The polymorphism of the 1:1 nicotinamide:adipic acid (NIC:AA) cocrystal system was re-examined by combining structural and thermodynamic approaches. Differential scanning calorimetry (DSC), solid-state NMR (ssNMR), and variable-temperature powder X-ray diffraction (VT-PXRD) confirmed an enantiotropic relationship between the two polymorphs, evidenced by a direct solid-solid transformation from triclinic form I to monoclinic form II at ∼ 370 K. Solubility data subsequently indicated that this temperature is ∼78 K higher than the equilibrium transition temperature (289.2 ± 0.7 K), consistent with a phase transition hindered by a substantial activation barrier. This also explained why the reverse process was not detected on cooling within the time scale of the DSC, ssNMR, and VT-PXRD experiments. The relative stabilities of forms I and II, as well as their stability relative to dissociation into the coformers, at 298 K, were quantitatively established based on Gibbs energy, enthalpy, and entropy data obtained from solution calorimetry and solubility measurements. The results indicated that at 298 K: (i) form II is thermodynamically more stable than form I, despite having a lower lattice enthalpy; (ii) this is consistent with the conclusion that the equilibrium transition temperature (289.2 ± 0.7 K) is lower than 298 K and suggests that the stabilization of form II (the high-temperature polymorph) versus form I (low-temperature polymorph) under ambient conditions is of an entropic nature; (iii) both polymorphs are stable with respect to dissociation into the coformers nicotinamide and adipic acid; and (iv) the stability gain upon cocrystallization is primarily of an enthalpic rather than entropic nature, reflecting a lattice enthalpy advantage relative to the pure components. Single-crystal X-ray diffraction further showed that at ∼298 K form I exhibits an ∼3% higher density and packing index than form II, in line with the observed lattice enthalpy difference Δlat H m o(crI) > Δlat H m o(crII). Finally, although cocrystallization is frequently used to produce solid forms with enhanced solubility or stability relative to the individual coformers, the formation of the NIC:AA cocrystal does lead to improved solid-state stability but not to solubility enhancement, at least when acetonitrile is used as solvent.

An all-atom force field for MD simulations on crystalline Active Pharmaceutical Ingredients (API) containing sulfur and halogens was developed and tested. Validation was performed by comparing the MD results with enthalpies of sublimation experimentally determined by Calvet microcalorimetry and reported single crystal X-ray diffraction data. The test set consisted of sulfanilamide, sulfapyridine, chlorzoxazone, clioquinol, and triclosan. The development was incremental. The OPLS-AA model was taken as the starting point. Then dihedral parameters missing in the OPLS-AA database were obtained from PES data computed at the MP2/aug-cc-pVDZ level of theory. Finally, several methods to determine atomic point charges were tested and a procedure based on the ChelpG methodology, with the inclusion of X-sites mimicking the σ-hole in the case of iodine, was found to provide the best overall accuracy in terms of unit cell dimensions and enthalpy of sublimation predictions.

In this work, insights into the structural rearrangements occurring in aqueous solution, prior to the nucleation of different 4'-hydroxyacetophenone (HAP) forms from water, were obtained, through a combination of thermomicroscopy, microdifferential scanning calorimetry, density and speed of sound measurements, and molecular dynamics simulations. The results confirmed our previous observation that cooling crystallization of HAP is intermediated by liquid-liquid phase separation (LLPS) and, depending on the initially selected concentration range, selectively leads to the formation of different crystal forms. Analysis of the solution properties before the onset of LLPS revealed that, in the HAP mole fraction range x(HAP) < 0.004 (Zone I), where hydrate H2 ultimately crystallizes, small, solvated clusters are initially present in solution, which remain approximately invariant in size, shape, and HAP/H2O proportion as the temperature decreases. For the x(HAP) > 0.005 range (Zone III), where anhydrous form I crystallizes, large HAP/water aggregates (that can even percolate the whole system as x(HAP) approaches the 0.005 limit) are already initially present in solution. As cooling progresses, they become more compact, a process accompanied by a reduction in water content, which is more significant as the solution concentration increases. The 0.004 < x(HAP) < 0.005 (Zone II) range corresponds to a transition region where, as x(HAP) increases, the physical properties of the solution initially evolve from those typical of Zone I and, at a certain point, abruptly change and start converging to those typical of Zone III. In all zones, the colloidal particles formed upon LLPS (from which crystallization results) can also reduce their water content on cooling, but the extent of this process increases as x(HAP) moves from Zones I and II, where hydrates are formed, to Zone III, where anhydrous form I is produced.

