Standard Enthalpy Change Research Articles

Green corrosion inhibitors for nickel in acidic media utilizing novel imine ligand and its Zn (II) metal chelate supported by DFT calculation

L and ZnL complex act as corrosion inhibitors were synthesized and their structural elucidation were characterized via various spectroscopic and physicochemical tools. Correlation of experimental data with DFT calculation affords that ZnL complex is octahedral. L and ZnL compounds were used as essential components and environmentally benign inhibitors to reduce the rate at which Nickel as metal and its alloys corroded. In the investigative research, 0.5 M H2SO4 was used as the corroding medium. Electrochemical impedance spectroscopy and the Tafel plot were used to analyse the electrochemical performances of L, its complex with Zn, and the inhibitory effect in the acid under test. Processes of Ni corroding in an acidic solution have been examined in relation to additive existence and deficiency. The obtained data demonstrate that while the inhibitory effect increases as the dose of the additives is increased, density of corrosion current Icorr. gradually decreases. It is noted that inhibition efficiency decreases with increasing temperature especially at high temperature (55 °C) in the case of presence of 1 × 10−3 M of L as an additive (η = 70.4 %). Although, in the case of utilizing ZnL complex as an additive, it in noted that inhibition efficiency η% is nearly the same and slightly changed with raising temperature. In the case of existence high dose of ZnL, η% slightly increases with temperature indicating chemisorption process of the additive on Ni surface in the acidic medium. When the additives are present in the solution, both the cathodic and anodic reaction processes are impacted. Furthermore, the presence of the ligand or its complex reduces the amount of NiO that forms on the electrode’s exterior sides. This finding implies that the adsorption mechanism of ZnL additive species follows Langmuir model and that kind of ligand and its complex adsorption on its outside are chemical in nature. These results have also been confirmed by electrochemical impedance spectroscopy. The ligand and its complex were included as additives, which significantly improved nickel’s corrosion resistance, according to the results. Studies on the effects of temperature have been done with different additive doses and Tafel plot method. High activation energy value of (−79.3 kJ. mol−1) was achieved when using 1 × 10−4 M of the L as well as (−82.8kJ. mol−1) in the presence of 1 × 10−3 M of ZnL in 0.5 M H2SO4. The standard enthalpy change ΔH0ads. for Ni in the acidic medium taking many dosages of L and ZnL were −31.16 and –32.72 kJ/mol, respectively. In light of this result, the adsorption process was chemisorption and the adsorption method was exothermic. Positive ΔS0ads values are correlated with an increase in solvent energy and a rise in the water desorption entropy. Employing scanning electron microscopy, the outward side morphology of the corroded samples was examined. Through a scanning electron microscope, the framework and texture of the films of oxide that are generated on Ni after potentiodynamic polarisation at different doses of ZnL additive are apparent.

Understanding the thermodynamic effects of chemically reactive working fluids in the Stirling heat pump

Within the realm of sustainable heating technologies, this study examines the performance of a Stirling heat pump employing chemically reactive working fluids in contrast to conventional inert counterparts. Reactive working fluids are energy vectors that enable the conversion of not only thermal but also chemical energy within the heat pump. The investigation spans a wide range of theoretical reactive gaseous mixtures, leveraging the ideal gas mixture thermodynamic model. Each fluid is characterized by an equilibrated chemical reaction, denoted as A2(g)⇄2A(g), and distinguished by a set of reaction coordinates: the standard entropy change of reaction and standard enthalpy change of reaction. The chemical reaction evolution and thermodynamic properties are observed in each transformation, and the overall coefficient of performance (COP) of the system is evaluated and benchmarked against that of comparable inert working fluids. It is observed that the exothermic reaction during isothermal compression significantly increases the thermal energy supplied to the heat sink, as well as the thermal energy density per unit maximum volume, by up to 269 %, compared to an inert gas system. However, for the majority of reactive fluids studied, chemical reactions introduce irreversibility in the internal regenerator due to heat transfer across a finite temperature difference, contrary to the case of inert working fluids, penalizing the COP. Consequently, a reduction of up to 28 % in the COP is observed. Nevertheless, there exists a range of reactive fluids, characterized by reversible heat exchange in the internal regenerator, offering increased thermal energy transfer to the heat sink without compromising the COP.

