Enthalpies Of Sublimation Research Articles

Vaporization enthalpies of self-associated aromatic compounds at 298.15 K: A review of existing data and the features of heat capacity correction. Part III. Polyphenols, polyanilines and aminophenols

The experimental data on the phase transition enthalpies and heat capacities of numerous polyphenols, polyanilines and aminophenols in the condensed and ideal gas state were analyzed to obtain the reliable values at 298.15 K. For this purpose, we combined experimental data on the crystal, liquid, and ideal gas heat capacities and fusion, sublimation and vaporization enthalpies. Significant part of these data, including the ideal gas heat capacities of 16 molecules, vapor pressures and vaporization enthalpies of 1,3-diaminobenzene and 1,6-dihydroxynaphthalene, were obtained in this work. A modified approach for the estimation of the temperature dependence of vaporization enthalpies of polyphenols, polyanilines and aminophenols showing performance competitive with the experimental one was proposed based on the analysis performed.

Thermal and sublimation properties of cardiovascular drugs sotalol and ivabradine hydrochlorides

The saturated vapor pressure of sotalol and ivabradine hydrochlorides was measured in the temperature range (413.15–437.15) K by the transpiration method. The sublimation thermodynamic functions (Gibbs energy, enthalpy and entropy) of the compounds were calculated from the temperature dependencies of saturated vapor pressure. The standard molar enthalpy of sublimation for sotalol and ivabradine hydrochlorides is (157.5 ± 1.4) kJ·mol−1 and (143.2 ± 1.2) kJ·mol−1, respectively. The thermal properties and crystal state of the drugs were studied by the DSC, TG/DTG and X-ray diffraction methods.

Data-efficient fine-tuning of foundational models for first-principles quality sublimation enthalpies.

Calculating sublimation enthalpies of molecular crystal polymorphs is relevant to a wide range of technological applications. However, predicting these quantities at first-principles accuracy - even with the aid of machine learning potentials - is a challenge that requires sub-kJ mol-1 accuracy in the potential energy surface and finite-temperature sampling. We present an accurate and data-efficient protocol for training machine learning interatomic potentials by fine-tuning the foundational MACE-MP-0 model and showcase its capabilities on sublimation enthalpies and physical properties of ice polymorphs. Our approach requires only a few tens of training structures to achieve sub-kJ mol-1 accuracy in the sublimation enthalpies and sub-1% error in densities at finite temperature and pressure. Exploiting this data efficiency, we perform preliminary NPT simulations of hexagonal ice at the random phase approximation level and demonstrate a good agreement with experiments. Our results show promise for finite-temperature modelling of molecular crystals with the accuracy of correlated electronic structure theory methods.

Enthalpies and entropies of sublimation and vaporization of aza crown ethers and cryptands measured by TGA

AbstractIn this work, the solid–gas and liquid–gas change of phase enthalpies of three aza crown ethers and two cryptands are derived from thermogravimetric data. For each of the compounds under study, the mass loss rate, dm/dt, was measured by isothermal thermogravimetry, then Pieterse and Focke equation combined with that of Clausius–Clapeyron was applied to correlate mass loss rate with temperature and to derive the respective vaporization or sublimation enthalpies at the experimental temperature and at 298.15 K. Such enthalpies are reported with the derived entropies and Gibbs energies of change of phase for the analyzed compounds. The results show a general trend of increasing value of the thermodynamic property as the number of the nitrogen atoms increases in the molecular structure of the macrocycle.

Molecular structure, thermodynamic and spectral characteristics of chloroboron(III) subphthalocyanine and its dodecafluorinated derivative

