Structural and electronic comparative analysis of aminopyridazines showing anti-GABA activity. Crystal structure of 2-(carboxy-3′-propyl)-3-amino-6-cyclohexylpyridazinium bromide.Ab initio Mulliken population analysis of the 6-phenyl-substituted analog compared to GABA

The crystal structure of 2-(carboxy-3-propyl)-3-amino-6-cyclohexylpyridazinium bromide has been determined by single-crystal X-ray diffraction techniques and refined by full-matrix least squares. The compound crystallized in the tri-clinic space groupP ¯1 witha=10.275(1),b=11.215(1),c=7.082(1) Å,=91.84(1),=102.21(1), =106.77(1)°, andZ=2. FinalR-factor is 0.045. The main structural results are very similar to the ones observed for the 6-phenyl analog. These two compounds are GABA-A antagonists.Ab initio molecular orbital calculations, with STO-3G and 4-31G basis sets, suggest that the exocyclic nitrogen accurately mimics the nitrogen atom of GABA.     

Structure (x-ray analysis) of Manicoline B,a mixture of two diastereoisomers of a new alkaloid from dulacia guianensis (olacaceae)

Manicoline B, isolated from the root bark of $\text{Dulacia guianensis}$ (Olacaceae), was shown by X-ray analysis to be an equimolecular mixture of two diastereoisomers of a new alkaloid and to have structure (3).     

Optimization of a nitrogen analyser based on the Dumas method

The objectives of this work was to obtain a total nitrogen concentration in milk with the Dumas method for industrial and research applications. This method was faster than the Kjheldal method (5 min against 2 h or 3 h) but less precise. A three factor experimental design was performed to optimize the instrument, a FP-2000 supplied by LECO. The first interpretation of the experimental design was disappointing and no conclusion could be done. It was not a failure of experimental design but a lack of thinking on the physical and chemical aspect of the problem. Selection and construction of composite responses based on chemical and physical consideration were the keys to optimize the Dumas method. This method is now as precise as the Kjheldal method, but considerably faster.     

Disorder effects in Mn12–acetate at 83 K

The structure of hexadeca‐μ‐acetato‐tetra­aqua­dodeca‐μ₃‐oxo‐dodecamanganese bis(acetic acid) tetrahydrate, [Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄]·2CH₃COOH·4H₂O, known as Mn₁₂–acetate, has been determined at 83 (2) K by X‐ray diffraction methods. The fourfold (S₄) molecular symmetry is disrupted by a strong hydrogen‐bonding interaction with the disordered acetic acid mol­ecule of solvation, which displaces one of the acetate ligands in the cluster. Up to six Mn₁₂ isomers are potentially present in the crystal lattice, which differ in the number and arrangement of hydrogen‐bonded acetic acid mol­ecules. These results considerably improve the structural information available on this molecular nanomagnet, which was first synthesized and characterized by Lis [Acta Cryst. (1980), B 36 , 2042–2046].     

MIL-50, an open-framework GaPO with a periodic pattern of small water ponds and dry rubidium atoms: a combined XRD,NMR, and computational study

A new fluorinated gallium phosphate, MIL-50, has been synthesized under mild hydrothermal conditions using 1,6-diaminohexane. The chemical formula of MIL-50 is Rb(2)Ga(9)(PO(4))(8)(HPO(4))(OH)F(6).2N(2)C(6)H(18).7H(2)O. The structure is a network of hexameric units of Ga(3)(PO(4))(3)F(2) and Ga(3)(PO(4))(2)(HPO(4))F(3) via corner sharing. It creates a three-dimensional open-framework delimiting 6- and 18-ring channels running along the c axis. The diprotonated 1,6-diaminohexane and water molecules are trapped within the 18-ring pores, whereas the rubidium cations reside in the 6-ring ones. A double quantum (31)P NMR experiment and partial charge calculations indicate that water molecules are present under the form of periodic small clusters, lowering the multiplicity of one phosphorus site, P3. Though water hops within the clusters, the motion leaves the water pattern periodic. Rubidium is so tightly embedded into the framework that water moving in the large 18-ring channels does not reach it, leaving it therefore dry. The crystal framework may be ascribed to the orthorhombic space group Cmc2(1) (n degrees 36), a = 32.1510(2), b = 17.2290(3), c = 10.2120(1) A. The periodic water pattern has a different symmetry than that of the framework. A method has been devised to superpose the two sublattices that coexist in the same unit cell in order to have full occupancy of each site and to perform Madelung summations. This original method is of general interest for most zeolitic materials exhibiting a different symmetry for the framework and the template sublattices.     