Biosurfactants are surface-active compounds of biological origin, stable over a wide range of temperature, pH, and salinity. In this work, the ability of the biosurfactants rhamnolipid (RAM), sophorolipid (SOFO) and surfactin (SURF) to stabilize a nanocrystal suspension of niclosamide (NCL) in water, and to enhance the drug solubility were evaluated. The performances were compared with those of the synthetic surfactants tween 80 (TW) and soluplus (SOLU). Overall, RAM, SOFO, and SURF proved to be as effective as TW and SOFO in terms of NCL nanocrystal suspension stabilization. Formulations containing 3 % (w/w) surfactant exhibited the best stability at 4 degrees C and 25 degrees C. The three biosurfactants also led to an improvement of aqueous NCL solubility, even when a slurry of the micronized drug was used without nanocrystal formulation. The best performance was observed for the SURF 3 % (w/w) nanocrystal formulation (1157.48 mu g/mL), which released more than twice the amount of NCL compared to the best synthetic surfactant formulation (TW 3 % (w/w), 542.57 mu g/mL), and 622 times more than the pure solid drug (1.86 mu g/mL). Cell viability was not compromised by the surfactants alone, indicating that the formulation cytotoxic effect is related to the enhanced solubilization of NCL. Consistently, the NCL/ SURF formulation was the most effective, achieving a maximum cytotoxicity effect of 80 % at a concentration of 1000 nM, while the other formulations reached a maximum effect of 71 % at concentrations starting from 1500 nM. Nevertheless, when the balance between formulation stability, drug release enhancement, and cytotoxicity is considered the three biosurfactants studied in this work showed significant potential advantages relative to synthetic analogues that can be explored in pharmaceutical development.

Fumaric acid and alkyl fumarates are a family of structurally related compounds with a wide spectrum of potential or effective therapeutic applications. The series consisting of fumaric acid (FA), monomethyl fumarate (MMF), dimethyl fumarate (DMF), monoethyl fumarate (MEF), and diethyl fumarate (DEF) was studied in this work to address the following main questions: how does the number of OHO hydrogen bonds that may be established due to systematic differences in molecular structure impacts on the molecular packing and lattice energetics? Is there evidence of a cooperative hydrogen bond strengthening when infinite 1D chains sustained by OHO hydrogen bonds are formed? How well can the structural and energetic features of this series of related molecules be predicted by state-of-the art force field and periodic DFT procedures that are used in the rationalization or prediction of crystal structures and physical properties of molecular organic solids? By combining results from a variety of experimental (X-ray diffraction, Raman spectroscopy, DSC, Calvet drop-sublimation calorimetry) and theoretical (quantum mechanical, molecular dynamics simulations) methods, it was found that (i) in all cases, the molecular packing leads to layered solids, where each layer consists of 1D chain motifs linked to each other through C-HO interactions. (ii) The 1D arrangements are determined by two main motifs: the R-2(2)(8) carboxyl dimer, typically found in mono- and di-n-alkyl carboxylic acids, and the staggered CH3H3C synthon, which is present in mono-n-alkyl carboxylic acids and n-alkanes. This leads to the formation of carboxyl-carboxyl and alkyl-alkyl domains that are structurally isolated from each other. (iii) The lattice energy, as measured by the enthalpy of sublimation (Delta H-sub(m)o), varies according to FA > MMF similar to MEF > DMF similar to DEF and is linearly correlated with the number of OHO hydrogen bonds present in the structures. (iv) The larger enthalpy of sublimation of FA compared to MMF and MEF is linked to the number of OHO hydrogen bonds but does not seem to be related to their individual strength. Examination of OO distance and C & boxH;O stretching frequency as well as theoretically computed dissociation energies of dimeric FA, MMF, and MEF species suggests that the OHO interaction is weaker in FA than in MMF and MEF. As such, the present study showed no evidence of a cooperative OHO bond strengthening in FA, relative to MMF and MEF, due to the presence of infinite 1D chains sustained by carboxylic acid dimers. (v) No evident connection between Delta H-sub(m)o and compactness indicators such as density or Kitaigorodski packing index was also found. Finally, (vi) MD simulations and periodic DFT calculations were both able to reproduce the above-mentioned Delta H-sub(m)o trend and capture the main structural features of the family of crystalline materials studied in this work. In terms of accuracy, better overall performance was observed for the force field method developed for this particular type of compounds.

