Negative Gibbs Free Energy Research Articles

Phase, chemical constitution and effective depth of oxide overgrowth and its influence on SmPrCo5 magnetic properties

Ternary Sm-Pr-Co magnets with CaCu5-type hexagonal structure exhibit superior magnetic properties and investigating their oxidation behavior is crucial for assessing their stability under the service conditions. In this regard, here thermal oxidation of sintered SmPrCo5 magnet is carried out by varying the oxidation temperature from 373 to 973 K for 5 hr under atmospheric pressure. Owing to their lower negative Gibbs free energy, rare earth oxides of Sm2O3 and Pr2O3 are found to initially form, making cobalt free from SmPrCo5 lattice. Cobalt is then observed to migrate to the oxide surface, because of the difference in chemical potential between the surface and inner layers, leading to Co3O4 formation. Moreover, here a comprehensive discussion on the occurrences of different oxide phases and their depth distributions in the oxide layer are being made. Finally, a correlation between these oxide phases and the alterations in their magnetic properties is discussed.

Acid-base treatment of lightweight expanded clay aggregate (LECA) for removal of paraquat from aqueous media

This study focuses on the modification of lightweight expanded clay aggregate (LECA) with sulfuric acid, potassium hydroxide, and sulfuric acid-potassium hydroxide to enhance the removal efficiency of the highly hazardous herbicide (paraquat) from the aqueous solution. The modification results showed that samples activated with sulfuric acid before KOH yielded higher removal efficiency (70.8%) than those activated with acid or base (25.6% and 35.8%, respectively). The paraquat uptake mechanism by LECA was investigated using XRD, XRF, FTIR, FESEM, BET, and zeta potential measurements. Batch adsorption tests were conducted under different conditions using LECA and acid-base-modified LECA. The results indicated the maximum removal efficiency for PQ at 240 min contact time, adsorbent dose of 3.5 g L−1, and pH 9 was achieved with the acid-base treated sample. Experimental data were evaluated with different isothermal, thermodynamic, and kinetic models. The pseudo-second-order model with a correlation coefficient of R2 > 0.99 was congruent with experimental results for LECA and acid-base-activated LECA through kinetic investigations. The highest adsorption capacities for the LECA and acid-base-activated LECA samples, respectively, were 6.12 mg g−1 and 21.23 mg g−1 according to the Langmuir equilibrium isotherm, which offered greater agreement with the experimental results. A negative standard enthalpy change (−21.09 kJ mol−1) and Gibbs free energy change for PQ uptake at 15, 25, and 35 °C indicated an exothermic and spontaneous process. Reusability studies confirmed that the treated adsorbent could successfully remove paraquat even after four regeneration cycles.

The depression mechanism on pyrite in a low-alkaline system with combined depressants: Experiment, HSC, DFT and ToF–SIMS studies

Depression of pyrite in a low-alkaline system has sparked soaring interests for the multi-metal sulfide minerals flotation recently. This study investigates effects of combined depressants (Ca(ClO)<sub>2</sub> and CaO) on pyrite flotation with butyl xanthate (KBX). Micro-flotation experiments indicate that the addition of 200 mg/L combined depressants (a mass ratios of CaO to Ca(ClO)<sub>2</sub> of 2:3) and 1.0×10<sup>−3</sup> mol/L KBX at pH 9.5 can effectively depresses the flotation of pyrite, and a minimum pyrite recovery rate of 12.5% is obtained. Basic thermodynamic evaluation results confirm the participation of Ca(ClO)2 significantly decrease the negative Gibbs free energies of pyrite oxidation reaction. Besides, the calcium species (Ca(OH)<sub>2</sub>, Ca<sup>2+</sup> and Ca(Cl)<sub>2</sub>) will spontaneously transform into CaCO<sub>3</sub>, and it is the ultimate dominant calcium species in the CO<sub>3</sub><sup>2-</sup> system. Density functional theory (DFT) results indicate that CaCO<sub>3</sub> can chemically adsorb onto the pyrite surface with an adsorption energy of –671.13 kJ/mol. The O1 and Ca atoms mainly contribute to the bonding process and are responsible for the stable adsorption of CaCO<sub>3</sub>. ToF-SIMS results provide strong evidence that the combined depressants increase the amount of hydrophilic species and decrease dixanthogen adsorption onto the pyrite surface. The thickness of the whole formed hydrophilic species is approximately 50 nm. Semiquantitative amounts of hydrophilic species follow the order of hydroxy calcium>iron carbonyl>calcium carbonate. Overall, hydrophilic species repulse adsorption of dixanthogen and significantly reduce the flotation performance of pyrite.

