Standard Enthalpy Change Research Articles

Calorimetric, spectroscopic and molecular modelling insight into the interaction of gallic acid with bovine serum albumin

Abstract Gallic acid (GA), a naturally occurring plant phenolic acid, effectively used as antioxidant, anti-carcinogenic, antifungal, anti-inflammatory and in anti-human rhinovirus activities. The present study reports in vitro interaction studies of Gallic acid (GA) with bovine serum albumin (BSA) by using isothermal titration calorimetric (ITC), fluorescence, circular dichroism (CD) and molecular modelling studies. The association constant (Ka), standard enthalpy change (ΔHo), standard entropy change (ΔSo) and standard Gibbs energy change (ΔGo) were obtained from ITC. The fluorescence results indicate that there was static quenching mechanism in the interactions of GA with BSA. The synchronous and 3D fluorescence spectroscopy confirms conformational alteration of BSA in presence of GA which is further supported by CD. Molecular docking analysis highlighted that GA binds at Sudlow site I of BSA which also confirmed from site probe experiments. In addition, the molecular dynamics (MD) simulation study of BSA and BSA-GA complex shows that binding of GA at site I of BSA is stable and the binding Gibbs energies from the molecular mechanics/Poisson-Boltzmann surface area method showed that van der Waals forces are the predominant intermolecular forces. This study reflects greater pharmacological significance of GA and highlights its importance in the clinical medicine.

Kinetics, isotherms, and thermodynamic studies of lead, chromium, and cadmium bio-adsorption from aqueous solution onto Picea smithiana sawdust.

Lead (Pb), chromium (Cr), and cadmium (Cd) removal capacity of sawdust (Picea smithiana) from aqueous solution was investigated by conducting batch experiments. Thermodynamic parameters, like change in standard free energy (ΔGΘ), enthalpy (ΔHΘ) and entropy (ΔSΘ) during bio-adsorption process were estimated using the Van't Hoff equation. The maximum metals adsorption was observed at pH8, 20gL-1 bio-adsorbent and at 60min of contact time. The metal adsorption kinetics was examined by fitting the pseudo-first-order as well as four forms of pseudo-second-order kinetic models. Type 1 pseudo-second-order equation described adsorption kinetics better than others. Langmuir model and Freundlich equations were used for calculation of sorption parameters. The Langmuir maximum adsorption capacity of Pb, Cr, and Cd was 6.35, 3.37, and 2.87mgg-1 at room temperature, respectively. The values of the separation factor (RL) were in between 0 and 1, indicating that bio-adsorption was favorable. Thermodynamics study revealed that the Pb, Cr, and Cd uptake reactions were endothermic and spontaneous. Results of the study asserted that the removal of heavy metal ions from aqueous solution is viable and the sawdust could be used in the treatment of effluents from industries, thereby reducing the level of water pollution.

Carbamate Formation and Amine Protonation Constants in 2-Amino-1-Butanol–CO2–H2O System and Their Temperature Dependences

The apparent protonation constant of an amino butanol (AB) and its carbamate formation constant in the CO2–H2O–AB system were determined at T = 298.15–328.15 K, and at various ionic strengths up to 0.2 mol·L−1 by potentiometric titration. The Debye–Huckel equation was used to extrapolate the protonation constants to zero ionic strength. The variation of the thermodynamic equilibrium constant for carbamate formation with temperature was modeled according to the relationship of log10 K1 = 280.91/T − 0.1105, while the temperature dependency of the amine protonation constant was correlated by log10 K2 = 1926.53/T + 2.9482. Van’t Hoff type plots of the pK values showed linear relationships indicating that the standard enthalpy changes of reaction are constant over this range of temperatures. Hence, our current findings are crucial for designing efficient unit operations involving separation of CO2 from natural or flue gases.

