On the dimorphism of prednisolone: The topological pressure-temperature phase diagram involving forms I and II

The dimorphism of the corticosteroid anti-inflammatory drug prednisolone has been investigated by the construction of a topological pressure-temperature phase diagram, using crystallographic and calorimetric data. The system is enantiotropic, because the temperature of the I-II equilibrium under atmospheric conditions (400 - 463 K) is lower than that of the two melting equilibria (518.7 K for form II and 526.3 K for form I). The slope of the I-II equilibrium in the pressure-temperature phase diagram is negative and relatively steep; therefore, form II, which is the stable form at room temperature, will not easily encounter conditions where form I will become stable even under industrial processing conditions. On the other hand, extreme small amounts of form I have been observed to spontaneously transform into form II in a time interval of about six years at room temperature and it can be concluded that although form I is very persistent under ambient conditions, it does slowly convert into form II. Moreover, the system does not obey the density rule.

On the dimorphism and the pressure-temperature state diagram of gestodene, a steroidal progestogen contraceptive

The pressure-temperature phase diagram of the dimorphism of the contraceptive drug gestodene is constructed using the temperature and enthalpy of fusion of form I (469.5K, 107Jg^-1), and those of the endothermic transition from form II to form I (311K, 8.52Jg^-1). At ordinary pressure, the sign of the enthalpy of this transition indicates that these polymorphs are enantiotropically related and that form II, whose melting temperature is calculated to be about 452K, is the stable form at room temperature. Considering the inequality in the specific volumes of the two polymorphs, it is shown that the two forms remain enantiotropically related on increasing pressure, because the I-II equilibrium and the melting equilibria I-L and II-L diverge as a consequence of the negative slope dP/dT of the solid-solid equilibrium. In addition, it is demonstrated that the heats of dissolution, inferred from solubility measurements, lead to virtually the same value of the heat of transition from II to I as for the differential scanning calorimetry measurements.

On the dimorphism and the pressure-temperature state diagram of racemic m-nisoldipine, a dihydropyridine calcium ion antagonist

The pressure-temperature phase diagram of the dimorphism of racemic m-nisoldipine is constructed using temperatures and enthalpies of fusion of forms A and B. At ordinary pressure, the transition from form B to form A is found to occur around 192K, which indicates that these polymorphs are enantiotropically related and that form A is stable at room temperature. Nevertheless, the phase relationship turns to be monotropic when pressures become greater than about 100MPa, which indicates that form B becomes the sole stable phase.

Pressure-temperature phase diagram of the dimorphism of the anti-inflammatory drug nimesulide

Understanding the phase behavior of active pharmaceutical ingredients is important for formulations of dosage forms and regulatory reasons. Nimesulide is an anti-inflammatory drug that is known to exhibit dimorphism; however up to now its stability behavior was not clear, as few thermodynamic data were available. Therefore, calorimetric melting data have been obtained, which were found to be T_I-L=422.4±1.0K, Δ_I→LH=117.5±5.2Jg^-1,T_II-L=419.8±1.0K and Δ_II→LH=108.6±3.3Jg^-1. In addition, vapor-pressure data, high-pressure melting data, and specific volumes have been obtained. It is demonstrated that form II is intrinsically monotropic in relation to form I and the latter would thus be the best polymorph to use for drug formulations. This result has been obtained by experimental means, involving high-pressure measurements. Furthermore, it has been shown that with very limited experimental and statistical data, the same conclusion can be obtained, demonstrating that in first instance topological pressure-temperature phase diagrams can be obtained without necessarily measuring any high-pressure data. It provides a quick method to verify the phase behavior of the known phases of an active pharmaceutical ingredient under different pressure and temperature conditions.

High Pressure Differential Scanning Calorimetry Investigations on the Pressure Dependence of the Melting of Paracetamol Polymorphs I and II

A high pressure differential scanning calorimeter (HP-DSC) has been used to investigate the pressure dependence of the melting of the monoclinic (Form I) and orthorhombic (Form II) polymorphs of paracetamol (acetaminophen). DSC scans obtained at ambient pressure show that the stable monoclinic form melts at 442 K while the metastable orthorhombic form melts at 430 K. HP-DSC scans obtained for pressures up to about 450 MPa show that the melting temperatures of both Forms I and II increase with increasing pressure, but the latter more rapidly than the former. This results in a cross-over at about 250 MPa, where the two forms have approximately the same melting temperature, while at higher pressures Form II becomes the more stable phase. Although no solid-solid transitions have been observed, the coordinates of the I-II-liquid triple point have been found experimentally (p = 258.7 MPa and T = 489.6 K) for the first time, and confirm those predicted by Espeau et al. from a topological p-T diagram based on theoretical arguments and experimental data at ambient pressure.

