1,721,195 research outputs found
The Historical Chemist
No full textIn the epilogue of this special issue, we will focus on the relationship between humanities and chemistry in the framework of the replication of ancient procedures.
In particular we will discuss how an ancient recipe can be interpreted and performed in a modern lab, analyzing the issues in identifying the correct ingredients and approximate the apparatus with what is available in a chemistry lab. This requires an interplay of knowledge between scientists and historians; the implication is that both parties are forced out of their comfort zones in order to reach a deeper understanding of both their fields.
Even though it may be obvious how the replications are beneficial to the interpretation of the sources, we will point out what can be gained from this interdisciplinary work by the chemists in terms of both dissemination and pure research
Quantifying API polymorphs in formulations using X-ray powder diffraction and multivariate standard addition method combined with net analyte signal analysis
Full text linkThe direct quantification of Active Pharmaceutical Ingredients in solid formulations is a challenging open issue. A consolidated analytical technique based on X-ray Powder Diffraction is available, being the definitive test for the identification of polymorphs and crystal phases. However, its application for quantitative analysis is hindered by matrix effects: refinement methods (e.g. Rietveld method) require a complete knowledge of samples’ composition, while univariate calibration methods require the matrix effect to be studied and severely suffer from the co-presence of crystalline and amorphous phases in the sample. Multivariate analysis is the only way to bypass problems affecting refinements procedures and univariate calibration. In particular, the multivariate standard addition method (SAM) is promising; however, it is straightforward only when the analytical blank (matrix devoid of analyte) is available: in that case SAM is applied by simply extrapolating the SAM model to the matrix experimental signal. In this work, the quantitative analysis of polymorphic forms of Active Pharmaceutical Ingredients based on X-ray Powder Diffraction is performed for the first time by a method based on multivariate standard addition method combined with net analyte signal procedure; it allows for reliable quantification of polymorphs of active principles in solid formulations, which are rapidly analyzed without any sample pre-treatment. Two test cases are presented: quantification of two polymorphs of piracetam in binary mixtures (forms II and III), and quantification of paracetamol (form I) in Tachifludec®
On the crystal forms of NDI-C6: annealing and deposition procedures to access elusive polymorphs
Full text linkNDI-C6 has been extensively studied for its semiconducting properties and its processability. It is known to have several polymorphs and a high thermal expansion. Here we report the full thermal characterization of NDI-C6 by combining differential scanning calorimetry, variable temperature X-ray powder diffraction, and hot stage microscopy, which revealed two different thermal behaviours depending on the annealing process. The ranking of stability was determined by the temperature and energy involved in the transitions: Form alpha is stable from RT up to 175 degrees C, Form beta is metastable at all temperatures, Form gamma is stable in the range 175-178 degrees C, and Form delta in the range 178-207 degrees C followed by the melt at 207 degrees C. We determined the crystal structure of Form gamma at 54 degrees C from powder. The analysis of the thermal expansion principal axis shows that Form alpha and Form gamma possess negative thermal expansion (X1) and massive positive thermal expansion (X3) which are correlated to the thermal behaviour observed. We were able to isolate pure Form alpha, Form beta, and Form gamma in thin films and we found a new metastable form, called Form epsilon, by spin coating deposition of a toluene solution of NDI-C6 on Si/SiO2 substrates
Quantification of polymorphs form in Pharmaceutical Compounds Based on Powder X-Ray Diffraction with partial least square
No full textOver the last few years, studies on quantification and determination of various polymorph forms in complex matrices have become a key point in research by pharmaceutical industries. Studies on their quantification are also requested by the FDA, because the various polimorphs are characterized by a different bioavailability in the organism. For these reasons, the method consists in an X-ray diffractometric analysis combined with the partial least square. The analyzed drugs are the Budesonide (BDS), a glucocorticoid used for the treatment ofasthmatic pathologies and the Tachifludec, whose API is paracetamol, commonly used for inflammatory diseases. This work is done by preparing – through the method of standard addition – specimens that will be submitted to XRPD. The obtained diffractograms are then submitted to multivariate analysis through partial least square 1, by using the Unscrambler 10.4 software. The main advantage of chemometrics is its easy applicability. Moreover, thanks to the data obtained by the multivariate regression, it can be confirmed that the chosen method is extremely valid to solve these kinds of problem