A comprehensive study of the structural, spectral and energetic properties of chloroboron(III) complexes of subphthalocyanine (H[Formula: see text]SubPc, for the first time) and dodecafluorosubphthalocyanine (F[Formula: see text]SubPc, reinvestigation) was performed by mass-spectroscopy (MS), gas-phase electron diffraction (GED), IR spectroscopy and quantum-chemical (QC) calculations. A synchronous GED/MS method showed that at T = 630 K and T = 540 K, thermally stable H[Formula: see text]SubPc and F[Formula: see text]SubPc molecular forms are present in the gas phase. The geometric structure of free molecules has been determined, in which the N3-B-Cl fragment has the structure of a distorted tetrahedron, and the phthalocyanine skeleton has a dome shape. QC calculations of the geometry agree well with the GED results. The similarities and differences of the molecular structure in the gas and solid phases were discussed. It is shown, that despite the similarity of most geometric parameters, the H[Formula: see text]SubPc and F[Formula: see text]SubPc have significant differences in electronic characteristics, which determines the differences in their physicochemical properties. The interpretation of the experimental IR spectra was carried out. The distribution of potential energy of normal vibrations over the internal vibrational coordinates has been analyzed. The sublimation enthalpies of H[Formula: see text]SubPc ([Formula: see text]H[Formula: see text](589 K) = 135(5) kJ ⋅ mol[Formula: see text] and F[Formula: see text]SubPc ([Formula: see text]H[Formula: see text](516 K) = 189(3) kJ ⋅ mol[Formula: see text] were determined by the mass spectrometric Knudsen effusion method. The obtained data is important for designing processes employed in fabricating optoelectronic devices based on subphthalocyanines by PVD. Experimental geometric parameters for free molecules and vibrational frequencies can be used to calculate the thermodynamic functions of gaseous H[Formula: see text]SubPc and F[Formula: see text]SubPc.

Practical feature filter strategy to machine learning for small datasets in chemistry

Many potential use cases for machine learning in chemistry and materials science suffer from small dataset sizes, which demands special care for the model design in order to deliver reliable predictions. Hence, feature selection as the key determinant for dataset design is essential here. We propose a practical and efficient feature filter strategy to determine the best input feature candidates. We illustrate this strategy for the prediction of adsorption energies based on a public dataset and sublimation enthalpies using an in-house training dataset. The input of adsorption energies reduces the feature space from 12 dimensions to two and still delivers accurate results. For the sublimation enthalpies, three input configurations are filtered from 14 possible configurations with different dimensions for further productive predictions as being most relevant by using our feature filter strategy. The best extreme gradient boosting regression model possesses a good performance and is evaluated from statistical and theoretical perspectives, reaching a level of accuracy comparable to density functional theory computations and allowing for physical interpretations of the predictions. Overall, the results indicate that the feature filter strategy can help interdisciplinary scientists without rich professional AI knowledge and limited computational resources to establish a reliable small training dataset first, which may make the final machine learning model training easier and more accurate, avoiding time-consuming hyperparameter explorations and improper feature selection.

Enthalpy and heat capacity of hydration of the cytostatic Dioxadet

Thermochemical data on hydration of the well-established anticancer agent Dioxadet were obtained. Its enthalpies of solution and sublimation at various temperatures were determined calorimetrically, and on their basis the standard enthalpy (ΔhydrH0 = −154.6 ± 3.6 kJ mol−1) and the standard heat capacity (ΔhydrCp0 = 384 ± 80 J mol−1 K−1) of the transfer of the solute from the state of an ideal gas to an aqueous solution at infinite dilution at 298.15 K were calculated.

Development of All-Atom Empirical Potentials for Phloroglucinol (Phg) and Hexachlorocyclotriphosphazene (HCCP) Based on their Crystal Phase Structures.

Two existing generic force fields have been augmented with partial charges and tuned in order to give intercompatible all-atom empirical potentials that can satisfactorily represent the known crystal phase structures of the organic phloroglucinol (Phg) (C6H6O3) and inorganic hexachlorocyclotriphosphazene (HCCP) (N3P3Cl6) molecules at several temperatures. It has been proposed that HCCP-Phg network polymers could act as efficient H2 barrier layers in hydrogen storage tanks for cars. However, essential requirements for modeling such networks are adequate representations of both monomers in their pure dense phases using a common form of force field. Tests of their ability to maintain stable crystal structures have been made using classical molecular dynamics (MD) simulations on large 800-molecule supercells. The force fields have been optimized to match the densities calculated from the experimental unit cell dimensions at ambient conditions as well as the intermolecular potential energy, as estimated from experimental enthalpies of sublimation. For Phg, the crystal structure is stabilized by a network of hydrogen bonds and the Coulombic interactions contribute to over 55% of the total intermolecular potential energy. In contrast, the crystal structure of HCCP is intrinsically stabilized by the van der Waals terms. Both optimized force fields reproduce very well the orthorhombic symmetry of their respective crystals under constant-pressure NPT conditions. The model parameters tuned at ambient temperature also give reasonable agreement with crystallographic data at lower temperatures.

How Accurate Are Simulations and Experiments for the Lattice Energies of Molecular Crystals?

