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  • Author or Editor: F. Giordano x
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Abstract  

This work aims to investigate the thermal behaviour of diclofenac, diclofenac sodium, and NaHCO3 both as single components and binary mixtures. In particular, the melting point and latent heat of fusion binary diagrams of the diclofenac sodium/diclofenac mixtures at different mole fraction compositions were investigated in order to gain information about the thermal behaviour of their solid mixtures. A good agreement between liquidus curves, calculated by the Schroeder-Van Laar equation from fusion enthalpies and temperatures, and the experimental results was found. For all binary compositions, an endothermic effect at 153�C, probably due to the eutectic fusion, is present.

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Differential scanning calorimetry DSC has been applied to the analysis of drugcyclodextrin binary systems in order to gain experimental evidence of the interaction and determine the stoichiometry of the inclusion compound. Two model systems, paracetamolbetacyclodextrin and vinburnineg-ammacyclodextrin were tested through the comparison of thermal behaviors of interacted and non-interacted mixtures containing excess drug. DSC allowed a confirmation of both interaction and stoichiometry of the inclusion compounds.

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Abstract  

The thermal and structural characteristics of two crystal forms of ambroxol, (trans-((amino-2-dibromo-3,5-benzyl)amino)-4-cyclohexanol), a drug with remarkable mucolytic and expectorant properties marketed in several drug products, were investigated. Form II (m.p. 92.4C) is obtained by spontaneous cooling from a hot water/ethanol solution while Form I (m.p. 99.5C) slowly separates from the mother liquor. The two forms can be identified by PXRD and DSC analyses. On the basis of both thermal and structural data the thermodynamic relationship of enantiotropy was deduced. No metastable (Form I)?stable (Form II) conversion was observed upon storage at ambient conditions. Form I crystallizes in the space group P21/n (alternative setting of P21/c) with Z=8. Form II crystallizes in the space group P21/c with Z=4 and a significantly different crystal packing arrangement from that in Form I. A third crystalline modification, Form III (space group P21/c with Z=16) was detected on cooling a single crystal of Form I down to -70C. On warming to ambient temperature Form III was found to revert to Form I. This reversible single crystal to single crystal transition was structurally characterised and found to involve subtle changes in the types and extent of molecular disorder as well as the hydrogen bonding arrangement.

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Summary Thermoanalytical techniques (TG, DSC) are frequently used in the investigation of the thermal properties of cyclodextrins and their inclusion complexes. However, the above techniques do not provide information on the chemical composition of the evolved fragments upon the thermal decomposition. In this study &-, &- and &-cyclodextrins and 4 methylated and 3 ethylated &-CD derivatives were investigated with a TG-MS combined thermoanalytical technique in order to get information about their fragmentation behaviour. By comparison of the TG/DTA curves, a different thermal behaviour was found for each of the native and the chemically modified cyclodextrins. Except for the water loss profiles and the solid-solid phase transformations, the thermal behaviour of the (investigated) native CDs do not show remarkable differences. However, the chemical modification of the native &-CD resulting in a new compound may change the strength of interactions between host and guest causing differences in the thermal stabilities of the derivatives. The mass spectrometry results supported the observed thermal differences and showed significant alterations in the fragmentation of ethylated and methylated compounds. The investigated natural CDs possess a very similar fragmentation profile, due to the common &-D-glucopyranose building units. In the case of modified CDs characteristic signals of the substituents are present.

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Journal of Thermal Analysis and Calorimetry
Authors: F. Giordano, A. Rossi, R. Bettini, A. Savioli, A. Gazzaniga, and Cs. Novák

Abstract  

The thermal behavior of binary mixtures of paracetamol and a polymeric excipient (microcrystalline cellulose, hydroxypropylmethylcellulose and cross-linked poly(vinylpyrrolidone)) was investigated. The physical mixtures, ranging from 50 to 90% by mass of drug, were submitted to a heating-cooling-heating program in the 35–180C temperature range. Solid-state analysis was performed by means of differential scanning calorimetry (DSC), hot stage microscopy (HSM), micro-Fourier transformed infrared spectroscopy (MFTIR), and scanning electron microscopy (SEM). The polymeric excipients were found to address in a reproducible manner the recrystallization of molten paracetamol within the binary mixture into Form II or Form III. The degree of crystallinity of paracetamol in the binary mixtures, evaluated from fusion enthalpies during the first and second heating scans, was influenced by the composition of the mixture, the nature of the excipient and the thermal history. In particular, DSC on mixtures with cross-linked poly(vinylpyrrolidone) and hydroxypropylmethylcellulose with drug contents below 65 and75%, respectively, evidenced the presence only of amorphous paracetamol after the cooling phase. Microcrystalline cellulose was very effective in directing the recrystallization of molten paracetamol as Form II.

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Journal of Thermal Analysis and Calorimetry
Authors: G. P. Bettinetti, C. Caramella, F. Giordano, A. La Manna, C. Margheritis, and C. Sinistri

Thermal analysis of the binary system benzoic acid (BA) and trimethoprim (TMP) provided evidence of the formation of two molecular compounds. BA-TMP and two crystalline forms of (BA)2-TMP were characterized on the basis of their thermodynamic parameters as well as of crystallographic and spectroscopic properties. The availability of these compounds (by recrystallization) allowed interpretation of thermal effects in the DSC curves of the mixtures and the theoretical phase diagrams could be drawn. The results are consistent with the model of a very slight dissociation of the molecular compounds in the melt.

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Journal of Thermal Analysis and Calorimetry
Authors: R. Bettini, G. Bertolini, E. Frigo, A. Rossi, I. Casini, I. Pasquali, and F. Giordano

Abstract  

The aim of this work was to study the solubility in supercritical CO2 of the hydrated phase of three model drugs, namely theophylline, carbamazepine, and diclofenac sodium, in comparison with the respective anhydrous form. Possible solid-state modifications, stemming from the interaction with supercritical CO2, were investigated by differential scanning calorimetry, thermogravimetric analysis, hot stage microscopy, Fourier Transform infrared spectroscopy and Karl-Fischer titrimetry. It was found that all three pharmaceutical hydrates exhibited higher solubility in supercritical CO2 than the relevant anhydrous phases. In the case of theophylline monohydrate, the instability of the crystal phase at the experimental temperature adopted has been evidenced. Diclofenac sodium tetrahydrate represents a peculiar case of chemical interaction with the acid supercritical fluid, mediated by crystal water.

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