Ciprofloxacin Antibiotics Removal from Effluent Using Heat-acid Activated Red Mud

In this study, the adsorption of Ciprofloxacin (CIP) antibiotics from a synthetic solution containing CIP is investigated using Red Mud (RM) and Red Mud that is activated by HCL (ARM). Scanning Electron Microscopy (SEM) techniques are used to morphological characteristics of Red Mud and activated Red Mud. The optimum conditions for both absorbents obtained with the highest adsorption include contact time=90 min and adsorbent dosage= 4 g/L. The highest adsorption of CIP was 25.44 mg/g for Red Mud and for activated Red Mud was 41.5 mg/g. The negative value of the standard enthalpy change indicates that the adsorption is physical in nature involving weak forces of attraction and is also exothermic, thereby demonstrating that the process is stable energetically. The results of this study show that the activated Red Mud is a relatively effective adsorbent for the adsorption of cerium from aqueous solution.

Application of treated eggplant peel as a low-cost adsorbent for water treatment toward elimination of Pb2+: Kinetic modeling and isotherm study

In this study, treated eggplant peel was used as an adsorbent to remove Pb2+ from aqueous solution. For this purpose batch adsorption experiments were performed for investigating the effect of contact time, pH, adsorbent dose, solute concentrations, and temperature. In order to assess adsorbent’s physical and chemical properties, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy were used. The results showed that the adsorption parameters for reaching maximum removal were found to be contact time of 110 min, adsorbent dose of 0.01 g/ml, initial lead(II) concentration of 70 ppm, pH of 4, and temperature of 25°C. Moreover, for the experiments carried out at pH > 4 the removal occurred by means of significant precipitation as well as adsorption. Furthermore, these results indicated that the adsorption followed pseudo-second-order kinetics model implying that during the adsorption process strong bond between lead(II) and chemical functional groups of adsorbent surface took place. The process was described by Langmuir model (R2 = 0.99; maximum adsorption capacity 88.33 mg/g). Also thermodynamics of adsorption was studied at various temperatures and the thermodynamic parameters including equilibrium constant (K), standard enthalpy change, standard entropy change, and standard free energy changes were obtained from experimental data.

Effects of N-methylation and amidination of cyclic β-amino acids on enantioselectivity and retention characteristics using Cinchona alkaloid- and sulfonic acid-based chiral zwitterionic stationary phases

In the present work the effects of N-methylation and N-amidination of ampholytic cyclic β-amino acids on their retention and enantioseparation characteristics on Cinchona alkaloid- and sulfonic acid-based zwitterionic chiral selectors, namely Chiralpak ZWIX(+)™ and ZWIX(−)™ columns are described. In a polar-ionic mobile phase, a double ion-pairing interaction mechanism takes place between the charged sites of the chiral analytes (the selectands) and the chiral selector moieties. As a support to correlate the chromatographic results with the structural details of the analytes, pKa values and van der Waals volumes of the substituted amino groups were calculated.In order to ensure better understanding of the mechanistic details of the chromatographic system the composition of the bulk solvent, the role of acid base additives, the concentration of the counter-ions, temperature and the structures of the ampholytic analytes have been investigated. Applying N-Fmoc protection, the ampholytic character of the analytes diminished, leading to a marked loss of retention. In the temperature range studied (5–40 °C) thermodynamic parameters, such as the difference in the standard enthalpy change Δ(ΔH°), entropy Δ(ΔS) and Gibbs energy Δ(ΔG°) were calculated from linear van’t Hoff plots derived from the ln α vs. 1/T curves. The values of the thermodynamic parameters depended on the structures of the chiral selectors applied and the analytes studied.

Thermodynamic aggregation behaviour of p-cymene in hydrotropic solution

The paper deals with the thermodynamic properties and aggregation behaviour of p-cymene through hydrotropy. Different hydrotropes namely urea, resorcinol, sodium cumene sulfonate and pyrogallol has been used to study the solubility under a wide range of hydrotrope concentrations (0 to 3.00 mol.kg–1) and different system temperatures (303.15 to 333.15 K). The effectiveness of hydrotrope with respect to the system was measured by Setschenow constant KS and reported for all hydrotropes used in this study. The influence of different system temperatures on thermodynamic properties like standard Gibbs free energy change (ΔG°), standard enthalpy change (ΔH°) and standard entropy change (ΔS°) of solubilisation with respect to p-cymene has been ascertained. The aggregation behaviour between the solute and the hydrotrope and among the hydrotrope molecules have also been studied using step wise association model.