Erlotinib hydrochloride (EtbHCl), whose polymorphism is still ill-characterized, is an essential component of the current armamentarium for the treatment of pancreatic and lung cancers. It recently became a textbook example of the importance of crystal polymorphism for drug development and patent litigation. In this work, a quantitative evaluation of the relative thermodynamic stability of the two most important EtbHCl polymorphs (forms A and B) was performed. Based on calorimetric and solubility studies, the standard molar Gibbs energy, enthalpy, and entropy of the B(cr) -> A(cr) transition at 298 K were obtained as Delta(trs)G(m)(degrees) (B -> A) = 2.4 +/- 1.0 kJ mol(-1), Delta H-trs(m)degrees (B -> A) = 6.1 +/- 1.1 kJ mol(-1), and T Delta S-trs(m)degrees (B -> A) = 3.7 +/- 1.5 kJ mol(-1), respectively. These results unequivocally indicate that form B is more stable than form A at, or close to, ambient temperature and that the larger stability of form B is enthalpically determined (hence of lattice energy origin). The solubility measurements (gastric fluid at pH 1.2, 298 +/- 1 K) evidenced a 2.6 times larger solubility of form A relative to form B. This suggests that a significant bioavailability enhancement may be potentially obtained if form A rather than form B is used in EtbHCl formulations. Differential scanning calorimetry and hot-stage microscopy experiments indicated that the two forms are monotropically related and exhibit considerably different thermal behaviors: on heating form B from 298 K, only fusion was observed; in contrast, the fusion of form A is followed by the formation of plate-like crystals that subsequently transform into a needle-like phase that subsequently melts. None of these two high-temperature phases should correspond to form B, given that melting occurs at a significantly lower temperature than the fusion of form B. Finally, insights into the structural differences between the two forms were provided by combining information from the previously reported crystal structure of form B and from FT-IR and Raman microspectroscopy experiments carried out on both forms. The overall results suggest that (i) the ethynylphenyl and quinazoline ring systems of the EtbHCl molecule are likely to be more coplanar and adopt a different conformation in form A (anti) than in form B (syn); (ii) a nonclassical C equivalent to C-HO hydrogen bond interaction, which is evident in the crystal structure of form B, is not present or is substantially weaker in form A.

The standard (p degrees = 0.1 MPa) molar enthalpy of sublimation of form I nicotinamide (NIC, cr I), at 298.15 K, was determined by drop-sublimation Calvet microcalorimetry. Experiments carried out under isothermal and non-isothermal conditions led to Delta H-sub(m)degrees(NIC, cr I) = 108.0 +/- 0.5 kJ center dot mol(-1). The present study allowed to resolve to a significant extent the large discrepancy observed between published Delta H-sub(m)degrees(NIC) results obtained by calorimetry and by vapor-pressure measurements, using samples of unspecified crystal form.

