Values Of Molar Enthalpies Research Articles

Protolytic Reactions at Electrified TiO2 P25 Interface: Quantitative and Thermodynamic Characterization

Protolytic reactions on the surface of a titania photocatalyst (TiO2 P25 containing chlorine impurities) were studied using potentiometric and calorimetric acid-base titration. The impurity was removed by either washing or heat treatment. The efficiency of purification was tested by chlorine (TOX) analysis and acid-base titration. Common intersection points of −0.023 and −0.021 mmol/g were obtained for the original and 400 °C heat-treated samples, which are in good agreement with the measured TOX value of 28 mmol/kg. The point of zero charge of the purified sample was determined to be 6.50. Titration data were fitted to simulate protolytic reactions during isothermal calorimetric titrations of purified titania. The evolved heat was measured, and data points were corrected with the heat of mixing and neutralization. The quantity of charged surface species formed in each step of titration was calculated using the parameters from the constant capacitance model fit. The partial molar enthalpy values of the exothermic and endothermic processes of surface protonation (ΔHpr, −17.47 to −16.10 kJ/mol) and deprotonation (ΔHdepr, 32.53 to 27.08 kJ/mol) depend slightly on the ionic strength of suspensions. The average standard enthalpy of one proton transfer reaction is −23.54 ± 1.75 kJ/mol, which is consistent with the literature.

Physicochemical studies of adenosine in the presence of aqueous caffeine and theophylline solutions, & sodium valproate with γ‐amino butyric acid in aqueous medium at T = (288.15–318.15) K and at p = 1 × 105 Pa

AbstractIn human body, drug‐neurotransmitter interactions have been the most significant process. Whereas, adverse reactions may be accompanied by unexpected interaction, which puts an individual in danger of life. Thus, the interactions between adenosine (ADN) and sodium valproate (SV) with caffeine (CAF), theophylline (TPY) and γ‐amino butyric acid (GABA) have been studied. Various properties like densities, ρ and speed of sound, u, have been used to calculate apparent molar volumes (V2,ϕ) and apparent molar isentropic compression (Ks,2,ϕ) for ADN and SV in aqueous (5, 10, 15 and 20 mmol kg−1) CAF, TPY and GABA solutions at T = (288.15–318.15) K and at pressure p = 1 × 105 Pa. The results of various interactions that occurred by mixing the solutions have been interpreted. Exothermicity is indicated by the negative values of standard molar enthalpy of transfer, ΔtrΔdilH0, obtained from the calorimetry. UV‐absorption and 1H NMR studies suggest that there is a dominance of solute‐cosolute interactions due to hyperchromic shift and shielding effect.

Excess Enthalpies Analysis of Biofuel Components: Sunflower Oil-Alcohols Systems.

This study addresses the pressing issues of energy production and consumption, in line with global sustainable development goals. Focusing on the potential of alcohols as "green" alternatives to traditional fossil fuels, especially in biofuel applications, we investigate the thermochemical properties of three alcohols (n-propanol, n-butanol, n-pentanol) blended with sunflower oil. The calorimetric analysis allows for the experimental determination of excess enthalpies in pseudo-binary mixtures at 303.15 K, revealing similarities in the trends of the curves (dependence on concentrations) but with different values for the excess enthalpies for each mixture. Despite the structural differences of the alcohols studied, the molar excess enthalpy values exhibit uniformity, suggesting consistent mixing behavior. The peak values of excess enthalpies for systems with sunflower oil and n-propanol, n-butanol and n-pentanol are, respectively, 3255.2 J/mole, 3297.4 J/mole and 3150.1 J/mole. Both the NRTL and Redlich-Kister equations show satisfactory agreement with the obtained values.

