Standard Free Energy Change Research Articles

Self-assembly of choline-based surface-active ionic liquids and concentration-dependent enhancement in the enzymatic activity of cellulase in aqueous medium.

The micellization of choline-based anionic surface-active ionic liquids (SAILs) having lauroyl sarcosinate [Sar]-, dodecylsulfate [DS]-, and deoxycholate [Doc]- as counter-ions was investigated in an aqueous medium. Density functional theory (DFT) was employed to investigate the net interactional energy (Enet), extent of non-covalent interactions, and band gap of the choline-based SAILs. The critical micelle concentration (cmc) along with various parameters related to the surface adsorption, counter-ion binding (β), and polarity of the cores of the micelles were deduced employing surface tension measurements, conductometric titrations and fluorescence spectroscopy, respectively. A dynamic light scattering (DLS) system equipped with zeta-potential measurement set-up and small-angle neutron scattering (SANS) were used to predict the size, zeta-potential, and morphology, respectively, of the formed micelles. Thermodynamic parameters such as standard Gibb's free energy and standard enthalpy change of micellization were calculated using isothermal titration calorimetry (ITC). Upon comparing with sodium salt analogues, it was established that the micellization was predominantly governed by the extent of hydration of [Cho]+, the head groups of the respective anions, and the degree of counter-ion binding (β). Considering the concentration dependence of the enzyme-SAIL interactions, aqueous solutions of the synthesized SAILs at two different concentrations (below and above the cmc) were utilized as the medium for testing the enzymatic activity of cellulase. The activity of cellulase was found to be ∼7- to ∼13-fold higher compared to that observed in buffers in monomeric solutions of the SAILs and followed the order: [Cho][Sar] > [Cho][DS] > [Cho][Doc]. In the micellar solution, a ∼4- to 5-fold increase in enzymatic activity was observed.

Solubilization study of antihypertensive drug Irbesartan in EO-PO based polymeric nanomicelle and optimization of its release behavior

Irbesartan (IRB) has low bioavailability due to its poor aqueous solubility and dissolution rate, thereby making it imperative to understand their absorption behavior. The present research work is aimed for improvement of solubilization of IRB, by investigating the effect of molecular characteristics/hydrophobicity of Pluronic® copolymers; P84 and F108 micelles with and without added salt (NaCl). The solubility of IRB was increased with copolymer concentration. Effect of added salt (NaCl) showed completely opposite behavior for both the copolymers; where F108 with NaCl has adverse effect on IRB solubilization and considerable decrease was observed. The micelle/water partition coefficient and the standard free energy change (∆G◦) were also evaluated from thermodynamic view point. The in vitro release kinetics of IRB drug was carried out for 1% P84 with and without 1 M NaCl and compared with its release in water. It was found that P84/NaCl reduces the release rate more efficiently for IRB compared to other systems. There are few reports about the solubilization improvement of IRB; but this is the first time where the study of Pluronic® micelle carried out for IRB solubilization with varying solvent condition as per best of our knowledge. This information can be useful to understand the solubilization behaviour of Pluronic® copolymers available in varieties of molecular weights and can be used to identify possible solvent condition for newer applications of Pluronic® copolymers in pharmaceutical field.

Corrosion Inhibition of Expired Cefazolin Drug on Copper Metal in Dilute Hydrochloric Acid Solution: Practical and Theoretical Approaches.

In this work, we studied the corrosion of Cu metal in 0.5 mol L-1 HCl and the inhibition effect of the expired Cefazolin drug. The inhibition efficiency (IE) of Cefazolin varied according to its concentration in solution. As the Cefazolin concentration increased to 300 ppm, the IE increased to 87% at 298 K and decreased to 78% as the temperature increased to 318 K. The expired drug functioned as a mixed-type inhibitor. The adsorption of the drug on the copper surface followed Temkin's adsorption model. The magnitudes of the standard free energy change (ΔGoads) and adsorption equilibrium constant (Kads) indicated the spontaneous nature and exothermicity of the adsorption process. Energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) techniques showed that the drug molecules were strongly attached to the Cu surface. The electrochemical frequency modulation (EFM), potentiodynamic polarization (PP), and electrochemical impedance spectroscopy (EIS) results were in good agreement with the results of the weight loss (WL) method. The density functional tight-binding (DFTB) and Monte Carlo (MC) simulation results indicated that the expired drug bound to the copper surface through the lone pair of electrons of the heteroatoms as well as the π-electrons of the tetrazole ring. The adsorption energy between the drug and copper metal was -459.38 kJ mol-1.

