New strategy to identify radicals in a time evolving EPR data set by multivariate curve resolution-alternating least squares

Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique that is able to characterize radicals formed in kinetic reactions. However, spectral characterization of individual chemical species is often limited or even unmanageable due to the severe kinetic and spectral overlap among species in kinetic processes. Therefore, we applied, for the first time, multivariate curve resolution-alternating least squares (MCR-ALS) method to EPR time evolving data sets to model and characterize the different constituents in a kinetic reaction. Here we demonstrate the advantage of multivariate analysis in the investigation of radicals formed along the kinetic process of hydroxycoumarin in alkaline medium. Multiset analysis of several EPR-monitored kinetic experiments performed in different conditions revealed the individual paramagnetic centres as well as their kinetic profiles. The results obtained by MCR-ALS method demonstrate its prominent potential in analysis of EPR time evolved spectra.     

Preparation of C8-amine and acetylamine adducts of 2'-deoxyguanosine suitably protected for DNA synthesis

[reaction: see text] C8-Amine and acetylamine adducts of 2'-deoxyguanosine were synthesized. Our approach provides solutions for the coupling of aromatic amines to a protected 8-bromo-2'-deoxyguanosine derivative, for the selective acetylation of the coupled adduct at N(8) and for a protecting group scheme preserving the integrity of the base-labile N(8) acetyl group during DNA synthesis.     

Light‐Driven Water Splitting Mediated by Photogenerated Bromine

Light‐driven water splitting was achieved using a dye‐sensitized mesoporous oxide film and the oxidation of bromide (Br^?) to bromine (Br₂) or tribromide (Br₃^?). The chemical oxidant (Br₂ or Br₃^?) is formed during illumination at the photoanode and used as a sacrificial oxidant to drive a water oxidation catalyst (WOC), here demonstrated using [Ru(bda)(pic)₂], ( 1 ; pic=picoline, bda=2,2′‐bipyridine‐6,6′‐dicarboxylate). The photochemical oxidation of bromide produces a chemical oxidant with a potential of 1.09 V vs. NHE for the Br₂/Br^? couple or 1.05 V vs. NHE for the Br₃^?/Br^? couple, which is sufficient to drive water oxidation at 1 (Ru^V/IV≈1.0 V vs. NHE at pH 5.6). At pH 5.6, using a 0.2 m acetate buffer containing 40 mm LiBr and the [Ru(4,4′‐PO₃H₂‐bpy)(bpy)₂]²⁺ ( RuP ²⁺, bpy=2,2′‐bipyridine) chromophore dye on a SnO₂/TiO₂ core–shell electrode resulted in a photocurrent density of around 1.2 mA cm^?2 under approximately 1 Sun illumination and a Faradaic efficiency upon addition of 1 of 77 % for oxygen evolution.     

AP-MALDI Mass Spectrometry Imaging of Gangliosides Using 2,6-Dihydroxyacetophenone

Matrix-assisted laser/desorption ionization (MALDI) mass spectrometry imaging (MSI) is widely used as a unique tool to record the distribution of a large range of biomolecules in tissues. 2,6-Dihydroxyacetophenone (DHA) matrix has been shown to provide efficient ionization of lipids, especially gangliosides. The major drawback for DHA as it applies to MS imaging is that it sublimes under vacuum (low pressure) at the extended time necessary to complete both high spatial and mass resolution MSI studies of whole organs. To overcome the problem of sublimation, we used an atmospheric pressure (AP)-MALDI source to obtain high spatial resolution images of lipids in the brain using a high mass resolution mass spectrometer. Additionally, the advantages of atmospheric pressure and DHA for imaging gangliosides are highlighted. The imaging of [M–H]^? and [M–H₂O–H]^? mass peaks for GD₁ gangliosides showed different distribution, most likely reflecting the different spatial distribution of GD_1a and GD_1b species in the brain.

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Graphical Abstract ?

