Soluble {[Rh2(μ-OOCCH3)2(dbbpy)2][BF4]}n molecular wire and [Rh2(μ-OOCCH3)2(dbbpy)2L2] complexes; dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine: Synthesis and physicochemical characterization

Binuclear Rh(II) compounds [Rh₂(μ-OOCCH₃)₂(dbbpy)₂(H₂O)₂](CH₃COO)₂ (1) (dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine), [Rh₂(μ-OOCCH₃)₂(dbbpy)₂(H₂O)₂](BF₄)₂·H₂O·CH₃CN (2), [Rh₂(CH₃COO)₂(C₁₈H₂₄N₂)₂(CH₃CN)₂](BF₄)₂·4CH₃CN (3) and {[Rh₂(μ-OOCCH₃)₂(dbbpy)₂][BF₄]}_n (4) have been synthesized and characterized with spectroscopic methods. Structure of complex 3 has been determined using X-ray crystallography. Rhodium atoms in compound 3 have distorted octahedral coordination with O and N atoms in equatorial positions and Rh atom and CH₃CN molecule in axial coordination sites. Reduction of rhodium(II) compounds with aqueous 2-propanol leads to the formation of polymetallic compound {[Rh₂(μ-OOCCH₃)₂(dbbpy)₂][BF₄]}_n (4) containing [Rh₂]³⁺ core. Compound 4 shows strong antiferromagnetic properties, μ = 0.18–1.73 M.B. in the range 1.8–300 K, J = −597 cm⁻¹. Electrochemistry of compounds 3 and 4 in CH₃CN has been investigated. Compound 4 exhibits a poorly reversible oxidation system at E_1/2 = −0.92 V (ΔE_p = 0.19 V) and in solution in DMF is slowly oxidized to 3 even in total absence of oxygen. Complex 3 is irreversibly oxidized to Rh(III) compound at E_pa = 1.48 V and irreversibly reduced at E_pc = −1.02 V to lead to the unstable polynuclear complex 4 in CH₃CN.     

Selectivity optimization in green chromatography by gradient stationary phase optimized selectivity liquid chromatography

Stationary phase optimized selectivity liquid chromatography (SOSLC) is a promising technique to optimize the selectivity of a given separation by using a combination of different stationary phases. Previous work has shown that SOSLC offers excellent possibilities for method development, especially after the recent modification towards linear gradient SOSLC. The present work is aimed at developing and extending the SOSLC approach towards selectivity optimization and method development for green chromatography. Contrary to current LC practices, a green mobile phase (water/ethanol/formic acid) is hereby preselected and the composition of the stationary phase is optimized under a given gradient profile to obtain baseline resolution of all target solutes in the shortest possible analysis time. With the algorithm adapted to the high viscosity property of ethanol, the principle is illustrated with a fast, full baseline resolution for a randomly selected mixture composed of sulphonamides, xanthine alkaloids and steroids.     

A Rigid Dinuclear Ruthenium(II) Complex as an Efficient Photoactive Agent for Bridging Two Guanine Bases of a Duplex or Quadruplex Oligonucleotide

The rigid dinuclear [(tap)₂Ru(tpac)Ru(tap)₂]⁴⁺ complex ( 1 ) (TAP=1,4,5,8‐tetraazaphenanthrene, TPAC=tetrapyridoacridine) is shown to be much more efficient than the mononuclear bis‐TAP complexes at photodamaging oligodeoxyribonucleotides (ODNs) containing guanine (G). This is particularly striking with the G‐rich telomeric sequence d(T₂AG₃)₄. Complex 1 , which interacts strongly with the ODNs as determined by surface plasmon resonance (SPR) and emission anisotropy experiments, gives rise under illumination to the formation of covalent adducts with the G units of the ODNs. The yield of photocrosslinking of the two strands of duplexes by 1 is the highest when the G bases of each strand are separated by three to four base pairs. This corresponds with each Ru(tap)₂ moiety of complex 1 forming an adduct with the G base. This separation distance of the G units of a duplex could be determined thanks to the rigidity of complex 1 . On the basis of results of gel electrophoresis, mass spectrometry, and molecular modelling, it is suggested that such photocrosslinking can also occur intramolecularly in the human telomeric quadruplex d(T₂AG₃)₄.     

(Thio)Amidoindoles and (Thio)Amidobenzimidazoles: An Investigation of Their Hydrogen‐Bonding and Organocatalytic Properties in the Ring‐Opening Polymerization of Lactide

The mechanism of the ring‐opening polymerization (ROP) of lactide catalyzed by two partner hydrogen‐bonding organocatalysts was explored. New amidoindoles 4 a , c , thioamidoindoles 4 b , d , amidobenzimidazoles 5 a , c , and thioamidobenzimidazoles 5 b , c were synthesized and used as activators of the monomer. In the solid state and in solution, compounds 4 and 5 showed a propensity for self‐association, which was evaluated. (Thio)Amides 4 and 5 do catalyze the ROP of lactide in the presence of a cocatalyst, tertiary amine 3 a or 3 b , which activates the growing polymer chain through hydrogen‐bonding. Reactions were conducted in 2–24 h at 20 °C; conversion yields ranged between 22 and 100 %. A detailed study of the intermolecular interactions undertaken between the participating species showed that, as expected, simultaneous weak hydrogen bonds do exist to activate the reagents. Moreover, interactions have been revealed between the partner catalysts 4 / 5 + 3 . ROP catalyzed by these partner activators is thus governed by multiple dynamic equilibria. The latter should be judiciously adjusted to fine‐tune the catalytic properties of (thio)amides and organocatalysts, more generally.     

