C,N‐chelated organotin(IV) compounds as catalysts for transesterification and derivatization of dialkyl carbonates

The potential catalytic activity of selected C,N‐chelated organotin(IV) compounds (e.g. halides and trifluoroacetates) for derivatization of both dimethyl carbonate (DMC) and diethyl carbonate (DEC) was investigated. Some tri‐, di‐ and monoorganotin(IV) species (L^CN(n‐Bu)₂SnCl (1), L^CN(n‐Bu)₂SnCl.HCl (1a), L^CN(n‐Bu)₂SnI (2), L^CNPh₂SnCl (3), L^CNPh₂SnI (4), L^CN(n‐Bu)SnCl₂ (5), L^CNSnBr₃ (6) and [L^CNSn(OC(O)CF₃)]₂(μ‐O)(μ‐OC(O)CF₃)₂ (7)) bearing the L^CN moiety (L^CN = 2‐(N,N‐dimethylaminomethyl)phenyl‐) were assessed as catalysts for reactions of both DMC and DEC with various substituted anilines. The catalytic activities of 4 and 7 for derivatization of DMC with p‐substituted phenols were studied for comparison with the standard base K₂CO₃/Silcarbon K835 catalyst (catalyst 8). The composition of resulting reaction mixtures was monitored by multinuclear NMR spectroscopy, GC and GC‐MS techniques. In general, catalysts 1, 3 and 7 exhibited the highest catalytic activity for all reactions studied, while some of them yielded selectively carbonates, carbamates, lactam or substituted urea. Copyright © 2012 John Wiley & Sons, Ltd.     

Solvatochromic Effect in the Optical Spectra of Calcofluor and its Relation to Fluorescent Staining of Yeast Cell Walls

Fluorescence spectral properties of calcofluor (a popular stain used to visualize cell walls of bacteria, yeast and fungi) has been studied. The analysis of calcofluor fluorescence emission spectra measured in a wide range of solvents (including media containing chitin), and in yeast cell suspensions has revealed that the solvatochromic properties of calcofluor ensue essentially from the by solvent-solute hydrogen bonding, or from the hydrogen bonding to cell wall polysaccharides with an eventual contribution of calcofluor aggregation at the cell surface. Preliminary data suggest that calcofluor emission spectra can be employed as a practical marker of variations in the quality of yeast cell wall.     

Characterization of metabolites of sibutramine in primary cultures of rat hepatocytes by liquid chromatography–ion trap mass spectrometry

Liquid chromatography–ion trap mass spectrometry was used for the detection and structural characterization of metabolites of the anti-obesity drug sibutramine. Metabolites were profiled from incubations of sibutramine in primary cultures of rat hepatocytes. In addition, enantioselectivity of sibutramine metabolism was investigated by carrying out separate incubations with (R)- and (S)-sibutramine. As a result, biotransformation profile for sibutramine with rat hepatocytes is proposed. Nineteen metabolites and several of their isomers formed via demethylation, hydroxylation, dehydrogenation, acetylation, attachment of CO₂, and glucuronidation were identified in MS² and MS³ experiments, though the exact position of the functionality, mostly hydroxylation, could not always be determined from the mass spectrometric information. However, clear enantioselective formation was observed for two hydroxyl derivatives and two glucuronide conjugates, indicating that the hydroxyl/glucuronic acid moiety in those structures is close to the chiral center. Most of the metabolites found in this study are new metabolites of sibutramine, which were not previously reported.     

Biomimetic surface modifications based on the cyanobacterial iron chelator anachelin

Siderophores are natural iron chelators that have been evolutionarily selected to bind to Fe ions with very high binding constants. We utilize these unique properties to bind to metal oxide surfaces using a fragment of the cyanobacterial siderophore anachelin. The resulting poly(ethylene glycol) conjugate forms stable adlayers on TiO2 as has been shown by variable angle spectroscopic ellipsometry and X-ray photoelectron spectroscopy. Moreover, these coated surfaces are highly protein-resistant against the adsorption of full human serum.     

Utilisation of separation methods in the analysis of chemical warfare agents

Chemical warfare agents and their degradation products represent a broad group of compounds with different chemical properties (polarity, volatility, thermostability, etc.). These chemicals often have to be detected and determined in complex matrices and therefore highly efficient separation techniques hyphenated to selective and sensitive detectors play an indispensable role. This review offers an overview of selected papers devoted to the title subject. It cannot be considered as a comprehensive literature compilation but should allow the reader to obtain an insight into the application of separation techniques in the important area of human protection and control of chemical weapons.     

Tungsten oxide-based materials as effective catalysts in isopulegol formation by intramolecular Prins reaction of citronellal

Research on Chemical Intermediates - Several types of mixed WO3/SiO2/Al2O3 materials were prepared using sol–gel and wet impregnation methods. Four different loadings of WO3 (1, 10, 25 and...     

