Thermochemical Study of 1-Methylhydantoin

Using static bomb combustion calorimetry, the combustion energy of 1-methylhydantoin was obtained, from which the standard molar enthalpy of formation of the crystalline phase at T = 298.15 K of the compound studied was calculated. Through thermogravimetry, mass loss rates were measured as a function of temperature, from which the enthalpy of vaporization was calculated. Additionally, some properties of fusion were determined by differential scanning calorimetry, such as enthalpy and temperature. Adding the enthalpy of fusion to the enthalpy of vaporization, the enthalpy of sublimation of the compound was obtained at T = 298.15 K. By combining the enthalpy of formation of the compound in crystalline phase with its enthalpy of sublimation, the respective standard molar enthalpy of formation in the gas phase was calculated. On the other hand, the results obtained in the present work were compared with those of other derivatives of hydantoin, with which the effect of the change of some substituents in the base heterocyclic ring was evaluated.

The melting properties of D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose and their solubility in water: A revision

Saccharides are still commonly isolated from biological feedstock by crystallization from aqueous solutions. Precise thermodynamic data on solubility are essential to optimize the downstream crystallization process. Solubility modeling, in turn, requires knowledge of melting properties. In the first part of this work, following our previous work on amino acids and peptides, D-α-glucose, D-β-fructose, D-sucrose, D-α-galactose, and D-α-xylose were investigated with Fast Scanning Calorimetry (FSC) in a wide scanning rate range (2000 K·s−1 to 10000 K·s−1). Using the experimental melting properties of saccharides from FSC allowed successfully modeling aqueous solubility for D-sucrose and D-α-galactose with the equation of state PC-SAFT. This provides cross-validation of the measurement methods to determine accurate experimental melting properties with FSC. Unexpectedly, the experimental FSC melting temperatures, extrapolated to zero scanning rates for thermal lag correction, were higher than results determined with DSC and available literature data. To clarify this inconsistency, FSC measurements towards low scanning rates from 10000 K·s−1 to 1 K·s−1 (D-α-glucose, D-β-fructose, D-sucrose) overlapping with the scanning rates of DSC and literature data were combined. At scanning rates below 1000 K·s−1, the melting properties followed a consistent non-linear trend, observed in both the FSC and the literature data. In order to understand the non-linear decrease of apparent melting temperatures with decreasing heating rate, the endothermic peaks were investigated in terms of isoconversional kinetics. The activation energies in the non-linear dependency region are in the range of $$300<{E}_{A}< 600 {\text{kJ}}\bullet {\text{mo}}{\text{l}}^{-1}$$ 300 < E A < 600 kJ ∙ mol - 1 . These values are higher than the enthalpy of sublimation for D-α-glucose, indicating that the non-linear behavior does not have a physical nature but attributes to chemical processes corresponding to the decomposition of molecular compounds within the crystal lattice before melting. The melting properties reported in the literature, commonly determined with conventional methods such as DSC, lead to inaccurate results due to the decomposition of these biomolecules at low heating rates. In addition, the FSC results at lower scanning rates coincide with results from DSC and literature in the overlapping scanning rate range, further validating the accuracy of FSC measurements to determine reliable melting properties of thermally labile biomolecules. The experimental FSC melting properties determined at higher scanning rates are considered as the correct equilibrium melting properties, which are not influenced by any chemical processes. The combination of FSC and PC-SAFT opens the door to model solubility of solid compounds that commonly decompose before melting.

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.

Molecular Structure, Thermodynamic and Spectral Characteristics of Metal-Free and Nickel Complex of Tetrakis(1,2,5-thiadiazolo)porphyrazine

The Knudsen effusion method with mass spectrometric control of the vapor composition was used to study the possibility of a congruent transition to the gas phase and to estimate the enthalpy of sublimation of metal-free tetrakis(1,2,5-thiadiazolo)porphyrazine and its nickel complex (H2TTDPz and NiTTDPz, respectively). The geometrical and electronic structure of H2TTDPz and NiTTDPz in ground and low-lying excited electronic states were determined by DFT calculations. The electronic structure of NiTTDPz was studied by the complete active space (CASSCF) method, following accounting dynamic correlation by multiconfigurational quasi-degenerate second-order perturbation theory (MCQDPT2). A geometrical structure of D2h and D4h symmetry was obtained for H2TTDPz and NiTTDPz, respectively. According to data obtained by the MCQDPT2 method, the nickel complex possesses the ground state 1A1g, and the wave function of the ground state has the form of a single determinant. Electronic absorption and vibrational (IR and resonance Raman) spectra of H2TTDPz and NiTTDPz were studied experimentally and simulated theoretically.

Learning to Fly: Thermochemistry of Energetic Materials by Modified Thermogravimetric Analysis and Highly Accurate Quantum Chemical Calculations

The standard state enthalpy of formation and the enthalpy of sublimation are essential thermochemical parameters determining the performance and application prospects of energetic materials. Direct experimental measurements of these properties...

