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In an effort to establish reliable thermodynamic data for amino acids, heat capacity and phase behavior are reported for L-cysteine (CAS RN: 52-90-4), L-serine (CAS RN: 56-45-1), L-threonine (CAS RN: 72-19-5), L-lysine (CAS RN: 56-87-1), and L-methionine (CAS RN: 63-68-3). Prior to heat capacity measurements, initial crystal structures were identified by X-ray powder diffraction, followed by a thorough investigation of the polymorphic behavior using differential scanning calorimetry in the temperature range from 183 K to the decomposition temperature determined by thermogravimetric analysis. Crystal heat capacities of all five amino acids were measured by Tian–Calvet calorimetry in the temperature interval (262–358) K and by power compensation DSC in the temperature interval from 215 K to over 420 K. Experimental values of this work were compared and combined with the literature data obtained with adiabatic calorimetry. Low-temperature heat capacities of L-threonine and L-lysine, for which no or limited literature data was available, were measured using the relaxation (heat pulse) calorimetry. As a result, reference heat capacities and thermodynamic functions for the crystalline phase from near 0 K to over 420 K were developed.

Knowledge of the active pharmaceutical ingredient (API) solubility in a polymer is imperative for successful amorphous solid dispersion design and formulation but acquiring this information at storage temperature is challenging. Various solubility determination methods have been established, which utilize differential scanning calorimetry (DSC). In this work, three commonly used DSC-based protocols [i.e., melting point depression (MPD), recrystallization, and zero-enthalpy extrapolation (Z-EE)] and a method that we have developed called "step-wise dissolution" (S-WD) were analyzed. For temperature-composition phase diagram construction, two glass-transition temperature equations (i.e., those of Gordon-Taylor and Kwei) and three solid-liquid equilibrium curve modeling approaches [i.e., the Flory-Huggins model, an empirical equation, and the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EOS)] were considered. Indomethacin (IND) and Kollidon 12 PF (PVP K12) were selected as the API and polymer, respectively. An annealing time investigation revealed that the IND-PVP K12 dissolution process was remarkably faster than demixing, which contradicted previously published statements. Thus, the recrystallization method overestimated the solubility of IND in PVP K12 when a 2-h time of annealing was set as the benchmark. Likewise, the MPD and Z-EE methods overestimated the API solubility because of unreliable IND melting endotherm evaluation at lower API loadings and a relatively slow heating rate, respectively. When the experimental results obtained using the S-WD method (in conjunction with the Kwei equation) were applied to the PC-SAFT EOS, which was regarded as the most reliable combination, the predicted IND solubility in PVP K12 at T = 25 °C was approximately 40 wt %. When applicable, the S-WD method offers the advantage of using a limited number of DSC sample pans and API-polymer physical mixture compositions, which is both cost- and time-effective.

Vapor pressures for liquid 1-heptanol (CAS RN: 111-70-6), 1-octanol (CAS RN: 111-87-5), 1-nonanol (CAS RN: 143-08-8), and 1-decanol (CAS RN: 112-30-1) were measured by a static method near ambient temperatures over an operating pressure range from 0.5 to 1270 Pa, thus complementing literature vapor pressure data obtained by ebulliometry at higher temperatures. Liquid heat capacities of 1-octanol, 1-nonanol, and 1-decanol were determined by Tian–Calvet calorimetry. Ideal-gas thermodynamic properties of 1-alkanols up to 1-heptanol were obtained by a combination of quantum chemistry and statistical mechanics and validated against available experimental data. Ideal-gas heat capacities and entropies for longer homologues were obtained by deriving a methylene increment due to having a too complex conformational shape for analogical treatment. The thermodynamic consistency of available data was validated by simultaneous correlation of selected vapor pressures, literature enthalpies of vaporization, and heat capacity differences between the ideal gaseous and the liquid phase. The results are represented by the Cox equation and compared with available literature data. Moreover, the results were used to examine the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state for its performance in describing vapor pressures, enthalpies of vaporization, residual liquid heat capacities, and liquid densities of neat 1-alkanols from 1-hexanol to 1-decanol. A new PC-SAFT parameter set for each of them was also regressed that improves the PC-SAFT performance for the studied properties in comparison to existing parameters published in the literature.

The present work deals with the precise experimental determination of the gas–liquid chromatography (GLC) retention factors (k) in a sufficiently large temperature range to allow the calculation of...

