Search results for "chemical stability"
showing 10 items of 96 documents
Zn(II)-alloferon complexes - Similar sequence, different coordination modes, no antibacterial activity.
2020
Often, in the search for a highly defined scientific phenomenon, a different one becomes apparent. This was also the case of this work, in the scope of which we planned to search for metal-enhanced, novel antibacterial/ antifungal compounds. Instead, we denied the existence of such and revealed the details of the bioinorganic chemistry of Zn(II)-alloferon complexes. Zinc(II) complexes of alloferon 1 and 2, ligands with a sequential difference of one amino acid only, show a substantially different coordination pattern at physiological pH. In the case of Zn(II)-alloferon 1 species, a histamine-like binding mode is observed (N-terminal amine and imidazole of His-1) and the coordination sphere …
Design of stable mixed-metal MIL-101(Cr/Fe) materials with enhanced catalytic activity for the Prins reaction
2020
[EN] This work highlights the benefit of designing mixed-metal (Cr/Fe) MOFs for enhanced chemical stability and catalytic activity. A robust and stable mixed-metal MIL-101(Cr/Fe) was prepared through a HF-free direct hydrothermal route with Fe(3+)content up to 21 wt%. The incorporation of Fe(3+)cations in the crystal structure was confirmed by(57)Fe Mossbauer spectrometry. The catalytic performance of the mixed metal MIL-101(Cr/Fe) was evaluated in the Prins reaction. MIL-101(Cr/Fe) exhibited a higher catalytic activity compared to MIL-101(Cr), improved chemical stability compared to MIL-101(Fe) and a higher catalytic activity for bulky substrates compared to MIL-100(Fe).In situinfra-red sp…
Three anhydrous forms and a dihydrate form of quifenadine hydrochloride: a structural study of the thermodynamic stability and dehydration mechanism
2015
Crystal structures of dihydrate (DH) and three anhydrous forms (A, B and C) of quifenadine (1-azabicyclo[2.2.2]oct-8-yl-diphenyl-methanol) hydrochloride are presented, and crystal structure information is used to explain and rationalize the relative stability of polymorphs and observed phase transformations. The dehydration mechanism of the hydrate is provided by interpreting the results obtained in studies of crystal structures, dehydration kinetics and thermal analysis. Structural analysis is used to explain the observed relative stability of the anhydrous phases and the hydrate. The crystal structures have been determined either from single crystal (form DH) or from powder diffraction da…
Conformational equilibrium and intramolecular hydrogen bond of 4′X and 4X substituted 2′(OH)chalcones
1999
Abstract By using the AM1 method on 4X and 4′X substituted 2′(OH)chalcones (X=H, OH, F, Cl, CH 3 , CH 3 O, N(CH 3 ) 2 , and NO 2 ), certain currently unclear structural characteristics, conformational equilibria, intramolecular hydrogen bonds and UV spectroscopic properties had been clarified. The compounds studied have non-planar structures. The 2′(OH),4′Xchalcones only present the trans - s - cis conformation. trans - s - cis and trans - s - trans conformers of 2′(OH),4X-chalcones have a comparable thermodynamic stability. For these chalcones, a conformational equilibrium at 298 K exists, with 91% of the trans - s - cis form. The proposal of analyzing the intramolecular hydrogen bond of 2…
Potential transbuccal delivery of l-DOPA methylester prodrug: stability in the environment of the oral cavity and ability to cross the mucosal tissue
2016
Levodopa (l-DOPA) is the most effective pharmacologic agent in Parkinson's disease and remains the "gold standard". Nevertheless, in long-term treatments, dyskinesias and motor complications can emerge. In this work, the combined use of l-DOPA methylester hydrochloride prodrug (LDME) with transbuccal drug delivery was supposed as a good alternative method to optimize the bioavailability of l-DOPA, to maintain constant plasma levels and to decrease the drug unwanted effects. The effects of environmental pH on buccal delivery of LDME were evaluated ex vivo. The increase of pH value from 5.8 to 6.2 implies an improvement of drug permeation. Since the pH increase causes the raising of hydrolyti…
Physico-chemical stability of eribulin mesylate containing concentrate and ready-to-administer solutions.
