Thermal properties and reactions towards nucleophiles of an iron complex displaying an acetyl and a pyruvoyl ligands

Thermal evolution at 4 °C of the structurally characterized cis(CO)₄Fe[C(O)C(O)CH₃][C(O)CH₃] (1(2)) gives rise to the cis(CO)₄Fe[C(O)CH₃]₂ (1(3)) which, probably owing to synthetic problems, has never been described in the literature. By reaction with anionic nucleophiles (Nu⁻), 1(2) affords anionic trifunctionalized metallalactones {(CO)₃Fe[C(O)CH₃][C(O)C(CH₃)(Nu)OC⁷(O);(Fe-C⁷)]}⁻ (3) formed by addition of the nucleophile reagent on the β carbon of the pyruvoyl moiety followed by the cyclization of this ligand on a terminal carbonyl of the complex. Anions 3 are characterized by ¹H and ¹³C NMR and by X-ray diffraction for the complex with Nu = C(H)(CO₂C₂H₅)₂. Complexes 3 are also prepared by reaction of CH₃Li with the neutral metallalactones (CO)₄Fe[C(O)C(CH₃)(Nu)OC⁷(O);Fe-⁷C] (2). The results of this study shed light on the reaction of cyclization of a pyruvoyl ligand as they clearly show that the presence of a second ligand (for example CO₂R) with a labile OR group is not required to perform the formation of the metallalactone ring and then that the observed reaction has no connection with organic chain-ring transformations.     

Détermination de la résonance de Bragg et des largeurs des bandes interdites par le modèle d'onde plane corrigéDetermination of the Bragg resonance and line width of forbidden bands using the corrected plane wave model

During the interaction of the swell with a sea bottom composed of a set of steps, using the model of plane wave corrected by the effective length: (1) We determine the exact position of the Bragg resonance in case of a periodic bottom or containing a periodic part; (2) The determination of forbidden band widths is brought back to the study of the sign of the discriminant of the polynomial characteristic of the matrix of transfer of the generating motive of the periodic part of the bottom; (3) One can increase the width of the forbidden band while using some slightly increasing or decreasing length steps. To cite this article: S. Naasse et al., C. R. Mecanique 331 (2003).     

Syntheses and Structures of Acetyl‐Acetonato‐Alumo‐Diphenylsilanolates with Magnesium(II), Iron(II), Iron(III), Cobalt(II), and Nickel(II)

Bis(acetylacetonate)alumo‐oxo‐tetraphenyldisiloxane‐metal(II) dihydrates [(acac)₂Al(O–SiPh₂–O–SiPh₂–O)]₂M(H₂O)₂ (M = Mg, Fe, Co, Ni) were obtained from the corresponding acetyl‐acetonate‐dihydrates (acac)₂M(H₂O)₂ by reaction with the alumosiloxane [O–Ph₂Si–O–SiPh₂–O]₄Al₄(OH)₄. These new compounds display two acac ligands at the aluminum atoms as well as disilatrioxy chains linking the two aluminum atoms forming a (Al–O–Si–O–Si–O)₂ cycle (X‐ray structure analyses). Within this cycle the divalent metal ions M²⁺, to which two water molecules in trans positions are linked, are installed in almost planar MO₄ coordination spheres. Using water free (acac)₂Ni a different product forms: both reactants combine in a 2:1 ratio to yield [O–Ph₂Si–O–SiPh₂–O]₄Al₄(OH)₂O(OH₂)Ni₂(acac)₄. Here, three of the acac ligands were transposed to the aluminum atoms. The nickel atoms are in a distorted octahedral coordination mode from oxygen atoms of the ligands. When iron(III)tris(acetylacetonate) reacts with the alumosiloxane [O–Ph₂Si–O–SiPh₂–O]₃Al₂O(OH)Fe₂(acac)₃ was isolated, in which the two iron atoms still display one of the acac ligands. One of the aluminum atoms is in a tetrahedral oxygen environment, whereas the other is in the center of a trigonal bi‐pyramid formed of oxygen atoms either of the siloxane or of acac. The iron atoms have five‐ or sixfold coordination from oxygen atoms of siloxane, acac, hydroxide or oxide.     