This work is part of the effort on establishing reliable thermodynamic data for amino acids and, in a broader context, benchmarking first-principles calculations of thermodynamic properties of molecular crystals against reliable experimental data. In this work, crystal heat capacities of l-alanine (CAS RN: 56-41-7), l-valine (CAS RN: 72-18-4), l-isoleucine (CAS RN: 73-32-5), and l-leucine (CAS RN: 61-90-5) were newly measured in the temperature range 262–450 K by Tian–Calvet calorimetry and power-compensation differential scanning calorimetry (DSC) and combined with the critically assessed literature data to obtain the reference data from near 0 to 450 K. The heat capacity measurements were accompanied by thermogravimetric analysis to determine the decomposition temperatures of the studied amino acids and phase behavior studies by X-ray powder diffraction and heat-flux DSC to identify the initial crystal structures and their possible transformations. The crystal heat capacities calculated by combining the...

For successful formulation of amorphous solid dispersions (ASDs) using hot-melt extrusion, it is imperative to understand the effect that heat and shear rate has on the physicochemical properties of the excipient. In this study, we investigated the influence of hot-melt extrusion parameters on solvent-free binary ASDs of ibuprofen (IBU), a model active pharmaceutical ingredient, in methacrylic acid-ethyl acrylate copolymer type A, 1:1, EUDRAGIT® L100-55 (EUD). To evaluate the impact of barrel temperature, screw speed, and residence time on EUD mass average molar mass and IBU release profile, size-exclusion chromatography and dissolution testing were used, respectively. The optimal conditions were established for IBU loadings less than 40 wt. %. For ASD formulations prepared using the ideal variables, spectral and thermal analyses confirmed that, under dry conditions at a temperature of 25°C, IBU remained amorphous during an 18-month storage period. After 28 months, formulations with active pharmaceutical ingredient content above 30 wt. % started to recrystallize. A temperature-composition phase diagram, constructed using melting point depression and glass-transition temperature measurements of IBU-EUD mixtures, correlated well with the long-term physical stability. The effect that minor-to-moderate polymer degradation within the extrudates has on their long-term physical stability and dissolution characteristics is analyzed and discussed.

This work aims to provide reliable heat capacities for ethylene glycol and selected oligo(ethylene glycol)s (diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and h...

Knowledge of the vapor pressure is one of the key parameters that determine the application of detection taggants for a given explosive and useful lifetime. The objective of this work was to determine the vapor pressures and thermodynamically linked properties of selected explosive taggants, namely 2,3-dimethyl-2,3-dinitrobutane, 2-nitrotoluene, and 4-nitrotoluene. Experimental studies included vapor pressure measurements using a static method, investigation of phase behavior by differential scanning calorimetry, and measurement of condensed-phase heat capacities. On the basis of the above-mentioned data and in combination with theoretically calculated ideal-gas thermodynamic properties, the recommended vapor pressure equations for the explosive taggants in a wide temperature range were developed by the method of simultaneous correlation of vapor pressures and thermodynamically linked properties.

In an effort to establish reliable thermodynamic data for amino acids, heat capacity and phase behavior is reported for l-arginine (CAS RN: 74-79-3), l-aspartic acid (CAS RN: 56-84-8), l-glutamic acid (CAS RN: 56-86-0), l-glutamine (CAS RN: 56-85-9), and l-asparagine (CAS RN: 70-47-3). Prior to heat capacities measurement, thermogravimetric analysis was performed to determine decomposition temperatures. Crystal heat capacities of all five amino acids were measured by Tian–Calvet calorimetry in the temperature interval (262–358) K and by power compensation DSC in the temperature interval (215–451) K. Experimental values of this work were combined with the literature data obtained with adiabatic calorimetry. Low temperature heat capacities of l-arginine and l-asparagine, for which no or limited literature data were available, were measured using the relaxation (heat pulse) calorimetry. As a result, reference heat capacities and thermodynamic functions for crystalline phase from near 0 K to 450 K were developed.

A combined experimental and computational thermodynamic study of 4-ethylmorpholine was undertaken in this work to resolve large discrepancies between the two vapor pressure data sets reported in th...

Anthracene (CAS RN: 120-12-7) is recommended as a primary standard for sublimation enthalpy measurements and it is also frequently used for testing apparatus for vapour pressure measurements. Two recent recommendations by ICTAC for sublimation enthalpy at 298.15 K obtained by extrapolation can be found in the literature. However, no recommended vapour pressure equation and sublimation enthalpy as a function of temperature were reported. The following steps were performed to develop recommended sublimation pressure and enthalpy data for anthracene in the temperature range in which the calibrations are typically performed: (i) analysis and reconciliation of the literature values on vapour pressures and examination of their thermodynamic consistency with related thermal properties; (ii) new extensive vapour pressure measurements in the temperature range (343–373) K; (iii) calculation of ideal-gas thermodynamic properties combining statistical thermodynamics and quantum chemistry methods, and (iv) multi-property correlation of selected vapour pressure and thermal data. The quality and range of available data needed for the multi-property correlation allowed to establish the recommended sublimation pressure equation in the temperature range (200–373) K while at higher temperatures and for the liquid phase only tentative data are provided. Recommended values at 298.15 K are (0.91 ± 0.09) mPa for sublimation pressure and (101.01 ± 0.52) kJ·mol−1 for sublimation enthalpy; the recommended enthalpy of sublimation at 0 K is (104.4 ± 0.9) kJ mol−1. Based on the recommended sublimation pressures, super cooled liquid vapour pressures required for environmental modeling were also calculated.