The lattice enthalpies and monotropic relationship of two dehydroepiandrosterone (DEHA) polymorphs (forms I and II) were evaluated through a combination of differential scanning calorimetry (DSC), isothermal solution microcalorimetry, and drop-sublimation Calvet microcalorimetry experiments. The standard molar enthalpy of transition between both forms was determined as & UDelta;trsHom(II & RARR;I, 298.15 K) =-0.90 & PLUSMN; 0.07 kJ mol-1 and & UDelta;trsHom(II & RARR;I, 417.8 K) =-1.7 & PLUSMN; 1.0 kJ mol-1, from measurements of standard molar enthalpies of solution in dimethyl sulfoxide and enthalpies of fusion, respectively. Drop-sublimation Calvet microcalorimetry experiments on form I led to & UDelta;subHom(cr I, 298.15 K) = 132.0 & PLUSMN;3.3 kJ mol-1. This result, when combined with the more precise & UDelta;trsHom(II & RARR;I) value obtained by solution calorimetry, afforded & UDelta;subHom(cr II, 298.15 K) = 131.1 & PLUSMN;3.3 kJ mol-1. The overall data indicate that on enthalpic grounds form I is more stable than form II from 298.15 K up to fusion. This conclusion, and the fact that DSC experiments indicated that form I has also a considerably higher tem-perature fusion, namely, Tfus(cr I)= 422.5 & PLUSMN;0.2 K and Tfus(cr II) = 413.1 & PLUSMN;0.2 K, suggest that the two polymorphs are monotropically related.

6,7-Dehydroroyleanone (DHR) is a caspase-induced cytotoxic abietane diterpene, frequently found on Plectranthus spp. A pharmaceutical formulation consisting of a DHR-squalene conjugate was synthesized and analyzed by different techniques such as scanning electron microscopy (SEM). The facile production of the dispersion of DHR-squalene conjugate nanoparticles in phosphate buffer (pH 7.4) suggests that this nanodelivery platform may be an effective system to improve the solubility and bioavailability of DHR, so that therapeutical systemic levels may be achieved.

SUMMARYMetabolic alterations have been recognized to underly the etiology of many diseases. Herein, cellular energy dissipation was evaluated as a novel non-specific global biomarker of metabolic alterations. Energy dissipation, measured as heat by microcalorimetry, was maximal during Saccharomyces cerevisiae adaptation to growth conditions before fast proliferation took place. This response was further augmented by 95 % in media where nutrient assimilation was more difficult, and by 133 % under sub-optimal non-carbon nutrient levels. In this last case, the increase in energy dissipation (1) reflected changes in amino acid and glycolytic metabolism and (2) anticipated changes in the growth curve significantly later observed by traditional microbiological measurements. It was, therefore, an early marker of adaptive responses that compensated for sub-optimal nutrient levels and maintained phenotypic stability. Compensatory responses buffer systems against perturbations and delay the onset of diseases. Microcalorimetry can, therefore, provide a biomarker development platform for early disease-diagnosis.HIGHLIGHTSEnergy dissipation measurements detect cell responses to metabolic challenges.The detection by microcalorimetry occurs considerably earlier than by traditional microbiological measurements.Sub-optimal non-carbon nutrient levels impact energy dissipation long before cell proliferation.Energy dissipation is highly sensitive to increased nutrient assimilation difficulty.

