Polyoxometalate Derivatives with Multiple Organic Groups. 3. Synthesis and Structure of Bis(phenyltin) Bis(decatungstosilicate), [(PhSnOH(2))(2)(gamma-SiW(10)O(36))(2)](10)(-)

A new phenyltin tungstosilicate derivative, [(PhSnOH(2))(2)(gamma-SiW(10)O(36))(2)](10)(-) (1), has been prepared by reaction of phenyltin trichloride with K(8)[gamma-SiW(10)O(36)].xH(2)O. The new heteropolyanion was characterized by elemental analysis, infrared spectroscopy, multinuclear NMR, and X-ray crystallography. The crystals of Cs(9)H[(PhSnOH(2))(2)(gamma-SiW(10)O(36))(2)].16H(2)O (Cs salt of 1) are triclinic, space group P&onemacr;, with lattice constants a = 12.401(3) ?, b = 13.832(3) ?, c = 16.313(3) ?, alpha = 96.17(2) degrees, beta = 109.73(2) degrees, gamma = 97.13(2) degrees, V = 2579.9(10) ?, and Z = 1. Anion 1 has a structure of virtual C(2)(h)() symmetry with two phenyltin groups sandwiched between two gamma-SiW(10) groups. Such a structure is different from all previously reported polytungstates derived from [gamma-SiW(10)O(36)](8)(-) lacunary anions.     

Modelling effects of subgrid-scale mixture fraction variance in LES of a piloted diffusion flame

A posteriori analysis of the statistics of two large-eddy simulation (LES) solutions describing a piloted methane–air (Sandia D) flame is performed on a series of grids with progressively increased resolution reaching about 10.5 million cells. Chemical compositions, density and temperature fields are modelled with a steady flamelet approach and parametrised by the mixture fraction. The difference between the LES solutions arises from a different numerical treatment of the subgrid scale (SGS) mixture fraction variance – an important quantity of interest in non-premixed combustion modelling. In the first case (model I), the variance transport equation is solved directly, while in the second (model II), an equation for the square of the mixture fraction is solved, and the variance is computed from its definition. The comparison of the LES solutions is based on the convergence properties of their statistics with respect to the turbulence resolution length scale. The dependence of the LES statistics is analysed for velocity and the mixture fraction fields, and tested for convergence. For the most part, the statistics converge for the finest grids, but the variance of the mixture fraction shows some residual grid dependence in the high-gradient regions of the jet near field. The SGS variance given by model I exhibits realisability everywhere, whereas in regions of the flame model II is non-realisable, predicting negative variances. Furthermore, the LES statistics of model I exhibit superior convergence behaviour.     

Is there a unique consistent theory of quantum gravity?

Superstrings have been proposed as a quantum-theoretical framework for unifying all the fundamental forces, including gravity. We consider the question of whether there might be more general supersymmetric possibilities, based on higher extended objects such as membranes, jellies, etc. We argue that all the possible extended objects in all possible spacetime dimensions are quantummechanically inconsistent except for the 10-dimensional superstring and the 11-dimensional supermembrane. These are also the only two such theories that contain massless gravitons and, thus, that can describe gravity at low energies. It is remarkable that the range of possibilities can be narrowed down to this extent. Whether these can be further narrowed down to just one consistent theory remains open to further research.This essay received the first award from the Gravity Research Foundation for the year 1988.-Ed.     

The structures and thermal decomposition of cupric mono,di and trichloracetates

Magnetic moment measurements and ultra-violet diffuse reflectance spectroscopy have been used to investigate the structure of the chloroacetates of copper(II). These studies indicate that cupric monochloroacetate dihydrate is dimeric and cupric trichloracetate tetrahydrate is monomeric. Cupric dichloracetate tetrahydrate forms an intermediate case. The thermal decomposition of these compounds under nitrogen has been studied using thermogravimetry and differential thermal analysis, together with analysis of the products of the decomposition. The major organic product formed in the thermal decomposition of the mono- and dichloracetates is the corresponding chlorinated acetic acid; the solid inorganic product is cuprous chloride. Thermal decomposition of the trichloracetate yields cupric chloride and a mixture of trichloracetic acid and trichloracetyl chloride.

