31P NMR Knight shifts in the UPY(Y = S,Se, Te) compounds

Nuclear magnetic resonance of ³¹P measurements have been made for UPY (where Y = S, Se and Te) compounds. The resonane lines show the effect of anisotropic Knight shifts. In the UPS, the NMR data indicate an axial symmetry of the phosphorus environment whereas for UPSe and UPTe the symmetry is lower than the axial one. The result for UPSe disagrees with earlier structural studies. An analysis of NMR spectra indicates that both the asymmetry parameter ε and the isotropic component of the Knight shift increase with the increase of atomic weight of the Y element.     

Magnetic ordering in NdRh2Si2 and ErRH2Si2

Neutron diffraction and magnetization study of polycrystalline NdRh₂Si₂ and ErRh₂Si₂ was performed in the temperature range from 4.2 to 293 K. Both compounds are of ThCr₂Si₂ type crystal structure and exhibit antiferromagnetic ordering below T_N = 53 K and T_N = 12.8 K respectively. The magnetic structure wave vector is τ = [0, 0, 1].     

Spectral Properties of Bacteriochlorophyll c in Organisms and in Model Systems

Polarized absorption and fluorescence spectra of bacteriochlorophyll c and green photosynthetic bacterium Prostheecochloris aestuarii cells and cell fragments embedded in stretched polymer film were measured. In pigment samples the artificial oligomers of bacteriochlorophyll c (with absorption about 750 nm) and other forms of this pigment and bacteriopheophytin (with absorption at 670 nm) were present. In bacteria samples, embedded in polymer, oligomers were in high degree disaggregated and as a result the absorption about 670 nm was observed. Previously for similar sets of samples the decay of fluorescence excited only at one wavelength was analyzed on three exponential components, but exact lifetime values of these components for various samples were different. The aim of present paper was to check if these differences occur because of various contributions to decay from three well defined forms or if they were related to the existence of several pigment forms with slightly different lifetimes. The global analysis of data obtained for various excitation and observation wavelengths of fluorescence were done. From this analysis it follows that the second situation occurs. For a model system containing artificial oligomers the largest component of decay has a ⁴ of about 0.183 ns or 0.136 ns depending on observation wavelength. For the bacteria sample, in which the emission at 680 nm is the superposition from various pigments, global analysis done for various excitation wavelengths shows also that the values differ depending on the regions of fluorescence observation. From polarized spectra, it follows that in the model system the pigments absorbing at 670 nm are randomly distributed whereas oligomers are highly oriented. In bacteria fragments absorbing at 670 nm pigment molecules can be divided into two groups: one oriented along the axis of film stretching and the second practically randomly distributed. In living organisms, under some conditions, small amount of 670 nm pigments can be present and can work as excitation energy traps or as antenna transferring the excitation. Present results show that the role of various pools of 670 nm absorbing pigments can be different because of their differing orientation.     

Herbicidal Activity of Phosphonic,Phosphinic and Phosphinous Acid Analogues of Aromatic Amino Acids

Abstract

Over 40 phosphonic, phosphinic and phosphinous acid analogues of phenylglycine and phenylalanine were synthesized and screened for their herbicidal activity on Lepidium sativum (crest) and Cucumis sativus (cucumber). The most active appeared to be 2-amino-1-hydroxy-3-phenylpropylphosphonic acid which was equipotent with popular herbicide glyphosate. Also aminobenzylphosphonic acids, analogues of phenylglycine, exhibited notable herbicidal activity and thus represent a group of the most active herbicides found among simple aminophosphonic acids. Other compounds showed moderate herbicidal activity. Preliminary results indicate that analogues of aromatic amino acids display their activity as effectors of biosynthesis of aromatic amino acids.     

