The preparation of bimetallic complexes with the ligand 1-oxy-2,6-di[N,N-biscarboxymethyl)aminomethyl]-4-chlorobenzol, and their physico-chemical characterization

With the binucleating ligand 1-oxy-2,6-di [(N,N-biscarboxymethyl)aminomethyl]- 4-chlorobenzol (H₅L) complexes of formulae FeH₂L · 2H₂O; FeH₃L(C1O₄) · H₂O; Fe₂L(OH) · 2H₂O; M₂HL · nH₂O (M = Co, Cu, n = 2; M = Ni, n = 4); FeCuL · 3H₂O; FeCrL(OH) · 3H₂O were prepared and characterized by elemental analysis, IR and electronic spectra and magnetic moment determinations. In addition, thermal analysis data of the complexes and Mössbauer effect spectra of the iron containing complexes are also given and discussed.     

Mechanism of reductive elimination of benzonitrile in cyanophenyl complexes of nickel(II) : II. Reactions of [cyano(phenyl)bis(tricyclohexylphosphine)nickel(II)]

The thermal decomposition of the complex Ni(CN)(C₆H₅)(PCy₃)₂ (Cy = cyclohexyl) in decalin has been examined. The complex reacts with P(OC₂H₅)₃ to give C₆H₅CN in quantitative yield. The mechanism of this reaction has been investigated and compared with that of the similar reaction shown by Ni(CN)(C₆H₅)(PEt₃)₂. The results indicate that the easiest path for the reaction involves a bimolecular attack of P(OC₂H₅)₃ at the metal atom before reductive elimination of C₆H₅CN.     

Further development of catalase, tyrosinase and glucose oxidase based organic phase enzyme electrode response as a function of organic solvent properties

Using three enzyme sensors (tyrosinase, catalase and glucose oxidase), capable of functioning also in non-aqueous solvents, we found new correlations between classical indicators, e.g. the log P value of several organic solvents and new empirical indicators such as ;maximum current variation' (MCV) and above all the ;current variation rate' (CVR), the values of which may be monitored with the biosensor considered dipping directly into the organic solvent. The trend of the immobilised specific activity of the tyrosinase enzyme dipping into different organic solvents was evaluated and compared with that determined by the spectrophotometric method. Lastly, an investigation was performed to experimentally verify the relation between hydrophobicity of the solvent and its ability to draw back the water from the enzyme microenvironment using the Karl Fischer method and thermogravimetric analysis to estimate the residual water in the enzyme microenvironment after having treated the enzyme with the organic solvent, then allowing it to dry.     

Selenium speciation in foods: Preliminary results on potatoes

The present paper deals with the speciation of selenium in potatoes (enriched or not in selenium). The study was carried out by using differential pulse cathodic stripping voltammetry (DPCSV) for quantifying selenium. Results obtained provide evidence that the selenium content in the protein fraction is rather independent from the selenium added to the plants during their growth. On the contrary, the amount of Se in the non-protein fraction (water and starch) in Se-enriched sample is significantly higher than in non-enriched one, suggesting that it is the main selenium-storing site. In this fraction the Se(VI)/Se(IV) ratio seems independent from selenium application but it may be related to the redox conditions. The accumulation of selenium in the non-protein fraction is tentatively ascribed to the “Se–starch interaction” that should be able to modulate both the Se absorption into proteins and, possibly, its toxic effect for the plant itself.     

Glutamate receptor incorporated in a mixed hybrid bilayer lipid membrane array, as a sensing element of a biosensor working under flowing conditions

The realization of a reliable receptor biosensor requires stable, long-lasting, reconstituted biomembranes able to supply a suitable biomimetic environment where the receptor can properly work after incorporation. To this end, we developed a new method for preparing stable biological membranes that couple the biomimetic properties of BLMs (bilayer lipid membranes) with the high stability of HBMs (hybrid bilayer membranes); this gives rise to an innovative assembly, named MHBLM (mixed hybrid bilayer lipid membrane). The present work deals with the characterization of biosensors achieved by embedding an ionotropic glutamate receptor (GluR) on MHBLM. Thanks to signal (transmembrane current) amplification, which is typical of natural receptors, the biosensor here produced detects glutamate at a level of nmol L(-1). The transmembrane current changes linearly vs glutamate up to 100 nmol L(-1), while the limit of detection is 1 nmol L(-1). In addition, the biosensor response can be modulated both by receptor agonists (glycine) and antagonists (Mg(2+)) as well, and by exploiting the biosensor response, the distribution of different kinds of ionotropic GluR present in the purified sample, and embedded in MHBLM, was also evaluated. Finally, one of the most important aspects of this investigation is represented by the high stability of the biomimetic system, which allows the use of biosensor under flowing conditions, where the solutions flow on both biomembrane faces.     

Eptastigmine,nicotinamide and nicotinic acid determination using an inhibition enzyme sensor; application to pharmaceutical analysis

An enzyme inhibition biosensor, developed in our laboratory and previously used for the analysis of compounds with anticholinesterase activity (e.g. physostigmine, neostigmine, pyridostigmine nicotine and organophosphorus compounds) has now been tested for the analysis of another recently synthesized cholinesterase inhibitor, i.e. eptastigmine. In addition nicotinic acid and nicotinamide, although displaying weaker inhibition properties, were also tested in pharmaceutical products using the same inhibition enzyme sensor. The biosensor consisted of a hydrogen peroxide amperometric electrode coupled to a functionalised nylon membrane chemically bonding both the enzymes butyrylcholinesterase and choline oxidase; a butyrylcholine standard solution in glycine buffer acted as substrate. The response of the system to all the inhibitors considered was characterised completely and the analysis of several pharmaceutical formulations containing nicotinamide or nicotinic acid was also performed.     

CH...O and CH...F links form the cage structure of dioxane-trifluoromethane

The molecular beam Fourier transform microwave spectrum of 1,4-dioxane-trifluoromethane has been assigned and measured. The two subunits form a cage stabilized by one C-H...O and two C-H...F weak hydrogen bonds. The C-H...O link involves the axial lone pair of one of the two equivalent ring oxygens, while the two C-H...F bridges connect trifluoromethane to the two axial hydrogens in positions 3 and 5. The dissociation energy has been estimated from the D(J) centrifugal distortion parameter to be approximately 6.8 kJ/mol.     

Conformational equilibrium and potential energy surface of 1-fluorobutane by microwave spectroscopy and Ab initio calculations

The rotational spectra of four (GT, TT, TG, and GG) of the five possible conformers of 1-fluorobutane have been assigned by combining free jet and conventional microwave spectroscopy. The geometry optimization was performed at the MP2 (full) level of theory with the 6-31G (d) and 6-311G (d, p) basis sets and by using the B3LYP (3df, 3pd) density functional method. The relative stability of the five rotamers is calculated at the QCISD (T)/6-311G (d, p) level of theory. In spite of the fact that ab initio calculations indicated the unobserved GG' conformer to be more stable than at least one of the observed conformers it was not possible to detect its rotational spectrum. GT and TG are the most and the least stable species, respectively. The rotational spectra of several vibrational satellites of the four conformers have been studied by conventional microwave spectroscopy. The overall conformational equilibrium is governed by the two-dimensional potential energy surface of the skeletal torsions MeC-CC and FC-CC, which have been evaluated by a flexible model analysis, based on the experimental values of the relative conformational and vibrational energy spacings, and on the shifts of second moments of inertia upon conformational change and vibrational excitation. The relative energy of the fifth stable conformer (GG') was determined to be 333 cm(-1) from flexible model calculations, and to be 271 cm(-1) from the most accurate ab initio calculations.