Thermodynamic aggregation behaviour of p-cymene in hydrotropic solution

The paper deals with the thermodynamic properties and aggregation behaviour of p-cymene through hydrotropy. Different hydrotropes namely urea, resorcinol, sodium cumene sulfonate and pyrogallol has been used to study the solubility under a wide range of hydrotrope concentrations (0 to 3.00 mol.kg–1) and different system temperatures (303.15 to 333.15 K). The effectiveness of hydrotrope with respect to the system was measured by Setschenow constant KS and reported for all hydrotropes used in this study. The influence of different system temperatures on thermodynamic properties like standard Gibbs free energy change (ΔG°), standard enthalpy change (ΔH°) and standard entropy change (ΔS°) of solubilisation with respect to p-cymene has been ascertained. The aggregation behaviour between the solute and the hydrotrope and among the hydrotrope molecules have also been studied using step wise association model.

Application of Coconut-Shell Activated Carbon as Heterogeneous Solid Catalyst for Biodiesel Synthesis

Biodiesel is a bio-based fuel for diesel engine synthesized from renewable oils isolated from oil crops or animal. Biodiesel can be produced through transesterification where the process involves a catalyst and an alcohol. The most common catalyst for this process is homogeneous liquid catalyst. However, this catalyst system suffers from environmental problems. In order to eliminate the problem, we developed potassium loaded on coconut-shell activated carbon (K/AC) as heterogeneous solid catalyst which is easily regenerated, leading to more secure and more environmental friendly application. The purpose of the present work is to demonstrate the biodiesel synthesis from palm oil using K/AC catalyst in stirred tank reactor. Reaction variables such as methanol-oil molar ratio and temperature were optimized to reach the highest conversion for 4 hours reaction time. The highest reaction conversion, 26.98%, was obtained at methanol-oil molar ratio of 6:1 and reaction temperature of 60 °C. Furthermore, the value of collision factor, activation energy and standard enthalpy change of reaction obtained are 5.40 x 103dm6.(mol.gcat.min)-1, 16.113 cal/mol and 5499.40 cal/mol, respectively.

Equilibrium in Protic Ionic Liquids: The Degree of Proton Transfer and Thermodynamic Properties.

The degree of proton transfer and thermodynamic parameters of six acetate-based protic ionic liquids (PILs) were measured using nuclear magnetic resonance spectroscopy and calculated by van't Hoff analytical method, respectively. The degree of proton transfer of these PILs at 298 K spread over a large range, which is from 39.6% (1-methylpyrrolidinium acetate, [MpyrH][AcO]) to 94.4% (1-butylimidazolium acetate, [BuimH][AcO]). The calculated standard enthalpy change of the reaction (ΔrHmθ) is from -23.30 to -7.80 kJ mol-1 and the standard entropy change of the reaction (ΔrSmθ) is from -42.70 to -8.07 J mol-1 K-1. The correlation between the degree of proton transfer and aqueous ΔpKa or ΔrHmθ was investigated as well. Furthermore, in some special cases, ΔrSmθ, especially the entropy change of symmetry, also plays an important role in affecting the degree of proton transfer.