Application of HS-SPME with Poly(1-Vinyl-3-Hexylimidazolium Chloride) Polymeric Ionic Liquid Coating Using GC–MS to Determine Volatile Fatty Acids in Dairy Wastewater

Volatile fatty acids were determined in this study using headspace solid-phase microextraction (HS-SPME) with a poly(1-vinyl-3-hexylimidazolium chloride) polymeric ionic liquid coated fiber followed by gas chromatography–mass spectrometry. Experimental parameters such as extraction time and temperature, sample volume as well as desorption time and temperature were optimized. Detection limits of the method were in the range of 0.13–0.26 mg/L. The coefficient of variation ranged from 0.12 to 6.9 %. The method was applied to determine volatile fatty acids in dairy wastewater from different operations and in bulk wastewater.     

Quantitative energy dispersive X-ray microanalysis of electron beam-sensitive alloyed nanoparticles.

An energy dispersive X-ray spectrometry (EDXS) method is developed to evaluate the composition of alloyed nanoparticles (NPs) where one of the alloying elements is removed under the electron beam during microanalysis with a transmission electron microscope (TEM). The method is demonstrated for alloyed Au-Ag NPs of a diameter ranging from 6 to 20 nm produced by laser evaporation of a water-suspended Ag-Au powder mixture of varying composition. Series of EDXS spectra are recorded for 30 NPs from samples with five different Ag:Au ratios revealing Ag depletion from NPs during electron irradiation. By studying the evolution of NPs composition as a function of dose, the initial Ag content for each NP is extrapolated. The rate of Ag depletion is discussed in terms of sputtering and knock-on damage. On average, approximately one Ag atom is lost from the NP for each Ag L X-ray detected. To assess the limitations of microanalysis in these sensitive nanoscale structures, the concept of detectability limit is adapted to our method. This benchmark is then evaluated for Ag in Au-Ag NPs of various sizes and acquisition times. This study should be regarded as a guide for the design of analytical TEM measurements of beam-sensitive NPs.     

Matrix Chebyshev polynomials and continued fractions

In the first part we expose the notion of continued fractions in the matrix case. In this paper we are interested in their connection with matrix orthogonal polynomials.

In the second part matrix continued fractions are used to develop the notion of matrix Chebyshev polynomials. In the case of hermitian coefficients in the recurrence formula, we give the explicit formula for the Stieltjes transform, the support of the orthogonality measure and its density. As a corollary we get the extension of the matrix version of the Blumenthal theorem proved in [J. Approx. Theory 84 (1) (1996) 96].

The third part contains examples of matrix orthogonal polynomials.     

Thermodynamics of titanium and vanadium reduction in non-aqueous environment calculated at various levels of theory

Reduction of titanium and vanadium compounds is a process accompanying the activation of coordinative olefin polymerization catalysts. Four density functional theory (DFT) functionals, coupled cluster with single, double, and perturbative triple excitations method CCSD(T) as well as complete active-space second-order perturbation theory method CASPT2 with a complete active-space self-consistent field CASSCF reference wave function were applied to investigate the thermodynamics of titanium and vanadium reduction. The performance of these theoretical methods was assessed and compared with experimental values. The calculations indicate that vanadium(IV) chloride is more easily reduced by trimethylaluminum than the corresponding titanium compound; the energies of reaction calculated at the CCSD(T) level are equal -57.21 and -33.10 kcal/mol, respectively. The calculations deal with the redox reactions of metal chlorides in the gas phase, rather than solvated ions in the aqueous solution. This approach may be more appropriate for olefin polymerization, usually carried out in nonpolar solvents.     

Confinement of charged dust particles by a hybrid-type electric curtain

The hybrid-type electric curtain (HTEC) comprises a planar electric curtain and a perpendicular planar condenser. Serial cylindrical electrodes are supplied with AC voltage, whereas the condenser is fed with DC voltage. HTEC allows for better control of the particle position shift in space. The particle oscillation path within the hybrid curtain has been photographically analysed. The changing particle path was recorded according to a DC changing voltage value and a constant AC voltage value. The aim of the paper is to describe a successful method that enables one to experimentally determine the region where the particle can be stably oscillated.