Theoretical and structural studies on mechanism of the Stec reaction

The mechanism of the Stec reaction between phosphoroselenanilidate or phosphonoanilidate and CS₂, activated by strong bases, has been studied computationally, using DFT methods, and experimentally, by low temperature ³¹P NMR spectroscopy. From molecular calculations, the reaction pathway of the reaction has been revealed with several transition states and intermediates, including a low energy spirocyclic pentacoordinate transition state and acyclic tetracoordinate intermediates, which eventually were correlated with short living molecules detected by NMR spectroscopy.     

EPR and optical properties of KYb(WO4)2 and KTb0.2Yb0.8(WO4)2 single crystals

Well oriented KYb(WO₄)₂ and KTb_0.2Yb_0.8(WO₄)₂ single crystals have been investigated for their magnetic and optical properties using the Raman and EPR techniques. The registered EPR signal is dominated by three lines ascribed to ytterbium ions: one main and two satellites. Tb ions, although non-paramagnetic, distinctly modify magnetic properties of the KYb(WO₄)₂ single crystal. Basic parameters of the spin Hamiltonian, including Zeeman and hyperfine terms (g and A matrices) as well the spatial orientation between principal and crystallographic axes systems were determined for both crystals.     

On strong approximation applied to post-widder operators

We introduce modified Post-Widder operators in polynomial weighted spaces of differentiable functions and we study strong approximation for them.     

Approximation by generalized MKZ-operators in polynomial weighted spaces

We prove some approximation properties of generalized Meyer-Konig and Zeller operators for differentiable functions in polynomial weighted spaces. The results extend some results proved in [1-3,7-16].     

Chemoselective activation of nucleoside 3'-O-methylphosphonothioates with 1,3,5-triazinyl morpholinium salts

Chemoselective and stereospecific O-activation of 2'-deoxynucleoside 3'-O-methylphosphonothioates 5 with N-methyl-N-4,6-dimethoxy-1,3,5-triazin-2-yl morpholinium salts results in formation with retention of configuration of 5'-O-DMT-2'-deoxynucleoside 3'-O-(4,6 dimethoxy-1,3,5-triazin-2-yl methylphosphonothioates (7). Active esters 7 are convenient intermediates for hydrolytic interconversion of RP-5 into SP-5 and can be used as monomers for stereoselective synthesis of dinucleoside (3',5')-methyl phosphonothioates.     

The Profile of Polyphenolic Compounds,Contents of Total Phenolics and Flavonoids,and Antioxidant and Antimicrobial Properties of Bee Products

This study aimed to characterize bee products (bee bread, bee pollen, beeswax, and multiflorous honey) with the profile of phenolic compounds, total phenolic (TPC) and flavonoid (TFC) contents, and antioxidant and microbiological properties. The TP and TF contents could be ordered as follows: bee pollen > bee bread > beeswax > honey. The UPLC−PDA−MS/MS analysis allowed identifying 20 polyphenols. Sinapic acid dominated in bee pollen, gallic acid in the bee bread and honey, while pinobanksin was the major compound of beeswax. The data showed that bee pollen and bee bread had a stronger antioxidant potential than honey and beeswax. Moreover, the antibacterial activity of the bee products was studied using 14 bacterial strains. Bee bread’s and bee pollen’s antimicrobial activity was higher towards Gram-negative strains. In comparison, honey was more potent in inhibiting Gram-positive bacteria. Our study indicates that bee products may represent valuable sources of bioactive compounds offering functional properties.     

Witt equivalence of local and global fields of characteristic 2

ABSTRACT

In this note it is proved that certain level sets of some real proper polynomial maps are nothing but spheres. As an application of this, we provide new proofs of Theorems 1.1, 1.2 and of the fundamental theorem of algebra. In addition, we show that every strictly convex (concave) polynomial map is proper. The latter implies that every real polynomial map g(x): R ⁿ  → R ⁿ , whose Jacobian matrix is symmetric and has nonzero eigenvalues of the same sign, is a homeomorphism of R ⁿ onto R ⁿ .     