The precipitation process for a rare earth leach solution with calcium oxide in the presence of ascorbate and calcination to oxide of high purity

Sulfate ions coprecipitate with rare earth metal ions to form alkaline rare earth sulfate (RE2(OH)4SO4) in the CaO precipitation process, leading to excessive content of sulfate in the mixed rare earth oxide. Due to the difference of coordination ability between ascorbate, sulfate, hydroxyl and rare earth metal ions, ascorbate is introduced into the pregnant leach solution (PLS) during the CaO precipitation process. It realizes the coprecipitation between ascorbate (C6H7O6−) and rare earth metal ions, reducing the formation of RE2(OH)4SO4 and improving the purity of mixed rare earth oxide. In this paper, the standard reaction Gibbs free energy changes of the possible reactions in the precipitation process were calculated using the group contribution method, to draw the species distribution equilibrium diagram with Newton's iteration method. When ascorbate exists, rare earth metal ions in the PLS tend to form the alkaline rare earth ascorbate (RE2(OH)4(C6H7O6)2) instead of RE2(OH)4SO4. Furthermore, the effect of the reaction conditions on the precipitation process were studied. When the molar ratio of rare earth metal ions to ascorbate was 1.17, the purity of the mixed rare earth oxide was 96.2 wt% and the sulfate content was 2.2 wt%. Finally, based on the results of the material balance calculation, FTIR, XRD and TG-DSC tests, it was further confirmed that ascorbate participated in the form of RE2(OH)4(C6H7O6)2, and effectively suppressed the generation of RE2(OH)4SO4. Consequently, the results facilitate the green and efficient extraction of rare earths from the ion-adsorption type ore.

Association of bovine serum albumin and cetyltrimethylammonium chloride: An investigation of the effects of temperature and hydrotropes

Interactions between bovine serum albumin (BSA) and cetyltrimethylammonium chloride (CTAC) were studied utilizing conductivity approach. The critical micelle concentration (CMC), micelle ionization (α) along with counter ion binding (β) of CTAC micellization in aqueous solutions of BSA/BSA + hydrotropes (HYTs) have been computed at 298.15−323.15 K. Increase in temperatures of CTAC + BSA/BSA mixtures in HYTs resulted in elevation of CMC due to the association of chemical species in the respective systems which reduced the degree of micelle formation. CTAC + BSA consumed greater extents of surfactant species to generate micelle formation in the corresponding systems at higher temperatures. Standard free energy change ∆Gm0 associated with the assembling processes of CTAC in BSA was found negative suggesting the spontaneous nature of micellization processes. Magnitudes of ∆Hm0 and ∆Sm0 obtained from CTAC + BSA aggregation revealed the existence of H-bonding, electrostatic interactions along with hydrophobic forces among the constituents employed in the respective systems. ∆Gm0 The estimated thermodynamic parameters of transfer (free energy (∆Gm,tr0), enthalpy (∆Hm,tr0) and entropy (∆Sm,tr0)) and compensation variables (∆Hm0,∗ and Tc) provided significant insights on the association behaviors of the CTAC + BSA system in the selected HYTs solutions.

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.

Solubilization and partitioning study of nickel fluoride complex [Ni(dmen)2F2].8H2O in the micellar media of sodium stearate by conductometric and spectroscopic techniques

This study was aimed to investigate the physicochemical behavior, solubilization and interaction of coordination complex [Ni(dmen)2F2].8H2O (NDC) with anionic surfactant sodium stearate (SS). The thermodynamic parameters of solubilization such as standard free energy (ΔGm0), enthalpy (ΔHm0) and entropy (ΔSm0) changes of micellization were evaluated by using conductometric measurements. These parameters revealed that the phenomenon of micellization is entropy driven and spontaneous due to the more negative value of (ΔGm0). The quantitative estimation of partitioning parameters such as partition coefficient (Kx), binding constant (Kb), standard energy of partition (ΔGpartO), and standard binding energy (ΔGbindO) revealed the complex-surfactant interaction. Spectroscopic study indicated the high degree of interaction and solubilization of NDC in SS micellar media.. The partitioning results not only governs the mechanism of solubilization but also gives understanding about the partitioning of NDC across membranes in biological systems.

