study deals with the grafting of barley husk (BH) with lauric acid, palmitic acid and arachidic acid in the presence of redox initiators. The grafting reaction parameters (reaction time, reaction temperature, dimethyl sulphoxide (DMSO) content, fatty acid concentration) were optimized by one variable at a time approach (OVAT) and response surface methodology (RSM) coupled with central composite design (CCD). The crystallinity of BH decreased after grafting of BH with long chain fatty acids. The grafted BH samples showed higher thermal stability as compared to BH and the thermal degradation rate of grafted BH decreased with increase in the chain length of fatty acid. Water contact angle (WCA) of BH was 45° and increased to 140–145° after grafting with lauric acid, palmitic acid and arachidic acid. After grafting, swelling (%) of BH decreased in polar solvents (water, ethanol), however, it increased in dimethyl formaldehyde (DMF). Chemical resistance and hydrophobic transformation of BH improved with an increase in % graft yield as well as with fatty acid chain length.

Inhibition of bacterial growth using false yam (Icacina oliviformis) extract as an additive in liquid soap

False yam (Icacina oliviformis) is a drought-resistant root crop found in Northern Ghana. Research confirms it to contain some levels of antimicrobial, antifungal, antidiarrheal, antioxidant, and antidiabetic activities. This study was carried out to determine the effectiveness of False yam extracts incorporated in liquid soap against selected microorganisms. Polar solvent (methanol, ethanol, and water) extracts from the leaves, tuber (root), peels (root bark), and seeds were diluted with liquid soap to give concentrations of 50 mg/mL, 25 mg/mL, and 12.5 mg/mL. Test organisms used were Staphylococcus aureus, Escherichia coli, and Vibrio species. The results revealed significant differences (P < 0.05) among the different solvents and concentrations of the plant materials used. The ethanol seed extract at a concentration of 50 mg/mL was most inhibitive on Vibrio species with an inhibition diameter of 13 mm. The methanol peel extract also had the greatest inhibition on Escherichia coli with average inhibition zone of 7 mm to 12.5 mm followed closely by the tuber with maximum inhibition zone of 9 mm. The leaf extract generally exhibited higher values of inhibition on Staphylococcus aureus with zone range of 10 mm to 15 mm. The highest activity occurred with an inhibition zone of 15 mm diameter. The tuber and peel extracts recorded the highest antibacterial activity. Staphylococcus aureus appeared to be the most susceptible organism and the methanol extracts exhibited a relatively high frequency of inhibition. Further research efforts should combine the tuber and peel extracts to determine the possible synergistic and/or antagonistic effect.

The density, dynamic viscosity and kinematic viscosity of protic and aprotic polar solvent (pure and mixed) systems: An experimental and theoretical insight of thermophysical properties

We report herein the thermophysical properties of pure protic and aprotic polar solvents (water, dimethyl sulfoxide and N,N-dimethyl formamide) and their mixed (binary and ternary) systems. The experimental density (ρ) and viscosity (η) were determined for these systems by varying temperature range from 293.15 K to 343.15 K. The excess properties (viz., excess molar volumes (VE), excess thermal expansion coefficient (αE), viscosity deviation (Δη) and excess Gibb's free energy (ΔGE) for viscous flow) were computed for mixed systems from experimental values. The excess properties of the mixed systems show clearly a non-ideal behaviour. Especially, a mixture of water with aprotic polar component show better thermophysical properties than pure systems. The pure (DMF) system shows increasing dynamic viscosity values at higher temperature region. Both the binary as well as ternary mixed systems show maximum activation energy (Ea) in the presence of water depicts their thermal stability of the mixed systems. The thermal expansion coefficient (α) also revealed increase in the thermal behaviour for the protic-aprotic systems. In addition to that, thermodynamic parameters are also evaluated for better understanding of thermal stability.

Adsorption behavior of metformin drug on boron nitride fullerenes: Thermodynamics and DFT studies

In this study, a density functional theory (DFT) calculation was carried out for the adsorption behavior and detection of metformin on the exterior surfaces of pure and doped boron nitride (BN) fullerenes by using B3LYP-D and PW91-D functionals. The results demonstrate that the NH group of metformin can chemisorb on the boron atom of B12N12 and B16N16 fullerenes. Presence of polar solvent (water) increases the adsorption energy of metformin on the pure and GaB11N12 fullerenes. However, at the presence of Ga doping and it was found that the doping increases the binding energy of the metformin molecule, while the Ge doping decreases the binding energy. So our calculations suggest that the GeB11N12 has a greater sensitivity for the metformin molecule compared with the GaB11N12 fullerene. Our results represented that the GeB11N12 fullerene has good potential as a biosensor for the determination of metformin in environmental systems.

