GC/MS analysis of pesticides in the Ferrara area (Italy) surface water: a chemometric study

The development of a network to monitor surface waters is a critical element in the assessment, restoration and protection of water quality. In this study, concentrations of 42 pesticides--determined by GC-MS on samples from 11 points along the Ferrara area rivers--have been analyzed by chemometric tools. The data were collected over a three-year period (2002-2004). Principal component analysis of the detected pesticides was carried out in order to define the best spatial locations for the sampling points. The results obtained have been interpreted in view of agricultural land use. Time series data regarding pesticide contents in surface waters has been analyzed using the Autocorrelation function. This chemometric tool allows for seasonal trends and makes it possible to optimize sampling frequency in order to detect the effective maximum pesticide content.     

The Strongest Brønsted Acid: Protonation of Alkanes by H(CHB11F11) at Room Temperature

What is the strongest acid? Can a simple Brønsted acid be prepared that can protonate an alkane at room temperature? Can that acid be free of the complicating effects of added Lewis acids that are typical of common, difficult‐to‐handle superacid mixtures? The carborane superacid H(CHB₁₁F₁₁) is that acid. It is an extremely moisture‐sensitive solid, prepared by treatment of anhydrous HCl with [Et₃Si? H? SiEt₃][CHB₁₁F₁₁]. It adds H₂O to form [H₃O][CHB₁₁F₁₁] and benzene to form the benzenium ion salt [C₆H₇][CHB₁₁F₁₁]. It reacts with butane to form a crystalline tBu⁺ salt and with n‐hexane to form an isolable hexyl carbocation salt. Carbocations, which are thus no longer transient intermediates, react with NaH either by hydride addition to re‐form an alkane or by deprotonation to form an alkene and H₂. By protonating alkanes at room temperature, the reactivity of H(CHB₁₁F₁₁) opens up new opportunities for the easier study of acid‐catalyzed hydrocarbon reforming.     

A new approach to 4,6-disubstituted-3,4-dihydropyran-2-ones by Domino Michael addition-cyclization reaction under PTC conditions

Domino Michael addition-cyclization reactions of α,β-unsaturated carbonyl compounds with activated 1,3-dithiane-2-carbothioate esters under solid-liquid phase transfer catalysis conditions provide 4,6-disubstituted-3,4-dihydropyran-2-one-3,3-dithioacetals in good chemical yield. Desulfurization proceeds chemoselectively under mild conditions affording 3,4-dihydropyran-2-ones in high yields.     

Structural Behavior of Pt–Sn Supported on MgO

Pt–Sn supported on magnesia and alumina were characterized, before and after treatment with hydrogen, by Mössbauer spectroscopy and X-ray diffraction. For the calcined samples on both supports tin is present as SnO₂ and platinum as metal. After reduction with hydrogen, platinum and tin diffuse into the magnesia lattice to form a solid solution. On alumina Sn(IV), Sn(II), Sn(0), Pt, Pt₃Sn, PtSn and PtSn₂ alloys are formed. The SnO interacts strongly with the alumina support. The catalytic activity of both Pt–Sn catalysts is strongly affected by the support. On alumina the dehydrogenation of cyclohexane is very high, whereas that on magnesia is almost non-active.     

Thermal properties of smoky quartz at very low temperatures

The existence of a distribution of low-lying energy levels associated with holes trapped at substitutional aluminium impurities is confirmed by measurements of low temperature specific heat and dielectric loss. A large linearly temperature-dependent contribution to the specific heat is observed at temperatures below 1 K, down to 30 mK. A localization temperature describing the width of the distribution of the energy levels is estimated to vary between 3 and 6 K.

We determined the thermal conductivity down to 30 mK and attribute the decrease below the boundary-scattering value to irradiation damage generally, arguing that it is not attributable to resonant scattering.     

Specific heat of smoky quartz

Specific heat measurements of smoky quartz are reported between 20 mK and 10 K. The linear temperature dependence observed below 1 K can be attributed to the widely distributed manifold of low-lying energy levels associated with a hole trapped at one oxygen near a substitutional aluminium impurity.     

Study of iron-zinc catalysts by Mössbauer spectroscopy

The Mössbauer parameters were determined on a series of catalyst mixtures of iron and zinc oxides with variable quantities of zinc. From these results, a change in the crystal structure of the iron oxide when introducing zinc into the samples was observed. The corundum structure of the -Fe₂O₃ phase was transformed into the spinel type of zinc ferrite when zinc oxide was present in any quantity. By means of these parameters a strong electronic interaction between the zinc ferrite and the zinc oxide present in excess was evident. The catalysts were analyzed using X-ray fluorescence /XRF/ and X-ray diffraction /XRD/.     

1H‐Azepine‐4‐amino‐4‐carboxylic Acid: A New α,α‐Disubstituted Ornithine Analogue Capable of Inducing Helix Conformations in Short Ala‐Aib Pentapeptides

A very efficient synthesis of orthogonally protected 1H‐azepine‐4‐amino‐4‐carboxylic acid, abbreviated as Azn, a conformationally restricted analogue of ornithine, was realized. It was obtained on a gram scale in good overall yield in five steps, three of which did not require isolation of the intermediates, starting from the readily available 1‐amino‐4‐oxo‐cyclohexane‐4‐carboxylic acid. Both enantiomers were used for the preparation of pentapeptide models containing Ala, Aib, and Azn. Conformational studies using both spectroscopic techniques (NMR, CD) and molecular dynamics on model 5‐mer peptides showed that the (R)‐Azn isomer possesses a marked helicogenic effect.