Reevaluation of copper(I) affinity for amyloid-β peptides by competition with ferrozine--an unusual copper(I) indicator

The association constant of ferrozine (5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine-4,4'-disulfonic acid) with Cu(I) to form the chromophoric [Cu(I)(Fz)(2)](3-) complex was determined by UV/Vis titration experiments in Hepes buffer (0.1 M, pH 7.4). An association constant close to 10(12) M(-2), which is significantly weaker than those of the well-known, water-soluble, Cu(I) chelators bicinchoninic acid and 2,9-dimethyl-4,7-diphenyl-1,10-phenantroline disulfonic acid, was found. The [Cu(I)(Fz)(2)](3-) chromophore was used in UV/Vis competition experiments to determine Cu(I) binding affinity for the amyloid-β peptide involved in Alzheimer's disease and for a series of pertinent mutants. An association constant of approximately 10(7) M(-1) was found; this is much weaker than that reported for dithiothreitol and confirms that imidazoles are harder ligands than thiolates. Each His mutation (H6A, H13A, and H14A) impacts the peptide affinity for Cu(I). The native human amyloid-β peptide was found to be a fourfold-stronger Cu(I) ligand than the murine peptide, which differs by three point mutations (R5G, Y10F, and H13R) from the human one.     

Nitroxyl radical self-assembled monolayers on gold: Experimental data vs. Laviron’s interaction model

Mixed SAMs of nitroxyl radical derivative and alkanethiol have been studied by cyclic voltammetry in both aqueous and non-aqueous solvents. Cyclic voltammograms exhibit shapes as a function of surface coverage deviating from an “ideal system”. Confronted to Laviron’s interaction model, the agreement observed between theory and experiments provides evidence of a random distribution of electroactive centers on surface and indicates that the local ionic environment of charged redox centers plays a major role in the electrochemical behaviour of SAMs.     

Effect of chelating agent on the oxidation rate of PCP in the magnetite/H2O2 system at neutral pH

The complex [Rh(CO)₂Cl]₂ reacts with two molar equivalent of pyridine carboxylic acids ligands Py-2-COOH(a), Py-3-COOH(b) and Py-4-COOH(c) to yield rhodium(I) dicarbonyl chelate complex [Rh(CO)₂(L^/)](1a) {L^/ = η²-(N,O) coordinated Py-2-COO⁻(a^/)} and non-chelate complexes [Rh(CO)₂ClL^//](1b,c) {L^// = η¹-(N) coordinated Py-3-COOH(b), Py-4-COOH(c)}. The complexes 1 undergo oxidative addition (OA) reactions with different electrophiles such as CH₃I, C₂H₅I, C₆H₅CH₂Cl and I₂ to give penta coordinated Rh(III) complexes of the types [Rh(CO)(CORⁿ)XL^/], {n = 1,2,3; R¹ = CH₃(2a); R² = C₂H₅(3a); X = I and R³ = CH₂C₆H₅ (4a); X = Cl}, [Rh(CO)I₂L^/](5a), [Rh(CO)(CORⁿ)ClXL^//] {R¹ = CH₃(6b,c); R² = C₂H₅(7b,c); X = I and R³ = CH₂C₆H₅ (8b,c); X = Cl} and [Rh(CO)ClI₂L^//](9b,c). The complexes have been characterized by elemental analysis, IR and ¹H NMR spectroscopy. Kinetic data for the reaction of 1a–b with CH₃I indicate a first order reaction. The catalytic activity of 1a–c for the carbonylation of methanol to acetic acid and its ester is evaluated and a higher turn over number (TON = 810–1094) is obtained compared with that of the well-known commercial species [Rh(CO)₂I₂]⁻ (TON = 653) at mild reaction conditions (temperature 130 ± 5 °C, pressure 35 ± 5 bar).     