Conductometric investigations of surfactant behavior in aqueous polar aprotic organic additives

Micellar properties of sodiumdodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) in aqueous polar aprotic additives viz., dimethylsulfoxide (DMSO), dimethylformamide (DMF), acetonitrile (AN) and 1,4-dioxane were determined between 25 and 45°C. The critical micelle concentration (CMC) determined using electrical conductivity measurements have been used to evaluate thermodynamic properties of micellization. By detailed experiments, it was observed that the DMSO and DMF have an inhibitory effect on micellization of the targeted surfactants, i.e. SDS and CTAB in aqueous solutions over the entire solvent composition range from 0.67–5.94mol% by weight. The addition of dioxane and AN initially increase CMC of CTAB and then it decreases gradually with further increase in the concentration of dioxane and AN. A contrary trend is observed in the micellar behavior of SDS in the presence of dioxane and AN. The changes in standard enthalpy and entropy of micellization values are found to be consistent with the observed behavior of the two surfactants in the presence of these additives. Near constant counter-ion binding values are indicative of the fact that no structural transition of the micelles of the two surfactants takes place in the range of the composition studied.

Research on synthesis and thermodynamic properties of 2-methoxycyclohexanol

2-Methoxycyclohexanol is synthesized through an alcoholysis reaction of cyclohexene oxide and methanol with Ag2CsPW12O40 as catalyst. The elemental analyzer, FT-IR, GC, and NMR are used to analyze and confirm elements, functional groups, purity, and molecular structure of 2-methoxycyclohexanol. The equation between the specific heat capacity (C p) and the temperature from 280 to 340 K is fitted by the results of differential scanning calorimeter to examine 2-methoxycyclohexanol. Bomb calorimeter is introduced to determine the standard enthalpy change of combustion of 2-methoxycyclohexanol (− 3938.6 ± 2.0 kJ mol−1). The standard enthalpy of formation has been calculated as − 816.88 ± 2.21 kJ mol−1, based on Hess’s law. These basic thermodynamic parameters are deemed to facilitate the exploitation of new production route of 2-methoxycyclohexanol.

Sequestering Ability of Oligophosphate Ligands toward Al3+ in Aqueous Solution

The interactions between Al3+ and ortho-phosphate (PO43–), pyro-phosphate (P2O74–, PP), tripolyphosphate (P3O105–, TPP) and hexa-metaphosphate (P6O186–, HMP) in aqueous solution have been studied. Formation constants, speciation models, and possible structures for the complexes formed are discussed on the basis of potentiometric, calorimetric, 31P–{1H} NMR, laser desorption mass spectrometric (LD MS) and MS/MS results. 31P–{1H} NMR experiments for Al3+–TPP system are in agreement with the speciation model drawn from analysis of potentiometric titration data, suggesting that TPP binds to Al3+ with two adjacent phosphate oxygen atoms, forming a six-membered ring. LD MS has provided identification and structural information for Al3+–PP, −TPP, and −HMP complexes which supports the reliability of speciation models proposed on the basis of the potentiometric data. Moreover, MS/MS spectra obtained from [ML]+ precursor ion show that the ion species involve linear HMP isomers and that two adjacent terminal phosphate groups probably bind Al3+. Standard enthalpy change values were obtained by titration calorimetry; all are endothermic, as is typical for hard–hard interactions. The dependence of formation constants on ionic strength over the range I = 0.1–1 mol kg–1 is also reported. The sequestering ability of all the ligands under study toward Al3+ was also evaluated by the empirical parameter pL0.5.

Kinetics, isotherms and thermodynamic evaluation of amine functionalized magnetic carbon for methyl red removal from aqueous solutions

Global fresh water demand increases as population increases. Thus, the demand for cost-effective materials and efficient technologies for water treatment is on the rise. Here, we modified rubber-derived carbon by iron oxide and then the obtained material was subjected to surface modification using typical branched polyethylenimine (BPEI) to produce a magnetic composite of AC-FexOy-BPEI. The composite was characterized. The efficiency of the polymer anchored material was examined for methyl red (MR) removal from aqueous media in the batch and column systems. The results indicated a high percentage of removal (≈100%) and eequilibrium was observed in 10mins. The process followed models of the Langmuir isotherm and Pseudo-second order, with a capacity of 526mg/g. The negative standard enthalpy change (∆Ho) suggests that the adsorption of MR on the material is exothermic. The breakthrough was observed after 150mins using a 1mM concentration of methyl red flow through a designed short column. The AC-FexOy-BPEI demonstrated remarkable efficiency in removing MR from aqueous solutions. The high adsorption capacity does indeed make the amine-modified material as an effective sorbent. The material leverages its cost-effective source, in addition to the ease of preparation along with its fast uptake capacities, it offers great promise for wastewater remediation.