Thermodynamic and CO2 sorption investigations on improved Li3BO3-based sorbents by NaOH addition

The development of new solid sorbents with high carbon capture capacity and good reversible sorption properties is considered a key factor for mitigating CO2 emissions. Tri-lithium borate (Li3BO3) has shown to be a high-capacity CO2 sorbent adequate for an intermediate temperature range (500–650 °C). However, the performance of this sorbent has been little studied in particular at low CO2 concentrations, requiring the introduction of changes in Li3BO3 to make it competitive. Here, highly efficient NaOH-modified Li3BO3 sorbents were synthesized by a simple two-step mechano-thermal method at low temperature using different amounts of NaOH. For the first time, the influence of increasing amounts of an additive on the standard enthalpy change of Li3BO3 as well as on the relation between CO2 pressure and temperature equilibrium was determined. A progressive rise in the standard enthalpy change and a decrease in the equilibrium CO2 pressure at a fixed temperature were observed with the increase in the amount of additive. Moreover, the NaOH addition to Li3BO3 improves its CO2 capture capacity, CO2 absorption rate and stability during carbonation/regeneration cycles. The CO2 capture capacity ranges between 50 wt% and 35 wt% at pure CO2 and 15 % CO2, respectively, for low amounts of NaOH added. Further studies showed that CO2 capture/desorption efficiency is kept high after 20 cycles at 525 °C and 15 % CO2. The improved performance of NaOH-modified Li3BO3 sorbents and the changes in the thermodynamic properties were associated with two factors: the partial substitution of boron by carbon in the Li3BO3 structure, and the formation of Li2CO3-Na2CO3 molten carbonates. Therefore, these NaOH-modified Li3BO3 materials represent attractive CO2 sorbents for moderate temperatures, applicable for post-combustion industrial processes.

Solubility enhancement of metronidazole using natural deep eutectic solvents: Physicochemical and thermodynamic studies

This research aimed to explore the utility of natural deep eutectic solvents (NADES) as the co-solvents for slightly water-soluble metronidazole (MNZ). After testing 70 wt% (percentage by weight) aqueous mixtures of seven NADESs, it was found that MNZ had the highest solubility in water solutions of NADES composed of choline chloride (ChCl) and citric acid (CA). The solubility of MNZ (expressed as 103 mol fraction) increased with the concentration of ChCl:CA NADES (from 6.7743 to 26.8518 at 298.5 K, for 30 and 70 wt% NADES-water mixtures, respectively), and it was more effective when compared to aqueous solutions of individual NADES components with wt% corresponding to these in the NADES-water mixtures. The study also found a preferable mixing of MNZ with aqueous solutions of NADES reflected by negative values of standard molar enthalpy change of mixing (approx. − 4.2 kJ·mol−1), compared with positive values in the case of MNZ mixing with water or ChCl aqueous solutions (approx. 7.3 kJ·mol−1). Comparative research conducted on the volume and acoustics of MNZ in water and aqueous solutions of ChCl, CA, and ChCl:CA NADES also confirmed stronger interactions between the drug and NADES and CA. The dominant interactions between MNZ and co-solvent were hydrophilic-hydrophobic and hydrophobic-hydrophobic. This effect increased in the following strength order: ChCl < NADES < CA. In conclusion, the obtained NADES seems to be a promising co-solvent which provides solid grounds for further research to evaluate the full potential in pharmaceutical design of MNZ liquid formulations.