---

Zusammenfassung Messungen des magnetischen Momentes sowie diffuse UV-Remissionspektroskopie wurden zur Untersuchung der Struktur der Kupfer(II)-chloracetate eingesetzt. Die Ergebnisse deuten darauf hin, daß Kupfermonochloracetat-Dihydrat dimer und Kupfertrichloracetat-Tetrahydrat monomer ist. Das Kupferdichloracetat-Tetrahydrat bildet hierbei eine Zwischenstufe. Die thermische Zersetzung dieser Verbindungen wurde in Stickstoffatmosphäre unter Anwendung der Thermogravimetrie und Differentialthermoanalyse untersucht, bei gleichzeitiger Analyse der Zersetzungsprodukte. Das bei der thermischen Zersetzung des Mono- und Dichloracetats gebildete organische Hauptprodukt ist die entsprechende chlorierte Essigsäure; der feste anorganische Rückstands das Kupfer(I)-chlorid. Die thermische Zersetzung des Trichloracetats ergibt Kupfer(II)-chlorid sowie eine Mischung von Trichloressigsäure und Trichloracetylchlorid.

---

Résumé La mesure du moment magnétique et la spectroscopie de réflexion diffuse dans l'U. V. sont utilisées pour étudier la structure des chloroacétates de cuivre (II). Les résultats indiquent que le monochloroacétate de cuivre (II) dihydraté est dimère et que le trichloroacétate de cuivre (II) tétrahydraté est monomère. Le dichloroacétate de cuivre (II) tétrahydraté représente un cas intermédiaire. La décomposition de ces composés dans l'azote a été suivie par thermogravimétrie et analyse thermique différentielle, en analysant simultanément les produits de décomposition. Le principal produit organique formé lors de la décomposition thermique des mono et dichloroacétates est l'acide chloroacétique correspondant; le produit solide inorganique est le chlorure de cuivre (I). La décomposition thermique du trichloroacétate fournit le chlorure de cuivre (II) et un mélange d'acide trichloracétique et de chlorure trichloroacétylique.

---

(II). , (II) , (II) - . (II) . , , . , - , , (I). (II) (II) .

     

The preparation and properties of BAB block copolymers based on polyethylene sulphide and polyisoprene

Block copolymers of ethylene sulphide (B) and isoprene (A) have been prepared by anionic synthesis using alkali metal complexes of naphthalene as initiator. Two series of block copolymers have been synthesized, one (based on sodium naphthalenide as initiator) having high molecular weights and the other (based on lithium naphthalenide) having low molecular weights.Physical properties of the block copolymers as a function of composition, molecular weight and polyisoprene microstructure have been studied. Polymers containing high molecular weight polyethylene sulphide sequences were difficult to process without degradation. By lowering the molecular weight of the polyethylene sulphide segment, block copolymers of improved processibility were obtained.The centre block polyisoprene microstructure has been varied from 100% 1,2/3,4 configuration to 80% 1,4 configuration by preparing a “seed” polymer in tetrahydrofuran followed by solvent removal and replacement by hexane. Changes in microstructure affect low temperature flexibility, resilience and tensile strength of the block copolymer.The BAB block copolymers are biphasic and exhibit elastomeric properties with improved network stability compared with polystyrene-polybutadiene-polystyrene ABA block copolymers.     

High-Valent Manganese in Polyoxotungstates. 3. Dimanganese Complexes of gamma-Keggin Anions

Dimanganese-substituted gamma-Keggin heteropoly tungstates have been synthesized by reaction of the lacunary species gamma-[(SiO(4))W(10)O(32)](8)(-) with appropriate mixtures of Mn(II) and MnO(4)(-). The crystal structure of [(CH(3))(3)(C(6)H(5))N](4)[(SiO(4))W(10)Mn(III)(2)O(36)H(6)].2CH(3)CN.H(2)O (anion 1) was determined by X-ray diffraction. Crystallographic data: space group P&onemacr;, a = 12.951(3) ?, b = 14.429(3) ?, c = 20.347(4) ?, alpha = 81.95(3) degrees, beta = 88.92(3) degrees, gamma = 67.48(3) degrees, V = 3475.2(13) ?(3), and Z = 2. The final R value is 7.29% for 15861 reflections with I > 2sigma(I). The anion has the anticipated gamma-Keggin structure with virtual C(2)(v)() symmetry. The two Mn cations occupy adjacent, edge-shared octahedra with bridging hydroxo and terminal aqua ligands. Anion 1 can be oxidized and reduced to the corresponding Mn(III)Mn(IV) (2) and Mn(II)(2) (3) species respectively. The magnetic susceptibility of 1 between 2 and 300 K indicates that the Mn(III) cations are antiferromagnetically coupled, with J = -17.0 cm(-)(1) and g = 1.965. No simple magnetic behavior was observed for 2 or 3.     