Solvent Mediation of Peptide Conformations: Polyproline Structures in Water, Methanol, Ethanol, and 1-Propanol as Determined by Ion Mobility Spectrometry-Mass Spectrometry.

Ion mobility spectrometry and circular dichroism spectroscopy are used to examine the populations of the small model peptide, polyproline-13 in water, methanol, ethanol, and 1-propanol over a range of solution temperatures (from 288 to 318K). At low temperatures, the less-polar solvents (1-propanol and ethanol) favor the all-cis polyproline I helix (PPI); as the temperature is increased, the trans-configured polyproline II helix (PPII) is formed. In polar solvents (methanol and water), PPII is favored at all temperatures. From the experimental data, we determine the relative stabilities of the eight structures in methanol, ethanol, and 1-propanol, as well as four in water, all with respect to PPII. Although these conformers show relatively small differences in free energies, substantial variability is observed in the enthalpies and entropies across the structures and solvents. This requires that enthalpies and entropies be highly correlated: in 1-propanol, cis-configured PPI conformations are energetically favorable but entropically disfavored. In more polar solvents, PPI is enthalpically less favorable and entropy favors trans-configured forms. While either ΔH0 or ΔS0 can favor different structures, no conformation in any solvent is simultaneously energetically and entropically stabilized. These data present a rare opportunity to examine the origin of conformational stability. Graphical Abstract ᅟ.

The mechanistic study of reaction between N-benzoyl carbamates and aliphatic/aromatic amines for synthesis of substituted N-benzoyl urea derivatives: a DFT approach

A thorough investigation on whether a stepwise or a concerted pathway is involved in the synthesis of substituted N-benzoyl urea derivatives by reaction of substituted N-benzoylcarbamates and aliphatic/aromatic amines using density functional theory (DFT) calculations at B3LYP/6–31 + G (d,p) level of theory has been reported. The study of effects of nature of leaving group present in N-benzoylcarbamate, structure of amines, and solvents on the reaction showed that the choice of reaction mechanism involved depends upon the nature of leaving group present on N-benzoylcarbamate. The effect of structure of amine on reaction mechanism depends upon the type of leaving group present on N-benzoylcarbamate. We have also observed that the reaction between aliphatic/aromatic amine with phenyl benzoylcarbamate is thermodynamically more favorable, while a reaction between phenyl/methyl benzoylcarbamates with methylamine is more preferred. The effect of polar solvent water and non-polar solvent toluene on reaction mechanism was also investigated to account the interactions of solvent molecules with polar transition states at the same level of theory.

&lt;i&gt;In-vitro&lt;/i&gt; antimicrobial activity of crude extracts of &lt;i&gt;Diospyros monbuttensis&lt;/i&gt;

Diospyros species in folklore medicine are used as anti-inflammatory, antibacterial, antioxidant, anticancer and antiviral agents. The in vitro antimicrobial activity of crude extracts of the leaves of Diospyros monbuttensis were evaluated against three bacterial species (Staphylococcus aureus, Escherichia coli and Micrococcus luteus ) and fungal strain (Aspergillus niger). Extraction was carried out using both polar and non-polar solvents (ethanol and water). The leaves were screened for phytochemical constituents and preliminary screening for antimicrobial activity carried out using the agar well diffusion method. The minimum inhibitory concentration (MIC) was determined using the agar well dilution method. The phytochemical screening revealed the presence of saponins, tannins, glycosides and alkaloids in the plant. The ethanolic leaf extract of D. monbuttensis had no activity against the test organisms, but antimicrobial activity was observed for the aqueous extract against S. aureus and E. coli at all concentrations tested. The MIC of the aqueous extract of D. monbuttensis on S. aureus and E. coli was 0.78 mg/ml. The results of this study indicate that Diospyros monbuttensis leaves may be used for treatment of infections caused by S. aureus and E. coli.Keywords: Diospyros monbuttensis; Antimicrobial activity; phytochemical screening

Reaction mechanisms of 3-amino-4-nitro-furoxan formation by 3-amide-4-nitro-furoxan and sodium hypochlorite in water and benzene solvents