Thermodynamic characteristics and surface free energy analysis of bifonazole and lecithin with sodium dodecyl sulfate in hydroethanolic solvent systems

The thermodynamic investigations of the well-recognised antifungal drug bifonazole and lecithin with anionic surfactant sodium dodecyl sulphate have been established. The experiments were conducted using five distinct hydro-ethanolic concentrations, namely 0% v/v, 10% v/v, 30% v/v, 70% v/v, and 90% v/v ethanol, throughout a range of five temperatures (ranging 20 ℃, 25 ℃, 30 ℃, 35 ℃ and 40 ℃) with an increment of drug concentration. The study involved the determination of several parameters, including surface tension (σ), density (ρ), conductivity (κ), contact angle (θ) and surface free energy. Conductivity and surface tension data was used for calculating critical micelle concentration (CMC). CMC was utilised to calculate various thermodynamic properties, such as the standard entropy change (ΔS°m), standard Gibbs energy change (ΔG°m) and standard enthalpy change (ΔH°m) of micellization. This study represents a comparative analysis of the critical micelle concentration (CMC) by utilising surface tension and conductivity measurements. Contact angle is used to determine the hydrophobicity and hydrophilicity of the system. These investigations are valuable for examining the magnitude of hydrophobic interactions within the system, which might be used to ascertain an optimal concentration of bifonazole, lecithin and surfactant to prepare ethosomal formulations.

In-Vitro Study of the Binding of Atorvastatin with Adenine using Multi-Spectroscopic Approaches.

Atorvastatin-an oral lipid regulating drug is a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase), which is the rate determining enzyme for cholesterol synthesis. Adenine is a purine nucleobase that is found in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) to generate genetic information. The binding mechanism of atorvastatin and adenine was studied for the first time utilizing various techniques, including UV-visible spectrophotometry, spectrofluorimetry, synchronous fluorescence spectroscopy (SF), Fourier transform infrared (FTIR), fluorescence resonance energy transfer (FRET), and metal ion complexation. The fluorescence spectra of the complex indicated that atorvastatin is bound to adenine via hydrophobic interaction through a spontaneous binding process, and the fluorescence quenching mechanism was found to be static quenching with a binding constant of 1.4893 × 104 Lmol-1 at 298 K. Various temperature settings were used to investigate thermodynamic characteristics, such as binding forces, binding constants, and the number of binding sites. The interaction parameters, including the standard enthalpy change (ΔHο) and standard entropy change (ΔSο) were calculated using Van't Hoff's equation to be 42.82 kJmol-1 and 208.9 Jmol-1K-1, respectively. The findings demonstrated that the adenine- atorvastatin binding was endothermic. Furthermore, the results of the experiments revealed that some metal ions (K+, Ca+2, Co+2, Cu+2, and Al+3) facilitate the binding interaction between atorvastatin and adenine. Slight changes are observed in the FTIR spectra of adenine, indicating the binding interaction between adenine and atorvastatin.

Activated carbon from macadamia nutshells for removal of p-Nitrophenol from real wastewater: Thermodynamic evaluation

