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- Crystal structure (3)
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- Knoevenagel condensation (2)
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Organisationseinheit der BAM
The preparation and characterization of tris-pyridyl bispidine (3,7-diazabicyclo[3.3.1]nonane) derivatives with benzimidazole and imidazole donor groups at the N-3 position of the bispidine Skeleton and their copper(II) complexes are reported. The impact of the hetaryl substituents on the configurational isomerism of piperidones and their corresponding bispidones has been studied by NMR spectroscopy, revealing the exclusive appearance in the enol form for the piperidones in solution and the trans-configuration regarding the two pyridyl substituents, as well as the sole formation of the unsymmetric exo-endo isomers for the corresponding bispidones. Thus, the bispidones are preorganized ligands for building pentacoordinated complexes, confirmed by the preparation and characterization of the corresponding Cu(II) complexes. Of the di-pyridyl piperidones with benzimidazole and imidazole substituents, and of the Cu(II) complex of the benzimidazole-containing bispidone, Crystals have become available for the analysis by X-ray diffraction, showing that the piperidones form the enol tautomers also in the solid state.
Triacetone triperoxide (TATP), an improvised explosive, is a potential security threat because of its cost-efficient synthesis and the difficulty in detecting it. A highly selective antibody could provide the necessary specificity to the detection process. To obtain antibodies, a hapten made from acetone, hydrogen peroxide, and 7-oxooctanoic acid has been designed, synthesized, and confirmed by NMR that displays the utmost similarity to the analyte. The single-crystal X-ray structures of the solvated species TATP·methanol (1:1) and the TATP derivate were determined. In both compounds, the molecules exhibit D3 symmetry and adopt a twisted boat-chair conformation. The hapten was coupled to bovine serum albumin, and mice were immunized. An immune response against TATP was elicited, and selective antibodies were detected in the mouse serum, which should be very useful for the development of a TATP biosensor system. An ELISA with a limit of detection for TATP of 65 µg L-1 is shown.
: Simvastatin is one of the most widely used active pharmaceutical ingredients for the treatment of hyperlipidemias. Because the compound is employed as a solid in drug formulations, particular attention should be given to the characterization of different polymorphs, their stability domains, and the nature of the phase transitions that relate them. In this work, the phase transitions delimiting the stability domains of three previously reported simvastatin forms were investigated from structural, energetics, and dynamical points of view based on single crystal X-ray diffraction (SCXRD), hot stage microscopy (HSM), and differential scanning calorimetry (DSC) experiments (conventional scans and heat capacity measurements), complemented with molecular dynamics (MD) simulations. Previous assignments of the crystal forms were confirmed by SCXRD: forms I and II were found to be orthorhombic (P212121, Z′/Z = 1/4) and form III was monoclinic (P21, Z′/Z = 2/4). The obtained results further indicated that (i) the transitions between different forms are observed at 235.9 ± 0.1 K (form III → form II) and at 275.2 ± 0.2 K (form II → form I) in DSC runs carried out at 10 K min−1 and close to these values when other types of techniques are used (e.g., HSM). (ii) They are enantiotropic (i.e., there is a transition temperature relating the two phases before fusion at which the stability order is reversed), fast, reversible, with very little hysteresis between heating and cooling modes, and occur under single crystal to single crystal conditions. (iii) A nucleation and growth mechanism seems to be followed since HSM experiments on single crystals evidenced the propagation of an interface, accompanied by a change of birefringence and crystal contraction or expansion (more subtle in the case of form III → form II), when the phase transitions are triggered. (iv) Consistent with the reversible and small hysteresis nature of the phase transitions, the SCXRD results indicated that the molecular packing is very similar in all forms and the main structural differences are associated with conformational changes of the “ester tail”. (v) The MD simulations further suggested that the tail is essentially “frozen” in two conformations below the III → II transition temperature, becomes progressively less hindered throughout the stability domain of form II, and acquires a large conformational freedom above the II → I transition. Finally, the fact that these transitions were found to be fast and reversible suggests that polymorphism is unlikely to be a problem for pharmaceutical formulations employing crystalline simvastatin because, if present, the III and II forms will readily convert to form I at ambient temperature.