Molecular crystals play a central role in a wide range of scientific fields, including pharmaceuticals and organic semiconductor devices. However, they are challenging systems to model accurately with computational approaches because of a delicate interplay of intermolecular interactions such as hydrogen bonding and Van der Waals dispersion forces. Here, by exploiting recent algorithmic developments, we report the first set of diffusion MonteCarlo lattice energies for all 23molecular crystals in the popular and widely used X23 dataset. Comparisons with previous state-of-the-art lattice energy predictions (on a subset of the dataset) and a careful analysis of experimental sublimation enthalpies reveals that high-accuracy computational methods are now at least as reliable as (computationally derived) experiments for the lattice energies of molecular crystals. Overall, this work demonstrates the feasibility of high-level explicitly correlated electronic structure methods for broad benchmarking studies in complex condensed phase systems, and signposts a route towards closer agreement between experiment and simulation.

Thermodynamic study of tin tetraiodide (SnI4) sublimation by effusion techniques

This study presents the first investigation of the sublimation behavior of tin tetraiodide, SnI4, using effusion-based techniques, within a low temperature range (313–340) K. The temperature range covered in the experiments was lower than in previously reported studies based on static methods. Knudsen Effusion Mass Loss (KEML) measurements were performed in the range of (317.1–339.6) K using effusion cells with different orifice sizes. The vapor pressures were measured in the range (0.13–1.13) Pa and were found to be independent of the orifice size. The standard molar enthalpy and Gibbs energy of sublimation at 298.15 K obtained by the Clarke and Glew fit of experimental data are (88.1 ± 0.9) kJ⋅mol−1 and (38.96 ± 0.08) kJ⋅mol−1, respectively. Knudsen Effusion Mass Spectrometry (KEMS) experiments were also performed in the range (313.3–331.7) K, resulting in a sublimation enthalpy value in good agreement with the KEML values and not negligibly higher vapor pressure values. KEMS vapor pressure data were also analyzed by the third-law method. A comparison of our experimental results with the literature data available for both sublimation and evaporation properties of SnI4 is reported. Additionally, ancillary DFT and ab initio calculations were performed to estimate the molecular properties of SnI4(g) and the extent of the gas-phase dissociation to SnI2 and I2.

Phase transition study of bathophenanthroline and bathocuproine: A multitechnique approach

The thermal behaviour of bathophenanthroline and bathocuproine has been studied using several techniques, namely, differential scanning calorimetry and thermogravimetry. To determine their respective enthalpies of sublimation, vapor pressure measurements were carried out using different methods, such as Knudsen effusion mass loss/mass spectrometry, isothermal thermogravimetry, and a quartz crystal microbalance technique. Furthermore, the enthalpies of sublimation were determined by measuring the heat change of the sublimation process using high-temperature Calvet microcalorimetry.The results obtained in this work allowed the determination of the standard molar enthalpies of sublimation at 298.15 K, for bathophenanthroline and bathocuproine. The values obtained were (183.8 ± 2.2) kJ⋅mol−1 and (206.2 ± 2.8) kJ⋅mol−1, respectively. Additionally, the standard molar enthalpies of fusion were determined to be (30.4 ± 0.4) kJ⋅mol−1 and (26.5 ± 1.6) kJ⋅mol−1 for bathophenanthroline and bathocuproine, respectively. The analysis of the results allows a deeper understanding of the phase transition behavior for these compounds from the condensed to the gaseous phases, elucidating molecular decomposition and the inherent intermolecular forces governing the species.

Thermodynamic parameters of L-carnosine dissolution and solvation in binary aqueous-organic mixtures at T = 298.15 K.

Isothermal calorimetry was used to measure the enthalpies of L-carnosine digestion in aqueous solutions of acetonitrile (AN) 1,4-dioxane (DO), acetone (AC), dimethyl sulfoxide (DMSO), ethanol EtOH), 1-propanol (1-PrOH), and 2-propanol (2-PrOH). The values of ΔsolH° obtained were combined with the standard enthalpies of L-carnosine sublimation to obtain the corresponding enthalpies of solvation ΔsolvH°. In addition, the enthalpic coefficients of pairwise interactions (hxy) of L-carnosine with organic solvent molecules and the enthalpy of transfer (ΔtrH°) from water in their mixture with the latter were calculated. It is established that the solvation of L-carnosine is weakened in a series of (H2O + EtOH) > (H2O + 1-PrOH) > (H2O + 2-PrOH). This may be due to an increase in the hydrophobicity of alcohols of the same order as well as the presence of CH3-groups within the alcohol molecule. The weakening of the solvation energy of L-carnosine by co-solvent molecules in a series of mixed solvents: (H2O + AN) < (H2O + AC) < (H2O + DO) < (H2O + DMSO) is associated both with an increase in the hydration energy of co-solvents in the same order and with their physicochemical properties. The enthalpic coefficients of water-organic solvent pairwise interactions were discovered to be linearly related to the corresponding coefficients of L-carnosine-organic solvent interactions. An increase in the polarity and acidity of an organic solvent increases the energy of pairwise interactions between L-carnosine and the organic solvent. Increasing the cohesion energy density, molar volume, and basicity of the organic solvent reduces the energy of the pairwise interactions between L-carnosine and the organic solvent.