Cohesive properties (lattice and cohesive energy of the crystal and corresponding sublimation enthalpy) of the complete set of twenty enantiopure anhydrous proteinogenic amino acids are investigated using first-principles calculations. In contrast to neutral amino acid molecules in the vapor phase, all amino acids form crystals in their zwitterionic form. Therefore, reliable ab initio calculations of the proton transfer energy are an indispensable step of such calculations. Simplifying procedures, designed to rationalize the computational cost of the quasi-harmonic approximation, which proves too demanding if performed fully at the given quantum level of theory, are presented and tested. For this purpose, atomic multipoles (up to the quadrupoles) for the amoeba force field are parametrized for all amino acid zwitterions. While the calculated lattice energies of the amino acids range from 235-458 kJ mol-1 in absolute value, the proton transfer energies typically amount to 100-220 kJ mol-1, which translates to sublimation enthalpies ranging from 117-202 kJ mol-1, appreciably exceeding the sublimation enthalpy values common for nonionic molecular crystals. Critically assessed experimental data on sublimation enthalpies are used as a benchmark for comparison of the data calculated in this work. Cohesive properties of most amino acids calculated in this work, combining the PBE-D3(BJ)/PAW and CCSD(T)-F12/aug-cc-pVDZ levels of theory used for predictions of the lattice energies and of the proton transfer energies, respectively, exhibit a reasonable agreement with the experiment. At the same time, this work contains the first published data on cohesive properties for several enantiopure amino acids.

The preparation of an amorphous solid dispersion (ASD) is a promising strategy for improving the poor oral bioavailability of many active pharmaceutical ingredients (APIs). However, poor predictability of ASD long-term physical stability remains a prevalent problem. The purpose of this study was to evaluate and compare the predictive performance of selected models concerning solid–liquid equilibrium (SLE) curve and glass-transition temperature (Tg) line modeling of ibuprofen (IBU) in cellulosic polymers (i.e., hydroxypropyl methylcellulose (HPMC) and hydroxypropyl methylcellulose acetate succinate (HPMCAS)). For SLE curve modeling, an empirical analytical approach (Kyeremateng et al., 2014) and the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equation of state (EOS) were chosen. Due to the unavailability of PC-SAFT parameters for both polymers, an approximation procedure for parametrization was applied. The Gordon–Taylor equation and Kwei equation were considered for Tg line determination. The impact of various computational set-ups (e.g., model parametrization or extrapolation length) on IBU solubility prediction at storage conditions was thoroughly investigated, assessed and confronted with the results from an 18-month physical stability study. IBU developed stable 20 wt% API content ASDs with both HPMC and HPMCAS. The extrapolation behavior and subsequent ASD thermodynamic stability prediction at storage conditions deduced from the aforementioned models were significantly different. Overall, the PC-SAFT EOS predicted higher IBU solubility in both polymers and, thus, a lower recrystallization tendency when compared to the empirical analytical approach. At higher IBU concentrations, liquid-liquid demixing in IBU–polymer systems was predicted by the PC-SAFT EOS, which was in qualitative disagreement with experimental observation.

An insight into current possibilities of obtaining the sublimation pressures for molecular crystals from first principles is presented. Due to their extreme sensitivity to any computational uncertainties, sublimation pressures are the strictest possible representation of first-principles data on the cohesive properties of molecular crystals, emphasizing the significance of any computational uncertainties of cohesive energies, sublimation enthalpies, or sublimation entropies which might seem acceptable from a purely energetic point of view. The sublimation pressure was computed for 20 selected molecular crystals by combining the calculated static cohesive energy, vibrational contributions to thermodynamic properties in the crystalline phase, and ideal-gas thermodynamic properties required to obtain the sublimation enthalpy and entropy as a function of temperature. The calculated sublimation pressures were compared to reference experimentally based values developed in this work. By an analysis of the uncert...

