The first structural characterisation of a group 2 metal alkylperoxide complex: comments on the cleavage of dioxygen by magnesium alkyl complexes

A new high-yield synthesis of [(PhCH(2))(2)Mg(thf)(2)] and [[(PhCH(2))CH(3)Mg(thf)](2)] via benzylpotassium has allowed a simple entry into benzylmagnesium coordination chemistry. The syntheses and X-ray crystal structures of both [(eta(2)-Me(2)NCH(2)CH(2)NMe(2))Mg(CH(2)Ph)(2)] and [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] (Ar'=2,6-diisopropylphenyl) are reported. The latter beta-diketiminate complex reacts with dioxygen to provide a 1:2 mixture of dimeric benzylperoxo and benzyloxo complexes. The benzylperoxo complex [[eta(2)-HC[C(CH(3))NAr'](2)Mg(mu-eta(2):eta(1)-OOCH(2)Ph)](2)] is the first example of a structurally characterised Group 2 metal-alkylperoxo complex and contains the benzylperoxo ligands in an unusual mu-eta(2):eta(1)-coordination mode, linking the two five-coordinate magnesium centres. The O[bond]O separation in the benzylperoxo ligands is 1.44(2) A. Reaction of the benzylperoxo/benzyloxo complex mixture with further [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] results in complete conversion of the benzylperoxo species into the benzyloxo complex. This reaction, therefore, establishes the cleavage of dioxygen by this system as a two-step process that involves initial oxygen insertion into the Mg[bond]CH(2)Ph bond followed by O[bond]O/Mg[bond]C sigma-bond metathesis of the resulting benzylperoxo ligand with a second Mg[bond]CH(2)Ph bond. The formation of a 1:2 mixture of the benzylperoxo and benzyloxo species indicates that the rate of the insertion is faster than that of the metathesis, and this is shown to be consistent with a radical mechanism for the insertion process.     

Comportement électrochimique des faces vicinales de Au(111) ; surfaces à marches {111}

Electrochemical behaviour of the Au(111) vicinal faces; {111} stepped surfaces. The Au(332) and Au(776) facets forming on Au(554) and Au(775) faceted vicinal faces have different electrochemical behaviours. The electrochemical study in NaF solutions of the Au(776) face reveals that the whole of the {111} steps of an Au(776) surface have the same electrochemical behaviour as the Au(332) face. On the other hand, the (111) terraces of Au(776) behave differently from the large (111) terraces of an Au(111) single-crystal electrode. The atomic reconstruction of the (111) terraces of the Au(776) facets, observed by vacuum STM, completely disappears in contact with the solution, whereas the reconstruction of the wide (111) terraces of a Au(111) single-crystal does not disappear completely. Measurements of the differential capacity C(E) also showed that faceted or non-faceted surfaces of Au(554) and Au(775) faces had the same electrochemical behaviour. This implies that non-faceted surfaces consist of Au(332) and Au(111)(1 × 1) domains that have independent electrochemical behaviours.     

The regularity of the Stokes operator and the Fujita-Kato approach to the Navier-Stokes initial value problem in Lipschitz domains

We study the regularity of the Navier-Stokes equations in arbitrary Lipschitz domains.     

Singlet oxygen in microporous silica xerogel: quantum yield and oxidation at the gas-solid interface.

The quantum yields of singlet oxygen ((1)O(2)) production (Phi(Delta)) and (1)O(2) lifetimes (tau(Delta)) at the gas-solid interface in silica gel material are determined. Different photosensitizers (PS) are encapsulated in parallelepipedic xerogel monoliths (PS-SG). PS were chosen according to their known photooxidation properties: 9,10-dicyanoanthracene (DCA), 9,10-anthraquinone (ANT), and a benzophenone derivative, 4-benzoyl benzoic acid (4BB). These experiments are mainly based on time-resolved (1)O(2) phosphorescence detection, and the obtained Phi(Delta) and tau(Delta) values are compared with those of a reference sensitizer for (1)O(2) production, 1H-phenalen-1-one (PN), included in the same xerogel. The trend between their ability to oxidize organic pollutants in the gas phase and their efficiency for (1)O(2) production is investigated through photooxidation experiments of a test pollutant dimethylsulfide (DMS). The Phi(Delta) value is high for DCA-SG relative to the PN reference, whereas it is slightly lower for 4BB-SG and for ANT-SG. Phi(Delta) is related to the production of sulfoxide and sulfone as the main oxidation products for DMS photosensitized oxidation. Additional mechanisms, leading to C--S bond cleaveage, appear to mainly occur for the less efficient singlet oxygen sensitizers 4BB-SG and ANT-SG.     

Characterization of Composite Networks Made of Type I Collagen,Hyaluronic Acid and Decorin

Summary: To ultimately assess the ability of macromolecular medicines e.g. liposomes, non viral gene delivery systems, to penetrate one of the least studied physiological barriers, the extracellular matrix (ECM), composite networks made of different ECM components i.e. type I collagen, hyaluronic acid and a proteoglycan, decorin, were prepared. These composite networks were characterized by rheology, Confocal Reflection Microscopy, Fluorescence Recovery After Photobleaching and Transmission Electron Microscopy. While being at the low end of its physiological concentration, collagen appears to be the backbone of the composite networks as it provides the elastic modulus. On the other hand, 15 kDa and 1.1 MDa hyaluronic acid, when present at physiological levels interpenetrate the collagen network. When approaching their overlap concentration, hyaluronic acid chains lead to an increase of the population of collagen fibrils. Finally, while decorin increased the population of fibrils in pure collagen networks, its role in presence of hyaluronic acid remains unclear as it does not alter the diameter of fibrils nor their population.     

Electropolymerization of [Ru(bpy)(CO)2Cl2] (bpy=2,2′-bipyridine: a revisited trans versus cis(Cl) isomeric influence study

The mono-bipyridine bis carbonyl complex [Ru(bpy)(CO)₂Cl₂] exists in two stereoisomeric forms having a trans(Cl)/cis(CO) (1) and cis(Cl)/cis(CO) (2) configuration. In previous work we reported that only the trans(Cl)/cis(CO) isomer 1 leads by a two-electron reduction to the formation of [Ru(bpy)(CO)₂]_n polymeric film on an electrode surface. This initial statement was overstated, as both isomers allowed the build up of polymers. A detailed comparison of the electropolymerization of both isomers is reported here, as well as the reduction into dimers of parent stereoisomer [Ru(bpy)(CO)₂(C(O)OMe)Cl] complexes 3 and 4 obtained as side products during the synthesis of 1 and 2.