A convenient approach to an advanced intermediate for (+)-lactacystin synthesis

A fully stereoselective preparation of the advanced intermediate 24 for the synthesis of (+)-lactacystin from known 1,2:5,6-di-O-isopropylidene-α-d-gulofuranose (2), as the source of chirality, has been achieved. The C-5 methyl group was introduced via a Wittig olefination followed by Pd/C-mediated hydrogenation of the conformationally restricted alkene 11 in a highly stereoselective manner. The stereogenic tetrasubstituted carbon centre at C-3, with an amino group, was installed stereoselectively via an Overman rearrangement, which was efficiently controlled by a saccharide environment.     

Determination of bromadiolone in pheasants and foxes by differential pulse voltammetry

Bromadiolone, a commercially used anticoagulant rodenticide, was determined in tissues of various animals by differential pulse voltammetry with a carbon-paste electrode. Under the most suitable experimental conditions (step potential of 25?mV?s^?1 and 0.2?mol?L^?1 acetate buffer, pH 4.2), the limit of detection was 0.5?ng?mL^?1. The electroanalytical method was consequently used to investigate the bromadiolone transport within the food chain. Pheasants were exposed to bromadiolone and then used as feed for a fox. The average levels were 528 and 198?ng of bromadiolone per gram of fresh weight of liver of pheasant and fox, respectively. Due to the surprisingly lower content of bromadiolone in the latter, a basic biochemical analysis, particularly blood coagulation, was performed. Among the parameters studied (thrombin time, prothrombin time, activated partial thromboplastin time, and fibrinogen), there was prolongation of the prothrombin time and activated partial thromboplastin time.     

On the Roter Type of Chen Ideal Submanifolds

Chen ideal submanifolds M ⁿ in Euclidean ambient spaces E ^n+m (of arbitrary dimensions n ?? 2 and codimensions m??? 1) at each of their points do realise an optimal equality between their squared mean curvature, which is their main extrinsic scalar valued curvature invariant, and their ???C(= ??(2)?C) curvature of Chen, which is one of their main intrinsic scalar valued curvature invariants. From a geometric point of view, the pseudo-symmetric Riemannian manifolds can be seen as the most natural symmetric spaces after the real space forms, i.e. the spaces of constant Riemannian sectional curvature. From an algebraic point of view, the Roter manifolds can be seen as the Riemannian manifolds whose Riemann?CChristoffel curvature tensor R has the most simple expression after the real space forms, the latter ones being characterisable as the Riemannian spaces (M ⁿ , g) for which the (0, 4) tensor R is proportional to the Nomizu?CKulkarni square of their (0, 2) metric tensor g. In the present article, for the class of the Chen ideal submanifolds M ⁿ of Euclidean spaces E ^n+m , we study the relationship between these geometric and algebraic generalisations of the real space forms.     

Micromorphology Characterization of SiO2-Based Composite Thin Films with Immobilized Terbium(III) Complex

The aim of this study was to investigate by atomic force microscopy and multifractal analysis the three-dimensional (3-D) of surface micromorphology of the complex of Tb(III) with the biscoumarin derivative 3,3′-[(4-hydroxyphenyl)methyl)]bis-(4-hydroxy-2H-1-benzopyran-2-one), Tb(C₂₅H₁₅O₇)₃ · 5H₂O immobilized in transparent SiO₂-based films by a simple casting technique. The 3-D surfaces contain irregularities of various orders spread on the surface due to the intrinsic method of surface preparation. We found that the micromorphology of all analyzed samples has multifractal characteristics. The generalized dimension D _q and the singularity spectrum f(α) provided quantitative values that describe the degree of heterogeneity in the 3-D surface geometry at nanometer scale. The results showed that the larger the spectrum width Δα (Δα = α _max  ? α _min ) of the multifractal spectra f(α), the more nonuniform is the surface micromorphology. These results demonstrate that multifractal analysis is a more precise and reliable tool for quantitative characterization of 3-D surface micromorphology.     