A β-glucosidase from Sclerotinia sclerotiorum

The filamentous fungus Sclerotinia sclerotiorum, grown on a xylose medium, was found to excrete one β-glucosidase (β-glu x). The enzyme was purified to apparent homogeneity by ammonium sulfate precipitation, gel filtration, anion-exchange chromatography, and high-performance liquid chromatography (HPLC) gel filtration chromatography. Its molecular mass was estimated to be 130 kDa by HPLC gel filtration and 60 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that β-glu x may be a homodimer. For p-nitrophenyl β-d-glucopyranoside hydrolysis, apparent K _m and V _max values were found to be 0.09 mM and 193 U/mg, respectively, while optimum temperature and pH were 55–60°C and pH 5.0, respectively. β-Glu x was strongly inhibited by Fe²⁺ and activated about 35% by Ca²⁺. β-Glu x possesses strong transglucosylation activity in comparison with commercially available β-glucosidases. The production rate of total glucooligosaccharides (GOSs) from 30% cellobiose at 50°C and pH 5.0 for 6 h with 0.6 U/mL of enzyme preparation was 80 g/L. It reached 105 g/L under the same conditions when using cellobiose at 350 g/L (1.023 M). Finally, GOS structure was determined by mass spectrometry and ¹³C nuclear magnetic resonance spectroscopy.     

Koordinative Verankerung von Nickelkomplexen an Hectorit-Schichtsilicaten mit Hilfe langkettiger Diphenylphosphinogruppen

Coordinative Anchoring of Nickel Complexes on Hectorite-Layer Silicates through long-chain Diphenylphosphine Groups The treatment of sodium and calcium hectorites with 2-diphenylphosphinoethyltriethoxysilane leads, by condensation of free hydroxyl groups, to functionalized layer silicates with long-chain diphenylphosphine groups onto which nickel chloride can be coordinated. In these modified hectorites the fourth coordination site of the tetrahedrally coordinated nickel is occupied by a labile solvent molecule. On the other hand, the complex bis(2-diphenylphosphinoethyltriethoxysilane)nickel(II) chloride prepared beforehand also reacts with sodium hectorite under condensation; but the square-planar coordination of the four stable ligands (two chloride and two phosphor atoms) is maintained. This finds its expression in a significant activity decrease in catalytic reactions as compared to the aforementioned products.     

Electroactive ligands: the first metal complexes of tetrathiafulvenyl-acetylacetonate

The reaction of tris(alkylthio)tetrathiafulvalene thiolates with 3-chloro-2,4-pentanedione affords tetrathiafulvalene (TTF) moieties substituted by the acetylacetone function (TTFSacacH), precursors of novel redox-active ligands: the acetylacetonate ions (TTFSacac). These TTFSacacHs have been characterized by X-ray diffraction analyses, and similar trends have been observed, such as a TTF core almost planar and the acetylacetone substituent located in a plane almost perpendicular to the plane formed by the TTF core. Their chelating ability has been demonstrated by the formation of the corresponding M(TTFSacac)2(pyridine)2 complexes in the presence of M(II)(OAc)2.H2O (M = Ni2+, Zn2+). These complexes with TTFSacac moieties, Ni(TTFSacac)2(pyridine)2, 6b, and Zn(TTFSacac)2(pyridine)2, 7b, have been characterized by X-ray diffraction analyses, showing in all structures the metal(II) center chelated by two TTFacac units in the equatorial plane and the octahedral coordination geometry around the metal completed by two axial pyridine ligands. Cyclic voltammetry and UV-visible-near infrared spectroscopic measurements have evidenced a sizable interaction between the two electroactive ligands and the stabilization of a mixed-valence state in the one-electron oxidized complexes.     

Can the presence of chemically inert species modify the face selectivity in asymmetric induction by cyclodextrins?

Reduction of-cyclodextrin (-CD) aromatic ketone (acetophenone and acetonaphthones) inclusion compounds were carried out in the presence of a large number of chemically inert species as potential co-guests. In several cases, it was observed that stoichiometric molar ratios of these compounds to ketone significantly modify the chiral induction yielding the inverted alcohol enantiomer and increasing the face selectivity. The results were found to depend strongly on the respective structure and shape of both the ketone and the additive, and on the molar ratio of-CD:ketone:third compound. These observations suggest the formation of a three-component inclusion complex in which the geometry of binding of the substrate and its mobility are changed with respect to the binary system.     

Numerical Study of Pore Sizes Distribution in Gels

We introduce a new numerical technique for the calculation of the pore size distribution in two-dimensional disordered systems. Our method is based on a triangulation technique which allows a closer measurement of pores surface without any morphological hypothesis.In this work, we focus our calculations in simulated gels. Such materials are modeled in two different conditions: by means of the Diffusion-Limited and Reaction-Limited Cluster-cluster Aggregation algorithms, DLCA and RLCA, respectively. In both situations, when the particles concentration decreases, the average pores size increases. The more compact cluster in RLCA, compared with DLCA, is consistent with the pore size distribution we have calculated. The simulated mean pore size is quantitatively in agreement with experimental data from literature.