Molecular dynamics simulation, thermodynamic parameters and solute–solvent molecular interactions of cilostazol (form A) dissolution in (ethylene glycol / ethanol + water) mixtures

This research work reports the cilostazol (form A) dissolution in (ethylene glycol / ethanol + water) mixtures. The co-solvency phenomenon only occurs in mixture of ethanol + water, the maximum solubility in mole fraction is 3.034 × 10-3 at the composition of 0.85. It was found that the solvation performance of cilostazol in two mixtures mainly depend on the ability of forming hydrogen bond (H-bond) of the solutions and van der Waals interaction. According to the preferential solvation results, it is conjecturable that cilostazol molecules are preferentially solvated by water in water-rich regions. With the increase of alcohol concentration, the destruction of water molecular ordered structure by alcohol through hydrogen bond, and solute molecules are preferentially solvated by ethanol and EG. Nonetheless, when 0.86 < x1 < 1 in mixture of ethanol + water, solute molecules are preferentially solvated by water again. The calculation of radial distribution function (RDF) between the atoms of H and O for ethanol and the atoms of N and H for solute is to achieve the interaction of the solute and solvents. The correlation fitting was performed for the solubility data through Jouyban Acree model and its derivative models, and the statistical analysis showed that the Apelblat-Jouyban Acree model is more suitable to present the solubility correlation. Meanwhile, the values of apparent molar standard dissolution enthalpy (ΔHsolo) and apparent molar standard dissolution entropy (ΔSsolo) are positive in each solvents, which reveals that the dissolution process of cilostazol form A is endothermic and entropy favorable within the given temperature range.

Separation potential of 1,5-pentanediol-based deep eutectic solvent: Infinite dilution activity coefficients and excess thermodynamic data

In the present study, the new data of the infinite dilution activity coefficient for 32 different solutes in {1-ethyl-1-methylpyrrolidinium bromide +1,5-pentanediol}, [[EMPYR] Br + 1,5-PDO] DES, were measured using the gas liquid chromatography (GLC) method with pre-saturation of the helium gas. The list of selected solutes included alkanes, alkenes, alkynes, cycloalkanes, cycloalkenes, aromatics, ketones, alcohols, and water. Because the solvents were volatile at the temperatures used for measurements, pre-saturation was deemed necessary. The measurements were taken at temperatures T = (313.15–343.15) K and atmospheric pressure. Values of partial molar properties, i.e., enthalpy, entropy, and Gibbs free energy, were computed at a reference temperature of Tref = 333.15 K. Moreover, the values of capacity and selectivity relating to [[EMPYR] Br + 1,5-PDO] DES for different sets of binary systems that are normally problematic in the separation through solvent extraction or distillation were also computed. These include cyclohexane/benzene; acetone/methanol; and hexane/benzene. The obtained data in the present work was then compared to the literature data, at similar temperatures. Thus, the thermodynamical data is important for pre-selecting solvents for industrial purposes.

Zn-Mo-O system: Insights into the thermodynamic stability and applicability in lithium ion batteries

A detailed experimental investigation on the thermochemical stability of Zn2Mo3O8(s) in the Zn-Mo-O system was reported for the first time using high temperature oxide melt solution calorimetry in conjunction with solid oxide based electrochemical measurements. The temperature dependence of molar heat capacity of this compound was determined employing thermal relaxation calorimetry and differential scanning calorimetry. The values of standard molar enthalpy of formation (∆fH298.15°), standard molar entropy (S298.15°), molar heat capacity (Cp) and Debye temperature (θD) for Zn2Mo3O8(s) were determined for the first time in this study. The present study also focuses on the investigation of electrochemical performance of α-ZnMoO4(s) for lithium ion battery applications which demonstrated the effective utilization of this compound as anode material due to its remarkable cycling stability and rate capability.

Thermodynamically Traceable Calorimetric Results for Aqueous Sodium Chloride Solutions from T = (273.15 to 373.15) K up to the Saturated Solutions: Part 1—The Quantities Associated with the Partial Molar Enthalpy