Development and characterization of a clay-HDTMABr composite for the removal of Cr(VI) from aqueous solutions with special emphasis on the electrochemical interface

This research aims to study the removal of chromium in its toxic form, Cr (VI), from wastewater, using clay and modified clay with Hexadecyltrimethyl ammonium bromide (HDTMABr)as adsorbents. The modified clay is obtained by impregnating a known quantity of HDTMABr into the clay. The two materials were characterized by different techniques, such as X-ray diffraction, which is used to determine the inorganic composition and the phyllite structures it contains. Thermal analysis TGA isused to understand the thermal behavior as function of the sintering temperature. Nitrogen adsorption/desorption is used to get the pores' size and surface area, using the Brunauer-Emmett-Teller (BET) theory. Scanning electron microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (SEM/EDAX) is used to study the surface morphology of the bare clay and the HDTMABr/clay. The operating conditions, such as contact times, pH, and adsorption temperatures, were studied, and optimized to improve the efficiency of the adsorption process. The adsorption is favored in acidic medium and room temperature, giving adsorption capacities for Cr(VI) of 12 mg/g and 250 mg/g for the clay and clay/HDTMABr, respectively. The reaction kinetics were studied and found to fit a pseudo-second-order model. The standard entropy (ΔS°), enthalpy (ΔH°), and Gibbs free energy (ΔG°) changes indicate that the chromium (VI) adsorption process is a physical, spontaneous, endothermic process. Cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS) are used for the electrochemical characterization of the raw clay and clay/HDTMABr in [Fe(CN)6]3-/4-/ 0.1 M KCl solution. The linear scan anodic stripping voltammetry (LSASV) is used for the reduction the Cr(VI) to Cr(III), indicating that Cr(VI) accumulates better at the surface of clay/HDTMABr compared to the bare graphite and the raw clay.

Investigation of the impacts of simple electrolytes and hydrotrope on the interaction of ceftriaxone sodium with cetylpyridinium chloride at numerous study temperatures.

Herein, interactions between cetylpyridinium chloride (CPC) and ceftriaxone sodium (CTS) were investigated applying conductivity technique. Impacts of the nature of additives (e.g. electrolytes or hydrotrope (HDT)), change of temperatures (from 298.15 to 323.15K), and concentration variation of CTS/additives were assessed on the micellization of CPC + CTS mixture. The conductometric analysis of critical micelle concentration (CMC) with respect to the concentration reveals that the CMC values were increased with the increase in CTS concentration. In terms of using different mediums, CMC did not differ much with the increase in electrolyte salt (NaCl, Na2SO4) concentration, but increased significantly with the rise of HDT (NaBenz) amount. In the presence of electrolyte, CMC showed a gentle increment with temperature, while the HDT showed the opposite trend. Obtained result was further correlated with conventional thermodynamic relationship, where standard Gibb's free energy change , change of enthalpy , and change of entropy ) were utilized to investigate. The values were negative for all the mixed systems studied indicating that the micellization process was spontaneous. Finally, the stability of micellization was studied by estimating the intrinsic enthalpy gain () and compensation temperature (Tc). Here, CPC + CTS mixed system showed more stability in Na2SO4 medium than the NaCl, while in NaBenz exhibited the lowest stability.

Insight of molecular interactions between short‐chain tetraalkylammonium bromides and cetyltrimethylammonium bromide: A spectroscopic and thermodynamic approach