A thermodynamic study of three ethanolamines, 2-(diethylamino)ethanol, 2-(ethylamino)ethanol and 2- (isopropylamino)ethanol, reporting the measurements of vapor pressure, liquid phase heat capacities, and phase behavior is presented in this work. The vapor pressures were measured using a static method in the temperature interval 238e343 K. After a critical assessment of literature data, selected experimental data were correlated using the Cox equation. The liquid phase heat capacities were measured in the temperature range 265e355 K using Tian-Calvet calorimetry and the phase behavior was investigated using differential scanning calorimetry (DSC) starting from 183 K. For 2-(ethylamino)ethanol and 2-(isopropylamino)ethanol, two monotropically related crystalline forms were identified. To our knowledge, vapor pressure and heat capacity for 2-(isopropylamino)ethanol and phase behavior data for 2-(ethylamino)ethanol and 2-(isopropylamino)ethanol are reported for the first time in this work. The authors acknowledge financial support from the Czech Science Foundation (GACR no. 17-03875S) and the project POCI-01- 0145-FEDER-006984 e Associate Laboratory LSRE-LCM funded by FEDER through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) e and by Portuguese national funds through FCT - Fundação para a Ciência e a Tecnologia The authors acknowledge financial support from the Czech Science Foundation (GACR no. 17-03875S) and the project POCI-01- 0145-FEDER-006984 e Associate Laboratory LSRE-LCM funded by FEDER through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) e and by Portuguese national funds through FCT - Fundação para a Ciência e a Tecnologia. info:eu-repo/semantics/publishedVersion

An environmentally benign concept based on waterborne systems is developed for preparation of novel nanocomposite materials with tunable properties. The designed nanocomposites are based on combination of core-shell latex nanoparticles, cellulose nanocrystals (CNC) and polyethylene glycol (PEG). First, core-shell latex nanoparticles from copolymer (methyl methacrylate-ethylene glycol dimethacrylate)-core and copolymer (methyl methacrylate-butyl acrylate)-shell (CS15) are prepared by starved emulsion polymerization. Likewise, incorporation of CNC aqueous suspension into the core-shell latex without any further chemical modification of the nanofiller while assuring good compatibility between both entities is achieved. PEG is effectively added to the suspension to assure multiple functions in the final material. After mixing of the ternary systems, the nanocomposites are prepared by three approaches, i.e. solution casting, solution casting followed by compression molding, and freeze drying followed by compression molding. SEM analysis shows that compression molding processes lead to the highest degree of coalescence of CS15 nanoparticles. This effect is however reduced in presence of PEG or PEG/CNC. It is further observed that the presence of PEG helps protecting CNC from thermal degradation. Thermal and thermo-mechanical analyses prove a high plasticizing performance of PEG and its good confinement between the nanoparticles and at interstitial spaces. Furthermore, it is revealed that the level of material reinforcement by CNC depends strongly on the ratio between CNC and PEG due to the establishment of strong interactions via hydrogen bonding between both components, which can affect the formation of CNC percolating network. These findings allow tuning the microstructure and related properties of the nanocomposites.

Isobaric heat capacities of ten selected aliphatic octanols (3-octanol, CAS RN: 589-98-0; 2,2,4-trimethyl-3-pentanol, CAS RN: 5162-48-1; 2,2-dimethyl-3-hexanol, CAS RN: 4209-90-9; 2,3-dimethyl-3-hexanol, CAS RN: 4166-46-5; 2,4-dimethyl-3-hexanol, CAS RN: 13432-25-2; 2,5-dimethyl-3-hexanol, CAS RN: 19550-07-3; 3,5-dimethyl-3-hexanol, CAS RN: 4209-91-0; 4-ethyl-3-hexanol, CAS RN: 19780-44-0; 3-methyl-4-heptanol, CAS RN: 1838-73-9; 4-methyl-4-heptanol, CAS RN: 598-01-6) were measured with a Tian–Calvet calorimeter in the temperature range from 257 to 358 K; this temperature range was extended up to 423 K with a heat-flux DSC. For all studied compounds, a maximum on temperature dependence of heat capacity was observed; this feature was corroborated by FTIR spectroscopy performed from 303 K to a maximum of 463 K. Such maxima are related to disintegration of oligomers kept together by hydrogen bonds. The role of steric hindrance on hydrogen bonding is discussed. It is apparent that temperature of maxima is very sensitive to steric hindrance; however, further effort is required for full understanding of hydrogen bonding in aliphatic octanols.

The influence of three generations of five different phosphonium carbosilane dendrimers and one ammonium carbosilane dendrimer as a reference (PMe3, PBu3, P(Et2)2(CH2)3OH, PPh3, P(MeOPh)3 and NMe3, peripheral functional groups) on dimyristoylphosphatidylcholine (DMPC) or a lipid mixture dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol (DMPC/DMPG) of liposomes was studied by fluorescence polarization measurements and differential scanning calorimetry. All types of dendrimers interacted with neutral as well as negatively charged liposomes, but the strength and observed influence were different. Concentration, type of peripheral functional group modification and dendrimer generation were the main factors influencing the interaction. Generally, weak interactions as well as destabilization of the lipid membranes at low concentrations, regardless of liposome type, were observed in the case of DmPMe3, DmNMe3, DmPBu3 and DmP(Et2)2(CH2)3OH. Dendrimers with PPh3 and P(MeOPh)3 peripheral functional groups interacted much more strongly and increased the rigidity of liposomes. Electrostatic interactions, the hydrophobicity of substituents and charge shielding on the peripheral phosphonium group are important factors in the interaction. We suggest that, among the other types of dendrimers, the dendrimer with the P(MeOPh)3 peripheral functional group is a highly promising candidate for the design of a drug delivery system due to its positive charge, efficient interaction with lipidic membranes and low cytotoxicity.

