Etude structurale d'un nouveau tellurate alcalin: Na2TeO4. Evolution de la coordination du tellure(VI) et du cation quand on passe du cation lithium au sodium

Single crystal Na₂TeO₄ has been prepared by hydrothermal synthesis and its structure determined from three dimensional X-ray analysis. The crystal is monoclinic, space group $\text{P}\text{P2}{}_1\text{c}$ with a = 10.632(5)Å, b = 5.161(2)Å; c = 13.837(11)Å, and β = 103.27(4)°. The crystal structure is built up of chains of Te(VI)O₆ octahedra parallel to the [010] axis which can be formulated as [TeO₄]_n^2n?. All sodium cations are in very distorted octahedral coordination.     

Force de la liaison Te-O: Coordination et localisation de la paire libre de l'atome de tellure IV dans les tellurites

The calculation of bond valences (S) from the bond lengths (R) observed in many accurate structure determinations of tellurites, Te^IV, using the relation S = S₀(R/R₀)^?N allows us to refine the R₀ and N values proposed by Brown. If we classify the different TeO_y surroundings by taking into account the three strongest bond valences in their relation to the weakest ones, it can be verified that the observed variation allows us to foresee the atomic coordination of tellurium IV atom with respect to the other components of the structure. On the other hand, the probable location of the lone pair 5s² of tellurium IV atom can be related to the evolution of its coordination.     

Sur les chalcogeno-iodures d'antimoine SbXI(X =S,Se, Te): Structures et spectroscopie Mo¨ssbauer de121Sb

The crystal structure of SbXI(X =Se, Te) compounds has been determined by means of three-dimensional intensity data. The crystal structure of SbSeI, orthorhombic, space groupPnma witha = 8.698(2), b = 4.127(1), c = 10.412(2) Å, was refined at several temperatures (180 K,R = 0.021; 293 K,R = 0.020; 320 K,R = 0.023) in correlation with the paraelectric structure or SbSI stable above 293 K. The crystal structure of SbTeI, triclinic, space groupP1¯, witha = 7.570(3), b = 7.159(3), c = 4.228(3) Å, α = 107.22(5), β = 106.18(4), γ = 77.19(3)° has been determined by symbolic addition method and refined to a finalR value of 0.035. These structures are built up from infinite weakly linked ribbons (SbX₂)_n of trigonal SbX₃ with SbX bonds of 2.605(1), 2.795(1)Å(X =Se), and 2.829(1), 2.953(1), 2.955(1)Å(X =Te). The nature of SbX and SbI bonds is discussed in terms of the S, Se, Te substitution. Antimony-121 Mo¨ssbauer spectra have been recorded at liquid helium temperature. The data are discussed with regard to the stereochimical activity of the antimony (III) lone pair of electrons. For SbTeI the Mo¨ssbauer parameters are interpreted in terms of direct population of conductance bands by nonbonding electron pairs.     

Determination of chemical shift anisotropy tensors of carbonyl nuclei in proteins through cross-correlated relaxation in NMR.

The principal components and orientations of the chemical shift anisotropy (CSA) tensors of nearly all 13C carbonyl nuclei in a small protein have been determined in isotropic solution by a combination of three complementary cross-correlation measurements.     

Synthesis and Electrochemical Characterization of a New Electropolymerizable Hydrophilic Viologen Designed for Enzyme Wiring

A new viologen derivative functionalized by an electropolymerizable pyrrole group via a long hydrophilic spacer has been synthesized. This redox monomer has been electrochemically characterized both for its presence in organic and in aqueous media. Its electrooxidation in both solvents leads to the formation of a polymeric film exhibiting the regular electrochemical behaviour of the viologen groups. The electropolymerization process was applied to the immobilization of isocitrate dehydrogenase as an enzyme model. An electrical connection between the redox polymer and the immobilized enzyme molecules has been observed in the presence of oxoglutarate and CO₂.     