Thermodynamic properties of 3-(1,5-diphenylpyrrol-2-yl)- propanoic acid

Using precision equipment, the enthalpies of vaporization, fusion and formation in the condensed state of 3-(1,5-diphenylpyrrol-2-yl)-propanoic acid were experimentally determined. The enthalpy of sublimation at 298 K and the enthalpy of formation in the gaseous state were calculated. A comparative analysis of the experimentally determined values with theoretically calculated values using additive calculation methods is given.

Health is the greatest wealth: Quest for a diagnostic check for thermochemistry of pure drug compounds

The development of pharmaceutical formulations and the optimisation of drug synthesis are not possible without knowledge of thermodynamics. At the same time, the quantity and quality of the available data is not at a level that meets modern requirements. A convenient diagnostic approach is desirable to assess the quality of available experimental thermodynamic data of drugs. A comprehensive set of available data on phase transitions of profens family drugs was analysed using new complementary measurements and structure–property correlations. The consistent sets of solid–gas, liquid–gas and solid–liquid phase transitions were evaluated for twelve active pharmaceutical ingredients based on alkanoic acid derivatives and recommended for the calculations of the pharmaceutical processes. A “centerpiece approach” proposed in this work helped to perform the “health check” of the thermochemical data. The evaluated data on the sublimation enthalpies were used to derive the crystal lattice energies of the profens and to correlate the water solubilities with the sublimation vapour pressures and molecular parameters. A “paper-and-pen” approach proposed in this work can be extended to the diagnosis of “sick” or “healthy” thermodynamic data for drugs with a different structure than those studied in this work.

A New Model to Correlate Solubility of Therapeutic Drugs in Supercritical Carbon Dioxide

In this work, a new solubility model was proposed based on the enhancement factor concept. The proposed model is validated with the literature available solubility data of seventeen therapeutic drugs in supercritical carbon dioxide. The correlating ability of the proposed model was compared with the Chrastil model and Bartle et al. model. The global average absolute relative deviation (AARD) percentages of Chrastil, Bartle et al. and new models were 19.42%, 19.57% and 16.43%, respectively. Sublimation enthalpies of therapeutic drugs were calculated with a new model as well as with Bartle et al. model. The calculated sublimation enthalpies ranged between 8.32 to 180.23 kJ/mol and 19.5 to 280.26 kJ/mol for the Bartle et al. model and the Improved Bartle model, respectively. Finally, a statistical analysis was performed in terms of Alaike's Information Criterion (AIC) to differentiate models considered in this work.

Thermochemistry of amino-1,2,4-triazole derivatives

AbstractThe present work is focused on determining the enthalpy of formation of several derivatives of amino-1,2,4-triazoles. Experimentally, the enthalpies of formation of the crystalline phase and the enthalpies of sublimation of 3-amino- and 3,5-diamino-1H-1,2,4-triazole were derived, respectively, from static-bomb combustion calorimetry and Calvet microcalorimetry or Knudsen effusion measurements. For 4-amino-4H-1,2,4-triazole, only the enthalpy of sublimation was measured. Gas-phase standard molar enthalpies of formation were also estimated using theoretical calculations performed with the G3(MP2) composite approach. The very good agreement of these estimates with the experimental results, support the extension of this study to the estimate of this property for the remaining compounds not studied experimentally. The results obtained are interpreted in terms of structural contributions.