Analysis of the Flow of Magnetoelastic Materials

We consider evolutionary models for magnetoelastic materials. The PDEs modeling the flow of the material were derived from variational principles in a continuum mechanical setting. In this article, we discuss the existence of weak solutions for two models, one with gradient flow type dynamics on the magnetic variable and in the other the dynamics of the magnetization is described by the Landau-Lifshitz-Gilbert equation. We highlight the main differences of the proofs in the two cases. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simultaneous identification of historical pigments Prussian blue and indigo in paintings by electrospray mass spectrometry

A new analytical protocol for identification of Prussian blue (PB) and indigo was proposed. Pigments useful for dating of artworks were detected by flow injection analysis/electrospray ionization mass spectrometry after alkalization of their suspensions in water, decomposition of PB to iron (III) hydroxide and hexacyanoferrate (II) and reduction of indigo to soluble leucoindigo using sodium dithionite. Limits of detection (PB 47 pg, indigo 59 pg) complied with requirements for analysis of microsamples of historical paintings. Potential of the developed method was proven in analysis of blue samples of two oil paintings from the 20^th century. Further, PB was confirmed in a microsample from a painting of ‘Crucifixion’, St. Sebestian church on St. Hill in Mikulov, Czech Republic. Copyright © 2013 John Wiley & Sons, Ltd.     

Dynamics of Phloridzin and Related Compounds in Four Cultivars of Apple Trees during the Vegetation Period

Apple trees (Malus domestica Borgh) are a rich source of dihydrochalcones, phenolic acids and flavonoids. Considering the increasing demand for these phytochemicals with health-benefitting properties, the objective of this study was to evaluate the profile of the main bioactive compounds—phloridzin, phloretin, chlorogenic acid and rutin—in apple tree bark, leaves, flower buds and twigs. The variety in the phenolic profiles of four apple tree cultivars was monitored during the vegetation period from March to September using chromatography analysis. Phloridzin, the major glycoside of interest, reached the highest values in the bark of all the tested cultivars in May (up to 91.7 ± 4.4 mg g⁻¹ of the dried weight (DW), cv. ‘Opal’). In the leaves, the highest levels of phloridzin were found in cv. ‘Opal’ in May (82.5 ± 22.0 mg g⁻¹ of DW); in twigs, the highest levels were found in cv. ‘Rozela’ in September (52.4 ± 12.1 mg g⁻¹ of DW). In the flower buds, the content of phloridzin was similar to that in the twigs. Aglycone phloretin was found only in the leaves in relatively low concentrations (max. value 2.8 ± 1.4 mg g⁻¹ of DW). The highest values of rutin were found in the leaves of all the tested cultivars (10.5 ± 2.9 mg g⁻¹ of DW, cv. ‘Opal’ in September); the concentrations in the bark and twigs were much lower. The highest content of chlorogenic acid was found in flower buds (3.3 ± 1.0 mg g⁻¹ of DW, cv. ‘Rozela’). Whole apple fruits harvested in September were rich in chlorogenic acid and phloridzin. The statistical evaluation by Scheffe’s test confirmed the significant difference of cv. ‘Rozela’ from the other tested cultivars. In conclusion, apple tree bark, twigs, and leaves were found to be important renewable resources of bioactive phenolics, especially phloridzin and rutin. The simple availability of waste plant material can therefore be used as a rich source of phenolic compounds for cosmetics, nutraceuticals, and food supplement preparation.     

Investigation of the metabolism of monepantel in ovine hepatocytes by UHPLC/MS/MS

Monepantel (MOP) belongs to a new class of anthelmintic drugs known as aminoacetonitrile derivatives. It was approved for use in veterinary practice in Czech Republic in 2011. So far, biotransformation and transport of MOP in target animals have been studied insufficiently, although the study of metabolic pathways of anthelmintics is very important for the efficacy of safety of therapy and evaluation of the risk of drug–drug interactions. The aim of this study was to identify MOP metabolites and to suggest the metabolic pathways of MOP in sheep. For this purpose, primary culture of ovine hepatocytes was used as a model in vitro system. After incubation, medium samples and homogenates of hepatocytes were extracted separately using solid-phase extraction. Analysis was performed using a hybrid quadrupole-time-of-flight analyzer with respect to high mass accuracy measurements in full scan and tandem mass spectra for the confirmation of an elemental composition. The obtained results revealed S-oxidation to sulfoxide and sulfone and arene hydroxylation as MOP phase I biotransformations. From phase II metabolites, MOP glucuronides, sulfates, and acetylcysteine conjugates were found. Based on the obtained results, a scheme of the metabolic pathway of MOP in sheep has been proposed.