Simvastatin (SV) is an important active pharmaceutical ingredient (API) for treatment of hyperlipidemias, which is known to exist in different crystalline and amorphous phases. It is, therefore, an interesting model to investigate how the outcome of evaporative crystallization in the contactless environment of an acoustically levitated droplet may be influenced by key experimental conditions, such as temperature, solvent properties (e.g., polarity and hygroscopicity), and dynamics of the evaporation process. Here, we describe a real-time and in situ study of simvastatin evaporative crystallization from droplets of three solvents that differ in volatility, polarity, and protic character (acetone, ethanol, and ethyl acetate). The droplet monitorization relied on synchrotron X-ray diffraction (XRD), Raman spectroscopy, imaging, and thermographic analysis. A pronounced solvent-dependent behavior was observed. In ethanol, a simvastatin amorphous gel-like material was produced, which showed no tendency for crystallization over time; in ethyl acetate, a glassy material was formed, which crystallized on storage over a two-week period to yield simvastatin form I; and in acetone, form I crystallized upon solvent evaporation without any evident presence of a stable amorphous intermediate. The XRD and Raman results further suggested that the persistent amorphous phase obtained from ethanol and the amorphous precrystallization intermediate formed in ethyl acetate were similar. Thermographic analysis indicated that the evaporation process was accompanied by a considerable temperature decrease of the droplet surface, whose magnitude and rate correlated with the solvent volatility (acetone > ethyl acetate > ethanol). The combined thermographic and XRD results also suggested that, as the cooling effect increased, so did the amount of residual water (most likely captured from the atmosphere) remaining in the droplet after the organic solvent was lost. Finally, the interpretation of the water fingerprint in the XRD time profiles was aided by molecular dynamics simulations, which also provided insights into the possible role of H2O as an antisolvent that facilitates simvastatin crystallization.

The energetics of the stepwise dissociation of a A:B2 bi-component crystal, according to A:B2(cr) → A:B(cr) + B(cr) and A:B(cr) → A(cr) + B(cr), was investigated using MA:Phe2 and MA:Phe (MA = maleic acid; Phe = L-phenylalanine) as model systems. The enthalpy changes associated with these sequential processes and with the overall dissociation reaction A:B2(cr) → A(cr) + 2B(cr) were determined by solution calorimetry. It was found that they are all positive, indicating that there is a lattice enthalpy gain when MA:Phe2 is formed, either from the individual precursors or by adding Phe to MA:Phe. Single-crystal X-ray diffraction (SCXRD) analysis showed that MA:Phe2 is best described as a protic salt containing a maleate anion (MA−) and two non-equivalent L-phenylalanine units, both linked to MA− by NH···O hydrogen bonds (H-bond): one of these units is protonated (HPhe+) and the other zwitterionic (Phe±). Only MA− and HPhe+ molecules are present in the MA:Phe lattice. In this case, however, NH···O and OH···O H-bonds are formed between each MA− unit and two HPhe+ molecules. Despite these structural differences, the enthalpy cost for the removal of the zwitterionic Phe± unit from the MA:Phe2 lattice to yield MA:Phe is only 0.9 ± 0.4 kJ mol−1 higher than that for the dissociation of MA:Phe, which requires a proton transfer from HPhe+ to MA− and the rearrangement of L-phenylalanine to the zwitterionic, Phe±, form. Finally, a comparison of the dissociation energetics and structures of MA:Phe and of the previously reported glycine maleate (MA:Gly) analogue indicated that parameters, such as the packing coefficient, density, hydrogen bonds formed, or fusion temperature, are not necessarily good descriptors of dissociation enthalpy or lattice enthalpy trends when bi-component crystals with different molecular composition are being compared, even if the stoichiometry is the same.

The solubility is generally thought to be higher if the solvent effectively solvates solute molecules that are well-separated from each other. The present work suggests, however, that the formation...

This work describes an exploratory experimental and in silico study of the influence of polymorphism, particle size, and physiology on the pharmacokinetics of lercanidipine hydrochloride (LHC). Equilibrium and kinetic solubility studies were performed on LHC forms I and II, as a function of pH and buffer composition. GastroPlus® was used to evaluate the potential effect of solubility differences due to polymorphism, particle size, and physiological conditions, on the drug pharmacokinetics. The results indicated that solubilities of LHC polymorphs are strongly dependent on the composition and pH of the buffer media. The concentration ratio (CI/CII) is particularly large for chloride buffer (CI/CII = 3.3–3.9) and exhibits a slightly decreasing tendency with the pH increase for all other buffers. Based on solubility alone, a higher bioavailability of form I might be expected. However, exploratory PBPK simulations suggested that (i) under usual fasted (pH 1.3) and fed (pH 4.9) gastric conditions, the two polymorphs have similar bioavailability, regardless of the particle size; (ii) at high gastric pH in the fasted state (e.g., pH 3.0), the bioavailability of form II can be considerably lower than that of form I, unless the particle size is < 20 μm. This study demonstrates the importance of investigating the effect of the buffer nature when evaluating the solubility of ionizable polymorphic substances. It also showcases the benefits of using PBPK simulations, to assess the risk and pharmacokinetic relevance of different solubility and particle size between crystal forms, for diverse physiological conditions.

