A novel multi-element coprecipitation technique for separation and enrichment of metal ions in environmental samples

A multi-element preconcentration-separation technique for heavy metal ions in environmental samples has been established. The procedure is based on coprecipitation of gold(III), bismuth(III), cobalt(II), chromium(III), iron(III), manganese(II), nickel(II), lead(II), thorium(IV) and uranium(VI) ions by the aid of Cu(II)-9-phenyl-3-fluorone precipitate. The Cu(II)-9-phenyl-3-fluorone precipitate was dissolved by the addition 1.0 mL of concentrated HNO₃ and then the solution was completed to 5 mL with distilled water. Iron, lead, cobalt, chromium, manganese and nickel levels in the final solution were determined by flame atomic absorption spectrometer, while gold, bismuth, uranium and thorium were determined by inductively coupled plasma mass spectrometer. The optimal conditions are pH 7, amounts of 9-phenyl-3-fluorone: 5 mg and amounts of Cu(II): 1 mg. The effects of concomitant ions as matrix were also examined. The preconcentration factor was 30. Gold(III), bismuth(III), chromium(III), iron(III), lead(II) and thorium(IV) were quantitatively recovered from the real samples. The detection limits for the analyte elements based on 3 sigma (n = 15) were in the range of 0.05-12.9 μg L⁻¹. The validation of the presented procedure was checked by the analysis of two certified reference materials (Montana I Soil (NIST-SRM 2710) and Lake Sediment (IAEA-SL-1)). The procedure was successfully applied to some environmental samples including water and sediments.     

Structure of the nitrogen-centered radical formed during inactivation of E. coli ribonucleotide reductase by 2'-azido-2'-deoxyuridine-5'-diphosphate: trapping of the 3'-ketonucleotide

Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides to deoxynucleotides providing the monomeric precursors required for DNA replication and repair. The class I RNRs are composed of two homodimeric subunits: R1 and R2. R1 has the active site where nucleotide reduction occurs, and R2 contains the diiron tyrosyl radical (Y*) cofactor essential for radical initiation on R1. Mechanism-based inhibitors, such as 2'-azido-2'-deoxyuridine-5'-diphosphate (N(3)UDP), have provided much insight into the reduction mechanism. N(3)UDP is a stoichiometric inactivator that, upon interaction with RNR, results in loss of the Y* in R2 and formation of a nitrogen-centered radical (N*) covalently attached to C225 (R-S-N*-X) in the active site of R1. N(2) is lost prior to N* formation, and after its formation, stoichiometric amounts of 2-methylene-3-furanone, pyrophosphate, and uracil are also generated. On the basis of the hyperfine interactions associated with N*, it was proposed that N* is also covalently attached to the nucleotide through either the oxygen of the 3'-OH (R-S-N*-O-R') or the 3'-C (R-S-N*-C-OH). To distinguish between the proposed structures, the inactivation was carried out with 3'-[(17)O]-N(3)UDP and N* was examined by 9 and 140 GHz EPR spectroscopy. Broadening of the N* signal was detected and the spectrum simulated to obtain the [(17)O] hyperfine tensor. DFT calculations were employed to determine which structures are in best agreement with the simulated hyperfine tensor and our previous ESEEM data. The results are most consistent with the R-S-N*-C-OH structure and provide evidence for the trapping of a 3'-ketonucleotide in the reduction process.     

On the solutions of analytic equations

Inventiones mathematicae -     

Abstract Hilbert Schemes

In analogy with classical projective algebraic geometry, Hilbert functors can be defined for objects in any Abelian category. We study the moduli problem for such objects. Using Grothendieck's general framework. We show that with suitable hypotheses the Hilbert functor is representable by an algebraic space locally of finite type over the base field. For the category of the graded modules over a strongly Noetherian graded ring, the Hilbert functor of graded modules with a fixed Hilbert series is represented by a commutative projective scheme. For the projective scheme corresponding to a suitable noncommutative graded algebra, the Hilbert functor is represented by a countable union of commutative projective schemes.     

Theoretical Characterization of End‐On and Side‐On Peroxide Coordination in Ligated Cu2O2 Models

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.