Centers and Generalized Centers of Near-Rings

Let N be a right near-ring. Denote by C(N) the multiplicative center of N, and by N _d the set of left-distributive elements of N. In general, C(N) need not be closed under the addition of N. However, the generalized center of N, GC(N) = {a ? N|an _d  = n _d a for all n _d  ? N _d }, is always a subnear-ring of N containing C(N). In this article, we study the problem of determining when C(N) is a subnear-ring of N. We show that, for certain classes of near-rings, C(N) is a subnear-ring of N if and only if C(N) = GC(N). Examples are given to show the limits of the theory.     

Raman microspectroscopy of organic inclusions in spodumenes from Nilaw (Nuristan, Afghanistan)

The color varieties of spodumene (green spodumene, kunzite) from Nilaw mine (Nuristan, Afghanistan) have been investigated by microthermometry and Raman spectroscopy analyses. These minerals are rich in primary and secondary fluid inclusions. Measured values of temperature homogenization (T(h)) and pressure (P) for selected fluid-inclusion assemblages (I-IV) FIA in green spodumene and (I-II) FIA in kunzite ranges from 370 to 430°C, 1.16 to 1.44 kbar and 300 to 334°C, 0.81 to 1.12 kbar, respectively. The brine content and concentration varies from 4.3 to 6.6 wt.% eq. NaCl. Numerous and diverse mineral phases (quartz, feldspars, mica, beryl, zirconium, apatite, calcite, gypsum) present in this mineral as solid inclusions were studied by Raman microspectroscopy. Raman spectra of selected fluid, organic and solid inclusions were collected as line or rectangular maps and also depth profiles to study their size and contents. There appeared very interesting calcite (156, 283, 711 and 1085 cm(-1)), beryl (324, 397, 686, 1068 and 3610 cm(-1)), topaz (231, 285, 707, 780 and 910 cm(-1)) and spodumene (355, 707 and 1073 cm(-1)) inclusions accompanied by fluid and/or organic inclusions (liquid and gas hydrocarbons) with bands at 2350 cm(-1) (CO(2), N(2)), 2550 cm(-1) (H(2)S) and 2900 cm(-1) (C(2)H(6)-CH(3)). Some solid inclusions contain carbonaceous matter (D-band at ca. 1320 cm(-1) and/or G-band at ca. 1600 cm(-1)).     

Optimization of LC method for the determination of testosterone and epitestosterone in urine samples in view of biomedical studies and anti-doping research studies

A sensitive and rapid liquid chromatographic (LC) method for the simultaneous determination of testosterone (T) and epitestosterone (E) in human urine samples has been developed and elaborated. The ratio of the both steroids (T/E) in human urine is a widely used as doping control indicator. A sample pretreatment by solid-phase extraction (SPE) after hydrolysis using 36% hydrochloric acid for determination of total level of T has been applied. Unconjugated (free) form of the both androgens were determined without hydrolysis steps, what makes novelty of the method, because simplifies the proposed procedure. In turn, the measurements of urinary free T and E provided the diagnostic information for excess adrenal production of steroids. The proposed LC assay was evaluated by analyzing a series of urine samples containing T, E and methyltestosterone (MT) as internal standard at the range of concentration 2-300 ng⁻¹ mL of both analyzed hormones. The proposed method was fully validated for specificity, linearity, limits of detection and quantitation, precision and trueness according to the current requirements concerning analytical methods. Interestingly, the developed LC method allows to obtain a sensitive enhancement with respect to UV detection with the quantitation limit for T and E equaled 2 ng mL⁻¹. The method was selective and reliable for identity and enable to detect changes of endogenous levels of T and E in urine independently of fluctuations characteristic for both analyzed endogenous hormone level in plasma.