The Physico-Chemical Properties of Glipizide: New Findings

The present work is a concrete example of how physico-chemical studies, if performed in depth, are crucial to understand the behavior of pharmaceutical solids and constitute a solid basis for the control of the reproducibility of the industrial batches. In particular, a deep study of the thermal behavior of glipizide, a hypoglycemic drug, was carried out with the aim of clarifying whether the recognition of its polymorphic forms can really be done on the basis of the endothermic peak that the literature studies attribute to the melting of the compound. A number of analytical techniques were used: thermal techniques (DSC, TGA), X-ray powder diffraction (XRPD), FT-IR spectroscopy and scanning electron microscopy (SEM). Great attention was paid to the experimental design and to the interpretation of the combined results obtained by all these techniques. We proved that the attribution of the endothermic peak shown by glipizide to its melting was actually wrong. The DSC peak is no doubt triggered by a decomposition process that involves gas evolution (cyclohexanamine and carbon dioxide) and formation of 5-methyl-N-[2-(4-sulphamoylphenyl) ethyl] pyrazine-2-carboxamide, which remains as decomposition residue. Thermal treatments properly designed and the combined use of DSC with FT-IR and XRPD led to identifying a new polymorphic form of 5-methyl-N-[2-(4-sulphamoylphenyl) ethyl] pyrazine-2-carboxamide, which is obtained by crystallization from the melt. Hence, our results put into evidence that the check of the polymorphic form of glipizide cannot be based on the temperature values of the DSC peak, since such a peak is due to a decomposition process whose Tonset value is strongly affected by the particle size. Kinetic studies of the decomposition process show the high stability of solid glipizide at room temperature.     

Boundary effects in finite Heisenberg antiferromagneticS = 1 chains:89Y NMR in Y2BaNi1−xMgxO5

By means of⁸⁹Y nuclear magnetic resonance (NMR) spectra direct evidence of staggered magnetization induced by a uniform field has been obtained in the Heisenberg antiferromagneticS = 1 chain Y₂BaNi_1?xMg_xO₅. A correspondence between the resonance lines and the lattice positions is established, providing an image of the alternating magnetic moments that develop around the Mg impurities at the chain boundaries. The amplitude of these moments is found to decrease exponentially from the edges, with a characteristic decay distance equal to the magnetic correlation length numerically evaluated for an infinite chain. While the magnetization pertaining to ions far from the boundaries behaves as in typical gapped systems, the edge spins exhibit anS = 1/2 Curie-like deviation. These results promote the NMR approach to access the spin-spin correlation function in antiferro-magnetic quantum spin systems at finite temperatures.     

Influence of solvent and crystallization method on the crystal habit of metronidazole

In the present study, metronidazole was crystallized in several solvents, according to both the “cooling crystallization” and the “crystallization by non‐solvent addition”. Particle properties, such as crystal habit, elongation ratio, and mean particle size, were determined by SEM analysis. Structural changes and development of polymorphic forms were excluded by both Differential Scanning Calorimetry (DSC) and X‐Ray Powder Diffractometry (XRPD). Crystal habit (and thus elongation ratio) was typically influenced by both the solvent polarity index and the crystallization method: solvents with higher polarity index tended to promote acicular or stick‐shaped crystals with a high elongation ratio, while isodimensional crystals were promoted by decreasing the polarity index, as was particle aggregation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Role of doping and CuO segregation in improving the giant permittivity of CaCu3Ti4O12

The dopant role on the electric and dielectric properties of the perovskite-type CaCu₃Ti₄O₁₂ (CCTO) compound is evidenced. Impedance spectroscopy measurements show that the relevant permittivity value attributed to sintered CCTO is due to grain boundary (g.b.) effects. The g.b. permittivity value of the pure CCTO can be increased of 1-2 orders of magnitude by cation substitution on Ti site and/or segregation of CuO phase, while the bulk permittivity keeps values 90<ε_r<180. Bulk and g.b. conductivity contributions are discussed: electrons are responsible for the charge transport and a mean bulk activation energy of 0.07 eV is obtained at room temperature for all the examined samples. The g.b. activation energy ranges between 0.54 and 0.76 eV. Defect models related to the transport properties are proposed, supported by electron paramagnetic resonance measurements.     