Synthesis of the first unnatural schisantherins and their effects in multidrug-resistant cancer cells

Schisandrol A, a dibenzocyclooctadiene lignan, was obtained by a simplified procedure from Schisandra chinensis fruits. Its reaction with carboxylic acids to give new esters (schisantherins) required special conditions such as microwave irradiation. An X-ray single crystal structure analysis of schisandrol A revealed a sterical shielding of the secondary OH group as the likely reason. The cinnamoate inhibited the P-gp drug transporters of multidrug-resistant human Kb-V1 cervix carcinoma cells better than the natural benzoate and comparable to the clinical sensitizer verapamil.     

Polyaniline-coated cellulose fibers decorated with silver nanoparticles

Cellulose fibers of 20 μm in diameter and aspect ratio of 2 or 10 were coated with protonated polyaniline (PANI) during the oxidation of aniline hydrochloride with ammonium peroxydisulfate in an aqueous medium. The presence of PANI has been proved by FTIR spectroscopy. The conductivity increased from 4.0 × 10⁻¹⁴ S cm⁻¹ to 0.41 S cm⁻¹ after coating the fibers with PANI. The percolation threshold in the mixture of original uncoated and PANI-coated fibers was reduced from 10 mass % PANI to 6 mass % PANI, as the aspect ratio changed from 2 to 10. The subsequent reaction with silver nitrate results in the decoration of PANI-coated cellulose fibers with silver nanoparticles of about 50 nm average size. The content of silver of up to 10.6 mass % was determined as a residue in thermogravimetric analysis. FTIR spectra suggest that the protonated emeraldine coating changed to the pernigraniline form during the latter process and, consequently, the conductivity of the composite was reduced to 4.1 × 10⁻⁴ S cm⁻¹, despite the presence of silver.     

The efficient preparation of α-substituted serine scaffolds as the chiral building blocks for the synthesis of SPT inhibitors

An efficient stereoselective synthesis of unusual substituted serine synthons 7, 10, 12 is reported. It was shown that highly functionalized furanose 6 has the suitable structure for further synthetic manipulations toward the inhibitors of SPT.     

H NMR and IR study of temperature-induced phase transition of negatively charged poly(N-isopropylmethacrylamide-co-sodium methacrylate) copolymers in aqueous solutions

¹H NMR and IR spectroscopies were used to investigate the temperature-induced phase transition behaviour of poly(N-isopropylmethacrylamide-co-sodium methacrylate) [P(IPMAAm/MNa)] copolymers, containing in aqueous solutions negatively charged MNa units (i = 1-10 mol%), and the obtained results were compared with those obtained for poly(N-isopropylmethacrylamide) (PIPMAAm) homopolymer. For PIPMAAm/H₂O solution, IR spectra indicate that the transition temperatures for the hydrophilic CO groups are slightly higher (by ∼ 2 K) in comparison with hydrophobic CH₃ groups. The decreasing values of phase-separated fraction p_max and the decrescent hysteresis during gradual heating and cooling, both with increasing content of MNa units i in the copolymer, show that for copolymers with i ? 5 mol% the globular-like structures formed at temperatures above the respective LCST are rather porous and disordered with relatively low degree of polymer-polymer hydrogen bonding. While for P(IPMAAm/MNa) copolymers with i ? 5 mol% most water molecules are expelled from globular structures, for i < 5 mol% a certain portion of water (HDO) molecules is rather tightly bound in globular structures; at the same time no releasing process was detected for the bound water even for 90 h.     

Phenol‐Substituted Tetrapyrazinoporphyrazines: pH‐Dependent Fluorescence in Basic Media

Tetrapyrazinoporphyrazines (TPyzPzs) bearing one, two, four or eight 3,5‐di(tert‐butyl)‐4‐hydroxyphenol moieties were synthesized as zinc(II) complexes and metal‐free derivatives. The deprotonation of the phenol using tetrabutylammonium hydroxide induced the formation of a strong donor for intramolecular charge transfer that switched OFF the red fluorescence (λ_F～660 nm) of the parent zinc TPyzPzs. The changes were fully reversible for TPyzPzs with one to four phenolic moieties, and an irreversible modification was observed for TPyzPzs substituted with eight phenols. The sensors were anchored to lipophilic particles in water, and a pK_a approximately 12.5–12.7 was determined for the phenolic hydroxyl based on fluorescence changes in different buffers. In addition, a novel concept for fluorescence OFF‐ON‐OFF switching in metal‐free TPyzPzs bearing phenolic moieties upon addition of specific amounts of base was demonstrated.