Condensed-phase heat capacities of selected pharmaceutical active pharmaceutical ingredients (APIs), namely (RS)-ibuprofen (CAS RN: 15687-27-1), (S)-ibuprofen (CAS RN: 51146-56-6), (S)-naproxen (CAS RN: 22204-53-1), indomethacin (CAS RN: 53-86-1), and carbamazepine (CAS RN: 298-46-4), were determined using Tian-Calvet calorimetry and power-compensated differential scanning calorimetry in the temperature range 216 to 471 K. In most cases, previously published heat capacities of the studied APIs are in significant disagreement both with each other and our measurements. By analyzing the literature values, many previously published data sets were shown to be erroneous. The heat capacities of supercooled liquid, an important parameter in the modeling of API solubility, were also measured in a wide temperature range when feasible. The phase behavior study of carbamazepine suggests that its thermal stability is lower than previously thought, which is in accordance with the most recent studies on carbamazepine decomposition. This work significantly extends the availability of reliable API heat capacity data for clearly defined polymorphic forms and liquid phase.

The heat capacity and thermal behavior trend along the 1-alkyl-3-methylimidazolium hexafluorophosphate [C n C 1 im][PF 6 ] (with n = 2–10, 12) ionic liquids series, is used to explore the effect of the alkyl chain length in the nanostructuration. The heat capacities of the studied ILs were measured with an uncertainty better than ± 0.15% and are in excellent agreement with the available data in the literature. An odd-even effect for the specific and volumic heat capacities of the [C n C 1 im][PF 6 ] series was found. The observed odd-even effect in the liquid heat capacity was rationalized considering the preferential orientation of the terminal CH 3 group. The higher specific/volumic heat capacities shown for the [C 6 C 1 im][PF 6 ] and [C 8 C 1 im][PF 6 ] are an indication of an additional conformational disorder increase in the liquid phase that could be related with a weaker alkyl chain interdigitation capability of the even number chain ILs. The melting temperatures and consequent ∆ s l H m o and ∆ s l S m o trend along the alkyl series present a V-shape profile that is explained based on the analysis of the balance between the initial decrease of the electrostatic interaction potential and the increase of the van der Waals interactions with the increasing size of the alkyl side chain of the cation. The inhibition of crystallization for intermediate alkyl chain size (from [C 5 C 1 im][PF 6 ] to [C 8 C 1 im][PF 6 ]) seems to arise from the overlapping of the hypothetical cold crystallization temperature by the melting temperature. Above the critical alkyl size, CAS, a regular increase in the entropy and enthalpy profiles presents a similar shape than the observed in other alkane series and is a strong support of the intensification of the ILs nanostructuration.

Three pure heptanol isomers were studied using infrared spectroscopy: n -heptanol, 2,4-dimethyl-3-pentanol, and 3-ethyl-3-pentanol. In order to analyze the branching effect of heptanol, investigations on the two symmetric branched isomers have been performed. Branching and steric hindrance highly influence the aggregation in associating systems. Therefore, a systematic comparison with the linear molecule n -heptanol is performed to better understand the experimental data. The vibrational structures were studied in the spectral range from 650 to 4000 cm − 1 and the individual peaks were assigned to the corresponding vibrational modes of the molecules. The OH-stretching band is significantly narrower in the spectra of the branched alcohols compared to n -heptanol. In particular, the low frequency components of the band are absent. This is a result of the steric hindrance leading to a less pronounced hydrogen bonding network.

The vapor pressures of 52 compounds including n-alkanes and their monosubstituted derivatives, as well as chloro- and alkylbenzenes were determined exploring the gas chromatographic relative retention time (GLC-RT) technique in its simplest form, that is, using a single reference standard and neglecting the activity coefficient effect (GLC-RT1S). The selection of compounds was limited to those which are in the liquid state under the measurement conditions and for which high-quality vapor pressures obtained by direct methods are available at temperatures of GLC measurements. This approach should eliminate possible secondary error sources (such as data extrapolation or recalculation from supercooled liquid to solid phase or vice versa). On the basis of a thorough comparison of the GLC-RT1S-based and directly measured vapor pressures for the group of (functionalized) n-alkanes and by exploiting n-alkanes as reference solutes it is clear that deviations from direct data are significant (in many tens of percen...