Artificial vitriols: a contemporary interpretation of historical ingredients
No full text"Vitriol" is a term that appeared during the Middle-Ages to indicate a wide range of ingredients widely used both in medicinal and alchemical recipes. Green, blue, or white vitriols are easily associated with iron(ii), copper(ii), and zinc sulphate respectively thanks to the historical sources composed in the time period when the ancient and modern nomenclatures overlapped. However, other colours of vitriols are attested throughout history, such as yellow, red, or black. The identification of these compounds is significantly less straightforward, and often chalked up to Decknamen (code names) or unspecified impure ores. Moreover, from several sources it is apparent that some of these compounds are artificial, or at least the result of technical operations rather than mineral ores used as they are. By thermal manipulation of iron(ii) sulphate, we managed to identify several compounds that fit with historical descriptions, which were later characterized through XRPD. Moreover, by using a Kofler bench and variable temperature XRPD, we were able to further investigate the transitions between these phases
Making crystals with a purpose; a journey in crystal engineering at the University of Bologna
Full text linkThe conceptual relationship between crystal reactivity, stability and metastability, solubility and morphology on the one hand and shape, charge distribution, chirality and distribution of functional groups over the molecular surfaces on the other hand is discussed, via a number of examples coming from three decades of research in the field of crystal engineering at the University of Bologna. The bottom-up preparation of mixed crystals, co-crystals and photoreactive materials starting from molecular building blocks across the borders of organic, organometallic and metalorganic chemistry is recounted
Anhydrous ionic co-crystals of cyanuric acid with LiCl and NaCl
No full textAnhydrous ionic co-crystals (ICCs) of cyanuric acid (CA) with sodium
and lithium chlorides have been prepared by solid state
methods and structurally characterized from X-ray powder diffraction
data (XRPD). Complete encapsulation of the Li+Cl− ion pair by
the organic molecules is observed in CA·LiCl, while the solid-state
solvation of piles of Na+ cations in CA·NaCl results in the markedly
increased dissolution rate (ca. 5 times) and solubility (ca. 20 times)
in water with respect to pure CA
Polymorph Screening of Core-Chlorinated Naphthalene Diimides with Different Fluoroalkyl Side-Chain Lengths
Full text linkIn this work, naphthalenediimide (NDI) derivatives are widely studied for their semiconducting properties and the influence of the side-chain length on the crystal packing is reported, along with the thermal properties of three core-chlorinated NDIs with different fluoroalkyl side-chain lengths (CF3-NDI, C3F7-NDI and C4F9-NDI). The introduction of fluorinated substituents at the imide nitrogen and addition of strong electron-withdrawing groups at the NDI core are used to improve the NDI derivatives air stability. The new compound, CF3-NDI, was deeply analyzed and compared to the well-known C3F7-NDI and C4F9-NDI, leading to the discovery and solution of two different crystal phases, form α and solvate form, and a solid solution of CF3-NDI and CF3-NDI-OH, formed by the decomposition in DMSO
AgX-based hybrid coordination polymers: mechanochemical synthesis, structure and luminescence property characterization
Full text linkHybrid coordination polymers are interesting for their ability to converge the properties of both inorganic and organic systems in one single compound and recently attention has been focused on silver based hybrid coordination polymers due to their luminescence properties. We searched the CSD to establish the propensity of AgXL (X = Cl-, Br- and I-) with L as an organic ligand to form hybrid coordination polymers. About 800 AgXL structures are deposited in the CSD, with huge structural variability: indeed, it is possible to recognize some structural preferences based on the halide nature. The formation of an inorganic polymeric unit is favoured by iodide but it is also possible with the other halides. This research continues with the synthesis of AgX (X = I-, Br-) based coordination polymers with 2-, 3- and 4-picolylamine (n-pica) as ligands. By mechanochemical synthesis five new hybrid coordination polymers and one coordination polymer have been obtained and their structures determined. While [(AgI)(n-pica)](n) are not luminescent, [(AgBr)(n-pica)](n) emit and their profile depends on the crystallinity of the sample
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