Micellar and antimicrobial activities of ionic surfactants in aqueous solutions of synthesized tetraalkylammonium based ionic liquids

A series of quaternary ammonium based ionic liquids (ILs) containing tetraalkylammonium cation has been synthesized and characterised by NMR as well as FT-IR analysis. Then their effect on aggregation behaviour of an anionic surfactant, Sodium dodecylsulphate (SDS) and a cationic surfactant, Dodecyltrimethylammonium bromide (DTAB) has been investigated using conductometric, fluorescence (emission spectra) and UV–vis (absorption spectra) techniques. To gain better insight into colloidal behaviour of surfactant in ILs, the critical micelle concentration (CMC) of surfactant has been calculated in the absence and presence of IL. The addition of IL has a depressing effect on CMC values of studied surfactants in aqueous medium. Also the observed variation in CMC values has been discussed in terms of structural modulation in surfactant-water complex caused by these additives. Furthermore, the thermodynamic parameters of micelle formation viz. change in standard free energy (ΔGmo), change in standard enthalpy (ΔHmo) and change in standard entropy (ΔSmo) have been investigated from the dependence of CMC on temperature using charged pseudo-phase model of micellization. All the calculated parameters have been used to elucidate the electrostatic and hydrophobic contributions of IL for the building up of the micellar aggregates of the surfactant. The effect of these ILs on the antibacterial activity of surfactants has also been tested by measuring zone of inhibition and minimum inhibitory concentration (MIC) for DTAB and SDS in the presence of ILs against gram positive and gram negative bacterial species.

Thermodynamic and kinetic analyses of curcumin and bovine serum albumin binding

Bovine serum albumin (BSA)/curcumin binding and dye photodegradation stability were evaluated. BSA/curcumin complex showed 1:1 stoichiometry, but the thermodynamic binding parameters depended on the technique used and BSA conformation. The binding constant was of the order of 105L·mol−1 by fluorescence and microcalorimetric, and 103 and 104L·mol−1 by surface plasmon resonance (steady-state equilibrium and kinetic experiments, respectively). For native BSA/curcumin, fluorescence indicated an enthalpic and entropic driven process based on the standard enthalpy change (ΔH○F=−8.67kJ·mol−1), while microcalorimetry showed an entropic driven binding process (ΔH○cal=29.11kJ·mol−1). For the unfolded BSA/curcumin complex, it was found thatp ΔH○F=−16.12kJ·mol−1 and ΔH○cal=−42.63kJ·mol−1. BSA (mainly native) increased the curcumin photodegradation stability. This work proved the importance of using different techniques to characterize the protein-ligand binding.

Probing Gas Adsorption in Zeolites by Variable-Temperature IR Spectroscopy: An Overview of Current Research.

The current state of the art in the application of variable-temperature IR (VTIR) spectroscopy to the study of (i) adsorption sites in zeolites, including dual cation sites; (ii) the structure of adsorption complexes and (iii) gas-solid interaction energy is reviewed. The main focus is placed on the potential use of zeolites for gas separation, purification and transport, but possible extension to the field of heterogeneous catalysis is also envisaged. A critical comparison with classical IR spectroscopy and adsorption calorimetry shows that the main merits of VTIR spectroscopy are (i) its ability to provide simultaneously the spectroscopic signature of the adsorption complex and the standard enthalpy change involved in the adsorption process; and (ii) the enhanced potential of VTIR to be site specific in favorable cases.