A computational methodology for calculation of sublimation enthalpies of molecular crystals from first principles is developed and validated by comparison to critically evaluated literature experimental data. Temperature-dependent sublimation enthalpies for a set of selected 22 molecular crystals in their low-temperature phases are calculated. The computational methodology consists of several building blocks based on high-level electronic structure methods of quantum chemistry and statistical thermodynamics. Ab initio methods up to the coupled clusters with iterative treatment of single and double excitations and perturbative triples correction with an estimated complete basis set description [CCSD(T)/CBS] are used to calculate the cohesive energies of crystalline phases within a fragment-based additive scheme. Density functional theory (DFT) calculations with periodic boundary conditions (PBC) coupled with the quasi-harmonic approximation are used to evaluate the thermal contributions to the enthalpy of the solid phase. The properties of the vapor phase are calculated within the ideal-gas model using the rigid-rotor harmonic-oscillator model with correction for internal rotation using a one-dimensional hindered rotor approximation and a proper treatment of the molecular rotational degrees of freedom in the vicinity of 0 K. All individual terms contributing to the sublimation enthalpy as a function of temperature are discussed and their uncertainties estimated by comparison to critically evaluated experimental data.

The thermodynamic properties, phase behavior, and kinetics of polymorphic transformations of racemic (DL-) and enantiopure (L-) menthol were studied using a combination of advanced experimental techniques, including static vapor pressure measurements, adiabatic calorimetry, Tian-Calvet calorimetry, differential scanning calorimetry (DSC), and variable-temperature X-ray powder diffraction. Several concomitant polymorphs (α, β, γ, and δ forms) were observed and studied. A continuous transformation to the stable α form was detected by DSC and monitored in detail using X-ray powder diffraction. A long-term coexistence of the stable crystalline form with the liquid phase was observed. The vapor pressure measurements of both compounds were performed using two static apparatus over a temperature range from 274 K to 363 K. Condensed-phase heat capacities were measured by adiabatic and Tian-Calvet calorimetry in the wide temperature interval from 5 K to 368 K. Experimental data of L- and DL-menthol are compared mutually as well as with available literature results. The thermodynamic functions of crystalline and liquid L-menthol between 0 K and 370 K were calculated from the calorimetric results. The thermodynamic properties in the ideal-gas state were obtained by combining statistical thermodynamics and quantum chemical calculations based on a thorough conformational analysis. Calculated ideal-gas heat capacities and experimental data on vapor pressure and condensed-phase heat capacity were treated simultaneously to obtain a consistent thermodynamic description. Based on the obtained results, the phase diagrams of L-menthol and DL-menthol were suggested.

In this work, a R1SM approach was applied for the calculation of ideal-gas thermodynamic properties of five amino acids with aliphatic side chains: glycine, alanine, valine, leucine, and isoleucine. The first step of the calculation was an extensive conformational analysis that located several conformers not reported previously. A new systematic and user-friendly nomenclature of the conformers was introduced, and the stable conformers were clearly assigned with the previously used labeling where possible. Stability and calculated relative energies of the conformers were compared between various levels of theory and with several experimental studies, demonstrating a good performance of the selected B3LYP-D3/6-311+G(2df,p) level of theory. As a second step, the theoretically calculated vibrational frequencies were compared to the previously reported experimental spectra to verify the performance of the applied double-linear scaling factor. Finally, ideal-gas heat capacities, enthalpies, and absolute entropies were calculated, accounting for all stable conformers using the R1SM model. The resulting thermodynamic data are presented for the first time, since they cannot be determined experimentally and their rigorous calculation requires a complex thermodynamic model.

First-principles calculations, coupled with statistical thermodynamics, can provide ideal-gas thermodynamic properties but get complicated and less reliable with an increasing number of conformers. An approach designed for calculation of ideal-gas thermodynamic properties of long-chain molecules, R1SM, and its simplified version, sR1SM, is tested in this work by calculation of ideal-gas heat capacities and entropies for a homologous series of n-alkanes up to n-tetradecane. The R1SM approach incorporates the rigid rotor-harmonic oscillator approximation in combination with a correction for internal rotations of methyl tops using the one-dimensional hindered rotor scheme and the mixing model accounting for the population of conformers based on the Boltzmann distribution. The R1SM approach is applicable for compounds with up to hundreds of conformers, while the simplified sR1SM approach can be used for molecules with up to 105 conformers when coupled with rules for enumeration of stable conformers and estimation scheme for their energies. The obtained results for n-alkanes are compared with experimental values and previously employed computational schemes. As the conformational behavior and conformer energies are inherent parts of the proposed approaches, a thorough conformational study of n-alkanes is performed and compared with experiments and the Tasi rules for enumeration of n-alkane conformers. Finally, the standard uncertainty of the R1SM-calculated ideal-gas thermodynamic properties is estimated based on the error propagation from the used input quantities and approximations as well as on comparison to experimental values and amounts to less than 1% for both ideal-gas heat capacity and standard ideal-gas entropy.