Anticorrosive properties of Eucalyptus (Nilgiris) leaves extract on 2S grade aluminium in acid solutions

The study is on the application of Eucalyptus leaves extract (ELE) as anticorrosive properties for aluminium alloy in 0.5 M HCl by using potentiodynamic polarization (PDP), gravimetric weight loss, and Electrochemical impedance spectroscopic (EIS) methods. The corrosion inhibition characteristics of ELE on aluminium in HCl solution have been examined. This investigation showed the finest inhibition efficiencies of 95.0%, 92.0% and 89.3% that were obtained from weight loss, PDP and EIS at concentration of 0.5% ELE at 303 K respectively. As per Langmuir adsorption isotherm models, an extract of Eucalyptus leaves was adsorbed on the metal surface. The effect of the temperature on the corrosion behaviour with adding of the best concentration of ELE was studied in the temperature range 313–333 K. It was found that inhibition efficiency is independent of temperature. The negative Gibb's free energy and activation parameters of the ELE were recorded and the results indicated that the adsorption rates were spontaneous. The results obtained from PDP and EIS shows that the corrosion inhibition procedure is charge transfer controlled, and the ELE works as a mixed-type inhibitor. The findings of SEM (Scanning electron microscopy) and AFM (Atomic forcemicroscopy) studies support the adsorption inhibition mechanism. The results of all the experiments conduct are consistent. The functional groups of the ELE were identified using Fourier transform infrared (FTIR) spectroscopy.

Efficient and environmentally friendly removal of azo textile dye using a low-cost adsorbent: Kinetic and reuse studies with application to textile effluent

Recently, there has been an increasing interest in environmentally friendly methods for the removal of toxic dyes to enable sustainable textile dyeing processes. In this study, a highly efficient, non-toxic, low-cost MgO particles were prepared by sol-gel technique and utilized for the removal of Reactive Red 21 azo dye by adsorption process. The prepared MgO particles were characterized by Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, and Particle Size Analysis. The batch adsorption studies were performed for optimizing the parameters affecting adsorption. The adsorption behavior of Reactive Red 21 was accurately characterized by the Langmuir model. The adsorption process was found to be thermodynamically spontaneous at room temperatures as indicated by the negative Gibbs free energy change (∆G) value of −30.65 kj/mol. The kinetic studies indicate that the pseudo-second-order model provides a good fit to the adsorption of Reactive Red 21. The adsorption capacity of the prepared MgO particles for Reactive Red 21 was determined to be 355 mg/g at room temperature over a wide pH range of 5–9, with a contact time of 20 min. The regeneration of dye-adsorbed MgO particles was conducted at 500 °C for 2 h. The regenerated MgO particles were then utilized for adsorbing Reactive Red 21 five times with a sufficiently high dye removal efficiency. The prepared MgO particles provided a 98 % dye removal in real textile wastewater containing Reactive Red 21 dye.

Insight into the Mechanism of Cobalt-Nickel Separation Using DFT Calculations on Ethylenediamine-Modified Silica Gel.

The separation of Co(II) and Ni(II) from leaching solution is gaining interest because Co(II) and Ni(II) are increasingly used in emerging strategic areas, such as power batteries. Herein, the surface of silica gel is functionalized with 1,2-ethylenediamine and used for the separation of Co(II) and Ni(II). The Co(II) removal efficiency of the modified silica is 80.2%, with a 4-fold improvement in the separation factor. The geometry, frequency, and electrostatic potential of the ethylenediamine modified silica gel (en/SG) are calculated. The corresponding properties of M2+ (M-Co, Ni) adsorbed on en/SG in an aqueous solution are simulated and analyzed. The results show that ethylenediamine tends to form [Men(H2O)4]2+ after binding to M2+, and the binding ability of Co(II) to ethylenediamine is stronger. Besides, the thermodynamic calculations show that en/SG has a more negative Gibbs free energy when absorbing Co(II) in aqueous solution, so en/SG is more inclined to bind with Co(II) preferentially. It is the difference in complexation ability between Ni, Co, and ethylenediamine that enlarges the difference in the original physical adsorption, thus strengthening the separation performance. This work will provide guidance for a rational design of high-performance nickel-cobalt adsorption materials.

