Zinc catalyst recycling in the preparation of (all-rac)-α-tocopherol from trimethylhydroquinone and isophytol

Recycling of ZnCl₂ as a catalyst in the cyclocondensation of trimethylhydroquinone and isophytol to all-rac-α-tocopherol was studied. ZnCl₂ was recycled at over 98 % efficiency in required purity by repeated extraction of the reaction streams with water, followed by switching of solvent to butyl acetate and then back to water. Recycled ZnCl₂ had no negative effect on the yield of all-rac-α-tocopherol (maintaining over 90 %) at nearly total conversion of isophytol and only a 3 % molar excess of trimethylhydroquinone.     

Photochemical preparation of ZnO nanoparticles

Preparation of zinc oxide nanoparticles from aqueous solutions containing zinc nitrate or formate using UV irradiation was investigated. Analysis of solid phase formed during irradiation confirmed the presence of zinc oxide or zinc peroxide nanoparticles ranging in size from 1 to 70 nm, depending on initial precursors. Annealing at temperatures 650–1000 °C results in forming of rice-like zinc oxide particles, up to hundreds of nm in size. Photochemical method yields material with high chemical purity and uniform particle size distribution. In addition, photo-induced doping of zinc oxide with lanthanum was studied. Presence of lanthanum in zinc oxide crystal lattice and post-preparation treatment in reduction atmosphere significantly increase the UV excitonic luminescence at 395 nm in radioluminescence spectra.     

Identification of phase I and phase II metabolites of benfluron and dimefluron in rat urine using high-performance liquid chromatography/tandem mass spectrometry

Biotransformation products of two potential antineoplastic agents, benfluron and dimefluron, are characterized using our integrated approach based on the combination of high-performance liquid chromatography (HPLC) separation of phase I and phase II metabolites followed by photodiode-array UV detection and electrospray ionization tandem mass spectrometry (MS/MS). High mass accuracy measurement allows confirmation of an elemental composition and metabolic reactions according to exact mass defects. The combination of different HPLC/MS/MS scans, such as reconstructed ion current chromatograms, constant neutral loss chromatograms or exact mass filtration, helps the unambiguous detection of low abundance metabolites. The arene oxidation, N-oxidation, N-demethylation, O-demethylation, carbonyl reduction, glucuronidation and sulfation are typical mechanisms of the metabolite formation. The interpretation of their tandem mass spectra enables the distinction of demethylation position (N- vs. O-) as well as to differentiate N-oxidation from arene oxidation for both phase I and phase II metabolites. Two metabolic pathways are rather unusual for rat samples, i.e., glucosylation and double glucuronidation. The formation of metabolites that lead to a significant change in the chromophoric system of studied compounds, such as the reduction of carbonyl group in 7H-benzo[c]fluorene-7-one chromophore, is reflected in their UV spectra, which provides valuable complementary information to MS/MS data.     

Laser ablation synthesis of new phosphorus nitride clusters from α-P3N5 via Laser Desorption Ionization and Matrix Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry

Phosphorus nitride clusters generated during Laser Desorption Ionization (LDI) and Matrix-Assisted Laser Desorption Ionization (MALDI) of solid P(3) N(5) were analyzed via Time-of-Flight Mass Spectrometry (TOF MS). The LDI TOF mass spectra show the formation of series of clusters: P(m)N(n)(+) {(m=1; n=8-11), (m=4; n=3-4), (m=5; n=1-5), (m=6; n=1-3, 5-8), (m=2-7; n=1), (m=5-10; n=2), (m=4-6; n=3), (m=4,5; n=4), (m=5,6; n=5)}, and P(m)N(n)(-) (m=4,5; n=1). Using 3-hydroxypicolinic acid (HPA) as a matrix the P(m)N(n)(+) species (m=1-4, 6, 8) with a high nitrogen content (n=4, 5, 8, 10-12, 20) were identified. The formation of a N(6)(-) cluster was also detected using a C(60) matrix. Under various conditions singly charged P(m)(+) (m=2-7, 9, 13), P(m)(-) (m=3-11, 13, 15, 17), N(n)(+) (n=5, 9, 10, 12, 13), and N(n)(-) (n=6, 10-15) clusters were identified in the mass spectra. Such high nitrogen content clusters (up to N(15)(-)) generated by laser desorption from a solid material are described for the first time. The stoichiometry of the P(m)N(n) clusters was determined via isotopic envelope analysis and computer modelling. The composition of the clusters with respect to the crystalline structure of α-P(3)N(5) is discussed.     