This Water pollution by organic pollutants have remained a matter of significant apprehension since they tend to accumulate in the body to toxic levels and are often resistant to degradation and consequently endure in the surroundings for an extended duration. Phenolic compounds are among organic pollutants that have gained significant attention in research, due to the various ways these compounds can be used in our everyday activities. Among the most common derivatives of phenols is P-Nitrophenol (PNP), which is one of the most common and toxic pollutants found in wastewater. The nutshells were first charred in a muffle furnace at 600 ͦ C. The resultant ash was then activated and utilized for the adsorption of PNP from the wastewater. In this study, we utilized macadamia nutshell waste, both in its untreated and activated forms, which had been prepared earlier, to investigate the thermodynamic aspects of adsorbing p-Nitrophenol ions from wastewater. The scanning electron microscopy (SEM) images demonstrated the existence of pores within the adsorbent material, which proved to be advantageous for the adsorption process. Furthermore, the Fourier-transform infrared spectroscopy (FTIR) results indicated the presence of functional groups in both the unaltered and modified resins, highlighting their significance as sites for studying the thermodynamics of adsorbing copper p-Nitrophenol ions. The thermodynamic analysis revealed that the standard Gibbs' free energy (ΔG°) values for all metals were negative, indicating that the adsorption process was not only feasible but also favorable. Additionally, the standard enthalpy change (ΔH°), standard entropy (ΔS°), and activation energy (Ea) were all positive and greater than 50 kJ mol-1. This observation confirmed that the adsorption of p-Nitrophenol ions onto both unaltered and modified adsorbents was primarily governed by chemical interactions between the PNP ions and the active sites of the adsorbent material. This conclusion was further supported by the exceedingly low values of sticking probability (S*). This investigation did not only show a good performance of the modified macadamia agricultural waste in adsorbing the PNP ions but also provided another way of reducing the negative effects caused by the nutshells disposed in the environment.

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.

Phase behaviour and thermodynamics of triton X-100 + metformin hydrochloride mixture: influences of several polyols and polymer media

The applications of surfactants and drugs in a wide variety of fields such as pharmaceuticals, food industry, textile, fabrics, etc. are increasing significantly. Herein, we investigated the clouding behavior and thermodynamics of triton X-100 (TX-100) and metformin hydrochloride (MNH) drug mixture in the effect of several polyols and polyethylene glycol (PEG) polymer. The phase separation behavior of the mixture of TX-100 + MNH has been deduced with the help of the cloud point technique. The cloud point (CP) values for the TX-100 and drug mixtures were documented in a decreased and increased manner with the augmentation of the concentration of polyol and PEG respectively. With the subsequent enhancement of polyol and PEG content, the CP values were recorded in the following order: C P H 2 O + PEG > C P H 2 O + fructose > C P H 2 O + glucose > C P H 2 O + galactose > C P H 2 O + maltose . The standard enthalpy change ( Δ H c o ) and entropy change ( Δ S c o ), of TX-100 + MNH mixture in aq. polyols solutions were documented as negative; the negative values reduce in magnitudes with the polyols contents and become positive at the highest polyol content while opposite trend was obtained in presence of PEG. The presence of electrostatic and hydrophobic interactions among TX-100/MNH/polyols/polymer has been recommended as the interaction forces.

Advanced Pyrene Copolymer/rGO Hydrogels for Efficient Congo Red Removal from Aqueous Systems

AbstractThis study investigates the use of hydrogel semi‐interpenetrating polymer networks (semi IPN) as efficient adsorbents for removing the dye congo red (CR) from aqueous solutions. Specifically, three hydrogel semi IPN, namely AH0–AH2, were synthesized through redox polymerization of acrylamide, polyethylenimine, polyhydroxylethylmethacrylate and (pyren‐1‐yl)methyl methacrylate/2‐acrylamido‐2‐methylpropane‐1‐sulfonic acid copolymer (pyrene−AMPS) using a reduced graphene oxide (RGO)‐N,N’‐methylene‐bis(acrylamide) (MBA)‐based crosslinker (GABC). Results indicated that these hydrogels were efficient in removing CR at pH 6.73, with the adsorption behaviour conforming to the Langmuir isotherm. This suggests a monolayer adsorption pattern, indicating a chemical nature. Thermodynamic analysis supports the practical feasibility of this process. The negative Gibbs free energy of adsorption (ΔG̊) indicates that adsorption is spontaneous and favorable. Conversely, the positive standard entropy of adsorption (ΔS̊) suggests an increase in molecular randomness during the process. Additionally, the standard enthalpy change (ΔH̊) suggests an endothermic activation energy for the binding process. Response Surface Methodology (RSM), utilizing four variables was employed to optimize the removal of CR. The model demonstrated high R2‐values and strong agreement between experimental and projected results, affirming its reliability. AH1 and AH2 showed significant efficacy in removing CR dye from aqueous solutions, underscoring their potential application in wastewater remediation.