     

Mu-28: an open-framework fluorogallophosphate with a three-dimensional 12-membered ring channel system

A new three-dimensional (3-D) microporous fluorogallophosphate, named Mu-28, was obtained by hydrothermal synthesis. It was obtained in the presence of fluoride ions with 1,4-dimethylpiperazine as organic template. This new fluorogallophosphate, with chemical formula [Ga₂₀P₂₀O₈₀(OH)₆F₆(H₂O)₄(C₆H₁₆N₂)₆] 8H₂O, crystallizes in the monoclinic system space group P2₁ with the following unit cell parameters: , , , β=95.10(9)° (Z=1, R₁=0.0435 [I>2σ(I)]). Its structure was determined by single-crystal X-ray diffraction with the help of ³¹P NMR spectroscopy. Mu-28 consists of a complex arrangement of GaO₃(OH,F)(H₂O)₂, GaO₄(OH)F and GaO₄(OH)₂ octahedra, GaO₄F trigonal bipyramids and GaO₃(OH,F) and PO₄ tetrahedra. It displays a 3-D channel system delimited by 12-membered ring openings.     

Palladium-mediated arylation of 3-aminopiperidines and 3-aminopyrrolidines

This paper describes the palladium-catalyzed arylation of 1-substituted 3-aminopyrrolidines or piperidines. Palladium(0) (1-2 mol %) in conjunction with "Buchwald's ligand" [2-(dimethylamino)-2'-(dicyclohexylphosphine)biphenyl] was shown to be the catalyst of choice for the coupling with aryl bromides or chlorides. When bromobenzene was used, a strong temperature effect was noticed. Whereas no reaction occurred at 100 degrees C, yields higher than 85% were obtained at 130 degrees C for each substrate. Such an effect was not observed when diphosphines were used. Whereas Xantphos and, to a lesser extent BINAP, were moderately efficient in the coupling of all diamines, the palladium-mediated arylation in the presence of monophosphines was strongly dependent on the substrate. The results suggest the participation of both nitrogens of the aminoheterocycle in the reactive intermediate. This participation could also account for the highly selective arylation of the endocyclic nitrogen of unsubstituted 3-aminopyrrolidine or piperidine. Optimal conditions were found for the arylation using 2- or 4-substituted electron-poor or enriched aryl halides.     

Redox state switching of transition metals by deprotonation of the tridentate ligand 2,6-bis(imidazol-2-yl)pyridine

The chemistry of the ligand 1, 2,6-bis(imidazol-2-yl)pyridine with manganese, cobalt, nickel and ruthenium has been investigated. The ligand binds as a meridional tridentate ligand as shown by the crystal structures of [Mn(1)2](CF3SO3)2 x Et2O and [Ru(1)2](PF6)2 x 2CH3CN x H2O. The coordinated ligand is deprotonated in mildly basic solution, and this leads to a drop in the metal M(III)/M(II) reduction potential for cobalt and ruthenium of roughly 1.3 V. The crystal structure of Na2(PPN)[Co(1 - 2H)2]2(OH) x MeOH x 2H2O confirms the deprotonation and shows sodium to bind to the deprotonated nitrogen atoms. No stabilisation of the M(III) oxidation state was observed for nickel and manganese.     

Bilan thermique d'un four sous vide comportant un certain nombre d'ecrans

Résumé Nous nous proposons d'indiquer une méthode de calcul facilement programmable permettant de déterminer les variations de température des éléments d'un four sous vide en fonction de la puissance dissipée; les hypothèses faites ont été confirmées par l'application des résultats du calcul à un four construit antérieurement au laboratoire, ce qui nous a permis de prévoir l'amélioration de ses performances.

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An easily programmable means of calculating temperature variations of vacuum furnace elements versus dissipated power is indicated; the hypothesis was tested in the case of a furnace built previously in our laboratory and this helped us in improving its characteristics.

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Zusammenfassung Es wurde eine leicht programmierbare Methode zur Errechnung der TemperaturÄnderungen der Elemente eines Vakuumofens als Funktion der verbrauchten Energie entworfen. Die Hypothese wurde bewiesen durch Anwendung der Rechnungsergebnisse an einem früher in unserem Laboratorium erbauten Ofen, wodurch wesentliche Verbesserung seiner LeistungsfÄhigkeit erreicht werden konnte.

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A new supported reagent for the parallel synthesis of primary and secondary O-alkyl hydroxylamines through a base-catalyzed Mitsunobu reaction

The growing field of applications of O-alkyl hydroxylamines in medicinal chemistry and chemical biology has motivated the search for a parallel synthesis. A solid-phase approach based on the alkylation by alcohols of a new supported N-hydroxyphthalimide reagent using a Mitsunobu reaction followed by methylaminolysis has been optimized. This study points out the importance of the linker and a specific base effect for the Mitsunobu reaction. A large variety of alcohols can be used to give with moderate to high yields diverse O-alkyl hydroxylamines in high purity.