Ruthenacarborane and Quinoline: A Promising Combination for the Treatment of Brain Tumors

Gliomas and glioblastomas are very aggressive forms of brain tumors, prone to the development of a multitude of resistance mechanisms to therapeutic treatments, including cytoprotective autophagy. In this work, we investigated the role and mechanism of action of the combination of a ruthenacarborane derivative with 8-hydroxyquinoline (8-HQ), linked via an ester bond (complex 2), in rat astrocytoma C6 and human glioma U251 cells, in comparison with the two compounds alone, i.e., the free carboxylic acid (complex 1) and 8-HQ, and their non-covalent combination ([1 + 8-HQ], in 1:1 molar ratio). We found that only complex 2 was able to significantly affect cellular viability in glioma U251 cells (IC₅₀ 11.4 μM) via inhibition of the autophagic machinery, most likely acting at the early stages of the autophagic cascade. Contrary to 8-HQ alone, complex 2 was also able to impair cellular viability under conditions of glucose deprivation. We thus suggest different mechanisms of action of ruthenacarborane complex 2 than purely organic quinoline-based drugs, making complex 2 a very attractive candidate for evading the known resistances of brain tumors to chloroquine-based therapies.     

Efficient Solution of a Class of Quantified Constraints with Quantifier Prefix Exists-Forall

In various applications the search for certificates for certain properties (e.g., stability of dynamical systems, program termination) can be formulated as a quantified constraint solving problem with quantifier prefix exists-forall. In this paper, we present an algorithm for solving a certain class of such problems based on interval techniques in combination with conservative linear programming approximation. In comparison with previous work, the method is more general—allowing general Boolean structure in the input constraint, and more efficient—using splitting heuristics that learn from the success of previous linear programming approximations.     

Geodesic mapping onto Kählerian spaces of the first kind

In the present paper a generalized Kählerian space Open image in new window of the first kind is considered as a generalized Riemannian space \(\mathbb{G}\mathbb{R}_N \) with almost complex structure F _i ^h that is covariantly constant with respect to the first kind of covariant derivative.Using a non-symmetric metric tensor we find necessary and sufficient conditions for geodesic mappings f: Open image in new window with respect to the four kinds of covariant derivatives. These conditions have the form of a closed system of partial differential equations in covariant derivatives with respect to unknown components of the metric tensor and the complex structure of the Kählerian space Open image in new window .     

The harmonic moment tail index estimator: asymptotic distribution and robustness

Asymptotic properties of the harmonic moment tail index Estimator are derived for distributions with regularly varying tails. The estimator shows good robustness properties and stands out for its simplicity. A tuning parameter allows for regulating the trade-off between robustness and efficiency. Small sample properties are illustrated by a simulation study.     

Crystal Structure and Physical Characterisation of [Zn<Subscript>2</Subscript>(Benzoato)<Subscript>4</Subscript>(Caffeine)<Subscript>2</Subscript>]·2 Caffeine

Abstract  

The crystal structure of [Zn₂(benzoato)₄(caffeine)₂]·(caffeine)₂ was determined by direct method and Fourier technique. The structure was refined by full-matrix least-squares method to a weighted R factor of 0.0582. The structure consists of centrosymmetric dimeric units where the two zinc(II) atoms are coordinated by four bridging benzoates in a syn–syn arrangement and two caffeine ligands at the apices of a bicapped square prism. Remaining two caffeines are bound only by hydrogen bonds. The Zn–Zn distance is 2.961(1) ?. The Zn(II) atoms are displaced by 0.365 ? from the basal plane containing four oxygen atoms towards the apical caffeine molecules. The dimeric structure of the complex is consistent with spectrum and thermal data. The structural data are compared with those found in similar [Zn₂(RCOO)₄(NL)₂] complexes.