Large‐Scale Synthesis of Helicene‐Like Molecules for the Design of Enantiopure Thin Films with Strong Chiroptical Activity

Helicenes are fascinating molecules owing to their unusual properties and applications in many fields from catalysis to organic electronics. Herein, we report a straightforward pathway for the synthesis of helicene‐like molecules on a gram scale in an enantiopure form. Thin‐film materials with good propagating optical properties and very high chiroptical responses have been grown by using pulsed laser ablation without altering the structure or the enantiopurity of the molecules. Moreover, electronic and vibrational circular dichroism spectroscopies coupled with theoretical calculations enabled some dependences of the chiroptical properties with the structure to be highlighted, for example, effects of rigidification, aromatization, or the state of matter (liquid versus solid).     

Influence of the degree of ionization on the growth mechanism of poly(diallyldimethylammonium)/poly(acrylic acid) multilayers

pH‐dependent growth laws of the mass coverage Γ(n) of poly(diallyldimethylammonium) chloride and poly(acrylic acid) (PAA) layer‐by‐layer films are analyzed by Quartz Crystal Microbalance‐D. (Attenuated Total Reflection)‐FTIR spectroscopy shows a degree of dissociation of acrylic acid groups in the films identical to that in solution. Apart from pH‐regimes of differently pronounced exponential and linear growth, the corresponding kinetics indicate pH‐dependent adsorption, reorganization, and diffusion processes. As the thickest films form with almost uncharged PAA (low pH), the results can only partly be explained by the dissociation degree of PAA in the film. For intermediate and high pH values chain interdiffusion as a mechanism for nonlinear growth is strongly dependent on the charge density of the PAA chains. However, at low pH other types of interactions, most likely ion–dipole interactions, play a major role in the multilayer growth. Furthermore, a change in the symmetry of growth can be observed in the low to intermediate pH range. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 425–434     

Thermal,Raman and dielectric study of 0.5K0.5Bi0.5TiO3–0.5PbTiO3 ceramics

The 0.5K_0.5Bi_0.5TiO₃–0.5PbTiO₃ ceramics were prepared by following a standard solid-state method. The Raman, thermal and dielectric properties of these ceramics were investigated. The X-ray measurements showed that samples have single perovskite-type structure with tetragonal symmetry. Dielectric study revealed that the dielectric behaviour of the investigated ceramics is rather of normal ferroelectrics with large thermal hysteresis. The transition temperature observed by means of differential scanning calorimetry measurements is in good agreement with that obtained from dielectric study.     

Transition Metal Complexes of Dis(thiosemicarbazone): Synthesis and Spectral,and Antifungal Studies

Mn(II), Co(II), Ni(II), and Cu(II) complexes have been synthesized with benzil bis(thiosemicarbazone) (L) and characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, thermogravimetric studies, infrared (IR), electronic, and electron paramagnetic resonance (eEPR) spectral studies. The molar conductance measurements of the complexes in DMF correspond to the non-electrolytic nature of the complexes. Thus these complexes may be formulated as [M(L)X₂] (where M = Mn(II), Co(II), Ni(II), Cu(II) and X = Cl^? and NO₃ ^?). On the basis of IR, electronic, and EPR spectral studies, an octahedral geometry has been assigned for Mn(II), Co(II), and Ni(II) complexes, whereas a tetragonal geometry for the Cu(II) complexes is presumed. The free ligand and its metal complexes were tested against the phytopathogenic fungi (i.e., Rhizoctonia baticola, Alternaria alternata) in vitro.     

Comparative studies in subsolidus areas of ternary oxide systems PbO–V2O5–In2O3 and PbO–V2O5–Fe2O3

Thermal stability of PbO was studied. Reactivity of oxides in the systems PbO–M₂O₃ (M = In, Fe) was investigated up to 650 °C. Using the DTA and XRD methods, parts of investigated ternary oxide systems, labelled by compounds: V₂O₅, Pb₈V₂O₁₃ and M₂O₃ (M = In, Fe), have been divided into partial ternary systems. IR spectra of compounds Pb₂MV₃O₁₁ (M = In, Fe) have been compared.     