Electrophoretic behavior of a highly water-soluble dendro[60]fullerene

The aim of the present study was to develop an analytical method for measuring amounts of a dendro[60]fullerene (DF) which is a highly water-soluble [60]fullerene derivative. We tried to define a straightforward methodology using capillary zone electrophoresis, a method which, to our knowledge, has not yet been used to that purpose. Preliminary assays showed that DF has almost the same mobility than the electroosmotic flow (EOF) but in the opposite direction. Attempts were carried out to reduce the EOF and positive results were obtained by adding hydroxypropylcellulose to the background electrolyte. In order to define optimal operating conditions, a Taguchi experimental plan was used to study simultaneously the effects of the main parameters that are pH, ionic strength, methanol amount and hydroxypropylcellulose concentration. Two parameters are of the utmost importance as to their effect on the migration time and separation efficiecy: pH and ionic strength whose actions are opposite.

Quantitative analysis of C60 fullerene in blood and tissues by high-performance liquid chromatography with photodiode-array and mass spectrometric detection

A high-performance liquid chromatographic (HPLC) assay method for C60 fullerene, in blood, liver and spleen using photodiode-array detection or mass spectrometric detection (LC-MS) and C70 fullerene, as the internal standard, is described. The recovery from mouse blood and tissues spiked with micronized C60 exceeds 90%. The method is linear from 0.05 to 200 mg of C60 per liter of blood and from 0.05 to 5.00% of C60 per tissue weight. The limit of detection of the method is 0.1 ng of C60 per injection. This method was applied to mouse blood and tissue samples after intraperitoneal administration of a micronized C60 suspension.

Polymorphism of sulfanilamide: (II) Stability hierarchy of alpha-, beta-, and gamma-forms from energy calculations by the atom-atom potential method and from the construction of the p, T phase diagram

PURPOSE

Sulfanilamide trimorphism was chosen as a model system for comparison between stability hierarchies obtained from lattice-energy calculations with those deduced from the relative locations of the sublimation curves of polymorphs in the sulfanilamide p, T diagram.

METHODS

The atom-atom potential (AAP) method was used for lattice-energy calculations. The p, T diagram was constructed by using crystallographic and thermodynamic data for alpha-, beta-, and gamma-forms, and by assigning the temperatures of the experimentally observed phase transitions to triple points involving the vapour phase.

RESULTS

The hierarchy obtained with the AAP method (E alpha > or = E gamma > > E beta) differs only slightly from that deduced from the positions of the sublimation curves (p gamma > p alpha > p beta) in the p, T diagram at room temperature. No stable phase region was found for form alpha. Thus it is really monotropic.

CONCLUSIONS

Provided enthalpy and volume changes at the transitions are accurate enough, it is possible to draw a p, T diagram that accounts for the stability hierarchy of polymorphs.

Thermodynamic study of sulfanilamide polymorphism: (I). Monotropy of the alpha-variety

PURPOSE

Sulfanilamide was chosen as a model compound in order to gain insights on the stability hierarchy of drug polymorphs from structural and thermodynamic criteria. Despite numerous studies, disagreements remained on the reported enthalpies associated with the mutual interconvertions of the alpha-, beta-, and gamma-forms of sulfanilamide. Therefore, the unambiguous determination of these enthalpies was the purpose of this work.

METHODS

Samples, free of solvent inclusions and made of only one form, were prepared, and analyzed combining X-ray powder diffraction and Differential Scanning Calorimetry (DSC).

RESULTS

The enthalpy values associated with the alpha- to gamma- and beta- to gamma-transitions were found to be + 10.2 and + 10.9 J g-1, respectively. The calculated enthalpy of the beta- to alpha-transition is consistent with the experimental one (+ 1 J g-1).

CONCLUSIONS

The monotropy of the alpha-form was ascertained over the explored temperature range at ordinary pressure.