Structure and Ultrafast X-ray Diffraction of the Hydrated Metaphosphate.

We study the pathway of metaphosphate hydration when a metaphosphate anion is dissolved in liquid water with an explicit water model. For this purpose, we propose a sequential Monte Carlo algorithm incorporated with the ab initio quantum mechanics/molecular mechanics (QM/MM) method, which can reduce the amount of ab initio QM/MM sampling while retaining the accuracy of the simulation. We demonstrate the numerical calculation of the standard enthalpy change for the successive addition reaction PO3-·2H2O + H2O ⇌ PO3-·3H2O in the liquid phase, which helps to clarify the hydration pathway of the metaphosphate. With the obtained hydrated structure of the metaphosphate anion, we perform ab initio calculations for its relaxation dynamics upon vibrational excitation and characterize the energy transfer process in solution with simulated ultrafast X-ray diffraction signals, which can be experimentally implemented with X-ray free-electron lasers.

Defective NH2-UiO-66 for effective Pb(II) removal: Facile fabrication strategy, performances and mechanisms

Defective NH2-UiO-66 adsorbent (named as NH2-UiO-66-SD) was successfully fabricated via post-synthesis method with the aid of both sodium carbonate anhydrous (Na2CO3) and diethylenetriaminepentaacetic acid (DTPA), in which the defective structure was confirmed by various characterizations. The as-obtained defective NH2-UiO-66-SD exhibited outstanding Pb(II) sorption capacity (172.21 ​mg ​g−1) and rapid diffusion rate (29.87 ​mg ​g−1 min−0.5) at room temperature with optimal pH being 5.47. The Pb(II) sorption behavior was conformed to pseudo-second-order kinetics and Langmuir model, demonstrating that the chemical sorption of the monolayer played a dominant model. As well, the thermodynamic parameters like standard Gibbs free energy change ΔGo (−31.21 ​kJ ​mol−1), standard enthalpy change ΔHo (12.79 ​kJ−1 ​mol−1) and standard entropy change ΔSo (146.73 ​J ​mol−1 ​K−1) revealed that the Pb(II) sorption process of NH2-UiO-66-SD was spontaneous, endothermic and disordered. Furthermore, the NH2-UiO-66-SD exhibited desirable desorption and recirculation performances (removal efficiencies >85 ​% in 5 runs) with ideal stability. Moreover, the Pb(II) sorption mechanism of NH2-UiO-66-SD mainly included the electrostatic attractions and coordinative interactions. Overall, this work offered an intriguing method of fabricating defective NH2-UiO-66 adsorbent, which vastly enhanced adsorption efficiency for toxic metal ions elimination from wastewater.

Removal of hexavalent chromium from electroplating wastewater by ion-exchange in presence of Ni(II) and Zn(II) ions

This study presents the ion-exchange elimination of hexavalent chromium [Cr(VI)] from electroplated industrial wastewater. The effects of experimental factors such as pH, contact time, adsorbent dose, temperature, and co-ions on Cr(VI) removal were investigated. The metal ions were maximally removed (up to 96.7 %) and obtained with a resin dosage of 3 g L−1 at pH 2 for 70 min. Thermodynamic parameters, such as the standard Gibbs free energy change (ΔG0), standard enthalpy change (ΔH0),and standard entropy change (ΔS0), were calculated. The negative value of ΔG0(−8.031 kJ/mol K)indicates the spontaneity of the ion exchange process. The Freundlich and Langmuir isotherms fit the adsorption data well. The adsorption kinetics of Cr(VI) on the Amberlite IRA400 resin were analyzed using reversible first-order kinetics. The presence of Zn(II) and Ni(II) increased the efficiency of the adsorption process in the order Zn(II) > Ni(II). Column experiments were conducted to determine the breakthrough point of the packed-bed resin column, and a break-even concentration of 0.1 mgL−1 was deducted after the treatment of 4.5 L of the effluent. The adsorption data from the column studies were fitted using the Adam–Bohart adsorption model and the results fit the model well. A mathematical approach to the regeneration process is described in this study. The reusability of the resin was tested for 30 cycles and its efficiency of the regenerated resin was found to be above 97 % after the 30th cycle.