The standard molar enthalpy of transition between the two known polymorphs of 4'-hydroxyacetophenone (HAP), at 298.15 K, was determined from measurements of their standard molar enthalpies of solution in dimethyl sulfoxide (DMSO). The obtained result Delta H-trs(m)o (cr II -> cr I) = (0.48 +/- 0. 10) kJ.mol(-1) is in excellent agreement with a previously reported value measured in ethanol with an isoperibol calorimeter, using similar to 7 times larger amounts of sample and solvent. The fact that the two polymorphs are easily prepared, and such good agreement was observed between results from two considerably different calorimetric techniques and solvents, suggests that HAP may be a convenient benchmark system for the validation of solution calorimetry measurements or force field predictions on the relative enthalpic stability of organic polymorphs. (C) 2021 Elsevier Ltd.

Compounds based on the HOC6H4C(O)R (R = H, alkyl, OH, etc.) framework have provided excellent models to investigate the complex interplay of structural and energetic effects behind polymorphism and crystallization as a whole. In this work, the polymorphic behavior of 4'-hydroxyvalerophenone (HVP, R = C4H9) was experimentally and theoretically explored from a holistic structural-energetics-dynamics perspective. The molecular and crystal structures of two new forms (II and III) were determined by single crystal X-ray diffraction. They share with the previously known form I, and with analogous systems (R = H, CH3) that do not contain a flexible R group, an infinite C-1(1) (8) chain sustained by "head-to-tail" OH center dot center dot center dot O=C hydrogen bonds as the main one-dimensional (1D) packing motif. The molecular organization within the chain ("herringbone" type in form I and planar in forms II and III) and the relative orientation of the CO and OH groups (Z in form I and E in forms II and III) are, however, different. These differences are reflected by the thermodynamic and kinetic relationships between the three polymorphs. Differential scanning calorimetry and microscopy experiments revealed that (i) the structurally very similar III/II pair is enantiotropically related by a fast and reversible phase transition at 247.5 +/- 0.4 K. (ii) In contrast, the form II -> form I transition is severely hindered, and, although form II is monotropic relative to form I, it can be observed to melt upon heating, or stored for days at ambient pressure and temperature without signs of transformation to form I, unless subjected to a perturbation (e.g., scratching, grinding). These findings are consistent with microscopy and molecular dynamics (MD) simulation results, suggesting that the III -> II transition occurs by a concerted displacement of the molecules in the crystal lattice, while the II -> I process is compatible with a diffusive nucleation and growth mechanism. It was also found that, despite being metastable, form II preferentially crystallizes from the melt in accordance with Ostwald's rule of stages. MD simulations indicated that this observation is most likely originated by the fact that the structure of liquid HVP is much closer to form II than to form I. Finally, a thermodynamic analysis suggested that the relative stability of the three HVP polymorphs, at 298 K, ranked in terms of Gibbs energy (I > II > III) does not follow the corresponding lattice enthalpy trend (I > III > II). This stresses the importance of accounting for entropy contributions when discussing polymorph stability.

Differential Scanning Calorimetry (DSC) is a widely accessible and versatile method for the determination of the heat capacities of organic materials as a function of temperature. In routine use, it is typically possible to obtain results with an accuracy better than 3 %. However, to achieve this level of accuracy, careful optimization of the experimental procedure for a specific apparatus must be performed. Using benzoic acid as a test substance, this work highlights some practical aspects of heat capacity measurements by DSC, such as crucible material and its geometry, heating rate, thermal lag, the selection of a suitable pre-stabilization stage before the measurement and the duration of the experiment, that can have a strong influence on the quality of the obtained results.