The three-parameter extended Hückel equations with parameters B, b1, and b2 have recently been successfully tested against existing vapor pressure, electrochemical, and solubility data for aqueous NaCl solutions at temperatures from (273 to 373) K (Partanen and Partanen in J. Chem. Eng. Data 65:5226–5239, 2020). In the present study, we extend this model to the apparent and partial molar enthalpy data of these solutions. The enthalpy equations were determined using a new calculation method that gives practically the same results as that used in another previous study (Partanen et al. in J. Chem. Eng. Data 62:2617–2632, 2017), but the new method is much simpler. In the previous enthalpy study, dilute NaCl solutions up to m = 0.2 mol⋅kg−1 were considered in the range from T = 273 to 353 K. Following the success of the three-parameter extended Hückel model within the whole concentration range at various temperatures, we tabulate new values for relative apparent and partial molar enthalpies for NaCl solutions at rounded molalities. The resulting values are extensively tested against the literature ones. The best agreement is obtained for temperatures below 288 K and between 313 and 353 K. Elsewhere, at least a reasonable agreement is obtained. As no enthalpy or heat capacity data were used in the estimation of our model’s parameters and as the model has excelled in explaining other high-precision thermodynamic data, we argue that the recommended enthalpy values should be preferred even for the temperatures where the agreement is only reasonable due to potential problems associated with the literature values. These problems are also considered in the study.Graphical

A comprehensive investigation on CdO-SnO2 system: Structure, thermal expansion and energetics

An extensive investigation into the thermochemical stability of two ternary oxides, ilmenite-type CdSnO3(s) and orthorhombic Cd2SnO4(s), in the Cd-Sn-O system was reported for the first time using high temperature oxide melt solution calorimetry in conjunction with differential scanning calorimetry and thermal relaxation calorimetry. The values of standard molar enthalpy of formation (∆fH298.15°), standard molar entropy (S298.15°), molar heat capacity and Debye temperature (θD) for ilmenite-type CdSnO3(s) and orthorhombic Cd2SnO4(s) were determined. Using the experimentally obtained thermochemical data, the standard molar Gibbs energy of formation of these compounds were derived and the corresponding expressions are given as follows:∆fGm°<CdSnO3>±1.3kJmol−1=−847.9+0.2781(T/K)(T:298.15−1000K)∆fGm°<Cd2SnO4>±3.6kJmol−1=−1138.1+0.3831(T/K)(T:298.15−1000K)Moreover, high temperature XRD experiments were conducted to evaluate their thermal expansion behaviour as well as for the in-situ identification of phase evolution resulting from decomposition of cadmium stannates.

Physicochemical insights into the micellar delivery of doxycycline and minocycline to the carrier protein in aqueous environment

Physicochemical understanding of the micellar drug delivery is essential for designing efficient drug carrier molecules. An in-depth analysis of the partitioning mechanism of drugs in a quantitative manner and the effects of partitioning on the delivery of drugs through micellar media is a subject of enormous research. This paper focuses on the quantitative measurements of the binding of two antibiotic drugs from tetracycline family, doxycycline and minocycline with the carrier protein human serum albumin (HSA). The partitioning of both the drugs in the micellar system of hexadecyltrimethylammonium bromide (HTAB) and their delivery to HSA through this micellar system was also studied applying spectroscopy and calorimetry. A combination of fluorescence spectroscopy, isothermal titration calorimetry (ITC) and docking studies suggest that both the drugs bind close to Site I of HSA. The ITC results establish that the association of drugs with the protein occurs with an affinity of 103-104 M−1 and the binding is mainly entropy driven. The partitioning mechanisms have been evaluated in terms of the values of the changes in values of standard molar Gibbs free-energy, enthalpy, entropy, and partitioning stoichiometry. The thermodynamic signatures associated with the drug-HSA binding in the presence of HTAB micelles suggest that the partitioning of doxycycline/minocycline in the micelles of HTAB changes their interaction behavior with HSA. These findings provide deep understanding about the micellar drug delivery systems, thereby suggesting their potential applications in strategies for more effective therapeutics.

Infinite Dilution Activity Coefficient Measurements for 1-Methyl-4-(1-methylethenyl)-cyclohexene as a Green Solvent for Separation