Adsorption of aqueous Cr (VI) onto UiO66NH2 MOF: Isotherm, thermodynamics and mechanism studies

As a member of the UiO-66 family, UiO66NH2 MOF (UNH) possessed enhanced stability, high surface area, increased pore size, and pore volume. Additionally, its amino groups offer spectacular affinity to capture Cr (VI). With these propitious features, UNH was fabricated by a facile solvothermal route in this study. It was then characterized by XRD and FTIR to confirm its successful formation. Its affinity towards efficacious capture of aqueous Cr (VI) was explored with the help of isotherm models and thermodynamic parameters. The Langmuir isotherm model fits best the experimental data, demonstrating monolayer Cr (VI) sorption on a homogenous UNH surface. The maximum adsorption capacity was determined as 51 mg/g. Negative ΔG° values suggested that the Cr (VI) uptake process is spontaneous and favorable, while the endothermic nature of the sorption was evident from positive values ΔH°. Thermodynamic parameters such as standard enthalpy change (ΔH°), standard entropy change (ΔS°), and standard Gibbs free energy change (ΔG°) were determined as 6.651 kJ mol−1, –3.216 kJ mol−1, and 33.76 KJ K−1.mol−1 respectively. FTIR and pH studies evidenced that the sequestration of Cr (VI) onto UNH proceeds through the electrostatic attraction mechanism, supported by the fitted isotherm model and thermodynamic parameters’ results.

Assessing hydrophobic deep eutectic solvents for intramolecular excimer formation.

Intramolecular excimer formation by a dipyrenyl probe, 6-(1-pyrenyl)hexyl-11(1-pyrenyl)-undecanoate [1-Py(CH2)10COO(CH2)61-Py], is used to assess hydrophobic deep eutectic solvents (HDESs) for the purpose. n-Decanoic acid (DA), L(-)-menthol (Men) and thymol (Thy) have been utilized to form HDESs with different pairs of constituents in different molar ratios, namely Men : DA (2 : 1, 1 : 1, and 1 : 2), Thy : DA (2 : 1, 1 : 1, and 1 : 2), and Thy : Men (5 : 1, 2 : 1, 1 : 1, 1 : 2, and 1 : 5). The maximum of the excimer-to-monomer emission intensity ratio, (IE/IM)max, is observed at 343.15-353.15 K for all DESs irrespective of the constitution, and it varies in a narrow range exhibiting no correlation with the dynamic viscosity (η) of the DES which varies between 2.05 and 3.56 mPa s. Excited-state intensity decay data reveal excimer dissociation back to the excited monomer to be negligible in all DESs at lower temperatures (T ≤ 323.15 K); the simplistic Birks scheme is followed at higher temperatures (T > 323.15 K). The rate constant for excimer formation/association, ka, ranges from (3.00 ± 0.50) × 106 s-1 to (103 ± 10) × 106 s-1, which is similar to that reported in other media. The temperature-dependence of the equilibrium constant for excimer formation follows the van't Hoff equation with recovered standard enthalpy (ΔaH*⊖) and standard entropy (ΔaS*⊖) changes, indicating the reversible intramolecular excimer formation to be exothermic and energetically-favorable but entropically unfavorable. A plot of kavs. T/η for all the DES systems investigated exhibits a fairly good linear correlation, indicating the adherence to the Stokes-Einstein formulation within the HDESs further emphasizing the homogeneous nature of the solubilizing media. The work helps to highlight the potential of HDESs for intramolecular excimer formation involving non-polar reactants.