AbstractThe influence of tetraalkylammonium salts, viz., tetraethylammonium, tetrapropylammonium, and tetrabutylammonium bromides (0.005, 0.010, 0.015 mol kg−1) on the micellar behavior of aqueous solutions of the cationic surfactant cetyltrimethylammonium bromide (CTAB, 0.2–2 mmol kg−1) over the 298.15–313.15 K temperature range has been studied by conductometric method. From conductivity versus surfactant concentration plots, the critical micelle concentration (CMC) of CTAB has been determined, which shows that the tetraalkylammonium bromides promote the formation of CTAB aggregates. Further, from the temperature dependence of CMC values, the degree of ionization, the counterion binding constant along with some thermodynamic parameters of micellization, such as standard free energy change (), standard enthalpy change (), standard entropy change () have been calculated. From the values of , and , it has been concluded that our ternary system is both enthalpy as well as entropy controlled. Similar CMC values were obtained from UV–Visible spectrometry measurements, using pyrene as a probe at ambient temperature. Also 1H‐NMR and FTIR methods give a greater understanding of the molecular scale interactions between the tetraalkylammonium bromides and the cationic surfactant.

Interaction Mechanisms and Predictions of the Biofouling of Polymer Films: A Combined Atomic Force Microscopy and Quartz Crystal Microbalance with Dissipation Monitoring Study.

Biofouling of polymeric membranes is a severe problem in water desalination and treatment applications. A fundamental understanding of biofouling mechanisms is necessary to control biofouling and develop more efficient mitigation strategies. To shed light on the type of forces that govern the interactions between biofoulants and membranes, biofoulant-coated colloidal AFM probes were employed to investigate the biofouling mechanisms of two model biofoulants, BSA and HA, toward an array of polymer films commonly used in membrane synthesis, which included CA, PVC, PVDF, and PS. These experiments were combined with quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The Derjaguin, Landau, Verwey, and Overbeek (DLVO) and the extended-DLVO (XDLVO) theoretical models were applied to decouple the overall adhesion interactions between the biofoulants and the polymer films into their component interactions, i.e., electrostatic (El), Lifshitz-van der Waals (LW), and Lewis acid-base (AB) interactions. The XDLVO model was found to predict better the AFM colloidal probe adhesion data and the QCM-D adsorption behavior of BSA onto the polymer films than the DLVO model. The ranking of the polymer films' adhesion strengths and adsorption quantities was inversely proportional to their γ- values. Higher normalized adhesion forces were quantified for the BSA-coated colloidal probes with the polymer films than the HA-coated colloidal probes. Similarly, in QCM-D measurements, BSA was found to cause larger adsorption mass shifts, faster adsorption rates, and more condensed fouling layers than HA. A linear correlation (R2 = 0.96) was obtained between the adsorption standard free energy changes (ΔGads°) estimated for BSA from the equilibrium QCM-D adsorption experiments and the AFM normalized adhesion energies (WAFM/R) estimated for BSA from the AFM colloidal probe measurements. Eventually, an indirect approach was presented to calculate the surface energy components of biofoulants characterized by high porosities from Hansen dissolution tests to perform the DLVO/XDLVO analyses.

Impacts of several salts on the clouding development, nature of interactions and associated physico-chemical variables of mixture of promethazine hydrochloride and conventional nonionic surfactant

Herein, in the presence of electrolytes, the cloud points (CPs) of the mixture of a conventional uncharged amphiphile (triton X-100 (TX-100)) and promethazine hydrochloride (PMH; phenothiazine medicine) were measured and explained in great details. The CP values of the employed surfactant + PMH system were reduced with enhancing salts contents (NaCl, Na2SO4, NH4Cl, and (NH4)2SO4)), while the CP values of the study system followed the trend: Na2SO4 < NaCl and (NH4)2SO4 < NH4Cl. The different thermodynamic parameters of phase separation, including standard free energy (ΔG 0 c), enthalpy (ΔH 0 c), and entropy (ΔS 0 c) changes were also calculated and discussed elaborately. The values of free energy change (ΔG 0 c) were obtained to be positive, indicating that the clouding phenomena are non-spontaneous. Different transfer properties (free energy (ΔG 0 c.t), enthalpy (ΔH 0 c,t ), and entropy (ΔS 0 c,t ) of transfer), intrinsic enthalpy gain (ΔH 0,*c) and compensation temperature (T c) of the inspected system have also been assessed and discussed.

