Physico-chemical characterization of crystalline phases in fly ashes

Fuel oil combustion in power plants, domestic heating systems and diesel engines, causes the emission in the environment of particles with a typical structure and composition: the cenospheres.These particles are produced during the microdrop fuel oil combustion, when air and fuel are injected into the combustion chamber; they have a spheroidal morphology and a spongy structure.Cenospheres are constituted by an amorphous component rich in C, S, Si, Fe and Al; phases composed by microcrystals of sulphates, oxides and pure metallic elements or their alloys, are frequently present in the cenospheres.These crystalline phases are important from environmental and toxicological points of view both because they are composed of heavy metals, and because they can play an important role in heterogeneous catalysis.We started to study these crystalline phases by analytical electron microscopy techniques and electron energy loss spectrometry to define and characterise their structure and composition.     

The crystal structure of triphenylallyltin

The crystal structure of (C₆H₅)₃SnCH₂CHCH₂ has been determined. The asymmetric unit consists of two molecules of triphenylallyltin having virtually the same conformation. Their geometrical parameters exclude p_π-d_π bonding between the metal and the allyl double bond, and seem to be in a better agreement with a σ-π conjugation effect.     

Functional and structural characterization of ovine ornithine transcarbamoylase

Ornithine transcarbamoylase from ovine liver has been purified to homogeneity. Like all anabolic OTCs, the ovine enzyme is a trimer, constituted by identical subunits of 34 kDa. Sequence analysis of the 54 N-terminal residues of ovine OTC shows a high degree of homology with the human enzyme. The optimum pH and the Michaelis constants for the catalytic reaction were determined. The ovine enzyme is the most thermostable one among mammals OTCs, its critical temperature being 6 degrees C higher than those measured for the other enzymes. The enzyme has been crystallised and the structure determined at 3.5 A resolution. Crystals belong to the cubic P4(3)32 space group, with a = b = c = 184.7 A and a solvent content of about 80%. There is no evidence of any ligand in the active site cavity, indicating that the crystals contain an unliganded or T state of the enzyme. The unliganded OTCase enzyme adopts a trimeric structure which, in the crystal, presents a three-fold axis coincident with the crystallographic one. The conformation of each monomer in the trimer is quite similar to that of the liganded human protein, with the exception of a few loops, directly interacting with the substrate(s), which are able to induce a rearrangement of the quaternary organisation of the trimer, that accounts for the cooperative behaviour of the enzyme following the binding of the substrates.     

The first example of a copper(II) chloride complex with 1,3-thiazolidine-2-thione

Summary The reaction of copper(II) chloride with 1,3-thiazolidine-2-thione in absolute ethanol yields the complex CuL₂Cl₂. This derivative has been studied by elemental analyses, molar conductance, magnetic moment measurements at different temperatures, electronic and infrared spectroscopy, thermal analyses (TG and DTG) and e.p.r. techniques. The complex has a pseudooctahedral stereochemistry, with bridging halides and with the ligands monodentate-S-bondedvia the exocyclic sulphur atom.     

Reactions of the unsaturated anion [Re3H4(CO)10]− with car☐ylic acids and x-ray characterization of the anions [Re3H3(CO)10(μ-O2CR)]− (R = H,CF3)

The novel anions [Re₃H₃(CO)₁₀(μ-O₂CR)]^? (R = H, CH₃, CF₃), obtained by reaction of [Re₃H₄(CO)₁₀]^? with the corresponding car?ylic acids, have been characterized by IR and NMR spectra and by X-ray analysis of the formate and trifluoroacetate derivatives. They contain a triangle of rhenium atoms, with the car?ylate group diaxially bridging on the shorter ReRe edge.     

Electrochemistry of coordination compounds: IX. An approach to the kinetic study of the reversible addition of carbon monoxide to di-(1,2-bisdiphenylphosphinoethane)rhodium(I) perchlorate by cyclic voltammetry

The reversible addition of carbon monoxide to [Rh(DPE)₂]⁺ has been studied by cyclic voltammetry. The greatest contribution of this technique is that the uptake and release of CO, occurring before electron transfer, can be characterized and their rates measured.The differences in the reversibility of the CO addition between this complex and the isoelectronic isostructural cobalt and iridium ones are compared. A suggestion is made on the possible relevance of kinetic factors in the release of the CO molecule.     

ENZYMATIC GENERATION OF ELECTRONICALLY EXCITED STATES BY ELECTRON TRANSFER

Abstract— The catechol oxidase promoted oxidation of catechols produces electronically excited states readily detected by chlorophyll sensitized fluorescence. Both the chemiexcitation step and the transfer step are efficient. The use of chlorophyll has confirmed that the peroxidase catalyzed oxidation of dihydroxyfumarate also generates electronically excited species. It is concluded that efficient enzymatic generation of electronic energy can occur not only through the dioxetane/dioxetanone route, but also via electron transfer processes.     

Fluoride ion induced reactions of organocilanes with saturated lactones and αβ-enones

Benzyl-, heteroaryl-, and allylsilanes, under the catalytic action of CsF or silica/TBAF, react in mild conditions with electrophiles such as σ-valero and ε-caprolactone, and with cyclohexen-2-one.