ELECTRON WORK FUNCTION OF LANTHANIDE TRIIODIDES

Desorption enthalpies of LnI4– and Ln2I7– associative ions (Ln = La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, and Lu) and the enthalpy of sublimation of LnI3 molecules were determined by Knudsen effusion mass spectrometric technique. These data were used to calculate the effective values of electron work function φe of polycrystalline samples of lanthanide triiodides LnI3 for the first time. The calculation methodology is based on the study of thermochemical cycles, which include atoms, molecules, ions, and electrons being in thermodynamic equilibrium with the LnI3 crystal inside the effusion cell. The values obtained for different lanthanides turned out to be close. They lie in the range of about 2.4 – 4.4 eV with an average value in the series: φe = 3.2 ± 0.3 eV. The latter value is close to those for previously studied lanthanide tribromides. No secondary periodicity of φe was found within the calculated errors along the lanthanide series. The results obtained are in quantitative agreement with the theoretical calculation of the values of the band gap of lanthanide triiodides. Comparison of φe with other classes of lanthanide compounds such as oxides, hexaborides, and lanthanide metals shows relatively high electron emission ability yielding only to alkali and alkali-earth metals.

Computational Study of Selected Amine and Lactam N-Oxides Including Comparisons of N-O Bond Dissociation Enthalpies with Those of Pyridine N-Oxides

A computational study of the structures and energetics of amine N-oxides, including pyridine N-oxides, trimethylamine N-oxide, bridgehead bicyclic amine N-oxides, and lactam N-oxides, allowed comparisons with published experimental data. Most of the computations employed the B3LYP/6-31G* and M06/6-311G+(d,p) models and comparisons were also made between the results of the HF 6-31G*, B3LYP/6-31G**, B3PW91/6-31G*, B3PW91/6-31G**, and the B3PW91/6-311G+(d,p) models. The range of calculated N-O bond dissociation energies (BDE) (actually enthalpies) was about 40 kcal/mol. Of particular interest was the BDE difference between pyridine N-oxide (PNO) and trimethylamine N-oxide (TMAO). Published thermochemical and computational (HF 6-31G*) data suggest that the BDE of PNO was only about 2 kcal/mol greater than that of TMAO. The higher IR frequency for N-O stretch in PNO and its shorter N-O bond length suggest a greater difference in BDE values, predicted at 10–14 kcal/mol in the present work. Determination of the enthalpy of sublimation of TMAO, or at least the enthalpy of fusion and estimation of the enthalpy of vaporization might solve this dichotomy. The “extra” resonance stabilization in pyridine N-oxide relative to pyridine was consistent with the 10–14 kcal/mol increase in BDE, relative to TMAO, and was about half the “extra” stabilization in phenoxide, relative to phenol or benzene. Comparison of pyridine N-oxide with its acyclic model nitrone (“Dewar-Breslow model”) indicated aromaticity slightly less than that of pyridine.

Thermodynamic properties of L-menthol in crystalline and gaseous states

Objectives. Menthol causes a cooling sensation and reduces the nerve activity when it is applied locally, ingested, or inhaled. This feature explains its extensive use as both an aromatizer and a flavoring agent in food manufacturing, tobacco industry, cosmetics production, as well as a mild anesthetic and antiseptic in dentistry. This work aimed to perform a comprehensive thermodynamic study of L-menthol in both crystalline and gaseous states.Methods. To determine the combustion energy of L-menthol in the crystalline state, combustion bomb calorimetry was used. The temperature dependence of L-menthol’s heat capacity in the range of 5–370 K and the melting (fusion) parameters were determined using adiabatic calorimetry. Quantum chemical calculations were performed on a standalone virtual machine in the Google Cloud Platform using an eight-core Intel Xeon Scalable Processor (Skylake) with a 2.0 GHz (up to 2.7 GHz at peak load) clock frequency and 8 GB RAM.Results. The energy and enthalpy of L-menthol combustion in the crystalline state were determined, and the standard enthalpy of L-menthol formation in the gaseous state was calculated using the standard enthalpy of sublimation. The standard thermodynamic functions (reduced enthalpy, entropy, and reduced Gibbs energy) of L-menthol in both crystalline and liquid states were obtained based on the smoothed values of heat capacity and melting parameters. The group of isodesmic reactions for the ab initio calculation of the enthalpy of formation for gaseous L-menthol was substantiated. Electronic energy and frequencies of normal modes of the molecules involved in these reactions were calculated using the Gaussian 4 composite quantum chemical method. Further, the sublimation enthalpy of L-menthol was calculated using the extended Politzer equation according to the electrostatic potential model.Conclusions. The first comprehensive thermodynamic study of L-menthol in various states of aggregation was performed, and the values calculated using semiempirical methods were consistent with the experimental values within error limits, which confirms the reliability of the results.

A Re-assessment of the Thermodynamic Properties of Osmium

The thermodynamic properties were reviewed by the author in 1995. A new assessment of the enthalpy of fusion at 68.0 ± 1.7 kJ mol-1 leads to a revision of the thermodynamic properties of the liquid phase and although the enthalpy of sublimation at 298.15 K is retained as 788 ± 4 kJ mol-1 the normal boiling point is revised to 5565 K at one atmosphere pressure.