Thermal and spectroscopic studies of the antioxidant food additive propyl gallate

Literature mentions propyl gallate (PG) as a non-toxic synthetic antioxidant that can be used as a food additive due to its high tolerance to heat. It is important to understand the thermal properties and to identify the decomposition products of this substance, since it has been reported to be thermally stable at temperatures as high as 300 °C. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry-photovisual (DSC-photovisual), coupled thermogravimetry-infrared spectroscopy (TG-FTIR) analyses and spectroscopic techniques were used to study the food additive PG. The TG-DTA curves, which were performed with the aid of DSC-photovisual, provided information concerning the thermal stability and decomposition profiles of the compound. From the TG-FTIR coupled techniques, it was possible to identify n-propanol as a possible volatile compound released during the thermal decomposition of the antioxidant. A complete spectroscopic characterization in the ultraviolet, visible, near and middle infrared regions was performed in order to understand the spectroscopic properties of PG

Radical bridged Ln₄ metallocene complexes with strong magnetic coupling and large coercive field

Abstract Inducing magnetic coupling between 4f elements is an ongoing challenge. To overcome this formidable difficulty, we incorporate highly delocalized tetrazinyl radicals, which strongly couple with f-block metallocenes to form discrete tetranuclear complexes. Synthesis, structure, magnetic properties of two tetranuclear [(Cp*₂Ln)₄(tz•)₄]·3(C₆H₆) (Cp* = pentamethylcyclopentadienyl; tz = 1,2,4,5-tetrazine; Ln = Dy, Gd) complexes are reported. An in-depth examination of their magnetic properties through magnetic susceptibility measurements, as well as computational studies, support a highly sought-after radical-induced “giant-spin” model. Strong exchange interactions between the LnIII ions and tz• radicals lead to a strong magnet-like behaviour in this molecular magnet with a giant coercive field of 30 kOe

Aufbau vs. non-Aufbau ground states in two-coordinate d⁷ single-molecule magnets

Abstract Single-molecule magnets (SMMs) with d⁷ electronic configurations often require designer ligands to satisfy the metals electronic conditions to achieve large angular momentum. Herein, the slow relaxation of the magnetization in two d⁷ metal complexes in near identical ligand fields is achieved from divergent origins. The two compounds, [CoII{N(SiMePh₂)₂}₂] and [K(2,2,2-crypt)][FeI{N(SiMePh₂)₂}₂] (2,2,2-crypt = 2,2,2-cryptand), display unusual electronic configurations giving rise to SMM behavior originating either from 3d–4s orbital mixing or a non-Aufbau ground state. The chracteristics contributing to the rare non-Aufbau ground state configurations are illuminated by the use of a highly donating amido-ligand, which would be expected to significantly split the respective orbitals. Magnetic circular dichroism provides experimental support for ab initio determined electronic structures. Moreover, computational models reveal that the relative electronic configurations are largely retained independently of coordination geometry, provided that some degree of pseudo-linearity is retained. Thus, providing generalized design principles in the pursuit of linear d⁷ SMMs

Thermoanalytical study of nimesulide and their recrystallization products obtained from solutions of several alcohols

Thermogravimetry, differential scanning calorimetry, and vibrational infrared spectroscopy were used to study nimesulide and its recrystallization products that were obtained from solutions of several alcohols. The thermoanalytical measurements were performed in both air and nitrogen atmospheres and the results suggest that, under the experimental conditions used in this paper, it was possible to obtain neither polymorphic nor pseudopolymorphic forms of this drug. In this investigation, quantum chemical approach methods were used to determine the molecular structures using the Becke three-parameter hybrid method and the Lee-Yang-Parr correlation functional. The performed molecular calculations were done with the Gaussian 09 routine and the theoretical calculation results were correlated with the experimental IR vibrational spectrum. © 2013 Akadémiai Kiadó, Budapest, Hungary

Thermal behavior of some antihistamines

Thermogravimetry (TG), differential scanning calorimetry (DSC), polarized light thermal microscopy (PLTM), as well as X-ray powder diffraction (XRD) and Fourier transformed infrared spectroscopy (FTIR) were used to study the thermal behavior and the chemical structure of cimetidine, famotidine, ranitidine-HCl, and nizatidine. The TG-DSC curves show that the famotidine and ranitidine-HCl suffer decomposition during melting and they are thermally less stable in comparison with cimetidine and nizatidine, the latter being the most stable of all the drugs studied in this study. The DSC curves of famotidine and ranitidine-HCl show exothermic peaks immediately after the melting, confirming the occurrence of thermal decomposition. The DSC curves also show that the cimetidine and nizatidine have some thermal stability after melting. The thermal events shown in the PLTM images are consistent with the results shown in the TG-DSC and DSC curves. The XRD patterns show that the cimetidine and famotidine are less crystalline compared with ranitidine-HCl and nizatidine. The theoretical FTIR bands are in agreement with those obtained experimentally, and in some cases, no difference is observed between the theoretical and experimental values, even being identical in one of the cases. © 2012 Akadémiai Kiadó, Budapest, Hungary