Prediction of extraction efficiency in supported liquid membrane with a stagnant acceptor phase by means of artificial neural network

An artificial neural network model of supported liquid membrane extraction process with a stagnant acceptor phase is proposed. Triazine herbicides and phenolic compounds were used as model compounds. The model is able to predict the compound extraction efficiency within the same family based on the octanol–water partition coefficient, water solubility, molecular mass and ionisation constant of the compound. The network uses the back‐propagation algorithm for evaluating the connection strengths representing the correlations between inputs (octanol–water partition coefficients logP, acid dissociation constant pK_a, water solubility and molecular weight) and outputs (extraction efficiency in dihexyl ether and undecane as organic solvents). The model predicted results in good agreement with the experimental data and the average deviations for all the cases are found to be smaller than ±3%. Moreover, standard statistical methods were applied for exploration of relationships between studied parameters.     

Mass spectrometric profiling of Bacillus cereus strains and quantitation of the emetic toxin cereulide by means of stable isotope dilution analysis and HEp-2 bioassay

A fast and robust high-throughput ultra-performance liquid chromatography/time-of-flight mass spectrometry (UPLC–TOF MS) profiling method was developed and successfully applied to discriminate a total of 78 Bacillus cereus strains into no/low, medium and high producers of the emetic toxin cereulide. The data obtained by UPLC–TOF MS profiling were confirmed by absolute quantitation of cereulide in selected samples by means of high-performance liquid chromatography with tandem mass spectrometry (HPLC–MS/MS) and stable isotope dilution assay (SIDA). Interestingly, the B. cereus strains isolated from four vomit samples and five faeces samples from patients showing symptoms of intoxication were among the group of medium or high producers. Comparison of HEp-2 bioassay data with those determined by means of mass spectrometry showed differences, most likely because the HEp-2 bioassay is based on the toxic action of cereulide towards mitochondria of eukaryotic cells rather than on a direct measurement of the toxin. In conclusion, the UPLC–electrospray ionization (ESI)–TOF MS and the HPLC–ESI–MS/MS–SIDA analyses seem to be promising tools for the robust high-throughput analysis of cereulide in B. cereus cultures, foods and other biological samples.

Enantioselective Extraction System Containing Binary Chiral Selectors and Chromatographic Enantioseparation Method for Determination of the Absolute Configuration of Enantiomers of Cyclopentolate

The distribution coefficients and enantioseparation of cyclopentolate were studied in an extraction system containing d-tartaric acid ditertbutyl ester in organic phase and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) in aqueous phase. Various parameters involved in the enantioseparation such as the type and the concentration of chiral selectors, pH value and a wide range of organic solvents were investigated. The maximum enantioselectivity (α = 2.13) and optimum distribution coefficients (K _R = 0.85, K _S = 0.40) were obtained under the following conditions: 0.10 mol/L HP-β-CD in aqueous phase and 0.20 mol/L d-tartaric acid ditertbutyl ester in decanol as organic phase. Cyclopentolate is present as a racemic mixture to the aqueous phase. The potentially different biological activities of cyclopentolate enantiomers have not been examined yet. Two chiral liquid chromatography methods have been developed for the direct separation of the enantiomers of cyclopentolate. First method was used for the quantification analysis of cyclopentolate enantiomers in aqueous phase. Second method used two chiroptical detectors: electronic circular dichroism (ECD) and optical rotation (OR) for the identification of individual cyclopentolate enantiomers from the organic phase enriched with (R)-enantiomer. The absolute stereochemistry was determined by means of the comparison of the experimental and computed ECD spectra and signs of OR. The ECD spectra of chiral analytes were measured on-line using HPLC-ECD technique.

     

Selective formation of non-conjugated olefins by samarium(II)-mediated elimination/isomerization of allylic benzoates

Aromatic allylic benzoates can be selectively transformed to the corresponding benzoate eliminated olefin by the action of samarium diiodide. Depending on the substrate and the elimination conditions, high selectivity for the non-conjugated alkene product can be achieved.