Deciphering the spectroscopic and thermodynamic aspects of binding of biologically important antioxidants with the alkali induced state of human serum albumin.

Protein-ligand interactions are crucial for developing and identifying novel therapeutic targets. In this study, we investigate the interaction of the alkali induced state of human serum albumin (pH 11.2) with three hydroxycinnamic acid derivatives (HCDs), ferulic acid (FA), sinapic acid (SA) and trans-o-coumaric acid, which are biologically important antioxidants, and compare the outcomes with the results obtained at physiological pH (7.4). This study aims to explore the interaction of altered protein conformation with small molecules. Spectroscopic characterization methods show that the conformation of HSA and the ionic properties of HCDs are pH-dependent. Fluorescence, FRET and lifetime measurements reveal that the binding of HCDs with HSA is different at both pH 7.4 and 11.2. Despite the moderate binding of HCDs to HSA, circular dichroism and thermal denaturation studies report no conformational changes in HSA in the presence of HCDs. Isothermal titration calorimetry is employed to assess their binding based on structure and energetics using thermodynamic parameters. Standard molar enthalpy change (ΔH0m) and standard molar entropy change (ΔS0m) values vary with the change of pH from 7.4 to 11.2 with the contributions from the exothermicity and hydrophobicity of functional and aromatic groups of HCDs. Ferulic acid (FA) and sinapic acid (SA) binding to HSA is entropically driven, whereas trans-o-coumaric acid (CA) acid binding is enthalpically favourable. Our ITC studies also reveal that the involvement of -OH functional groups present in CA in binding with HSA is greater than that present in FA and SA at pH 11.2. Overall, this experimental study shows the comparable binding strength of HCDs to both the alkali-induced state of HSA and native HSA (pH 7.4). However, the mechanism of their binding is different.

Molecular interactions of cationic/anionic surfactants in presence of anionic antibiotic drug cloxacillin sodium at different temperatures: Micellization and thermodynamic studies

The physicochemical properties and interactions of surfactant–drug aggregates are regarded as essential features to achieve optimum therapeutic action of the drug. In this article, the effect of various concentrations of anionic antibiotic drug cloxacillin sodium (ClxNa) on the micellization of cationic surfactants such as cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB) and anionic surfactant sodium dodecyl sulphate (SDS) have been investigated using electrical conductance measurement at different temperatures (288.15 K, 293.15 K, 298.15 K, 303.15 K, 308.15 K, and 313.15 K). The results suggest an increase in critical micelles concentration (CMC) values for cationic surfactants (CTAB/TTAB) with a rise in drug concentration (0 mM up to 10 mM) whereas anionic surfactant SDS shows a decrease in CMC at higher drug concentrations (from 2.5 mM up to 10 mM) at all the studied temperatures. The degree of counterion dissociation (α) values for TTAB aggregates show a slight increase with [ClxNa], except at a few lower temperature ranges whereas such a regular trend was not obtained for CTAB and SDS aggregates. Temperature-dependent CMC values show a nonlinear nature with a rise in temperatures and follow a U-shaped curve for all studied pure surfactant and surfactant–ClxNa systems. Micellization for all surfactant-drug systems is found to be spontaneous. Investigation of other temperature-dependent thermodynamic parameters such as change in standard enthalpy (ΔHm0), and entropy (ΔSm0) of micellization suggest that surfactant–drug interactions are both endothermic (ΔHm0 < 0, particularly at lower temperatures) and exothermic (ΔHm0 < 0, at higher temperatures), whereas micellization is largely entropically driven (ΔSm0 > ΔHm0).