Docking macromolecules with flexible segments

We address a major obstacle to macromolecular docking algorithms by presenting a new method that takes into account the induced conformational adjustment of flexible loops situated at a protein/macromolecule interface. The method, MC2, is based on a multiple copy representation of the loops, coupled with a Monte Carlo conformational search of the relative position of the macromolecules and their side chain conformations. The selection of optimal loop conformations takes place during Monte Carlo cycling by the iterative adjustment of the weight of each copy. We describe here the parameterization of the method and trials on a protein-DNA complex of known 3-D structure, involving the Drosophila prd paired domain protein and its target oligonucleotide Wenqing, X. et al., Cell 1995, 80, 639. We demonstrate that our algorithm can correctly configure and position this protein, despite its relatively complex interactions with both grooves of DNA.     

Lipid A components from Pseudomonas aeruginosa PAO1 (serotype O5) and mutant strains investigated by electrospray ionization ion-trap mass spectrometry

The lipid A components of the Pseudomonas aeruginosa strains PAO1 (wild-type) and derived mutants PAO1 algC::tet and PAO1 PDO100 were isolated after mild acetic acid hydrolysis of LPS. Their structural heterogeneities were characterized using electrospray ionization (ESI) ion-trap mass spectrometry (MS) with direct infusion in the negative ion mode without prior derivatization. The ESI-mass spectra revealed monophosphorylated molecules corresponding to known tetra-, penta- and hexaacylated structures of P. aeruginosa lipid A. The MS/MS fragmentation patterns allowed the location of fatty acyl chains on the disaccharide backbone of lipid A. In addition, a hexaacylated lipid A containing a hexadecanoyl chain was detected for the first time in strain P. aeruginosa PAO1. With multiple stages of fragmentation (MS(n)), the position of this hexadecanoyl chain O-linked to the decanoyl chain at the C-3(') position of the glucosamine backbone was determined. This sensitive method is suitable to reveal lipid A heterogeneity, i.e. the nature, number and distribution of acyl chains, without prior lipopolysaccharide purification. The lipid A from mutant strains were also characterized and significant differences were shown in the abundance of monophosphorylated lipid A components between the wild-type and the mutant strains.     

Multi-residue method for the determination of thyreostats in urine samples using liquid chromatography coupled to tandem mass spectrometry after derivatisation with 3-iodobenzylbromide

Thyreostats are banned compounds in Europe since 1981 (directive 81/602/EC) because of their carcinogenic and teratogenic properties. The control of their illegal use in breeding animals is amongst the most difficult because of their low molecular weight, high polarity and the existence of tautomeric forms. The analytical procedure described in this paper involves, after a derivatisation step with 3-iodobenzylbromide, the detection and identification at low level (microg/L) by LC-ESI(-)-MS/MS of eight thyreostats in various biological matrices (urine, muscle, liver, thyroid, animal feed, faeces and hair). The urine method has been validated according to the EU criteria (2002/657/EC decision): CCalpha and CCbeta were found in the range (0.1-5.2 microg/L) and (2.6-23.2 microg/L), respectively. The performances fulfil the requirements of the EU regarding the provisional minimum required performance limit (MRPL) fixed at 100 microg/L in urine.     

Ruthenium-catalyzed [2 + 2] cycloadditions of ynamides

Ruthenium-catalyzed [2 + 2] cycloadditions between norbornene and ynamides were investigated. The ynamide moiety was found to be compatible with the ruthenium-catalyzed cycloaddition conditions, giving the corresponding cyclobutene cycloadducts in moderate to good yields (up to 97%). [reaction: see text]     

Structure Cristalline du Sulfure d'Étain(II) et de Thallium(I) Tl2Sn2S3

Crystal Structure of Tl₂Sn₂S₃ The compound Tl₂Sn₂S₃ had been prepared from SnS? Tl₂S mixtures. The cell is monoclinic, space group C2/c with a = 13.887(7), b = 7.742(4), c = 7.267(4) Å, β = 105.39(3)° and Z = 4. The structure was solved by the symbolic addition method and refined by least-squares to a final R = 0.086 for the 382 observed reflections. From this structure it is apparent that Tl₂Sn₂S₃ is of defect NaCl type with the thallium and tin atoms distributed over the cation positions, the sulfur atoms and vacancies over the anion positions. Tl and Sn atoms have four bonds to S atoms of 2.81–3.13 Å and 2.68–3.11 Å respectively. The thallium and tin lone pairs of electrons are stereochemically active.