We report on the temperature- and structural-dependent optical properties and photophysics of a set of boron dipyrromethene (BODIPY) dyes with different substitution patterns of their meso-aryl subunit. Single-crystal Xray diffraction analysis of the compounds enabled a classification of the dyes into a sterically hindered and a unhindered group. The steric hindrance refers to a blocked rotational motion of the aryl subunit around the bond connecting this moiety to the meso-position of the BODIPY core. The energy barriers related to this rotation were simulated by DFT calculations. As follows from the relatively low rotational barrier calculated to about 17 kcal/mol, a free rotation is only possible for sterically unhindered compounds. Rotational barriers of more than 40 kcal/mol determined for the sterically hindered compounds suggest an effective freezing of the rotational motion in These molecules. With the aid of temperature-dependent spectroscopic measurements, we could show that the ability to rotate directly affects the optical properties of our set of BODIPY dyes. This accounts for the strong temperature dependence of the fluorescence of the sterically unhindered compounds which show a drastic decrease in fluorescence quantum yield and a significant shortening in fluorescence lifetime upon heating. The optical properties of the sterically hindered compounds, however, are barely affected by temperature. Our results suggest a nonradiative deactivation of the first excited singlet state of the sterically unhindered compounds caused by a conical intersection of the potential energy surfaces of the Ground and first excited state which is accessible by rotation of the meso-subunit. This is in good agreement with previously reported deactivation mechanisms. In addition, our results suggest the presence of a second nonradiative depopulation pathway of the first excited singlet state which is particularly relevant for the sterically hindered compounds.
The identification of different forms of dihydroergocristine (DHEC) was carried out by crystallization from different organic solvents. DHEC was identified as potential template for molecularly imprinted polymers (MIPs) for the epimeric specific analysis of ergot alkaloids (EAs) in food. DHEC was crystallized from different solvents in order to mimic the typical MIP synthesis conditions. Four new solvatomorphs of DHEC were obtained. All solvatomorphs contain a water molecule in the crystal structure, whereas three compounds contain an additional solvent molecule. Based on the conformation of DHEC a comparison with typical EA molecules was possible. The analysis showed that DHEC is a suitable template for MIPs for EAs.
The title compound [systematic name: (2R,3R,4S,5R,6R) 2-(acetoxymethyl)-6-propoxytetrahydro-2H-pyran-3,4,5-triyl triacetate], C17H26O10, was formed by a Koenigs-Knorr reaction of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide and n-propanol. The central ring adopts a chair conformation. The crystal does not contain any significant interactions such as hydrogen bonds.
The Keggin type polyoxotungstate [Ti2W10PO40]7- forms stable associates with the biopolymer chitosan in the nanometer size range. The cluster compound crystallizes from aqueous solution as K4H3[Ti2W10PO40] · 15H2O having a tetragonal structure. Both, the cluster compound and the chitosan/[Ti2W10PO40] associates show a high hydrolytic stability at pH 7.4. The associates formed between the cluster anion [Ti2W10PO40]7- with the polyaminosaccharide chitosan have been characterized by photon correlation spectroscopy, scanning electron microscopy, filtration, centrifugation and zeta potential measurements. The size of the associates formed is in the range of ca. 5×101 to 5×102 nm. These particles have a defined stoichiometry with 56 cluster anions bound per molecule chitosan. The isoelectric point determined by zeta potential measurements was found for a cluster anion to chitosan molar ratio of 5.5, indicating the charge neutralization between protonated chitosan and [Ti2W10PO40]7- anions. Cellular uptake studies with [Ti2W10PO40]7- using tumor cell lines FaDu (human squamous carcinoma) and HT-29 (human adenocarcinoma) showed that the tungsten amount inside the cells is remarkably enhanced in the presence of chitosan.
Formation Mechanism of a Nano-Ring of Bismuth Cations and Mono-Lacunary Keggin-Type Phosphomolybdate
(2022)
A new hetero-bimetallic polyoxometalate (POM) nano-ring was synthesized in a one-pot procedure. The structure consists of tetrameric units containing four bismuth-substituted monolacunary Keggin anions including distorted [BiO8] cubes. The nano-ring is formed via self-assembly from metal precursors in aqueous acidic medium. The compound (NH4)16[(BiPMo11O39)4] ⋅ 22 H2O; (P4Bi4Mo44) was characterized by single-crystal X-ray diffraction, extended X-ray absorption fine structure spectroscopy (EXAFS), Raman spectroscopy, matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF), and thermogravimetry/differential scanning calorimetry mass spectrometry (TG-DSC-MS). The formation of the nano-ring in solution was studied by time-resolved in situ small- and wide-angle X-ray scattering (SAXS/WAXS) and in situ EXAFS measurements at the Mo−K and the Bi−L3 edge indicating a two-step process consisting of condensation of Mo-anions and formation of Bi−Mo-units followed by a rapid self-assembly to yield the final tetrameric ring structure.