Exploring the interactions of anionic dye tartrazine with cationic surfactants in aqueous solution: Insights into micellization and interfacial properties

Different techniques such as conductometric, tensiometric and spectroscopic methods were deployed to investigate the interactions of tartrazine (TZ) dye with cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) in aqueous media at four temperatures. Results revealed a lower cmc values for CPB as compared to CTAB in presence/or absence of aqueous TZ solutions. A qualitative analysis, using UV–vis spectroscopy, was carried out to understand the interactions between the dye TZ and CTAB/CPB in the premicellar and post micellar phase. Interfacial properties such as surface excess concentration (Γmax), area occupied per surfactant molecule (Amin), surface pressure (πcmc), standard Gibbs energy of adsorption (ΔGado), packing parameter (P), etc., were evaluated at air–water/aqueous TZ solution of CTAB/CPB. The equilibrium model was used to determine the change in standard Gibbs energy (ΔGm0), enthalpy (ΔHm0), and entropy (ΔSm0) of micellization. Due to the interruption of the structured water molecules encasing the hydrophobic groups of the surfactant, the critical micelle concentration (cmc) rose with temperature. For both the studied systems, the values of ΔGm0 and ΔHm0 were negative, implying that the process of micellization is thermodynamically spontaneous and exothermic. The -TΔSm0 values, which were found to be greater than ΔHm0 values, suggest the gain in entropy primarily governs the process of micellization.

Phase partitioning nature, interaction forces and thermodynamic parameters of triton X-100 and bovine serum albumin mixture: impacts of the composition of Na-salt

Herein, the assessment of interactions between a non-ionic surfactant (NIS) triton X-100 (TNX-100) and a globular protein bovine serum albumin (BSA) was explored through the determination of clouding nature in aqueous solution of sodium salts (Na-salts). Sodium chloride (NaCl), sodium acetate (NaOAc), sodium carbonate (Na2CO3), sodium oxalate (Na2Oxal), sodium sulphate (Na2SO4), and sodium phosphate (Na3PO4) have been chosen to assess their impacts on the clouding nature of TNX-100 + BSA mixture. The estimated cloud point (CP) values were noticed to be lowered with the enhancement of [Na-salts]. The lessening of CP values has been explained by the salting out effect of anions. The calculated standard Gibbs free energy change ( Δ G c o ) was positive at all examined conditions which illustrates the nonspontaneity of phase change. The standard enthalpy ( Δ H c o ) and entropy ( Δ S c o ) changes exhibited negative values at low contents of aq. Na-salts and positive values at high aq. Na-salts content. These consequences illustrate the presence of electrostatic interactions at low Na-salts concentration and hydrophobic interactions at high Na-salts concentration. Furthermore, enthalpy-entropy parameters were successfully computed and explained with proper clarification.

Adsorption behavior and mechanisms of the emerging antibiotic pollutant norfloxacin on eco-friendly and low-cost hydroxyapatite: Integrated experimental and response surface methodology optimized adsorption process

In this study, hydroxyapatite derived from bovine bone (nat-HAp) was used to remove norfloxacin antibiotic (NOR) from an aqueous solution. The nat-HAp properties were interpreted by analysis of the structure, specific surface area, functional groups, morphology, and composition. The pseudo-second-order kinetic and Langmuir isotherm suit the experimental data on NOR adsorption very well. Maximum absorption was shown to be 166.01 mg g−1. Using a response surface methodology (RSM), the highest NOR elimination of 96.20 % was obtained under optimum conditions: NOR of 132.57 mg L–1, pH of 7.88, nat-HAp dose of 0.99 g L–1, and temperature of 25.06 °C. Thermodynamic studies demonstrated that the adsorption process was favorable, spontaneous, and exothermic. The value of standard enthalpy change (ΔH0) shows that physisorption controlled the adsorption, and for this purpose, a viable mechanism for the adsorption of NOR onto nat-HAp was suggested. Based on the reusability experiment, the nat-HAp remained stable after four cycling runs. These results show that nat-HAp effectively absorbed NOR and might be a cost-effective alternative adsorbent to eliminate fluoroquinolone antibiotics during wastewater treatment.