Influence of polyvinyl alcohol coated porous Al2O3 ceramic waste particles on cement properties in geothermal applications

To improve the low strength of the existing geothermal temporary sealing cement (GTSC) and figure out the influence of PACW on cement performances in geothermal applications, the hard porous Al2O3 ceramic waste (PACW) was introduced into oil well cement. The water-soluble PVA was coated on PACW particles to wrap the porous ceramic at relatively low temperature for geothermal drilling, and dissolve in water at ≥ 90 ℃ for hot water flow. The compressive strength, hydrates, pore structures and interface transition zone of cement with raw or modified PACW were tested. The results showed that 10% raw and modified PACW enhanced the compressive strength of oil well cement by 57.69% and 60.31% respectively, during the 90 ℃ water immersing. For the cement containing 10% raw and modified PACW, thermal weight loss related to degradation of hydrates and CH increased, meso pores fraction rose to 52.73% and 51.93 % respectively, and the deeper etch pits on surfaces of the mineral suggested the promoting effect of PACW on cement hydration. The promoted cement hydration and formed hydrates with their filling effect contributed to the cement strength enhancement. As the thermal weight loss attributed to AFm increased after immersion, the thermodynamic parameters of the possible transformation reaction of AFt to AFm were calculated. The standard molar Gibbs free energy change of the reactions are negative, and microstructure images showed that the PACW surface was covered by lots of flaky AFm crisscrossed with large hexagonal AFt crystals, proving that the alumina in PACW participated in and promoted the transformation of AFt to AFm. In addition to reservoir protection, simplifying construction procedures and reducing the time cost of geothermal development, the high-strength GTSC will further strengthen the hole wall and reduce the risk of borehole collapse.

Sorption characteristics and thermodynamic parameters of bispyribac-sodium and metribuzin on alluvial soil with difference in particle size and pH value

The behavior of bispyribac-sodium and metribuzin herbicides was investigated into alluvial soil. Effect of pH, temperature, and particle size of soil on the sorption process was studied. Sorption isotherms by bulk soil and its sand, silt, clay and humic acid (HA) fractions were quantified using the batch equilibration technique. The results showed that sorption of herbicides tested was significantly affected by temperature and was a spontaneous interfacial process into soil. Freundlich equation accurately predicted the sorption behavior of two herbicides. Thermodynamic parameters summarized that the negative values of the standard free energy changes (ΔG˚) were obtained therefore, the adsorption of tested pesticides in soil was spontaneous and small negative values indicate the sorption is physical in nature involving weak forces of attraction. The negative ΔH˚ value, indicating metribuzin and bispyribac-sodium interactions are exothermic processes and products are energetically stable with a high binding of compound to soil sites. There was an increase in the entropy of tested pesticides-soil systems as shown by positive values of ΔS˚. The highest adsorption in soil was at pH 5 for bispyribac-sodium and at pH 7 for metribuzin. The sorption of metribuzin and bispyribac-sodium were significantly greater on HA fraction followed by clay fraction than the bulk soil. The KF and Kd values increase with decreasing particle size particularly in the case of adsorption of metribuzin.

Applications of spectroscopic techniques to the study of monomer–dimer equilibria for methylene blue in aqueous solutions containing ionic liquid: Probing the structural interactions involving water and ionic liquids

An understanding of the nature of interaction and bonding in dye aggregation process is important for such diverse problems and applications such as stacking interactions in biomolecules, staining properties, photodynamic therapy for cancer, energy transfer in lasing technology and energy transfer and electron transfer processes. In present communication we report visible absorption spectrums and their analysis for the dye methylene blue (MB) in concentration range of 1∙10–6 – 1∙10–4 M in aqueous solutions containing ionic liquids namely, 1–ethyl–3–methyl–imidazolium bromide, 1–butyl–3–methyl–imidazolium bromide and 1–hexyl–3–methyl–imidazolium bromide at 298 ± 1. In this concentration range of MB only Monomer ⇌ Dimer equilibria for the dye exist and hence the spectral characteristics in the visible range of 550–700 nm have been examined. The spectrums obtained are compared with those obtained in aqueous solutions of NaCl. Using suitable developed method of estimating molar absorption extinction coefficient values, the equilibrium constant values are obtained at various ionic strengths of imidazolium ions. It has been found that monomer and dimer absorption maximum occur at 665 and ≈605/610 nm, respectively, do not get much altered on addition of imidazolium ions. The extent of interaction between the MB and imidazolium cations varies with the concentration of imidazolium cations as well as the nature of imidazolium cations, that is, the chain length of the substituents. The dimer dissociation constant values extrapolated to zero ionic strength of ionic liquids exhibit systematic alteration with respect to alteration of chain length in imidazolium cations. The different interactional phenomena such as the formation of ion–pairs, ion–pair complexes, dimer dissociation, solubilization of monomers and binding of MB with imidazolium cations have been examined. The transfer standard free energy changes have been calculated for the transfer of dimers from aqueous solutions to aqueous solutions containing ionic liquids. The changes in dimer geometry from sandwich type and end–on–end types also have been studied. It is observed that the contribution to the interaction energy is mainly from van der Waals type and dispersion forces, in addition to short range forces involving multipoles. The binding of monomers with imidazolium cations is also examined in terms of formation of micellar type aggregates in solution phase. It is proposed that the water structural interaction and hydrophobic interactions are the major factors in the formation and dissociation of aggregates.

