The chemistry of peroxovanadium species in aqueous solutions. Structure and reactivity of a neutral diperoxovanadium complex as provided by V-NMR data, ab initio calculations and kinetic results

The addition of hydrogen peroxide to vanadium (V) precursors in aqueous acidic solutions leads to the formation of a cationic monoperoxospecies [VO(O₂)]⁺ and an anionic diperoxocomplex [VO(O₂)₂]⁻, depending on the pH and on the excess of H₂O₂. The latter may undergo protonation to form the neutral complex [HVO(O₂)₂]. ⁵¹V-NMR data and ab initio calculations suggest that the neutral complex is formed via protonation of a peroxide oxygen and that in such a species, as well as in the other two peroxovanadium derivatives, the usual η² arrangement of the peroxo groups is maintained. The comparison of reactivity data of the three complexes in the self-decomposition reaction and in the oxidation of uracil, indicates that the neutral diperoxocomplex exhibits an oxidizing power considerably larger than that of the other two peroxovanadium species.     

1,4-Diaryl and Schiff's base [1,2,3]-triazole derivative liquid crystalline compounds

Regioselective synthesis of [1,2,3]-triazoles based on the 'click-reaction', involving the Cu(I)-catalysed 1,3-dipolar cycloaddition of aryl azide to terminal arylacetylenes, was successfully employed in the preparation of two series of non-linear mesogens, based on 1,4-diaryl-[1,2,3]-triazole (Ia-e) and with Schiff's base units (IIa-c). Their mesophases were characterized by polarizing optical microscopy and differential scanning calorimetry. All final compounds exhibited preferentially the SmC phase. In addition, compounds of series I showed weak blue fluorescence in solution (λ_{max. em.} = 380-386 nm) with poor quantum yields and a Stokes shift of around 90 nm.     

NMR and pressure correlated analysis of metabolic changes in soft-X-rays irradiated yeast cells

An NMR technique for the identification of the energy related molecules, AMP, ADP and ATP, is suitably taylored to follow up the dynamics of the glycolitic metabolism in a suspension of yeast cells. Such a technique proves to be efficient to investigate soft X-ray radiation damage as complementary to other physical and chemical assessment. Received: 13 October 1998 / Accepted: 30 October 1998     

Hayman’s classical conjecture on some nonlinear second-order algebraic ODEs

In this paper, we study the growth, in terms of the Nevanlinna characteristic function, of meromorphic solutions of three types of second-order nonlinear algebraic ordinary differential equations (ODEs). We give all their meromorphic solutions explicitly, and hence show that all of these ODEs satisfy the classical conjecture proposed by Hayman in 1996.     

1,4‐Diaryl and Schiff's base [1,2,3]‐triazole derivative liquid crystalline compounds

Regioselective synthesis of [1,2,3]‐triazoles based on the ‘click‐reaction’, involving the Cu(I)‐catalysed 1,3‐dipolar cycloaddition of aryl azide to terminal arylacetylenes, was successfully employed in the preparation of two series of non‐linear mesogens, based on 1,4‐diaryl‐[1,2,3]‐triazole (Ia–e) and with Schiff's base units (IIa–c). Their mesophases were characterized by polarizing optical microscopy and differential scanning calorimetry. All final compounds exhibited preferentially the SmC phase. In addition, compounds of series I showed weak blue fluorescence in solution (λ_{max. em.} = 380–386 nm) with poor quantum yields and a Stokes shift of around 90 nm.     

High performance liquid chromatography-mass spectrometry based chemometric characterization of olive oils

In this study the effective discrimination of extra virgin olive oils is described using HPLC-MS, combined with chemometric evaluation. The presented method is simple since the diluted oil sample is directly injected into the system, without any preliminary chemical derivatization or purification step. Separation of diacylglycerols, triacylglycerols and sterols occurs within 20 min and is achieved using an octadecyl-silica column. Detection is performed by positive APCI mass spectrometry which provided sensitivity to detect over 50 compounds in the sample. After extraction of data, stepwise discriminant function analysis is used to select the variables with the highest discriminative power. These variables are used to perform linear discriminant analysis and classify/predict the samples. One-hundred per cent classification and 99% prediction rate was achieved for olive oils obtained from Nocellara, Biancolilla and Cerausola cultivars. Reliability of prediction was tested by cross validation.     

Detailed elucidation of hydrocarbon contamination in food products by using solid-phase extraction and comprehensive gas chromatography with dual detection

The present work is focused on the development/optimization of a comprehensive two-dimensional gas chromatography method, with dual detection [flame ionization (FID) and mass spectrometric], for the simultaneous identification and quantification of mineral-oil contaminants in a variety of food products. The two main classes of contaminants, namely saturated and aromatic hydrocarbons, were previously fractionated on a manually-packed silver silica solid-phase extraction (SPE) cartridge. The quantitative results were compared with those obtained by performing a large volume injection, in a GC-FID system, after the same SPE process and by an on-line liquid–gas chromatography method, with very similar results observed. The presence of a series of unknown compounds, that appeared when using the off-line methods, was investigated using the mass spectrometric data, and were tentatively-identified as esterified fatty acids, most probably derived from vegetable oil based ink.     

Comparative X‐ray study of three nickel(II)–thio­cyanate compounds

Three cis nickel–di­thio­cyanate (SCN) complexes with different N,N′‐bidentate bases have been prepared and their crystal structures determined: bis(2,2′‐bi­pyridine‐N,N′)­bis­(thio­cyan‐­ato‐N)­nickel(II), [Ni(SCN)₂­(C₁₀H₈N₂)₂], bis(1,10‐phen­anthroline‐N,N′)­bis­(thio­cyanato‐N)­nickel(II), [Ni(SCN)₂­(C₁₂H₈N₂)₂], and bis(2,9‐di­methyl‐1,10‐phenanthroline‐N,N′)­bis­(thiocyanato‐N)nickel(II) mono­hydrate, [Ni(SCN)₂­(C₁₂H₈N₂)₂]·H₂O. Distortions due to ligand size are discussed.     

Free radical generation upon plasma treatment of cotton fibers and their initiation efficiency in surface-graft polymerization

Low-temperature plasma was used to activate mercerized cotton fabrics, to be followed by grafting with various methacrylates. Careful analysis of the experimental electron spin resonance (ESR) lineshapes of cotton samples treated at different RF powers made it possible to recognize and quantify four different species of free radicals still persistent 30 h after irradiation in the samples maintained under inert atmosphere. The decay rate of these species at room temperature was also evaluated with the analysis of the time evolution of the ESR spectra. The nature of the free radical species actually involved in the monomer grafting reaction has been discussed for cotton fabrics prepared under different plasma treatment conditions by analyzing the ESR lineshapes.