Determination of calcium, magnesium, sodium, and potassium in foodstuffs by using a microsampling flame atomic absorption spectrometric method after closed-vessel microwave digestion: method validation

This paper describes a validation process in compliance with the NFIEN ISO/IEC 17025 standard for the determination of the macrominerals calcium, magnesium, sodium, and potassium in foodstuffs by microsampling with flame atomic absorption spectrometry after closed-vessel microwave digestion. The French Standards Commission (Agence Francaise de Normalisation) standards NF V03-110, NF EN V03-115, and XP T-90-210 were used to evaluate this method. The method was validated in the context of an analysis of the 1322 food samples of the second French Total Diet Study (TDS). Several performance criteria (linearity, LOQ, specificity, trueness, precision under repeatability conditions, and intermediate precision reproducibility) were evaluated. Furthermore, the method was monitored by several internal quality controls. The LOQ values obtained (25, 5, 8.3, and 8.3 mg/kg for Ca, Mg, Na, and K, respectively) were in compliance with the needs of the TDS. The method provided accurate results as demonstrated by a repeatability CV (CVr) of < 7% and a reproducibility CV (CVR) of < 12% for all the elements. Therefore, the results indicated that this method could be used in the laboratory for the routine determination of these four elements in foodstuffs with acceptable analytical performance.     

Access to functionalised silver(I) and gold(I) N-heterocyclic carbenes by [2 + 3] dipolar cycloadditions

A new strategy was developed for the modification of silver(I) and gold(I) N-heterocyclic carbenes. Azido groups were grafted and used either by copper-catalysed azide-alkyne cycloaddition before metallation or by thermal and "strain-promoted" 1,3-dipolar cycloaddition after metallation to functionalise the metal-NHCs.     

Lanthanide-binding peptides with two pendant aminodiacetate arms: impact of the sequence on chelation

Lanthanide complexes with a series of hexapeptides-incorporating two unnatural chelating amino acids with aminodiacetate groups, Ada(1) and Ada(2)-have been examined in terms of their speciation, structure, stability and luminescence properties. Whereas Ada(2) acts as a tridentate donor in all cases, Ada(1) may act as a tetradentate donor thanks to the coordination of the amide carbonyl function assisted by the formation of a six-membered chelate ring. The position of the Ada(1) residue in the sequence is demonstrated to be critical for the lanthanide complex speciation and structure. Ada(1) promotes the coordination of the backbone amide function to afford a highly dehydrated Ln complex and an S-shape structure of the peptide backbone, only when found in position 2.     

Influence of the electrochemical conversion of [(LH)Mn(II)Cl2] into [(L)Mn(III)Cl]+ on the protonic state of a phenol-containing ligand

A bischloromanganese(II) complex [(LH)MnCl2] (1), where LH is the pentadentate ligand N,N-bis(2-pyridylmethyl)-N'-salicylidene- ethane-1,2-diamine, has been synthesized. Elemental analysis, UV-visible, and cyclic voltammetry experiments showed that the phenol function of the ligand LH remains protonated. Exhaustive electrolysis at 1.0 V vs SCE led to the formation of the Mn(III) derivative [(L)MnCl]+ (3) with the concomitant expulsion of H+ and Cl-. The formation of the Mn(III) species was confirmed by UV-visible spectroscopy and X-ray crystallography. Complex 1 could be regenerated by the reduction of complex 3 in the presence of H+ and Cl-.     

Adsorption of paracresol in silicalite-1 and pure silica faujasite. A comparison study using molecular simulation

This paper presents the results on the Grand-Canonical Monte Carlo simulations of the adsorption of the paracresol uremic toxin and water into the silicalite-1 and pure silica faujasite zeolites. The co-adsorption of water and paracresol seems to proceed along a cooperation effect between the toxin and the solvent. A model of adsorption that accounts for the effect of the solvent has been elaborated and verified using experimental isotherms. The model is based on the Langmuir isotherm in which an apparent adsorption enthalpy is used that changes with the concentration of the solute. The new expression for the isotherm reproduces the experimental isotherm with good accuracy and physical interpretation is given to justify the model.     

Unusual entry to the novel 8-halo-N1-ribosyl hypoxanthine system by degradation of a cyclic adenosine-5'-diphosphate ribose analogue

Cyclic 8-bromo-inosine-5'-diphosphate ribose (8-Br-N1-cIDPR) was cleanly degraded at acidic pH by N9 ribosyl scission and subsequent pyrophosphate cleavage to give 8-bromo-N1-ribosyl hypoxanthine 5'-monophosphate (8-Br-N1-IMP), a novel class of mononucleotide, as the sole product.     

Tandem intermolecular Suzuki coupling/intramolecular vinyl triflate-arene coupling

Treatment of a benzyl substituted meso-ditriflate with boronic acids in the presence of palladium acetate, triphenylphosphine and caesium fluoride results in intermolecular Suzuki coupling followed by vinyl triflate-arene cyclisation to provide, in high yields, single regioisomers of tricyclic-carbocycles.