Nanosized LiMn2O4 from mechanically activated solid-state synthesis

The synthesis of pure and Cr-doped nanosized LiMn₂O₄ particles has been carried out by solid-state process on high-energy ground mixtures. In situ X-ray analysis demonstrates the spinel forms as single phase at 623 K passing through the Mn₃O₄ precursor at temperatures as low as 573 K. In the doped high-energy ground mixture Li-rich spinel phase forms at 623 K and Cr ions insert in the spinel octahedral site only at 723 K.A mean particle size value of 60 Å, quite independent of the reaction time, is obtained for T<673 K. For higher temperature the growing of the particles as a function of time is observed, independent of doping. The mechanical grinding seems to be the most suitable way to obtain impurity-free spinel phases at lower temperature and with smaller particle size with respect to manually ground mixtures by solid-state reaction and via sol-gel synthesis.     

Febantel: looking for new polymorphs

The aim of this work was to search for new polymorphic forms of febantel, an anthelminthic drug of great present interest for the veterinary industry. Solvent-based recrystallization, thermal and mechanical treatments and spray drying were chosen to discover new solid forms. The solids obtained were physicochemically characterized by thermal techniques (DSC and TG), FTIR spectroscopy, laboratory and synchrotron X-ray powder diffraction and scanning electron microscopy. Our work leads to obtain a new solid form never described in the literature. In particular, the new polymorph was obtained by the anti-solvent method and the crystallization from isopropanol. The experimental conditions of crystallization favorable to the formation of the highest amount of the new solid phase were selected. The new phase shows a thermal, spectroscopic and diffractometric behavior unique. Furthermore, the preliminary structure investigation suggests two possible crystal systems: an orthorhombic or a monoclinic one, with really comparable lattice parameters and cell volume. Measurements put into evidence that the new phase is a metastable polymorph that is in monotropic relationship with the stable and known form.

     

ARDESIA: A fast silicon drift detector X-ray spectrometer for synchrotron applications

ARDESIA, a four-channel X-ray spectrometer based on silicon drift detectors (SDDs), is presented. It has been developed for synchrotron applications targeting especially X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) with good energy resolution at high count rates (a few Mcps per second). The main target applications are XRF and XAFS techniques. The system features a 2 × 2 monolithic array of 5-mm-pitch SDDs cooled with a double Peltier scheme and coupled to a four-channel CUBE charge preamplifier. Different digital pulse processors allowing operation in Mcps per second count rates are employed. The results of preliminary characterization measurements performed at both the LNF DAΦNE-Light DXR1 beamline and the ESRF LISA BM-08 are reported, in particular, XRF measurements on low atomic number elements (down to the Carbon K-line, 270 eV) and extended X-ray absorption fine structure of trace materials in pyrite.     

Optical properties of sol–gel prepared Cerium doped Lutetium and Yttrium oxyorthosilicates

The optical properties of sol–gel prepared Cerium doped Lutetium and Yttrium oxyorthosilicates are investigated in the vacuum ultraviolet energy range by means of synchrotron radiation. The excitation and emission properties are compared to commercial samples grown by Czochralski method. The sol gel polycrystals do show emission features comparable to the ones of the monocrystals but with a slightly smaller decay time. Preliminary radioluminescence measurements indicate the possibility to apply the sol gel synthesized polycrystals as scintillating materials in the low X-ray energy range.     

Probenecid and benzamide: cocrystal prepared by a green method and its physico-chemical and pharmaceutical characterization

Journal of Thermal Analysis and Calorimetry - The eco-friendly method of kneading was here used to synthesize a cocrystal of probenecid, an uricosuric drug used in treating gout and hyperuricemia,...     

Structural and magnetic properties of Ni-Li oxides

Mixed Li-Ni oxides, Li_xNi_1-xO, are prepared by solid state reaction in the range 0.2≤x≤0.46 by annealing around 1000 K for various times. As reported in literature, above x=0.31 an ordered solid solution (OSS) is formed in which planes of pure Ni alternate with Li-Ni planes, whereas below x=0.2 only a fully disordered solid state solution (SSS) exists. We analyze the intermediate composition region 0.22≤x≤0.31 by fitting the X-ray patterns with a two-phases model using the Rietveld method: a SSS phase and an OSS phase where partial occupancy of the Ni-planes by lithium is allowed. The two phases coexist in the intermediate region, and no lithium is allowed in the Ni planes of the OSS phase; furthermore, the lithium contents of the OSS and SSS phases are approximately x ∼ 0.4 and x ∼ 0.2, respectively, and loss of lithium is associated with transformation of the OSS phase into SSS.⁷Li NMR data find evidence of a common magnetic behaviour of the samples containing the OSS phase which agrees with the X-ray findings. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995