Photogenic MnO2/Ag metal nanocomposites and their dye adsorbing activities

Manganese dioxide/silver (MnO2/Ag) nanoparticles were fabricated by using KMnO4-NaBH4 redox reaction at room temperature. The optical and structural properties of MnO2/Ag were determined using UV–visible and Fourier transform infrared spectroscopies. The morphology was established with scanning and transmission electron microcopies, and X-ray diffraction. MnO2/Ag showed excellent adsorbing activity to the removal of Congo red. The various kinetic models were used to determine the rate of dye removal. Congo red adsorption onto MnO2Ag proceeds through the pseudo-second-order kinetic model. Langmuir adsorption capacity (Q0max = 97.1 mg/g), and sorption intensity (n = 1.6) were estimated with Langmuir and Freundlich adsorption isotherm models for 250 mg/L Congo red. Elovich model suggest the adsorption of Congo red with the MnO2Ag proceeds through the film diffusion. The positive values of enthalpy changes (ΔH0), entropy changes (ΔS0), and negative Gibbs free energy changes (ΔG0) showed that the Congo red adsorption process was endothermic, spontaneous, and chemisorption process followed with physical mechanism. The results showed that the removal efficiency decreases from 98% to 89% after the six consecutive experiments.

FliA-Dependent Surface Macromolecules Promote Initial Biofilm Development of Escherichia coli by Influencing the Bacterial Surface Properties

FliA is an important regulatory component for the synthesis of surface macromolecules which are involved in motility and biofilm development of Escherichia coli. In this study, the roles of FliA-dependent surface macromolecules in E. coli surface tension, surface heterogeneity and surface roughness, and initial biofilm development consisting of reversible and irreversible adhesion were investigated using E. coli MG1655 wild-type strain and fliA gene deleted mutant strain. Negative Gibbs free energy change values calculated using bacterial surface tensions obtained by a spectrophotometric method showed that both wild-type and mutant cells in water can reversibly adhere to the surface of the model solid, silicon nitride (Si3N4). The calculations further showed that bacterial reversible auto-adhesion and co-adhesion were also thermodynamically favorable. In comparison, the reversible adhesion and auto-adhesion capacities of wild-type cells were higher than the mutant cells. Direct measurements by atomic force microscopy (AFM) and thorough analysis of the recorded adhesion data showed that the irreversible adhesion strength of wild-type cells to Si3N4 in water was at least 2.0-fold greater than that of the mutants due to significantly higher surface heterogeneity resulting in higher surface roughness for the wild-type cells compared to those obtained for the mutants. These results suggest that strategies aimed at preventing E. coli biofilm development should also consider a combined method, such as modifying the surface of interest with a bacterial repellent layer and targeting the FliA and FliA-dependent surface macromolecules to reduce both reversible and irreversible bacterial adhesion and hence the initial biofilm development of E. coli.

Investigation of Newly Synthesized Bis-Acyl-Thiourea Derivatives of 4-Nitrobenzene-1,2-Diamine for Their DNA Binding, Urease Inhibition, and Anti-Brain-Tumor Activities

