Comparison between DAX-8 and C-18 solid phase extraction of rainwater dissolved organic matter

Rainwater is a very low concentrated matrix and, for dissolved organic matter (DOM) characterization, an efficient extraction procedure is essential. Isolation procedures based on the adsorption onto XAD-8 and C-18 sorbents have been used in the literature for rainwater DOM isolation, but a comparison between these procedures is lacking. In this work, UV-visible and molecular fluorescence spectroscopies highlighted differences between rainwater DOM isolated by DAX-8 (replacement for XAD-8) and by C-18. It was possible to recover higher rainwater DOM percentage by the C-18 based procedure than by the DAX-8 one. Rainwater protein-like compounds were better concentrated by the C-18 procedure than by the DAX-8 one, while humic-like compounds were similarly concentrated by both procedures. Furthermore, rainwater DOM extracted by the C-18 procedure was more representative of the global matrix, while DAX-8 preferentially extracted humic-like compounds.     

Electrochemical Determination of Uric Acid,Dopamine and Tryptophan at Zinc Hexacyanoferrate Clay Modified Electrode

A Cameroonian smectite clay has been transformed into Zn²⁺ homoionic form and then used to prepare film modified glassy carbon electrodes and carbon paste electrodes. These electrodes containing Zn²⁺ were exploited to prepare a mixed valence zinc hexacyanoferrate (ZnHCF). Cyclic voltammetry has been employed to monitor the in situ growth of ZnHCF on clay modified electrodes. Although interesting electrocatalytic properties toward UA were observed with these modified electrodes, the modified carbon paste electrodes were the most suitable for dopamine, uric acid and tryptophan detection and exhibited for these analytes extended linear range, high sensitivities, selectivity and low limit.     

Higher homotopy of groups definable in o-minimal structures

It is known that a definably compact group G is an extension of a compact Lie group L by a divisible torsion-free normal subgroup. We show that the o-minimal higher homotopy groups of G are isomorphic to the corresponding higher homotopy groups of L. As a consequence, we obtain that all abelian definably compact groups of a given dimension are definably homotopy equivalent, and that their universal covers are contractible.     

[ReIII(thiourea-S)6]Cl3 · 4 H2O and [ReIII(N-methylthiourea-S)6]Cl3 as Precursors to other ReIII Complexes: a Kinetic Study in Aqueous Media. Crystal Structure of [ReIII(N-methylthiourea-S)6](PF6)3 · H2O

Capability of [Re^III(tu-S)₆]Cl₃, where tu = thiourea, as a precursor to other Re^III complexes by ligand substitution in aqueous medium is studied. For the decomposition of [Re(tu-S)₆]Cl₃, experiments suggest pseudo first order kinetics and observed rate constants vary from 1.3 × 10^–2 to 9.6 × 10^–2 min^–1 in the pH range 2.80–5.04. Experiments in presence of incoming ligand (ethylendiaminetetraacetic acid or diethylentriaminepentaacetic acid) show that ligand substitution is significantly slower than decomposition of the precursor, even when pH and temperature are modified. Similar results were obtained working with [Re^III(Metu-S)₆]Cl₃, where Metu = N-methylthiourea. Molecular structure of [Re^III(Metu-S)₆](PF₆)₃ · H₂O was determined by single crystal X-ray diffractometry. The coordination polyhedron around the Re ion is a distorted octahedron. The six methylthiourea ligands are bonded to the metal through the sulfur atoms [bond lengths range from 2.409(2) to 2.451(2) Å].     

On Groups and Rings Definable In O-Minimal Expansions of Real Closed Fields

Let R, >,+,• be a real closed field, and let M be ano-minimal expansion of R. We prove here several results regardingrings and groups which are definable in M. We show that everyM–definable ring without zero divisors is definably isomorphicto R, R((–l)) or the ring of quaternions over R. One corollaryis that no model of T_exp is interpretable in a model of T_an.     

Inhibiting and Reversing Amyloid‐β Peptide (1–40) Fibril Formation with Gramicidin S and Engineered Analogues

In Alzheimer’s disease, amyloid‐β (Aβ) peptides aggregate into extracellular fibrillar deposits. Although these deposits may not be the prime cause of the neurodegeneration that characterizes this disease, inhibition or dissolution of amyloid fibril formation by Aβ peptides is likely to affect its development. ThT fluorescence measurements and AFM images showed that the natural antibiotic gramicidin S significantly inhibited Aβ amyloid formation in vitro and could dissolve amyloids that had formed in the absence of the antibiotic. In silico docking suggested that gramicidin S, a cyclic decapeptide that adopts a β‐sheet conformation, binds to the Aβ peptide hairpin‐stacked fibril through β‐sheet interactions. This may explain why gramicidin S reduces fibril formation. Analogues of gramicidin S were also tested. An analogue with a potency that was four‐times higher than that of the natural product was identified.     

Expanding Catch and Release DNA Decoy (CRDD) Technology with Pyrimidine Mimics

Catch and release DNA decoys (CRDDs) utilize photochemically responsive nucleoside analogues that generate abasic sites upon exposure to light. Herein, we describe the synthesis and evaluation of four candidate CRDD monomers containing nucleobases that mimic endogenous pyrimidines: 2-nitroimidazole ( 2-NI ), 2-nitrobenzene ( 2-NB ), 2-nitropyrrole ( 2-NP ) and 3-nitropyrrole ( 3-NP ). Our studies reveal that 2-NI and 2-NP can function as CRDDs, whereas 3-NP and 2-NB undergo decomposition and transformation to a higher-ordered structure upon photolysis, respectively. When incorporated into DNA, 2-NP undergoes rapid photochemical cleavage of the anomeric bond (1.8 min half-life) to yield an abasic site. Finally, we find that all four pyrimidine mimics show significantly greater stability when base-paired against the previously reported 7-nitroindole CRDD monomer. Our work marks the expansion of CRDD technology to both purine and pyrimidine scaffolds.     

Poly(phenylene oxide); electropolymerization on mild steel and anticorrosive properties of the layer: A new corrosion test

The electropolymerization of phenyl salicylate by cyclic potential sweeps over mild steel gives rise to the formation of a poly(phenylene oxide) (PPO) film. In order to study the anticorrosive properties of PPO a new rapid corrosion test has been devised.