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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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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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Abstract  

The thermal behaviour of binary mixtures between β-cyclodextrin (β-CD) and either carbamazepine polymorphic Form I (CBZ I), Form III (CBZ III) or dihydrate was investigated in order to assess possible interactions of CBZ solid phases with β-CD. Physical mixtures and kneaded binaries of β-CD and different CBZ crystal forms were studied by differential scanning calorimetry, thermogravimetric analysis and hot stage microscopy. The pattern of transition of CBZ Form III into Form I is strongly influenced by β-CD. The liquid-solid transition is practically absent when anhydrous CBZ/β-CD mixes are tested, as a consequence of an interaction between β-CD and liquid CBZ that hinders CBZ recrystallisation as Form I occurring after CBZ Form III melting. Water loss on heating of CBZ dihydrate in the presence of β-CD leads in all cases to the formation of CBZ Form I.

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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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Abstract  

Aim of this work was to investigate the solid-state characteristics of micronized acetylsalicylic acid (ASA), produced by rapid expansion of a supercritical carbon dioxide solution (RESS) and to assess whether a correlation could be found between process parameters and solid-state characteristics. Drug solubility in supercritical CO2 was first assessed under various pressure and temperature conditions. DSC, FT-IR, PXRD, SEM, laser light scattering and HPLC were used to characterise the solid phases produced by the RESS. The obtained particles were crystalline, with spectroscopical and diffractometrical pattern overlapping those of the starting available product. However, a strong reduction of particle size was obtained, linearly correlated to pressure imposed during the RESS process, while temperature did not seem to have a major effect. Similar influence of pressure was observed on the final melting temperature of the micronized ASA. The application of a mathematical model allowed to conclude that the melting temperature depression of RESS-prepared ASA powders can be attributed to the decrease of particle dimension rather than to the formation of different solid phases or impurities.

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Journal of Thermal Analysis and Calorimetry
Authors: F. Giordano, A. Rossi, I. Pasquali, R. Bettini, E. Frigo, A. Gazzaniga, M. Sangalli, V. Mileo, and S. Catinella

Abstract  

The thermal behaviour of Diclofenac was investigated using Differential Scanning Calorimetry, Hot Stage Microscopy, and Thermogravimetric Analysis. A discrepancy was observed between the melting point values recorded under dynamic flow of either dry nitrogen (180C) or air (160C). By means of High Performance Liquid Chromatography/Mass Spectrometric analyses, it has been possible to ascribe this difference in melting points to the formation of three degradation products as a result of intramolecular cyclization and condensation reactions during the heating process in an oxidative atmosphere.

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