Bis-acyl-thiourea derivatives, namely N,N'-(((4-nitro-1,2-phenylene)bis(azanediyl)) bis(carbonothioyl))bis(2,4-dichlorobenzamide) (UP-1), N,N'-(((4-nitro-1,2-phenylene) bis(azanediyl))bis(carbonothioyl))diheptanamide (UP-2), and N,N'-(((4-nitro-1,2-phenylene)bis(azanediyl))bis(carbonothioyl))dibutannamide (UP-3), were synthesized in two steps. The structural characterization of the derivatives was carried out by FTIR, 1H-NMR, and 13C-NMR, and then their DNA binding, anti-urease, and anticancer activities were explored. Both theoretical and experimental results, as obtained by density functional theory, molecular docking, UV-visible spectroscopy, fluorescence (Flu-)spectroscopy, cyclic voltammetry (CV), and viscometry, pointed towards compounds' interactions with DNA. However, the values of binding constant (Kb), binding site size (n), and negative Gibbs free energy change (ΔG) (as evaluated by docking, UV-vis, Flu-, and CV) indicated that all the derivatives exhibited binding interactions with the DNA in the order UP-3 > UP-2 > UP-1. The experimental findings from spectral and electrochemical analysis complemented each other and supported the theoretical analysis. The lower diffusion coefficient (Do) values, as obtained from CV responses of each compound after DNA addition at various scan rates, further confirmed the formation of a bulky compound-DNA complex that caused slow diffusion. The mixed binding mode of interaction as seen in docking was further verified by changes in DNA viscosity with varying compound concentrations. All compounds showed strong anti-urease activity, whereas UP-1 was found to have comparatively better inhibitory efficiency, with an IC50 value of 1.55 ± 0.0288 µM. The dose-dependent cytotoxicity of the synthesized derivatives against glioblastoma MG-U87 cells (a human brain cancer cell line) followed by HEK-293 cells (a normal human embryonic kidney cell line) indicated that UP-1 and UP-3 have greater cytotoxicity against both cancerous and healthy cell lines at 400 µM. However, dose-dependent responses of UP-2 showed cytotoxicity against cancerous cells, while it showed no cytotoxicity on the healthy cell line at a low concentration range of 40-120 µM.

Design and optimization of the composition and mechanical properties for non-equiatomic CoCrNi medium-entropy alloys

• The essential criterion was provided for the composition design of CoCrNi medium-entropy alloys (MEAs) with exceptional strength-ductility combinations. • The analysis on phase stability, deformation mechanisms and mechanical properties is combined in the essential criterion. • The optimal composition space of CoCrNi MEAs was predicted with the adoption of the essential criterion and first principles calculations. • The validity of essential criterion was proved by systematic comparison with numerous experimental data. The development of multi-principal element alloys (MPEAs, also called as high- or medium-entropy alloys, HEAs/MEAs) provides tremendous possibilities for materials innovation. However, designing MPEAs with desirable mechanical properties confronts great challenges due to their vast composition space. In this work, we provide an essential criterion to efficiently screen the CoCrNi MEAs with outstanding strength-ductility combinations. The negative Gibbs free energy difference ∆ E FCC-BCC between the face-centered cubic (FCC) and body-centered cubic (BCC) phases, the enhancement of shear modulus G and the decline of stacking fault energy (SFE) γ isf are combined as three requisites to improve the FCC phase stability, yield strength, deformation mechanisms, work-hardening ability and ductility in the criterion. The effects of chemical composition on ∆ E FCC-BCC , G and γ isf were investigated with the first principles calculations for Co x Cr 33 Ni 67- x , Co 33 Cr y Ni 67- y and Co z Cr 66- z Ni 34 (0 ≤ x, y ≤ 67 and 0 ≤ z ≤ 66) alloys. Based on the essential criterion and the calculation results, the composition space that displays the negative Gibbs free energy difference ∆ E FCC-BCC , highest shear modulus G and lowest SFE γ isf was screened with the target on the combination of high strength and excellent ductility. In this context, the optimal composition space of Co-Cr-Ni alloys was predicted as 60 at.%–67 at.% Co, 30 at.%–35 at.% Cr and 0 at.%–6 at.% Ni, which coincides well with the previous experimental evidence for Co 55 Cr 40 Ni 5 alloys. The validity of essential criterion is further proved after systematic comparison with numerous experimental data, which demonstrates that the essential criterion can provide significant guidance for the quick exploitation of strong and ductile MEAs and promote the development and application of MPEAs.

Preparation and Physio–Chemical characterisation of activated carbon derived from prosopis juliflora stem for the removal of methylene blue dye and heavy metal containing textile industry effluent