Physico-chemical parameters of phase separation of the mixture of BSA and triton X 100 in aqueous solutions of monohydroxy compounds

Clouding behavior and thermodynamic properties for the TX 100 + BSA mixture were investigated in aqueous and aq. alcoholic media. In an aqueous environment, the values of cloud point (CP), at which a clear solution becomes cloudy, for TX 100 decreases with augmentation of the concentration of BSA. The reverse result was obtained in the aq. alcoholic media. In this study, we have used ethanol (EtOH), 1-propanol (1-PrOH), and 2-butanol (2-BuOH) as alcohols. The changes of CP values in alcoholic media have been obtained in the following order: CPH2O+EtOH > CPH2O+2−BuOH > CPH2O+1−PrOH. The standard free energy (∆Gco), standard enthalpy (∆Hco), and standard entropy (∆Sco) changes of clouding were derived at CP. The ΔGc0 values of TX 100 + BSA decreases in the aqueous and alcoholic media with increasing the concentration of BSA and alcohol. This process becomes endothermic in the aq. alcoholic media. Different thermodynamic properties of transfer and entropy-enthalpy compensation parameters for the phase partitioning of the TX 100 + BSA mixture have been calculated and assessed properly.

Double open mouse-like terpyridine parts based amphiphilic ionic molecules displaying strengthened chemical adsorption for anticorrosion of copper in sulfuric acid solution

In this study, the benign target double terpyridine parts based amphiphilic ionic molecules (AIMs 1, 2) and the reference single terpyridine segment included AIMs (AIMs 3, 4) were synthesized through a multi-step method, and the molecular structures were fully characterized. The excellent anticorrosion of the target AIMs for copper surface in H2SO4 solution was demonstrated by the electrochemistry analysis, which was more superior over those of the reference AIMs. The standard adsorption free energy changes of the target AIMs calculated by the adsorption isotherms were lower than –40 kJ·mol−1, suggesting an intensified chemical adsorption on metal surface. The molecular modeling and molecular dynamic computation of the studied AIMs were performed, demonstrating that the target AIMs exhibited lower highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps and greater adsorption energies than the reference ones. The chemical adsorption of the AIMs on metal surface was revealed by various spectroscopic methods including scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, attenuated total reflection infrared spectroscopy, Raman and X-ray diffraction.

Efficient Adsorption Removal of an Anionic Azo Dye by Lignocellulosic Waste Material and Sludge Recycling into Combustible Briquettes

In recent years, the removal of dyes has emerged as a significant problem that attracted several researchers. The search for green and eco-friendly adsorbents has been a never-ending task in environmental protection to overcome this issue. Herein, almond shells (AS) were used as an adsorbent to remove methyl orange (MO) from aqueous solutions. The AS was characterized using several techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). Adsorption experiments were carried out under different pH, temperature, and AS particle size conditions. Kinetic and isothermal studies revealed that MO adsorption on the AS reached equilibrium at 90 min, following the pseudo-second-order (PSO) kinetic model. The Langmuir adsorption isotherm was found the suitable adsorption model for MO adsorption on AS, showing a maximum adsorption capacity of 15.63 mg/g. Thermodynamic parameters such as the change in standard enthalpy (ΔH°), the change in standard entropy (ΔS°), and the change in standard free energy (ΔG°) indicated that the MO dye adsorption process is non-spontaneous, endothermic, and physical, which was further confirmed from FTIR analysis of AS samples after adsorption. The contaminated sludge was converted into biochar by slow pyrolysis at a temperature of 400 °C for 2 h. Biochar has been exploited for the manufacture of combustible briquettes.