Ionic Liquid Influenced Synergistic Interaction between Amitriptyline Hydrochloride and Cetyltrimethylammonium Bromide

The mixed micellization behavior of amitriptyline hydrochloride (AMT) with cetyltrimethylammonium bromide (CTAB) has been studied at different mole fractions in the presence of imidazolium based ionic liquid 1-butyl-3-methyl imidazolium hydrochloride (Bmim·Cl), by using electrical conductivity at different temperatures from 298 to 318 K. A shift in the Tmax value (i.e., the temperature at which the cmc value is maximized) has been observed with the rise in CTAB mole fraction. Synergistic interaction is explained by the deviations in critical micelle concentration (cmc) from an ideal critical micelle concentration (cmc*) and micellar mole fraction (Xm) from ideal micellar mole fraction (Xideal) values. The calculated thermodynamic parameters (viz., the standard Gibbs energy change, ΔGm°, the standard enthalpy change, ΔHm°, and the standard entropy change, ΔSm°) suggest the dehydration of hydrophobic part of the drug at higher temperatures in the case of AMT as well as in CTAB-AMT binary systems in the pres...

Aluminate treated Casuarina equisetifolia leaves as potential adsorbent for sequestering Cu(II), Pb(II) and Ni(II) from aqueous solution

In the present study, a novel biosrbent was prepared by treating Casuarina equisetifolia leaves with sodium aluminate (SATCEL) and utilized for the removal of heavy metals from single and multi-metal system. The biosorbent was characterized by various different techniques. Brunauer-Emmett-Teller (BET) analysis showed increase in surface area of biosorbent from 5.902 m2 g−1 (in its raw form) to 10.582 m2 g−1 (after chemical modification). Response surface methodology (RSM) using central composite design (CCD) was employed for Optimization of process variables and evaluating their interactive effect Isotherm data were fitted in Langmuir, Freundlich, Temkin and SIPS by non-linear curve fitting. Maximum biosorption capacity (qm) calculated from Langmuir isotherm in single metal system for Cu(II), Pb(II) and Ni(II) were 44.0, 28.0 and 39.0 mg g−1, respectively. In multi-metal system competition among metal ions caused the qm values to decrease drastically. Thermodynamic parameters, standard Gibb's free energy change (ΔGo), enthalpy change (ΔHo) and entropy change (ΔSo) showed that the biosorption of metal ions onto SATCEL was spontaneous and endothermic in nature. Analysis of kinetic data showed that Pseudo-second order kinetic model was well obeyed. Regeneration study indicated that SATCEL could be reused successfully upto four consecutive cycles.

Effect of intramolecular hydrogen bonding of α, ω–diamines on the structure and exchange affinity of 18–crown–6-amine host-guest complexes in gas phase: A collision cross section measurements by ion mobility spectrometry

The effect of intramolecular hydrogen bonding on the thermodynamics of the host–guest interactions have been investigated through the gas phase exchange studies of protonated normal primary amines and α,ω–diamines with ammonium ion in 18–crown–6 (18C6) cavity using ion mobility spectrometry (IMS). The cross sectional areas were calculated for α, ω–diamines and normal primary amines in free and complex form. The results showed that protonated α, ω–diamines have more compact structure than that of the protonated normal primary amines in the free forms. This is attributed to the formation of intramolecular hydrogen bridges in protonated α, ω–diamines. In addition, we found that 18C6 attachment prevents from the formation of intramolecular hydrogen bond in α, ω–diamines. The exchange reactions were also investigated for different amines and diamines. The values of the standard molar enthalpy change for exchange reactions were obtained from temperature dependence of exchange constants (Kex) of complexes using the Van’t Hoff plots. The results show that the tendency of diamines to interaction with 18C6 is lower than the normal amines due to the intramolecular hydrogen bond formation. The Kex of diamines to interaction with 18C6 follows the order 1,2–diaminoethane (1,2–DAE)>1,3–diaminopropane (1,3–DAP)>1,5–diaminopentane (1,5–DAP)>1,4–diaminobutane (1,4–DAB). This trend indicates that the most stable intramolecular hydrogen bond is formed in 1, 4–DAB through the formation six-member cycles.