Infinite dilution activity coefficients for various solutes, which include alkanes, alkenes, alkynes, cycloalkanes, heterocycles, alcohols, aromatics, ketones, ethers, nitrile, and water, in a 1-methyl-4-(1-methylethenyl)-cyclohexene solvent were measured using gas–liquid chromatography at 303.15, 313.15, and 323.15 K. The focus of this study was to assess 1-methyl-4-(1-methylethenyl)-cyclohexene as a green solvent for separation processes. 1-Methyl-4-(1-methylethenyl)-cyclohexene, a nonpolar monoterpene solvent extracted from essential oils of citrus peels, was investigated as an alternative solvent to currently employed conventional organic solvents in separation processes. Through experimental infinite dilution activity coefficients, γ13∞, the values of partial molar excess enthalpy at infinite (ΔHiE,∞) were obtained using the Gibbs–Helmholtz equation. The infinite dilution selectivity (Sij∞) and capacity (Δkj∞) values were calculated from the experimental limiting activity coefficients and were compared with deep eutectic solvents, ionic liquids, and industrial solvents. From this study, it was observed that 1-methyl-4-(1-methylethenyl)-cyclohexene is not suitable to be used as an alternative for separation processes. In addition, activity coefficients at infinite dilution of different organic solutes in hexadecane were measured at various temperatures to validate the reliability and accuracy of gas–liquid chromatography. Finally, the experimental data were modeled using Aspen Plus, compared with experimental data, and found to be in good agreement.

A thermodynamic approach to understand the partitioning of tetracycline family antibiotics in individual and mixed micellar systems

Micelle-mediated drug delivery is an efficient and smart way of delivering drugs to the target sites. This method of drug delivery increases the concentration of the drugs specifically to the affected tissues/organs and hence increases the bioavailability of the drug and reduces the side-effects of the drug. Quantitative understanding of the mechanism of partitioning of drugs in micellar structures is crucial for developing guidelines to design effective drug delivery systems. In this background, we have done quantitative studies of the mechanism of partitioning of four drugs doxycycline, minocycline, tetracycline and oxytetracycline which belong to tetracycline family of antibiotics in the HTAB, TX-100 and mixed surfactant micellar system using isothermal titration calorimetry (ITC). The insights into the partitioning mechanisms have been investigated in a temperature range T = 288.15 K–310.15 K in terms of the values of standard molar enthalpy, standard molar entropy, the standard molar Gibbs free-energy change, and stoichiometry of partitioning. The thermodynamic parameters for the interaction of the drugs with the surfactants suggest involvement of ionic/H-bonding as well as hydrophobic interactions between the drugs and the surfactant micelles and monomers. The effects of the drugs on the critical micellar concentration of the surfactants are studied using ITC and fluorescence spectroscopy. The results are essential in establishing structure-properties-energetics correlations and will help in designing enhanced strategies for improved drug delivery systems.

Calorimetric studies and thermodynamic calculations of the Ag-Mg system

The experimentally determined integral enthalpy of mixing of liquid Ag-Mg alloys has been presented. Three separate measurements have been made at 991, 1141, and 1272 K with the use of an MHTC 96 Line Evo line drop calorimeter. The values of integral molar mixing enthalpy are characterized by negative deviations from the ideal solutions in the entire concentration range. Based on the obtained calorimetric results and other thermodynamic data available in the literature, the Ag-Mg system has been re-optimized. Additionally, the mechanical properties of the Ag-Mg intermetallic phases have been calculated based on the ab initio calculations.

Isavuconazole: Thermodynamic Evaluation of Processes Sublimation, Dissolution and Partition in Pharmaceutically Relevant Media.

A temperature dependence of saturated vapor pressure of isavuconazole (IVZ), an antimycotic drug, was found by using the method of inert gas-carrier transfer and the thermodynamic functions of sublimation were calculated at a temperature of 298.15 K. The value of the compound standard molar enthalpy of sublimation was found to be 138.1 ± 0.5 kJ·mol−1. The IVZ thermophysical properties—melting point and enthalpy—equaled 302.7 K and 29.9 kJ mol−1, respectively. The isothermal saturation method was used to determine the drug solubility in seven pharmaceutically relevant solvents within the temperature range from 293.15 to 313.15 K. The IVZ solubility in the studied solvents increased in the following order: buffer pH 7.4, buffer pH 2.0, buffer pH 1.2, hexane, 1-octanol, 1-propanol, ethanol. Depending on the solvent chemical nature, the compound solubility varied from 6.7 × 10−6 to 0.3 mol·L−1. The Hansen s approach was used for evaluating and analyzing the solubility data of drug. The results show that this model well-described intermolecular interactions in the solutions studied. It was established that in comparison with the van’t Hoff model, the modified Apelblat one ensured the best correlation with the experimental solubility data of the studied drug. The activity coefficients at infinite dilution and dissolution excess thermodynamic functions of IVZ were calculated in each of the solvents. Temperature dependences of the compound partition coefficients were obtained in a binary 1-octanol/buffer pH 7.4 system and the transfer thermodynamic functions were calculated. The drug distribution from the aqueous solution to the organic medium was found to be spontaneous and entropy-driven.