New static apparatus STAT9 for vapor pressure measurements at temperatures up to 463 K

In this work, a state-of-the-art static apparatus for vapor pressure measurements in a temperature range of 363−463 K and a wide pressure range of 1−13,330 Pa is introduced and described. The performance of the apparatus was evaluated by a meticulous procedure of measuring the vapor pressure of five reference materials of different volatility, anthracene, benzophenone, ferrocene, naphthalene, and dibenzothiophene. The last two compounds were studied in the blind test regime, i.e., the results were compared to literature only after finishing the experiments. During benchmarking the performance of the apparatus, it was found appropriate to develop new vapor pressure equations for ferrocene and anthracene that included high-temperature data from the STAT9 apparatus. By combining the new data with previously selected vapor pressures, sublimation enthalpies, and ideal-gas and condensed phase heat capacities, we have obtained a consistent sublimation pressure equation for anthracene and ferrocene. For anthracene, the correlation procedure covered melting properties and liquid-phase vapor pressure data to support the description of the high-temperature region. The revised vapor pressure equations and sublimation enthalpies may serve as solid foundation for future research in this field.

Phase transition thermodynamics of organic semiconductors: N,N,N’,N’-tetraphenylbenzidine and 4,4′-bis(N-carbazolyl)-1,1′-biphenyl

In this work, we report a comprehensive study of the phase change thermodynamics of two compounds, N,N,N’,N’-tetraphenylbenzidine (TPB) and 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), used in the production of organic light-emitting diodes and photovoltaics. The vapor pressures and phase transition enthalpies of these compounds have been previously studied at the elevated temperatures which may not be relevant to the conditions during fabrication and use TPB- and CBP-based materials. In this work, a combination of experimental and computational methods was employed to establish the reliable temperature dependences of the sublimation, fusion, and vaporization enthalpies of TPB and CBP in a wide temperature range. The vapor pressures of both compounds over solid and liquid phases were measured using fast scanning calorimetry. The fusion enthalpies at the melting point were determined by DSC. The isobaric heat capacities of the compounds in crystalline and liquid phases, including the supercooled liquids, were measured using scanning calorimetry. For the first time, the heat capacities of the ideal gas TPB and CBP were computed, considering internal rotation effects. The solution enthalpies in benzene at 298.15 K were measured, providing an independent estimate of the fusion enthalpy temperature dependence. Its consistency with the data on the fusion enthalpies was confirmed using Hess’s and Kirchhoff’s laws of Thermochemistry. Using the obtained results, the available literature data were critically evaluated. The obtained thermodynamic parameters may facilitate optimization of vapor deposition conditions and description of the thermodynamic and kinetic stability of the glassy state of TPB and CBP.

Thermodynamics of reversible hydrogen storage: Does alkoxy-substitution of naphthalene yield functional advantages for LOHC systems?

The reversible hydrogenation/dehydrogenation of aromatic molecules, known as liquid organic hydrogen carriers (LOHCs), is considered an attractive option for the safe storage and release of elemental hydrogen. The LOHC systems based on the alkoxy-naphthalene/alkoxy-decalin studied in this work can become potentially attractive from the point of view of the thermodynamic conditions of the reversible hydrogenation/dehydrogenation processes. This work reports the results of a complex experimental investigation of the thermochemical properties of the reactants of the LOHC systems. The enthalpies of formation were measured using high-precision combustion calorimetry, the enthalpies of vaporization and sublimation were derived from the vapor pressure–temperature dependencies measured using the transpiration method, and the melting temperatures and enthalpies of fusion were measured using the differential scanning calorimetry method. The liquid-phase enthalpies of formation of methoxy- and ethoxy-substituted naphthalenes and methoxy- and ethoxy-substituted decalins were derived and used for the thermodynamic analysis of hydrogenation/dehydrogenation reactions and transferhydrogenation reactions.

First Sublimation Thermodynamics and First Gas‐Phase Experimental Molecular Structure of Heteroporphyrins: 5,10,15,20‐Tetraphenyl‐21‐X, 23‐Y‐Porphyrins (X=O or S; Y=N or S)

AbstractFirst sublimation enthalpies of heteroporphyrins: 10,15,20‐tetraphenyl‐21‐oxa‐ (HOPP), 5,10,15,20‐tetraphenyl‐21‐thia‐ (HSPP) and 5,10,15,20‐tetraphenyl‐21,23‐dithia‐ (S2PP) were measured by Knudsen effusion mass spectrometry: ΔsublH (T)=209±2 (561 K), 224±2 (552 K) and 219±2 (577 K) kJ/mol, respectively. Geometry and force field of a free molecule of HSPP was studied by quantum chemistry, and first gas‐phase experimental molecular structure of heteroporphyrins was derived by gas‐phase electron diffraction. Theoretically observed changes of the coordination cavity geometries due to heteroatomic intracavity substitution were experimentally confirmed with good agreement. Molecular structures of the dimeric associates of the heteroporphyrins were tested simulated to reveal tendencies in sublimation thermodynamics.