An experimental work endeavoured and presented in this article focuses on the removal of Methylene Blue (MB) dye and Heavy Metals (HM) such as lead and copper from textile industry effluent by the adsorption process with ZnCl2-activated carbon. Initially, carbon was prepared using the cheapest and environmentally hazardous precursor of Prosopis Juliflora plant (Stem) and called Prosopis Juliflora Stem Carbon (PJSC). Then the PJSC was chemically activated by impregnating ZnCl2 with a ratio of 1:0.5 at a temperature of 800 °C in muffle furnace about 1 h and named as ZnCl2-activated Prosopis Juliflora Stem Carbon (ZAPJSC). The physio–chemical characteristics such as yield, pH, conductivity, bulk density, moisture content, ash content, volatile matter, fixed carbon content, as well as solubility in acid and water were calculated. Surface textures of PJSC and ZAPJSC were characterised by Scanning Electron Microscopy (SEM); functional group characterisation was performed by Fourier Transform Infrared Spectroscopy (FTIR); elements in the adsorbents were identified by Energy Dispersive X-Ray Analysis (EDX); and Brunauer-Emmett-Teller (BET) surface area analysis was carried out to find the surface area, pore volume, and pore radius of the adsorbents. Surface area was found to be 252.730 m2/g which showed that ZAPJSC was having enormous bores meanwhile surface area of PJSC was 85.508 m2/g. In this context, the central composite design (CCD) approach-based response surface methodology (RSM) was performed to investigate and optimise the effects of process parameters on the adsorption of MB by ZAPJSC. The optimum level of process parameters such as contact time of 5.4 min and dosage of 85 mg were achieved with MB adsorption efficiency of 99.05%. Further, pseudo-first-order and pseudo-second-order models were used to fit the present experimental data. Pseudo-second-order rate equation was perfectly fit to provide a realistic description of adsorption kinetics. Equilibrium isotherms were investigated by Langmuir and Freundlich equations. Langmuir equation was found to best represent the equilibrium data for MB-ZAPJSC system. Thermodynamic study showed that the adsorption of MB on ZAPJSC (with a more negative Gibbs free energy value) was more favoured. Next, batch adsorption experiments for methylene blue dye and heavy metals (lead, copper, manganese, iron, cobalt) were carried out as parameters of effect of contact time and adsorbent dosage. Lastly, ZAPJSC adsorbent showed a reuse efficiency of 73.34% after four consecutive adsorption-desorption cycles in MB removal. These results indicate that the ZAPJSC could provide base for more low-cost activated carbon to be used as adsorbents for MB dye removal and heavy metals.

Performance of Organic Salts as Salting-Out Media on Recovering Nicotine from Water

Three degradable organic salts, sodium formate (NaCHO2), sodium succinate (Na2C4H4O4), and sodium citrate (Na3C6H5O7), were evaluated for the extraction of nicotine from aqueous solutions by forming two-phase systems. The detailed phase diagrams, including the binodal curves and tie-lines, were experimentally determined at 298.15 K and atmospheric pressure by the cloud point method. The three empirical equations including Merchuk, Pirdashti, and Hu models gave a perfect correlation of the experimental binodal data, and the reliability of liquid–liquid equilibrium data was evaluated using the Othmer–Tobias and Bancroft equations. It could be found that all adopted organic salts promoted the expansion of two-phase regions and had a high partition yield for nicotine extraction from water. The relative tendency of the anions to form aqueous two-phase systems being C6H5O73– > C4H4O42– > CHO2– was consistent with their valence order, which could be explained by the Gibbs hydration free-energy theory. Furthermore, the salting-out ability of salt anions was also in accordance with the parameter order (Na3C6H5O7 > Na2C4H4O4 > NaCHO2) of the calculated effective excluded volume. Increasing the temperature from 298.15 to 318.15 K and the pH value from 8.0 to 11.0 at 298.15 K was conducive to the two-phase formation of the ternary nicotine + Na3C6H5O7 + water system to increase the distribution coefficients and recovery percentages of nicotine. Computational thermodynamics of cloud point indicated that the more negative Gibbs free energy with temperature promoted the desolvation of nicotine to migrate preferentially to the top phase. It was concluded that degradable organic salts would be effective for nicotine extraction at an industrial scale.

Unveiling the gemcitabine drug complexation with cucurbit[n]urils (n = 6–8): a computational analysis