2013
Objectives The aim of this study was to determine the stability of commercially available eribulin mesylate containing injection solution as well as diluted ready-to-administer solutions stored under refrigeration or at room temperature. Methods Stability was studied by a novel developed stability-indicating reversed-phase high-performance liquid chromatography (RP-HPLC) assay with ultraviolet detection (detection wavelength 200 nm). Triplicate test solutions of eribulin mesylate containing injection concentrate (0.5 mg/mL) and with 0.9% sodium chloride solution diluted ready-to-administer preparations (0.205 mg/mL eribulin mesylate in polypropylene (PP) syringes, 0.020 mg/mL eribulin mesyl…
Studying the stability of Solvent Red 19 and 23 as excise duty components under the influence of controlled factors
2020
Abstract In this study, we examine the chemical stability of two disazo dyes, namely Solvent Red 19 and 23 (SR 19 and SR 23), under simulated conditions. Both dyes are considered to be chemically stable under normal exploitation conditions and therefore, are used extensively as excise duty components that enable a rapid visual verification of the tax levels that were imposed on fuel products as well as identifying fuel usage. However, the results from this study confirmed that the colour of the samples that had been fortified with either SR 19 or SR 23 fades under the influence of external conditions such as UV-A irradiation and temperature over time. The UV-A irradiation was the dominant f…
The tetrameric α-helical membrane protein GlpF unfolds via a dimeric folding intermediate.
2011
Many membrane proteins appear to be present and functional in higher-order oligomeric states. While few studies have analyzed the thermodynamic stability of α-helical transmembrane (TM) proteins under equilibrium conditions in the past, oligomerization of larger polytopic monomers has essentially not yet been studied. However, it is vital to study the folding of oligomeric membrane proteins to improve our understanding of the general mechanisms and pathways of TM protein folding. To investigate the folding and stability of the aquaglyceroporin GlpF from Escherichia coli, unfolding of the protein in mixed micelles was monitored by steady-state fluorescence and circular dichroism spectroscopy…
Heterometallic Titanium-Organic Frameworks as Dual Metal Catalysts for Synergistic Non-Buffered Hydrolysis of Nerve Agent Simulants
2020
Heterometallic metal-organic frameworks (MOFs) can offer important advantages over their homometallic counterparts to enable targeted modification of their adsorption, structural response, electronic structure, or chemical reactivity. However, controlling metal distribution in these solids still remains a challenge. The family of mesoporous titanium-organic frameworks, MUV-101(M), displays heterometallic TiM2 nodes assembled from direct reaction of Ti(IV) and M(II) salts. We use the degradation of nerve agent simulants to demonstrate that only TiFe2 nodes are capable of catalytic degradation in non-buffered conditions. By using an integrative experimental-computational approach, we rational…
Expanding the Variety of Zirconium‐based Inorganic Building Units for Metal–Organic Frameworks
2019
Two new zirconium-based metal-organic frameworks with the composition [Zr6 O4 (OH)4 (OAc)6 (BDC)3 ] (CAU-26) and [Zr5 O4 (OH)4 (OAc)4 (BDC)2 ] (CAU-27) are reported, which were synthesized from acetic acid, a rarely utilized but green and sustainable solvent (BDC2- : 1,4-benzenedicarboxylate). Structure determination aided by automated electron diffraction tomography revealed that CAU-26 is composed of layers of well-known {Zr6 O8 } clusters interconnected by terephthalate ions. In contrast CAU-27 exhibits a three-dimensional structure with a so far unknown type of one-dimensional inorganic building unit (IBU), which can be rationalized as condensed polyhedron-sharing chains of {Zr6 O8 } cl…