Polyoxometalate Derivatives with Multiple Organic Groups. 2. Synthesis and Structures of Tris(organotin) alpha, beta-Keggin Tungstosilicates

Eight tris(organotin)-substituted Keggin tungstosilicate heteropolyanions have been synthesized and characterized by elemental analysis, infrared and M?ssbauer spectroscopy, multinuclear NMR, and X-ray crystallography. The new anions contain alpha- or beta-SiW(9)O(34)(10)(-) moieties and are of two structural types, [(RSn)(3)(SiW(9)O(37))](7)(-) (R, isomer: Ph, alpha-, 1; n-Bu, alpha-, 2; Ph, beta-, 3; n-Bu, beta-, 4) and [(RSnOH)(3)(SiW(9)O(34))(2)](14)(-) (Ph, alpha-, 5; n-Bu, alpha-, 6; Ph, beta-, 7; n-Bu, beta-, 8). Crystals of Cs(4)H(3)[(PhSn)(3)(SiW(9)O(37))].8H(2)O (anion 3) are monoclinic, space group C2/c, with lattice constants a = 48.91(2) ?, b = 12.111(3) ?, c = 20.334(9) ?, beta = 102.30 degrees, and Z = 8. The anion has nominal C(3)(v)() symmetry and has a structure with three corner-shared WO(6) octahedra of the beta-Keggin anion replaced by three PhSnO(5) groups. Crystals of Cs(9)H(5)[(BuSnOH)(3)(SiW(9)O(34))(2)].36H(2)O (anion 6) are tetragonal, space group P&fourmacr;2(1)m, with lattice constants a = b = 29.005(4) ?, c = 13.412(4) ?, and Z = 4. The anion has the anticipated D(3)(h)() symmetry and contains three BuSnOH groups sandwiched between A,alpha-SiW(9)O(34)(10)(-) anions.     

Metal-catalyzed organosulfur cathodes for rechargeable lithium batteries

Extensive studies were carried out to apply composite materials composed of polyaniline (PAn) and 2,5-dimercapto-1,3,4-thiadiazole (DMcT) to develop cathode materials which exhibit high energy densities. Previous results have established that composites of PAn and DMcT which are coated onto copper substrates exhibit greatly enhanced charge and discharge performance. It is shown that composite materials composed of DMcT, PAn, and Cu ion have the ability to be reversibly charged and discharged at ca. 260 A h per kg-cathode (ca. 830 W h per kg-cathode) for more than 80 cycles. These two results are explored in general in this contribution via investigation of the electron transfer reactions between the components using UV/Vis and investigation of the copper substrate/DMcT chemistry using electrochemical quartz crystal microbalance and phase modulated interferometric microscopy.     

Rapid,sensitive fluorimetric assay for proteases using fluorescein-labelled albumin coupled to Fractogel activated with 2-fluoro-1-methylpyridinium salt in flow-injection analysis

A rapid and sensitive flow-injection method is described for the fluorimetric determination of the proteolytic activity of a number of enzymes. The substrate, fluorescein-labelled bovine serum albumin coupled to a 2-fluoro 1-methylpyridinium salt-activated Fractogel support, is packed in a small reactor (35 × 2 mm i.d.) and inserted into a flow manifold. Under the reaction conditions the amount of fluorescein released from enzymatic cleavage of the substrate is found to be directly proportional to the activity of the proteolytic enzyme. Sample throughput is 30–35 h^?1. The calibration range for trypsin is linear up to at least 0.35 μg ml^?1. Linear responses were also obtained for otherproteolytic enzymes such as papain, chymotrypsin, ficin and bromelain.