Calorimetric studies and thermodynamic properties of Li-Pb-Pd liquid alloys

The first ever calorimetric results of integral enthalpies of mixing of liquid Li-Pb-Pd alloys were investigated with the use of an MHTC 96 drop calorimeter. Five separate measurements were performed for such liquid alloys as (Li0.5Pb0.50)1−xPdx, (Li0.25Pb0.75)1−xPdx at 926 K, (Pb0.90Pd0.10)1−xLix at 1005 K, as well as (Li0.75Pb0.25)1−xPdx, and (Pb0.60Pd0.40)1−xLix at 1026 K. Based on the authors' own equations describing the excess Gibbs energy of binary Li-Pb, Li-Pd, and Pb-Pd liquid solutions, and the experimental values of integral molar enthalpy of mixing of liquid Li-Pb-Pd alloys presented in this work, the ternary interaction parameters were calculated. Finally, the values of molar thermodynamic functions of liquid Li-Pb-Pd alloys were calculated and presented in the form of tables and figures.

Correlating the Properties of Antibiotics with the Energetics of Partitioning in Colloidal Self-Assemblies and the Effect on the Binding of a Released Drug with a Target Protein.

The bioavailability of drugs and the monitoring of efficient dosage requires drug delivery through suitable vehicles. The partitioning characteristics of the drugs in the delivery vehicles is determined by their molecular features and structure. A quantitative understanding of the partitioning of drugs into delivery media and its subsequent release and binding to the target protein is essential to deriving guidelines for rational drug design. We have studied the partitioning of aminoglycosides and macrolide antibiotic drugs kanamycin, gentamicin, azithromycin, and erythromycin in cationic, nonionic, and the mixture of cationic and nonionic self-assemblies. The quantitative aspects of drug partitioning followed by the monitoring of its interaction with target model protein bovine serum albumin on subsequent release have been performed by using a combination of spectroscopy and high-sensitivity calorimetry. The mechanisms of partitioning have been analyzed on the basis of the values of standard molar enthalpy, entropy, the Gibbs free-energy change, and stoichiometry of interaction. The integrity of the binding sites and the effects of the components of the self-assemblies and the released drug on the serum albumin were analyzed by using differential scanning calorimetry and circular dichroism spectroscopy. The thermodynamic signatures of drug partitioning and subsequent binding to target protein have enabled an in-depth correlation of the structure-property-energetics relationships which are crucial for the broader objective of rational drug design.

On the Mg-Pb system. Calorimetric studies and thermodynamic calculations

In this paper, the experimentally determined integral and partial molar enthalpy of mixing of liquid Mg-Pb alloys is presented. Five separate measurements were performed at 1012 and 1014 K with the use of MHTC 96 Line Evo line drop calorimeter. The values of integral molar mixing enthalpy are characterized by negative deviations from the ideal solutions in the entire concentration range. Based on obtained results and other thermodynamic quantities available in the literature the Mg-Pb phase diagram was optimized. The calculated and experimentally obtained values of the integral molar mixing enthalpy are also compared with the Miedema model prediction of the integral molar mixing enthalpy. The formation enthalpy for the Mg2Pb phase is computed by ab initio calculations and equals −5978 J/mol of atoms at 0 K. For the Mg2Pb intermetallic phase, the calculated bulk isothermal and adiabatic modulus, as well as a variation of primitive cell volume and thermal expansion coefficient with the temperature, are presented. Moreover, the heat content of the Mg2Pb intermetallic phase is shown and compared with experimental data for temperatures from 0 K to its melting temperature.

Molar Entropy and Enthalpy of CO Adsorbed in Zeolites as Derived from VTIR Data: Role of Intermolecular Modes.