Despite being a very common compound in the industry as well as in the nature, the thermodynamic description of oxalic acid is far from being complete and reliable. The literature is contradictory considering both preparation of the two known polymorphs and the triple point temperature above which β-form should be more stable. The published vapour pressure data for α-phase show also a considerable disagreement. In this work, the polymorphs of anhydrous oxalic acid are subjected to a combined thermodynamic and X-ray diffraction study since a single technique cannot give an exhaustive answer on the phase behaviour of the compound. The simultaneous correlation procedure that combines vapour pressure data, calorimetric phase-transition properties, and heat capacities of the crystalline and ideal-gas phase is used to develop a consistent thermodynamic description. Finally, the triple point temperature and transition enthalpy are derived.

Recommended vapor pressure data for three polycyclic aromatic hydrocarbons, acenaphthylene (CAS RN: 208-96-8), fluoranthene (CAS RN: 206-44-0), and fluorene (CAS RN: 86-73-7), were developed by the simultaneous correlation of vapor pressure and related thermal data (heat capacities of condensed phases, ideal-gas heat capacities and calorimetrically determined enthalpies of sublimation). For acenaphthylene, new experimental data on vapor pressure, enthalpy and temperature of fusion and solid and liquid heat capacity were obtained. New solid heat capacity data were measured also for fluorene. For fluoranthene, relevant thermodynamic data were taken from the literature. The thermodynamic properties in the ideal gaseous state were calculated using the methods of statistical thermodynamics based on experimental as well as calculated fundamental vibrational frequencies and molecular structure data. Supercooled vapor pressures were calculated using the relations suggested for polycyclic aromatic hydrocarbons in the literature. Comparisons with literature values are shown for all measured and derived properties.

The uncertainty analysis of the calculation of ideal-gas thermodynamic properties using the one-dimensional hindered rotor (1-DHR), which is designed for quantum chemical treatment of internal rotations, is presented. The sensitivity of ideal-gas heat capacities and entropies to the input parameters of the 1-DHR model, that is, the reduced moments of inertia and barriers to internal rotation, is analyzed and evaluated. The calculations of energy barriers to internal rotations using the B3-LYP functional coupled with six basis sets and the empirical D3 correction accounting for dispersion interactions for a set of 60 molecular structures containing internal rotation motions were also performed, compared with available experimental values, and statistically evaluated to estimate the impact of uncertainty associated with the calculated barriers to internal rotation (15% on average, underestimated in two-thirds of cases) on ideal-gas thermodynamic properties.

The vapor pressure, liquid heat capacity, and heat of combustion were measured for distillation cuts obtained from several heavy oils using a deep vacuum fractionation apparatus. Derivatives of fitted vapor pressure equations were used to determine heats of vaporization based on the Clausius–Clapeyron equation. Existing correlations were evaluated against these data and new correlations were proposed including a generalized Cox vapor pressure correlation (as a function of molecular weight and boiling point temperature) and a correlation for the heat of vaporization based on the generalized Cox equation. Two versions of Tsonopoulos correlations were developed for liquid heat capacity: one using the Watson Factor and another using the H/C ratio. In general, the new correlations improved the prediction of heavy cut properties compared with correlations from the literature and performed similarly for light cuts (both for the development dataset and for independent test datasets). In addition, the heats of combustion of some cuts were measured and used to validate the elemental analysis based correlations from the literature.

Isobaric liquid phase heat capacities of nine selected aliphatic heptanols (1-heptanol, CAS RN: 111-70-6; 3-heptanol, CAS RN: 589-82-2; 4-heptanol, CAS RN: 589-55-9; 2-methyl-2-hexanol, CAS RN: 625-23-0; 5-methyl-2-hexanol, CAS RN: 627-59-8; 2-methyl-3-hexanol, CAS RN: 617-29-8; 3-ethyl-3-pentanol, CAS RN: 597-49-9; 2,2-dimethyl-3-pentanol, CAS RN: 3970-62-5; 2,4-dimethyl-3-pentanol, CAS RN: 600-36-2) were measured with a highly sensitive Tian-Calvet calorimeter in the temperature range from 261 K to 382 K. Experimental heat capacity data were correlated as a function of temperature. For eight compounds, a maximum on temperature dependence of heat capacity was observed. The phase behavior was investigated with a differential scanning calorimeter. Calorimetric measurements were complemented by FTIR spectroscopy from room temperature to a maximum of 428 K. The main aim of this work was to fill the gap in reliable heat capacity data for these compounds and to extend the knowledge base required for a better understanding of alcohols self-association.