In this work, we have investigated the complex formation capability of gemcitabine drug with host cucurbit[n]urils, Q[n] (n = 6, 7, and 8) using density functional theory (DFT). The DFT studies demonstrate that the most stable configuration is a fully encapsulated complex. In the encapsulated gemcitabine@Q[6] and gemcitabine@Q[7] complexes, the gemcitabine amino -NH2 and the alcoholic groups bond with the carbonyl units of Q[n]. The addition of sodium ions leads to the partial exclusion of the gemcitabine molecule and the sodium atoms lie close to the carbonyl portal of Q[7]. Thermodynamic parameters computed for the complexation process exhibit high negative Gibbs free energy change, implying that the encapsulation process is spontaneous and is an enthalpy-driven process. Frontier molecular orbitals are located mainly on the gemcitabine uracil ring, before and after encapsulation, indicating that the encapsulation occurs by pure physical adsorption. Quantitative molecular electrostatic potentials demonstrate a shift in electron density during the complex formation and are more pronounced in gemcitabine@Q[7]. Atoms-in-molecule (AIM) topological analysis illustrate that these complexes are stabilized by various non-covalent interactions including hydrogen bonding (HBs) and C···F interactions. The reduced density gradient (RDG) graph exhibits the presence of strong HBs and weak van der Waals interactions and the presence of steric repulsion. The isosurface non-covalent interactions (NCI) diagram shows predominant steric interaction in the gemcitabine@Q[6] complex. The NCI isosurface for gemcitabine encapsulated complexes with Q[7] and Q[8] host displays that the green patches are uniformly distributed in all directions. Finally, EDA results demonstrate Pauling’s repulsive energy is predominant in gemcitabine@Q[6] complex, while the orbital and dispersion energies stabilize the gemcitabine@Q[7] complex.

Adsorptive Removal of Rhodamine B Dye Using Carbon Graphite/CNT Composites as Adsorbents: Kinetics, Isotherms and Thermodynamic Study.

The study of the adsorption efficiency of new carbon/CNT composites was undertaken to remove a cationic dye, Rhodamine B (RhB), from dye-contaminated wastewater. Indeed, we investigated the effect of different experimental parameters such as time, initial concentration of dye and temperature on the adsorption of RhB by the carbon composites (KS44-0 and KS44-20). The results showed that the adsorption uptake increased with the initial concentration and solution temperature while maintaining a relatively constant pH. The presence of the carbon nanotubes provided more active sites for dye removal and improved the adsorption behavior of Rhodamine B dye. The analysis of the experimental data was conducted using model equations, such as Langmuir, Freundlich and Temkin isotherms. As regards the Freundlich isotherm model, it was the best fit for the equilibrium data obtained from the experiments. The applicability of the pseudo-second-order equation could be explained assuming that the overall adsorption rate is limited by the rate of adsorbate transport that occurs on the pore surfaces of adsorbents. Furthermore, the intraparticle diffusion and Bangham models were used to investigate the diffusion mechanism of RhB absorption onto carbon composites. They showed that multiple adsorption stages occurred simultaneously via pore surface diffusion. Concerning the thermodynamic parameters (∆G°, ∆H°, and ∆S°), they were calculated and explained in the mean of the chemical structure of the adsorbate. Negative standard Gibbs free energy change values (ΔG°ads) at all temperatures suggested that the adsorption process was spontaneous, and the positive values of the standard enthalpy change of adsorption (∆H°ads) revealed the reaction to be endothermic. The values of standard enthalpy (ΔH°ads) and activation energy (Ea) indicated that the adsorption process corresponds to physical sorption. The mechanisms for the removal of Rhodamine B dye from wastewater using carbon composite were predicted. RhB is a planar molecule that is readily adsorbed, in which adsorbed molecules are bound by hydrophobic or other weak interactions due to the π-π interactions between the dyes' aromatic backbones and the hexagonal skeleton of graphite and carbon nanotubes. Thus, the graphite carbon/carbon nanotube composite is believed to play a major role in organic pollutant reduction.

Molecular interaction of di-ester bonded cationic Gemini surfactants with pepsin: in vitro and in silico perspectives

The implications of surfactant–enzyme/protein interactions in a variety of fields, including biotechnology, cosmetics, paints and pharmaceuticals, have attracted a lot of attention in contemporary studies. Herein, we have employed several in vitro and in silico techniques such as excitation and absorption spectroscopies, circular dichroism and FT-IR spectroscopies, density functional and molecular dynamics simulations to understand the interaction behavior of oxy-diester-based green cationic Gemini surfactants, N1,N1,N14,N14-tetramethyl-2,13-dioxo-N1,N14-dialkyl-3,6,12-tetraoxateradecane-1,14-diaminiumdichloride (abbreviated as Cm-E2O2-Cm, where ‘m’ stands for alkyl chain length, m = 12 and 14) with one of the main digestive proteins, pepsin. The spectroscopic techniques confirm the static quenching effect of surfactants on pepsin. The calculated physical parameters (Ksv , Kb and ΔG) and their order reveal the distinguished implications for the surfactants’ chain lengths. The spontaneity of interaction was also confirmed by negative Gibbs free energy change values. The extrinsic spectroscopic study with pyrene as fluorescence probe, FT-IR and CD techniques indicated a potential conformational change in pepsin induced by the Gemini surfactants. DFT, docking and MD simulations provided the theoretical understanding regarding the quantum mechanical environment, location of binding and stability of the protein–surfactant complexation in energy terms. We believe this study will be a humble addition to our existing knowledge in the field of protein–surfactant interactions. Communicated by Ramaswamy H. Sarma