Moisture driven aging mechanism of LiFePO4 subjected to air exposure

The impact of air exposure on LiFePO₄–C nanocomposites has been investigated at moderate temperature. We show here that the storage in 120 °C hot air for 30 days leads not only to the material delithiation but also to the formation of an amorphous ferric phosphate side-phase, accounting for 38% of the total iron. The formed phase is found to be partially hydrated, suggesting a water-driven aging mechanism and a proposed hypothetic formula: Li_xFePO₄(OH)_x. The side-phase displays new electrochemical activity but poor cyclability and the overall battery performance is thus deteriorated. The regeneration of pristine structure, together with the performance recovery can be achieved by a simple thermal treatment under inert atmosphere.     

Shear induced clay organo‐modification: application to plasticized starch nano‐biocomposites

The present paper reports the successful development of a straightforward clay organo‐modification protocol named “Shear Induced Clay Organo‐modification” process, or SICO. To develop such a fast process, natural montmorillonite has been organo‐modified with cationic starch (surfactant) under shearing. According to the obtained results, this process allows the preparation of a pre‐exfoliated montmorillonite, organo‐modified by cationic starch (OMMT‐CS). Then, the OMMT‐CS has been dispersed into different plasticized starch‐based plastics, varying the polysaccharide botanical source, to obtain nano‐biocomposites displaying an exfoliated morphology. To establish the efficiency of this protocol and highlight this nano‐structuration, uniaxial tensile tests have been performed on these materials. The mechanical properties have been compared with those obtained with nano‐biocomposites elaborated with OMMT‐CS prepared with the conventional and efficient Exfoliation/Adsorption technique. Since comparable properties are obtained, we assume that the SICO process is a powerful technique to easily and quickly organo‐modify the montmorillonite clay and to obtain exfoliated nano‐biocomposites. Copyright © 2009 John Wiley & Sons, Ltd.     

Internal stress influence on the coercivity of FeCuNbSiB thin films

Thin films of Finemet-type alloy with thickness varying from 50 to 1000 nm have been deposited by RF sputtering and annealed at temperature ranging from 150 to 450 °C. Their magnetic and structural properties have been characterized using alternating gradient field magnetometry and X-ray diffraction. In addition, the stress in the films has been measured as a function of temperature from the curvature of the wafers using a laser scanning technique.The coercive field of the films first decreases with annealing temperature due to stress relaxation, and then increases again when crystallisation begins. The optimal annealing conditions comprises between the glass transition and the crystallisation temperature.Its is observed that the coercivity of the as-deposited material is continuously decreasing as the thickness increases, following an inverse square root dependence, in relation with the stress-induced magneto-elastic contribution to the total anisotropy. By opposition, it has been found that the coercive field of devitrified and totally relaxed films is inversely proportional to film thickness. In order to explain this evolution, a model is proposed, based on random anisotropy considerations applied to thin films in which the anisotropy was considered localised in the dimension of thickness.     

Study by ESI‐FTICRMS and ESI‐FTICRMSn of zinc and cadmium thiophenolate complexes used as precursors for the synthesis of II–VI nanosemiconductors

[M₄(SC₆H₅)₁₀][(CH₃)N]₂, [M₁₀L₄(SC₆H₅)₁₆][(CH₃)N]₄ and [Cd₁₇S₄(SC₆H₅)₂₈][(CH₃)N]₂(M = Cd or Zn, and L = S or Se) zinc and cadmium thiophenolates have been studied by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (ESI‐FTICRMS) and tandem ESI‐FTICRMS (ESI‐FTICRMSⁿ). ESI‐FTICRMS demonstrated its ability to characterize and study such compounds, which may be used as precursors of II–VI nanomaterials. The obtained mass spectrum has been found to be highly relevant of the investigated thiophenolate and the fragmentation behavior of some of the detected ions is indicative of its stability. More specifically, it has been demonstrated that ESI in‐source activation or fragmentation experiments conducted in the Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) cell induced the formation of a very stable entity, which corresponds to the general formula M₄L₄ (M = Zn or Cd and L = S or Se). The elimination of SC₆H₅^? and/or M(SC₆H₅)₂ moieties by various activation processes from the studied thiophenolates led systematically to this structure. Copyright © 2009 John Wiley & Sons, Ltd.     

Tunability of the optical properties in the Y6(W,Mo)(O,N)12 system

New fluorite-type solid solution domains have been evidenced in the system Y₆(W,Mo)(O,N)₁₂ using precursors prepared by the amorphous citrate route. The oxynitrides as well as the low temperature oxides (600 °C) crystallize in a cubic-type symmetry while the oxides annealed above 1200 °C exhibit a rhombohedral symmetry. Either cationic (W/Mo) or anionic (O/N) substitutions bring the possibility to tune the optical absorption of the yttrium tungstate Y₆WO₁₂, which potential as inorganic UV absorbers is discussed.