Detailed analysis of recently reported variable‐temperature IR (VTIR) spectra of carbon monoxide adsorbed in alkaline zeolites shows how, not only the corresponding values of standard adsorption enthalpy (ΔH0 ) and entropy (ΔS0 ) can be obtained, but also the thermodynamic values of molar entropy and enthalpy which characterize the adsorbed gas phase. In addition, it is shown that the so obtained molar entropy data can lead to new insights into soft molecular modes, which would be hardly accessible by conventional IR spectroscopic techniques.

Betulin/2-hydroxypropyl-β-cyclodextrin inclusion complex: Physicochemical characterization and hepatoprotective activity

The thermodynamic and spectroscopic parameters of the betulin/2-hydroxypropyl-β-cyclodextrin (HPβCD) inclusion complex and its hepatoprotective activity were investigated in rats with nonalcoholic steatohepatitis (NASH). The pentacyclic triterpene betulin was isolated from birch bark and complexed with HPβCD. The parameters of inclusion complex formation were evaluated by infrared spectroscopy and differential scanning and isothermal titration calorimetries. The aqueous solubility and stability of betulin were significantly increased due to the formation of a stable inclusion complex with a stoichiometry of 1:1. The determined changes in molar enthalpy (ΔH < 0), entropy (ΔS > 0) and free energy (ΔG < 0) values indicate energetically favorable and spontaneous nature of the ligand-receptor interaction. The association constant of the betulin/HPβCD complex formation was equal to 1330 ± 111 M−1, as was determined by a calorimetric method. The complex formation was enthalpy and entropy driven. In rats with NASH induced by a high-fat diet, the oral administration of the betulin/HPβCD complex at 50 mg/kg betulin equivalent resulted in marked liver protective effects exceeding those of a higher dose (100 mg/kg) of betulin alone. Specifically, the betulin/HPβCD complex decreased lipid accumulation, the number of inflammatory foci in the liver, the activities of the serum marker enzymes, and the circulating TNFα level. Therefore, the complexation of betulin with HPβCD, improving aqueous solubility and, in turn, bioavailability, could be a prospective strategy to enhance antioxidative, anti-inflammatory, and hepatoprotective properties of betulin as a promising candidate for treatment of NASH.

Hydrogen bond dynamics in aqueous Malonamide system: An experimental and theoretical approach

Dielectric relaxation properties of aqueous solutions of Malonamide (MAL) with different compositions are studied using Time Domain Reflectometry (TDR). The Molecular interactions and dipole properties are described using excess dielectric parameters and effective Kirkwood factors. Thermal properties show dissociation effects with an increase in solute concentration within the mixture. The positive values of molar enthalpy suggest heat energy is being absorbed during the dipole reorientation process. Luzar model has been used to determine theoretical values of static dielectric constant and adequately it determines Kirkwood correlation values. The theoretical vibrational spectroscopy of MAL-Water complexes was performed which shows the carbonyl group (C=O) of MAL acts as a hydrogen bonding site. The Mulliken charge plot of MAL in its gaseous and solution phase shows that the compound is more electronegative in its solution phase. The hydrogen-bonding interactions between the solute-solvent molecules are verified by FTIR spectroscopy. The experimental and theoretical IR frequencies were found to be consistent.

Influence of the functional groups −NH2, −OCH3, and −OH on the thermochemistry of indanes

This work is a contribution to the thermochemical characterization of bicyclic hydrocarbons, reporting the study of six indane derivatives: 4-aminoindane, 5-aminoindane, 5-methoxyindane, 1-indanol, 2-indanol, and 5-indanol. The combustion calorimetry technique was used to measure the massic energy of combustion of each compound in the condensed state, which has been used to derive the corresponding standard (p° = 0.1 MPa) molar enthalpy of formation, at 298.15 K. The standard molar enthalpies of sublimation or vaporization of the compounds were determined by high-temperature Calvet microcalorimetry. For each indane derivative, the results obtained for those two properties, allowed to derive the respective value of standard molar enthalpy of formation, in the gaseous phase. Additionally, a theoretical study at the G3(MP2)//B3LYP level has been carried out, and the calculated enthalpies of formation have been compared with the experimental values. The values of the enthalpy of formation, in the gaseous phase, were analysed in terms of correlations between the structural (different substituents in the indane core) and energetics characteristics.