Physicochemical parameters and modes of interaction associated with the micelle formation of a mixture of tetradecyltrimethylammonium bromide and cefixime trihydrate: effects of hydrotropes and temperature.

The interaction between an antibiotic drug (cefixime trihydrate (CMT)) and a cationic surfactant (tetradecyltrimethylammonium bromide (TTAB)) was examined in the presence of both ionic and non-ionic hydrotropes (HTs) over the temperature range of 300.55 to 320.55 K. The values of the critical micelle concentration (CMC) of the TTAB + CMT mixture were experienced to have dwindled with an enhancement of the concentrations of resorcinol (ReSC), sodium benzoate (NaBz), sodium salicylate (NaS), while for the same system, a monotonically augmentation of CMC was observed in aq. 4-aminobenzoic acid (PABA) solution. A gradual increase in CMC, as a function of temperature, was also observed. The values of the degree of counterion binding (β) for the TTAB + CMT mixture were experienced to be influenced by the concentrations of ReSC/NaBz/NaS/PABA and a change in temperature. The micellization process of TTAB + CMT was observed to be spontaneous (negative standard Gibbs free energy change (ΔG0m)) at all conditions studied. Also, the values of standard enthalpy change (ΔH0m) and entropy change (ΔS0m) were found negative and positive, respectively (with a few exceptions), for the test cases indicating an exothermic and enthalpy-entropy directed micellization process. The recommended interaction forces between the components in the micellar system are electrostatic and hydrophobic interactions. In this study, the values of ΔC0m were negative in aqueous NaBz, ReSC, and PABA media, and positive in case of NaS. An excellent compensation scenario between the enthalpy and entropy for the CMT + TTAB mixed system in the investigated HTs solutions is well defined in the current work.

Investigating the physicochemical properties of solid dispersions based on semicrystalline carriers: A case study with ketoprofen

Hydrophilic semicrystalline carriers represent an alternative to amorphous polymers due to their low melting temperature, useful for the production of solid dispersions (SDs) by melting-based technologies. This research aims to compare SDs of ketoprofen (KET) and three different semicrystalline carriers (PEG, Poloxamer and Gelucire) regarding miscibility, phase behavior, molecular interactions and stability. KET was chosen owing to its low solubility and high glass forming ability. Estimation of drug-excipient miscibility was performed by Flory-Huggins theory. Negative Gibbs free energy indicated a spontaneous mixing of KET with the three carriers and miscibility in the order PEG > Poloxamer > Gelucire. SDs up to 40 % w/w of drug were produced by melting process at a temperature below KET melting point. Characterization of SDs was performed by differential scanning calorimetry, polarized light microscopy and powder X-ray diffraction. In case of PEG and Poloxamer, the drug incorporation did not affect carrier crystallinity, while KET was in the amorphous state. Differently, KET retarded the crystallization of Gelucire and at high drug loadings the SDs were amorphous and semisolid. FT-IR analysis revealed a strong interaction between KET and the three carriers. Finally, PEG-based SDs above 20 % KET loading displayed drug crystallization after 6 months of storage; while Poloxamer and Gelucire-based SDs showed KET crystallization only at 40 % KET. Due to its less hydrophilic character and limited water uptake, Gelucire showed the best stability among the three excipients.

