Walter Marconi

Synthesis and structure of a π-arene complex of uranium(III) - aluminum chloride

Abstract The synthesis of a π-arene uranium(III) complex with aluminium chloride obtained from UCl 4 , AlCl 3 and Al in benzene, is reported. The isolated big black crystals are thermally stable up to 100°C and are immediately decomposed by moisture. The crystal and molecular structure of the complex is reported as determined by single crystal X-ray method.

A contribution to the organometallic chemistry of uranium: tetra(allyl)uranium

Abstract The synthesis of tetra-allyl Uranium obtained from UCl4 and C3H5 Mg Br, is reported. The isolated crystalline dark-red complex is not thermally stable above −20°C and burns spontaneously in the air. Its infrared spectra could be reasonably in agreement with π-bonded allylic groups. Thermal decomposition and cleavage with H2O gave the expected hydrocarbon products.

[18] Fiber-entrapped enzymes

Publisher Summary This chapter discusses the analytical determination, properties, and application of fiber-entrapped enzymes. Entrapment of invertase is reported in the chapter. It is stressed that any other enzyme can be entrapped using the same procedure. The activity of a fiber-entrapped enzyme is determined by incubating the enzyme fibers and the substrate solution while stirring. The physical properties of enzyme fibers depend on the chemical nature of the polymer and are generally different from those of fibers normally obtained in the textile industry. These differences arise chiefly from the fact that, while in the normal wet-spinning procedure a homogeneous solution of the polymer is spun, in the technology of enzyme entrapment an emulsion is extruded. The catalytic properties of fiber-entrapped enzymes are generally different from those of the corresponding free enzymes. The principal differences are ascribed to, the restricted diffusion of substrates and products inside the porous enzyme support. Because of their excellent activity and stability, fiber-entrapped enzymes have potential technological application in industry, medicine, and analytical chemistry. The easy and inexpensive preparation procedures for enzyme fibers show a clear economic advantage in a large number of applications, which include both replacement of currently used free enzymes and the use of sophisticated enzymes considered too expensive in the soluble form.

Reactions Between AIRCl2 and Ti (OR)4 and Activity in Diolefin Polymerization

Abstract Through the use of a Ti(OR′)4-AlRCl2 catalyst system, high 1,4-cis isoprene polymers and crystalline 1,4-trans polybutadiene are obtained. Neither monomer is polymerized at a Al/Ti mole ratio of less than 4. The maximum activity and stereospecificity for isoprene is observed at Al/Ti = 4. For 1,4-trans butadiene polymers the activity increases progressively with increasing Al/Ti ratio. The investigations carried out on this catalyst system show that at a AI/Ti mole ratio of 4 the formation of crystalline β-TiCl3 takes place, while at lower ratios insoluble chloro-alkoxide derivatives of TiIII with different compositions separate. Soluble complexes containing aluminium and titanium are initially formed before precipitation occurs. Chemical data and investigations by IR and NMR spectroscopy indicate exchange reactions between Al-Cl, Al-R, and Ti-OR groups, together with reduction of the transition metal. A reaction mechanism and a hypothesis on the nature of the active catalyst are given.

Reaction of π-allylic nickel complexes with quinones and their catalytic activity☆

Abstract The reaction between bis(π-crotyl)Ni and π-crotyl-Ni-Cl with some quinones such as chloranil, bromanil and monochloro-p-benzoquinone have been studied. The preferred Ni-quinone mole ratio is one or two depending on the oxidation state of Ni in the starting complex. On the basis of analytical data and infrared spectra, the reaction products may be formulated as charge transfer complexes in which electrons are transferred from Ni to the quinone. All the complexes are brown solids, unstable in the air and insoluble in all solvents, except those in which complete solvolysis takes place, in agreement with a proposed salt-like structure. Catalytic activity of these complexes in the stereospecific polymerization of butadiene is briefly reported and discussed in terms of acceptor-donor properties of those starting Ni and quinone derivatives.

A contribution to the chemistry of N-alkylalazanes☆

Abstract By reaction of a primary amine with halogenalanes (mole ratio 1:2), derivatives such as Cl 2 AlN(R) AlCl 2 .O(C 2 H 5 ) 2 are obtained. Reducing these compounds with LiH, a mixture of LiAlH 4 and polymeric (HAlNR) n is obtained, instead of the expected H 2 AlNRAlH 2 . When halogenalanes were reacted with aluminum amides (mole ratio 3:1) compounds of type Al(NRAlCl 2 ) 3 resulted. Also it is possible to synthesize these complexes reacting halogenalanes with primary amine and then with aluminum-hydride. They were isolated as complexes with Lewis bases such as diethyl ether, tetrahydrofuran, trialkylamines. Reduction of these complexes in suitable conditions gives stable aluminum tris-(N-alkylalazanes) Al(NRAlH 2 ) 3 . A possible structure is suggested for these compounds.

[24] Microbial cells entrapped in cellulose acetate beads

Publisher Summary This chapter describes the preparation of the biocatalysts and some of their industrial applications. Cellulose acetate derivatives, having a polymerization degree of around 300, can be used for biocatalyst immobilization. Enzymatic cells have been entrapped in cellulose triacetate (CTA) fibers following the procedure used for the immobilization of free enzymes, but the results obtained were not satisfactory. Cellulose diacetate (CDA) is found to be suitable for the entrapment of cells because of its physical and chemical properties. CDA has a degree of polymerization lower than CTA, it is soluble both in acetone and acetone-water mixtures, and coagulates in water taking different physical shapes (fibers, disks, and beads) according to the viscosity of the extruded dispersion. The entrapment is therefore carried out under mild conditions generally compatible with the enzymatic activity.

Synthesis of l-Tryptophan from Indole and dl-Serine by Tryptophan Synthetase Entrapped in Fibres: I. Preparation and Properties of Free and Entrapped EnzymeII. Reactor Studies

Optimal culture conditions for microbial production of tryptophan synthetase were studied. It was found that on cultivation of Escherichia coli 476, a tryptophan auxotroph, in a medium containing 5g/liter glycerol as C source, supplemented with 1 g/liter of acid-treated peptone, cells with high tryptophan synthetase activity could be obtained.The enzyme was extracted from cells and 3-fold purified by heat treatment and ammonium sulfate precipitation. The overall yield of the isolation procedure was 60%.The partially purified tryptophan synthetase was entrapped in cellulose triacetate fibres. Under storage conditions, in refrigerator, the entrapped enzyme was stable at least for 6 months. The activity of the entrapped enzyme was about 75% with respect to the free enzyme.Similar behaviour for the free and entrapped enzyme was observed as to the effect of temperature and pH on the enzymic activity. The operational stability of the entrapped tryptophan synthetase was very good (activity unchanged after 50 day...