Determinations of low atomic number elements in real uranium oxide samples using vacuum chamber total reflection x‐ray fluorescence

Conditions for the total reflection x‐ray fluorescence (TXRF) analysis of real uranium samples for low atomic number elements using vacuum chamber TXRF spectrometer were optimized. It was observed that for analysis of low atomic number elements, almost complete removal of uranium matrix is required. Two certified reference materials of uranium containing trace elements in different concentrations were dissolved in minimum amount of high purity nitric acid. The uranium matrix from these solutions was separated by solvent extraction using tri‐n‐butyl phosphate as extracting reagent. Low atomic number elements in TXRF spectrum of the aqueous phase could be seen only after six tri‐n‐butyl phosphate equilibrations in extraction. The TXRF determinations of the certified low atomic number elements Mg and Al were made in these aqueous solutions after addition of Sc as an internal standard. The TXRF determined values for Mg were in good agreement with the certified values, whereas TXRF determined Al values differed from the certified values appreciably, probably due to the interference of Al Kα peak with escape peak of U Mα and the neighboring Si Kα peak. Copyright © 2013 John Wiley & Sons, Ltd.     

A solution method for linear variational relation problems

In this paper, we consider a particular class of variational relation problem namely linear variational relation problem wherein the sets are defined by linear inequalities. The purpose is to study the existence of the solution set and its nature for this class of problem. Using these results, we provide algorithms to obtain the solutions of the problem based on which we present some numerical illustrations.     

X-Ray Crystallographic Investigation of Fully Acetylated N-(2-Deoxy-2-Acetamido-β-D-Glucopyranosyl)Alkanamides as N-Glycoprotein Linkage Region Analogs

To understand the structural significance of the linkage region of N-glycoproteins, three title sugar amides have been prepared as analogs and their molecular assembly and crystal structures have been solved to explore the effect of acetyl protection and aglycon variation on the conformation, particularly of the N-glycosidic linkage. Comparative analysis of these structures with those of free sugar amides reported earlier showed that conformation of the amido aglycon moiety is not altered significantly by the masking of hydroxyl groups in the form of acetate. The bifurcated antiparallel pattern involving N?H…O and C?H…O hydrogen bonds, a hallmark of the N-glycoprotein models GlcNAcβNHAc and GlcNAcβAsn, is absent in all of the fully protected title alkanamides. The asymmetric unit of the tri-O-acetylated GlcNAcβNHAc contains two different conformations, in one of which the double-pillared hydrogen bond network involving C1 and C2 acetamido groups is antiparallel, while it is parallel in the other. The co-occurrence of a molecular assembly motif—a double-pillared parallel and antiparallel hydrogen bonding pattern—is hitherto unknown in the crystal structures of N-glycoprotein linkage region models and analogs.     

Synthesis of Hydroxy-Functional PMMA Macromonomers by Anionic Polymerization

Living anionic polymerization has been utilized to synthesize hydroxy end-functionalized PMMA macromonomers with styryl or allyl functionalities as the polymerizable end-groups. Protected hydroxy-functionalized alkyl lithium initiators have been used to initiate anionic polymerization of MMA. Subsequently the living chains with protected hydroxyl function have been terminated using 4-vinylbenzyl chloride (4-VBC) or allyl methacrylate (ALMA) to form α-hydroxy-ω-styryl and α-hydroxy-ω-allyl PMMA, respectively. These protected hydroxy-functionalized PMMA macromonomers have been characterized by GPC and ¹H-NMR. Termination using 4-VBC led to 50% functionalization, whereas that using allyl methacrylate led to 100% functionalization of the hydroxy-PMMA.     

Synthesis and spectroscopic investigation of a novel solvatochromic dye

Optical response of a novel dye has been studied in various media like neat and mixed binary solvents, aqueous SDS micelles and β-cyclodextrin (β-CD) nanocavities. Fluorescence parameters in pure and mixed binary solvents have been found to be sensitive to the nature of the microenvironment. The emitting state of the dye in protic solvent is different from that in aprotic solvents. In presence of cations (H⁺, Mg²⁺), the dye exists in two tautomeric forms at equilibrium in solution. The values of the equilibrium constant (K) and ΔH⁰ have been measured. Values of local dielectric constant (ε) and microviscosity (η) at the region of solubilisation of the dye in aqueous SDS micellar media have been found out. The dye has also been found to form complex with β-CD. The equilibrium constant and the energy of maximum fluorescence of the dye encapsulated by β-CD have been determined.     

A missing enzyme in thiamin thiazole biosynthesis: identification of TenI as a thiazole tautomerase

In many bacteria tenI is found clustered with genes involved in thiamin thiazole biosynthesis. However, while TenI shows high sequence similarity with thiamin phosphate synthase, the purified protein has no thiamin phosphate synthase activity, and the role of this enzyme in thiamin biosynthesis remains unknown. In this contribution, we identify the function of TenI as a thiazole tautomerase, describe the structure of the enzyme complexed with its reaction product, identify the substrates phosphate and histidine 122 as the acid/base residues involved in catalysis, and propose a mechanism for the reaction. The identification of the function of TenI completes the identification of all of the enzymes needed for thiamin biosynthesis by the major bacterial pathway.     

Low-temperature neutron diffraction structures of N-glycoprotein linkage models and analogues: structure refinement and trifurcated hydrogen bonds

The biological addition of oligosaccharide moieties to asparagine residues of N-glycoproteins influences the properties and bioactivities of these macromolecules. The low-temperature neutron crystal structures of three N-glycoprotein linkage models and analogues provide accurate characterization of the three-dimensional structure of the conserved GlcNAc-Asn linkage. These first crystal structures of N-acetylated carbohydrates obtained by neutron diffraction provide high-resolution geometrical parameters that can be used for force-field parametrization and subsequent molecular dynamics simulation of N-glycoproteins. The correct localization of hydrogen atoms demonstrates the occurrence of trifurcated hydrogen bonds and hydrophobic contacts.