The thermal behavior, solid and liquid heat capacities of the 1-benzyl-3-methylimidazolium, [Bzmim]+, based ionic liquid series with Cl−, PF6−, BF4−, CHF2CF2SO3− and NTf2− as anions were used to evaluate the effect of the insertion of an aromatic character (benzyl group) and the expected increase of the π–π interactions as well as the impact in the cation–anion hindrance and charge delocalization in the ionic liquid properties. It was found that the molar liquid heat capacities of [Bzmim][X] are in the same order as the 1-pentyl-3-methylimidazolium, [C5C1im][X] analogs. A good correlation between the molar (solid and liquid) heat capacity and the number of atoms of the anion was found. Two different crystalline forms for [Bzmim][BF4] differing by 10 K in the melting temperature and about 10% in the heat capacity were found. The crystallization behavior, melting temperatures, and enthalpies and entropies of fusion show that the insertion of an aromatic character (benzyl group) in the imidazolium cation leads to a significant and systematic change of the thermophysical properties of the ionic liquids associated with an increase of the glass transition and melting temperatures arising from the additional π–π interactions.

A newly developed static apparatus, capable of measuring the vapor pressure in the temperature range 273–368 K and in the pressure range 0.1–1333 Pa, is presented. The apparatus was calibrated by measuring the vapor pressure of recommended reference materials, naphthalene, n-decane, and ferrocene, and thoroughly tested. Subsequently, new vapor pressure data for benzophenone were measured in the temperature range 293–365 K with the aim to establish revised thermophysical data for this compound. Although benzophenone is another material recommended as the reference material for sublimation pressure and enthalpy measurements, the published sublimation thermodynamic data show a significant spread, and the recommendation was made with reservations which involved a reported metastable crystalline phase. We clarify this point based on reviewing the literature reporting the phase behavior and crystallographic studies and an extensive study on the polymorphic behavior of benzophenone performed in the present work....

Given the recent interest in multi-functional oxygen-containing organic compounds and the need of accurate and consistent data, a complete review and systematic analysis of available experimental vapor pressure data, as published in the original work of (Asher et al., 2002), was performed with the ThermoData Engine (TDE). A revised set of critical evaluated vapor pressure data, including their uncertainties based on the principles of dynamic data evaluation, is here recommended for a total of 58 compounds. COSMO-RS was further used for vapor pressure estimations for these compounds. The quality of the results is discussed in terms of the chemical functionalities of the molecules. To illustrate the partition behaviour of the title compounds under ambient conditions, a simple comparison of volatility binning between estimates and measurements was performed. Since the encountered vapor pressures are rather high, with respect to pressure range of semi-volatile organic compounds (SVOC), a large fraction is expected to stay in the atmosphere rather than to form secondary organic aerosol.

An extensive thermodynamic study of acetamide and its derivatives, N-methylacetamide, and N,N-dimethylacetamide, is presented in this work. Phase behavior was investigated by a heat-flux differential scanning calorimetry (DSC) from 183 K confirming the previously reported polymorphism of acetamide and N-methylacetamide. Two different polymorphic forms of N,N-dimethylacetamide were observed for the first time. Two static apparatus were employed for the vapor pressure measurements over a wide temperature range focusing on the ambient temperatures. Vapor pressures of metastable phase of acetamide were determined for the first time. Heat capacities of liquid and crystalline phases were measured by Tian-Calvet calorimetry at temperatures between 265 and 355 K. The ideal-gas thermodynamic properties were calculated using a combination of the density functional theory (DFT) and statistical thermodynamics. A consistent thermodynamic description was developed using the method of simultaneous correlation, where the experimental data for phase behavior, vapor pressures, and condensed phase heat capacities and calculated ideal-gas heat capacities are treated together to ensure overall thermodynamic consistency of the results. The observed trends in the thermodynamic properties of liquid phase were rationalized based on molecular interactions.

The thermodynamic properties and phase behaviour of 1,3-diisopropylnaphthalene were studied for the first time using static vapour pressure measurements, Tian-Calvet calorimetry, and differential scanning calorimetry (DSC). Polymorphic behaviour of the compound was detected and studied in detail by combination of DSC and variable-temperature X-ray powder diffraction. The crystal structure of the disordered metastable phase was obtained using a single-crystal X-ray diffraction for the first time. The experimental study was supplemented by calculating thermodynamic properties in the ideal-gas state using a combination of statistical thermodynamics and quantum-chemical calculations. Recommended vapour pressure equation was derived by simultaneous treatment of vapour pressures, experimental heat capacities of the condensed phases, calculated ideal-gas heat capacities, and temperature and enthalpy of fusion, assuring their mutual thermodynamic consistency.