Synthesis of new furoxan-based compounds has been a hot research topic in order to explore the energetic materials with good application prospect. 3-amino-4-nitro-furoxan is a precursor for synthesis of furoxan derivatives because that the amino groups are prone to be substituted by nucleophiles. A theoretical research is conducted for the formation reaction of 3-amino-4-nitro-furoxan by 3-amide-4-nitro-furoxan and sodium hypochlorite in water and benzene solvents using the density functional theory (DFT) and CCSD coupled cluster method to reveal the formation mechanism and explore new synthesis routes. The structures and energies of intermediates and transition states in the possible reaction pathways are given, and the potential energy surfaces of the every reaction channels are mapped. The results indicate that the formation mechanism is mainly through two stages: generation and hydrolysis of isocyanate. Hydrogen bond plays an important role for the hydrolysis process. The formation mechanism is shown to be dependent on the polarity of solvent. The hydroxyl ion (OH−), originated from the basic properties of sodium hypochlorite solution, is shown to be more likely first attacker than the hypochlorite ion (OCl−) for the reactant 3-amide-4-nitro-furoxan due to the low active barrier in the polar water solvent. But the OCl− dominates the reaction in benzene solvent where the isocyanate is formed via the dehydration chlorination by OCl− and Hofmann rearrangement with the elimination of chloride ion. The isocyanate is then hydrolyzed through addition of a H2O molecule to the NC double bonds, rotation of the hydroxyl hydrogen, transfer of hydrogen to the N atom in the amide group and the removal of a CO2 molecule to form the final product. The benzene solvent is more suitable than water solvent for the formation reaction due to the lower active barrier of 46.4 kcal/mol. The reaction is not feasible at room temperature and raising properly temperature of system would be requisite to realize the synthesis reaction.

The density, dynamic viscosity and kinematic viscosity of protic polar solvents (pure and mixed systems) studies: A theoretical insight of thermophysical properties

The densities (ρ) and viscosities (η) have been studied for pure and mixed systems of protic polar solvents water, methanol, ethanol and propan-1-ol for entire composition range at temperature from 293K to 343K in 5K intervals at atmospheric pressure. With increase in temperature the density values as well as the dynamic viscosity values were decrease. The obtained values are used to calculate the excess properties such as excess molar free volume (VE), thermal expansion coefficient (α), excess thermal expansion coefficient (αE), viscosity deviation (Δη) and excess Gibb's free energy (ΔG⁎E) for the activation of viscous flow for mixed systems. The calculated excess properties of binary mixtures were correlated with Redlich-Kister type polynomial equation by least square regression method and fitting parameters were found for all binary systems. The temperature dependence of viscosities for mixed systems has been explained using Arrhenius type equation of Newtonian classic solvents and Eyring transition state equation. The thermodynamic parameters were also evaluated for mixed systems which show the thermal stability of system.

Antioxidant Properties of Camelina sativa Oil and Press-Cakes

Abstract Camelina sativa is well known due to high content of polyunsaturated fatty acids in its oil. Till now this oil has been studied mainly for applications as raw material for synthesis of resins, biodiesel and hydrocarbon fuels. This study examines the oxidative stability of cold-pressed Camelina sativa (also known as camelina, false flax or gold-of-pleasure) oil and its extracts of spices. Despite the high content of polyunsaturated fatty acids, Camelina sativa oil appeared more rigid against oxidation than rapeseed or flax oil. Extracts of different spices were prepared by maceration in camelina oil at room temperature for 24 h. The stability of extracts was determined under accelerated oxidation conditions and monitored by peroxide values. Most of the tested additives (e.g., bay leaves, allspice, clove, barley sprouts, coriander, ginger) did not influence or even decreased oxidative stability of the oil. However, oil with thyme additive demonstrated remarkably higher stability then Camelina sativa oil alone. Press-cakes of camelina seeds were extracted with two polar solvents (ethanol or water) and their mixtures under variable conditions (room temperature or reflux). Prepared polar extracts of press-cakes were characterised by total polyphenol content (Folin–Ciocalteu method) and antiradical activity against 1,1-diphenyl-2-picryl hydrazyl and galvinoxyl.

Dendritic polyelectrolyte brushes

The current state of the theory of brushes formed by dendritically branched ionized macromolecules attached by the root segment to a planar substrate and immersed in a polar solvent (water) is discussed. The theory makes it possible to unravel the most distinctive features of such brushes associated with the branched architecture of brush-forming chains and to systematically compare them with the properties of brushes formed by linear polyelectrolyte chains. Owing to their peculiar properties, dendritic polyelectrolyte brushes show promise for designing smart functional polymeric materials.