Simultaneous adsorption removal of organic and inorganic phosphorus from discharged circulating cooling water on biochar derived from agricultural waste

A high level of organic and inorganic phosphorus exists in discharged circulating cooling water (DCCW), therefore, the efficient removal of phosphorus from DCCW is necessary. Herein, the adsorption performance and mechanism of hydroxyethylidene diphosphonic acid (HEDP) and phosphate from DCCW on pyrolysis biochar derived from agricultural waste (wheat and corn straw wastes, and peanut shell powder) were systematically investigated. Among them, biochar prepared from wheat straw and modified with MgCl2 and CeCl3 (molar ratio 3:1), i.e., WS-3Mg/Ce, showed optimal phosphorus removal from DCCW. The pseudo-second-order and Freundlich model well described the adsorption of HEDP, PO43−, and total phosphorus (TP) on WS-3Mg/Ce. Further, negative Gibbs free energy (ΔG) indicated that WS-3Mg/Ce adsorbed HEDP and phosphate through physical adsorption and chemical reactions, with the chemical reaction being dominant. Scanning electron microscopy-energy dispersive X-ray spectroscopy and X-ray diffraction results revealed that CePO4 and Mg3(PO4)2 appeared on WS-3Mg/Ce after adsorption, and the diffraction bands of metal oxides or hydroxides decreased. Fourier transform infrared and X-ray photoelectron spectroscopy results showed that O–H, M-O, M-O-P, and O–P on the surface of WS-3Mg/Ce participate in the reaction. This suggests that the adsorption of HEDP and phosphate on WS-3Mg/Ce mainly involves metal binding via Ce and Mg, and chemical complex via OH−. This study provides a promising approach for removing different forms of phosphorus simultaneously from DCCW via biochar and contributes to the resource recovery of agricultural and forestry waste. Future work is needed for the optimization of the biochar to promote the adsorption capacity and renewability in treating real DCCW.

What is the role of phytochemical compounds as capping agents for the inhibition of aggregation in the green synthesis of metal oxide nanoparticles? A DFT molecular level response

To control the size of metal oxide nanoparticles, capping agents are often employed in the green synthesis of metal oxide nanoparticles. To guide the role of phytochemical-based capping agents, the interactions between the phytochemicals and nanoparticles have been investigated by DFT method. For this purpose, aucubin, an iridoid glycoside compound, was selected as a model. In this work, an in-depth analysis of the interactions between aucubin and ZnO nanoparticles with different sizes were conducted in gas and water phases. The adsorption Gibbs free energies of all bio-nanocomposites with different sizes were observed to be negative, which indicates the spontaneous nature of the adsorption process. The Eg and Gibbs free energy values of aucubin was found to depend on the size of ZnO nanoparticles. The bio-nanocomposite aucubin-(ZnO)6 has the most negative Gibbs free energy due to the formation of four hydrogen bonds between the aucubin and the nanoparticles. The evaluation of charge decomposition analysis showed that the direction of charge transfer is from aucubin to ZnO. Indeed, we found that both the vdW and electrostatic interactions are present in ZnO-aucubin bio-nanocomposites. The molecular level information provided in this work can be considered as a model for using phytochemicals as capping agents in green synthesis of nanoparticles.

Fabrication of a novel magnetic high entropy alloy with desirable mechanical properties by mechanical alloying and spark plasma sintering

In this study, a novel magnetic CoCuFeMnNi high entropy alloy (HEA) was synthesized using mechanical alloying (MA) and spark plasma sintering (SPS). Thermodynamic analysis showed that the solid solution state of the CoCuFeMnNi alloy system has the highest negative Gibbs free energy (−59.34 kJ/mol), meaning that the solid solution state is very stable. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis confirmed the formation of an FCC solid solution after 50 h mechanical alloying. The vibrant sample magnetometer (VSM) test illustrated a soft magnetic behavior with 48 emu/g magnetic saturation (MS) and 15 Oe coercivity field (HC) in 1 T (T) applied magnetic field. The maximum of densification and microhardness were attained at 850 °C, and the ultimate values of shear strength and tensile strength were 320 MPa and 576 MPa, respectively. The CoCuFeMnNi HEA was subjected to a pin-on-disc dry sliding wear test at various temperatures from room temperature to 600 °C. A detailed microscopic characterization of the worn surfaces revealed a transition in the predominant wear mechanism from delamination wear at room temperature to oxidative and delamination wear at elevated temperatures. The formation of an oxidized tribo-layer at 600 °C on the worn surfaces led to a low wear rate and low coefficient of friction, enabling the CoCuFeMnNi HEA for high-temperature applications.