Cytotoxic and Antioxidant Activities of Imine Analogs of Trans-Resveratrol towards Murine Neuronal N2a Cells

Trans-resveratrol is a natural polyphenol showing numerous biological properties, especially anti-tumoral and antioxidant activity. Among numerous resveratrol derivatives, aza-stilbenes, which bear an imine bound, show interesting biological activities. In the present study, we synthesized a series of imine analogs of trans-resveratrol (seven aza-stilbenes) following an easy and low-cost procedure of green chemistry. The toxicity of synthesized aza-stilbenes, which is currently unknown, was evaluated on murine neuronal N2a cells, comparatively to trans-resveratrol, by considering: cell density evaluated by staining with sulforhodamine 101; esterase activity, which is a criteria of cell viability, by staining with fluorescein diacetate; and transmembrane mitochondrial potential, which is known to decrease during cell death, by staining with DiOC₆(3) using flow cytometry. In addition, the antioxidant activity was quantified with the KRL (Kit Radicaux Libres) assay, the DPPH (2,2′-diphenyl-1-picrylhydrazyl radical) assay and the FRAP (ferric reducing antioxidant power) assay. The PAOT (Pouvoir Antioxidant Total) score was also used. The aza-stilbenes provide different cytotoxic and antioxidant activities, which are either higher or lower than those of trans-resveratrol. Based on their cytotoxic and antioxidant characteristics, all synthesized aza-stilbenes are distinguished from trans-resveratrol.     

A competitive transport across polymeric membranes. Study of complexation and separation of ions

The removal and separation of Cu(II), Zn(II) and Ni(II) from nitrate aqueous solutions were studied by competitive transport across cellulose triacetate plasticized membranes modified with polyelectrolytes: polyethyleneimine (PEI) and polyethyleneglycol (PEG). Competitive transport of trace ions from aqueous solutions across polymer inclusion membranes containing a mixture of the three polymers (cellulose triacetate as the support) and tris(2-ethylhexyl-phosphate) (TEHP) as the plasticizer provide the selectivity order: Cu(II) > Ni(II) > Zn(II). A long-term transport experiment was carried out to demonstrate the durability of polymer inclusion membranes. A separation of bivalents cations (Cu²⁺, Ni²⁺, Zn²⁺) and monovalent cations (K⁺ and Na⁺) is achieved.     

Catalytic oxidation of α-pinene by transition metal using t-butyl hydroperoxide and hydrogen peroxide

The allylic oxidation of α-pinene 1 was investigated using various catalytic systems. By a proper choice of the latter, the reaction can be directed toward the selective synthesis of verbenol 2 or verbenone 3. High yield into verbenone was achieved under mild conditions with copper salts as catalysts and t-butyl hydroperoxide (TBHP) as oxidant. On the other hand, when Pd(acac)₂ was used with hydrogen peroxide, verbenol was obtained as the main product.     

POSITIVE SOLUTIONS FOR SINGULAR BVPs ON THE POSITIVE HALF-LINE ARISING FROM EPIDEMIOLOGY AND COMBUSTION THEORY

In this work,we are concerned with the existence and multiplicity of positive solutions for singular boundary value problems on the half-line.Two problems from epidemiology and combustion theory set on...     

Photocatalytic degradation of ammonia and butyric acid in plug-flow reactor: Degradation kinetic modeling with contribution of mass transfer

Photocatalytic treatment of polluted air by odorous contaminants – ammonia and butyric acid – is investigated in a plug-flow reactor covered by non-woven fiber textile coated with TiO₂. For the first time, the single-component degradation pathway of ammonia by photocatalysis at ambient condition is highlighted. It appears fundamentally different compared to the butyric acid degradation pathway. The ammonia degradation pathway highlights a possible auto-accelerated behavior of the reaction. The chemical degradation kinetics follows the Langmuir–Hinshelwood model, though observed oxidation rates depend upon flow conditions in the reactor. Thus, interpretation of degradation results through a model considering the Langmuir–Hinshelwood approach and mass transfer phenomenon is presented. This model succeeds with a pair of determined kinetic constants and mass transfer coefficients to describe experimental results for different flow rates and for both pollutants, though they present wide dissimilarities in their degradation pathways.