On automorphisms fixing non-normal subgroups of groups

This work was carried out when the last named author visited the Department of Mathematics of the University of Napoli Federico II in March 1994. He is very grateful for the hospitality he enjoyed and for the support by the C.N.R.     

Groups with many normal-by-finite subgroups

A subgroup of a group is said to be normal-by-finite if the core of in has finite index in . In this article groups satisfying the minimal condition on subgroups which are not normal-by-finite and groups with finitely many conjugacy classes of subgroups which are not normal-by-finite are characterized.

     

Spontaneous dehydration mechanism of aromatic aldehyde reactions with hydroxyl and non‐hydroxyl amines

The plot of rate constants vs. pH for the dehydration step of the reaction between furfural and 5‐nitrofurfural with hydroxylamine, N‐methylhydroxylamine, and O‐methylhydroxylamine, shows two regions corresponding to the oxonium ion‐catalyzed and spontaneous dehydration. The oxonium ion‐catalyzed dehydration region of the reaction of furfural with the above mentioned hydroxylamines exhibits general acid catalysis with excellent Brønsted correlation (Brønsted coefficients: 0.76 (r = 0.986), 0.68 (r = 0.987), and 0.67 (r = 0.993) respectively). However, the rate constants of the spontaneous dehydration of these hydroxylamines, where water is considered the general acid catalyst, exhibit a large positive deviation from the Brønsted line. This fact was not observed in the reaction of non‐hydroxyl amines with different aromatic aldehydes by other authors, thus supporting that the spontaneous dehydration steps for these reactions proceed by intramolecular catalysis. The mechanism of intramolecular catalysis might be stepwise. First, a zwitterionic intermediate is formed. It can then evolve in the second step by loss of water, or follow a concerted pathway, with the transference of a proton through a five‐membered ring (general intramolecular acid catalysis). In the case of non‐hydroxyl amines, data suggested the possibility of a mechanism of intramolecular proton transfer through one or two water molecules, from the nitrogen of the amine to the leaving hydroxide ion. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 685–692, 2002     

Amperometric Glucose Determination by Means of Glucose Oxidase Immobilized on a Cellulose Acetate Film: Dependence on the Immobilization Procedures

Glucose microelectrodes were prepared by immobilizing glucose oxidase onto a cellulose acetate film coating a platinum wire. Hexamethylenediamine (HMDA) and Glutaraldehyde (GA) were employed as spacer and coupling agent, respectively. Sensitivities and linear response ranges were studied as a function of the relative amounts of HMDA and GA. The best sensitivity was found when HMDA and GA were 5% and 2.5% in aqueous solutions, respectively. Taking as a reference the functioning of this biosensor, the roles of HMDA and GA percentages appear to be opposed when the extension of the linear response range is considered. Indeed, an increase of one unit in HMDA percentage (from 5 to 6 %) induces an increase in the extension of the linear response range equal to that obtained with a decrease of one unit of GA percentage (from 2.5 to 1.5%).     

Metallocene derivatives as active supports of zirconium‐based catalysts for ethene polymerization

Cyclopentadienyl magnesium chloride (MgClCp) and its functionalized derivatives represent original and interesting supporting materials to heterogenize metallocene catalysts for olefin polymerizations. The synthesis of MgClCp, its functionalization, and the preparation of a catalytic system in which the ZrCl₂(Flu)⁺ moiety is joined on the support through a cyclopentadienyl ligand are reported. This catalyst was tested in ethene polymerization, and both the catalytic activity and properties of the produced polymer were measured. Its performance was compared with that shown by the catalyst ZrCl₂CpFlu employed under the same conditions for both unsupported and conventional supports, such as MgCl₂. The results showed a remarkable improvement in terms of the activity and polymer properties with these heterogenized catalysts. Moreover, this system showed stability toward leaching processes and was characterized by good morphological control of the growing polymer. Finally, catalysts in which [HB(3,5‐Me₂pyrazolyl)₃]ZrCl and [HB(3,5‐Me₂pyrazolyl)₃]ZrClOtBu⁺ moieties were bonded to a functionalized MgClCp^? support were also synthesized and tested. The results showed that the proposed supports could be usefully used to heterogenize tailored metallocene homogeneous catalysts. In fact, new catalysts were prepared that combined the peculiar advantages of both heterogeneous and homogeneous catalysts and overcame the disadvantages of the latter, such as a lack of morphology and reactor fouling. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4243–4248, 2001     

Mineral composition of fruit by-products evaluated by neutron activation analysis

Brazil is one of the largest producers of fruits cropping 40 million tons per year. In agro-food processing, approximately 50 % of raw material is discarded generating large amounts of by-products. The lack of information on the nutritional quality of agroindustrial by-products precludes their potential use in the manufacture of food products accessible to all. In this context, the objective of this work was to investigate the nutritional quality of by-products of the industrial processing of fruits. Samples of bagasse, peel and seeds of several fruits (banana, camu camu, coconut, cupuaçu, guava, jackfruit, mango, orange, papaya, pineapple, and soursop) were analysed by neutron activation analysis for the determination of Br, Ca, Co, Cr, Cs, Fe, K, La, Na, Rb, Sc and Zn. In general, higher levels of minerals were found in the by-products rather than in the pulps of fruits. This indicates that the use of the by-products should be encouraged, thereby reducing the economic and environmental impact of waste generated by agroindustrial processing.     

Utilization of deuterium labelling and 13C NMR spectroscopy in the investigation of the condensation of 1-Methyl-5-nitroimidazole-2-aldehyde and 2-Amino-4-methylpyrimidine

The product obtained condensing l-methyl-5-nitroimidazole-2-aldehyde with 2-amino-4-trideuteriomethyl-pyrimidine and showing total deuterium incorporation at one of the olefinic carbons and partial deuterium incorporation para to the amino group, served to assign ¹³C and ¹H resonances in the condensation products 3. The nature of the species undergoing condensation has been inferred from labelling experiments and from ¹H and ¹³C nmr spectra of precursors and products in dimethylsulfoxide and trifluoroacetic acid.     

Inter‐ and intramolecular hydrogen bonds in polyamines: variable‐concentration 1H‐NMR studies

Inter‐ and intramolecular hydrogen bonding play an important role in determining the arrangement, physical properties, and reactivity of a great diversity of structures in chemical and biological systems. Several aromatic nucleophilic substitutions (ANS) in nonpolar aprotic, (non‐HBD), solvents recently studied in our laboratory have demonstrated the importance of self‐association of amines by hydrogen‐bond interactions. In this paper, we describe ¹H‐NMR studies carried out at room temperature on bi‐ and polyfunctionalized amines, namely: N‐(3‐amino‐1‐propyl)morpholine (3‐APMo), histamine, 2‐guanidinobenzimidazole (2‐GB), 1,2‐diaminoethane (EDA), 3‐dimethylamino‐l‐propylamine (DMPA), and 1‐(2‐aminoethyl)piperidine (2‐AEPip). By ¹H‐NMR measurements of amine solutions at variable concentrations we have shown that 3‐APMo, histamine and 2‐GB are able to form a six‐membered ring by intramolecular hydrogen bonding, while EDA, DMPA, and 2‐AEPip form dimers by intermolecular hydrogen bonds. Likewise, variable concentration ¹H‐NMR studies allowed estimation of the corresponding equilibrium constants for the dimerization. These results are correlated with experimental kinetic results of ANS, confirming hereto the relevance of the “dimer mechanism” in reactions involving these amines. Copyright © 2011 John Wiley & Sons, Ltd.