Role of core-shell structure in binary mixture of amino sulfonate amphoteric surfactant with nonionic surfactant in solubilization behavior of pyrene

In order to understand the role of core-shell structure of mixed surfactant micelle and the effect of hydrophilicity of amphiphile in the enhanced remediation of contaminated soils and water, a novel amphoteric sodium 3-(N-dodecylethylenediamino)− 2-hydroxypropyl sulfonate (C12AS), three nonionic octylphenol polyoxyethylated ethers with unit number n of oxyethylene glycol ether (OP-n, n = 4, 7 and 10) and these binary mixtures of C12AS/OP-n were adopted to probe the solubilization behavior of pyrene by both the UV–vis spectrometric and the 1H NMR techniques. Some parameters including the molar solubilization ratio (MSR), the partition coefficient (Pm), the standard free energy change (∆Gp) of partition, the interaction parameter (B) based on regular solution theory and the ratio (K1/n) of first stepwise association coefficient (K1) and aggregation number (n) in mixed micelle were estimated using different models. In these single surfactants, the values of MSR and Pm depend mainly on the hydrophilic-lipophilic balance (HLB) of amphiphiles for the homologues of OP surfactants. The solubilization behavior in these mixtures, however, does not again follow the HLB effect, but is subjected to the mixing ratio of component in mixed micelle and the micellar structure. The data from these B and K1/n values can gain some understanding in tune with these parameters, e.g., MSR, Pm, R, etc. Based on the chemical shift of hydroxyl group, the core-shell structure of mixed micelle assumed in this investigation is proposed to demonstrate the solubilization locus and rationally describe the spontaneous process of solubilization and the related behaviors. These findings will help with understanding the solubilization behavior of hydrophobic organic compounds in these surfactants with a core-shell structure of micelle and designing the surfactant formulations in the surfactant enhanced remediation of contaminated soils and water.

Mode of interaction of altretamine with calf thymus DNA: biophysical insights

Insights into drug-DNA interactions have importance in medicinal chemistry as it has a major role in the evolution of new therapeutic drugs. Therefore, binding studies of small molecules with DNA are of significant interest. Spectroscopy, coupled with measurements of viscosity and molecular docking studies were employed to obtain mechanistic insights into the binding of altretamine with calf thymus DNA (CT-DNA). The UV-visible spectroscopic measurements study confirmed altretamine-CT-DNA complex formation with affinity constant ([15.68 ± 0.04] × 103 M−1), a value associated with groove binding phenomenon. The associated thermodynamic signatures suggest enthalpically driven interactions. The values of standard molar free energy change () -(23.93 ± 0.23) kJ mol−1, enthalpy change () -(50.84 ± 0.19) kJ mol−1 and entropy change () -(90.29 ± 0.12) JK−1 mol−1 indicate the binding is thermodynamically favorable and an important role of the hydrogen bonds and Van der Waals interactions in the binding of altretamine with CT-DNA. Circular dichroism spectroscopy indicated insignificant conformational changes in the DNA backbone upon interaction with altretamine suggesting no distortion and/or unstacking of the base pairs in the DNA helix. UV-melting study suggested that the thermal stability of the DNA backbone is not affected by the binding of the drug. Competitive displacement assays with ethidium bromide, Hoechst-33258 and DAPI established the binding of altretamine with CT-DNA in the minor groove. The mode of binding was further confirmed by viscosity and molecular docking studies. Molecular docking further ascertained binding of altretamine in the minor groove of the CT-DNA, preferably with the A-T rich sequences. Highlights Altretamine binds CT-DNA which is enthalpically driven with Ka of the order of 103 Insignificant conformational change is observed due to DNA-altretamine complexation Altretamine binds favorably with A-T rich sequences in the minor groove of CT-DNA Mechanistic insights obtained based on thermodynamic signatures Communicated by Ramaswamy H. Sarma